PCB surface treatment process
Summary of content: The most basic purpose of PCB surface treatment is to ensure good solderability or electrical performance. Since copper in nature tends to exist in the form of oxides in the air, it is unlikely to remain as copper for a long time, so other treatments of copper are needed.
1 hot air leveling (spray tin)
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 PCB surface and leveling (blowing) with heated compressed air to form a layer that resists copper oxidation. It can also provide a coating with good solderability. During hot air leveling, solder and copper form a copper-tin intermetallic compound at the joint. PCB hot air leveling should sink in molten solder; the air knife blows the liquid solder before the solder solidifies; the air knife can minimize the meniscus of the solder on the copper surface and prevent solder bridging.
2 Organic Solderability Protective Agent (OSP)
OSP is a RoHS-compliant process for the surface treatment of printed circuit board (PCB) copper foil. OSP is the abbreviation of Organic Solderability Preservatives. The Chinese translation is organic solder mask, also called copper protection agent, and it is also called Preflux in English. To put it simply, OSP is to chemically grow an organic film on a clean bare copper surface. This film has anti-oxidation, thermal shock resistance, and humidity resistance. It is used to protect the copper surface from rusting (oxidation or sulfurization) in the normal environment. However, in the subsequent welding high temperature, this protective film must be very It is 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 strong solder joint in a very short time.
3 full plate nickel-plated gold
Full-plate nickel-plated gold is coated with 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: soft gold (pure gold, the surface of the gold does not look bright) and hard gold (smooth and hard surface, wear-resistant, containing other elements such as cobalt, the gold surface looks brighter). Soft gold is mainly used to wire gold when chip packaging; hard gold is mainly used to electrically interconnect non-soldering places.
4 sinking gold
Shenjin is a thick layer of nickel-gold alloy with good electrical properties 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 Shen Tin
Since all solders are currently tin-based, the tin layer can match any type of solder. The process of sinking tin can form a flat copper-tin intermetallic compound. This characteristic makes sinking tin as good as hot air leveling without the troublesome flatness problem of hot air leveling; Shen tin plates cannot be stored for too long , Assembly must be carried out according to the sequence of Shen Tin.
6 Shen Yin
The immersion silver process is between organic coating and electroless nickel / immersion gold. The process is relatively simple and fast; even if exposed to heat, humidity and pollution, silver can still maintain good solderability, but it will lose its 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
Compared with immersion gold, electroless nickel-palladium has a layer of palladium between nickel and gold. Palladium can prevent the corrosion phenomenon caused by the substitution reaction, and is fully prepared for immersion gold. Gold tightly covers the palladium, providing a good contact surface.
8plated hard gold
In order to improve the wear resistance of the product, the number of mating cycles is increased and the hard gold is plated.