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

Zhiping, static applications where flex is used to make non-planar shapes 
are fine with solid planes.

Regards,


Steve.
At 06:10 PM 8/23/2005 -0700, Zhiping Yang \(zhiping\) wrote:
>Hi,
>
>I had an impression that the planes on flex are not really solid plane.
>It is more like a mesh with small holes.  Is it also true for embedded
>capacitance on flex?  If so, I assume it will reduce the total available
>capacitance.  Can someone confirm it?  Thanks.
>
>Best regards,
>
>Zhiping
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of steve weir
>Sent: Tuesday, August 23, 2005 5:48 PM
>To: Larry.Smith@xxxxxxx
>Cc: ray.anderson@xxxxxxxxxx; adsurevv@xxxxxxxxx; si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: [SI-LIST]: Embedded capacitance on Flex..??
>
>Larry, they are fun materials, aren't they?
>
>Best Regards,
>
>Steve.
>At 05:42 PM 8/23/2005 -0700, Larry SMITH wrote:
> >Steve - Yes, we have sampled both DuPont and 3M.  Dupont is very
> >flexible, almost like saran wrap.  The 3M material is good for hard
> >boards but is about as flexible as a potato chip.  Snaps like one too,
> >I tried it..
> >
> >regards,
> >Larry
> >
> >steve weir wrote:
> > > 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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