System-in-Packages (SiPs) and methods for producing SiPs are provided. In one embodiment, the above-described SiP fabrication method includes the step or process of forming a through-hole in a core package, the core package containing an electrically-conducive routing feature exposed at a sidewall surface of the through-hole. A leaded component is positioned adjacent the core package such that an elongated lead of the leaded component extends into the through-hole. An electrically-conductive material, such as solder, is then applied into the through hole to electrically couple the elongated lead of the leaded component to the electrically-conductive routing feature of the core package.