Stabilization formation characterization of metal single droplet by pneumatic drop-on-demand

Metal single droplets are widely used in electronic packaging and flexible circuit printing. However, liquid metals are characterized by high density and interfacial tension, so that stable injection of single droplet occurs only in an extremely small printable region, which limits the application of metal droplets. In this study, based on a drop-on-demand pneumatic injection device, the evolutionary process and mechanism of metal droplet generation are analyzed through experiments and numerical simulations, the theoretical solution of the injection velocity is obtained, the printable region that can stably generate the single droplet dimensionless parameters Wej (Jet Weber number) and Z (1/Ohnesorge number) is plotted, and the prediction model of the single droplet dimensionless limit jet length is established. Results show that in the range 400 < Z < 1100, the printable region where single droplets can be generated is extremely narrow (1.3 < Wej < 2). When Wej < 1.3, the inertial force of the jet is not sufficient to overcome the interfacial capillary force, and no droplets can be generated. When Wej > 2, the inertial force of the jet is so large that satellite droplets are generated. The prediction results obtained by the prediction model of single droplet dimensionless limit jet length are consistent with the experimental results and can accurately predict whether a single droplet can be generated or not. The results can reveal the mechanism of stable generation of on-demand pneumatic metal droplets. Furthermore, the results can serve as theoretical references for the further development of on-demand pneumatic metal droplet injection technology.