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Footprints

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).

Shapes

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:

  • Lines
  • Arcs
  • Polygons
  • Circles
  • Rectangles



Padstack

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 stage.

Symbols

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.




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