Figures of Merit Design Tools for Surface Mount Solder Joint Reliability

In early 1989 the original version of the Reliability Figures of Merit (FM) for the solder attachments of surface mount (SM) assemblies was published. That version of the FM was specifically tailored for telecommunications environments. Misapplications of FMs to use environments, such as military applications and accelerated tests, pointed to a real need for generally applicable FMs. Adequate reliability of SM solder connections can only be assured with a ‘Design for Reliability’ based on solder joint behaviour and the underlying fatigue damage mechanisms. Perceived difficulties with a ‘Design for Reliability’ stem from the very complex and only partially understood nature of the interacting mechanisms underlying thermally induced solder joint fatigue, combined with the highly temperature, time, and stress‐dependent behaviour of some of the materials involved, especially solder. In this paper generic FMs are presented. These are simple design tools, easily applied by users unfamiliar with the underlying complexities of solder fatigue and the reliability assessment results are in Go/No‐go format. The oversimplifications contained in Version 1 of the FMs (originally thought necessary for simple design tools and limiting their applicability) are omitted, making these generic FMs more readily understood.