An improved interconnect substrate having high density routings for a chip package assembly, a chip package assembly having a high density substrate, and methods for fabricating the same are provided that utilize substrates having a region of high density routings disposed over a region of low density routings. In one example, a method for fabricating an interconnect substrate is provided that includes forming a high density routing region by depositing a seed layer on a top surface of a low density routing region, patterning a mask layer on the seed layer, forming a plurality of conductive posts on the seed layer, removing the mask layer and the seed layer exposed between the conductive posts, and depositing a dielectric layer between the between the conductive posts, wherein at least some of the conductive posts are electrically coupled to conductive routing comprising the low density routing region.