A heat sink core assembly includes a base plate fabricated from a first material. The base plate comprises an opening therein, and the opening defines an insert engagement surface. An insert is fabricated from a second material different from the first material. The insert includes a base plate engagement surface and the insert is inserted into the opening. At least one of the insert engagement surface and the base plate engagement surface includes a curved portion. The curved portions oppose one another when the insert is engaged to the opening to produce a predetermined contact force in directions parallel and perpendicular to the opening in the base plate. When the opposed surfaces are crimped together, gaps or voids between the surfaces are avoided.