Homebrew PCBs

"Barry Demers" <sdad@...> writes:

> Those of you who have used photresist films would you care to
> comment?  I noticed different application methods, self adhesive and
> laminate.  I assume that in either case, I apply to board, use a uv
> light through a positive or negative film above it, and then remove
> the unexposed film?

In a nutshell, yes.

> Maybe I print via a laser/inkjet onto the film rather than use a
> second transparency?

Laser doesn't block enough UV light to be useful here.  Also, you
can't really run the film itself through the printer, because it's too
flimsy, heat sensitive, and light sensitive.

> How about leakage under the film during the etching process?  Is
> this a concern and does either the self adhesive or the laminate
> provide better results?

That depends on how well it's stuck to the board.  I've found that
tiny "bubbles" in the film cause etched spots in the board, even if
that spot is supposed to have copper.

> How does this compare with using a liquid photosensitized coating on
> the board?

Film resists tend to be negative acting (ink = no copper), liquid
coatings tend to be positive (ink = copper).  Film gives you a much
more consistent film thickness, if you can apply it consistently.
Liquid applies consistently, but the thickness is harder to control.

> How is the unwanted film removed from the board prior to etching?

That's what the developer is for.  The process goes:

* laminate
* expose
* develop (various chemicals, depends on the film)
* etch
* strip (usually NaOH)

> If the laminating procedure is superior to the self adhesive, can a
> flat household iron be used to laminate the film to the board?

Unlikely.  I don't think an iron gives you the pressure/heat control
you need.  However, we've seen good results on this list with both
laminators (dry) and heat guns (wet).  See also:
http://members.optusnet.com.au/~eseychell/index.html