Parylene coating

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Vapour deposition is a completely different process to all of the other liquid based application methods. It is a dry process compared to the standard “wet” liquid conformal coatings.

The conformal coating is deposited onto the circuit board from a gas phase in a vacuum chamber.

Parylene is a room temperature deposition process.

Parylene is the trade name for a variety of chemical vapor deposited poly(p-xylylene) polymers which are deposited this way.

The key areas for Parylene vapour deposition

Parylene Machine 1
Vapour Deposition is a completely different process to all of the other liquid based application methods. It is a dry process compared to the standard “wet” liquid conformal coatings.

How does vapour deposition coating work?

Parylene is a conformal coating that is deposited as a gas in a vacuum chamber.

All components that must not be coated must be masked. The process is unselective.

Find out more in Parylene section on processing.

Paratronix Parylene Process
Parylene is a conformal coating that is deposited as a gas in a vacuum chamber.

Which conformal coatings can be used in vapour deposition coating?

Materials are specifically designed for vapour deposition and can only be used in the process.

Traditional conformal coatings cannot be applied in a Parylene system.

There is a range of Parylene coating materials with different properties. Find out more from the materials section: Parylene.

What equipment do you need for vapour deposition coating?

For vapour deposition coating a specialist system designed for vacuum application of coatings is required.

This is a not a low cost set up. It normally requires considerable capital investment.

The set up is also a low to medium volume batch process.

Is Parylene vapour deposition coating a complex process?

The actual application of the coating in the vacuum chamber can be very simple.

The complex part is developing the process initially.

The Parylene material may require surface preparation of the circuit or substrate to be coated.

This can be very difficult to achieve and experience of processing Parylene is normally required.

Also, the coating thickness can be a critical parameter. The control of the coating thickness is achieved by calculating the volume of material required to cover the substrates.

However, the coating can only be applied once and cannot be stopped once started.

So, the weight of material to be applied is critical.

Parylene Vertical Static Coating System
A Parylene coating system is a complex piece of equipment that requires knowledge of the process

How cost effective is vapour deposition coating as a process?

The vapour deposition coating process is one of the most costly processes.

However, it also produces the best conformal coating finish.

The properties of Parylene make it highly desirable as a material to be used and the cost of processing needs to be balanced against the coatings performance in the field.

Is vapour deposition coating a low, medium or high volume technique?

The Parylene process is generally a low volume batch process.

It can be scaled for medium and high volume but there are no economies of scale to be made.

Also, the time taken to apply the coating can take many hours, dependent on the coating thickness desired.

What variables control the quality of the vapour deposition coating finish?

Variables that influence the quality of the coating process in Vapour Deposition Coating are:

  • The operator skill: The control of the Parylene system and the material variables require a high level of skill and knowledge.
  • Preparation knowledge: The Parylene material may require surface preparation If the circuit or substrate to be coated. This can be very difficult to achieve and experience of processing Parylene is normally required.
  • Cleanliness: The Parylene type materials do not adhere well to some surfaces. Cleanliness of the surface and their treatment can be critical.
  • Masking: The Parylene process is a vapour deposition process. Therefore, the masking must be perfect to avoid leakage into the wrong areas of the circuit board or substrate.
  • Circuit Board Design: Some circuits are just not suited to the vapour deposition process.

What are five advantages of the vapour deposition process?

  1. True conformal coatings being completely homogeneous
  2. Very Low Permeability giving excellent protection against moisture
  3. Solvent and salt protection is high
  4. Excellent electrical properties compared to other conformal coatings
  5. 100% Clarity means Parylene can coat optical parts without problem

What are five disadvantages of the parylene coating process?

  1. It is a batch process so not suitable for high volume processing
  2. Capital Costs are high
  3. Cost per circuit coated can be very high
  4. Preparation of the surface can be difficult
  5. Masking level is the highest

More Information can be found in the Alternative Coatings Section: Parylene.

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