Homebrew PCBs

Per Mattsson <per@...> writes:

> Next question, what wavelengths are of interest here - different
> wavelengths for different materials I suppose?  300nm?

For UV etch resist films, something around 390 nm is normal, but each
film has its own specs.  Think&Tinker film, for example specs "350-420
nm".  I suspect anything in the 380-400 nm range, common for UV LEDs,
would work.

As for exposure, the math only gets you part way - you should calibrate
the film against your actual setup using something like a step
transmission wedge:  http://www.stouffer.net/TransPage.htm

Expose your film through the wedge, and based on which step "holds" you
adjust your exposure time accordingly.

http://www.thinktink.com/stack/volumes/volvi/filmimag.htm#Calibration