Re: [CAD_CAM_EDM_DRO] Re: making PC boards

>
> 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
>
> I used to do boards with Kodak KPR using an intense UV lamp to polymerize the photoresist, then develop with toluene. Still have
> some KPR if someone can't resist. :-)