Re: [SI-LIST] : Cross hatched planes

Adrian Shiner (adrian.shiner@virgin.net)
Sat, 19 Jun 1999 21:46:03 +0100

Considering the flexing stresses on sharp corners, whether diamond or square cross hatch:-

Why go for sharp corners, these are mechanical stress raising areas?

Why not make the ground plane solid and perforated with a mesh of round holes?

Holes can be variable (choatic) size to control impedance in critical areas.

Should be easy for the PCB layout tools software makers to get their heads around.

Adrian

Fred Balistreri wrote:

> fabrizio zanella wrote:
> >
> > I have a question regarding high frequency (over 500MHz) signals running
> > over ground planes that are cross hatched, which is commonly done on flex
> > circuits. The issue is how to accurately model the characteristic and
> > differential impedance for the flex circuit traces. If, for example, I use
> > a 2D field solver (where I assume an ideal ground plane) and am designing
> > for 100 ohms differential impedance, what percent increase in impedance
> > should I expect if the ground plane will actually be cross hatched?
> >
> > thanks and regards,
> >
> > Fabrizio Zanella
> > EMC, Hardware Engineering
> > fzanella@emc.com
> > 508-435-2075, x4645
> >
> > **** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at
>
> This will depend on how the cross hatch is done. If the cross hatch is
> square and the traces are routed directly above/below the hatch then
> a 2d field solver can be applied and get good answers. However if the
> cross hatch is diamond w.r.t. the traces then more work is necessary to
> get a reasonable result from a 2d field solver. Electrically speaking
> the square cross hatch is a better solution. However for manufacturing
> and mechanical reasons flex is usually made with diamond cross hatching.
> That being the case, care has to be taken to make sure the return paths
> are not being increased substanually due to the hatching. And as
> mentioned its much harder to model.
>
> Best Regards,
> --
> Fred Balistreri
> fred@apsimtech.com
>
> http://www.apsimtech.com
>
> **** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****

**** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****