Integrated heat sink and air plenum for a heat-generating integrated circuit

An electronic device includes an integrated circuit and a heat exchanger. The heat exchanger includes a heat pipe and a first plurality of cooling fins and a second plurality of cooling fins. The heat pipe is thermally coupled to the integrated circuit and has an evaporator portion and a condenser portion, where the condenser portion extends away from the evaporator portion. The first plurality of cooling fins are attached to the condenser portion and proximate to the evaporation portion and form a plenum having a first associated pressure drop when a cooling fluid flows across the first plurality of cooling fins at a first velocity. The second plurality of cooling fins are attached to the condenser portion and distal from the evaporation portion and form a flow path having a second associated pressure drop when the cooling fluid flows across the second plurality of cooling fins at the first velocity.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present invention relate generally to computer systems and, more specifically, to an integrated heat sink and air plenum for a heat-generating integrated circuit.

Description of the Related Art

In modern computing devices, central processing units (CPUs), graphics processing units (GPUs), and other integrated circuits (ICs) generate significant quantities of heat during use. This heat needs to be removed for the proper operation of the integrated circuit and computing device. For example, a single high-power chip, such as a CPU or GPU, can generate hundreds of watts of heat during operation, and, if this heat is not efficiently removed, the temperature of the chip can increase to a point at which the chip is at risk of being damaged. To prevent thermal damage during operation, many system implement clock-speed throttling when the operating temperature of the processor exceeds a certain threshold. Thus, in these systems, the processing speed of the high-power chip is constrained by both the chip design and how effectively heat is removed from the chip.

To reduce the impact that thermal constraints have on high-power chip performance, heat exchangers can be employed that allow high-power chips to operate at greater processing speeds and generate greater amounts of heat. As is well-understood, a heat exchanger transfers heat from a chip to ambient air, and the air then carries the heat away from the chip. Heat exchangers can include passive devices, such as heat sinks, or more complex heat-transfer devices, such as heat pipes. Heat sinks generally include an array of fins that increases the effective surface area of the chip exposed to ambient air, while heat pipes rely on phase transition (e.g., evaporation of a liquid) to efficiently transfer heat between two solid interfaces. In some instances, heat pipes are used in conjunction with heat sinks to increase the amount of heat that can be removed from a high-power chip.

Despite the use of heat exchangers and other thermal solutions, as the processing power of CPUs and GPUs and other integrated circuits continues to increase, the processing speeds of such high-power chip continue to be constrained by the rate at which heat can be removed from those chips. Furthermore, many modern chip-package architectures add thermal resistance between the high-power chip and the associated heat exchanger. For example, some chip-package architectures now include structures between the high-power chip and the heat exchanger, such as a protective lid or additional heat-generating chips stacked on the heat-generating chip. These intervening thermal resistances reduce the effectiveness of the heat exchanger.

As the foregoing illustrates, what is needed in the art are more effective techniques for removing heat from integrated circuits during operation.

SUMMARY

One embodiment of the present invention sets forth an electronic device that includes an integrated circuit (IC) and a heat exchanger. The heat exchanger includes at least one heat pipe and a first plurality of cooling fins and a second plurality of cooling fins. The at least one heat pipe is thermally coupled to the IC and has an evaporator portion and a condenser portion, where the condenser portion extends away from the evaporator portion. The first plurality of cooling fins are attached to the condenser portion and proximate to the evaporation portion and form a plenum having a first associated pressure drop when a cooling fluid flows across the first plurality of cooling fins at a first velocity. The second plurality of cooling fins are attached to the condenser portion and distal from the evaporation portion and form a flow path having a second associated pressure drop when the cooling fluid flows across the second plurality of cooling fins at the first velocity.

At least one technological advantage of the disclosed heat exchanger design relative to the prior art is that heat generated by an IC can be more efficiently removed from the IC, thereby enabling the IC to operate at higher processing speeds without overheating. A further advantage is that pressure drop across the disclosed heat exchanger is typically less than the pressure drop across conventional heat exchangers, which reduces fan power consumption and fan noise relative to conventional heat exchanger designs. These technological advantages provide one or more technological advancements over prior art approaches.

DETAILED DESCRIPTION

Heat Exchanger Description

FIG.1Ais a perspective view of a heat exchanger100according to various embodiments of the present invention.FIG.1Bis a side view of heat exchanger100, according to various embodiments of the present invention. Heat exchanger100is a heat exchanger for an integrated circuit (IC)101and includes an integrated heat sink120and a low pressure-drop air plenum130. Together, heat exchanger100and IC101form an electronic device that can be mounted on a printed circuit board (PCB)104. In the embodiments, heat sink120includes one or more heat pipes140thermally coupled to IC101and a plurality of cooling fins121attached to heat pipes140.

In some embodiments, IC101includes a single microchip, such as a graphics processing unit (GPU) or central-processing unit (CPU). Alternatively, in some embodiments IC101includes multiple microchips, such as a processor die101A and one or more stacks101B of memory dies that are all mounted on a common packaging substrate101C. In such embodiments, packaging substrate101C can be configured for mounting IC101onto PCB104, for example via solder balls (not shown). In addition, in such embodiments, IC101may include a package lid101D, which protects processor die101A and the one or more stacks101B of memory dies from physical damage, but also increases thermal resistance associated with the packaging of IC101. Further, in some multi-microchip embodiments, IC101can include other configurations of chips, such as a system-on-chip (SoC) configuration.

