8 - PCB Netlists and Back Annotation

Abstract

The two major issues that arise when preparing a netlist for printed circuit board (PCB) design are PCB design software requires PCB footprint values to identify the physical layout of parts on the schematic and the pin number sequence used by Capture may differ from that used by the PCB design software to represent the physical layout of actual devices. Problems are most prevalent with discrete parts, especially transistors. The most efficient approach to preparing a netlist for PCB design is by using Capture's Browse tool to add PCB footprints and then using a text editor to clean up the pin numbers. This chapter focuses on the preparation of a netlist suitable for input into PowerPCB by Pads Software. PowerPCB is widely used and considered by many to be the leading edge PCB design software for the Windows environment. Although PowerPCB imposes some specific requirements, the techniques are applicable to most PCB design software. The chapter introduces the subject of back annotation and the Gate and Pin Swap tool. As one works on a PCB design, the software may swap device gates and pins in order to improve trace routing. Reference designators may be renumbered to correspond to the spatial sequence of parts on the board. Updating the schematic to incorporate these changes is referred to as back annotation. The Gate and Pin Swap tool uses the information in a swap file to automatically back annotate the schematic.