On Thu, Aug 10, 2017 at 9:01 AM, mike.valk@gmail.com mike.valk@gmail.com wrote:
2017-08-09 15:23 GMT+02:00 Luke Kenneth Casson Leighton lkcl@lkcl.net:
next set...
GND shielding parallel to the differentials is interrupted quite often.
because there's simply not enough space to do otherwise. if i could move the entire CPU and RAM up another 0.5mm it would be doable. but then i would have to re-route 12 signals which go around the top area of the board and that's (a) risky and (b) not enough space to do it.
Those GND tracks act as shields, for emission and reception. I'd try to put as much parallel GND as possible.
And trace the parallel GND around the via's, see attachment.
ah, got it - thanks for the tip, i thought i'd done that on all diffpairs, but i missed one. good call.
yes there's only one, because the layer 1 and layer 6 will be flood-filled and that will fill the areas that "appear" to be missed.
Make sure the'res as much solid GND on the layer above and below the traces, again shielding.
these are layer 1 and layer 6, and layer 2 and 5 are solid GND.
Also I'd personally not use curved wriggles. HF signals travel in a straight direction. With curves they start diffracting and start bouncing cross each other and might start to radiate or echo back.
mmmmm.... *stress*! anyone else feel the curves are "Bad"?
But I see that the community is divided on that stance.
If tight for space you can use 90% corners with a chamfered outer edge. I suppose the chamfer acts like a mirror.
i'd *really* prefer not to do that :)
https://www.maximintegrated.com/en/app-notes/index.mvp/id/5100 Figure 6
wow that's pretty bad-ass.