Microstructure and fracture behavior of non eutectic Sn–Bi solder alloys

The microstructure and mechanical properties of Sn–xBi (x = 10, 20, 25, and 35) solder alloy were investigated by scanning electronic microscope and notch tensile test. The results showed that the microstructure of Sn–10Bi and Sn–20Bi solder alloy was constituted by Bi particle and β-Sn phase. The microstructure of Sn–25Bi and Sn–35Bi solder alloy was consisted of eutectic phase and primary phase. The ultimate tensile load of Sn–20Bi solder alloy was higher than that of Sn–10Bi in notch tensile test. The ultimate tensile load of Sn–25Bi and Sn–35Bi was declined gradually compared with that of Sn–20Bi solder alloy. The fracture energy of Sn–xBi was decreased continuously when the Bi fraction increased. Crack observation, fracture surface observation, and finite element analysis revealed that the crack initiation and propagation of Sn–25Bi and Sn–35Bi was dominated by the fracture of brittle eutectic phase. Therefore, the ultimate tensile load and fracture energy of Sn–25Bi and Sn–35Bi were damaged compared with that of Sn–20Bi.