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BoardMaker3 PCB symbols - Methodology and Structure
Many PCB layout programs only allow you to use pad styles which are built into the software.
BoardMaker3 provides a mechanism which allows the user to define the exact shape of the
copper for a layer on a pad.
For example, a plated through hole pad could
have a smaller copper diameter on an inner layer where it will not be used for soldering.
This approach allows the designer to transfer footprints quickly and accurately from the
data sheet and into the software without compromise.
In BoardMaker3 this fundamental object is called a padstack. Symbols are made out of
padstacks (pads) and padstacks are made up from shapes. Shapes are built up from the
standard graphical primitives (lines, arcs, circles, polygons, rectangles etc).
The image to the left shows the centre
pad from a SOT89. This was created using a single polygon.
Most pad shapes of course are much simpler that this and the required shape will either
be a rectangle or circle. However, when the requirement is more complex, the software
will not limit the designer. Simple pads shapes are trivial to create.
For convenience to the user, a library of standard shapes has been provided with the
software. This library contains all the shapes that have been used to create the
footprints that are supplied with the software. For many symbols, it is likely that the
required shapes will already exist within this library.
The designer is free to use the following
primitives to create pad shapes:
Padstack is a "stack" of shapes, there
are two basic types of padstack with their
own layer configurations:
- Surface Mount
- Plated Through Hole
The example shown here is a plated through
padstack where all the layers are connected
by a plated hole.
As previously mentioned, the designer is free
to place any valid shape on any of the layers
of the padstack.
For example, in the case of a large surface
mount pad it is possible to create a paste
mask which has embedded strengthening bars
to increase paste volume. Further options
are available to automatically expand or contract
resist and paste mask layers at the output
BoardMaker3 incorporates some powerful
functions to aid in symbol creation. One
such function is the Pad Matrix command.
Once the designer has provided a number
of parameters including pad pitch and column
spacing etc, the system will automatically
place the pads. The tool allows SIL, DIP,
Flatpack, BGA as well as numerous connectors
to be created quickly and accurately. The
sister function to pad matrix is the pad
naming function. The designer can select
any number of pads, choose an appropriate
numbering scheme (e.g. 1,2,3 or 1A,2A,3A
etc) and then specify the direction of numbering
(eg. left to right, top to bottom etc).
The final stages of creating a symbol include
placing any required silkscreen outlines
and setting the default designator position.
BoardMaker3 also allows the designer to
place attributes which have been carried
forward from the schematic onto silkscreeen,
so it is possible, for example, to dynamically
display the value of a component on the
silkscreen as well. If the component is
surface mount, then a centroid can be added.
This defines the centre of gravity of the
component and it preferred direction for
the pick and place machine.