Evaluation of the microstructure, distribution of the intermetallic compounds, and mechanical behavior of SC07 solders with In, Ni, and TiO₂ NPs minor additions

In this paper, the impact of small additions of indium (In), nickel (Ni), and Titanium dioxide nanoparticles (TiO₂ NPs) in the microstructure and characterization of eutectic Sn–0.7 Cu (SC07)-based solder were investigated. The third element In, Ni, or TiO₂ NPs were added in varying amounts 0.4 or 0.8 wt% to SC07 alloy by replacing an equal amount of Sn for each addition. Structural analysis of the investigated samples showed that the addition of Ni or In modified the eutectic composition, leading to the appearance of primary phases (Cu₆Sn₅) followed by the formation of intermetallic compounds (IMCs) (Cu, Ni)₆Sn₅ and Cu₆(Sn, In)₅. However, addition of TiO₂ NPs did not lead to formation of any new IMCs but refine β-Sn dendrites grains with a decrease in the volume fraction of Cu₆Sn₅ IMC. The crystallite size, lattice strain, and dislocation density of the SC07 solder alloy were improved in terms of third addition. The results indicated that the smallest crystallite size for SC07–0.8In associated with largest lattice strain and highest dislocation density. Microhardness tests were performed for all samples at room temperature. The results illustrate the enhancement indentation creep resistance of SC07 reinforced solder, which inherently correlates to the microstructure refinement and the formation of intermetallic phases (Cu, Ni)₆Sn₅ and Cu₆(Sn, In)₅ with higher hardness values. The obtained stress exponent values are in the range 9.26–11.46 for all tested alloys which close to that creep mechanisms associated with dislocation movement such as dislocation creep are predominant. Thus, we conclude that the greatest value of stress exponent for SC07–0.8In (10.9–11.46) at different loads suggested to be more resistant to indentation creep which improves the mechanical strength compared to other solders.