Plating solution

Electroless plating on metal substrates can be improved by addition of pentaerythritol, either to a photosensitive composition of a noble metal salt (99), or with glycerine to nickel plating solutions (100). Both resolution and covering power of the electrolyte are improved. 

Numerous variations exist in the electroless plating solutions, processes, and techniques employed both in laboratory and commercial form, to create a great variety of products (39). AH produce a layer of highly conductive copper in specified areas. Modem electroless copper films have a ductiHty and conductivity identical to that of electrolytic copper (40). The three basic classes of copper baths are... 

Plate Thickness. In plating processes, plate thickness can be predicted knowing the cathode efficiency of a particular plating solution, the current density, and time of plating. 

Examples of plating solutions having good throwing power include cyanide plating baths such as copper, zinc, cadmium, silver, and gold, and noncyanide alkaline zinc baths. Examples of poorer throwing power baths are acid baths such as copper, nickel, zinc, and hexavalent chromium. 

Copper anodes for use in acid copper plating solutions preferably contain a small amount of phosphoms [7723-14-0] usually 0.03—0.04 wt %, which retards chemical dissolution of the copper and thus the subsequent copper build-up. Typically, acid copper plating solutions increase in copper and require periodic dilution. Additionally, additives for brightening acid copper baths tend to last longer in plating tanks using phosphorized copper anodes. In cyanide copper solutions, phosphorized copper anodes should not be used. 

Since the 1960s titanium mesh anode baskets have been used (21), especially in nickel plating solutions. Nickel anodes in the form of small round buttons and pellets combined with the titanium anode basket allows a constant anode area to be maintained with a minimum of effort. 

Whenever insoluble anodes are used, the pH of the plating solution decreases along with the metal ion concentration. In some plating baths, a portion of the anodes is replaced with insoluble anodes in order to prevent metal ion buildup or to reduce metal ion concentration. Lead anodes have been used in acid copper sulfate baths, and steel anodes have been used in alkaline plating baths. 

Heat scales and mst on steel are not of even composition or thickness, and parts are subject to uneven pickling. To minimize over-etching, inhibitors are sometimes used to slow the attack on the clean steel. Many inhibitors produce strong adverse effects if carried into the plating solution. A second electrocleaning step is used after the pickle when inhibitors are employed. 

Reference 38 is a good guide to the selection of plate thickness test methods. Test methods may vary with the purity and electrochemical activity of the deposit. Metals deposited from commercial plating solutions are seldom pure. For example, zinc deposits from the three commonly used baths, ie, cyanide, chloride, and zincate, vary significantly in purity and activity (39). Standard ASTM test methods for determining plate thickness are... 

Ductility Tests. The ductihty of plated metals differs considerably from the corresponding thermally cast metals. Additionally, ductihty which is an important property if parts are to be deformed after plating, varies with the chemical composition of the plating solution, as well as the operating conditions of a given plating process. Ductihty can also be important when plated parts are stressed in use. Some metal deposits have coefficients of... 

Plating Bath Purification. Purification, often needed once a plating bath is made, is used periodically to maintain the plating solutions. Alkaline ziac plating solutions are sensitive to a few mg/L of heavy-metal contamination, which can be precipitated usiag sodium sulfide and filtered out. 

Nickel plating solutions may contain excess iron and unknown organic contaminants. Iron is removed by peroxide oxidation, precipitation at a pH of about 5, then filtered out. The more complex, less water-soluble organic contaminants along with some trace metals are removed with activated carbon treatments in separate treatment tanks. About 5 g/L of plating-grade activated carbon is mixed in the plating solution for at least 1—2 hours, usually at warmer temperatures. 

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