GENERIC RELIABILITY FIGURES OF MERIT DESIGN TOOLS FOR SURFACE-MOUNT SOLDER ATTACHMENTS

In early 1989 the original version of the reliability figures of merit (FM's) for the solder attachments of surface mount (SM) assemblies was published. This version of the FM's was specifically tailored for telecommunications use environments and precluded their application to other use environments, such as military applications and accelerated tests, with substantially different degrees of completion of the cyclic stress-relaxation. Misapplications of the FM's to other use environments pointed to a real need for generally applicable FM's. Adequate reliability of SM solder attachments can only be assured with a ''design for reliability'' (DFR) based on solder joint behavior and the underlying fatigue damage mechanisms. The perceived difficulties with a DFR 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 behavior of some of the involved materials, especially solder. In this paper generic FM's are presented. These FM's are simple design tools that can easily be utilized by nonexpert users unfamiliar with the underlying complexities of solder fatigue and give reliability assessment results in a GO/NO-GO fashion. These FM's not only avoid the oversimplifications-originally thought necessary for simple design tools and limiting the applicability of the FM's-contained in Version 1 of the FM's, but are also simpler to apply.