Fabrication Of The Metal Micro Screen By Combination Of UV-LIGA With Micro Electro-machining Technology

As the improve of the MEMS and mciro-fabrication technology, micro-screen has been used in a wide range of applications, such as grid mesh, inkjet plate, spinneret plate, filter screens and test sieves et al. How to fabricate the micro screens by a low cost and high effciency way is a big challenge to the academia and industry.For fabricating Micro/Meso metal micro screens, the combination of UV-LIGA with micro electro-machining is presented in this paper, and relative researches have been carried out. The dissertation consists of five sections, including:(1) The parameters of UV lithography process including coating method, pre-bake temperature & time, exposure dose, post bake temperature & time and development time et al. have been studied to pattern SU-8 photoresist on a metal substrate. Using orthogonal array technique, an optimization experiment is performed to characterize the processing of SU-8 photoresist. Using the optimized process parameters, SU-8 moulds up to 1mm thick of different shapes with high definition, good topography, fewer defects and excellent adhesion with metal substrate have been produced successfully.(2) Two methods are advanced to solve the SU-8 removal problem. For the negative resist mould, before the electroforming process, a through-mask electrochemical micromachining (through-mask EMM) procedure was carried out to make micro roots on the substrate, the micro roots could improve the adhesion of micro electrode array electroformed on the substrate, so the electrode array could not be peeled after the resist removed. For the positive resist mould, after electroformed, the cross-linked SU-8 resist can be burned directed.(3) Two processes are adopted to fabricate the metal electrode array: The micro ECM aided UV-LIGA technology and the combination of UV-LIGA with the Micro electro-discharge machining (Micro-EDM) process. The micro ECM aided UV-LIGA technology was using the through-mask EMM to make micro roots to improve the adhesion of micro electrode array electroformed on the substrate, a mathematical model is presented to simulate the through-mask EMM process by finite element method (FEM), through the optimized parameter of the through-mask EMM, the ultra-thick cross-linked SU-8 resist is completely removed without destroying the electroformed microstructures. The combination of UV-LIGA with the Micro-EDM process both solved the problem of resist removal and the difficulty of micro-EDM electrode fabrication, using the optimized parameter of micro-EDM, electrode array of 1.5mm long and aspect ratio up to 17.65 was fabricated.(4) Using the fabricated electrode arrays to machine micro screens on the 100μm thick stainless steel. The effects of various parameters on the machining accuracy and stability are investigated, including electrolyte, electrode feeding speed,electrical parameters, et al.. Results indicate that pulse current, low concentration electrolyte, low voltage could attribute good performance of micro ECM. Machining accuracy and stability could be improved. After the electrode arrays are insulated, micro hole arrays of profiled holes are machined.(5) The over-plating method is introduced to fabricate the super micro hole array (size less than 10μm). A mathematical model is presented to simulate the over-plating process by finite element method (FEM). Finally, the micro hole array of diameter 4μm was fabricated by the over-plating technology. The result indicates that over-plating is a simple, low cost method to fabricate micro hole array, and it's suitable to batch production.