[SI-LIST] Re: Number of Power Planes in a Stack up

Sivarajan,

There is no thing like "a 62 mils thick stack up there are 3 power planes". The 
number of power planes will be required by the number of different powers 
required by board ( IO voltage, memory IO, processor core, to example some), 
impedance requirements, current carrying capacity requirements, power to ground 
plane capacitance requirement, cost criteria ( increasing number of power plane 
is always good, bust cost more).

I will try to minimize the number of power plane required to keep the cost down 
while still satisfying the power and signal integrity requirements of the board.

Split planes are useful to keep the number of layers and cost down. But we need 
to include stitching capacitors where required. It also has implications on 
impedance discontinuity which should be addressed if required.

How do you think that use of split plane will reduce noise ?

Vikas Shukla

http://referencedesigner.com




--- On Wed, 7/30/08, Sivarajan, Vysakh (S&T-Student) <vshdc@xxxxxxx> wrote:

> From: Sivarajan, Vysakh (S&T-Student) <vshdc@xxxxxxx>
> Subject: [SI-LIST] Number of Power Planes in a Stack up
> To: si-list@xxxxxxxxxxxxx
> Date: Wednesday, July 30, 2008, 3:37 PM
> Hello All,
>  
> Is there any criteria for deciding the number of power
> planes in a PCB stack up ? I read in a paper that for a 62
> mils thick stack up there are 3 power planes.  What decides
> this ? Is it the number of active devices and their power
> requirements that decides ?
>  
> Along with that, can we use the spilt planes for reducing
> the number of power planes ? Or are the split planes used
> only for more and more dender designs ?
>  
> I was just thinking that use of split planes instead of
> more seperate planes will reduce the power plane noise. Is
> it correct ? Please give me your suggestions. Thank you.
>  
> ------------------
> Vysakh Sivarajan
> Graduate Research Assistant
> Electromagnetic Compatibility Laboratory
> Missouri University of Science and Technology
>  
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