US How conformal coating protects a board
Conformal coating is a thin polymer film applied over an assembled circuit board, so that it follows, or conforms to, the shape of the components and solder joints beneath it. It insulates the surface and seals it against moisture, condensation, dust, salt spray and many chemicals.
A circuit board inside a sealed enclosure can still see moisture. Air trapped inside condenses when the temperature drops, and salt or sulphur in the atmosphere slowly corrodes exposed copper and solder. Conformal coating puts a thin insulating barrier over the assembled board, with connectors and contacts masked so they still mate.
The film is thin, typically tens of microns, so it adds almost no weight and does not stop heat leaving the components. It is not a substitute for a sealed enclosure. Coating and sealing work together: the enclosure keeps water and dust out, and the coating protects the board from what gets in or forms inside. Our explainer on the printed circuit board covers the board itself.
Types of conformal coating
IPC, the electronics assembly standards body, groups coatings by chemistry, each with its own letter code. The choice is a trade-off between protection, temperature range and how easily a board can be repaired later.
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Acrylic (AR). Easy to apply and to remove for rework, with good moisture protection. The most common general-purpose choice.
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Silicone (SR). Stays flexible across a wide temperature range, so it suits boards that cycle between hot and cold.
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Urethane (UR). Tough and resistant to solvents and fuels, at the cost of harder rework.
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Epoxy (ER). Hard and abrasion resistant with strong chemical resistance, but very difficult to remove, so it is used less on boards that may need repair.
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Parylene (XY). Vapour-deposited in a very thin, pinhole-free layer that covers every surface, used where reliability is critical.
Conformal coating thickness and properties
IPC-A-610, the acceptability standard for electronic assemblies, gives a typical thickness range for each type. Manufacturers then specify their own target within it.
| Coating type | IPC code | Typical thickness | Main strength | Rework |
|---|---|---|---|---|
| Acrylic | AR | 30 to 130 µm | Moisture protection, easy to apply | Easy, dissolves in solvent |
| Silicone | SR | 50 to 210 µm | Flexible over wide temperatures | Moderate |
| Urethane | UR | 30 to 130 µm | Solvent and fuel resistance | Difficult |
| Epoxy | ER | 30 to 130 µm | Hard, abrasion resistant | Very difficult |
| Parylene | XY | 10 to 50 µm | Thin, pinhole-free full coverage | Very difficult, needs abrasion |
Coating materials are qualified to IPC-CC-830, which replaced the older MIL-I-46058C military specification. Many coatings carry a UV tracer that glows under ultraviolet light, so inspectors can check coverage and spot gaps or bubbles.
How conformal coating is applied
Before coating, the board is cleaned, because flux residues and fingerprints trapped under the film cause problems later. Connectors, test points, sockets and anything that must make electrical contact are masked with tape, boots or a selective process.
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Spray. Manual or automated spray suits low and medium volumes and gives an even film over complex boards.
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Dip. The board is lowered into a bath of coating, which gives full coverage but needs more masking.
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Selective robot. A programmed nozzle coats only the areas that need it, avoiding connectors without masking, which suits volume production.
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Vapor deposition. Parylene is deposited from a gas in a vacuum chamber, coating every exposed surface evenly, including under components.
Common coating defects
A coating only protects a board if it is continuous and well bonded. Inspection, usually under UV light, looks for a handful of familiar faults.
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Bubbles and voids. Trapped air leaves thin spots or holes where moisture can reach the copper, often caused by spraying too thickly or curing too fast.
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De-wetting. The coating pulls back from a surface that was not clean, leaving bare patches around residues of flux or release agent.
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Cracking. Hard coatings applied too thickly can crack under temperature cycling, opening paths for moisture.
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Delamination. The film lifts away from the board, which can trap water underneath and make corrosion worse rather than better.
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Coating where it should not be. Film on a connector, socket or test point causes intermittent contacts, which is why masking matters as much as coverage.
When a rugged computer needs coating
For a rugged computer, coating closes the gap that sealing leaves: an IP-rated enclosure keeps water out, but it cannot stop condensation forming inside during a cold start. Coated boards are common in rail, marine, agricultural and outdoor deployments, and coating is available as an option on many rugged boards and systems, so ask for it when you specify.
The rolling stock standard EN 50155 has its own classes for board coating, and many vehicle and defense specifications call for it too. Our guide to what makes a computer rugged covers the other protections, and our rugged single board computers show board-level options.
Quick answers on conformal coating
Conformal coating: common questions
Is conformal coating conductive?
No. Coatings are electrical insulators. That is the point: they stop moisture and contaminants from forming leakage paths between conductors.
Does conformal coating make a board waterproof?
No. It protects against humidity, condensation and splashes, but it is not designed for immersion. Use a sealed, IP-rated enclosure for that.
How do you remove conformal coating?
It depends on the type. Acrylics dissolve in solvent. Silicones and urethanes need specialist strippers, and epoxy and parylene usually need careful abrasion or micro-blasting.
Does conformal coating protect against ESD?
Not reliably. A coating adds some insulation, but it is not an electrostatic discharge protection measure. Handle coated boards with normal ESD precautions.
Does coating affect cooling?
Very little. At tens of microns, the film adds little thermal resistance. Heatsinks and thermal pads still sit directly on the components.
Where the site calls for it, we specify conformally coated boards in the rugged computers we supply, then integrate and validate the complete system as standard before it ships.