Role Does Conformal Coating Play in Circuit Board Assembly

Conformal coating is a layer of protective material applied to the surface of a printed circuit board (PCB). It is used in electronic products to protect against environmental hazards such as corrosion, dust, vibration, salt fog, moisture and extreme temperatures. It also helps to improve a device’s durability and lifespan. It can be applied to a wide range of materials including acrylics, polyimides, urethanes, epoxy and silicones. Parylene and potting compounds are also conformal coatings but are typically considered to be a separate category as they don’t form part of the circuit board assembly process.

When deciding on the best conformal coating to use for an application, manufacturers must consider many factors including coating thickness requirements, coating materials compatibility with the operating environment of the PCB and its components, production throughput needs and cost. The coating must have good adhesion to the circuit board substrate and be able to withstand the operating conditions that will be experienced by the finished product, such as humidity testing.

Humidity is a common problem that can cause corrosion of metal components and connections on a printed circuit board, and it is essential that the conformal coating can offer protection against this condition. The thickness of the coating is also important, and a too thin coat may crack or create mechanical stress points in the area where it has been applied. A thicker coat, however, is more likely to block out airborne contaminants and provide longer-term surface insulation resistance.

What Role Does Conformal Coating Play in Circuit Board Assembly?

The choice of a conformal coating application method is also dependent on production throughput and the amount of masking that will need to be done to prevent areas that don’t require coating from being coated. It is also crucial to choose a coating that can be easily inspected for compliance with standards, and automated inspection systems (AOI) are available which can be camera or scanner-based.

The most popular conformal coating application methods include manual spraying, dip processing and selective spraying. Manual spraying can be done with an aerosol can or a handheld spray gun and is often used in low volume production where capital equipment costs are a concern. This method is time consuming and requires careful preparation of the circuit boards with masking to avoid coating unwanted areas.

Dipping is a more labour-intensive process but is popular for high volumes of production and allows for the dipping of both sides of the circuit board. Selective spraying is a more automated process that can be programmed to a particular target area and can help to reduce the need for masking. This process is often preferred for mission critical applications because of its consistency and reliability.

After soldering, the assembled PCB undergoes inspection to ensure quality and functionality. This may involve visual inspection, automated optical inspection (AOI), or functional testing. Visual inspection checks for solder defects, misaligned components, or any other visible issues. AOI uses cameras and software to detect defects that may not be visible to the naked eye, such as solder bridges or missing components. Functional testing verifies that the circuit operates correctly according to its intended function.