US20070151275A1

US20070151275A1 - Methods and apparatus for microelectronic cooling using a miniaturized vapor compression system

Info

Publication number: US20070151275A1
Application number: US11/324,875
Authority: US
Inventors: Victor Chiriac
Original assignee: Freescale Semiconductor Inc
Current assignee: NXP USA Inc
Priority date: 2006-01-03
Filing date: 2006-01-03
Publication date: 2007-07-05

Abstract

A miniaturized refrigeration system (100) is used to cool a semiconductor component (104). The system includes an evaporator (e.g., a microchannel evaporator) (106), a compressor (108), a condenser (e.g., a microchannel condenser) (112), a throttling component (110), and a refrigerant. The condenser (112) may be attached to the backside (304) of the board (102) opposite the semiconductor component (104) being cooled. The compressor (108) may be used in conjunction with a number of evaporators (106), and may therefore be located outside of an enclosure (306) that houses the various components.

Description

FIELD OF THE INVENTION

The present invention generally relates to microelectronic cooling systems and, more particularly, to miniaturized cooling systems employing a refrigeration cycle.

BACKGROUND OF THE INVENTION

Semiconductor devices continue to increase in size and power-density, resulting in a number of challenges for system designers. One of the primary challenges relates to microelectronic device cooling—i.e., how to efficiently remove heat generated by the device during operation.
Traditional cooling techniques include, for example, the use of finned heat sinks operating under forced convection produced by one or more fans. Such systems are capable of significant heat transfer, but are becoming increasingly less effective as devices become larger and more powerful. Furthermore, this cooling problem is exacerbated by the trend toward miniaturization, which leaves little room for large heat sinks and the like.
Advanced cooling techniques now being developed include thermoelectric cooling systems (which utilize the Peltier effect to transfer heat under application of a current), liquid-cooling (using a pump to move water or another liquid through a heat exchanger), and heat-pipe devices (which use phase-change as a method of moving heat from one place to another). These methods have the same shortcomings as indicated above, and are not typically able to handle the high power densities generated by microprocessors and other large devices.
Furthermore, while refrigeration cycles are capable of very high heat transfer rates, such systems are large, cumbersome, include many components, and have not yet been effectively employed on a small scale as is required in semiconductor applications.
Accordingly, there is a need for microelectronic cooling systems that overcome these and other shortcomings of the prior art. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
FIG. 1 is a schematic block diagram of a cooling system in accordance with one embodiment of the present invention;
FIG. 2 is a schematic block diagram of a cooling system in accordance with another embodiment of the present invention;
FIG. 3 is a schematic block diagram of a cooling system in accordance with another embodiment of the present invention;
FIG. 4 is a block diagram illustrating a refrigeration cycle in accordance with the present invention;
FIG. 5 is an isometric depiction of an evaporator in accordance with one embodiment of the present invention;
FIG. 6 is an isometric depiction of a condenser in accordance with one embodiment of the present invention; and
FIG. 7 is a conceptual Venn diagram illustrating exemplary spatial relationships between the various components in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, or the following detailed description. Conventional terms and processes relating to heat transfer, thermodynamic, and fluid dynamics are known to those skilled in the art, and are therefore not discussed in detail herein.
Referring to FIG. 1, a microelectronic cooling system (or simply “cooling system”) 100 in accordance with one embodiment of the present invention generally includes an evaporator 106, a compressor 108, a condenser 112, a fan 114 optionally associated with condenser 112, and a throttling element 110. Evaporator 106 is attached to or otherwise placed in thermal communication with a microelectronic component (or simply “component”) 104 which itself is typically attached to a printed circuit board (PCB) or other such substrate 102. A working fluid (or “refrigerant”) circulates through the system via tubes or other suitable pathways 120, 122, 124, and 126 that are configured to providing transport of a liquid and/or vapor through the system. Evaporator 106, compressor 108, condenser 112, and throttling element 110 together implement a refrigeration cycle—as further described below—in which the heat generated by component 104 is transferred to cooling system 100.
Component 104 may be a semiconductor die, a semiconductor device package, a module, or any other heat-generating component. In accordance with the illustrated embodiment, described below, component 104 is a device capable of generating heat in the range of about 20 to 100 Watts. In this regard, an exemplary vapor compression refrigeration cycle applicable to the illustrated embodiments is shown in FIG. 4. In general, heat generated by component 104 (Q_e) is transferred via thermal conduction to evaporator 106. The thermal resistance between evaporator 106 and component 104 is modeled as a resistance 402, which would typically be minimized by applying a thermally conductive material (such as a paste or pad) at the interface of component 104 and evaporator 106. Heat absorbed by evaporator 106 vaporizes the refrigerant circulating through the evaporator, and the resulting vapor is compressed and absorbed by compressor 108 (subject to external work W_c). Compressed vapor is transferred to condenser 112 which, in conjunction with forced convection provided by fan 114, cools the vapor, resulting in a gas-to-liquid phase-change and concomitant heat loss Q_c. The resulting liquid then passes through throttling element 110 to evaporator 106, thereby completing the refrigeration cycle. Further information regarding exemplary refrigeration cycles may be found in standard reference books, including, for example, Kenneth Wark, Thermodynamics, 708-731 (1983).
