I. Definition of Three-Proof Coating

Three-proof coating is a specially formulated coating used to protect printed circuit boards and related equipment from environmental hazards, thereby enhancing and extending their service life while ensuring safety and reliability in use. Additionally, since three-proof coatings prevent electrical leakage, they allow for higher power levels and closer component spacing on printed circuit boards, thus helping to achieve the goal of component miniaturization.

Three-proof coatings go by various names, such as three-proof sealant, moisture-proof sealant, insulating sealant, moisture-proof paint, protective paint, safeguarding paint, conformal coating, coating sealant, waterproof sealant, moisture-proof oil, three-proof oil, moisture-proof agent, conformal coating material, conformal coating, conformal film, and conformal coating—whose English name is Conformal Coating.

II. What are the three protections?

1. Moisture-proof

Moisture prevention involves guarding against excessive humidity in the air from eroding circuit boards, which could lead to issues such as short circuits and rusting.

2. Mold-resistant

Mold prevention refers to preventing mold growth on circuit boards.

3. Apply salt spray

Mainly in coastal areas, the salt spray is very heavy and can corrode metals. To extend the service life of various equipment, it’s generally necessary to employ special measures to protect against salt spray.

However, its protective effects are not limited to these three aspects alone. It provides excellent protection against a wide range of external environmental factors, including static electricity, corrosion, electrical leakage, dust, and aging. After application, it hardens on the surface of the object to form a transparent protective film, effectively shielding the treated object from environmental degradation.

III. Classification of Three-Proof Coatings

Including solvent-based conformal coatings, UV-curable conformal coatings, polyurethane conformal coatings, and silicone conformal coatings;

1. Solvent-based three-proof coating

Solvent-based acrylic resin conformal coating (currently the most widely used and mainstream product on the market);

Features: Quick surface drying and curing time, excellent three-proof performance, low price, transparent color, flexible texture, and easy repairability.

Under real-world conditions—such as chemical environments (e.g., fuels, coolants), vibrations, high dust levels, salt spray, humidity, and high temperatures—circuit boards may experience issues like corrosion, softening, deformation, and mold growth, leading to circuit failures.

The conformal coating is applied to the surface of the circuit board, forming a lightweight and flexible film with a thickness of approximately 25 to 50 microns. It protects the circuit from damage under the harsh conditions mentioned above.

2. Silicone-based three-proof coating

The silicone-based three-proof coating is a soft, elastic material that effectively relieves stress. It withstands high temperatures up to 200 degrees and is easy to repair.

Silicone-based conformal coatings come in two types: solvent-resistant and solvent-removable. Both are suitable for use under high-temperature conditions and exhibit excellent chemical resistance and salt-spray resistance.

Although solvent-resistant products can undergo welding operations, they are difficult to remove using organic solvents. Their most distinctive feature is that the chemical bonds become increasingly stronger over time. To achieve optimal performance, these products can be thermally cured if necessary.

Silicone products possess remarkable electrical insulation properties, making them an ideal choice for applications in high-voltage and highly integrated circuit boards.

3. UV-resistant, waterproof, and dustproof coating

Solvent-free acrylic resin three-proof coating features: UV-curable, surface-dry within a few seconds to ten-odd seconds, transparent in color, relatively hard in texture, and boasting excellent resistance to chemical corrosion and abrasion.

The three-proof coatings that are initially cured using ultraviolet light do not require solvents. They are non-flammable and free of volatile organic compounds, fully complying with both current and proposed environmental regulations.

They offer excellent chemical resistance and heat resistance, high flexibility, a glossy surface, strong adhesion, and superior coverage. Their curing time is short—just a fraction of that required by other products (measured in seconds)—and by boosting productivity, they significantly reduce product costs.

IV. Application Fields

Including civil commercial applications, the automotive industry, aerospace, marine navigation, and the electronics industry, among others;

1. Civil and commercial applications

Three-proof coatings can protect the electronic circuits in household appliances, enabling them to withstand: water, moisture, insects, and harmful substances found in offices and homes.

