Additive Manufacturing for Microelectronics Packaging ... · PDF fileAdditive Manufacturing for Microelectronics Packaging Applications ... Role of the NDML ... Need for Additive Manufacturing

Additive Manufacturing for Microelectronics Packaging Applications

Michael CullinanAssistant Professor

Department of Mechanical EngineeringUniversity of Texas at Austin

Overview of the NDML • Nanoscale Design and Manufacturing

Laboratory• Director: Professor Michael Cullinan

• 8 current graduate students

• Will host 4 undergraduate, 3 high school students and 1 high school teacher as researchers this summer

• Numerous collaborations with local industry and national labs

• Member of the NSF NanosystemsEngineering Research Center (NERC) for Nanomanufacturing Systems for Mobile Computing and Mobile Energy Technologies (NASCENT) at UT-Austin

5/11/2016 Nanoscale Design and Manufacturing Laboratory 2

Role of the NDML

5/11/2016 3

•Research Challenges• Need for more integrated manufacturing approach

• Need increased flexibility in types of devices produced and materials used

• Need improved process metrology and in-line inspection systems

Nanostructure and

Nanomaterial

Manufacturing

Nanosystem and

Nanodevice

ManufacturingNDML

Demand for nanoscale

sensors and devices

Manufacturable,

Engineered

Device

The Nanomanufacturing Process:

From Physical Properties to End Product

Marketable

Product

Prototype Test

Structure

Nanoscale

Physical

Phenomena1) Improved Methods for

Integrating Nanomaterials/

Mechanisms into Micro/

Macro Devices

Focus Areas for

Nanomanufacturing

Research:

2) New Design for

Manufacturability Rules/

Procedures for Designing

Nanoscale Devices

3) Novel High-Rate, Low

Cost Nanomanufacturing

Equipment and Processes

Nanoscale Design and Manufacturing Laboratory

• Development of Novel Nanomanufacturing Processes and Equipment• Micro/Nanoscale Additive Manufacturing

• Project: Microscale Selective Laser Sintering

• Assembly of Micro/Nanoscale Components• Project: Assembly of Micron-Scale Feedstock at Megahertz Rates• Project: Exfoliation of Thin-Film Silicon Devices for Wearable Electronics

• Metrology Systems for Nanomanufacturing• In-line Wafer-scale and Roll-to-Roll Inspection

• Project: In-Line Tip-Based Metrology Systems with Multiple Scanning Tips

• In-situ Process Metrology• Project: Tip-Based Metrology Systems for Quantifying the CVD Growth Processes

• Scalable Production of Nanoscale Systems• Design of Nanoscale Systems for Compatibility with Current Manufacturing Systems

• Project: Graphene-based Tunable NEMS Resonators

• Development of Wafer-scale and Roll-to-Roll Nanomanufacturing Processes• Project: Wafer-Scale Manufacturing of Graphene-Based Devices

Major Projects in the NDML

5/11/2016 4Nanoscale Design and Manufacturing Laboratory

Micro/Nanoscale Additive Manufacturing• Opportunities

• Additive manufacturing of microscale metal features will allow for precise control 3D electronic interconnect structures

• Challenges• Submicron layer heights

• Need nanoscale powders

• Precise control of heat effected zone

• Use ultrafast lasers

• Microscale spot sizes• Use micromirror arrays and 10x

focusing objectives


Need for Additive Manufacturing to Enable 3D Packaging

• Conventional PCB based interconnect technologies such as wire bonding and flip chip assembly have reached their design/process capabilities limit

• Would like to get rid of the PCB substrates and assemble all devices directly on the silicon wafers.


• The benefits offered by direct integration include:• Integration all of the key components into a single

package including the processor, memory, voltage regulation, shielding, etc.

• System routing/optimization done within the package

• High speed interfaces possible

• Simplify board design and shorten time to market for the customer

Common Additive Manufacturing Systems• Vat photopolymerization (i.e. Stereolithography)

• Light used to cure polymer resin layer-by-layer

• Polymers only and requires support structures

• Material Jetting• Uses a printer head to jet layer of material down

onto surface and build up 3D structure

• Limited materials and requires support structures

• Binder Jetting• Print binder onto powder bed, spread new layer of

powder, and repeat process to build up 3D structure

• Fabrication of conductive parts requires high temperature anneal step to remove binder material


Schematic of Stereolithography

Common Additive Manufacturing Systems Continued• Material Extrusion (i.e. Fused

Deposition Modeling, Robocasting)• Thermoplastic polymer or ink injected

through nozzles into a platform. The nozzles trace the cross-section of the pattern in layers.

