A cooling apparatus for an electronics assembly having a substrate and one or more electronics devices includes an enclosure sealably engaging the substrate to form a cavity, with the electronics devices and a heat exchange assembly being disposed within the cavity. The heat exchange assembly defines a primary coolant flow path and a separate, secondary coolant flow path. The primary coolant flow path includes first and second chambers in fluid communication, and the secondary flow path includes a third chamber disposed between the first and second chambers. The heat exchange assembly provides a first thermal conduction path between primary coolant in the first chamber and secondary coolant in the third chamber, and a second thermal conduction path between primary coolant in the second chamber and secondary coolant in the third chamber. The heat exchange assembly further includes coolant nozzles to direct primary coolant towards the electronics devices.