A Novel NanoCopper-Based Advanced Packaging Material

Dr. Alfred A. Zinn

Kuprion Inc.

alfred.zinn@kuprioninc.com

Core Team: Dr. Randall Stoltenberg, Jerome Chang, Yenling Tseng, Shannon Clark

Lockheed Martin Space Systems Company Advanced Technology Center

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Flowable, nanoCopper “metal-adhesive”

and printable ink – pressure-less

sintering as low as 200C forms solid

metal with high electrical and thermal

conductivity.

• Large-scale manufacture

• Product formulation

• System application & assembly

• Many products / markets

Scaled-up productionnanoCu paste

Solder-free electronics

HIGH PERFORMANCE, HIGH RELIABILITY SOLDER-FREE

ELECTRONICS

NanoCopper Metal Adhesive

Thermal interface

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Electronic Solder-like

Pastes

3D Printable

Inks

Emulsions/ Coatings

High-Reliability Electronics & Packaging

1 kgPilotplant

PhotovoltaicsFlexible / Printed Electronics (e.g phased array antennas)

Flat Panel Displays /Touchscreens

Thermal Interface Applications3D Electronics

Packaging

Low Temp.Cu / Al Brazing

Courtesy NASA

Co

urte

sy NA

SA

CuantumFuse™ Materials PlatformAddresses Many Applications & Markets

CUANTUMFUSETM COMBINES THE BENEFITS OF COPPER (PERFORMANCE, COST)WITH INDUSTRY-COMPATIBLE LOW-TEMPERATURE PROCESSING

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Demonstrate Scaleability for Cost Reduction

• Industrial scale production

– Economy of scale = minimizes materials & labor cost

– Commodity material requires competitive pricing

• Enabled by single “pot” process:

– Mix precursor and surfactants

– Add reducing agent

– Isolate powder

• Setting up & qualifying supply chain

– Yield increased to over 1 kg per batch

100 L PILOT PROCESS >1 KG NANOCOPPER

100 L reactor>1 kg / batch

ATC pilot plant

The Future:

IndustrialScale

(>100 kgper batch)

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2015-2016 Process Improvements

• Raw nanoCopper Cost Reduction

– Yield approaching 95%

• Process Chemistry Improvements

– Replace original solvent due to phase-out (REACH)

• Improved process characteristics (no foaming)

• Manufacturing Process Scale-Up

– Cost reduction through further scale-up and process stream-lining

• >1 kg batches

YIELD APPROCHING 95%

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Fuses to form solidcopper slugs

Hard, dense, metallic luster, behaves like Cu

Agglomerated raw nanoCu powder

NanoCopper Morphology (TEM / SEM)

PRESSURE-LESS FUSION TO SOLID COPPER

Fusion

Raw nanoCopper paste

Fused state: crystalline copper grains

20 nm20 nm

Energy (keV)

Cou

nts

50

3000

2000

1000

0

C

Cu

Cu

CuCu

Au

O

C & Au are from TEM Grid

Agglomerated Raw Powder

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• Bonds well to low activity bulk copper surface

• Widespread cohesive ductile failure

– Responsible for high strength = true metal bond

• Average range around 6000 psi

– Equals current space qualified solder (4-8ksi)

EQUALS STRENGTH OF SPACE QUALIFIED SOLDER

Fracture Surface Analysis

Cohesive ductile failure

Effective bonding to bulk Cu

Extensive shear deformation

Stress – Strain Curve

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LED Bonding Application• Over 130 formulations evaluated

– Repeatable dispensing of less than 0.1 mg

• Improved Rheology

– Can readily dispense >4g/mL dense paste

• using standard solder dispensing equipment

– Paste is stable, does not “cream”

• Paste density can now be controlled

– Can dial-in to over 5 g/mL

• Over 90% Cu by weight!

DENSITY > 3.7 g/mL, > 90% BY WEIGHT CU

Assembled Emitter

Dispensed nCu

After die placement

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Cross-Section and Porosity• Very thin bond layer

– 2-10 micron

– High heat transfer rate

• Conforms well to rough surface

• Low porosity

• X-ray analysis comparison

NO LARGE VOIDS – HIGHLY UNIFORM

No voidsPotential for long life

Commercial AuSn solder

Multiple large voids

– Chance of early failure due to burn-out

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MMIC onENiPG/Metgraf

SIGNIFICANT IMPROVEMENTS IN SHEAR STRENGTH AND REPRODUCIBILITY

LED Shear Test ResultsComparison with AuSn

Mil-spec

• LEDs as test vehicles

• 5 LEDs per run

• Shear test as high as 9 kg

– Mil-standard for 1 mm2 is ~ 600g

• Starting to test larger dies– 2 x 4 mm MMICs

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Shelve-Life Investigation

• One large batch split into 12

samples

• Periodic testing and retesting

over 8 months

• Doubled shear strength over

first 4 months

• After 7 months start to see drop

off in strength

FOUND 7 MONTH SHELF-LIFE

Test vehiculelayout

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SMT Bonding

• Good bonding to Cu, Ag, Au,

ENIG, Sn / SAC

– In some cases over 80MPa

– Average around 50 MPa

– Voltage regulators

– BGA and QFP packages

– 26 pin through-hole connector

Broken ResistorContact ripped off

BGA (208)

68 pin QFP

26-pin through-hole connector

5-lead voltage regulators

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Printing Applications

• Initial demonstration of:

– As narrow as 25 micron

– 250 nm to 2 micron thick

– Six passes on top of each other

– Bumps / pillars >60 micron tall

(10 x 10 arrays)

• Applications in 3D printing &

additive manufacturing

– Potential for injection molding

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Overall Materials Advantages

• Special features:

– Processing temperature as low as 200C

– Drop-in replacement for solder

– Good adhesion to Cu, Ag, Sn*, SAC*, ENIG

• Up to 10x higher thermal / electr. conductivity compared to solder once fully optimized

• Tin-whisker-free

• No Cu dissolution or pad weakening / failure

• No brittle IMC formation / no gold embrittlement

ENABLES RELIABLE ALL-COPPER SYSTEMS

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