Heat pipes140are sealed vessels, such as copper tubes, that include an evaporative working fluid (not shown), such as water or alcohol. One embodiment of heat pipes140is illustrated inFIG.2.FIG.2is a perspective view of an array of multiple heat pipes140, according to various embodiments of the present invention. Heat pipes140efficiently transfer heat, through a combination of evaporation and condensation, from IC101to cooling fins121(not shown for clarity) and on to cooling air that passes over cooling fins121. More specifically, in heat pipes140, evaporation of the working fluid into a vapor takes place in an evaporator portion241of each heat pipe140, while condensation of the working fluid takes place in one or more condenser portions242. Each evaporator portion241is coupled to a surface from which thermal energy is to be removed, and each condenser portion242extends away from the surface from which the thermal energy is to be removed. In the embodiment illustrated inFIG.2, each heat pipe140includes two condenser portions242, but in other embodiments, each heat pipe140can include more than or fewer than two condenser portions242. Condensed working fluid from condenser portions242flows to a corresponding evaporator portion241, where thermal energy from IC101is absorbed and the working fluid vaporizes. The vapor then moves to condenser portions242and condenses in the condenser portion242, releasing latent heat. In some embodiments, each heat pipe140also includes a wicking structure or material (not shown) on some or all inner surfaces, to facilitate the return of condensed cooling liquid to the evaporator portion241of the heat pipe140.

Returning toFIGS.1A and1B, in the embodiment illustrated, heat pipes140are mounted on a metallic plate150, such as a copper or aluminum plate, that is thermally coupled to IC101. In such embodiments, metallic plate150can be thermally coupled to a major surface101E of IC101via a thermal interface material (TIM)151, for example a highly thermally conductive paste. Metallic plate150spreads heat over a surface area that is greater than that of IC101. As a result, a larger number of heat pipes140can be thermally coupled to IC101on metallic plate150than when directly attached to IC101. In some embodiments, a high density of heat pipes140is mounted on metallic plate150in a high-density heat-pipe area152and a low density of heat pipes140is mounted to metallic plate150in a low-density heat-pipe area153. Thus, in such embodiments, a portion of metallic plate150that is closest to IC101, and therefore is at the highest temperature during operation of IC101, has a higher density of heat pipes140coupled thereto. By contrast, lower-temperature portions of metallic plate150, such as low-density heat-pipe area153, has a lower density of heat pipes140coupled thereto.

Cooling fins121can be any material that conducts heat efficiently, such as copper or aluminum. Cooing fins121are attached along condenser portions242of heat pipes140, and are oriented to allow cooling air to flow in an airflow direction103between cooling fins121and past condenser portions242. As shown, cooling fins121form one or more low pressure-drop plenums130and a high-pressure-drop path102. The one or more low pressure-drop plenums130form a path for cooling air flowing proximate to evaporator portions241and high-pressure-drop path102is for cooling air flowing distal to evaporator portions241of heat pipes140. Low pressure-drop plenum130causes higher velocity, lower temperature cooling air to flow over portions of condenser portions242that are closer to IC101, while high-pressure-drop path102causes lower velocity, higher temperature cooling air to flow over portions of condenser portions242that are distal to IC101. Thus, portions of heat pipes140closest to IC101, which are most able to affect the temperature of IC101, are exposed to the higher velocity, lower temperature cooling air. For example, lower portions143of heat pipes140disposed in high-density heat-pipe area152are exposed to such higher velocity, lower temperature cooling air, as illustrated by a velocity profile190included inFIG.1A.

Velocity profile190graphically illustrates the velocity of cooling air (or other cooling fluid) passing through cooling fins121as a function of height h above metallic plate150. The higher pressure drop generated by cooling air flowing through cooling fins121via high-pressure-drop path102causes the cooling air to flow through cooling fins121at a lower velocity than via low pressure-drop air plenum130. That is, when cooling air flows through cooling fins121, the reduced length of cooling fins121in a low pressure-drop region125corresponding to low pressure-drop air plenum130results in less pressure drop being generated at a specific velocity than in an adjacent high-pressure drop region126(corresponding to high-pressure-drop path102) at the specific velocity. Consequently, the velocity of the cooling air flowing in low pressure-drop region125is significantly higher than in high-pressure drop region126. As a result of the higher velocity cooling air flowing across the lower portions of heat pipes140within low pressure-drop region125, the highest temperature portions of heat pipes140are able to transfer more heat to the cooling air, and heat sink120can more effectively transport heat away from IC101than conventional heat sinks.

In addition, the cooling air flowing through low pressure-drop air plenum130and across the lower portions of heat pipes140(within low pressure-drop region125) is not pre-heated by passing along cooling fins121in low-density heat-pipe area153. Instead, there are few or no cooling fins121in low-density heat-pipe area153proximate lower portions143of heat pipes140in high-density heat-pipe area152. Therefore, little or no heat is transferred to cooling air prior to flowing across lower portions143. As a result of the cooling air flowing across lower portions143not being pre-heated by passing along cooling fins121, more heat can be transferred from the highest temperature portions of heat pipes140(i.e., lower portions143) to the cooling air, and heat sink120can more effectively transport heat away from IC101than conventional heat sinks.

According to various embodiments, low pressure-drop air plenum130is formed by the termination of a portion of cooling fins121prior to an edge region123or edge region124of heat sink120. Thus, the portion of cooling fins121that terminate prior to edge region123and/or124have a shorter length in airflow direction103than cooling fins that form high-pressure-drop path102and extend from edge region123to edge region124. For example, in some embodiments, some or all of the cooling fins121in the portion of cooling fins121forming low pressure-drop air plenum130terminate at an interface region between high-density heat-pipe area152and low-density heat-pipe area153. In some embodiments, each of the cooling fins121forming low pressure-drop air plenum130terminate at different lengths that correspond to a termination profile155. In the embodiment illustrated inFIGS.1A and1B, termination profile155is depicted as a parabolic function for the length of certain cooling fins121. In other embodiments, termination profile155can be a linear function for the length of certain cooling fins121that is at or near a minimum for cooling fins121closest to IC chip101. In other embodiments, termination profile155can be a step function; that is, in such embodiments, the cooling fins121forming low pressure-drop air plenum130have the same (shorter) length and the cooling fins121forming high-pressure-drop path102have the same (longer) length and terminate at edge region123and/or edge region124of heat sink120. In yet other embodiments, any other suitable termination profile155can be employed to cause higher velocity cooling air to flow through low pressure-drop air plenum130and lower velocity cooling air to flow through high-pressure-drop path102.

