System for maintaining uniform copper etching efficiency
AssigneeGeneral Dynamics Corporation
InventorH. Ben Snyder
Life of this patent
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Abstract
System and apparatus for the controlled etching of copper work pieces with ferric chloride etchants. The working solution is constantly monitored with regard to its oxidation reduction potential (ORP) by comparison with a standard solution or voltage. To reduce the build up of etched copper in the working solution, an ORP controller activates the removal of specific quantities of that solution which are then replaced in precise stoichiometric proportions with fresh etchant. Simultaneously, oxidant is injected into the fluid to reoxidize ferrous ions to ferric ions. The solution is constantly monitored and the ORP control means repeats the above procedure as often as necessary to maintain the ORP of the fluid within an acceptable range.
Claims10
Apparatus to etch copper work pieces which comprises;
- a. etching machine means which utilize a working solution of etchant in which there is a tendency to convert ferric ions to ferrous ions, and in which the copper ion content of the solution has a tendency to increase as the etching progresses;
- b. oxidation reduction potential detection means to continuously monitor the changes in concentration of ferric, ferrous and copper ions and to compare the same to the concentration in a reference solution;
- c. oxidation-reduction potential control means adapted to adjust the ion concentrations in the working solution responsive to the change in oxidation reduction potential monitored by said detector means;
- d. working solution dumping means responsive to said control means to dump a signaled quantity of working solution;
- e. etchant solution rejuvenating means activated by said control means to add fresh etchant solution in a quantity at least equal to that dumped by said dumping means;
- whereby, said control means, according to the oxidation-reduction potential change continuously monitored by said detection means, dumps old etchant and rejuvenates with fresh etchant to reduce the copper ion content of the solution and maintain a constant etch rate.
Dependencies are inferred from the claim text.