UV-resistant encapsulation: conformal coating is primarily applied to the printed circuit boards (PCBs) of already soldered plug-in components to form a very thin protective layer. This protective layer enhances the moisture resistance, mold resistance, and salt spray resistance of electronic circuits and components; it protects solder joints and conductors from corrosion, while also providing shielding against electromagnetic interference, preventing circuit short circuits, and improving the insulation performance of the PCB.
UV three-proof varnish, also known as circuit board three-proof varnish, three-proof paint, insulating paint, covering varnish, coating varnish, moisture-proof oil, common-coverage film, patterned coating, electronic coating material, and other similar terms.
Advantages of UV-resistant encapsulant:
1. Environmental friendliness
Solvent-based anti-static paint: contains 40–60% volatile organic compounds (VOC), with emissions of 0.3–0.5 tons of hazardous gases per ton of product. UV moisture-cured dual-cure type: 100% solid content, zero VOC emissions, and compliant with national environmental protection policies.
2. Process Efficiency
Solvent-based hermetic coating: requires 8–24 hours for complete curing; production line cycle time ≤ 200 boards/hour. UV moisture-dual-curing type: surface dryness/initial curing in 3–30 seconds; production line cycle time can reach 1,200 boards/hour, thereby enhancing production line efficiency.
3. Energy consumption costs
Solvent-based hermetic coating: baking energy consumption is approximately 2.8 kW·h/kg. UV moisture-curable coating: photopolymerization energy consumption is 0.4 kW·h/kg (resulting in long-term savings on baking equipment maintenance costs).
4. Address the challenge of shadow hardening
Utilizing a dual curing mechanism—UV photopolymerization followed by moisture post-curing—the treated areas achieve surface dryness and initial curing within 3–30 seconds, while untreated areas undergo deep curing via ambient moisture, thereby fully addressing curing challenges in concealed areas such as the bottom of connectors and component gaps.
5. A broader range of construction environments
The operating temperature range is-40 °C to 130 °C, which meets the requirements for most electronic devices.
Common application techniques for UV three-proof coating:
1. Brush coating: This method is widely used; applying it with a wool brush on a smooth substrate can yield superior coating results.
2. Spraying: Spray can-type products can be conveniently used for maintenance and small-scale production applications, while spray guns are suitable for large-scale production. Both of these spraying methods require high operational precision and may result in shading effects (i.e., areas of components not covered with the three-proof coating).
3. Dip coating: Dip coating ensures complete coverage of the three-proof coating without causing material waste due to over-spraying.
4. Selective coating: Provides precise coating with minimal material waste, making it suitable for large-scale film coating operations; however, it imposes higher requirements on the coating equipment.
Key operational precautions for UV adhesive and EMI/EMI-resistant adhesive:
1. Clean and dry the circuit board to remove moisture and water. First, thoroughly remove dust, moisture, and oil contaminants from the surface of the component to be coated, ensuring optimal performance of the protective properties. Thorough cleaning guarantees complete removal of any corrosive residues and promotes excellent adhesion of the UV triple-protection varnish to the circuit board surface. Drying conditions: 60°C for 10–20 minutes; applying the varnish while the board is still warm after removal from the oven yields superior results.
2. Apply using a brush; the brushing area should exceed the footprint of the component to ensure complete coverage of both the component and the pads.
3. When applying the coating, the plate should be placed as flat as possible; no drips should remain after application; the coating should be applied evenly without any exposed areas, with a preferred thickness range of 0.1–0.3 mm.
4. Before brushing or spraying, ensure that the diluted product has been thoroughly mixed, and allow it to stand for 2 hours prior to application. Use high-quality natural fiber brushes to apply the coating gently by brushing or dipping at room temperature. If mechanical equipment is used, measure the viscosity of the coating (using a viscosity meter or flow cup), and adjust the viscosity as necessary with a thinner.
5. The circuit board assemblies shall be vertically immersed in the coating bath. Connectors shall not be immersed unless they are carefully covered; the circuit boards shall be immersed for 1 minute until bubbles disappear, after which they shall be slowly removed. A uniform film shall form on the surface of the circuit boards. Most coating residues shall be allowed to flow back from the circuit boards into the immersion machine. TFCF has specific coating requirements. The immersion speed of circuit boards or components shall not be too high to avoid excessive bubble formation.
6. When reusing after dipping, if scaling occurs on the surface, remove the surface layer, and the product may then be continued to be used.
7. After brushing, place the coating flat on a support frame for curing; if heating is required, this is known as accelerated curing of the coating. If the coating surface is uneven or contains bubbles, the coating should be placed in the curing oven under appropriate conditions.
Moisture-curing mechanism of UV three-proof adhesive
The core mechanism of moisture-curing is the chemical reaction between the isocyanate groups (-NCO) and water molecules.
The reaction process can be briefly described as follows:
Initial interaction: The-NCO group reacts with water molecules, initiating the reaction to form a carbamate (-NHCOO-) intermediate.