In the embodiment illustrated inFIGS.1A and1B, low pressure-drop air plenum130includes a termination profile155at edge region123and edge region124. In other embodiments, low pressure-drop air plenum130is formed at either edge region123or edge region124.

Base Plate Cooling Fins

In some embodiments, condenser portions242of heat pipes140include one or more straight segments that extend away from IC101and metallic plate150. In such embodiments, condenser portions242may also include one or more curved segments that connect the straight segments of condenser portions242with corresponding evaporator portions241. In such embodiments, attachment of cooling fins121to heat pipes140along such curved portions is generally impracticable. As a result, heat sink120can include an airflow region109that is free of cooling fins121and is disposed between metallic plate150and low pressure-drop air plenum130. As shown, airflow region109encompasses the curved portions of heat pipes140that connect the straight segments of condenser portions242with corresponding evaporator portions241.

According to some embodiments, one or more sets of plate-mounted cooling fins are attached to metallic plate150and extend away from metallic plate150and into airflow region109. Such plate-mounted cooling fins effectively add more surface area to metallic plate150, further increasing how effectively heat sink120can transport thermal energy away from IC101.FIG.3is an end view of heat sink120, IC101, and plate-mounted cooling fins356, according to various embodiments of the present invention. The view illustrated inFIG.3is looking in airflow direction103. As shown, plate-mounted cooling fins356extend from metallic plate150into airflow region109. Thus, in such an embodiment, in addition to low pressure-drop region125and high-pressure drop region126, cooling fins are also present in airflow region109. As a result, the heat removal efficiency of heat sink120is increased. In some embodiments, plate-mounted cooling fins356are attached to a mounting plate357that is in turn coupled, soldered, or otherwise attached to metallic plate150.

Alternatively or additionally, in some embodiments, cooling fins extending into airflow region109are mounted on or otherwise thermally coupled to a surface of one or more of heat pipes140. One such embodiment is illustrated inFIG.4.FIG.4is an end view of heat sink120, IC101, and heat pipe-mounted cooling fins456, according to various embodiments of the present invention. The view illustrated inFIG.4is looking in airflow direction103. As shown, heat pipe-mounted cooling fins456(cross-hatched for clarity) extend into airflow region109and transfer heat from a surface441(dashed line) of one or more of heat pipes140, thereby extending heat exchanging surfaces into airflow region109. In some embodiments, heat pipe-mounted cooling fins456are attached to a mounting plate457that is in turn coupled, soldered, or otherwise attached to surface441or surface441and metallic plate150. Heat pipe-mounted cooling fins456can be disposed in portions of airflow region109into which plate-mounted cooling fins356cannot be positioned easily, as illustrated inFIG.5.

FIG.5is a perspective view of a heat sink520that includes heat pipes140, plate-mounted cooling fins356, and heat pipe-mounted cooling fins456, according to various embodiments of the present invention. InFIG.5, cooling fins121are omitted for clarity. As shown, heat pipe-mounted cooling fins456can be positioned between the two condenser portions242of each heat pipe140, thereby increasing the heat removal efficiency of heat sink520.

Base Plate Heat Pipes

In some embodiments, a heat sink can include a set of one or more heat pipes configured to transport thermal energy outward along a metallic plate coupled to an IC. As a result, portions of the metallic plate that are distal to the IC are increased in temperature, further enhancing the heat removal efficiency of the heat sink. One such embodiment is illustrated inFIGS.6A and6B.

FIG.6Ais a schematic end view of a heat sink620, according to a various embodiments of the present invention. The view of heat sink620inFIG.6Ais taken in airflow direction103, i.e., airflow direction103is into the page.FIG.6Bis a schematic side view of heat sink620, according to a various embodiments of the present invention. In the embodiment illustrated inFIGS.6A and6B, heat sink620includes heat pipes640for transporting thermal energy away from IC101and across a base plate650of heat sink620.FIG.6Balso shows low pressure-drop plenum130, heat pipes140, and plate-mounted cooling fins356. Heat pipes640are formed within and/or on a surface of metallic plate650, and increase the heat removal effectiveness heat pipes140that are coupled to metallic plate650in low-density heat-pipe area153. Specifically, heat pipes640increase the heat removal effectiveness of such heat pipes140by increasing the temperature of the portions of metallic plate650in low-density heat-pipe area153with thermal energy transferred from IC101.

In some embodiments, heat pipes that transport thermal energy away from an integrated circuit across a base plate of the heat sink are coupled to a surface of the base plate. One such embodiment is illustrated inFIGS.7,8, and9.

FIG.7is a perspective view of a first array710of heat pipes720coupled to a surface of a base plate750and a second array730of heat pipes740coupled to the heat pipes720of first array710, according to various embodiments of the present invention. For clarity, cooling fins121, which are typically coupled to heat pipes740, are omitted inFIG.7. Heat pipes720of first array710transport thermal energy away from an integrated circuit (not shown inFIG.7) and to the heat pipes720of first array710. To that end, some or all of heat pipes720are thermally and mechanically coupled to an evaporator portion741of each heat pipe740of second array730. As a result, heat transported away from base plate by heat pipes720heats evaporator portions741of heat pipes740.

Heat pipes740can be coupled to heat pipes720via soldering or any other technically feasible technique. In some embodiments, in addition to solder between heat pipes740and heat pipes720for mechanically and thermally coupling heat pipes740to heat pipes720, a solder fill material (not shown) can be employed to fill air gaps between heat pipes720, air gaps between heat pipes740, and air gaps between first array710and second array730. In such embodiments, first array710and second array730are more robustly couple together and heat transfer therebetween is enhanced.

