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.
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.
- 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.
- 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.
- Many wet chemistry cleaning processes can be eliminated. Methods using cleaning chemistries, water processing and drying energy become unnecessary.
- 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.
- The plasma cleaning process is a simple, safe and environmentally friendly technology.
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.
There are several reasons why a conformal coating may need to be removed from a printed circuit board or component.
However, the two main reasons I normally see are:
- The board or component may need to be reworked for electrical repair or improvement of functionality
- Poor conformal coating application has led to the requirement to repair the material and reapply the coating
Whatever the reason for removing the conformal coating the process is a challenge.
Whether it has been a localised repair to a component or a complete strip of the conformal coating it has always been difficult for the unlucky technician stuck with the job.
What are options for conformal coating repair and removal?
There are several main methods now available for both localised repair and complete stripping of the conformal coating.
- Soldering through the coating
- Chemical stripping of the material
- Mechanical abrasion with a tool like a blade
- Micro abrasion using particulates to “shot blast” the coating
- Plasma processing using a plasma gas for removal
So which is the right removal process for conformal coating?
None of the options are perfect.
All of them have there advantages and disadvantages. The key is to review the circuit board and its needs on an individual basis.
Some of the factors that influence the conformal coating removal process include:
- Conformal coating material type
- The size of the area to repair
- The components sensitivity to the repair process (will they get damaged?)
- The cost of the repair versus the value of the circuit board
- The health and safety implications to the operator carrying out the repair
All of these factors and more can influence the choice or even whether the operation takes place.
After all, the cost of most electronics nowadays can be so low that the repair process is not cost effective!
To find out more go to the Nexus eBook section on conformal coating removal or contact us directly and we can help.
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Dr Lee Hitchens is the Author of the Nexus eBook and a main contributor to Nexus.