[SI-LIST] R: AW: 8 layer stackup recommandation

Dear Gert,
there is a direct connection between a good SI practice and a good EMC-PCB 
design.
 
Just to make an easy example, it is simple to see that the reduction of ripple 
on a fast signal ( using approppriate termination load) will produce a 
reduction of the field radiated by the net.
 
In general good SI practive is the first step (not the only one) towards a good 
EMC design.
 
Giancarlo
________________________________

Da: si-list-bounce@xxxxxxxxxxxxx per conto di Havermann, Gert
Inviato: ven 19/09/2008 11.15
A: Mustafa Özgür TUTUM; si-list@xxxxxxxxxxxxx
Oggetto: [SI-LIST] AW: 8 layer stackup recommandation



Mustafa,

Is it correct that your first stackup has two signal layers between Power and 
GND? Does that mean your routing broadside coupled? If not, I think you will 
have a very hard time routing that to be sure that your GND-return paths are 
all correct. Even with broadside coupling you need to be very careful when 
using the Power plane as GND-return path. I recommend the second stackup to 
avoid hidden errors in your design.

I've never seen a reliable relationship between good SI- and good EMC- PCB 
designs. You can have both, but you can not rely on getting good EMC 
performance just by careful selecting Stackup and routing. A good Stack and 
routing does at least assure that your high speed lines will be resistant to EM.

BR
Gert


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-----Ursprüngliche Nachricht-----

Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im 
Auftrag von Mustafa Özgür TUTUM
Gesendet: Freitag, 19. September 2008 10:52
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] 8 layer stackup recommandation

Dear all, I have 2 questions


1) We are planning to use 8 layer PCB for high speed circuit having max 1.5GHz 
clock frequency. Which stackup do you recommend?



First Stackup:



Signal

Ground

Signal

Signal (includes a few power islands)

Power (includes ground island for 4th layers' high speed signals' return path)

Signal

Ground

Signal



OR



Second Stackup:



Signal

Ground

Signal

Ground

Power

Signal

Ground

Signal





Second choice seems good  but  very hard for routing, Do you think it worths to 
try second choice?

Which is the best stack up for 8  layer PCB for good Signal integrity and EMC 
performance?



2)  Can we say that if any stackup is the best for Signal Integrtiy, it is also 
the best for EMC? or reverse?



Thanks for your interest



Regards

Mustafa




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