Embodiments herein relate to systems, apparatuses, or processes for packages that include substrates that include one or more die in a cavity within the substrate, where sides and a bottom of the cavity are lined with a heat spreader, or TIM, material that is thermally coupled to a side of the substrate using thermally conductive vias. In embodiments, thermally conductive vias may be thermally coupled with the heat spreader at the side of the substrate. Other embodiments may be described and/or claimed.