Electronic chip having a composite stratified metal back and method of making it in which strata of metal and/or metal alloys are deposited on the back of the silicon base or a wafer carrying a plurality of circuit components on its face at least one of the strata being resistant to passage of copper...http://www.google.de/patents/US4451972?utm_source=gb-gplus-sharePatent US4451972 - Method of making electronic chip with metalized back including a surface stratum of solder
