Reference cited in this section

9. Electroplating Engineering Handbook, Reinhold, 1971, p 748, 750 Plating in Noncyanide Copper Baths

The development and refinement of proprietary noncyanide copper baths continues today. The copper deposit from these systems is a fine-grain, dense deposit (Ref 3). The noncyanide copper systems exhibit excellent throwing and covering power, even in deeply recessed areas. In addition to eliminating the cyanide, these processes operate at much lower copper metal concentrations of 7.5 to 13.5 g/L (1 to 2 oz/gal). As a result, they offer additional savings in lowering waste treatment costs. Copper sulfate is the source of copper ions for these systems. The plating electrolytes producing these deposits are very stable compared to those of cyanide copper processes, because there is no decomposition of cyanide resulting in carbonate buildup.

Over the typical current density range of 0.5 to 3.5 A/dm2 (5 to 35 A/ft2), the cathode efficiency of noncyanide systems approaches 100%. The good efficiency tends to offset the lower deposition rate of divalent copper electrolysis compared to that of monovalent copper systems. Agitation has a dramatic effect on deposit appearance and cathode efficiency. To obtain a uniform, fine-grain deposit over a wide current density range, air agitation is required for these systems. Lack of agitation produces dull, burned deposits at average current densities of 1.5 to 2.0 A/dm2 (15 to 20 A/ft2).

Of the commercially available systems, one process is affected by the buildup of cuprous ions in the cupric phosphonate system, which results in rough, nonadherent copper deposits (Ref 10). To overcome this effect, the process uses continuous electrolysis carried out in an auxiliary tank with special ceramic or platinized anodes to oxidize the cuprous to cupric.

Because the operating pH of these systems is in the range of 9 to 10, these baths can be used as both strikes and plates. There are no special adjustments required for processing zinc diecast and zincated aluminum, as there are in cyanide copper plating. At pH values below 9, the deposits are brighter but adhesion is adversely affected. Values greater than 10 cause high-current-density dullness and can reduce the limiting current density.

These systems, unlike the cyanide systems, are more susceptible to metallic and organic contaminants. Iron, lead, and silver are critical impurities that should be removed by low-current-density electrolytic treatments. Organic impurities are treated using hydrogen peroxide and carbon treatments on a regular basis. Continuous filtration through a 10 pm retention-size cartridge is beneficial for the noncyanide systems. Occasional carbon filtration using a sulfur-free carbon can be used to control organic contamination. Noncyanide systems have very little tolerance to cyanide contamination. When converting cyanide plating lines to noncyanide processes, it is essential to clean and leach out all the cyanide from the tank linings, racks, filters, heaters, plating barrels, and any associated equipment.

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