Abstract: Aimed at the problem of fine solder in large power devices, the microstructure and components of SnPb soft solder of device are analyzed and the failure modes for polishing are documented. The failure causes are discussed: the remains of Aluminum Oxide are still in the solder and result in the deterioration of soft solder . According to the analysis, improved measures are suggested. Experiment results significantly favored the processing of SnPb soft solder in large power devices.