How thick should I apply my conformal coating?

So, here is a question I am regularly asked. How thick should the conformal coating be on the circuit board?

Well, the simple answer is thick enough so the conformal coating works and protects the circuit board.

But not too thick as this can cause problems for the circuit board in the long term.

After all, the performance of the conformal coating is dependent on the thickness applied.

But, it is possible to quantify this a little more.

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Find out how one company saved 60% of their process costs by changing to custom conformal coating masking boots

Diamond MT, a conformal coating and Parylene coating service provider in the USA, found they saved more than 60% of their current masking costs by switching to the SCH range of conformal coating masking boots.

Sean Horn, Diamond MT, explains how they did it.

“We had initially wanted to try SCH’s conformal coating masking boots for price savings. However, once we began to work with Lee on our specific masking application, we realised that we could extend the life of our boots over 200%. We switched immediately!

We then realised the importance of working with someone who understands coatings. We will not being going back to our previous supplier.”

Sean Horn, Director, Diamond MT, Parylene and conformal coating subcontract service provider.

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How do I correctly dip coat my circuit board in conformal coating?

Dip coating is a traditional conformal coating application method that has been used to conformal coat circuit boards for a very long time.

The process in its simplest form is as follows:

  • The printed circuit board (PCB) is dipped into a tank of conformal coating liquid.
  • This can be complete submersion or partial dip.
  • The board can be dipped vertically, horizontally or at another angle.
  • The board can be dipped manually or automatically.
  • The board is removed from the coating and the excess coating drains away.

This process is highly effective in applying a conformal coating to a printed circuit board (PCB).

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How do I brush coat my conformal coating?

The correct technique for applying conformal coating by brush is to flow the coating on.

The material should not be brushed on like you are decorating with paint.

The coating should be loaded on to the brush and flowed onto the printed circuit board.

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How do I measure conformal coating thickness?

There are several ways to measure the conformal coating thickness on a printed circuit board (PCB).  They can be either used on dry or wet film coating.

These techniques include:

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

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What are the alternative materials to liquid conformal coatings?

There are several alternative coatings available to the traditional conformal coating materials.

These alternative coatings include:

  • Parylene and other Chemical Vapour Deposition (CVD) films
  • Fluorinated ultra-thin and thin film coatings
  • Molecular Vapour Deposition (MVD) coatings
  • Atomic Layer Deposition (ALD) coatings

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Is there a free guide on conformal coating defects?

Nexus, the independent conformal coating information site, provide an information section on conformal coating defects in their free online Ebook.

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Why does cleaning improve the adhesion of the conformal coating?

In general it is important that conformal coatings have good adhesion in order to be effective. However, there is no single theory that describes the property of adhesion for conformal coatings.

There are three basic mechanisms for conformal coatings that are known to help with good adhesion.

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What are the different techniques for cleaning a circuit board?

Nowadays, there are many different methods and media for cleaning circuit boards. That includes low, medium and high volume production levels.

However, when considering a new process then you the key issues can be broken down into two different categories.

These are the:

  1. Different chemistries / media to be used
  2. Different methods / techniques to be used

Lets consider the categories in a little more detail.

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Are there design rules for applying conformal coatings?

Conformal coating is not simply a consumable material. Unfortunately, for too many designers, conformal coating is simply a part number, to be applied to circuit boards.

However, this can be a major problem especially in the conformal coating production stage of the process.

There are guidelines in the IPC standards that may help with Design for Manufacture (DFM) principles. These are worth considering.

Unfortunately, there are no official design guidelines that will help directly with the application process and conformal coating.

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Do you need MiL spec qualification for your conformal coating?

Normally, customers know if they require MIL-I-46058C qualification for their conformal coating. It normally is required if it is a military product.

However, caution should be shown when examining conformal coating datasheets that state MEET the requirements of MIL-I-46058C since the conformal coating will likely not be on the Qualified Product List (QPL).

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What is plasma cleaning?

Plasma cleaning is a process of using plasma energy to clean and modify the surface of a substrate like a circuit board assembly.

It is a highly effective surface cleaning and treatment process before application of conformal coatings and is gaining more popularity due its highly effective performance.

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How to clean “no clean” flux residues and get it right

Cleaning the residues left behind by a no clean flux process is one of the most difficult tasks when considering cleaning.

After all, the residues left on the circuit board are not formulated to be cleaned away easily.

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The ABCs of Atomic Layer Deposition (ALD)

What is ALD?

Atomic Layer Deposition (ALD) belongs to the family of Chemical Vapour Deposition methods (CVD).

It is a deposition process at a nano-scale level within an enclosed vacuum chamber.

The deposition process forms ultra-thin films (atomic layers) with extremely reliable film thickness control.

This provides for highly conformal and dense films at extremely thin layers (1-100nm).

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Introducing a new coating that could offer the ultimate protection for LEDs without compromise to performance or process cost!

The need to protect LEDs from the long –term exposure of a harsh environment is becoming more and more required. This is doubly so for LEDs used outdoors.

The alternative coatings used to protect LEDs are many. They include Parylene, conformal coatings, ultra-thin fluoropolymer materials and encapsulates.

However, none of the material processes offer the perfect protection without adding significant cost to the production process, and ultimately the circuit board and product.

Further, to reduce costs in production some of the coating materials used compromised performance. So, there is a typical balance of costs versus protection.

Now, this may all change with the introduction of a very new coating process that takes many of the performance benefits of the best coatings but does not suffer the associated problems of increased production costs.

This process is a hybrid ALD (Atomic Layer Deposition)/CVD (Chemical Vapor Deposition) technique.

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What are conformal coating masking boots and how can they save you money?

The use of masking materials such as tapes, dots and liquid latex can be a highly effective process in protecting components from ingress of conformal coating.

However, the masking process can be labour intensive, difficult and time consuming.

Using reusable, custom masking boots offers a labour saving alternative in both the masking and de-masking stages of the coating process.

This can save you lots of time and money.

masking boots

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What is Plasma coating?

Plasma treatment of the surface of a circuit board before conformal coating

Plasma coating is the application of a nano-coating material onto a surface via a plasma.

Using a jet nozzle the material is supplied to the plasma. Next, the plasma excites the material and this increases the coatings reactivity.

This extra reactivity allows the material to optimally cover the surface of the substrate and bond much tighter.

The plasma coating process can be adjusted individually to the substrate. It can be used to coat different materials like metals, glass, ceramics and plastics.

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The ABCs of plasma cleaning for conformal coating

Plasma cleaning is a process that is gaining more popularity in thin film applications due its highly effective performance on cleaning and modifying surfaces.

It is also a highly effective surface cleaning and treatment process before application of conformal coatings.

Plasma circuit treatment of circuit board narrow

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The ABCs of Parylene

What is Parylene?

Parylene is an organic polymer, generically known as Poly (p-xylylene).

It is not a liquid like typical acrylic and urethane conformal coatings. It is not therefore processed like standard liquid conformal coatings.

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