Conformal coating is a thin polymer film applied over an assembled PCB to protect it from moisture, dust, chemicals and contamination. The five families you will see specified are acrylic (AR), silicone (SR), urethane (UR), epoxy (ER) and parylene (XY) — the type codes come from IPC-CC-830, the qualification standard for conformal coatings. The right one depends on four practical questions: will the board ever need rework, how much does it flex or thermally cycle, what chemicals or moisture does it see, and how is it applied? There is no best coating; there is the one whose trade-offs match the product.
This guide compares the five types on those questions, shows where coating stops and potting or an IP-rated enclosure takes over, and lists what to put on the drawing so the coating that reaches your finished unit is the one you chose.
The five conformal coating types at a glance
The comparison below is qualitative and general. Exact performance depends on the specific product and its datasheet, so treat it as a way to shortlist, not a substitute for the supplier’s data.
| Type (IPC-CC-830) | Main strength | Main limitation | Rework | Typical application |
|---|---|---|---|---|
| Acrylic (AR) | Easy to apply, good moisture protection, dries quickly | Modest chemical and abrasion resistance | Easy — dissolves in solvent | Brush, spray, dip, selective |
| Silicone (SR) | Flexible, tolerant of wide temperature swings and thermal cycling | Softer film, weaker abrasion resistance; can contaminate other processes | Harder — removal is difficult | Spray, dip, selective |
| Urethane (UR) | Strong chemical and solvent resistance | Harder to remove; slower cure | Difficult — thermal or chemical removal | Spray, dip, selective |
| Epoxy (ER) | Hard, tough film with strong chemical and abrasion resistance | Rigid; can stress components and is very hard to remove | Very difficult, often not practical | Spray, dip, brush |
| Parylene (XY) | Very thin, uniform, pinhole-resistant film that reaches tight gaps | Vacuum-deposition process, more costly, masking is more involved | Difficult | Vapor deposition in a chamber |
Two other terms appear alongside the list: UV-cure coatings, which cure under UV light for fast throughput and often include a fluorescing tracer, and fluorescing tracers in general, which let inspectors confirm coverage under UV light. Both are properties of a specific product, not separate chemistries.
When each type fits
Read the table as a set of trade-offs and pick against the product’s real duty:
- Acrylic — the default when the board may need repair or reprogramming after coating. Its solvent removability is the reason it is common on assemblies that see field service. It is a sensible starting point for general humidity and dust protection.
- Silicone — when the assembly sees wide temperature swings or repeated thermal cycling and needs a flexible film that moves with the board. Check compatibility with the rest of the process first, since silicone residue can interfere with adhesion of other materials later.
- Urethane — when chemical, solvent or fuel-adjacent exposure is the main threat and the board will not be reworked. It gives up repairability for resistance.
- Epoxy — when hardness and abrasion or chemical resistance matter most and rework is not expected. Its rigidity can load fragile parts, so it is usually a deliberate choice, not a default.
- Parylene — when a very thin, highly uniform film is needed, for example on dense or geometry-critical assemblies, and the cost and chamber process are justified.
If the board is inaccessible once the unit is built, choose with rework in mind first: a coating that cannot be removed turns a small defect into a scrapped module.
Thickness and coverage: what is actually specified
Coating performance depends on the film being present where it should be and absent where it must not be. Common practice is to control both:
- Coverage map — which areas are coated and which are keep-outs.
- Thickness target — IPC-A-610 and IPC-CC-830 give typical ranges by type, in the tens of micrometres for most types and thinner still for parylene. Your drawing’s value governs; state it as a range with a measurement method, not a single number.
- Masking — connectors, test points, switches, mating surfaces and adjustment features are masked so coating does not block contact, and labels or marks stay readable.
Coating applied outside the approved area is a defect just as much as missing coating is, so both belong in the inspection criteria.
Where coating stops: potting and IP-rated enclosures
Coating is a thin film on the assembly; it is not a sealed enclosure and not a fill compound. Keep three protections separate:
- Conformal coating protects the PCB surface against moisture, dust and contamination.
- Potting or encapsulation fills a defined cavity around a module or connector for mechanical support and heavier protection, and is largely irreversible — see our conformal coating and potting capability for how both fit inside a Box Build.
- An IP-rated enclosure seals the finished unit as a system. Coating a board does not give the product an IP rating, and an IP-rated box may still benefit from coating inside it — read IP rating and ingress protection for enclosures for the enclosure side.
Choosing one does not replace the others; the design decides how they are layered.
How coating fits into the Box Build sequence
Coating is applied to the assembled PCBA, usually after test and cleaning and before the board is integrated into the enclosure. That ordering matters because coating changes what can be tested and touched afterward — probing through a coated surface is harder, and re-work means removing film first. In PCBA integration, the PCBA arrives with the coating step already placed in the process plan. Anything that will need a test point or adjustment after coating should be identified up front and masked.
In regulated products the coating step also feeds the unit record — material and batch, coverage checks and cure confirmation. The box build for medical devices guide covers how that kind of evidence is expected to be kept.
What to put on your drawing
- The coating type and product — for example “acrylic per IPC-CC-830 type AR, product and datasheet named” — so the exact material is unambiguous. The material identity and its performance are owned by the design, and a Box Build supplier applies the approved one rather than choosing it.
- The coverage map and keep-out zones, marked on the assembly drawing.
- Thickness range and how it is checked, plus the inspection method such as UV-tracer inspection where the product supports it.
- Cure method and time as defined for the product.
- Masking requirements for connectors, test points and adjustment features.
- Rework expectation — whether a coated board may be repaired, so the type and process match.
State the type, the area, the thickness and the rework rule, and the coating that ends up on the finished unit is the one your design intended. For help planning coating inside a complete build, talk to the team behind our conformal coating and potting capability.
FAQ
What are the main types of conformal coating?
The five common families are acrylic (AR), silicone (SR), urethane (UR), epoxy (ER) and parylene (XY), named in IPC-CC-830. They differ in flexibility, chemical resistance, ease of rework and application method: acrylic is easy to apply and repair, silicone is flexible, urethane and epoxy resist chemicals but are hard to remove, and parylene is a vapor-deposited thin film.
Acrylic vs silicone conformal coating: which should I choose?
Choose acrylic when the board may need rework or repair, since it dissolves in solvent. Choose silicone when the assembly sees wide temperature swings or thermal cycling and needs a flexible film, accepting that it is harder to remove. Check the datasheet and process compatibility for your specific product before committing.
Is conformal coating the same as potting?
No. Conformal coating is a thin film over the PCB surface, while potting fills a defined cavity or module with a compound for support and heavier protection, and is usually irreversible. They can be used together, and neither gives an enclosure an IP rating on its own.
Does conformal coating make a product waterproof or IP-rated?
No. Coating protects the board surface against moisture and contamination; an IP rating applies to the sealed enclosure as a whole, verified under IEC 60529. A coated board inside a poorly sealed enclosure does not earn an IP rating.
Can a coated board be reworked?
It depends on the type. Acrylic can be removed with solvent, which is why it suits boards that may be repaired. Silicone, urethane and epoxy are harder or impractical to remove, and parylene is difficult. Decide the rework expectation before choosing the coating.
Who chooses the coating type in a Box Build?
The design owner. The product’s coating type, coverage areas, thickness target and cure method are defined by the customer’s design and datasheets, and the Box Build supplier applies and inspects the approved coating rather than selecting the material.
