Evaluating the efficiency of current reverse method applied to solder joints

The method of applying a reverse current to counterbalance electromigration was examined using the Cu/eutectic Pb-Sn/Cu solder joints in this study. Upon current stressing test, a square-wave alternating current (AC) was delivered with a fixed frequency of 0.05 min^-1, 1 h^-1, and 1/(84 h) for a known cycles. It was found that in the AC-stressed solder joints, there were no significant DC-induced microstructural damages. For instance, there were no enormous valley/hillock observed in the whole joint (1); no electromigration-induced phase segregation of Pb-rich and Sn-rich (2); no polarity effect on the growth of Cu-Sn IMCs at the interfaces (3); less Cu₆Sn₅ precipitates nucleated inside the solder matrix (4); no excessive depletion in the Cu pad on either side (5). This is especially true for a high AC frequency treatment. More interesting findings related to the AC behavior in solder joints will be presented in this study.