[SI-LIST] Re: Vias on decoupling pads
- From: "Patrick Jabbaz" <patrick@xxxxxxxxx>
- To: <vincenzo@xxxxxxxxxxxxxx>, <Sol.Tatlow@xxxxxxxxxxxxxxx>,<cchalmers@xxxxxxxxxxx>
- Date: Tue, 6 Apr 2004 09:08:18 -0700
Vincenzo
The problem that occurs when you have a standard via in Pad is not
related to the Fabrication, instead the concern is related to the solder
paste being drawn away from the component land into the via plated hole.
There are methods to avoid this, by using microvias, very small hole
that has no impact on the solder reflow process.
Inkra Networks
Patrick Jabbaz CID
Sr Board Layout Eng.
40971 Encyclopedia Circle=20
Fremont, CA 94538
Work (510) 249-4835
Mobile (408) 621-6533
patrick@xxxxxxxxx
-----Original Message-----
From: Vincenzo Kreft-Kerekes [mailto:vincenzo@xxxxxxxxxxxxxx]=20
Sent: Tuesday, April 06, 2004 8:33 AM
To: Sol.Tatlow@xxxxxxxxxxxxxxx; cchalmers@xxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Vias on decoupling pads
I've always wondered about this, from both the design and manufacturing
standpoint, how is a via-in-pad any different from a via with a
non-circular
capture pad? Why would you use a microvia instead of lets say a 14 mil
via
in the center of a 40x40 mil 0603 pad which would practically be a large
via
capture pad with corners? Why would a fab house worry about the shape of
the
capture pad, they don't seem to handle octagonal capture pads for
through
hole vias differently? Or plane stitching vias with practically board
size
capture pads? Thanks a lot for your help.
Best,
Vincenzo
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Sol Tatlow
Sent: Tuesday, April 06, 2004 7:23 AM
To: cchalmers@xxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] AW: Vias on decoupling pads
Hi Chris,
>Is it ok to put vias actually on the pads of
>a ceramic decoupling cap in terms of manufacture?
>Do other people do this?
yes, you CAN do this, BUT it can require technologies
(micro-via or via-plugging techniques) that are
otherwise not needed - this can make the PCB more
expensive, as well as extending delivery times, plus
can limit your choice of PCB manufacturers: it is NOT
simply a case of placing normal vias in pads at the
layout stage and end of story (solder paste disappears
into the holes=3D3Dbad/no joints, solder paste application
difficulties on other side, etc.).
Obviously, via-in-pad CAN give you the best technical
result/performance with very small decoupling caps,
where there is no space to put the vias for the
individual pads BETWEEN the pads (0603 and smaller),
and in the case of micro-vias allows the placement
of caps directly under full matrix BGAs where it might
otherwise not be possible (good against 'bounce'),
but needs to be weighed against cost requirements.
On a more detailed level, before you use something like
micro-vias, you perhaps also need to do analysis
(comparison) of the impedances of the various
possibilities of connecting the pads to the planes,
since micro-vias are (obviously!) small. Plus, micro-
vias (normally) only connect between neighbouring
layers - stacking is possible, but EXPENSIVE! - which
means they are perhaps ok for GND (L1-L2) but not
for PWR (L1-Lx).
Plugging is yet another different story, with different
methods and (plugging) materials.
If you want more info, let me know, and I can give
you more info on manfg. techniques that will help
you evaluate the pros and cons.
Hope this helps!
____________________________________
Sol Tatlow, M.Eng. (Oxon)
ProDesign Electronic & CAD Layout GmbH
Product Developer
Albert-Mayer-Str. 16
D-83052 Bruckmuehl
Phone: +49 (0) 8062-808-302
Fax: +49 (0) 8062-808-333
Mailto:sol.tatlow@xxxxxxxxxxxxxxxxxxxx
www.prodesign-europe.com
____________________________________=3D20
-----Urspr=3DFCngliche Nachricht-----
Von: Chris Chalmers [mailto:cchalmers@xxxxxxxxxxx]=3D20
Gesendet: Dienstag, 6. April 2004 12:48
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Vias on decoupling pads
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl
List technical documents are available at:
http://www.si-list.org
List archives are viewable at: =20
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
=20
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl
List technical documents are available at:
http://www.si-list.org
List archives are viewable at: =20
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
=20
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
