Research On Fabrication Process Of 50 μm Metallic Microchannel Of Heat Sink

With the development of electronic technology,integration level of electronic devices is getting higher and higher and heat flux is also increasing.Therefore,how to dissipate heat efficiently is one of the most attracting issues in the field of electronics.Metallic micro channel has a great cooling efficiency which earns it more and more attention.In this paper,cooper micro channels were fabricated based on UV-LIGA technology.The width was 50μm and the height was 250μm.Some processing problems were researched as follow:On the basis of drawing up the fabricating scheme of the metallic micro channel,a new method to measure the thickness of thick SU-8 film was proposed based on refractive index in view of the difficulty of measuring the thickness of SU-8 film before exposing.First the visual thickness of SU-8 film was measured by optical microscope.Then the refractive index of SU-8 photoresist at yellow light was obtained by experiment.The actual Thickness was the product of the visual thickness and the refractive index.Meanwhile,according to the dimensional characteristic and fabricating requirements,the micro channel cooling device was confirmed to be fabricated based on UV-LIGA technology consisted of SU-8 lithography and micro electroforming on copper substrate by two-time photoresist spinning and one-time exposing.The thickness non-uniformity of SU-8 film and the difficulty to fabricate thick SU-8 film were studied.At first,grinding and polishing technique was applied to improve the thickness uniformity.Experimental result showed that non-uniformity of SU-8 film was reduced by79.4%and dimension error was reduced from 5.1μm to 0.5μm after grinding and polishing treatment.Then lithography experiment was conducted to study the effect of exposure dose on the quality of SU-8 film.It was found that the film had the best quality when exposure dose was 640mJ/cm².Electroforming non-uniformity of micro channels was researched by finite element method and electroforming experiment.At first,simulation model was built to study the effect of the width of the auxiliary cathode and the distance between auxiliary cathode and micro channels on the electroforming uniformity.According to the simulation results,electroforming uniformity would get better as the distance between auxiliary cathode and micro channels increased,while worse as the width of the auxiliary cathode increased.Then electroforming experiment with and without auxiliary cathode was conducted.Experimental results showed that with auxiliary cathode,electroforming uniformity was improved by 37.1%after electroforming for 10h,while 72.2%after 20h.Based on the above research results,copper micro channel of heat sink was fabricated on copper substrate and SU-8 removal issue was studied.Due to small linewidth and high aspect ratio,highly cross-linked SU-8 was difficult to be removed by SU-8 remover.Therefore,SU-8removal methods by CO₂ laser,high-temperature ashing in vacuum and nitrogen were researched.The experimental results shown that CO₂ laser assisted by ultrasonic cleaning can effectively remove the SU-8 photoresist in micro channels on the premise of soundness of copper micro channels.