A novel approach of equivalent circuit model extraction is developed for modeling of integrated package and PCB power distribution networks (PDN). The integrated PDNs are formulated from a full-wave finite-difference algorithm, and the resulting matrix equations are converted to equivalent circuits. The equivalent circuits, as well as the decoupling capacitors and the attached circuit components, can be analyzed with a SPICE-like solver in both the time and frequency domains. The modeling of dielectric loss is also addressed. The method is used to model three PDN problems including a simple power bus, a BGA package mounting on a PCB, and a 3-D power bus structure. The results are compared to either measurement data or other numerical results. The limitations of the method are also discussed.