Research On The Principle And Experiment Of Solder Micro-jetting Driven By Electromagnetic Force

Solder micro-jetting driven by electromagnetic force is a new type of non-mechanical jetting. The principle of this technology is the Ampere's law. Compared with other jetting methods, the advantages of this technology is very outstanding. It has high energy utilization rate and, secondly, it can provide reverse force to the liquid, which is the other jetting methods can not realize. Due to its unique advantages, Solder micro-jetting driven by electromagnetic force will be expected to be widely applied in semiconductor packaging with high-density, high reliability.In this thesis, firstly the theory of the electromagnetic hydrodynamics was analyzed, and the main factors that impact the electromagnetic force was concluded. Under the base of the conclusion, the total structure of the jetting system was designed. Then a constant magnetic field was established according to the experimental requirement. The pulse circuit and power amplifier was designed to provide control signal for the jetting system. Problems in experiments are primarily solder oxidation under the high temperature, bad insulation and seal and high damping of nozzle. The incorrect choose of these parameters will lead to failure for successive research. To solve the above problems, the experimental devices was improved, such as adding nitrogen to solder reservoir while heating to prevent solder from oxidation; divided the total structure into several parts, making different parts connected by transition joint and using high temperature gaskets seal to solve insulation and sealing problem; Designed a simple glass stretching device, with it the glass nozzles with small caliber and smaller internal friction was made.By calculating and testing we got a conclusion that the main factors affect the size of micro-droplets are the current pulse frequency, pulse duty cycle and so on. The higher the pulse frequency of electromagnetic force is, the smaller the droplet is; the pressure in the solder reservoir also has a significant influence on the formation of micro-droplets. With higher pressure, the liquid will flow out even there is no electromagnetic force. With lower pressure droplet can not be formed. So the air pressure should be fine-tuned to enable the system reach critical state, which is under static state the orifice liquid is near meniscus form. And then it will jet under slight electromagnetic force .