How to make Printed Circuit Boards (PCBs)
There are several methods of making electronic
circuits, like point-to-point soldering , but these methods are
only suitable for simple projects (and look very ugly).
It's more professional to use copper-clad boards and to etch
the copper away where you don't want it.
1. How to transfer the layout to the board
2. UV exposeure and development
How to transfer the layout to the board
How to make traces in the copper?
If you don't need high quality you can buy special pens with
etch-resistant ink and draw the traces directly on the copper,
but that's almost impossible for complex boards or boards with
SMD components. It 's better to design the pattern with a special
PC program. (a good choice is Eagle
Light). The pattern is then printed on
transparencies (or normal paper if you have 'Pausklar-spray' to
make the paper UV-transparent).
In this case you buy special copper-clad boards that carry a
photo-positive coat on the copper. You first expose this to UV
light with the transparency pattern placed against it. After
putting it in a special developer, the coat will be dissolved
where the light got to the board. The etch-resistant film
remains.
Exposure to UV Light and development
There are special UV light bulbs and tubes. The sun
will work, too.
If you use a 300-W UV bulb and the distance is about
20 cm, the exposure takes about 4 minutes. The distance should be
at least the diagonal of the board. There is a relation between
distance and exposure time: doubling the distance needs 4 times
greater exposure.
A special device with UV tubes (self made) will work
faster (1 - 2 min).
First you remove the protective black foil on the board (do that
in a dim place), put the transparency on the board, hold
everything with a heavy glass plate (although not too thick;
Plexiglass is best because it lets UV through much better) and
expose it. Then put the board into the developer (of course make
that first).
After about 2 minutes, the image should be visible on the board,
and on the exposed parts you should see the bare copper. If
everything's OK, you can etch the board.
The most popular etchant is ferric chloride (FeCl3).
It's very cheap, doesn't need heating and is easy to dispose of.
However, it makes stains that are almost impossible to remove.
Ferric chloride does not attack the skin, but avoid getting it in
your eyes. It will corrode metals immediately.
Without heating, ferric chloride takes about 30 minutes to
dissolve all the copper. If you move the board in the etchant,
it's faster.
After etching, the remaining photo-resist must be removed with
acetone.
Finally, it's helpful to apply soldering lacquer.
Note that the required chemicals are toxic and should be safely disposed of!
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