Drop-on-Demand Solder Droplet Jetting System for Fabricating Microstructure

The novel drop-on-demand (DOD) solder droplet jetting system, which can be characterized as the non-heat affection of the piezoelectric actuator, the control mechanism of the piston head-to-nozzle distance, and disposable nozzle parts, is devised. This system consists of the piezoelectric actuator, insulator, piston head-to-nozzle distance control apparatus, pressure control unit, and furnace. For the modulation of the droplet size, the distance from piston head-to-nozzle exit can be controlled by using the piston head-to-nozzle distance control apparatus. The working temperature is improved by locating the piezoelectric actuator outside of the furnace and by inserting the insulation block between the print head and the actuator. From a practical point of view, the DOD solder droplet jetting system has a simple structure for easily interchangeable nozzle parts. We derived the equation of the ejected droplet volume as a function of design parameters and operating conditions. The prototype of the DOD solder droplet jetting system was fabricated and the performance was verified. The diameter, volume and velocity of the ejected solder droplet are around 65-150 mum, 140 pl-1.8 nl, and 2.8-4 m/s, respectively. We also experimented with the effect of varying the chamber pressure, piston head-to-nozzle distance, and operating frequency on the ejected droplet diameter and velocity. The high aspect ratio vertical columns and inclined columns were fabricated by using the DOD solder droplet jetting system.