1. Hot air leveling applied on the surface of PCB molten tin lead solder and heated compressed air leveling (blowing flat) process. Making it form an oxidation resistant coating can provide good weldability. The hot air solder and copper form a copper-sikkim compound at the junction, with a thickness of approximately 1 to 2mil.
2.   Organic Solderability Preservative (OSP) by chemically growing an organic coating on clean bare copper. This PCB multilayer film has the ability to resist oxidation, heat shock, and moisture to protect the copper surface from rusting (oxidation or sulfurization, etc.) under normal conditions. At the same time, at the subsequent welding temperature, welding flux is easily removed quickly.

        3. Ni-au chemical coated copper surface with thick, good ni-au alloy electrical properties to protect PCB multilayer board. For a long time, unlike the OSP, which is only used as a rustproof layer, it can be used for long-term use of PCB and obtain good power. In addition, it has environmental tolerance that other surface treatment processes do not have.

        4. Electroless silver deposition between OSP and electroless nickel/gold plating, PCB multilayer process is simple and fast.

Exposure to hot, humid and polluted environments still provides good electrical performance and good weldability, but tarnish. Because there is no nickel under the silver layer, the precipitated silver does not have all the good physical strength of electroless nickel plating/gold immersion.

        5.The conductor on the surface of PCB multilayer board is plated with nickel gold, first with a layer of nickel and then with a layer of gold. The main purpose of nickel plating is to prevent the diffusion between gold and copper. There are two types of nickel-plated gold: soft gold (pure gold, which means it doesn’t look bright) and hard gold (smooth, hard, wear-resistant, cobalt and other elements that look brighter). Soft gold is mainly used for chip packaging gold line; Hard gold is mainly used for non-welded electrical interconnection.

       6. PCB mixed surface treatment technology choose two or more methods for surface treatment, common ways are: nickel gold anti-oxidation, nickel plating gold precipitation nickel gold, nickel plating gold hot air leveling, heavy nickel and gold hot air leveling. Although the change in PCB multilayer surface treatment process is not significant and seems far-fetched, it should be noted that a long period of slow change will lead to great change. With the increasing demand for environmental protection, the surface treatment technology of PCB is bound to change dramatically in the future.