Experimental Study of the Solder Paste Jet Printing Process Using High Speed Photography and Rheological Methods

Abstract

The jet printing process of Sn-58Bi lead-free solder paste involving expansion, necking, pinch-off and satellite droplet formation was observed and analyzed with the aid of high-speed photography. The viscosity and phase angle of the solder paste at three temperatures were measured using a rheometer. Spattering behavior of the solder paste was observed at 55°C. The spatter on the substrate came from a second satellite droplet which was produced in the second pinch-off of the solder paste and collided with the nozzle. Satellite droplets were produced at three temperatures when droplets break off, and the number of satellite droplets was determined at each temperature. The appropriate temperature could reduce the viscosity of the solder paste and improve the liquid-like behavior, which is conducive to realizing the jet printing process with an ideal ratio of height to diameter of the solder joints. According to the demand for jet solder paste, high-speed photography and rheological methods can help establish the relationship between jet printing performance and materials design.