Nexus has been examining Molecular Vapor Deposition (MVD), a new novel coating technique that may be able to offer superior protection to electronic circuit boards compared to the standard coating technologies like conformal coatings and Parylene.
The MVD process is a hybrid ALD (Atomic Layer Deposition) / CVD (Chemical Vapor Deposition) technique that uses multiple layers of ultra-thin coatings with differing properties to build a completely protective coating.
The results are proving to be highly effective and could change the industry in time.
But where did the MVD technology come from originally?
The Molecular Vapor Deposition (MVD®) process was found in 2003 by the SPTS MVD group located in San Jose, California.
SPTS provided nano-film technology processing, equipment and coating services, supplying to multiple markets including:
MEMS (Microelectromechanical systems)
Industrial Inkjet Heads
Data Storage Industry
How is the MVD coating process used in the different industries?
The MVD process provides low temperature vapor deposition of coatings with many different properties in many sectors.
Consider the examples of MVD coating use below:
Surface Energy Control
Device Protection / Package Sealing
Conformal films on high A/R
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.
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.
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.
Parylene is the trade name for a variety of chemical vapor deposited poly (p-xylylene) polymers used as moisture and dielectric barriers.
Although Parylene is a conformal coating it is different compared to the standard “wet” liquid conformal coatings in that it is deposited as a gas in a vacuum chamber and it is a dry process.
Although Parylene is a conformal coating it is different compared to the standard “wet” liquid conformal coatings in that it is deposited as a gas in a vacuum chamber and it is a dry process. Image courtesy of Plasma Rugged Solutions
This method of chemical vapour deposition (CVD) and the Parylene dimer material itself give Parylene unique properties compared to other traditional conformal coatings.
For Parylene there are five key areas that Nexus can help with.
There are a lot of different reasons for using a conformal coating material or Parylene to protect a printed circuit board (PCB).
These reasons can include:
High insulation protection
High moisture and humidity protection
Chemical and temperature resistance
Improve dielectric properties
A conformal coating can create a barrier against attack during the lifetime of the circuit board.
The coating material can prevent various types of particulate contamination reaching the surface of the circuit board, which can lead to problems such as corrosion.
High insulation protection
Conformal coatings can provide a high degree of insulation protection for the circuit board during its lifetime when applied as a protective lacquer.
The circuit board normally starts with a high level of insulation when it is first manufacture as it is normally clean.
However, with time in the field and its natural environment the circuit can degrade in different ways.
The conformal coating can slow this degradation down.
High moisture and humidity protection
Printed circuit boards can be vulnerable to moisture and humidity whilst in the field during its lifetime.
Most conformal coatings are highly resistant to moisture and humidity and this can lead to a reduction in leakage currents, cross talk, electrochemical migration, dendrite growth and arcing across the circuit board.
Chemical and temperature resistance
Some conformal coatings can be highly resistant to many types of solvents, chemical attack and be heat resistant.
Normally, a circuit board exposed to chemically aggressive environment would be attacked but the conformal coating can slow down the effects or even prevent them.
Conformal coating can prevent damage from rough handling, installation and reduction of mechanical and thermal stress.
Improved dielectric properties
Just as the conformal coating can protect the circuit from moisture it can also help to increase the dielectric strength on the circuit board between components and lead interconnects.
This enables the design of the PCB to be more compact and small.
Need to find out more?
For further information on using conformal coatings then contact us directly.
Analysing your conformal coating production process, whether its a conformal coating line or a Parylene batch system, can create huge benefits due to improvements made in the production performance.
Using our expert knowledge and experience from Nexus, we can examine your individual production processes and examine your output for your coating line.
This can save you money, time, and improve quality, depending on your needs.
A typical audit would include:
A site visit to audit your conformal coating facilities and processes surrounding the conformal coating area.
Discussions with staff members regarding the conformal coating processes, understanding their needs for production, the requirements for the product to be protected by the conformal coating and any other issues such as commercial or health & safety restraints
Analysis of the conformal coating process findings with recommendations for further improvements delivered in a report for future reference
We would work with you to understand your requirements an priorities. We can then tailor the system to fit your needs, whilst employing the best knowledge available for your field of production.
Let us help you and audit your conformal coating process line.