Patent ID: 12189441

DETAILED DESCRIPTION

The present disclosure relates generally to systems and methods for thermal management of electronic devices or other heat-generating components. In some embodiments, heat spreaders and wicking structures according to the present disclosure promote the boiling and vapor bubble formation and/or release during vaporization of working fluid.

Immersion chambers surround the heat-generating components in a liquid working fluid, which conducts heat from the heat-generating components to cool the heat-generating components. As the working fluid absorbs heat from the heat-generating components, the temperature of the working fluid increases. In some embodiments, the hot working fluid can be circulated through the thermal management system to cool the working fluid and/or replace the working fluid with cool working fluid. In some embodiments, the working fluid vaporizes, introducing vapor into the liquid of the working fluid which rises out of the liquid phase, carrying thermal energy away from the heat-generating components in the gas phase via the latent heat of boiling.

In large-scale computing centers, such as cloud-computing centers, data processing centers, data storage centers, or other computing facilities, immersion cooling systems provide an efficient method of thermal management for many computing components under a variety of operating loads. In some embodiments, an immersion cooling system includes a working fluid in an immersion chamber and a heat exchanger to cool the liquid phase and/or a condenser to extract heat from the vapor phase of the working fluid. The heat exchanger may include a condenser that condenses the vapor phase of the working fluid into a liquid phase and returns the liquid working fluid to the immersion chamber. In some embodiments, the liquid working fluid absorbs heat from the heat-generating components, and one or more fluid conduits direct the hot liquid working fluid outside of the immersion chamber to a radiator, heat exchanger, or region of lower temperature to cool the liquid working fluid.

In some embodiments, a high-compute application assigned to and/or executed on the computing devices or systems in the immersion cooling system requires a large amount of thermal management. A working fluid boiling absorbs heat to overcome the latent heat of boiling. The phase change from liquid to vapor, therefore, allows the working fluid to absorb a comparatively large amount of heat with a small associated increase in temperature. Further, the lower density allows the vapor to be removed from the immersion bath efficiently to exhaust the associated heat from the system.

In some embodiments, a thermal management system includes an immersion tank with a two-phase working fluid positioned therein. The two-phase working fluid receives heat from heat-generating components immersed in the liquid working fluid, and the heat vaporizes the working fluid, changing the working fluid from a liquid phase to a vapor phase. The thermal management system includes a condenser, such as described herein, to condense the vapor working fluid back into the liquid phase. In some embodiments, the condenser is in fluid communication with the immersion tank by one or more conduits. In some embodiments, the condenser is positioned inside the immersion tank.

A conventional immersion cooling system100, shown inFIG.1, includes an immersion tank102containing an immersion chamber104and a condenser106in the immersion chamber104. The immersion chamber104contains an immersion working fluid that has a liquid working fluid108and a vapor working fluid110portion. The liquid working fluid108creates an immersion bath112in which a plurality of heat-generating components114are positioned to heat the liquid working fluid108on supports116.

Referring now toFIG.2, in some embodiments, an immersion cooling system200includes an immersion tank202defining an immersion chamber204with an immersion working fluid positioned therein. An immersion working fluid in the immersion tank202has a boiling temperature that is at least partially related to one or more operating properties of the immersion cooling system, the electronic components and/or computing devices in the immersion tank202, computational or workloads of the electronic components and/or computing devices in the immersion tank202, external and/or environmental conditions, or other properties that affect the operation of the immersion cooling system200. As the operating conditions of the immersion cooling system200change, the immersion cooling system200can change a mixing ratio of the immersion working fluid to change at least one property (such as boiling temperature) of the immersion working fluid.

In some embodiments, the immersion working fluid transitions between a liquid working fluid208phase and a vapor working fluid210phase to remove heat from hot or heat-generating components214in the immersion chamber204. The liquid working fluid208more efficiency receives heat from the heat-generating components214and, upon transition to the vapor working fluid210, the vapor working fluid210can be removed from the immersion tank202, cooled and condensed by the condenser206(or other heat exchanger) to extract the heat from the working fluid, and the liquid working fluid208can be returned to the liquid immersion bath212.

In some embodiments, the immersion bath212of the liquid working fluid208has a plurality of heat-generating components214positioned in the liquid working fluid208. The liquid working fluid208surrounds at least a portion of the heat-generating components214and other objects or parts attached to the heat-generating components214. In some embodiments, the heat-generating components214are positioned in the liquid working fluid208on one or more supports216. The support216may support one or more heat-generating components214in the liquid working fluid208and allow the working fluid to move around the heat-generating components214. In some embodiments, the support216is thermally conductive to conduct heat from the heat-generating components214. The support(s)216may increase the effective surface area from which the liquid working fluid208may remove heat through convective cooling.

In some embodiments, the heat-generating components214include electronic or computing components or power supplies. In some embodiments, the heat-generating components214include computer devices, such as individual personal computer or server blade computers. In some embodiments, one or more of the heat-generating components214includes a heat sink or other device attached to the heat-generating component214to conduct away thermal energy and effectively increase the surface area of the heat-generating component214. In some embodiments, the heat sink of the heat-generating component214is a vapor chamber with one or more three-dimensional structures to increase surface area.

As described, conversion of the liquid working fluid208to a vapor phase requires the input of thermal energy to overcome the latent heat of vaporization and may be an effective mechanism to increase the thermal capacity of the working fluid and remove heat from the heat-generating components214. Because the vapor working fluid210rises in the liquid working fluid208, the vapor working fluid210can be extracted from the immersion chamber204in an upper vapor region of the chamber. A condenser206cools part of the vapor working fluid210back into a liquid working fluid208, removing thermal energy from the system and reintroducing the working fluid into the immersion bath212of the liquid working fluid208. The condenser206radiates or otherwise dumps the thermal energy from the working fluid into the ambient environment or into a conduit to carry the thermal energy away from the cooling system.

In some embodiments of immersion cooling systems, a liquid-cooled condenser is integrated into the immersion tank and/or the chamber to efficiency remove the thermal energy from the working fluid. In some embodiments, an immersion cooling system200for thermal management of computing devices allows at least one immersion tank202and/or chamber204to be connected to and in fluid communication with an external condenser206. In some embodiments, an immersion cooling system200includes a vapor return line218that connects the immersion tank202to the condenser206and allows vapor working fluid210to enter the condenser206from the immersion tank202and/or chamber204and a liquid return line220that connects the immersion tank202to the condenser206and allows liquid working fluid208to return to the immersion tank202and/or chamber204.

The vapor return line218may be colder than the boiling temperature of the working fluid. In some embodiments, a portion of the vapor working fluid210condenses in the vapor return line218. The vapor return line218can, in some embodiments, be oriented at an angle such that the vapor return line218is non-perpendicular to the direction of gravity. The condensed working fluid can then drain either back to the immersion tank202or forward to the condenser206depending on the direction of the vapor return line218slope. In some embodiments, the vapor return line218includes a liquid collection line or valve, like a bleeder valve, that allows the collection and/or return of the condensed working fluid to the immersion tank202or condenser206.

In some examples, an immersion cooling system200includes an air-cooled condenser206. An air-cooled condenser206may require fans or pumps to force ambient air over one or more heat pipes or fins to conduct heat from the condenser to the air. In some embodiments, the circulation of immersion working fluid through the immersion cooling system200causes liquid working fluid208to flow past one or more heat-generating components214. In the example of a heat-generating component214with a vapor chamber heat sink, the dynamics of liquid working fluid208may be used to move vapor chamber working fluid within the vapor chamber and/or the boiling of the immersion working fluid by the vapor chamber may drive flow of the immersion working fluid.

