Sequential Versus Concurrent Effects in Combined Stress Solder Joint Reliability

Reliability risk in solder joints has been commonly linked to various failure mechanisms, with electromigration (EM) and fatigue among the prominent drivers. Even though these failure mechanisms often occur simultaneously, typical accelerated tests are based on a single failure mechanism. Consequently, the effect of multiple interacting failure mechanisms is ignored, which may underestimate reliability risk. This common practice has the potential to reduce life prediction accuracy. To address this gap, in this paper, we present an experimental setup that is developed and used to simultaneously evaluate SAC 305 solder joint lifetime under electromigration and fatigue failure mechanisms using sequential and concurrent approaches. The sequential approach involves prestressing the solder joint using a fixed current density and temperature until the test vehicle attains a specified rise in resistance. After that, an isothermal fatigue load was applied at three prescribed temperatures. The data collected enable the estimation of parameters used for reliability prediction. On the other hand, the concurrent case involves the simultaneous application of current density, temperature, and cyclic mechanical load to the solder joint. The correlation of the experiment and complementary numerically simulated strain energy density (SED) resulted in an improved, physic-based reliability model, which has the added benefit of reduced time and cost of data collection, especially during new product development. Unlike the concurrent approach, the sequential approach shows a defect-driven failure mode. The prediction accuracy of the concurrent-based derived characteristic life model compared to that of experiment-derived characteristic life was found to be ±25%.