PCB Technical - PCB surface treatment process is fully summarized

The basic purpose of PCB board surface treatment is to ensure good solderability or electrical properties. Since natural copper tends to exist in the air as oxides and is unlikely to remain as raw copper for long, other treatments are needed.

1. Hot air leveling (tin spraying)

Hot air leveling, also known as hot air welding leveling (commonly known as tin spraying), is a process of coating the PCB surface with molten tin (lead) solder and heating compressed air leveling (blowing) to form a coating layer that is not only resistant to copper oxidation, but also provides good solderability. Hot air finishing solder and copper form intermetallic cu-tin compounds at the junction. PCB for hot air conditioning to sink in molten solder; Air knife blows liquid solder flat before solder solidifies; Wind knife can meniscate solder on copper surface and prevent solder bridge.

2. Organic solderability protective agent (OSP)

OSP is a process for copper foil surface treatment of printed circuit boards (PCB) in accordance with the RoHS directive. OSP is short for Organic Solderability Preservatives, also known as Organic Solderability Preservatives or Preflux in English. Simply put, OSP is the chemical growth of an organic skin film on a clean, bare copper surface. This film has anti-oxidation, heat shock resistance, moisture resistance, to protect the copper surface in the normal environment no longer continue to rust (oxidation or vulcanization, etc.); However, in subsequent welding at high temperatures, this protective film must be easily and quickly removed by the flux, so that the exposed clean copper surface can be immediately combined with the molten solder into a solid solder spot in a very short time.

3. The whole plate nickel plating gold

Nickel plating is to first coat the PCB surface conductor with nickel and then with gold, nickel plating is mainly to prevent the diffusion between gold and copper. There are now two types of nickel plated gold: soft gold (pure gold, the surface of gold looks dull) and hard gold (smooth and hard, wear-resistant, containing cobalt and other elements, the surface of gold looks shiny). Soft gold is mainly used for chip packaging gold line; Hard gold is mainly used for electrical interconnections in non-welded areas.

4. Zedoary

Gold sink is a thick layer of nickel gold alloy with good electrical properties wrapped on the copper surface, which can protect the PCB for a long time. It also has a tolerance to the environment that no other surface treatment process has. In addition, the gold can also prevent the dissolution of copper, which will benefit lead-free assembly.

5, Tin

Since all current solders are tin-based, the tin layer can be matched with any type of solder. Tin sinking process can form flat intermetallic compounds of copper tin gold, which makes tin sinking have the same good weldability as hot air leveling without the headache of hot air leveling flatness problem; Tin plate can not be stored for too long, the assembly must be carried out according to the sequence of tin.

6. Heavy silver

The silver deposition technology is between organic coating and electroless nickel plating/gold deposition, which is simple and fast. Silver retains good solderability even when exposed to heat, humidity, and pollution, but loses luster. Silver plating 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

Chemical nickel palladium compared with gold precipitation is in the nickel and gold between a layer of palladium, palladium can prevent corrosion caused by the substitution reaction, for gold precipitation is fully prepared. Gold is tightly coated over palladium, providing a good interface.

8. Hard gold plating

In order to improve the wear resistance of the product, increase the number of plug and pull hard gold plating.