A cooling package for an electronic component comprising: a supply port communicating with a plurality of outer supply channels, and a return port communicating with a plurality of outer return channels, said outer supply channels and said outer return channels communicating with distinct ones of openings in a slot layer and into return and supply slots, respectively; and an orifice layer for supplying fluid to an electronic component to be cooled from said supply slots and for receiving return fluid after having cooled the electronic component and returning the received fluid into said return slots; the orifice layer comprises a plurality of supply orifices and a plurality of return orifices (142, 146), the supply orifices configured to receive fluid from the supply port to be directed to the electronic component and the return orifices are configured to receive the return fluid after it has cooled the electronic component; and wherein said orifice layer is spaced from the electronic component to be cooled by an impingement channel layer, with the impingement channel layer having impingement channels communicating with said orifices (142, 146) in said orifice layer, such that fluid flows into the impingement channels from a supply orifice associated with a supply slot, flows along the impingement channels to cool the electronic component and then returns through others of said return orifices (142, 146) in the orifice layer associated with said return slots; characterised in that there is a first zone of higher density of said orifices in said orifice layer, and a second zone of lesser density of said orifices (142, 146) in said orifice layer. a supply port communicating with a plurality of outer supply channels, and a return port communicating with a plurality of outer return channels, said outer supply channels and said outer return channels communicating with distinct ones of openings in a slot layer and into return and supply slots, respectively; and an orifice layer for supplying fluid to an electronic component to be cooled from said supply slots and for receiving return fluid after having cooled the electronic component and returning the received fluid into said return slots; the orifice layer comprises a plurality of supply orifices and a plurality of return orifices (142, 146), the supply orifices configured to receive fluid from the supply port to be directed to the electronic component and the return orifices are configured to receive the return fluid after it has cooled the electronic component; and wherein said orifice layer is spaced from the electronic component to be cooled by an impingement channel layer, with the impingement channel layer having impingement channels communicating with said orifices (142, 146) in said orifice layer, such that fluid flows into the impingement channels from a supply orifice associated with a supply slot, flows along the impingement channels to cool the electronic component and then returns through others of said return orifices (142, 146) in the orifice layer associated with said return slots; characterised in that there is a first zone of higher density of said orifices in said orifice layer, and a second zone of lesser density of said orifices (142, 146) in said orifice layer.