Ternary intermetallic compounds in Au–Sn soldering systems—structure and properties

The intermetallic compound AuSn is essential for the wetting of Au-rich AuSn solders. On the addition of In or Sb, pseudo-binary compounds AuSn1−x In x (x ≤ 0.33) and AuSn1−y Sb y (y ≤ 0.17) are formed. Both adopt the AuSn structure type (P63/mmc, Z = 2). This single-crystal X-ray diffraction study reveals that there is an absence of superstructure ordering upon long-time annealing (years). This behavior constitutes a surprising contrast to the related compounds in the systems Cu–In–Sn and Cu–Sn–Sb. As subsequent total energy calculations disclose, superstructure ordering is neither expected at 0 K nor by the application of high pressure. Hence, decomposition to AuSn and its neighboring phases in the ternary phase diagrams is the only way to release chemical pressure quickly. However, the ternary phases are formed at the expense of the binary compound AuSn, when moving away from the ideal composition. To give an idea how additions of In and Sb will affect the performance of AuSn in the solder joint, we studied the physical properties such as magnetism and resistance as well as mechanical properties such as hardness, elastic modulus, and fracture behavior.