For most of what we did, there was enough copper to get to 50 ohms within
10% or so. Traces were 5 mils on the inners directly under/over the 25
mil grid traces going perpendicular per layer. .

I don't have my notes with me, but most often, as I recall, we used 25 mil
wide copper grid "traces" on 60 or 100 mil centers with square via pads and
dummy pads that were 60 mils for 100 centers and 20 for 60 mil centers.
Variations on the design sometimes were mixed.

These were balanced stripline designs as well. Little was available as
unbalanced requirements though the equations were available - board shops
and their understanding of TDR were not.

Via sizes in those days were nearly always 4 to 6 to 1 aspect ratios in what
usually were 10 to 16 layer boards. Examples were Magnuson Computer,
Trillium, Fairchild, BNR, what was that other one?, etc.

Most all designs were constructed using 5 core materials and prepregs. This
meant using mostly all two ply 1080 resin to glass ratio whether epoxies or
polyimides. Soon thereafter, we started using 106 and 2113 materials to
achieve better dimensional stability and electrical performance.

Anyway, don't see grid reference planes anymore. Hope you revive the
practice.

Earl Moon

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