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1 of 23Introduction to LTCC for engineers
How to manufacture 3D circuits for microtechnique applications?
With LTCC !
Monday 4 September 2006Thick-film Technology Group, Prof. P. Ryser Laboratoire de Production Microtechnique
http://lpm.epfl.ch/ltcc
Introduction for engineers
2 of 23Introduction to LTCC for engineers
The LTCC ?
Low-Temperature, Cofired Ceramic
•Sheets of sintered ceramics (blue, white or black)
•You’re carrying it unaware (mobile phone, car ignition)
•Relatively new material (<20 yrs)
•Developed for highly integrated electronics
raw sheets of LTTC (micro-reactor)
micro-flow sensor assembled
fluidic circuit, management of valves with SMD
electronics
3 of 23Introduction to LTCC for engineers
Objectives
•Objectives of my thesisTo integrate in a circuit:- sensors (pressure, temperature, flow)- actuators (electrovalves)- electronics (SMD)by an industrially viable process.
•Objectives of this presentationTo make you discover the LTCC technologyand its multiples possibilities.
Hybrid micro-reactor in LTCC and alumina
Modular gas viscosity sensor
4 of 23Introduction to LTCC for engineers
Content
1. The principle of LTCC
2. Properties
3. Realisations at the LPM
4. Concurrent methods
5. State of the art
6. In practice
7. Conclusion
5 of 23Introduction to LTCC for engineers
1.1) The principle of LTCC
1. Raw sheets easily cut(laser, punch tool)
2. Layers individually printed(multilayer circuits )
3. Stacking of layers to geta 3D structure
4. Firing-> sintering, monolithic circuit
5. Individualisation and post-firing(assembly by soldering)
6 of 23Introduction to LTCC for engineers
1.2) Types of realisations
Circuits:
• fluidic
• electronic
• mechanical
Hybrid micro electrovalve in LTCCM. Gongora-Rubio et al., 2001
M. Gongora-Rubio et al., 1999
www.ltcc.de
7 of 23Introduction to LTCC for engineers
1.3) Acronym
The LTCC is dissociated from HTCC:
•Low- LTCC 875°C
•Temperature HTCC 1400-1600°C
•Cofired co-firing of (di)electric pastesLTCC: precious metals (Au, Ag, Pd,
Cu)HTCC: refractory metals (W, Mo,
MoMn)
•Ceramic mix of:- alumina Al2O3
- glasses SiO2 - B2O3 - CaO - MgO- organic binders
- HTTC: essentially Al2O3
8 of 23Introduction to LTCC for engineers
1.4) Processing
Raw material comes as:
•sheets or rollsthickness 50-320μm5-6 big manufacturers:DuPont, ESL, Ferro, Heraeus…
•powder: to mix oneself, proprietary LTCC (mass production like automotive, military etc.)
•Simple, yet complex process
•Incompressible times :- lamination 5-15 min- firing 2-8 hrs- post-firings 45 min each www.ltcc.de
9 of 23Introduction to LTCC for engineers
2) Physical properties
1. Chemically stable, inert to HCl, NaOH…
2. Thermically stable (>600°C)
3. Low thermal conductivity (3 W/mK)
4. High hardness (8 Mohs)
5. Very good dielectric (low losses at high frequencies, application for GHz antennas)
6. rupture=320 MPa, E=120 GPa, density=3.1
7. High reliability and hermeticity
10 of 23Introduction to LTCC for engineers
3) Realisations at the LPM
1. Flow sensor and micro-reactor
2. Gas viscosity sensor Wobbe
3. Force sensor Millinewton
4. Circuit for managing pneumatic valves
5. Hermetic case for sealing tests
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3.1) Flow-sensor and micro-reactor
1. Flow sensor- 3 layers of LTCC- principle of the hot-wire anemometer- channel 1 to 2 mm wide
2. Micro-reactor- 2 reactants- 2 flow sensors- 1 calorimeter
Microreactors and micro flowsensor (bottom)Hybrid micro-reactor
12 of 23Introduction to LTCC for engineers
3.2) Gas viscosity sensor Wobbe
Modular sensor measuring the Wobbe index:
- 1 base plate- 1 heating module- 1 membrane pressure sensor module
Application: optimisation of combustion in oil-fired boilers
Sensor with its external modules disassembled
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3.3) Force sensor Millinewton
Alumina version (200..2000 mN)
• rectangular beam soldered on base plate
• double-side serigraphy (4 R in Wheatstone bridge)
LTCC version (10..100 mN)
• Optimised T-shaped beam
• Young modulus 2.6x smaller
• Better sensitivity
