Abstract
The melt structure transition behaviors of SnBi₁₇Cu_0.5 solder alloy were investigated in detail. By Differential Scanning Calorimetry (DSC) and electrical resistivity method, an anomalous change has been found in 835–875 °C during heating process on the ρ-T and DSC curves. It reveals that a liquid-liquid structure change (LLSC) occurs in the melt. Through melt overheating treatment, the influence of LLSC on solidification process and material properties has been further studied: bigger solidification undercooling degree in the solidification process, finer and more dispersing solidification structure, and more importantly, the mechanical and welding properties of the solder alloy have also been obviously improved.

Key words
melt structure, liquid structure change, SnBi₁₇Cu_0.5 solder, soldering property, solidification

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