[SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz frequency

What does FR-4 actually stand for? Does anyone know the history of this
material?

Anand



> Stuart, for common dielectrics, somewhere in the high hundreds of MHz
> dielectric loss overtakes loss from skin effect.
>
> Steve.
> At 05:16 PM 11/24/2003 -0500, Stuart Brorson wrote:
>>True enough, but aren't the dielectric losses in FR-4 more or less
>>frequency independent (i.e. to the <10% level that the dielectric
>>function is constant)?
>>
>>Anyway, Tom is right:  you need to consider the frequency variation of
>>both Dk (the dielectric function) and Df (the dielectric loss
>>function).   However, both are typically dominated by skin effect
>>losses, particular in the GHz range.
>>
>>Stuart
>>
>>
>> > To make the answer complete you need also to include dielectric losses
>> which
>> > also are frequency dependent.
>> >
>> > Tom Dagostino
>> > Teraspeed Consulting Group LLC     Teraspeed Consulting Group LLC
>> > 2926 SE Yamhill St.                Device Modeling Division
>> > Portland, OR 97214                 13610 SW Harness Lane
>> >                                    Beaverton, OR 97008
>> > http://www.teraspeed.com           503-430-1065
>> > tom@xxxxxxxxxxxxx
>> >
>> >
>> > -----Original Message-----
>> > From: si-list-bounce@xxxxxxxxxxxxx
>> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Stuart Brorson
>> > Sent: Monday, November 24, 2003 1:22 PM
>> > To: andyk@xxxxxxxxxx
>> > Cc: si-list@xxxxxxxxxxxxx
>> > Subject: [SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz
>> > frequency
>> >
>> >
>> > If I am not mistaken, your question is equivalent to this one:  Is the
>> > dielectric function constant over the 1 MHz -- 1 GHz range?  The
>> > answer is: It is not constant, but varies by several percent or more
>> > over that range for many FR-4s.  (FR-4 is not a single material, but
>> > is a family of materials, each different depending upon your PCB
>> > vendor, and whatever batch of materials he was shipped on any
>> > particular day.)
>> >
>> > However, the bigger problem for you to think about is the loss due to
>> > the skin effect in your copper traces.  The skin effect losses vary as
>> > the square root of the frequency, IIRC.  The frequency-dependent loss
>> > due to the skin effect dominates over the frequency variation of the
>> > FR-4's dielectric constant.
>> >
>> > Here are some references:
>> >
>> > http://www.tdasystems.com/library/appnotes/siml0803.pdf
>> > http://signalintegrity.com/Pubs%5Cnews%5C4_5.htm
>> >
>> > Stuart
>> >
>> >
>> > > Hi all,
>> > >
>> > > I am designing a high speed PCB at over 1Ghz frequency using FR4
>> material=
>> > > .
>> > > I am wondering how much the dielectric constant will be affected by
>> the
>> > > frequency over 1Ghz as compared to 1Mhz?
>> > >
>> > > Thank you
>> > >
>> > > Regards,
>> > > Andy
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