Growth behavior of interfacial Cu–Sn intermetallic compounds of Sn/Cu reaction couples during dip soldering and aging

Abstract

The formation and growth of intermetallic compound (IMC) layer at the interface between pure Sn and a Cu substrate during dip soldering and aging were studied. The soldering was conducted at 250 °C using dipping method, followed by aging treatment at 150 °C for up to 10 days. The results showed that the IMC layer flattened with aging duration because the grooves in scallop-like IMC provide a more convenient access for Cu atoms to dissolve and react with solders and previous IMCs. And when isothermal aging was subjected, the growth rate of Cu₆Sn₅ was lower than that of Cu₃Sn due to Cu₃Sn growing rapidly with aging time by consuming Cu₆Sn₅ at the interface of Cu₃Sn/Cu₆Sn₅. Kirkendall voids were observed at Cu₃Sn/Cu interface as well as inside the Cu₃Sn layer as the Sn/Cu couple was aged at 150 °C for prolonged time, with which the Cu₃Sn IMC dominates the interfacial IMCs growth. During solid-state aging, the mean diameter (d) of interfacial Cu₆Sn₅ grains increased dramatically with the increasing time (t). The relationships between d and t were given to be d = 1.22 t ^0.291 for samples formed at 250 °C for 1 min and d = 1.53 t ^0.259 for samples formed at 250 °C for 5 min, respectively.