Improved Uniformity and Anisotropy of Through-Mask Electrochemical Micromachining by Localized Etching and Homogeneous Flow

This contribution aims to point out the potential of through-mask electrochemical micromachining (TMEMM) as an environmentally friendly alternative for thin metal layer patterning for applications such as printed circuit boards (PCBs). Two process chamber concepts with shearing and impinging electrolyte flow, based on the concept of localized etching, are introduced. The etching results, obtained with simple mask designs, were investigated regarding homogeneity in etch depth and anisotropy. Compared to a simple setup with unspecific electrolyte flow and full area etching, a significant improvement in microscopic and macroscopic homogeneity (deviations reduced from >100 to <10%) and anisotropy (etch factors increased from ~4 to >7) could be shown. A comparison to an industrial chemical etching process using a simple mask design revealed equal macroscopic homogeneity and higher etch factors in TMEMM. Only the microscopic homogeneity leaves still room for improvement. It is presented for the first time that island formation can be prevented completely over a large area (5 × 20 mm2) with TMEMM. These results demonstrate the advantages and the potential that can be achieved with TMEMM by designing appropriate tools.