Assemblies including heat sink elements and methods of assembling

A heat sink assembly comprises a plurality of components and a plurality of mounting tabs. A component attachment surface of each mounting tab is attached to a component and heat sink attachment surfaces of the plurality of mounting tabs are at least substantially coplanar. A heat sink element is attached to at least some of the plurality of mounting tabs at the heat sink attachment surface thereof. A method of assembling a heat sink assembly comprises attaching a plurality of mounting tabs to at least one substantially planar assembly surface of an assembly fixture. Each mounting tab is attached to a heat-generating component to form a mechanical and thermal coupling therebetween. The assembly fixture is removed from the plurality of mounting tabs, and a heat sink element is attached to mounting tabs of the plurality.

TECHNICAL FIELD

Embodiments of the present invention relate to assemblies including heat sink elements and to methods of assembling. More specifically, various embodiments relate to enabling use of a single heat sink element to provide cooling multiple heat-generating components provided on a substrate.

BACKGROUND

Cooling heat-generating components, such as integrated circuit devices, is often desirable to ensure their proper operation and to extend their useful life. A trend in contemporary circuit design is to provide multiple heat-generating components on a printed circuit board. A consequence of providing multiple heat-generating components on a printed circuit board, which may include integrated circuit devices operating at relatively high speeds, is substantial heat production that may be detrimental to the operation and life of those components. Conventionally, heat sinks are used to transfer heat from the heat-generating components to an area where the heat can be dissipated, such as the atmosphere. Alternatively, or in addition, adequate forced ventilation is provided to remove the heat from the heat sink.

Some conventional approaches to thermal management of packaged electronic devices require the mating of individual heat sinks with individual components. The use of individual heat sinks can be expensive and the associated installation may be labor intensive. Further, as more heat-generating components are provided onto ever-smaller printed circuit boards, each heat sink must be accurately aligned with its neighbor to ensure proper function.

Other conventional heat sinks are also adapted for cooling a multiplicity of heat-generating components. Variations in the manufacturing and assembly processes, however, frequently result in seemingly identical components that have top attachment surfaces, over which the heat sink is provided, at slightly different heights. Possible sources of height differences include, for example, variances in the size of solder balls used to attach components to a substrate, variances in bends of leads used for component attachment, variances in thickness of solder connections, and dimensional variances in other attachment features used for this purpose. Moreover, different components having top attachment surfaces located at different heights may often be provided on the same printed circuit board. In a conventional configuration resulting in different component height, highly compressible thermally conductive gap pads or gap filler materials may be used to fill gaps between the bottom of the heat sink and the top surfaces of the components to be cooled, enabling effective thermal transfer to the heat sink from the shorter components. Gap pads may be attached between the heat sink and the components by thermally conductive epoxy or by mechanical means, such as clamps or fasteners. Alternatively, the heat sink may be configured to deform in response to an applied downward force to contact the top surfaces of components and be attached thereto. Further, gap filler material, such as a thermal interface material (TIM), may also be provided to fill gaps between the heat sink and the components. Conventionally, TIMs are able only to fill relatively thin gaps because a thicker layer of TIM may not provide adequate heat dissipation. Any of these configurations, however, may result in inadequate heat transfer from components due to suboptimal, or failed, thermal attachments or may introduce unacceptable stress on thicker components having top surfaces most out of plane with the top surfaces of the remainder of the components.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable a person of ordinary skill in the art to practice the invention. However, other embodiments may be utilized, and structural, logical, and configurational changes may be made without departing from the scope of the invention. The illustrations presented herein are not meant to be actual views of any particular heat sink, assembly fixture, or heat-generating components, but are merely idealized representations that are employed to describe embodiments of the present disclosure. The drawings presented herein are not necessarily drawn to scale. Additionally, elements common between drawings may retain the same numerical designation.

FIG. 1shows a partially exploded perspective view of an assembly fixture10according to an embodiment of the present disclosure. The assembly fixture10includes an assembly member12and a plurality of legs14depending from the assembly member12. The assembly fixture10further includes a plurality of recesses16formed in a surface of the assembly member12. Each recess16may be of a size and shape configured to receive a mechanical attachment feature, such as, for example, an affixer, an assembler, a bolt, a button, a carrier, a cinch, a clamp, a clasp, a clencher, a clinch, a clip, a connector, a contact, a coupler, a fastener, a fitter, a fixer, a hanger, a harness, an interconnect, a joiner, a latch, a lead, a link, a mount, a nail, a peg, a pin, a reaffixer, a reattachment, a refastener, a refixer, a resecurer, a rivet, a rod, a screw, a securer, a staple, a stick, a strap, a tab, a tack, a tie, a uniter, or, as shown inFIG. 1, a heat sink mounting tab18of a plurality of heat sink mounting tabs18, partially therein such that a heat sink attachment surface26(seeFIG. 2) of each mounting tab18abuts against and is flush with an at least substantially planar assembly surface28forming a floor of each recess16of the plurality. The assembly surfaces28of the recesses16are at least substantially coplanar. In other embodiments, the assembly member12may not have recesses16formed therein, but may comprise a uniform, at least substantially planar surface to which heat sink mounting tabs18may be attached.

