Electroplating

Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current. The part to be coated acts as the cathode (negative electrode) of an electrolytic cell; the electrolyte is a solution of a salt whose cation is the metal to be coated, and the anode (positive electrode) is usually either a block of that metal, or of some inert conductive material. The current is provided by an external power supply.

Electroplating is widely used in industry and decorative arts to improve the surface qualities of objects—such as resistance to abrasion and corrosion, lubricity, reflectivity, electrical conductivity, or appearance. It is used to build up thickness on undersized or worn-out parts and to manufacture metal plates with complex shape, a process called electroforming. It is used to deposit copper and other conductors in forming printed circuit boards and copper interconnects in integrated circuits. It is also used to purify metals such as copper.

The aforementioned electroplating of metals uses an electroreduction process (that is, a negative or cathodic current is on the working electrode). The term "electroplating" is also used occasionally for processes that occur under electro-oxidation (i.e positive or anodic current on the working electrode), although such processes are more commonly referred to as anodizing rather than electroplating. One such example is the formation of silver chloride on silver wire in chloride solutions to make silver/silver-chloride (AgCl) electrodes.

Electropolishing, a process that uses an electric current to selectively remove the outermost layer from the surface of a metal object, is the reverse of the process of electroplating.^[1]

Throwing power is an important parameter that provides a measure of the uniformity of electroplating current, and consequently the uniformity of the electroplated metal thickness, on regions of the part that are near to the anode compared to regions that are far from it. It depends mostly on the composition and temperature of the electroplating solution, as well as on the operating current density.^[2] A higher throwing power of the plating bath results in a more uniform coating.^[3]