[SI-LIST] To remove reference planes under the gold finger areas
- From: "Cortex Chen" <Cortex.Chen@xxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 15 Jun 2005 12:16:46 +0800
Dear SI experts,
I'm working to design a FB-DIMM add-in card. To recall previous experiences for
PCI-E, I'm confused why it's recommended to remove reference planes under the
gold finger areas of an add-in card. In detail, refer to section 2.3.2.6 (page
28 ~ 29) of PCI Express Design Guide (rev. no, 0.5, 12978). Who can tell me
what the main reason is?
By the way, refer to section 6.11.10 (page 417 ~ 418) from Howard Johnson's new
book, I like to quote some sentences for your reference as below:
"......In a differential-pcb pair, most of the returning current from each
trace still flows on the solid plane, not the other trace, because each
differential trace couples much more strongly to the big, solid nearby plane
than it does to its little, skinny differential buddy....".
If it's true, then it will cause some effects like "Differential U-Turn"?
Please give me your comments.
Thanks & Sincerely
Cortex Chen ³¯¥ÃªN
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