🚀 go-pugleaf

   What follows is a quick introduction into the way most double-sided
printed circuit boards are manufactured. There are other techniques,
and they get much more involved especially when manufacturing multi-layer
boards. After this intro, I have included steps as to how this might be
done at home.

   A) An image of the board is transferred to the raw copper board using
      photographic techniques.
   B) The holes are drilled in the board, using the photo as a reference.
   C) The board is dipped in a chemical solution called "Electroless
      Copper". This solution deposits a thin layer of copper everywhere
      on the board (including the sides and inside the holes). The layer
      is generally between .001 - .002 thick, which is just enough to
      support electo-plating.
   D) The board is electro-plated with another .002 - .004 inches of
      copper, using the Electroless Copper layer as a plating conductor.
   E) A reverse image of the board is applied using photo techniques.
      That is, all copper areas that you want to remain are left exposed,
      while all copper that will eventually be removed are covered.
   F) Solder is electro-plated to the exposed areas of the board, using
      the copper previously applied as a plating conductor. About .002
      inches of solder is applied.
   G) The image is "stripped" from the board.
   H) The board is etched. The solder that was previously plated to the
      board acts as the resist.
   I) Once the board has been etched, it is "fused". This process melts
      the solder on the board so that it flows and covers all exposed
      copper. This step is necessary to prevent the copper from oxidizing.

   The board is now completed. The plating process has plated though the
holes, so traces on one side of the board are electrically connected to 
traces on the other. Here is how to do this at home:

   A) Apply the image to the raw pc board.
   B) Using small hand tools, drill the board using the image as a guide.
   C) Dip the board into the Electroless Copper solution. This can be
      obtained locally from most chemical supply houses, and instructions
      as to usage and amount of time in the solution will be included.
   D) Apply a reverse image to the raw pc board.
   E) Dip the board in rosin and then into molten solder. How you get the
      solder molten is up to you.
   F) Now etch the board in your favorite etchant. If you don't want to
      wait for the Ferric Chloride you purchased at Radio Shack to etch
      the board, check for something stronger when you buy your Electroless
      solution at the chemical supply house.

   Your board is done. You may find some of the holes are plugged with
solder. To unplug them, simply melt the solder in the hole and remove it.
That pretty well does it, except for a few notes:

   A) In some (most) states, the chemicals used in this procedure require
      special disposal techniques. DO NOT FLUSH THEM DOWN YOUR TOILET!
      Toxic waste fines can be very expensive, so check with the chemical
      supply house on disposal tips. They may even offer a service for a
      nominal fee.
   B) Wear appropriate clothing, as well as hand and eye protection.
      These chemicals can be nasty. Remember those little chemistry sets
      you got for Christmas? Chicken feed compared to these chemicals.
   C) Do this in a well-ventilated area. And I don't mean turning on the
      bathroom fan. Try it in the garage with a fan going, or outside.
      I know of people who have landed in the hospital because of too much
      exposure.
   D) There are several books on the subject. I don't have the titles and
      author names handy, but if any of you are interested, e-mail me and
      I'll post them.
   E) The example above was greatly simplified. It was meant as an overview,
      not as instructions. I'm sure that there are pcboard gurus out there.
      If I botched something, please post the corrections. No flames!

                            *** Disclaimer ***
   The opinions expressed above are my own. Neither myself or my employer
   shall be liable for any damages, either incidental or consequential,
   with regard to the use of this information.

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Dave Tubbs                         UUCP:{ihnp4,decvax}!decwrl!esunix!dtubbs
Evans & Sutherland Computer Corp.  INET:          esunix!dtubbs@cs.utah.edu
580 Arapeen Drive                 PHONE:           (801) 582-5847 Ext. 3277
Salt Lake City, Utah 84108          FAX:                     (801) 582-8208
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