In some embodiments, the liquid working fluid receives heat in a cooling volume of working fluid immediately surrounding the heat-generating components. The cooling volume is the region of the working fluid (including both liquid and vapor phases) that is immediately surrounding the heat-generating components and is responsible for the convective cooling of the heat-generating components. In some embodiments, the cooling volume is the volume of working fluid within 5 millimeters (mm) of the heat-generating components.

The immersion working fluid has a boiling temperature below a critical temperature at which the heat-generating components experience thermal damage. The immersion working fluid can thereby receive heat from the heat-generating components to cool the heat-generating components before the heat-generating components experience damage.

For example, the heat-generating components may be computing components that experience damage above 1000 Celsius (C). In some embodiments, the boiling temperature of the immersion working fluid is less than a critical temperature of the heat-generating components. In some embodiments, the boiling temperature of the immersion working fluid is less about 900° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is less about 800° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is less about 700° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is less about 600° C. at 1 atmosphere of pressure. In some embodiments, the boiling temperature of the immersion working fluid is at least about 350° C. at 1 atmosphere of pressure. In some embodiments, the working fluid includes water.

In some embodiments, the working fluid includes glycol. In some embodiments, the working fluid includes a combination of water and glycol. In some embodiments, the working fluid includes an aqueous solution. In some embodiments, the working fluid includes an electronic liquid, such as FC-72 available from3M, or similar non-conductive fluids. In some embodiments, the heat-generating components, supports, or other elements of the immersion cooling system positioned in the working fluid have nucleation sites on a surface thereof that promote the nucleation of vapor bubbles of the working fluid at or below the boiling temperature of the working fluid.

FIG.3is a side cross-sectional view of an example of a conventional heat spreader. In an example, a heat-generating component314includes a die324positioned on a printed circuit board (PCB)326. The die324may be a generalized device, such as a central processing unit (CPU) or graphical processing unit (GPU), or a specialized device application-specific integrating circuit (ASIC). The die324generates heat during use. The heat is transmitted by a thermal interface material (TIM)328to a heat spreader330that is in contact with the liquid phase308of the working fluid in the immersion chamber304.

The heat spreader330transfers heat to the liquid phase308of the working fluid to vaporize the working fluid into a vapor phase310of the working fluid. As described herein, the formation of the vapor bubbles332allows the working fluid to receive heat to overcome the latent heat of vaporization without substantially increasing the temperature of the working fluid. The vapor bubbles332then, through the buoyancy of the vapor phase310, rise out of the liquid phase308of the working fluid, and liquid phase308of the working fluid replaces the vapor phase310contacting the surface of the heat spreader330, allowing the process to repeat and continue.

However, the heat transfer of the heat spreader330to the liquid phase308of the working fluid is limited by the surface area of the heat spreader330in contact with the liquid phase308of the working fluid. A conventional, solid heat spreader330has a limited surface area given the amount of space on the PCB326and/or in the immersion chamber304relative to other components, devices, or structures immersed in the working fluid. In some embodiments, vapor formation on the surface of the heat spreader330further limits the available surface area of the heat spreader330in contact with the liquid phase308of the working fluid. A heat transfer rate from the heat spreader330to the vapor phase310of the working fluid is lower than for the heat spreader330to the liquid phase308of the working fluid. For example, while the vapor bubble332remains in contact with a surface of the heat spreader330, such as due to cohesion, the heat spreader330can continue to increase in temperature above the boiling temperature of the working fluid, which may be undesirable for thermal management of the heat-generating component314and/or preventing dryout in the immersion cooling system.

In some embodiments, one or more features that increase surface area and promote bubble formation and release from the heat spreader can improve heat transfer rates from the heat spreader to the working fluid.

FIG.4is a side cross-sectional view of an embodiment of a thermal management device including a wicking heat spreader436according to the present disclosure. In some embodiments, the wicking heat spreader436is a three-dimensional heat spreader with a plurality of channels therein or therethrough that allow flow of working fluid through an interior volume446of the heat spreader. A three-dimensional heat spreader conducts heat within a plane of the heat spreader that is parallel to a plane of the heat source (such as a surface of a die), as well as in a vertical direction away from the plane. In some embodiments, the wicking heat spreader436includes both horizontal channels440and vertical channels442. For example, the horizontal channels440may draw a liquid phase408of the working fluid into the wicking heat spreader436from the sides of the wicking heat spreader436, while vertical channels442allow exhausting of both liquid phase408and vapor phase410working fluid from the wicking heat spreader436.

In some embodiments, the vapor bubbles432floating out of the channels440,442of the wicking heat spreader436contribute to the flow of liquid phase408working fluid into the channels440,442of the wicking heat spreader436. For example, the bubbles432vacating the space in the channels440,442of the wicking heat spreader436can draw liquid phase408working fluid into the channels440,442to replace the volume of the vapor bubbles432. In some embodiments, the fluidic drag of the vapor bubbles432moving through the liquid phase408working fluid can drag the liquid phase408in the direction of movement of the vapor bubbles432, which may move hot liquid phase408working fluid out of the wicking heat spreader436and encourage cool liquid phase408working fluid to enter the wicking heat spreader436.

It should be understood that while some embodiments of a wicking heat spreader are described with horizontal and vertical channels, the wicking heat spreader may be oriented in any direction relative to gravity. The embodiments described herein will describe the horizontal channels as being oriented substantially parallel to a plane of a surface of the die and vertical channels as being oriented substantially perpendicular to the plane of a surface of the die, but the channels may have other orientations, as well, as will be described in greater detail herein.

In some embodiments, a wicking heat spreader436has an outer surface444. The outer surface has openings therein to allow ingress and egress of working fluid to an interior volume446of the wicking heat spreader436. The wicking heat spreader436has at least one horizontal channel440and at least one vertical channel442with interior surfaces448that are oriented toward the interior volume446(e.g., toward the channels440,442) and away from the outer surface444of the wicking heat spreader436. The interior surfaces448and outer surfaces444of the wicking heat spreader436increase the surface area of the wicking heat spreader436relative to a conventional heat spreader with a continuous outer surface and no working fluid flow through the frame of the heat spreader. Increased surface area relative to volume allows for greater heat transfer to the working fluid and greater thermal management capacity.

In some embodiments, the interior surfaces448have at least one boiling enhancement surface feature (BESF) thereon. For example, the BESF may include one or more surface treatments, recesses, or protrusions on the interior surfaces that promote the formation of vapor bubbles on and/or the release of vapor bubbles from the interior surfaces448. In some embodiments, the BESF is or includes a boiling enhancement coating (BEC) applied to the interior surface448of the wicking heat spreader436. For example, the wicking heat spreader436may have a frame450with channels440,442therein, and the BEC may be applied to the surface(s) of the frame450such that the BEC is located on at least one interior surface448of the frame450. In some embodiments, the BEC is located on at least 50% of the interior surface area of the frame450. In some embodiments, the BEC is located on substantially all of the interior surface area of the frame450. In some embodiments, the BEC is located on substantially all of the surface area of the frame450in contact with or configured to contact working fluid (i.e., outer surfaces444and interior surfaces448).

