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Polymer Micromachining
Packaging of MEMS sensors
Mikrosensorer
Project meeting 1
Sensor Time
Accelerometer 184 915
Pressure sensor 184 1015
Flow sensor 184 1115
Polymer Micromechanics
Cheaper materials
Low cost fabrication
Allow single use
rdquothermal recyclingrdquo
Rapid prototyping
Very flexible electronic
components (design amp state)
Polymer Micromachining
Polymer Micromechanics
bull Thin Film Litography
bull Hot Embossing
bull Injection Moulding
bull Laser Fabrication
bull 3D-printing
Polymer classes
Plastic materials that can be formed into shapes
Thermoplastic materials that can be shaped more than once
Thermosetting plastic material that can only be shaped once
Elastomer material that is elastic in some way If a moderate amount of deforming force is added the elastomer will return to its original shape Useful for fibers
Properties of Polymers
bull Chain length
bull Structure orientation of chains
bull Identity of side groups
bull Degree of cross‐linking
ndash Cross linking with covalent bonds formed
between chains make the polymer stiffer
more crystalline
Thermoplastics
Melting (Tm)
Rubbery flow
OSTE(+)
Saharil F et al microTAS 2012Carlborg et al Lab on a chip 2011
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Project meeting 1
Sensor Time
Accelerometer 184 915
Pressure sensor 184 1015
Flow sensor 184 1115
Polymer Micromechanics
Cheaper materials
Low cost fabrication
Allow single use
rdquothermal recyclingrdquo
Rapid prototyping
Very flexible electronic
components (design amp state)
Polymer Micromachining
Polymer Micromechanics
bull Thin Film Litography
bull Hot Embossing
bull Injection Moulding
bull Laser Fabrication
bull 3D-printing
Polymer classes
Plastic materials that can be formed into shapes
Thermoplastic materials that can be shaped more than once
Thermosetting plastic material that can only be shaped once
Elastomer material that is elastic in some way If a moderate amount of deforming force is added the elastomer will return to its original shape Useful for fibers
Properties of Polymers
bull Chain length
bull Structure orientation of chains
bull Identity of side groups
bull Degree of cross‐linking
ndash Cross linking with covalent bonds formed
between chains make the polymer stiffer
more crystalline
Thermoplastics
Melting (Tm)
Rubbery flow
OSTE(+)
Saharil F et al microTAS 2012Carlborg et al Lab on a chip 2011
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Polymer Micromechanics
Cheaper materials
Low cost fabrication
Allow single use
rdquothermal recyclingrdquo
Rapid prototyping
Very flexible electronic
components (design amp state)
Polymer Micromachining
Polymer Micromechanics
bull Thin Film Litography
bull Hot Embossing
bull Injection Moulding
bull Laser Fabrication
bull 3D-printing
Polymer classes
Plastic materials that can be formed into shapes
Thermoplastic materials that can be shaped more than once
Thermosetting plastic material that can only be shaped once
Elastomer material that is elastic in some way If a moderate amount of deforming force is added the elastomer will return to its original shape Useful for fibers
Properties of Polymers
bull Chain length
bull Structure orientation of chains
bull Identity of side groups
bull Degree of cross‐linking
ndash Cross linking with covalent bonds formed
between chains make the polymer stiffer
more crystalline
Thermoplastics
Melting (Tm)
Rubbery flow
OSTE(+)
Saharil F et al microTAS 2012Carlborg et al Lab on a chip 2011
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Cheaper materials
Low cost fabrication
Allow single use
rdquothermal recyclingrdquo
Rapid prototyping
Very flexible electronic
components (design amp state)
Polymer Micromachining
Polymer Micromechanics
bull Thin Film Litography
bull Hot Embossing
bull Injection Moulding
bull Laser Fabrication
bull 3D-printing
Polymer classes
Plastic materials that can be formed into shapes
Thermoplastic materials that can be shaped more than once
Thermosetting plastic material that can only be shaped once
Elastomer material that is elastic in some way If a moderate amount of deforming force is added the elastomer will return to its original shape Useful for fibers
Properties of Polymers
bull Chain length
bull Structure orientation of chains
bull Identity of side groups
bull Degree of cross‐linking
ndash Cross linking with covalent bonds formed
between chains make the polymer stiffer
more crystalline
Thermoplastics
Melting (Tm)
Rubbery flow
OSTE(+)
Saharil F et al microTAS 2012Carlborg et al Lab on a chip 2011
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Polymer Micromechanics
bull Thin Film Litography
bull Hot Embossing
bull Injection Moulding
bull Laser Fabrication
bull 3D-printing
Polymer classes
Plastic materials that can be formed into shapes
