Hello Guan,
Insulation resistance is a dc measurement of resistance and it therefore
must be in units of Ohms. It is usually specific to a particular test setup
since the conductance across the surface of the laminate and through the
body of it are not the same. If you were interested in sheet resistance of
the raw laminate material (two-dimensional properties), the appropriate
units would be Ohms per square. If you were interested in three-dimensional
properties, the parameter is volume resistivity and the units are typically
Ohm-centimeters.
When you talk about electrical isolation and mention dBm, you are referring
to ac performance. I am just guessing at what you meant, but it sounds like
you are looking for steady-state coupling from one trace to another at a
given frequency, which could be measured in dB or dBm. This is dependent on
the geometry of the conductors and laminate, the laminate properties plus
the source and load impedances. The ac laminate properties (dielectric
constant and loss factor) are only two factors in this calculation, and not
really the major ones. Since the ac impedances are usually orders of
magnitude less than the dc insulation resistance, this quantity does not
usually contribute at all. For this reason, we don't really talk about
electrical isolation properties of a laminate, except for the one case of
insulation resistance at dc.
Hope this helps. If I have misinterpreted your question, please try again.
Regards,
Seth Goodman
Goodman Associates, LLC
tel 608.833.9933
fax 608.833.9966
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Goh Guan Chye
> Sent: Wednesday, May 15, 2002 10:29 PM
> To: [log in to unmask]
> Subject: [TN] Electrical Isolation in dbm ?
>
>
> Hi Technetter,
>
> Noticed from FR4's materials properties that the unit used in the
> Insulation Resistance is in "ohm", just wonder is there anyway or
> logical to interpret as "dbm" ?
>
> Appreciate kindly advise please.
>
> Regards,
> Guan Chye
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