[SI-LIST] Re: Power - Ground Swap in PCB

Mehrdad, it depends on your goals.  Ground near the bottom of a six layer 
stack-up has the advantage that you likely have more free real estate on 
the bottom layer to route with.  If you use Lee's trick of a capped design, 
( quasi eight layer ), then you have two well controlled impedance layers 
both referenced to ground, like they should be.  The more signals that you 
reference against ground versus a power layer, generally, the easier your 
life will be.  It also means that higher speed signals are pushed down in 
the stack and see less of a via stub.  OTOH, ground near the top can be 
better for EMI.

Regards,

Steve.
At 12:03 PM 4/26/2004 +1000, Mehrdad Salami wrote:
>Hello All,
>
>I have a question about layer stack in PCBs. For a simple six layer like
>(configuration 1)
>
>Top (Signal1)
>Ground
>Signal2
>Signal3
>Power
>Bottom (Signal4)
>
>What would be the effect if the Ground and Power planes are swapped
>(configuration 2)
>
>Top (Signal1)
>Power
>Signal2
>Signal3
>Ground
>Bottom (Signal4)
>
>Assuming the same distance between Power or Ground to signal layers and
>also the same track routing on the signal layers.
>
>
>Regards
>
>
>
>Sal
>
>==========================================
>Mehrdad Salami
>Hardware Design Engineer
>
>Colour Vision Systems
>11 - Park St - Bacchus Marsh
>Victoria - 3340 - Australia
>
>
>
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