Philip Pemberton <
ygroups@...> writes:
> Can anyone explain how to do this? The laminate I was going to try and
> calibrate is some really old Maplin "Economy Single-Sided SRBP Photo-Etch
> Board" that one of my friends wants testing. Frankly it saves me digging into
> my own stocks of (FR4) board...
Check the archives; I've described this before a few times, but in a nutshell:
You put the gauge on some PCB and expose it for some time, like 8
minutes, and develop it. One of the steps will have some but not all
resist remaining; this is the "step" of that exposure. Near the "1"
end of the gauge it will be overexposed (one hopes), and near the "21"
end it will be unexposed.
If the step is too low, increase your exposure time - for the ST21,
twice the exposure moves you TWO steps (1.414x per step).
If the step is too high, decrease your exposure time similarly.
> Also, does anyone know how the procedure for setting UV exposure levels
> differs when using positive photoresist?
It doesn't, you just need to know what step to use for your particular
film. If you can't find that info, use 8, which is what Riston uses.