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How Are Conformal Coating Thinnesses Controlled in Surface Mount PCB Assembly?

Conformal Coating Thinnesses Controlled in Surface Mount PCB Assembly

Printed circuit boards (PCBs) contain intricate electronic components. These components are delicate and must be protected from corrosion, dust, chemicals, heat, and other environmental hazards. This is why PCB conformal coating is so important. Conformal coatings protect PCBs by preventing metal migration between closely spaced conductors, and they also suppress moisture absorption and leakage current. They are also used to prevent shorting due to thermal shock, mechanical impact, and other factors.

Typical conformal coatings for PCB assemblies are silicone and acrylic, but urethane, parylene, and epoxy are also used. These materials are semi-permeable, meaning they allow some water and oxygen to pass through them. However, they are impervious to most solvents and gases. This allows them to resist corrosion, impact, and degradation from UV radiation, ozone, and other environmental factors that may harm electronics.

In addition to their ability to provide resistance to external factors, conformal coatings for pcb help prevent electrical failure by improving the dielectric strength between adjacent traces on a PCB. This improves the quality of electrical performance and allows for higher component density in PCBs. This allows manufacturers to build more complex and powerful electronics, such as smart phones, computers, and tablets.

The application of conformal coating is not always an easy task. It requires precise measurement, thorough coverage, and attention to “keep out” areas and optional areas that can be coated but are not required to be. An improperly applied coat can result in an exposed board that is vulnerable to environmental hazards, which can make the entire assembly unusable.

How Are Conformal Coating Thinnesses Controlled in Surface Mount PCB Assembly?

There are several ways to measure conformal coating thicknesses, including using a black light and measuring points on the uncoated substrate with micrometers. Another method uses a non-contact digital coating gauge that measures changes in magnetic or electric fields to determine film thickness. This technique is faster and easier than the micrometer approach, but it is not suitable for use on conductive surface mount pcb such as solder mask and insulated parts.

There are also rubbing and grinding methods for removing conformal coating, but these can damage the substrate of a pcb. A better option is a miniature sandblasting machine that propels finely-graded abrasive powder through streams of compressed air and out tiny nozzles at the workpiece. This method can be very effective for removing conformal coating without damaging the substrate, and it is fast. In addition, it is less expensive than other rework techniques.

Controlling the thickness of conformal coatings in surface mount printed circuit board (PCB) assembly is crucial for ensuring the protection of electronic components while maintaining their functionality. Conformal coatings are applied to PCBs to protect them from environmental factors such as moisture, dust, and chemicals. The process involves several techniques and careful monitoring to achieve the desired coating thickness.

The entire PCB is submerged in the coating solution. This method ensures uniform coverage but requires careful control of the dipping speed and withdrawal to achieve the desired thickness and prevent excess coating from dripping off. Coating is manually applied using a brush. This method is labor-intensive and typically reserved for touch-up or rework applications, where precise control over coating thickness is necessary.


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