Since your question asked what is the smallest minimum annular ring, I know of one very complex 52 layer PWB that is designed and built using a pad size that is 6-mils larger than the drill size, giving nominal annular ring of 3-mils. 6-mils over the drill size is a nice rule of thumb for the "smallest minimum" annular ring. Regards, Lyle Wallig ################################################################ 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 web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################