Patent Application
20240263890
The present disclosure relates to improvements in embedding phase change material (PCM) in heat sinks.
Electronic systems, particularly integrated circuit (IC) devices, are known to sometimes generate a substantial amount of heat, which can adversely affect IC device reliability and functionality. Various embodiments of heat sinks have been implemented to remove heat from active areas of IC devices, most notably, for present purposes, embodiments employing phase change material (PCM). The PCM removes heat from a device by changing phase from a solid to a liquid at its phase change temperature. During a phase change the PCM absorbs heat without a corresponding increase in temperature. By absorbing heat at the point where the maximum desired operational temperature of the managed components would be reached, the temperature that is actually reached can be reduced.
Two important parameters of PCM for heat sink applications are its phase change temperature and the quantity of PCM used. By having the phase change temperature of the material near the specified maximum operational temperature of a protected device, the melting of the PCM occurs just prior to the maximum permissible operational temperature being reached. By providing a suitable quantity of PCM, such that, under normal operating conditions, the PCM remains part liquid and part solid, the temperature of the protected devices can effectively be clamped at the melting temperature.
A few of the many examples of prior art heat sinks employing phase change material are disclosed in U.S. Pat. No. 6,848,500 (Langari et al), US2011/0156245 (Wu et al), U.S. Pat. No. 10,151,542 (Wood), U.S. Pat. No. 10,748,837 (Kedem) and U.S. Pat. No. 10,262,920 (Rafai-Ahmed et al), the entire disclosures in which are incorporated herein by reference. As disclosed in these documents, PCM heat sinks are typically provided with a sealed cavity that serves as an internal reservoir for the phase change material.
As size requirements for the packaging of electronic components become smaller, the size of heat sinks used with those components must likewise become smaller. However, reductions in the size of the electronic components do not necessarily result in a reduction of the heat they generate, thereby requiring increased thermal capacitance for smaller heat sinks. To illustrate, and referring to the schematic illustration in
More specifically, to create a reservoir cavity for the PCM with prior art manufacturing techniques, the thermally conductive heatsink body must typically be split transversely into two halves so that an interior cavity can be created between them and filled with the phase change material. The two halves are then sealed together so that the created cavity serves as a reservoir for the PCM. This approach becomes substantially unviable from a manufacturing standpoint when heat sinks, in order to accommodate required system functions not necessarily associated with thermal management, are configured with significant complexity including many through holes, deep recesses, and irregular and complex features.
It is an object of the present invention to increase the thermal capacity of PCM heat sinks without increasing the outer dimensions thereof.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended as an aid in determining the scope of the claimed subject matter.
The embodiments disclosed herein focus primarily on maximizing thermal capacitance of PCM heat sinks while minimizing heat sink length. Stated otherwise, disclosed herein are heat sink configurations, and methods of their manufacture, that enable maximizing the volume and effectiveness of PCM that can be contained in the heat sink.
Broadly stated, disclosed herein is a PCM heat sink for use in thermally managing components of a system having a maximum permissible operating temperature that is significantly higher than ambient temperature, wherein the heat sink comprises; a thermally conductive body member having mutually perpendicular axial and transverse dimensions and a plurality of PCM-receiving bores defined therein from at last one surface thereof; a plurality of pre-cast PCM rods disposed in respective bores, wherein the rods are in solid phase at ambient temperature and have a phase change temperature from solid to liquid at or just below the maximum permissible operating temperature; and a plurality of sealing members disposed in respective bores to seal the rods in the bores. The sealing members may be plugs or thin disc-like lids that are brazed, welded or otherwise secured to the body member at the bore openings.
In one example embodiment, a heat sink body member, with a short axial length relative to its transverse diameter, is formed with an array of multiple axially extending through-holes to accommodate functional requirements unrelated to thermal management. It would be extremely challenging and costly to manufacture such a heat sink configuration with a conventional reservoir for the PCM. Instead, in accordance with one concept disclosed herein, multiple blind holes or bores are formed in the top and/or bottom surface of the heat sink body and are configured to be filled with PCM and then sealed. Typically, the PCM is selected to have a solid phase (e.g., a rod) at ambient temperatures during manufacture and to have a phase change temperature at or just below the maximum specified operating temperature of the system components to be thermally managed. Sealing of the PCM in the bores may be effected with respective plugs (e.g., Lee Plugs R), or lids that may be welded or brazed in place as covers at the open ends of the bores. We have found that the resulting heat sink assembly has a significantly increased thermal capacitance without requiring increasing the axial length or transverse dimension of the heat sink. Moreover, the increased thermal capacity is achieved without requiring expensive advanced manufacturing processes.
