Heat pipe fin stack with extruded base

Details Heat pipe fin stack with extruded base Heat pipe fin stack with extruded base

2003-06-09

2004-12-14

Flanigan, Allen (Department: 3753)

Heat exchange

Intermediate fluent heat exchange material receiving and...

Liquid fluent heat exchange material

C165S104210, C165S080300, C361S700000

Reexamination Certificate

active

06830098

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to the structure of heat exchangers, and in particular a heat dissipation tower arrangement or heat sink for transferring heat energy collected at a conductive base in contact with a thermal source such as an integrated circuit package. The heat is transferred via heat pipes carrying a phase-change fluid, into a set of fins in contact with the ambient air. The heat pipe tubes fit in complementary channels in the base, which extend parallel to one another and parallel to an edge of the base. The tubes are diverted upwardly to serve as columnar supports of the fins. This structure is simple and inexpensive in that the base can be a cut section of an extruded form to which the heat pipes and fins are simply assembled. Yet the structure has a substantial heat dissipation capacity.
BACKGROUND OF THE INVENTION
Certain semiconductor devices in electrical and electronic circuits, such as large scale integrated circuits, voltage regulators, current switching devices, high current drivers and other similar devices, generate heat that is deleterious to their operation and must be dissipated. An individual semiconductor junction may be subject to thermal runaway current conduction leading to further heating and damage. In large scale digital integrated circuits, operation at or above the maximum rated temperature can result in spurious switching operations and functional failure.
In a highly integrated semiconductor device such as a computer processor, a single semiconductor switching transistor may conduct little concurrent on its own, but is densely mounted with many other transistors. A single integrated device may generate heat energy of a hundred Watts or more. Supplemental cooling arrangements may be needed in addition to convective cooling by heat driven circulation of ambient air, conduction of heat through circuit lands and the like, for maintaining operational temperatures within design ranges. For this purpose, thermally conductive heat sink devices, normally of cast or sheet metal and having a substantial surface area exposed to the air, are mounted on a base that is clamped to bear physically against the heat generating circuit element.
A large-scale integrated circuit such as a computer processor or similar device typically is mounted removably in a receptacle that is soldered to a printed circuit board. The receptacle has inward-facing resilient contacts for conductively coupling to contacts on the circuit package, which package may be several cm on a side. The receptacle or auxiliary structures associated with the printed circuit board carry spring-clip clamping mechanisms that engage over part of the heat sink, rested atop the circuit package. The clamping mechanism physically presses a heat sink against the circuit package when mounted. The heat sink typically comprises a base block that is relatively thick, integrally cast with an array of thin fins functioning as a heat exchanger to release heat into the ambient air. The array of fins and/or the base has structure to cooperate with the clamping mechanism, and can also provide a point of attachment for a fan for forcing a flow of air over the fins.
Heat energy diffuses from the active circuit elements into the circuit substrate and into the circuit packaging structure, which comprises thermally conductive plastic or ceramic. The heat energy diffuses by conductive contact into the base of the heat sink, and then diffuses through the integral or thermally conductively attached structures of the heat sink to the surfaces at which air contact heat exchange convection carries the heat away. The array of fins typically is cast integrally with the heat sink base, but also can be thermally conductively attached in contact with the base. The function of the fins is to present a relatively large surface area, preferably within a relatively small total volume, for efficient thermal energy release. The electrically powered fan, mounted on the heat exchanger by screws or clamps, forces air over the heat exchanger fins and may improve thermal transfer. However, the fan also dissipates a certain amount of heat into the air. The heat sink spreads out the heat energy from the source, primarily the integrated circuit; into the cabinet or housing volume of the device. Another fan may be provided to circulate air between the housing and the ambient room air.
Integrated circuit devices are available according to more or less demanding temperature specifications. Devices that have a relatively wider temperature range are more expensive. Standard commercial computer processor components, for example, may be rated up to 70° C. (about 160° F.). The most durable military application devices may be rated up 125° C. (about 260° F.). These devices are sometimes required to operate in ambient air temperature conditions ranging from −40 to +55° C. (about −40 to +130° F.).
Movement of thermal energy from an integrated circuit or other localized heat source, toward a remote area or toward a structure that carries the heat away, occurs from one or more of thermal conduction, convection and radiation. Conduction of heat energy requires contact between thermally conductive masses and proceeds at a rate that depends in part on the difference in temperature between the masses. Convection involves conduction between a heated body and adjacent heat transfer fluid (gas or liquid), typically air, involves differences in fluid density due to differences in fluid temperature, and is substantially affected by forced air currents. Radiation also dissipates heat, but its contribution is normally small at the temperature ranges of interest.
Heat transfer arrangements can involve passing a current of cooler air or other heat transfer fluid over a hotter surface to be cooled. A captive heat transfer fluid can be provided in closed volume and arranged to circulate. The fluid is heated by a source of heat energy that is in heat transfer relationship with one part of the closed volume. A heat sink is arranged in heat transfer relationship with another part of the closed volume, releasing heat (provided that the heat exchange medium, such as air, is kept cooler than the heat sink), and cooling the fluid. The heat transfer fluid advantageously undergoes cyclic changes of phase. Each change of phase either stores or releases a quantity of heat energy due to the latent thermal energy involved in the phase change itself.
In this way, a liquid phase change heat transfer fluid can be evaporated (vaporized) into gas at the heat source and condensed again into liquid at the heat sink. Different techniques can be used to return the condensed liquid from the condenser to the evaporator, which need not be powered by outside energy sources. A return path is possible, for example, over a gravity flow path in a thermo-siphon arrangement. In a heat pipe arrangement, a return path for the condensed liquid can be provided by lining the vessel confining the heat transfer fluid with a wicking material that supports capillary flow, such as a sintered particulate or powder lining. The capillary flow is driven substantially by surface tension and can proceed regardless of orientation and gravity.
Assuming that the heat transfer fluid is confined in an integral metal vessel, some thermal conduction from the heat source to the sink can occur through the vessel walls. It is desirable on grounds of efficiency to separate the evaporator and condenser sections by a distance or otherwise to interpose a thermal barrier that permits maintenance of a temperature difference. Nevertheless, phase change heat exchange circuits as described can operate with a very modest temperature difference between the source and the sink and can efficiently move heat energy to assist in heat dissipation.
There are a number of design considerations for thermal transfer arrangements such as heat pipes. In addition to the ability to handle the necessary flow of thermal energy to keep the heat source within desired temperature limits, the evaporator and the c

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