Wes In the "olden days" there was a problem with Z axis shorting, or "punch through" between layers in a multilayer board In order to prevent this, the mil spec required 2 layers of prepreg. . This became a standard call out in the U S because of the mil spec Agruable whether it was ever really needed, but that is the history. Do you need it now? Depends on your board, but you should be open to dropping the requirement if you don't need it, or the added cost Good Luck Jerry Sallo Sallo Consulting Services --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------