Conformal Coating – Protect PCBs from adverse environment conditions

By Mer-Mar Electronics Date posted: Last updated: September 16, 2022
Conformal coating for pcb and environment hazards

The conformal coating has a very important role to play when it comes to protecting circuit boards against unfavorable environmental conditions. In environments that have extremes of temperature, moisture, and dust, circuit boards can often suffer from defects, compromising the shelf life of the product. The conformal coating acts like a protective film that keeps the PCB moisture-f, and dust-proof protects it against temperature variances, keeps it free from corrosion & more. Another common aspect that impacts printed Circuit Boards wide variety of pollutants. They can lead to corrosion and even failure of PCBs. While several pollutants could accrue from the operating environment, oftentimes there are a lot of contaminants on account of residues during the PCB manufacturing process.

Uses of Conformal Coating in different sectors

The application fields of conformal coating include, but are not limited to:

1. Consumer Electronics

Consumer electronics particularly must face harsh external conditions. Be it water and detergent in the case of washing machines and dishwashers or contaminants as in the case of computers, microwaves and others.

2. Automobiles

With break fluids, gasoline vaporization & more, there are enough and more reasons for the use of conformal coatings in automotive.

3. Aerospace

With compression and decompression being the norm, it only stands to reason that the aerospace industry should see a widespread application of conformal coating.

Components that shouldn’t have conformal coating

It is also important to remember that some components cannot receive conformal coating. Some such components include:

  • High power components
  • Adjustable resistor
  • Battery holders
  • DIP Switch and more

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Benefits of Conformal Coating for PCB Protection

While the benefits of using conformal coating are well established, however, to reap the benefit of conformal coating, it is imperative that some preparations be made in the design phase itself.

You need to make sure that there are no contaminants on the board as contaminants can be sealed in and can create issues in the long run. In fact, the boards need to be thoroughly cleaned as well as dried. This will go a long way in ensuring that long-term performance isn’t impacted.

Conformal coating is also not effective in the case of applications that are exposed to water significantly. In such cases, it is advisable to offer protection through the process of encapsulation.

Ideally PCB conformal coating works best for applications which have:

  • Good electrical properties
  • Chemical resistance
  • Are durable mechanically

Also, the conformal coating does not work well over sharp edges as it results in edge crawling where the coating isn’t present on such edges. To prevent edge crawling it is necessary to check the viscosity of the coating and use multiple coats. A specialized coating of 100 microns works best for improved edge cover.

Some of the tests that might be carried out on conformal coated boards include:

  • Damp heat testing
  • Thermal cyclic performance
  • Chemical resistance test
  • Flammability test

Conformal coating is normally applied by the process of dipping or spraying. Typically, the thickness of the coating is 20-50 micron, even though specialist coatings can be applied at up to 100-micron thickness. In the case of PCB Prototypes or small batch production, it is also possible to apply the coating by the process of brushing.

Types of Conformal Coating for PCBs

Conformal coatings can be of several broad types:

1. Acrylic coatings

This comprises thermoplastic polymer dissolved in organic solvents. Typically, low boiling solvents are used that in turn leads to rapid touch dry. However, these solvents are flammable and hence have environmental hazards associated with them.

2. Epoxy coatings

They resist both moisture and chemicals. Also, they rate highly in terms of abrasion resistance. The flip side, however, is that they are very hard to remove from the board.

3. Urethane coatings

These are known for their moisture resistance, however, their removal and hence board repair is extremely difficult.

4. Silicone cover

These can vary from tough abrasion resistant material to soft coatings. These coatings are especially known for their high temperature performance.

5. Specialist coatings

These are of various kinds including UV cure coatings. These are especially useful where the production is high volume.

6. Water based conformal coatings

These are largely developed in response to the use of organic solvents. However, these take time to dry and with high coating thickness cracks can develop.

7. Parylene coating process

This comes in handy in evenly coating components and coating the underside of board components. The process, however, is expensive compared to conventional coating.

While there are environmental pressures in terms of use of solvent-based conformal coatings, the fact is currently it is hard to match the performance of these coatings. Going forward there will be further development of UV cures as well as water-based coatings to further improve their performance.

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