This depends on the base material system. FR4 tends to have a broader range when different glass to resin ratios are evaluated. 30% is a higher deviation than I have seen - 10% I would say for FR4 is about what deviations you can expect from a glassy build to a resin rich build - 3.8 range to 4.6. A material like RO4000 has a tighter variation as the system is delta in permittivity is less across the plane, but part of this also is the refined glass systems used in the lower loss materials. Much is also dependant on how you are measuring the loss - neat material measurements will return more accurate results than estimations made from a completed stripline. Jeffrey Bush Director, Quality Assurance and Technical Support VERMONT CIRCUITS INCORPORATED 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302 Voice - 802.257.4571 ext 21 Fax - 802.257.0011 <http://www.vtcircuits.com/> -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Smith, Richard Sent: Friday, September 15, 2006 11:46 AM To: [log in to unmask] Subject: [TN] Laminate Material DK I've seen differences of as much as 30% between a laminate manufacturer's specified DK value and the board fabricators "effective DK" value for the same material (FR4). Often the disparity is well outside of the range specified by the material manufacturer. I understand that DK values can change due to resin/content and frequency however, a 30% difference just seems awful big. Here's the part where I seek help from the experts. Thanks! Is 30% difference in manufacturer DK versus Effective DK really possible? Assuming the same material, will the DK difference be the same from fabricator to fabricator? Thanks Much! Rick --------------------------------------------------- Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------