🚀 go-pugleaf

 
   Wow!   I got about 14 E-Mail requests for the article I wrote!   I E-Mailed
a few responses before I realized it would be much easier to just post it.
 
   Maybe the word "article" is misleading.   What I wrote is simply a document
of what I know about the method.
 
   
Personally, I prefer wire-wrapping for prototyping, but this method has
potential.  In fact, a few companies are trying to making this method a
commercial product.   
 
   Anyway, here's what I've got.   Please let me know what you think, any
questions you have, and any experience you gain trying out the method...
 
 
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                  Making PC Boards Using Xerox Transparencies
          
          
          
          
     This method is not perfect, but its simplicity makes it worth
     trying.   I have successfully made a few simple PC boards using
     this method and have tried a more complicated board.  Due to a
     design error with the complicated board, I never figured out
     whether the circuit board was OK (I ended up wire wrapping the
     thing).
     
     The beauty of this method is that you can create the artwork for
     the board using regular pens and drafting supplies- much as you
     would be able to for the standard photographic technique.  This
     is welcomed by those of use who have tried to use etch resist
     pens or lacquer.  The cost of making boards this way is much
     cheaper than regular photographic techniques.
     
     Make sure all lines on the finished artwork are as black as
     possible (use black ink).  
     
     The artwork must be Xeroxed onto transparency plastic.  Beware! 
     You can NOT use just any kind of clear plastic sheets.  The
     temperature inside a Xerox machine will melt most plastics and
     ruin the machine.   There is a specific type of plastic made just
     for Xeroxing things onto transparencies.  I got a pack of 25
     sheets for $14 at my university's bookstore.
 
     There are different types of this stuff, and some types work
     better than others.  I was fortunate in that I was able to try
     out a few sheets of different types before I bought an entire
     pack.  The types that don't work too well have an extra layer of
     thin plastic laminated onto the thicker sheet of transparency. 
     This is not apparent until later in the process.   You might be
     able to tell by looking at light reflecting off the surface of
     the transparency- both sides should be shiny.  If one side is
     shiny, and one side is somewhat dull, then chances are the sheet
     is of the laminated type.  Perhaps these types of sheets would
     work if you Xeroxed onto the shiny side but I haven't bothered to
     experiment with this.
     
     Once you have located the right kind of transparency (or have
     decided to try whatever transparency plastic you could get),
     Xerox your artwork onto the transparency with the machine set at
     its darkest contrast.   This assures that the most toner gets
     deposited onto the plastic.  Its a good idea to make more than
     one copy as a backup.   Another tip:  try Xeroxing onto paper
     first to see what the image quality is like.  If the image looks
     less than acceptable, try another machine. 
 
     When a Xerox is made onto paper, the porous surface of the paper
     absorbs the toner.  But, on the transparency plastic, the toner
     can be removed...
     
     The next step requires a vise and a clothes iron.  Set the iron
     to a moderately high temperature (again, there is a lot of room
     for experimentation here).   Mount the bare circuit board
     (cleaned well with steel wool) vertically in the vise so that you
     have access to both sides.  Cut the circuit image out of the
     transparency and line it up on the copper board.  Tape the
     plastic's edge to the board's edge so that you have a hinge of
     sorts (masking tape is best).  You should be able to lift the
     plastic up like a book cover, and be able to put it back down
     against the board without the image shifting.
     
     I have used double sided circuit boards every time I have used
     this method, even though I was making a single sided board. 
     Reason: I'm not sure if the non-metal side of the board will hold
     up to the iron's heat (I haven't tried because I didn't want to
     ruin the iron).  I suppose its possible to heat the board from
     the one metal side.
     
     I have not tried making a double sided board.  The only
     difficulty I anticipate is in lining up the two sides' images so
     that the holes will match up.
     
     The copper must be heated to a high enough temperature to re-melt
     the toner.   I have had success, like I stated above, heating the
     board from behind while I press the transparency plastic hard
     against the front part of the board.   I use a bundled up rag to
     press against the copper since it gets VERY hot..  Press the
     plastic against the board using a "smoothing"  wiping away from
     the tape hinge.   Continue this for a couple minutes.   The time
     is a big variable - too short of a time and the toner won't
     melt.   Next, carefully start to peel the transparency from the
     board.   Do this SLOWLY.  If you see some of the toner lift off,
     you can put the plastic back against the board and continue
     heating/smoothing.   Eventually you should be able to get the
     plastic off and a nice sharp black image of your circuit will be
     left behind on the copper, most of the toner should come off the
     transparency.
     
     If the transparency is laminated, chances are that the layers
     will separate at some time during this stage.  In my case, the
     transparency left the thin layer of plastic on the copper, and it
     was a hassle to get it all removed.
     
     Don Lancaster, of CMOS Cookbook, TTL Cookbook, and
     Radio-Electronics fame (Hardware Hacker column) suggested to me
     that the board be placed in a freezer for a while after the
     plastic is removed to "fuse" the toner.
     
     If the image looks pitted in some areas, touching up the lines
     may help.  An etch-resist pen might work, or lacquer could be
     used.
     
     
     Finally, etch the board using standard etchant.  The toner makes
     an excellent etch resist (ie. it doesn't dissolve).  When the
     board's finished, the toner can be removed using many different
     solvents.
     
     
     
     Let me know what experiences any of you have with this.  I'm
     especially interested in tips and success/failure stories.
     I can be reached on USENET or on the Circuit Cellar BBS at 
     203-871-1988.
 
     By the way, I first read this idea in a letter in
     Radio-Electronics.   Don't bother trying to look up the original
     letter because it wasn't very long or detailed.
     
     
                                                Greg Bell
                                                serene!pnet12!gbell
 
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for a better return address, see my sig below... 

Incidentally, I need to find out what brand/part number the particular
transparency plastic I use is.  But I don't have the package here, so I will
post that information when I get it.

    Greg Bell_________________________________________________________
      Hardware hacker          |
      Electronics hobbyist     | UUCP:  uunet!serene!pnet12!gbell
      EE major at UC San Diego |