What are the different techniques for cleaning a circuit board before conformal coating application?

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Cleaning circuit boards before conformal coating is a huge topic by itself. This is because cleaning circuit boards can be challenging.

However, successful cleaning of electronic circuits can be achieved by a variety of techniques.

The main methods of cleaning can include:
• Aqueous wash
• Semi-aqueous wash
• Solvent & chemical wash
• Plasma cleaning

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.


Why clean circuit boards before conformal coating?

The cleaning of a printed circuit board (PCB) before conformal coating application is normally done for two key reasons:

These are:
• Contamination removal
• Process improvement

They have different effects on the lifetime of the circuit board but can be equally important.


What types of contamination may be present on a circuit board?

Cleaning is used to remove many different types of contaminants from the manufacturing and assembly processes.

The residues can come from:
• Board laminate manufacture
• Component manufacture
• Soldering assembly processes (fluxes)
• Glue and ruggedizing processes
• Operator handling (finger prints, hair)
• Machine contamination (oils and greases)
• Environmental contamination (dust)

Removing the contamination may be a priority depending on their harmfulness.


Need to find out more?

Click conformal coating cleaning for further information or contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

How do I selective apply my conformal coating without using masking?

Selective spraying of conformal coating using an automated robot system is one of the widest used application methods in high volume processing.

The principle is that the conformal coating is applied selectively by a small spray gun to the circuit board to the areas requiring coating only.

The selective process deliberately does not apply the conformal coating to areas that normally require masking such as connectors and other components.

This selective application of the conformal coating to the circuit board can avoid using a time consuming masking process and costs can normally be reduced.


What equipment do you need for selective spraying?

A specialist robotic system designed for application of conformal coatings is normally required for selective coating.

The robotic system will be fitted with various conformal coating spray valves that apply the different types of conformal coating material to the circuit board using different spray patterns.

The level of movement of the robot can vary with systems having three, four, five and even six axes of movement for the spray valves.

Want to find out more about application of conformal coatings to circuit boards by selective robots?

Click to find out more about questions such as:

  1. What equipment do you need for selective spraying?
  2. What specialist valves are required for applying different types of conformal coating?
  3. Which conformal coatings can be used in selective spraying?
  4. Is selective spraying of conformal coating a complex process?
  5. How cost effective is selective spraying of conformal coating as a process?
  6. What variables control the quality of the conformal coating finish in selective spraying?
  7. What are five advantages of the selective spray conformal coating process?
  8. What are five disadvantages of the selective spray conformal coating process?

Need to find out more?

Go directly to our conformal coating selective spray application section or contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

Images 1 and 2 courtesy of PVA (Precision Valve Automation).

How do I spray coat my printed circuit board with conformal coating?

Nexus 1Batch spraying of conformal coating on printed circuit board assemblies (PCBA) is one of the most widely used techniques in low and medium volume production processing.

Typically, using either a compressed air spray gun or an aerosol, the conformal coating is sprayed across the whole of the circuit board to provide the protection it requires.

The batch spray process can produce a high quality conformal coating finish that gives the best protection due to good tip edge coverage of components.

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

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


What is a typical spray process for application of the conformal coating to the circuit board?

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Batch spraying using an aerosol or hand spray gun is normally a simple process.

A typical method of application for spraying is as follows:

  1. Dilute the conformal coating with thinners according to the manufacturers recommended instructions (typically the viscosity is close to 24cps and almost like water).
  2. Mix the blend thoroughly but without creating bubbles (if bubbles occur wait for them to dissipate) and apply a test pattern to ensure the material from the spray gun is flowing properly.
  3. If “spider webs” occur (similar to candy floss in the air) then dilute further with more thinning solvents.
  4. Position the circuit board horizontally
in front of the spray gun operator.
  5. Hold the spray gun at a 45° angle and at the recommended distance (typically 20 to 25 cm from the circuit board).
  6. Spray a thin and uniform coat onto the circuit board with an even motion using “spray and release” strokes in a raster pattern. Do not over apply too much liquid.
  7. Turn the circuit board 90°and repeat until the board has completed one complete 360° rotation.
  8. If a second coat is required, wait 2-3 minutes (may be longer with certain solvent types so check manufacturers recommended instructions) and repeat steps 5-7.

Once complete follow the cure instructions for the coating on the circuit board.


Need to find out more?

Go directly to our conformal coating batch spraying section or contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

The science behind fluoropolymer coatings for protecting electronic circuit boards

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Recently, fluoropolymer coatings are being used more often to protect printed circuit board assemblies. This is because they have very specialized properties that are very different to traditional conformal coatings and these properties are being utilized highly effectively.

To understand these properties you have to understand what a fluoropolymer coating is made of.

Typically, the coating is comprised of fluorocarbons and characterized by carbon-fluorine bonds.