Such as: soybean milk makers, coffee machines, induction cookers, dryers, dishwashers, air conditioners, computers, bathroom electronics, electric vehicles, and more.

2. Automotive Industry

The automotive industry requires conformal coatings to protect circuits from hazards such as gasoline vapors, salt spray, and brake fluids. With the rapid and continuous growth in the use of electronic systems in automobiles, applying conformal coatings has become a fundamental requirement for ensuring the long-term reliability of automotive electronic components.

For example: computer control systems, air conditioning, and automotive electronics.

3. Aerospace

Due to the unique characteristics of their operating environments, aerospace and aviation applications place stringent requirements on electronic devices—especially under conditions of rapid pressurization and depressurization—where the devices must continue to maintain excellent circuit performance. Consequently, the voltage stability of three-proof coatings has become widely adopted.

For example: satellite systems, military control systems, and flight route control systems.

4. Electronics Industry

Three-proof coatings protect electronic devices from erosion caused by water, moisture, external chemicals, and special operating environments, ensuring their continued stability. Their application scope is extremely broad.

For example: LED displays, LED guardrail tubes, solar energy, instruments and meters, power supplies, frequency converters, consumer electronics, anti-theft and fire alarm systems, and more.

5. Navigation

Both fresh water and saltwater can damage the electrical circuits of ship equipment. Applying a three-proof coating can provide maximum protection for equipment both above and below the waterline, even when fully submerged.

For example: navigation systems, radar control systems.

V. Coating Method

Including brush coating, dip coating, flow coating, and spray coating;

1. Brush coating

The brush-coating method is the simplest coating technique. It’s typically used for localized repairs and maintenance, and can also be applied in laboratory settings or for small-batch trials and production—generally in situations where the quality requirements for coating are not particularly high.

Advantages: Virtually no investment required in equipment or fixtures; saves on coating materials; generally eliminates the need for masking operations.

Disadvantages: narrow application scope; lowest efficiency; when applying the coating to an entire board, there’s a masking effect, leading to poor coating consistency. Due to manual operation, defects such as bubbles, ripples, and uneven thickness are prone to occur. It also requires a large amount of labor.

2. Dip coating

The brush-coating method is the simplest coating technique. It’s typically used for localized repairs and maintenance, and can also be applied in laboratory settings or for small-batch trials and production—generally in situations where the quality requirements for coating are not particularly high.

Advantages: Virtually no investment required in equipment or fixtures; saves on coating materials; generally eliminates the need for masking operations.

Disadvantages: narrow application scope; lowest efficiency; when applying the coating to an entire board, there’s a masking effect, leading to poor coating consistency. Due to manual operation, defects such as bubbles, ripples, and uneven thickness are prone to occur. It also requires a large amount of labor.

3. Coating by spraying

The dip-coating method is a less commonly used technique for applying conformal coatings.

The three-proof coating stored in the elevated tank is sprayed or flowed through a narrow slot, forming a curtain-like film that evenly coats the substrate driven by a conveying mechanism. Excess three-proof coating flows back into the container and is pumped back to the elevated tank for recycling.

In small-batch production, manual operations are typically used to directly apply the three-proof coating onto the product; therefore, the dip-coating method is also referred to as the pour-coating method.

In mass production, automated assembly lines are typically used. The thickness of the three-proof coating applied to the product is controlled by adjusting the size of the nozzle or the width of the narrow slot. If the coating is too thick, bubbles will form on the product as it exits the drying oven via the conveyor belt. On the other hand, if the coating is too thin, the substrate will show through, resulting in uneven application. For this reason, the curtain-coating method is also referred to as curtain spraying.

Depending on the characteristics of different products, sulfurization may sometimes be required to enhance the adhesion of the conformal coating film onto the product. To increase the coating thickness, it may also be necessary to apply the coating by spraying and then subject the product to one or more sulfurization treatments.

4. Spraying

Spraying is the most commonly used coating method in the industry, and it is further divided into two types: automated machine spraying and manual spraying.

Among these, automated machine spraying is suitable for customers engaged in large-scale production, as well as those with high-volume or long-term production needs.

