Scott, Moisture in and of itself is non-conductive. It's the ionic contamination or under etching or surface finish dendrite growth that typically causes shorts, or voltage break over failures. All things being equal, I would expect that the shop that did the boards skipped baking them before applying the solder mask... This may have allowed dendrites to form between conductors through the moisture which would have performed as an electrolyte. I would suggest making a section of the bad area and take microscopic pictures of the affected area and you might see the failure mode for the boards. Best regards, Bill Brooks PCB Design Engineer , C.I.D., C.I.I. Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 http://pcbwizards.com -----Original Message----- From: Scott Lefebvre [mailto:[log in to unmask]] Sent: Tuesday, June 08, 2004 11:32 AM To: [log in to unmask] Subject: [TN] Soldermask Dielectric DC properties We have a PCB that two traces have shorted and blown a set of traces on the PCBs. The trace width and spacing is correct for 150 V and is not a new design. We recently changed PCB shops. We found some residual moisture about 1/8" square in close proximity of two traces after assembly and after test. The traces were entirely covered with LPI soldermask. I understand that the moisture should be removed prior to test. My question is shouldn't the soldermask have insulated the two traces from the moisture? Scott --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------