De-masking and conformal coating

Co-authors and contributors

  • Dr Lee Hitchens, Nexus

What is the de-masking process in conformal coating?

conformal coating de-maskingWhen masking has been used to prevent conformal coating penetrating into wrong areas, then normally the masking has to be removed.

This is because the masking is a temporary process.

That is, after completion of the coating application, the masking should be removed.

The removal of the masking can lead to the next stage that is Finishing.

Conformal coating demasking in an inspection booth cropped
De-masking is the removal of masking materials after the conformal coating application.

What is the finishing process in conformal coating?

When the masking is removed the conformal coating process stage of the circuit board should be complete and the board ready for final inspection.

However, in many cases the conformal coating process is not complete.

This is because of several reasons including:

  • Masking removal: The masking damaged the conformal coating when removed from the circuit
  • Shadowing: Conformal coating did not reach certain areas of the board that should have been coated due to the masking blocking it, the design of the board causing shadowing or the application technique was unable to reach the areas
  • Qualify of coating: The finish of the conformal coating is not to the standard required (defects appear in the conformal coating) and it needs repairing.
  • Masking leakage: The masking failed to prevent coating going into areas it was designated to avoid so it must be removed.

The amount and type of finishing required for the circuit board and conformal coating will be down to several factors. These include:

  • Standards: The conformal coating standards that the circuit board is being processed to need to be considered.
  • Work instructions: The work drawings defining the conformal coating requirements for the board should state what must and must not be coated, the coating thickness and critical instructions.
  • Coating defects: The type of conformal coating defect present will determine the finishing and rework required.
  • Operator skill: The ability of the operator to de-mask correctly and not cause excess damage to the finish will determine how much extra rework is required
  • Degree of cure: When the masking is removed, the time after coating and level of cure can be critical to the removal of the masking materials.

Further information can be found in Conformal coating removal.