Formation Mechanism and Suppression Strategies of Satellite Droplets for Piezoelectric Jet Dispensing within Short Distance

Jet dispensing is the core technology in the field of microelectronic packaging. The problems including substrate pollution, irregular shape of glue spots, etc., will be caused by the satellite droplets generating in jet breakup, which is a serious problem for the dispensing technology. The distance between nozzle and substrate is very short (0.7-1.2 mm) during piezoelectric driven dispensing, and jet breakup usually occurs after the droplet contact with the substrate. The process of jet breakup is complex, and the mechanism of satellites formation is still unclear. Numerical and experimental analysis for the dispensing of epoxy glue within short distance is implemented aiming to explore the mechanism of satellites formation, and the strategies to suppress satellites are presented. The results show that the formation modes of satellites can be classified into three types: the second breakup occurs under the satellite droplets, two breakups occur simultaneously at different positions, the second breakup occurs above the satellite droplets, and the third mode is worst, for which the satellites will become scattered spots. There is a negative relation between generation rate of satellite droplets and jet breakup time. The generation rate of satellites can be reduced by raising breakup time through decreasing the jet velocity, shortening the distance between nozzle and substrate, and reducing the temperature. In addition，the jet velocity can be decreased by increasing the angle of nozzle and the ratio of length to diameter of nozzle, or designing steps in the nozzle. © 2024 Chinese Mechanical Engineering Society. All rights reserved.