What is conformal coating for PCB?

We often heard "let's apply conformal coating" on the boards, we therefore know it is something that can protect PCB from damages, but what are the "damages?" and how the coating functions?

Humidity has always been the main factor that can hurt a PCB, a board placed in moist enviorment can largely reduce the insulativity between conductors and Q value, also cause corrosion on the conductors.

Currently there are three popular method for protection: conformal coating, electronic wax and nano-coating.

For conformal coating, it is a coating with special formula to protect circuit boards from damages from enviorments, therefore can extend the life of boards and ensure its reliablitiy and safety.

Conformal coating ingredients include acrylate, silicone and polyurethane (PU) layer. It is applied with brushing, painting and steep process, once the coating goes dry and solidified, the layer can prevent boards from humidity, salt fog and mildew.

The nano coating is another way to protect PCB. It is a special water-resistant layer which is clear, non-toxic and fireproof, still work to provent salt fog, humidity and mildew to harm the boards.

How the conformal coating is applied on board?

1. Brushing: it is widely used and the effect is very well accepted by users, mostly on flat surface board.

2. painting: it is popular for applying conformal coating in large scale production, but it requires high precision, sometimes there will be small shadow which is not painted under components;

3. Steep: using steep can ensure all boards are applied with conformal coating, and it will not cause waste by over painting;

There are some components area that can't apply conformal coating: Lacquer high power radiator, heat sink, power resistance, high power diode, cement resistors, drawing code switch, potentiometer (adjustable resistance), buzzer, battery holder, fuse holder, IC, light touch switch, relay and other types of socket, row needle, terminals and the DB9, plug-in or patch type light emitting diode (directive role), digital tube, grounding screw holes.