What Role Do Conformal Coating Materials Play in SMT Circuit Board Assembly?

Conformal Coating Materials Play in SMT Circuit Board Assembly

Electronics are used in a variety of challenging environments, exposing delicate connections to potential hazards like extreme temperatures and moisture. These risks can damage components, leading to failure of the finished product. To prevent this, conformal coating is applied during the smt circuit board production process to protect the assembly from harmful elements.

A number of factors are involved in choosing the best conformal coating material for a given application. These include the operational requirements of the final product, equipment availability, and quality requirements. Ideally, the choice of coating material should be specified as part of the electrical design of the circuit board, allowing the specification to be shared with a manufacturing partner early in the process. Tools such as Altium Designer allow for this to be done easily, allowing the conformal coating process to be planned from the very beginning of the assembly cycle.

There are a wide range of conformal coatings available to meet the requirements of different applications. These materials are grouped into categories based on the base resin that they contain. These categories then are further broken down by the attributes that they offer. An epoxy-based conformal coating is typically the lowest cost option and provides good durability and resistance to corrosion. This coating is semi-permeable and does not fully seal the coated surface, making it ideal for general use. This type of coating can be cured using controlled heat or UV exposure, which is generally more convenient than a chemical-curing process.

What Role Do Conformal Coating Materials Play in SMT Circuit Board Assembly?

Polyurethane, or urethane-based conformal coatings, provide high durability and are resistant to abrasion, chemicals, and moisture. They also provide a strong resistance to solvent contamination and are approved by the US Food and Drug Administration for medical devices. These types of conformal coatings are often used in high-volume production where the investment in additional equipment makes sense.

Acrylic resins are durable and easy to apply, but they are not fully hermetic and do not seal the board. These are good options for most industrial applications, including harsh environments where there is the risk of abrasion. Acrylic resins also offer a high level of corrosion protection and are highly abrasion-resistant, making them suitable for most applications.

The choice of application method is dependent on the size and complexity of the circuit board, component types and placement, and production volume. Brushing and spraying are the most common methods, but other techniques can be used as well. In order to measure the thickness of a conformal coating, a tool known as an eddy current probe is often utilized. This is a non-destructive tool that measures the thickness of the coating by sending out an electromagnetic field and measuring the resulting reflections, providing very accurate measurements.

The thickness of the conformal coating is important to consider, as it must be thick enough to provide an appropriate degree of protection without interfering with electrical conductivity. It is also important to ensure that the coating covers all required surfaces, and that any areas that are not supposed to be coated are masked or protected in some other way. Finally, the coating should be allowed to cure properly before the circuit board is put into service.

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