In accordance with another embodiment of the present invention, multiple components are cooled using a single compressor. More particularly, referring to FIG. 2, two components 104(a) and 104(b) are thermally coupled to respective evaporators 106(a) and 106(b). The vapor produced by evaporators 106(a) and 106(b) is transferred (via a T-connector or other suitable tubing 220) to a shared compressor 108. The compressed vapor 108 from compressor 108 is received by condensers 112(a) and 112(b) (having associated fans 114(a) and 114(b)) and experiences a phase change as described above. The liquid refrigerant then passes through throttling elements 110(a) and 110(b) back to respective evaporators 106(a) and 106(b).
In accordance with one embodiment of the present invention, the condenser is placed on the backside of the PCB, adjacent to the component being cooled. More particularly, referring to FIG. 3, evaporator 106 is coupled to component 104 on one side 302 of PCB 102, and condenser 112 is coupled to the opposite side 304 of PCB 102. Condenser 112 may be coupled to PCB 102 using any convenient technique, including various adhesives, fasteners, or the like. Throttling valve 110 may also be located adjacent condenser 112 and/or coupled to backside 304. Inasmuch as side 302 of PCB 102 may be populated by a greater number of components than side 304, side 302 is occasionally referred to herein as the “frontside,” and side 304 is referred to as the “backside.” Those skilled in the art will recognize, however, that these designations are arbitrary and do not limit the range of geometries and topologies contemplated by the present invention. The illustrated cooling system operates with higher efficiency when the condenser and evaporator are placed on opposite sides of PCB 102, minimizing their thermal interaction. The condenser operates at higher efficiency when exposed to lower ambient temperature, and frontside 302 of PCB 102 is pre-heated by any heat-dissipating components placed on that side.
With continued reference to FIG. 3, and in accordance with yet another embodiment of the present invention, PCB 102 is provided within a housing 306 that separates board compressor 108 from an external environment 308. In such an embodiment, it is convenient to place the compressor (which may be shared with multiple components, as previously described) within environment 308 rather than inside enclosure 306. The compressor could of course be placed either inside or outside of enclosure 306, but it is advantageous to place it outside the system due to size limitations it may impose on the system.
Referring again to FIG. 1, evaporator 106 includes any suitable structure capable of absorbing heat from component 104 and using that heat to vaporize a working fluid. In accordance with one embodiment of the present invention, for example, evaporator 106 is a micro-channel evaporator having a size on the order of the size of component 104. More particularly, with reference to FIG. 5, an evaporator 106 in accordance with one embodiment of the present invention comprises a body 504 having a number of microchannels 502 extending therethrough. Side 506 of evaporator 106 is thermally coupled to the component being cooled (not shown), and side 508 is preferably thermally insulated (e.g., via a layer of material having a low thermal conductivity). The refrigerant employed may be selected in accordance with known refrigeration design principles. In one embodiment, a fluorocarbon refrigerant such as R134a (1,1,1,2-Tetrafluoroethate) is used.
In the illustrated embodiment, microchannels 502 have a substantially rectangular cross-section and are configured in parallel with respect to the refrigerant flow direction; however, any suitable number, shape, and configuration of microchannels may be used. In accordance with a particular embodiment, a total of six microchannels 502 are incorporated into body 504, wherein each channel has a height a of about 1.2 mm, a width c of about 2.8 mm, and a length e of about 16 mm. In the illustrated embodiment, body 504 has an overall width d of 18 mm and a height b of about 2 mm.
A variety of materials, including various metals, ceramics, or combinations thereof, may be used for body 504 of evaporator 106. In a preferred embodiment, evaporator 106 comprises a suitable high-conductivity metal, for example, copper, steel, aluminum, or the like.
Compressor 108 is any apparatus capable of suitably compressing the incoming vapor from evaporator 106. In one embodiment, compressor 108 has a volumetric flow rate of about 39 cm³/s, a maximum flow rate of about 100 cm³/s a heat transfer rate of about 116 Watts, a physical diameter of about 15 cm, and a height of about 15 cm. In accordance with a particular embodiment, compressor 108 is a Model No. AZ47YD scroll compressor manufactured by Copeland Corporation.
Condenser 112 is any suitable condenser capable of removing heat from a vapor in order to produce a phase-change. In accordance with one embodiment of the present invention, for example, condenser 112 is a microchannel condenser having an associated heat sink and fan. Referring to FIG. 6, a condenser 112 in accordance with one embodiment of the present invention includes a number of heat fins (or other such structures) 605, a body 604, and a number of microchannels 602. Air flows through or onto fins 605 via an associated fan (not shown), and vapor flowing through channels 602 experiences a phase-change as a result of heat rejected from the system via fins 604.
