[SI-LIST] : A 10 layer stackup

Peterson, James F (jfpeterson@space.honeywell.com)
Mon, 4 May 1998 07:47:34 -0400

I read what DC said about the stackup mentioned below, and he brings up
some good points. One point he missed, though, was a better (and more
efficient) stackup for a 10 layer board. This stackup has 6 signal
layers, plus adjacent pwr/gnd layers (an excellent high-freq. cap).
Sure, it's not perfect, some of you're return currents might not take
the shortest path "home", which means you've increased your loop area a
little and thus you're radiated emissions. But the pwr plane should
provide a low inductance path for both the lower freq. return currents
and the very high freq. return currents (remember the intrinsic
capacitance of the pwr/gnd layers). The frequencies of concern are
probably in the area of 100-300 MHz and this could be minimized by
spreading out some 0.01uf sm cap's.
In my humble opinion this stackup approach (dual stripline) has some
concerns, but is an effective and efficient one.
Respectfully,
Jim Peterson
Honeywell Space Systems

> ----------
> From: D. C. Sessions[SMTP:dc.sessions@tempe.vlsi.com]
> Sent: Friday, May 01, 1998 10:57 AM
> To: SI-LIST
> Subject: Re: [SI-LIST] : another stack-up question
>
> Andrew Phillips wrote:
> >
> > Hi,
> >
> > There was a recent discussion on this list regarding a stack-up
> proposal
> > for a 10-layer board. Here's another one:
> >
> > signal
> > GND
> > signal
> > signal
> > PWR
> > GND
> > signal
> > signal
> > GND
> > signal
> >
> > I'd be interested in any comments on the merits (or lack of) for
> this
> > arrangment
>
> Return currents will see a different impedance on PWR vs GND, for one.
> Worse, the returns on 7 & 8 will have to cross layers to get to PWR,
> which should make for (1) much more noise, and (2) assymetrical edges
> at the receiver.
>
> --
> D. C. Sessions
> dc.sessions@tempe.vlsi.com
>