Electromigration behavior of liquid Sn-58Bi/Cu joints through minor Zn alloying substrates

This study aims to investigate the interfacial reactions of Sn-58Bi/Cu and Sn-58Bi/Cu-Zn solder joints during liquid-solid electromigration (L-S EM). L-S EM behavior of Sn-58Bi/Cu and Sn-58Bi/Cu-2.29Zn solder joints about external microstructure under 1.5 × 10⁴ A/cm² at room temperature was studied using scanning electron microscopy (SEM). For the two types of solder joints, the thickness of IMC layer at the anode side was much higher than that at the cathode side with the same stressing time, respectively. At the anode side of Sn-58Bi/Cu and Sn-58Bi/Cu-2.29Zn solder joints, the rod-like Cu₆Sn₅ grew rapidly and showed an obvious “Ripening phenomenon”. It is also found that doping 2.29Zn into Cu substrate reduced the average thickness of IMC layers at both sides. The “Ripening phenomenon” happened in the two types of solder joints, which indicated that the doping Zn did not change the direction of Cu atoms. There was no back-stress in L-S EM, and the flux induced by EM and chemical potential gradient during L-S EM was discussed.