How does Parylene material differ from liquid conformal coatings and where can you buy it?

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Parylene is very different to typical liquid conformal coatings like acrylic, epoxy, silicone and polyurethane resin based materials.

When you buy Parylene it is a white powdered dimer.

This powder cannot be applied to circuit boards in its current state. The dimer requires specialist Parylene equipment that uses a Chemical Vapour Deposition (CVD) process. That is the dimer is placed inside the machine, a vacuum created and the dimer is then transformed to a gas vapour by being heated up.

This vapour created during the pyrolysis process can then be deposited on the printed circuit board as the Parylene coating.

This is very different to liquid conformal coatings. They start off as a “varnish” in a can or container and are applied to circuit boards by brushing, dipping or spraying. They then dry either naturally or artificially in some manner and the circuit board is now protected.


Where to buy Parylene

When purchasing Parylene it is important to find a source that provides a quality product. The purity of the coating is one of the key points in creating a successful Parylene process. Neglecting this fact can cause endless problems.

Remember that buying Parylene cheaply is easy. Buying cheap Parylene that is pure enough to protect the circuit board is another issue.

Thin film Partners can inform you of the right vendors who supply high-quality material and the pricing for each type. Then you can compare which vendor you would like to buy from.

This is a cost effective method to ensure you get the right Parylene coating at the right price.


Want to find out more about Parylene?

Contact us to discuss your needs and let us explain how we can help you.

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Why is it harder to mask and de-mask Parylene on a circuit board assembly compared to traditional liquid conformal coatings?

There are four key reasons why Parylene masking and de-masking is more difficult compared to liquid conformal coatings.

These are:

  1. Parylene is a vapour. When you are masking against a gas rather than a liquid then there is more of a challenge. So you need to provide a much better barrier with the masking process compared to the liquid coatings.
  2. Parylene is immersion. Most liquid conformal coatings are sprayed and so the capillary is less compared to immersion in a limitless supply of material.
  3. Stripping Parylene is hard. It is much harder to remove unwanted Parylene material on components that should not have been coated. Parylene is chemically inert (therefore harder to strip off or remove) and more difficult to see (no UV trace in most Parylene coatings). Mistakes can be more costly.
  4. The Parylene can bond more to the masking materials. When the Parylene is deposited on the masking materials and circuit board it can bind the two together and it can take significant effort and care to remove the masking materials without damaging the board or the Parylene coating integrity.

Need to find out more?

Click Parylene coating to protect electronic circuit boards to find out further information 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.

Why are polyurethane conformal coatings used for protecting electronic circuit boards and in which sectors?

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The majority of conformal coatings used in the world to protect electronic circuit boards are made from organic based resins.

These organic conformal coatings can be further subdivided into resin types such as

  • Acrylic
  • Polyurethane
  • Epoxy
  • Acrylic urethane blends

Although the majority of conformal coatings being used in this group are acrylic materials there is a considerable amount of coatings made from polyurethane.

Solvent based acrylic conformal coatings have been historically the number one choice for moisture protection of printed circuit boards and they provide excellent humidity resistance.

They also dry quicker than nearly all the other conformal coating types, they are easy to use in production and are easily repaired.

However, acrylic conformal coatings have very little chemical resistance. So, they are poor at protecting circuit boards in harsh chemical environments.

This is where polyurethane conformal coatings are considered.


Using polyurethane conformal coatings to protect against chemical attack

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Polyurethane (UR) coatings also provide good humidity & moisture protection compared to acrylic materials.

But, what is key to their selection as a protective conformal coating is that they also offer excellent chemical resistance to the circuit board.

The reason for this is that UR coatings cure rather than dry. That is they cross-link once applied to the circuit board by one of the many methods including solvent evaporation (initial stages), heat, UV, moisture and catalysed cure.

This cross-linking of the polymer chain provides the chemical resistance for which the UR coatings are generally selected.

This makes them excellent conformal coatings where the chemical attack is a potential hazard for the electronic circuit boards. This includes sectors such as aerospace, military and industrial sectors plus other diverse areas such as medical and commercial electronics.


Need to find out more?

Find out more about using polyurethane conformal coatings to protect printed circuit boards in a chemical environment here 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.

Factors to consider when setting up a conformal coating production line for printed circuit boards

The conformal coating production line, whether it is an operator manually brush coating printed circuit boards (PCBs) or an inline robotic spray coating process is typically made up of several stages.

However, not all the stages are mandatory or may be required. These stages are shown below:

 

Chart

Consider each stage below.


Boards In / Boards Out

This is very straightforward. The PCBs are delivered to the conformal coating area ready for processing.


Inspection

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Inspecting the circuit boards before starting the conformal coating application process starts helps avoid stopping the line if there is a problem.

The initial inspection process can also identify which PCBs are to be coated, the material to be used and how they are to be coated.

This can be done automatically as part of the production process or completed by the operator.


Cleaning

Cleaning the circuit boards before application of conformal coating may or may not be required.

This is a decision that should be made earlier on in the design stage before production actually starts.

However, if you do decide to clean then consider these guidelines:

  • Ensure that the cleaning process does not add more contaminants to the PCB than it started with due to entrapment of cleaning fluids.
  • Make sure the PCBs are dry enough for the conformal coating process and the cleaning process not leave water entrapped under components that could impede the application.
  • Ensure the cleaning process actually removes residues that may cause defects like de-wetting to minimise finishing at the end of the process.

Again, cleaning is for the engineers to decide.  The option of whether you need to clean your circuit boards for conformal coating is a whole topic on its own.


Masking

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Masking may not be required on the circuit board.  However, generally there are very few circuit board assemblies that can be completely coated and have no areas that must not be conformal coated.

Some components on PCBs generally need to avoid having conformal coating applied to them.

