OVERVIEW OF ADVANCED THERMAL MATERIALS Carl Zweben, PhD Life Fellow ASME Fellow SAMPE and ASM Associate Fellow, AIAA Advanced Thermal Materials Consultant 62 Arlington Road Devon, PA 19333-1538 Phone: 610-688-1772 E-mail: [email protected] http://sites.google.com/site/zwebenconsulting

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The information in these slides is part of a short course on composite materials that is presented publicly and in-house Contact author for information

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OUTLINE • Introduction • Semiconductors, ceramic substrates and traditional thermal materials • Advanced thermal materials • Applications • Summary and conclusions • Appendix (terminology and abbreviations)

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INTRODUCTION

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INTRODUCTION • Critical thermal management problems: – Heat dissipation – Thermal stresses cause • Warping, fracture, fatigue, solder creep • Primarily due to CTE mismatch • An issue for all cooling methods • Problems similar for – Microprocessors, power modules, RF – Diode lasers – Light-emitting diodes (LEDs) – Plasma and LCD displays – Photovoltaics – Thermoelectric coolers (TECs) Copyright Carl Zweben 2010

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INTRODUCTION (cont) • Microelectronic thermal problems well known – Xbox 360 $1 billion “Red Ring of Death” failure widely cited as thermal issue – Nvidia $150-200 million GPU thermal problem – “Burned groin blamed on laptop” (BBC 11//02) • Solder thermal fatigue limits laser pulsing • Higher process temperatures for lead-free solders – Increased thermal stresses & warping • Higher ambient temperatures – E.g. automotive under hood

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INTRODUCTION (cont) • Weight (mass) important – Portable systems – Vibration and shock loads • Volume and thickness decreasing • Cooling significant part of total cost of ownership – System – Building, data center • System cooling power increases building cooling load • Low-CTE “Thermount” PCB withdrawn from market in 2006 – No current thin-ply replacement Copyright Carl Zweben 2010

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INTRODUCTION (cont) • Traditional thermal materials inadequate – Decades old: mid 20th Century – Impose major design limitations (see later) • In response to critical needs, an increasing number of advanced materials have been developed • Many with ultrahigh-thermal-conductivity – k = 400 to 1700 W/m-K – Low CTEs – Low densities – R&D to high-volume production

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INTRODUCTION (cont) • Can now match CTEs of chips, lids, heat sinks, and PCBs – Reduces thermal stresses and warping – Possibly eliminates need for underfill – Enables use of hard solder attach • Low thermal resistance – Low-CTE solders under development • Thermally conductive PCBs provide heat path

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CTE MISMATCH CAUSES THERMAL STRESSES

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PACKAGING LEVELS

Source: USAF (modified) Copyright Carl Zweben 2010

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SEMICONDUCTORS, CERAMIC SUBSTRATES AND TRADITIONAL THERMAL MATERIALS

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SEMICONDUCTOR AND CERAMIC SUBSTRATE PROPERTIES MATERIAL Silicon GaAs GaP InP SiC Alumina (96%) AlN BeO LTCC

CTE (ppm/K) 2.5-4.1 5.8-6.9 5.9 4.5-4.8 4.2-4.9 6.0-7.1 3.5-5.7 6-9 5.8

CTE RANGE ~ 2 – 7 ppm/K Copyright Carl Zweben 2010

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TRADITIONAL THERMAL AND PACKAGING MATERIALS k CTE Specific k/SG MATERIAL (W/m-K) (ppm/K) Gravity (W/m-K) Copper 400 17 8.9 45 Aluminum 218 23 2.7 81 “Kovar” 17 5.9 8.3 2 Alloy 42 10.5 5.3 8.1 1.3 W/Cu (85/15) 167 6.5 17 10 Mo/Cu (85/15) 184 7.0 10 18 Cu-Invar-Cu* 172* 6.7* 8.4 20 Cu-Mo-Cu* 182* 6.0* 9.9 18 E-glass/epoxy 0.3* 12-24* 1.6-1.9 0.2 Epoxy 0.2 45-65 1.3 0.2 *Inplane isotropic (x,y) Copyright Carl Zweben 2010

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WHAT’S WRONG WITH TRADITIONAL THERMAL MATERIALS? • Copper and aluminum – High CTEs • Thermal stresses, warping • Require compliant polymeric and solder thermal interface materials (TIMs) – Higher thermal conductivities desirable – Copper has high density • What’s wrong with compliant polymeric TIMs? – Pump-out and dry-out for greases – High thermal resistance for most – Increasingly, the key contributor to total thermal resistance Copyright Carl Zweben 2010