The assembly fixture10and the mounting tabs18may be attached using other, releasable attachment features, such as screws. For example, holes20may be formed in the assembly fixture10and holes52may also be formed in the mounting tabs18, which holes20and52may be threaded to receive screws22therein. In some embodiments, only the holes52in the mounting tabs18may be threaded, while holes20in the assembly fixture10are smooth-walled and sized to provide clearance for screws22passing therethrough. The screws22attach the mounting tabs18to the assembly fixture10, attaching them within the recesses16and ensuring that the heat sink attachment surfaces26(seeFIG. 2) of the mounting tabs18abut against and are flush with the at least substantially coplanar assembly surfaces28of the recesses16. The screws22may comprise, for example, spring-loaded captive screws22. In other embodiments, other attachment features may be used to releasably attach the mounting tabs18to the assembly fixture10, such as, for example, clamps, snap-fit mating features, etc.

When the mounting tabs18are attached to the assembly fixture10, heat sink attachment surfaces26of the mounting tabs18are at least substantially coplanar, such as due to their abutment against an at least substantially planar surface, such as the substantially coplanar assembly surfaces28of each recess16of the plurality of recesses16. The mounting tabs18may be attached to the assembly fixture10in a predetermined configuration. For example, the mounting tabs18depicted inFIG. 1are mounted in recesses16forming two arrays, each array comprising eight mounting tabs18in four rows and two columns. In other embodiments, any number of mounting tabs18may be attached to the assembly fixture10in any desired configuration. The recesses16formed in the assembly fixture10may also be configured to orient the mounting tabs18in a desired manner. For example, the recesses16depicted inFIG. 1are formed such that, when the mounting tabs18are attached to the assembly fixture10, the mounting tabs18are at least partially disposed within the recesses16, and movement of the mounting tabs18is at least substantially restrained in all directions. In other words, the sidewalls of the recesses16shown inFIG. 1substantially prevent rotation or other displacement of the mounting tabs18in the plane of the assembly fixture10, while spring-loaded captive screws22attach the mounting tabs18to the assembly member12of the assembly fixture10. The arrangement of the mounting tabs18may correspond to an arrangement of heat-generating components24(seeFIG. 2) to which the mounting tabs18attach.

Though the mounting tabs18shown inFIG. 1are depicted as being of substantially rectangular shape, having a length, width and depth, the mounting tabs18may be of any suitable shape or size for cooperative attachment to heat-generating components24(seeFIG. 2) and for cooperative receipt with recesses16to substantially prevent movement therein. For example, the mounting tabs18may have a predetermined size and shape to optimize dissipation of heat from a given type of heat-generating component. In the embodiment shown inFIG. 1, where the mounting tabs18comprise a three-dimensional, substantially rectangular peripheral shape, the mounting tabs18may have a length of about 20 millimeters, a width of about 9 millimeters, and a depth of about 3 millimeters. The shape, length, width, and depth of the mounting tabs18, however, may be designed and manufactured to be any suitable shape or size to enable the mounting tabs18to attach to an assembly fixture10, to attach to heat-generating components24(seeFIG. 2), and to transfer heat from the heat-generating components24. Optimal shape and size of the mounting tabs18may depend on, for example, the size and shape of the heat-generating components24and the wattage or power rating of the heat-generating components24. The mounting tabs18may also comprise a thermally conductive material to facilitate heat dissipation. For example, the mounting tabs18may comprise aluminum, gold, copper, silver, indium, tin, alloys of these, a thermally conductive composite material, or any combination of these. Specifically, the mounting tabs18may comprise tin-plated copper, which may increase the wettability or solderability of the mounting tabs18.

