TECHNICAL FIELD

The present principles relate generally to providing a thermally conductive interface for heat management in electronic equipment.

BACKGROUND

Electronic equipment generates heat when operating and the heat may adversely affect the operation and the reliability of the equipment. Typically, design of such equipment must include components to dissipate excessive heat and maintain desired operating temperatures of the equipment. In particular, active devices such as integrated circuits and other power-consuming components both active and passive such as power transistors, power diodes and power resistors included in electronic equipment may generate heat that requires adding features to the equipment to properly dissipate undesirable heat.

Features added for heat dissipation may include components such as heat sinks and heat spreaders. A component intended to dissipate heat from a device such as an integrated circuit (IC) must be thermally coupled to the device to ensure efficient conduction of heat from the device to the heat-dissipation component. Achieving thermal coupling typically involves positioning a surface of the heat dissipation component in close proximity to a surface of the device, e.g., the top surface of an IC.

Despite the surfaces being in close proximity when the heat dissipation component is initially positioned during production, an air gap or space may exist initially between the surfaces due to production tolerances (e.g., to allow space for component movement). Even if the surfaces are touching initially, a gap or space may subsequently occur due surface irregularities, component aging, movement of the equipment, or other movement of the components, e.g., due to repeated cycles of heating and cooling of the apparatus. Any such air gaps significantly reduce the efficiency of the thermal interface between the heat dissipation component and the device.

To minimize such air gaps and increase the thermal efficiency of the interface to an acceptable level, a high-viscosity thermally conductive substance such as a thermal putty may be placed between the surfaces prior to positioning of the passive heat dissipation component. As the heat dissipation component is moved into close proximity to the device during production of the equipment, the putty is compressed and spreads between the surfaces to fill any gaps that exist and create a thermally efficient interface.

The described thermal interface functions well for equipment, e.g., a digital set top box used for cable television or digital satellite television reception, that typically has been rectangular in shape, installed in a horizontal position flat on a shelf and moved infrequently or not at all. In such conventional installations, the PCBs inside the equipment would usually be in a horizontal position when the equipment was installed. Active components and the heat dissipation components coupled thereto were mounted flat on the PCBs and were also oriented horizontally as were the thermal interfaces between the heat dissipation components and the heat-generating devices. However, modern electronic equipment may have shapes other than rectangular or be relocated frequently or installed in an unconventional orientation. For example, today rectangular set top boxes may be positioned on edge rather than flat or may have unusual configurations such as a pyramid to create a particular look or aesthetic effect. Printed circuit boards in a rectangular box that is installed on edge or in a box having a configuration other than rectangular may be oriented vertically or in an orientation other than horizontal when the equipment is in operation. As a result, the heat dissipation components and devices mounted on the boards and the thermal interfaces between them may be oriented vertically or have some orientation other than horizontal.

A thermal interface having an orientation other than horizontal may result in gravity causing a thermal putty to flow out of the thermal interface. The potential for thermal putty to flow may be exacerbated by high temperature in the thermal interface and by movement of components due to vibration of the equipment, e.g., by movement or relocation of the equipment, and thermal cycling. A loss of thermal putty in the interface may result causing a loss of thermal efficiency in the interface and excessive heating of devices that could lead to premature device failure. In addition, a substance such as thermal putty flowing out of an interface might contaminate areas or components in the vicinity of the thermal interface and result in reduced performance, improper operation or failure of such nearby components. SUMMARY

These and other drawbacks and disadvantages of the prior art are addressed by the present principles.

According to an aspect of the present principles, there is provided apparatus comprising a component configured to be thermally coupled to a device to dissipate heat from the device wherein the component comprises a first surface to be thermally coupled to the device with a thermal putty included in a region between the first surface and the device, and a pattern of features on the first surface configured to decrease migration of the thermal putty out of the region.

According to another aspect of the present principles, there is provided apparatus comprising a component configured to be thermally coupled to a device to dissipate heat from the device wherein the component comprises a first surface including a region to be thermally coupled to a surface of the device using a thermally conductive substance included in at least a portion of the region and between the first surface and the surface of the device, and a recessed area in at least a portion of the region of the first surface; wherein the recessed area comprises a first portion providing a target for application of the thermally conductive substance.

These and other aspects, features and advantages of the present principles will become apparent from the following detailed description of exemplary embodiments, which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present principles can be readily understood by considering the following detailed description in conjunction with the accompanying drawings in which:

FIG. 1 is a diagram showing an exemplary thermal interface apparatus to which the present principles can be applied, in accordance with an embodiment of the present principles;

FIG. 2 is a diagram showing an apparatus in accordance with an exemplary embodiment of the present principles;

FIG. 3 is a diagram showing enlarged detail of the exemplary embodiment shown in Figure 2;

FIG. 4 is a diagram showing a plurality of exemplary embodiments of aspects of the present principles; and FIG. 5 is a diagram showing a plurality of various embodiments of aspects of the present principles.

