Using custom masking boots for the conformal coating masking process saves time, money and improves quality. Find out why….
The use of various masking materials such as tapes, dots, and liquid latex can be an effective process in protecting components from ingress of conformal coating on a printed circuit board assembly.
However, the masking process can be difficult and time-consuming. This can increase the process costs significantly.
In fact, in many cases, the masking and de-masking processes can be >75% of the actual conformal coating process time and costs.
Using recyclable masking boots as an alternative to masking tapes, dots, and latex
Here are three good reasons to change to masking boots and save up to 80% of your costs compared to traditional methods like masking tape and dots:
- The masking time is reduced significantly. Masking boots can be 4-5 times quicker to use than masking tape.
- De-masking time is reduced significantly. Again it is much quicker to remove masking boots than tape.
- Masking boots don’t leak as easily as masking tape. So, there is less likely to be repaired.
These reasons mean you can save a lot of money very quickly when switching to masking boots.
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Why does the solids content of my conformal coating matter for costing a printed circuit board for application?
The amount of solids content in a conformal coating is the amount of actual material available to be applied to the circuit board and that will protect the circuit board assembly.
The more solids you have the more circuit boards you can coat.
So, you want to have as much solids as possible per liter when you buy the material.
Caution –Check the conformal coating solids is at the right viscosity for application!
You also need to take care when comparing individual materials from different companies.
The differences in both solids content and viscosity can be striking and you can be wasting a lot of money on solvents that literally evaporate away.
The first stage in checking this is to determine the final solids content of the material that you will use in production. That is the correctly blended coating ready for application at the right viscosity.
Take the following example that is typical of conformal coatings sold commercially around the world.
Material X is 35% solids as sold.
Its viscosity is 190 cps approx. at this solids content.
However, to spray the coating it must be at 24 cps approx. So, the coating must be diluted by 50% with thinners to reach this viscosity.
This means material X is now 17.5% solids and a viscosity of 24 cps approx. This also means there is >80% of the material that evaporates away!
Check the market!
You cannot assume that all conformal coating materials are similar.
For example, SCH have a UL approved acrylic conformal coating that is 44% solids at 24 cps and ready to spray.
Comparing Material X (17.5%) and this particular material means that the higher solids coating has more than twice as much coverage power for the same liter of material.
If the coatings are similar in price at this viscosity then you need to buy at least 2x more of material X than the higher solids product to get the same coverage.
Quite a saving can be made if care is taken!
Want to find out more about coating coverage?
If you would like a spreadsheet that you can just punch the values in to calculate coating coverage and costs per PCB then contact us directly and we can send it through to you to help you.
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What are the main uses of Molecular vapor deposition (MVD) in protecting components?
Molecular vapor deposition (MVD) is a combined Atomic Layer Deposition (ALD) and Chemical Vapour Deposition (CVD) process that was developed to improve the protective performance properties of the individual ALD and CVD processes.
The MVD process provides protective thin films to many industries including:
- MEMS (Microelectromechanical systems)
- Semiconductors
- Industrial Inkjet Heads
- Display Technology
- Advanced Packaging
- Data Storage Industry
- Biomedical
- Genome Sequencing
- µfluidics
How is the MVD coating process used in different industries?
The MVD process provides low temperature vapor deposition of coatings with many different properties in many sectors.
Consider the examples below where an MVD coating has been used to provide the appropriate film properties:
Surface Energy Control
- Anti-stiction
- Hydrophobic
- Hydrophilic
- Oleophobic
- Oleophilic
- Lubrication
- Bio-functional layer
Device Protection / Package Sealing
- Moisture barrier
- Corrosion barrier
- Chemical barrier
- Gas/Oxygen barrier
Optical Films
- Anti-reflection coatings
Dielectric Films
- Electrical insulation
- Conformal films on high A/R
Adhesion
- Adhesion promotion
- Improved thermal stability
- Improved mechanical durability
The MVD process offers great flexibility of processing thin films and it has now been considered for electronics protection.
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Requirements for setting up a conformal coating facility
The set up of a conformal coating production line regardless of the application method has many similar characteristics.
Any coating facility will need the basic requirements put in place that would be standard for any piece of electronic manufacturing process.
These include ESD systems, facilities for the machines, the environmental requirements and the normal Health & Safety (HSE) considerations.
Also, the conformal coating production line, whether it is an operator manually brush coating printed circuit boards (PCBs) or an inline robotic spray coating process is typically made up of several stages.
These stages are shown below:
Not all the stages are mandatory or may be required. However, each should be considered on an individual basis.
Want to find out more about setting up a conformal coating facility?
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Three key points you should know about polyurethane conformal coatings when using them for protecting electronic circuit boards
A polyurethane (urethane for short and designated UR by IPC) conformal coating is part of the organic family of coating materials that also includes the acrylic and epoxy coatings.
Here are three key facts to consider when examining polyurethane conformal coatings:
- Most conformal coatings provide good humidity and moisture protection although some are slightly better in performance than others. UR type coatings are just as good on average as acrylic materials.
- A polyurethane coating has traditionally been used to protect electronic circuit boards against chemical attack due to their excellent chemical resistance. This protection allows electronic circuit boards to survive in highly aggressive environments and atmospheres such as the aerospace, military and industrial sectors. However, it does make repair a little more difficult as chemical resistance to a coating means more difficult to remove.
- Times are changing and whereas acrylic conformal coatings used to dominate 70-80% of the market, there is a shift in emphasis towards alternative materials due to higher specifications for protecting electronics. Many new conformal coatings (UV cure, two part thin film coatings) now comprise of urethane resin bases and are becoming more popular in high volume sectors such as automotive electronics. This is because the urethane resin lends itself to this type of technology more easily than the acrylic based resins.
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What are the different methods available for cleaning electronic circuit boards?
The topic of cleaning printed circuit board assemblies (PCBAs) effectively before application of conformal coating can be daunting. This is because the process of cleaning circuit boards can be difficult especially with so many variables to consider.
When considering cleaning the circuit you need to assess many factors including:
The board and component compatibility with the cleaning method
The ability of the cleaning method to remove the contamination effectively from the circuit
Any residues the cleaning process may leave behind that may be harmful to the circuit in the long term.
The reasons for cleaning the circuit (e.g. contamination removal, adhesion promotion etc.)?
After considering these factors you can compare with the processes available.
The main methods of cleaning printed circuit boards
The main methods of cleaning used in everyday electronics processing before conformal coating application can include:
- Aqueous washing
- Semi-aqueous washing
- Solvent & chemical washing
- Plasma surface cleaning
These processes can be mixed, the method can be varied but the fundamental concepts still apply.
However, whatever method you choose you still have to consider that the key to success in cleaning circuit boards is similar to the success made with conformal coating.
You need to match the cleaning process, the cleaning materials and the circuit board together.
If you do this then this will give you the best results for cleaning the circuit board assembly.
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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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How do I selective apply my conformal coating?
Selective application of conformal coating is this case is applying the conformal coating without using masking to shield components from ingress.
Technically using masking tapes, latex and boots is a selective process. But, we want to look at coating application without masking.
This leaves a couple of different options.
The first is brushing. This is a simple selective process that can be highly effective.
The second, and the more obvious option, is selective robot.
This process uses a small spray valve (there are many conformal coating spray valve types) that is attached to a robot that follows a set pattern applying the conformal coating selectively to the circuit board.
To read more about how to selective apply conformal coating, click here…
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Conformal Coating 