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

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 A degrees C using dipping method, followed by aging treatment at 150 A degrees 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 A degrees 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 A degrees C for 1 min and d = 1.53 t (0.259) for samples formed at 250 A degrees C for 5 min, respectively.