Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, DJ Delorie <dj@...> wrote:
>
> 
> "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
>
dj.... Thanks for a great response.  The included link is fascinating and I do believe I will give this wet approach a try.