Closed-Cycle Expansion-Valve Impingement Cooling System

This invention is related to the following application which is assigned to the assignee of the present invention and concurrently filed herewith in the name of the inventor of the present invention:

Ser. No. 367,369, now abandoned.

1. Field of the Invention

This invention relates to a method and apparatus for cooling integrated circuit devices. More particularly, it relates to a closed-cycle coolant medium impingement cooling system and method that does not require a refrigeration cycle after the compression stage of the cooling system.

2. Prior Art

Each generation of semiconductor integrated circuits develops smaller and more closely packed devices. This higher integration generates greater component density and permits more circuit functions to be performed on a single semiconductor chip. On the other hand, packing more and more circuit elements closer and closer together generates greater heat and concentrates this heat in a smaller chip area. To ensure proper circuit performance, durability, and reliability, a way must be found to remove this heat to maintain device junction temperatures below some maximum value.

Conventional methods of cooling integrated circuits or a printed circuit board having a number of integrated circuits mounted on them include natural convection, forced convection (fan cooling), liquid cooling, various forms of heat sink, and a combination of two or more of these methods. However, all of these known methods are unsatisfactory because they are ineffective at present heat flux densities, inefficient, and/or expensive to operate. Known methods particularly suffer from a low power-density limitation.

In most known mounted component cooling systems, the heat removal capability of the system is limited by the thermal resistance of the interface of the device and its mounting. By cooling a coolant medium gas with an expansion valve, an interface thermal resistance can be tolerated. Other methods developed to pre-cool impingement air or other coolant medium include an additional refrigeration cycle, where the coolant passes through a refrigeration (cold) heat exchanger. In open-cycle cooling systems, condensation of water can be a major problem. In addition, the integrated circuit chips may be cooled directly, minimizing the interface resistance between the chips and the cooling medium.

It would therefore be advantageous to provide a cooling system to maintain electronic component junction temperatures below a prescribed maximum at high heat flux densities. Further, the present closed cycle system provides high heat transfer by utilizing gases other than air which have high heat transfer properties, such as helium, freon and the like, thus providing very efficient heat transfer. Such a system also eliminates the introduction of impurities, contaminants, or moisture into the cooling system.

The present invention effectively removes high density heat from electronic components, heat flux, for example at greater than 20 watts per square centimeter. A compressor pressurizes a cooling medium and provides this pressurized cooling medium to a first heat exchanger. The heat exchanger may use air at ambient temperature to reduce the temperature of the pressurized cooling medium, preferably to close to room temperature. The cooling medium passes to a cooling chamber which can be an impingement plenum or a flow distribution chamber. The impingement plenum is fed the cooling medium through an expansion valve which cools the medium and then directs the expanded and cooled cooling medium directly onto the chips to be cooled. The flow distribution chamber is first pressurized by the cooling medium at approximately compressor outlet pressure, and then uses a number of expansion valves to direct the cooling medium onto the chips. In either embodiment, the cooling medium is collected, directed through another heat exchanger, and sent back to the inlet of the compressor.

In this way, the system removes high heat densities from the semiconductor chips to ensure that device junction temperatures are maintained below a specified limit.

FIG. 1 is an exploded, partially cut-away diagram of one embodiment of the present invention.

FIG. 2 is an exploded, partially cut-away diagram of another embodiment of the present invention.

FIG. 1 depicts a closed-cycle expansion-valve impingement cooling system of the present invention. The cooling system comprises a compressor 10, a containment chamber 12, an inlet or supply heat exchanger 14, and an outlet or return heat exchanger 16. The supply and return heat exchangers 14 and 16 may be of various designs such as tube-in-tube, counterflow, crossflow, or the like, and may use air or other gas as the heat exchange medium to eliminate the need for a separate refrigerant cooling system. The inlet heat exchanger 14 may include one or more outlet ports 18 to accommodate a number of containment chambers like that of the containment chamber 12. Similarly, the outlet heat exchanger 16 may include one or more inlet ports 20 to receive the cooling medium from a number of containment chambers.

