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Operating Procedures for Applying Three-Proof Coating (Part 1)

Release time:

2025-04-27 07:26

Operating Procedures for Applying Three-Proof Coating (Part 1)
Operating Procedures for Applying Three-Proof Coating (Part 1)

Among the many methods for applying conformal coatings, the brush-coating method is widely used—particularly in small-batch production, localized coating applications, and scenarios that demand high coating precision—thanks to its flexible operation and versatility across various application environments. However, despite its seemingly simple nature, the brush-coating method actually has stringent requirements for operational standards. Every single detail can affect the final coating result and, consequently, the protective performance of the circuit board.

The brush-coating method is a coating technique that uses a brush to evenly apply conformal coating onto the surface of a circuit board. It is suitable for small-batch production, localized coating, or scenarios with high requirements for coating accuracy. The following are detailed specifications for brush-coating operations:

I. Choose a brush

Choosing the right brush is crucial for ensuring high-quality brushing application. The brush material should be selected based on the type of conformal coating used—for example, for solvent-based conformal coatings, bristle brushes or nylon brushes are suitable; whereas for water-based conformal coatings, synthetic fiber brushes are recommended. The brush size should be chosen appropriately according to the PCB’s dimensions and the complexity of the coating area; generally, the bristle length should be sufficient to cover the entire coating area while remaining convenient for operation. Before use, the brush must be cleaned and pre-treated to remove any impurities and oils from the bristles, ensuring that the brush is clean and free from contamination.

II. Control of Paint Dipping Amount

When dipping the brush into the conformal coating, it’s important to control the amount of coating applied to avoid over-saturating the bristles, which could cause dripping or running. As a general guideline, the amount of coating should not exceed half the length of the bristles. If too much coating is applied, the conformal coating may easily drip onto the PCB during brush movement, leading to coating buildup or contamination of other areas. On the other hand, if too little coating is applied, the brushing will be uneven, resulting in exposed substrate.

3. Trial Printing

Perform a trial brush application on discarded circuit boards or test samples, adjust the brushing pressure and speed, and observe the uniformity and thickness of the paint film to ensure that the desired coating effect is achieved.

4. Brushing Direction and Pressure

When applying the coating, keep the brush at a certain angle to the PCB surface. Generally, use a unidirectional brushing technique, moving from one end of the circuit board to the other—either from left to right or from top to bottom—while avoiding back-and-forth motions to minimize brush marks. For large-area PCBs, you can adopt an alternating horizontal and vertical brushing pattern to ensure even coverage of the coating film. The brushing pressure should be consistent and moderate: not too light, which could result in insufficient coating thickness, nor too heavy, which might deform the brush bristles or damage the PCB surface. Gently press the brush onto the circuit board surface so that the bristles flex slightly.

V. Brushing Speed

Maintain a steady brushing speed—typically 2–3 cm per second. Moving too quickly may result in uneven paint coverage, while moving too slowly could cause the paint to accumulate and lead to sagging.

6. Coating Thickness Control

To control the coating film thickness according to product requirements, multiple coats can be applied to achieve the desired thickness. Each coat should be applied with an interval of 5 to 10 minutes, allowing sufficient drying time for the previous coat to prevent dissolution or peeling between layers.

7. Edge and Corner Finishing

Pay special attention to thoroughly brushing the edges, corners, and component leads of the circuit board. Use a smaller brush or the tip of the brush for careful application, ensuring that no areas are missed.

8. Multi-layer coating

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 layers 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 could compromise the adhesion between layers.

9. Summary

Adhering to the rigorous operational guidelines for applying three-proof coatings is crucial to ensuring that circuit boards receive high-quality protective coatings. Every step in the application process is closely interconnected and leaves no room for even the slightest carelessness. Only by strictly following these guidelines can personnel effectively prevent various defects such as bare substrate exposure, brush marks, and sagging, thereby enabling the three-proof coating to fully unleash its protective performance and safeguard the stable operation of circuit boards in a wide range of challenging environments.

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