This document provides an overview of advanced thermal materials. It begins with an introduction that outlines the need for improved thermal management in electronics due to issues like heat dissipation, thermal stresses from CTE mismatch, and limitations of traditional materials. It then discusses semiconductors, ceramic substrates, and traditional thermal materials like copper and aluminum. The document outlines some of the deficiencies of traditional materials. It introduces several advanced thermal materials like SiC particle-reinforced aluminum composites and describes their properties and advantages over traditional materials. Potential applications and benefits of advanced materials are also summarized.

1. 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: c.h.zweben@usa.net
http://sites.google.com/site/zwebenconsulting
Copyright Carl Zweben 2010 1

2. 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
Copyright Carl Zweben 2010 2

3. OUTLINE
• Introduction
• Semiconductors, ceramic substrates and
traditional thermal materials
• Advanced thermal materials
• Applications
• Summary and conclusions
• Appendix (terminology and abbreviations)
Copyright Carl Zweben 2010 3

4. INTRODUCTION
Copyright Carl Zweben 2010 4

5. 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 5

6. 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
Copyright Carl Zweben 2010 6

7. 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 7

8. 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
Copyright Carl Zweben 2010 8

9. 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
Copyright Carl Zweben 2010 9

10. CTE MISMATCH CAUSES THERMAL STRESSES
Copyright Carl Zweben 2010 10

11. PACKAGING LEVELS
Source: USAF (modified)
Copyright Carl Zweben 2010 11

12. SEMICONDUCTORS, CERAMIC
SUBSTRATES AND TRADITIONAL
THERMAL MATERIALS
Copyright Carl Zweben 2010 12

13. SEMICONDUCTOR AND CERAMIC SUBSTRATE
PROPERTIES
MATERIAL CTE (ppm/K)
Silicon 2.5-4.1
GaAs 5.8-6.9
GaP 5.9
InP 4.5-4.8
SiC 4.2-4.9
Alumina (96%) 6.0-7.1
AlN 3.5-5.7
BeO 6-9
LTCC 5.8
CTE RANGE ~ 2 – 7 ppm/K
Copyright Carl Zweben 2010 13

14. 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 14

15. 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 15

16. 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 16

17. 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 17

18. ADVANCED THERMAL MATERIALS
Copyright Carl Zweben 2010 18

19. 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 19

20. 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
Copyright Carl Zweben 2010 20

21. 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 21

22. 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
Copyright Carl Zweben 2010 22

23. 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 23

24. 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)
Copyright Carl Zweben 2010 24

25. COMPOSITE MATERIAL REINFORCEMENTS
Discontinuous Fibers,
Continuous Fibers Whiskers
Particles Fabrics, Braids, etc.
Copyright Carl Zweben 2010 25

26. CTE OF SILICON-CARBIDE-PARTICLE-REINFORCED
ALUMINUM (Al/SiC) vs PARTICLE VOLUME FRACTION
25 Aluminum
COEFFICIENT OF THERMAL
Powder Metallurgy
EXPANSION (ppm/K)
20 Infiltration
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 26

27. THERMAL CONDUCTIVITY vs CTE FOR
PACKAGING MATERIALS
1200 Si, GaAs, Silica, Alumina, Beryllia,
THERMAL CONDUCTIVITY (W/mK)
Aluminum Nitride, LTCC
600
HOPG
(1700)
500 Diamond-Particle-Reinforced Metals
and Ceramics
C/Cu Silver
400
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 27

28. 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
Copyright Carl Zweben 2010 28

29. SPECIFIC THERM. COND. vs CTE FOR PACKAGING MATERIALS
670
350
SPECIFIC THERMAL CONDUCTIVITY
Si, GaAs, Silica, Alumina, Beryllia,
Aluminum Nitride, LTCC
HOPG (740)
300
Diamond-Particle-Reinforced Metals
and Ceramics
250
C/C
(W/mK)
200
C/Ep SiC/Al (Al/SiC)
150
C/Al
Aluminum
100 C/Cu
Si-Al
50 Copper
Invar Kovar
Cu/W
0
-5 0 5 10 15 20 25
COEFFICIENT OF THERMAL EXPANSION (ppm/K)
Copyright Carl Zweben 2010 29

30. MODERATE-THERMAL-CONDUCTIVITY MATERIALS
(k < 300)
k CTE Specific k/SG
MATERIAL (W/m-K) (ppm/K) Gravity (W/m-K)
Copper 400 17 8.9 45
Industrial Gr 95 7.9 1.8 53
Carbon Foam* 135-145 -1 0.6-0.9 220-270
Disc. CF/Ep* 20-290 4-7 1.6-1.8 12-160
SiC/Al (Al/SiC) 170-255 4.8-16.2 2.9-3.0 57-85
Cont. CF/Al* 218-290 0-16 2.3-2.6 84-126
Disc. CF/Al* 185 6.0 2.5 74
Industrial Gr/Cu 175 8.7 3.1 56
Beryllia/Be 240 6.1 2.6 92
Be/Al 210 13.9 2.1 100
Silver/Invar 153 6.5 8.8 17
Si-Al 126-160 6.5-14 2.5-2.6 49-63
* Inplane isotropic values
Copyright Carl Zweben 2010 30

31. 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 31

32. ULTRAHIGH-THERMAL-CONDUCTIVITY MATERIALS
(k > 400) – Part 1
k CTE Specific k/SG
MATERIAL (W/m-K) (ppm/K) Gravity (W/m-K)
Copper 400 17 8.9 45
CVD Diamond 500-2200** 1-2 3.5 143-629
HOPG* 1500-1700 -1 2.3 650-740
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
Copyright Carl Zweben 2010 32

33. ULTRAHIGH-THERMAL-CONDUCTIVITY MATERIALS
(k > 400) – Part 2
k CTE Specific k/SG
MATERIAL (W/m-K) (ppm/K) Gravity (W/m-K)
Copper 400 17 8.9 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 33

34. EXPERIMENTAL LOW-CTE COMPOSITE SOLDER
Wt % Mo CTE Thermal
(ppm/K) Conductivity
(W/m-K)
0 21 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 34

35. APPLICATIONS
Copyright Carl Zweben 2010 35

36. 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 36

37. THE FIRST SILICON-CARBIDE-PARTICLE-
REINFORCED (AL/SiC) MMC MICROWAVE PACKAGE
Source: GE
Copyright Carl Zweben 2010 37

38. SUMMARY AND CONCLUSIONS
Copyright Carl Zweben 2010 38

39. 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 39

40. 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 40

41. WE ARE THE INFANCY OF A
PACKAGING MATERIALS REVOLUTION
Copyright Carl Zweben 2010 41

42. APPENDIX
Copyright Carl Zweben 2010 42

43. 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 43

44. 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
Copyright Carl Zweben 2010 44

45. 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 45

46. 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
Copyright Carl Zweben 2010 46