The science behind fluoropolymer coatings for protecting electronic circuit boards
Nano-coatings are being used regularly to protect printed circuit board assemblies.
This is because the material they are made of fluorinated polymers and these materials have very specialized properties that produce very different results to traditional conformal coatings.
So, what are the unique properties of a Nano-coating?
To understand the properties of a Nano-coating you have to understand what a fluoropolymer coating is made of.
Typically, the coating itself is comprised of fluorocarbons and characterised by carbon-fluorine bonds.
Since the coating is made of fluorocarbons then the film surface is not susceptible to Van der Waals forces (interfacial electrostatic bonds).
Therefore, the surface energy of the fluoropolymer coating is extremely low and hydrophobic (water repellent). It acts like Teflon on a frying pan.
This non-wetting of water on the circuit board is one of the many key properties making them so popular.
What other properties do Nano-coatings have that may help protect circuit boards?
For electronic circuit board assemblies there are several key properties that are being used.
These include being:
• Hydrophobic: Being highly water repellent
• Ultra-thin: Protection whilst being extremely thin
• High moisture barrier: Low water vapor transmission rate provides excellent corrosion resistance
• Chemically resistant: Having a high chemical resistance helps protect the circuits from chemical attack.
• Good dielectrics: fluoropolymer coatings have high dielectric properties
However, to really understand the benefits you have to look at the key difference compared to a conventional conformal coating.
That is that no masking is required when applying the Nano-coating.
The key reason for using a Nano-coating in protecting electronics is that no masking is required whilst applying the coating to the printed circuit board.
In the image above the connector is coated completely in the Nano-coating. It was just dipped in the coating. The image shows the water is being repelled from the connector. However, electrically the connector works perfectly fine.
So, why is there no need to mask when using a Nano-coating?
First, consider a normal conformal coating is applied at typical thicknesses of 25um or more.
Also, the conformal coating is a high insulation material.
Therefore, at this thickness the conformal coating would electrically insulate components like connectors and it must not be applied to any part that needs electrical conductivity.
However, this is not a problem for a Nano-coating.
Since the Nano-coating can be applied at ultra-thin thicknesses (1-2um in thickness or less) without any protection performance reduction, then the extremely soft coating is easily removed or scratched away when the connectors are joined and the electrical circuit is easily made.
This key parameter of not requiring masking during Nano-coating application combined with the hydrophobic nature of the coating material makes the Nano-coatings highly effective in protecting electronic circuit boards at a very low cost per unit.
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Five key facts about Parylene when protecting printed circuit board assemblies
- The Parylene conformal coating process is a very specialised vapour deposition application method using specialist vacuum chamber systems. This differs significantly to all of the other liquid conformal coatings available on the market that are applied by spraying, brushing and dipping.
- Parylene coating is completely conformal and uniform to the surface of the Printed Circuit Board (PCB) or product. It is also pinhole free. Therefore, components with sharp edges, points, flat surfaces, crevices or exposed internal surfaces are coated uniformly without voids.
- Parylene coating provides an excellent moisture and gas barrier due its very low permeability. This means that electronics circuit boards coated in Parylene generally are more “waterproof” than the same electronics coated in a liquid conformal coating.
- Parylene is unaffected by solvents (it has very high chemical resistance) and is very effective against salt attack.
- Parylene has excellent electrical properties. This includes having low dielectric constant and loss with good high-frequency properties, good dielectric strength, and high bulk and surface resistance.
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What is a fluoropolymer nano coating and how can it protect my circuit board?
A fluoropolymer Nano-coating is an ultra-thin film comprised of fluorocarbons and characterised by carbon-fluorine bonds.
Chemically inert, fluorocarbons are not susceptible to Van der Waals force. This means that films formed using these materials are non-stick (hydrophobic and water repellent) and friction reducing.
Also, due to the fluorine bonds, these Nano-coatings demonstrate a high level of chemical resistance to acids, bases and most solvents.
This makes them interesting materials for protecting electronic circuits.
Click here to read more about Fluoropolymer nano-coatings.
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What application methods are available for applying conformal coating?
What application methods are available for applying conformal coating?
Conformal coatings can be applied to printed circuit boards (PCB) in the production process environment in many alternative ways.
Listed below are the common methods of applying the conformal coating materials.
