The Hitchhiker's Guide to PCB Design

The Hitchhiker's Guide to PCB Design

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Page 26 of 115

27 The electronics industry foresaw this issue many years ago and as a result, organizations formed to standardize the way schematic symbols are depicted. ASME Y14.44-2008 and IEEE 315-1975 define how to reference and annotate components of electronic devices. The table to the left is a quick list of reference designators and their matching symbols. A complete list is on the IEEE association's website. Successful schematic capture is basically the process of creating simple schematic symbols which contain basic nodal contacts. These symbols represent simple part configurations which are each documented on a page of the manufacturer's data sheet. Individual component symbols are placed within the schematic's electronic database drawing sheets and connected with lines to form a schematic diagram. For organizational purposes, each symbol is assigned a unique alpha-numeric reference designation. Assignment of reference designator numbers can be performed manually or automatically. However, use caution in this area as some tools will allow duplications of symbol reference designators within the same schematic. After placement and connectivity of the schematic symbols are established, editing of the symbol and net information can take place to finalize the design intent. It is important to recognize the goal of capturing the schematic for PCB design: to define or "capture" as much data as required to be imported into the layout database so it can be leveraged to create the physical aspects of the design. As previously mentioned, the schematic is a simplified, symbolic representation of what will materialize as a physical PCB assembly. Click to Enlarge

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