There are many pcb surface treatment processes, the common ones are hot air leveling, organic coating, electroless nickel/immersion gold, immersion silver and immersion tin, which will be introduced one by one below.

　　1, hot air leveling HASL (spray tin)

Hot air leveling is also known as hot air solder leveling (commonly known as tin spraying). It is a process of coating molten tin (lead) solder on the surface of the PCB and flattening (blowing) it with heated compressed air to form a layer that is resistant to copper oxidation. It can also provide a coating layer with good solderability. During hot air leveling, the solder and copper form a copper-tin intermetallic compound at the joint. When the PCB is leveled with hot air, it must be submerged in the molten solder; the air knife blows the liquid solder before the solder solidifies; the air knife can minimize the meniscus of the solder on the copper surface and prevent the solder from bridging.

　　2, organic solderability preservative (OSP)

　　OSP is a process for surface treatment of printed circuit board (PCB) copper foil that meets the requirements of the RoHS directive. OSP is the abbreviation of Organic Solderability Preservatives, which is translated as Organic Solderability Preservatives in Chinese, also known as Copper Protector, or Preflux in English. Simply put, OSP is to chemically grow a layer of organic film on the clean bare copper surface.

This layer of film has anti-oxidation, heat shock resistance, and moisture resistance to protect the copper surface from rusting (oxidation or sulfidation, etc.) in a normal environment; but in the subsequent welding high temperature, this kind of protective film is ** *It is easy to be quickly removed by the flux, so that the exposed clean copper surface can be immediately combined with the molten solder to form a firm solder joint in a very short time

　　3, the whole plate is nickel-plated gold

　　Plating nickel and gold on the PCB surface conductor is plated with a layer of nickel and then with a layer of gold. Nickel plating is mainly to prevent the diffusion between gold and copper. There are two types of electroplated nickel gold: soft gold plating (pure gold, the gold surface does not look bright) and hard gold plating (the surface is smooth and hard, wear-resistant, contains cobalt and other elements, and the gold surface looks brighter). Soft gold is mainly used for gold wire in chip packaging; hard gold is mainly used for electrical interconnection in non-welded areas.