Study of microstructure evolution and temperature distribution in eutectic SnBi solder joints under high current density

Microstructure evolution and temperature distribution of eutectic SnBi solder joint under high current density of 1×10⁴A/cm² at room temperature were investigated in the current study. With the increase of current stressing time, a continuous Bi segregation layer was formed and grew along the interface at the anode side, and a Sn rich region was found at the cathode side. Due to the microstructure changes in solder alloys, temperature distribution tended to be nonuniform. Because of the aggregation of Bi atoms, which have higher electrical resistivity and lower thermal conductivity, at the anode side, the temperature of anode was higher than the cathode. Due to the formation of severe cracks in the solder joints, the local Joule Heating effect was enhanced and the local temperature was much higher. It was found that the microstructure evolution induced by electromigration (EM) could alter the temperature distribution. By using the infrared microscope to record temperature in the solder joint during current stressing, the relationship was established between microstructural changes and temperature filed in the SnBi joint under high current density.