Thermal stability of epoxy-based Sn-58Bi solder joint

Abstract

The epoxy(EP)-based Sn-58Bi solder paste consists of a curable flux and Sn-58Bi particles. In addition to its function as a flux, the curable flux forms a cured shell on the periphery of the solder joint. Under appropriate process parameters, the EP-based Sn-58Bi solder paste can form solder joints with a shell-core structure on the Cu substrate. Compared to conventional Sn-58Bi solder paste, the solder joint of EP-based Sn-58Bi solder paste has a higher heat resistance and joint strength. To investigate the heat resistance of the solder joint of EP-based Sn-58Bi solder paste, the thermal cycle test was carried out in the temperature range of 130-170°C. Metallographic microscopy and scanning electron microscopy (SEM) were used to observe the interfacial microstructure of the solder joints and to analyze the difference in the microstructure of the solder joints in relation to the thermal history. The results show that the solder joint interface of the EP-based Sn-58Bi solder paste is more stable than that of the conventional Sn-58Bi solder paste, indicating that the cured EP shell on the periphery of the solder joint can effectively improve the thermal stability of the solder joint.