Like Paul said, there are two ways to effect the structure. I haven't designed, built, or used 4 layer boards in years. Most all 4 layer boards, in ancient times, were core laminated wherein two double sided "boards" were laminated together with whatever amount of preg was needed to effect the required thickness. Mass lamination techniques were, and maybe still, used extensively using core lamination after printing and etching the inner layer details. Most all, if not all, "sophisticated" MLB's are foil laminated with preg facing the outer most layers with thin core materials making up the rest as printed and etched details. Everyone else pointed to oxides and double treat foils. They would impact you visually as pointed out. In any event, your boards should be reliable and functional unless your supplier looses the recipe for effective process management. Enjoy Genny, MoonMan --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------