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.
The authors would like to thank the National Natural Science Foundation of China (51004039), Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology (ASMA201602) and Open Fund of Key
Laboratory of Materials Preparation and Protection for Harsh Environment (Nanjing University of Aeronautics and Astronautics), Ministry of Industry and Information Technology No. 56XCA17006-1. The authors also wish to thank Dr. Jie Zhu at Jiangsu University of Science and Technology for his help on the high-speed photography.