Coating Ingress into Keep-Out Areas in Conformal Coating
Coating ingress into keep-out areas occurs when conformal coating unintentionally enters regions that must remain uncoated, such as connectors, test pads, mating surfaces, contacts, or defined electrical interfaces. Unlike insufficient coverage or shadowing, this defect is not about missed protection. It is a violation of functional boundaries, often leading to contact resistance, intermittent connections, test failures, or mechanical interference.
This page focuses specifically on coating where it should not be. If coating has been blocked from required areas, see
insufficient coverage & shadowing. If coating has migrated underneath components, see capillary (wicking)
Examples of conformal coating ingress into keep-out areas such as connectors, test pads and mating surfaces
Article Quicklinks
| Topic | More |
|---|---|
| Definitions: what constitutes a keep-out violation | π |
| Root Causes: masking, geometry and process drivers | π |
| Prevention: masking strategy and application control | π |
| Troubleshooting & Diagnosis | π |
What is Coating Ingress into Keep-Out Areas?
- Keep-out areas β regions intentionally left uncoated to preserve electrical contact, mechanical fit, or test access.
- Ingress β conformal coating entering or contaminating these regions during application, flow, or cure.
- Common locations β connectors, sockets, test pads, edge fingers, mating faces, press-fit contacts, and switch mechanisms.
- Primary risk β increased contact resistance, intermittent faults, failed testing, and long-term reliability issues.
This defect is fundamentally different from coverage loss: the coating may be perfectly applied elsewhere, but its presence in a prohibited zone creates a functional failure.
Causes of Coating Ingress into Keep-Out Areas
- Inadequate masking β incomplete coverage, poor mask fit, degraded tapes, or incorrect mask placement.
- Mask edge leakage β coating creeping under mask edges due to pressure, over-wet films, or solvent attack.
- Over-application β excessive flow, pressure, or dwell time overwhelming the masking barrier.
- Geometry effects β recessed connectors, cavities, or capillary paths drawing coating into protected zones.
- Process variability β inconsistent operator technique, robot offsets, or changes in coating viscosity.
Sanity check (look-alikes):
- If coating has flowed under components leaving adjacent thin zones, see capillary (wicking).
- If coating has been removed during demasking, see mask-edge lift & demask damage
.
How to Prevent Coating Ingress into Keep-Out Areas
- Correct masking selection β choose tapes, boots, dots or custom masks matched to geometry and solvent exposure.
- Defined mask application rules β consistent placement, overlap, and pressure during mask application.
- Controlled film build β avoid over-wet coats that can overwhelm mask edges.
- Process tuning β reduce flow, pressure and dwell near protected regions.
- Inspection before cure β identify early ingress while removal is still possible.
Detailed masking methods and best practices are covered in the Masking Hub.
Troubleshooting & Diagnosis
- Visual and UV inspection β confirm coating presence in prohibited zones.
- Mask review β inspect mask integrity, fit and removal condition.
- Pattern analysis β determine whether ingress is localised or systematic.
- Process audit β review application parameters at the time of failure.
- A/B trials β adjust masking method or application settings to confirm the root cause.
Looking for Other Defect Types?
This page focuses on coating ingress into keep-out areas. For other conformal coating defect mechanisms and diagnostic guides, explore the full index:
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