overview of advanced thermal materials

Copyright Carl Zweben 2010 1

OVERVIEW OF ADVANCED THERMAL MATERIALS

Carl Zweben, PhD Life Fellow ASME

Fellow SAMPE and ASMAssociate Fellow, AIAA

Advanced Thermal Materials Consultant 62 Arlington Road

Devon, PA 19333-1538 Phone: 610-688-1772

E-mail: [email protected]://sites.google.com/site/zwebenconsulting

http://sites.google.com/site/zwebenconsulting


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


OUTLINE

• Introduction• Semiconductors, ceramic substrates and

traditional thermal materials• Advanced thermal materials• Applications• Summary and conclusions• Appendix (terminology and abbreviations)


INTRODUCTION


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)


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


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• Low-CTE “Thermount” PCB withdrawn from market in 2006– No current thin-ply replacement


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


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


CTE MISMATCH CAUSES THERMAL STRESSES


PACKAGING LEVELS

Source: USAF (modified)


SEMICONDUCTORS, CERAMIC SUBSTRATES AND TRADITIONAL

THERMAL MATERIALS


SEMICONDUCTOR AND CERAMIC SUBSTRATE PROPERTIES

MATERIAL CTE (ppm/K)Silicon 2.5-4.1GaAs 5.8-6.9GaP 5.9InP 4.5-4.8SiC 4.2-4.9Alumina (96%) 6.0-7.1AlN 3.5-5.7BeO 6-9LTCC 5.8

CTE RANGE ~ 2 – 7 ppm/K


TRADITIONAL THERMAL AND PACKAGING MATERIALS

k CTE Specific k/SGMATERIAL (W/m-K) (ppm/K) Gravity (W/m-K)Copper 400 17 8.9 45Aluminum 218 23 2.7 81“Kovar” 17 5.9 8.3 2Alloy 42 10.5 5.3 8.1 1.3W/Cu (85/15) 167 6.5 17 10Mo/Cu (85/15) 184 7.0 10 18Cu-Invar-Cu* 172* 6.7* 8.4 20Cu-Mo-Cu* 182* 6.0* 9.9 18E-glass/epoxy 0.3* 12-24* 1.6-1.9 0.2Epoxy 0.2 45-65 1.3 0.2

*Inplane isotropic (x,y)


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


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


• 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)

WHAT’S WRONG WITH TRADITIONAL THERMAL MATERIALS? (cont)


ADVANCED THERMAL MATERIALS


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


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


SiC-PARTICLE/ALUMINUM (Al/SiC) SUPPLIERS

v/o k CTE SpecificSupplier (%) (W/m-K) (ppm/K) GravityAmetek 68 220 7.5 3.03CPS 63 200 8.0 3.01DWA 55 200 8.8 3.00Denka - 200 7.5 2.96MC-21 20-45 150-180 10-16 2.7-2.9PCC-AFT* 70 175 7 3.01Sumitomo - 150-200 8-15 2.60-2.78TTC - 165-255 4.8-16.2 2.77-3.10

*Purchased by Rogers Corporation


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


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)


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)


COMPOSITE MATERIAL REINFORCEMENTS

Continuous Fibers

Particles

Discontinuous Fibers, Whiskers

Fabrics, Braids, etc.


0 20 40 60 80 100 PARTICLE VOLUME FRACTION (%)

CO

EFFI

CIE

NT

OF

THER

MA

L EX

PAN

SIO

N (p

p m/K

)

25

20

15

10

5

0

Aluminum

Copper

Beryllium

Titanium, SteelAluminaSilicon

Powder MetallurgyInfiltration

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

E-glass PCB

NEW MATERIAL


Silver

Copper

Aluminum

E-glass PCB

SiC/Al (Al/SiC)

C/Al

C/Cu

C/C

C/Ep

Cu/W

Kovar

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

Si-Al

Diamond-Particle-Reinforced Metals and Ceramics

SiC/Cu

HO

PG

(170

0)

-5 0 5 10 15 20 25COEFFICIENT OF THERMAL EXPANSION (ppm/K)

THER

MA

L C

ON

DU

CTI

VITY

(W/m

K)

