Current-Induced Interfacial Reactions in Sn Solder Joints with Electroplated FeNi/Cu Substrate

The effect of polarity on interfacial reactions under high-density electric current was investigated in Cu/FeNi/Sn/FeNi/Cu solder interconnects. A reverse polarity effect was found where the FeSn2 intermetallic compound (IMC) layer at the cathode grew significantly thicker than that at the anode under electric loading. Such an abnormal polarity effect was shown to result from electromigration of Fe in the direction opposite to the electron flow. At the same time, a Cu-rich layer developed next to the FeSn2 layer at the anode side. Kinetic analysis of Fe and Cu mass transport explained the differential growth of the IMCs at the two electrodes, in good agreement with the experimental data.