Microstructures and Properties of Sn-Bi-In Low-temperature Lead-free Solders

The characteristics of microstructures, thermal properties, wettabilities and mechanical properties of Sn-Bi-In solders with different composition were studied. The results show that the microstructure of Sn-Bi-In solders consists of beta-Sn, Bi and InBi phases. The reduction of Bi content can result in the proportion decrease of Bi and InBi phases. There are three endothermic peaks with different magnitudes on the DSC curves, and the onset melting temperature of solders are between 101.3 similar to 103.4 degrees C. With the increase of Sn concentration, the melting range of solders firstly decreases and then increases, while the spreading area firstly increases and then decreases. The microhardness of solders increases with the rising of Bi content; in addition, the hardness is remarkably higher than that of Sn-Bi eutectic alloy when the In element is added to solder. The tensile strength and elongation of solders decrease with increase of Bi content.