The advantages are: selective spraying, high precision, uniformity, high efficiency, and automatic detection capability.

The drawbacks are: high cost, high requirements for operational accuracy, and the potential to create shadows (areas beneath components that remain uncovered by the conformal coating).

6. UV-resistant, three-proof coating

1. Dual curing

Dual-curing refers to the combination of light curing with other curing methods, which complement each other and highlight their respective advantages. This approach offers rapid curing at low temperatures and excellent stability, effectively preventing uncured resin separation and yielding cured products with outstanding mechanical properties and dimensional stability. The development of dual-curing systems that integrate light curing with other curing methods has proven highly effective in overcoming the weaknesses of light-curable adhesives, expanding their application scope, and enhancing their competitiveness. Other curing methods include thermal curing, moisture curing, oxidative curing, and anaerobic curing.

2. Why adopt dual curing with light and moisture?

Since the curing process of UV-curable systems is initiated by light, these systems also have the following drawbacks: limited curing depth; difficulty in use with colored systems and opaque materials; and inability to cure objects with excessively complex shapes. To address these limitations, a dual-curing system has been developed, combining light curing with other curing methods.

In this system, the crosslinking or polymerization reaction of the system is accomplished through two independent stages, each with a different reaction mechanism. One stage proceeds via UV light-induced reactions, while the other stage involves dark reactions such as thermal curing, moisture curing, oxidative curing, or anaerobic curing.

This allows the system to rapidly cure—or achieve “surface dry”—using UV light, while the dark-curing reaction ensures that the “shadowed” areas or inner layers are fully cured to reach “full dry.” The dual-layer curing process expands the application of UV adhesives to opaque substrates, substrates with complex geometries, ultra-thick adhesive layers, and colored adhesive layers. This system gives UV adhesives greater competitiveness.

3. UV-resistant, waterproof, and dustproof coating

Definition: UV three-proof coating is a UV-light dual-curing electronic coating.

Basic introduction: Areas not fully cured by light can be cured by moisture. This UV-resistant conformal coating offers the highest level of protection for electronic circuits, making it a fast-application, high-performance conformal coating that remains effective even under harsh operating conditions.

Feature Introduction: UV triple-proof coating is a single-component, low-viscosity electronic conformal coating that cures both via ultraviolet light and moisture. Under irradiation by ultraviolet light of a specific wavelength, it can achieve surface dryness within just a few seconds. This coating boasts excellent resistance to yellowing, moisture, and chemical exposure, making it suitable for coating various types of printed circuit boards. It provides protection for solder joints and pins, and is particularly well-suited for application methods such as spraying, dispensing, and manual brushing. The UV triple-proof coating is a UV-light dual-curing electronic conformal coating that combines surface UV curing with intermediate-layer moisture curing. Leveraging the principle of multi-stage UV curing, this PCB protective coating achieves rapid curing in just tens of seconds.

4. Main advantages

Environmentally friendly and safe: UV three-proof coatings contain no VOCs, posing no pollution to the ambient air; few of the ingredients in UV three-proof coatings are restricted or prohibited under environmental regulations; they are solvent-free and have low flammability.

Economic and cost-saving: UV three-proof coating cures rapidly, which is conducive to automated production lines and boosts labor productivity. After curing, the coating can be inspected and handled immediately, saving space. Its compact size requires less floor space, further conserving area. The UV three-proof coating only needs to be applied in a very thin layer, reducing material consumption and lowering costs. It’s a single-component system that doesn’t require mixing, making it easy to use.

Compatibility: Suitable for materials sensitive to temperature, solvents, and moisture; adjustable curing time and degree of cure for smarter, more convenient operation; allows for repeated application and multiple curing cycles; UV-resistant, three-protection adhesive that can undergo secondary moisture curing even in shaded areas where UV light cannot reach.

As a manufacturer of UV resins, Boxing New Materials has launched light- and moisture-curable resins for UV three-proof coatings, such as product models B-404 and B-405. These products have received unanimous recognition from numerous three-proof coating manufacturers. We welcome your inquiries and invite you to request samples for testing.

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