Full intermetallic compound (IMC) solder joints present fascinating advantages in high-temperature applications. In this study, the mechanical properties and elastic anisotropy of η′-Cu₆Sn₅ and Cu₃Sn intermetallic compounds were investigated using first-principles calculations. The values of single-crystal elastic constants, the elastic (E), shear (G), and bulk (B) moduli, and Poisson’s ratio (ν) were identified. In addition, the two values of G/B and ν indicated that the two IMCs were ductile materials. The elastic anisotropy of η′-Cu₆Sn₅ was found to be higher than Cu₃Sn by calculating the universal anisotropic index. Furthermore, an interesting discovery was that the above two types of monocrystalline IMC exhibited mechanical anisotropic behavior. Specifically, the anisotropic degree of E and B complied with the following relationship: η′-Cu₆Sn₅ > Cu₃Sn; however, the relationship was Cu₃Sn > η′-Cu₆Sn₅ for the G. It is noted that the anisotropic degree of E and G was similar for the two IMCs. In addition, the anisotropy of the B was higher than the G and E, respectively, for η′-Cu₆Sn₅; however, in the case of Cu₃Sn, the anisotropic degree of B, G, and E was similar.

In this paper, the mechanical properties of Cu 3 Si were researched by the first-principles method. And the method based on density functional theory (DFT). The exchange correlation energy function adopts the generalized gradient approximation (GGA). Approximately calculate the bulk modulus, Young's modulus, shear modulus and Poisson's ratio of Cu 3 Si crystal by Voigt-Reuss. The B/G value of Cu 3 Si is 3.66, and it can be considered that Cu 3 Si is a ductile material. The anisotropy index A ^U is 6.169, indicating that the anisotropy of Cu 3 Si is extremely obvious. The anisotropy indexes A B and A G are 0.004 and 0.381, respectively, revealing the weak anisotropy for bulk modulus and obvious anisotropy for shear modulus. The shear anisotropy indexes A 1 , A 2 and A 3 are 0.605, 0.605, 1.005, respectively, showing that the Cu 3 Si crystal exhibits obvious shear anisotropic characteristics at {100} and {010} planes, and there is almost no anisotropy at {001} plane. Moreover, The orientation of the bulk modulus, Young's modulus and shear modulus, as well as their maximum and minimum values were identified.