Techniques and mechanisms for promoting heat conduction in a packaged device using a heat spreader that is fabricated by a build-up process. In an embodiment, 3D printing of a heat spreader successively deposit layers of a thermal conductor material, where said layers variously extend each over a respective one or more IC dies. The heat spreader forms a flat top side, wherein a bottom side of the heat spreader extends over, and conforms at least partially to, different respective heights of various IC dies. In another embodiment, fabrication of a portion of the heat spreader comprises printing pore structures that contribute to a relatively low thermal conductivity of said portion. An average orientation of the oblong pores contributes to different respective thermal conduction properties for various directions of heat flow.