Seishi Masaki

Mirror-bright silver plating from a cyanide-free bath

ilver has good electric conductivity and solderability and possesses S excellent electric characteristics as a contact and is thus widely used for plating electronic industrial parts. A cyanide plating bath is most often used, but the cyanide compounds have strong toxicity and a large amount of the cost is rxpkd for securing safe working conditions and waste treatment. Because of this, many cyanide-free baths have been proposed and reported, such as the silver chloride-sodium thiosulfate system, the silver nitrate-tartaric acid system? and the silver iodide system added with gelatin: but none of them is in practical use. The authors found that a plated coat having performance comparable to that of the cyanide silver plating bath can be obtained from a silver methane sulfonate-potassium iodide bath to which N-(3-hydroxyl1 -butylidene)-p-sulfanilic acid (HBPSA) is added and has succeeded for industrialization; however, the plated coat obtained from this bath bas poor brightness. The authors have carried out research and development work on a cyanide-free bath capable of providing a bright silver plate.G It was determined that a bright coating can be obtained from silver succinimide.7,8 Jayaknshnan and Natarajan9 reported an alkaline silver plating using succinimide, but they gave no information for the stabilization of the bath. The authors found that the bath can be stabilized by adding boric acid and that mirror-bright silver plating can he obtained by adding polyethyleneimine (PEI) as a brightener. In the development work reported in this article the influences of adding PEI on the appearance of the plate coat, current efficiency, surface morphology, cathodic polarization characteristics, and the like were examined. The solderability, contact electric resistance, and hardness obtained were compared with those obtained from a conventional cyanide bath.

The Properties of the Bright Silver Deposit from Cyanide-Free Bath

The properties of electrodeposited silver films from succinimide baths were iuvestigated using a bath composed of 0.45mol/L of CH3SO3Ag and 1.5mol/L of succinimide. The silver film grain size was similar to that from a bright cyanide bath. The optimum conditions for bright silver plating were a pH of 10, a bath temperature of 25°C, and a current density of 2A/dm2.The plating bath throwing power was 40-42% and increased with the pH. The solderability of these silver deposits was better than those from a bright cyanide bath and the film electric contact resistance was less than 2mΩ at a load of 5g. The deposited silver hardness was Hv (125-130) and became Hv (86-90) after backing at 200°C for 1h.

Correlation between Differential Capacity of Electrical Double Layer and Surface Morphologies in Silver-electrodeposits

A solution of silver methane sulfate and potassium iodide with HBPSA added was employed for the test solution and the electroplating bath. Differential capacity was found to decrease with increases in the concentration of HBPSA as did the grain size of the electrodeposits.

Silver Plating from Silver Methane Sulfonate-Potassium Iodide Baths

It was found that silvery-white, smooth electrodeposits were obtained by adding N-(3-Hydroxy-1-buthylidene)-p-sulfanilic acid (HBPSA) to silver methane sulfonate-potassium iodide baths.The bath composition and operating conditions most conductive to obtaining a smooth surface on the electroplated silver were 0.27mol/L of CH3SO3Ag, 3mol/L of KI, 2.06×10-2mol/L of HBPSA, with a pH of 5, bath temperature of 50°C, and current density of 0.5∼3A/dm2.Cathode current efficiency was over 95% at current densities between 1 and 3A/dm2, and throwing power was 30% at HBPSA 2.06×10-2mol/L The solderability and contact electric resistance of these silver deposits were approximately Similar to those from cyanide baths