Electronics that operate at altitude face a problem sea-level designs ignore: as air pressure drops, its dielectric strength drops with it, and voltages that were safely separated on the ground can arc. Incure Pyra-Sil™ 905 is a UV-cure silicone sealant formulated to conformal-coat boards against moisture and against high-altitude arcing.
The high-altitude arcing problem
Air is an insulator, but a weak one, and its insulating ability falls with pressure. A circuit with high-voltage nodes, a power supply, an ignition driver, a sensor excitation rail, that is reliable at sea level can flash over between conductors at cruise altitude or in a depressurized bay. A dielectric conformal coating fills the space around and between those conductors with a solid insulator, raising the breakdown voltage well above what thin air provides.
905 is designed for that role: a silicone film that both seals against moisture and provides the dielectric barrier that suppresses corona and arcing at altitude.
What Pyra-Sil™ 905 is
905 is a one-part UV/moisture-cure silicone adhesive sealant. It cures primarily under UV light, fixing exposed material in seconds, with a secondary moisture cure that completes shadowed regions within about 72 hours. The cured film is flexible and durable and resists ozone, weathering, and elevated temperature.
It is specifically formulated for use as a conformal coating on printed circuit boards and components, and it also serves general bonding, sealing, and encapsulation.
Where it is used
- Aerospace: avionics, power electronics, and instrumentation operating at altitude or in unpressurized zones.
- Consumer and industrial electronics: boards exposed to humidity that also carry higher-voltage nodes.
- Renewable energy: string inverters and combiner electronics with high DC bus voltages in outdoor enclosures.
- General industrial manufacturing: sealing and encapsulation where a flexible, dielectric silicone is needed.
Application and cure control
905 is applied by manual brushing for repair and low volume, or by automated dispensing or spray for production. The UV step needs a measured dose, verified with a radiometer, with allowance for lamp aging. Batch fixturing under Incure L-Series UV LED flood lamps covers trays at a set intensity, and inline curing runs on an Incure CDM UV conveyor.
For arcing suppression, coverage between high-voltage conductors has to be complete and of adequate thickness. A thin spot or a bubble at a critical gap is where flashover starts. Inspect under magnification, and if inspectability is required, ask about the Pyra-Sil™ grades that fluoresce under blacklight.
For help matching Pyra-Sil™ 905 to a board’s voltage map and altitude requirement, Email Us with the details.
Failure modes to design against
- Voids or bubbles at a high-voltage gap: air pockets in the film defeat the dielectric barrier. Dispense to avoid entrapment and allow the film to wet out fully.
- Thin coverage between conductors: control film thickness where it matters most, not just overall.
- Assuming the UV fix is a full cure: shadowed material needs its moisture-cure time, up to about 72 hours, before the board is qualified.
- Contamination under the film: clean and dry the board; residue undermines both sealing and dielectric performance.
Coverage where the dielectric barrier has to work
For moisture sealing, coverage needs to be continuous everywhere. For arcing suppression, coverage also needs adequate thickness precisely in the gaps between high-voltage conductors, which are often the hardest places to reach: narrow channels between a transformer’s pins, the space under a large component, the creepage path across a connector body.
Two defects defeat the barrier. A void or entrapped air bubble at a critical gap leaves a low-pressure air pocket exactly where the coating was supposed to displace it, and that pocket can ionize and arc. A thin spot between conductors reduces the breakdown margin below what the altitude requirement assumes. Dispense technique that lets the sealant wet fully into tight channels, plus a degassing or vacuum step for potted regions, keeps the film solid. Inspect the high-voltage areas specifically, not just overall coverage, and document the film thickness achieved between the biased conductors.
Frequently asked questions
Q: How does a coating stop arcing that air cannot?
A: A cured silicone film has a much higher dielectric strength than low-pressure air and fills the gap between conductors with solid insulation, so the breakdown path no longer exists.
Q: How long until the board is fully cured?
A: Exposed material fixes in seconds under UV. Shadowed regions complete their moisture cure within about 72 hours; qualify the board after that.
Q: Can it be used as a general sealant too?
A: Yes. Besides conformal coating, it works for bonding, sealing, and encapsulation where a flexible silicone is appropriate.
Getting support
Incure can help select a silicone grade, define the cure process, and address dielectric or coverage requirements. Contact Our Team to discuss your application and request technical data.
Visit www.incurelab.com for more information.