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Operating Procedures for Applying Three-Proof Coating (Part 3)
Release time:
2025-04-28 07:12
The spray-coating method, with its advantages of high coating efficiency and strong adaptability, occupies an important position in large-scale production as well as in the protection of circuit boards with complex structures. However, although the spray-coating method may seem easy to operate, it actually places extremely high demands on various parameters and operational details. From securing the circuit board, to fine-tuning parameters during the trial-spray phase, and then to precisely controlling factors such as spraying sequence, pressure, speed, distance, and angle during formal spraying—any deviation at any stage can lead to defects in the paint film, seriously compromising the protective performance of the circuit board.
The spray-coating method for applying conformal coatings is a widely used technique for protecting electronic and electrical products. By evenly spraying the conformal coating onto the surface of the circuit board, a protective film is formed to prevent damage to electronic components caused by environmental factors such as moisture, salt spray, mold, and dust, thereby extending the product's service life. The following are the key points of the spray-coating operation procedure:
I. Fixed Circuit Board
Place the circuit board to be coated onto the coating fixture, ensuring that the board is positioned stably and accurately.
II. Trial Spray
Before performing the formal spray coating, first conduct a trial spray on a scrap circuit board or a test specimen. Adjust the spray gun’s spraying distance, spraying angle, and spraying speed, and observe the spray results—such as the thickness and uniformity of the paint film—until you achieve satisfactory spray parameters.
3. Apply the spray coating officially.
Apply the coating according to the predetermined spraying path. The spraying path should be uniform and continuous, avoiding issues such as missed spots or excessive overlap. For large-area circuit boards, a “well”-shaped or “S”-shaped spraying pattern can be used to ensure that the entire surface is evenly coated. Control the number of spray passes and the thickness of the paint film. For typical protective requirements, one to two spray passes are usually sufficient to achieve an appropriate paint film thickness. After spraying, use a paint film thickness gauge to inspect the circuit board and ensure that the paint film thickness meets the product specifications.
4. Spraying Sequence
Spraying should be carried out in a specific sequence: first spray the edges and corners of the PCB, then proceed to the central areas; first spray the back side of components, then spray the front side. This approach helps prevent uneven coating thickness on already sprayed areas caused by paint mist rebound.
V. Spray Pressure
The spray pressure should be adjusted according to the viscosity of the conformal coating and the type of spray gun used. Generally, for air spray guns, the spray pressure should be maintained between 0.2 and 0.4 MPa; for high-pressure airless spray guns, the spray pressure should be controlled within the range of 10 to 20 MPa. If the pressure is too low, the conformal coating will not atomize adequately, resulting in a rough coating surface. If the pressure is too high, the coating mist will scatter excessively, leading to material waste and potentially polluting the environment.
6. Spray Gun Moving Speed
The spray gun’s moving speed should be uniform and stable, typically maintained between 10 and 30 cm/s. If the speed is too fast, the coating thickness will be insufficient; if it’s too slow, the coating will be excessively thick, increasing the risk of sagging and buildup. The spray gun’s moving speed can be adjusted according to the PCB’s size and shape to ensure even coating coverage. For small PCBs, the spray gun’s moving speed can be slightly increased; for large or complex-structured PCBs, the spray gun’s moving speed should be slowed down.
7. Spray Distance
The spray distance refers to the distance between the spray gun nozzle and the PCB surface, typically maintained within the range of 15–30 cm. If the distance is too close, paint mist may bounce back, easily causing sagging and orange-peel texture; if the distance is too far, the paint mist will disperse, resulting in uneven coating thickness.
8. Spraying Angle
The spray gun should be held at a vertical or nearly vertical angle when spraying onto the PCB surface. If the angle is too steep or too shallow, it will result in uneven coating thickness and cause shadowing or bare substrate exposure.
9. Multi-layer spraying
If multiple layers of conformal coating are required to meet specific protection requirements, the next layer should be applied only after the previous layer has completely dried. Generally, the interval between two consecutive coats should be determined based on the type of conformal coating and the drying conditions, typically ranging from 30 minutes to 2 hours. Applying the next layer too early may result in defects such as wrinkling or delamination of the coating film; applying it too late, on the other hand, could compromise the adhesion between layers.
X. Summary
Applying conformal coating is a task that demands intense focus and precise execution. Every step is closely interconnected and mutually dependent, collectively determining the quality of the final coating film and the circuit board’s protective performance. Only by strictly adhering to these operational guidelines—carefully adjusting various parameters in a flexible yet precise manner according to the characteristics of the conformal coating, the structure of the circuit board, and specific production requirements—can the conformal coating fully unleash its protective efficacy and build an impenetrable barrier of protection for the circuit board.
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Operating Procedures for Applying Three-Proof Coating (Part 2)
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Three-proof coatings, also known as three-proof paints or electrical protective adhesives, are specialized coating materials that offer protection against moisture, dust, mold, and electrical insulation. By being applied to the surface of electronic device circuit boards, these coatings form a uniform and dense protective film, effectively shielding the circuit boards from environmental hazards. 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.
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