The basic purpose of PCB surface treatment is to ensure good solderability or electrical properties.Since natural copper tends to exist in the air as an oxide, it is unlikely to remain raw copper for long periods of time, so additional treatment of copper is required.
1, hot air leveling (spray tin)
Hot air leveling is also known as hot air solder leveling (commonly known as tin spraying). It is a process of coating the surface of PCB with molten tin (lead) solder and heating compressed air leveling (blowing), so that it forms a coating layer that is not only resistant to copper oxidation, but also can provide good solderability.During the hot air process, the solder and copper form intermetallic compounds at the junction.PCB for hot air to sink in the molten solder;The air knife flattens the liquid solder before it sets;The blade minimizes the crescent shape of the solder on the copper surface and prevents solder bridging.
2. Organic Solderable Protective Agent (OSP)
OSP is printed circuit board (PCB) copper foil surface treatment in line with the ROHS directive requirements of a process.OSP is the abbreviation of Organic Solderability Preservatives, also known as copper Preservatives, and also known as Preflux in English.Simply put, OSP is a chemical method to grow a layer of organic skin film on a clean, bare copper surface.This film has anti-oxidation, heat shock, moisture resistance, to protect the copper surface in the normal environment will not continue to rust (oxidation or vulcanization, etc.);However, in the subsequent welding high temperature, the protective film must be easy to be quickly removed by the flux, so that the exposed clean copper surface can be immediately combined with the molten solder into a solid solder joint in a very short time.
3. The whole plate is plated with nickel gold
Nickel plating is to coat the conductor on PCB surface with a layer of nickel first and then a layer of gold. The main purpose of nickel plating is to prevent the diffusion between gold and copper.There are two types of nickel gold plating: soft gold plating (pure gold, gold surface does not look bright) and hard gold plating (smooth and hard surface, wear resistance, containing cobalt and other elements, gold surface looks bright).Soft gold is mainly used for chip packaging gold wire;Hard gold is mainly used in electrical interconnections at non-welded areas.
Immersion is a thick layer of electrically good nickel-gold alloy on the copper surface, which can protect the PCB for a long time.In addition, it also has the environmental tolerance that other surface treatment processes do not have.It also prevents copper from dissolving, which would benefit lead-free assembly.
Since all solders are currently tin-based, the tin layer can be matched with any type of solder.The tin settling process can form flat copper-tin intermetallic compounds, which makes the tin settling have the same good solderability as hot air leveling without the flatness problem which is troublesome by hot air leveling.Immersed tin plate can not be stored too long, assembly must be according to the order of the tin.
6, heavy silver
Silver deposition process is between organic coating and electroless nickel/gold deposition, and the process is simple and fast.Even when exposed to heat, moisture, and pollution, silver retains good solderability, but loses its luster.Immersed silver does not have the good physical strength of electroless nickel/gold plating because there is no nickel underneath the silver layer.
7, chemical nickel palladium gold
Compared with gold deposition, there is a layer of palladium between nickel and gold. Palladium can prevent corrosion caused by replacement reaction and make full preparation for gold deposition.The gold is tightly coated with palladium, providing a good contact surface.
8, plating hard gold
In order to improve the wear resistance of the product, increase the number of insertion and extraction of hard gold plating.