WO1999006782A1

WO1999006782A1 - Apparatus and method for cooling an electronic component using a porous material

Info

Publication number: WO1999006782A1
Application number: PCT/US1998/009081
Authority: WO
Inventors: Debabrata Pal
Original assignee: Motorola Inc.
Priority date: 1997-07-31
Filing date: 1998-05-04
Publication date: 1999-02-11

Abstract

The apparatus includes a plate (10) which is configured to carry an electronic component (11) and which has a thermally-conductive porous medium (16) disposed therein. The porous medium is sized to receive a fluid (45). When an electronic component is disposed on the plate and a fluid passes through the thermally-conductive porous medium, at least a portion of the fluid boils and heat is removed from the electronic component by conduction and phase change effects.

Description

APPARATUS AND METHOD FOR COOLING AN ELECTRONIC COMPONENT USING A POROUS MATERIAL

Field of the Invention

This invention relates generally to cooling for electronic components, and, more particularly, to an apparatus and a method for cooling an electronic component using a porous material.

Background of the Invention

Electronic components such as integrated circuits, multi-chip modules, passive components and power transistors, which are generally mounted to surfaces such as circuit boards or carrier plates, may be heat sources which require cooling during normal operation and during testing and tuning.

Traditionally, electronic components have been cooled by natural or forced air convection which involves moving large volumes of air past the components or past heavy heat sinks attached to the components. Advances in electronic devices, however, have resulted in some electronic devices having power densities which exceed the capabilities of traditional natural or forced convective air cooling.

Evaporative spray cooling, cold plates and jet impingement cooling are examples of thermal management techniques which use liquid coolants, rather than air, to dissipate heat generated by electronic components. Evaporative spray cooling and/or jet impingement cooling are suitable methods of heat removal for many electronics applications, but these cooling techniques generally require the spraying of fluid directly onto the surfaces of electronic components. The fluid will often capture particulate matter from the electronic components being cooled, and the particles may clog spray nozzles and impede the effective spraying of the fluid. In addition, extensive sealing may be required prior to operation of such cooling systems, so that operation of the cooling systems during the testing and tuning processes of electronic components may be impractical .

The cold plate is typically a direct replacement for an air-cooled heat sink in which water or another fluid flows through internal passages where the heat sink was originally mounted. Typically, the heat transfer capabilities of cold plates have been much less than those achievable using evaporative spray or jet impingement cooling, and high flow rates (up to several gallons per minute) have generally been required for successful application of cold plate technology. In addition, the complexity of flow passages in cold plates may make it difficult to accurately predict heat transfer characteristics at or near locations of individual electronic components. Moreover, the material and manufacturing costs of cold plates may be high.

There is therefore a need for an apparatus and method for cooling an electronic component which, among other things, uses a fluid but which does not require a cooling fluid to contact the electronic component, which features low flow rates, which allows for localized cooling of the component and which allows the electronic component to be cooled during the testing and tuning process.

Summary of the Invention

According to an aspect of the present invention, the foregoing needs are addressed by an apparatus for cooling an electronic component which includes a plate which is configured to carry an electronic component and which has a thermally-conductive porous medium disposed therein. The porous medium is sized to receive a fluid. When an electronic component is disposed on the plate and a fluid passes through the thermally-conductive porous medium, at least a portion of the fluid boils and heat is removed from the electronic component by conduction and phase change effects.

According to another aspect of the present invention, an apparatus for cooling an electronic component includes a first layer configured to carry an electronic component, a second layer and a fluid distributing channel disposed between the first layer and the second layer. The fluid distributing channel has a first end, a central portion defining a chamber and a second end. The chamber is positioned proximate the electronic component when the electronic component is disposed on the first layer. A thermally- conductive porous foam which is sized to receive and to mix a fluid is disposed in the chamber. When the electronic component is disposed on the first layer and the fluid is received and mixed, the electronic component is cooled via conduction and two-phase heat transfer. According to a further aspect of the present invention, a method for cooling an electronic component includes providing a first layer and a second layer; disposing a thermally-conductive porous medium between the first layer and the second layer; disposing the electronic component on the first layer, proximate the thermally-conductive porous medium; and passing a fluid through the thermally-conductive porous medium.

