Conformal coating is one of the most effective ways to safeguard printed circuit boards against moisture, dust, chemicals, and temperature extremes. Yet applying the coating is only half the equation. If the film is too thin, the board remains vulnerable to environmental damage; if it is too thick, it can cause cracking, stress on components, or interference with connectors. Understanding how to measure conformal coating thickness is therefore a critical quality-control step that separates reliable PCB assemblies from failure-prone ones.
The purpose of conformal coating is to form a uniform protective film — typically 25 to 210 micrometres — over the PCB surface and its components. This film acts as a barrier against moisture ingress, salt spray, dust contamination, chemical corrosion, and fungal growth. When the coating thickness falls outside the recommended range for a given material, the protective function is compromised.
Too little coating leaves traces of bare board exposed, creating paths for electrochemical migration and dendrite growth under humid conditions. Too much coating can trap solvents, produce bubbles during curing, or build up excess material around tall components, leading to mechanical stress and eventual delamination. For industries such as automotive, medical devices, and industrial controls — where boards operate in harsh environments for years — precise thickness control is not optional but mandatory.
Industry standards such as IPC-A-610 and IPC-CC-830 define acceptable coating coverage and thickness ranges for different chemistries. Manufacturers that follow these standards can demonstrate that their conformal coating electronics processes meet the reliability requirements demanded by global OEM customers.
Wet film thickness measurement is performed immediately after the coating is applied, while the material is still in its liquid state. This approach allows operators to verify coverage before the coating cures, making it possible to adjust spray parameters or rework the board if the deposit is off-target.
The most common tool for wet film measurement is a wet film gauge — a small comb-like instrument with teeth of varying known lengths. The gauge is placed directly onto the wet coating surface, and the teeth that make contact with the coating indicate the wet film thickness. Once the wet thickness is known, the dry film thickness can be estimated by multiplying it by the solid-content ratio of the coating material, which is typically provided on the manufacturer's technical data sheet.
Works best on flat, accessible areas of the board. Provides immediate feedback during the spraying process. Low cost and simple to use. Does not damage the coating since measurement happens before curing. However, it is less suitable for complex geometries or selective-coated areas with heavy masking.
Dry film thickness is measured after the coating has fully cured. This is the value that ultimately determines whether the board meets specification, so it serves as the final verification step in the coating process.
Eddy-current instruments use a probe that generates an alternating magnetic field. When placed over a non-conductive coating on a conductive substrate, the instrument calculates thickness based on the change in the field. This method is fast, non-destructive, and can deliver readings accurate to within one micrometre on films in the 25 to 50 micrometre range. It is widely used on production lines where speed and repeatability matter.
Ultrasonic gauges send a pulse through the coating and measure the time it takes for the echo to return from the coating-substrate interface. Because this method does not rely on a conductive substrate, it can be used on a wider range of board materials. It is particularly useful for silicone and polyurethane coatings where eddy-current probes may not perform well.
Coating coupons — small bare-board samples processed alongside production boards — provide a convenient surface for measurement and can be archived as a physical record of the coating applied during a given production run. Coupons are especially valuable when the production board itself has too many components or irregular surfaces for reliable direct measurement.
No single measurement method is ideal for every situation. Wet film gauges are inexpensive and provide real-time feedback, but they cannot tell you the final cured thickness. Eddy-current gauges are fast and precise on conductive substrates but require flat surfaces. Ultrasonic gauges offer material versatility but may need more setup time per measurement. Coupons add traceability but represent the coating on a separate sample rather than the actual product board.
In practice, the most effective quality programmes combine methods: wet film measurement during application for process control, dry film measurement after curing for final verification, and archived coupons for traceability. This layered approach ensures that both the process and the product meet the thickness specification required for long-term reliability.
At Farway Electronic, conformal coating is performed on an automated spraying line designed for consistent, repeatable film deposition. The line supports boards up to 550 mm by 470 mm and handles dense, high-pin-count assemblies through selective masking, double-sided spraying, and baking. Fan and needle spraying options accommodate different coating chemistries, and the average spraying time of 0.5 to 3 minutes per board keeps throughput efficient without sacrificing uniformity.
Coating quality is verified under IPC-oriented inspection controls that include manual visual inspection, AOI, and thermal imaging. The company operates under ISO 9001, ISO 13485, IATF 16949, and ISO 14001 certified management systems, and its PCBA assemblies are produced to the IPC-A-610 standard. This combination of automated application, multi-method inspection, and internationally recognised quality systems helps ensure that every coated board meets the thickness and coverage requirements demanded by customers in automotive, medical, industrial, and communications markets.
Beyond coating, Farway provides a full electronics manufacturing chain — from PCB fabrication and component sourcing through SMT, DIP, testing, and finished product assembly — at its 2,000-square-metre facility in LongGang, Shenzhen. This integrated capability means coating parameters can be co-optimised with upstream assembly and downstream testing, reducing the risk of coating-related field failures.
| Farway Coating Line Capability | Detail |
|---|---|
| Maximum board size | 550 mm x 470 mm |
| Spraying methods | Fan spray, needle spray, selective masking |
| Processing modes | Single-sided and double-sided spraying with baking |
| Throughput | 0.5 to 3 minutes average per board |
| Inspection methods | Visual, AOI, thermal imaging |
| Quality standards | IPC-A-610, ISO 9001, IATF 16949, ISO 13485 |
Whether you need acrylic, silicone, or polyurethane coating applied with precise thickness control, Farway Electronic's automated line and IPC-oriented inspection process can help you protect your boards for the environments they will face. Contact the engineering team at sales@farway.hk or visit the conformal coating service page to discuss your coating requirements and request a quotation.
Hey there! Your message matters! It'll go straight into our CRM system. Expect a one-on-one reply from our CS within 7×24 hours. We value your feedback. Fill in the box and share your thoughts!