Characteristics of Wet Etching of Copper Foil for Printed Circuit Boards by using Ferric Chloride Solution

The kinetics of dissolution of copper in an agitated vessel containing aqueous solutions of FeCl₃ was investigated to clarify the wet etching mechanism in turbulent flow. The dependences of dissolution rate of copper upon the agitation speed, liquid temperature, and the concentration of FeCl₃ were investigated. From these results, this etching process appears to be controlled by a liquid phase mass-transfer. In general, it is thought that CuCl is precipitated on a copper surface during the wet etching of copper. To study about this mechanism and determine the rate-limiting species, dissolution rate of CuCl was measured and compared with that of copper. From these results, it is concluded that CuCl is not precipitated on the copper surface and the etching rate of copper is controlled by the diffusion rate of Fe³⁺. Wet etching experiments of line-patterned copper specimen were performed in an agitated vessel containing aqueous solutions of FeCls. By using of observed diffusivity of Fe³⁺, a mass-transfer model in wet etching for printed circuit boards has been developed and applied to the analysis of the pattern etching. In conclusion, it is found that this model is almost reliable to evaluate the cavity formation for the pattern etching. However, the calculated cavity shape appears to be inconsistent with the observed one slightly in the case of wide line spacing. It seems that this deviation is caused by the effect of bulk convection.