Introduction to Important PCB Surface Coatings and Their Functions

Introduction to Important PCB Surface Coatings and Their Functions

Circuit board manufacturing, circuit board design, PCBA processing manufacturers explain important PCB surface coatings and their functions

Many small white people who just started the PCB industry are not very clear about the process details of the surface coating, and do not know how to improve the reliability of the PCB surface coating. Now the electronic engineer editor will give you a brief introduction.

The coating of PCB is used to protect the surface of circuit copper foil. Copper is the main material of PCB surface solder joints, which is a good surface for welding components. However, copper is easy to react with air and oxidize; Copper oxide hinders the wetting of solder. Although gold precipitation process is used now, because gold will not be oxidized, covering copper with gold can slow down the copper oxidation process; Gold and copper will rapidly diffuse and infiltrate each other. One method is to use a nickel "barrier layer" that prevents the transfer of gold and copper and provides a durable, conductive surface for component assembly.

In terms of surface coating process, almost all PCB manufacturers in China currently operate in accordance with the international standard IPC-A-610 electronic component acceptance standard. The ultimate goal of this IPC standard is to make the surface coating evenly cover the circuit board, solder joints and components. The coating coverage depends on the coating method. However, it should be noted that most surface coatings at present contain optical brighteners, which will emit fluorescence when PCB is exposed to ultraviolet light. This makes it easier to check the surface coating. However, under ultraviolet light, the uneven distribution defects of the coating will be difficult to find, and may need to be inspected under white light. The properties of different materials are different, and the fluorescence is also quite different. Some coatings, such as ultraviolet fluorescence, are very weak. This condition can be seen in many silicon surface coatings, which may make inspection more difficult.

At present, the commonly used OSP coating is the organic welding aid protective film on Cu surface that appeared in the 1990s. Technically, these cyclic nitrogen compounds, such as those containing benzotriazole (BTA), imidazole, alkyl imidazole, benzimidazole and other substances, can easily react with the clean copper surface in aqueous solution. The nitrogen heterocycles in these compounds form complexes with the copper surface. This protective film prevents the copper on the surface of the solder joint from being oxidized.

In addition, I would like to add that non electrolytic nickel and gold have only recently become a commonly used PCB surface coating, and some industrial procedures may not be suitable. The above are some instructions about the surface coating. If you think it is useful, you can collect it as soon as possible. The company will continue to maintain its reputation, let China's PCB proofing brand go global, and become a world-renowned PCB producer as soon as possible. Circuit board manufacturers, circuit board designers and PCBA processors will introduce important PCB surface coatings and their functions.