[PCB_FORUM] Re: GND Clearance Under SMD Pads
- From: "Jean Bratton" <jean.bratton@xxxxxxxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Wed, 13 Oct 2010 04:56:02 -0700
I've seen this request for AC Blocking caps on high speed nets, reasons
as suggested by Gerry, but not decoupling caps...
Jean Bratton
Senior PCB Designer
Freedom CAD Services, Inc.
Phone: 603-864-1349
Skype: jean.bratton
Email: jean.bratton@xxxxxxxxxxxxxx <mailto:jean.bratton@xxxxxxxxxxxxxx>
Visit us at http://www.freedomcad.com <http://www.freedomcad.com>
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Randy Dawson
Sent: Wednesday, October 13, 2010 4:43 AM
To: icu-pcb-forum
Subject: [PCB_FORUM] Re: GND Clearance Under SMD Pads
Hi Alexis,
Unless I am missing something here, you want that decouple cap signal to
launch immediately to the GND layer...
No voids underneath in it either. Question them.
Randy
________________________________
From: kathy_descoteaux@xxxxxxxxxxx
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: GND Clearance Under SMD Pads
Date: Tue, 12 Oct 2010 20:17:36 -0400
Hi Alexis..
Did you try to add a route keepout on the second layer? It should clear
out the gnd plane on the second layer if its a dynamic shape. There may
be an issue when it's placed on a brd with a different layer name for
the second layer... a minor update to the footprint and you should be
good to go. Just thinking... not sure if it will work.
Kathy Descoteaux
________________________________
Date: Tue, 12 Oct 2010 20:07:19 -0400
From: ameehan@xxxxxxxxxxxxxx
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] GND Clearance Under SMD Pads
For a high speed application, we've had a request from engineering to
create a special footprint for decouplers (0402, 0201) with a GND
clearance under the pads. The clearances will be the same size as the
pads, and will just affect the ground plane on layer 2. I'm trying to
figure the best way to do this. I thought I could just build a special
padstack, but Allegro (using XL 16.3) won't allow me to build an SMD
padstack with an anti-pad unless I define a drill, bottom side pad, etc.
But I'm not seeing a clean way to build this into the footprint symbol
either. Any ideas?
Thanks.
Alexis Meehan
Violin Memory Inc.
Mtn View, CA
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