FIG.8is a perspective view of first array710of heat pipes720coupled to base plate750, according to various embodiments of the present invention. For clarity, second array730is omitted inFIG.8. As shown, each of heat pipes720of first array710is coupled to a surface of base plate750. In some embodiments, heat pipes720are coupled to the surface of base plate750via a soldering process. In such embodiments, additional solder material (not shown) can be employed to fill air gaps between heat pipes720and base plate750, thereby enhancing thermal transport from base plate750and heat pipes720. In other embodiments, any other technically feasible technique can be employed to mechanically and thermally couple heat pipes720to base plate750.

FIG.9is a bottom perspective view of first array710of heat pipes720, according to various embodiments of the present invention. As shown, base plate750is coupled to heat pipes720, forming an assembly901. When first array710and base plate750are included in a heat sink, such as heat sink120ofFIGS.1A and1B, a surface902of base plate750is configured to be thermally coupled to an IC (not shown), for example IC101inFIGS.1A and1B. Thus, assembly901is configured to transmit heat generated by the IC through base plate750and into heat pipes720.

In the embodiment illustrated inFIGS.7,8, and9, base plate750is configured to be coupled to a middle portion of each of heat pipes720, rather than along most or all of the length of each heat pipe720. In such embodiments, assembly901can be further configured to mate with a larger base plate that includes a suitably configured opening for base plate750. An embodiment of one such larger base plate is illustrated inFIG.10.

FIG.10is a perspective view of a base plate1050configured to mate with a smaller base plate to which heat pipes are coupled, according to various embodiments of the present invention. As shown, base plate1050includes an opening1051that is configured to substantially match the shape of a smaller base plate (e.g., base plate750inFIGS.7,8, and9) to which heat pipes720are coupled. In addition, in some embodiments, base plate1050includes walls1052, which extend away from a central surface1053and are configured to accommodate heat pipes720when assembly901is coupled to base plate1050. In some embodiments, walls1052are configured to at least partially encircle heat pipes720when assembly901is coupled to base plate1050. Thus, in some embodiments, heat pipes720can first be coupled to base plate750to form assembly901ofFIG.9, then assembly901can be coupled to base plate1050by inserting base plate750into opening1051. Assembly901and base plate1050can then be mechanically and thermally coupled to each other, for example via a soldering process. In such embodiments, additional solder material can be employed to fill air gaps between heat pipes720and walls1052and/or air gaps between heat pipes720and central surface1053.

In some embodiments, walls1052of base plate1050include one or more notches1054or other mechanical features configured to accommodate a mounting plate for plate-mounted cooling fins. For example, when plate-mounted cooling fins356ofFIG.3are attached to mounting plate357, notches1054can be configured to accommodate a suitably configured tab or other feature of mounting plate357.

An embodiment of a heat sink that includes features of the above-described embodiments is illustrated is illustrated inFIG.11.FIG.11is a perspective view of a heat exchanger1100, according to other various embodiments of the present invention. As shown, heat exchanger1100includes base plate1050with notches1054for accommodating plate-mounted cooling fins356. Heat exchanger1100further includes heat pipe-mounted cooling fins456and heat pipes140mounted on and coupled to an array of heat pipes720. Heat pipes720are coupled to base plate750, which is inserted into an opening (not shown) of base plate1050.

Multiple IC Configuration

In some embodiments, multiple ICs may be mounted on a single PCB. In such embodiments, multiple heat exchangers can also be mounted on the single PCB. One such embodiment is illustrated inFIG.12.FIG.12is a schematic side view of an electronic device1201that includes multiple heat exchangers1211and1212and multiple ICs101, all mounted on a single PCB1202, according to various embodiments of the present invention. In some embodiments, heat exchangers1211and1212are positioned on PCB1201so that cooling air (or any other cooling fluid) may flow sequentially through a first heat exchanger of an electronic device (for example heat exchanger1211and a second heat exchanger of the electronic device (for example heat exchanger1212). That is, heat exchangers1211and1212are positioned on PCB1201so that cooling air can flow through the first heat exchanger and then flow through the second heat exchanger. For example, as shown inFIG.12, cooling fins coupled to the heat pipes of heat exchanger1211are oriented parallel to the cooling fins coupled to the heat pipes of heat exchanger1212. Thus, sequential flow of a cooling fluid through heat exchangers1211and1212is facilitated.

Computing Device

In some embodiments, electronic device1201, which includes multiple ICs and heat exchangers, is included in a larger computing device. One such embodiment is illustrated inFIG.13.

FIG.13is a schematic view of a computing device1300that includes one or more electronic devices1201, according to an embodiment of the invention. Computing device1300can be configured for use in high-performance applications, such as in a data center. As such, computing device1300includes a plurality of electronic devices1201. In the embodiment illustrated inFIG.13, computing device includes multiple trays1310of electronic devices1201. In addition, computing device1300includes, in some embodiments, a fan box1301with a plurality of fans configured to force cooling air across the heat exchangers included in electronic devices1201. In some embodiments, computing device1300further includes additional ICs, PCBs, and other electronic components1302that are cooled by the air forced across the heat exchangers included in electronic devices1201. While the heat transfer efficiency of the heat exchangers included in electronic devices1201is superior to that of conventional heat exchangers, it is noted that the low pressure-drop air plenums130included in the heat exchangers of electronic devices1201generally have similar or even less pressure drop than conventional heat exchangers.

