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)
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4.
INTRODUCTION
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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)
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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
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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• Low-CTE “Thermount” PCB withdrawn from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
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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
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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
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10.
CTE MISMATCH CAUSES THERMAL STRESSES
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11.
PACKAGING LEVELS
Source: USAF (modified)
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12.
SEMICONDUCTORS, CERAMIC
SUBSTRATES AND TRADITIONAL
THERMAL MATERIALS
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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
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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)
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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
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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
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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)
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18.
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
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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
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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
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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
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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)
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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)
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25.
COMPOSITE MATERIAL REINFORCEMENTS
Discontinuous Fibers,
Continuous Fibers Whiskers
Particles Fabrics, Braids, etc.
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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 (%)
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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)
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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
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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)
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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
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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)
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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
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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
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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
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35.
APPLICATIONS
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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
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37.
THE FIRST SILICON-CARBIDE-PARTICLE-
REINFORCED (AL/SiC) MMC MICROWAVE PACKAGE
Source: GE
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38.
SUMMARY AND CONCLUSIONS
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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
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41.
WE ARE THE INFANCY OF A
PACKAGING MATERIALS REVOLUTION
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42.
APPENDIX
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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
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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
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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