How do I spray coat my conformal coating?

May 11, 2017 Blog, conformal coating

SCH UK Image 3conformal coating batch spraying Collage 640x480

Batch spraying is one of the widest used techniques used in low and medium volume conformal coating processing.

Whether you are using a compressed air spray gun or an aerosol can, the conformal coating is sprayed across the whole of the circuit board.

It can produce a high quality coating finish that gives the best protection due to good edge coverage.

However, it is not a selective process. All parts are coated on the circuit board.

Therefore, masking may be required to protect components that must not be coated.

What equipment do you need for batch conformal coating spraying?

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If you are not using aerosols then for conformal coating spraying a typical set up is:

Spray gun
Air Compressor for the Air Supply
Spray booth

This is a low cost set up that can handle a fairly high volume of product.

However, the quality of the finish is dependent on the quality of the spray equipment itself and the operator.

How do you apply the conformal coating by spraying?

Although the process can be material specific there are a few general guidelines for applying conformal coating by spraying.

These include:

Only apply thin, consistent coats. It may be necessary to apply more than one coat.
Apply the coating in a narrow raster pattern across the circuit.
Rotate the board 90 degrees and repeat. Continue until the whole board is coated to avoid 3D effects.
Allow the coating to dry enough to avoid problems like bubbles before applying a second coat.

Following a few simple guidelines can save a lot of problems.

What variables control the quality of the conformal coating in batch spraying?

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Variables that influence the quality of the coating process in spraying are:

The operator skill
Quality of the spray equipment
Viscosity of the conformal coating
Blending the conformal coating to the right viscosity is critical.
The level of masking required

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How thick should I apply my conformal coating?

April 27, 2017 Blog, 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.

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.

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

April 25, 2017 Blog, 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.

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

April 21, 2017 Blog, 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.

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.

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How do I measure conformal coating thickness?

April 13, 2017 Blog

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.

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.

Need to know more about conformal coating thickness measurement?

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

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What are the alternative materials to liquid conformal coatings?

April 11, 2017 alternative, Atomic layer deposition (ALD), Blog, conformal coating, Molecular vapour deposition, Parylene

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.

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?

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Is there a free guide on conformal coating defects?

April 6, 2017 Blog, conformal coating

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?

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Why does cleaning improve the adhesion of the conformal coating?

April 4, 2017 Blog

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:

Adsorption
Chemical Bonding
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?

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Are there design rules for applying conformal coatings?

March 30, 2017 Blog, Uncategorized

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.

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.

Nexus Design Rules

Nexus, the independent conformal coating knowledge base, has developed both guidelines for conformal coating reliability and conformal coating process.

Their philosophy is that for companies embracing lean philosophies and applying conformal coatings, a failure to appreciate the subtleties of the application process can result in an uncoatable (at least as specified) assembly process.

They also state that if the rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.

Nexus have design rules for both general processing and for specific application processes such as dipping, selective coating and batch spraying.

For further information visit conformal coating design rules to learn more.

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Do you need MiL spec qualification for your conformal coating?

March 29, 2017 Blog, Uncategorized

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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).

What is the Qualified Product List (QPL)?

The Mil Standard for conformal coating has been inactive for new designs since November 1998. However, the standard is still widely used for independent certification of conformal coatings.

All companies tested to the MIL-I-46058C standard are listed on the QPL. It is still possible to register the coating on the list.

Conformal coatings listed on the QPL will have been through rigorous 3rd party testing to confirm they meet the standard. They are not self-certified.

So, if you require a conformal coating material that is Mil-spec approved then it will have to be on the QPL and it will have been independently tested.

Need to know more about Mil Standard conformal coatings?

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