At 12:32 PM 11/24/2008, you wrote:
>Hi to all,
>
>I am doing PCB layout that has 12v and 5v. 12v has 2A load
>and it is used to power leds and 5v is to supply logic.
>The board is only 4 layers and I am not sure about power plane
>Should I use 12v as part of power plane or 5v. for example
>
>Layer1: 12v
>Layer2: signal
>Layer3: signal
>Layer4: ground  or sould I do this

Generally the signal planes are on the outside. It is easier to get 
the bonding process to work properly with large areas of copper on 
the inner planes. If you have significant non-copper areas then you 
might need to use a "balancing pattern" so that the board doesn't 
develop hollow spots.

Splitting a plane is not a problem either. I have one design I am 
checking right now which is the fourth in a series where we have a 
single ground plane, but the power plane is split into 5V, 3.3v and 
1.2v areas. You could easily split yours into 5V and 12V if it makes 
sense in terms of your layout.

John



>Layer1: 5v
>Layer2: signal
>Layer3: signal
>Layer4: ground  or sould I do this
>
>
>Layer1: signal
>Layer2: 12v
>Layer3: ground
>Layer4: signal   or sould I do this
>
>
>Layer1: signal
>Layer2: 5v
>Layer3: ground
>Layer4: signal
>
>
>I do not have any requirement this is for my own use.
>any suggestion will appreciate.
>
>Thanks
>
>Andre
>
>
>
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