Hi Kelly - May I direct your attention to an interesting little requirement out of IPC-SM-840C? A portion of para. 3.4.10 reads: "The board fabricator shall confirm that the minimum thickness is sufficient to withstand 500 VDC per solder mask vendor's specification. The coating thickness shall be measured by any micrometer or inidcator accurate to 0.0025 mm [0.0001 inch] or microsection in accordance with TM 2.1.1 of IPC-TM-650." "If a specific thickness or breakdown voltage is required it shall be specified by the end user on the procurement document." Thickness of the solder mask is considered critical only in an electrical performance sense. There is no relief for any areas which are to be coated with permanent solder mask on the circuit board from this requirement. Regards - Kelly ################################################################ TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################