Ultimate Guide to PCB Conformal Coating

The operating environments of various electronic devices are complex and changeable. Moisture, dust, high temperatures, salt spray, chemical corrosion and even physical wear and tear during daily use can all cause circuit boards to fail or be scrapped prematurely.

To avoid these problems, engineers apply a layer of conformal coating on the surface of the circuit board, which is like putting on an invisible protective coat for the PCB. It can prevent moisture, corrosion and dust, enhance insulation strength, and ensure that PCBS can still operate stably in damp, high-salt fog or polluted environments. Whether it is consumer electronics, automotive ECUs, industrial control boards, medical devices or aerospace systems, the use of PCB conformal coating can effectively reduce the failure rate and extend the product life.

This article will focus on introducing what conformal coating is, common types of conformal coating, the process of conformal coating, as well as its practical applications in various electronic products. After reading this article, you will be able to determine whether a certain type of PCB needs coating, which PCB coating material should be chosen, and how to correctly apply conformal coating to enhance product reliability.

What is PCB Conformal Coating?

Conformal coating is a thin protective layer applied to the surface of circuit boards, mainly used to prevent damage to PCBs caused by moisture, salt spray, dust, chemical contaminants, and electrical discharges. Unlike potting, it does not encapsulate the entire circuit board. Instead, it covers the surface of the PCB in a very thin way and closely adheres to the components and solder joints, just like putting on a transparent and lightweight protective coat for the PCB.

This kind of PCB protective coating can enhance electrical insulation, prevent short circuits, reduce metal oxidation and corrosion, and at the same time resist a certain level of mechanical stress and temperature changes. Therefore, whether in automotive electronics, aerospace, industrial equipment, medical devices, or outdoor LED lamps, conformal coating for electronics is an effective way to enhance the reliability of circuit boards and extend the lifespan of equipment.

Types of Conformal Coating

Different types of conformal coatings have their own characteristics in terms of protective performance, flexibility, chemical resistance and ease of rework. Common PCB coating materials include the following types:

PCB Conformal Coating Types – Comparison Table

How Conformal Coating is Applied

Common Application Methods

Pre-Coating Preparation

Before applying conformal coating for PCBs, it is necessary to ensure that the surface of the circuit board is clean and dry, and any areas that should not be coated must be properly protected.

First, the PCB needs to be cleaned using deionized water or ultrasonic methods to thoroughly remove flux residues, dust, oil and moisture. This prevents contaminants from affecting the adhesion of the coating or insulation performance.

Subsequently, for areas such as connectors, gold fingers, and test points that need to remain exposed or conductive, masking should be carried out in advance to prevent the conformal coating from covering these critical positions, thereby ensuring that subsequent soldering, testing, or connector mating are not affected.

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Thickness & Quality Control

After the conformal coating is applied to the PCB, the coating thickness is usually controlled between 25 and 127 μm (1 - 5 mils). If the thickness is too thin, it will affect the protective effect; if it is too thick, it may crack or affect the heat dissipation of components. Therefore, thickness and quality inspections need to be carried out after the coating is completed.

Common measurement methods include immediate checks using a wet film thickness gauge or calculating the coating thickness by measuring the thickness difference of the plate with a micrometer before and after coating. For more precise applications, non-contact methods such as eddy current or ultrasonic testing are also adopted to confirm whether the coating is uniform and meets the standards.

Conformal Coating Curing Methods

After the conformal coating is applied, it does not immediately form a final protective film. Instead, it needs to go through a curing process to firmly adhere to the surface of the PCB. Different types of conformal coatings adopt different curing methods, which will affect the hardness, adhesion, production speed and reliability of the coating. The following are several common curing methods.

Industry Standards & Certifications for Conformal Coating

•  IPC-CC-830B / MIL-I-46058C – Industry standard for conformal coating for electronics

•  UL94 V-0 – Flammability classification

•  UL746E – Electrical insulation performance

•  RoHS / REACH – Environmental compliance

Applications in Electronic Devices

The working environments of different electronic devices vary greatly. Some are exposed to high temperatures and vibrations, while others are exposed to moisture, salt spray or chemical substances. Therefore, it is particularly important to apply PCB conformal coating to the circuit board.

Conclusion

Conformal coating for electronics is no longer optional, but a necessary process to ensure the reliability of circuit boards. Whether it is ordinary consumer electronics or highly demanding aerospace equipment, as long as PCB conformal coating is used reasonably, the circuit board can be effectively protected from moisture, dust, corrosion, chemical pollution, vibration or extreme temperatures.

When using conformal coating, choosing the right conformal coating types, mastering the correct conformal coating process, and operating in accordance with industry standards can significantly enhance the stability of electronic products, reduce malfunctions, and extend their service life at the same time.

Whether it is acrylic conformal coating, silicone conformal coating, or parylene PCB protective coating, each type of PCB coating material has its own advantages and applicable environments. As long as this circuit board coating is considered and correctly applied during the product design and production stages, electronic devices can operate stably in harsher environments and be durable and reliable.