FIG.5is a side cross-sectional view of another embodiment of a thermal management device including a wicking heat spreader536according to the present disclosure. In some embodiments, the wicking heat spreader536is thermally connected to a heat-generating component514through an intermediate heat spreader552. For example, some heat spreaders, such as vapor chambers or graphite sheets have high in-plane thermal conductive to spread heat laterally, but such planar heat spreaders may have comparatively low surface area to volume ratios to efficiently transfer heat to the working fluid.

In some embodiments, the intermediate heat spreader552receives heat from the die524or other portion of a heat-generating component514through a first TIM528-1, and the intermediate heat spreader552provides lateral heat spreading within a plane of the intermediate heat spreader552. The intermediate heat spreader552then allows the heat to be transferred more or substantially uniformly to the wicking heat spreader536through a second TIM528-2.

FIG.6is a perspective view of an embodiment of a wicking heat spreader636according to the present disclosure. In some embodiments, the wicking heat spreader636includes a plurality of horizontal rails654with horizontal channels640therebetween and a plurality of vertical rails656with vertical channels642therebetween.

In some embodiments, the horizontal channels640allow for intakes658to the horizontal channels640on the lateral sides660of the wicking heat spreader636. The horizontal channels640connect to vertical channels642to flow working fluid through the wicking heat spreader636. The working fluid can then exhaust from the wicking heat spreader636.

In some embodiments, at least one of the horizontal channels640is straight and continuous from a front surface (e.g., a lateral side660) to a rear surface (e.g., a lateral side opposite the front surface). In some embodiments, all of the horizontal channels640between the front surface and the rear surface are straight and continuous. In some embodiments, at least one of the horizontal channels640has a curve, a bend, a corner, or another deviation that causes fluid flow to change direction compared to a straight channel. In some embodiments, at least one of the horizontal channels640terminates between a first lateral side660and a second lateral side660.

In some embodiments, at least one of the horizontal channels640allows fluid flow from a front surface of the wicking structure to a rear surface of the wicking structure. In some embodiments, at least one of the horizontal channels640terminates between a first lateral side660and a second lateral side660and/or exhausts out a top surface662of the wicking heat spreader636.

In some embodiments, at least one of the vertical channels642is straight and continuous from a bottom surface664to the top surface662. In some embodiments, all of the vertical channels642between the bottom surface664and the top surface662are straight and continuous. In some embodiments, at least one of the vertical channels642has a curve, a bend, a corner, or another deviation that causes fluid flow to change direction compared to a straight channel. In some embodiments, at least one of the vertical channels642terminates between a bottom surface664and the top surface662.

In some embodiments, at least one of the vertical channels642allows fluid flow from a bottom surface664and the top surface662. In some embodiments, at least one of the vertical channels642terminates between a bottom surface664and the top surface662and/or exhausts out a lateral side660of the wicking heat spreader636.

FIG.7is an end view of the embodiment of a wicking heat spreader636ofFIG.6. The wicking heat spreader636has a plurality of horizontal channels640with intakes658on the lateral side660. In some embodiments, the horizontal channels640have uniform transverse dimension (e.g., perpendicular to a direction of flow through the horizontal channel640) such as a channel width666or channel height668. In other embodiments, at least one horizontal channel640has a transverse area (e.g., channel width666by channel height668) that changes along a length670of the horizontal channel640. For example, vapor bubbles forming in the horizontal channel640may create a pressure in the wicking heat spreader636that resists ingress of additional working fluid. In some embodiments, the horizontal channel640may increase in cross-sectional area toward a center of the wicking heat spreader636to accommodate the increase in volume of the working fluid upon vaporization.

The wicking heat spreader636has a plurality of vertical channels642with openings on the top surface662. In some embodiments, the vertical channels642have uniform transverse dimension (e.g., perpendicular to a direction of flow through the vertical channels642) such as a channel width666or channel height668illustrated in relation to the horizontal channels640. In other embodiments, at least one vertical channel642has a transverse area that changes along a length of the vertical channel642toward the top surface662. For example, vapor bubbles forming in the vertical channel642may create a pressure in the wicking heat spreader636that resists ingress of additional working fluid. In some embodiments, the vertical channel642may increase in cross-sectional area toward the top surface662of the wicking heat spreader636to accommodate the increase in volume of the working fluid upon vaporization.

In some embodiments, the wicking heat spreader636has a plurality of horizontal rails672. In some embodiments, the horizontal rails672have uniform transverse dimension (e.g., perpendicular to a direction of flow through the horizontal channel640) such as a rail width676or rail height678. In other embodiments, at least one horizontal rail672has a transverse area (e.g., rail width676by channel height678) that changes along a length of the horizontal rail672. For example, vapor bubbles forming in the horizontal channel640may create a pressure in the wicking heat spreader636that resists ingress of additional working fluid. In some embodiments, one or more horizontal rails672may decrease (e.g., taper) in cross-sectional area to allow the horizontal channel640to increase in cross-sectional area toward a center of the wicking heat spreader636to accommodate the increase in volume of the working fluid upon vaporization.

In some embodiments, the wicking heat spreader636has a plurality of vertical rails674. In some embodiments, the vertical rails674have uniform transverse dimension (e.g., perpendicular to a direction of flow through the vertical channel642) such as analog to the rail width676or rail height678described in relation to the horizontal rails. In other embodiments, at least one vertical rail674has a transverse area that changes along a length of the vertical rail674. For example, vapor bubbles forming in the vertical channel642may create a pressure in the wicking heat spreader636that resists ingress of additional working fluid. In some embodiments, one or more vertical rails674may decrease (e.g., taper) in cross-sectional area toward the top surface662to allow the horizontal channel640to increase in cross-sectional area toward a center of the wicking heat spreader636to accommodate the increase in volume of the working fluid upon vaporization.

FIG.8is a detail view of a channel of the wicking heat spreader636ofFIG.6andFIG.7. To promote the formation of and/or release of vapor bubbles on the interior surface of the channels, in some embodiments, the channels includes one of more BESF.FIG.8is a detail view of a portion of a horizontal channel640of the wicking heat spreader636, but it should be understood that any BESF described in relation to a horizontal channel may be applicable to a vertical channel or to an outer surface of the wicking heat spreader. In some embodiments, the BESF includes a BEC, a recess, a protrusion, or combinations thereof.

For example, a BEC680may be deposited on an interior surface648of a horizontal rail672or a vertical rail674of the wicking heat spreader636. The BEC680may be deposited by physical vapor deposition, chemical vapor deposition, sputtering, electroplating, or other coating deposition methods to create a surface roughness, texture, or chemical composition that promotes the formation of and/or release of vapor bubbles on the interior surface of the channels. In some embodiments, the BEC680is etched into the interior surface648of a horizontal rail672or a vertical rail674of the wicking heat spreader636. For example, the BEC680may be etched by ion etching or chemical etching to create a surface roughness or texture that promotes the formation of and/or release of vapor bubbles on the interior surface of the channels.

In some embodiments, the BESF includes or is a recess682in the interior surface648. The recess682may include a curve or a corner. In some embodiments, the recess682is positioned in the interior surface648to promote the formation of a vapor bubble that is smaller than the cross-sectional area of the channel (e.g., the horizontal channel640). For example, the recess682may have an opening683that is no more than half of the transverse dimension (such as the channel width or height) of the channel such that the vapor bubble that forms in the recess682is smaller than the channel area. In other examples, the opening683is no more than ⅓ of the transverse dimension of the channel.