FIG. 2shows a partially exploded view of the assembly fixture10and heat sink mounting tabs18ofFIG. 1, depicting a method of attaching the mounting tabs18to heat-generating components24according to an embodiment of the present disclosure. Once the mounting tabs18are attached to the assembly fixture10such that heat sink attachment surfaces26are at least substantially coplanar, the assembly fixture10and at least some of the mounting tabs18may be provided over a like plurality of heat-generating components24attached to a common substrate. For example, the heat-generating components shown inFIG. 2may be provided on a substrate, for example, on a printed circuit board38. Mounting tab18component attachment surfaces30(seeFIG. 1) opposing the heat sink attachment surfaces26may be brought proximate to upper surfaces32of the heat-generating components24, and aligned therewith. The upper surfaces32of the heat-generating components24are not necessarily coplanar. For example, the upper surfaces32of heat-generating components24may have a difference in height of up to about one millimeter (1 mm). In some embodiments, at least one mounting tab18component attachment surface30(seeFIG. 1) may contact and abut the upper surface32of the tallest heat-generating component24, while a space (e.g., a gap) may remain between the remaining mounting tabs18and heat-generating components24. In other embodiments, a space may be present between each mounting tab18and each corresponding heat-generating component24. The allowable space may depend on the thermal impedance of the attachment medium. Thus, an attachment medium with a low thermal impedance, such as, for example, an impedance of about fifty Watts per meter (50 W/m) may enable attachment of a mounting tab18to a heat-generating component24across a relatively large space. For example, a mounting tab18and a corresponding heat-generating component24may be up to one millimeter (1 mm) apart.

In addition to the assembly fixture10, a cooperative assembly fixture base34may also be provided. The assembly fixture base34may include various features to facilitate accurate alignment and attachment of the mounting tabs18to the heat-generating components24. For example, the assembly fixture base34may include a ledge36proximate the perimeter of the assembly fixture base34. The ledge36may be configured such that a portion of the printed circuit board38, a portion of the assembly fixture10, or a portion of each may abut against and rest on the ledge36during the assembly process. The assembly fixture base34may also include holes40. Cooperating holes42may be formed in the assembly fixture10and in the printed circuit board38, to facilitate attachment to the assembly fixture base34. For example, the holes40in the assembly fixture base34may be threaded, and the holes42formed in the assembly fixture10may permit clearance of a screw (not shown) extended therethrough to attach the assembly fixture10to the assembly fixture base34. In other embodiments, the holes40in the assembly fixture base34may not be threaded, and a rod or peg, for example, may be inserted through the holes40,42to facilitate alignment of the assembly fixture10and the printed circuit board38with the assembly fixture base34. In addition, the legs14depending from the assembly member12may have a selected height such that, when the legs14are brought into contact with the assembly fixture base34, the mounting tabs18are vertically proximate the heat-generating components24. For example, when the legs14contact the assembly fixture base34, the upper surface32of the tallest heat-generating component24may abut a corresponding mounting tab18. The weight of the assembly fixture10may hold at least one mounting tab18against the tallest of the heat-generating components24.

Once the mounting tabs18are aligned with the heat-generating components24, the mounting tabs18may be attached to the heat-generating components24. Attaching the mounting tabs18to the heat-generating components24may comprise thermally and mechanically attaching the mounting tabs18to the heat-generating components24. For example, a solder may be provided on upper surfaces32of heat-generating components24and/or on the component attachment surfaces30of mounting tabs18to attach the mounting tabs18to the heat-generating components24and to at least substantially fill any gaps therebetween using, for example, conventional soldering techniques. A suitable, relatively low-temperature solder may be selected so as to not damage the heat-generating components or substantially impact the thermal budgets of the various heat-generating components. For example, a eutectic solder, such as a solder comprising sixty-three percent (63%) tin and thirty-seven percent (37%) lead, may be selected. In embodiments where the mounting tabs18are soldered to the heat-generating components24, the assembly member12may comprise a thermally stable, insulating material to enable sufficient heating of the solder. In other embodiments, the mounting tabs18may be attached to the heat-generating components24using a thermally activated epoxy, screws, rivets, or other suitable attachment feature.

The mounting tabs18may be arranged in a manner corresponding to the heat-generating components24provided on the printed circuit board38. In the embodiment shown inFIG. 2, both the heat-generating components24and the mounting tabs18are configured in two arrays comprising two columns and four rows. In other embodiments, any desirable configuration of heat-generating components24and corresponding mounting tabs18may be used. As shown inFIG. 2, some heat-generating components24may not have mounting tabs18attached thereto. In other embodiments, each heat-generating component24may be attached to a corresponding mounting tab18.

