[SI-LIST] Re: High Speed Traces Under Card Edge Fingers
- From: bala <balaseven@xxxxxxxxx>
- To: Stefan Milnor <stefan.milnor@xxxxxxxxxxxxxx>
- Date: Mon, 9 Jan 2012 09:28:22 +0530
Whats your connector's SMT pad width&HS pair width.if they are almost
equal,then no need to provide cutout.better get the models and simulate
using HFSS or ADS.
Thanks
Bala
On Jan 9, 2012 6:54 AM, "Stefan Milnor" <stefan.milnor@xxxxxxxxxxxxxx>
wrote:
> 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
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>
> --
> Steve Weir
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