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Understanding Conformal Coatings and Their Types

 Oct 27, 2015

Conformal Coatings

Circuitry protection is an important aspect] when manufacturing Printed Circuit Boards (PCBs). One of the primary methods of protection is applying conformal coatings.

Conformal coatings comprise dielectric materials, which protect the circuit board and its components from environmental contaminants. These include dust, fungus, and moisture. The coatings also enhance the board’s service life when used in industrial applications.

The coatings can be applied onto the substrate in different ways. Today, the most common method is using computer controlled coating systems. This machine ensures that the coating is applied evenly over all the PCB components. Prior to the use of this machine, PCB manufacturers would either hand spray the coating, or dip the circuit board directly into the coating fluid.

Types of Coatings

There are four basic types of conformal coatings applied onto PCBs.

  • Type AR: This stands for acrylic resins. Acrylic conformal coatings are primarily used to protect the PCB from contaminants like fungus. However, they do provide a moderate dielectric constant. These coatings are very easy to apply and can dry within minutes. Repairing the PCB will not damage the coating.
  • Type ER: Also known as epoxy resins, ER coatings are chosen for their strength, and resistance to abrasion, chemicals, and humidity. The downside is that they are difficult to remove if the PCB requires repairs. Only a knife or a soldering iron can remove them.
  • Type SR: Silicone resins or silicone conformal coatings perform exceptionally in applications with high temperatures. They provide immense resistance to humidity and corrosion. However, as a material, silicone is not soluble in solvents. Hence, they require chemical strippers for removal.
  • Type UR: This type is a polyurethane coating, and is popular for its strength and resilience. The coating provides immense resistance to solvents, abrasions, and humidity. It also possesses excellent dielectric properties. Similar to type SR, polyurethane coatings require chemical strippers when it comes to repairs.

The type of PCB Conformal coating that you require will depend on the PCB design. It is always best to discuss the design with the PCB manufacturer and let him suggest the most optimum coating. The right choice will enhance the performance of your circuit board, as well as its service life.

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