Alloying effects on the phase stability and mechanical properties of doped Cu-Sn IMCs: a first-principle study

Cu-Sn phases are important intermetallic compounds formed at the interface between solder and substrate in the soldering process. They exist in several crystal structures (η′, η, η and η etc.). The solid-state phase transformation that occurs among Cu-Sn intermetallic compounds is a crucial issue for industry applications, because the associated volume change inevitably leads to microstructural instability. Generally, four alloying elements, i.e., Ni, Au, Zn, and indium (In), are used as alloying elements to stabilize the high temperature hexagonal η-phase. However, the physical mechanism of this stabilization effect, especially on the high temperature η and η phases, is still unclear. In the present study, first-principle calculations were performed to study the stability and mechanical properties of CuSn (η and η) and CuSn (η′) when doped with Ni, Au, Zn, and indium alloying elements. It is shown that their phase stability and mechanical properties could be enhanced by these elements in some circumstances. Ni-doping can significantly enhance both the stability and the mechanical properties of the three phases, whereas Zn-doping exhibits a significant effect on that of the η phase