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A methodology to characterize and predict fatigue failure of BGA package solder joints under vibration loading is presented. The results show that the board strain versus number-of-cycles-to-failure (or E-N) curve has a linear trend with little scatter in data points, similar to that of a classical fatigue theory using cyclic stress versus number-of-cycles-to-failure (or S-N) curves. Using finite element analysis (FEA), the solder joint stress was shown to be linearly correlated to the board strain. Therefore, board strain can indeed be used as an optimum engineering metric to study the fatigue of ball grid array (BGA) solder joints. In addition, the E-N curve approach was shown to be applicable to cyclic bend and cyclic shock loading conditions as well. The E-N curves of lead-free and leaded solder systems also have been generated and compared to demonstrate that the lead-free system has a better high-cycle fatigue performance. In addition, a fatigue-life prediction methodology based on the Miner's cumulative damage theory is proposed. The effectiveness of this methodology was demonstrated with promising results through random vibration testing of actual motherboards. Finally, a novel approach to study solder joint reliability (SJR) under vibration loading at the system level, using a fatigue curve generated at the component level is presented.
Date of Conference: May 29 2007-June 1 2007