Interfacial behavior between copper foil and tin upon thermal aging

This study investigated the thermal effect on the interfacial IMC (Cu₃Sn and Cu₆Sn₅) formation at the interface between pure tin and a copper substrate at 125degC. During thermal aging, the morphology of Cu₆Sn₅ transformed from a scallop to a layer shape. The thickness of IMCs (Cu₃Sn, Cu₆Sn₅) changed with an increase in aging time. It was observed that scallop Cu₆Sn₅ decomposed during heat aging for up to 420 hours; in contrast, upper Cu₃Sn grew rapidly. Between 420 hours and 2693 hours, both Cu₃Sn and Cu₆Sn₅ increased with increasing aging time. However, between 2693 hours and 2854 hours of thermal aging, the shrinkage of Cu₃Sn and the growth of Cu₆Sn₅ were induced as a result of the segregation of voids formed at the Cu₃Sn/Cu interface. On a free surface, Cu₆Sn₅ and Cu₃Sn tended to grow in the X-Y and Z planes, respectively.