The most basic purpose of surface treatment is to ensure good solderability or electrical properties. Since copper in nature tends to exist in the form of oxides in the air, it is unlikely to remain as original copper for a long time, so other treatments are required for copper. Although in the subsequent assembly, strong flux can be used to remove most of the copper oxides, but the strong flux itself is not easy to remove, so the industry generally does not use strong flux. There are 8 common surface treatment processes as follows:

1. HASL

HASL, also known as Hot Air Solder Leveling (commonly known as tin spray), is a process of coating molten tin (lead) solder on the surface of the PCB and leveling (blowing) the level 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 hot-air leveled, it should sink in the molten solder; the air knife blows off 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. OSP

OSP, Organic Solderability Protectant, is a process that conforms to the RoHS directive requirements for printed circuit board (PCB) copper foil surface treatment. OSP is the abbreviation of Organic Solderability Preservatives, Chinese translation is organic solder mask, also known as copper protector, also known as Preflux in English. Simply put, OSP is to grow a layer of organic film chemically on a clean bare copper surface.

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

3. Full Plate Nickel -Plated Gold

Full plate nickel-plated gold is to plate a layer of nickel on the surface conductor of the PCB and then a layer of gold. Nickel plating is mainly to prevent the diffusion between gold and copper. There are two types of electroplated nickel-gold now: 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 other elements such as cobalt, and the gold surface looks brighter). Soft gold is mainly used for gold wire bonding in chip packaging; hard gold is mainly used for electrical interconnection at non-welded locations.

4. Immersion Gold

Immersion Gold is a thick layer of nickel-gold alloy with good electrical properties wrapped on the copper surface, which can protect the PCB for a long time; in addition, it also has environmental tolerance that other surface treatment processes do not have. In addition, immersion gold can also prevent the dissolution of copper, which will benefit lead-free assembly.

5. Immersion Tin

Since all solders are currently based on tin, the tin layer can match any type of solder. Immersion Tin process can form a flat copper-tin intermetallic compound, this feature makes Shen tin have the same good solderability as hot air leveling without hot air leveling headache flatness problem; Immersion Tin plate can not be stored for too long , but must be assembled according to the technical requirements of Immersion Tin.

6. Immersion Silver

Immersion Silver process is between organic coating and electroless nickel/immersion gold, with relatively simple and fast process; even if exposed to heat, humidity and contaminated environment, silver can still maintain good solderability, but will lose luster. Immersion silver does not have the good physical strength of electroless nickel/immersion gold because there is no nickel under the silver layer.

7. Chemical Nickel Palladium Gold

Compared with Immersion Gold, Chemical Nickel Palladium Gold has an extra layer of palladium between nickel and gold. Palladium can prevent the corrosion phenomenon caused by the replacement reaction and make full preparation for immersion gold. Gold closely covers the palladium to provide a good contact surface.

8. Hybrid surface treatment technology

Choose two or more surface treatment methods for surface treatment, the common forms are: Immersion Nickel Gold + OSP, Electroplating Nickel Gold + Immersion Nickel Gold, Electroplating Nickel Gold + Hot Air Solder Leveling, Immersion Nickel Gold + Hot Air Solder Leveling.

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