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.


Help for determining the right conformal coating thickness

First off it’s probably best to use guidelines from International Standards like IPC A 610.

These standards specify the conformal coating thickness based upon the generic material types like acrylics, polyurethanes, and silicones.

Further, you can also reference this data against the material manufacturers technical recommendations.

Combining these two pieces of information should give you a target range for the conformal coating thickness.

However, ultimately, the coating thickness is down to the user.

How you decide if the conformal coating thickness is good enough is up to you. Too thin and you will not protect the circuit as effectively as you may need. Too thick and you could have reliability issues in the future. So, monitor your conformal coating thickness with care.
How you decide if the conformal coating thickness is good enough is up to you. Too thin and you will not protect the circuit as effectively as you may need. Too thick and you could have reliability issues in the future. So, monitor your conformal coating thickness with care.

So what do the IPC Standards recommend when considering conformal coating thickness?

The IPC A 610 standard defines ideal liquid conformal coating thickness values as:

  • Acrylic: 30-130μm
  • Polyurethane: 30-130μm
  • Silicone: 50-210μm

However, this is not the end of the story.

Using the target coating thicknesses as an absolute value can be problematic.

The reality is that the conformal coating thickness will vary massively across the circuit board due to many factors including the surface tension of the liquid, the surface energy of the board surface, the design of the board, the material properties and the application method used.

So, there may be areas on the board that could fall outside of the range where the coating thickness will be less or more than the ideal values.

Therefore, it is highly recommended that the range should be considered as an average value across the board for the conformal coating thickness.

In fact, the IPC go further and suggest using flat test coupons coated in the same way as the process you use for the circuit boards. Then, these test coupons are measured against the standards.

In the end how you decide if the coating thickness is good enough is up to you.

Too thin and you will not protect the circuit as effectively as you may need. Too thick and you could have reliability issues in the future.

So, monitor your conformal coating thickness with care.

Using the target coating thicknesses as an absolute value across the circuit board can be problematic. The reality is that the thickness will vary across the circuit board due to many factors including the surface tension of the liquid, the surface energy of the board surface, the design of the board, the material properties and the application method used.
Using the target coating thicknesses as an absolute value across the circuit board can be problematic. The reality is that the thickness will vary across the circuit board due to many factors including the surface tension of the liquid, the surface energy of the board surface, the design of the board, the material properties and the application method used.

Need to know more about measuring conformal coating thickness in your application process?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com

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.

Diamond MT saved more than 60% of their current masking costs by switching to the SCH range of conformal coating masking boots.

Diamond MT saved more than 60% of their current masking costs by switching to the SCH range of conformal coating masking boots.


So why did Diamond MT switch to our range of masking boots?

When the analysis was completed, it was found pricing for our conformal coating masking boots was lower by 30% compared to their current supplier.

This made a significant saving to Diamond MT and immediately a trial production run was started.

What was really interesting was after using them in the first month, Diamond MT found the masking boots lasted twice as long as their original boot from the alternate supplier.

This meant that now Diamond MT has halved the volume of boots they order and this has reduced their costs by 60% for the year.

This meant what started as a simple trial led to a huge saving to Diamond MT as a partner with SCH.


Need to know more about using conformal coating masking boots in your application process?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com

 

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).


What equipment may you need for dipping circuit boards in conformal coating?

A simple process is a board dipped by hand into a container of conformal coating. This can give some reasonable results.

However, normally dip coating equipment is used. This is especially true if medium and high volume processing is required.

The reason for using dipping machines is because the process has variables that are critical to film integrity and they are controlled by the machine system.

The variables that are critical for film quality and thickness are:

  • The speed of immersion
  • Dwell time in the coating
  • The withdrawal speed of the board

These factors, plus the viscosity of the conformal coating, are important to create a high quality finish and reduce costs.

A simple process is a board dipped by hand into a container of conformal coating. This can give some reasonable results. However, normally dip coating equipment is used. This is especially true if medium and high volume processing is required.
A simple process is a board dipped by hand into a container of conformal coating. This can give some reasonable results. However, normally dip coating equipment is used. This is especially true if medium and high volume processing is required.

 


How cost effective is the dip process for conformal coating?

The conformal coating process itself can be extremely low cost.

The cost of a dip system can be low compared to many other processes and when balanced against the speed of application.

However, if the circuit board demands a lot of components be masked before processing then the overall coating process can be expensive.

Masking for dipping can be very demanding and very difficult to complete successfully.


Need to know more about using a conformal coating in your application process?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com

 

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.

The correct technique for applying by brush is to flow the conformal coating on to the circuit board. The material should not be brushed on like you are decorating with paint.
The correct technique for applying by brush is to flow the conformal coating on to the circuit board. The material should not be brushed on like you are decorating with paint.

What conformal coatings can be applied by brush?

All conformal coatings can be applied by brush. Most conformal coatings lend themselves well to the technique.

Key factors that

The key points to be aware of are the material pot life and the conformal coating viscosity.

Material pot life

The pot life of the material may be finite so the conformal coating could cure during use. This may make the material useless to apply after a certain amount of time.

Conformal coating viscosity

The way the conformal coating flows is critical when applied by brush coating.

Therefore, the viscosity of the coating material is highly influential on the flow so control of the viscosity is critical to allow good coverage.

A highly viscous coating will be harder to apply correctly than a lower viscosity material.


What factors control the quality of conformal coating finish with brushing?

