It is important that your organization only pulls schematic symbols from one database. It may be the CIS, Oracle, SAP, Proprietary Data Base or other data bases that is managed centrally. Thus everything should be well defined regarding Schematic Symbol, Footprint References and other related info that reflects in the BOM with a specific part number. This ensures uniformity of the entire data package from Schematic to PCB layout program.
However do you use a Schematic Symbol Library or even worse a Shared Common Schematic Symbols Library you should be particularly vigilant how to define a Schematic Symbol and link it to a Footprint Name and how you use it. You create a symbol that match you schematic for a particular project and assign pin numbering as you please. Later your colleague utilize the same symbol but he modifies it just a little regarding pin numbering. Next time you grab that same symbol your pin numbers do not match as expected and subsequently errors are introduced in the PCB layout.
Symbol Pin Definition.
Examples of various pin numbering. Please note that this is only one example on pin numbering for that specific footprint. In real several variations will occur depending of various part numbers.
Transistors could be named several ways:
It could be : E-B-C, 1-2-3, 3-1-2 etc.
Connectors require special considerations:
Pin numbering CW, CCW, Up-Down, pin 1 is left or right Z-count numbering etc.
SOT23 diode
SOT23 transistor
SOT143 dual diode
There are many pitfalls and especially asymmetric, unique and exotic components gives rise to an additional review of definition and coherence with the footprint.
Be aware that some data sheets showing the component as seen from the bottom and again other data sheets are not complete with respect to the number of physical pins that must be defined in the schematic symbol so it match the PCB footprint for the real component.
Light Emitting Diode
Switch from Tyco
TO252 diode
Related Information
Thorough and careful data discipline can jumpstart your design project and optimize the process
Coherence between schematic symbols and PCB footprints are a must.
Benefit from our Footprint SmartBrowser
Check your netlist with our Netliste SmartChecker
Run DRC! It's a virtue.
Create your constraint set up with our Constraint SmartEditor
