Study On Uniformity Of Electroforming Layer Of Metallic Microchannel Plate Based On Micro Electroforming Process

With the development of microelectronics technology,the integration of electronic components in electronic circuits is getting higher and higher,which leads to the increase of heat flux around the integrated devices.How to dissipate heat of highly integrated electronic components has become a hot topic in the electronic field.Microchannel heat sink is an efficient heat sink designed to meet the development of microelectronic technology,and its processing method has received extensive attention.Based on the process of SU-8 photoresist lithography and micro electroforming,metallic microchannel heat sink plate with line width of100?m and height of more than 500?m has been fabricated in this paper.The thickness non-uniformity problem of the electroforming layer in the fabrication process was analyzed and the corresponding solutions were put forward.The main work of this paper is as follows:In order to solve the thickness non-uniformity problem of microchannel electroforming layer caused by the current edge effect in the electroforming process of microchannel structure,a method of adding secondary cathode on the surface of cathode was put forward.Firstly,the simulation model was established according to the software of COMSOL,the horizontal distance between secondary cathode and cathode,the width of secondary cathode and the current density applied on secondary cathode were examined by L₉?3⁴?orthogonal test.Then according to the simulation results,the optimal secondary cathode was processed and a set of contrast experiments were carried out.The experimental results show that the thickness uniformity of microchannel electroforming layer increased by 54.2%with the optimal secondary cathode after 10 hours of micro electroforming.In order to solve the thickness non-uniformity problem of microchannel electroforming layer caused by uneven distribution of the reactive ions in the electroforming process,a method of introducing megasonic waves in the electroforming process was proposed and a set of comparative experiments was carried out.The experimental results show that the thickness uniformity of electroforming layer of microchannel structure increases with the increase of megasonic power.Compared with the absence of megasonic,the thickness uniformity of microchannel electroforming layer increased by 17.9%,50.9%and 67.6%respectively after addition of 30W,60W and 90W megasonics.In order to study the mechanism of megasonic improvement on thickness uniformity of micro-structure electroforming layer in megasonic assisted electroforming process,the effect of the megasonic on the diffusion layer thickness on cathode surface was analyzed.The diffusion layer thickness was obtained by measuring copper cathode polarization curve.The measurement results show that the diffusion layer thickness on the surface of copper cathode decreases with the increase of megasonic power.The acoustic streaming and resonant bubbles generated by megasonic in the electroforming solution can stir the electroforming liquid,accelerating the convolution of electroforming fluid,reducing the thickness of the diffusion layer on cathode surface,promoting the diffusion of the reaction ions on cathode surface,improving the distribution of reative ions on cathode surface,so that the thickness uniformity of electroforming layer of micro structure can be improved.Based on the results above,the microchannel heat sink plate structure was formed by UV-LIGA technology based on SU-8 lithography process and micro electroforming process.The fabrication process is that the copper substrate was baked twice and once exposure,development and electroforming were performed.The thickness uniformity of electroforming layer was solved by adding secondary cathode and applying bidirectional alternative vibration by megasonic.Finally,the microchannel heat sink plate with dimension precision meeting the design requirements has been fabricated.