very interesting....

Just out of curiosity, you inspired two related questions:
1) Do you ever find that in your 3-layer configurations, one
side is tightly controlled dielectric because it is a core, but
the other side being pre-preg fluctuates? Have you ever had
a problem in that regard?

2) By saying you stitch as tightly as possible, are you
going above and beyond a quarter wavelength of your highest
frequency? Do you even calculate that, or do you just shotgun
every available space with GND vias?

Jack
(aka "the blasted on SI-LIST for mentioning stitching" guy)
.



On 1/4/07, Haldor Husby <[log in to unmask]> wrote:
>
> I think you had just the right amount of coffee today. Your observation is
> good, if the return planes for vertical and horizontal routing are not the
> same net, you essentially loose control of the return path every time you
> make transition between the routing layers. Since transitions often happen
> close to IC's ther is usually a lot of decoupling around, but somtimes
> there
> are clusters of transitions away from any circuitry, and much crosstalk
> can
> happen there.
>
> For several years now I have used board stackups consisting of closely
> spaced substacks of 3 layers with the return plane in the centre as far as
> possible. The substacks are then separated with layers that are more than
> 2x
> the distance between layer internal to the substack. This approach
> resembles
> what you are suggesting, and it has worked very well for me in terms of
> noise control and signal integrity. Applications span wireless networks,
> FM
> radio, sensitive analog measurement circuits and GBethernet over copper.
> (also switching power supplies creating large noise currents at 100 MHz
> close a couple of cm away from a FM receiver with no loss of sensitivity).
>
> I also use a single GND if at all possible, and only use GND as return.
> The
> GND layers are stitched as tightly as space will allow, and I always use
> GND
> stitching around the edge of the board.
>
> Several of our customers have remarked that boards we have re-developed
> for
> them are remarkably more quiet than earlier versions and that it has had a
> real impact on perfromance.
>
> I know everyone cannot afford such extravagant use of copper, but I warmly
> recomend the approach you suggest, and it can be realized in other ways
> than
> the one I have suggested here.
>
>
> Med vennlig hilsen/Best regards
> ________________________________________________
> Haldor Husby, Senior Development Engineer
> Data Respons Norge AS
> Kongsberg Næringspark
> P.O. Box 1022
> N-3601 Kongsberg, Norway
>
> Tel: +47 32 29 94 00    Fax: +47 32 29 94 40
> Dir: +47 32 29 94 18    Mob: +47 48 04 83 68
> [log in to unmask]
>
>
>

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