Michael... Unless you are forming a transmission line using a conductor over a ground plane with solder mask as the dielectric, it does not much matter. If you are concerned about solder mask over the top of a microstrip line (for example), the e-fields above the line is so weak that you'll never be able to tell (by measurement) if there is solder mask there or not. We commonly use solder mask on our 2 GHz CDMA test boards (on top of microstrip or coplanar waveguide lines) and it has no effect whatsoever. Ray Raymond W. Waugh Agilent Technologies -----Original Message----- From: Chan, Michael (Eng Hou) [mailto:Michael.Chan@xxxxxx] Sent: Thursday, March 06, 2003 9:23 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Loss Tangent of Solder Mask Hi: Anybody has any idea what is the loss tangent of solder mask? Thanks. Regards, Michael Chan H-P Corp. ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list 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 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list 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