How do I spray coat my conformal coating?

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

Find out how we can help you with your conformal coatings now.

Contact us to discuss your needs and let us explain how hydrophobic coatings could work for you.

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The ABCs of ultra-thin fluoropolymer coatings for electronic circuit boards

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Nano coatings are no mask conformal coatings with great water repellent properties

What is a fluoropolymer coating?

A fluoropolymer coating is typically comprised of fluorocarbons and characterised by carbon-fluorine bonds.

They have many interesting properties and especially for printed circuit boards.

However the three key properties for electronics are that the coatings are:

  • Hydrophobic
  • Chemically resistant
  • No masking required

These properties can be key to protecting the electronics and providing a highly cost effective production process.

Hydrophobic coating

Fluorocarbons are not susceptible to Van der Waals force.

This gives the coatings their signature characteristics. That is they are non-stick, hydrophobic and friction reducing.

Therefore, water does not like to wet the surface of the circuit board and this gives the circuit excellent protection.

Chemically Resistant

These fluorinated coatings are chemically inert.

Owing to the fluorine bonds, fluoropolymer coatings demonstrate a high level of durability as well as resistance to acids, bases and most solvents.

This gives the circuit board a high degree of protection from chemical attack.

No masking required

Finally, what is really interesting is that these properties are exhibited at ultra-thin film thicknesses.

Typically a dry film can be 1-2um or even less.

This means that masking generally is not required for circuit boards before application.  Therefore, you can dip the whole product into the liquid and there is no issue with electrical contact.

This can lead to significant cost savings in production.

What other properties do the fluoropolymer coatings have that may be relevant in electronics?

SCHUK 2

As already mentioned these hydrophobic coatings have very specialised properties.

They can include:

  • Being highly hydrophobic (water repellent)
  • Having a high moisture barrier
  • Requiring no masking before application
  • Being highly oleophobic (oil repellent)
  • Having a high chemical resistance
  • Having a high lubricity
  • Having high dielectric properties
  • Providing high corrosion resistance
  • Providing good abrasion / wear resistance

Note, not all fluoropolymer coatings have all of the above properties. But, some coatings can in fact have almost all of the properties.

The fluoropolymer coatings are extremely flexible coatings and becoming more prolifically used throughout engineering.

What sectors of industry are fluoropolymer coatings being used in protecting electronics?

SCHUK3

Fluorinated coatings are used to protect electronics in almost all industrial sectors.

They include:

  • Aviation
  • Aerospace
  • Defence
  • Automotive
  • Industrial
  • Oil & Gas
  • LEDs
  • Medical
  • Optics
  • Telecommunications
  • White goods / Commercial

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

What are the major differences between a fluoropolymer coating and a conformal coating for protecting an electronic printed circuit board or assembly?

There are several key differences between a conformal coating and a fluoropolymer coating.

They include:

  • Hydrophobic Properties – A fluoropolymer coating is generally hydrophobic in nature. It repels water when the water is on the surface of the coating.
  • Extremely thin coating – The fluoropolymer coating is normally applied a lot thinner than a typical liquid conformal coating. This is due to its superior performance when repels liquids
  • No masking – Due to the extremely thin fluoropolymer coating applied (<1-2um), the components that normally require protecting (connectors, switches etc) from the insulating liquid conformal coating may not need to be masked for the fluoropolymer. The circuit board can be completely submerged in the liquid with no masking applied without fear of damaging the connections.
  • Simple process – No masking means an extremely fast application process
  • Fast drying – due to the thin nature of the fluoropolymer coating and the solvents normally used the coating dries extremely quickly.

Find out how we can help you with your ultra-thin hydrophobic coatings now.

Contact us to discuss your needs and let us explain how hydrophobic coatings could work for you.

Contact us now.

How thick should I apply my conformal coating?

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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

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

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.
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

 

What are the alternative materials to liquid conformal coatings?

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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?

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?

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

 

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