In the illustrated embodiment, microchannels 602 have a substantially rectangular cross-section and are configured in parallel with respect to the refrigerant flow direction; however, any suitable number, shape, and configuration of microchannels may be used. As with evaporator 106, a variety of materials, including various metals, ceramics, or combinations thereof, may be used for body 604 of condenser 112. In a preferred embodiment, condenser 112 comprises a suitable high-conductivity metal, for example, copper, steel, aluminum, or the like.
In the illustrated embodiment, microchannels 602 have a substantially rectangular cross-section and are configured in parallel with respect to the refrigerant flow direction. Any suitable number, shape, and configuration of microchannels may be used, however. In accordance with a particular embodiment, a total of six microchannels 602 are incorporated into body 604, wherein each channel has a height a of about 1.2 mm, a width c of about 2.8 mm, and a length e of about 67 mm. In the illustrated embodiment, body 604 has an overall width d of 18 mm and a height b of about 2 mm. Fins 605 extend outward from both sides of body 604 by about 6.5 mm.
Throttling element 110 acts to regulate flow of the refrigerant through the system—e.g., by modifying the pressure and velocity of the working fluid. In this regard throttling element 110 may include any combination of throttling valves or other such components known in the art. Suitable throttling elements include, for example, expansion valves, capillary tubes, and the like.
While the embodiments described above show specific locations for the various cooling system subsystems, it will be understood that the invention is not so limited. FIG. 7, for example, shows a conceptual overview of a system in accordance with the present invention. Generally, the heat-generating semiconductor packages and other components are attached to a board having a frontside 722 and a backside 724, where there may be any number of boards 720. The boards are typically provided within an enclosure 710 (e.g., a computer cabinet or the like), and that enclosure is situated within an environment 702. In accordance with one embodiment, a series of evaporators 106 (a)-(c) are coupled to respective heat-generating components provided on board frontside 722. Corresponding condensers 112 and throttling components 110 are attached to board backside 724. In the illustrated embodiment, compressor 108 is located outside enclosure 710 in environment 702. In an alternate embodiment, compressor 108 is located off-board (i.e., not on board frontside 722 or backside 724) within enclosure 710. In further embodiments, the condensers 112 are located either on board frontside 722, off-board within enclosure 710, or outside of enclosure 710. Stated another way, the present invention contemplates that the various components of the cooling system may be distributed in any fashion with respect to design spaces 702, 710, 720, and 724.
In summary, one embodiment of the present invention includes an evaporator configured to be thermally coupled to the component, a compressor coupled to the evaporator, a condenser (and an optional fan) coupled to the compressor, a throttling element coupled to the condenser and the evaporator, and a refrigerant configured to flow in a circuit through the evaporator, compressor, condenser, and throttling element to complete a refrigeration cycle.
In accordance with one embodiment, the evaporator and/or the condenser are microchannel devices, with the evaporator being in intimate contact with the component being cooled, further including a fan thermally coupled to the condenser. In one embodiment, the compressor is a scroll compressor.
In one embodiment, the refrigerant is a fluorocarbon such as R134a. In accordance with another embodiment, the system includes a printed circuit board having a frontside and a backside, wherein the component is attached to the frontside of the board, and the condenser is attached to said backside of said board. In yet another embodiment, further including an enclosure, the component is internal to the enclosure and the compressor is external to the enclosure.
In accordance with another embodiment of the present invention, a system for cooling a component involves coupling an evaporator to the component, wherein the evaporator has an input, an output, and a refrigerant flowing through the evaporator from the input to the output. Heat is removed from the component via the evaporator, wherein the refrigerant undergoes a phase change in the evaporator from a liquid form to a vapor form and exits through the output. The refrigerant is then returned to the evaporator in liquid form. In one embodiment, the method includes coupling a condenser to the board on a side opposite from the component and producing, within the condenser, a phase change in the refrigerant from vapor form to liquid form.
In accordance with another embodiment, a system for cooling a semiconductor component includes a microchannel evaporator in intimate contact with the semiconductor component, wherein the microchannel evaporator is part of a refrigeration cycle. In one embodiment, the system includes a condenser that is part of the refrigeration cycle and a board having a first side and a second side, wherein the semiconductor component is attached to the first side of the board and the condenser is attached to the second side of the board adjacent the semiconductor component. In a further embodiment, the system includes an enclosure enclosing the board, wherein the compressor is external to the enclosure.
It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.

