Effect of electron flow on the microstructure and mechanical property of Cu/Sn–30Bi/Cu solder joint

Non-eutectic Sn–30Bi solder alloy/joint always formed during surface mounting of BGA component, due to the application of pure Sn bump and Sn–58Bi solder paste. In order to investigate the microstructure and mechanical property evolution of Sn–30Bi solder joint electro-migrated at the temperature between solidus and liquidus, the electro-migration test of Cu/Sn–30Bi/Cu joint was conducted at 160 °C. The microstructure was observed by optical microscope and scanning electron microscope. The mechanical property of solder joint was tested by universal testing machine. The results showed that the eutectic phase would migrate towards the anode side and segregate on the surface of Cu pad of anode side. The anode side interfacial IMCs layer was between liquid Sn–58Bi and Cu pad. The cathode side interfacial IMCs layer was between solid Sn–11Bi and Cu pad. The interfacial IMCs layer thickness of anode side and cathode side was all thicker than the interfacial IMCs layer without electron flow.