Effect of Zn Additions on the Mechanical Properties of Cu6Sn5-Based IMCs: Theoretical and Experimental Investigations

The influences of Zn solubility on the mechanical properties of Cu6Sn5-based intermetallic compounds are investigated by first principles calculations and experimental work. A stress-strain approach is employed to calculate elastic properties. The polycrystalline elastic properties are obtained from single-crystal elastic constants to understand the mechanical properties, which are compared with our experimental results by nanoindentation. Our results demonstrate that doping small amounts of Zn into Cu6Sn5 can stabilize the hexagonal structure during the thermal aging process, and that Zn affects the mechanical stability, ductility, and modulus of eta'- and eta-Cu6Sn5 compounds. By calculating the electronic structure and charge density distribution, we find that the covalent bonding of the nearest-neighbor Sn and Zn atoms to Cu atoms are stronger than the previous Cu-Sn bonding, which can yield an energy gain when bonding states are created.