In an embodiment, a method of making a heat sink assembly can include: forming a heat sink assembly comprising a polymer heat sink around a metal insert, the polymer heat sink comprising a thermally conductive polymer material, wherein the heat sink assembly has a contact pressure between the polymer heat sink and the metal insert; and increasing the contact pressure. In an embodiment, a method of making a heat sink assembly includes: heating a mold and subsequently introducing a metal insert to the mold, wherein the metal insert has an insert temperature of 30° C. to 70° C. when it is inserted into the mold; closing the mold; and in less than or equal to 10 seconds of closing the mold, over-molding the metal insert with a thermally conductive polymer material to form a heat sink assembly.