Effects of the melt state on the microstructure of a Sn-3.5%Ag solder at different cooling rates

► Liquid-liquid structure transition (LLST) does occur in lead-free Sn-3.5%Ag solder. ► The increases of solid-liquid interface energy results in the melts need a larger undercooling to nucleate and a slower rate to grow when the melt experiences LLST. ► The solidification microstructures of Sn-3.5%Ag alloy are refined when the melt experiences LLST. ► When LLST occurs, the eutectic growth pattern would be changed.