[SI-LIST] Re: 8-layer PCB stackup

Kevin,

Stackup A is better as all signals have a continuous ground reference
even when layers are changed.  Adjust(increase) the separation between
layers 3 & 4 and layers 5 & 6 to get the required PCB thickness.  Keep
the minimum separation between layers 1, 2, 3 and layers 6,7,8 to
increase the above effect and to get your required impedance on signals.
The only low point of this is lack of plane decoupling for 5V and 12V.
But this can be compensated by broadband decoupling of these supplies.

In the stackup B, it is difficult to control the reference plane for
signals as they will see different reference planes when they switch
layers.  This is a huge disadvantage.

Regards,
Prasad

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Kevin Khuu
Sent: Thursday, June 24, 2004 9:07 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] 8-layer PCB stackup

Which of these two PCB stackups is better?


Stackup A:

1 Signals
2 GND
3 Signals
4 +5V
5 +12V
6 Signals
7 GND
8 Signals


Stackup B:
1 Signals
2 GND
3 +5V
4 Signals
5 Signals
6 +12V
7 GND
8 Signals

Thanks,
Kevin

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