On a populated circuit board, some areas must stay sealed and some must stay coating-free. Connectors, test points, switches, and displays cannot be conformal coated, but they still need protection from the coating process and from moisture in service. A UV-curable gasket dispensed onto the board solves both problems in one fast step.

The PCBA Sealing Problem

Conformal coating protects a board from humidity, dust, and corrosion, but it must be kept off certain components. The traditional approach is hand-applied masking dots, tape, and boots, which are labor-intensive, inconsistent, and generate waste. They also do nothing for in-service sealing around a connector or a board-to-enclosure interface.

A dispensed UV gasket replaces masking with a precise, automated bead. It defines a keep-out boundary the coating cannot cross, seals the perimeter of components that need it, and stays on the board as a permanent gasket where a board-to-housing or connector seal is required.

Incure Uni-Seal 3393

Incure’s Uni-Seal 3393 is a UV-curable form-in-place gasket and sealant developed with PCBA work in mind. Its characteristics:

• Fast LED cure for high-volume board assembly, cured before the board moves to the next station.
• Soft yet tough, balancing enough compliance to seal against uneven surfaces with enough toughness to resist tearing during handling.
• Ease of peel for rework, so a sealed area can be reopened to replace a component and re-gasketed, without damaging the board or pads.
• Air-tight sealing around connectors and enclosure interfaces.
• Moisture and temperature resistance for the board’s service environment.
• Chemical resistance, consistent with the electronics and automotive use where the chemistry is common.

Applied along a keep-out boundary before conformal coating, the cured gasket gives the coating a clean edge to stop against. Applied around a connector footprint, it provides the in-service seal.

For guidance on bead placement and cure setup for a specific board, Email Us with the board layout and coating process details.

Dispensing and Bead Design

• Bead width and height: Match the bead to the gap it has to seal and the compression the mating part applies. For a masking boundary with no compression, a low, wide bead that adheres firmly to the laminate is enough.
• Standoff from components: Program the path with enough clearance that the bead does not creep onto a pad or lead, while staying close enough to keep the coating out.
• Adhesion to the laminate: Boards should be clean and dry. Residual flux or handling oils reduce gasket adhesion and can let coating wick underneath.
• Automated dispense: A programmable dispenser gives repeatable bead volume and position, which manual masking cannot match.

Curing

Cure the dispensed bead under a UV LED flood lamp sized to the board, or run boards through a conveyor curing system for volume. Verify delivered dose at the board with a radiometer. Tall components can shadow a nearby bead, so check that beads next to connectors and headers get full exposure, or expose from a second angle. Cure the gasket fully before applying conformal coating so the coating solvent does not attack a soft bead.

Rework

The peelable character of the cured gasket is what makes board rework practical. To replace a component inside a sealed area, lift the gasket, do the rework, clean the area, and dispense and cure a fresh bead. Confirm the replacement bead ties into the surrounding original cleanly.

Comparing With Traditional Masking

Hand masking with dots, tape, and latex boots is slow, needs a skilled operator, and produces inconsistent boundaries. Peel-off latex maskants leave residue and can pull pads if over-applied. Reusable boots wear and lose their seal. A dispensed UV gasket replaces all of these with one programmed operation: consistent boundary position, no residue, and a bead that doubles as an in-service seal rather than a consumable that gets thrown away after coating. The labor saving alone is often the justification, before counting the reduced coating rework from cleaner keep-out edges.

Placement Around Tall Components

Connectors, electrolytic capacitors, and headers cast shadows that can leave a nearby bead undercured. Where a gasket has to run close to a tall part, plan the cure exposure to come from an angle that clears the shadow, or add a second exposure pass from the opposite side. On a conveyor lamp, orienting the board so the bead runs parallel to the lamp travel keeps the exposure even along its length.

Validation

• Coating containment: Coat a test board and confirm the coating stops cleanly at the gasket with no wicking underneath.
• Seal integrity: Leak or humidity test around gasketed connectors.
• Thermal cycling: Cycle boards across the service range and recheck adhesion and seal, accounting for expansion differences between the gasket, the laminate, and component bodies.
• Rework cycle: Peel and re-gasket a sample and confirm the repaired seal performs like the original.

Summary

A UV-curable PCBA gasket replaces hand masking with a fast, repeatable dispensed bead that defines coating keep-out zones and seals connectors, and it peels cleanly for rework. Design the bead for the gap and the compression, cure fully before coating, and validate containment and seal integrity. Incure supports PCBA gasketing from material selection to line integration.

Contact Our Team to discuss a board sealing and masking application.

Visit www.incurelab.com for more information.