Simulation And Optimization Of Drop-on-demand Molten Metal Droplet Printing

Surface-mounting technology has become the mainstream of packing technologysince its high density, high reliability and excellent electrical properties comply with thetrend of miniaturization, integration and precision. Quality of the bump determines thereliability of the packaging. A fine bump is supposed to have smooth surface, uniformdiameter and shape without holes and precise location without displacement. Bumpscan be fabricated by micro-droplet inkjet printing technology. However, the quality ofthe bump would be affected by many factors such as the surroundings during printingprocess and structure parameters. Thus it’s important to investigate the rules betweenparameters and bump quality.In this paper, a piezoelectric droplet ejector is studied. Simulation is conducted tolearn the mechanism of molten metal tin printing process based on FLUENT. Thecharacteristics of droplet ejection are obtained by varying working parameters(amplitude of the piston, dwell time of the signal and the retracting time) and structureparameters(the interspace between piston and chamber wall, the angle of the piston backwall). Influences of installation error are also discussed.Simulations of the deposition and solidification process are conducted. Both thevariation of surface tension as the temperature changes and the heat transfer betweendroplet and substrate are taken into considers. The flow field and volume fraction ofliquid are observed. The effect of impact velocity, droplet temperature, substratetemperature and diameter are investigated.Structure parameters are optimized based on the simulation results. Comprehensiveinfluence of amplitude of the piston, the interspace between piston and chamber walland the angle of the piston back wall are studied. Based on Response surfacemethodology, a range of parameters which show excellent ejection characteristics areobtained. The reliability of the optimization is proved.