🚀 go-pugleaf

Greetings all,

	I thought I would share some ideas on PCB prototyping I have done. I have made
my first 2-sided PCB using the photographic method. The minimum track width I used was
20mil (0.5mm) and the resolution seemed good although I got some shorts between
closely spaced pads (are you meant to remove the clear plastic coating off the PCB
*before* exposing?). I used Protel 3.1 (Grrr, etc) to generate a Gerber output, then
used Camcad Graphic to read in the Gerber file so I could invert the image (I am using
negative PCB emulsion) before printing it out.
	Central to this method is being able to get a sharp, high-contrast printout
onto a transparency. After some investigating and testing, I chose an Epson Stylus 400
ink-jet printer and printed onto Epson transparency slides ($3 each tho). I used
black ink only and selected 720dpi in the driver (even tho 720dpi is labelled for
photo-quality paper). The printout was excellent with sharp lines (at 1:1 scaling) and
solid black. I used the negative process because large copper planes are printed out
clear thus saving ink.
	I mirrored the top layer printout so that the ink would be closest to the
copper when exposed. For alignment, I placed both films together and matched the
tracks, then drilled a 0.5mm hole thru selected large pads on both films, at
opposite corners of the sheets. Then in the dark area, I placed the top film on the
PCB, and drilled thru the film holes thru the PCB. I then removed the top film and
got the bottom film and put it on the UV lightbox. Then placed PCB on it and aligned
it looking thru the holes in the PCB to the holes in the film. Then black plastic was
placed on top to prevent the top layer being exposed. Then the lid was clamped down
and exposure was 3 minutes (my lightbox needs preheating for 15 minutes before use).
I then did the same for the other side. After exposure, you can see the film pattern
on the PCB even before developing.
	Now the PCB was stuck in the developer (NaOH?) dish and brushed with a 
paint-brush to dissolve the unexposed resist. Then the PCB was stuck in the bubble-etcher 
tank to etch all that is unwanted (using ferric chloride). Some stubborn areas would not
go, and I realised that there was still some undesolved resist, so I washed the PCB and
brushed over it with more developer (after 2 hours etching!). After more etching, these
areas were quickly removed. Then the PCB was washed, dried, and brushed over with
stripper (at 50degC) which quickly removed all the remaining resist. Finally, the PCB
was drilled. It is most useful (and probably essential) that you use a drill stand
for your small PCB drill.
	I think the next time round I could probably make the PCB in 2 hours total (it
was 4"x6" and had 200+ holes). A real dark room isn't really needed, just some fairly
darkish areas lit with non UV sources. I used a yellow 60W "bug globe"; the theory
being that bugs can see the shorter wavelength light which these globes avoid.
	Some PCB fab places will sell you the PCB cut to the size you want, and cheaper
than most retail outfits.

	Hope this helps...

--
Regards,
    Russell, VK3KRS.

MARTIN COMMUNICATIONS Pty. Ltd
87 Peters Ave. Mulgrave Vic. 3170
Ph. +61 3 9560 9999   Fx. +61 3 9560 9055
http://www.ozemail.com.au/~mcomltd

    /\  /\  /\  /   / MARTIN COMMUNICATIONS
   /  \/  \/  \/   /  Russell Shaw, B.Eng, M.Eng, MIREE
  /   /\  /\  /\  /   Electronic RnD Engineer
 /   /  \/  \/  \/    EMAIL: russell@martin.com.au