Think & Tinker, Ltd.
P.O. Box 1606, Palmer Lake, CO 80133
Tel: (719) 488-9640, Fax: (866) 453-8473
Sales: Sales@thinktink.com, Support: Support@thinktink.com
The technique of analyzing the concentration of dissolved copper in an acid copper plating bath is identical to that for analyzing the copper in "peroxy-sulfuric" type etchants. The only real difference is the range of allowable concentrations and the methods used to reduce the copper level in an overdosed bath. In the following, the basic technique is presented, followed by specific discussions of plating and etching baths.
If you have not done so, please read the DOs and DON'Ts section now.
Acid Copper Plating Baths
The acceptable range of NumCop is:
In normal operation (after the bath stabilizes through regular use), the copper concentration will never be outside the acceptable range.
Low copper levelToo low a level is usually an indication that:
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 levelOf 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:
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.
Peroxy-sulfuric EtchantsThe 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 log book will alert you when the need for this test is becoming critical.
The acceptable range of NumCop is:
A reading in excess of 450 drops indicates that the bath has become supersaturated with copper. To prevent accelerated H2O2 consumption, the excess dissolved copper should be precipitated out of the bath.