Why use Parylene to protect printed circuit boards?

Parylene2

Parylene is a conformal coating film that is applied using a specialised vapour deposition application process.

This means it is very different to all of the other liquid conformal coatings available on the market.


Three reasons why Parylene is better than traditional liquid conformal coatings

The fact that the Parylene film is deposited onto circuit boards in a vacuum leads to many unique advantages.

Here are three key reasons to use Parylene:

  1. The Parylene coating is completely conformal to the surface of the Printed Circuit Board (PCB) or product. The coating has a uniform thickness and is pinhole free. Therefore, components with sharp edges, points, flat surfaces, crevices or exposed internal surfaces are coated uniformly without voids.
  2. Parylene coating provides an excellent barrier that exhibits a very low permeability to moisture and gases compared to traditional liquid conformal coatings. This means that circuit boards coated in Parylene generally are more “waterproof” than the same circuits coated in a liquid conformal coating.
  3. Parylene has excellent electrical properties compared to normal conformal coatings. These include low dielectric constant and loss with good high-frequency properties, good dielectric strength, and high bulk and surface resistance.

Need to find out more?

Go directly to our Parylene section in Nexus  or contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

What is Parylene?

Parylene is the trade name for a variety of chemical vapor deposited poly (p-xylylene) polymers used as moisture and dielectric barriers.

Although Parylene is a conformal coating it is different compared to the standard “wet” liquid conformal coatings in that it is deposited as a gas in a vacuum chamber and it is a dry process.

nexusphoto1Although Parylene is a conformal coating it is different compared to the standard “wet” liquid conformal coatings in that it is deposited as a gas in a vacuum chamber and it is a dry process. Image courtesy of Plasma Rugged Solutions

This method of chemical vapour deposition (CVD) and the Parylene dimer material itself give Parylene unique properties compared to other traditional conformal coatings.

For Parylene there are five key areas that Nexus can help with.

These are:


Need to find out more?

For further information on Parylene then contact us directly or go to our Parylene section in Nexus. See how we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

 

How do you remove Parylene completely from a printed circuit board?  

Parylene is the trade name for a variety of chemical vapor deposited poly (p-xylylene) polymers used as moisture and dielectric barriers.

Although Parylene is a conformal coating it is different compared to the standard “wet” liquid conformal coatings in that it is deposited as a gas in a vacuum chamber and it is a dry process.

This method and the material itself give Parylene unique material properties that give it a lot of advantages compared to other traditional conformal coatings.

However, these unique properties also make it an extremely difficult material to remove.

Why is Parylene difficult to remove?

Compared to typical liquid conformal coatings like acrylics and polyurethanes that more easily dissolve in mildly aggressive solvents then Parylene is much tougher to remove.

The reasons are many why but a key point is that the Parylene coating itself is chemically inert. It has a high chemical resistance so the solvents don’t work well.

This means any chemical attack tried with solvents or other liquid chemicals on the Parylene is as much likely to damage the circuit board than remove the actual coating.

So, chemical removal is almost impossible.

This leaves another well know method for Parylene removal that is mechanical abrasion.

Mechanical abrasion of a coating can be done crudely by scraping off the Parylene with a knife or tool. Or, removal can be done with a media blast system that gradually erodes the Parylene coating away.

However, mechanical abrasion is a time consuming process and is highly skilled. Any wrong action could result in irreparable damage.

Further, mechanical abrasion tends to be a localised repair and removal technique. The concept of completely removing all of the Parylene of a circuit by mechanical abrasion is considered almost impossible unless a ridiculous amount of time and effort is injected into the process.

Therefore, a specialist method is required to remove Parylene completely from a whole circuit board.

A new method for completely stripping Parylene from a PCBA

Due to new research two processes have been developed for completely removing Parylene coating from the surface of a circuit.

They are:

  • A method for <15um thickness of Parylene coating on the board
  • A method for >15um thickness of Parylene coating on the board

Removal with <15um thickness of Parylene coating on the circuit

When the Parylene coating is under 15um then the removal from the whole circuit is a relatively simple process.

To successfully remove the Parylene a technique has been developed involving plasma etching.

The plasma-etch process uses a proprietary blend of gasses, and a custom system to mechanically etch off the Parylene. This specially designed alchemy of gasses specifically attacks Parylene rather than the solder mask.

The technique successfully removes the Parylene from all over the board.

Also, the etching process is quick relative to the other mechanical methods. Typically, the circuit can be completely etched of Parylene in under an hour.

Further, the process is safe. It does almost no harm to the circuit and is one of the safest methods for complete removal of Parylene.

Removal with >15um thickness of Parylene coating on the circuit

When the Parylene coating is greater than 15um then the removal from the whole circuit is a little more complex. In fact, it becomes a two-stage process.

First, you can use the plasma etch treatment to loosen the Parylene from the surface of the circuit. Normally the Parylene is bonded well to the surface and this loosening allows for a second stage process.

In the second stage a media blaster like the SWARM system can be used to remove the coating. Since the coating has been loosened it does tend to come off much easier and quicker.

That said it is still a little slow and costs are higher. But, it still can be removed more easily.


Need to find out more?

For further information on Parylene removal then contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

 

Things you should know about Parylene

What is Parylene?

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

It is a completely different process to the liquid conformal coatings and its properties offer advantages and disadvantages in comparison.

Parylene is a dry process compared to the standard “wet” liquid conformal coatings.

Since Parylene is deposited as a gas its thickness is almost uniform across the whole circuit board.

 

The ABCs of Parylene

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

Therefore, the Parylene application process is a completely different process to the liquid conformal coatings.