After the mounting tabs18are attached to the heat-generating components24, the spring-loaded captive screws22may be removed. The assembly fixture10and assembly fixture base34may also be removed, leaving the mounting tabs18attached to the heat-generating components24. Due to prior attachment of the mounting tabs18to the at least substantially coplanar assembly surfaces28, the heat sink attachment surfaces26of the mounting tabs18may be at least substantially coplanar. For example, the heat sink attachment surfaces26of the mounting tabs18may be a maximum of thirteen-hundredths of a millimeter (0.13 mm) out of plane with one another. Stated another way, the heat sink attachment surfaces26of the mounting tabs18may be coplanar with a tolerance of, for example, plus or minus about thirteen-hundredths of a millimeter (±0.13 mm). When a heat sink44(seeFIG. 3) is attached to a group of mounting tabs18, as further described hereinbelow, the force or stress condition on the heat-generating components24may be zero or at least substantially near zero because the heat sink attachment surfaces26of the mounting tabs18are at least substantially coplanar.

FIG. 3is a partially exploded perspective view of a plurality of heat sinks44depicting a method of attaching the heat sinks44to groups of mounting tabs18in accordance with one embodiment of the present disclosure. Heat sinks44, which may also be characterized as heat sink elements as such structures may also perform one or more functions in addition to heat transfer, may be brought proximate the mounting tabs18in superimposition thereover. Each heat sink44is configured for attachment to at least some of a plurality of heat sink mounting tabs18. In addition, the heat sinks44are configured to dissipate heat from the heat-generating components24. The heat sinks44may enable sharing of thermal mass from a location of one heat-generating component24with locations of other heat-generating components24. For example, the heat sinks44shown inFIG. 3are monolithic-style heat sinks44having a plurality of laterally separated, vertically protruding fins46configured to dissipate heat. The fins46, however, may be of any size, shape, or arrangement suitable to dissipate heat from the heat-generating components24. In other embodiments, the heat sinks44may not be monolithic-style heat sinks44, but may have any profile, configuration, or structure desirable to dissipate heat from the heat-generating components24, either through natural radiation and convection, or in combination with forced ventilation. For example, heat sinks44may include channels or bores therethrough, through which cooling air or other fluid may pass or be forced through. The heat sinks44may also comprise a thermally conductive material to facilitate heat dissipation. For example, the heat sinks44may comprise aluminum, gold, copper, silver, indium, alloys of these, a thermally conductive composite material, or any combination of these.

The heat sinks44each include a mounting tab attachment surface48(seeFIG. 4) of sufficient size and shape to attach to at least two mounting tabs18. The heat sinks44further include structures for attachment to the mounting tabs18. For example, the heat sinks44shown inFIG. 3each include a plurality of holes50formed therein and arranged in a manner corresponding to at least some of the heat sink attachment surfaces26of the mounting tabs18. Likewise, the mounting tabs18include threaded holes52that are axially aligned with the holes50in the heat sinks44. Attachment features, such as screws54, may be inserted through the holes50in the heat sinks44and engage the threaded holes52to attach the heat sinks44to at least some of the mounting tabs18. The screws54may be used to form a thermal and mechanical attachment between the heat sinks44and the mounting tabs18. In other embodiments, the heat sinks44may be attached to the mounting tabs18using a soldered connection, a thermal epoxy, a rivet, or any other suitable attachment feature. Heat sinks44may be thermally attached to, but not necessarily mechanically attached to, each mounting tab18. In summary, heat may be dissipated from the heat-generating components24by providing a continuous, effective thermal attachment from the heat-generating components24to the heat sinks44using mounting tabs18and the attachment features between each of these structures.

Though the heat sinks44depicted inFIG. 3are each configured to attach to eight mounting tabs18on two sections of a printed circuit board38, persons of ordinary skill in the art will understand that embodiments of heat sinks44in accordance with the present disclosure may be configured to attach to any desirable number of mounting tabs18. Moreover, in some embodiments, a single heat sink44may be configured to attach to every mounting tab18of each heat-generating component24provided on a printed circuit board38. In other embodiments, a heat sink44may be configured to attach to a first plurality of mounting tabs of a first plurality of heat-generating components provided on a first printed circuit board or other substrate and a second plurality of mounting tabs of a second plurality of heat-generating components provided on a second printed circuit board or other substrate. In this way, multiple substrates bearing heat-generating components24may be thermally and mechanically attached together using a single heat sink44or multiple heat sinks44. Though the two sets of eight mounting tabs18shown inFIG. 3are at least substantially coplanar, different sets of mounting tabs18may have upper surfaces in different planes at different heights, and a single heat sink44may be attached to each set of mounting tabs18having coplanar upper surfaces at each different height.

