The conformal coating of printed circuit board is used to enhance the performance and reliability of printed circuit board assembly, so that it can be applied in harsh environments such as underwater, aerospace and military applications. Manufacturers of electronic products are increasingly using conformal coatings as an economical method to improve product reliability.
When the printed circuit assembly board without protective coating is exposed to humid air, a thick film of water molecules will be formed on its surface, which reduces the surface insulation resistance (SIR) of the circuit board. The lower the surface insulation resistance, the worse the transmission performance of the electrical signal will be. The typical consequence will be crosstalk, electrical leakage and transmission interruption, which may lead to permanent interruption of the signal, that is, short circuit.
The moisture film on the printed circuit board without conformal coating also provides favorable conditions for metal growth and corrosion, which will eventually in turn affect the insulation strength and high-frequency signal. Dust, dirt and other environmental pollutants falling on the assembly board constantly absorb moisture, thus expanding its negative impact. Conductive particles such as metal fragments can also cause electrical bridging.
The protective coating is a coating around the printed circuit board. The thickness of this film is 0. 005 inch, which seals dust and environmental pollutants outside the circuit board. Of course, the conformal coating may also seal the pollutants that were not removed during the pre-cleaning, so it is very important to clean the surface of the circuit board before applying the conformal coating.
The protective coating has the following functions:
1) Protect the circuit from extreme environment, and prevent it from being affected by moisture, fungi, dust and corrosion;
2) Prevent the circuit board from being damaged in the process of manufacture, assembly and use, reduce the mechanical stress on components and protect them from thermal oscillation;
3) reduce the wear during use;
4) As the conformal coating increases the insulation strength between conductors, it strengthens the performance of the circuit board and allows greater component density.