In short, gold deposition is to produce a layer of metal coating on the surface of circuit board by chemical oxidation-reduction reaction. The copper on the circuit board is mainly red copper. The copper solder joint is easy to be oxidized in the air, which will cause poor conductivity, i.e., poor tin eating or poor contact, and reduce the performance of the circuit board. Therefore, the surface treatment of the copper solder joint is required. Gold deposition is gold plating on it. Gold can effectively prevent copper metal and air from being oxidized, so gold deposition is a kind of surface anti-oxidation The treatment method is to cover the copper surface with a layer of gold through chemical reaction, which is also called metallization.

Immersion gold is mainly used for boards with connection functional requirements and long storage life. Gold is uniform in thickness, good in flatness, contact and wettability. Good electrical performance, can be stored for a long time (generally 1 year). However, black pad and gold embrittlement welding are easy to occur, and the production cost is high. Immersion silver is mainly used in boards with high frequency signal requirements. The electric properties of immersion Ag plate are good, the coating is uniform and the surface is flat. It has good weldability and can withstand multiple assembly operations.

As a new environment-friendly surface treatment process, immersion silver deposits a layer of 6-18u "thick silver on the surface of copper to ensure the reliable welding of electronic devices on string theory. The production cost of immersion silver is high, and it has high requirements for storage environment. It is easy to turn yellow and discolored, which will affect the weldability and the storage period is relatively short (generally 2-3 months). The resistance welding of the former process is required to be higher by immersion silver, otherwise, the Galvanic effect  is likely to occur, resulting in fatal defects of the open circuit.

The purpose of immersion gold and immersion silver is to better increase the conductivity, weldability and hardness. However, the purpose of immersion gold and immersion silver is to better connect gold (or silver) and copper foil. Of course, the cost of immersion gold is much higher than that of immersion silver. If it's a general solder joint, it's OK to make silver deposition, but if it's a finger insertion, immersion gold or gold plating is the best choice.