Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Table XI. Copper Fluoborate Baths Copper fluoborate Fluoboric acid pH (colorimetric) Temperature Baum|fe Current density High Concentration 60 oz/gal (459 g/L) 5.4 oz/gal (40.5 g/L) 0.2-0.6 65-150O F 37.5-39.5° 125-350 A/ft2 Low Concentration 30 oz/gal (225 g/L) 2 oz/gal (15 gal/L) 1.0-1.7 65-150° 21-22° F 75-125 A/ft2 ing. Major sources are decomposition products of brighteners, drag-in of previous process chemistries, tank liners, unleached anode bags, stop-offs, resists, and impure salts or acid. Contaminants will adversely affect the appearance and the phys- ical properties of the deposit. A green coloration of the bath indicates significant organic contamination. Organic impurities are removed by treatment with activated carbon. In cases of severe contamination, potassium permanganate, hydrogen peroxide, or even bleach, if the chloride ion is monitored, may be necessary to break down the organics so that the activated carbon can effectively remove them. Carbon itself may contaminate or have no effect if the activated carbon was not designed for use in high acid baths. Cellulose filter aids should not be used. Some common metallic contaminants and their effects are as follows: Antimony (10-80 ppm): rough, brittle deposits. Gelatin or tannin added to the bath will inhib- it its codeposition. Arsenic (20-100 ppm): same as antimony. Bismuth: same as antimony. Cadmium (>500 ppm): can cause an immersion deposit and polarization of the anode dur- ing idle time. Can tie up chloride ions. Iron (>1,000 ppm): reduces bath conductivity and throwing power. Nickel (>1,000 ppm): same as iron. Selenium (>10 ppm): anode polarization, roughness. Tellurium (>10 ppm): same as selenium. Tin (500-1,500 ppm): immersion deposits and polarization of anodes during idle time. Zinc (>500 ppm): same as cadmium. A guide for troubleshooting acid copper baths is given in Table X. COPPER FLUOBORATE BATH This bath allows the use of high current densities and increased plating speed, as copper fluoborate is extremely soluble and large amounts can be dissolved in water. The main drawback is its corrosivity, consequently, construction materials are normally limited to hard rubber, polypropylene, polyvinyl chloride (PVC), and carbon/Karbate. In all other aspects, the copper fluoborate bath is similar to copper sulfate plating. The anodes should be high-purity copper that is oxide free. Anode bags should be made of Dynel or polypropylene. Normally, the bath is made up with copper fluobo- rate concentrate (1.54 g/ml or 50.84O B|fe), which contains 92.0 oz/gal cupric fluobo- rate (26.9% by weight copper metal), 1.4 oz/gal fluoboric acid, and 2 oz/gal boric acid (to prevent the formation of free fluoride due to fluoborate hydrolysis). The fluoboric acid (1.37 g/ml or 39.16° Bé typically contains 90 oz/gal of fluoboric acid and 0.9 208

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