[SI-LIST] Re: Why are PCIe card edges beveled and DIMMs aren't?
- From: Hermann Ruckerbauer <Hermann.Ruckerbauer@xxxxxxxxxxxxx>
- To: msharpes@xxxxxxxxxx
- Date: Thu, 26 Mar 2015 08:16:27 +0100
Hello,
In the mechanical outline spec (e. g. MO-269H.pdf) this feature is
defined the spec, but as optional and not as required feature.
"Note 22: The addition of this Bevel is a fabrication option and is not
required. The bevel is not to hit the plated contacts."
So the vendor can take the effort/cost if he thinks that this is
required for his high quality products for the reason Mike described.
Hermann
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Am 25.03.2015 um 20:03 schrieb Mike Sharpes (msharpes):
> Jeff et al. - DIMMs as a whole have not had a consistent specification for
> bevel/no-bevel. The reason we (being module OEMs in general or Micron
> specifically) would bevel are for reasons such as: customer spec/preference,
> lower insertion force (esp. on high pin count DIMMs), and better overall
> product (not so many customer returns for tie bar or connector tab related
> issues). Since it is an extra process that is not without its own
> yield/scrap issues, there is a cost associated with it. DIMMs with lower
> margin that are more impacted by cost may not have beveled tabs. I might
> hazard a guess these DIMMs are in the consumer channel, not necessarily
> server grade type modules. ..mike
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Joseph.Schachner@xxxxxxxxxxxxxxxxxx
> Sent: Wednesday, March 25, 2015 10:26 AM
> To: jeff.loyer@xxxxxxxxx
> Cc: si-list (si-list@xxxxxxxxxxxxx)
> Subject: [SI-LIST] Re: Why are PCIe card edges beveled and DIMMs aren't?
>
> Content-Type: text/plain; charset="US-ASCII"
> I listen to the PCI EWG calls. All I can say is: Signal integrity I've heard
> the following discussed for SI as they debate what changes will be needed to
> support Gen 4 (at 16GT/s): height of the ground fingers until the via that
> connects them to the "ground" layer; height of the wiper contact on the
> fingers; width of the wipers and the fingers; whether adjacent ground fingers
> are joined and have two or three vias or separate each to its own via; and
> there is likely something else that I'm not remembering right now. But I am
> sure that the bevel on the bottom has never been raised in any call or any
> document I am aware of as an SI concern.
>
> Looking all the back to PCI Express CEM 1.0a, it says: " The edge-finger
> portions of the PCI Express cards are required to have bevels or chamfers as
> defined in Figure 5-3."
> The relevant part of that figure is:
>
> Note 2 says the chamfer must be free of burrs. There is no explanatory text
> about why the spec specifies this beveled edge. Just my thought:
> Perhaps it is to avoid damage to the wipers in the connector. If a square
> edge board was inserted it might be more likely to damage the wiper
> contacts in the connector. I've never heard this raised as an SI
> concern.
>
> --- Joe S.
>
>
>
> From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
> To: "si-list (si-list@xxxxxxxxxxxxx)" <si-list@xxxxxxxxxxxxx>,
> Date: 03/25/2015 12:06 PM
> Subject: [SI-LIST] Why are PCIe card edges beveled and DIMMs
> aren't?
> Sent by: si-list-bounce@xxxxxxxxxxxxx
>
>
>
> Does anyone know why they bevel PCIe cards but don't bevel DIMMs? We're
> guessing that they want less insertion force for PCIe cards which ostensibly
> get swapped more often, but wonder if anyone knows the actual
> history/explanation. It seems (to me) that removing the bevel from PCIe
> cards would be a welcome change for manufacturing and signal integrity folks.
> Thanks,
> Jeff Loyer
>
>
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