Recent Advances in Sn-Based Lead-Free Solders for Electronic Packaging: A Review

With the global enforcement of environmental regulations restricting the use of lead-based solders, the development of lead-free solder alloys for electronic packaging has become a central topic in ensuring both device reliability and sustainable manufacturing. This review summarizes the current research progress on lead-free solders for electronic packaging, focusing on the performance characteristics and modification strategies of major alloy systems such as Sn-Cu, Sn-Zn, Sn-Bi, Sn-Ag, and Sn-Ag-Cu. Although each system exhibits unique advantages, challenges such as high melting temperature, poor wettability, oxidation susceptibility, and high material cost remain unresolved. Performance optimization can be effectively achieved through alloying element doping and nanoparticle reinforcement. Alloying elements refine the microstructure via solid-solution strengthening, grain refinement, and secondary-phase strengthening while suppressing the coarsening of intermetallic compounds (IMCs). Meanwhile, nanoparticles enhance interfacial stability through dispersion strengthening and diffusion barrier effects, thereby improving wettability, mechanical strength, and long-term reliability. Finally, this paper proposes potential research directions for the next generation of lead-free solders and provides an outlook on their future applications in advanced electronic packaging.