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 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 <[email protected]> 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, <[email protected] > mailto:[email protected] > 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 > > > <[email protected] mailto:[email protected] > 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, <[email protected] > > > mailto:[email protected] > 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 -- [email protected] > > > > > mailto:[email protected] > > > > > To unsubscribe, go to > > > > > > > > > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > > > > and follow the instructions there. > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > volt-nuts mailing list -- [email protected] > > > > mailto:[email protected] > > > > To unsubscribe, go to > > > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > > > and follow the instructions there. > > > > > > > > > > > > > > > > > > > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
