Gold plating

1. Characteristics and properties

Pure gold is a yellow, very soft and corrosion-resistant metal. It has good electrical conductivity, has the lowest tendency of all metals to form insulating coatings and is not subject to oxidation or sulphur attack. Pure gold is not attacked by acids, with the exception of hydrochloric acid with the addition of oxidizing agents. Gold is also dissolved in cyanide solutions in the presence of oxygen.

Fine gold has a hardness of 40-80 HV 0.1, the hardness of the layer can be increased to 140-160 HV 0.1 by co-depositing approx. 0.3% nickel or cobalt. Alloying elements reduce the conductivity of gold, which is particularly important in electrical engineering. At Metoba, components are coated with gold/cobalt or gold/nickel alloys. Deposited gold layers retain their gloss, but do not form it. For this reason, decorative components are highly polished and nickel-plated before coating.

2. Benefits and areas of application

Galvanic gilding used to be used exclusively for decorative purposes. The layers were usually very thin and not very resistant to abrasion. By co-depositing alloying elements, it is now standard to produce hard, abrasion-resistant layers.

Electronics and electrical engineering is the largest consumer of gold-plated components, since gold coatings not only have excellent physical properties, such as high ductility, tarnish resistance, good solderability and even at higher temperatures the specific resistance and contact resistance remain constant. Gold layers are mainly used on contact components. Due to the constantly increasing distribution of electronic devices, a large number of contact or interfaces are required at which information is transmitted in the form of very small currents. There, very high demands are placed on the reliability of the connections, which can usually only be met with a gold layer.

Depending on the field of application, gold with layer thicknesses of 0.1 to 4µm is predominantly deposited on intermediate layers such as nickel.

3. Basic material

Base materials that can be directly gold-plated are copper, brass, nickel, nickel silver or silver. Other metallic base materials can also be provided with a gold coating by means of intermediate layers. In order to prevent diffusion processes, it is usual to provide the workpieces with a diffusion barrier layer, which usually consists of a layer of semi-bright or bright nickel.

4. Required delivery condition

The goods provided must be largely metallically bright. Residual oils or residual impurities must be removable with conventional aqueous alkaline degreasers. Oils containing silicone, alkali/alkaline earth and high-pressure additives must be avoided at all costs.