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.

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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.

How do I measure conformal coating thickness?

 

nexus1Measuring the exact thickness of your conformal coating across the whole of a circuit board is not simple.

In fact, due to the geometry of the components and the fact that the coating is measured in microns, it makes this task almost impossible.

However, what you can do is measured the thickness of the conformal coating in a few key places and use the thickness information found to infer how the coating coverage is for the rest of the board.

This is how nearly all companies measure conformal coating thickness.


So, how is the conformal coating thickness measured on a circuit board?

There are several ways to measure the conformal coating thickness on a printed circuit board (PCB).

The methods used can be for either a dry or wet conformal coating.

These techniques include:

  • Non-destructive eddy current system
  • Micrometer screw gauge
  • Wet film gauge

These techniques are explored further below.


Non-destructive eddy current system

A fast method for measuring conformal coating thickness after drying is a system using eddy currents.

The process works by placing the test probe head flat on the surface of the conformal coating and a measurement taken.

The system provides an immediate repeatable result for thickness measurement of conformal coating.

The process is quick and accurate to ±1 um. Using a gauge and flying probe also means the measurement system is extremely easy to use.

positector
Using a test probe system can quickly give you conformal coating thickness measurements without damaging the circuit board. Image from SCH Technologies

There are a couple of issues using an eddy current system like this.

First, there needs to be metal in the circuit board directly below the tested point. Otherwise, the system cannot function correctly as the eddy current will pass directly through the board.

Second, there needs to be a flat area on the board large enough for the test probe. The smallest practical probe is approximately 6mm diameter so any area smaller than this is not practical.

Finally, the surface measured for the probe needs to be flat. If not then there will be errors in the measurement. So, measuring components is extremely difficult.

To overcome these problems it may be better to measure test coupons.

Apply the conformal coating to the test coupons at the same time as the circuit board allows an easy measurement process. It also provides a permanent measurement.

In fact, test coupons are the ideal method for measuring the coating thickness, whatever the conformal coating process and method of measurement.


Micrometer screw gauge

An alternative to the eddy current system for dry film measurement is a calibrated micrometer screw gauge.

It’s a low cost, low-tech method for measuring conformal coating thickness and can normally measure down to ± 10 um.

The process is relatively simple.

First measure a point on the board or test coupon before coating. Next, apply the coating. Cure the coating well and finally re-measure at the same point.

The difference in the two measurements gives you the conformal coating thickness.

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A couple of pitfalls to avoid with this technique are ensuring the conformal coating is cured hard enough since if it is soft it could compact and give a false reading.

Also, do not measure one point. Take an average of at least 3 or 4 points across the coupon since this will give a better result statistically.

Again, for this technique test coupons are the ideal method.


Wet film gauge

A final method that can be used is a wet coating measurement technique that is very cost effective.

The technique uses a comb with different size patterns that is placed in the wet conformal coating and the imprint left indicates the wet film thickness.

Knowing the solids content of the material means that the material thickness can be calculated.

wet
A wet film gauge is a low cost method for measuring coating thickness while the conformal coating is wet. Using the solids content in the material and the wet film thickness allows the dry film thickness to be estimated.

Need to find out more?

Click conformal coating thickness measurement 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.

Five important facts about polyurethane (UR) conformal coatings

conformal coated PCBs Collage 640x480_NEXUS

  1. Polyurethane (UR) conformal coatings generally provide good humidity & moisture protection although not always as good as the acrylics. However, it normally is enough to protect the circuit board.
  2. Normally, urethanes are selected for their excellent chemical resistance. This is because the coatings cure rather than dry. That is they cross-link by one of many different methods including heat, UV, moisture and catalysed cure.
  3. Typically they have higher dielectric properties compared to the acrylic conformal coatings.
  4. Their chemical resistance, however, can be a limitation since rework and repair generally is more difficult than the acrylic coatings.
  5. UR coatings are normally available as either single or two-component formulations. Pot life is dependent on the cure mechanism but can be more limited than the acrylic coatings.

Need to find out more?

Click organic conformal coatings to find out about polyurethanes 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 application methods are available for applying conformal coating?

