Metal Finishing Guide Book


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Maintenance and Control Constituents Ammonia aids in anode corrosion and acts as a grain refiner. Ammonia is replenished daily because of evaporation loss. Nitrate increases the high current density plating range and is a cathode depolarizer. The pH is controlled by using pyrophosphoric acid or potassium hydroxide as required. Temperature Operating the baths above 60°C (140°F) causes the rapid hydrolysis of pyrophosphate to orthophosphate. Agitation Copper pyrophosphate baths need vigorous agitation for a normal operating current density plating range. The most common form used is air agitation, by itself or in combination with mechanical agitation. Ultrasonic and solution jet agitation can also be used. Contaminants Copper pyrophosphate baths are sensitive to organic contamination such as oil, breakdown products, or organic addition agents. Organic, cyanide, and lead contamination can cause dull, nonuniform deposits with a narrow plating range. Carbon treatment will remove organic contamination and treating with hydrogen peroxide or potassium permanganate before carbon treatment will remove cyanide and severe organic contamination. Lead can be removed by dummying. Orthophosphate In addition to high temperature, localized overheating or too low a pH can cause the rapid buildup of orthophosphate. OTHER ALKALINE BATHS There has been work on the development of other types of alkaline, noncyanide copper plating baths; but their use in industry has been too specialized or limited to discuss at this time. COPPER SULFATE BATHS Copper sulfate baths are economical to prepare, operate, and waste treat. They are used in printed circuits, electronics, semiconductor, rotogravure, electroforming, decorative, and plating-on-plastics applications. The chemistry of the solution is simple, with copper sulfate and sulfuric acid forming the ionized species in solution. The baths are highly conductive. Previous problems with throwing power have been overcome with the advent of the modern high throw formulations and additives. Steel parts must be cyanide copper- or nickel-plated in strike formulations to prevent immersion coatings and poor adhesion. Zinc die castings and other acid sensitive metals must have sufficient deposit to prevent attack by the sulfuric acid. The baths are operated at room temperature for most applications. Anodes should be phosphorized (0.02-0.08% by weight phosphorus), oxide-free, high-purity, rolled copper. Copper anode nuggets in titanium baskets can be used. Anodes should be bagged. The anode current density should range from 15 to 30 A/ft2. Excessively high current densities can cause the anode to lose its black, protective film and cause rough deposits; exces276

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