Abnormal phase segregation induced by void formation in Cu/Sn-58Bi/Cu solder joint during current stressing

This work focused on the electromigration (EM) behavior of the Cu/Sn-58Bi/Cu solder joint affected by the large void formation. The as-reflowed one-dimensional solder joint was stressed with current density of 5×10³ A/cm² at 80°C continuously for 144h. The microstructural evolution was observed and analyzed by SEM. Results indicated that the abnormal Sn/Bi phase segregation was observed at the cathode interface of the solder joint owing to the early serious defects formation. Local current flow was aggregated surrounding the large void, resulting in the Joule heating accumulation there. Therefore, the original straight direction of the electrons was altered near the void region, leading to the unusual Bi migration.