The most basic purpose of PCB surface treatment is to ensure good solderability or electrical properties. Since natural copper tends to exist as an oxide in the air, it is unlikely to remain as a raw copper for a long period of time, and therefore other treatments of copper are required.
1 Hot Air Leveling (Spraying)
Hot air leveling, also known as hot-air solder leveling (commonly known as spray tin), is the process of applying molten tin (lead) solder on the surface of the PCB and flattening (flattening) it with heated compressed air to form a layer that is resistant to copper oxidation. It also provides a good solderability coating. When the hot air is leveled, the solder and copper form a copper-tin intermetallic compound at the junction. When the PCB is hot-air levelled, it sinks into the molten solder; the air knife blows the liquid solder before the solder solidifies; the air knife minimizes the solder meniscus on the copper surface and prevents the solder from bridging.
2 Organic Solderability Protection Agent (OSP)
The OSP is a process that complies with the RoHS directive for surface treatment of printed circuit board (PCB) copper foils. OSP is the abbreviation of Organic Solderability Preservatives. Chinese translation is organic solder mask, also known as copper protector. English is also called Preflux. Simply put, OSP is to chemically grow a layer of organic film on the surface of clean bare copper. This layer of film has anti-oxidation, thermal shock resistance, moisture resistance, to protect the copper surface in the normal environment no longer continue rust (oxidation or vulcanization, etc.); but in the subsequent welding temperature, this protective film must be very It is easily removed by the flux quickly, so that the exposed clean copper surface can be immediately combined with molten solder in a very short time to become a solid solder joint.
3 full plate nickel plated gold
The full-surface nickel-plated gold is coated on the surface of the PCB with a layer of nickel and then a layer of gold. The nickel plating is mainly to prevent the diffusion between gold and copper. There are two types of electroplated nickel gold: gold-plated (pure gold, gold surface does not look bright) and gold plated (surface smooth and hard, wear-resistant, containing cobalt and other elements, the gold surface looks brighter). Soft gold is mainly used for gold wire in chip packaging; hard gold is mainly used in non-welded electrical interconnections.
4 Immersion gold
Immersion gold is a thick layer of nickel-gold alloy coated on the copper surface, which can protect the PCB in the long-term; it also has the endurance to the environment that other surface treatment processes do not have. Immersion Gold can also prevent the dissolution of copper, which will benefit lead-free assembly.
5 Immersion tin
Since all current solders are 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 it possible to have the same good solderability as hot air leveling without the headache flatness problem of hot air leveling; it can not be stored for too long. The assembly must be carried out according to the order of sinking tin.
6 Immersion silver
The silver immersion 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 maintain good solderability but it will lose its luster. . Shen Yin does not have the good physical strength of electroless nickel/immersion gold because there is no nickel below the silver layer.
7 Chemical nickel palladium gold
The chemical nickel palladium gold has a layer of palladium between nickel and gold compared with the gold sink. The palladium can prevent the corrosion phenomenon caused by the substitution reaction and make full preparation for the heavy gold. Gold is tightly covered on the palladium, providing a good contact surface.
8 plating hard gold
In order to improve the wear resistance of the product, the number of plugs and pulls is increased and the hard gold plating is performed.