KEY AREAS TO AVOID WHEN COATING A PCBA WITH CONFORMAL COATING

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Conformal coating is a protective layer applied to a printed circuit board (PCB) to safeguard it from external contaminants and prevent corrosion. These coatings provide insulation and protect sensitive components, but they must be applied selectively to avoid interfering with the board's functionality. Over-coating or incorrect application can lead to problems with electrical connections or the performance of sensitive components.

Areas on PCBA That Should Not Be Coated

While the benefits of conformal coating are clear, there are specific regions on a PCBA where coating should be avoided. These areas include those where electrical connections are made, components that need to remain accessible for maintenance or operation, and places where the coating could impact performance.


1. Electrical Connection Points

Gold Pads and Fingers: Areas that are used for electrical connections, such as gold-plated pads, gold fingers, and metal vias, should not be coated. These areas are critical for electrical integrity, and any coating could create resistance or prevent proper connection.
Test Points: Test points, used for diagnostics or performance testing, must be left uncoated to ensure accurate measurements and to maintain the integrity of the testing process.

2. Connectors and Switches

Connectors: Connectors (e.g., USB, HDMI, power connectors) should be shielded from the coating process as they need to maintain a direct, clean connection for signal or power transmission.
Switches: Non-sealed switches should not be coated, as the coating could interfere with their mechanical function, leading to operational failure.

3. Thermal Components

Heat Sinks and Thermal Management Components: These areas should be left uncoated to ensure efficient heat dissipation. Conformal coatings could act as an insulating layer, preventing effective cooling and causing thermal issues.

4. Battery and Battery Holders

Batteries and their holders should be kept free from coatings to avoid the risk of short circuits, overheating, or other potential safety issues.

5. Optical and Sensitive Components

Optical Devices: Any components that rely on light transmission, such as lenses or light sensors, should not be coated. Conformal coatings could obstruct light paths, affecting the device's performance.
Sensors and Potentiometers: These sensitive components must remain uncoated to ensure their correct operation. For example, applying a coating to a sensor can impede its ability to detect environmental changes, compromising functionality.

6. Fuses and External Enclosures

Fuses and external protective housings should be left uncoated. Conformal coating could prevent the fuse from functioning properly in case of an overload or short circuit.

7. Jumpers and Wire Links

These are used for specific configurations and should not be coated, as the coating could affect their function, especially in high-frequency circuits or low-resistance paths.


Areas That Should Be Coated

Aside from the aforementioned areas that must be left uncoated, all other exposed components on the board—such as solder joints, component leads, and conductors—should be coated to ensure protection against moisture and contaminants. The coating should be applied uniformly, ensuring that the protection layer is intact without obstructing any electrical connections.

Final Thoughts

When applying conformal coating to a PCBA, it's essential to understand the specific requirements of your design and the function of each component. Failure to selectively coat or shield the necessary components can result in performance degradation or even damage to the board. As a general rule, anything that is involved in the electrical connection or physical manipulation (like switches, connectors, or test points) should remain uncoated, while other parts of the board should be adequately protected. Always remember to conduct thorough testing to ensure that the coating has not affected the performance or safety of your assembly.

KINGSHENGPCBA specializes in the PCBA industry, providing one-stop services from electronic component procurement to custom PCBA solution design, development, and manufacturing. If you have custom PCBA development needs, please feel free to contact us.