Crosslinking: Multiple-NCO groups undergo sequential reactions with water molecules to form a network structure.
The rate and extent of moisture-curing reactions are significantly influenced by ambient humidity. (All coating operations shall be conducted under conditions where the ambient temperature is not lower than 16 °C and the relative humidity is below 75 %.)
Common Test Parameters for UV Waterproof, Dustproof, and Moistureproof Adhesives
Application Scenarios for UV Waterproof, Dustproof, and Shockproof Coating
1. Civil and Commercial Applications: Three-proof paint can protect electronic circuits in household appliances, enabling them to withstand exposure to water, moisture, insects, and other harmful agents in both commercial and residential environments. Examples of such appliances include soy milk makers, coffee machines, induction cookers, dehumidifiers, dishwashers, air conditioners, computers, bathroom electronics, and electric vehicles.
2. Automotive Industry: The automotive industry requires hermetic coatings to protect circuits from the following hazards: gasoline vapors, salt spray, brake fluid, etc. Given the rapid growth of electronic system applications in automobiles, the use of hermetic coatings has become a fundamental requirement to ensure the long-term reliability of automotive electronic devices, such as computer control systems, air conditioning systems, and automotive electronics.
3. Aerospace: Due to the unique nature of operating environments, aerospace applications impose stringent requirements on electronic equipment—particularly the need to maintain optimal circuit performance under rapid pressurization and decompression conditions. Consequently, the pressure resistance stability of hermetic coatings has found widespread application in satellite systems, military control systems, and flight path control systems.
4. Navigation: Both fresh freshwater and saltwater can pose hazards to the electrical circuits of marine equipment. The use of three-proof paint can maximize protection for equipment on the water surface, as well as for equipment submerged in or beneath the water—such as navigation systems and radar control systems.
5. Electronic Industry: EMI/ESD/Corrosion-resistant coatings protect electronic devices from damage caused by water, moisture, external chemical agents, and harsh operating environments, ensuring their continuous and stable performance; consequently, these coatings have a wide range of applications, including LED displays, LED guardrails, solar energy systems, instrumentation, power supplies, frequency converters, consumer electronics, and anti-theft and fire alarm devices.
Specialized Resin for UV-Rating Encapsulation: Concise Overview
I. Polyurethane-modified acrylate (PUA) resin [Standard Model]
❶ Curing method: UV + moisture dual-curing
❷ Key Features: Moderate viscosity, exceptional adhesion (compatible with PCB substrates such as FR4, copper, and tin), excellent flexibility, resistance to thermal shock, humidity and salt spray, low coefficient of contraction, no stress cracking, and high cost-performance ratio.
❸ Application Scenarios: General consumer electronics, industrial control, and automotive general-purpose PCBs
II. Silicone-Modified Acrylate (Si-PUA) Resin [High-Performance Weather-Resistant Grade]
❶ Curing method: UV + moisture dual-curing
❷ Key Features: Extremely wide temperature resistance range (-60 °C to 200 °C), resistance to UV yellowing, resistance to outdoor aging, resistance to sulfidation, excellent dielectric properties, and a smooth, stain-resistant surface finish.
❸ Weakness: adhesion is slightly inferior to PUA
❹ Application Scenarios: outdoor electronics, 5G base stations, new energy BMS, automotive-grade high-reliability circuit boards
III. Epoxy-modified acrylate (EPA) resin [High-insulation grade]
❶ Curing method: Primarily UV curing, with optional combination of thermal curing.
❷ Key features: high hardness, scratch and wear resistance, excellent insulation strength, resistance to acids, bases, and solvents, and superior dimensional stability
❸ Weakness: Poor ductility; prone to embrittlement at low temperatures
❹ Application scenarios: high-frequency, high-voltage PCBs, power modules, and thick-film protection applications
IV. UV + Moisture Dual-Curing NCO-Modified Acrylate [Specialized for shaded applications]
❶ Curing method: UV curing with rapid surface drying and deep-diffusion dark curing
❷ Key Features: Completely resolves issues related to component shading and incomplete curing of thick coatings (50–200 μm); requires no mixing for single-component application; exhibits low stress; ensures complete curing.
❸ Applicable scenarios: PCBs with high component density, irregular shapes, and numerous shadows
V. Flexible Low-Tg Acrylate Resin [Specialized for Soft Boards]
❶ Curing method: UV curing
❷ Key features: soft texture, bend-and fold-resistant, low-shrinkage crack-resistant film, and excellent adhesion to FPC and PI flexible substrates.
❸ Application scenarios: flexible PCBs, foldable devices, flexible flex cables
The potting and encapsulating compound range named above is one part of the JOME production line. For the earlier discussion of Technical Analysis Synthesis Principles and Key Applications, follow the link, or browse the the complete JOME industrial adhesive line; specifications and samples go through the start a conversation with the JOME team.