The coating itself is not susceptible to Van der Waals forces (interfacial electrostatic bonds). Therefore, the surface energy of the fluoropolymer coating is extremely low.

This means that there is no adsorption of another coating or liquid on the surface of the fluoropolymer and the coating shows the familiar, hydrophobic, non-wetting characteristics with water and oil.

This non-wetting is one of many of the key properties making them so popular.

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The surface energy of the fluoropolymer coating is extremely low. There is no adsorption of water on the surface of the fluoropolymer and the coating shows the familiar, hydrophobic, non-wetting characteristics.


So, what other properties do fluoropolymer coatings have that help protect circuit boards?

Generally, fluoropolymer materials have very specialized properties.

For electronics the five key properties that are driving the interest in fluoropolymer technology are:

  • Being highly hydrophobic (water repellent)
  • Being extremely thin whilst still providing protection
  • Having a high moisture barrier and corrosion resistance
  • Having a high chemical resistance
  • Having high dielectric properties

To really understand the benefits you have to look at the key difference compared to a conventional conformal coating.


The key reason for using a fluoropolymer coating in electronics: No masking required

First, consider a conformal coating applied at normal thicknesses of 25um or more.

The coating is a high insulation material. Therefore, it must not be applied to a connector or part that can be damaged or needs electrical conductivity.

Further, the conformal coating naturally has good mar resistance and it cannot be easily abraded. It is tough to the touch and not easily removed.

So, if it was applied to the wrong component it would ruin the connection.

On the reverse side, a fluoropolymer coating can be applied at 1-2um in thickness and can still show the same performance characteristics.

Further, it is also extremely soft and shows almost no mar resistance when rubbed or abraded.

This allows the fluoropolymer coating to be applied to all connectors without fear of damage as the coating is easily removed or scratched away and the electrical circuit is easily made when the mating parts are connected together.

This key parameter of not requiring masking combined with the hydrophobic nature of the material and its other key characteristics makes the fluoropolymer coatings highly desirable in protecting electronic circuit boards.


Need to find out more?

Go directly to our Nano-coating fluoropolymer section or contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

Why use Parylene to protect printed circuit boards?

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Parylene is a conformal coating film that is applied using a specialised vapour deposition application process.

This means it is very different to all of the other liquid conformal coatings available on the market.


Three reasons why Parylene is better than traditional liquid conformal coatings

The fact that the Parylene film is deposited onto circuit boards in a vacuum leads to many unique advantages.

Here are three key reasons to use Parylene:

  1. The Parylene coating is completely conformal to the surface of the Printed Circuit Board (PCB) or product. The coating has a uniform thickness and is pinhole free. Therefore, components with sharp edges, points, flat surfaces, crevices or exposed internal surfaces are coated uniformly without voids.
  2. Parylene coating provides an excellent barrier that exhibits a very low permeability to moisture and gases compared to traditional liquid conformal coatings. This means that circuit boards coated in Parylene generally are more “waterproof” than the same circuits coated in a liquid conformal coating.
  3. Parylene has excellent electrical properties compared to normal conformal coatings. These include low dielectric constant and loss with good high-frequency properties, good dielectric strength, and high bulk and surface resistance.

Need to find out more?

Go directly to our Parylene section in Nexus  or contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

How do I dip coat my circuit board with conformal coating?

 

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Dip coating is a traditional conformal coating application method that has been used to conformal coat circuit boards for a very long time.

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 conformal coating drains away.

This leaves a conformal coated circuit board.


The key areas for dipping with conformal coating

Find out more by clicking these links:


Need to find out more?

Go directly to our conformal coating dip section or contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

Outsourcing your conformal coating project – The key points

So, you are considering outsourcing your conformal coating or Parylene process to a subcontract supplier.

What’s the next step?

Assuming you have decided this is the right choice then the next task is to choose the right service provider.

This can be as difficult as selecting the right PCB manufacturer or laminate provider. There are good contractors and there are others. There are small providers and there are large-scale turnkey solutions.

The obvious answer is “the right one for me” but how do you ensure that you make the right decision?

Here are a few of the questions you should ask before signing up to the wrong coating solution provider and stop you wishing you had kept the coating process in house.

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There are several questions you should ask before signing up to the wrong coating solution provider and stop you wishing you had kept the coating process in house!

The three key points to consider when choosing a subcontractor

When considering the supplier look at the three main areas.

The order you look at is up to you but ultimately you need to be happy in all three to keep sending the work out.

These three key areas are:

  1. Quality
  2. Turnaround time
  3. Price

If you get these three key areas correct then you have succeeded. Everyone will be happy and there are no more problems with conformal coating.

However, within each of these areas, lie a lot of questions to be asked and if one of them isn’t working properly then who knows what the consequences are around the corner.

