# Patent

## Title
Thermal management of electronic devices

## Abstract

Thermal management is provided for a device. The device may include a substrate having a mounting area on a first surface of the substrate. The device may also include first thermal vias extending from the mounting area to at least an interior of the substrate. The device may also include at least one thermal plane substantially parallel to the first surface of the substrate, the at least one thermal plane being in thermal contact with at least one of the first thermal vias. The device may also include a heat sink attachment area, and second thermal vias extending from the heat sink attachment area to the interior of the substrate, the at least one thermal plane being in thermal contact with the second thermal vias.

## Background
FIELD OF THE INVENTION
Implementations consistent with the principles of the invention relate generally to heat dissipation and, more particularly, to systems and methods of heat transfer through a substrate supporting electronic components to control operating temperatures of the electronic components.
BACKGROUND OF THE INVENTION
Physical compactness of electronic devices, such as interface devices mounted at a user interface edge of an electronic assembly, impedes cooling of the electronic devices, which is a particular concern for electronic devices that consume a substantial amount of power, and thus generate a significant amount of heat. For example, when transceivers, such as small form-factor pluggable (SFP) modules, are ganged into multiple cages, the transceivers in the middle of the cluster may generate and retain an undesirable amount of heat. Very little airflow may reach individual modules in certain positions of the cluster for cooling purposes. Unlike stand-alone devices, which have relatively large surface areas that may radiate heat, clustered devices may have only limited surface area from which to radiate heat.
SUMMARY OF THE INVENTION
According to one aspect, a device may include a substrate that may include a first mounting area on a first surface of the substrate. The device may also include a group of first thermal vias extending from the first mounting area to at least an interior of the substrate. The device may also include at least one thermal plane substantially parallel to the first surface of the substrate, the at least one thermal plane being in thermal contact with at least one of the first thermal vias. The device may also include a heat sink attachment area. In addition, the device may include a group of second thermal vias extending from the heat sink attachment area to the interior of the substrate, the at least one thermal plane being in thermal contact with the second thermal vias.
According to another aspect, a method of heat transfer in a substrate may include conducting heat from a component to a component mount mounted on a first mounting surface of the substrate. The method may also include conducting the heat from the component mount to a first set of thermal vias that extend from the first mounting surface to at least an interior of the substrate. The method may also include conducting the heat from the first set of thermal vias to one or more thermal planes disposed along a length of the substrate. The method may also include conducting the heat from the one or more thermal planes to a second set of thermal vias. The method may also include conducting the heat from the second set of thermal vias to a heat sink attachment surface of the substrate. In addition, the method may include conducting the heat from the heat sink attachment surface of the substrate to a heat sink mounted to a heat sink attachment surface of the substrate.
According to yet another aspect, a method of forming a substrate may include disposing one or more thermal planes in the substrate. The method may also include providing a first set of thermal vias in a component mounting area on a first side of the substrate, the first set of the thermal vias being thermally coupled to the component mounting area and to the one or more thermal planes. In addition, the method may include providing a second set of thermal vias extending from a heat sink attachment area on the first side of the substrate, the second set of the thermal vias being thermally coupled to the one or more planes and to the heat sink attachment area.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an implementation of the invention and, together with the description, explain the invention. In the drawings,
FIG. 1 is a diagram illustrating an exemplary device in which methods and systems consistent with the principles of the invention can be implemented;
FIG. 2 is an exemplary diagram of the interface card of FIG. 1 according to an implementation consistent with the principles of the invention;
FIG. 3 is a cut-away view of an exemplary interface card in which methods and systems consistent with the principles of the invention can be implemented;
FIGS. 4A, 4B, and 4C illustrate an exemplary interface unit in which methods and systems consistent with the principles of the invention can be implemented;
FIG. 5 is a line image of the exemplary daughterboard of FIGS. 4A-4C; and
FIG. 6 is a flow diagram of an exemplary thermal management process according to an implementation consistent with the principles of the invention.



