Electronic devices such as semiconductor integrated circuits can generate a great deal of internal heat due to inefficiencies including resistance to electrical current. If heat is not dissipated from the electronic devices, they can easily be damaged or destroyed by the heat they generate during normal use. For example, computer systems commonly include fans to increase convective cooling of hot integrated circuits. Networked computer equipment is commonly housed in refrigerated rooms. The problem of cooling electronics is so great that even liquid cooling systems have been experimented with. Electronic devices have become increasingly small and complex, with semiconductor processes shrinking for example from 130 microns, to 65 microns, then to 40 microns, etc. More transistors are packed into a smaller area, using more power and generating more heat in increasingly small packages. The problem of drawing heat out from the inside of integrated circuits so that it can be dissipated externally has therefore become increasingly difficult and important.
The problem is even more complex for electronic devices that do not uniformly generate heat. For example, integrated circuits containing multiple processing cores or other extremely active circuits may be surrounded by relatively cooler circuits. This results in multiple hot spots on the integrated circuit that are more difficult to cool than the overall device. Conventional cooling techniques such as heat sinks require a large amount of space and do not address the problem of drawing heat from the inside of an integrated circuit and out through the package around the integrated circuit to the heat sink.