It should be understood that the drawings are for purposes of illustrating exemplary aspects of the present principles and are not necessarily the only possible configurations for illustrating the present principles. To facilitate

understanding, throughout the various figures like reference designators refer to the same or similar features.

DETAILED DESCRIPTION

The present principles are directed to apparatus providing a thermal interface addressing problems such as those described above and, as will be apparent to one skilled in the art, may be applied to other situations. While one of ordinary skill in the art will readily contemplate various applications to which the present principles can be applied, the following description will focus on exemplary embodiments of the present principles applied to a passive heat transfer component referred to herein as a heat spreader for removing heat generated by a heat-generating device such as an integrated circuit (IC) packaged in a ball grid array (BGA) package mounted on a printed circuit board (PCB). However, one of ordinary skill in the art will readily contemplate various other embodiments of the present principles including, for example, other heat transfer components, both active and passive, such as heat sinks, fins (structures to expand surface area), cavities (inverted fin structures), cold plates, forced air cooling (structures operating in conjunction with cooling fans), heat pipes and others. Also, one skilled in the art will readily recognize that devices other than ICs included in electronic products may create thermal transfer situations suitable for application of the present principles, e.g., power transistors, power supplies, power resistors and others. In addition, devices and applications to which the present principles can be applied include devices such as ICs and other devices in various configurations including various packages and mounting approaches. For example, the present principles may be applied to ICs in packages including BGA as mentioned above or flat packages, pin grid arrays, chip carriers, surface mount, through hole packages, multi-chip packages and others. Also, the present principles are applicable to thermal interfaces occurring in various types of electronic equipment including set-top boxes, gateway devices, routers, servers, computers, televisions, monitors, and others. It is to be appreciated that the preceding listing of potential applications of the present principles is merely illustrative and not exhaustive.

Referring now to Figure 1 , an exemplary embodiment of a thermal interface suitable for application of the present principles is shown. The left side of Figure 1 illustrates an exploded perspective view 100 of aspects of the thermal interface prior to assembly of the interface. The right side of Figure 1 shows a side sectional view 105 illustrating a cross section of the assembled thermal interface. In more detail, Figure 1 shows a heat removal component 1 10 such as a heat spreader including a large planar area from which a portion 150 protrudes. Protrusion 1 50 is formed during manufacturing of heat spreader 1 10, e.g., by stamping or molding, and has a planar region 1 60. Also shown in Figure 1 , a heat-generating device 140, such as an IC in a BGA package, is mounted on a surface of PCB 120. IC 140 has a top planar portion 170. During assembly of electronic equipment including the exemplary apparatus shown in Figure 1 , heat spreader 1 10 is positioned to place region 1 60 of heat spreader 1 10 in close proximity to planar region 170 of IC 140. Before moving regions 160 and 170 into close proximity, a small amount, e.g., a small pellet 130 in Figure 1 , of a high-viscosity thermally conductive substance such as thermal putty is placed between regions 160 and 170. Movement of the two regions into close proximity causes the pellet to deform and fill at least a portion of the space between regions 160 and 170 as the regions are moved into close proximity and reach their final locations in the assembled apparatus, thereby providing a thermally conductive interface to move heat generated by device 140 to heat dissipating component 1 10.

As described above, if a thermal interface as shown in Figure 1 is oriented horizontally, a thermally conductive substance such as high-viscosity thermal putty may be expected to remain in place between regions 160 and 170 and operate as intended to move heat from device 140 to heat dissipating component 1 10.

However, also as described above, if a thermal interface such as that illustrated in Figure 1 is positioned in an orientation other than horizontal, effects such as gravity, vibration, high temperature, thermal cycling and others may cause a substance such as thermal putty 130 to flow or migrate within the area between regions 1 60 and 1 70 and, potentially, move out of the intended area for the putty into surrounding areas of the electronic equipment. Any such migration may cause a decrease of the heat transfer efficiency of a thermal interface and/or contamination of surrounding components, reduced reliability and failure of components and/or the electronic equipment.

