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Vias or long track in groud connection.

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elektryk

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I have to design PCB for some kind of computer. I will have 4 layers without burried via. It has to fulfil some EMC rules. I have designed it with one groud plane (inside board) divided to two areas (digita and analog groud). Top and bottom layers will be covered with ground planes at all free space. The question is what is better for conecting ground for chip (high scale integrated, with lot of ground pins). I have two option, both with positive and negative consequences.
:arrow: via to ground plane
+short conection to ground
-current loop in ground (via-ground plane-via- another ground plane)
:arrow: long conection by "external" ground layers (on bottom and top layer)
+ no "holes" in internal ground plane
+ no current loops in ground
- high impedance in ground connections
 

signal return

You should connect to the layer that the signal traces use for ground return. (the inner plane) Otherwise you will get bit loops for the return signal currents which will radiate and also distort the pulses.

Put plenty of bypass capacitors on the opposite side of the board very close to the power pins and have the other end of the caps go to the inner plane.
 

Re: signal return

flatulent said:
You should connect to the layer that the signal traces use for ground return. (the inner plane) Otherwise you will get bit loops for the return signal currents which will radiate and also distort the pulses.
Click to expand...
So how about closed loop in ground? Should I remove them or just leave? I mean loop between 2 layers conected by 2 (or more) vias.
 

Keep the grounds on other layers and connect them to the main ground plane with many vias. The signal currents will return on the grounds directly under the signal traces and not flow on other shielding pieces of copper. These other grounded areas are good for reducing radiation and also for reducing crosstalk between traces.
 

And should I avoid curent loops in "external" power layers or have so many conection as possible?
 

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