Think & Tinker Instrument Prototyping

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P.O. Box 1606, Palmer Lake, CO 80133
Tel: (719) 488-9640, Fax: (866) 453-8473
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Acid-Copper Electroplating Module Model 1000 Manual
Chemical Analysis - Copper Concentration Analysis II

Low copper level
Too low a level is usually an indication that:

the surface area of the anode material is insufficient to source the amount of copper being removed from the bath during plating, or
the bath has become contaminated and the anodes are not sourcing adequate copper.

In the first case, you should check with the vendor who supplied your plating bath to find out the optimum ratio between the anode and cathode (workpiece) surface areas. Unfortunately, determing the actual area of the anodes in your bath is not as straightforward as one might like. Surface roughness typically contributes the majority of the total area and is almost impossible to reliably estimate. Luckily, this is not much of a problem since, if you have determined that the low level of copper is not due to organic contamination, all you have to do is add more material (phosphorized copper) to your anode arrays. If the copper level continues to decline, add a bit more material until stability is achieved (or at least approximated) Using anode baskets as opposed to anode bars makes it much easier to tweak the anode area to the optimum value.
Contamination is usually evidenced by a thick, muddy gray coating on the anodes. This coating effectively insulates the copper surface from the electrolyte and significantly reduces the dissolution of copper into the plating bath. Ultimately, the bath becomes depleted of copper ions, the conductivity goes down, and plating ceases. If organic contamination is found to be the culprit, it is necessary to carbon treat the bath before proceeding.

High copper level
Of greater concern is the situation where the level of dissolved copper has gotten too high and begins to interfere with the proper operation of the bath. The usual causes of a bath becoming "overdosed" on copper are:

a significant imbalance exists in the organic components of the electrolyte, and/or;
too much copper anode surface area for the workpiece being plated.

Assuming that you do not to own a liquid chromatagraph, spectraphotometer, or a CVS (cyclic voltametric stripper), the most practical way to determine if the various organic components of the electrolyte are out of balance is through a technique known as "dilution Hull-cell analysis".

If the dilution Hull cell indicates that the organic additives are within operating parameters, it is likely that there is simply too much anode surface area contributing copper to the electrolyte. If the copper level was slowly drifting up, remove about 10 to 15% of the anode material and dummy plate for a couple of hours at the maximum current available from your power supply. Analyze the copper ion content. If the copper level has risen or stayed the same, remove 10% of the remaining anode material. Continue plating, testing,and removing anode material until the level of dissolved copper begins to fall.

Continue dummy plating until the level of dissolved copper in the bath is within operating limits. Return 10% of the anode material (the pieces you removed just before the copper level began to fall) and dummy plate at full power for 1 hour. If the copper concentration continues to fall, return a bit more of the anode stock to the bath. Continue in this fashion until stability is achieved. Carefully record the total amount of anode material remaining. This should represent the ideal charge of anode material for your setup, assuming that you are always plating the same size board. You might also want to calculate the effective area of the anode material by dividing the apparent geometric area by the area of the panel you were dummy plating. This ratio will come in handy if you routinely plate boards of varying sizes since it relates the "ideal charge" of anode stock to the unit area of the workpiece.

Established 1990

On the web since 1994