[SI-LIST] trade-off between using vias and longer trace length
- From: "Ethan Tsai" <ethantsai@xxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 24 Sep 2003 22:41:19 +0800
In a 4 layer PCB, the stack-up is signal(layer-1), ground(layer-2),
power(layer-3) and signal(layer-4). For a crowded routing, some signals need to
be routed through vias from layer-1 to layer-4, that means signals will change
reference plane. If we make the reference plane in layer-3 also be ground,
there will be no reference-plane issue. But it needs two vias for each signal
to transition between layer-1 and layer-4. In another way, not using vias,
signal path (trace length) will be routed longer to avoid crossing. The longer
trace length will result in more attenuation and increasing loop inductance.
There is a trade-off between the two approach, which way is preferable?
The frequency will be 400MHz
And the over routed length is about 2 ~ 3 inch.
Thanks a lot
Ethan Tsai
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