What you have to know about the surface treatment process of the printed circuit board industry

1. Hot air leveling (spray tin)

Hot air leveling, also known as hot air solder leveling (commonly known as spray tin), is a process of coating molten tin (lead) solder on the surface of the PCB and flattening (blowing) it with heated compressed air to form a layer that resists copper oxidation. It can also provide a coating with good solderability. Solder and copper form a copper-tin intermetallic compound at the junction during hot air leveling. PCBs are submerged in molten solder during hot air leveling; 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 Preservative (OSP)
OSP is a process for surface treatment of printed circuit board (PCB) copper foil that meets the requirements of the RoHS directive. OSP is the abbreviation of Organic Solderability Preservatives, which is translated as organic solder protection film in Chinese, also known as copper protection agent, also known as Preflux in English. Simply put, OSP is to chemically grow an organic film on the clean bare copper surface. This layer of film has anti-oxidation, thermal shock resistance, moisture resistance, and is used to protect the copper surface from rusting (oxidation or vulcanization, etc.) in the normal environment; but in the subsequent high temperature welding, this protective film must be very It is easily and quickly removed by the flux, so that the exposed clean copper surface can be combined with the molten solder to form a strong solder joint in a very short time.

3. Nickel gold plating on the whole board

Nickel-plated gold is to first coat a layer of nickel and then a layer of gold on the surface conductor of the PCB. Nickel plating is mainly to prevent the diffusion between gold and copper. Now there are two types of electroplated nickel gold: soft gold plating (pure gold, the gold surface does not look bright) and hard gold plating (the surface is smooth and hard, wear-resistant, contains other elements such as cobalt, and the gold surface looks brighter). Soft gold is mainly used for gold wire in chip packaging; hard gold is mainly used for electrical interconnection in non-soldering places.

4. Immersion Gold

Immersion gold 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; 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. Immersion tin

Since all current solders are based on tin, the tin layer can be matched to any type of solder. The immersion tin process can form a flat copper-tin intermetallic compound, which makes the immersion tin have the same good solderability as the hot air leveling without the headache of the flatness problem of the hot air leveling; the immersion tin board cannot be stored for too long , the assembly must be carried out according to the order of immersion tin.

6. Shen silver

The immersion silver process is between organic coating and electroless nickel / immersion gold, the process is relatively simple and fast; even when exposed to heat, humidity and pollution, silver can still maintain good solderability, but 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. Electroless nickel palladium gold

Compared with immersion gold, chemical nickel palladium gold has an additional layer of palladium between nickel and gold. Palladium can prevent corrosion caused by replacement reaction and be fully prepared for immersion gold. Gold covers the palladium tightly, providing a good contact surface.

8. Plating hard gold

In order to improve the wear resistance of the product and increase the number of insertion and removal, hard gold is plated.

Post time: May-07-2022