Applying conformal coating to a printed circuit board is only half the job. If the coating is too thin, the board remains vulnerable to moisture, dust, chemical corrosion, and thermal shock. If it is too thick, the coating may crack during curing, trap solvents, or interfere with delicate components and connectors. Getting the thickness right — and proving it through repeatable measurement — is what separates a protected board from a reliably protected one.
Why Coating Thickness Matters in Electronics Manufacturing
Conformal coating is a thin protective film — typically 25 to 210 micrometres — applied across a PCB to shield it from environmental threats such as humidity, salt spray, dust contamination, chemical exposure, and temperature extremes. Whether you are working with acrylic, silicone, polyurethane, or epoxy-based chemistries, the dry-film thickness directly determines how well the coating performs over the product's service life.
For manufacturers assembling boards that must survive in automotive engine compartments, outdoor security enclosures, or medical devices subjected to repeated sterilisation, thickness is not a "nice to have" data point. It is a process-control parameter tied to recognised standards. IPC-A-610, the widely used PCBA acceptability standard, includes criteria for conformal coating coverage and thickness. Boards that fall outside the specified range risk field failures, warranty claims, and qualification failures during customer audits.
Two Core Approaches: Wet-Film and Dry-Film Measurement
There are two principal ways to verify coating thickness, and each answers a different question in the production process. Wet-film measurement tells you what is happening during application, before the coating cures. Dry-film measurement tells you what you actually delivered on the finished board. A well-controlled process uses both.
Wet-Film Gauge Measurement
A wet-film thickness gauge — a notched comb or wheel — is placed into the wet coating immediately after application. The teeth that make contact with the coating reveal the wet thickness, which can then be converted to a dry-film value using the coating's known solid-content percentage. This method lets operators catch over-application or under-application in real time, before the coating enters the curing oven. It is inexpensive, fast, and especially useful during process setup or when qualifying a new coating material on a new board layout.
Dry-Film Eddy-Current Measurement
After the coating has fully cured, a non-contact eddy-current probe can measure dry-film thickness without damaging the surface. Instruments such as the PosiTest series place a flat probe on the coated area and return a reading precise to roughly ±1 micrometre in the 25–50 micrometre range. The measurement is nearly instantaneous and repeatable, making it suitable for production-line quality control and for creating permanent inspection records.
Test Coupons
Test coupons — small bare-board fragments coated alongside the production batch — offer a practical way to verify thickness without probing the actual assembly. Because the coupon receives the same coating pass under the same conditions, its measured thickness serves as a reliable proxy for the boards in the run. Coupons can be archived as physical quality records, which is particularly valuable for industries that require traceability.
Typical Thickness Ranges by Coating Chemistry
Different coating materials have different optimal thickness windows. Understanding these ranges helps you interpret measurement readings and set the right process targets.
| Coating Type |
Typical Dry-Film Range |
Key Characteristics |
| Acrylic (AR) |
30–75 µm |
Easy to apply and rework; good moisture resistance |
| Silicone (SR) |
50–200 µm |
High flexibility; excellent high-temperature performance |
| Polyurethane (UR) |
25–75 µm |
Strong chemical and solvent resistance |
| Epoxy (ER) |
30–80 µm |
Hard, durable finish; difficult to remove once cured |
These ranges are general industry guidance; always confirm the specification for your particular material grade and end-use environment with the coating supplier and your applicable customer standard.
Integrating Thickness Control Into the Production Line
Knowing
how to measure conformal coating thickness is only useful if the measurement is embedded in a controlled, repeatable production workflow. At Farway Electronic, the conformal coating service runs on an automated Anda spraying line capable of handling boards up to 550 mm × 470 mm. The line supports selective masking, double-sided spraying and baking, and both fan and needle spray modes, with average spray times of 0.5 to 3 minutes per board — giving operators the consistency needed to hold a target thickness across a full batch.
Process tip: When you
spray conformal coating on dense, high-pin-count assemblies, use wet-film gauges during the initial setup pass to dial in the spray parameters, then verify the cured result with eddy-current dry-film readings on test coupons. This two-stage approach catches drift before it affects the entire batch.
Thickness verification does not stand alone, either. It sits within a broader inspection framework. Farway's PCBA test capability includes AOI, X-ray inspection, thermal imaging, and high- and low-temperature reliability testing, all conducted under IPC-oriented controls. When a coated board passes this combined inspection regime, the thickness reading gains meaning because it is corroborated by visual, structural, and functional data.
Choosing the Right Measurement Strategy
Selecting a measurement method depends on your production stage, your coating material, and your documentation requirements:
• During process setup or new-product qualification — use wet-film gauges to establish spray parameters and confirm you are in the target range before committing a full batch.
• For routine production quality control — rely on dry-film eddy-current readings on test coupons taken from each batch, archiving the coupons as physical records.
• For high-reliability or regulated industries — combine coupon measurement with full-board AOI and functional testing so that thickness, coverage, and electrical performance are all verified before shipment.
If you are new to the topic and wondering
what conformal coating actually does for your electronics beyond thickness numbers, the short answer is that it forms a barrier against the environmental factors that cause field failures — but only when applied at the correct thickness and verified through a disciplined process.
A Partner That Controls Thickness End to End
Thickness measurement is one link in a chain that runs from PCB fabrication through component sourcing, SMT and DIP assembly, coating, testing, and finished-product box-build. Farway Electronic, established in 2018 and operating a 2,000-square-metre facility in LongGang, Shenzhen, manages that entire chain under one roof. The company holds ISO 9001, ISO 13485, IATF 16949, and ISO 14001 certifications, and builds to IPC-A-610 assembly standards — giving customers confidence that coating thickness is controlled within a system designed for automotive, medical, security, and new-energy applications.
With
conformal coating services integrated alongside SMT lines, DIP through-hole welding, low-pressure injection moulding, PCBA functional testing, and finished-product assembly, Farway provides a single point of accountability for boards that must perform in demanding environments.
Need controlled, verified conformal coating on your next PCBA project? Farway Electronic combines automated spraying, thickness measurement, and full IPC-oriented testing in a one-stop manufacturing workflow. Contact the team at
Farway's conformal coating service or email sales@farway.hk to discuss your coating requirements, thickness specifications, and production schedule.