Advantages of the present invention will become readily apparent to those skilled in the art from the following description of the preferred embodiment ( s ) of the invention which have been shown and described by way of illustration. As will be realized, the invention is capable of other and different embodiments, and its details are capable of modifications in various respects. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

Brief Description of the Drawings

FIG. 1 is a cross-sectional view of an apparatus for cooling an electronic component according to a preferred embodiment of the present invention.

FIG. 2 is a perspective view of the (disassembled) apparatus depicted in FIG. 1. FIG. 3 is a top view of the apparatus illustrated in FIGs . 1 and 2 , depicting a manner of operation of the apparatus and further illustrating a closed-loop fluid flow for the apparatus .

Detailed Description of the Preferred Embodiments

Turning now to the drawings, wherein like numerals designate like components, FIG. 1 is a cross-sectional view of an apparatus 10, such as a plate, for cooling an electronic component according to a preferred embodiment of the present invention. Plate 10 preferably includes a first layer 12 and a second layer 14. Layers 12 and 14 are preferably Aluminum Silicon Carbide (AlSiC) , stainless steel, aluminum, copper alumina or ceramic, but may be any suitable circuit board- or carrier plate- type material, such materials being well-known and widely available. It is also contemplated that plate 10 may be a single layer.

An electronic component 11, which may be, for example, an NPN Silicon Radio Frequency (RF) Power

Transistor such as a flangeless RF power transistor, is disposed on first layer 12. Component 11 may be attached to a mounting plate (not shown) , which is in turn secured to first layer 12, or may be mounted directly to layer 12. References to electronic component 11 will be understood to apply not only to component 11 as depicted and described in connection with FIG. 1, but also to completely different components, including but not limited to passive components, all types of integrated circuits, multi-chip modules and hybrid circuits.

A thermally-conductive porous medium 16, such as an aluminum or ceramic foam, is disposed between first layer 12 and second layer 14. Medium 16 is proximate, preferably directly underneath, component 11. A suitable medium 16 is commercially available from Energy Research and Generation, Inc., Oakland, California.

At least one fluid inlet channel 18 is disposed in the plate and is in communication with a first end of medium 16. At least one fluid outlet channel 20 is also disposed in the plate and is in communication with a second end of medium 16. Ports 19 and 21 serve to supply and remove, respectively, a fluid (discussed further below) from plate 10.

As illustrated in FIG. 2, where plate 10 is formed from two separate layers 12 and 14, fluid inlet channel 18 and fluid outlet channel 20 may be formed in second layer 14 and/or in first layer 12, so that, when mated, layers 12 and 14 form channels 18 and 20. In addition, at least one chamber 22, in which medium 16 is disposed, may be formed in one or both of layers 12 and 14.

Channels 18 and 20 and chamber 22 may be formed in any desired configuration, and each may have a cross- sectional shape which is conical, cylindrical, rectangular or another suitable shape. Layers 12 and 14 may be fabricated separately, and porous foam 16 placed in chamber 22 created between the layers . Foam 16 may be secured to layers 12 and/or 14 by brazing, but may be attached using various other methods, including but not limited to well-known techniques such as fasteners, compliant gaskets, ultrasonic welding, brazing, soldering, swaging, adhesives or other methods. Layers 12 and 14 may be permanently secured to each other using similar techniques .

Alternatively, channels 18 and 20 and chamber 22 may be formed integrally within plate 10 using well- known casting techniques .

FIG. 3 is a top view of second layer 14 of plate 10, which further depicts operation of a closed-loop system for cooling electronic component 11. A fluid pump 50, which is connected via tube 52 to port 19, supplies a coolant fluid 45, which may be any coolant such as water or a dielectric coolant such as 3M's Fluorinert™ dielectric fluid, to fluid inlet channel 18. Tube 52 may be coupled to port 19 using a barbed fitting (not shown) , for example, or by any other suitable means.

