Electromigration reliability for Al₂O₃-reinforced Cu/Sn–58Bi/Cu composite solder joints

The Sn–58Bi based composite solder was fabricated via mechanical mixing 0.5 wt% Al₂O₃ particle, and the effect of electromigration (EM) behavior on the microstructure and mechanical properties of the Al₂O₃-reinforced Cu/Sn–58Bi–0.5Al₂O₃/Cu lead-free solder joints was investigated under the current density of 0.6 × 10⁴ A/cm² at room temperature. The results indicated that the EM failure behavior occurred at the cathode side as increasing EM time to 280 h for Cu/Sn–58Bi/Cu and 410 h for Cu/Sn–58Bi–0.5Al₂O₃/Cu, respectively. A continuous white Bi-rich layer was caused by heavy electron wind flow observed among the bulk solder in the two joints. The remarkable interfacial morphologies change was not found in the 0.5 wt% Al₂O₃ reinforced joint, and the EM-induced IMC layer growth rate of Cu/Sn–58Bi–0.5Al₂O₃/Cu was slower than that of the non-composite joint. The mechanical properties, including UTS, shear strength and hardness, of the Cu/Sn–58Bi–0.5Al₂O₃/Cu solder joint were improved slightly by adding 0.5 wt% Al₂O₃. Consequently, the EM reliability is enhanced for the Cu/Sn–58Bi–0.5Al₂O₃/Cu solder joint with adding Al₂O₃ concentration to 0.5 wt%.