DETAILED DESCRIPTION
The following detailed description of embodiments of the principles of the invention refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims and equivalents.
Systems and methods consistent with the principles of the invention may provide controlled cooling of a component, such as an input/output device, that may be located in a compact configuration at a user interface edge of an interface card, by conducting heat away from the component using a system of thermally coupled thermal vias and thermal planes on and/or in a substrate to a heat sink that may be disposed in an available airflow that may flow by the interface card.
Exemplary Device Configuration
FIG. 1 illustrates an exemplary device 100 in which systems and methods consistent with the principles of the invention may be implemented. As illustrated, device 100 may include a housing 110 that houses various modules 120 (e.g., controller, power supply, etc.) and card slots 130 which operably receive interface cards 140.
In one implementation, device 100 may include any device that receives, processes, and/or transmits data, such as a server, a router, or a switch.
In one implementation, housing 110 may include any structure configurable to retain and/or support a chassis, removable cards, and/or other modules that may be used in operation of device 100. The number and type of cards, modules, and other system components illustrated in FIG. 1 are provided for simplicity. In practice, a typical device could include more or fewer cards, modules, and other removable or fixed components that aid in receiving, processing, and/or transmitting data, than what is illustrated in FIG. 1. Housing 110 may be fabricated from metal, plastic, and/or composite and may be sized for particular applications. In one implementation, housing 110 may be sized to fit an industry standard mounting structure, such as an equipment rack.
FIG. 2 illustrates exemplary interface card 140 in an orientation representative of being configured in card slot 130 in housing 110 (FIG. 1), for which airflow may be represented by the directional arrows shown. It should be appreciated that the cooling effect produced by the airflow may not be uniform over the various surfaces of interface card 140.
FIG. 3 illustrates an internal view of one end of an exemplary interface card 340. Interface card 340 may include a motherboard 350 and an interface unit 360. Motherboard 350 may include any substrate, such as a circuit board, e.g., a printed circuit board (PCB). Interface card 340 may include more than one interface unit 360.
Interface unit 360 may include a daughterboard 362, interface module cages 364 for receiving interface modules 366, and heat sinks 368. In one implementation, interface modules 366 may attach directly to daughterboard 362 and interface module cages 364 are omitted. Interface unit 360 may include any input/output device, such as a small form-factor pluggable (SFP) interface, an XFP (10 Gigabit SFP), or any type of transceiver. Interface unit 360 may electrically, structurally, and/or thermally connect to motherboard 350. Interface unit 360 may be located at a user-accessible end of motherboard 350. Other configurations are possible.
Daughterboard 362 may include any substrate, such as a PCB. Daughterboard 362 may have any dimensions corresponding to the dimensions of interface card 340. In one implementation, motherboard 350 may include interface unit 360. That is, motherboard 350 and interface unit 360 may be an integral PCB, without a separate daughterboard 362.
Interface module cages 364 may include any device for receiving and retaining interface modules 366. Interface module cages 364 may include ganged individual module cages. Other configurations of interface module cages 364 are possible. As shown, interface module cages 364 may be arranged on opposing sides of daughterboard 362. Interface modules 366 may include any electronic component and/or circuitry, such as an SFP module, e.g., an SFP optical modular transceiver. In one implementation, interface modules 366 are hot-swappable.
Heat sinks 368 may include any device that may absorb, conduct, radiate, and/or dissipate heat. Heat sinks 368 may include any material having any thermal conductivity. Heat sinks 368 may have any shape or dimensions. Any number of heat sinks 368 may be used. Thermal conductivity properties of any one heat sink 368 may vary from another heat sink 368. As shown, heat sinks 368 may be disposed at a remote end of daughterboard 362. Other configurations of the heat sinks 368 are possible. For example, heat sinks 368 may be disposed on two or more surfaces on daughterboard 362. In one implementation, the location of heat sinks 368 is based on an airflow in device 100.
FIGS. 4A and 4B illustrate opposing views of an exemplary interface unit 360. As shown, interface unit 360 may include four interface module cages 364, two side-by-side mounted at a mounting area of a first surface of daughterboard 362, and two side-by-side mounted at a mounting area of an opposite second surface of daughterboard 362 along an accessible edge of interface unit 360. Other configurations may be used. Any mechanism may be used to mount interface module cages 364 to daughterboard 362. In one implementation, a thermal interface material (not shown) is interposed between a mounting surface of interface module cages 364 and the mounting area on the surface of daughterboard 362. As shown, two interface modules 366 are respectively plugged into two interface module cages 364. Interface unit 360 may include heat sinks 368 attached to daughterboard 362 at an attachment area by attachment members 470 (FIG. 4B). Other attachment mechanisms may be used. In one implementation, a thermal interface material (not shown) is interposed between a mounting surface of heat sinks 368 and the attachment area on the surface of daughterboard 362.
