In these examples and others that have been put forth to say mother and other boards' microstrip traces radiate enough to cause EMC issues, how are the tests used to indicated that there is a radiation issue separated emissions from: The well designed microstrips The poorly designed microstrips The cables running to chassis mounted connectors The cables to drives The power supply cables Etc. In my experience, which I'm sure is not as broad as many who are contributing to this thread, is the cables were the big problem. Any noise on the ground, power or signals that were connected to the cables was radiated. This was much higher than anything on the board. Tom Dagostino Teraspeed Consulting Group LLC Teraspeed Consulting Group LLC 2926 SE Yamhill St. Device Modeling Division Portland, OR 97214 13610 SW Harness Lane Beaverton, OR 97008 http://www.teraspeed.com 503-430-1065 tom@xxxxxxxxxxxxx -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of phillip.r.wellington@xxxxxxxxxx Sent: Wednesday, October 22, 2003 2:34 PM To: MikonCons@xxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Traces don't cause EMI - really? I think there are many of us who lived through these early PC days who can substantiate Mike's (and many others) assertions that a good enclosure is required to contain emissions from microstrips. My experiences (at another company) was with motherboards, video cards and monitors (even back when VGA Video cards had 6 oscillators on them), SCSI, and ethernet. We ran into the same problem with vendor provided product and tried to find compliant "hanger queen" devices to perform our FCC Class-B tests with. Enclosures were always an EMC reliability problem. Surface microstrips do radiate and their emissions need to be contained either by planes or an enclosure. The emissions from microstrip traces fill the enclosure looking for a return path. The image plane can't contain all the EM field lines. The emissions couple to internal cabling, ungrounded heatsinks, sub-assemblies, etc, and cause self compatibility and/or external compatibility problems. This can also happen with internal cabling connected to motherboards that do not have local decoupling to keep those emissions off of the cables. They are essentially microstrips without a reference plane nearby. A low impedance return path must be provided for a PREFERRED return path for those emissions inside the cabinet. If you don't provide it, currents split, and they will surely find the return path that you least desire (Reset circuits, Analog/RF circuitry, Power traces, etc). It may not be a failure at the time of test, but degraded noise margins may lead to "spooky" problems in adverse environments (Electro-magnetic, thermal, voltage margin sensitivities, etc). Good Stripline (symmetrical and asymmetrical) design solves many EMC problems. As with all designs, there are trade-offs based on multiple pain thresholds. Often, surface microstrips are a susceptibility path for ESD failures as well. This has been a good thread with a lot of good input from seasoned, very talented people. Congratulations. Ross Wellington L-3 Communications CSW -----Original Message----- From: MikonCons@xxxxxxx [mailto:MikonCons@xxxxxxx] Sent: Wednesday, October 22, 2003 12:59 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Traces don't cause EMI - really? In a message dated 10/20/2003 6:02:12 PM Pacific Standard Time, chris.cheng@xxxxxxxxxxxx writes: To hide behind claims that since PC's or workstations have surface trace passing EMI and magically deduced that traces does not cause EMI problem makes as much sense as driving in the highway seeing no cops pulling people over for speeding and extending that to no one is speeding in the highway.. I love this analogy. Excellent comment, Chris. Jeff Loyer stated the following. " I don't believe a case of "well behaved" microstrip traces generating enough EMI to fail FCC standards has been demonstrated - all failing instances seem to be accompanied with the caveat of including a design error, or unreasonable geometries (.062" above the ground plane)." Absolutely not true. Several papers over the past decade from respectable sources (e.g., IBM, Ott, Paul, and me, sorry--don't want to sound arrogant) have demonstrated FCC Class B failure for boards that are NOT shielded by an appropriately designed enclosure. Following is another personal experience that should put this contention to rest. At the time of launch of the AMD K6 microprosser, I supported AMD with EMI evaluations that required testing of multiple vendor PCs. I performed analyses, near-field probe tests, and microprocessor package measurements that predicted not only emission levels, but CPU package resonances that would aggravate the expected emissions. We tested about 10 separate PCs from vendors that included Acer, HP, Dell, Compaq, and others. Tests were conducted at two different certified facilities (one in Santa Clara, CA and another in Dallas, TX). The PCI bus at that time was only 33 MHz, and the the microprocessor (typically 100-300 MHZ clocks) technology used was predominately 0.25 microns or larger (which inherently produces slower edge rates than todays 0.09 to 0.18 micron technology). Nevertheless, ALL VENDOR PCs FAILED EMI WHEN THE CASES WERE OPEN---MISERABLY. The resonances I had predicted were confirmed to contain the worst offending frequencies. In the same time frame, I consulted to Motorola on their Power PC motherboards, with the exact same result---you had better have a good enclosure to pass FCC (or CISPR) Class B levels. Shipping PCs from Phoenix, AZ to Europe loosened marginally designed case sufficiently to cause EMI test failures in Europe that passed fine in the US. The cases were redesigned to increase seam contact ruggedness to resolve the problem. BOTTOM LINE: It is pure folly to mislead todays junior designers with thoughts of successful EMI performance unless an adequate shielded enclosure is doing an excellent job of suppressing emissions generated directly from the motherboards. Multiple, objective tests of products from the largest PC suppliers have unquestionably confirmed this fact. And, it IS possible to analytically predict emission levels and their consequences (i.e., failure to pass regulatory requirements). Do your own analyses with the appropriate software, than confirm your results and your analytical techniques by radiated emission tests. Only then will you have adequate confidence in how to execute a "works the first time" design. If my comments offend some, sorry; but I'm old and wise enough that I accept reality, whether I like it or not (at $2800/day, my clients seem to think so too). 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 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 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 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