Manufacture, microstructure and microhardness analysis of Sn-Bi lead-free solder reinforced with Sn-Ag-Cu nano-particles

This paper investigates a composite solders obtained by adding Sn-3.0Ag-0.5Cu (SAC) nano-particles into conventional eutectic Sn-58Bi solder paste. The microstructure analysis and the measurement of the Vickers microhardness have been carried out. Utilizing the self-developed consumable-electrode direct current arc (CDCA) technique, the Sn-3.0Ag-0.5Cu nano-particles with an average particle size between 20 and 80 nm are prepared. The reinforced lead-free Sn-Bi solder was prepared by thoroughly blending the nanometer-sized SAC particles into the eutectic Sn-Bi solder paste. The SAC reinforced Sn-Bi composite solder paste was printed onto ENIG/Cu metalized substrate and reflowed in a conventional reflow oven. After reflow, the morphology of the as-solidified reinforced composite solder was observed by means of SEM and TEM. The Vickers microhardness measurements indicated that the addition of SAC nano-particles enhances the overall strength of the eutectic solder, and the results agree well with the theory of dispersion strengthening.