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Homebrew_PCBs@yahoogroups.com, "gmanca101" <gmanca101@...> wrote:
>
> Sorry, I chose this post as the most recent of yours to reply to; I used to dabble in trying various methods of DIY PCB's and I did try the plotter method with a 7440, trying to figure out which Staedler red pen will suffice,(argh!) but I couldn't do double-sided boards without figuring how to register the board in a way for the plotter to do the second side.
>
> Even with a laser, I'm not sure if this an obvious issue or not a concern as you are only doing single-sided work.
>
> For me, I find Sunday coupon pages printed on my old laser printer adequate enough but the real issue that eludes me from quick PCB fabrication is through-plating.
>
> I am intrigued though, why did you stop going with the direct laser method? The pictures you provided were most impressive but perhaps you ran into the same issue with double-sided boards?
Direct laser? I have never done anything with direct laser, if that means exposing resist directly on the board with a laser.
This photoplotter has been running since 1996 with minimal change. I have had to change films a couple times as one film became obsolete. Agfa is no longer in the silver film business, so I have just had to qualify another film.
I used to do double-sided boards all the time. What I did is generate the two films on the photoplotter, one in mirror image. I took a scrap of PCB material and a sheet of .060" Plexiglas and put it on a light table. Using a magnifier, I align the two films with the emulsion facing together, and glue them in alignment with rubber cement. I use Riston dry film resist fro Think and Tinker, who resell it at a VERY reasonable price. I have a Kepro dry film laminator machine with heated rubber rollers to laminate the film to the board. Oh, the board has to be cleaned with fine sandpaper or Scotchbrite and washed very well for the best dry film adhesion.
I then slip the board between the two aligned phototools and print for one minute on each side with a bank of fluorescent blacklights.
You wait for 15 minutes for the reaction to complete, then develop the resist with warm sodium carbonate solution for about a minute.
I don't have a through-hole process. I do have a CNC milling machine, and a system for putting an air bearing drill spindle on it, and have drilled boards that way. a LOT of setup time and tedious work to make one board.
With FPGAs, I can usually prototype anything I want now in a single chip, using a hacked over board left from some previous project, so I just don't do a heck of a lot of one-off boards anymore.
But, I use this entire setup to make solder stencils out of .003" brass shim stock, just like it was a double-sided PC board without the fiberglass substrate in the middle.
This process is now working extremely well, and I can make apertures down to .010" with excellent results.
I have a huge old Calcomp pen plotter here, I rigged a mercury short arc lamp with ellipsodal mirror and a small loudspeaker moving a brass vane as a light "switch" feeding an optical fiber. I mounted a set of lenses to the pen carriage and it exposed low-sensitivity litho film with a .010" beam. Complex boards took close to an hour to plot out, and the plotter was so dynamic it actually caused a lens to self-disassemble. I should have totally skipped this mess and just kept plugging away on the raster machine. The advantage was no software needed, just plot as if it was a pen plot on paper. The raster machine required a program to convert Gerber to raster, and that program is ten times more complicated than the plotter hardware.
Jon