An innovative process to fabricate interphase-free

copper / diamond composite films

Thomas Guillemet 1, 2 *, Jean-Marc Heintz 1, Namas Chandra 3,

Yongfeng Lu 2 and Jean François Silvain 1Yongfeng Lu 2 and Jean-François Silvain 1

1 Institute of Condensed Matter Chemistry of Bordeaux, CNRS, Pessac, France2 Department of Electrical Engineering, 3 Department of Mechanical and Materials

Engineering, University of Nebraska-Lincoln, Lincoln, NE, USA

www.icmcb-bordeaux.cnrs.fr / * thomas.guillemet@gmail.com 1

Contents

1. Background & Motivations

2. Processing

3. Characterization and Results

4. Conclusions and Prospective

5. Acknowledgements

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Contents

1. Background & Motivations

2. Processing

3. Characterization and Results

4. Conclusions and Prospective

5. Acknowledgements

3

1. Background – Copper / diamond composites

Diamond: high thermal conductivity, low thermal expansion

Copper: high thermal conductivity, ductility

Thermal management applications

Raw diamond particleRaw diamond particle

Various processes:

High Pressure / High Temperature

Infiltration Cr-coated diamond particleCr-coated diamond particle

Permanent issue: low Cu C chemical affinity

Spark Plasma Sintering

Permanent issue: low Cu-C chemical affinity

Current solution: carbide forming additives: B, Cr

HHowever:

K. Chu et al., Journal of Alloys and Compounds 490 (2010), 453-458

Carbide interphases degrade the thermal performances

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1. Motivations

What? Diamond dispersed copper matrix composite films

with high thermal performances

and no carbide interphaseRaw diamond particleRaw diamond particle

How? Tape casting of Cu/D filmsHow? Tape casting of Cu/D films

Cu coated diamond particleCu coated diamond particleCopper coating of diamond particles Cu-coated diamond particleCu-coated diamond particle

Vacuum hot pressing

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1. Motivations

Why? Thermal management of power electronic modules

Silicon chips SnAgCu Solder joints

Copper films

Small CTESmall CTE

Large CTELarge CTE

Copper heat-sink Alumina substrate

Large CTELarge CTE

Trends: Packing density

Power / Heat flux density

Demand for efficient cooling materials at minimum cost

6Copper-Diamond films as heat-spreading layers in electronic packages

Contents

1. Background & Motivations

2. Processing

3. Characterization and Results

4. Conclusions and Prospective

5. Acknowledgements

7

2. Processing – Flowchart

Formulation Tape casting and drying Shaping

Hot pressing

DebindingReduction

400°C, 2h, under air400°C, 2h, under air400°C, 1h, under Ar/H2400°C, 1h, under Ar/H2650°C, 50 MPa, 30 min650°C, 50 MPa, 30 min8

2. Processing – Formulation

Chemical Role

MatrixMatrixDendritic copper powderDendritic copper powder

ReinforcementsReinforcementsMBD6 50 µm diamond powder

MBD6 50 µm diamond powder

SolventSolvent

pp

Ethanol / 2-butanone (60/40)

Ethanol / 2-butanone (60/40)

Dispersant + Functionalization agent

Dispersant + Functionalization agentPhosphate EsterPhosphate Ester

(60/40)(60/40)

PMMAPMMA

DiButyl PhtalateDiButyl Phtalate

BinderBinder

PlasticizerPlasticizerDiButyl PhtalateDiButyl Phtalate PlasticizerPlasticizer

Mixing 15h at 20 rpm9

2. Processing – Tape casting

Doctor blade

Motorized guide rail

Doctor blade Slurry

Silicon film SupportTape casting direction

Silicon film Support

Viscosity: 1 Pa sViscosity: 1 Pa.s

Doctor blade speed: 2 cm.s-1

G t thi k [300 1 5 ]Green tape thickness: [300 µm – 1.5 mm]

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2. Processing – Tape casting

Organics Diamond

Thickness controlGood surface finishL t

Net shapingEasy handlingL l bilit

Copper matrix

Low cost Large scale capability

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2. Processing – Debinding

2 hours / 400°C / under air: organics burnout

CuO nanowires growthCopper matrix oxidation

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2. Processing – Reduction

1 hour / 400°C / under Ar/H2: copper matrix reduction

Cu particlesCopper particles deposition onto diamond powders through phosphorus chemical bonds: C-O-P-O-Cu

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2. Processing – Copper / Carbon interface

Reduction step Hot pressing stepOxidation step

CuCuO

CuCuCuCuOCuO

Carbon

CarbonCarbon

Cu|

Cu|

CuP |P|O|

Cu|

P-O|C

P|O|C C CC

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2. Processing – Vacuum hot pressing

30 minutes / 650°C / 50 MPa30 minutes / 650 C / 50 MPaFast and low-cost sintering techniqueMultilayered Cu/D samples for thermal measurements purposes (4 mm thick)

2 cm

Cu / 20 vol.% DCu / 20 vol.% D

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Contents

1. Background & Motivations

2. Processing

3. Characterization and Results

4. Conclusions and Prospective

5. Acknowledgements

16

3. Characterization and Results – Relative density

The Cu coating effectively actsas interfacial chemical bonding agent

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3. Characterization and Results – Thermal conductivity

The Cu coating enablesefficient interfacial heat transfer

λ = 470 W.m-1.K-1 with 40 vol.% diamondHigher conductivity is expected from single tape samplesHigher conductivity is expected from single tape samples

λ = 600 W.m-1.K-1 with 40 vol.% diamond using direct PM processing

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3. Characterization and Results – Thermal expansion coefficient

The Cu coating enablesefficient thermal expansion load transfer

12 × 10 6 °C 1 ith 40 l % di dα = 12 × 10-6 °C-1 with 40 vol.% diamond

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Contents

1. Background & Motivations

2. Processing

3. Characterization and Results

4. Conclusions and Prospective

5. Acknowledgements

20

4. Conclusions

Advantageous tape casting process

Innovative and low-cost Cu coating process of diamond particlesof diamond particles

Dense Cu/D composite films with high thermal performances and no interphase

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4. Conclusions – Integration to power modules

As single thin filmAs single thin film

As multilayered system

As complementAs complement to Cu and/or Cu/CF for composite heat sink

Cu/DCu/D Cu/CFCu/CF

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4. Prospectives Influence of…

Diamond particles size? 40 µm40 µm 80 µm80 µm

Cu particles size/coverage?Copper coating tunability

(t, T)1(t, T)1 (t, T)2(t, T)2

Single tape systems?Single tape systems?

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Contents

1. Background & Motivations

2. Processing

3. Characterization and Results

4. Conclusions and Prospective

5. Acknowledgements

24

5. Aknowledgements

The authors are grateful to the Région Aquitaine (France) and the

Office of Naval Research (USA) for their financial support.

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