Heat sinks with millichannel cooling

A heat sink (10, 50) for cooling at least one electronic device package (20) includes a lower lid (12), an upper lid (14) and a body (16) formed of at least one thermally conductive material. The body (16) is disposed between and sealed to the lower and upper lids (12, 14) and defines inlet manifolds (30) configured to receive a coolant and outlet manifolds (32) configured to exhaust the coolant. The inlet and outlet manifolds (30, 32) are interleaved and are disposed in a circular or spiral arrangement. Millichannels (34) are formed in the body (16) or in the lids, are disposed in a radial arrangement, and are configured to receive the coolant from the inlet manifolds (30) and to deliver the coolant to the outlet manifolds (32). The millichannels (34) and inlet and outlet manifolds (32, 34) are further configured to cool one of the upper and lower contact surfaces (22, 24) of the electronic device package (20). Heat sinks (10, 50) with a single lid are also provided.