Homebrew PCBs

grantfair2001 wrote:
> 
> By positive, I mean that the copper tracks will appear white when
> printed on paper, and etched portions will be black. My PCB software
> does the usual "negative" print - copper tracks are black, etched
> areas white, but not the positive print.
> 

   As someone already pointed out, you have your terminology reversed by 
trying to label it what you want it to do.  On screen is a positive, 
what you're describing is a negative, and then the exposure process 
negates it again to make a positive PCB with correct tracks.  Note that 
your reversed terminology will make you want a 'positive' and when you 
print a 'positive' it'll be backwards to what you want.  What you really 
need to find is the program's way to print a negative image.

   Keep in mind that you can always reverse the sense of positive and 
negative in anything, electronic or mechanical or photo or anything 
else, and it'll still work logically as long as you keep the senses 
consistent.  That means you are REQUIRED to correctly determine and 
match the normal conventions, or you will be thinking the wrong thing 
and be getting results that you think don't work correctly when really 
you just chose the wrong result by being backward to normal polarity. 
It's not that the program's 'positive' output or 'negative' output 
aren't correct.  You just chose their 'positive' when you really wanted 
their 'negative' and have your choices reversed to the conventional 
direction..

Alan