Re: [SI-LIST] : GND on the outer layers

Bill Dempsey (bdempsey@dnaent.com)
Wed, 14 Jul 1999 15:04:38 -0500

Douglas McKean wrote:
>
> Jon,
>
> I worked with a vendor who just did this recently.
> The answer is - it depends.
>

> My recommendation to them prior to this little
> experiment in order to keep rerouting costs and
> time to market to a minimum was to ADD gnd planes
> as you suggested for a 8-layer stackup such as
>
> gnd
> signal
> signal
> gnd
> pwr
> signal
> signal
> gnd
>
>
> Regards, Doug McKean
>

Doug,

How do you address pads & pin escapes with this stackup?
Are you in fact assuming a 10 layer board? Or did you intend
to flood areas of the top and bot with gnd? The flooding method isn't
nearly as robust as your previous (3db only) stackup.

You could alleviate the problem, add xtalk isolation, and no cost
change by restacking as follows:

signal
gnd
signal
gnd
pwr
signal
gnd
signal

This also allows x&y routing on internal layers (by avoiding parallelism
rules). It may prove to be easier to route because of that (not
guaranteed).

My 3c worth.

Bill Dempsey
DNA Enterprises, Inc.

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