These guidelines are
associated with the constraints of the overall board - size, shape, and some of
the factors that affect the overall design or concept of the PCB.
Choose reference points that
suit the manufacturing process : It is normally necessary to have
reference holes or points on the board. These are used for pick and place machines
and test fixtures. They should be chosen to suit the PCB manufacturing process.
Often they may be holes for fixtures, but they may also be crossed marks for
optical sensors. They must be clear of components, and not obscured.
Allow adequate board area for
the circuit : Often the dimensions of the board will be defined by the
overall product size, but before the PCB design starts, estimates should be made
regarding the size of the board and whether it can accommodate the components and
Determine the number of layers
required : It is advisable to determine the number of track layers that
are needed within the printed circuit board at the beginning of the design.
Additional layers increase the production costs, but may mean that the tracks can
be accommodated. Complex designs may have many tracks, and it may not be possible
to route them unless sufficient layers are available.
Consider the board mounting method :
It is necessary to consider how the printed circuit board will be mounted at the
beginning of the design. Different methods of mounting may require different areas
of the board to be kept free, or they may take up different areas on the board.