Shear test parameters for brittle fracture of flip chip solder joint

Abstract

Compared to conventional Sn-Pb solder, ternary Pb free solder alloys are particular susceptible to brittle fracture through the formation of intermetallic compound layers. However, the conventional shear test of the solder ball joint has been reported to be inappropriate for confirming the susceptibility to brittle fracture of ball grid array solder joints. In this study, we investigated the effects of two shear test parameters, the shear height and shear speed to determine the optimum shear conditions for the brittle fracture of flip chip solder joints. The solder composition and process used in this study were Sn-3·0Ag-0·5Cu and low cost bumping with electroless nickel immersion gold followed by solder paste screen printing. Increasing shear height, at a fixed shear speed, decreased the shear force, whereas increasing the shear speed, at a fixed shear height, increased the shear force. The experimental and computational simulation results indicated that a low shear height and high shear speed improve the bonding force and are generally more appropriate for the brittle fracture of flip chip solder joints. The failure mechanisms were discussed in terms of the von Mises stresses and equivalent plastic strain distributions.