[SI-LIST] Re: 6-layer vs 7-layer PCB Stackup
- From: steve weir <weirsp@xxxxxxxxxx>
- To: kevin98146@xxxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Tue, 01 Jun 2004 14:10:28 -0700
Kevin,
I would not reference signals with any kind of rise time under 5ns against
a 12V supply that has nothing to do with your logic.
For a six layer backplane with very directional routing where you need a
whole plane for each +5V and 12V, I would put both of those in the middle:
1 Ground
2 Signal / 3.3V
big space
3 +12
4 +5
big space
5 High speed differential
6Ground
The routes on layer 2 can be denser than before so hopefully you would not
need to go to eight layers.
Steve
At 01:41 PM 6/1/2004 -0700, Kevin Khuu wrote:
>Hi All,
>
>I'm working on a backplane design and come up with the following 7-layer PCB
>stackup:
>
>1) Signal (Single Ended Signals)
>2) +5V
>3) GND
>4) Signal (Diffential Signals, high speed)
>5) GND
>6) +12V
>7) Signal (Single Ended Signals and +3.3V trace)
>
>I don't really need two GND planes, but the reason I added the second GND
>plane (layer 5) was because of symmetry and balancing PCB stackup. How does
>this stackup compare to the 6-layer stackup (without the second GND layer on
>layer 5)?
>
>Your comments/ideas would be greatly appreciated.
>
>Thanks,
>Kevin
>
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