- Brushing
- Aerosol spray
- Batch spray
- Selective spray
- Dipping
- Vapour deposition
Click to read more on about application methods available for applying conformal coating
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What is a hydrophobic acrylic conformal coating?
There are several reasons for using a conformal coating or Parylene to protect a printed circuit board (PCB).
They include:
- High insulation protection
- High moisture and humidity protection
- Chemical and temperature resistance
- Ruggedisation
- Improve dielectric properties
- Barrier protection against particulates
However, one property that most liquid conformal coatings do not possess that is extremely useful to have is being water repellent or hydrophobic.
Click to read more about hydrophobic acrylic conformal coatings.
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Improve your conformal coating masking process reliability with custom boots
One of the most underestimated reasons for using conformal coating masking boots is that they improve the reliability of the process.
This is because they don’t leak as easily as conformal coating masking tape can!
The reality is that a well-designed boot will not allow conformal coating to penetrate into a component if it’s placed correctly; and the fact is that this is a very easy thing to do.
An operator using masking tape has to continuously show care and attention when applying the tape to the components. The level of skill required is high.
The level of skill required to apply a masking boot is much lower.
So, fewer errors are made and there are less costly repairs due to leaks.
Therefore, not only do you save up to 60% of your conformal coating masking costs due to reduced process times with boots but you can also improve the reliability of the masking process.
Need to know more about conformal coating masking boots in your application process?
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Conformal Coating Outsourcing: What are the “Range of services” you should expect when you subcontract your coating work?
A conformal coating subcontract service should be able to provide:
- Many methods of conformal coating application techniques so that the best option is chosen for your circuit board. This includes selective robotic spraying, dip coating, and batch spray.
- Be able to apply many different conformal coating materials including both liquid and parylene conformal coatings so the correct coating is chosen for the project
- a high level of process control through an ISO 9000 system that provides full control of the conformal coating process.
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We guarantee to offer the lowest price solutions on a like for like basis for our subcontract coating services through our North America, Europe and Asia facilities.
How can we say guarantee this?
- We are experts in what we do! that means you get the best prices
- We provide conformal coating services at the source to the customer where we can
- This means we benefit from lower costs in our facilities which we can pass on as savings
- We have the full range of conformal coating processes and materials to offer so the customer gets the right application method and not a process which is isn’t fit for purpose.
This helps SCH provide the lowest cost solution without compromise to the customer.
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Links of Interest
Want help in Selecting a Conformal Coating Material. Then use our New Technical Bulletin
Choosing the right conformal coating material for your process can be difficult. You need to consider several factors which if you are lucky will all add up to at least one material choice. If not, then compromises are required.
Factors to be considered are:
- Temperature Operating Range
- International, Customer or National Standards
- Environmental Considerations
- Chemical Resistance
- Requirement to Rework the Conformal Coating
- Application Process Considerations
- Curing the conformal coating
- National, State, Regional Legislation and Insurance
- Supplier Performance
- Price
Each of these factors is examined briefly in our new Technical Bulletin How Select a Conformal Coating Material. It is written to allow an insight into the complexity of selecting a conformal coating material and gives you everything you need to ask to ensure you get it right.
Click Technical Bulletin How Select a Conformal Coating Material to download the PDF to understand what we can offer you.
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What information do I need to provide to get a conformal coating quotation for subcontract service?
When deciding to look at outsourcing your conformal coating process there are fundamental questions you need to answer and information to be provided to allow us to provide an accurate quote.
Questions to be answered include:
- Do you require the circuit boards to be cleaned or is this a no clean process?
- What are your expected volumes of PCBs to be processed?
- What turnaround time do you require on the service?
- What conformal coating material do you want applied?
- Do you have photos and /or masking drawings of the PCBs?
- How big are the PCBs for costing purposes?
- Do you have a particular coating process you prefer to be used?
- Do you have any masking requirements before coating application?
- What conformal coating standards do you require the PCBs to be inspected to?
- Are there any materials on the PCB such as silicone RTV that can cause problems when processing?
- Are there any special requirements?
These are the basic questions and each of them will lead to further questions. As with many projects, many answers are unknown and SCH can help develop the conformal coating process with you.
Take a look at our conformal coating services introduction to understand what we can offer you.
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Conformal Coating 