Hi David, You could perhaps send some of that white material to Mike's Electric Stuff, he has a mass spectrogram, which could tell you what it is.
On Mon, 17 Apr 2017 04:31 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]> > 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.
