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]> 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]> 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]> 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] > 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. > > _______________________________________________ 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.