Thermoplastic materials that can be shaped more than once
Thermosetting plastic material that can only be shaped once
Elastomer material that is elastic in some way If a moderate amount of deforming force is added the elastomer will return to its original shape Useful for fibers
Properties of Polymers
bull Chain length
bull Structure orientation of chains
bull Identity of side groups
bull Degree of cross‐linking
ndash Cross linking with covalent bonds formed
between chains make the polymer stiffer
more crystalline
Thermoplastics
Melting (Tm)
Rubbery flow
OSTE(+)
Saharil F et al microTAS 2012Carlborg et al Lab on a chip 2011
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Polymer classes
Plastic materials that can be formed into shapes
Thermoplastic materials that can be shaped more than once
Thermosetting plastic material that can only be shaped once
Elastomer material that is elastic in some way If a moderate amount of deforming force is added the elastomer will return to its original shape Useful for fibers
Properties of Polymers
bull Chain length
bull Structure orientation of chains
bull Identity of side groups
bull Degree of cross‐linking
ndash Cross linking with covalent bonds formed
between chains make the polymer stiffer
more crystalline
Thermoplastics
Melting (Tm)
Rubbery flow
OSTE(+)
Saharil F et al microTAS 2012Carlborg et al Lab on a chip 2011
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Properties of Polymers
bull Chain length
bull Structure orientation of chains
bull Identity of side groups
bull Degree of cross‐linking
ndash Cross linking with covalent bonds formed
between chains make the polymer stiffer
more crystalline
Thermoplastics
Melting (Tm)
Rubbery flow
OSTE(+)
Saharil F et al microTAS 2012Carlborg et al Lab on a chip 2011
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Thermoplastics
Melting (Tm)
Rubbery flow
OSTE(+)
Saharil F et al microTAS 2012Carlborg et al Lab on a chip 2011
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
OSTE(+)
Saharil F et al microTAS 2012Carlborg et al Lab on a chip 2011
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Particle doped polymers
bull Magnetic particles
bull Silver
bull Carbon graphene
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Hot Embossing
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Nano Imprint Litography (NIL)
Thin Films
Higher Temperatures
Curable Polymers
Limit in aspect ratio rather than linewidth
Very high resolution
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Injection Moulding
High throughput massfabrication
Expensive initial cost
Limited resolution (10 microm)
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
3D printing
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Stereolitography
bull Polymerisation by
multi photon
absorption
bull High energy density
achieved by fs-
pulses
bull Resolution down to
120nm
bull Completely arbitrary
3D -structures
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Microfluidic filters
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Cell Gym
Adv Mater 23 (2011)
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Microrobots
Adv Materials 24 2012
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Laser Ablation
bull Evaporation
ndash Long wavelength (~1microm)
ndash Gaussian profile
ndash Condensation rdquobumpsrdquo
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Laser Ablation
bull Ionisation
ndash Short wavelength (200 ndash 300 nm)
ndash High power bursts
ndash Smaller spot size (5 microm)
ndash High aspect ratio
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Materials
bull Metals
bull Polymers
bull Semiconductors
bull Glass
bull Ceramics
bull Crystalline materials
bull Delicate materials
bull Flammablesexplosives
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Cutting
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Drilling
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Structuring in 25 D
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Packaging
bull MEMS Packaging Issues
bull MEMS Packaging Approaches
bull Electrical connections
bull Sealing
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Recommended Literature
Handbook of silicon based MEMS
Materials amp technologies
Author Lindroos Veikko
Available as eBook on
httpwwwlubluseensearchlubsearchhtml
Part V
Encapsulation of MEMS Components
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Packaging
bull One of least explored MEMS components
bull Litterature is scarce
bull No unique and generally applicable packaging method for
MEMS
bull Each device works in a special environment
bull Each device has unique operational specs
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Design Issues in MEMS
packaging
bull Up to and exceeding 80 of total cost
