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 ---------- 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 [log in to unmask]