A protrusion684may be located on the interior surface648to promote the promote the formation of and/or release of vapor bubbles on the interior surface of the channels. In some embodiments, the protrusion684is formed by three-dimensional printing on the interior surface648. In some embodiments, the protrusion684is formed by etching or machine material to leave the protrusion684remaining.

The BESF described herein may be combined in any manner. In some embodiments, the protrusion684is located on a recess surface in the recess682. In some embodiments, the protrusion684has a BEC located thereon. In some embodiments, the recess682has a BEC positioned therein.

FIG.9is a flowchart illustrating an embodiment of a method786of manufacturing a wicking heat spreader. In some embodiments, the method includes obtaining a frame of a wicking structure at788and forming at least one boiling enhancement surface feature positioned on at least one interior surface of the frame at790. In some embodiments, the frame includes at least one horizontal channel and at least one vertical channel that intersect and allow fluid flow therethrough.

In some embodiments, obtaining a frame includes machining the frame from a billet. In some embodiments, obtaining a frame includes three-dimensional printing of the frame. In some embodiments, obtaining a frame includes casting the frame. In some embodiments, obtaining a frame includes sintering of the frame. In some embodiments, obtaining a frame includes injection molding of the frame. In some embodiments, obtaining a frame includes a combination of machining, three-dimensional printing, casting, sintering, and injection molding. In some embodiments, obtaining a frame includes obtaining a first portion of the frame by any method described herein and subsequently additively manufacturing a second portion of the frame onto the first portion of the frame. For example, the first portion of the frame may have a BEC deposited thereon, and the second portion of the frame is additively manufactured over the first portion, thereby allowing an interior surface of the frame to have a BEC that would otherwise be inaccessible for some deposition techniques.

In some embodiments, forming at least one BESF on an interior surface of the frame includes depositing or etching a BEC on the interior surface. In some embodiments, forming at least one BESF on an interior surface of the frame includes forming a recess in the interior surface. In some embodiments, the recess is formed by etching. In some embodiments, the recess is formed by machining. In some embodiments, the recess is formed during three-dimensional printing of the frame. In some embodiments, forming at least one BESF on an interior surface of the frame includes forming a protrusion on the interior surface. In some embodiments, the protrusion is printed on the interior surface. In some embodiments, the protrusion is deposited on the interior surface. In at least one embodiment, the protrusion is formed in a recess of the interior surface.

FIG.10is a cross-sectional view of an embodiment of a wicking heat spreader836with a porous frame892according to the present disclosure. A vapor bubble832may form in a recess882of the interior surface858of the frame892. In some embodiments, the recess882includes protrusions884. Liquid phase808flow through the channels of the wicking heat spreader promotes the release of the vapor bubbles832. In some embodiments, refilling of the vacated volume and/or release of the vapor bubble832from the frame892can be increased by the use of a porous frame892. For example, a porous frame892may allow the liquid phase808of the working fluid to enter the wicking heat spreader836more easily and/or create a fluid pressure behind the vapor bubble832to aid in releasing the vapor bubble832.

In some embodiments, working fluid (either two-phase or single-phase working fluid) can be directed adjacent to and/or directly contacting a die in a heat-generating component.FIG.11is a side schematic representation of a stacked die processor (e.g., a heat-generating component914) including a first die924-1and a second die924-2with a microfluidic volume994therebetween. In some embodiments, the microfluidic volume994allows flow of a liquid phase908of a working fluid through the microfluidic volume994and around a plurality of pin fins996positioned between and connected to the first die924-1and the second die924-2. In some embodiments, the pin fins996are integrally formed with one or both of the first die924-1and the second die924-2to allow direct on-chip cooling of the first die924-1and the second die924-2.

In some embodiments, the working fluid is a single-phase working fluid, and the liquid phase908of the working fluid flows through the microfluidic volume from a first lateral side of the stacked-die processor to a second lateral side of the stacked die processor. In some embodiments, the first lateral side and second lateral side are opposite one another. In some embodiments, the first lateral side and second lateral side are abutting one another at a corner of the stacked-die processor, such as allowing a 90° turn to the flow of working fluid through the microfluidic volume994. In some embodiments, the top surface of the first die924-1and the bottom surface of the second die924-2are planar and parallel to one another such that a height of the microfluidic volume994is constant through the microfluidic volume994.

The pin fins996connect the first die924-1and the second die924-2to one another and may provide thermal conductivity therebetween, such as conducting heat from the first die924-1and the second die924-2into the pin fins to assist in transferring the heat into the liquid phase908of the working fluid. In some embodiments, at least one of the pin fins996has a through-silicon via (TSV)998positioned therein to provide electrically connection and communication through the pin fins between the electronic components and circuitry of the first die924-1and the second die924-2. In some embodiments, the TSV998is vulnerable to thermal damage, and efficient removal of heat from the pin fin996may increase the performance and/or operational lifetime of the TSVs998and/or the stacked-die processor.

In some embodiments, the pin fins996have BESFs on the pin surface901, such as a BEC, recess, protrusion, or combinations thereof, such as described in relation toFIG.8. The BESFs may be positioned on all of the pin surface901contacting the working fluid, or the BESFs may be positioned on less than all of the pin surface901. For example, the BESFs may increase drag on the working fluid, inhibiting flow of the working fluid through the microfluidic volume994. In some embodiments, the BESFs are selectively located on the pin surface901relative to the direction of flow of the working fluid to promote the formation of and/or release of vapor bubbles (e.g., of the vapor phase910of the working fluid) while lessening the drag on the flow of the working fluid.

FIG.12is a side schematic view of closed-loop microfluidic cooling system with a working fluid therein. In some embodiments, a closed loop system for cooling a stacked-die heat generating component1014includes an inlet conduit1003connected to a first lateral side1060-1and an outlet conduit1005connected to a second lateral side1060-2. In other embodiments, the inlet conduit1003and outlet conduit1005connected to the same lateral side1060-1to circulate working fluid in the microfluidic volume1094.

FIG.13is an embodiment of a method of manufacturing of a stacked-die processor. Step A illustrates the initial blank wafer1107, and holes1109in what will be the pin fins1196are created by high plasma etching, reactive ion etching, or other etching process to remove at least a portion of the silicon wafer1107at B. A dielectric layer or liner1111is applied to the pin surfaces1101at C, and a conductive material is positioned in the holes1109to form the TSVs1198at D before the wafer1107is mechanically polished to the desired thickness1113at E. In some embodiments, the TSVs1198are tested by fabricating interconnects1115across the contact surfaces of the TSVs1198as F before the wafer1107around the TSVs1198is removed at G, such as by etching, at G to form the pin fins1196with the TSVs1198therethrough and the microfluidic volume1194around the pin fins1196. In some embodiments, the microfluidic volume is at least partially closed or capped at H to enclose the microfluidic volume and/or direct working fluid through the microfluidic volume.

FIG.14is a side view of an embodiment of a stacked-die processor including a first die1224-1, a second die1224-2, and a third die1224-3stacked with pin fins1296-1,1296-2containing TSVs1298-1,1298-2therebetween. In some embodiments, a first microfluidic volume1294-1is located between the first die1224-1and the second die1224-2, and a first set of pin fins1296-1couples the first die1224-1and the second die1224-2through the first microfluidic volume1294-1. In some embodiments, a second microfluidic volume1294-2is located between the second die1224-2and the third die1224-3, and a second set of pin fins1296-2couples the second die1224-2and the third die1224-3through the second microfluidic volume1294-2.

