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

Cu6(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 Cu24Sn19In1 is a new IMC, and its structural stability is better than that of Cu6Sn5. Moreover, the anisotropy of Cu24Sn19In1 is stronger than that of Cu6Sn5. Based on first-principles calculations and VRH methods, the bulk modulus, shear modulus, Young’s modulus, and Poisson's ratio of polycrystalline Cu6Sn5 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 Cu24Sn19In1, respectively. All elastic moduli of the latter are larger than those of the former. The formation of a Cu24Sn19In1 IMC can improve the mechanical properties of the IMC layer.