From: Paul M Fly
Hi gang,
I work for an OEM and not a board fabricator, so I would like to add a
different twist to what
Mike had to say.
Being able to put power and ground planes very close together (without
shorting!) also builds
a nice capacitor into your board. With materials that have higher
dielectric constants comes even
more capacitance! This is a great benefit in todays world of extremely fast
edge rates. No offense
to Mike ar any other fabricators reading this but that built in bypass
capacitance is more of a
benefit (to us at least) than being able to squeeze 16 layers into an
0.062" thick board!
The reason why is simple. We want to provide low impedance return paths
for all that high frequency
energy todays ICs spit out. Having discrete capacitors sprinkled around has
two disadvantages, first
no matter how small the footprint of those parts take up valuable real
estate. Second is those capacitors
may have been chosen without regard to the inductance in the routing to
them. Which means the
low impedance return path may not be as low as you would like, or need.
With the power and ground
planes configured as a "capacitor" inside the board the situation improves
a lot! Now that unwanted
high frequency noise has a place to go.
My explanation is a little on the crude side, but I think any EE's
reading this will understand.
Just my $0.02,
*********************************
Paul Fly
Eastman Kodak Company
Engineering Technology Center
901 Elmgrove Rd.
Rochester, New York 14653-5313
Phone: (716) 726-5670
Fax: (716) 726-0275
E-mail: [log in to unmask]
*********************************
"Mcmaster, Michael" <[log in to unmask]> on 26/07/2000 10:53:41
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
to "Mcmaster, Michael" <[log in to unmask]>
To: [log in to unmask]
cc: (bcc: Paul M Fly/243609/EKC)
Subject: Re: [TN] Plane Capacitors
Bill
I'm running a little behind in reading my Technet. I'm busy trying to keep
our lead times down to 6 weeks :-). I noticed you haven't gotten a
response
on this so I thought I'd still post a reply to your question.
We build boards with standard cores as thin as 2.5 mils (single-ply 1080
prepreg). These can be signal/signal, signal/plane or plane/plane. Of
course there is also the ZBC 2.0 mil core, but it's pretty limited to
plane/plane applications. The challenges are about what you'd expect,
handling, handling and handling.
We also fabricate prepreg openings down to around 3 mils in thickness, too.
Most of these are single-ply applications of 2313 (or similar) style
prepreg. The challenges here are optimizing both process and design to
avoid low pressure areas which could result in voids and entrapped air.
Cleanliness can also be an issue, at the material supplier and in the board
fabrication process. We and our suppliers had to invest a lot of effort in
cleaning up our material handling areas to avoid shorts due to
contamination
from conductive particles.
The benefits are fairly obvious. How else are you going to fit 16 layers
in
an 0.62" thick board or maintain "reasonable" PTH aspect ratios for 26
layer
boards with BGAs that require .012" drilled holes unless you have
dielectric
openings this thin?
> ----------
> From: Brooks Bill[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Brooks Bill
> Sent: Thursday, July 13, 2000 8:37 AM
> To: [log in to unmask]
> Subject: [TN] Plane Capacitors
>
>
>
>
>
>
>
>
> To: PCB guys and gals...
>
> Plane Capacitors... it was the topic for discussion at PCB West in Santa
> Clara... have any of you had experience with manufacturing boards with a
4
> mil gap between the gnd plane and the signal layer?
> What are the challenges you see... and did you realize any benefits from
> the
> exercise?
>
> Bill Brooks
> Senior PCB Designer - <mailto:[log in to unmask]> [log in to unmask]
> Zoneworx, Inc.
> 40925 County Center Drive, STE 200
> Temecula, CA 92591
> <http://www.zoneworx.com/> http://www.zoneworx.com
> Tel: (909) 296-1226 x 1037
> Co-Director / Education Officer / Webmaster
> for the San Diego Chapter of the IPC Designers Council
> <http://www.ipc.org/SanDiego/index.html>
> http://www.ipc.org/SanDiego/index.html
>
>
>
>
>
>
>
>
>
>
> Thanks,
>
>
>
> Bill Brooks
> Senior PCB Designer - [log in to unmask] <mailto:[log in to unmask]>
> Co-Director / Education Officer / Webmaster
> for the San Diego Chapter of the IPC Designers Council
> http://www.ipc.org/SanDiego/index.html
> <http://www.ipc.org/SanDiego/index.html>
>
>
>
> Expand Your Domain!
> _____
>
>
>
>
> Zoneworx, Inc.
> 40925 County Center Dr., Suite 200
> Temecula, CA 92591-6037
>
>
> Ph: 909.296.1226 (x1037)
> Fx: 909.296.1227
> Visit us on the Web: zoneworx.com <http://www.zoneworx.com>
>
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