Interfacial reactions in Cu/Sn/Cu(Ni) systems during soldering under temperature gradient

The diffusion behavior of Cu and Ni atoms undergoing liquid-solid thermomigration in Cu/Sn/Cu and Cu/Sn/Ni solder joints was investigated under the temperature gradients of 136.5 °C/cm and 154.0 °C/cm at 250 °C, respectively. Asymmetrical growth of the interfacial IMCs was observed in the Cu/Sn/Cu solder joints, i.e., the IMCs at the cold end were much thicker than those at the hot end. The Cu-Ni cross-solder interaction occurred in the Cu/Sn/Ni solder joints during reflow on hot plate. Cu and Ni atoms arrived to the opposite sides under the concentration gradients, resulting in the formation of (Cux,Ni1−x)6Sn5 IMCs at both interfaces. The interfacial reaction was accelerated by the combined effect of Cu concentration gradient and thermomigration. While in Cu/Sn/Cu solder joints, the thermomigration process was weakened by Cu concentration gradient. As a result, the IMCs layers at both cold and hot ends in Cu/Sn/Ni solder joints were thicker than those in Cu/Sn/Cu solder joints after the same reflow time.