During inspection of coated assemblies, we occasionally observe conformal coating creeping along exposed wire strands well beyond the intended coated area. This is often flagged as “over-application”, but in practice the root cause is usually more subtle.
In this scenario, the coating is not flowing excessively during application. Instead, capillary forces draw low-viscosity material along fine wire strands, braid structures, or conductor interfaces after deposition. This effect is amplified where flux residues, incomplete cleaning, or high surface energy materials are present.
We most often see this behaviour:
- At wire terminations and soldered pigtails
- Where insulation stripping exposes fine conductor bundles
- When low-viscosity acrylics or urethanes are used without sufficient flash-off
From a process perspective, this is not something that can be “sprayed out”. Masking strategy, cleanliness, and controlled flash times are far more influential than spray parameters alone.
For definitive technical guidance on this phenomenon, see our Defects Hub page on capillary wicking in conformal coating.
