Effect of In-Doping on Mechanical Properties of Cu6Sn5-Based Intermetallic Compounds: A First-Principles Study

Cu 6 (Sn, In) 5 phase intermetallic compounds (IMCs) were generated by In doping in Sn-Ag-Cu(SAC) solders. First, the optimum site of the In atom replacing the Sn atom was determined. Subsequently, the elastic constants of the IMCs were calculated based on the determined structure. All calculations were performed using first-principles calculations. The results show that Cu 24 Sn 19 In 1 is a new IMC, and its structural stability is better than that of Cu 6 Sn 5 . Moreover, the anisotropy of Cu 24 Sn 19 In 1 is stronger than that of Cu 6 Sn 5 . Based on first-principles calculations and VRH methods, the bulk modulus, shear modulus, Young’s modulus, and Poisson's ratio of polycrystalline Cu 6 Sn 5 are 78.31 GPa, 39.00 GPa, 100.35 GPa, and 0.2864 GPa, respectively, and 88.08 GPa, 41.42 GPa, 107.43 GPa, and 0.2967 GPa of Cu 24 Sn 19 In 1 , respectively. All elastic moduli of the latter are larger than those of the former. The formation of a Cu 24 Sn 19 In 1 IMC can improve the mechanical properties of the IMC layer.