Pcb includes an autorouter which can greatly speed up the layout of a circuit board. The autorouter is a rectangle-expansion type of autorouter based on “A Method for Gridless Routing of Printed Circuit Boards” by A. C. Finch, K. J. Mackenzie, G. J. Balsdon, and G. Symonds in the 1985 Proceedings of the 22nd ACM/IEEE Design Automation Conference. This reference is available from the ACM Digital Library at //www.acm.org/dl for those with institutional or personal access to it. It's also available from your local engineering library. The reference paper is not needed for using the autorouter.
Before using the autorouter, all elements need to be loaded into the layout and placed and the connectivity netlist must be loaded. Once the elements have been placed and the netlist loaded, the following steps will autoroute your design.
1.Turn off visibility of any layers that you don't want the router to use.
2.Turn of via visibility if you don't want the router to use any new vias.
3.Use only plain rectangles for power/ground planes that you want the router to use [use the rectangle tool!]
4.Make at least one connection from any plane you want the router to use to the net you want it to connect to.
5.Draw continuous lines (on all routing layers) to outline keep-out zones if desired.
6.Use routing styles in the netlist to have per-net routing styles. Note that the routing style will be used for an entire net. This means if you have a wide metal setting for a power net you will need to manually route breakouts from any fine pitch parts on their power pins because the router will not be able to change to a narrow trace to connect to the part.
7.Set the current routing style to whatever you'd like the router to use for any nets not having a defined route style in the netlist.
8.Disable any nets that you don't want the autorouter to route (double-click them in the netlist window to add/remove the *)
NOTE: If you will be manually routing these later not using planes, it is usually better to let the autorouter route them then rip them up yourself afterwards. If you plan to use a ground/power plane manually, consider making it from one or more pure rectangles and letting the autorouter have a go at it.
9.Create a fresh rat's nest. ('E' the 'W')
10.Select “show autorouter trials” in the settings menu if you want to watch what's happening
11.Choose “autoroute all rats” in the connection menu.
12.If you really want to muck with the router because you have a special design, e.g. all through-hole components you can mess with layer directional costs by editing the autoroute.c source file and changing the directional costs in lines 929-940. and try again. Even more mucking about with costs is possible in lines 4540-4569, but it's probably not such a good idea unless you really just want to experiment.
