Homebrew PCBs

Dwayne,
Thanks for the interesting insight.
What if anything is your solution for via connections ?

BTW I think  "stripper is Caustic Soda (Sodium Hydroxide)" is the same
as Red Devil Lye ! I buy it at Krogers, may be somewhat cheaper.

Best Regards
Hans Wedemeyer


Dwayne Reid wrote:

>  At 08:02 AM 5/3/02 -0500, hans@... wrote:
> >Been following all this about perf. boards and milling etc.
> >
> >I like the idea of milling but it seems the prep. work is tremendous.
>
> >
> >Doing pref. boards then PCB seems like hard labor.
> >
> >I'd like to have comments as to why pre-sensitzed PCB and etching is
> not
> >mentioned and what you consider is so bad with it ?
>
> We do both.
>
> The photo process uses DuPont Riston 4215 laminate film, a much
> modified
> Ibico laminator supplied by Kepro, developer is Soda Ash (Potassium
> Carbonate), etch is Ammonium Persulphate, stripper is Caustic Soda
> (Sodium
> Hydroxide), drilling is by Gordon Robineau's PCB drill.  This is a
> very
> mature process - we have made thousands of boards with the process
> over the
> past 18 years or so.
>
> The downside is the prep time.  The raw board has to go through a 5
> step
> cleaning process before being laminated.  The negative has to be done
> at a
> local print shop - someone takes over a floppy and comes back with a
> negative.  Drilling used to be done by hand but is now with Gordon
> Robineau's seriously cool PC drill - I simply feed it the drill file
> from
> my CAD program.  The bottom line is that it is a half day process from
>
> start to finish - 1 board or 20 boards takes about the same amount of
> time.  The boards turn out perfect - it is a great process.  But it
> ties up
> somebody for that half day.
>
> One of my techs purchased a dead engraving machine from the local
> repair
> outfit.  The computer part of it was completely dead but the
> mechanical
> stuff was just fine.  He cut the stepper motor drive section off of
> the CPU
> card - he now had a stepper controlled X-Y-Z mill, complete with
> stepper
> drivers.  I wrote a simple PIC stepper controller (12c508) that takes
> in
> step and direction commands and generates the step sequences for the
> stepper drivers.
>
> Ryan spent a couple of months in his spare time learning how make the
> system work.  He now uses a somewhat modified version of Kevin
> Carroll's
> Stepster as the G-code interpreter - its what drives the stepper
> controllers.
>
> It takes Ryan about 40 minutes to process the plot file from my CAD
> package
> into G-code suitable for feeding to Stepster.  I don't know the exact
> steps
> involved: I do know that he uses Corel Draw, Adobe Photoshop, and
> Desk-NC
> in the process.  I'll document the procedure sometime soon and post
> it.
>
> The milling bits are standard high speed steel engraving machine
> bits.  For
> milling PC boards, Ryan has the bits ground to what the re-grinder
> calls a
> .005" flat.  That means the tapered bit does not come to a point but
> instead has a .005" wide flat surface at the very tip of the
> bit.  Apparently any finer than that results in a tip that is too
> fragile.
>
> Milling a board takes anywhere from 20 minutes to an hour, depending
> upon
> the size of the board and how much copper has to be removed.  The
> boards
> turn out OK - Ryan can get a trace between 2 IC pads reliably.  The
> sides
> of the traces are somewhat jagged - not perfectly smooth like the
> photo
> process.  The isolation path is probably about 0.015" or so - it means
> you
> have to take a little care when soldering to make sure you do not
> bridge
> the gap.
>
> The boards are drilled after the isolation paths have been milled.
> Ryan
> simply changes the milling bit to a drill bit, loads the (edited) .NCD
>
> file, hits GO, and walks away.  When all the holes for that size have
> been
> milled, he changes the bit to the next size and the machine drills
> those.  The PC board is not moved between any of those steps so
> registration remains perfect.
>
> We now rarely use the photo process!  The milled boards don't look
> quite as
> nice as the photo etched boards but it takes less time to get a board
> made
> and the milled board takes only about 1/4 of the total man-hours of
> actual
> labor.
>
> I've been planning on doing a bit of a write-up on the whole process -
> lack
> of time has stopped me.  But I'll try to get some pictures of actual
> boards
> made on the machine - soon.
>
> dwayne
>
> PS - Ryan has done one hell of a great job in turning a dead engraver
> into
> a wonderfully useful CNC tool.  He was the driving force behind this -
> I
> assisted him with some things but Ryan deserves all the credit.  I
> want to
> be clear on this - it was his idea, he found and purchased the dead
> engraving machine, he figured out how to make the software available
> to him
> do the job he needed.
>
> dwayne
>
>
> Dwayne Reid   <dwayner@...>
> Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> (780) 489-3199 voice          (780) 487-6397 fax
>
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