Influence of Alloying Elements on the Phase Structure, Stress-Strain Behavior, and Fracture Toughness of Ni(3)Sn: A First-Principles Study.

Transient liquid-phase bonding (TLPB) enables the low-temperature fabrication of encapsulated solder joints with high-temperature resistance and electromigration resilience; yet, Ni-Sn TLPB joints suffer from brittle fracture due to intermetallic compounds (IMCs). This study investigates the Co, Cu, and Pt alloying effects on Ni(3)Sn via formation energy, molecular dynamics, and first-principles calculations. Occupancy models of Ni(6-x)M(x)Sn(2) (M = Co, Cu, and Pt) were established, with the lattice parameters, B/G ratios, fracture toughness (K(IC)), and stress-strain behaviors analyzed. The results reveal that Co enhances fracture toughness and reduces Ni(3)Sn anisotropy, mitigating microcrack risks, while Cu/Pt introduce antibonding interactions (Cu-Sn and Pt-Sn), weakening the bonding strength. The classical B/G brittleness criterion proves inapplicable in Ni-M-Sn systems due to mixed bonding (metallic/covalent) and the hexagonal structure's limited slip systems. The Ni(6-x)Co(x)Sn(2) formation improves toughness with a low Co content, supported by an electronic structure analysis (density of states and Bader charges). The thermodynamic stability and reduced molar shrinkage (Ni + Sn → Ni(3)Sn) confirm Co's efficacy in optimizing Ni-Sn solder joints.