Alternative Plenum Configuration in Heat Exchanger

In embodiments described above, cooling fins of a heat exchanger are configured to form one or more low pressure-drop plenums that cause higher velocity, lower temperature cooling air to flow over heat pipe condenser portions that are proximate to an IC. Concurrently, a high-pressure-drop path through the cooling fins of the heat exchanger causes lower velocity, higher temperature cooling air to flow over portions of heat pipe condenser portions that are distal to the IC. In some alternative embodiments, the one or more low pressure-drop plenums are formed by a group of the cooling fins having a larger fin pitch than one or more other groups of the cooling fins. One such embodiment is illustrated inFIGS.14and15.

FIG.14is a perspective view of a heat exchanger1400according to various embodiments of the present invention.FIG.15is a side view of heat exchanger1400, according to various embodiments of the present invention. Heat exchanger1400is a heat exchanger for IC101and includes an integrated heat sink1420with a low pressure-drop air plenum1430.

Heat exchanger1400is similar to heat exchanger100inFIG.1, with the exception that low pressure-drop air plenum1430is formed by a first group1525of cooling fins121having a larger fin pitch1501than one or more other groups of the cooling fins, such as second group1526of cooling fins121. As shown, second group1525is configured with cooling fins121that have a fin pitch1502that is significantly less than fin pitch1501. As a result, higher pressure drop is generated by cooling air flowing at a specific velocity through second group1526than by cooling air flowing at the same velocity through first group1525. Consequently, in operation, the velocity of the cooling air flowing through a low pressure-drop region formed by low pressure-drop air plenum1430is significantly higher than in the high-pressure drop region formed by second group1526. In addition, first group1525is disposed proximate to IC101while second group1526is disposed distal to IC101. As a result of the higher velocity cooling air flowing across the lower portions of heat pipes140within low pressure-drop air plenum1430, the highest temperature portions of heat pipes140are able to transfer more heat to the cooling air, and heat sink1420can more effectively transport heat away from IC101than conventional heat sinks.

In the embodiment illustrated inFIGS.14and15, each cooling fin121in first group1525and in second group1526has a fin length1527. In other embodiments, cooling fins121in first group1525have a different fin length than cooling fins121in second group1526. On such embodiment is illustrated inFIG.16.

FIG.16is a side view of a heat exchanger1600, according to various embodiments of the present invention. Heat exchanger1600is a heat exchanger for IC101and includes an integrated heat sink1620with a low pressure-drop air plenum1630. Heat exchanger1600is similar to heat exchanger1400inFIGS.14and15, with the exception that low pressure-drop air plenum1630is formed by a first group1625of cooling fins121having a larger fin pitch1601and shorter length1627than one or more other groups of the cooling fins, such as second group1626. As shown, second group1625is configured with cooling fins121that have a fin pitch1602that is significantly less than fin pitch1601and a fin length1628that is significantly greater than length1627. As a result, higher pressure drop is generated by cooling air flowing at a specific velocity through second group1625than by cooling air flowing at the same velocity through first group1626.

In some embodiments, multiple groups of cooling fins121in a heat exchanger have fin lengths that correspond to a termination profile. That is, a first group of cooling fins121in the heat exchanger have fin lengths that correspond to a first termination profile and a second group of cooling fins121in the heat exchanger have fin lengths that correspond to a second termination profile. One such embodiment is illustrated inFIG.17.

FIG.17is a side view of a heat exchanger1700, according to various embodiments of the present invention. Heat exchanger1700is a heat exchanger for IC101and includes an integrated heat sink1720with a low pressure-drop air plenum1730. Heat exchanger1700is similar to heat exchanger1400inFIGS.14and15, with the exception that heat exchanger1700includes two or more groups of cooling fins121, where the cooling fins121of each group have respective lengths that correspond to a particular termination profile. Thus, in the embodiment illustrated inFIG.17, heat exchanger1700includes a first group1725of cooling fins121that have respective lengths corresponding to a first termination profile1701and a second group1726of cooling fins121that have respective lengths corresponding to a second termination profile1702. In such embodiments, the configuration of multiple groups of cooling fins121that each form a termination profile enables further tuning of the pressure drop and/or cooling fluid velocity associated with each group of fins. That is, a flow rate of a cooling fluid through first group1725can be selected relative to a flow rate of the cooling fluid though second group1726, for example by modifying the morphology of first termination profile1701and/or second termination profile1702.

In the embodiment illustrated inFIG.17, cooling fins121of first group1725are formed in first termination profile1701on leading edge region1723and on a trailing edge region1724of heat exchanger1700. In alternative embodiments, cooling fins121of first group1725are formed in first termination profile1701on either leading edge region1723or on trailing edge region1724of heat exchanger1700, but not on both. Alternatively or additionally, cooling fins121of second group1726are formed in second termination profile1702on either leading edge region1723or on trailing edge region1724of heat exchanger1700, but not on both.

In the embodiment illustrated inFIG.17, first termination profile1701of first group1725is substantially similar to second termination profile1702of second group1726. Alternatively or additionally, in some embodiments, first termination profile1701differs significantly from second termination profile1702of second group1726. Examples of such embodiments are illustrated inFIGS.18A-18C.

FIG.18Aschematically illustrates a side view of a heat exchanger1810, according to various embodiments of the present invention. InFIG.18A, heat exchanger1810includes a first portion1811of cooling fins (not shown individually for clarity) that are collectively configured to form a first termination profile1813. In addition, heat exchanger1810includes a second portion1812of cooling fins (not shown individually for clarity) that are collectively configured to form a second termination profile1814. As shown, first termination profile1813differs from second termination profile1814.

FIG.18Bschematically illustrates a side view of a heat exchanger1820, according to various embodiments of the present invention. InFIG.18B, heat exchanger1820includes a first portion1821of cooling fins (not shown individually for clarity) that are collectively configured to form a first termination profile1823and a second portion1822of cooling fins (not shown individually for clarity) that are collectively configured to form a second termination profile1824. As a consequence of the relative shapes of first termination profile1823and second termination profile1824, higher pressure drop across heat exchanger1820is generated by cooling air flowing at a specific velocity through second portion1822than by cooling air flowing at the same velocity through first portion1821. As a result, during operation more cooling air tends to flows through first portion1821and at a higher velocity than through second portion1822.

