Indeed, someone I asked elsewhere hinted that ceramic filled PTFE is a good idea for curbing hook.
On Mon, 17 Apr 2017 06:20 Bruce Griffiths, <bruce.griffi...@xtra.co.nz> wrote: > When the glass fibre bunch periodicity approaches a significant fraction > of a wavelength the periodic spatial modulation of the substrate dielectric > constant under or surrounding transmission lines has interesting effects > on the properties of the transmission line. At even higher frequencies the > surface texture of the copper also becomes an issue. Ditching glass fibre > in favour of small ceramic particles eliminates the effect of the periodic > spatial modulation of the substrate dielectric constant. Just as with > dielectric absorption it should be possible to fit a Cole-Coles or similar > model to the variation of dielectric properties (including loss) with > frequency. > > Bruce > > On 17 April 2017 at 15:54 cheater00 cheater00 <cheate...@gmail.com> wrote: > > Thanks, that second article had exactly what I had in mind. I would love > to see that permittivity vs freq graph in more detail around one of the > flat crossings of the saw graph with the smooth fitted curve, maybe +/- 10 > MHz around that crossing (not around the steep jump) > > If ceramic is fragile and FR4 can be hook less then I assume FR4 is > better, testing anyways doesn't hurt. > > The periodicity of the "saw" graph is telling. Could this have to do with > the size of layers created by the fibers, or the size of fibers themselves > or their spacing? Maybe a random fiber dimension (diameter, spacing) would > be better here than using a constant dimension of fibers. > > On Mon, 17 Apr 2017 05:35 Bruce Griffiths, <bruce.griffi...@xtra.co.nz> > wrote: > > There's little out there on the frequency dependence of dielectric > constant at audio and sub audio frequencies. > > A bit more for 10MHz and above like: > > > http://www.edn.com/design/analog/4398951/2/What-PCB-material-do-I-need-to-use-for-RF- > > > http://ac.els-cdn.com/S1474667015373043/1-s2.0-S1474667015373043-main.pdf?_tid=2e1d6d30-231a-11e7-84ab-00000aab0f26&acdnat=1492398280_a0295abea04d2b08db9f227ee52506fc > > > There's also the article in The October 8 1978 issue of electronics on > > Getting rid of hook: The hidden pc-board capacitance by authors from > Tektronix and Norplex. > > This article is in the files section of the Tekscopes yahoo group. > > Otherwise there are various values given in the literature and on the web > for the low frequency relative permittivity of FR4 which are all noticeably > higher than the value at 10MHz. > > Bruce > > On 17 April 2017 at 14:31 cheater00 cheater00 <cheate...@gmail.com> wrote: > > Thank you. Do you have a plot of the effect on impedance due to hook out > into high frequencies, measured on a real world material? It would tell me > a lot. > > On Mon, 17 Apr 2017 04:19 Bruce Griffiths, <bruce.griffi...@xtra.co.nz> > wrote: > > Hook is merely a manifestation of the variation of dielectric constant > with frequency. > > It affects the frequency response and transient of resistive attenuators > by requiring more complex compensation than merely adjusting a trimmer cap > to equalise the low frequency and high frequency attenuation. Since the > dielectric "constant" (relative permittivity) of all dielectrics is > frequency dependent all dielectrics will exhibit hook to some extent. Some > PCB substrates like some versions of FR4 and G10 exhibit a significant > variation in the dielectric constant from the dc value to a somewhat lower > value for frequencies even in he audio range let alone frequencies of > several MHz. Achieving a flat frequency response where the dielectric > associated with circuit board capacitances exhibits significant hook is a > complex task. Circuit board hook even affects the impedance of printed > transmission lines (eg stripline, microstrip, CPW etc). > > Bruce > > On 17 April 2017 at 13:54 cheater00 cheater00 <cheate...@gmail.com> wrote: > > Are conformal coatings the right way to handle this? > > I understand there are kinds of FR4 and G10 that don't have hook. What does > one do about hook - how are those substrates improved? How does hook > manifest in circuits? > > On Mon, 17 Apr 2017 03:48 David, <davidwh...@gmail.com> wrote: > > FR4 has problems with consistency. Samples can have problems with > hook, dielectric absorption, leakage, and sensitivity to humidity. > > On Sun, 16 Apr 2017 12:08:07 +0100, you wrote: > > Hi Chuck > > But the context is "PCBs with ceramic substrates". Are any of *those* > tough? They may well be, perhaps you know of some? It does not help us > with the subject much if there are ceramics with these amazing > properties if they are not available as PCBs. > > There is also the question of exactly what properties of FR4 are > limiting for "metrology" use. > > John > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > > _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
