| Metal micro-column arrays have broad application prospects in the industrial field due to their large specific surface area,excellent electrochemical properties and high strength.Meanwhile,More and more researchers have focused on its production methods.Although UV-LIGA technology is known as one of the main production methods of metal micro-column arrays,there are still some challenges in the production process,especially "incomplete electroforming" phenomenon due to serious side reaction of hydrogen evolution in the process of micro-blind-vias electroforming.In this paper,the "incomplete electroforming" phenomenon of nickel electroforming in micro-blind-vias is analyzed and studied,and a method of megasonic-assisted micro-electroforming is proposed to solve the "incomplete electroforming" problem.The influence of megasonic assistance on mass transfer process of micro-electroforming is quantitatively studied by numerical simulation,and the influence of megasonic assistance on electrode reaction in micro-electroforming process is studied.Finally,the megasonic-assisted micro-electroforming experiment is carried out to solve the "Incomplete electroforming" problem.The specific research work of this paper is as follows:(1)The fabrication process of metal micro-column array was introduced,and the reason why the “incomplete electroforming” phenomenon due to hydrogen evolution was prone to occur during electroforming process of nickel micro-column arrays was analyzed.To solve the problem of "incomplete electroforming" in micro-blind-via electroforming,based on the hydrogen evolution reaction steps,hydrogen generation was researched from the perspectives of equilibrium potential,hydrogen evolution overpotential and current density,and the factors influencing hydrogen escape were studied from the force of bubbles in electroforming solution.(2)On the basis of conventional mode of cathode moving stirring,a method of megasonic-assisted micro-electroforming was proposed to solve the problem of "Incomplete electroforming" caused by hydrogen evolution.The mechanism of increasing flow rate of electroforming liquid and enhancing mass transfer by megasonic assistance was studied.Simulation study on the effect of megasonic assisted micro-electroforming on the mass transfer process of electroforming liquid was carried out,and the mass transfer coefficient was used for quantitative characterization under different stirring conditions.Based on the connection among sound field,flow field and mass transfer process,the theoretical model of megasonic-assisted micro-electroforming was established.The results show that megasonic agitation can significantly enhance the mass transfer effect,and the mass transfer coefficient increases with the increase of mega power and the increase of aspect ratio leads to the decrease of mass transfer coefficient.As a internal stirring method,megasonic-assisted electroforming is better than cathode moving method in enhancing mass transfer.(3)The influence of megasonic-assisted Ni micro-electroforming on the electrode reaction was explored.The Tafel polarization curve measurement experiment was carried out.Based on the Tafel linear extrapolation method,the effect of megasonic power density on electrode dynamic parameters in Ni micro-electroforming system was studied.The experiment results of Tafel polarization curve measurement experiment indicate that,the equilibrium potential and exchange current density of the Ni electroforming system increase with the assistance of megasonic agitation.Meanwhile,the equilibrium potential and exchange current density increase with the increase of megasonic power density.(4)The experiment of megasonic-assisted electroforming nickel micro-column array was carried out to verify the feasibility of solving the problem of "incomplete electroforming" of Ni electroforming in micro-blind-vias.with the assistance of megasonic agitation during electroforming,Ni electroforming layer with good filling quality was obtained,and the "incomplete electroforming" problem was solved.In addition,to address the problem of micro-blind-vias development,ultrasonic-assisted development was put forward.The binding force between the microcolumn and the substrate was enhanced by oxygen plasma treatment before electroforming.Finally,the Ni micro-column array with an average edge length of194.7μm and an average height of 304.0μm was obtained by photoresist stripping process.The actual size of the micro-column array structure met the design requirements. |
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