What is conformal coating and what is it used for? In short, conformal coating is a thin, transparent film that can be applied to the surface of a circuit board. This film contours to the PCB’s shape, protecting components from environmental conditions without impacting functionality.
But is conformal coating necessary? While not all applications are best served by conformal coating, it can be an excellent choice for specific types of PCBs. Some of the benefits conformal coating offers include the following:
- Protection: Conformal coatings protect assemblies from environmental hazards such as chemicals, corrosion and dust.
- Lightweight: PCB conformal coatings do not significantly increase the board’s weight.
- Insulation: Conformal coating provides insulating properties, allowing a reduction in PCB conductor spacing.
These benefits are all provided without needing sophisticated or highly designed protective elements.
What is the working principle of conformal coating on PCB?
Conformal coatings may be applied to circuit boards using various methods, which differ in quality level, reliability and production level. The most notable application methods include the following:
- Brush method: In this technique, conformal coating materials are applied by hand using a brush. These coatings tend to be thick and less consistent than those applied by other methods. This process is simple and labor-intensive and best suited for low-volume production and rework and repair operations.
- Spray method: The spray method involves using an aerosol spray to apply conformal coating materials to PCB surfaces. Ideal for low-volume production, this technique provides an excellent surface finish consistency but is also time-consuming as it requires a thorough application to cover the entire board.
- Dipping method: The dipping method involves applying conformal coating to circuit boards by submerging them in the coating solution. Fast, accurate and thorough, this method is ideal for high-volume production. However, it is only useable on certain types of PCBs with designs that prevent leakage and can be coated on both sides of the board.
- Selective coating: The selective coating method uses robotic spray nozzles to apply coating materials to specified areas of a PCB assembly. This automated process is ideal for high-volume applications, offering a fast and accurate procedure that can be used on a wide range of boards. Like the dipping method, the board must be designed to be compatible with selective coating.
With each of these application methods, the conformal coating must be very thin to minimize heat entrapment and weight increase, among other concerns. Typically, conformal coatings are between 3 to 8 mil thick. How do you measure conformal coating? This is usually done with a micrometer, current probe or specialized gauge that uses physical measurements, electromagnetic fields or ultrasonic waves to take measurements of the coating after it is dry.