technical pcb question - reason older board don't use square edge traces?

[johngreene]

You want the real reason?

The older boards were largely laid out with black crepe tape, much like masking tape, in various widths, including quite skinny. It's easer to snake around skinny masking tape than to be continuously cutting corners.

And more reliable. The cut corners were likely to gap apart before the tape masters could be shot to litho film. It's hard to get enough overlap on skinny tapes overlaid on 90 degree or even 45 degree corners.

How do I know this?

I was there.

and rubylithe for ground planes....

12 inch square Multilayer boards at 3X were a real pain! (flip, flip, flip, flip, flop, flop, flop, flop...).

--john