Semiconductor device packages and stacked package assemblies including high density interconnections

A semiconductor device package includes: a redistribution stack including a dielectric layer defining a first opening; and a redistribution layer (RDL) disposed over the dielectric layer and including a first trace, wherein the first trace includes a first portion extending over the dielectric layer along a first longitudinal direction adjacent to the first opening, and a second portion disposed in the first opening and extending from the first portion of the first trace, wherein the second portion of the first trace has a maximum width along a first transverse direction orthogonal to the first longitudinal direction, the first opening in the dielectric layer has a maximum width along the first transverse direction, and the maximum width of the second portion of the first trace is less than the maximum width of the first opening.