Homebrew PCBs

Philip Pemberton <ygroups@...> writes:
> DJ Delorie wrote:
> > I've found that ink blocks UV better than toner (8 steps vs 3 for
> > toner).
> 
> What do you mean by "steps"?

The standard measure of exposure is a "transmission step wedge" - it's
a film with various calibrated steps of opacity from "clear" to
"opaque".  If you put one of these over a striped pattern and expose
it long enough, you end up with three sections on your board - a solid
copper section (too much exposure) on one end, a solid bare section
(too little exposure) on the other end, and a striped section in the
middle.  The width, in steps, of that section, tells you how well your
stripe mask blocks UV - the difference between "step alone blocks
enough" and "step plus mask blocks enough".

Each step is 1.414 times as dark as the previous one, so two steps =
twice as dark, or twice the exposure time equivalent.

So, my black inkjet ink is 8 steps, or a 16:1 range of exposure times
that "work".  The black toner is only 3 steps, or about a 3:1 range of
working exposure times.