What is the purpose of coating the waterproof connector housing and copper pin surface?

The waterproof connector housing and copper pin surface coating will affect the quality of the product, after all, the material selection and manual labor need to be carefully controlled, so that we can ensure that the product we make is good for the user.
1. Cyanide free alkaline bright copper: Pre plated and thickened on copper alloy waterproof connectors, with a coating thickness of over 10 μ m and a color similar to acidic bright copper coating. If blackened, it can achieve a dark effect. It has been operating normally in a 10000 liter tank for 2 years.
2. Cyanide free bright gold plating: The universal type uses thiosulfate as the main chelating agent, while the high polarity type uses organic compounds without sulfur content as the main chelating agent. The thickness of the fully bright coating can reach over 40 μ m, the surface resistivity of the coating is~54 μ Ω· cm, the tensile strength is~HV101.3, and the thermal shock reaches the standard at 350 ℃, which is very close to the performance of cyanide gold plating.  
3. Cyanide free self ionic liquid organic chemical gold plating: The main salt used for the contact of waterproof connectors is Na3 [Au (SO3) 2], and the thickness of the gold layer can reach 1.6 μ m. It is used for gold plating on high-density flexible circuit boards and electronic ceramics.
4. Non formaldehyde content self ionic liquid organic chemical roll coating: used for through-hole plating and non-conductive surface metallization of PCB circuit boards. Eliminating harmful formaldehyde content and replacing it with cheap and harmless hypophosphite has not yet been politicized domestically and internationally. We have mainly conducted laboratory discussions, with a rotational speed of 3-4 μ m/h for igneous rocks and a service life of over 10 cycles per system (MTO). The coating is high-density and bright. But it still needs continuous improvement and pilot testing.
5. Pure palladium electroplating: Ni can cause allergic dermatitis, and the European Commission has long rejected the import of Ni containing jewelry. Palladium is a good substitute for Ni alloy. This project was carried out in 1997 and includes two processes. The second is thin palladium transfer, with a thickness of 0.0~0.3 μ m, which is used as an anti rust abstract coating and anti silver anti discoloration layer on white copper tin; The second is the thick palladium ferry, with a thickness of up to 3 μ m and no cracks (current international standard). Due to the high price of palladium, it has never entered the domestic market.
6. Trivalent chromium zinc coating white blue and colorful passivator: a hexavalent chromium salt that acts as a carcinogen with trivalent chromium salt. The white blue passivation treatment color is like a coating layer, which has been tested in the neutral salt spray laboratory for more than 27 hours and has undergone 20 years of market experience. The colorful passivation treatment has been discussed in the laboratory, and the color is bright, but it needs to be tested in the pilot test.
The above six coatings each have their own characteristics. Whether it is the surface of the waterproof connector or the contact part, the type of material must be confirmed first, and then the method of changing the coating should be determined to determine the main parameters of the coating.