Five key facts about plasma cleaning for conformal coating processing

  1. Plasma cleaning can clean surfaces of the circuit board 100% to improve adhesion and surface energy of the product. Generally, conformal coatings must exhibit good adhesion in order to be effective.
  2. There is no single theory that describes the property of adhesion for coatings. There are several basic mechanisms for coatings that are known to define good adhesion. They are adsorption, chemical bonding, and mechanical interlocking:
  • Adsorption is where the molecules in the conformal coating wet or flow freely over the substrate and make intimate contact with the substrate. This forms interfacial (electrostatic) bonds with van-der-Waal forces.
  • Chemical bonds are formed at the interface between the conformal coating and the substrate.
  • The conformal coating film penetrates the roughness on the substrate surface. This results in mechanical interlocking once the coating dries.

All three of mechanisms do not have to occur to form good adhesion. Depending on the specific conformal coating system, substrate, and application method, different mechanisms could work. However, good wetting or adsorption is normally required.

  1. Many wet chemistry cleaning processes can be eliminated. Methods using cleaning chemistries, water processing and drying energy become unnecessary.
  2. The significant improvement in adhesion enables the use of alternative conformal coatings and other chemical vapour deposition coatings (CVD) that may have difficulty adhering to circuit boards without the treatment.
  3. The plasma cleaning process is a simple, safe and environmentally friendly technology.

Plasmatreatment of circuits collage

Plasma cleaning can clean surfaces of the circuit board 100% to improve adhesion and surface energy of the product. Generally, conformal coatings must exhibit good adhesion in order to be effective.

 


Need to find out more?

For further information on plasma cleaning for conformal coating processing then contact us directly.

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.

 

What application methods are available for applying conformal coating?

 

Conformal coatings can be applied to printed circuit boards (PCBs) in the production process environment in many different ways.

Listed below are the common methods of applying conformal coating materials:

Click on each to review each conformal coating application technique in our free ebook online.

Nexus
Conformal coatings can be applied to printed circuit boards (PCBs) in the production process environment in many different ways including spraying selectively, batch spraying and dipping.

The holistic approach to conformal coating application methods 

It is possible to split the different application methods and their suitability in many different ways including:

  • Compatibility with the conformal coating material
  • Design of the circuit board
  • Suitability to low, medium and high volume
  • Manual versus automatic process
  • Type of method of application
  • Level of control required

Each of the various coating methods has different advantages and disadvantages.

This relates to the holistic approach to conformal coating processing. It states that you should consider the conformal coating material itself, the application process and the circuit board together and not as three separate entities.

However, when considering the application methods it is possible to make some assumptions that help in selection.


Need to find out more?

For further information on conformal coating application methods then 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 thick should I apply my conformal coating?

 

positector

The measurement of the conformal coating thickness on a printed circuit board (PCB) to ensure internal and international standards are met is now a standard process in production.

There are several methods for measurement of conformal coating thickness including dry and wet film processing. However, the most important factor is how thick should the coating be?

First, you can reference both internal and international standards like IPC A 610 for conformal coating application.  They can help a lot.

These standards will help guide you in the coating thickness required for a particular coating materials since the coating thickness suggested will be dependent on the resin of the conformal coating.

For example, an acrylic or polyurethane based conformal coating has a different coating thickness requirement to silicone-based materials.

Below are the suggested conformal coating thicknesses from the IPC A 610 standard:

  • Acrylic            30-130 μm
  • Urethane        30-130 μm
  • Epoxy             30-130 μm
  • Silicone          50-210 μm
  • Parylene        10-50 μm

Note, that this is the average thickness across the circuit board. It is almost impossible to achieve a homogeneous coating thickness with the liquid conformal coatings due to surface tension issues during drying.

Using this information you can now move forward and look at the application of the conformal coating.


Need to find out more?       

For further information on process control and conformal coating thickness then contact us directly.

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.

Things you should know about Parylene

What is Parylene?

Parylene is a conformal coating that is deposited as a gas in a vacuum chamber.

It is a completely different process to the liquid conformal coatings and its properties offer advantages and disadvantages in comparison.

Parylene is a dry process compared to the standard “wet” liquid conformal coatings.

Since Parylene is deposited as a gas its thickness is almost uniform across the whole circuit board.

 

The ABCs of Parylene

Parylene is an organic polymer conformal coating that is deposited as a gas in a vacuum chamber.

Therefore, the Parylene application process is a completely different process to the liquid conformal coatings.

This gives Parylene unique properties that are not possible with the typical liquid conformal coatings normally used in electronics protection.

 

Five key facts about Parylene

  1. Parylene is the trade name for a variety of poly(p-xylylene) polymers
  2. It is a conformal coating that is deposited as a gas in a vacuum chamber. This is different to liquid conformal coatings.
  3. The Parylene film is created via a controlled Chemical Vapor Deposition (CVD) process.
  4. It is a dry process compared to the standard “wet” liquid conformal coatings.
  5. This process makes Parylene a highly effective moisture and dielectric barrier that outperforms most liquid conformal coatings.