In another example embodiment, where the heat sink configuration itself has axial and/or transverse irregularities, deep transversely extending bores may be formed at axially thick locations along the peripheral surface of the heat sink. These bores may be filled with PCM rods and sealed, as noted, with plugs or lids.
In another aspect, the use of relatively thin brazed or welded lids to cover PCM receiving cavities provides significant flexibility in designing shapes and locations of PCM reservoir cavities in a heat sink body member.
By way of example, specific illustrative embodiments of the present disclosure will now be described with reference to the accompanying drawings.
The present system and methods are described more fully hereinafter with reference to the accompanying drawings, in which several exemplary embodiments are shown. It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended drawings may be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the drawings, is not intended to limit the scope of the present disclosure but is merely representative of various embodiments. While the various aspects of the embodiments are presented in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
The subject matter disclosed herein may be embodied in other specific forms without departing from its spirit or essential characteristics; that is, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention(s) is/are, therefore, indicated by the appended claims rather than by this detailed description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the disclosed apparatus, system and method should be or are in any single embodiment. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.
Furthermore, the described features, advantages, and characteristics of the disclosed systems may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the embodiments can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments.
Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment. Thus, the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The relative terms “top”, “bottom”, “upper’, “lower” “above”, “below”, “forward”, “rear”, “height”, “length”, “width”, “thickness”, and the like as used herein are for ease of reference in the description to merely describe points of reference and are not intended to limit any particular orientation or configuration of the described subject matter.
Referring specifically to
Multiple local PCM-receiving pockets (i.e., deep blind holes or bores) 13 are defined in top surface 12, typically by simple machining but possibly by any metal forming technique. The number, depth and transverse dimension of the bores 13 are typically determined by the desired thermal capacitance to be achieved by PCM located in the bores. In this regard, the PCM received in the bores is in the form of pre-cast rods 14 that are in solid phase at ambient temperature (i.e., when the heat sink is assembled) and have a phase change temperature from solid to liquid that is typically at or just below the maximum specified operating temperature of the system components to be thermally managed or protected by the heat sink. The PCM chosen may be any phase change material having a melting point suitable to achieve this function. For example, various forms of INDALLOY®, (e.g., INDALLOY® 51, INDALLOY® 60, et al), manufactured by Indium Corporation of America of Utica, N.Y., are available with respective phase change temperatures that will serve the purposes described.
The PCM is sealed in bores 13 at surface 12 with respective plugs 15, for example, Lee Plugs®, manufactured and sold by The Lee Company of Westbrook, Connecticut and described, for example, in U.S. Pat. No. 5,160,225 (Lee), the entire disclosure of which is incorporated herein by reference. When surface 12 is disposed proximate or adjacent the managed heat load, the locally embedded PCM rods significantly increase heatsink performance (thermal capacitance) without adding heatsink length. Moreover, the enhanced thermal capacitance is achieved with a low-cost manufacturing process.
Referring to
The same volume maximization approach can be used for any conventional or unconventional PCM reservoir configuration as illustrated diagrammatically in
Reservoir 81 in
As noted above, in prior art PCM heat sinks, increased thermal capacity is typically obtained by increasing the size of the internal cavity or reservoir. Such cavities are typically created by advanced manufacturing procedures, such as a vacuum braze process, which are expensive and involve difficulty in properly filling the heatsink with PCM. The present solution avoids these problems simply and inexpensively without advanced manufacturing processes. In addition, and importantly, with the present solution, PCM can be easily introduced in localized areas of the heat sink that, when the heat sink is in use, are located proximate the heat load being managed by the heat sink, thereby significantly increasing heat sink efficiency and overall performance without increasing the heat sink dimensions.
The above description is intended by way of example only. Although the techniques are illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made within the scope and range of equivalents of the claims.
