Parts - Symbols and Footprints

A PCB design consists of several parts connected together on a PCB using copper tracks.

Parts consist of 4 separate representations, The logical, simulation, PCB Footprint ( Land Pattern) and 3D solid model (Package).

This displays the part as an abstract/logical symbol.

The symbols usually consists of a rectangle or box.

Attached to the edges of the box are a several symbol terminals.

In addition there is a part reference used to uniquely identify the part. (U1 in this case).

Finally there is a Symbol Value used to indicate the part's generic type. 6821 in this case.

SchematicSymbol

The Spice Model defines the electrical characteristics of the part and is used when simulating the electrical behaviour of a circuit.

The footprint represents the part when placed on the final PCB.

It consists of a number of pads.

( Shown in red with a yellow perimeter).

There is also a Footprint Reference symbol to uniquely identify the part. Here it is U1. This will be associated with a symbol on a schematic sheet.

The 3D package is the actual 3D model of the part and is used to visualize the final PCB.

It is also used to export a 3D model of the PCB to third party 3D CAD programs.

package