The PCBA three anti-coating process, referred to as Conformal Coating in IPC-A-510D, is called "three-proof" and generally refers to moisture-proof, anti-salt spray, and mold-proof. But this is a narrower understanding. In fact, the meaning of "three defenses" far exceeds these three contents. For example, it also has the functions of anti-vibration, anti-friction, improving the insulation strength, preventing the failure of the printed circuit assembly board (PCBA), ensuring and prolonging the service life of the product. Coating technology is widely used in strategic defense systems, aerospace systems, automotive electronics and power systems, industrial control systems, and more. Coating technology is also used in civilian products to extend the life of the product. The three-proof protection coating process of the electronic assembly is at the back end of the PCBA. After the general process is SMT chip processing and testing, after passing the quality inspection, the SMT patch process has been completely finished, and then the three defense treatments are processed. The process has various methods such as dip, brush, spray, and selective coating. The selective coating process is a new type of protection technology for electronic assemblies, also known as the digital coating process. This chapter combines the three-proof protective coating process, focusing on the new protective technology of electronic assembly - a selective coating process.

The environment is not only closely related to human life, but also has a significant impact on the service life and stability of electronic devices. Among many environmental factors, moisture, salt spray and mold directly threaten the use and storage of electronic products. High-tech products, especially military weapons and equipment, aerospace, navigation, power, electricity, automobiles, and all electronic equipment that work in the wild, especially in humid environments, are more susceptible to these factors due to the particularity of their use environment influences.

Therefore, the patch processing factory generally paints three anti-paint according to the customer's requirements. Currently, the good three anti-paints on the market is K50, and there is a foreign brand.