Conformal Coating


What exactly is a conformal coating? 

What exactly is a conformal coating?

A conformal coating is a protective film that conforms to the surface of a circuit board assembly.

The conformal coating can be used to create a protective barrier between contaminants in the environment and the assembly. 

It is also usually used on electronic products that are exposed to adverse environments where contamination, heat, chemicals and / or moisture are prevalent.

This means that the printed circuit board assembly may be protected from damage due to contamination, salt spray, moisture, fungus, dust and corrosion caused by harsh or extreme environments.


What does a conformal coating look like?

What does a conformal coating look like?

When the conformal coatings are applied, some materials are clear and glossy on the surface of the circuit board assembly.  Some conformal coatings may be translucent or opaque. Others are too thin to be easily seen.

Some coatings are hard while others are softer with a more rubbery texture.

Conformal coatings may include a fluorescent trace that glows a bright blue /green when illuminated by ultraviolet or black light.  This fluorescence allows for easy inspection of the applied liquid coating.


Why use a conformal coating to protect a circuit board?

Why use a conformal coating to protect a printed circuit board assembly?

There are several reasons for using a conformal coating or Parylene to protect a printed circuit board (PCB).

These reasons include:

  • High insulation protection
  • High moisture and humidity protection
  • Chemical and temperature resistance
  • Ruggedisation
  • Improved dielectric properties
  • Barrier protection

High Insulation protection

Conformal coatings can provide a high degree of insulation protection for the circuit board assembly during its lifetime when it is applied as a protective film.

The circuit board normally starts with a high level of insulation when it is first manufactured, as it is normally clean.

However, as time passes in the field then the natural environment can degrade the circuit in different ways.

A conformal coating may slow this degradation down.

High moisture and humidity protection

Circuit boards can be very vulnerable to moisture and humidity whilst in the field of operation during its lifetime.

Most conformal coatings are resistant to moisture and humidity.

This can lead to a reduction in affects such as leakage currents, cross talk, electrochemical migration, dendrite growth and arcing across the circuit board.

Chemical and temperature resistance

Some conformal coatings can be resistant to many types of solvents, chemical attack and be heat resistant.

Normally, a circuit board exposed to these types of environment would be degraded but a chemically resistant conformal coating can slow down the effects or even prevent them.

Ruggedisation

Conformal coating can prevent damage from rough handling, installation and reduction of mechanical and thermal stress.

They can strengthen the board.

Improved dielectric properties

Just as the conformal coating can protect the circuit from moisture it can also help to increase the dielectric strength between the conductor parts.

This enables the design of the PCB to be more compact and small.

Barrier protection

The coating material can prevent various types of particulate contamination reaching the surface of the circuit board, which can lead to problems such as corrosion.

The conformal coating is effectively creating a barrier from the contamination during the lifetime of the circuit board.


How are conformal coatings applied to circuit boards?

Different conformal coating application methods including Parylene, spraying, dipping and brushing

Some coatings, such as acrylics, polyurethanes, silicones and epoxies, are usually applied in a liquid state, using spray, dip or brush application methods.

They harden and dry through solvent evaporation or chemical cure reactions.

However, there are many coatings that are not liquids such as Parylene and ALD coatings. They are applied in a chemical vapor deposition process.


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