Synergistic Effect of Current Stressing and Temperature Cycling on Reliability of Low Melting Point SnBi Solder

In this paper, we report the acceleration on the failure of eutectic SnBi solder through simultaneous application of current stress and temperature cycling. For this purpose, electromigration (EM) and temperature cycling test (TCT) is conducted synchronously on a test vehicle with daisy-chain structure containing 6 eutectic SnBi solders. After experiment, Sn- and Bi-rich phase separation is observed and a stress-induced crack type failure is discovered in the sample. Simulation of stress distribution in the sample is conducted to locate the preferred failure generation site in the sample. The experimental result of EM + TCT is compared with the result of the same type of sample under single EM/TCT condition, and the failure under EM + TCT condition appeared to be more severe than single EM/TCT condition, demonstrating the synergistic effect of EM and TCT in the failure generation in eutectic SnBi solder. To achieve this, we stressed SnBi solder joints with electromigration (EM) and temperature cycling tests (TCT) at the same time. The test vehicle has six eutectic SnBi solder joints connected in a daisy-chain structure. Phase separation happens between Sn- and Bi-rich regions and a stress-induced crack pass through in the solder joints, leading to a failure. To explain the failure mode, simulations are done to analyze the stress distribution within the sample. Furthermore, we compare the experimental results of the EM + TCT tests with those obtained from identical samples subjected to either single EM or TCT stressing conditions. We have a much faster failure under the EM + TCT stressing condition while the failure resulting from the individual EM or TCT tests is much slower (sic). This result highlights the synergistic effect of electromigration and temperature cycling on failures in eutectic SnBi solder.