Study of the satellite droplet formation in piezoelectric jetting at short nozzle-to-substrate distances

Jet dispensing is a foundational technology in microelectronics packaging. Piezoelectric-driven jet dispensing involves short-distance jet processes, typically ranging between 0.7 and 1.2 mm. During this process, jet breakup occurs after the droplet contacts the substrate, leading to substrate contamination, irregular adhesive dot shapes, and various other challenges. The underlying mechanism of jet breakup is complex, and the formation mechanism for satellite droplets remains unclear. To address this issue, in this paper, a certain epoxy resin adhesive is investigated to analyze the mechanism of satellite droplet formation during short-distance jet dispensing through experiments, theoretical model, and numerical simulations. The results indicate that the second jet breakup above satellite droplets is most likely to form scattered spots, and the probability of satellite droplet generation is negatively correlated with jet breakup time. Reducing jet velocity, lowering jetting height, and adjusting nozzle temperature can effectively increase jet breakup time and reduce the generation of satellite droplets. Additionally, decreasing jet velocity by modifying parameters such as the length-to-diameter ratio of the micro-jet orifice and the nozzle cone angle can help suppress satellite droplet formation.