[SI-LIST] Re: 6 Layer Stack-up
- From: Ravinder.Ajmani@xxxxxxxx
- To: vishrampandit@xxxxxxxxxxx
- Date: Wed, 10 Sep 2003 12:54:02 -0700
Vishram,
I have mostly used the stackup no. 2 of your example. I have also
compared the performance of identical design in stackup 1 and 2, and found
out that for frequencies over 500 MHz, stackup 2 is superior. With the
present day sub-nano second edge rates, it is very easy to have even 50
MHz clock harmonics well up to a GHz or more.
However, there are following issues in using stackup no. 2:
1) In order to get the benefit of buried capacitance, the spacing between
Power and Ground should be 4 mils or less. If you can afford it, go for
ZBC-2000, which is a 2 mil core patented by Zycon.
2) The signals on adjacent layers (1 & 2, and 5 & 6) need to be carefully
routed so that there is no overlapping of traces.
3) Impedance matching will be difficult for the traces that move between
outer and inner layer (traces on outer layer have to be much wider than
traces on inner layer). Hence, try to route most of the signals on the
inner layers, and preferably against the Ground plane as reference.
After experimenting with both types of stackup, I have settled on the
stackup 2. Even from EMI perspective, I have seen lower emissions with
this stackup if the signal impedance is matched properly with transmission
line design and terminations.
Regards, Ravinder
Server PCB and Flex Development
Hitachi Global Storage Technologies
Email: Ravinder.Ajmani@xxxxxxxx
"Vishram Pandit" <vishrampandit@xxxxxxxxxxx>
Sent by: si-list-bounce@xxxxxxxxxxxxx
09/10/2003 11:14 AM
Please respond to vishrampandit
To: larry.smith@xxxxxxx
cc: si-list@xxxxxxxxxxxxx
From: si-list-bounce@xxxxxxxxxxxxx
Subject: [SI-LIST] 6 Layer Stack-up
We have been using the stackup S-G-S-S-P-S.(stack up no. 1). Now, with
suggestion from SI-List, on newer high speed designs, I would like to use
G
adjacent to P with 4-6 mils of separation. It will give me very good
decoupling. However, I have only 6 layers so I have to have my stack-up as
S-S-G-P-S-S (stack up no. 2). Will it be okay?
Here are pros and cons as per my analysis:
1] Stack up no. 1 gives you poor P/G decoupling, wheras stack up no. 2
gives
you very good P/G decoupling.
2] P/G Decoupling caps at higher frequencies (>500MHz) are not required
for
stack up no. 2
3]Stack up no. 1 will shield the EMI radiation from internal traces
because
of G(Layer 2) and P(Layer 5).we will loose this benefit for the stack up
no.
2.
4] For stack up no. 1, signals on Layer 1, 3, 4, and 6 had a reference
plane.For stack up no. 2, only signals on Layer 2 and 5 have reference
planes. So I have to be careful routing high speed signals on Layer 1 and
Layer 6.
Has anyone implemented stack up no. 2 on 6 layer board? Which stack up is
advisible for 6 layer board? What are pros and cons for stack up no. 1 and
2
for a 6 layer board?
Thanks,
Vishram
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