A common inspection finding is localised de-wetting of conformal coating, particularly on solder joints or around component leads, even when a cleaning process has been applied beforehand.
In many cases, the boards are genuinely clean in a visual sense. However, de-wetting is often caused by residues that are invisible to the naked eye — including low-level ionic contamination, surfactant residues from aqueous cleaning, or incompatible cleaning chemistries.
Typical characteristics include:
- Circular pull-back around solder joints
- Patchy coating coverage on ENIG or HASL finishes
- Repeatable locations across multiple assemblies
Crucially, operators may notice the effect during coating but assume it is cosmetic. In reality, de-wetting is a strong indicator of a surface energy problem and should always trigger escalation and investigation rather than acceptance.
Detailed causes, acceptance criteria, and corrective actions are covered in our Defects Hub guidance on de-wetting in conformal coating.
