Effects of Mixed Percentage on the Microstructure and Mechanical Properties of Sn-52In/Sn-3.0Ag-0.5Cu Hybrid Solder Joints

The microstructural evolution and mechanical properties of Sn-52In/Sn-3.0Ag-0.5Cu hybrid solder joints soldered at different reflow temperatures (150°C, 175°C, 200°C) were investigated. The mixed percentage of as-soldered hybrid solder joints increased with increasing reflow temperature. With increasing mixed percentage, finely dispersed Ag₂In and Ag₃Sn particles led to significant refinement of the size of β-Sn grains, and consequently, the combined effect of fine grain strengthening and second-phase dispersion strengthening improved the shear strength, ductility, and fracture energy of the hybrid solder joints. The fracture site of the hybrid solder joints shifted from the Cu₆(Sn, In)₅ intermetallic compound (IMC)/solder interface to the mixed zone of the solder, and the fine β-Sn grains attenuated crack propagation, enabling more fracture energy to be absorbed before fracture. The hybrid solder joint with 100% mixed percentage exhibited the highest shear strength of 87.8 MPa, highest displacement of 251 μm, and highest fracture energy of 1.4 J.