Hi Rudy, Your explanation sounds good, but is incorrect--it is not the surface roughness that is the problem, it is the variability of the ED copper density. The specific gravity (density) of ED copper is less than the specific gravity (density) of rolled copper because of organic co-deposits and micro-voids. This uncertainty in specific gravity (density) prevents a direct conversion of oz./ft2 to thickness, and that is why ED copper is specified in oz./ft2. The reason weight is used in specifying copper foil is because copper is bought and sold by weight. So, foil vendors sell copper foil by weight; the laminators resell the foil, laminated to epoxy, by area. Want to guess how much foil is produced near the upper weight tolerance for any given foil weight class? None of thus of course excuses the lazy stupidity in this country that has killed the use of the metric system time and again. Regards, Werner Engelmaier Fornercahairman of IPC Copper Fopil Committee --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/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 -----------------------------------------------------