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

The issue of getting people to utilize thin dielectrics (1 mil and 
under) is to make them understand that these materials have been 
engineered to provide the necessary minimum break down voltage, both 
during initial testing and in the long term.  They are not like 
typical FR4 laminates.  The PCB shops test the power/ground inner 
layers at 500 volts before putting them in the boards and again at 
final electrical test.  Additionally the material suppliers have 
done significant testing on the long term reliability of these thin 
dielectrics.  Also, Sanmina-SCI has done extensive testing to insure 
the reliability of the products made under their license (this is 
one of the benefits of using licensed products and fabricators).

As for the issue of Er versus dielectric strength, there is a 
tradeoff as was mentioned.  The BC12TM material from Oak-Mitsui 
(www.oakmitsui.com) balances the properties and obtains a product 
with an Er of 10 and a dielectric strength over 6000 V/mil.  
Dupont's HK-11 is similar. These types of materials also are easier 
to process as they can flex and won't snap like a "potato chip".   
Products like Oak-Mitsui's BC16T (Er of 30) and 3M's C-Ply (Er of 
16) could be used for distributed capacitance in backpanels, 
motherboards and cards, but I feel they are best suited 
as "singulated" (a term we are kicking around in the IPC for 
discrete capacitors formed inside the board) capacitors (and tested 
at voltages similar to discretes) or as distributed capacitance in a 
module (which typically see lower voltages). 

Finally, another reason why it is hard to get people to evaluate the 
technology is that the ones who are currently using it (and there 
are several) are not talking about it.  They are keeping it as a 
competitive advantage and do not want to share their experiences at 
conferences or in published papers.   Most of the literature is from 
academia or the material suppliers.



--- 
In si-list@xxxxxxxxxxxxxxx, steve weir <weirsi@xxxx> wrote:
> 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@xxxx [mailto:si-list-bounce@xxxx]
> >On Behalf Of steve weir
> >Sent: Tuesday, August 23, 2005 5:48 PM
> >To: Larry.Smith@xxxx
> >Cc: ray.anderson@xxxx; adsurevv@xxxx; si-list@xxxx
> >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@xxxx
> > > >>>[mailto:si-list-bounce@xxxx]
> > > >>>On Behalf Of Virendra
> > > >>>Sent: Tuesday, August 23, 2005 12:11 PM
> > > >>>To: si-list@xxxx
> > > >>>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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