Computer Science Department
School of Computer Science, Carnegie Mellon University
PCB - A Printed Circuit Board Editor User Manual
PCB is an integrated router and editor to design printed circuits. It adopts the correct by construction principle, that is it will enforce a certain set of design rules such as copper traces have to maintain a minimal separation, holes have to aligned, etc. . PCB maintains a data base of the desired circuit so that it can make sure that signals of different net cannot be shorted.
Building a PC board usually involves a number of steps, such as placement of the components, routing the various connections, preparing a geometry file for the photographic masks, adding design changes. PCB aids these steps by:
Placement aids : Components can be moved on a graphic screen. For a given placement, the wire densities can be displayed to give hints on how to improve the placement.
Automatic router : Depending on the complexity and density of the circuit, PCB can route up to 95% of all connections without human intervention.
Manual editing facilities : Wires can be entered with a pointing device like a mouse or graphics tablet. Existing wires can be moved without loss of connectivity and the router can be used interactively on a certain connection, on a certain net or on a certain area of the board. There are commands to erase wires on an individual basis or on entire areas.
Output facilities : PCB can generate a CIF file that complies with the MOSIS design rules for 4 layer boards. It takes care of power and ground connections, can improve the wires by removing unnecessary jogs, adds fillets to holes in order to ease the removal of components and calls external supplied pieces of geometry. In addition, topological bitmaps can be plotted directly on a Versatec plotter which is much faster than using CIF for intermediate plots.
Change facilities : The internal database can be updated in order to add or remove nets a list of points that should form an electrical connection , components a particular IC or any other actual device on a PC board or types a generic description for a class of components, say the layout of a 7400 without rebuilding the entire board.