Homebrew PCBs

"lcdpublishing" <lcdpublishing@...> writes:
> I have tried using that dry-film etch resist that you buy on a roll,
> apply it to the board with a laminator and have had mixed results.

If you mean photofilm, it took me a while to get reliable results from
it.  Some thoughts...

It wants around 220-240 F temperature, far cooler than most
laminators.  I added the temp control to mine just for this purpose.

I cut the film a few inches longer than needed so I can hold it up and
pulled away from the board during lamination, letting the rollers be
the first to press them together.  Far fewer air bubbles this way.
Adam's wet lamination gets the same results, for mostly the same
reasons, using a wet squeegie.

I have to bloat all my prints by 2 mils per edge (think "bigger
copper") to get the resulting sizes I want.

Don't forget the 15 minute wait between exposure and peeling the
backing film off!

I ended up writing my own software to do the prints for this.  Using
either Silkjet or Jetstar films, I can put down a 100% ink coating at
2880 DPI, which is good for 8 or so steps on a 21 step transmission
wedge.

Very important to get the exposure right!  I use a step transmission
wedge (step gauge) to make sure I'm giving it the right amount of
exposure time.  To little and you risk breaks; too much and you risk
shorts.

I did a 6/6 board recently that had a grand total of one gap, due to
one air bubble I didn't catch (the gap is just left of dead center):
http://www.delorie.com/electronics/sdram/sdram-toppcb.jpg