• Generally limited to polymer materials and inks

• Powder Bed Fusion (i.e. Selective Laser Sintering, Electron Beam Melting)• Laser or electron beam used to fuse

particles in a powder bed together layer-by-layer to form 3D part

• Can be used to make 3D structures in metals


Schematic of Fused Deposition Modeling

How Macroscale SLS Systems Work• SLS processing steps

• Roller used to spread a layer of powder onto powder bed

• Laser scans surface of powder bed to fuse together powders in desired cross-section

• Platform is lowered and a new layer of powder is spread onto the power bed

• Process is repeated until 3D part formed

• Challenges moving to microscale• Powders typically 10’s of μm in diameter

• Laser spot size typically on the order of 100’s of μm

• Large heat effected zones from lasers


Key Aspects of μ-SLS System• Use of nanoparticles to generate truly

micron sized features

• Use of ultrafast lasers to minimize the heat affected zone

• Use micromirror arrays focused to ~1μm spots to increase throughput

• Properties like specific heat capacity, sintering temperature and melting point are size dependent• Thus, need for an exhaustive study of

physical and thermal properties to• model and simulate the sintering process• estimate the power requirements for

sintering


High Throughput Laser Sintering System

μ-SLS Process Schematic


Z axis Positioning of Slot Die

Coater

Slot Die Coater

Heated Chip Holder

Powder Bed

X-Y Nanopositioner

Part

Photodetector and IR CameraFocusing

Objectives

Computer Control System

Nanosecond Laser

Objective Lens/ Fiber Coupler

Micro-Mirror Array

Focusing Objective

Silicon Chip

Powder Bed

Laser Spot

Objective Lens

Excitation Light

Heated Chip Holder

Air Bearing Linear Guide Rails

Part

X-Y Nanopositioner

Silicon Chip

Dispensing pump

Long Range Positioner Scan Direction

Optical Table

Focusing of Objective

Lens

Vacuum Chamber

Silicon Chip

Linear Actuator

Model of μ-SLS Optical Subsystem System• Tube lens and focusing

objective used to focus output from micromirrors

• XY nanopositioning stage used to position chuck below objective lens

• Linear air bearings and servomotor used to move stage between optical and slot die coating stations


Light Engine for Micromirror Array

Tube Lens

10x Focusing Objective

Heated Chuck

XY Positioning Stage

Voice Coil Actuator

Linear Air Bearings

Linear Servo Motor

• To improve throughput, TI’s DLP 5500 micromirror array was used as it is• Compact and >2 million independent micromirrors can be illuminated

• 10x microscope objective used to focus laser down to 1 μm spot size

• Spectra-Physics Talon 532nm – 20W laser with 25 ns pulse width

Ti Micro-Mirror Array

10x Focusing

Optics

Coupler from Fiber Laser to Micro-Mirror

Array

Optical System


μ-SLS System Throughput• Pulse energy to sinter a spot size of

diameter, D, and layer thickness, h, in npulses,

• With 1 micron spot size• Areal scan speed- 293 mm2/s

• With 1 micron layer thickness• Volumetric throughput – 1 cm3/hr

• Throughput can be increased by increasing spot size or layer thickness

Based on pulse energy calculation, Talon-532nm-20W laser was chosen

No. of mirrors along length 1920

No. of mirrors along width 1080

Mirror pitch 7.6 μm

Max laser power used 18 Watts

Repetition 100 kHz

Laser Pulse Width 25 ns

Duty Cycle 0.25%


Nanopositioning System• XY positioning with nm level precision

• Voice coil actuators used to move stage

• Flexure mechanisms used to guide motion

• Interferometry probes used to measure position


Double Parallelogram Flexure Mechanism

Voice Coil Actuators

Heated Wafer Chuck

XY Flexure Stage

Ground Points

Challenges with Nanoscale Powders:Agglomeration of Copper Nanopowders

5/11/2016 16

40nm Average

Diameter Particles APS-100nm

Shape

Spherical Irregular

Agglomerates


Nanoparticle Spreading System• Potential Solution – Slot die coating of nanoparticle ink


Nanoparticle Inks• Spread nanoparticle inks instead of powders

• 10-200nm diameter particles, viscosity 10-20 cP, 50% weight loading

• More uniform layer thickness, fewer agglomerates

Nanoparticles Spread on Surface 10-200nm Diameter Individual Particles


Nanoparticle Systems Tested• In order to understand nanoparticle sintering we have tested numerous

different Cu powers and inks


S.No SampleAverage Particle

Size (nm)

