Depiction of the elastic anisotropy of AuSn4 and AuSn2 from first-principles calculations

As the solder joints become increasingly small and contain only a few grains, their mechanical properties cannot be determined from conventional mechanical tests as with bulk samples, and there may be a considerable variation in mechanical behavior from joint to joint because of the anisotropy of mechanical properties. In this paper, elastic constants of single-crystal AuSn₄ and AuSn₂ were preliminarily determined through first-principles calculations to characterize their polycrystalline elastic behavior and elastic anisotropy. The ideal bulk, shear, and Young's moduli, as well as Poisson's ratios were determined using the Voigt-Reuss-Hill method. These compounds exhibited distinct anisotropy in Young's modulus, which may be partially responsible for the discrepancy in the experimental results.