As described herein, the pin fins1296-1,1296-2have, in some embodiments, at least one BESF position on a pin surface thereof. In some embodiments, the first set of pin fins1296-1and the second set of pin fins1296-2have the same BESF(s) thereon. For example, the first set of pin fins1296-1may have a BEC thereon and the second set of pin fins1296-2may have the same BEC thereon. In other examples, the first set of pin fins1296-1may have a plurality of recesses in a pin surface thereof, and the second set of pin fins1296-2may have a plurality of recesses in a pin surface thereof. In other examples, the first set of pin fins1296-1may have a plurality of protrusions on a pin surface thereof, and the second set of pin fins1296-2may have a plurality of protrusions on a pin surface thereof.

In some embodiments, the first set of pin fins1296-1and the second set of pin fins1296-2have different BESFs thereon. For example, the first set of pin fins1296-1may have a BEC thereon and the second set of pin fins1296-2may lack a BEC or have a different BEC thereon. In other examples, the first set of pin fins1296-1may have a plurality of recesses in a pin surface thereof, and the second set of pin fins1296-2may lack recesses in a pin surface thereof or have recesses in a different pattern or with different dimensions. In other examples, the first set of pin fins1296-1may have a plurality of protrusions on a pin surface thereof, and the second set of pin fins1296-2may lack protrusions on a pin surface thereof or have protrusions in a different pattern or with different dimensions. In some embodiments, the thermal management requires of the dies1224-1,1224-2,1224-3may be different, and the BESFs of the first set of pin fins1296-1and the second set of pin fins1296-2may be different to effect the different thermal management properties.

In some embodiments, the working fluid is urged through the first microfluidic volume1294-1and through the second microfluidic volume1294-2at the same flow rate. For example, a manifold forming at least a portion of the side wall of the microfluidic volume1294-1,1294-2is connected to an inlet conduit may provide equal flow rate and/or equal fluid pressure to both the first microfluidic volume1294-1and the second microfluidic volume1294-2. In some embodiments, the flow rate is different, such as when different thermal management is required by different portions of the stacked-die processor. For example, a first inlet conduit may provide a first flow rate and/or fluid pressure to the first microfluidic volume1294-1and a second inlet conduit may provide a second flow rate and/or fluid pressure to the second microfluidic volume1294-2.

In some embodiments, the working fluid in the first microfluidic volume1294-1is the same working fluid in the second microfluidic volume1294-2. In some embodiments, the working fluid in the first microfluidic volume1294-1is shared with the second microfluidic volume1294-2. In other embodiments, a first working fluid is provided to the first microfluidic volume1294-1, and a second working fluid is provided to the second microfluidic volume1294-2. The first working fluid and second working fluid may have different boiling temperatures, different latent heat of boiling, different thermal capacities, different viscosities, or different reactivities, depending on different thermal management requirements of the different dies of the stacked-die processor.

While some embodiments described herein have a plurality of dies that are the same area, in other embodiments, at least one die of a stacked-die processor has a different shape or area than another die in the stacked-die processor.FIG.15is a side view of an embodiment of a heat generating component1314including a stacked-die processor including dies1324-1,1324-2,1324-3of varying sizes. A first die1324-1and second die1324-2(such as a CPU and GPU) have substantially the same area, while a third die1324-3(such as memory) has a different area. In some embodiments, different dies may have the same in-plane aspect ratio and have different areas, such as two different size squares. In some embodiments, different dies may have different in-plane aspect ratios and have the same area, such as two rectangles turned 900 relative to one another. In some embodiments, different dies may have different areas but share at least one dimension of their area, such as the second die1324-2and third die1324-2having different lengths in the direction of flow, but having equal widths perpendicular to the direction of flow. In another example, the first die1324-1and the second die1324-2may have equal lengths in the direction of flow, but having different widths perpendicular to the direction of flow.

Different size dies may have different thermal management requirements. In some embodiments, a first set of pin fins1396-1and a second set of pin fins1396-2have different BESFs thereon. For example, the first set of pin fins1396-1may have a BEC thereon and the second set of pin fins1396-2may lack a BEC or have a different BEC thereon. In other examples, the first set of pin fins1396-1may have a plurality of recesses in a pin surface thereof, and the second set of pin fins1396-2may lack recesses in a pin surface thereof or have recesses in a different pattern or with different dimensions. In other examples, the first set of pin fins1396-1may have a plurality of protrusions on a pin surface thereof, and the second set of pin fins1396-2may lack protrusions on a pin surface thereof or have protrusions in a different pattern or with different dimensions. In some embodiments, the thermal management requires of the dies1324-1,1334-2,1324-3may be different, and the BESFs of the first set of pin fins1396-1and the second set of pin fins1396-2may be different to effect the different thermal management properties.

In some embodiments, the working fluid is urged through the first microfluidic volume1394-1and through the second microfluidic volume1394-2at the same flow rate. For example, a manifold forming at least a portion of the side wall of the microfluidic volume1394-1,1394-2is connected to an inlet conduit may provide equal flow rate and/or equal fluid pressure to both the first microfluidic volume1394-1and the second microfluidic volume1394-2. In some embodiments, the flow rate is different, such as when different thermal management is required by different portions of the stacked-die processor. For example, a first inlet conduit may provide a first flow rate and/or fluid pressure to the first microfluidic volume1394-1and a second inlet conduit may provide a second flow rate and/or fluid pressure to the second microfluidic volume1394-2.

In some embodiments, the working fluid in the first microfluidic volume1394-1is the same working fluid in the second microfluidic volume1394-2. In some embodiments, the working fluid in the first microfluidic volume1394-1is shared with the second microfluidic volume1394-2. In other embodiments, a first working fluid is provided to the first microfluidic volume1394-1, and a second working fluid is provided to the second microfluidic volume1394-2. The first working fluid and second working fluid may have different boiling temperatures, different latent heat of boiling, different thermal capacities, different viscosities, or different reactivities, depending on different thermal management requirements of the different dies of the stacked-die processor.

In some embodiments, the pin fin height can vary between sets of pin fins. For example, a first pin fin height1317-1of the first set of pin fins1396-1may be different from a second pin fin height1317-2of the second set of pin fins1396-2.

FIG.16is a top cross-sectional view of the first set of pin fins1396-1ofFIG.15. In some embodiments, a pin fin has a pin fin aspect ratio of the pin fin height (e.g., first pin fin height1317-1ofFIG.15) to pin fin maximum transverse dimension1319-1. In some embodiments, a pin fin has a circular shape in transverse cross-section (such as illustrated inFIG.16), and the pin fin maximum transverse dimension1319-1is a diameter of the pin fin. In some embodiments, a pin fin has a square shape in transverse cross-section, and the pin fin maximum transverse dimension1319-1is a diagonal dimension of the pin fin. In some embodiments, a pin fin has an oval shape in transverse cross-section, and the pin fin maximum transverse dimension1319-1is a major axis of the pin fin. In some embodiments, the maximum transverse dimension1319-1is no more than 100 micrometers. In some embodiments, the maximum transverse dimension1319-1is no more than 75 micrometers. In some embodiments, the maximum transverse dimension1319-1is no more than 50 micrometers.