Production

Method

Coating

layer

140nm Cu NPs (US Research

Nanomaterials,Inc) 40

Electric Explosion

of Wire (EEW)None

2 100nm Cu NPs (USRN,Inc) 100Electric Explosion

of WireNone

325nm Carbon coated Cu NPs

(USRN, Inc)25

Laser Ablation

SynthesisCarbon

425nm Passivated Cu NPs

(MKNano)25

Laser Ablation

Synthesis

Copper

oxide

5100nm Cu ink (Applied

Nanotech, Inc.)10-200

Chemical

SynthesisUnknown

690nm Cu ink for glass substrate

(Intrinsiq Materials, Inc)90

Chemical

SynthesisPVP

790nm Cu ink for polyimide

substrate(Intrinsiq Materials, Inc)90

Chemical

SynthesisPVP

Heat Flow Rate/Weight of the 40nm Cu Powder Sample

• Exothermic peak at 229°C, Melting peak at 1069°C

• 1.95% weight loss of the sample

• Organics removed during sintering process

5/11/2016 20

Exothermic Peak (could be due to re-crystallizaton or surface sintering)

Melting Peak


Heat Flow Rate and Mass of the Re-heated 40nm sample• No re-crystallization/surface sintering peak

• Weight change of 0.07%

• This suggests that • the amorphous metal particles have fully crystallized

• organics have been completely vaporized from the sample


Sintering of 40nm Cu Sample• 40 nm Cu sample heated

to 260°C where recrystallization peak observed in previous experiments

• Necking between particles observed in heated samples

• Sintering rate increases as temperature increases

5/11/2016 22

USRN-40nm sample (room temperature) USRN-40nm (after being heated to 260 C)


Cu Sintered Part• Powder converted to a solid pellet during heating

• Volumetric shrinkage

• Organics completely removed from sample

SEM Images of Fully Sintered 40 nm Particles


NP Ink Sintering• Dynamic Scanning Calorimetry measurements of nanoparticle inks

• Sharp peaks in 90 nm inks show removal of organics

• Peak at 320 °C in 100 nm ink shows onset of particle necking

• Increase in heat flow for 90 nm ink at 425 °C indicates start of sintering


Removal of Organic Solvents Onset of Sintering

100 nm Cu Ink with No Coating• Sintering starts around 320 °C for uncoated NP ink samples


Room Temperature After Heating to 350 °C

Composition of Uncoated Ink vs Temperature• Organics quickly decompose during heating for uncoated ink

• Samples start to oxidize at high temperature


22.3

0.0

50.5

27.2

65.4

0.0

14.220.4

67.0

0.0

10.4

22.7

56.6

6.310.3

26.7

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

Metallic Cu Cu satellites Carbon Oxygen

WEI

GH

T %

Room T 300°C 350°C 1085°C

X-Ray Photoelectron Spectroscopy Results for Uncoated Inks

90nm Cu Ink with PVP coating• Sintering for PVP coated ink starts between 400 °C and 450 °C


After Heating to 400 °C After Heating to 450 °C

Composition of PVP Coated Ink vs Temperature• Organics decompose as temperature increases above 400 °C

• Surface carbon forms at very high temperatures• Energy dispersive x-ray spectroscopy shows high carbon concentrations only present at

the surface of particle


22.8

7.8

45.8

2.7

20.9

36.2

0.0

41.4

3.4

19.0

28.3

0.0

46.3

4.1

21.3

55.2

0.0

27.0

3.1

14.8

60.1

12.3 11.6

0.1

15.817.8

8.6

63.6

1.6

8.3

68.9

0.0

24.5

1.65.0

-10.0

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

Cu Cu satellites C N O

WEI

GH

T %

Room T 150°C 200°C 350°C 450°C 1085°C EDX@1085

X-Ray Photoelectron Spectroscopy Results for PVP Coated Inks

Nanoparticle Sintering Recommendations• Composition of nanoparticle ink has a strong influence on sintering properties

• Need temperature above 400 °C to ensure removal of all organic solvents

• Want to keep temperature below melt point to prevent excess oxidation and surface carbons from forming


PVP coated ink after heating beyond melt point shows balling up Cu particles on surface

PVP coated ink after heating to 450 °C shows smooth sintered surface forming

Preliminary Laser Sintering Tests• Sintered spots with femtosecond laser

• Power – 720 μW to 3.6 mW

• Exposure time – 5 ms to 500 ms

Sintered Spots500 ms

200 ms5 ms50 ms

1.4 mW


Sintered Test Spots

Before Sintering After Sintering

• 720 μW for 50 ms -> Particles well sintered


Next Challenge: Modeling of μ-SLS Process• Goal

• To be able to model μ-SLS process accurately enough to predict the quality of parts produced

