If the ink is forming globules of any description then that
automatically means the media you are using is not compatible with the
ink. There should be no density difference between large areas and
narrow line features. I suggest you give up on the media your
experimenting with. I found a number of inkjet transparency sellers for
the screen printing industry were happy to provide free samples of film.
The JetStar brand was mentioned before.
For example, I bought a 100 sheets of "HP everyday semi-gloss gloss
photo paper" that would simply not absorb ink correctly in either my
Epson or Canon printers. Some inkjet clear films I came across were
similarly ineffective.
Adam
DJ Delorie wrote:
> Some follow-up notes from today's experiments...
>
> It occurred to me that I've got negative acting film, so I need ink
> where there will be NO copper. This changes the rules a bit :-)
>
> Specifically - the printer can print dark fine lines, even if I say "1
> mil" it can print dark enough (I hope) to properly expose the
> photofilm. The problem with the positive print was that bleeding
> would cause shorts, but I needed to make the pads as big as they
> needed to be, which put lots of ink there.
>
> So what I tried tonight was something different. I printed a
> negative, which is a lot less ink because I normally flood copper onto
> the board to reduce etchant usage Thus, rather than print a big pad,
> I'm printing a thin outline around it.
>
> I also told PCB to bloat all the copper by 1.5 mil to compensate for
> the blurring caused by dot misalignment. With a 5 mil space, this
> leaves 2 mil of ink, plenty for the printer to print with. It also
> moves the ink away by more than the misalignment amount. If this
> works out, I'll just change my design rules to use larger traces and
> smaller spaces, like 8/4 instead of 6/6, or 7/3 instead of 5/5. That
> will handle the copper floods properly.
>
> I also tried printing on an old laser transparency film. Note that
> inkjet ink pretty much doesn't dry on this, as it is not absorbed at
> all. I haven't experimented with a heat gun on this; I assume that
> something like JetStar will resolve the ink issues. Anyway...
>
> I'll have to experiment with the ink density. What happens is that in
> large ink areas, there's so much ink that the surface tension pulls
> the ink away from the edges. So for this to be useful, either a more
> absorbant transparency will be needed (as noted :), or software to
> find these areas and checkerboard their interiors (much like we have
> to break up big solder paste areas under thermal pads). If ink lines
> are kept to a few mil, they seem to hold their shape and density
> nicely - they're pretty much solid black. Since they don't dry
> though, they will eventually bleed enough to corrupt the plot.
>
> I tried printing on heavy cardstock (8 mil thick vs 3 for paper) with
> no change in ink drop misalignment. Of course, I have no idea how far
> the print head is from the paper, or how to change it with my
> software. If I get too close, it smears the ink all over the paper.
>