Since no commercial PCB routing tools can solve the routing problem for today's complex PCBs, these circuit boards have to be routed manually, taking about 2 months of time per board. Bus planning is one of the most time-consuming steps of PCB routing. It consists of assigning buses to multiple layers of the PCB and routing them in a planar fashion on each layer. Routing congestion between on-board components and the min-max length bounds of the buses must also be considered during routing. In this paper, we present the first automatic bus planner. We tested our system on a state-of-the-art industrial circuit board with over 7000 nets and 12 signal layers. All the nets on this board were already manually routed. Our bus planner is able to achieve 100% routing completion using the layer assignment extracted from manual design. For simultaneous layer assignment and bus routing, we are able to successfully route 98.5% of the nets. The remaining 1.5% can be routed either manually or by using vias. The runtime of our bus planner is less than 3 hours on a 3 Ghz workstation.