Hi Richard, Everyone could be correct - - It all Depends ! All standard FR-4's from a laminator will vary by 27% in general. This is because the Dk of each core is different, due to its glass fabric and resin content is different for each core. If you look at the cores below, you can see that the Dk varies by construction, as well as it varies with frequency (a 10.4% additional contribution). Now add to that the 'normal' variation in Dk of any of these cores from lot-to-lot, month-to-month (see 2-sigma chart)and you have another 1.5%. Now also add to that that Temperature and humidity will change the Dk of any of these cores by 5.7% and 11.8% respectively, and you can see how everyone may be "correct", they are just reporting on a different core, at a different temperature and humidity, at a different frequency, but all about the same 'Laminate". FR-4 is inexpensive but it varies a lot as a stable electrical platform. Happy Holden Asian Pacific Materials Direct line: 203-283-3097 t: 203-283-3000 ext 297 f: 203-283-3100 email: [log in to unmask] CELL: 203-464-6466 "Smith, Richard" <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 09/15/2006 11:46 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to "Smith, Richard" <[log in to unmask]> To [log in to unmask] cc 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 -----------------------------------------------------