FIG.18Cschematically illustrates a side view of a heat exchanger1830, according to various embodiments of the present invention. InFIG.18C, heat exchanger1830includes a first portion1831of cooling fins (not shown individually for clarity) that are collectively configured to form a first termination profile1833. In addition, heat exchanger1830includes a second portion1832of cooling fins (not shown individually for clarity) that are collectively configured to form a second termination profile1834. As shown, first termination profile1833differs from second termination profile1834, which significantly affects the flow rate of cooling air though first portion1831relative to second portion1832.

Alternative Heat Pipe Configuration in Heat Exchanger

In embodiments described above, a first set of heat pipes is thermally coupled to an IC to distribute heat away from the IC, while a second set of heat pipes is thermally coupled to the first set of heat pipes and to a plurality of cooling fins. In such embodiments, each heat pipe in the second set of heat pipes includes an evaporator portion and at least one condenser portion that is perpendicular to the evaporator portion and is directly coupled to the plurality of cooling fins. In addition, each heat pipe in the first set of heat pipes includes an evaporator portion that is thermally coupled to the IC and perpendicular to the evaporator portions of the second set of heat pipes. In other embodiments, each heat pipe in the first set of heat pipes further includes at least one condenser portion that extends away from and is perpendicular to the evaporator portion of that heat pipe. In such embodiments, the condenser portion can also be directly coupled to the plurality of cooling fins. One such embodiment is illustrated inFIGS.19A-19D.

FIG.19Aschematically illustrates a perspective view of a heat exchanger1900with cooling fins and an auxiliary metallic plate omitted, according to various embodiments of the present invention. Heat exchanger1900includes a first set of heat pipes1950and a second set of heat pipes1940. Each heat pipe1950in the first set includes an evaporator portion1951and at least one condenser portion1952, and each heat pipe1940in the second set includes an evaporator portion1941and at least one condenser portion1942.

In some embodiments, in the first set of heat pipes1950, the evaporator portion1951of each heat pipe1950is thermally coupled to an IC-contacting metallic plate1970that is in turn coupled to an IC (not shown). For example, in some embodiments, IC-contacting metallic plate1970is coupled to the IC in the same way that metallic plate150inFIG.1is coupled to IC101. In such embodiments, evaporator portions1951may be embedded at least partially within IC-contacting metallic plate1970. One such embodiment is illustrated inFIG.20.

FIG.20schematically illustrates a cross-sectional view of evaporator portions1951and IC-contacting metallic plate1970, according to an embodiment of the present invention. Also shown are an IC2002coupled to a first surface1973of IC-contacting metallic plate1970, an evaporator portion1941of heat pipes1940coupled to a second surface that is opposite to the first surface, portions of a condenser portion1942of one heat pipes1940, and an array of plate-mounted cooling fins2056. In the embodiment illustrated inFIG.20, the array of plate-mounted cooling fins2056is coupled to one or more evaporator portions1941via an auxiliary metallic plate2057.

In the embodiment, multiple cavities2001are formed in IC-contacting metallic plate1970and are each configured to accommodate at least a portion of one evaporator portion1951as shown. In some embodiments, space or air gaps between evaporator portions1951and corresponding surfaces of cavities2001are filled with a material that facilitates heat transfer from IC-contacting metallic plate1970and evaporator portions1051, such as solder, thermal paste, and the like. In addition, in some embodiments, metallic plate1070further includes cover plate2070that facilitates coupling of evaporator portions1941of heat pipes1940onto IC-contacting metallic plate1970. In such embodiments, cover plate2070may be soldered in place over cavities2001and evaporator portions1951. Additionally or alternatively, in some embodiments, evaporator portions1941may be soldered in place onto cover plate2070to enhance heat transfer from IC-contacting metallic plate1970to evaporator portions1941.

Returning toFIG.19A, the at least one condenser portion1952of a particular heat pipe1950is perpendicular to the evaporator portion1951of that particular heat pipe1950. That is, the condenser portion1952of each heat pipe1950extends away from IC-contacting metallic plate1970(and IC2002, shown inFIG.20). Further, the at least one condenser portion1952of each heat pipe1950is directly coupled to cooling fins (not shown) of heat exchanger1900. For example, in some embodiments, the at least one condenser portion1952of each heat pipe1950is coupled to cooling fins in the same way that heat pipes140are coupled to cooling fins121inFIGS.1A and1B.

FIG.19Bschematically illustrates a perspective view of heat exchanger1900with cooling fins omitted and auxiliary metallic plate2057included, according to an embodiment of the present invention. As shown, auxiliary metallic plate2057is coupled to IC-contacting metallic plate1970and/or to evaporator portions1941of heat pipes1940. In some embodiments, auxiliary metallic plate2057facilitates coupling of plate-mounted cooling fins2056onto IC-contacting metallic plate1970and/or onto evaporator portions1941of heat pipes1940. One such embodiment is illustrated inFIG.19C.

FIG.19Cschematically illustrates a perspective view of heat exchanger1900with cooling fins omitted and auxiliary metallic plate2057, plate-mounted cooling fins2056, and a base plate1975shown, according to an embodiment of the present invention. Plate-mounted cooling fins2056are coupled to auxiliary metallic plate2057and are positioned proximate evaporator portions1941of heat pipes1940and IC-contacting metallic plate1970. It is noted that cooling fins oriented parallel to IC-contacting metallic plate1970can be difficult to install proximate IC-contacting metallic plate1970, due to the curved portions of evaporator portions1941and evaporator portions1951. Thus, plate-mounted cooling fins2056facilitate heat transfer from evaporator portions1941of heat pipes1940and from IC-contacting metallic plate1970to cooling air flowing through a region that does not include cooling fins oriented parallel to IC-contacting metallic plate1970.

