PCB board eight kinds of surface treatment process


The most basic purpose of surface treatment is to ensure good solderability or electrical properties. Since naturally occurring copper tends to exist as oxides in the air and is unlikely to remain as raw copper for long periods of time, other treatments of copper are required. Although a strong flux can be used to remove most copper oxides in subsequent assembly, the strong flux itself is not easy to remove, so the industry generally does not use a strong flux.

Now there are many PCB circuit board surface treatment processes, commonly hot air leveling, organic coating, chemical nickel plating / immersion gold, silver immersion and tin immersion of the five processes, which will be introduced one by one.

Hot Air Leveling (Tin Spraying)

Hot air leveling, also known as hot air solder leveling (commonly known as tin spraying), it is coated with molten tin (lead) solder on the surface of the PCB circuit board and heated compressed air leveling (blowing) process to form a layer of both anti-oxidation of copper, but also to provide good solderability of the coating layer. Hot air leveling of solder and copper in the combination of copper and tin intermetallic compounds.

PCB circuit boards for hot air leveling to be sunk in the molten solder; wind knife in the solder before the solidification of the liquid solder blowing flat; wind knife will be able to minimize the copper surface of the solder crescent shape and prevent solder bridging.

Organic Solderability Protectors (OSP)

OSP is a RoHS compliant process for the surface treatment of copper foil on printed circuit boards (PCBs). OSP is Organic Solderability Preservatives for short, the Chinese translation of the organic solder film, also known as copper protector, also known as the English Preflux. Simply put, OSP is in the clean surface of the bare copper, in order to chemically grow a layer of organic skin film.

This film has anti-oxidation, thermal shock, moisture resistance, to protect the copper surface in the normal environment will not continue to rust (oxidation or sulfidation, etc.); but in the subsequent welding high temperature, such a protective film and must be easy to be flux quickly removed, so that the exposed clean copper surface can be in a very short period of time and the molten solder immediately combined with a solid solder joints.

Full Plate Nickel-Gold Plating

Board nickel gold plating is in the PCB circuit board surface conductor first plated with a layer of nickel and then plated with a layer of gold, nickel plating is mainly to prevent the diffusion of gold and copper between.

Now there are two types of nickel plating: soft gold plating (pure gold, gold surface does not look bright) and hard gold plating (smooth and hard surface, wear-resistant, containing cobalt and other elements, the gold surface looks brighter). Soft gold is mainly used for chip packaging when playing gold wire; hard gold is mainly used in non-soldered electrical interconnections.

Immersion gold

Sinking gold is wrapped in a thick layer of copper surface, electrical good nickel-gold alloy, which can protect the PCB circuit board for a long time; in addition, it also has other surface treatment process does not have the endurance of the environment. In addition, immersion gold can also prevent the dissolution of copper, which will be beneficial to lead-free assembly.

Immersion Tin

Since all current solders are tin-based, the tin layer is compatible with any type of solder. The tin sinking process creates a flat copper-tin intermetallic compound, a property that gives tin sinking the same good solderability as hot air leveling without the headache of hot air leveling's flatness problems; tin sinking boards should not be stored for too long, and must be assembled in accordance with the sequence of tin sinking.

Silver Immersion

The silver immersion process is between organic coating and chemical nickel/gold plating, the process is relatively simple and fast; even when exposed to heat, humidity and contamination, the silver still maintains good solderability, but loses its luster. Immersion silver does not have the good physical strength of electroless nickel/gold because there is no nickel underneath the silver layer.

Electroless Nickel-Palladium

Electroless nickel-palladium has an additional layer of palladium between the nickel and the gold. The palladium prevents corrosion due to displacement reactions and prepares the metal for gold deposition. The gold is tightly covered with palladium to provide a good contact surface.

Hard Gold Plating

Hard gold plating is used to improve wear resistance and increase the number of insertions and removals.

As the user requirements are getting higher and higher, the environmental requirements are getting more and more stringent, the surface treatment process is getting more and more, no matter what, to meet the user's requirements and protect the environment of the PCB circuit board surface treatment process must be the first to do!

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