Bridging & Webbing Defects in Conformal Coating

← Back to Defects Hub
← Knowledge Hub

Bridging (webbing) occurs when conformal coating forms a continuous film between two adjacent features that should remain electrically or functionally isolated — most commonly between pins, leads, pads, or test points in fine-pitch areas. This page explains how bridging forms, how to diagnose the dominant mechanism, and how to prevent recurrence.

For a complete index of defect types and links to each technical article, use the Conformal Coating Defects Hub.

Article Quicklinks

Topic	More
Definitions: what bridging/webbing is and when it matters	🔗
Root Causes: film build, viscosity, geometry and masking	🔗
Prevention: control window & recipes	🔗
Troubleshooting & Diagnosis: isolate the mechanism	🔗
Repair: when to remove vs rework	🔗

What is Bridging / Webbing in Conformal Coating?

• Bridging — coating creates a continuous path between two adjacent conductors or features.
• Webbing — a thin “film web” spanning between pins/leads/pads (often seen in fine pitch or tight clearances).
• Typical locations — connector pins, fine-pitch leads, adjacent test pads, closely spaced terminations, and tight RF keep-outs.
• Main risk — reduced creepage/clearance, trapped residues/moisture, leakage under bias, or interference with test/mating functions.

Bridging should be assessed against the drawing/specification (keep-outs, minimum clearances, and acceptance rules). A bridge that is acceptable in one design may be a nonconformance in another.

↑ Back to Quicklinks

Root Causes of Bridging & Webbing

Process & Technique

• Over-wet film build — heavy single-pass application leaves a mobile film that can span gaps before skinning or set.
• Keep-wet overlap effects — repeated overlaps or slow application speed maintain a continuously wet zone that promotes web formation.
• Application angle and distance — poor approach angles or excessive standoff can deposit film across gaps rather than around individual features.
• Orientation and gravity — pooling at low points allows coating to flow between adjacent leads or pads.
• Thick fillets acting as stress concentrators — heavy build between adjacent features cures into a rigid fillet that is more prone to cracking or crazing under thermal or mechanical stress, creating secondary moisture ingress paths.

Material & Condition

• Low viscosity / high flow — increases the tendency for coating to span fine gaps and tight clearances.
• Long open time — extended film mobility allows bridges to form before the coating locks.
• Solvent imbalance — unintended dilution or retained solvent alters flow behaviour and increases bridging risk.

Geometry & Masking

• Fine pitch / tight spacing — closely spaced pins and pads naturally promote bridging and webbing.
• Connector and recessed geometries — cavities and interfaces encourage local film build and web formation.
• Incorrect masking strategy — keep-outs that are unmasked or under-masked at high-risk features (connectors, test pads, mating faces) allow coating to bridge prohibited areas.

Sanity check (look-alikes):
If coating is found within defined keep-out or prohibited areas, refer to coating ingress into keep-out areas. Where the issue is primarily excessive build or pooling at low points, see pooling / puddling. If thin or bare zones are observed behind tall components, refer to insufficient coverage / shadowing. Where cracking initiates at bridged or over-built areas, consult cracking in conformal coating for stress- and cure-related mechanisms.

↑ Back to Quicklinks

How to Prevent Bridging / Webbing

Stabilise the control window

• Multiple thin coats with defined flash-off rather than one heavy wet deposit.
• Control viscosity: measure/record and keep within a validated range.
• Manage open time: avoid films that remain mobile long enough to span tight gaps.

Reduce keep-wet bridging behaviour

• Optimise overlap and speed in dense component fields to avoid persistent wet zones.
• Tune local parameters near fine pitch: flow, pressure, distance and dwell should be reduced where practical.
• Use multi-angle strategy carefully to avoid laying continuous films across pin rows.

Keep-out protection (where required)

• Mask high-risk features (connectors, test pads, mating surfaces) using suitable tapes, boots, dots or custom masks.
• Mask-edge sealing where appropriate to stop creep under the boundary.
• Inspect pre-cure so ingress/webbing can be removed before full cure.

For masking methods and keep-out control strategies, use the Masking Hub. For inspection planning and acceptance routines, use the Inspection & Quality Hub.

↑ Back to Quicklinks

Troubleshooting & Diagnosis

1) Confirm the bridge and the risk

• UV + white-light inspection: confirm continuous films spanning adjacent conductors/features.
• Confirm keep-out and clearance rules: check drawings/specs for prohibited zones and minimum separation.

2) Identify the dominant mechanism

• Pattern repeatability: recurring bridge locations usually indicate geometry + recipe/path issues.
• Film mobility: determine whether bridging occurs while wet, during flash, or during cure.
• Keep-wet behaviour: look for overlaps and dwell that maintain wet films in dense fields.

3) Validate with A/B trials

• Reduce flow/overlap or add flash steps; confirm bridging reduces without creating shadowing elsewhere.
• Where required, add or improve masking and verify ingress is eliminated.

↑ Back to Quicklinks

Repair: When to Rework vs Remove and Recoat

• Localised webbing in accessible areas: controlled local removal may be possible if you can re-inspect and verify clearance.
• Bridging in connectors, contacts, or defined keep-outs: treat as a high-risk nonconformance — removal and rework is usually required.
• Recurring bridging: fix the process window and application recipe before reworking, otherwise the defect will repeat.

For structured removal workflows and best-fit methods, see the Removal & Rework Hub.

↑ Back to Quicklinks

Looking for Other Defect Types?

This page covers bridging and webbing. For the complete index of defect types and links to each technical article:

Explore the Defects Hub ↗

Training on Conformal Coating Defects

SCH offers conformal coating training that goes beyond theory—recognising and preventing bridging/webbing,
coating ingress into keep-outs, insufficient coverage, wicking, pinholes/bubbles/foam, orange peel, de-wetting, and corrosion mechanisms. We cover process analysis, troubleshooting, materials, and application methods.

Explore Conformal Coating Training ↗

Industry Standards We Work To

SCH Services aligns coating services, training, equipment supply and materials to relevant IPC standards, including:

• IPC-A-610 – Acceptability of Electronic Assemblies
• IPC-CC-830 – Qualification & Performance of Conformal Coatings
• IPC-HDBK-830 – Conformal Coating Handbook (guidance and best practice)

For further details on IPC standards: electronics.org/ipc-standards ↗

Why Choose SCH Services?

You gain a complete, integrated platform for Conformal Coating, Parylene & ProShieldESD—plus equipment, materials and training—backed by decades of hands-on process support.

• 🛠️ End-to-End Support – Selection, masking, inspection and troubleshooting.
• ✅ Process Discipline – Recipes, control windows and repeatability.
• 🌍 Global Reach – Support across Europe, North America and Asia.

📞 Call: +44 (0)1226 249019   | ✉ Email: sales@schservices.com |   💬 Contact Us ›

Note: This article provides general technical guidance only. Final design, safety, and compliance decisions must be verified by the product manufacturer and validated against the applicable standards.