Size and geometry effects on microstructural evolution in Sn microbumps during isothermal aging

A phase field model on the Sn-Cu binary reaction is used to systematically study the effects from the size, geometry and stress on the microstructural evolution in Sn microbumps with Cu pads during aging at 150°C. It is found that a thicker interfacial Cu₃Sn layer, a thinner interfacial Cu₆Sn₅ layer and a faster consumption rate of the Cu pad can be obtained by increasing the pad size of the microbump, no matter whether the bulk Cu₆Sn₅ is considered or not. In addition, there are more bulk Cu₆Sn₅ Particles remained by increasing the bump height or by adopting an hourglass-shaped microbump with the latter resulting in a faster consumption of the Cu pads. Furthermore, the amount of the interfacial Cu₆Sn₅ and Cu₃Sn phases is found to be controllable by applying external mechanical loads. A compressive load is in favor of the growth of the interfacial Cu₃Sn phase, while a tensile load can enhance the growth of the interfacial Cu₆Sn₅ phase.