Claims

1. A system for cooling an electronic component, said system comprising:

an evaporator configured to be thermally coupled to the component;

a compressor coupled to said evaporator;

a condenser coupled to said compressor;

a throttling element coupled to said condenser and said evaporator; and

a refrigerant configured to flow in a circuit through said evaporator, compressor, condenser, and throttling element to complete a refrigeration cycle.

2. The system of claim 1, wherein said evaporator is a microchannel evaporator configured to intimately contact the component.

3. The system of claim 1, wherein said condenser is a microchannel condenser.

4. The system of claim 1, further including a fan thermally coupled to said condenser.

5. The system of claim 1, wherein said refrigerant is a fluorocarbon.

6. The system of claim 5, wherein said refrigerant is R134a.

7. The system of claim 1, further including a printed circuit board having a frontside and a backside, wherein said component is attached to said frontside of said board, and said condenser is attached to said backside of said board.

8. The system of claim 1, further including an enclosure, wherein said component is internal to said enclosure and said compressor is external to said enclosure.

9. The system of claim 1, wherein said compressor is a scroll compressor.

10. The system of claim 1, further including a second component, a second evaporator, and a second condenser, wherein said second evaporator is thermally coupled to said second component and

11. A method for cooling a component, said method comprising the steps of:

coupling an evaporator to the component, wherein the evaporator has an input, an output, and a refrigerant flowing through said evaporator from said input to said output;

removing heat from said component via said evaporator, wherein said refrigerant undergoes a phase change in said evaporator from a liquid form to a vapor form and exits through said output;

returning said refrigerant to said evaporator in said liquid form.

12. The method of claim 11, wherein the component is attached to a board, further including the steps of:

coupling a condenser to said board on a side opposite from said component;

producing, within said condenser, a phase change in said refrigerant from said vapor form to said liquid form.

13. A system for cooling a semiconductor component, said system comprising a microchannel evaporator configured to intimately contact the semiconductor component, wherein said microchannel evaporator is part of a refrigeration cycle.

14. The system of claim 13, further including:

a condenser that is part of said refrigeration cycle; and

a board having a first side and a second side, wherein the semiconductor component is attached to said first side of said board and said condenser is attached to said second side of said board adjacent the semiconductor component.

15. The system of claim 13, further including:

a compressor that is part of said refrigeration cycle; and

an enclosure enclosing said board, wherein said compressor is external to said enclosure.

16. The system of claim 13, wherein said evaporator is a microchannel evaporator.

17. The system of claim 13, wherein said condenser is a microchannel condenser.

18. The system of claim 13, further including a fan thermally coupled to said condenser.

19. The system of claim 13, wherein said refrigerant is a fluorocarbon.

20. The system of claim 13, further including a printed circuit board having a frontside and a backside, wherein said component is attached to said frontside of said board, and said condenser is attached to said backside of said board.