Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

Issue link: https://metalfinishing.epubxp.com/i/49721

Contents of this Issue

Navigation

Page 205 of 707

tamination, and are made from purified liquid concentrates. Maintenance and Control Constituents Ammonia aids in anode corrosion and acts as a grain refiner. Ammonia is replen- ished daily because of evaporation loss. Nitrate increases the high current density plating range and is a cathode depolarizer. The pH is controlled by using pyrophos- phoric acid or potassium hydroxide as required. Temperature Operating the baths above 60° phate to orthophosphate. C (140° F) causes the rapid hydrolysis of pyrophos- Agitation Copper pyrophosphate baths need vigorous agitation for a normal operating cur- rent 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 con- tamination 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 cop- per 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 mod- ern 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 tem- perature 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 den- sity should range from 15 to 30 A/ft2 . Excessively high current densities can cause 204

Articles in this issue

view archives of Metal Finishing Guide Book - 2011-2012 Surface Finishing Guidebook