Much time and planning are invested in the choice of the ideal conformal coating material and process to adequately protect your printed circuit boards. This often includes multiple qualification trials. There is also what can be long and detailed testing in areas such as electrical performance, flame resistance, and thermal or mechanical cycling.
By Matt Eveline, HumiSeal
Unfortunately, the qualification and testing process for conformal coatings is simply a snapshot of the process at the start. In order to maintain consistency, there remains an often-overlooked activity: regular cleaning and flushing of your selective conformal coating equipment.
In general, the following comments and guidelines from HumiSeal are designed for a discussion involving typical modern selective coating equipment as shown in the schematic below. However, nearly all of the principles are applicable to manual spraying operations as well.
Before discussing the specific considerations involved in the clean and flush process, it is probably best to 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 your 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:
Here are the basic steps to cleaning and flushing your manual or selective coating equipment. (Note: Please consult your equipment manufacturer to discuss details before attempting).
(Important: Use thinners provided by your coating manufacturer, not stripping agents, which are used for removing cured coatings from PCBs.)