[SI-LIST] Re: [SI-LIST]: Embedded capacitance on Flex..??

Don't forget that ultra thin dielectrics can result in unreliable PCBs due
to dielectric breakdown.  Gr86 core requires a 4 mil minimum separation
between planes.

Lee W. Ritchey
Speeding Edge
P. O. Box 2194
Glen Ellen, CA 95442
Phone- 707-568-3983
FAX-    707-568-3504

I just used the energy it took to be angry to write some blues.
Count Basie


> [Original Message]
> From: steve weir <weirsi@xxxxxxxxxx>
> To: <Larry.Smith@xxxxxxx>; <ray.anderson@xxxxxxxxxx>
> Cc: <adsurevv@xxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> Date: 8/23/2005 4:30:46 PM
> Subject: [SI-LIST] Re: [SI-LIST]: Embedded capacitance on Flex..??
>
> Larry, DuPont and 3M both have thin dielectric with elevated Ers that is 
> nice stuff.
>
> Some caution is warranted though depending on the specific 
> application.  High Er material can do good things as you said.  For a
given 
> skin and dielectric loss, the peak magnitude of the parallel resonant
peak 
> falls approximately as the inverse square root of Er.  It tends to be
even 
> better than that as higher dielectric loss pulls down the peak as 
> well.  But there are some potential rocks in that stream:
>
> 1. Reduced board modal resonant frequencies, good for damping,
potentially 
> bad if too low
> 2. Reduced board to discrete capacitor parallel resonant frequency.  Can
be 
> a good or bad thing.  Introduces more variables to discrete bypass design.
> 3. Increased risk of quarter wave resonance within power delivery band 
> between discrete caps and IC die.
> 4. Much higher material cost.
>
> Best Regards,
>
>
> Steve.
> At 01:24 PM 8/23/2005 -0700, Larry Smith wrote:
> >Virendra - I believe that Dupont has some thin, flexible dielectric
> >that can be loaded with ceramic to bump up the dielectric constant.
> >
> >We have found that the best value comes from thin dielectric because
> >it both reduces inductance and increases capacitance resulting in
> >lower impedance.  The lower power plane impedance produces more
> >damping, which is a good for reducing power plane resonances.
> >
> >By increasing the dielectric constant alone (no dimensional changes)
> >the capacitance per square area is increased but it turns out that the
> >capacitance available to a power consumer with in a given time frame
> >(i.e. 1 nSec) is the same.  This is because the velocity of
> >electromagnetic propagation goes down with increasing dielectric.  The
> >cylindrical wavefront that goes out from a disturbance "uncovers" the
> >same amount of capacitance per time, independent of the dielectric
> >constant.
> >
> >So if you are looking for high frequency capacitance to satisfy those
> >fast edges, thin dielectric is good, high dielectric constant is
> >neutral.
> >
> >regards,
> >Larry Smith
> >Sun Microsystems
> >
> >Ray Anderson wrote:
> > >
> > > Typically the way I've seen it done in the past is to use a very thin
> > > dielectric material (~2 mil thick) to achieve the higher than usual
> > > capacitance.
> > >
> > > Most hi-k materials are loaded with some sort of ceramic material
which
> > > tends to make them somewhat less than flexible which could be an issue
> > > with a flex board.
> > >
> > > Note that the materials people are always developing new and
innovative
> > > solutions, so what was true a couple of years ago when I looked at the
> > > issue may no longer be the case.
> > >
> > > -Ray
> > >
> > > -----Original Message-----
> > > From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> > > On Behalf Of Virendra
> > > Sent: Tuesday, August 23, 2005 12:11 PM
> > > To: si-list@xxxxxxxxxxxxx
> > > Subject: [SI-LIST] [SI-LIST]: Embedded capacitance on Flex..??
> > >
> > > Hello All,
> > > Does anyone have experience with embedded capacitance
> > > (wih high K) on a flex circuit board? If yes, are
> > > there any issues with bending the part of the flex
> > > with the high k material..?
> > >
> > > thanks in advance,
> > >
> > > virendra
> > >
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