DOUG, YES INDEEDY THERE IS A HONKING BIG DIFFERENCE, (ALL THINGS BEING EQUAL), BETWEEN THE COEFFIECENTS OF EXPANSION OF FR4 AND CERAMIC PACKAGE MATERIAL. POLYIMIDE MATERIALS MAY ALLEVIATE THIS SLIGHTLY, (DEPENDS ON THE DELTA OF YOUR THERMAL EXCURSIONS AND NUMBER OF REPITIONS). ANOTHER METHOD IS TO USE A CONSTRAINING CORE MATERIAL SUCH AS COPPER-INVAR-COPPER, (Cu/In/Cu). AND OF COURSE THE ULTIMATE IS DOING BOTH A HIGH TEMP MATERIAL AND A CONSTRAINING CORE. DISADVANTAGES ARE INCREASED COST AND FEWER QUALIFIED FAB HOUSES. ADVANTAGES ARE THAT YOU DON'T HAVE TO SWEEP UP ALL THOSE BROKEN CERAMIC PIECES. ANOTHER POSSIBILITY, DEPENDING ON ENVIROMENT, IS TO HAVE COMPLIANT LEADS ATTACHED TO THE COMPONENTS. AGAIN COST IS AN ISSUE AS IS ELECTRICAL PERFORMANCE. REGARDS, ROB BUTTERWORTH ADC VIDEO SYSEMS WALLINGFORD, CT [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: FAB: Heat Expansion Author: [log in to unmask] at internet-mail Date: 6/26/96 9:25 AM 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]