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WHAT’S WRONG WITH TRADITIONAL THERMAL MATERIALS? (cont) • What’s wrong with compliant solders? – E.g. indium alloys – Process problems (voiding, poor wetting) – Poor fatigue life (low yield stress) – Creep – Intermetallics – Corrosion – Electromigration – Relatively low melting point – Cost higher than many solders DIRECT ATTACH WITH HARD SOLDERS DESIRABLE Copyright Carl Zweben 2010

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WHAT’S WRONG WITH TRADITIONAL THERMAL MATERIALS? (cont) • Low-CTE materials seriously deficient – E.g. alloy 42, Kovar, tungsten/copper, molybdenum/copper, copper-Invar-copper, etc. – Conductivities < aluminum (200 W/m-K) – High densities – High cost • CVD diamond – High thermal conductivity – Low CTE – Expensive – Thin flat plates only (i.e. CVD diamond films) Copyright Carl Zweben 2010

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ADVANCED THERMAL MATERIALS

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NEW THERMAL MANAGEMENT MATERIALS • Many advanced materials – Various stages of development – R&D to large scale production – New ones continuously emerging • Monolithic materials – Primarily carbonaceous (graphitic) • Composites – Polymer matrix – Metal matrix – Metal/metal alloys-composites – Carbon matrix (e.g. carbon/carbon) – Ceramic matrix Copyright Carl Zweben 2010

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NEW THERMAL MANAGEMENT MATERIALS (cont) • Al/SiC first, and most successful advanced thermal material – First used by speaker and colleagues at GE for electronics and optoelectronics in early 1980s – New processes developed – Millions of piece parts produced annually – Part cost dropped by orders of magnitude – Microprocessor lids now $1-5 in high volume – CVD diamond and highly-oriented pyrolytic graphite inserts increase heat spreading • “Hybrid materials” approach

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SiC-PARTICLE/ALUMINUM (Al/SiC) SUPPLIERS v/o k CTE Specific Supplier (%) (W/m-K) (ppm/K) Gravity Ametek 68 220 7.5 3.03 CPS 63 200 8.0 3.01 DWA 55 200 8.8 3.00 Denka 200 7.5 2.96 MC-21 20-45 150-180 10-16 2.7-2.9 PCC-AFT* 70 175 7 3.01 Sumitomo 150-200 8-15 2.60-2.78 TTC 165-255 4.8-16.2 2.77-3.10 *Purchased by Rogers Corporation Copyright Carl Zweben 2010

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ADVANCED MATERIALS PAYOFFS • Lower junction temperatures • Reduced thermal stresses and warpage • Simplified thermal design – Possible elimination of fans, heat pipes, TECs, liquid cooling, refrigeration • Increased reliability • Improved performance • Weight savings up to 90% • Size reductions up to 65% • Dimensional stability • Improved optical alignment

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ADVANCED MATERIALS PAYOFFS (cont) • • • • • •

Possible elimination of underfill Increased manufacturing yield Reduced electromagnetic emission Reduced power consumption Longer battery life Reduced number of devices (e.g. power modules, LEDs) • Low cost potential – Component – System – Total cost of ownership (TCO) Copyright Carl Zweben 2010

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DISADVANTAGES OF SOME ADVANCED MATERIALS • • • • • • • • • • •

Higher cost (low volumes, reinforcements) Limited service experience Low fracture toughness Possible hysteresis Ceramic materials hard to machine Some particulate materials hard to metallize Surface roughness and flatness Edge sharpness (laser diodes) Direct attach during infiltration complicates rework Galvanic corrosion potential Porosity (not hermetic)

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COMPOSITE MATERIAL REINFORCEMENTS

Continuous Fibers

Discontinuous Fibers, Whiskers

Particles

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Fabrics, Braids, etc.

