The Importance of Conformal Coatings for PCBA
A polymer coating called a "conformal coating" is used to protect circuit boards and components from adverse environmental conditions. The conformal coating adheres completely to the shape of the PCBA, covering every component. Each coating has unique chemistries that can be tailored for specific protective properties, giving products higher insulation resistance and protecting circuit boards from corrosive environments, humidity, and contaminants such as dirt and dust.
Standard coating thickness requirements
The standard thickness for most circuit board products is 25 to 127 microns, with some products requiring lower coating thicknesses. Thinner coatings provide better heat dissipation and minimize heat trapping, providing maximum protection for the circuit board.
Many users mistakenly believe that a thicker coating is better, but in fact, the effectiveness of a coating depends on more than just its thickness. Conformal coatings can be made from acrylic, silicone or polyurethane resins, as well as other application-specific polymers such as epoxies.
Different industries and products have different requirements for coating thickness. Conventional electronic products have lower coating requirements, and a thickness of 20-30 microns is usually sufficient. However, for industrial or military products that have higher requirements for coating performance, the coating thickness is usually between 30-50 microns. Choosing a higher-performance coating can provide better protection for the circuit board.
Painting method
There are three common methods of applying conformal coatings
1. Automatic spraying: This is a programmable spraying system that moves circuit boards on a conveyor belt and sprays coatings at specific locations.
2. Selective coating: This is an automated coating technology that sprays coating on specific areas of the circuit board, similar to selective wave soldering. This method is suitable for mass production.
3. Manual spraying: The coating can be sprayed manually with an air tank or hand-held spray gun. This method is suitable for small batch production.
Conformal coating application steps
1. Clean the surface of the board to ensure there is no oil, dirt, or dust;
2. Dry and wipe the surface to remove any remaining cleaning solution and moisture;
3. Prepare coating according to manufacturer's instructions, adjusting viscosity as needed;
4. Start spraying the conformal coating;
5. Put the coated PCB board into the oven and bake it (for vertical ovens, it is recommended to leave it outside for 3-5 minutes and then bake it in an oven not exceeding 80 degrees for 5-10 minutes. )
6. Check the plate to ensure that there are no bubbles in the coating and the surface is smooth and even to complete the spraying of the conformal coating.
Conformal coatings are necessary for PCBs and PCBAs that must operate in harsh environments. It should also be noted that conformal coating and PCB surface treatment are different processes. Conformal coating is performed after the circuit board is assembled, while surface treatment is part of the PCB manufacturing process. Depending on the use environment and needs, you can decide whether to spray conformal coating or not.
