Quantitative study of mass transfer in megasonic micro electroforming based on mass transfer coefficient: Simulation and experimental validation

Mass transfer is a key process in micro electroforming, especially for electroformed microstructures with high aspect ratio. Mass transfer coefficient is a key parameter that can be used to quantitatively characterize the degree of mass transport. Based on mass transfer coefficient, a computational model is developed to quantitatively study the mass transfer during megasonic (1 MHz) micro electroforming in this paper. The factors that affect mass transfer are investigated, such as input power, aspect ratio and distance between microchannel and transducer. The simulated results show that when the megasonic power increases, the mass transfer coefficient of micro electroforming increases. In addition, under the same megasonic power, mass transfer coefficient increases with decreasing aspect ratio and distance between microchannel and transducer. The effectiveness and feasibility of the simulated method are investigated by sonoelectrochemical experiments. The experimental and simulated mass transfer coefficients without megasonic agitation are 0.47 and 0.44 (10(-5) m/s), respectively. Under the megasonic power of 30 W, 60 W, 90 W, the experimental mass transfer coefficients are 0.88, 1.19 and 1.47 (10(-5) m/s), and the corresponding simulation values are 1.04, 1.39 and 1.68 (10(-5) m/s), respectively. The tendency of simulated values is consonant with the experimental values. The research provides a new option for the study of deposition process and is helpful for the design of megasonic electroforming equipment. (C) 2018 Elsevier Ltd. All rights reserved.