FIG. 4C illustrates an exploded view of interface unit 360. Daughterboard 362 may include thermal vias 480A that terminate on a surface of daughterboard 362 in an area of interface module cages 364 and terminate on an opposing surface of daughterboard 362. Daughterboard 362 may include thermal vias 480B that terminate on a surface of daughterboard 362 in an area of heat sinks 368 and extend to an interior of daughterboard 362. Daughterboard 362 may include thermal planes 490. Thermal planes 490 may be exposed at the edge of daughterboard 362. Thermal planes 490 may alternatively not be exposed at the edge of daughterboard 362. Thermal planes 490 may be electrically insulated from electrical connections, electrical vias, or electrical planes. Thermal planes may alternately include power planes, ground planes, and the like.
FIG. 5 illustrates a partial line image of daughterboard 362, showing an internal construction thereof. Thermal vias 480A and 480B may include one or more through-holes that extend from a surface of daughterboard 362 to an interior of daughterboard 362. In one implementation, thermal vias 480A and 480B may extend from one surface of daughterboard 362 to an opposing surface of daughterboard 362. Thermal planes 490 may include one or more thermal conducting layers separated by substrate layers of daughterboard 362. Thermal planes 490 may be configured substantially parallel to daughterboard 362. Thermal planes 490 may extend from thermal vias 480A to thermal vias 480B. Thermal planes 490 may be exposed at an edge of daughterboard 362. Any of thermal vias 480A may thermally couple to any or each of thermal planes 490, and any of thermal planes 490 may thermally couple to any or each of thermal vias 480B.
Thermal vias 480A and 480B may form a uniform pattern on the surface of daughterboard 362. Thermal vias 480A and 480B may alternatively be non-uniformly arranged on the surface of daughterboard 362. Thermal vias 480A and 480B may extend substantially perpendicularly from the surface to an interior of daughterboard 362. Thermal vias 480A and 480B may alternatively extend at any angle from the surface to an interior of daughterboard 362. Thermal vias 480A and 480B may have a substantially circular cross-section. Thermal vias 480A and 480B may alternatively have cross-sections of any other regular or irregular shape. Thermal vias 480A and 480B may have any diameter that is substantially constant from end to end. Thermal vias 480A and 480B may alternatively have diameters that vary over a length thereof. Any of thermal vias 480A and 480B may vary one from another in any of the above respects.
A periphery of thermal vias 480A may correspond to a perimeter of interface module cages 364, i.e., define a mounting area for interface module cages 364 on a surface of daughterboard 362. The total effective surface area of thermal vias 480A at the surface of daughterboard 362 may constitute any portion of the total area of the mounting area of interface module cages 364. Some of thermal vias 480A may alternatively not be covered by interface module cages 364. Alternatively, the mounting surfaces of interface module cages 364 may overlap the periphery of thermal vias 480A.
A periphery of thermal vias 480B may correspond to a perimeter of heat sinks 368, i.e., define a mounting area for heat sinks 368 on a surface of daughterboard 362. The total effective surface area of thermal vias 480B at the surface of daughterboard 362 may constitute any portion of the total area of the mounting area of heat sinks 368. Some of thermal vias 480B may alternatively not be covered by heat sinks 368. Alternatively, the mounting surfaces of heat sinks 368 may overlap the periphery of thermal vias 480A.
Thermal vias 480A and 480B may include blind vias that extend from a surface of daughterboard 362 to a predetermined depth of daughterboard 362. Thermal vias 480A and 480B may include backdrilled vias that extend from a predetermined depth of an interior of daughterboard 362 to another predetermined depth of an interior of daughterboard 362. In one implementation, backdrilled vias may interconnect one or more thermal layers 490.
Thermal vias 480A and 480B may include plated through-holes. The plating may be disposed on all or any portion of the circumference of the through-holes. The plating may be any one or more materials having any thermal conductivity. The plating may occupy any portion of the volume of the through-holes. The plating may form a hollow cylinder having an outer diameter and an inner diameter. In one implementation, the inner diameter of the plating may be filled or partially filled with a second material, for example, a soldering material. Any of thermal vias 480A and 480B may vary one from another in any of the above respects.
Thermal planes 490 may include any of one or more materials having any thermal conductivity. In one implementation, thermal planes 490 may include a thermal conductive layer on all or any portion of a surface of daughterboard 362. Thermal planes 490 may have a substantially constant cross-section. Thermal planes 490 may alternatively have a varying cross-section along a length thereof. Any of thermal planes 490 may vary one from another in any of these respects. In one implementation, for example, an inner-most thermal plane 490 may have the largest effective cross-sectional area relative to other thermal planes 490. In another implementation, a thermal plane 490 that is the greatest distance from interface module cages 364 may have the largest effective cross-sectional area relative to other thermal planes 490.
