[volt-nuts] PCBs with ceramic substrates

cheater00 cheater00 cheater00 at gmail.com
Sun Apr 16 22:33:19 EDT 2017


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, <cheater00 at 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.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
>>
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