> Just a suggestion, but would it be too much to ask people > who did some of the tremendous studies in simulations > and analysis scenerios with printed circuit boards > to do best case and worst case scenerios with a RANGE > of FR-4 values and then to have the Dk of the board > for the frequencies of interest actually MEASURED? > > I found that ALL simulations presented used the typical > Dk = 4.7 value that can vary with great latitude from > mfr to mfr (dependent upon mfr-ing techniques) and > can vary with frequency. > > I even took one person aside after their presentation, > (a very good one I might add) and discussed this point > with them. They hadn't thought of this. We're talking > at the Ph.D. level. Now maybe that isn't such a big > concern for them, but it is for me. The 4.7 value is > at best a fantasy. > > Am I being to overly something-or-other?
Not at all. In several years of measurements I've never found a commercially produced FR4 (high temp or not) board with an effective Dk > 4.6. The ratio of resin to glass-fibre varies between vendors, boards, layers and even across layers. One might also ponder the reasons for differences between time-domain measurements (which is what most design engineers need to see) versus time-domain simulation results based upon frequency-domain measurements. regards, Richard Schumacher Hewlett Packard HPSL (nee' Convex) --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], or [email protected] (the list administrators).
