The problem with coeficients of expansion of different substrate materials 
has been a problem in the printed wiring board industry for many years. The 
use of Kevlar, Copper-Invar-Copper and Thermount has been common. The X and 
Y expansion differences between the substrates in our electronic components 
and the printed wiring substrates has cause millions of dollars of 
additional expense in the use of exotic materials in our printed wiring 
substates. This is not a simple nor cheap problem to address and many 
problems have been realized by this situation. It is much better to utilize 
plastic components to place on plastic boards.

             Phil Elias
             Honeywell Air Transport Systems
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From: [log in to unmask]
To: [log in to unmask]; [log in to unmask]
Subject: FAB: Heat Expansion
Date: Wednesday, June 26, 1996 9:11AM

Has anyone had problems with the different rates of expansion among IC chips 
made of ceramic material, copper for traces/pads, and say FR4?

The result would be cracks in the traces/pads?

Doug

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