[volt-nuts] PCBs with ceramic substrates

[cheater00 cheater00]

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.griffiths at 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 <cheater00 at 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, <davidwhess at 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 at 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 at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
> and follow the instructions there.
>
>