The disclosed technology generally relates to integrated circuit (IC) packages, and more particularly to integrated circuit packages comprising perforated diamond-based heat spreading substrates. In one aspect, a heat spreading substrate for an IC die is configured to be attached to an IC die and to spread heat away therefrom. The diamond-based heat spreading substrate can have an electrically conductive surface and an array of vias formed therethrough. At least one of the vias is configured to overlap an edge of the IC die when attached to the diamond-based heat spreading substrate.