[SI-LIST] Re: High Speed Traces Under Card Edge Fingers
- From: "Stefan Milnor" <stefan.milnor@xxxxxxxxxxxxxx>
- To: "steve weir" <weirsi@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Sun, 8 Jan 2012 17:23:21 -0800
My PCB crew was routing some HS pairs along the edge under the fingers,
I was the bad cop and stopped them.
If the planes are not pulled back, and the traces are isolated from the
fingers by planes, it would seem that the trace sig int would be OK.
But I am getting the message that the "pullback is necessary" for the
connector sig int performance.
Although - Devil's advocate - the only place I can recall seeing this in
print is in the PCIe CEM spec. I don't see this recommendation in the
MXM3 spec, or in the connector vendor's materials.
Thanks, SM
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of steve weir
Sent: Sunday, January 08, 2012 5:46 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: High Speed Traces Under Card Edge Fingers
The pullback is necessary to maintain a relatively constant impedance.
Were you routing high speed signals on inner layers in the finger area?
That's something I would avoid with or without the PCIe pullback
requirement.
Steve.
On 1/7/2012 10:28 PM, Stefan Milnor wrote:
> Hello Experts
>
> The "DDR3 Clock Failing Radiation Tests" discussions have been quite
> interesting. But here is a different topic:
>
> "Remove Planes Under Card Edge Fingers?"
>
> In the PCIe CEM document, one finds the following statement:
>
> "On the add- in card, the ground and power planes underneath the PCI
> Express high-speed signals (edge fingers) shall be removed. Otherwise
> the edge fingers will have too much capacitance and greatly degrade
> connector performance"
>
> Is this really a concern?
>
> We are making small form factor boards with MXM3 connectors, and are
> wondering if we have to relieve the planes in the "edge finger" area.
If
> we do so, then we lose some routing space, for high speed signals at
> least, as we want to route these against a plain. This is a bit
> painful.
>
> Thanks,
>
> Stefan
> ------------------------------------------------------------------
> 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 technical documents are available at:
> http://www.si-list.net
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
All contents Copyright (c)2012 IPBLOX, LLC. All Rights Reserved.
This e-mail may contain confidential material.
If you are not the intended recipient, please destroy all records
and notify the sender.
------------------------------------------------------------------
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 technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
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 technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
