In a practical sense, solder mask alone may not give you the protection you need if your PWB assembly ends up in high temperature/humidity and/or corrosive environment. Enen though the solder mask will protect all your circuits in a harsh enviroment, you will still have metallic solder joints exposed. Therefore, you would run the risk of shorting, the metallic circuits reacting with the corrosive materials, etrc. Conformal coatings were developed to completely seal the printed wiring board assembly after all the components were soldered or joined in place. At this point, the protective conformal coating covers everything and there are no conductors exposed to the environment. Hope this helps Larry Fisher Dexter Electronic Materials [log in to unmask] ############################################################## 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. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################