In accordance with the present principles, the described problem is addressed by thermal interface apparatus such as an exemplary embodiment shown in Figure 2. The left side of Figure 2 shows a top view 200 of a heat dissipation component 210 including a protruding area 240 formed in a manner similar to that described in regard to protrusion 1 50 shown in Figure 1 . Sectional view 204 in the center of Figure 2 illustrates a side view of a slice through heat dissipation component 210 at line A-A clearly showing protruding area 240. Protrusion 240 includes a planar portion 260 similar to region 160 of Figure 1 . An aspect of the present principles comprises providing a region 220 of planar portion 260 having an arrangement or pattern of features configured to decrease migration of a thermally conductive substance out of a thermal interface region. A magnified view 208 on the right side of Figure 2 includes an area 235 providing a magnified representation of area 230 of section view 204 to more clearly illustrate the exemplary embodiment of region 220 in Figure 2.

In the exemplary embodiment illustrated in Figure 2, the arrangement or pattern of features comprises a plurality of recesses formed in region 220 of surface 260. In the example of Figure 2, the plurality of recesses may comprise a plurality of parallel grooves formed in a portion of surface 260 and configured to be

perpendicular to a direction of potential migration of a thermal substance such as thermal putty. For example, Figure 2 illustratively shows a heat dissipation component having an arrangement of features 220 oriented to be suitable for decreasing migration of a thermal substance along line A - A in view 200. That is, in the example of Figure 2, heat dissipation component 210 may be oriented such that line A - A is vertical or in an orientation other than horizontal. In such an orientation, an effect such as gravity will act along line A - A and might increase likelihood that a thermally conductive substance such as a thermal putty will flow along line A - A and move out of a thermal interface formed with heat dissipation component 210. However, in accordance with the present principles, the arrangement of features 220 is perpendicular to line A - A and will resist the flow of the thermally conductive substance.

Figure 3 further illustrates the exemplary embodiment of Figure. In Figure 3, top view 300 on the left side of Figure 3 shows a portion of planar area 260 and region 220 within planar area 260 of the exemplary embodiment of heat dissipation component 210 shown in Figure 2. Figure 3 further illustrates a small amount 1 30 of a thermally conductive substance such as thermal putty positioned over region 220 of planar area 260. As can be seen in side view 310 on the right side of Figure 3, region 220 includes an arrangement or pattern of features, e.g., a plurality of parallel grooves, oriented for decreasing migration of, for example, thermal putty 130 along a line extending from the top to the bottom of views 300 and 31 0.

In accordance with another aspect of the present principles, the arrangement of features 220 shown in the exemplary embodiment of Figure 2 and Figure 3 as parallel recesses or grooves may be implemented in various forms. Various exemplary embodiments are shown in Figure 4. In Figure 4, the arrangement of features suitable for decreasing or impeding migration or flow of a thermally conductive substance such as thermal putty may take the form of a plurality of recesses or grooves that are parallel and perpendicular to the expected direction of flow of the thermal putty as previously discussed and shown in view 410 of Figure 4. Other possible forms of the arrangement or pattern of features may include recesses or grooves arranged in a rectangular grid as shown in view 420 of Figure 4, or an arrangement of a plurality of crossed recessed areas as shown in view 430 of Figure 4, or an arrangement of circular recessed areas as shown in view 440 of Figure 4, or a starburst pattern of recessed areas as shown in view 450 of Figure 4. As will be apparent to one skilled in the art, other patterns or arrangements of features not shown in Figure 4 are also possible and in accordance with the present principles, e.g., a spiral groove or recess. Also, the patterns shown may be combined in various ways to create other embodiments of arrangements or patterns of features in accordance with the present principles, e.g., a starburst in the center of one or more circles or a plurality of crosses combined with circles or combined with the rectangular grid or other patterns.

In accordance with another aspect of the present principles, improper positioning of a thermally conductive substance may occur when the substance is applied to a heat dissipation component prior to assembly of the component to a device for heat removal. For example, to ensure proper distribution of a substance such as a thermal putty in a thermal interface, the substance should be applied properly, e.g., approximately centered in a planar region of the heat dissipation component intended to form a thermal interface with a device. Proper positioning may occur in a factory environment using automated computer-controlled production equipment. However, outside of a factory, proper positioning may be problematic. For example, in a repair facility or when repairs are made in the field, e.g., a consumer's home, if equipment is disassembled such that existing thermal interfaces are separated or disassembled, e.g., a heat dissipation device is removed to access or replace a device coupled thereto, the thermally conductive substance must be reapplied before reassembly of the equipment. Improper positioning may occur in such a situation.

