It’s important to remember that, while conformal coatings do have incidental insulative functions, test houses (in general) only accept them for the purposes of keeping the underlying surface clean, thereby reducing the PD.
Some solder masks have been tested in end-products as conformal coatings, but not many have certifications for that application. Peter Tarver From: Richard Nute Sent: Wednesday, May 17, 2017 12:43 Solder mask is, necessarily, a reasonable solid insulator. The trace-to-trace insulation construction is trace - solder mask - air - solder mask - trace The solder mask is thin, so there is a depression between the traces. This depression makes air a part of the insulation between the traces. The construction is three capacitors in series. Assuming the areas of each capacitor plate is the same, the capacitance of each is a function of the dielectric constant (and the distance through the dielectric). The dielectric constant of air is 1; the dielectric constant of the solder mask is greater than 1. The voltage divides according to the capacitance of each capacitor. The air is the weakest link, and will break down. The heat of the arc may damage the solder mask. A conformal coating is thicker, and would not have as much depression between traces; its dielectric strength would be higher than a solder resist coating scheme. Rich The information contained in this message may be privileged and confidential. It is intended to be read only by the individual or entity to whom it is addressed or by their designee. If the reader of this message is not the intended recipient, you are on notice that any distribution of this message, in any form, is strictly prohibited. If you have received this message in error, please immediately notify the sender and delete or destroy any copy of this message! - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
