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Mark E. Skeels wrote:
> Ok, so my question is about the stack up order.
> 
> I would have thought this was the best for my needs:
> 
> 1. Signal #1
> 2. Ground
> 3. Signal #2
> 4. Power/VCC.
> 
> In my mind, it places the two signal layers in the closest proximity to 
> the ground plane, and since I have reasonably low (relatively speaking) 
> intentional RF type activity on the PCB, I am most concerned with 
> isolating the digital and analog return currents and separating digital 
> and analog areas of the PCB, and not too concerned about what I 
> understand as the advantageous capacitive or shielding actions of having 
> the ground plane/power plane interaction.
> 
> However, I see nobody doing this.
> 
> Instead, I see the most frequently recommended stack up order is
> 
> 1. Signal #1
> 2. Ground
> 3  Power/VCC
> 4. Signal #2
> 
> Even my PCB program (Altium Designer) defaults to this configuration.
> 
> I have also seen a few other stack-ups but by placing the planes on the 
> outside, (for example) they force the breakup of the plane for component 
> connections, which I see as not very useful for me, all things considered.
> 
> Does anybody have any input or advice on this? Thanks?
> 

The difference between the inner and outer layers (in terms of distance
from the ground plane) is tiny: measured in tenths of a millimeter. The
extra performance you may get will probably be outweighed by the
additional difficulty you will encounter if you need to probe that
internal signal layer. Also, most of the connections to and from
components will be on the signal layer (usually more so than power
connections) so more vias will need to be used.

- --
Brendan Gillatt | GPG Key: 0xBF6A0D94
brendan {a} brendangillatt (dot) co (dot) uk
http://www.brendangillatt.co.uk
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