Conformal Coating for Aerospace Electronics: Specs, Thickness and Rework

Updated October 12, 2026

Material qualification and workmanship are separate documents

One document qualifies the coating material and others control how it is applied and inspected on your board. A callout that names only the material leaves cleaning, thickness, masking and acceptance undefined, and a callout that names only a workmanship standard leaves the chemistry open.

For wire harness and cable work done alongside the board, see the wire harness service page, since potting and harness protection often share the same material controls.

The five coating types

The type letter tells you the resin family, and the resin family largely decides how hard the coating is to remove, how much stress it puts on parts and what thickness is allowed. The NASA thickness ranges below are from Table 10-1 of NASA-STD-8739.1B.

The IPC handbook also covers coating chemistries outside these five letters, such as amorphous fluoropolymers, fluorocarbons and atomic layer deposition films. If a supplier proposes one of them, ask how it is qualified, because the five letter types are what most flight drawings and acceptance criteria assume.

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Thickness: why both limits matter

Too thin and the coating leaves edges and lead tips exposed. Too thick and it cracks during thermal cycling, traps solvent, or clamps parts so that solder joints carry the stress. NASA-STD-8739.1B notes in its appendix that thickness is of special importance with rigid materials such as epoxies.

• Measure cured thickness on test specimens. NASA-STD-8739.1B applies its thickness limits to the final cured film on a test specimen, which is a spare board, coupon or similar substrate processed with the flight assemblies, so the flight hardware is not damaged by measurement.
• Wet film gauges are allowed in process if they are calibrated to a cured thickness that meets the table.
• Brush coating outside the table limits is nonstandard and needs prior approval under the NASA standard.
• Touchup must meet the minimum thickness but may exceed the maximum.
• Watch bridging. Where coating webs between packages and the board at a thickness above the limit, the standard asks for an evaluation of the effect on stress relief.

Thickness control comes mainly from viscosity and the number of passes. The NASA standard describes spray application as one pass across the board with the gun at about 45 degrees, then rotating the board 90 degrees and repeating until all four directions are sprayed.

Cleaning, demoisturizing and masking come first

Most coating failures start before the coating is applied. Residues under the film cause poor adhesion and can drive corrosion or leakage, and moisture sealed into the board can blister or delaminate the coating.

• NASA-STD-8739.1B requires boards to be cleaned, tested for cleanliness and demoisturized within 8 hours before coating.
• Its demoisturizing example is an oven bake at 90 °C ±5.5 °C for at least 4 hours, or a vacuum bake at lower temperature, with time and temperature recorded. Process controls are required at or above 100 °C to avoid damaging parts from trapped vapor.
• Staking is done before conformal coating unless the design says otherwise.
• Areas to stay clean are masked with approved tape, boots or covers, and the mask must leave no residue. For parylene, unsealed parts must be masked so the vapor cannot penetrate small openings.

Typical keep out areas are connector mating surfaces, test points, adjustable components, switches, grounding pads, heat sink interfaces and anything the next assembly level must contact. Put them on the drawing as a coating map rather than a list in a note. The NASA standard's post cure checks include that coating does not extend into keep out areas or cover connector mating surfaces.

Outgassing for spacecraft and vacuum hardware

For space hardware, the coating has to pass outgassing screening as well as electrical and environmental tests. ASTM E595 heats the material to 125 °C under vacuum for 24 hours and collects condensables on a 25 °C plate, giving total mass loss (TML) and collected volatile condensable material (CVCM).

The standard itself does not set pass or fail limits. It notes that 1.0 percent TML and 0.10 percent CVCM have historically been used as screening levels for spacecraft materials, and NASA Goddard's outgassing database applies those levels when it lists materials. Water vapor regained (WVR) is an optional measurement of how much of the lost mass is water reabsorbed at 50 percent relative humidity.

Two practical points. First, outgassing depends on cure, so a coating that passes in its data sheet cure can fail if the shop shortens the cycle; require the cure schedule on the traveler and the cure record in the cert package. Second, NASA-STD-8739.1B asks that materials be stable under the project's thermal vacuum conditions and traceable to a production lot and manufacturing date. Silicone grades vary widely, so name the specific low outgassing product. Polymer outgassing in general is covered on the engineering plastics page.

