Nanocrystalline (NC) Cu–Ta thin films were successfully fabricated by unbalanced magnetron sputtering on crystal silicon and glass substrates. Thin films doped with different Ta contents were prepared by altering the sputtering current of the Ta target. The micromorphology, microstructure, mechanical properties, electrical properties, and thermal stability of the films were investigated. The results on the microstructure of the as-deposited films demonstrated that Ta forms an FCC Cu (Ta) metastable supersaturated substitutional solid solution in Cu. In addition, with the increase of Ta content, the NC Cu–Ta films tended to be amorphous. Furthermore, the grain size of the post-annealed Cu–Ta films increased slightly due to recrystallization and in the metastable solid solution, Ta was exsolved and precipitated from the Cu matrix. The lowest resistivity (3.165 × 10⁻⁷ Ω·m⁻¹) and the highest elastic modulus (125.2 GPa) were obtained with a Ta target current of 0.5 A.

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 Ni₃Sn via formation energy, molecular dynamics, and first-principles calculations. Occupancy models of Ni_6−xM_xSn₂ (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 Ni₃Sn 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−xCo_xSn₂ 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 → Ni₃Sn) confirm Co’s efficacy in optimizing Ni–Sn solder joints.

Cr alloyed Cu exhibits puzzlingly high electrical conductivity compared with other 3d elements alloying. Here, we present a theoretical understanding based on standard electronic band structure calculations. The influence of local spin-polarization on electrical conductivity was first investigated. It is found that the non-magnetic calculation produces a high density of states peak at the Fermi level, and then it fails to explain the high electrical conductivity of Cu-Cr alloy. When spin polarization is taken into account, the density of states is significantly reduced, and the results are in good agreement with experimental measurements. Meanwhile, the calculation results can explain the increase in strength and also lead to some interesting deductions. Finally, a computational program is proposed to select a high electrical conductivity Cu alloy based on a simple calculation model.