Effects of cooling rate on microstructure and microhardness of lead-free Sn-3.0Ag-0.5Cu solder

The effects of cooling rate on the microstructure and microhardness of Sn-3.0Ag-0.5Cu solder was studied. The results showed that the undercooling of the solder increases with the cooling rate increasing, resulting in eutectic composition shifting to the hypoeutectic region, thus increasing the volume ratio of the primary β-Sn and decreasing its grain size, Simultaneously, Ag₃Sn in the eutectic region transforms from the large lamellar-like to uniformly distributed fine granular-like. Due to the grain refinement of the primary β-Sn and dispersion strengthening of the fine Ag₃Sn in SAC305 solder, its microhardness markedly increases.