Electrokinetic Behavior of Solder Powders in Non-aqueous Media

Solder paste dispensing is a key process in the electronics assembly. The increased global demand for smaller, lighter, faster and cheaper assemblies drives the electronics industry to use dispensers with finer apertures. However, reduction in the aperture size of dispensers faces the industry with increased clogging of dispensers and incomplete transfer of paste to the printed circuit board (PCB) pads. One factor contributing to the clogging of dispensers is the agglomeration of the solder powder suspensions which depends on the electrokinetic behavior of the particles. When suspensions are close to the point of no charge, wherein zeta potential is equal to zero, the particles tend to agglomerate. This work focuses on the determination of the zeta potential of Sn, SAC305 and PbSn5Ag2.5 suspensions in isopropyl alcohol (IPA) through microelectrophoresis. The effect of acid, base and flux additives were studied. Results showed that the zeta potential of the solder suspensions are negative in pure IPA and charge reversal occurs in both acidic and basic region. In systems containing flux additives, the zeta potential of the suspensions is highly dependent on the type efflux. FTIR spectroscopy, conductivity measurement, and surface analysis was done in order to explain the observed electrokinetic behavior.