UV (UVA) Inspection: Coverage & Edge Definition

UV (UVA) inspection is one of the most widely used inspection methods in conformal coating processes. Because most conformal coatings contain a fluorescent tracer dye, exposure to UV-A light makes coating presence, coverage continuity, and masking boundaries immediately visible.

This article explains how UV inspection should be used correctly β€” what it reliably shows, what it does not, and how it fits into a controlled inspection workflow.

Infographic showing UV (UVA) inspection for conformal coating, highlighting coverage assessment, edge definition, and limitations.

The Role of UV Inspection in Conformal Coating

UV inspection is a screening and verification tool. It provides rapid visual confirmation that coating has been applied where required and that masking has performed as intended.

  • Confirms coating presence and continuity
  • Highlights missed areas, skips, and shadowing
  • Reveals edge behaviour around masking boundaries
  • Identifies obvious leakage or overspray into keep-out zones

It is typically the first inspection stage, not the final acceptance authority.

Coverage Assessment Under UV

  • Uniform fluorescence indicates continuous coating coverage
  • Dark or dull regions indicate missing or very thin coating
  • Shadowed zones beneath, around or actually on components often indicate spray path obstruction or poor access

Coverage failures identified at this stage are typically caused by shadowing, poor spray access, masking interference, or surface energy effects.

In contrast, defects such as de-wetting may appear as apparent β€œmissing coverage” under UV.

Edge Definition & Masking Performance

UV inspection is particularly effective at evaluating mask boundary behaviour.

  • Acceptable: smooth, continuous boundary with no coating ingress into keep-out areas
  • Concern: uneven pull-back, feathered boundaries, or inconsistent edge definition
  • Rejectable: coating penetration into defined keep-out zones or unstable edges that may lift or propagate

Edge-related findings almost always point to masking selection, application, dwell time, or removal technique.

PCB being inspected inside a UV inspection booth under UVA light

Limitations of UV (UVA) Inspection

UV inspection does not provide a complete assessment on its own.

  • Does not reliably confirm coating thickness
  • Cannot fully characterise bubbles or voids
  • Cannot assess adhesion or cure state
  • May mask texture defects

How UV Inspection Fits Into Inspection Control

  • Use UV to confirm coverage and masking behaviour
  • Use white light and magnification to assess surface defects
  • Use defined plans for thickness verification
  • Apply documented acceptance criteria for final disposition

Final accept/reject decisions should follow Conformal Coating Inspection Acceptance Criteria.

Need Help Improving UV Inspection Consistency?

If UV decisions vary between operators or shifts, SCH can help you standardise the method, lighting, and decision rules.

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Note: This article provides general technical guidance only. Final inspection criteria and compliance decisions must be validated against applicable standards and customer requirements.