Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 238 of 707

electroplating solutions PALLADIUM AND PALLADIUM-NICKEL ALLOY PLATING BY RONALD J. MORRISSEY TECHNIC INC., PROVIDENCE, R.I.; Palladium has been electroplated from a wide variety of systems, which can be broadly characterized as ammoniacal, chelated, or acid processes. Of these, the most numerous are the ammoniacal systems, in which palladium is present as an ammine complex, such as palladosamine chloride, Pd(NH3 )4Cl2 dinitrite, Pd(NH3 )2 (NO2 P-SALT/SULFAMATE Palladium as Pd(NH3 )2 sentative formulations are shown as follows: )2 (NO2 )2 , 10-20 g/L Ammonium sulfamate, 100 g/L Ammonium hydroxide to pH 7.5-8.5 Temperature, 25-35°C Current density, 0.1-2.0 A/dm2 Anodes, platinized PALLADOSAMINE CHLORIDE Palladium as Pd(NH3 )4 Cl2 , 10-20 gL Ammonium chloride, 60-90 g/L Ammonium hydroxide to pH 8.0-9.5 Temperature, 25-50°C Current density, 0.1-2.5 A/dm2 Palladium electrodeposits are notably susceptible to microcracking induced by codeposition of hydrogen. For this reason, it is important to plate at current effi- ciencies as high as possible. Proprietary brightening and surfactant systems are available, which increase the range of current densities over which sound deposits may be obtained. Ammoniacal electrolytes, particularly at higher temperature and pH, tend to tarnish copper and copper alloys. Proprietary palladium strike solu- tions have been developed. In most cases, however, a nickel strike is sufficient. Chelated palladium plating solutions contain palladium in the form of an organometallic complex. These solutions operate in the pH range of 5 to 7 and are in almost all cases proprietary. Requisite details may be obtained from the manufacturers. Acid palladium plating solutions have been used for producing heavy deposits of very low stress. Such systems are ordinarily based on the chloride, although a proprietary sulfate solution brightened with sulfite has been reported. A repre- sentative formulation for the chloride systems is as follows: ACID CHLORIDE Palladium as PdCl2 , 50 g/L 237 , or diamino- , which is known popularly as the P-salt. Some repre-

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