Effect of thermomigration on evolution of interfacial intermetallic compounds in Cu/Sn/Cu and Cu/Sn0.7Cu/Cu solder joints

The growth behaviors of the interfacial intermetallic compounds (IMCs) in Cu/Sn/Cu and Cu/Sn0.7Cu/Cu solder joints were systematically investigated under a temperature gradient of 1046 °C/cm for 250, 500, and 750 h, respectively. Thermomigration (TM) caused the interfacial IMCs accumulation at the cold end and disintegration at the hot end, and the evolution rate in Cu/Sn0.7Cu/Cu solder joint was faster than that in Cu/Sn/Cu solder joint. In addition, it was observed that both Cu₆Sn₅ and Cu₃Sn IMC at the cold end grew with TM time in Cu/Sn0.7Cu/Cu solder joint, and the Cu₃Sn at the hot end grew faster than at the cold end. However, no obvious change was observed in Cu/Sn/Cu solder joint. Therefore, we conclude that Cu/Sn0.7Cu/Cu solder joint has a more serious TM damage compared with Cu/Sn/Cu solder joint. The microhardness detection indicates that TM can cause microhardness reduction in the two solders, and the microhardness gradually increased from the hot end to the cold end, which was attributed to grain coarsening and higher vacancy concentration at the hot end.