As noted,FIG.19Calso shows an embodiment of a base plate1975that is configured to couple to IC-contacting metallic plate1970, according to some embodiments. As shown, base plate1975is substantially similar in configuration to base plate1050ofFIG.10. Thus, in some embodiments, base plate1975is configured to mate with IC-contacting metallic plate1970, to which heat pipes1941and1951are coupled. Base plate1975has a greater length1976and a greater width1977than IC-contacting metallic plate1970, and therefore facilitates conductive heat transfer away from an IC across a wider surface than IC-contacting metallic plate1970.

In some embodiments, condenser portions1952of heat pipes1950are disposed in a low-density heat-pipe area1953and condenser portions1942of heat pipes1940are disposed in a high-density heat-pipe area1954. In such embodiments, a portion of IC-contacting metallic plate1970, which is closest to IC2002and therefore is at the highest temperature during operation of IC2002, has a higher density of heat pipes1940coupled thereto. By contrast, lower-temperature portions of IC-contacting metallic plate1970, such as low-density heat-pipe area1953, has a lower density of heat pipes1940coupled thereto.

FIG.19Dschematically illustrates a perspective view of heat exchanger1900with cooling fins omitted and an IC-contacting surface1971of IC-contacting metallic plate1970shown, according to an embodiment of the present invention. In the embodiment illustrated inFIG.19D, evaporator portions1951of heat pipes1950are at least partially embedded or otherwise disposed within IC-contacting metallic plate1970. In addition, evaporator portions1941of heat pipes1940are coupled to a surface of IC-contacting metallic plate1970that is opposite to IC-contacting surface1971.

In sum, embodiments of the present invention provide a heat exchanger for an IC that includes an integrated heat sink and at least one low pressure-drop plenum formed by cooling fins of the integrated heat sink. The low pressure-drop plenum is disposed proximate the IC, and causes a cooling fluid moving flowing across the heat exchanger to have higher-velocity proximate the IC. As a result, the heat transport capability of the heat exchanger is increased. Thus, for a specific pressure drop of the cooling fluid across the heat exchanger, the plenum formed by the cooling fins enables greater heat removal from the IC.

