Definition

Co-authors and contributors

  • Dr Lee Hitchens, Nexus

Mealing is a form of delamination of the conformal coating that occurs across the circuit board.

It is a blistering (vesication) affect.

Download our PDF guide Solving conformal coating problems in the application process now.


Examples of conformal coating mealing

Examples are shown in the images where the conformal coating where mealing has occurred.

Mealing Low res


Causes of mealing defects in conformal coating

Similar to delamination, the causes of mealing in conformal coating include:

  • Cleanliness: Poor cleanliness of the surface reduces good adhesion. If the surface is contaminated across a wide area then mealing can occur due to the poor adhesion of the coating to the laminate.
  • Material Compatibility: Compatibility between the coating and the surface adhered to due to surface energies mismatch. If the conformal coating is not matched to the laminate then mealing can occur.
  • Permeability to moisture of the coating: If the coating allows the moisture to permeate into the region between the coating and the laminate, then a difference in vapour pressure occurs. This could lead to osmotic pressures building due to a change in temperature and pressure, which lift the coating away from the laminate.
  • Degree of coating cure: If the coating is not cured correctly then this can lead to adhesion problems.

How to prevent mealing problems in conformal coating

  • Clean the Board: Clean the surface of the board to improve the adhesion of the coating. Remove contamination such as mould release agents on components before application.
  • Material Compatibility: Match the conformal coating to the solder resist and laminate so that good adhesion is achieved. Change the coating and / or surface finish so the surface energies are more favourable.
  • Coating Thickness: Reduce the coating thickness. This reduces the problems associated with CTE mismatch with the components and laminate that lead to flexing of the coating.
  • Lower Curing Heat: Reduce force drying (thermal profile) during curing to avoid excess stress and strains on the coating.
  • Prime the Substrate: Apply a primer to treat the board surface. This will increase the bonding of the conformal coating to the substrate.

Download our PDF guide Solving conformal coating problems in the application process now.


 Links

BlisteringBlushingBubbleContamination
Capillary FlowCorrosionCrackingDelamination
De-wettingDiscolourationFish EyesLayering
MealingOrange PeelShadowingUneven coating