This paper describes a solution for global routing and track assignment of flip-chip I/O nets. Voronoi Diagram (VD) is used to partition the open routing space and the geometrical properties of VD graph are exploited to create global routing channels with capacity and congestion considerations. A network flow algorithm is used to achieve optimal global routing. The regularity of the flip-chip bump placement is observed and allows us to reduce the size of global routing channel graph by over 50% to speed up computation. A track assignment algorithm avoids crossing wires before completing the final route with a detailed router. Experiment results using actual silicon chip data demonstrate that our solution achieves good quality of results compared to an implementation used in a commercial tool.