An aspect of the present principles comprises providing apparatus including a target for application of or proper positioning of a the thermally conductive

substance, e.g., a thermal putty. An exemplary embodiment of such apparatus comprises a component configured to be thermally coupled to a device to dissipate heat from the device. The component includes a first surface and the first surface includes a region to be thermally coupled to a surface of the device using a thermally conductive substance. The substance is to be included in at least a portion of the region and between the first surface and the surface of the device. The first surface further includes a recessed area in at least a portion of the region of the first surface, wherein the recessed area comprises a first portion providing a target for application of, or proper positioning of, a the thermally conductive substance, e.g., a thermal putty. In an exemplary embodiment such as that shown in Figure 4, view 410 illustrates an arrangement of features, e.g., a recessed area or a plurality of recesses in a region such as that shown in Figure 2 as region 220 in heat dissipation component 210. In addition, the exemplary recessed area in view 410 further includes feature 460 comprising a crossed pair of features, e.g., crossed grooves, forming an "X" pattern in the approximate center of the region or the recessed area. Feature 460 is configured to provide a target for application of the thermally conductive substance. That is, placement of a small portion or pellet of thermally conductive substance on the target will approximately center the substance in the area intended to form a thermal interface and increase the likelihood that the substance, e.g., a thermal putty, will properly spread through the thermal interface area as intended when the interface is assembled to ensure efficient heat transfer through the thermal interface area. A target such as target 460 may be incorporated in any of the patterns of features used to decrease thermal compound migration as shown in the various views of Figure 4. It should be apparent that although target 460 is shown in each of the views in Figure 4, a target is not required and may be included or not as appropriate for a particular application of the present principles.

Also, various embodiments of a target for application of a substance such as thermal putty are possible in accordance with the present principles. As shown in Figure 5, and in accordance with the present principles a target may take various forms other than the cross 460 shown in Figure 4 such as the exemplary

embodiments 570 in views 510 through 560, e.g., a cross inside a rectangle such as in view 510, a rectangle such as in view 520, a plurality of nested rectangles such as in view 530, a cross inside a circle such as in view 540, a circle such as in view 550, or a plurality of nested circles such as in view 560.

In accordance with another aspect of the present principles, in the exemplary embodiment depicted in Figure 2, region 220 is shown to occupy a portion of planar area 260 and region 220 may be increased or reduced in area to occupy more or less of area 260 than that depicted in Figure 2, e.g., more or less than 50% of planar area 220 or all of planar area 220. Also, although region 220 may, e.g., occupy more than 50% of planar area 220 or all of planar area 220, the surface area occupied by the plurality of features included in the pattern of features included in region 220 may be less than 50% of the surface area of planar area 220. For example, for an exemplary embodiment such as a pattern of a plurality of recesses, e.g., grooves, shown in view 41 0 of Figure 4, the spacing between the grooves (i.e., the portions of planar area 220 between grooves) is greater than the width of the grooves causing the surface area occupied by the grooves to be less than 50% of the surface area of planar area 220 even if a pattern such as that shown in view 41 0 occupies all of planar area 220. However, as will be apparent to one skilled in the art, characteristics of one or more features included in a pattern may be varied. For example, recesses such as grooves may be varied in width and depth. Also, although the exemplary embodiment illustrated in view 410 suggests that each feature, e.g., each recess or groove, is uniform as to length, width and depth, characteristics of the features may vary for one particular feature in a pattern, e.g., one groove may be wider and/or deeper than others in a pattern, or may vary throughout a pattern, e.g., each groove has a width and/or depth different than each of the other grooves in a pattern such as the pattern shown in view 410.

In accordance with another aspect of the present principles, including an arrangement or pattern of features such as that shown in view 410 of Figure 4 in a region of a surface of a heat dissipation component increases a total surface area of the surface of the heat dissipation component. For example, each feature such as a recess or groove increases surface area over that of the planar area where the groove is created due to, e.g., adding the sidewall area of the recess or groove. Increasing surface area increases the surface area for transmission of heat, thereby increasing a heat dissipation efficiency of the heat dissipation component and of the thermal interface.

The present description illustrates the present principles. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the present principles and are included within its spirit and scope. For example, the

arrangement or pattern of features included in region 220 of Figure 2 may be formed using one or more of various techniques such as embossing, molding, shaping, stamping, machining, etc.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the present principles and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. For example, use in the description when referring to the drawings of "top", "bottom", "left", "right" and other such terms indicating an orientation or relative relationship between areas of the Figures are illustrative only and not limiting as to the present principles.

Moreover, all statements herein reciting principles, aspects, and

embodiments of the present principles, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof.

Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

Reference in the specification to "one embodiment" or "an embodiment" of the present principles, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the embodiment is included in at least one embodiment of the present principles. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment", as well any other variations, appearing in various places throughout the specification are not necessarily all referring to the same embodiment.

Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the present principles are not limited to those precise embodiments, and that various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the scope or spirit of the present principles. All such changes and modifications are intended to be included within the scope of the present principles as set forth in the appended claims.