<p>Presently, high-stress and wear-resistance solder alloys are increasingly required due to the dynamic growth of the electrical and electronic sector. The mechanical and functional integrity of solder joints serves as a key factor in determining the reliability of modern electronic assemblies. In this study, Sn-based lead-free solder alloys micro alloyed with 0.1 wt.% nickel (Ni) was synthesized, using silver (Ag), copper (Cu), and bismuth (Bi) as base alloying elements. The role of Ni incorporation on tensile strength, microhardness, wettability, and electrical resistivity was systematically investigated. Tensile and hardness measurements revealed a notable improvement in mechanical strength with the incorporation of Ni. Wettability tests demonstrated enhanced spreading behavior, indicating better solder-substrate interaction, while electrical resistivity measurements confirmed that Ni additions did not significantly compromise conductivity. Microstructural analysis via scanning electron microscopy (SEM), showed that Ni promotes the formation of fine, uniformly distributed intermetallic compounds (IMCs), contributing to grain refinement and improved load-bearing capacity. Ni effectively suppressed the generation and evolution of brittle IMCs at the solder-substrate interface during thermal loading. These enhancements result from the combined effects of microstructural refinement and interfacial stabilization. The findings suggest that Sn–X–0.1Ni alloys offer superior reliability for applications subjected to mechanical and thermal stresses.</p>