First‐Principles Investigation of Structural, Elastic, and Electronic Properties of Co‐Doped η‐Cu ₆ Sn ₅

During bonding and service processes, the remarkable anisotropic behavior of hexagonal Cu 6 Sn 5 (η‐Cu 6 Sn 5 ) intermetallic compound (IMC) in Sn‐based solder/Cu joints may result in abnormal IMC growth and subsequent failure of the solder joints. In this work, the crystalline structure, elastic properties, fracture toughness and electronic features of hexagonal η‐Cu 6 Sn 5 with Co atoms doped at the various unfilled Cu2 sites were systematically analyzed using first‐principles methods. The Young's and bulk modulus of the Co‐free η‐Cu 6 Sn 5 and its doping systems were characterized by three‐dimensional plane projections constructions, and the Young's and shear modulus were characterized by two‐dimensional plane projections. The results revealed that doping Co atoms can change the elastic anisotropy and shear resistance of η‐Cu 6 Sn 5 . Doping Co into most sites can enhance the fracture toughness of η‐Cu 6 Sn 5 to varying degrees. Electronic structure analyses demonstrated that the doping of Co changed both the electronic configuration and structural stability of η‐Cu 6 Sn 5 . Specifically, hybridization between Co‐d and Sn‐p orbitals was observed, which results in a higher peak intensity near −1.51 eV. Notably, Co‐doping at particular sites led to significant improvement in the structural stability of η‐Cu 6 Sn 5 .