Cracking of conformal coating is most often discovered not during initial inspection, but after thermal cycling, environmental testing, or extended service exposure.

In field investigations, cracking is rarely caused by a single factor. Instead, it is usually the result of combined stresses, such as excessive coating thickness, rigid material selection, and differential thermal expansion between the coating and substrate.

We commonly see cracking:

• Over sharp component edges or solder fillets
• Where coating thickness exceeds recommended limits
• On assemblies exposed to wide thermal excursions

Importantly, coatings that appear compliant and defect-free at room temperature may still fail under thermal stress if thickness and material flexibility are not properly controlled.

A deeper technical breakdown of cracking mechanisms and prevention is available in our Defects Hub article on cracking in conformal coating.

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.

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.