Fabrication of micro pits based on megasonic assisted through-mask electrochemical micromachining

Through-mask electrochemical micromachining (TMEMM) is the primary method to fabricate micro pits with controlled size, location, and density. In order to improve the machining localization and deep etching capability in TMEMM process, a novel method which combined megasonic vibration to TMEMM process is presented in this paper. Firstly, the coupling relationship between sound field, gas-liquid two-phase flow field and electrolytic process was theoretically analyzed. Theoretical analysis results indicate that acoustic wave agitation can promote the electrolytic process by increasing the conductivity of the electrolyte. Based on this theory, a numerical simulation method was used to predict anodic profiles under different megasonic intensity. The simulation results show that the addition of megasonic agitation can obviously improve the machining localization and deep etching capability in TMEMM process. Etching depth of the micro pit increased from 48.22 μm to 77.98 μm with megasonic agitation compared to the without megasonic one. Depth-diameter ratio of the micro pit increased from 0.30 to 0.45. Meanwhile, the etching factor (EF) increased from 1.55 to 2.10. Then, a megasonic electrolyser at 1 MHz was set up, micro pits were etched under different megasionc intensity. The experiment results show that megasonic assisted through-mask electrochemical micromachining (MA-TMEMM) had best process performance when it worked with the increase of megasionc intensity. When the megasonic intensity was 8 W/cm2, micro pits with average diameter of 167.77 μm and 79.62 μm in depth were successfully fabricated. The average depth-diameter ratio of the micro pits was as high as 0.47, and the EF was as high as 2.35. The working mechanism of megasonic in MA-TMEMM process was analyzed too.