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P.O. Box 1606, Palmer Lake, CO 80133
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Peroxy-Sulfuric Etching Module
Chemical Analysis/Copper Concentration Analysis

Copper Concentration Analysis
If you have not done so, please read the DOs and DON'Ts section now.

Equipment Required:
  • Titration flask (125 ml)
  • 10 ml Automatic pipette
  • Digital titrator
Reagents Required:
  • Deionized water
  • pH 9.5 Buffer
  • PAN indicator
  • .800M EDTA tetrasodium salt (titrant)
Procedure:
  1. Measure 50 ml of heated deionized water into the titration flask. (about 40 degrees C will yield optimum results)
  2. Using a pipette, add .50 ml of sample etchant (5 charges from automatic pipettor).
  3. Add the pH 9.5 buffer one drop at a time until the solution turns a light blue or violet color (two or three drops max.). This point is rather subtle so watch for it closely.
  4. Add 2 drops of PAN indicator to yield a bright violet solution. Swirl flask to mix thoroughly.
  5. Using the digital titrator, titrate with the .800M EDTA tetrasodium salt to a green (or yellow-green) end point. Record the number of drops of titrant from the digital indicator.
  6. The concentration of dissolved copper present (as cupric ion in grams per liter (g/L)) can be directly calculated using (digital titrator reading for copper analysis is denoted NumCop):
Copper concentration (g/L) = 0.127 x NumCop

The presence of too much dissolved copper in the etching bath will lead to excessive etch times, accelerated peroxide consumption and a reduction of the edge quality of an etched circuit. This analysis will need to be performed after every 30 sq.ft. of copper clad is etched and should be done on a Friday or at any time that the etcher can be idle for one or two days. A marked increase in the consumption of hydrogen peroxide is a fairly reliable indicator that there is too much dissolved copper in the etchant. Careful attention to your logbook will alert you when the need for this test is becoming critical.

The acceptable range of NumCop is
Optimum Range:
(grams/Liter)
37 to 56
NumCop: 295 to 441

A reading in excess of 450 drops indicates that the bath has become supersaturated with copper. To prevent accelerated H2O2 consumption and spontaneous precipitation of copper sulfate in the etching tank, the excess dissolved copper should be precipitated out of the bath.

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