So, let’s consider each of these areas in turn in the order they are listed.


Quality

Everyone wants good quality. But what does that mean?

Whose quality are we judging against and how do we reach agreement?

One of the most important factors in subcontract conformal coating services is to agree what the PCB coating finish should look like.

Sound simple?

It can be if you define exactly what you want as a customer. The problem comes when you don’t know!

The reality is most customers have a preconceived idea of what a conformal coated printed circuit board should look like and the key for the customer is to communicate this to the provider.

Let me give you an example.

Consider a simple connector on a circuit board like the one below.

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Then decide on what statement you agree with below:

  1. Only the pins must not have coating on but the rest of the connector body does not matter.
  2. The whole of the connector must have no coating on it all but there can be a gap of 1-2mm around it free of coating.
  3. The whole of the connector must have no coating on it all and there can be no area around the connector free of coating.

All three options provide a connector free of coating.  All three options work. All three options could be considered fine by various different customers.

However, the order they are stated is also lowest difficulty (aka cost) to highest difficulty to actually complete the work in a coating production line.

So, defining how you want to coat the board intimately impacts on the price of the project.


A key issue highlighted

Unfortunately, this highlights a key problem in conformal coating processing.

There are no standards that state what is the best solution and only guidelines. Ultimately, it comes down to a decision made by the customer as to how the PCB should be coated.

This means it is a crucial factor for both the customer and the supplier to define the level of quality. Get this right and most of your problems are sorted.

If the coating house is good they will help you define this from the beginning. They will not assume any level of quality but ask you what you need.

If they don’t help you then hope that they can guess what they need to provide you with.

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A key problem in conformal coating processing is that there are no standards that state what is the best conformal coating finish and only guidelines. Ultimately, it comes down to a decision made by the customer as to how the PCB should be coated.

So what’s the next stage in quality?

So, you have agreed what quality of finish you want. Assuming that you know which conformal coating material you want then the rest should be easy.

Well, that statement is right as long as:

  • The supplier knows how to use your coating material correctly
  • Has the right equipment to apply the conformal coating
  • Has selected the right process for your PCB
  • Knows what to do when things go wrong

So, what you really need to do is find a subcontract conformal coating supplier that knows a lot about conformal coatings or Parylene.


Turnaround Time

So, you are considering outsourcing the coating work to an outside contractor but want the PCB coated when you need it.

Unfortunately, conformal coating is normally one of the last processes in a long line of operations so any delays in the manufacture of the PCB is normally being compounded by sending it out to a coating house.

Therefore, you need a fast turnaround option and your coating service should be flexible on this, allowing you choices on getting the PCBs coated.

However, you may want to consider the speed you require the PCB to be coated since it can lead to:

  • Extra costs
  • Potential problems with the process
  • Mistakes due to staff and machine availability
  • Availability of material
  • Local or global supply
  • Low cost offshore facilities
  • Capacity

These factors can influence the price significantly.

So, we have examined quality and turnaround time. The critical factor that ties these two areas together is price. Let’s take a look at this area.


Price

“I want this PCB coated for 45 cents”, says the customer.

“Okay can we see the board”, says the coating service provider.

The customer produces a 12”x6” PCB with 25 surface mount connectors with via’s everywhere and asks for coating both sides and wants all of the connectors not to be coated.

Okay, we have a mismatch in perception and this sounds ridiculous. But, it happens more regularly than it should.

Some customers have no idea of what it costs to coat a PCB. After all it’s just coating.

However, it’s up to the coating house to educate them so that they can get what they need and reach the happy point of all three areas satisfied.

So, what price should it be?

Well factors to be considered by the subcontractor are:

  • Material specified by the customer
  • Process to be used on the PCB
  • Volume of PCBs to be supplied
  • Amount of masking / keep out areas on the PCB
  • Amount of coating to be used per PCB
  • Is there cleaning involved before coating?
  • Yes cleaning is required, extra cost added in
  • No cleaning is not required, may be extra cost for finishing process if a lot of contamination
  • Speed of turnaround required (impact on resources, drying, curing)
  • Quality required (how much time finishing, inspecting, how close to look?)

So, the last two factors, turnaround and quality, tie directly back to the price and in reality have a huge impact.

Therefore, we find unsurprisingly all free factors should be considered as a whole and not separately.

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Some customers have no idea of what it costs to conformal coat a circuit board. After all it’s just coating….

Summary

Subcontracting out your conformal coating process isn’t difficult if you look carefully at the three areas of quality, turnaround time and price.

If you can achieve all three with your subcontract coating house then you will be happy.

If you ignore one of the factors then it may be a less pleasant position.


Need to find out more?

Contact us directly and we can help you. Or go to our supplier pages and look up coating services globally.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.