In looking at meeting CSA and UL spacing requirements for some of our PCB's (in power supplies up to 600 V) some questions concerning the use of conformal coatings (allowing reduction of spacing) have come up. The information that I am seeking is for both CSA and UL; the wording that they use concerning "coatings" on boards is similar, but not the same.
"Coatings" on a PCB could include both a solder mask, and a strict conformal coating. Does anybody have real-world knowledge as to whether or not a solder mask is accepted by UL/CSA as a "coating", and if so, under what conditions? Also, the method by which a coating is applied to a board could have considerable impact on the effectiveness of that coating. For instance, spraying a board will not get at any traces that are buried underneath components, whereas dipping will have a better chance of accessing those "hidden" areas. The standards that I am looking at say nothing about method of applying a coating (the process). I assume that the decision as to how a coating will be applied is left up to the manufacturer and board supplier. Does anybody out there have best practices that are worth considering when looking at our options for coating methods? Arjen Dragt