 

Three important points you should know about Parylene

  1. Parylene has unique properties that are not possible with the liquid conformal coatings.
  2. Parylene is a conformal coating that is deposited as a gas in a vacuum chamber.
  3. This is different to liquid conformal coatings that can be brushed, dipped or sprayed.

NEXUS FEATURE: Ask the Experts – What Challenges do subcontract coating services have when working with OEMs

One of the trickiest jobs is a take a PCB and conformal coat it. For a coating house this could be a board they haven’t even made. What issues arise that the subcontractors see that may help users of coating services get a better service? Experts from a variety of conformal coating services and houses around the world share their knowledge on issues that arise with them.

Ask The Expert: Dr Lee Hitchens, Nexus on Key Conformal Coating Material Challenges

“Out of all the Key Material Challenges I see on a regular basis, one of the most prolific is difficulties in adhesion to solder resist or to no clean residues and contaminants.“
 “It can be as basic as the coating just will not stick to the PCB or it runs away from areas on the PCB. At other times, it’s interpreting just how well the coating is stuck and determining if it’s good enough for the customer? Normally, this cannot be answered instantly and leads to some serious thinking!”

Visit the Nexus Associate Experts Section and read what other experts have to say about conformal coating material challenges.

Ask The Expert: Karl Hardcastle, SCH Services Ltd, Subcontract Conformal Coating Service on Key Conformal Coating Material Challenges

“One of the biggest issues we face is availability of the materials. As a subcontract coating house we generally have to use the coating selected by the customer. This can have dramatic issues occasionally when lead times on products can stretch into weeks or months and the customer wants the product now!”
“Conformal coating is one of the last processes on the PCB. Coating houses are normally making up the time lost in other areas. If you can plan the production to coincide with the material supply chain it’s a great help!”

Visit the Nexus Associate Experts Section and read what other experts have to say about conformal coating material challenges.

Ask The Expert: Gordon Watson, SMS Automation, Conformal Coating Equipment on Key Conformal Coating Material Challenges

“Our greatest Challenge is establishing good communication at an early stage with the key decision makers to determine the critical factors such as material specification, performance and requirements. Customers should also think of future needs when discussing conformal coating application systems rather than limit their choices to what is available on a standard machine.”

“Our skill is in combining machine building and automation skills with knowledge of the process of conformal coating and so it is important that we obtain a thorough understanding of our customers’ requirements and quickly formalise them into a  plan as quickly as possible.”

Visit the Nexus Associate Experts Section and read what other experts have to say about conformal coating material challenges.

Ask The Expert: Frank Hart, Sales and Marketing Director, PVA Conformal Coating Robotic Systems on Key Conformal Coating Material Challenges

“There has been much segmentation in the coating industry and this has driven chemical companies to the most prominent current trend in the marketplace, customization.  No longer is one coating chemistry versatile enough for the changing demands of the consumer.  It is no longer unusual to take a long standing coating material and have 8-10 versions of the formulation on the market.  Viscosity modifications, sometimes from 20 cps all the way to a non-slumping gel version, tend to be the most popular.  If you are looking to modify the flow characteristics, limit wicking into keep out areas, produce a dam, or control the solvent to resin ratio, there is typically a product tailored to your requirements.”

“Maybe the appearance of the coating is of greater importance to the end user.  This can be as radical as the physical color of the coating itself or maybe just the level of fluorescence under black light.  Some end users do specify the coating needs to be visible to the operator from a predetermined distance from the application, or perhaps they are using an automated AOI system.  Maybe your technology is proprietary to the point that an opaque coating protects your design in lieu of clear transparent materials.  Such requirements may drive an end user to request a custom formulation with these properties.”

“No matter what the request may be, from appearance to viscosity, to the cure mechanism or even changing the solvent carrier to a VOC friendly alternative, customizing formulations has become the norm more than the exception and chemical manufacturers are marketing these products as standard solutions.  End users should always work with formulators to assure that any modification to the original chemistry does not affect performance properties such as adhesion, protection, or curing. From an application standpoint, having your chemistry slightly altered may affect a variety of process parameters so always consult your material manufacturer and equipment manufacturer’s applications experts prior to making any formulation change.  In an automated process the changes may be as simple as modifying the robot speed or adjusting the path spacing to compensate for the new flow characteristics, or it may require a complete redesign of the fluid system and spray/dispensing valves….  But these factors can always be pre-qualified in a test laboratory.”

Visit the Nexus Associate Experts Section and read what other experts have to say about conformal coating material challenges.

Ask The Expert: Dave Prouse, Diamond SCH, Conformal Coating Equipment on Key Conformal Coating Material Challenges

“One of the biggest challenges is talking to a customer and finding that a conformal coating material and a conformal coating system has already been specified and the two are not easily compatible.”
“Linking the two in the design stages is critical in stopping the cost of the project multiplying by 2-3 times and causing untold misery and difficulties downstream.”

Visit the Nexus Associate Experts Section and read what other experts have to say about conformal coating material challenges.