 

Conformal coatings can be applied to printed circuit boards (PCBs) in the production process environment in many different ways.

Listed below are the common methods of applying conformal coating materials:

Click on each to review each conformal coating application technique in our free ebook online.

Nexus
Conformal coatings can be applied to printed circuit boards (PCBs) in the production process environment in many different ways including spraying selectively, batch spraying and dipping.

The holistic approach to conformal coating application methods 

It is possible to split the different application methods and their suitability in many different ways including:

  • Compatibility with the conformal coating material
  • Design of the circuit board
  • Suitability to low, medium and high volume
  • Manual versus automatic process
  • Type of method of application
  • Level of control required

Each of the various coating methods has different advantages and disadvantages.

This relates to the holistic approach to conformal coating processing. It states that you should consider the conformal coating material itself, the application process and the circuit board together and not as three separate entities.

However, when considering the application methods it is possible to make some assumptions that help in selection.


Need to find out more?

For further information on conformal coating application methods 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.

 

Why use conformal coatings to protect a printed circuit board?

 

There are a lot of different reasons for using a conformal coating material or Parylene to protect a printed circuit board (PCB).

These reasons can include:

  • Barrier protection
  • High insulation protection
  • High moisture and humidity protection
  • Chemical and temperature resistance
  • Ruggedising
  • Improve dielectric properties
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There are a lot of different reasons for using a conformal coating material to protect a circuit board including barrier protection, increased insulation resistance, chemical protection and increased dielectric properties

Barrier protection

A conformal coating can create a barrier against attack during the lifetime of the circuit board.

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.


High insulation protection

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

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

However, with time in the field and its natural environment the circuit can degrade in different ways.

The conformal coating can slow this degradation down.


High moisture and humidity protection

Printed circuit boards can be vulnerable to moisture and humidity whilst in the field during its lifetime.

Most conformal coatings are highly resistant to moisture and humidity and this can lead to a reduction in leakage currents, cross talk, electrochemical migration, dendrite growth and arcing across the circuit board.


Chemical and temperature resistance

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

Normally, a circuit board exposed to chemically aggressive environment would be attacked but the conformal coating can slow down the effects or even prevent them.


Ruggedising

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


Improved dielectric properties

Just as the conformal coating can protect the circuit from moisture it can also help to increase the dielectric strength on the circuit board between components and lead interconnects.

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


Need to find out more?

For further information on using conformal coatings then contact us directly.

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 sectors are fluoropolymer coatings used? 

I am regularly asked where fluoropolymer coatings are used? After all they are a relatively new coating type in the world of conformal coatings and printed circuit boards.

Well to be honest, fluorinated coatings are used in almost all industrial sectors.

They include:

  • Aviation
  • Aerospace
  • Defense
  • Automotive
  • Industrial
  • Oil & Gas
  • Electronics
  • Medical/Pharmaceutical
  • Optics
  • Telecommunications
  • White goods / Commercial

This list is limited and there are a lot more areas that they are used.

In terms of products that are actually coated right now in fluoropolymer coating materials there are many.

They include:

  • Circuit boards
  • Mobile phones
  • Tablets
  • Automotive parts (gears, rotors, pistons)
  • Commercial bake-ware
  • Glassware, labware
  • Machine parts/components
  • Printing equipment
  • Sintered metal parts
  • Catheters, guidewires
  • Fasteners
  • Screen (metal/synthetic)
  • Filter media (cloth, synthetic)
  • O-rings, gaskets, seals
  • Silicone rubber
  • Solenoid, springs, coils

What is really interesting is that these coatings are really advancing in technology and changing all the time. Companies are tailoring the coating technology to the problem.

They are a wonderful material waiting for a project or problem to solve.

They are also being used in new and different ways.

For example, we are now experimenting with depositing the fluorinated films by plasma coating. This actually makes the bonding stronger and improves the overall performance without significant cost.

Fluoropolymer nano coating repels water 600

Fluoropolymer coatings are also being used in new and different ways. They are being depositing by plasma coating. This actually makes the bonding stronger and improves the overall performance without significant cost.


Need to find out more?

For further information on fluoropolymer coating 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.