Inspection and acceptance

Inspect for coverage, thickness and defects against the workmanship standard named on the order. With fluorescent coatings, NASA-STD-8739.1B requires coverage to be verified under ultraviolet light, which is the fastest way to find thin spots and missed areas.

The NASA post cure criteria include uniform color, thickness and texture, tack free surface, adhesion to all coated surfaces, no lifting or peeling, no contamination, and no bubbles that bridge non-common conductors, expose bare conductors or exceed 0.762 mm (0.03 in) in any dimension. Minor pull back from sharp points and edges is permitted. Discoloration from excessive cure temperature or contamination is a defect, while color change from normal test temperature exposure is allowed.

IPC-A-610 and J-STD-001 carry their own coverage and defect criteria by class. If the contract invokes both a NASA or program standard and an IPC standard, the order of precedence should be on the PO so the inspector knows which wins.

Rework and repair

Plan for rework when you choose the material. NASA-STD-8739.1B tells suppliers to give preference to materials that allow repair and rework without damaging the assembly, and to apply NASA-STD-8739.6 requirements when removing and replacing coating.

The IPC handbook lists removal methods including solvent or chemical stripping, thermal removal, micro abrasive blasting and laser ablation, and combinations of them. Acrylic generally strips with solvent. Urethane, epoxy and parylene usually need mechanical, thermal or abrasive removal, each with ESD and damage risks to nearby parts and the laminate. After repair, the area is cleaned, the new coating is applied and touched up to minimum thickness, and the repaired area is inspected again, under UV where the coating fluoresces.

Record each rework on the traveler. A board that has been stripped and recoated several times can look acceptable but carry hidden laminate or pad damage, which matters for flight hardware.

What to call out on the drawing or PO

• Coating material by type and qualified product, for example IPC-CC-830 Type UR, product named, with any substitution requiring approval.
• Workmanship standard, class and revision: J-STD-001 and IPC-A-610 Class 3, NASA-STD-8739.1, or the program standard, with order of precedence.
• A coating map with coat, do not coat and overspray acceptable zones, and the masking method for parylene.
• Cured thickness range, measured on test specimens processed with the lot.
• Cleanliness test method and limit, demoisturizing schedule, and the cure schedule.
• Outgassing requirement (ASTM E595 with the program's TML and CVCM limits) for space and vacuum use.
• Records: material lot and date code, cure chart, thickness readings, UV inspection, rework history.

Related coatings: spacecraft thermal control coatings, chemical conversion coating for enclosures, and the coatings hub. Cleanliness levels and packaging after cleaning are on the precision cleaning page.

Get flight boards coated and documented

If you need assemblies built or coated to IPC-CC-830 materials with J-STD-001, IPC-A-610 or NASA workmanship requirements, send the drawing, coating map and workmanship callout. We source the work from assembly and coating shops that work to the standard you name, flow down material, thickness, outgassing and inspection requirements, check the records before boards ship, and a person replies within one business day. We sign a mutual NDA before files. Controlled designs follow the process on controlled programs, and our handling of your data is described on the confidentiality page.

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Part, quantity and date are enough to start. Drawings and the mutual NDA follow by reply, and controlled programs never send technical data through this site.

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Related

• Engineering Plastics for Flight and Ground Hardware
• Precision Cleaning and Oxygen Service Cleaning
• Inspection and Metrology for Aerospace Parts
• Spacecraft Thermal Control Coatings: Optical Properties, Degradation and Callouts

Sources

• NASA-STD-8739.1B Change 2: Workmanship Standard for Polymeric Application on Electronic Assemblies
• NASA Technical Standards: NASA-STD-8739.1 listing
• IPC-HDBK-830A table of contents (IPC)
• ASTM E595-15(2021): total mass loss and collected volatile condensable materials
• NASA Goddard outgassing database user guide
• NASA Goddard outgassing database