Novel accelerated failure mode of eutectic SnBi Solder joints under simultaneous electromigration and temperature cycling test

Abstract We studied the reliability of eutectic SnBi solder joints and discovered a new failure mode that resulted from the synergistic effect of simultaneously conducted electromigration (EM) and temperature cycling (TC) tests. After the test, we observed the EM induced phase separation and a crack-type failure induced by TC stress which propagates through the Bi-rich phase of the solder joint. The experimental result of the solder joints under EM + TC condition is compared with the experimental result of solder joints under individual EM/TC conditions. The EM + TC condition results in the most severe and fast failure in SnBi solder compared to only EM or TC tests. Due to the inherent brittleness of Bi, we could attribute the failure to EM induced phase separation, which embrittles the anode side and accelerates crack propagation. This crack propagation is further exacerbated by metal fatigue in the Bi-rich phase caused by the stress induced by TC. Our research provides insights into the reliability of advanced packaging structures using eutectic SnBi ball-grid-array under real application scenarios when structures will have to go through current stressing and temperature variation at the same time.