[SI-LIST] Re: Stack up for EMI reduction

Dear Nima

According to my experience, in the power integrity of PCB, there are always 
some anti-resinance pole at about 200MHz-400MHz. Could you tell me the dimesion 
of your PCB?

These kind of poless are because of resonance between discrete caps and plane 
caps. In this situation, some thin dielectric(<3mil) should be used in the 
stack-up. If the embedded cap is not useful, I suggust you to use some 
termination in the power supply net. This will eliminate the  poles.

Besides the measurement about EMI, some power integrity analysis at PCB level 
is suggested.

I hope this will help.

Best Regards

Zhangkun
2004.1.31

----- Original Message -----
From: Nima Lotfi <lnima@xxxxxxxxxxxxxxxxxx>
Date: Saturday, January 31, 2004 7:11 am
Subject: [SI-LIST] Stack up for EMI reduction

> Hi,
> I'm looking at re-layout of a 10 layer board because of EMI 
> problems.  The
> board contains 4 differential serial signals a ~700Mhz, and about 
> 20 single
> ended signals at 70 MHz.  The main problem frequencies are around 
> 350 Mhz.
> There are 4 large BGA components on the board.
> 
> I would ideally like to move into a 12 layer board, however there 
> is quite a
> bit of (non technical) resistance to doing that.
> 
> I like to eliminate 2 signal layers, by making my other 2 signal layer
> denser.  Then I'll use the eliminated signal layers as 
> ground/power layers,
> but I will need to use these new gnd/power layers to assist with 
> breakout of
> 4 high density (500pins) BGA.   
> 
> My question is can any one comment on whether I should in theory 
> get an EMI
> improvement?  What should I look out for?
> 
> 
> My current stack up is:
> 
> 1 Mainly GND with some breakout
> 2 Signal
> 3 Gnd
> 4 Signal
> 5 Power
> 6 Gnd
> 7 Signal
> 8 GND/Power (mixed)
> 9 Signal
> 10 mainly GND with some breakout
> 
> 
> 
> New proposed stack up
> 
> 1 GND with some breakout
> 2 power with some breakout
> 3 Gnd
> 4 Signal
> 5 Power
> 6 Gnd
> 7 Signal
> 8 GND/Power (mixed)
> 9 Power with some breakout
> 10 mainly GND with some breakout
> 
> 
> Thanks,
> Nima
> 
> 
> 
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