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Printed circuit boards
(PCB's) are laminates.
This means that they are
made from two or more
sheets of material stuck
together; often copper
and fibreglass. Unwanted areas of the
copper are etched away
to form conductive lands
or tracks which replace
the wires carrying the
electric currents in
other forms of
construction.
Some parts of the side
with copper tracks is
coated with solder
resist (usually green in
colour) to prevent
solder sticking to those
areas where it is not
required. This avoids
unwanted solder bridges
between tracks.
Sometimes the boards are
double-sided with copper
tracks on both sides.
Tracks on one side can
be joined to tracks on
the other by means of
wire links. Plated
through holes are
available which do the
same thing but these
make the PCB more
expensive.
Components are stuffed
into the board by hand
or by pick and place
machines.
Soldering is done by
hand or by flow wave
soldering where the PCB
passes over a wave of
molten solder.
Most recent PCB's use
surface mount techniques
where components are on
the same side of the
board as the tracks.
Components are stuck to
the board with adhesive
and the solder caused to
flow by heating the
board in a hot gas or by
some other technique.
When fitting components
ensure that they are
orientated correctly and
lay flat on the board
unless otherwise stated.
When the board is
assembled avoid flexing
it which may crack
tracks.
Avoid touching the board
which may cause
contamination due to
dirty fingers or damage
due to static
electricity carried on
your body.
It is best to handle
PCB's by holding them by
two edges only, between
thumb and forefinger. |
