In this paper, the Broadband Green's function with low wavenumber extraction (BBGFL) is applied to modeling of traces connecting vias in printed circuit boards, particularly arbitrarily shaped power/ground planes. The proposed method is a hybrid technique based on mode decomposition: BBGFL is used to fast compute the vias in power/ground planes, method of moments (MoM) is used to calculate the impedance matrix of the traces, and then physical circuit model is applied to cascade the vias and traces in the power/ground planes. The present method is compared to MoM and commercial tool HFSS. Results show the present technique has good agreement with MoM and HFSS on the S-parameters, while is several hundred times faster than in CPU time for broadband simulations. It provides a fast technique for system level high-speed interconnect designs and applications.