Effect of Cu6Sn5 particles on microstructure formation and mechanical properties of Sn-58Bi solder

With the development of surface mount technology, solders are required for applications that require high reliability and dimensional stability. Composite solders, reinforced with particles in a conventional solder alloy, is an attractive and potential method. This study presents series results on the binary eutectic Sn-Bi composite solders reinforced with Cu₆Sn₅ particles (0.5wt.% and 1wt.%). With this process, the wettability of composite solders was accepted although they were worse than that of Sn-58Bi. Compared with the spread area of Sn-58Bi, that of Sn-58Bi-1wt.% Cu₆Sn₅ was reduced about 10% after reflowing for 30min. The reinforcement particles were well dispersed in the solder matrix and refined the grain size of β-Sn and Bi-rich phase. During the liquid interfacial reaction, the size of interfacial IMC was increased with reflowing time and it got larger for the addition of Cu₆Sn₅. The shear strength of composite solder joints was higher than that of Sn-58Bi/Cu. The fracture modes of composite solder were mainly ductile while that of Sn-58Bi/Cu was brittle when ε̇ =9×10^-3s^-1.