Effects of pre-stressing on solder joint failure by pad cratering

The present work addresses a significant risk generally overlooked in the design and accelerated testing of high reliability electronics. Manufacturers of servers and other expensive high reliability electronics equipment are becoming increasingly concerned with the risk of solder pad cratering. Their focus is, however, on cratering in testing, handling or transport, while the risk of premature wear-out due to thermal excursions (cycling) in service is completely ignored. This is a result of reliability testing that almost invariably addresses individual loading conditions separately. Under such conditions it is for example extremely rare for electrical failures in thermal cycling or high-cycle vibration testing to be associated with pad cratering. The present paper shows how manufacturers of high reliability equipment intended for mechanically protected or benign service conditions may be missing a significant risk of invisible damage induced in testing, handling or transport which may change the failure mode in service. We present first results of a systematic effort aimed at redefining currently proposed pad cratering test protocols.