Conformal coating is a thin polymeric film applied to a printed circuit board assembly to conform to the contours of the board and its components. The coating acts as a barrier between the electronic circuitry and the surrounding environment. If you have ever asked what is conformal coating, the short answer is that it is a protective layer designed to keep moisture, dust, chemicals, and temperature extremes from reaching sensitive conductors and solder joints.
The film is typically between 30 and 210 micrometres thick. Despite being thin, it significantly improves the surface insulation resistance of the board, reduces the risk of corrosion on copper traces, and helps prevent short circuits caused by condensation or conductive contaminants. For products that must meet reliability standards in automotive, medical, industrial, and outdoor applications, conformal coating is not optional but a required step in the assembly process.
A bare circuit board, even after soldering, is exposed to whatever the environment throws at it. Humidity condenses on metal traces and slowly corrodes them. Salt spray in coastal or automotive environments accelerates electrochemical migration. Dust and industrial chemicals settle on the board surface and can create conductive bridges between closely spaced pads. Thermal cycling causes expansion and contraction that stresses solder joints over time.
PCB conformal coating addresses these threats directly. The coating seals the board surface against moisture ingress, blocks airborne contaminants from reaching conductors, dampens mechanical vibration stress on solder joints, and improves dielectric strength between adjacent traces. The result is a board that maintains its electrical performance longer and survives field conditions that would otherwise cause early failure.
Key point: Conformal coating does not make a board waterproof in the sense of submersion. It provides resistance against humidity, condensation, and chemical exposure. For full waterproofing, low-pressure injection moulding or potting may be required.
Several chemistries are used for conformal coating, each with distinct properties. Selecting the right material depends on the operating environment, the required temperature range, and any rework needs.
| Material | Key Characteristics |
|---|---|
| Acrylic (AR) | Fast curing, good moisture resistance, easy to rework and remove, moderate chemical resistance. |
| Silicone (SR) | Flexible and elastic, excellent thermal stability across wide temperature ranges, good vibration damping. |
| Urethane (UR) | Hard durable finish, superior abrasion and chemical resistance, stable at low temperatures, harder to rework. |
| Epoxy (ER) | Very rigid, strong moisture and chemical barrier, good dielectric properties, difficult to remove once cured. |
Most coatings cure either at room temperature or with applied heat. Heat-cured coatings tend to form a harder surface that resists abrasion, while room-temperature-cured coatings retain more flexibility. The choice depends on the product requirements and the manufacturing process available.
Understanding how to apply conformal coating correctly is critical because the method affects coating uniformity, thickness control, and production throughput. There are four common application methods:
1. Spraying: The most widely used method for medium to high volume production. Coating is atomised and directed onto the board. Automated spray systems with selective nozzles can target specific areas while masking connectors and contacts. Thickness depends on spray pressure, traverse speed, and number of passes.
2. Brushing: Suitable for low volume or rework. A brush applies coating manually. It is inexpensive but thickness uniformity depends heavily on operator skill, and bristle hairs can contaminate the coating.
3. Dipping: The entire board is submerged in coating liquid. Economical for uniform boards, but thickness varies with immersion speed, temperature, and withdrawal rate. Not suitable for boards with components that cannot be coated.
4. Selective coating: A programmable automated system applies coating only where needed. This is the preferred method for complex boards with many keep-out areas, offering consistency and repeatability for production runs.
Regardless of method, certain components must be masked before coating. Connectors, switches, speakers, LEDs, and adjustable components should not be coated, because the insulating film can interfere with electrical contact, sound output, or light transmission.
Farway Electronic operates an automated conformal coating line at its production facility in LongGang, Shenzhen. The coating service is designed to protect circuit boards from moisture, leakage, shock, dust, corrosion, ageing, corona, and harsh temperature environments. The line supports boards up to 550 mm by 470 mm, accommodating dense assemblies with high pin-count components.
The process includes selective masking for keep-out areas, double-sided spraying and baking, and both fan and needle spray modes. Average spraying time ranges from 0.5 to 3 minutes per board, making the line suitable for both prototype and production-volume runs. This coating service is part of Farway's broader one-stop electronics manufacturing chain, which covers SMT PCB assembly, DIP through-hole welding, PCBA OEM manufacturing, and finished product assembly under one roof.
Equipment and standards: Farway's coating line uses Anda automatic spraying equipment. The company operates under ISO 9001, ISO 13485, IATF 16949, and ISO 14001 management system certifications, and follows IPC-A-610 as its PCBA assembly standard. Product certifications within scope include UL, RoHS, SGS, and REACH.
Applying coating is only half the job. Verifying that the coating is present, uniform, and effective requires a structured inspection and testing process. Farway conducts a range of inspections on coated assemblies, including:
UV inspection to verify coating coverage and detect gaps or thin spots
AOI optical inspection of solder joints beneath the coating
X-ray inspection for hidden solder connections on BGAs and QFNs
Thermal imaging to detect hot spots under operating load
High and low temperature reliability testing
FCT functional testing to confirm the board works as designed after coating
These steps are part of Farway's comprehensive PCBA testing capability, which covers the full inspection chain from solder paste verification through final functional test. The company also offers a one-year free-repair commitment for eligible non-external defects arising during standard customer use, giving buyers additional confidence in the reliability of coated assemblies.
Conformal coating is not needed for every product, but for many industries it is essential. Automotive electronics face temperature swings from engine heat to winter cold, plus humidity and road salt exposure. Medical devices must maintain reliable operation in sterilisation environments and during long service lives. Industrial controls operate in factories with chemical fumes, dust, and vibration. Security and communication equipment deployed outdoors must resist rain, condensation, and UV exposure.
Farway serves customers across all of these sectors. The company's Service Area catalog spans transportation, new energy, security, medical, communication, and other industrial applications. With experience across more than 100 industry customers and over 20 countries and regions, Farway understands the coating requirements that different applications demand.
For applications where conformal coating alone is not sufficient, Farway also offers PCBA low-pressure injection moulding. This process encapsulates sensitive components under a thicker protective layer, providing a higher level of environmental protection than surface coating alone. Applications include medical and industrial sensors, LED lighting, battery packs, connector harnesses, and microswitches. When combined with conformal coating, low-pressure moulding creates a layered defence that protects boards against both everyday humidity and direct water exposure.
This combination of coating and encapsulation services, integrated with PCB fabrication, component sourcing, SMT and DIP assembly, testing, and finished product assembly, is what makes Farway a true one-stop manufacturing partner. Customers can move from prototype through volume production without managing multiple vendors for each process step.
Ready to protect your PCBAs? Whether you need conformal coating for a prototype run or a production batch, Farway Electronic can help. Contact the engineering team at sales@farway.hk or call 181 2472 7402 to discuss your coating requirements, request a quotation, or learn more about the full range of electronics manufacturing services available at the Shenzhen facility.
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