Page 45 - PCMI Summer Journal 2021

An Overview of the Operation of Ferric Chloride Regeneration Systems in Photochemical Etching Machines
Presented by: Kirk Lauver, the Marketing Specialist, Chemcut Corporation, US
7/27/21
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• Both sodium chlorate and electrolytic regeneration generate chlorine in the solution from hydrochloric acid. Problems will result if the free acid concentration is too low.
Ferric Chloride Hydrolyzes In Water FeCl3 + 3H2O è Fe+3 3OH- + 3H+ + 3Cl-
Both regeneration methods will take HCL where they find it. If there is not enough free HCl in the solution, the HCl from the hydrolysis will be used to make chlorine. This will cause the pH to rise resulting in metal hydroxides precipitating in the etching machine.
• When using the sodium chlorate regeneration method, low hydrochloric acid will make the regeneration slow. If the free acid is inadequate, there may be unreacted sodium chlorate in the etching solution. DO NOT ADD A LARGE AMOUNT OF HCl AT ONE TIME. Raise the low acid by adding small amounts of acid at timed intervals. Monitor the ORP value to sure that the solution is not “over regenerated” which might release chlorine gas. Titrate to verify that the free acid has been returned to the normal level.
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Adding Ferric Chloride While Regenerating
• New ferric chloride is sometimes added during regeneration.
• Reasons for adding it are:
• Maintain a higher iron concentration when etching a large volume of metals that have a low concentration of iron, ex. Kovar, Inconel 600 etc.
• Lower the concentration of trace elements, such as silicon, which can cause scale buildup in the etching machine.
• Reduce the sodium chloride crystal buildup when regenerating with sodium chlorate.
• Both the consumption of new ferric chloride and the production of spent solution will increase when this is done.
Issue 137 August 2021 PCMI Journal 45