1. Hot air leveling (TIN)
Hot air leveling, also known as hot air solder leveling (commonly known as tin spray), is the process of coating the molten tin (lead) solder on the surface of the FPC and using the heated compressed air (blowing) to form a coating that can resist copper oxidation and provide good weldability. During hot air, copper tin intermetallic compounds are formed at the junction of solder and copper.

2. Sink tin
Since all the solder is tin based, the tin layer can match any type of solder. The tin sinking process can form a flat copper tin intermetallic compound, which makes the SN having the same weldability as the hot air leveling without the hot air leveling. The tin plate can not be stored for too long, and the assembly must be carried out in the order of the tin.

3. Sink Silver
The process of sedimentation is between organic coating and electroless nickel plating / gold deposit. The process is simple and fast. Even if exposed to hot, wet and polluted environment, silver can still maintain good weldability, but it will lose its gloss. Silver immersion does not possess good physical strength due to electroless nickel plating and gold deposition, because nickel is not found below the silver layer.

4. Chemical nickel and palladium gold
Chemical nickel palladium gold is a layer of palladium more than gold and nickel and gold. Palladium can prevent corrosion caused by replacement reaction and prepare well for gold deposit. Gold is tightly covered with palladium, providing a good contact surface.

5. Full plate nickel plated gold
Nickel plated gold is plated on the surface of FPC conductor with a layer of nickel and then plated with a layer of gold. Nickel plating is mainly to prevent the diffusion of gold and copper. There are two kinds of electroplating nickel gold: soft gold plating and hard gold plating.

6. Sinking gold
Gold deposit is a thick, electrically good nickel gold alloy coated on the copper surface, which can protect the FPC for a long time, and it also has the tolerance to the environment that other surface treatment processes do not possess. In addition, sunk can also prevent copper from dissolving, which will be beneficial to lead-free assembly.