Key variables that influence the quality of the process include:

  • Operator skill
  • Quality of the brush
  • Viscosity of the coating
  • The coating environment
  • Complexity and size of the board
  • Conformal coating material type

Need to know more about using a conformal coating in your application process?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com

 

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

These techniques are explored further below.


Non-destructive eddy current system

A fast method for measure coating thickness is a system using eddy currents. The process can be extremely quick and accurate to ±1 um.

Using a gauge and flying probe for the measurement the system is extremely easy to use.

The process works by placing the test probe head flat on the surface of the conformal coating and the measurement is almost instantaneous. The system provides an immediate repeatable result for thickness measurement of conformal coating.

Using a test probe system like the Positector 6000 can quickly give you conformal coating thickness measurements without damaging the circuit board.
Using a test probe system like the Positector 6000 can quickly give you conformal coating thickness measurements without damaging the circuit board.

Test coupons are the ideal method for measuring the coating thickness, whether is it spraying or dipping, and can be kept as a physical record of the performance.

Apply the coating to the test coupons at the same time as the circuit board then provides a permanent measurement and an accurate guide to the coating thickness.

There are a couple of issues using a system like this.

First, there needs to be metal in the circuit board directly below the tested point. Otherwise, the system cannot work.

Second, there needs to be a flat area 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.


Micrometer screw gauge

The low cost method is using a calibrated micrometer screw gauge that can measure down to ± 10 um. First measure a point on the board or test coupon, apply the coating, cure and measure the test coupon again at the same point. The difference gives you the coating thickness.

A couple of pitfalls to avoid are ensuring the 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 since this will give a better result statistically.

Test coupons are the ideal method for measuring the coating thickness, whether is it spraying or dipping, and can be kept as a physical record of the performance.


Wet film gauge

A final method is a wet film measurement technique that is very cost effective.

The technique uses a comb with different size patterns that is placed in the wet 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.

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.
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 know more about conformal coating thickness measurement?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com

 

 

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

They can provide extremely high protection to circuit boards if used correctly for the right product.

There are several new and old alternative coatings available to the traditional conformal coating materials. They include Parylene, fluorinated Nano-coatings, Molecular Vapour Deposition (MVD) and Atomic Layer Deposition (ALD) thin films.
There are several new and old alternative coatings available to the traditional conformal coating materials. They include Parylene, fluorinated Nano-coatings, Molecular Vapour Deposition (MVD) and Atomic Layer Deposition (ALD) thin films.

Parylene (XY) coatings

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

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

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

Fluoropolymer (FC) coatings

Surface Modifiers are ultra thin coatings that are applied at less than a few microns in thickness.

Liquid conformal coatings are applied in the range of 25-75um so they are considerably thicker in nature.

There are several variations in ultra thin conformal coatings out in the market now but two of the most popular types are liquid materials and partial vacuum deposition.

Atomic layer deposition (ALD)

ALD belongs to the family of chemical vapor deposition methods (CVD).

It is a deposition process at a Nano-scale level within a 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).

Molecular vapour deposition (MVD)

MVD belongs to both the families of chemical vapor deposition (CVD) and atomic layer deposition (ALD) methods.

Unlike traditional CVD and ALD flow systems the MVD reaction takes place in a chamber under static pressure resulting in extremely low chemical use.

The MVD process produces highly conformal thin film coatings, typically less than 100nm in thickness.

The coating provides excellent barrier properties and surface energy control.


Need to know more about alternative materials to the traditional liquid conformal coatings?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com

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.

According to Nexus, problems in conformal coating can be broken down into two areas.

  • Problems relating to conformal coating process
  • Problems relating to product reliability

In their troubleshooting section they focus on troubleshooting the problems associated with conformal coating processing and production.

You can download the PDF guide Solving conformal coating problems in the application process now.


Need to know more about conformal coating defects?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com

 

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.

They are:

  1. Adsorption
  2. Chemical Bonding
  3. Mechanical Interlocking
There are three basic mechanisms for conformal coatings that are known to help with good adhesion. They are adsorption, chemical bonding and mechanical Interlocking
There are three basic mechanisms for conformal coatings that are known to help with good adhesion. They are adsorption, chemical bonding and mechanical Interlocking

Adsorption

This is where the molecules in the conformal coating wet or flow freely over the substrate and make intimate contact with the substrate. This forms interfacial (electrostatic) bonds with van-der-Waal forces.

Any contamination between the two will weaken the adsorption. Any de-wetting (prevention of wetting) will also hinder the adsorption.

Cleaning the surface of contamination will help with adsorption.

Chemical bonds

The bonds are formed at the interface between the conformal coating and the substrate.

Good bonding gives strong adhesion of the conformal coating to the substrate. If bonding cannot be achieved due to contamination then poor adhesion may result.

Cleaning the surface of contamination will help the chemical bonding process.

Mechanical interlocking

The conformal coating film penetrates the roughness on the substrate surface and is achieved once the coating dries.

If the surface is smooth then the mechanical bonding is less effective. If the surface can be cleaned, leaving a rough surface, then more effective bonding can be achieved.

Cleaning the surface of contamination will help.


Achieving the best conformal coating adhesion

Surface contamination can be critical when considering conformal coating and the process. If you can clean the contamination from the surface then the adhesion of the conformal coating should improve.

All three mechanisms do not have to occur to form good adhesion. Depending on the specific conformal coating system, substrate, and application method, different mechanisms could work.

However, good wetting or adsorption is normally required for good bonding.

So, if in doubt clean the surface of the substrate to achieve good conformal coating bonding.


Need to know more about conformal coating adhesion?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com

0
    0
    Your Cart
    Your cart is empty
      Calculate Shipping