Study of cooling rate on lead-free soldering microstructure of Sn-3.0Ag-0.5Cu solder

Compared to traditional Sn-Pb solder, the microstructure of lead free solder Sn-3.0Ag-0.5Cu is more complex. The cooling rate significantly affects the secondary dendrite arm size and the IMC morphology, which influence the solder joint mechanical behavior. In this paper, the solder joint microstructure and morphology of three different cooling rates: air cooling, forced air cooling and water cooling were studied. The morphology of the Ag₃Sn was relatively spherical under water cooling, and had a needle-like morphology under air cooling. The IMC of the joint was a relatively planar Cu₆Sn₅ layer under water cooling while a nodular Cu₆Sn₅ layer was formed under air cooling.