Did you have to make any adjustments to your impedance calculation?
Or is there enough copper there (assume something like 75%?) where the
field doesn't notice(?) the difference?


 -----Original Message-----
From:   Earl Moon [mailto:[log in to unmask]]
Sent:   Saturday, December 09, 2000 5:02 AM
Subject:        Re: Controlled Impedance Question

Doug,

Did considerable work with Lee Ritchey back in 1984, or so, with impedance
controlled, ECL, MLB's. We decided first, from a dimensional stability and
laminate integrity standpoint, x-hatched reference planes would be the way
to go. It was and I have some, or at least one, pretty picture to show the
inner layer details.

Without the graphic, the hatches were/are on whatever centers required. The
traces were two directly associated/under/over the reference plane grid
traces of about 25 mils, as I recall.

The system did as proposed. The laminate integrity and dimensional stability
was excellent and the electrical performance was as specified.

Today's boards may find issue with the grid system. They often are so dense,
they almost make something equal to the x-hatching as hole locations and
sizes make swiss cheese out of everything.

Earl

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