Daughterboard 362 may be formed according to any standard technique for forming a PCB. For example, a layer of copper may be affixed to a layer of an insulating substrate. Patterns may be etched in the copper layer. Additional copper/insulating layers may be laminated to the substrate with etched patterns. In one implementation, a four-ounce copper is used for the copper layers. Other thicknesses of copper may be used. The thickness of the copper may be thicker by any factor than a copper layer thickness (e.g., 1⁄2 oz.) used for electrical connections. Through-holes may be drilled, backdrilled, or otherwise formed in the copper/insulator layers. The through-holes may be plated by electrolytic plating or any other suitable technique. In one implementation, a soldering material is then flowed in the plated through-holes.
The dimensions and geometries of thermal vias 480A and 480B and/or thermal planes 490 may be based on factors such as structural integrity, electrical connectivity, and optimal thermal conductivity. For example, thermal vias 480A and 480B and thermal planes 490 may be electrically insulated from electrical connections (not shown) in daughterboard 362. As another example, thermal vias 480A and 480B and/or thermal planes 490 may be formed based on heat generation and/or thermal sensitivity of particular interface modules 366, as described in more detail below.
Exemplary Thermal Management
FIG. 6 is a flowchart of exemplary thermal management 600 in a device, such as device 100, according to an implementation consistent with principles of the invention. Thermal management 600 may begin with generation of heat from interface module 366, such as an active transceiver, during operations performed by device 100 (act, 610). At least a portion of the generated heat may be conducted to an interface module cage 364, in which interface module 366 is plugged (act 620). At least a portion of the heat absorbed by interface module cage 364 may be conducted to thermal vias 480A having a terminal end in an area directly under or near a mounting surface of interface module cage 364 (act 630). In one implementation, one or more thermal vias 480A may directly contact interface module cage 364. At least a portion of the heat conducted to the one or more thermal vias 480A may be conducted to one or more thermal planes 490 (act 640). At least a portion of the heat conducted by the one or more thermal planes 490 may be conducted to thermal vias 480B (act 650). At least a portion of the heat conducted to thermal vias 480B may be conducted to heat sink 368, an attachment portion thereof which may be directly over or near a terminal end of thermal vias 480B (act 660). At least a portion of the heat absorbed by heat sink 368 may be dissipated into available airflow in device 100 (act 670).
It will be appreciated that thermal management 600 may instead be initiated by interface module 366, such as an inactive transceiver, which acts as a secondary heat source, having absorbed heat from a primary source that has generated the heat (e.g., an active transceiver or other component).
In one implementation, the heat path described above may be specific to an associated individual interface module cage 364 in interface unit 360. That is, the effective heat conductivity of an associated heat path may be managed for any given interface module cage 364. The effective heat conductivity of an associated heat path may be based on such factors as the location of the individual interface module cage 364 in interface unit 360, the performance level (i.e., heat generation) of interface module 366 associated with the individual interface module cage 364, the heat sensitivity of interface module 366 associated with the individual interface module cage 364, and thermal gradients experienced over interface unit 360, generally. In this manner, the heat transfer rate (i.e., cooling effect) may be managed from one interface module 366 to another.
Optimizing thermal transfer among interface modules 366, or varying the effective thermal conductivity associated with particular heat paths, may be achieved through the geometries of and interconnection formed by thermal vias 480A and 480B and thermal planes 490. For example, thermal vias 480A may have effective thermal conductivities that differ one from another; thermal planes 490 may have effective thermal conductivities that differ one from another; and/or thermal vias 480B may have effective thermal conductivities that differ one from another. Sets of thermal vias 480A associated with particular areas of daughterboard 362 may differ one from another.
CONCLUSION
Implementations consistent with the principles of the invention make possible efficient heat management in a device employing PCBs having clustered components, including an interface device, a memory, a processor, and other types of devices. For example, heat transfer may be optimized for any given input/output module through interconnected vias and thermal planes in a substrate of an interface unit of an interface card, thereby controlling the temperature of the input/output module.
The foregoing description of exemplary embodiments of the invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention.
For example, implementations consistent with the principles of the invention can be implemented using assemblies and parts other than those illustrated in the figures and described in the specification without departing from the spirit of the invention. Parts may be added and/or removed from device 100, interface unit 360, and/or daughterboard 362 depending on specific deployments and/or applications. Further, disclosed implementations may not be limited to any specific combination of components.
No element, act, or instruction used in the description of the invention should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Where only one item is intended, the term “one” or similar language is used. Further, the phrase “based on,” as used herein is intended to mean “based, at least in part, on” unless explicitly stated otherwise.
The scope of the invention is defined by the claims and their equivalents.