100

200

300

400

500

600

0 Invar

THERMAL CONDUCTIVITY vs CTE FOR PACKAGING MATERIALS

1200


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


Copper

Aluminum

SiC/Al (Al/SiC)

C/Al

C/Cu

C/C

C/Ep

Cu/WKovar

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

Si-Al

Diamond-Particle-Reinforced Metals and CeramicsH

OPG

(740

)

-5 0 5 10 15 20 25COEFFICIENT OF THERMAL EXPANSION (ppm/K)

SPEC

IFIC

TH

ERM

AL

CO

ND

UC

TIVI

TY

(W/m

K)

50

100

150

200

250

300

350

0

SPECIFIC THERM. COND. vs CTE FOR PACKAGING MATERIALS

Invar

670


MODERATE-THERMAL-CONDUCTIVITY MATERIALS (k < 300)

k CTE Specific k/SGMATERIAL (W/m-K) (ppm/K) Gravity (W/m-K)Copper 400 17 8.9 45Industrial Gr 95 7.9 1.8 53Carbon Foam* 135-145 -1 0.6-0.9 220-270Disc. CF/Ep* 20-290 4-7 1.6-1.8 12-160SiC/Al (Al/SiC) 170-255 4.8-16.2 2.9-3.0 57-85Cont. CF/Al* 218-290 0-16 2.3-2.6 84-126Disc. CF/Al* 185 6.0 2.5 74Industrial Gr/Cu 175 8.7 3.1 56Beryllia/Be 240 6.1 2.6 92Be/Al 210 13.9 2.1 100Silver/Invar 153 6.5 8.8 17Si-Al 126-160 6.5-14 2.5-2.6 49-63

* Inplane isotropic values


HIGH-THERMAL-CONDUCTIVITY MATERIALS (300 < k < 400)

k CTE Specific k/SGMATERIAL (W/mK) (ppm/K) Gravity (W/mK)Copper 400 17 8.9 45Natural Graphite/Ep* 370 -2.4 1.9 190Cont. CF/Ep* 330 -1 1.8 183Disc. CF/Cu* 300 6.5-9.5 6.8 44Carbon/carbon* 350 -1.0 1.9 210 (363)------------------------------------------------------------------------------------------Graphite Foam/Cu 342** 7.4 5.7 60SiC/Cu 320 7-10.9 6.6 48

Materials below line are experimental* Inplane isotropic values** k(z)


ULTRAHIGH-THERMAL-CONDUCTIVITY MATERIALS (k > 400) – Part 1

k CTE Specific k/SGMATERIAL (W/m-K) (ppm/K) Gravity (W/m-K)Copper 400 17 8.9 45CVD Diamond 500-2200** 1-2 3.5 143-629HOPG* 1500-1700 -1 2.3 650-740Natural Graphite* 140-500+ -0.4 1.1-1.9 127-263------------------------------------------------------------------------------------------Cont. CF/Cu* 400-420 0-16 5.3-8.2 49-79Gr Flake/Al* 400-600 4.5-5.0 2.3 174-260GR particle/Al* 650-700 4-7 2.3 283-304

Materials below line are experimental* Inplane isotropic values ** k(z) – somewhat anisotropic


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

k CTE Specific k/SGMATERIAL (W/m-K) (ppm/K) Gravity (W/m-K)Copper 400 17 8.9 45Diamond/Al 325-600 7-9 3-4 93-171Diamond/Cu 400-1200 5-8 5.5-7 62-185Diamond/Co >600 3.0 4.1 >146Diamond/Ag 550-650 5-8 6-7 85-100Diamond/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


EXPERIMENTAL LOW-CTE COMPOSITE SOLDER

Matrix: Sn96.5Ag3.5

Lewis, Ingham and Laughlin, Cookson

Wt % Mo CTE(ppm/K)

Thermal Conductivity

(W/m-K)0 21 55

20 15 6840 8 7660 5.2 97100 5.1 137


APPLICATIONS


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


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

Source: GE


SUMMARY AND CONCLUSIONS


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


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


WE ARE THE INFANCY OF APACKAGING MATERIALS REVOLUTION


APPENDIX


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)


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


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


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

overview of advanced thermal materials

Technology