Making A Circuit Board:

People often think that in manufacturing a circuit board, you plate the board
with the copper traces which make up the circuits. That's not how it works.
In actuality, a blank circuit board is completely covered with copper
already, and the unwanted bits of copper are melted off using a powerful
acid, leaving the lines of copper which are the circuit.

The basic circuit board is really just a flat panel of fiberglass epoxy. The
first step to making it into a circuit board is to coat it with a sheet of
copper. However, the blank circuit boards which you buy from the store are
usually already coated with this copper, so you won't have to worry about
doing it yourself, unless you're really starting with just a bare sheet of
fiberglass. (Placing the layer of copper over the fiberglass base is
sometimes called "laminating" the circuit board.)

Usually the very first step in preparing a copper-clad circuit board is
simply to clean the board; The copper must be free from oxidization and other
impurities which might interfere with the etching process, and so it is
scoured clean. Any simple solvent, even common household cleaners, can be
used for this purpose.

The blank copper-coated board is drawn with a pattern of "etch resist", a
layer of tin or tin-lead (usually; other chemicals are sometimes used) which
protects the copper from the acid. Some etching processes use special tape to
lay out the traces on the circuit board; This tape is very narrow (since it's
forming the actual lines on the board), and resists the acid. There is also a
wide variety of stickers available for specific patterns which you want to
place on the circuit board; These stickers can simply be pasted on the board
and they protect the circuit from the acid in the same way. There are even
specially-manufactured pens which look like regular felt-tip markers, but
which draw with an ink that is designed to resist the acid just like other
resist substances; Etch resist pens are usually only used to "touch up" minor
details in a circuit design.

Once the circuit pattern has been drawn on the board using etch resist, the
whole board is dipped in an acid bath, which burns away the unwanted copper.
(Cupric chloride, ferric chloride, or ammoniacal is usually used for the
acid.) It is a bad idea to use a metal container to hold the acid; Use
plastic or glass instead. (Acid only corrodes metal; It does not react with
plastic or glass.) The acid bath is often heated, since heat makes chemical
reactions take place faster, and so considerably speeds up the process of
burning away the copper. However, if a heat source is used for etching, great
care must be taken so as not to make the acid hot enough to boil, since
boiling liquids tend to bubble and splash. The acid bath must be stirred
constantly while the board is burning (and don't use a metal stir stick
either; This must also be plastic or glass). The board must also not be left
in the acid too long, or else the acid will start to undercut the resist,
burning away copper that was intended to be left on the board. The board must
therefore be carefully supervised, and removed once the acid has eaten away
only the unwanted copper. The board must of course be handled with either
protective gloves, or tongs (which, once again, must not be metal). Wearing
protective glasses or goggles is also a good idea throughout this process.

Once etching is complete, the acid is washed off the board and the etch
resist is cleaned away (which may require special cleaning chemicals,
although many resist materials can easily be scrubbed off by hand), and what
remains is the completed circuit on the board. Then, small holes are drilled
through the board to mount the components on. This requires special tiny
drills and strong (usually carbon-steel) drill bits (generally holes of 0.02"
to 0.04" are used on PCBs). This drilling leaves an epoxy residue, or "drill
smear" on the holes, so the holes are chemically cleaned, and then plated to
make them conductive. The result is a circuit board ready for components to
be soldered to it. Often the board is coated with a final layer of tin or
some similar glazing to ward off oxidization and corrosion caused by exposure
to the air.