First-principles study of Ni additions on mechanical properties of η'-Cu6Sn5-based intermetallic compound

Amorphous NiP layers have been employed as barrier layers to regulate the formation and growth of intermetallic compounds (IMCs) within industrial contexts. The doping of Ni atoms into the crystal structure of η'-Cu₆Sn₅ resulted in the formation of the IMC of η'- (Cu,Ni)₆Sn₅. An examination of the mechanical properties of IMCs is crucial for the evaluation of solder joint longevity. Based on first-principles calculations and VRH methods, the bulk modulus, shear modulus and the elastic modulus and hardness values of η'-Cu₆Sn₅, η'-Cu_5.75Ni_0.25Sn₅, η'-Cu_5.5Ni_0.5Sn₅ and η'-Cu_5.25Ni_0.75Sn₅ IMCs were analyzed, which showed that η'- (Cu,Ni)₆Sn₅ possessed a stronger anisotropy and hardness. The K_IC of all η'-Cu₆Sn₅-based IMCs are 1.830, 1.933, 1.961, and 1.960, respectively, indicating that the doping of Ni atoms into the η'-Cu₆Sn₅ cells can favourably affect their mechanical properties reducing the likelihood of microcracking at the interface during use and increasing the shear resistance of the joint. The thermodynamic disorder parameter (TDOS) for all η'-Cu₆Sn₅-based IMCs is primarily influenced by the Sn-s and Cu-d states, which exhibit metallic properties. It has been demonstrated that the compound η'- (Cu,Ni)₆Sn₅ is more stable than the compound η'-Cu₆Sn₅. This phenomenon can be attributed to the formation of robust covalent bonds between the Ni atoms and their neighbouring Cu and Sn atoms, which occurs when Ni atoms are doped. The findings of this research can serve as a valuable reference point and theoretical foundation for future applications of NiP barrier layers in soldering.