In some embodiments, the pin fin aspect ratio is approximately 1.0. In some embodiments, the pin fin aspect ratio is greater than 1.0. In some embodiments, the pin fin aspect ratio is no more than 1.0. In some embodiments, the pin fin aspect ratio varies from one pin fin to another in a set of pin fins. For example, the pin fin aspect ratio may increase in a direction of flow of working fluid through the microfluidic volume. By decreasing the maximum transverse dimension1319of the pin fins in the direction of flow, there may be greater amounts of microfluidic volume between the pin fins as vapor bubble formation occupies a larger proportion of the microfluidic volume.

The pin fin aspect ratio is at least partially based on the number and diameter of TSVs1398in the pin fin. For example, a higher pin fin aspect ratio reduces the volume of the pin fin, allowing greater surface area-to-volume ratio and more efficient cooling by working fluid in the microfluidic volume1394-1. However, a higher pin fin aspect ratio also reduces the volume of the pin fin, limiting the quantity and/or size of the TSVs1398positioned therethrough, which may limit performance of the processor.

A volume ratio of the stacked-die processor is the amount of total volume of the microfluidic volume that is occupied by the pin fins. For example, a volume ratio of 1.0 means there is no microfluidic volume and the entire space between the first die and the second die is filled with silicon and/or TSVs. A volume ratio of 0.5 means that there is an equal amount of pin fins and microfluidic volume between the first die and the second die. In some embodiments, the volume ratio is no more than 0.9. In some embodiments, the volume ratio is no less than 0.5. In some embodiments, the volume ratio is approximately 0.75.

A pin fin1396-1may have any quantity of TSVs1398therethrough. In some embodiments, a pin fin1396-1has at least one TSV1398therethrough. In some embodiments, a pin fin1396-1has at least three TSVs1398therethrough. In some embodiments, a pin fin1396-1has at least 7 TSVs1398therethrough. In some embodiments, the TSVs1398of a pin fin1396-1are arranged in a square (such as illustrated inFIG.16). In some embodiments, the TSVs1398of a pin fin1396-1are arranged in a hexagonal close-pack arrangement.

In some embodiments, a stacked-die processor includes a first set of pin fins with a first pin fin aspect ratio and a second set of pin fins with a second pin fin aspect ratio.FIG.17is a side view of an embodiment of a stacked-die processor including three dies1424-1,1424-2,1424-3with TSVs1498-1,1498-2of varying sizes and aspect ratios in each set of pin fins1496-1,1496-2.

FIG.18is a system diagram of a system for working fluid delivery to the microfluidic volume1594of a stacked-die heat-generating component1514. In some embodiments, a flow of the liquid phase1508of the working fluid is controlled by a controller1521that is in data communication with a pump1523and one or more sensors, such as a flow meter1525, temperature gauge1527, or other sensors that measure operating conditions of the working fluid in the inlet conduit1503and/or the outlet conduit1505. The outlet conduit1505, in some embodiments, circulates the hot working fluid (which may include both liquid phase and vapor phase) to a condenser1506or heat exchanger.

In some embodiments, the controller1521is in data communication with the heat-generating component to receive operating metrics of the heat-generating component, such as clock frequency, core voltage, core temperature, power draw, etc. In some embodiments, a flow rate of the working fluid through the inlet conduit1503into the microfluidic volume1594is controlled by the controller1521based at least partially on the operating conditions of the working fluid in the inlet conduit1503and/or the outlet conduit1505and/or the operating metrics of the heat-generating components. The controller1521may adjust the flow rate of the working fluid by sending instructions to the fluid pump1523and/or to a valve or baffle in the conduits. In some embodiments, the flow rate of the working fluid from the fluid pump is less than 1.0 liters per minute. In some embodiments, the flow rate of the working fluid from the fluid pump is less than 0.5 liters per minute.

FIG.19is a side view of an embodiment of a stacked-die processor with a wicking heat spreader1636with horizontal channels1660and vertical channels1662positioned therebetween. The stacked-die processor includes a first die1624-1and a second die1624-2. The wicking heat spreader1636, such as any embodiment of a wicking heat spreader described in relation toFIG.3throughFIG.10, is positioned between the first die1624-1and the second die1624-2. In some embodiments, at least a portion of the wicking heat spreader1636is integrally formed with silicon of one or more of the first die1624-1and the second die1624-2. In some embodiments, the wicking heat spreader1636is manufactured as a separate and discrete component, and the wicking heat spreader1636is affixed to one or both of the first die1624-1and the second die1624-2. For example, at least a portion of a vertical rail1674has one or more TSVs1698positioned therein, similar to the embodiments of pin fins described in relation toFIG.11through18.

FIG.20is a side view of an embodiment of a stacked-die processor with a wicking heat spreader1736with a plurality of BESFs positioned thereon. In some embodiments, the wicking heat spreader1736includes one or more BESFs located on an interior surface1748of the horizontal channels1760and vertical channels1762. In some embodiments, the BESFs include a BEC1780, a recess1782, a protrusion1784, or combinations thereof.

For example, a BEC1780may be deposited on an interior surface1748of a horizontal rail1772or a vertical rail1774of the wicking heat spreader1736. The BEC1780may be deposited by physical vapor deposition, chemical vapor deposition, sputtering, electroplating, or other coating deposition methods to create a surface roughness, texture, or chemical composition that promotes the formation of and/or release of vapor bubbles on the interior surface of the channels. In some embodiments, the BEC1780is etched into the interior surface1748of a horizontal rail1772or a vertical rail1774of the wicking heat spreader1736. For example, the BEC1780may be etched by ion etching or chemical etching to create a surface roughness or texture that promotes the formation of and/or release of vapor bubbles on the interior surface of the channels.

In some embodiments, the BESF includes or is a recess1782in the interior surface1748. The recess1782may include a curve or a corner. In some embodiments, the recess1782is positioned in the interior surface1748to promote the formation of a vapor bubble that is smaller than the cross-sectional area of the channel (e.g., the horizontal channel1740). For example, the recess1782may have an opening that is no more than half of the transverse dimension (such as the channel width or height) of the channel such that the vapor bubble that forms in the recess1782is smaller than the channel area. In other examples, the opening is no more than ⅓ of the transverse dimension of the channel.

A protrusion1784may be located on the interior surface1748to promote the promote the formation of and/or release of vapor bubbles on the interior surface of the channels. In some embodiments, the protrusion1784is formed by three-dimensional printing on the interior surface1748. In some embodiments, the protrusion1784is formed by etching or machine material to leave the protrusion1784remaining.

The BESF described herein may be combined in any manner. In some embodiments, the protrusion1784is located on a recess surface in the recess1782. In some embodiments, the protrusion1784has a BEC1780located thereon. In some embodiments, the recess1782has a BEC1780positioned therein.

FIG.21is a side view of another embodiment of a stacked-die processor with a wicking heat spreader1836located between the first die1824-1and a second die1824-2and a set of pin fins1896between the second die1824-2and the third die1824-3. In some embodiments, the BESFs described herein may be used in any combination with the wicking heat spreaders and pin fins described herein. For example, the wicking heat spreader1836may be similar to that described in relation toFIG.20, while the pin fins1896may have a BEC, a recess, a protrusion, or combinations thereof.