## Claims

1. A device comprising:
a substrate including:
a first mounting area on a first surface of the substrate;
a plurality of first thermal vias extending from the first mounting area to at least an interior of the substrate;
at least one thermal plane disposed in the interior of the substrate and being substantially parallel to the first surface of the substrate, the at least one thermal plane being in thermal contact with at least one of the first thermal vias, where the at least one thermal plane is exposed at one surface edge of the substrate and is not exposed at another surface edge of the substrate;
a heat sink attachment area; and
a plurality of second thermal vias extending from the heat sink attachment area to the interior of the substrate, the at least one thermal plane being in thermal contact with the second thermal vias.

2. The device of claim 1, the substrate further comprising:
a second mounting area located on a second surface of the substrate opposing the first surface of the substrate, at least one of the first thermal vias extending from the first mounting area to the second mounting area.

3. The device of claim 1, where the at least one thermal plane thermally connects to at least a portion of the first mounting area and at least a portion of the heat sink attachment area.

4. The device of claim 3, where at least one of the first thermal vias has a thermal conductivity that differs from a thermal conductivity of another one of the first thermal vias.

5. The device of claim 1, where the at least one thermal plane comprises two or more thermal planes, a first of the two or more thermal planes having a first cross-sectional area and a second of the two or more thermal planes having a second cross-sectional area, where the first cross-sectional area differs from the second cross-sectional area.

