Variable eutectic temperature caused by inhomogeneous solute distribution in Sn–Zn system

The microstructure and thermal properties of Sn–Zn–(Bi, In, Ga) solder alloys were examined in this study. Results show that the addition of those alloying elements gave rise to a reduced melting point, more broadened melting range and a less uniform microstructure comprising alternate normal–irregular eutectic cells. It was also found that the formation of an abnormal eutectic structure and a unique phenomenon, namely, continuously varying eutectic temperature and thus an enlarged solidus–liquidus temperature range, are due to the inhomogeneous dissolution feature of the solute elements.