In some embodiments, the pin fins1896have BESFs on the pin surface1801, such as a BEC, recess, protrusion, or combinations thereof, such as described in relation toFIG.20. The BESFs may be positioned on all of the pin surface1801contacting the working fluid, or the BESFs may be positioned on less than all of the pin surface1801. For example, the BESFs may increase drag on the working fluid, inhibiting flow of the working fluid through the microfluidic volume1894. In some embodiments, the BESFs are selectively located on the pin surface1801relative to the direction of flow of the working fluid to promote the formation of and/or release of vapor bubbles (e.g., of the vapor phase of the working fluid) while lessening the drag on the flow of the working fluid.

INDUSTRIAL APPLICABILITY

The present disclosure relates generally to systems and methods for thermal management of electronic devices or other heat-generating components. In some embodiments, heat spreaders and wicking structures according to the present disclosure promote the boiling and vapor bubble formation and/or release during vaporization of working fluid.

Immersion chambers surround the heat-generating components in a liquid working fluid, which conducts heat from the heat-generating components to cool the heat-generating components. As the working fluid absorbs heat from the heat-generating components, the temperature of the working fluid increases. In some embodiments, the hot working fluid can be circulated through the thermal management system to cool the working fluid and/or replace the working fluid with cool working fluid. In some embodiments, the working fluid vaporizes, introducing vapor into the liquid of the working fluid which rises out of the liquid phase, carrying thermal energy away from the heat-generating components in the gas phase via the latent heat of boiling.

In large-scale computing centers, such as cloud-computing centers, data processing centers, data storage centers, or other computing facilities, immersion cooling systems provide an efficient method of thermal management for many computing components under a variety of operating loads. In some embodiments, an immersion cooling system includes a working fluid in an immersion chamber and a heat exchanger to cool the liquid phase and/or a condenser to extract heat from the vapor phase of the working fluid. The heat exchanger may include a condenser that condenses the vapor phase of the working fluid into a liquid phase and returns the liquid working fluid to the immersion chamber. In some embodiments, the liquid working fluid absorbs heat from the heat-generating components, and one or more fluid conduits direct the hot liquid working fluid outside of the immersion chamber to a radiator, heat exchanger, or region of lower temperature to cool the liquid working fluid.

In some embodiments, a high-compute application assigned to and/or executed on the computing devices or systems in the immersion cooling system requires a large amount of thermal management. A working fluid boiling absorbs heat to overcome the latent heat of boiling. The phase change from liquid to vapor, therefore, allows the working fluid to absorb a comparatively large amount of heat with a small associated increase in temperature. Further, the lower density allows the vapor to be removed from the immersion bath efficiently to exhaust the associated heat from the system.

In some embodiments, a thermal management system includes an immersion tank with a two-phase working fluid positioned therein. The two-phase working fluid receives heat from heat-generating components immersed in the liquid working fluid, and the heat vaporizes the working fluid, changing the working fluid from a liquid phase to a vapor phase. The thermal management system includes a condenser, such as described herein, to condense the vapor working fluid back into the liquid phase. In some embodiments, the condenser is in fluid communication with the immersion tank by one or more conduits. In some embodiments, the condenser is positioned inside the immersion tank.

In an example, a heat-generating component includes a die positioned on a printed circuit board (PCB). The die may be a generalized device, such as a central processing unit (CPU) or graphical processing unit (GPU), or a specialized device application-specific integrating circuit (ASIC). The die generates heat during use. The heat is transmitted by a thermal interface material (TIM) to a heat spreader that is in contact with the liquid phase of the working fluid in the immersion chamber.

The heat spreader transfers heat to the liquid phase of the working fluid to vaporize the working fluid into a vapor phase of the working fluid. As described herein, the formation of the vapor bubbles allows the working fluid to receive heat to overcome the latent heat of vaporization without substantially increasing the temperature of the working fluid. The vapor bubbles then, through the buoyancy of the vapor phase, rise out of the liquid phase of the working fluid, and liquid phase of the working fluid replaces the vapor phase contacting the surface of the heat spreader, allowing the process to repeat and continue.

However, the heat transfer of the heat spreader to the liquid phase of the working fluid is limited by the surface area of the heat spreader in contact with the liquid phase of the working fluid. A conventional, solid heat spreader has a limited surface area given the amount of space on the PCB and/or in the immersion chamber relative to other components, devices, or structures immersed in the working fluid. In some embodiments, vapor formation on the surface of the heat spreader further limits the available surface area of the heat spreader in contact with the liquid phase of the working fluid. A heat transfer rate from the heat spreader to the vapor phase of the working fluid is lower than for the heat spreader to the liquid phase of the working fluid. For example, while the vapor bubble remains in contact with a surface of the heat spreader, such as due to cohesion, the heat spreader can continue to increase in temperature above the boiling temperature of the working fluid, which may be undesirable for thermal management of the heat-generating component and/or preventing dryout in the immersion cooling system.

In some embodiments, one or more features that increase surface area and promote bubble formation and release from the heat spreader can improve heat transfer rates from the heat spreader to the working fluid.

In some embodiments, the wicking heat spreader is a three-dimensional heat spreader with a plurality of channels therein or therethrough that allow flow of working fluid through an interior volume of the heat spreader. A three-dimensional heat spreader conducts heat within a plane of the heat spreader that is parallel to a plane of the heat source (such as a surface of a die), as well as in a vertical direction away from the plane. In some embodiments, the wicking heat spreader includes both horizontal channels and vertical channels. For example, the horizontal channels may draw a liquid phase of the working fluid into the wicking heat spreader from the sides of the wicking heat spreader, while vertical channels allow exhausting of both liquid phase and vapor phase working fluid from the wicking heat spreader.

In some embodiments, the vapor bubbles floating out of the channels of the wicking heat spreader contribute to the flow of liquid phase working fluid into the channels of the wicking heat spreader. For example, the bubbles vacating the space in the channels of the wicking heat spreader can draw liquid phase working fluid into the channels to replace the volume of the vapor bubbles. In some embodiments, the fluidic drag of the vapor bubbles moving through the liquid phase working fluid can drag the liquid phase in the direction of movement of the vapor bubbles, which may move hot liquid phase working fluid out of the wicking heat spreader and encourage cool liquid phase working fluid to enter the wicking heat spreader.

It should be understood that while some embodiments of a wicking heat spreader are described with horizontal and vertical channels, the wicking heat spreader may be oriented in any direction relative to gravity. The embodiments described herein will describe the horizontal channels as being oriented substantially parallel to a plane of a surface of the die and vertical channels as being oriented substantially perpendicular to the plane of a surface of the die, but the channels may have other orientations, as well, as will be described in greater detail herein.

In some embodiments, a wicking heat spreader has an outer surface. The outer surface has openings therein to allow ingress and egress of working fluid to an interior volume of the wicking heat spreader. The wicking heat spreader has at least one horizontal channel and at least one vertical channel with interior surfaces that are oriented toward the interior volume (e.g., toward the channels) and away from the outer surface of the wicking heat spreader. The interior surfaces and outer surfaces of the wicking heat spreader increase the surface area of the wicking heat spreader relative to a conventional heat spreader with a continuous outer surface and no working fluid flow through the frame of the heat spreader. Increased surface area relative to volume allows for greater heat transfer to the working fluid and greater thermal management capacity.

