Still looking.... Is there any thoughts on reverse treated copper foil versus standard? Jim -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Valerie St.Cyr Sent: Monday, November 21, 2005 10:23 AM To: [log in to unmask] Subject: Re: [TN] impedance testing It is 3.8. That value "works" best and, in fact, if you were to take a Dk reading at 1 GHz of a high layer count multilayer you would get about 3.8. That's because the multilayer probably has a net, effective resin content above 50%; we have a lot of boards that are probably closer to 55 to 60% resin. When the laminators test their laminates for Dk, they use a thin double-sided laminate which is usually 45 to 50% resin. I find about a .4 difference between published spec sheet values and measured values for multilayers. The impedance calculators don't have a fudge factor; they are built on formulas, which get tweaked occasionally and get better. The "fudging" is nothing more that knowing what values to use for the variables: Dk (3.8 for FR4), copper height (especially for outerlayers) and copper sidewall cutback; if you get those numbers right, you will have a pretty good first pass that meets the targets. As for the original problem, I don't know if it has been unraveled ... Jim, do you have the answer yet or are you still seeking advice ? Valerie Ken <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 11/18/2005 07:25 PM Please respond to TechNet E-Mail Forum; Please respond to Ken To: [log in to unmask] cc: Subject: Re: [TN] impedance testing You are welcome to give my calc a try (pitiful plug I know :p) but I used a formula from Linear Tech and I have had good results with it. I too have seen some odd numbers in the past with measured results. I have a vender in Singapore that swears the dk of his FR-4 is 3.8. Well, give it a shot... Ken http://www.saturnpcb.com/Software.htm ---------------------------------------------------------------------------- --- Kenneth J. Wood C.I.D Saturn PCB Design 2737 Bishop Lane Deltona, Fl 32725 407-340-2668 www.saturnpcb.com -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Eddie Rocha Sent: Friday, November 18, 2005 7:00 PM To: [log in to unmask] Subject: Re: [TN] impedance testing Wrong. The dielectric constant is a separate factor. Thank you, Eddie Rocha South Bay Circuits Eddie All Z0 calculators have a built in "fudge factor" to make modelled results agree with emperical data. It is called "dielectric constant" Gerry From: Eddie Rocha <[log in to unmask]> Reply-To: TechNet E-Mail Forum <[log in to unmask]>, Eddie Rocha <[log in to unmask]> To: [log in to unmask] Subject: Re: [TN] impedance testing Date: Tue, 15 Nov 2005 11:53:11 -0700 I've evaluated multiple impedance calculators. I did as you are doing, used actual x-section data with actual TDR results and compared it to the calculators results. Some calculators worked well with some stack-ups but not with all types of stack-ups. A good calculator should have a "fudge factor" that allows you to determine the best "factor" that works for a particular stack-up. Actual data is needed to make an impedance calculator accurate. Thank you, Eddie Rocha South Bay Circuits Hello, If there are any impedance testing gurus out there I have a question for you. We are testing an edge coupled offset strip line coupon. We modeled the stack up to give us 100 ohms differential. When we test the coupon we get around 130 ohms. We have done a microsection of the coupon and modeled the coupon data and Polar says we should have 105 ohms, within tolerance. We had a 4 panel lot and it is consistent across the board. The coupon is constructed correctly. My question is, other than what I am seeing on the microsection should I look for to find the culprit of the high reading? Any help would be great. Jim Henderson Colonial Circuits --------------------------------------------------- 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 -----------------------------------------------------