This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
• 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• Low-CTE “Thermount” PCB withdrawn from market in 2006– No current thin-ply replacement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 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 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 10
CTE MISMATCH CAUSES THERMAL STRESSES
Copyright Carl Zweben 2010 11
PACKAGING LEVELS
Source: USAF (modified)
Copyright Carl Zweben 2010 12
SEMICONDUCTORS, CERAMIC SUBSTRATES AND TRADITIONAL
• 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 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 17
• 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)
Copyright Carl Zweben 2010 18
ADVANCED THERMAL MATERIALS
Copyright Carl Zweben 2010 19
NEW THERMAL MANAGEMENT MATERIALS
• Many advanced materials– Various stages of development– R&D to large scale production– New ones continuously emerging
• 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
– 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 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 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 25
COMPOSITE MATERIAL REINFORCEMENTS
Continuous Fibers
Particles
Discontinuous Fibers, Whiskers
Fabrics, Braids, etc.
Copyright Carl Zweben 2010 26
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
THE FIRST SILICON-CARBIDE-PARTICLE- REINFORCED (AL/SiC) MMC MICROWAVE PACKAGE
Source: GE
Copyright Carl Zweben 2010 38
SUMMARY AND CONCLUSIONS
Copyright Carl Zweben 2010 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 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 41
WE ARE THE INFANCY OF APACKAGING MATERIALS REVOLUTION
Copyright Carl Zweben 2010 42
APPENDIX
Copyright Carl Zweben 2010 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