[SI-LIST] Re: [SI-LIST]: Embedded capacitance on Flex..??
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Larry.Smith@xxxxxxx, ray.anderson@xxxxxxxxxx
- Date: Tue, 23 Aug 2005 16:27:45 -0700
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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