6. The device of claim 5, the first cross-sectional area being based on a distance of the first of the two or more thermal planes from the first mounting area, and the second cross-sectional area being based on a distance of the second of the two or more thermal planes from the first mounting area.

7. The device of claim 1, where the first thermal vias comprise a non-uniform configuration in the first mounting area.

8. The device of claim 1, where a number of the first thermal vias per unit area of the first mounting area is based on a predetermined location on the first surface of the substrate.

9. The device of claim 1, further comprising:
a component mount mounted to the substrate at the first mounting surface area, where at least one of the first thermal vias thermally contacts the component mount.

10. The device of claim 1, further comprising:
a heat sink mounted to the substrate at the heat sink attachment area; and
a thermal interface material interposed between a mounting surface of the heat sink and the heat sink attachment area, where the thermal interface material is in thermal contact with the second thermal vias.

11. The device of claim 1, where the at least one thermal plane comprises two or more thermal planes, one or more layers of the substrate being interposed between the two or more thermal planes.

12. The device of claim 11, where a first of the two or more thermal planes and a second of the two or more thermal planes are in thermal contact with a same group of the first thermal vias.

13. The device of claim 11, where a first of the two or more thermal planes thermally contacts at least some of the first thermal vias that do not thermally contact a second of the two or more thermal planes.

14. A substrate comprising:
a first area, on a first surface of the substrate, to which to mount a first component;
a plurality of first thermal vias extending from the first area to at least an interior of the substrate;
a number of thermal planes disposed in the interior of the substrate and being substantially parallel to the first surface of the substrate and thermally contacting at least one of the first thermal vias, where a first one of the number of thermal planes is exposed only at a surface edge of the substrate and a second one of the number of thermal planes is not exposed at the surface edge of the substrate;
a second area to which to attach a second component, where the first and second areas differ; and
a plurality of second thermal vias extending from the second area to the interior of the substrate and thermally contacting at least one of the number of thermal planes.

15. The substrate of claim 14, the substrate further comprising:
a third area, on a second surface of the substrate that opposes the first surface of the substrate, at least one of the first thermal vias extending from the first area to the third area.

16. The device of claim 14, where the at least one thermal plane thermally connects at least a portion of the first area to at least a portion of the second area.

17. The substrate of claim 14, where at least one of the first thermal vias has a thermal conductivity that differs from a thermal conductivity of another one of the first thermal vias.

18. The substrate of claim 14, where the at least one thermal plane comprises a plurality of thermal planes, a first of the plurality of thermal planes having a first cross-sectional area and a second of the plurality of thermal planes having a different, second cross-sectional area.

19. The substrate of claim 18, the first cross-sectional area being determined based on a distance of the first of the plurality of thermal planes from the first area, and the second cross-sectional area being determined based on a distance of the second of the plurality of thermal planes from the first area.

20. The substrate of claim 14, where the first thermal vias comprise a non-uniform configuration in the first area.

21. The substrate of claim 14, where a number of the first thermal vias per unit area of the first area corresponds to a predetermined location on the first surface of the substrate.

22. The substrate of claim 14, further comprising:
a component mounted to the substrate at the first area, where at least one of the first thermal vias thermally contacts the component.

23. The substrate of claim 14, further comprising:
a heat sink mounted to the substrate at the first area; and
a thermal interface material interposed between a mounting surface of the heat sink and the first area, where the thermal interface material thermally contacts the second thermal vias.

24. The substrate of claim 14, where one or more layers of the substrate are interposed between adjacent ones of the number of thermal planes.

25. The substrate of claim 24, where a first one of the adjacent thermal planes and a second one of the adjacent thermal planes thermally contact a same group of the first thermal vias.

26. The substrate of claim 24, where a first one of the adjacent thermal planes thermally contacts at least some of the first thermal vias that do not thermally contact a second one of the adjacent thermal planes.

27. The substrate of claim 24, where the first one of the number of thermal planes is exposed at least one other surface edge of the substrate.