In an embodiment, a device includes: a die stack over and electrically connected to an interposer, the die stack including a topmost integrated circuit die including: a substrate having a front side and a back side opposite the front side, the front side of the substrate including an active surface; a dummy through substrate via (TSV) extending from the back side of the substrate at least partially into the substrate, the dummy TSV electrically isolated from the active surface; a thermal interface material over the topmost integrated circuit die; and a dummy connector in the thermal interface material, the thermal interface material surrounding the dummy connector, the dummy connector electrically isolated from the active surface of the topmost integrated circuit die.