This gives Parylene unique properties that are not possible with the typical liquid conformal coatings normally used in electronics protection.

 

Five key facts about Parylene

  1. Parylene is the trade name for a variety of poly(p-xylylene) polymers
  2. It is a conformal coating that is deposited as a gas in a vacuum chamber. This is different to liquid conformal coatings.
  3. The Parylene film is created via a controlled Chemical Vapor Deposition (CVD) process.
  4. It is a dry process compared to the standard “wet” liquid conformal coatings.
  5. This process makes Parylene a highly effective moisture and dielectric barrier that outperforms most liquid conformal coatings.

 

Three important points you should know about Parylene

  1. Parylene has unique properties that are not possible with the liquid conformal coatings.
  2. Parylene is a conformal coating that is deposited as a gas in a vacuum chamber.
  3. This is different to liquid conformal coatings that can be brushed, dipped or sprayed.

What are my options for conformal coating application methods?

This is a question I am asked time and again.

Of course most people know of the selective robot and how it applies conformal coating.

However, there are many different application methods available for both liquid conformal coatings and Parylene and listed below are the common techniques:

Click on each to examine individually for details or click conformal coating application techniques for an overview.

Note, each of the various methods has different strengths and weaknesses.

However, each of these application methods should be considered in relation to the holistic approach to conformal coating processing 

What is the holistic approach to conformal coating?

The holistic approach states that you should consider the conformal coating material, the application process and the circuit board together and not as three separate entities.

I consider this approach the most fundamental issue and crucial factor in all of conformal coating processing.

Ironically, it is ignored on a regular basis.

In fact, I find that the failure to apply the holistic approach at the beginning of the conformal coating selection process is normally the root cause of many conformal coating problems.

 

Click conformal coating application techniques to find out more.


Need help with your conformal coating process?

Contact Nexus now and let us show you how we can help you.


Dr Lee Hitchens, Author of Nexus website and ebook

Dr Lee Hitchens is the Author of the Nexus eBook and a main contributor to Nexus.

 

What type of problems can you have with conformal coating?

Normally, when I am working with customers I see two types of problems.

Those are problems relating to the conformal coating process and those relating to the actual product reliability.

They are two very different issues to deal with.

Conformal coating reliability problems

Ultimately, there are many factors that can affect the short, medium and long-term reliability of a circuit board.

It is not just the conformal coating that can influence this.

However, if the conformal coating material is not correctly specified at the reliability design stage then this could be the major issue and the reason for failure.

Once the product reliability requirements have been defined as part of the conformal coating design procedure then the resulting information needs to be combined with the data from the conformal coating holistic approach.

This will ensure that the risks of a failure due to the conformal coating are minimised.

if the conformal coating material is not correctly specified at the reliability design stage then this could be the major issue and the reason for failure.
If the conformal coating material is not correctly specified at the reliability design stage then this could be the major issue and the reason for failure.

Conformal coating process problems

Typical failure mechanisms in conformal coating processing normally come from the conformal coating masking process or the application process.

Conformal coating masking failures

Failures in the masking process are generally a known quantity and easy to understand.

Adopting best practice methods for conformal coating masking can help to minimise these problems.

Masking with tape and latex 1 600
Using best masking techniques can minimise some problems found in conformal coating processing

Conformal coating application failures

Failures in the conformal coating application process are very well understood.

Typical failure mechanisms include:

  • Bubbles
  • Blushing
  • Contamination
  • Capillary Flow
  • Orange Peel
  • Shadowing
  • Cracking
  • Delamination
  • De-wetting
  • Fish Eyes

Understanding and troubleshooting why these conformal coating failures occur can quickly lead to a solution to the failure in the conformal coating process.


Need help with your conformal coating process?

Contact Nexus now and let us show you how we can help you.


Dr Lee Hitchens, Author of Nexus website and ebook

Dr Lee Hitchens is the Author of the Nexus eBook and a main contributor to Nexus.

 

What You Need to Know About The Parylene Vapour Deposition Method

 

Paratronix Parylene ProcessVapour Deposition is a unique conformal coating technique as it is a dry process unlike other methods that are liquid-based.

The coating is applied on circuit boards through a vacuum chamber where the components are coated in batches. Parylene is a material applied during the deposition process at room temperature.

All parts that shouldn’t be coated ought to be masked prior to the vapour deposition.

The Basics:

  • It requires a specialist system that is designed for vacuum application.
  • The set up may cost significant investment initially
  • The process can handle low and medium volumes
  • Vapour deposition application is relatively simple but the initial process development can be complex
  • Coating thickness is an important parameter and calculations should be exact.
  • It is one of the most expensive coating processes but produces the best finish.

Variables to consider in vapour deposition conformal coating:

  • The operator’s skill and extensive training
  • Knowledge in preparation particularly in handling Parylene material
  • Cleanliness of the surface
  • Masking requirements
  • Circuit board design

Just like other conformal coating application process, there are advantages and disadvantages to using vapour deposition.

Some of the benefits include excellent protection due to very low permeability, high solvent and salt protection, and 100% clarity as Parylene can coat optical components. On the flipside, the capital costs are high, preparation can be challenging, and it requires the highest masking level.

Read more at Conformal Coating Application Methods: Vapour Deposition

Who is Nexus?

Nexus brings together the accumulated knowledge of a group of conformal coating and electronics material dispensing consultants who provide a unique service, focused on helping electronics manufacturing clients improve their conformal coating and electronics materials processes.

Nexus operate across North America, Europe and Asia and can provide a unique perspective to the rapidly growing conformal coating and electronics materials industry. Expertise is held in liquid and parylene coating, capital equipment sales and specifications and material, equipment and process specification, troubleshooting and training.