The compressor 10 compresses a cooling medium, which may be air, helium, freon, and the like, and delivers the compressed cooling medium to the supply heat exchanger through a tube 22. At least one tube 24 carries the cooling medium to a containment chamber 12, but the supply heat exchanger 14 may accommodate more tubes like that of the tube 24 at the outlet ports 18.

The tube 24 continues to a tube 26, by way of a path shown schematically as a line 28. The tube 26 mates to the cooling chamber 12 through an inlet nozzle 30. The cooling chamber 12 primarily comprises an upper seal-plate 32, a seal-ring 34, and a lower housing 36. The cooling chamber assembly may be held together by bolts 38 or other appropriate means.

The cooling medium exiting the inlet nozzle 30 enters a space 40 within the upper seal-plate 32. The space 40 allows the cooling medium to rapidly expand and thereby drop substantially in temperature. The bottom of the space 40 forms an impingement plenum 42. The impingement plenum 42 supports a plurality of coolant exit or exhaust tubes 44 that direct the flow of coolant onto the objects, such as semiconductor integrated circuit chips 46, to be cooled. Alternatively, the coolant may exit the space 40 directly through a plurality of holes or orifices 70, rather than through the exhaust tubes 44. There may be one or more tubes 44 or orifices 70 for each chip 46 to be cooled.

After impinging on the elements to be cooled, the heated coolant exits the lower housing 36 by way of an outlet port 48. The heated coolant passes to the return heat exchanger 16 by a path shown graphically as a line 50. The coolant passes into the return heat exchanger 16 through an inlet tube 52. The return heat exchanger 16 may accommodate a number of inlet tubes like inlet tube 52 at the inlet ports 20.

The return heat exchanger 16 cools the heated cooling medium and the compressor 10 draws the cooling medium through a tube 54, over a path shown graphically as a line 56, and into the compressor inlet port 58.

FIG. 2 depicts an alternative embodiment of the present invention. Elements in FIG. 2 that perform the same functions as like elements in FIG. 1 bear the same reference numbers and their functions will not be reiterated.

The embodiment of FIG. 2 differs from that of FIG. 1 within the cooling chamber 12. The cooling medium enters the cooling chamber through an inlet port 60. The inlet port 60 may attach to the upper seal-plate 32 by way of a quick air-disconnect 62 in a manner known in the art. The incoming cooling medium pressurizes a flow distribution plenum 64. A lower support plate 66 supports a plurality of expansion valves 68. The valves 68 direct the expanded and cooled coolant directly onto the chips 46 that require cooling. Again, there may be one or more valves 68 directed toward each of the chips 46 that require cooling. Further, the direction of the valve openings may be so selected that the coolant is directed to one or more portions of the surface of the chip 46. The cooling medium, as it expands from the valves 68, drops in temperature, and carries away heat from the chips 46.

Rather than using a cooling medium that remains in a gaseous state throughout the cycle, the present invention may advantageously employ a cooling medium that is a liquid or partially a liquid in the supply portion of the cycle and a gas in the return portion. Such a system would direct a liquid onto the objects to be cooled and the temperature of the cooling liquid should preferably be at or near its vaporization temperature when it impinges on the hot objects. In this way, when the cooling medium evaporates or vaporizes (changes phase), it removes heat from the objects equivalent to its heat of vaporization which is many times more effective than just raising the temperature of a gas or a liquid (sensible heat transfer). In this embodiment of the present invention, the air or other medium that cooled the system's cooling medium in the heat exchanger 14 could be used in the heat exchanger 16 to ensure the cooling medium is in a gaseous state at the inlet 58 to the compressor 10. In this embodiment, the heat exchanger 16 acts as an evaporator or heater rather than as a cooler and the heat exchanger 14 may act as a condenser. Further, temperatures and pressures within this embodiment depend on the selected cooling medium.

Although the invention has been described with reference to specific embodiments, these embodiments should not be construed as limiting the scope of the invention. It will be clear to those skilled in the art with the benefit of this disclosure that certain modifications can be made without deviating from the spirit of the invention. For example, a chip 46 may be any element that requires cooling.