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

Amorphous Ni-P 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 fl'-Cu6Sn5 resulted in the formation of the IMC of fl'- (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 fl'-Cu6Sn5, fl'-Cu5.75Ni0.25Sn5, fl'-Cu5.5Ni0.5Sn5 and fl'-Cu5.25Ni0.75Sn5 IMCs were analyzed, which showed that fl'- (Cu,Ni)6Sn5 possessed a stronger anisotropy and hardness. The KIC of all fl'-Cu6Sn5-based IMCs are 1.830, 1.933, 1.961, and 1.960, respectively, indicating that the doping of Ni atoms into the fl'-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 fl'-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 fl'- (Cu,Ni)6Sn5 is more stable than the compound fl'-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 Ni-P barrier layers in soldering.