Effects of temperature and humidity on the formation of solder bead and microstructure in Sn-58Bi Solder joint

Throughout the development of electronic packaging technology, Sn-58Bi lead- free solder has been widely applied because of its low-temperature welding. However, during the production process, the formation of solder bead is a terrible problem that is commonly encountered with Sn-58Bi solder joint. This problem not only damages the macroscopic appearance of the solder joint, but may encompass other solder joints as well. Due to factors such as vibration and temperature variation, the formation of solder bead could potentially lead to circuit fault. The purpose of this study is to investigate how the oxidation of Sn-58Bi solder powder, under different temperature and humidity, impacts the formation of solder bead and microstructure of the solder joint. The scanning electron microscope and auger electron spectroscopy were used to analyze the oxidation process of Sn-58Bi solder powder. The results indicated that, the formation of solder bead was enhanced with the increased temperature and humidity which also led to the deteriorated microstructure and poor wettability. In addition, the oxidation behavior of Sn-58Bi solder powder revolved around the adsorption and decomposition of O molecules and the subsequent interaction between the O atoms with the Bi atoms.