Effect of applying air pressure during wet etching of micro copper PCB tracks with ferric chloride

Abstract

Abstract Copper is an important commercial material used in various industries, especially in interconnections of microelectronics devices and printed circuit boards (PCBs). Wet etching has been widely used to machine copper tracks for producing micro-components. This process is simple and easy to implement. The selection of a suitable chemical etchant is one of the most important factors for the wet etching process, as it affects the etch rate and surface profile. Ferric chloride is considered an effective copper etchant as it possesses significant advantages. However, when etched pattern structures decrease beyond certain dimensions, ferric chloride falls short due to its isotropic nature which causes etch undercut that adds severe limitations to the process. To improve the etch rate and etch factor for the etched copper tracks, applying pressure (both positive and negative) during wet etching is suggested. Test structures with different geometry using copper spiral coils were patterned and wet etched using ferric chloride under different pressure values. The experimental study showed that the etch rate increases almost linearly with increasing pressure. Etch factor also varies with structure geometry and increases with pressure, reaching a maximum of about 2.4 at the maximum available pressure of 50 psi.