Hi Joe,

Ehm what do you want me to elaborate, the "uninterrupted" part or the "not achievable" part, or both ;-)


A ground plane 'works' by allowing the return current to flow very close to the signal current, thus keeping the loop area between them as small as possible. Any interruption in the ground plane will increase the loop area, greatly diminishing its effectiveness. Since on an SMT board, you need room for the device's pads, vias to other layers and the traces from pads to vias, it will be impossible to get even close to an uninterrupted copper area on that layer. Furthermore, making the available copper area continuous will be a lot of work, at the very least.

On boards with more than four layers, you could sandwich the signal layer(s) between two ground layers. This is often done on backplanes.


If you have any more questions, please go ahead and shoot.


Best regards,
Rob.

[EDIT] Take a look at http://www.elmac.co.uk/desfremc.htm under the heading "Grounding and PCB layout". It explains things in a bit more detail. That whole page is interesting for Lukas, too. [/EDIT]