SMTA International Conference Proceedings


Authors: Linlin Yang, et al.
Company: Binghamton University and Universal Instruments Corporation
Date Published: 10/4/2009   Conference: SMTA International

Abstract: Reports on the limitations of the Palmgren-Miner rule of linear damage accumulation are not uncommon, but the rule is still implicitly assumed in most interpretations of test results and predictions of life in service. The complete fundamental breakdown of the rule in testing of lead free soldered BGA assemblies is therefore of considerable concern for high reliability applications.

Previous experiments on BGA assemblies with SAC305 and SAC205 solder joints involved repeated drops, cyclic bending or vibration at room temperature, and led to failures through the solder, the intermetallic bonds to the contact pads, or the laminate resin under the pads. In either case, preconditioning in cyclic loading with a lower peak load was found to extend life in the subsequent test. In the present work isothermal load controlled fatigue testing of individual SAC305 and SAC405 solder joints of two different sizes and on two different solder pad finishes, using a Dage solder bump tester, helped further elucidate the systematics. As expected not all preconditioning served to extend life, in fact Miner’s rule was found to overestimate the remaining life by more than an order of magnitude in one experiment. Overall, indications are that Miner’s rule will underestimate life in scenarios where mild cycling is followed by cycling to a higher peak load, but overestimate it in the reverse case. This is consistent with other existing models, but the extension of life in the original tests is not. We conclude that no current models are suitable for the extrapolation of accelerated test results to life under realistic service conditions.

Key words: Reliability, damage accumulation, combined loading, varying loads, Pb-free solder.

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