Conformal Coating Masking: Methods & Materials

This guide explains conformal coating masking methods & materials—when to choose boots, tapes, dots, liquid mask, or custom 3D plugs—plus best practice, standards, and troubleshooting so your coating process is fast, consistent, and rework-friendly.

Illustration of PCB with masking boots, tape, and dots alongside training icons such as graduation cap and checklist, representing conformal coating masking and operator training

What is masking? Masking prevents conformal coating from covering keep-out areas such as connectors, test points, edge fingers, heat sinks, switches and threaded holes. The “right” approach balances speed, seal quality, reusability, temperature/solvent compatibility and total cost.

Why Masking Matters

  • Function: Maintains electrical contact at edge fingers, test points and connector pins.
  • Reliability: Prevents capillary wicking into switches, relays and connectors.
  • Productivity: Reduces rework, labour, and damage risk when demasking.

Masking Methods & Where They Fit

Method Best For Strengths Watch-outs
Silicone / EPDM Masking Boots & Caps Headers, connectors, LEDs, odd-form components Fast, repeatable, reusable; strong seal; less operator skill Up-front cost; correct sizing critical; check temp/chem compatibility
Polyimide / Crepe Tapes Edge fingers, flat keep-outs, board perimeters Flexible, low cost, quick to cut; temperature rated options Adhesive residue; lifting in wash or cure; operator variability
Masking Dots & Shapes Test pads, vias, BGA keep-outs, screw holes Precise, fast placement, consistent diameters Need clean, dry surface; risk of edge feathering if removed hot
Liquid Mask (Peelable / UV-gel) Irregular geometries, temporary dams, potting windows Conforms to complex shapes; good seals when applied correctly Cure & removal time; compatibility with coating solvent system
Custom 3D Plugs / Fixtures High-volume builds; repeat features; automation cells Maximum throughput, minimal skill dependency, durable Design/lead time; validate seal lines and demask ergonomics

Choosing Masking Materials

  • Boot Elastomers: Silicone for high temp & flexibility; EPDM/fluoroelastomers for solvent & fuel resistance.
  • Tapes: Polyimide (Kapton®) for heat; crepe for general use; check adhesive class (silicone vs acrylic) for residue.
  • Dots/Shapes: Die-cut polyimide or polyester; ensure clean removal profile.
  • Liquids: Peelable latex/UV gels—verify cure, edge definition, and compatibility with your coating chemistry.
Best Practice: Standardise a masking BOM for each assembly (boot IDs, tape widths, dot sizes, liquid mask lot) and include photos of correct placement to reduce variability.

Process Sequence & Tips

  1. Clean & Dry: Mask only on clean, dry surfaces to maximise adhesion and seal integrity.
  2. Apply Boots First: Press firmly along seal lines; verify no trapped leads or skew.
  3. Add Tape/Dots: Burnish edges; avoid bridging over sharp edges; label pull tabs for easy demask.
  4. Coat & Cure: Observe tape/boot temperature ratings; for UV coats, check shadowing around masks.
  5. Demask Window: Remove when coating is firm-tack free but before full cure to prevent edge tear; pull back over itself at 180° to minimise feathering.
  6. Inspect & Touch-up: Verify keep-out cleanliness; use approved solvents or removal tools only.

Standards & References

Align your masking plan with recognised guidance and customer specs:

Troubleshooting Common Issues

  • Tape lifting in wash/cure: Switch to higher-tack/temperature tape; reduce wash dwell; ensure fully dry before coat.
  • Leakage under masks: Change to boots or liquid mask for complex edges; burnish tape; review spray angle & pressure.
  • Residue after demask: Use silicone-adhesive polyimide or low-residue tapes; demask at defined window; solvent-wipe per WI.
  • Edge feathering: Demask earlier; reduce film build at edges (angle/off-part air); consider negative masks.

SCH Masking Solutions

We supply and specify complete masking kits for production and NPI:

Training & Support

SCH provides dedicated conformal coating training programmes to help your team achieve consistent results and reduce rework.
Our modules cover both general coating process training and specialist masking techniques, ensuring operators
understand how to apply boots, tapes, dots, and liquid masks effectively.

  • Masking Training: Best practices for applying and removing boots, tapes, and dots with minimal residue or leakage.
  • General Conformal Coating Training: Process setup, application methods (spray, dip, selective, Parylene), curing, and inspection.
  • Advanced Modules: Troubleshooting common issues, coating removal methods, and customer-specific standards.
  • Flexible Delivery: On-site operator workshops, online training modules, or full consultancy support packages.

Learn more about SCH training or contact us to discuss a tailored programme for your production team.

Need a masking BOM or custom boot?
Send your assembly photos and BOM—our team will specify fast, leak-free conformal coating masking methods & materials tailored to your line.

Why Choose SCH Services?

Partnering with SCH Services means more than just outsourcing — you gain a complete, integrated platform for
Conformal Coating, Parylene & ProShieldESD Solutions, alongside equipment, materials, and training, all backed by decades of hands-on expertise.

  • 🛡️ Safety-Critical Focus – Process control, documentation, and verification built-in.
  • 🛠️ End-to-End Support – Selection, masking, application, inspection, ProShieldESD integration.
  • 📈 Scalable Solutions – From small assemblies to full facility control.
  • 🌍 Global Reach – Support across Europe, North America, and Asia.
  • ✅ Proven Reliability – Quality and consistency across services and materials.

📞 Call: +44 (0)1226 249019
✉ Email: sales@schservices.com
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