Homebrew PCBs

Phil wrote:
>  My 
> best effort got creases and spacial distortion of the transfer 
> pattern.


   The only thing such statements are a true indicator of is that not much 
effort has yet gone into trying many variations on the technique.  It's never an 
indicator of the usefullness of anything until the technique is known and correct.


   I'm skeptical of this working well for 8 mil traces and
> tqfp packages.  I've got some 90 lb paper that might maintain its 
> integrity during starch treatment and will give it a try.  There may 
> be other products that don't wet the paper but decrease the paper-
> toner bonding. a very thin coating of a light oil (wd40 springs to 
> mind) might do it.
> 

   All you're likely to get is a splotchy mess.  Yes you want to increase the 
ratio of one to the other, but they still have to be relatively close for the 
bonding to do well through both steps.  You're not expecting melted plastic to 
stick to oil?  And unlikely you'd ever be able to put on so sparse an oil layer 
evenly enough to modify the paper's adhesion without having a very inconsistent 
process.




   Just got finished trying a board myself.  Didn't even worry about wrinkling, 
that is an issue to be controlled after a correct process is known.  Still, got 
poor toner adhesion to the board, although I didn't do the normal acetone rub so 
that may have been some of it.  Even without acetone though my other paper will 
still tack the toner down easily enough, but it has a more solid surface than 
this will make so the toner is in better contact.

   What is promising is that the pattern did stick fine to the paper, but under 
water didn't take that much rubbing effort with my finger to rub most of it off 
the paper.  So it is allowing the toner to stick fine for the print, but 
allowing it to release fairly easily from the page with water.  It has very good 
initial characteristics, so likely just needs process tuning.  It may actually 
work better with a bit coarser toner, the fine toner I have may need the more 
heavily coated pages to make it stay against the board.  But I may also just 
need to do a few coats etc, so several things to try.

   And paper only wrinkles because it's allowed to expand unevenly.  Put the 
paper on a sheet of glass, coat another sheet of glass with glue and then lay it 
on top.  It'd take forever to dry but it won't wrinkle.  We'll need to find 
something stiff enough to hold the paper flat, porous enough to let it dry in a 
reasonable time while holding it flat, and that the glue won't stick to.  May 
take some looking around but no doubt there's something common and reasonably 
cheap to develop a paper making system.

   Also there are premade products to look at.  There are ready made paper mache 
strips, don't know about the widths though.  And there is preglued wallpaper and 
border paper, which are already dried and flat and may be quite reasonable for 
this use and have a very similar glue.

   There's a heck of a lot of stuff to try before making any major 
pronouncements about the process.  And even though I got poor results on an 
initial swipe at it, several observations lead me to believe it could end up 
being superior to what I'm doing with the photo paper, which is already 
excellent.  So well worth persuing a bit further.

   LOL heck it wouldn't really surprise me to find out that some of the 
commercial stuff is just water soluable dried glue on film with some blue food 
coloring added in to throw people off the trail.  For $4 a sheet even..  :)

Alan