Theoretical And Experimental Study On Pneumatic Diaphragm-Based Micro Molten Metal Droplet Jetting System

In this dissertation, a new type microdrop generation technology is proposed for molten metal solder jetting under high temperature.Firstly microdrop generation status quo of drop on demand(DOD) jetting technologies are reviewed, including piezoelectric-driven method and pneumatic-driven method et al. Then a pneumatically-actuator diaphragm-driven DOD microdrop generator, aiming at working on high temperature for molten metal and other materials, is proposed. The apparatus consists of five parts: a throttle, a solder reservoir, a diaphragm, a vent hole and a dispensing nozzle. Derived form the advantage of piezoelectric-driven method and pneumatic-driven method, the strength of the generator is simple structure, low-cost, drive force near the nozzle et al.Secondly, according to the deformation and vibration of the diaphragm, the mathematical model of jetting process is proposed. The description of the dispensing process requires the coupling of three physical domains: pneumatic, mechanical, and hydraulic. Equations for the fluid motion in the working chamber such as reservoir, are derived from Bernoulli's equation, when viscous effects are not important, or from the general integral momentum balance, when viscous effects are important. parametric study describing the relationships between variables is presented.In order to fabricated suitable micronozzle two home made apparatus have been made. One is glass tube puller for micro-scale glass nozzle, the other is composite micro electric discharge machining system for stainless nozzle.Thirdly, microdrop generating system has been made up, which including four sub-systems: temperature control system, motion control system, pneumatic system and high speed image system are used for the mechanism of pneumatic diaphragm-based microdrop generating.In the sake of recording and analyzing of the jetting process, the high speed imaging system is put up. Several factors affecting jet printing: back pressure, driven pressure, driven pulse width, driven pulse frequency, vent hole and hydrophobic surface of nozzle, of which vent hole and hydrophobic surface of nozzle are considered to be extremely important.Using the home made microdrop generator, we have obtained uniform water micro droplets. The water droplets' size variation is less than 3% of droplet diameter, and the ration of diameter of water droplets to diameter of nozzle is 2 - 3.In addition, the microdrop generator is applied to various fluids, including water solution, low viscous paste and molten Sn63Pb37 solder. The dissertation investigated the effect of surface oxidation on the process of jet printing and using Nitrogen gas co-flow to prevent surface oxidation. We have obtained ideal micro solder balls of 85μm in diameter which ejected from a micro nozzle of 80μm in diameter. The microdrop generator shows features of low cost, less requirement of environment, easily maintaining.Moreover, as for microelectronic packaging and light emitting diode manufacturing, a kind mechanical microdrop generator has been proposed. The equipment used for high viscosity fluid in electronic engineering, For the consistency of this dissertation, description of this generator are presented in appendix A. System driven parameters such as drive force, pulse width, back pressure, and working temperature are studied, micro dot array and line are produced by the system.