Gold plating happens through an electrical current or circuit created by placing both the object to be plated and the gold to cover it in a chemical bath and then turning on a current of electricity that runs through the mixture. The chemical solution usually comprises metal salts and ions that can carry electrical currents. All items to be plated must be thoroughly cleaned and dried before the plating process begins. The rack method requires the pieces being gold plated to be hung from a rack and then dropped into the chemical bath. The metal is charged negatively and attracts the gold metal ions to its surface, depositing the metal across the piece. This process is repeated for each layer of metal added before the gold is plated.

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Each type of industry using electronics plating has developed its own gold plating bath recipes. Most desire to minimize the amount of gold used, for obvious reasons, but still retain the best thickness of the plate to prevent corrosion. They are also concerned with minimizing the amount of bath solution while making it as pure as possible, and making the process occur quickly. Electronics plating, also called industrial plating, is broken down into four categories or types of gold used. They are soft and pure gold used on semiconductors, hard and bright gold used for contact points and connectors, hard and bright gold used on printed-circuit tabs and soft and pure gold used in chip-on-board products, which involves plating the whole circuit board.

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Gold plating is used in the electronics industry on printed circuit boards and connectors. The gold in this type of application is used to create a corrosion barrier over copper components. Plating methods, until electronics came along, were created mainly for decorative purposes. Electronics plating has caused gold plating processes to develop further due to electronic requirements. The process involves plating a metal barrier, usually nickel, on the copper components and then plating the gold on top of the nickel. Once completed, the gold plated components are corrosion resistant and conductive.

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The process of depositing a thin layer of gold over another metal for added beauty and durability has been used commercially since the late 1800s. Besides the glamor of having gold detailing or the appearance of solid gold on a piece, gold is plated for industrial purposes and is important for use in circuit boards. There are two main electroplating methods, tank and brush. Both involve use of electric current, electrodes (anode and cathode) and an electrolyte solution or preparation containing gold.

Cleaners
The object or areas to be plated have to be absolutely clean for plating to occur properly. In order to remove both organic and inorganic materials as well as grit and soil, a combination of different treatments are used, including acid cleaners, alkaline cleaners, abrasives and solvents.

Pretreaters
Depending on the type of metal to be plated, treatment may be needed to deposit an intermediate plating metal or smooth the surface layer for gold deposition. For instance, in plating gold onto a copper alloy, nickel is plated first, then gold. Sometimes other finishes, such as chrome, need to be removed with a chemical stripping agent.

Electrolyte Solutions
In order to get an electrolyte, the metal has to be in a state where it can disassociate and form ions. Gold is a stable metal and it takes harsh chemicals to accomplish this. Usually gold is complexed with cyanide, called cyanaurate, although techniques using sulfites and thiosulfites exist. There are many proprietary formulae for these solutions. In tank electroplating, cyanaurate is dissolved in an acidic bath that receives the electrodes. In brush electroplating, an applicator with a stainless steel core puts on the cyanaurate as a gel. Electric current passes from the steel applicator to the metal object being plated as the gel goes on.

Acids
The pH of the electroplating solutions for tank electroplating have to be adjusted to prevent formation of hydrogen cyanide, a lethal gas, at pH values above eight. However, below pH three, cyanaurate precipitates out of solution. Both inorganic and organic acids have been used to adjust pH in the workable range, including phosphoric acid, sulphuric acid and citric acid.

Other Additives
Brighteners are metal salts of transitional metals like cobalt, nickel and iron. They give improved wear resistance and brighter colors to the gold deposit. Some organic compounds are added to improve the density of the gold plating. Some of these organic additives are polyethyleneimine, pyridine sulphonic acid, quinoline sulphonic acid, picoline sulphonic acid and substituted pyridine compounds. Buffering agents such as a citrate/oxalate buffer can be added to help keep pH in the proper range. Wetting agents may be added as well.

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