I have heard and read about a phenomenon which sounds kind of scientific
but which I have never seen.  This is that if you have an acute angle in
an etched circuit trace it will "trap" etchant and thus over-etch.  This
is actually mentioned in Joseph Fjelstad's flex circuit book people have
been talking about.

I've done lots of etching and haven't seen this effect at all.
Actually, my experience has been that inside corners under-etch, not
over-etch, which I presume to be the result of the same hydrodynamic
phenomenon quoted by the proponents of the over-etch theory:  Surface
tension causes the etchant to stick in the corners.  This "stuck"
etchant quickly becomes saturated with copper, and the etching process
stalls because not as much hot, high pressure etchant can get to the
affected area.

Not that I intentionally design circuits with acute angles in the
traces--I think they are non-optimal for other reasons, but I want to
make sure I'm doing the right thing for the right reason.

Wayne Thayer

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