All, I'm doing a board that needs 8 stripline layers running edge-coupled diff traces at circa 115 ohms, and a total of 22 layers. Using Fr4 with an er of 3.85 gets me 25 mils per stripline layer (ie ground plane to ground plane). Makes the board a tad thick to say the least. Using an er of 2.5 gets me 12 mils per. Anyone know of a usable and ecconomic material that can be used in this application, and which we can get UL approval for? Thanks Dave Instone. Compliance Engineer Storage Systems Development, MP24/22 Xyratex, Langstone Rd., Havant, Hampshire, P09 1SA, UK. Tel: +44 (0)23-92-496862 (direct line) Fax: +44 (0)23-92-496014 http://www.xyratex.com Tel: +44 (0)23-92-496000 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu