Re: [SI-LIST] : Effective Dielectric

Weber Chuang (WeberChuang@via.com.tw)
Tue, 24 Mar 1998 09:47:32 +0800

Dear D.C.,

I can guess that the value should be somewhere in between 4 and 7,
but can the fringing effect just be totally ignored and then apply the
static EM theory to solve the effective dielectric constant, I am
curious about that.

Best Regards

Weber Chuang(ChingFu Chuang)
SI Engineer, System Team.
VIA Technologies, Inc.
Taipei, Taiwan, ROC
http://www.via.com.tw
Very Innovative Architecture
******* Re: [SI-LIST] : Effective Dielectric
*******************************************

> dfall@thin-film.com wrote:
> >
> > I have a question regarding the effective dielectric of two layered
> > materials (such as ceramics, etc.). For example, say I have two
> materials
> > with dielectric constants of 4 and 7. When a signal passes through
> these
> > two materials, what is the effective or total dielectric constant
> that it
> > sees. Any help on this matter is greatly appreciated.
>
> Think of it as two caps in series, with a virtual plate at the
> material interface. 1/C = (t1/e1) + (t2/e2), so
>
> (t1+t2)/e' = (t1/e1) + (t2/e2)
> e' = e1*e2*(t1+t2)/(t1*e2 + t2*e1)
>
> Of course, this only applies if the layers are close together
> relative to the size of the conductor; if the space near the
> conductor is dominated by one material or the other (eg a
> 75-micron trace with 150 microns of FR4 and a few light-years
> of air and vacuum above it) then the farther dielectric
> has less effect.
>
> --
> D. C. Sessions
> dc.sessions@tempe.vlsi.com