Homebrew PCBs

"lcdpublishing" <lcdpublishing@...> writes:

> While developing, all the resist washed off.

I agree this sounds like underexposure.

If you don't have a step gauge, you can sort of calibrate your
exposure by making a lot of small boards (like 1 in2) with a striped
print on your film.  Mark the back with exposure times in powers of
two - 15s, 30s, 1m, 2m, 4m, 8m, 16m (more if needed).  Expose each for
the marked time and develop.  Note the shortest time that exposes the
clear areas, and the longest time that doesn't expose the covered
areas, and pick a time between those.  You don't have to etch these
boards - just expose and develop, and inspect the film.

If you have a step gauge, one exposure is all you need to calibrate.

> I am wondering what actually holds the resist to the board though.  

Heat.  Try peeling the film off by hand, it should be really hard to
do so.

Also, you need to let the film "rest" for 15 minutes after exposure -
before you peel off the second backing - to let the polymerization
complete, before developing.