Re: making PC boards

Jon,

That's quite impressive. Must be for more then a "hobby"! I'd heard
that the laser printer wasn't exactly scaled. But how do you build a
laser photoplotter? What are the plots from? I can guess that the
heart of it is an X-Y positioning system, then several apertures of some
sort? Also obviously a laser! Do you use Gerber format (which seems
somewhat related to RS274D?? g-code??)? Do you use protel
(http://www.protel.com/)? There is a freeware and a commercial
version. The NC file (holes) from the PCB program is then correct for
CNC? Do you convert Gerber to CNC to run your photoplotter? That's all
quite impressive!

Sorry for all the questions, but it's all !!! VERY INTERESTING !!! This
whole process would ALSO be a good addition to the Tutorial section.
Thanks again for taking the time to answer questions!

Alan

Jon Elson wrote:

> Alan Marconett KM6VV wrote:
>
> > Do you do double sided boards? Purple (?) sheet "negatives" from a
> > laser jet? Then etch them? I've seen the CNC-type mechanical board
> > etches like LPKF, and often thought about writing code to generate CNC
> >
> > "g-code" to cut boards on a Sherline mill. Anyone doing something
> > along
> > these lines?
>
> I do double sides, but without the plated through holes.
> No, laser printers are not accurate enough to register the two
> sides together. Any board over 2" square will have serious
> misregistration, such that holes drilled dead center from
> one side will completely miss the pads on the other side.
>
> I built my own laser photoplotter, which records images directly to
> red-sensitive
> silver litho film at 1000 dots/inch. The blacks are totally black,
> about a log
> density scale of 5 or so, and the clear is very clear (high contrast).
> The films match up, over 10" or so, to within a few thousandths.
> I align the films with a plexi sheet the same thickness as the board
> between them, and tape to a piece of PC board scrap to hold the
> alignment. I use boards coated with DuPont Riston dry film resist,
> and expose in a fluorescent vacuum frame. Development is done
> with a sodium carbonate solution, leaving a resist that is almost as
> tough as solder mask. It will take extensive overetching without
> much damage. The boards are etched in a heated spray etcher.
>
> I drill the boards with a mod that mounts on the quill of my Bridgeport.
>
> It is a Westwind air bearing drill spindle that now runs at up to
> 24,000 RPM. (With a better inverter I could go to 80,000 RPM.)
>
> I've seen the LPKF machines, they seem to work, and do get rid
> of the nasty chemical processes, that are also time consuming.
> But, on the other hand, the etching process develops both sides
> of the board at the same time, and it takes no longer to make a
> board that is 10 times more complex.
>
> Jon