In a message dated 97-08-01 00:10:33 EDT, Mark Ploughman asked for coefficients of thermal expansion (CTEs): ANSWERS: below are orders of magnitude: Polyimide materials: ~ 60 ppm/C. Polyimide based boards: x-y CTE ~ 15 to 18 ppm/C, z-CTE ~ 65 ppm/C FR-4: x-y CTEs ~ 16 to 18 ppm/C. This is typical of in-plane CTEs for double-sided boards, but measurements have given numbers in the range 12 to 21 ppm/C, depending on construction and board features (vias, solder filled holes, amount of copper etc...). z-CTE: 60 to 85 ppm/C. Copper: ~ 17. ppm/C Jean-Paul _______________________________________________________________ Jean-Paul Clech EPSI Inc., P. O. Box 1522, Montclair, NJ 07042 - USA tel: +1 (973)746-3796 fax: + 1 (973)655-0815 Home page: <A HREF="http://members.aol.com/Epsiinc1/index.html">http://members.aol.com/Ep siinc1/index.html</A> (last updated on June 28, 1997). SMT / BGA /CSP assembly reliability specialists. - click on the above or copy: http://members.aol.com/Epsiinc1/index.html __________________________________________________________________