The heat sinks44may also include a plurality of recesses56formed in a surface48, as shown inFIG. 4. Like the recesses16that may be formed in the assembly fixture10(seeFIG. 1), the recesses56formed in the heat sinks44may be configured to receive the mounting tabs18at least partially therein. The recesses56may be configured to facilitate attachment of the heat sinks44to the mounting tabs18. For example, the recesses56may be at least one of a size, shape, and arrangement configured to enable the mounting tabs18to at least partially enter the recesses56only when the recesses56and the mounting tabs18are mutually aligned to enable attachment of the mounting tabs18to the heat sink44. Once the mounting tabs18are aligned with and at least partially disposed in the recesses56, the mounting tabs18may be attached to the heat sink44in any of the previously described ways. In other embodiments, however, the heat sink44may not include recesses56formed therein. In such embodiments, the mounting tabs18may be attached directly to a planar surface48of the heat sinks44. In still further embodiments, a heat sink44may include a plurality of frames projecting from an underside thereof, each frame sized and shaped to define a recess56to at least partially receive a mounting tab18therein.

FIG. 5is a schematic view of a heat sink44attached to heat-generating components24disposed on multiple, laterally offset printed circuit boards38or other substrates. The heat sink44is attached to the heat-generating components24using mounting tabs18. In this way, multiple printed circuit boards38, or other substrates, may be thermally and mechanically attached together using a single heat sink44. In other embodiments, multiple heat sinks44may be used to attach multiple printed circuit boards38thermally and mechanically to one another. When attached to multiple printed circuit boards38, the heat sink44may enable sharing of thermal mass between multiple printed circuit boards38, or other substrates.

Referring toFIG. 6, a schematic view of stacked substrates38in a mezzanine configuration is shown. Each substrate38has a plurality of components24provided thereon. The substrates38may be attached to one another in a stacked mezzanine configuration using mounting tabs18, or other suitable attachment features, having substantially coplanar attachment surfaces. The stacked substrates38may be in complete vertical superimposition as depicted, or comprise a partially offset, so-called “shingle stack.” Moreover, different-sized substrates38may be superimposed and two or more laterally offset, smaller substrates38may be secured to a larger substrate38. The mounting tabs18may provide thermal and mechanical attachment of one substrate38to another substrate38while enabling simple disassembly and reassembly of the stacked substrates38for repairs, service, and cleaning. In some embodiments, a heat sink44, such as a metal heat sink plane as shown in broken lines, may be embedded within, or attached to an underside of some or all of substrates38. Attachment of multiple substrates38bearing heat generating components24using attachment features such as mounting tabs18may enable increased potential power of electronic systems while providing adequate cooling and simple disassembly and reassembly.

CONCLUSION

In some embodiments, the present disclosure includes assemblies comprising a plurality of components provided on a substrate and a plurality of attachment features. Each attachment feature comprises a component surface and a heat sink surface. The component surface of each attachment feature of the plurality is attached to a component of the plurality of components, and the heat sink surfaces of the plurality of attachment features are at least substantially coplanar. A heat sink element is attached to the plurality of attachment features at the heat sink surface of at least some attachment features of the plurality.

In additional embodiments, the present disclosure includes an assembly, comprising a first plurality of heat-generating components and at least a second plurality of heat-generating components. A first plurality of attachment features is thermally and mechanically attached to the first plurality of heat-generating components and at least a second plurality of attachment features is thermally and mechanically attached to the at least a second plurality of heat-generating components. Heat sink surfaces of attachment features of the first plurality are at least substantially coplanar and heat sink surfaces of attachment features of the at least a second plurality are at least substantially coplanar. A first heat sink element is attached to at least some of the first plurality of attachment features at the heat sink surfaces of attachment features of the first plurality. At least another heat sink element is attached to at least some of the at least a second plurality of attachment features at the heat sink surfaces of attachment features of the at least a second plurality.

In further embodiments, the present disclosure includes assemblies, wherein at least two substrates, one or more of which may comprise a circuit board, are placed in vertical superimposition and mechanically and thermally attached using the aforementioned techniques.

In further embodiments, the present disclosure includes methods of assembling, comprising attaching a plurality of first attachment features to at least one substantially planar assembly surface of an assembly fixture such that heat sink surfaces of the plurality of attachment features are substantially coplanar. At least some of the plurality of attachment features attached to the assembly fixture are aligned with a like plurality of heat-generating components. The at least some of the plurality of attachment features are attached to the plurality of heat-generating components. The assembly fixture is removed from the plurality of attachment features, and a heat sink element is attached to at least some of the attachment features of the plurality.