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 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.

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.

How do I brush coat my conformal coating?

The application of a conformal coating using a brush to “paint” on the material to the circuit board is a common practice all over the world.

Generally, it is done as a final touch up process after the main application method is used.

However, it can also be done in mainstream production.

Conformal coating brushing in an inspection booth_NEXUS1

Applying the conformal coating

The operator according to the requirements of the circuit board applies the conformal coating selectively with the brush.

Areas not be coated are avoided.

The key for success with brushing conformal coating is the technique of application.

The correct method is to flow the coating on. The coating should be loaded on to the brush and flowed onto the circuit.

The material should not be brushed on like paint.

Screenshot of Nexus brush coating
Watch a video on brushing conformal coating.

Need to find out more?

Click conformal coating brushing 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.