Effects of Bi and Sb co-doping at Sn sites on the structure, mechanical properties and electronic structure of η′-Cu6Sn5: A first-principles study

As an important intermetallic compound at the interface of tin-silver-copper(SAC) solder joints, studying the properties of η′-Cu₆Sn₅ is of great significance. This paper employs first-principles calculation methods to investigate the effects of 4.55 at.% Sb and Bi co-doping on the structure, elastic anisotropy, electronic structure, and fracture toughness of η′-Cu₆Sn₅. Calculation results show that the lattice constants of the doped structures increase, and the formation energies are less than 0 eV/atom, indicating that stable compounds are easily formed. Mechanical property calculations reveal that doping alters the mechanical properties of η′-Cu₆Sn₅ and significantly reduces its electronic anisotropy. Electronic structure and fracture toughness calculations demonstrate that doping modifies the metallic properties and fracture toughness of η′-Cu₆Sn₅. Among different doping structures, the Bi-2 Sb-2 structure shows the optimal performance in all aspects of properties. This provides a theoretical basis for studying the doping of Bi and Sb to improve the reliability of SAC solder joints.