bull Sensors need direct access to the environment
bull Package must be specifically designed for device
bull Reliability
bull Media compatibility
bull Modularity
bull Small quantities
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Example Accelerometerbull Key Issues
- Free standing microstructures
- Temperature sensitive microelectronics
- Hermetic sealing
- Alignment
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Example Pressure Sensor
Key Issues
ndash Exposure to external pressure
ndash Housing for harsh environment
ndash Interface coating
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Example Microfluidic DeviceKey Issues
ndash Micro-to-Macro interconnections
ndash Good sealing
ndash Temperature sensitive materials
ndash Optical access
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Packaging serves
two main functions
bull Protection from environment
ndash Electrical isolation from electrolytes and moisture
ndash Mechanical protection to ensure structural integrity
ndash Optical and thermal protection to prevent undesired effects
on performance
ndash Chemical isolation from harsh chemical environment
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Packaging serves
two main functions
bull Protection from device
ndash Material selection to eliminate or reduce host response
ndash Device operation to avoid toxic products
ndash Device sterilization
ndash Size and contacts
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Major Issues in MEMS
packaging
bull Release and stiction
bull Die handling and dicing
bull Stress
bull Outgassing
bull Testing
bull Electrical contacts
bull Encaptulation Hermetic seals
bull Integration
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Die Packaging Operations
bull Die separation (dicing)
bull Die pick
bull Die attach (a)
bull Inspection
bull Wire Bonding (b)
bull Preseal inspection
bull Packaging and Sealing (c)
bull Plating
bull Lead trim
bull Final Tests
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Packaging levels
bull Wafer
bull Die
bull Device
bull System
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Wafer Level Packaging
bull To adopt IC packaging processes
as much as possible
bull Stay in Batch process as long as
possible
bull Includes both interconnections
and Encapsulations
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Electrical ContactsWire bonding
bull Wire bonding
ndash Most common method
ndash Uses variety of metals
depending on bondpad
Ball bond Wedge bond
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Electrical ContactsWire bonding
Wedge bonding
ndash Aluminium or Gold wire
ndash Aluminium is ultrasonically bonded at room temperature
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Electrical ContactsWire bonding
Ball bonding
ndash Gold or Copper (Need inert atmosphere)
ndash Ball is formed with high voltage arc or hydrogen torch
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Electrical Contactsbull Flip chips
ndash Solder bumps used to attach flipped chip
ndash Quick universal connection
ndash Allows individual chip optimization
ndash Connect dissimilar materials
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Anisotropic Conductive Film
bull Polyester film with 10microm Particles of Gold coated polymer
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Sealing Methods
bull Hermetic
ndash Soldering Brazing Welding (Metals)
ndash Anodic bonding Glass frit (Glass)
ndash Wafer bonding (Silicon)
bull Nonhermetic
ndash Epoxy molding
ndash Blob top (polymers)
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Sealing Methods
Issues
bull Thermal expansion
bull Permeability
bull Surface Roughness
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Package Encapsulation
bull Protection from corrosion mechanical damage
bull Moisture is one of the major sources of corrosion
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Metal sealing methods
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Soldering and Brazing
bull Soldering
ndash Tin-Lead solder (indium and
silver are sometimes added)
ndash Tin-Lead oxidizes easily and
should be stored in nitrogen
bull Brazing
ndash Eutectic Au-Sn (8020) at 280oC
ndash 350oC for stronger more
corrosion-resistant seal and the
use of flux can be avoided
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Eutectic Bondingbull Formed by heating two
materials (Au and Si)
so they diffuse
together
bull The resulting alloy
composition melts at a
lower temperature than
the base materials
(97Au - 3Si eutectic
melts at 363degC)
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Eutectic Bonding
bull Benefits
bull Good thermal conductivity
bull Electrically conducting
bull Good fatiguecreep
resistance
bull Low contamination
bull High processoperating
temperature capability