Fluid 45 passes into chamber 22 and through porous medium 16, where it is mixed by the randomly interrupted pores of medium 16. Boiling of fluid 45 is initiated as the temperature of fluid 45 exceeds its boiling point. As a result of the boiling, heat is removed from electronic component 11 by a combination of convective and phase change effects. Heat transfer may be increased when chamber 22 and/or medium 16 are positioned such that the flow of fluid 45 is approximately aligned with the largest heat generating region or regions of component 11.

Heated fluid 45 continues on through fluid outlet channel 20 before exiting plate 10 through port 21. Of course, a portion of fluid 45 may remain for a period of time in medium 16 and/or in chamber 22. A heat exchanger 53, connected to pump 50 by tube 54, and to port 21 by tube 56 (which may be coupled to port 21 using a barbed fitting (not shown) , for example, or by any other suitable means) , receives fluid from port 21. Heat exchanger 53 rejects heat from the fluid, returning it to primarily a liquid phase. Fan 58 may be used to extend the cooling capacity of heat exchanger 53. Cooled fluid is supplied from heat exchanger 53 to pump 50. Thus, a closed-loop flow of coolant is formed. It will be appreciated that at any given point the coolant may be a vapor, a liquid or a vapor and liquid mixture .

It is contemplated that any conventional means for providing flow of a coolant may be used in conjunction with the described embodiments of the present invention, and that more than one apparatus may be connected to a single source of coolant or that one or more sources of coolant may be connected to a single apparatus, for example, for redundancy purposes. Sizes of fluid pump 50, heat exchanger 53 and fan 58 should be selected based on heat removal and flow rate requirements. For example, a typical closed-loop fluid flow is 500 to 1000 milliliters per minute for 500 to 1000 Watts of heat dissipation. Pump and heat exchanger assemblies in various sizes, as well as acceptable tubing and fittings, are available from Cole- Parmer in Vernon Hills, Illinois, as well as other common sources .

An electronic component or a group of electronic components may be effectively cooled using the disclosed apparatus and method. Use of a thermally-conductive porous medium increases heat transfer and provides additional surface area over which two-phase heat transfer may occur. Thus, a lower flow rate of coolant is required for a given heat load. And the removal of heat from individual electronic components helps to reduce operating temperatures of the components, increasing reliability through reduction of thermal variation and associated thermal stresses . Because fluid does not have to contact electronic components directly, the potential for contamination of the fluid is reduced. And various fluid coolants may be used, for example, water, which has very low toxicity and few handling problems . In addition, the placement of the porous medium is simpler and less costly to manufacture than a traditional cold plate having microchannels .

Embodiments of the present invention are also desirable for cooling an electronic component during the testing and tuning process. For example, a test fixture may be designed to cool high heat-dissipating electronic components, and extensive sealing at or about the electronic component is not necessary.

It should be appreciated that the present invention is not limited to cooling an electronic component, but may be adapted to cool any heat source, for example, a heat sink or flange which is mounted to a substrate in a traditional fashion.

It will be apparent that other and further forms of the invention may be devised without departing from the spirit and scope of the appended claims and their equivalents, and it will be understood that this invention is not to be limited in any manner to the specific embodiments described above, but will only be governed by the following claims and their equivalents.

Claims

-ex¬ claims I claim:

1. An apparatus for cooling an electronic component, comprising: a first layer configured to carry an electronic component ; a second layer; a fluid distributing channel disposed between the first layer and the second layer, the fluid distributing channel having a first end, a central portion defining a chamber and a second end, the chamber positioned proximate the electronic component when the electronic component is disposed on the first layer; and a thermally-conductive porous foam disposed in the chamber, the thermally-conductive porous foam sized to receive and to mix a fluid and, when the electronic component is disposed on the first layer and the fluid is received and mixed, to cool the electronic component via conduction and two-phase heat transfer.