The combined effect of reflow soldering time and Bi doping on the interfacial behavior and shear properties of Sn-0.7Cu-0.8Zn/Cu solders joint

The interfacial intermetallic compounds (IMC) layers evolution and shear properties in Sn-0.7Cu-0.8Zn/Cu and Sn-0.7Cu-0.8Zn–5Bi/Cu solder joint at different reflow soldering time were investigated. The results demonstrated that the IMC layers of solder joint with/without Bi doping and the increase of reflow soldering time are Cu 6 Sn 5 phase. However, Bi addition will increase the γ-Cu 5 Zn 8 phase closed to the IMC layer in solder matrix. The doping Bi can decrease the growth rate and voids of IMC layer. The decrease in IMC layer thickness is associated with the decline in the availability of Cu atoms and hindering the diffusion path for Cu atoms. In the case of short-time reflow soldering time, the grain size of the IMC layer in Bi-free solder joint is smaller compared to Bi-added solder joint. However, the grain size of the IMC layer of Bi-free solder joint is larger than that of Bi-added solder joint after long reflow soldering time. Although the shear strength of Bi-free and Bi-added solder joints decreases as reflow soldering time are prolonged, the shear strength of Bi-added solder joints is higher compared to Bi-free solder joints, which is the combined effect of solution strengthening, thickness reduction and grain refinement of IMC layer.