[SI-LIST] Re: Stack up for EMI reduction
- From: "mediwheel_js" <mediwheel_js@xxxxxxxxxxxxx>
- To: <lnima@xxxxxxxxxxxxxxxxxx>
- Date: Fri, 30 Jan 2004 19:37:33 -0800
Nima,
If you have an existing design, it's best to find out where the issues
are. Have your EMI specialist scan your board for failing frequencies
and what locations have the highest dB. Then address those signals
by observing the noise present in the system while the worst case
operability occurs. Then you'll have your baseline for corrections
in the design. You can use a spectrum analyzer to further isolate
the odd band frequencies that are getting you in trouble and attempt
to repopulate those areas with band-aids to observe changes or
worsening of the issues. Without this knowledge you are shooting
in the dark and will never resolve your issues.
jm2c's
jack ~
----- Original Message -----
From: "Nima Lotfi" <lnima@xxxxxxxxxxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Friday, January 30, 2004 3:11 PM
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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