Acidic copper plating baths are essentially constituted by copper sulphate and sulphuric acid. These copper plating baths, together with cyanide alkaline baths, are the most common.
Acidic copper plating baths, unfortunately, have a very poor penetrating power, so they do not uniformly cover the surface of the metal base, giving it a different degree of protection. It is, therefore, natural that, in order to achieve the minimum thickness allowed in the zones of minimum current density, it is necessary – unless resorting to elaborate screens – that in high current density zones the thickness reaches very high values of the minimum allowed.
This is, of course, a true economic disadvantage, as it requires much longer plating times and, possibly, mechanical levelling. Despite this drawback, acidic sulphate baths are mainly used for copper plating with high thickness. Indeed, through acidic baths, it is easier to use higher current density and, therefore, special kinds of electroforming can be obtained.
With special equipment, quick copper plating of cylinders by gravure is also possible; however, this type of copper plating is performed more proficiently with fluoroborate baths.
Their main disadvantage resides in the fact that iron cannot be directly copper-plated by acidic solutions, since the deposited copper is so spongy, due to cathodic polarization, that the coating is unusable. For all metals preceding copper in the electrochemical series, direct copper plating by acidic baths is very difficult and, in some cases, unworkable.