IMC Growth and Mechanical Properties of Cu/In-48Sn/Cu Solder Joints

The growth and shear properties of intermetallic compound (IMC) in Cu/In-48Sn/Cu solder joints at different bonding times have been studied, and the growth kinetics of interfacial Cu₃(In,Sn) phase at different bonding temperatures investigated. The results show that the IMC of the Cu/In-48Sn/Cu joint is composed of Cu₆(In,Sn)₅ and Cu₃(In,Sn) but transforms to Cu₃(In,Sn) after 120 min of bonding at 260°C and pressure of 3 MPa. The morphology of the Cu₆(In,Sn)₅ layer changed from flat to scallop, and the growth rate of Cu₃(In,Sn) located directly below the convex part of the Cu₆(In,Sn)₅ sector was significantly higher than that of Cu₃(In,Sn) located directly below the concave part of the Cu₆(In,Sn)₅ sector. The shear strength of the solder joints first increased then slowly decreased, reaching 21.8 MPa when increasing the bonding time to 60 min. The shear strength of the solder joints was improved by the formation of Cu₆(In,Sn)₅ and Cu₃(In,Sn), and Cu₃(In,Sn) phase played a greater role in improving the shear strength of the solder joints than did Cu₆(In,Sn)₅ phase. The growth kinetics index n of Cu₃(In,Sn) was 0.478 to 0.495, and the growth mechanism of Cu₃(In,Sn) was controlled by diffusion at bonding temperatures of 250°C to 280°C.