Excluding the specialty and continuous-strip plating industries, more copper is plated than any other decorative metal except for nickel. There are several reasons for this: Copper is an excellent undercoat for subsequent deposits, since it’s a good metal to cover substrate defects that can accelerate corrosion. Buffing copper even improves its ability to be an excellent substrate. Copper, and especially buffed copper, can provide an easy-to-plate, highly level and bright substrate.Copper is among the least expensive metals and is in relatively stable supply. More levelling can be obtained for the cost of the metal electroplated than for any other metal.Copper has a high plating efficiency, and many copper plating processes offer good coverage and throwing power.Copper metal is less environmentally hazardous than many other plated metals, although the EPA limits the discharge of copper and copper plating solutions. The waste treatment processes for copper plating solutions and copper-containing rinse waters are well known and in most cases easy to accomplish. Also, many times the copper metal and even the plating bath can be recycled.Copper’s high electrical conductivity is exceeded only by silver, making it an excellent and inexpensive coating for products such as printed circuit boards. Used as a topcoat on steel wire, it produces high-strength, conductive electrical cable.The percent elongation of most electroplated copper deposits is greater than other electroplated metals. This property helps substrates such as plastic and aluminium withstand thermal expansion without cracking their electrodeposited coatings.Three basic types of processes are available based upon the complexing system used: alkaline (several modifications of cyanide and non-cyanide); acid (sulphate and fluoborite) and mildly alkaline (pyrophosphate) complexed baths.
Alkaline Cyanide Solutions
Alkaline copper solutions have better throwing power (uniform deposit thickness) than acid copper solutions. However, they cannot be used at as high a current density as acid copper. They are also relatively more difficult to control than acid sulphate solutions. Also, cyanide involves special handling and treatment procedures because of its acute health hazards and waste disposal requirements. But, the procedures are well understood, and, with care, cyanide can be handled safely.
Carbonate, typically as sodium carbonate, is added to strike and Rochelle salt processes at bath makeup. It controls pH by acting as a buffer and reduces anode polarization.
Carbonate is not added to high-efficiency baths. However, carbonate forms naturally during operation in all cyanide baths. This is a result of the decomposition of free cyanide through hydrolysis and cyanide oxidation at the anode. Carbonate also builds up in the bath by absorption of carbon dioxide from the atmosphere, an effect promoted by air agitation.
If carbonate concentration reaches 75-100 g/L, some should be removed since it reduces the bright plating range. Remove carbonates by precipitation through the addition of calcium (lime) or barium hydroxide to form insoluble calcium or barium salts. Barium cyanide, which also lowers carbonate content, prevents an increase in the hydroxide level of the bath.
Another approach is to chill the sodium-based bath to form sodium carbonate, which is much less soluble at lower temperatures. If the temperature is reduced below 32°F, copper salts also will precipitate. Carbonates cannot be chilled out of a potassium-based bath, since potassium carbonate is too soluble. For all these purposes you can take the help of copper plating company experts who are action oriented and knows what is to be done.