B25 Copper Circuit Board Etching and Plating

Description
A commercial circuit board with a positive resist is exposed and etched. A mask, prepared from a computer drawing and transferred to a transparency, is placed over the resist before exposing to light. The resist is etched from the exposed areas with a strong base. The copper layer is then etched with a ferric chloride solution. A brown precipitate of mixed copper(I) and copper(II) oxidation states is characteristic of solutions of copper(II) chloride in contact with copper. The resist is removed with acetone. Next, a solution of tin (II) and cyanide plates tin on top of the copper. The tin layer forms an alloyed joint with the lead-tin alloy used for soldering.

Equation
2 Fe³⁺ + Cu --> Cu²⁺ + 2 Fe²⁺

2 Cu + Sn²⁺ + 6 CN^---> Sn + 2 Cu(CN)₃²^-

Other copper(I)complexes are present also.

Reference
Deforest, "Photoresist", McGraw Hill, N.Y., N.Y., (1975).

MetalsFinishing 50th Guidebook Directory, Metals and Plastics Publications, Inc.,Hackensack, N.J., (1982) p514.