Cleaning and conformal coating

Co-authors and contributors

  • Dr Lee Hitchens, Nexus

It may not be necessary to clean a circuit board before conformal coating.

Cleaning of a circuit board before conformal coating application is desirable but not essential.

However, the cleanliness of the circuit can be crucial for both the short-term production process and the long-term reliability of the circuit.

Key questions

There are many questions relating to conformal coating and cleanliness that are regularly asked.

These include:

Why clean for conformal coating application?

The cleaning of the circuit is normally done for two main reasons before conformal coating application.

These are

  • Contamination removal
  • Process improvement

Contamination removal

The removal of harmful contaminants from the surface of the board before coating application could be important as it  may affect the long-term reliability of the circuit.

Defects like corrosion can be devastating to a circuit performance in the field.

Process improvement

Cleaning can aid the conformal coating application and avoid conformal coating defects like de-wetting and delamination.

It can also promote adhesion of the coating to the circuit board.

This surface preparation can be important, especially where coatings may have compatibility issues with the circuit board.

Cleaning a circuit board before conformal coating may improve the coating quality and minimise defects.
Cleaning a circuit board before conformal coating may improve the coating quality and minimise defects. Photo courtesy of SCH Technologies

What is being cleaned when circuit boards are washed?

Cleaning in conformal coating processing is used to remove many different types of contaminants.

The residues can come from many areas including

  • Board laminate manufacture
  • Component manufacture
  • Soldering assembly processes (fluxes)
  • Glueing and ruggedising processes
  • Operator handling (finger prints, hair)
  • Machine contamination (oils and greases)
  • Environmental contamination (dust)

Removing these residues may be a priority depending on their harmfulness.

Cleaning is used to remove many different types of contaminants from the manufacturing and assembly processes. They can affect the long term reliability of the circuit after conformal coating.
Cleaning circuit boards before conformal coating can be critical to removing resides from the manufacturing process. Photo courtesy of SCH Technologies

How should I clean the circuit board?

Cleaning circuit boards before coating is a huge topic by itself.

Successful cleaning of circuits can be achieved by a variety of techniques.

These cleaning techniques include:

  • Aqueous chemistries
  • Solvent / chemical cleaning
  • Plasma cleaning

The key to success in cleaning is similar to the success made with coating.

You need to match the cleaning process, materials and the circuit board together.

This will give the best results for application of the conformal coating.

How do I validate my cleaning process?

There are many techniques that can be used to measure cleanliness.

They include many IPC test methods. The techniques available include

  • Ionic Contamination Testing (ROSE)
  • Ion Chromatography (IC) or High Performance Ion Chromatography (HPLC)
  • Surface Insulation Resistance (SIR) testing
  • Further information can be found in the IPC HDBK 001 on different cleanliness assessment methods.

 

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