There are four key reasons why Parylene masking and de-masking is more difficult compared to liquid conformal coatings.
Parylene is a vapour. When you are masking against a gas rather than a liquid then there is more of a challenge. So you need to provide a much better barrier with the masking process compared to the liquid coatings.
Parylene is immersion. Most liquid conformal coatings are sprayed and so the capillary is less compared to immersion in a limitless supply of material.
Stripping Parylene is hard. It is much harder to remove unwanted Parylene material on components that should not have been coated. Parylene is chemically inert (therefore harder to strip off or remove) and more difficult to see (no UV trace in most Parylene coatings). Mistakes can be more costly.
The Parylene can bond more to the masking materials. When the Parylene is deposited on the masking materials and circuit board it can bind the two together and it can take significant effort and care to remove the masking materials without damaging the board or the Parylene coating integrity.
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.
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:
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.
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.
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.
Then decide on what statement you agree with below:
Only the pins must not have coating on but the rest of the connector body does not matter.
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.
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.
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.
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:
Potential problems with the process
Mistakes due to staff and machine availability
Availability of material
Local or global supply
Low cost offshore facilities
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.
“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.
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.
Polyurethane (UR) conformal coatings generally provide good humidity & moisture protection although not always as good as the acrylics. However, it normally is enough to protect the circuit board.
Normally, urethanes are selected for their excellent chemical resistance. This is because the coatings cure rather than dry. That is they cross-link by one of many different methods including heat, UV, moisture and catalysed cure.
Typically they have higher dielectric properties compared to the acrylic conformal coatings.
Their chemical resistance, however, can be a limitation since rework and repair generally is more difficult than the acrylic coatings.
UR coatings are normally available as either single or two-component formulations. Pot life is dependent on the cure mechanism but can be more limited than the acrylic coatings.
Normally, conformal coatings must exhibit good adhesion to the PCB in order to be effective in the long term in protecting the circuit.
Therefore, the surface properties of the circuit board can be critical to the success of the coating adhesion.
Cleaning of circuit boards before conformal coating has taken place for many years.
The reasons for doing this have always remained the same:
Improve the surface cleanliness of the circuit to protect against corrosion and the effects of contamination on the surface from the process.
Improve the surface energy of the surface to improve the adhesion of conformal coating.
Traditionally, cleaning and adhesion promotion has been achieved by either using a wet chemistry treatment like washing or applying extra undercoats (priming).
Now, there are new methods and techniques appearing on the market for improving cleaning, adhesion and actually coating circuit boards differently to the traditional methods.
One of these techniques is plasma treatment.
Why use Plasma to clean circuit boards?
Here are a few key reasons to use plasma cleaning and surface treatment of printed circuit boards:
Plasma cleaning can clean surfaces of a product 100% to improve adhesion and surface energy of the product.
Many wet chemistry cleaning processes can be eliminated. Methods using cleaning chemistries, water processing and drying energy are unnecessary.
Activate the surface of the circuit by changing the surface energy. This allows easier bonding and better adhesion to the surface. The significant improvement in adhesion enables the use of alternative coatings that may have difficulty adhering to surfaces without the treatment.
The plasma process is a simple, safe and environmentally friendly technology.
The plasma process has both batch (offline) and inline capability.
This means the plasma process can be highly effective on printed circuit boards.
Need to find out more?
Contact us directly and we can help you with your plasma treatment requirements.
Nexus has been examining a new, novel technique that may be able to superior protection for electronic circuit boards compared to the standard coating methods like conformal coatings and Parylene but also actually be cost-effective.
This process is a hybrid ALD (Atomic Layer Deposition)/CVD (Chemical Vapor Deposition) technique called Molecular Vapor Deposition (MVD).
This method uses multiple layers of ultra-thin coatings with differing properties to build a completely protective coating.
So, why is this new coating so good compared to Parylene and other conformal coatings?
The final MVD coating built up is much thinner than the other traditional coatings including Parylene. However, its protective performance has been found to be superior to them all in most categories of testing so far.
Key performance indicators like Water Vapor Transmission Rate (WVTR), optical clarity, temperature resistance and hydrophobicity have been found to be much better than the other coatings.
Further, the really exciting part about this technology is the cost of processing that is extremely low.
Since the coating is extremely thin then it has been found that no masking is required. This is because when components like connectors are joined together then the ultrathin coating does not prevent electrical connection.
This means that the cost of process is purely the cost of application of the material and nothing else.
Since the process is relatively low cost then this does offer a very interesting alternative to the traditional coating materials.
So what does the science of Molecular Vapor Deposition coating (MVD) look like?
The actual film is built up of alternating layers of ALD and CVD thin coating layers.
The ALD is a ceramic-based material providing the insulating properties. The CVD film provides the barrier protection.
First, an ALD layer is applied to the substrate. Then a CVD layer is applied. Then a further ALD layer is applied and so on.
This continues until the correct number of layers is built that has the right protection.
Finally, once the required film thickness is achieved with the alternating layers, then a final hydrophobic thin film layer is applied, that combines with the ALD and CVD layers to provide a highly effective barrier.
So, just how good is the hybrid coating as a protective material for electronic circuit boards?
Generally, with protective coatings for electronics then Parylene is considered the gold standard in most cases.
So, Nexus compared Parylene with the MVD material.
Wear resistance/Handling Ease
Water Vapor Transmission Rate
Temperature Resistance (extended time)
Adhesion to various materials
Scalable to large production
8 – 12 hrs
8 – 12 hrs
Good – Excellent
Low – Med
What Nexus also identified for the material were some key properties.
The Water Vapor Transmission Rate (WVTR) is superior to Parylene so the coating is far more waterproof.
Coating adhesion is superior as it covalently bonds to the substrate. So, the lifetime of the material will be better on the circuit.
The temperature range of the material can be up to 350C without any degradation.
The hybrid coating is UV stable whereas Parylene in general is not. This is an important criteria for coatings exposed to UV light.
The coating stayed 100% transparent during testing (no loss of lux).
The coating thickness of the hybrid material is x10 LESS than the Parylene. This aids light transmission and electric connectivity
So, in reality the MVD material could just be what industries like the automotive and LED sectors are looking for in protecting their circuits where cost and protection abilities are critical.
Need to find out more?
Contact us directly and we can help you with this new material.