Printed circuit boards (PCBs) are a vital part of any electronics product. They are also one of the most vulnerable—highly susceptible to the environment where they are being used. Any number of factors can affect the PCB including heat or abrupt fluctuations in temperature, humidity, water, dust, salt, solvents, and levels of UV, leading to corrosion or a breakdown.
No matter where your PCB is eventually going to live, it’s beneficial to protect it with a conformal coating. The coating conforms to the contours of the board which allows the board to function while extending its life and not adding to the size. As a protective, insulating layer, the conformal coating will need to withstand the required operating conditions of where the PCB is located. For example, if your PCB will be operating in a location subject to condensation, it’s important to use a conformal coating that is known to resist water.
The conformal coating process is one of the last processes on the PCB assembly line. This is due to the fact that once a PCB is coated it is very difficult to repair or modify.
Conformal coatings are typically classified by polymer type. There are five major categories:
But you can also find hybrids and special types: acrylated urethanes, acrylic-modified silicones, or polyamides.
There are components of a PCB that cannot or should not be coated. When designing the board and picking a coating application method, the areas which will not be coated should be taken into consideration in the layout.
Just as important as which type of conformal coating is used, is how it is applied. As with most processes in the electronics industry, there are several ways to apply conformal coatings to the product. Some of the methods are typically performed manually while others are automated.
Many times a single board requires more than one dispense method for proper coating.
Once coated, the last important variable to consider is how to cure it. There are several options for curing the conformal coating and the variations are very important when considering the long-term reliability of the product and circuit board.
While the cure mechanism isn’t a primary criterion when selecting a coating, it does have a direct impact on the type of application method that will be feasible so it’s important to understand the different methods.
Conformal coating means the equipment is only as flexible as the material allows it to be, so consider what the end-product requirements are when choosing a PCB coating product. Also, material viscosity changes with temperature so if your PCB will be housed in an environment with drastic temperature fluctuations, you will want to find a conformal coat that will maintain the viscosity throughout the day to avoid a film build up.
Because conformal coating requires a great deal of process knowledge, including an understanding of material characteristics, curing and in-line integration issues, it’s important to work with a manufacturer who provides a comprehensive service and understands the advantages and disadvantages of each variety.
ACDi has the resources and experience with conformal coating services to provide a single source of support throughout your product lifecycle. We are familiar with each of the types, methods and uses, and can help you determine the best one for your application.
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