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Introduction to Surface Treatment Process of FPC

  1. Hot air leveling (tin spraying)

Hot air leveling, also known as hot air solder leveling (commonly known as tin spraying), is a process of coating molten tin (lead) solder on the surface of FPC and leveling (blowing) it with heated compressed air to form a coating that is both resistant to copper oxidation and can provide good solderability. Copper tin intermetallic compound is formed at the joint of solder and copper during hot air leveling.

  1. Tin precipitation

At present, all solders are based on tin, so the tin layer can match any type of solder. The tin deposition process can form a flat copper tin intermetallic compound, which makes the tin deposition have the same good solderability as the hot air leveling without the headache flatness problem of the hot air leveling; The tin plate cannot be stored for too long, and the assembly must be carried out according to the sequence of tin deposition.

  1. Sink silver

Silver deposition process is between organic coating and electroless nickel/gold plating, which is relatively simple and fast; Even if exposed to heat, humidity and pollution, silver can still maintain good solderability, but it will lose luster. Silver deposition does not have the good physical strength of electroless nickel/gold plating because there is no nickel under the silver layer.

  1. Chemical nickel palladium

Compared with gold precipitation, chemical nickel palladium has an additional layer of palladium between nickel and gold. Palladium can prevent corrosion caused by displacement reaction and make full preparation for gold precipitation. Gold tightly covers palladium, providing a good contact surface.

  1. Full plate nickel plated gold

Plate nickel gold plating is to coat the conductor on the FPC surface with a layer of nickel first and then a layer of gold. Nickel plating is mainly used to prevent the diffusion between gold and copper. Now there are two types of nickel gold plating: soft gold plating and hard gold plating.

  1. Sinking gold

Gold deposition is to wrap a thick layer of nickel gold alloy with good electrical properties on the copper surface, which can protect FPC for a long time; In addition, it also has the environmental tolerance that other surface treatment processes do not have. In addition, gold deposition can also prevent the dissolution of copper, which will be beneficial to lead-free assembly.

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