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