Masking is one of the simplest steps in conformal coating — and one of the most common causes of defects, rework and customer complaints when it goes wrong.
Coating on connector pins. Adhesive residue left behind. Silicone boots leaking. Latex that tears or pulls the coating away. These issues cost time and money — but most are preventable.
The solution isn’t only better operator training — it starts with using the right masking materials and adhesives, the same paper-based tapes, dots and pre-cut shapes we use in our own coating services every day.
To understand all available masking materials, see Conformal Coating Masking: Methods & Materials to review different tapes, dots, custom boots, latex and pre-cut shapes.
Why Masking Goes Wrong
Masking protects connectors, test pads, gold fingers, housings and other areas that must remain coating-free. Most masking failures are caused by:
- Coating wicking under tape, dots, shapes or silicone boots
- Coating de-wetting away from the tapes and dots due to the adhesive used.
- Adhesive residue left behind after removal
- Using general-purpose tape instead of conformal coating tested materials
- Silicone boots that don’t seal or are worn out
- Liquid latex applied too thick or removed too late
- No inspection during demasking
To better understand leak paths and barrier methods, see Conformal Coating Masking Strategies – Barrier vs Shielding.
Three Ways to Reduce Masking Defects
1. Choose the Right Masking Method — and the Right Adhesive
Masking Tape
- Best for: General areas, edges and flat surfaces
- Benefits: Low cost, flexible, easy to apply
- Important: Must be paper-based, low-tack, clean-release. Avoid Kapton or painter’s tape — they leave residue or pull coating off.
Masking Dots & Discs
- Best for: Test pads, vias, screw holes
- Benefits: Fast, consistent sizing, no cutting needed
- Important: Use paper-based coating-safe masking discs. Vinyl stickers, labels or strong adhesives will leave residue or lift coating.
Pre-Cut Masking Shapes (Custom Paper Shapes on Sheets/Rolls)
- Best for: Complex flat areas, precision masking, gold fingers, connector faces, repeat PCB builds
- Benefits: No hand-cutting, accurate placement, speeds up production
- Important: Made from specialist paper masking material with low-tack adhesive — same type we use daily in conformal coating services.
Silicone Masking Boots & Caps
- Best for: Connectors, pin headers, test points
- Benefits: Reusable, quick to apply, clean edges
- Important: Must fit properly and seal. Cheap silicone swells, tears or leaks. See Reusable Masking Boots – cost, speed, repeatability.
Liquid Latex / Hybrid Barrier Systems
- Best for: Board edges, non-flat surfaces, irregular shapes
- Benefits: Seamless coating barrier where tape cannot reach
- Important: Apply in thin coats, peel at the correct time. See Liquid Latex & Hybrid Barrier Systems – sealing tapes & keep-out edges.
Want materials? Visit Masking Boots, Tapes, Dots & Pre-Cut Shapes from SCH.
2. Apply Masking Correctly — Clean, Seal and Fit
Even the right masking materials fail if they’re not applied properly.
Best Practice:
- Clean the board before masking — oils and flux stop adhesives sealing.
- Press tape/dots/shapes firmly, especially around edges.
- Use Pre-Cut Masking Shapes for speed and consistency in repeat jobs.
- Fit boots fully — no lifted edges or gaps. For guidance, see How to Mask a PCB with Boots – A How to Guide.
- Latex must be applied in thin layers and peeled before it fully hardens.
For understanding the benefits of reusable boots in production environments, see Reusable Masking Boots – cost, speed, repeatability.
3. Inspect During Demasking — Not After Testing
Most masking failures are found too late — after coating cures or during electrical test. The best time to detect problems is while removing masking.
During demasking, check for:
- Coating on pins, connectors or gold fingers
- Adhesive residue or paper fibres
- Coating lifting with the tape or shapes
- Silicone boots pulling coating at the edges
- Latex tearing or leaving fragments
Early detection = repair before full cure.
More masking advice can be found in Conformal Coating Masking: Methods & Materials –and Designing Effective PCB Masking Strategies.
Bonus Tips — Speed Up Masking, Reduce Rework
- Use Pre-Cut Masking Shapes for intricate masking, complex areas, gold fingers and flat surfaces in repeat builds.
- Replace silicone boots when they swell, crack or don’t seal.
- Use latex or hybrid barrier approaches on difficult edges — see Liquid Latex & Hybrid Barrier Systems – sealing tapes & keep-out edges.
- Add masking diagrams and photos to work instructions.
- Train operators specifically in masking and demasking — not just coating.
Conclusion
Most masking problems aren’t caused by operator error — they’re caused by using the wrong tape, dots, shapes or boots.
Using the correct conformal coating masking tapes, dots, custom pre-cut shapes, silicone boots or peelable latex, applied and removed at the right time, will drastically cut defects, rework and costs.
