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

Flame Retardant Class 4.

Steve.
At 08:27 PM 11/24/2003 -0500, Anand Mohan Pappu wrote:
>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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