Hi Curt,
Good to hear from you again.
The reason I am continuing to build a small EDM PCB
Mill is because the machine can be left on it's own to
plug away at the spark erosion, time is not really a
factor. Secondly, the cost of importing the inks for
direct resist printing is not inconsiderable here in
Europe. Also there is the etchant cost. Lastly the
direct resist method still seems to be subject to a
certain 'black art', and few people seem to have had
success to date. I was one who never really had 100%
consistent results with toner transfer for example.
No doubt the black art will eventually be overcome,
but the EDM mill does not require any substantial
black art for successful board production, but of
course, you have to build a cnc as well.
Roger
--- curt_rxr <cwrxr@...> wrote:
> --- In Homebrew_PCBs@yahoogroups.com,
> "lcdpublishing"
> <lcdpublishing@...> wrote:
> >
> > Hi guys,
> >
> > About a year ago or so there was some talk of
> using EDM for
> > isolation milling and such. Stefan was tinkering a
> bit with it and
> > another fellow did some heavy, indepth work in the
> process,
> > including making a power supply to do the grunt
> work.
> >
> > I remember the initial approach was to use a
> bitmap image for
> > processing of the machining. There was a good
> reason why this
> > approach was used and I don't recall why - does
> anyone remember?
> >
> > Last night I was giving thought to this process.
> The one problem I
> > see with EDM and isolation milling is keeping the
> PCB conductive.
> > For example, if the output from the isolation
> milling routine
> > creates and island in the middle of the board -
> then further
> > machining needs to be done in that island area, it
> would no longer
> > be conductive. So I suspect that is part of the
> problem with using
> > vector data as opposed to bitmap data.
> >
> > Chris
> >
>
>
> Sure thing Chris,
>
> I started an EDM project about the same time the
> list was started.
>
> The reasons for choosing raster instead of vector
> were twofold.
> Firstly, I was trying to adapt a printer and use the
> built in PCL 5
> routines to "print" the layout directly to the
> circuit boards.
> Secondarily, as you have noted it's the easier way
> to maintain a
> ground return path.
>
> I ended up custom building a stepper driven XY table
> as the printer
> was incapable of the needed accuracy and the built
> in software was
> dependant on a parallel row of jets in a cartridge.
> While printing
> one dot after another was possible, the speed was
> glacial. Even with
> the XY table the speed was limited by the resolution
> needed for fine
> pitch packages. Using high speed IGBTs for the
> pulse circuitry and
> incorperating breakdown voltage control of the
> electrode gap. the best
> speed I was able to obtain for a an 8 inch by 11
> inch board was 45
> minutes.
>
> Another system that might be faster would the vector
> or pen plotter
> approach with a ground return incorperated into a
> dielectric pipe
> surrounding the electrode. The return path would
> travel with the
> electrode.
>
> With the advent of the Volkan direct resist printing
> system there no
> reason to continue with EDM for PCBs since you can
> print and etch
> multiple copies of your layout in less time than you
> can burn one.
>
> There are several folks in Europe continuing the EDM
> work so you may
> want to look on other lists.
>
> Curt Richards
>
>
>
>
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