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COEFFICIENT OF THERMAL EXPANSION (ppm/K)

CTE OF SILICON-CARBIDE-PARTICLE-REINFORCED ALUMINUM (Al/SiC) vs PARTICLE VOLUME FRACTION 25

Aluminum Powder Metallurgy Infiltration

20 Copper E-glass PCB

15

Beryllium

10

NEW MATERIAL

Titanium, Steel Alumina

5

Silicon

0 0

20

40

60

80

100

PARTICLE VOLUME FRACTION (%) Copyright Carl Zweben 2010

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Si, GaAs, Silica, Alumina, Beryllia, Aluminum Nitride, LTCC

1200

600 HOPG (1700)

THERMAL CONDUCTIVITY (W/mK)

THERMAL CONDUCTIVITY vs CTE FOR PACKAGING MATERIALS

500

Diamond-Particle-Reinforced Metals and Ceramics C/Cu

400

Silver

C/C

Copper SiC/Cu

300

C/Ep

C/Al Aluminum

200

Cu/W

SiC/Al (Al/SiC) Si-Al

100 Invar

Kovar

E-glass PCB

0 -5

0 5 10 15 20 25 COEFFICIENT OF THERMAL EXPANSION (ppm/K) Copyright Carl Zweben 2010

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SPECIFIC PROPERTIES • Specific property is absolute property divided by density • Figure of merit when weight is important • If specific gravity (S.G.) is used for density, absolute and specific properties have same units, e.g. – Thermal conductivity, k = W/m-K – Specific thermal conductivity, k/S.G = W/m-K

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SPECIFIC THERM. COND. vs CTE FOR PACKAGING MATERIALS 350

Si, GaAs, Silica, Alumina, Beryllia, Aluminum Nitride, LTCC

HOPG (740)

SPECIFIC THERMAL CONDUCTIVITY (W/mK)

670

300

Diamond-Particle-Reinforced Metals and Ceramics

250 C/C

200

C/Ep

SiC/Al (Al/SiC)

150 C/Al Aluminum

100

C/Cu Si-Al

50 Invar

Copper

Kovar

Cu/W

0 -5

0 5 10 15 20 25 COEFFICIENT OF THERMAL EXPANSION (ppm/K) Copyright Carl Zweben 2010

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MODERATE-THERMAL-CONDUCTIVITY MATERIALS (k < 300) k CTE MATERIAL (W/m-K) (ppm/K) Copper 400 17 Industrial Gr 95 7.9 Carbon Foam* 135-145 -1 Disc. CF/Ep* 20-290 4-7 SiC/Al (Al/SiC) 170-255 4.8-16.2 Cont. CF/Al* 218-290 0-16 Disc. CF/Al* 185 6.0 Industrial Gr/Cu 175 8.7 Beryllia/Be 240 6.1 Be/Al 210 13.9 Silver/Invar 153 6.5 Si-Al 126-160 6.5-14 * Inplane isotropic values Copyright Carl Zweben 2010

Specific Gravity 8.9 1.8 0.6-0.9 1.6-1.8 2.9-3.0 2.3-2.6 2.5 3.1 2.6 2.1 8.8 2.5-2.6

k/SG (W/m-K) 45 53 220-270 12-160 57-85 84-126 74 56 92 100 17 49-63 30

HIGH-THERMAL-CONDUCTIVITY MATERIALS (300 < k < 400) k CTE Specific k/SG MATERIAL (W/mK) (ppm/K) Gravity (W/mK) Copper 400 17 8.9 45 Natural Graphite/Ep* 370 -2.4 1.9 190 Cont. CF/Ep* 330 -1 1.8 183 Disc. CF/Cu* 300 6.5-9.5 6.8 44 Carbon/carbon* 350 -1.0 1.9 210 (363) -----------------------------------------------------------------------------------------Graphite Foam/Cu 342** 7.4 5.7 60 SiC/Cu 320 7-10.9 6.6 48 Materials below line are experimental * Inplane isotropic values ** k(z) Copyright Carl Zweben 2010

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ULTRAHIGH-THERMAL-CONDUCTIVITY MATERIALS (k > 400) – Part 1 k (W/m-K) 400

CTE (ppm/K) 17

Specific Gravity 8.9

k/SG (W/m-K) 45

CVD Diamond

500-2200**

1-2

3.5

143-629

HOPG*

1500-1700

-1

2.3

650-740

MATERIAL Copper

Natural Graphite* 140-500+ -0.4 1.1-1.9 127-263 -----------------------------------------------------------------------------------------Cont. CF/Cu*

