Influences of Ag and In alloying on Sn-Bi eutectic solder and SnBi/Cu solder joints

摘要

In this study, the Ag and In were alloyed to the Sn-58Bi solder, and their individual and combined influences on the SnBi solder and the SnBi/Cu solder joints were investigated. The results indicate that the In can effectively decrease the melting temperature and improve the wettability of the solder, while the Ag shows slight impacts on the melting behavior and the wetting properties. During the isothermal aging at 100 ℃, growth rate of the intermetallic compounds (LMCs) layer at the Ag-bearing solders/Cu interfaces are lower, while that at the In-bearing solders/Cu interfaces are much higher, because the substitution of Sn in the Cu_6Sn_5 IMC by In alters the interfacial diffusion behavior and assist in faster growth of IMCs layer. The Bi segregation at the long-term aged SnBi/Cu interface is eliminated in the aged SnBiAg/Cu, SnBiln/Cu and SnBiAgIn/ Cu solder joints. Tensile strength of all the solders joints decreases with increasing aging time, while the sharp decrease in the strength of the long-term aged SnBi/Cu solder joints is inhibited once the Bi segregation is eliminated, and fracture occurs mainly around the IMCs/solder interface. For the In-bearing solder joints, the Cu_6(Sn,In)_5 decrease the adhesion force between the solder and the interfacial IMCs, while the SnBiAg/Cu joints shows the highest strength. Based on the results, a more practicable method to inhibit the Bi embrittlement at the aged SnBi/Cu solder joints is proposed.