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December 2005
library  >  PAPERS  >  Design

Thermal conductivity of composite materials


 

a composite material can be defined as a material in which two or more different materials are bonded together. it is sensible to make a distinction between macrocomposites and microcomposites. the first group usually has a layered structure, and pcbs are the main application. the second group looks uniform to the naked eye; materials from this group are often used for packages and heat spreaders.

 

it appears that a combination of two or more materials can have much better overall properties than the individual materials.

 

the following quote is taken from ref. 1:

 


"various new advanced composite materials are now available, which provide great advantages over conventional materials for electronic packaging thermal control, including:

 

extremely high thermal conductivities

low, tailorable coefficients of thermal expansion

extremely high strength and stiffness

low densities

low cost, net shape fabrication processes"

 

apart from the topic of the last bullet, the other claims are related to physical properties. this technical brief focuses on thermal conductivity only, but i would like to stress that solving thermal mismatch problems is one of the great challenges for the future. promising materials are for example al/sic, with a thermal conductivity about equal to al, but with a lower density and a much more attractive cte.

 

back to thermal conductivity. as becomes evident from the table, many composite materials tend to be anisotropic.

 

composite

source

thermal conductivity
(w/mk) at 20°c

   

x,y direction

z direction

42.5cu / 15mo / 42.5cu

amoco

170

170

20cu / 60invar / 20cu

amoco

160

18

90w / 10cu

amoco

180

180

85mo / 15cu

sumitomo

160

 

80w / 20cu

sumitomo

200

 

6al / 40si

sumitomo

130

 

al / sic

ref.1

170-220

 

tpg graphite fiber

adv. ceramics

1700

25

polymer / tpg

adv. ceramics

1180

 

cu / tpg

adv. ceramics

1140

 

k1100 graphite fiber

amoco

1100

 

thermalgraph 8000

amoco

700

20

20 cu / 80thermalgraph

amoco

892

 

k1100 / epoxy

amoco

595

1

k1100 / cu

amoco

709

135

 

ref. 1: c. zweben, high performance thermal management materials, ecm vol.5: 3, pp. 36-42.

 

clemens j.m. lasance
associate editor
philips research laboratories

 

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