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Conformal Coating Protect PCB Assys From Environmental Factors

A circuit board’s operating environment is a big concern when it comes to the longevity of the device and reducing failure rates. A pcb assy conformal coating adds a layer of protection that shields the circuit board from environmental factors, improving performance and extending working life. There are many different conformal coating materials that provide specific protective benefits. The choice of the proper material requires balancing the required protective properties with the practicalities of application. This is important because some materials require expensive industrial equipment and can be difficult to apply without disrupting the integrity of the circuit board.

The basic resin that a conformal coating is based on determines its major attributes and functions. This includes its insulating qualities, moisture resistance, surface hardness, and color options. Some of the most common conformal coatings include silicone, acrylic, urethane and parylene. The coating’s thickness is also a consideration. Most conformal coatings are only about 1 to 5 mils thick, which is very thin and minimizes heat entrapment and unnecessary additional weight. Anything thicker than this is typically a potting compound and provides significantly more mass and insulation.

Humidity testing is one of the most common conformal coating tests that is carried out to ensure the coating can resist humidity. Moisture on a circuit board can cause corrosion to metal components and connections. A conformal coating can prevent this corrosion by preventing moisture from contacting the components and connections. The test process can also include exposing the boards to corrosive gases in order to simulate the conditions of a harsh environment. Other testing processes can include water immersion tests to verify the conformal coating’s ability to resist water molecules.

How Does Conformal Coating Protect PCB Assys From Environmental Factors?

During the conformal coating process, certain parts of the circuit board must be masked to protect them from the coating. The masking process can be accomplished using a variety of materials such as spray nozzles, stencils and masking tapes. The masking is especially necessary if there are components that should not be coated, such as connectors or solvent sensitive components.

Once the conformal coating process is complete, inspection is essential. During this stage the inspector checks for defects like blistering, cracks and bubbles. The conformal coating is also tested for its ability to withstand thermal cycling. Depending on the type of conformal coating, testing can include electrical resistance and mechanical shock. The inspector can check for appearance as well, including a UV lamp inspection and automated optical inspection (AOI).

Lastly, the conformal coating must be inspected to verify it has adhered to the circuit board. The coating is usually measured by a non-destructive ultrasonic thickness measurement system. This system measures the time it takes for an ultrasonic wave to travel from a transducer through the conformal coating, reach the circuit board’s surface and return to the transducer. The thickness is then calculated from the measured times. This method is much faster than the traditional eddy current probe, which is slow and labor intensive.

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