At least one technological advantage of the disclosed heat exchanger design relative to the prior art is that heat generated by an IC can be more efficiently removed from the IC, thereby enabling the IC to operate at higher processing speeds without overheating. A further advantage is that pressure drop across the disclosed heat exchanger is typically less than the pressure drop across conventional heat exchangers, which reduces fan power consumption and fan noise relative to conventional heat exchanger designs. These technological advantages provide one or more technological advancements over prior art approaches.1. In some embodiments, an electronic device, includes: an integrated circuit; and a heat exchanger that includes: at least one heat pipe that is thermally coupled to the integrated circuit and has an evaporator portion and a condenser portion, wherein the condenser portion extends away from the evaporator portion; and a first plurality of cooling fins that are attached to the condenser portion and proximate to the evaporation portion and form a plenum having a first associated pressure drop when a cooling fluid flows across the first plurality of cooling fins at a first velocity; and a second plurality of cooling fins that are attached to the condenser portion and distal from the evaporation portion and form a flow path having a second associated pressure drop when the cooling fluid flows across the second plurality of cooling fins at the first velocity.2. The electronic device of clause 1, wherein the heat exchanger further comprises: a second heat pipe that is thermally coupled to the integrated circuit and has an evaporator portion and a condenser portion; and a third plurality of cooling fins that are thermally coupled to the IC and disposed between the evaporator portion of the first heat pipe and the evaporator portion of the second heat pipe.3. The electronic device of clauses 1 or 2, wherein the cooling fins in the third plurality of cooling fins extend away from the integrated circuit into an airflow region that encompasses a curved portion of the first heat pipe and a curved portion of the second heat pipe.4. The electronic device of any of clauses 1-3, wherein the cooling fins in the third plurality of cooling fins are mounted on a first side of a metallic plate and the integrated circuit is mounted on a second side of the metallic plate opposite to the first side.5. The electronic device of any of clauses 1-4, wherein the evaporator portion is parallel to a first surface of the integrated circuit and the condenser portion is perpendicular to the first surface of the integrated circuit.6. The electronic device of any of clauses 1-5, wherein the plenum is formed in an edge region of the heat exchanger.7. The electronic device of any of clauses 1-6, wherein each fin in the first plurality of fins has a respective length in a direction of cooling fluid flow that is less than a length of fins in the second plurality of fins in the direction of cooling fluid.8. The electronic device of any of clauses 1-7, wherein the second pressure drop is greater than the first pressure drop.9. The electronic device of any of clauses 1-8, wherein the integrated circuit is coupled to a first side of a metallic plate and the evaporator portion is coupled to a second side of the metallic plate opposite to the first side.10. The electronic device of any of clauses 1-9, wherein: the condenser portion comprises a first straight segment coupled to the evaporator portion via a first curved segment and a second straight segment coupled to the evaporator portion via a second curved segment, and the heat exchanger further comprises a third plurality of cooling fins that are thermally coupled to the metallic plate and disposed between the first curved segment and the second curved segment.11. The electronic device of any of clauses 1-10, wherein the at least one heat pipe includes a heat pipe embedded in the metal plate.12. The electronic device of any of clauses 1-11, wherein the evaporator portion comprises a straight section and the heat pipe embedded in the metal plate is perpendicular to the straight section.13. The electronic device of any of clauses 1-12, wherein each cooling fin in the first plurality of cooling fins is separated by a first fin pitch, each cooling fin in the second plurality of cooling fins is separated by a second fin pitch, and wherein the first fin pitch is greater than the second fin pitch.14. The electronic device of any of clauses 1-13, wherein each cooling fin in the first plurality of cooling fins has a first fin length, and each cooling fin in the second plurality of cooling fins has a second fin length.15. The electronic device of any of clauses 1-14, wherein the first fin length is equal to the second fin length.16. The electronic device of any of clauses 1-15, wherein the respective lengths of the cooling fins in the first plurality of cooling fins correspond to a first termination profile, and the respective lengths of the cooling fins in the second plurality of cooling fins correspond to a second termination profile.17. An electronic device that includes an integrated circuit and a heat exchanger, the heat exchanger comprising: at least one heat pipe that is thermally coupled to the integrated circuit and has an evaporator portion and a condenser portion, wherein the condenser portion extends away from the evaporator portion; a first plurality of cooling fins that are proximate to the evaporation portion and form a plenum; and a second plurality of cooling fins that are distal from the evaporation portion and form a flow path, wherein the plenum is configured to cause a first portion of cooling fluid to flow through the plenum at a first velocity and through the flow path at a second velocity, wherein the first velocity is greater than the second velocity.18. The electronic device of clause 17, wherein the plenum is formed in an edge region of the heat exchanger.19. The electronic device of clauses 17 or 18, wherein each fin in the first plurality of cooling fins has a respective length in a direction of cooling fluid flow that is less than a length of cooling fins in the second plurality of fins in the direction of cooling fluid.20. The electronic device of any of clauses 17-19, wherein the respective lengths of the cooling fins in the first plurality of cooling fins correspond to a termination profile.21. In some embodiments, a heat exchanger includes: a first heat pipe that includes a first evaporator portion and a first condenser portion, wherein the first condenser portion extends away from the first evaporator portion; a second heat pipe that is thermally coupled to the first heat pipe and includes a second evaporator portion and a second condenser portion; and a plurality of cooling fins, wherein each cooling fin included in the plurality of cooling fins is attached to the second condenser portion.22. The heat exchanger of clause 21, wherein the second evaporator portion is mechanically coupled to the first heat pipe.23. The heat exchanger of clauses 21 or 22, further comprising a metallic plate having a first surface to which the first heat pipe is coupled.24. The heat exchanger of any of clauses 21-23, further comprising an integrated circuit that is coupled to a second surface of the metallic plate, wherein the second surface of the metallic plate is opposite to the first surface of the metallic plate.25. The heat exchanger of any of clauses 21-24, wherein the first surface is directly coupled to the first evaporator portion.26. The heat exchanger of any of clauses 21-25, wherein the first heat pipe is included in a plurality of heat pipes that are directly coupled to the first surface of the metallic plate.27. The heat exchanger of any of clauses 21-26, wherein the first heat pipe is at least partially disposed within the metallic plate.28. The heat exchanger of any of clauses 21-27, wherein the plurality of cooling fins includes: a first group of fins that are proximate to the second evaporation portion and form a plenum; and a second group of fins that are distal from the second evaporation portion and form a flow path.29. The heat exchanger of any of clauses 21-28, wherein the plenum has a first associated pressure drop when a cooling fluid flows across the first group of cooling fins at a first velocity, and the flow path has a second associated pressure drop when the cooling fluid flows across the second group of cooling fins at the first velocity.30. The heat exchanger of any of clauses 21-29, wherein the second evaporator portion is perpendicular to the second condenser portion.31. The heat exchanger of any of clauses 21-30, wherein the second heat pipe is included in a plurality of heat pipes, where each heat pipe in the plurality of heat pipes has an evaporator portion and a condenser portion that is perpendicular to the evaporator portion.32. The heat exchanger of any of clauses 21-31, wherein the first evaporator portion is perpendicular to the first condenser portion.33. The heat exchanger of any of clauses 21-32, wherein the second evaporator portion is perpendicular to the second condenser portion, and the first condenser is parallel to the second condenser portion.34. The heat exchanger of any of clauses 21-33, wherein each cooling fin included in the plurality of cooling fins is attached to the first condenser portion.35. In some embodiments, an electronic device includes a first integrated circuit thermally coupled to a first heat exchanger, the first heat exchanger comprising: a first heat pipe that includes a first evaporator portion and a first condenser portion, wherein the first condenser portion extends away from the first evaporator portion; a second heat pipe that is thermally coupled to the first heat pipe and includes a second evaporator portion and a second condenser portion; and a plurality of cooling fins, wherein each cooling fin included in the plurality of cooling fins is attached to the second condenser portion.36. The electronic device of clause 35, wherein the second evaporator portion is mechanically coupled to the first heat pipe.37. The electronic device of clause 35 or 36, further comprising a metallic plate having a first surface to which the first heat pipe is coupled.38. The electronic device of any of clauses 35-37, further comprising: a printed circuit board on which the first integrated circuit is mounted; a second integrated circuit that is mounted on the printed circuit board; and a second heat exchanger that is thermally coupled to the second integrated circuit.39. The electronic device of any of clauses 35-38, wherein the first heat exchanger and the second heat exchanger are positioned on the printed circuit board to allow a cooling fluid to flow first through the first heat exchanger and then through the second heat exchanger.40. The electronic device of any of clauses 35-39, wherein: the first heat exchanger includes a first plurality of cooling fins; and the second heat exchanger include a second plurality of cooling fins that are disposed parallel to the first plurality of cooling fins.41. The electronic device of any of clauses 35-40, wherein: the first heat pipe is included in a first plurality of heat pipes, wherein each heat pipe included in the first plurality of heat pipes has a third condenser portion; the second heat pipe is included in a second plurality of heat pipes, wherein each heat pipe included in the second plurality of heat pipes has a fourth condenser portion; and the third condenser portions are arranged within the first heat exchanger at a first density, and the second condenser portions are arranged within the first heat exchanger at a second density that is less than the first density.