High impact reliability and high temperature performance of Fe and Bi added Sn-1Ag-0.5Cu solder alloys

In this paper, the impact performance of the novel Fe and Bi added Sn-1Ag-0.5Cu solders has been thoroughly evaluated under severe thermal aging at 200 °C temperature for 100, 200 and 300 h. Impact absorbed energy was determined using Charpy impact testing machine having a 5.4 m/s impact speed. The impact absorbed energy increased from 8.1 to 9.7 J with 0.05 wt.% Fe and 1 wt.% Bi addition to SAC105, raising by about 20%. With the increase in Bi content, the impact energy of the alloy did not further increase. The changes in the impact absorbed energies were corroborated by the corresponding modulus of toughness. Microstructure study via optical microscopy as well as field emission scanning electron microscopy showed that Bi reduces the sizes of the β-Sn dendrites as well as IMCs particles (Ag₃Sn and Cu₆Sn₅₎ and, thereby, strengthens the alloy. These microstructural modifications improve the strength but decrease the ductility and, as a result, influence the impact toughness of the alloys. The microstructures of Fe and Bi added SAC105 solder alloys showed better stability than SAC105 during high thermal aging due to the Fe and Bi presence in the solder, which then led to their mechanical stability during severe thermal aging.