Thickness of Resist and Rate of Penetration for Cupric Ions in Various Molar Solutions of Ferric Chloride.

The time required for penetration of reactants and products through a gelatin resist transferred on the copper plate, in copper-ferric chloride reaction, was investigated. The results obtained indicate that, in each molar solution of ferric chloride, the relationship between thickness (1) of the resist and rate (t) of penetration can be approximated by the following equation: t = bl0al2 where a and b are constants at each molarity. From the point of view of the diffusion of cupric ions produced on the copper surface, the equation above was analyzed and it was found that the relationship was explicable in terms of the solution of the equation of Fick's second law. It became clear that the constants a and b were defined by the properties of the resist and by the molarity of the etching solution.