Finished electronics generally don't handle adversity well. Once an electronic board leaves the factory, it can be exposed to dirt, moisture, mold, dust, and all sorts of nasty stuff. When exposed to these elements, it can cause corrosion, short-circuiting, component failure, and, potentially, complete device failure. To combat this, sometimes a coating will be applied to the boards to keep them safe, clean, and dry. In this article, we'll discuss the basics of PCB coating.
Some types of protective coatings that are commonly used are acrylic resin, epoxy resin, polyoxyester resin, silicone resin, and p-xylene resin. These protective coatings have good resistance to high and low temperature. They are cured into a transparent protective film that can protect the circuit from damage under conditions such as vibration, chemical exposure (such as fuel, coolant, etc.), moisture, salt, fog, humidity, and high temperature. Under these conditions, the circuit board may be corroded, mold growth and short circuit. With these coatings, the boards get superior insulation and protection from moisture, leakage, dust, corrosion, aging, and mildew while also protecting from the loosening of parts.
1. Coating Techniques
Brushing is widely used to produce excellent coating effects on smooth surfaces.
Using a spray canister can be easily used for maintenance and small-scale production while spray guns are suitable for large gauge production. These two spraying techniques, however, require high operational accuracy. If not done correctly, the boards may have a shadow under some components where the lower part of the component is not covered with three protective coating.
The most accurate technique is automatic impregnation. This ensures complete coating and does not cause material waste due to over-spraying.
2. Basic Steps for Manual Coating
The first step is to clean and heat the board to remove moisture, dust, and oils. Any of these on the surface can dull the full effect of the protection. A thorough cleaning ensures that the coating properly adheres to the boards. The application of the coating is better after the board is heated for 8-15 minutes at around 60 °C .
If using brushing, the brushing area should be larger than the device in order to cover all of the device and its pads. The painting plate should be as flat as possible. Once the brushing is completed, there should be no drips and the brush strokes should be smooth. There should be no exposed parts between 0.1 and 0.3 mm.
Before brushing or spraying, check that the diluted coating agent is well mixed and allowed to stand for 2 hours before application. For brushing, use a high-quality, natural fiber brush. The solution should be at room temperature for application. The brushing or spraying should be even, slow and consistent.
As the size of electronic boards becomes smaller and the density becomes higher, the effect of environmental factors on the devices becomes more significant. The reliability requirements, as a consequence, becomes much higher. These types of coatings can help with making the products more reliable.
NexPCB offers a full line of conformal coatings for our PCBA productions. If you're interested in adding this to your project, don't hesitate to let us know and we'll be happy to help keep you keep you boards clean, dry, and operating at peak efficiency for many years.