Roger First of all make sure that your boards are as clean as poss before coating - you don't mention what soldering/cleaning process you use. Then I recommend any coating OTHER than silicone, which is the world's worst for moisture penetration. Choose between good acrylic or 2 part flexible epoxy or polyurethane products. Personally, if coating, I prefer not to have soldermask, if possible, but my friends say I'm being controversial. Do it all in one fell swoop with the coating (cheaper and less risk of compatibility problems). If you e-mail me privately with more details, I may be able to be a lot more specific. Brian "Roger M. Stoops" wrote: > > Hey y'all: > > We have seen some problems on SMD boards using 0805 package Rs and Cs. > These boards have soldermask and are silicone-coated twice. They are used > in machine control products (machines such as bulldozers, motor graders, > drag scrapers), and so moisture presents a constant problem, as well as > temperature extremes (-20C to +70C). > > We are having product failures after the product has been installed and > functioned normally for a few months. A typical example would be a 4.75K > resistor on a failed unit would measure about 200 ohms after product > failure. We take the part off; R between pads is in the meg-ohms (what we > expect). Replace the part, problem goes away. > > Does anyone know of a service that would help us find out what the probable > problem is, and maybe the cause and solution? We think it might be > contamination left over from assembly process (vendor doesn't think so) > that moisture may affect after time in field. > > Immense thanks. > > Roger Stoops > Spectra Precision Inc. > > ############################################################## > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c > ############################################################## > To subscribe/unsubscribe, send a message to [log in to unmask] with following text in > the body: > To subscribe: SUBSCRIBE TECHNET <your full name> > To unsubscribe: SIGNOFF TECHNET > ############################################################## > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional > information. > If you need assistance - contact Keach Sasamori at [log in to unmask] or > 847-509-9700 ext.5315 > ############################################################## -- Brian Ellis Protonique SA PO Box 78 CH-1032 Romanel-sur-Lausanne, Switzerland Voice: +41 21-648 23 34 Fax: +41 21-648 24 11 E-mail: [log in to unmask] URL: Technical and consultancy divisions: http://www.protonique.com Web services division: http://www.protonique.com/webserv ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################