This leaves three options:

  1. You can avoid coating the component or area using a selective application process.
  2. You can apply some form of masking that the conformal coating can be applied to and remove the masking materials after application.
  3. You can apply a conformal coating that does not need masking against.

Again, engineers need to consider their options on whether to use conformal coating masking as soon as possible.


Pre-Coating Inspection

Generally, it is more efficient to double check the masking process is correct before conformal coating application rather than repair the PCB after the process goes wrong because the masking process was incorrect.

This check can be manual or automated but it is highly valuable.


Coating Application

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The one stage that cannot be avoided is the conformal coating applied to the PCB.

There are many different methods for applying conformal coatings and probably the most important factor in all of them is training. The operator needs to understand the process to be able to work correctly.


Drying and Curing

A conformal coating is a wet process (unless you use Parylene) and therefore the coating has to dry.

The difference between drying and curing in conformal coating is very different. However the process required depends on the conformal coating itself.

Care needs to be taken in deciding how to achieve the right result.


De-masking

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Like masking, there is skill in removing the masking materials from the circuit board and not damaging the coating.

This is also where touch up (finishing) is carried out to ensure the final finished PCB is fit to pass the inspection criteria.

Work instructions are needed along with training on the specific methods of finishing to ensure this can be achieved.

Again, the work environment can be critical to achieve the right results.


Inspection

When the PCB is conformal coated and finished, you need to know if the product meets the inspection criteria.

The conformal coating inspection process can be done manually or automatically. This can depend on the volume of PCBs and the level of sophistication required.

Again, it is down to operator training and using the right equipment to ensure that this is possible.

Also, at this stage it is possible to measure process factors like coating conformal thickness to check that the criteria are met.


Other factors to consider

The set up of a conformal coating production line regardless of the application method has many similar characteristics.

General requirements

Any coating facility will need the basic requirements put in place that would be standard for any piece of electronic manufacturing process. These include ESD systems, facilities for the machines, the environmental requirements and the normal Health & Safety (HSE) considerations.

Health & Safety (HSE)

HSE tends to be more important for conformal coatings since in general the coatings themselves are hazardous, or the way they are applied makes them potentially harmful to operators

Environment

Conformal coatings are sensitive to the environment that they are processed. Cleanliness could be critical, as can temperature and humidity.


Summary

Setting up a conformal coating production facility can be a straightforward process as long as all factors are considered.

Get this right and many of the problems that could occur during production will be avoided.


Need to find out more?

Click conformal coating production processes for further information 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.r

What sectors are polyurethane conformal coatings used to protect electronic circuit boards?

 

NEXUS1Polyurethane conformal coatings are used in nearly all sectors where electronic circuit boards are used including:

  1. Aerospace
  2. Defence
  3. Marine
  4. Transport
  5. Automotive
  6. Control drives
  7. Industrial electronics
  8. LEDs
  9. Telecommunications
  10. Mobile technology
  11. White goods

In fact there are few sectors they are not used.


Why use a polyurethane conformal coating in electronics protection?

Conformal coatings made from polyurethane resin are part of the organic family of coating materials that also includes the acrylic and epoxy materials.

All organic conformal coating materials provide good humidity & moisture protection.

What differentiates the polyurethane coating from the other coatings like the acrylic resins is that the urethanes also offer high chemical resistance.

This makes them excellent conformal coatings where chemical attack is a potential hazard for the electronic circuit.


Need to find out more?

Click polyurethane conformal coatings as part of the organic coatings for further information 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.

The ABCs of Parylene coating for electronic circuit boards

NEXUSParylene is a conformal coating that can be applied to electronic circuit board assemblies that is deposited as a gas in a vacuum chamber.

It is a completely different process to the normal liquid conformal coatings that are applied by alternative methods such as dip, brush and spray.

This difference means Parylene offer advantages and disadvantages in comparison.

For Parylene coating and electronics here are six key areas to consider.

These are:

Click on each link to find out more Parylene, the process and its properties.


Need to find out more?

Click Parylene conformal coating for electronics for further information 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.

Do you need UL qualification for your conformal coating?

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What is UL and how does it relate to conformal coating?

UL stands for Underwriter Laboratories. They are a global safety certification body for consumer electronics.

When a conformal coating states that it has a UL qualification, it means that the material has been independently tested by UL in one of their laboratories and passed a particular standard.

UL carry out the testing. It is independent. There is no self-certification available.

UL qualified conformal coatings are used in all areas of electronics protection including aerospace, industrial controls, automotive and telecommunication sectors.


What UL standard tests are used with conformal coating?

For conformal coating materials there are two standard tests typically used.

These are UL94 and UL 746E.

UL 94 Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing.

UL 94 is a plastic material flammability standard. It classifies plastics according to how they burn in various orientations and thicknesses.

UL 94 measures a conformal coating material’s ability to extinguish or to spread the flame once a test specimen has been ignited.

This ability is ranked as a classification as below.

Classifications

For conformal coatings the coupons are normally tested Horizontally (HB).

Tests are normally conducted on coupons of the minimum approved thickness with different types of laminate.

The conformal coating thickness range also is normally specified.

  • V-2 burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed.
  • V-1: burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
  • V-0: burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.

Most conformal coatings aim to achieve V-0 status.

UL 746E Standard Polymeric Materials: Industrial Laminates, Filament Wound Tubing, Vulcanized Fiber and Materials Used in Printed-Wiring Boards

The UL 746 test measures the resistance of the conformal coating to electrical ignition sources.

The conformal coating material’s resistance to ignition and surface tracking characteristics is described in UL 746E.


Need to find out more?

Click UL standards and conformal coating for further information on whether you need UL qualified conformal coatings 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.