Think & Tinker, Ltd.
P.O. Box 1606, Palmer Lake, CO 80133
Tel: (719) 488-9640, Fax: (866) 453-8473
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Carbon Treating Acid
Copper Plating Baths

Periodically, it becomes necessary to remove organic contaminants from virtually every commercial electroplating bath. The sources of these "pollutants" can include:
  • leaching from tanks, filters, and tank plumbing
  • leaching from dry-film and liquid plating resists, and
  • poorly cleaned copperclad substrate.
In the case of a relatively small plating bath (100 liters or less), removing these contaminants is fairly straightforward. The easiest systems to purify are those that are equipped with a recirculation pump (min. 30 lpm into 1 meter of head) and an in-line filter housing that will accommodate commercially available activated carbon packs, . Such an in-line filter is assumed in the following.

Supplies needed

  1. 19% to 50% hydrogen peroxide ( H2O2)
  2. activated carbon pack
  3. 5 micron polypropylene filter cartridge (leached)

Procedure

  1. Remove all racks and anode banks from the plating bath.
  2. Thoroughly clean the surfaces of the anodes with a wire brush and set aside completely immersed in a 10% solution of sulfuric acid.
  3. Put a 5 micron pre-leached wound polypropylene filter cartridge into the in-line filter housing. If a pre-leached cartridge is not available. soak a food grade polypropylene filter in a 10% solution of sulfuric acid for 5 to 8 hours before inserting into the housing.
  4. To the bath, add 8 mL of 19% H2O2 (3 mL of 50% H2O2) for every liter of electrolyte, and allow to circulate overnight (min. 8 hours). Circulating the bath overnight will consume virtually all of the peroxide and prevent a harmful interaction with the acitvated carbon pack.
  5. The next morning, replace the 5 micron filter element with an activated carbon pack (same size and form factor as the wound filter) and circultate for another 8 hours.
  6. Run a Hull Cell test to make certain that all organics have been removed. The test plate will be completely matte from the high current density area nearest the anode to the low current density area. If a bright plated stripe is seen anywhere on the plate, organic components remain and must be removed by adding more H2O2 (about 50% of the original addition) and circulating for another 4 hours. Carbon treat for another 4 hours.
  7. Remove the filter pack (it can be reused at least one more time) and insert a 1 to 5 micron pre-leached wound polypropylene filter cartridge into the housing.
  8. Analyze the copper, sulfuric acid, and chloride ion content of the electrolyte and make additions as necessary. Allow the bath to circulate at least 10 minutes after any addition before proceeding.
  9. Return the anodes to the bath and electrolyze by dummy plating at 5 ASF for 2 hours, at 12 ASF for 2 hours and finally at your normal operating ASF (typically 20 ASF) for 2 hours.
  10. Using a Hull Cell, determine the amount of carrier and additive needed to bring the electrolyte up to specifications. Add the indicated volumes to the tank and allow to circulate for at least 10 minutes.
  11. Run another Hull cell test and make additions as necessary.
  12. Record the additions in your equipment log to insure that a comprehensive record is kept of everything that is added to the plating tank.
  13. Your plater is now ready to put back into service.


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On the web 1994

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Copyright © 1994 - 2011 Think & Tinker, Ltd. Updated 2/13/2014 8:36:58 AM