Mike, whatever term you want to use for it, we agree that the field is almost completely confined. Away from the edges, I think you have to work at it to get an antenna of any efficiency. Ordinary traces aren't much of an issue. Regards, Steve. At 11:15 AM 2/2/2004 -0600, Brown, Mike (Austin, TX) wrote: >Actually, Lee has stated that he uses a pad cap layer, followed by the >first signal route, followed by a plane. That configuration can be made >to have little radiation, assuming proper plane continuity under the >traces. Most of the field is confined to the dielectric surrounding the >trace. Whether you can make an efficient antenna with that configuration >is less clear to me. > >Mike > >-----Original Message----- >From: si-list-bounce@xxxxxxxxxxxxx >[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of steve weir >Sent: Monday, February 02, 2004 10:15 AM >To: Grasso, Charles; 'MikonCons@xxxxxxx'; 'leeritchey@xxxxxxxxxxxxx' >Cc: 'si-list@xxxxxxxxxxxxx' >Subject: [SI-LIST] Re: Buried uStrip question > > >Charles, no as I have read him, Lee promotes putting prepreg w/o foil on >the outside. > >Regards, > > >Steve. >At 09:01 AM 2/2/2004 -0700, Grasso, Charles wrote: > >Steve, AFAIK, a buried ustrip is a ustrip with soldermask. > >Is there another definition? I am unsure as to why one > >would advocate a buried ustrip over a "true" surface ustrip > >when (for typical boards) only buried ustrips prevail. > > > >Best Regards > >Charles Grasso > >Senior Compliance Engineer > >Echostar Communications Corp. > >Tel: 303-706-5467 > >Fax: 303-799-6222 > >Cell: 303-204-2974 > >Email: charles.grasso@xxxxxxxxxxxx; > >Email Alternate: chasgrasso@xxxxxxxx > > > > > >-----Original Message----- > >From: steve weir [mailto:weirsp@xxxxxxxxxx] > >Sent: Monday, February 02, 2004 5:44 AM > >To: MikonCons@xxxxxxx; leeritchey@xxxxxxxxxxxxx > >Cc: si-list@xxxxxxxxxxxxx > >Subject: [SI-LIST] Re: Traces don't cause EMI - really? > > > >Mike, I think the issue is worth reviewing under current > >circumstances. Some understandings have improved greatly with regard to > >antenna design and/or detuning, and geometries have definitely changed for > >the better. Lee advocates a buried microstrip for the outermost routing > >layer. That captures the vast majority of the field in the dielectric. > > > >It's been a long time since I read those old papers going back to the mid > >eighties when stripline started getting promoted for EMI. But I am > >confident that we will find all of those studies compared surface > >microstrip to stripline. It would be interesting to repeat your 50 ohm > >tests with this "buried microstrip" versus a true surface microstrip for > >EMI. > > > >Regards, > > > >Steve > > > >At 03:30 PM 2/1/2004 -0500, MikonCons@xxxxxxx wrote: > > >In a message dated 2/1/2004 9:35:10 AM Pacific Standard Time, > > >leeritchey@xxxxxxxxxxxxx writes: > > >Wow! This topic keeps coming up. Wasn't so long ago that we had a very > > >long exchange where proponents of this notion provided the research papers > > >that supported it. I got copies of all of them and looked for some > > >objective measurement of the EMI caused by a trace routed on an outer > layer > > >over a plane and then moved below the plane. > > >None of the papers did such an experiment in a way that could be used to > > >bet money on. I pointed out that the real source of EMI from a PCB were > > >the lead frames of components that stick up from the PCB. While at > Maxtor, > > >we had this very problem with disc drives. We fixed the problem by > > >changing lead frames from PLCCs to QFPs- packages that don't stick up very > > >far from the PCB. If you want to see this in action, go to Frys or any > > >place else that sells stand alone disc drives and look at how the PCBs are > > >designed. All of the signal traces are on outside layers and all of the > > >disc drives comply with CISPRB B. > > > > > >We used a pedicel of equipment that allowed the PCB to be laid on it and > > >then scanned to provide a 2D picture of where emission were coming > from. I > > >cannot remember the name of the tool, but it had a table with a grid on it > > >on which the PCB was mounted. The output looked a lot like what one gets > > >from a thermal mapping tool showing places with higher emissions. The > > >sources of EMI were very clear- the IC lead frames. > > >Thanks, Lee, for including me on your distribution. > > > > > >I absolutely agree that high-speed boards can be designed with many traces > >on > > >the PCB surfaces IF there is a high integrity enclosure. > > > > > >The tool you mentioned was likely of thick, planar construction with many > > >separate pickup coils in a grid. I have seen several test labs with this > > >tool. As > > >you indicated, the lead frames DO radiate substantially. Assuming buried > >PCB > > >traces, some of this radiation can be cancelled by routing the lead pad > >back > > >under the package before dropping the via. Aside from that, the tool > pickup > > >coils detect near fields; hence, the lead frames (because of their closer > > >proximity to the pickup coils) indicate a disproportionately high field > >level > > >relative to any PCB surface (microstrip) traces. The field strength is > > >comprised of > > >first-order, second-order, and third-order rolloff terms. Therefore, the > > >field > > >signature would show much less relative differences (even with very small > > >spacing displacements) because of an exponential rolloff in the coupled > > >signal; > > >hence, some test results may be misleading. Please be aware that I am in > > >agreement with you on the benefits of low-profile lead packages. Any > > >disbeliever > > >should measure the fields from a small daughter board connected via > > >standoffs of > > >1/4 to 3/8 inch length, as the results will scare you. > > > > > >Re: your statement, "None of the papers did such an experiment in a way > >that > > >could be used to bet money on." > > > > > >As (many months) before, I disagree. I demonstrated the relative radiation > > >and crosstalk performance of microstrip (50 & 100 Ohm lines), guarded > > >microstrip > > >(50 Ohms), stripline (50 Ohms), and guarded stripline (50 Ohms) as part of > > >the (now ancient) Hewlett-Packard High-Speed Digital Design Seminar Series > > >(that > > >included such respected pros as Ed Sayre, Eric Bogatin, and Henri > Merkelo). > > >The results were clear that either containment (via an enclosure) or the > > >use of > > >stripline was needed for FCC or CISPR Class B compliance. The data and > > >knowledge gained from these findings led to the redesign of scores (yes, > > >hundreds) > > >of EMI-deficient PCBs over the following decade that achieved a typical 20 > >dB > > >(some as high as 40 dB) reductions in radiated emissions. No one has > yet to > > >find that the HP spectrum analyzers, HP near-field probes, EMCO > (far-field) > > >antennas and near-field probes that I used (and still use) were > technically > > >deficient in any way. Additionally, my software predictions support the > > >empirical > > >test data as well. > > > > > >My concern (and the only reason I'm sending these comments) is that less > > >experienced designers than yourself will think surface traces are "no > > >problem" and > > >NOT employ the many other routing techniques that you and I have learned > >over > > >the years to be beneficial (or mandatory) for a successful design. > >Obviously, > > >non-enclosed/shielded designs will suffer most from this oversight. > > > > > >Good engineering to all, > > > > > >Mike > > > > > >Michael L. Conn > > >Owner/Principal Consultant > > >Mikon Consulting > > > > > >*** Serving Your Needs with Technical Excellence *** > > > > > > > > >------------------------------------------------------------------ > > >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.org > > > > > >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.org > > > >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.org > >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.org 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