Build-in cleaning time during chemistry changeovers and after extended line shutdowns.
Much time and planning are invested in the choice of the ideal conformal coating material and process to adequately protect printed circuit boards. This often includes multiple qualification trials. There is also sometimes long and detailed testing in areas such as electrical performance, flame resistance, and thermal or mechanical cycling. Unfortunately, the qualification and testing process for conformal coatings is simply a snapshot of the process at the start. To maintain consistency, an often-overlooked activity remains: regular cleaning and flushing of the selective conformal coating equipment.
In general, the following comments and guidelines are designed for a discussion involving typical modern selective coating equipment (FIGURE 1). However, nearly all the principles are applicable to manual spraying operations as well.
Why clean and flush? Before discussing the specific considerations involved in the clean and flush process, let’s explain the reasoning behind it. Beyond the obvious answer that it is simply good practice, there are a few reasons to regularly clean and flush the selective coating system:
(Note: When a silicone coating chemistry is used, never use the same fluid lines, valves or pressure pot when converting to other chemistries, such as acrylics, urethanes, synthetic rubbers, and so forth.)
When to clean and flush? There are a number of fairly obvious circumstances and times when it is advisable to thoroughly clean and flush your selective conformal coating equipment. They include the following:
How to clean and flush? Here are the basic steps to cleaning and flushing manual or selective coating equipment. (Note: Please consult the respective equipment manufacturer to discuss details before attempting.)
To restart the process, flush the remaining solvent from the fluid reservoir/fluid lines/valves. Now the machine and valve are ready to be filled with fresh coating.
is senior technical specialist at Chase Corp. (Humiseal).