Microstructure of a lead-free composite solder produced by an in-situ process
A composite solder, which consisted of solder matrix and intermetallic reinforcements, was manufactured by an innovative method. The cast ingot of the Sn-6.9Cu-2.9Ag alloy has primary Cu6Sn5 intermetallics in dendritic form. After rolling, the intermetallic dendrites are crushed into fine particles and distributed uniformly in the solder matrix. The crushed intermetallic particles do not melt, and they retain their shape during spheroidizing and reflow because of their high melting temperature. Coarsening and gravitational segregation of the particles was observed during reflow and analyzed theoretically.