Metal Finishing Guide Book


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Gold plating baths: Several types of gold plating baths have been formulated based on end uses, such as decorative, soft gold, nickel- and cobalt- hardened gold for industrial electronics, and miscellaneous applications involving repairs and electroforming. Low-speed and high-speed gold baths have been designed for use in rack, barrel, and reel-to-reel applications, namely: 1. Alkaline gold cyanide for gold and gold alloys 2. Neutral gold cyanide for high-purity gold plating 3. Acid gold cyanide for bright, hard gold and its alloys 4. Non-cyanide gold with sulfite, thiosulfate 5. Electroless gold Non-cyanide gold and electroless gold baths are used for special applications. The analytical methods for gold baths are summarized in Table 4. Silver plating baths: Both cyanide and non-cyanide silver baths are used in the electroplating industry. Parameters such as silver metal, free cyanide, pH, and brighteners are routinely measured by common analytical methods. Electroless silver baths are employed in special applications. Palladium, palladium-nickel, and Pd-cobalt baths: Palladium , Pd-Ni, and Pd-Co (80/20 alloy composition) baths containing sulfate and chloride at acid and alkaline pH have been employed in engineering finishes. The analysis methods are summarized in Table 5. Tin and tin-lead baths: Tin-lead baths—(with electrolytes fluoboric acid, sulfuric acid, alkyl sulfonic acid, and methane sulfonic acid (MSA)—have been employed in the industry in conjunction with proprietary brighteners. With the advent of new technologies and RoHS compliance requirements, several new tin chemistries have been developed. Presently, MSA-based chemistries are more popular than sulfate-based chemistries, especially the proprietary additive packages claiming whisker resistance in highly reliable electronic applications. Immersion tin baths are used in special applications where low tin thickness is required. Tin and lead metal concentrations are conveniently determined by AA, ICP, and titrimetric methods, whereas additives are estimated using hull cell, HPLC, IC, or spectrophotometric methods (Table 6). Copper baths: Several electrolytic copper baths, namely acid copper (sulfuric acid, fluoboric acid), cyanide copper, alkaline non-cyanide, and pyrophosphate copper are available. Copper metal may be determined by AA, ICP, and titrations. Pyrophosphates and orthophosphates are determined by EDTA titrations. Additives consist of organic chemicals, such as carriers, levelers, and brighteners, which are estimated using chromatographic methods, IC, CVS, and CPVS for aged baths. Electroless copper baths containing Cu, EDTA, formaldehyde, and proprietary additives are used for dedicated applications. Copper is analyzed by AA, ICP, and titrations. Formaldehyde may be measured by titration and colorimetric procedures. 468

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