Adequate reliability of surface mount (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. Generic figures of merit are presented. These figures of merit 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 figures of merit not only avoid the over simplifications-originally thought necessary for simple design tools and limiting the applicability of the figures of merit-contained in Version 1 of the figures of merit, but are also simpler to apply.
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