Influence of Hydrochloric Acid in Etching Solution on Penetration of Cupric Ions Through Gravure Resist.

In the etching of copper covered with a gelatin resist by various ferric chloride-hydrochloric acid solutions, we measured the opening time or penetration time. We found that this time was shortened with the increase of the concentration of hydrochloric acid. In order to clarify the fact mentioned, we estimated the diffusion coefficient (D) of cupric ions in etching solutions from Fick's second law. Examining the diffusion coefficient by Crank's Equation, we confirmed that its value could be appropriate. With these values we could explain the mechanism of penetration of cupric ions through the resist in the same way as that in simple ferric chloride solutions. From characteristics of the diffusion coefficient in the gelatin resist-etching solution system, it was considered that the addition of hydrochloric acid to an etching solution was unfavorable to the gelatin resist.