Solder paste metamorphism

Solder paste quality can be improved from microstructure and surface status of the solder powder. In this work, the micro-morphology of solder paste was observed and the particle surface condition was analyzed. Also, the conditions of corrosion and the corrosion products in different organic acid groups (activators) were analyzed. The result shows that the SnO passive film on the solder powder surface reacts with the COO- in the active agent of the solder paste. This reaction led the passivation layer to be peeled off. It also caused the change in solder powders' physical and chemical properties and made the metal boundary to be cold-welded. This is the root cause of solder paste exsiccation and deterioration. The study on the details shows that to obtain high-quality solder paste, one of the key methods is using the solder powder with ideal passivation shell structure and defect-free surface.