Conformal coatings are non-conductive coating which is applied to PCBs during the assembly process to prevent damage from salt sprays, moisture, fungi, and corrosion. It is most commonly applied to PCBs that are used in consumer electronics such as appliances and cellular products that are likely to be exposed to wet, humid, dusty, or other harsh environments during transport or prolonged storage. Such coating provides increased dielectric resistance, operational integrity thus they conform to the irregularity of PCB.
How does it protect PCBs?
It inserts a layer of protection between board-level components and the outside environment. It is a protective layer that functions as a one-way street, permitting moisture contained beneath to travel across the conformal coating whilst preventing contaminants in the ambient environment from transferring into board-level parts. This protection allows for higher voltage gradients and closer track spacing.
Other benefits of conformal coating.
This coating is made from lightweight material which gives the PCB a relatively small footprint. Furthermore, it also provides a support bridge between conductors, increasing overall strength and durability. This coating not only protects a PCB, but it also expands the working life of the board.
What are the different kinds of the conformal coating?
There are four main types of conformal coating depending upon the level of protection needed i.e. silicone, acrylic, urethane, and Paraxylene. These coatings are semi-permeable and they provide resistance to environmental exposure by increasing the PCB durability.
How does conformal coating get applied?
There are four different way of applying this coating on PCBs:
- Dipping– immerse the board in the coating solution. The result will depend on the immersion speed, withdrawal speed, immersion time, and viscosity. It is commonly used for large volume manufacturing processes.
- Selective coating– It is an automatic coating process in which a robotic spray nozzle is used for the application of the conformal coating. It eliminates the use of masking.
- Spraying – It is a manual spraying method in which a handheld spray gun is used for the application of coating hence it can be time-consuming also areas not required are needed to be masked.
- Brushing- Coating is applied with a brush on the board. It is well suited for small production runs.
After a coating is applied it must be cured. The curing process is executed via air drying, thermally, or by UV light. There are six steps to apply conformal coating on PCBs and these are:
- Cleaning the board
- Removal of terminal pins and connectors
- Apply the desired type of coating to the board
- Apply the desired curing method to the board
- Reinstall parts onto the board
- Test the board to ensure the functionality
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