Research On Thickness Uniformity Of Micro Lensarray Mold Insert Fabricated By Electroforming

Micro lens array is important micro-optics part and has been widely used in high-technology fields, it is mass produced by micro-injection molding technology and nano-imprinting technology. Electroforming technology is the key working procedure of LIGA or UV-LIGA technology, it is used in fabricating the micro mold insert for micro injection or nano-imprinting process and determine the qualification of polymer micro lensarrays. However, non-uniform thickness of micro lensarray mold insert fabricated by electroforming usually is consistently observed. In this paper, electrodeposition theory is used to analysis the formation mechanism of the non-unform thickness distribution, focusing on electric field distribution and flow field distribution in electroforming system, and studying the effect of the two factors on thickness distribution both numerically and experimentally, finding methods to improve thickness uniformity of micro lensarray electroformed mold insert.Numerically studied the effect of non-conducting shields and secondary cathode in improving the uniformity of current density distribution on micro lensarray cathode. With Faraday’s law and electrodeposition theory, researching the relationship between current density distribution and thickness distribution of the electroformed insert. A series of electroforming experiment were conducted to obtain nickel mold inserts by using a non-conducting shield or a secondary cathode with4different structure size, thickness distribution of them were measured by electronic digital display micrometer. Designing experiment to analyze the improvement of non-conducting shield and secondary cathode in thickness uniformity of electroformed insert. The experimental results were in accordance with the numerical data well.Using VOF model, researching how the two different movement (rotating vertically and reciprocating moving horizontally) of the cathode effect the flow field. Studying the relationship of flow field distribution and thickness distribution of the electroformed insert, a series of electroforming experiment were conducted to obtain by using different cathode motion parameters, thickness distribution of nickel mold inserts obtained by the experiment were measured by (profile meter) and surface quality of the were observed by image measurement instrument, designing single factor experiment to analyze the two movement of cathode on improving the thickness uniformity and surface quality of electroformed insert, experimental results were compared with numerical data and showed good agreement.Considering the costs and feasibility of each optimized methods of improving thickness uniformity, using a non-conduction shield combined with vertical rotary cathode in the electroforming process. Regarding PS micro lensarrays as a master and coating50nm copper film as conductive layer, a1mm thick micro lensarray mold insert was dabricated by electroforming. thickness variation of it are10.99%, by using this method, a4mm thick mold insert was also made. Their surface quality were observed by optical surface profiler, the results showed that both the inserts have a good micro structure and a low surface roughness of the electroformed mold insert, but warp were also found.