• Half-bridge version(single-sided)
• Easier manufacturing
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3.4) Circuit for electrovalves
• Up to 22 layers of LTCC
• 2 levels of interconnections
• Channels 0.3..3 mm wide
• Piloting by SMD electronics
• Brass adapters
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3.5) Hermetic case for sealing tests
• Base plate in LTCC, glass lid
• Co-fired electric tracks
• Sn-Pb soldered tungsten wires
• Post-fired sealing cord
• Sn-Bi 138°C solder for the lid
• From drawing board to assembled product: 2 weeks
16 of 23Introduction to LTCC for engineers
4.1) Concurrent methods
• SLS (Selective Laser Sintering)- slow- piece by piece prototyping- more for forms than for circuits- porous
• Alumina + classical thick-films- mono-substrate (assembly by sealing)- multilayer, but sequential process- less advantageous for numerous layers- 1400°C (HTCC)
17 of 23Introduction to LTCC for engineers
4.2) Concurrent methods
• PCB- Tmax 150°C- difficult machining for fluidics- losses in high frequencies- not hermetic- cheaper for a simple electric circuit
• Alu and epoxy resin- easier processing- only for fluidics
• Silicon- clean room- heavy and complicated processes- partial concurrency because Si ~ m, LTCC ~ 0.1mm-> to use in complement
Stacked fluidic mini-PCB of Fraunhofer IZM Berlin
Pneumotech
18 of 23Introduction to LTCC for engineers
5.1) State of the art
M. Gongora-Rubio et al., 1999
J. Kita, Bayreuth, Germany, 2005Peterson, Sandia National Lab, 2005
19 of 23Introduction to LTCC for engineers
5.2) State of the art
Fraunhofer IZM Berlin
20 of 23Introduction to LTCC for engineers
6.1) Technological problems
In practice one must take into account of:
• Variations of final dimensions due to shrinkage variability (batches + inherent)
• Shrinkage different than announced by manufacturer (10..15% in X-Y, 15-40% in Z)
• Crushing of cavities when following manufacturer’s lamination recommendations
• Delamination of layers at edgeswhen reducing lamination pressureor temperature
21 of 23Introduction to LTCC for engineers
6.2) Experimental setup at the LPM
pre-conditioningdrying oven 30min-
120°C
LTCC sheetsthick. 50-320μm6”x6”
laser cutting +air blowing
stackingpin
alignment fixture
lamination uniaxial press 5min - 70°C -
200bar
removal of protection
firingair furnace
8hrs - 875°C
ready for screenprinting and post-
firings
serigraphy of pastes
on raw layers
22 of 23Introduction to LTCC for engineers
7) Conclusions
•Robust and reliable technology
•Mature for electronics; under development for fluidics
•Automatisable
•Moderate costs and investments (semi-clean room)
•Infinite possibilities of forms and combinations
•Quasi-unlimited number of layers
•Price for industrial quantities : 1€ / dm2 / layer
•Finesse of structures ~ 50 m
23 of 23Introduction to LTCC for engineers
The end
Thank you for your attention!
More information onhttp://lpm.epfl.ch/ltcc
http://personnes.epfl.ch/yannick.fournier
All images without legend are copyrighted from LPM-EPFL.
24 of 23Introduction to LTCC for engineers
Appendix – air furnace temperature profile
LTTC Oven Temperature Profile "Yannick 16"
0
100
200
300
400
500
600
700
800
900
1000
000 060 120 180 240 300 360 420
Time [min]
Te
mp
era
ture
[°C
]
burnoutdwell 450°C
100 min(LTCC is at 440°C)
sinteringdwell 895°C
30 min
sinteringramp 895°C
2.5K/min
ramp 200°C-20 K/min
for the LTCC samples to reach a peak temp of 875°C, the oven must be higher ->
ramp 450°C2.4K/min
ramp 230°Cslope 8K/min
ramp 400°C-16 K/min
ramp 660°C10 K/min
Duration [h:min]
Total time
[h:min]
Final temp [°C]
Slope [K/min]
1 Fast ramp 00:25 00:25 230 82 Ramp to 440°C 01:30 01:55 450 2.43 Burnout dwell 100 mins 01:39 03:34 450 04 Fast ramp 00:21 03:55 660 105 Sintering ramp to 875°C 01:35 05:30 895 2.56 Sintering dwell 30 mins 00:30 06:00 895 07 Natural furnace cooling 00:30 06:30 400 -16.58 Fast cooling 00:10 06:40 200 -209 Back to ambiant 00:10 06:50 70 -13
Step
25 of 23Introduction to LTCC for engineers
Appendix – comparison of properties
26 of 23Introduction to LTCC for engineers
Appendix – specs of two common pastes