Material: Use of Two-Phase Components and Liquid Cooling

Designing Heatsinks and Thermal Solutions for Xilinx Devices (XAPP1377)

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For less demanding thermal needs, generally an aluminum base is used as it is relatively inexpensive and light while still delivering good thermal conductivity. For more demanding thermal needs, copper is generally chosen as it has a higher thermal conductivity leading to more heat spreading as well as conduction to the fins or other thermal outlets. However, this is at the tradeoff of cost and weight. For even more demanding applications, engineers are turning to two-phase thermal transport in the form of either heat pipes or vapor chambers. Heat pipes are two-phase thermal conduction apparatuses consisting of an enclosed pipe with a liquid tuned to a specific vaporization temperature from liquid to gas. A vapor chamber operate similar to a heat pipe. However, it consists of an enclosed plane rather than a pipe structure which generally can spread heat to a much larger area compared to a heat pipe. A very good compromise for cost, weight, and performance is using an aluminum base with embedded press fit heat pipes. Heat pipes generally have a very high and extremely fast thermal conduction property that far surpasses most materials.

The heat pipes allow for very good heat spreading within the base, generally higher than pure copper while the aluminum is very light and cost effective. Another option is the use of vapor chambers which generally have even better heat spreading than embedded heat pipes. However, this option can be more expensive and difficult to control coplanarity. Finally, for the most demanding situations, some customers turn to liquid cooling generally in the form of a cold plate. Although used more rarely, other methods such as immersion and impingement cooling can be used. Xilinx recommends the use of a heatspreader base. This is especially true for lidless devices when using these alternative methods of cooling. Any of these base types can be used with Xilinx devices depending on application need and selection.