The basic purpose of PCB surface treatment is to ensure good weldability or electrical performance.Because the natural copper in the air tends to be in the form of oxides, it is unlikely to remain copper for a long time, so copper is needed for other treatments.
1.Hot Air Leveling (HAL/HASL)
Hot air leveling, also known as hot air solder leveling (commonly known as HAL/HASL),which is coated on the PCB surface heating molten tin solder (lead) and use compressed air to the whole (blow) flat technology, make its form a layer of copper oxidation resistance, and can provide good weldability of the coating layer.The solder and copper are formed in the joint to form a compound.The PCB should be immersed in molten solder during hot air conditioning.The wind knife flushes the liquid solder before the solder solidifies.The wind knife can minimize the bending of the solder on the copper surface and prevent welding bridge.
2.Organic Weldable Protective Agent (OSP)
OSP is printed circuit board (PCB) copper foil surface treatment of a kind of technology to meet the requirements of RoHS directive.OSP is an abbreviation of Organic Solderability preservative. It is also known as the Organic soldering film, also known as the copper protector, and also known as Preflux in English.In a nutshell, the OSP is a chemically modified layer of organic skin on the surface of clean, bare copper.This film has anti-oxidation, thermal shock and moisture resistance, which can protect the copper surface from rust (oxidation or vulcanization) in normal environment.But in the subsequent welding heat, the protective film and must be quickly removed by flux easily, so just can make clean copper surface of the show is in a very short period of time with molten solder immediately become a solid solder joints.
3.Full Plate Nickel/ Gold
Plate Nickel/ Gold is plated on the surface of PCB and then plated with a layer of gold. The nickel plating is mainly to prevent the diffusion of gold and copper.Now there are two types of electroplating nickel gold: soft gold plating (gold, gold surface looks not bright) and hard gold plating (surface is smooth and hard, wear-resisting, contain other elements such as cobalt, gold looks more light).Soft gold is mainly used for chip packaging gold wire;The hard gold is mainly used for electrical interconnection in non-welding areas.
4.Immersion Gold
Immersion gold is coated with a thick, electrically good nickel-gold alloy on the copper surface, which can protect PCB for a long time.In addition, it has the tolerance of other surface treatment technologies.In addition, sinking gold can also prevent the dissolution of copper, which will be beneficial to lead-free assembly.
5.Immersion Tin
Since all solders are based on tin, the tin layer can match any type of solder.Tin process between flat copper tin compounds can be formed, this feature makes heavy tin has like hot air leveling of good weldability and no hot air leveling flatness of headache problem;immersion tin cannot be stored for too long and must be assembled according to the order of settling tin.
6.Immersion Silver
The silver process is between organic coating and electroless nickel plating. The process is simple and fast.Even when exposed to heat, humidity and pollution, silver can maintain good weldability but will lose its luster.The silver does not have the good physical strength of the chemical plating nickel/sinking gold because there is no nickel under the silver layer.
7.ENEPIG（Electroless Nickel Electroless Palladium Immersion Gold）
Compared with ENEPIG and ENIG,there is an additional layer of palladium between nickel and gold. Palladium can prevent the corrosion phenomenon caused by the substitution reaction, and make full preparation for immersion gold.Gold is closely covered with palladium, providing a good interface.
8.Plating Hard Gold
In order to improve the wear-resisting property of the product, increase the insertion number and the plating hard gold.
