Why do the terminals in a terminal block need to be gold plated?

Why most of the terminal wire terminals, terminals should be made surface treatment,. Mainly from three aspects:
First, first from the producer
      Operators must clean the machine every day, remove the machine surface dust and debris as well as excess oil, terminal machine stamping guide rail must be added once an hour oil lubrication refueling holes in the top of the terminal machine, each refueling to 2-3 drops is appropriate not too much. Terminal machine main speed bearing every week to add grease oh.
Second, protect the terminal reed substrate from corrosion;
      Most of the terminal reed is made of copper alloy, usually corroded in the use of the environment, such as oxidation, vulcanization, etc.. Terminal plating is to make the reed and environmental isolation, to prevent the occurrence of corrosion. Plated material, of course, if it does not corrode, at least in the application environment.
Third, optimize the performance of the terminal surface, the establishment and maintenance of the contact interface between the terminals, especially the film layer control. In other words, to make it easier to achieve metal-to-metal contact.
      1, surface optimization: optimization of terminal surface performance can be achieved in two ways. (1) lies in the design of the terminals to establish and maintain a stable terminal contact interface. (2) the establishment of metallic contact, the requirements of the insertion, any surface film layer is not present or will rupture. There is no film layer and film layer rupture the difference between these two forms is also the difference between precious metal plating and non-precious metal plating. Precious metal plating, such as gold, palladium, and their alloys, is inert and has no film layer of its own. Therefore, for these finishes, metallic contact is "automatic". What we need to consider is how to maintain the "nobility" of the terminal surface, unaffected by external factors such as contamination, diffusion from the substrate, terminal corrosion, etc. Non-metallic plating, especially tin and lead and its alloys, covered with a layer of oxide film, but in the insertion, the oxide film is easy to rupture, and the establishment of a metallic contact area.
      2, increase the strong plating adhesion of the terminal (such as copper) for poor adhesion of the metal, plating is usually played before the copper bottom to enhance adhesion.
      3, enhance the conductivity of the terminals (such as gold, silver) the original material such as iron, phosphorus copper conductivity are usually below 20%, for low impedance requirements of the connector can not meet the requirements, so the surface layer of gold plating and other high conductivity metal can be reduced after its impedance.
      4, improve the solderability of the terminals (such as tin, gold, etc.) cause material for the poor adhesion of tin, surface plating a certain thickness of tin and other substances can improve the solderability of the parts.

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