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Introduction to the Three-Proof Coating Process (Part 3)
Release time:
2025-04-26 12:45
Three-proof coatings, also known as three-proof paints or electrical protective adhesives, are specialized coating materials endowed with properties such as moisture resistance, dust prevention, mold resistance, and insulation. By being applied onto the surface of electronic device circuit boards, they form a uniform and dense protective film that effectively shields the circuit boards from environmental degradation. Among the various application techniques for three-proof coatings, spray coating has become one of the most widely used methods in the industry due to its high efficiency and even distribution characteristics.
I. Overview of the Spraying Method
As an important method in the application of conformal coatings, the spray coating process operates on the principle of liquid atomization. When the conformal coating is sprayed through the nozzle of a spray gun, it is atomized into tiny droplets under the action of high-pressure gas. These droplets are then ejected at high speed onto the surface of the object to be coated and, influenced by surface tension and gravity, spread out to form a uniform coating. During the spray-coating process, factors such as the size of the atomized droplets, the spraying velocity, and the distance between the spray gun and the surface of the object being coated all affect the uniformity and quality of the resulting coating. The spray-coating method is not only suitable for large-area coating applications but also enables selective spraying, thereby meeting the requirements of various application scenarios.
II. Operation Procedure for the Spraying Method
1. Equipment calibration
Spraying equipment is the core tool for implementing the process, and before operation, it must undergo a comprehensive inspection and adjustment. It is crucial to verify that the atomization effect of the spray gun is fine and uniform, that the paint supply system maintains stable pressure within a reasonable range, and that the exhaust system can effectively remove paint mist. Precise calibration of these fundamental parameters is essential to ensure high-quality spraying results.
2. Workpiece Preprocessing
The cleanliness of the workpiece surface to be coated directly affects the adhesion of the three-proof coating. It is necessary to employ ultrasonic cleaning technology in conjunction with a neutral detergent to thoroughly remove impurities such as oil stains and oxide layers. Subsequently, the workpiece must be completely dried to ensure that no water marks remain on its surface. For areas that need to retain conductivity or avoid coating altogether, specialized masking materials should be used for precise protection, preventing the coating liquid from seeping in and compromising functionality.
3. Apply three-proof coating
Spraying methods can be divided into two types: machine-assisted automatic spraying and manual spraying.
(1) Automatic machine spraying
In automated machine spraying, a motion platform is typically used to mount liquid jet valves or spray valves. The conformal coating is applied onto the product surface by means of pressure tanks or pumping equipment. In some applications, inline machine designs are employed, enabling seamless integration with the entire production line and achieving fully automated, unmanned spraying operations. This approach is well-suited for large-scale production and offers advantages such as high efficiency and stable quality. During automated machine spraying, it is essential to precisely control parameters such as the nozzle’s movement trajectory, spraying speed, and droplet size to ensure uniformity and high quality of the coating.
(2) Hand spraying
Hand spraying is typically carried out using a handheld spray gun. This method is well-suited for small-batch production or repair applications and offers the advantage of flexibility and adaptability. During hand spraying, operators need to master certain spraying techniques—such as controlling parameters like the distance between the spray gun and the surface being coated, the spray rate, and the movement speed—to ensure the uniformity and quality of the coating.
4. Proceed with curing.
Curing is a critical step in forming a stable protective layer with the conformal coating. The curing process must follow a predetermined temperature profile, involving staged curing: first, a low-temperature pre-cure to allow the coating film to take its initial shape; then, gradually increase the temperature to promote cross-linking reactions, ultimately achieving complete curing. During the curing process, it is essential to strictly control temperature fluctuations to prevent performance variations in the coating layer caused by uneven temperatures.
5. Quality inspection
The cured workpiece must undergo a comprehensive quality inspection. The appearance of the paint surface shall be visually inspected, and key parameters such as insulation performance and temperature resistance shall be tested using specialized instruments. For nonconforming products, the type of defect must be clearly identified, and a rework plan must be developed to ensure that the final product meets the standards.
III. Conclusion
As an efficient and uniform coating method, the spray-coating technique plays a crucial role in protecting printed circuit boards in electronic devices. By providing a detailed introduction and analysis of its working principles and operational procedures, we can gain a better understanding and more effectively apply the spray-coating technique, thereby enhancing the quality and reliability of electronic products.
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