Corrosion Behavior of Ultrasonic Atomized and Centrifugal Atomized SnAgCu Solder Powders in Solder Paste

Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to comparatively study the corrosion behavior of ultrasonic atomized and centrifugal atomized SnAgCu solder powders in solder paste. The results show that the ultrasonic atomized solder powders had a smooth surface where Ag-rich phase particles distributed evenly. The surfaces of centrifugal atomized solder powders were covered with dendrites, and the Ag-rich phase particles aggregated at the grain boundaries. The corrosion of the ultrasonic atomized solder powders occurred in the position of large Ag rich particles, showing the characteristic of localized pitting corrosion, while the centrifugal atomized powders showed the characteristic of general corrosion, and the corrosion was particularly serious at the grain boundaries. The statistics show that only a small amount ultrasonic atomized solder powders had corrosion pits, while all the centrifugal atomized solder powders had morphological changes due to corrosion. With the extension of storage time, i.e. corrosion time, the oxide layers on the surfaces of centrifugal atomized solder powders thinned more rapidly, and their corrosion resistance was inferior to that of ultrasonic atomized solder powders. The distribution of alloy phases and grain boundaries was a key factor in the differences of solder paste in the storage stability of solder paste.