The goal of automating PWB solder joint fatigue life calculations into a design environment is to make reliability assessment information available to the designer as early as possible and in an easily understood and implemented manner. This paper discusses the assumptions and details of the fatigue life calculations under a combined thermal and vibrational load. A methodology is presented to evaluate the combined effects of simultaneous vibration and thermal cycling of solder joints. This combined loading situation is simulated by superposing the effects of the vibrational and thermal loads. The damage due to each load-type acting individually is determined and then superposed to assess the overall effective fatigue life of the joint. As a first order approximation. Palmgren-Miner's linear superposition rule is utilized.

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