Definition

Author

  • Dr Lee Hitchens, Nexus

The orange peel defect is an uneven textured surface of the conformal coating, often appearing dull, which can look like the skin of the orange or golf ball.

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Example of conformal coating orange peel

orange peel 2


Causes of orange peel in conformal coating

Factors that can cause orange peel effect include:

  • Spray Setup: Orange peel is often caused because of poor gun adjustment as the conformal coating is being applied.
  • Application: An incorrect application technique. This manifests in aerosol or spray gun application where the coating is applied too far away from the PCB and the coating is too “dry” on the surface to level out.
  • Viscosity: Incorrect viscosity of the conformal coating before application.
  • Coating Thickness: The incorrect thickness of the coating where not enough coating is deposited so that there is insufficient conformal coating to self level.
  • Curing: The incorrect cure profile when using an accelerated curing mechanism. This could be that the flash off zone before heat curing is inadequate or the oven profile is incorrect.

How to prevent orange peel effects in conformal coating

  • Gun Setup: Set the spray gun up correctly. Gun setup and adjustment are critical to a smooth and flat appearance of a conformal coating.
  • If the needle/nozzle combination is not specifically matched to the coating being applied, the air pressure (especially when using an HVLP (high volume low pressure) gun) may not be sufficient to correctly atomise the conformal coating.
  • Viscosity: Reduce the viscosity of the conformal coating. If a coating is mixed at the wrong viscosity and it is too thick (high viscosity), orange peel is likely.
  • Spraying Technique: Optimise the distance for spray application to the manufacturer specification when applying the conformal coating.
  • Material Volume: Ensure enough layers of coating are applied to form a level coating. This is especially true for aerosols that are susceptible to this issue.
  • Drying: Increase the flash off time for the solvents to evaporate before increasing the temperature for elevated curing of the conformal coating. Re-profile the curing oven using the conformal coating material suppliers recommended profile.

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


Links

BlisteringBlushingBubbleContamination
Capillary FlowCorrosionCrackingDelamination
De-wettingDiscolourationFish EyesLayering
MealingOrange PeelShadowingUneven coating