bull Limitations bull High stresses on Si chip due to
CTE mismatch on larger dies
bull Relatively high processing
temperatures
bull Die back metallisation may be
required
bull Rework is difficult
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Metal sealing methods
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Glass Sealing
bull Hermetic glass-to-metal seals or glass-ceramic seal
bull Chemical inertness oxidation resistance electrical
insulation impermeability to moisture and other gasses
wide choice of thermal characteristics
bull Soft glass sealing are made by lead-zinc-borate glasses
below 420oC -gtlow water content good chemical
durability thermal expansion closely matched to that of
the ceramic
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Glass Sealing
Disadvantages
bull low strength and brittleness
bull Water is absorbed on glass network and may get
released into the sealed cavity
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Anodic bondning
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Anodic Bonding
bull Sodium-rich glass (Pyrex)
bull Operation temperature is well below the melting
temperature of glass
bull Surface roughness lt 1 microm
bull Native oxide on Si must be thinner than 02 microm
bull Bonding temperature below 500oC or the
thermal properties of materials begin to deviate
seriously
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Glass Frit Bonding
bull Low melting point glass (lead-glass 430C)
bull Screen printed as grained glass paste
bull Burn-out (melting to real glass)
bull Bonding (Melting)
bull Excellent Hermetic sealing to most materials
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Silicon Fusion Bondingbull Clean surface roughness lt 4 nm
bull Activated (Hydrated) in warm sulfuric acid
bull Weak Hydrogen bond
bull Dehydration in 1000oC
bull Forms stable
silicondioxide bond
bull Possible to do
hydrophobic bond
with weak H-F binding
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Low temperature Si bonding
bull Plasma Activation Based Low-
Temperature Bonding
bull UHV Low-Temperature Hydrophobic
Bonding
bull Direct Bonding of CVD Oxides
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Wafer Bonding Processes
bull Anodic Bonding
ndash Temperature ~450oC voltage ~1000 volts
ndash Silicon (metal) to glass
bull Glass Frit Bonding
ndash Temperature ~450oC voltage
ndash Silicon (metal) to glass
bull Fusion Bonding
ndash Temperature ~1000oC
ndash Silicon to silicon (glass oxide)
bull Eutectic Bonding
ndash Silicon to metal (silicon-to-gold ~363oC)
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
LPCVD encapsulation
(a) Standard surface
micromachining
process
(b) Additional thick PSG
(phosphosilicate glass)
deposition to define
encapsulation regions
(c) Additional thin PSG
deposition to define
etch channels
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
LPCVD encapsulation
(d) Nitride shell deposition
etch hole definition
(e) Removal of all sacrificial
PSG inside the shell
supercritical CO2 drying
global LPCVD sealing
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
CVDChemical Vapor Deposition
bull Chemical reaction in vapor phase forms a solid film
bull Pressure and temperature dependent
bull Activation energy (heat radiation plasma)
Polysilicon Nitrides Oxides Semiconductors (III - V)
Metals Polymers Diamond
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
CVDChemical Vapor Deposition
Critical deposition temperature of niobium as a function of NbCl5 initial pressure
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
CVDChemical Vapor Deposition
bull Atmospheric-pressure CVD (APCVD)
bull Low-pressure CVD (LPCVD)
bull Plasma-enhanced CVD (PECVD)
bull Photo-enhanced CVD (PHCVD)
bull Laser-induced CVD (PCVD)
bull Metalorganic CVD (MOCVD)
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Polymer Sealing
bull Advantages
ndash Low bonding temperature
ndash No metal ions
ndash Elastic property of polymer can reduce bonding stress
bull Disadvantages
ndash Not a good material for hermetic sealing
ndash High vapor pressure
ndash Poor mechanical properties
bull Examples
ndash Silicone (Blob top)
ndash UV-curable encapsulant resins
ndash Thick ultraviolet photoresists such as polyimides AZ-4000
and SU-8
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Thermal bonding of polymers
The substrates are heated above Tg and pressed together
Melting (Tm)
Rubbery flow
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Laser bonding of polymers
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Other bonding methods
bull UV Curable Materials
bull Photoresists
bull Adhesives (Glues Silicones)
bull Waxes
bull Chemical Bonding
bull Hydrophilic bond
Adhesive application on
structured surfaces
Adhesive application on
structured surfaces
