What are the main methods for cleaning contamination from a printed circuit board before conformal coating?

Successful cleaning of electronic circuit board assemblies can be achieved by a variety of techniques.

These include:

• Aqueous wash
• Semi-aqueous wash
• Solvent & chemical wash
• Plasma cleaning

Each of these methods can effectively remove contamination. However, the key to achieving success in cleaning the contamination is similar to being successful with applying conformal coating. You need to match the process, the materials (the contamination) and the circuit board together.

If you do this then this may give you the best results for cleaning the circuit board assembly.

So why clean circuit boards before conformal coating?

Cleaning printed circuit boards (PCBs) before conformal coating application is usually done for two reasons:

These reasons are:

• Contamination removal
• Adhesion improvement

Contamination removal is normally done to stop long term problems like electrochemical migration and corrosion from occurring.

Adhesion improvement is normally done for improving the process (especially around de-masking) and also for the long-term reliability of the circuit board and to prevent problems like coating delamination.

Both reasons have different effects on the lifetime of the circuit board but both can be equally important.

What types of contamination can be found on a printed circuit board?

Cleaning can be used to remove many different types of contamination from the circuit board that were deposited during the manufacturing and assembly processes upstream.

The contamination 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 these contaminants may be a priority depending on their harmfulness.

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 What are the main methods for cleaning contamination from a printed circuit board before conformal coating?

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