What is conformal coating?
Conformal coating is a thin protective polymer film applied to an assembled PCB so that it follows the contours of the board and components. It shields the assembly from moisture, dust, chemicals and corrosion. The main types are acrylic, silicone, urethane, epoxy and parylene, each with different protection, reworkability and application methods.
Conformal coating explained
Conformal coating is applied after assembly and cleaning, once the board has passed inspection and test. The coating forms a thin, continuous layer over solder joints, component leads and exposed copper, reducing the risk of leakage currents, dendritic growth and corrosion caused by humidity, condensation and contamination.
The coating can be applied in several ways. Spraying, either manually or with a selective coating robot, is the most common method for production. Dipping gives full coverage but requires good masking. Brushing suits small volumes and repairs. Parylene is different: it is deposited as a vapour in a vacuum chamber and forms a very thin, uniform, pinhole-free layer.
Areas that must stay uncoated — connectors, test points, switches, sockets, heat-sink contact areas and some sensors — are protected with masking tape, boots or dots before coating, or excluded by a selective coating program. A keep-out drawing tells the assembler exactly which areas to avoid.
Most coatings contain a UV tracer, so coverage can be inspected under ultraviolet light. Qualification of coating materials is covered by IPC-CC-830, and IPC-A-610 includes acceptance criteria for coating coverage, bubbles, voids and de-wetting on finished assemblies.
Each chemistry has a different balance of properties. Acrylics are easy to apply and to remove for rework. Silicones tolerate high temperatures and flex well. Urethanes resist solvents and abrasion. Epoxies are very hard. Parylene gives the most uniform coverage but needs specialised equipment.
When conformal coating matters
Conformal coating matters when an assembly will see humidity, condensation, salt, dust, chemicals or large temperature swings — typical for outdoor, automotive, marine, industrial and some medical products. It also helps on dense designs with fine pitch, where small amounts of moisture and contamination can cause leakage between closely spaced conductors.
Coating is not a cure for a dirty board. Flux residues or other contamination trapped under the coating can cause adhesion loss, blistering and corrosion, so cleanliness before coating is critical. Other common failure modes include coating wicking into connectors, bridging over parts that must stay open, too thin coverage on sharp component edges, and cracking of hard coatings under thermal cycling.
Coating also affects rework and testing. Once a board is coated, probing test points or replacing parts requires local removal of the coating. Decide early whether test access and repairability matter, because that influences the choice of chemistry and the masking plan.
Conformal coating types compared
Acrylic is the common general-purpose choice because it is easy to apply, inspect and remove for rework. Silicone suits high-temperature environments and assemblies that flex or vibrate. Urethane is chosen where solvents, fuels or abrasion are a concern. Parylene gives the most uniform, thin and complete coverage, including under components, but requires vacuum deposition equipment and makes rework difficult.
Conformal coating in your quote request
In your quote request, state the coating type or chemistry you need, the required thickness range if specified, and whether one or both sides are coated. Add a coating drawing that marks keep-out areas such as connectors, test points and switches, and note any standard the coating must meet, for example IPC-CC-830 for the material. If you are unsure which coating fits your environment, describe the operating conditions and we will raise the question with the manufacturer.
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PCB assembly →FAQ about conformal coating
What is conformal coating used for?
Conformal coating is used to protect assembled PCBs from moisture, condensation, dust, chemicals and corrosion. By covering solder joints and exposed conductors with a thin insulating film, it reduces leakage currents and corrosion-related failures. It is common in automotive, industrial, outdoor, marine and medical electronics, and anywhere boards operate in humid or contaminated environments.
What types of conformal coating are there?
The main types are acrylic, silicone, urethane, epoxy and parylene. Acrylic is easy to apply and remove for rework. Silicone handles high temperatures and flexing. Urethane resists solvents and abrasion. Epoxy forms a very hard layer that is difficult to remove. Parylene is vapour-deposited and gives a very thin, uniform and pinhole-free coating.
How do I specify conformal coating for PCB assembly?
Specify the coating chemistry, the sides to be coated and any thickness requirement, and supply a drawing that marks keep-out areas such as connectors, test points and switches. Reference the relevant standards, such as IPC-CC-830 for the coating material and IPC-A-610 for acceptance on the finished assembly. Also state whether coverage must be inspected under UV light.
Related terms
- PCBA
PCBA (Printed Circuit Board Assembly) is the process of populating a bare PCB with electronic components — resistors, capacitors, ICs, connectors, and other parts — to produce a functional electronic assembly ready for testing or integration into a finished product.
- IPC-A-610
IPC-A-610 is the IPC standard that defines visual acceptance criteria for electronic assemblies. It describes what acceptable and defective solder joints, component placement, cleanliness and damage look like on a populated PCB, using photographs and illustrations, across three product classes. It is the most widely used inspection standard in PCB assembly.
- AOI
AOI (Automated Optical Inspection) uses high-resolution cameras to inspect solder joints, component placement, and orientation after assembly. Modern 3D AOI measures joint height and volume volumetrically, catching defects like lifted leads and insufficient solder that 2D systems miss. Limited to visible surfaces — hidden joints under BGAs require X-ray inspection.
- Reflow soldering
Reflow soldering is the process used to solder surface-mount components to a PCB. Solder paste is printed onto the pads, components are placed on the paste, and the board passes through an oven that follows a controlled temperature profile. The paste melts, wets the pads and leads, and forms solder joints as it cools.
- Functional testing
Functional testing powers up the assembled PCB and verifies that it performs its intended function, typically using customer-supplied test scripts or fixtures. Unlike ICT, it tests behaviour rather than individual components. Often combined with programming (loading firmware) and calibration as a final assembly step.