Effects of zinc on the interfacial reactions of tin-indium solder joints with copper.

Sn-20.0 wt%In (Sn-20.0In) alloy is a promising base material in Pb-free solders for low-temperature applications. Zn is often used as an additive to Pb-free solders to reduce the extent of undercooling during reflow. Cu is the most commonly used substrate in electronics industry. Interfacial stability at Sn-In-Zn/Cu joints is crucial to reliability of electronic products. In this study, interfacial reactions between Sn-20.0 wt%In- x wt%Zn (Sn-20.0In- xZn) solders and Cu where x = 0.5, 0.7, 1.0, 2.0, 3.0, and 5.0 at 150, 230, and 260 °C were experimentally examined. It is found that the reaction phase formation and interfacial morphologies are strongly influenced by Zn concentrations. The reaction phases evolve from the CuSn phase, CuZn and CuZn phase, to CuZn phase with higher Zn doping in the solders. The CuZn phase acted as a diffusion barrier and suppressed the growth of the CuSn phase. The results indicate that 2.0 wt%Zn addition resulted in the gentlest reactions during both soldering and solid-state ageing in Sn-20.0In- xZn/Cu couples. [ABSTRACT FROM AUTHOR]