Why Is It Used During PCB Assembly

Conformal coating is applied to circuit boards to protect against environmental hazards like chemicals, moisture, and dust. It is also useful for protecting the board’s components from damage during manufacturing and assembly. However, there are several issues that must be considered when choosing a conformal coating to suit the board’s requirements and environmental conditions.

One consideration is the worst-case operating temperature of the circuit board, as different conformal coatings have varying thermal performance. High temperatures may restrict which coating types are suitable or necessitate redesigning the printed circuit board and assembly layout to reduce the maximum operating temperature.

Another important issue is rework and repair, as the choice of conformal coating can affect how easy it is to remove for rework, repairs, or field upgrades. A tougher conformal coating, for example, can be more difficult to remove and can create an extra step in the rework process. This can increase both the cost and time required for rework, and it is important to choose a material that will not affect the board’s electrical performance.

The application method of the conformal coating is another crucial consideration when selecting a product. Different methods of application can influence the coating’s characteristics and quality, including the thickness of the layer. For this reason, it is important to understand the process used by a circuit board manufacturer before selecting a conformal coating.

What Is Conformal Coating and Why Is It Used During PCB Assembly?

Some of the most common methods for applying a conformal coating to a circuit board are dip, spraying, and selective automated spraying. These processes all have their own advantages and disadvantages, and each may be better suited to certain production methods or environmental conditions.

Dip coating is the most traditional way to apply a conformal coating, where a board is dipped into a liquid coating solution. This method is highly effective in high-volume production runs and can be used with a variety of coating solutions. The downside to dipping, however, is that the surface of the board can become damaged during the immersion process, and the coating may not adhere well to sharp edges or other contours of the circuit board.

Selective automated spraying is a more efficient method of applying a conformal coating than the dipping process. It uses the same basic process as dipping, but with a programmable sprayer head that can be controlled to only target specific areas of a circuit board. This method is particularly suitable for high-density circuit boards with lots of connectors and other solvent sensitive parts.

A final consideration when choosing a conformal coating is its ability to self-extinguish if it comes into contact with flame. Many conformal coatings are tested to ensure that they meet industry standards like UL94 and UL746 for this purpose. Other tests include measurement of the coating’s resistance to water and abrasion, its electrical insulation properties, and the ease with which it can be removed from the board for rework or repairs.