Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Hmmm...

I'm a (relatively) new member here. I've been lurking. This is the first
urination competition I've seen in this group but, human nature being what
it is, I suppose they are inevitable. When I was in the first grade we used
to see who could stand farthest back from the urinal. I could do more than
six feet. Now that I'm almost 60 (yikes!) well, you don't want to know. A
sad story.

Anyway, the topic: This is in fact the reason I joined. I make double sided
PCBs with plated-thru holes, but have trouble going beyond 2 or 3 inches on
a side because of the distortion caused by printing laser transparencies. I
used negative file photoresist which works quite well, bit printing
negatives exacerbates the distortion problem because of the large areas of
black.

The contrast of the laser printer (I have a Brother MFC8500) is fairly poor
so I have to stack up 3 prints to make it dark enough. Last time I tried
inkjet (HP 932C) the ink wouldn't stick well enough to the plastic, so large
dark areas had lots of gaps (too much surface tension in the ink.) Recently
I picked up a used Epson Workforce 630 for my wife [only $25 :-) but $70 for
ink :-( ] and decided to try printing a mask on that. I was thrilled! It
looked perfect, with excellent contrast. But the test was a positive image,
no flood fill.

Next board I made I printed on the Epson, but found the ink smearing and
bleeding wherever there were large dark areas, and the fine traces (~12mil)
tending to close up. Back to the laser. I know I could use flood fill to
reduce the black areas on negatives, but that is not foolproof because the
flood fill often cannot reach some spaces.

I recently picked up some Oracal to experiment with, but even with that I
doubt TT will work for me because of inadequate contrast (too many pinholes
in the black areas) though I am in the process of making a temperature
controller for my Royal PL2112 laminator. I looked at replacing the
thermostats but decided I'd rather have continuous control from hand-warmer
to melt-down. Who knew a simple 1N4148 made such a swell temp. sensor? I
have actually tried multiple applications of toner to a PCB. Too hard to
align. But there are other interesting applications for TT.

Anyway, I would be very interested in learning which printers produce the
best contrast with little or no distortion. I can't afford to keep buying
inkjet and/or laser printers till I get it right, and I don't want to spend
a fortune on equipment or consumables. If I could just throw money at the
problem I wouldn't bother with DIY. I have a pretty good supply of NuKote
laser transparencies and would prefer to continue using those. They seem to
work pretty well with the Epson inkjet, though I'd grant there may be
something that works better. If so, I'd like to know why. But again, I don't
want to accumulate a stack of useless transparencies searching for The One
That Works.

OT; FWIW, I've found that conductive ink made from Silver Acetate is very
effective as a hole wall activator. After drying and annealing at ~92C it
forms a layer of metallic silver with a very strong mechanical bond to the
hole walls, and as such is impervious to solvents. It is more expensive than
conventional DIY activators, and is quite toxic, but the shelf life is
virtually indefinite, and I can make it in small batches. I thought about
selling it in small vials but the toxicity argues against that. Some putz
would probably sue me because his kid tried to snort it or something.
Anyway, FWIW.
--
Phil M.