Effect of aging time on interfacial microstructure of Sn-3.8Ag-0.7Cu solder reinforced with Co nanoparticles

This paper investigates the growth of intermetallics in Sn-3.8Ag-0.7Cu (SAC) solder with and without Co nanoparticle reinforcement. Co reinforced composite was prepared by mechanically mixing 0.5 wt% and 1.5 wt% Co nanoparticles respectively into Sn-3.8Ag-0.7Cu solder paste. The formation and growth of the intermetallic compounds (IMC) at the solder joint interface were evaluated after thermal aging at 150degC for up to 1008 hours. In the solder joint, Cu₆Sn₅ intermetallic was observed on Cu substrate, followed by Cu₃Sn intermetallic formation between Cu₆Sn₅ and Cu after prolonged aging. The thickness of both IMC increased linearly as a function of square root of aging time. The Co nanoparticle reinforcement tended to suppress the growth of Cu₃Sn intermetallic layer. However, the total of IMC thickeness was almost the same for the specimen with or without Co nanoparticle reinforcement.