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.