• Challenges• Heat transfer dominated by near-field

radiation not conduction or far-field radiation

• Nanoparticles are smaller than wavelength of light so must account for wave nature of light

• Agglomeration of nanoparticles in powder bed driven by van der Waals forces

Simulation of Particle Bed Generation


Modeling Approach

V. Kumar, “Simulations and Modeling of Unequal Sized Particles Sintering,” University of Utah, 2011.

Nanoparticle Sintering over Time

MFIX Simulations

μ-SLS Process Modeling Strategy

Multi-Physics Simulations and Phase Field Models

3D Finite Element Simulations

Model of Individual Nanoparticles and Particle interactions

In Situ Layer Analysis in μ-SLS

Testbed

Materials Characterization by

TEM, XRD, EBSD, Micro-CT, ect.

Model of Particle Interactions within a Single SLS Layer and

Between Layers

Full Part Simulation Model

Model of Electrical and Mechanical Properties of Part

Mechanical Testing of Parts Fabricated

in μ-SLS Testbed


Thermal Simulations of μ-SLS Testbed• Laser-Nanoparticle interactions simulated

Electric Field Phasor (Imag) (V/m)

Real Conductivity (S/m) for Loosely Packed Particles

Simulated Temperature

Profile

Courtesy of Esgee Technologies

• Nanosecond laser used• Solve Maxwell’s equations to account for wave

nature of light• Heat transfer by conduction/near-field radiation• Model phonon scattering in nanoparticles• Assumes uniform distribution of Nanoparticles


Simulations of individual nanoparticles• Cu nanoparticles simulated on 200 nm of SiO2

• Distribution of particles has large effect on local field enhancement

• Need more complex analysis of thermal heating in nanoparticle powder beds


Analysis of Local Field Enhancement of Near-field Thermal Emission

Air

Cu

SiO2

Air

CuCuOne 100 nm Cu Particle

Two 100 nm Cu Particles

Three Cu Particles of different sizes

Powder Bed Simulation• Particles randomly placed within 1 μm3

volume

• Particles randomly assigned velocity vector

• Particles allowed to interact to dissipate energy

• Particles settle due to gravity

• Week van der Waals interactions assumed

Simulation of Particle Bed Generation with 100 nm Particles in 1 μm Area with Only Gravitational Forces


Simulations of Agglomeration• Agglomeration occurs when van der Waals forces are strong (Dry Powders)

• Size of agglomerates tuned by adjusting strength of van der Waals forces

• Agglomerates can be reduces using solvents (Nanoparticle Inks)

Cluster Groups


Simulation of Agglomeration• Strong van der Waals interactions

assumed between particles and base

• No van der Waals on sides

• Particles randomly placed within 1 μm3

volume

• Particles randomly assigned velocity vector

• Particles allowed to interact to dissipate energy

• Particles settle due to gravity

Simulation of Particle Bed Generation with 100 nm Average Diameter and 10 nm Standard Deviation


Melt Model• Current model we have for macro SLS

• Updates needed for μ-SLS process• Plasmonic interactions between light and

nanoparticles need to be included

• Nanoparticles sinter before they melt• Need to include mass diffusion between

nanoparticles

• Heat transfer dominated by near field radiation


Multi-layer Simulation• Continuum thermal model to determine melt fraction from temperature

profile

• Enables prediction of part geometry from process inputs


Conclusions on μ-SLS and Future Work• Conclusions

• Nanoparticles used to increase resolution of SLS system• Nanoparticle inks used to reduce agglomeration problems

• Custom spreader system used to precisely control layer thickness• Thickness down to 100 nm achievable

• Ultrafast lasers used to control heat affected zone in powder beds

• Micromirror arrays used to increase throughput• 10x focusing objective used to reach 1 micron spot size

• Areal scan speed - 293 mm2/s

• Future work• Assembly and testing of complete μ-SLS system

• Improved computational modeling of μ-SLS process• Accurately simulate laser heating and heat transfer in powder bed

• Model sintering of nanoparticles and formation of parts


Acknowledgments• Graduate Students

• Nilabh Roy

• Anil Yuksel

• Dan Moser

• Collaborators• CS Foong

• Leo Higgins


Questions?

Documents

Additive Manufacturing for Microelectronics Packaging ... · PDF fileAdditive Manufacturing for Microelectronics Packaging Applications ... Role of the NDML ... Need for Additive Manufacturing