Package assemblies with a molded substrate comprising fluid conduits. The fluid conduits may be operable for conveying a fluid (e.g., liquid and/or vapor) through some portion of the package substrate structure. Fluid conduits may be at least partially defined by an interconnect trace comprising a metal. The fluid conveyance may improve thermal management of the package assembly, for example removing heat dissipated by one or more integrated circuits (ICs) of the package assembly.