Scott, Lee, Dorin and others interested in Dk discussion, I have been following this thread on Dk measurement with interest and wanted to add some input from a PCB fabrication standpoint. All of your points and concerns are valid. Please consider the following: 1. No two laminate material manufacturers measure or report electrical properties Dk or Df the same way. Some use Beraskin some use Split Post Cavity, others Full Sheet Resonance etc. In many cases, laminators prefer to use methods which make the electricals for their materials look better. No big surprise. Or they stick with methods that they are accustomed to. 2. When they do measure, it's usually done on a specific core thickness and at several, usually lower discrete frequencies. Higher frequency data is usually extrapolated. Again, samples are picked to make the electricals look good. Along with concerns regarding resin/glass ratio and pre-preg Dk effects, there are other variables that haven't been mentioned.. like copper foil roughness, glass weave etc. The reality of life is that laminate vendor Dk data in most cases is only useful for rough calculations or benchmarking comparisons. Any serious modeling or simulation , specifically at higher frequencies , requires empirically validated test data representative of the specific resin and stackup being evaluated. Here at SSCI, we were forced years ago to measure laminate properties ourselves,in order to obtain data we could reliably use in our impedance models and SI simulations which would then correlate with actual VNA and TDR measurements once we built the PCB. We adopted a method we call Modified Full Sheet Resonance . There is a DesignCon 2003 presentation on our website co-authored with Istvan Novak at Sun which discusses some of the early work utilizing this method. Try this link to access http://www.sanmina-sci.com/Solutions/pdfs/pcbres/SANM_Resonance_Test.pdf We found this method effective up to about 4GHZ. We have migrated towards developing microstrip and stripline based test structures for extracting Dk/Df up to 20 GHz using a high frequency VNA. Although we prefer frequency domain analysis, we have also benchmarked high speed time domain methods such as those published by Alina Deutsch et al at IBM and feel both domains have merit. We now have a pretty comprehensive data base on all the leading materials from FR-4 to the low Dk/Df materials which allows us to accurately select and substitute different materials and stackups. Bottom line...you have to measure. My SI folks will be at DesignCon if anyone wants to compare notes. Regards George Dudnikov Sr.VP & CTO PCB Division Sanmina-SCI -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Scott McMorrow Sent: Friday, January 19, 2007 10:06 AM To: Dorin.Oprea@xxxxxxxxxxxxxxxxxx Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: R: Re: Question on varying the coupling ratio on a differential pair Dorin If you want to accurately know what your Er is, the only way to be sure is to measure it yourself, or have a lab measure it for you. All measurements of FR4 Er have errors inherent in the measurement technique and the physical size of the sample. You just have to choose a method that is as close as possible to your board stackup and traces of interest. Some manufacturer's data only gets you in the ballpark. Regards, Scott Scott McMorrow Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 (401) 284-1827 Business (401) 284-1840 Fax http://www.teraspeed.com Teraspeed(r) is the registered service mark of Teraspeed Consulting Group LLC OPREA Dorin wrote: > Lee, > > Can I ask if you get also the data for the prepeg and how do you take > in to account for the change in the dielectric properties due to the > PCB manufacturing process? > > Thanks, > Dorin > > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx > [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of Lee Ritchey > Sent: Friday, January 19, 2007 12:09 PM > To: ryansatrom; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: R: Re: Question on varying the coupling ratio > on a differential pair > > Ryan, > > Most laminate manufacturers have a dielectric constant vs. frequency > curve for their materials. This is the place to start. In most > cases, the er starts at some level for 1 MHz and goes down until about > 2 GHz at which point it flattens out. This is true for all "FR-4" > class materials as well as Rogers RO 4350. > > I'd get that data from the laminate manufacturer as a starting point. > > If there is any good news in this as far as logic is concerned, the > edges are so fast with modern logic that the frequencies of concern > are above 1 GHz, where er is approaching a constant value. > > It's from 1 MHz to 500 MHz where the greatest slope is for the er > curves.=20 Not all that much a problem for most logic, but a potential > issue for RF engineers. > > Lee Ritchey =20 > > > >> [Original Message] >> From: ryansatrom <ryan.satrom@xxxxxxxxxxx> >> To: <si-list@xxxxxxxxxxxxx> >> Date: 1/17/2007 9:44:10 AM >> Subject: [SI-LIST] R: Re: Question on varying the coupling ratio on a >> > differential pair > >> Thanks for your feedback. Sometimes, living in the simulation >> world,=20 you forget the real-world effects of boards. >> >> Lee: Is there any way to predict this frequency dependency of er? >> >> Fred: Is the frequency dependence of R and G caused by the same=20 >> issues Lee is discussing (dielectric constant over frequency)? >> Are=20 there any other causes of this? >> >> (As a side note, the equation suggests R and G to be fixed in=20 >> frequency, while L and C are the frequency dependent values. I >> guess=20 that's why the lumped element model breaks down and models >> are more=20 accurately viewed as distributed full-wave EM models) >> >> Thanks again for the comments. >> >> Ryan >> >> ------------------------------------------------------------------ >> 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 technical documents are available at: >> http://www.si-list.net >> >> List archives are viewable at: =20 >> //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 >> =20 >> > > > ------------------------------------------------------------------ > 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 technical documents are available at: > http://www.si-list.net > > List archives are viewable at: =20 > //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 > =20 > > ------------------------------------------------------------------ > 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 technical documents are available at: > http://www.si-list.net > > 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 technical documents are available at: http://www.si-list.net 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 ________________________________________________________________________ _____ Scanned by Sanmina-SCI eShield ________________________________________________________________________ _____ CONFIDENTIALITY This e-mail message and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. 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