400-420

0-16

5.3-8.2

49-79

Gr Flake/Al*

400-600

4.5-5.0

2.3

174-260

GR particle/Al*

650-700

4-7

2.3

283-304

Materials below line are experimental * Inplane isotropic values

** k(z) – somewhat anisotropic

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ULTRAHIGH-THERMAL-CONDUCTIVITY MATERIALS (k > 400) – Part 2 MATERIAL Copper

k (W/m-K) 400

CTE (ppm/K) 17

Specific Gravity 8.9

k/SG (W/m-K) 45

Diamond/Al

325-600

7-9

3-4

93-171

Diamond/Cu

400-1200

5-8

5.5-7

62-185

Diamond/Co

>600

3.0

4.1

>146

Diamond/Ag 550-650 5-8 6-7 85-100 Diamond/SiC 600-680 1.8 3.3 182-206 -----------------------------------------------------------------------------------------Diamond/Si 525 4.5 Diamond/Mg

575

5.5

-

-

Diamond+SiC/Al

575

5

-

-

Materials below line are experimental Copyright Carl Zweben 2010

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EXPERIMENTAL LOW-CTE COMPOSITE SOLDER Wt % Mo

CTE (ppm/K)

0

21

Thermal Conductivity (W/m-K) 55

20

15

68

40

8

76

60

5.2

97

100

5.1

137

Matrix: Sn96.5Ag3.5 Lewis, Ingham and Laughlin, Cookson Copyright Carl Zweben 2010

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APPLICATIONS

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APPLICATIONS • Microelectronic applications – CPU, RF, Power, etc. • Optoelectronic applications – LEDs – Diode Lasers – Displays – Detector/sensors – Photovoltaics – Thermoelectric coolers • Thermally conductive, low-CTE printed circuit boards • Advanced thermal interface materials Copyright Carl Zweben 2010

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THE FIRST SILICON-CARBIDE-PARTICLEREINFORCED (AL/SiC) MMC MICROWAVE PACKAGE

Source: GE Copyright Carl Zweben 2010

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SUMMARY AND CONCLUSIONS

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SUMMARY AND CONCLUSIONS • Thermal management now critical problem for microelectronics and optoelectronics • Traditional thermal materials inadequate – Mid-20th century • Low-CTE, low-density materials with thermal conductivities up to 1700 W/m-K available • Can now match CTEs of chips, lids, heat sinks, and PCBs – Reduces thermal stresses and warping – Possibly eliminates need for underfill – Enables use of hard solder attach • Low thermal resistance Copyright Carl Zweben 2010

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SUMMARY AND CONCLUSIONS (cont) • Several advanced materials well established – SiC particle/aluminum – Silicon-aluminum – Carbon fiber/polymer – Natural graphite – Pyrolytic graphite sheet – Highly-oriented pyrolytic graphite • Diamond composites used in production microelectronic and optoelectronic systems • Short (2-3 year) cycle from introduction to production demonstrated • Applications increasing steadily Copyright Carl Zweben 2010

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WE ARE THE INFANCY OF A PACKAGING MATERIALS REVOLUTION

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APPENDIX

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TERMINOLOGY • Homogeneous – Properties constant throughout material • Heterogeneous – Properties vary throughout material – E.g. different in matrix and reinforcement – Composites always heterogeneous • Isotropic – Properties the same in every direction • Anisotropic – Properties vary with direction • Inplane isotropic (transversely isotropic) – Properties the same for every direction in a plane (different perpendicular to the plane) Copyright Carl Zweben 2010

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ABBREVIATIONS • • • • • • • • • • •

C: carbon CAMC: carbon matrix composite CCC: carbon/carbon composite C/C: carbon/carbon CF - carbon fiber CMC: ceramic matrix composite Cond: conductivity Cont: continuous CTE: coefficient of thermal expansion Dens: density Disc: discontinuous

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ABBREVIATIONS (cont) • • • • • • • • • • •

Elect: Electrical Ep: epoxy HOPG: highly oriented pyrolytic graphite Gr: graphite MMC: metal matrix composite PAN: polyacrylonitrile PCB: printed circuit board Pitch: carbonaceous petroleum or coal byproduct PMC: polymer matrix composite LTCC: low-temperature cofired ceramic Mod: modulus Copyright Carl Zweben 2010

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ABBREVIATIONS (cont) • • • • • • •

PGS: pyrolytic graphite sheet SG, S.G.: specific gravity SiCp: Silicon carbide particle TEC: thermoelectric cooler Therm: thermal UHM: ultrahigh modulus UHS: ultrahigh strength

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