In some embodiments, the interior surfaces have at least one boiling enhancement surface feature (BESF) thereon. For example, the BESF may include one or more surface treatments, recesses, or protrusions on the interior surfaces that promote the formation of vapor bubbles on and/or the release of vapor bubbles from the interior surfaces. In some embodiments, the BESF is or includes a boiling enhancement coating (BEC) applied to the interior surface of the wicking heat spreader. For example, the wicking heat spreader may have a frame with channels therein, and the BEC may be applied to the surface(s) of the frame such that the BEC is located on at least one interior surface448of the frame. In some embodiments, the BEC is located on at least 50% of the interior surface area of the frame. In some embodiments, the BEC is located on substantially all of the interior surface area of the frame. In some embodiments, the BEC is located on substantially all of the surface area of the frame in contact with or configured to contact working fluid (i.e., outer surfaces and interior surfaces).

In some embodiments, the wicking heat spreader is thermally connected to a heat-generating component through an intermediate heat spreader. For example, some heat spreaders, such as vapor chambers or graphite sheets have high in-plane thermal conductive to spread heat laterally, but such planar heat spreaders may have comparatively low surface area to volume ratios to efficiently transfer heat to the working fluid.

In some embodiments, the intermediate heat spreader receives heat from the die or other portion of a heat-generating component through a first TIM, and the intermediate heat spreader provides lateral heat spreading within a plane of the intermediate heat spreader. The intermediate heat spreader then allows the heat to be transferred more or substantially uniformly to the wicking heat spreader through a second TIM.

In some embodiments, the wicking heat spreader includes a plurality of horizontal rails with horizontal channels therebetween and a plurality of vertical rails with vertical channels therebetween.

In some embodiments, the horizontal channels allow for intakes to the horizontal channels on the lateral sides of the wicking heat spreader. The horizontal channels connect to vertical channels to flow working fluid through the wicking heat spreader. The working fluid can then exhaust from the wicking heat spreader.

In some embodiments, at least one of the horizontal channels is straight and continuous from a front surface (e.g., a lateral side) to a rear surface (e.g., a lateral side opposite the front surface). In some embodiments, all of the horizontal channels between the front surface and the rear surface are straight and continuous. In some embodiments, at least one of the horizontal channels has a curve, a bend, a corner, or another deviation that causes fluid flow to change direction compared to a straight channel. In some embodiments, at least one of the horizontal channels terminates between a first lateral side and a second lateral side.

In some embodiments, at least one of the horizontal channels allows fluid flow from a front surface of the wicking structure to a rear surface of the wicking structure. In some embodiments, at least one of the horizontal channels terminates between a first lateral side and a second lateral side and/or exhausts out a top surface of the wicking heat spreader.

In some embodiments, at least one of the vertical channels is straight and continuous from a bottom surface to the top surface. In some embodiments, all of the vertical channels between the bottom surface and the top surface are straight and continuous. In some embodiments, at least one of the vertical channels has a curve, a bend, a corner, or another deviation that causes fluid flow to change direction compared to a straight channel. In some embodiments, at least one of the vertical channels terminates between a bottom surface and the top surface.

In some embodiments, at least one of the vertical channels allows fluid flow from a bottom surface and the top surface. In some embodiments, at least one of the vertical channels terminates between a bottom surface and the top surface and/or exhausts out a lateral side of the wicking heat spreader.

The wicking heat spreader has a plurality of horizontal channels with intakes on the lateral side. In some embodiments, the horizontal channels have uniform transverse dimension (e.g., perpendicular to a direction of flow through the horizontal channel) such as a channel width or channel height. In other embodiments, at least one horizontal channel has a transverse area (e.g., channel width by channel height) that changes along a length of the horizontal channel. For example, vapor bubbles forming in the horizontal channel may create a pressure in the wicking heat spreader that resists ingress of additional working fluid. In some embodiments, the horizontal channel may increase in cross-sectional area toward a center of the wicking heat spreader to accommodate the increase in volume of the working fluid upon vaporization.

The wicking heat spreader has a plurality of vertical channels with openings on the top surface. In some embodiments, the vertical channels have uniform transverse dimension (e.g., perpendicular to a direction of flow through the vertical channels) such as a channel width or channel height illustrated in relation to the horizontal channels. In other embodiments, at least one vertical channel has a transverse area that changes along a length of the vertical channel toward the top surface. For example, vapor bubbles forming in the vertical channel may create a pressure in the wicking heat spreader that resists ingress of additional working fluid. In some embodiments, the vertical channel may increase in cross-sectional area toward the top surface of the wicking heat spreader to accommodate the increase in volume of the working fluid upon vaporization.

In some embodiments, the wicking heat spreader has a plurality of horizontal rails. In some embodiments, the horizontal rails have uniform transverse dimension (e.g., perpendicular to a direction of flow through the horizontal channel) such as a rail width or rail height. In other embodiments, at least one horizontal rail has a transverse area (e.g., rail width by channel height) that changes along a length of the horizontal rail. For example, vapor bubbles forming in the horizontal channel may create a pressure in the wicking heat spreader that resists ingress of additional working fluid. In some embodiments, one or more horizontal rails may decrease (e.g., taper) in cross-sectional area to allow the horizontal channel to increase in cross-sectional area toward a center of the wicking heat spreader to accommodate the increase in volume of the working fluid upon vaporization.

In some embodiments, the wicking heat spreader has a plurality of vertical rails. In some embodiments, the vertical rails have uniform transverse dimension (e.g., perpendicular to a direction of flow through the vertical channel) such as analog to the rail width or rail height described in relation to the horizontal rails. In other embodiments, at least one vertical rail has a transverse area that changes along a length of the vertical rail. For example, vapor bubbles forming in the vertical channel may create a pressure in the wicking heat spreader that resists ingress of additional working fluid. In some embodiments, one or more vertical rails may decrease (e.g., taper) in cross-sectional area toward the top surface to allow the horizontal channel to increase in cross-sectional area toward a center of the wicking heat spreader to accommodate the increase in volume of the working fluid upon vaporization.

To promote the formation of and/or release of vapor bubbles on the interior surface of the channels, in some embodiments, the channels include one of more BESF. In some embodiments, the BESF includes a BEC, a recess, a protrusion, or combinations thereof.

For example, a BEC may be deposited on an interior surface of a horizontal rail or a vertical rail of the wicking heat spreader. The BEC may be deposited by physical vapor deposition, chemical vapor deposition, sputtering, electroplating, or other coating deposition methods to create a surface roughness, texture, or chemical composition that promotes the formation of and/or release of vapor bubbles on the interior surface of the channels. In some embodiments, the BEC is etched into the interior surface of a horizontal rail or a vertical rail of the wicking heat spreader. For example, the BEC may be etched by ion etching or chemical etching to create a surface roughness or texture that promotes the formation of and/or release of vapor bubbles on the interior surface of the channels.

In some embodiments, the BESF includes or is a recess in the interior surface. The recess may include a curve or a corner. In some embodiments, the recess is positioned in the interior surface to promote the formation of a vapor bubble that is smaller than the cross-sectional area of the channel (e.g., the horizontal channel). For example, the recess may have an opening that is no more than half of the transverse dimension (such as the channel width or height) of the channel such that the vapor bubble that forms in the recess is smaller than the channel area. In other examples, the opening is no more than ⅓ of the transverse dimension of the channel.

A protrusion may be located on the interior surface to promote the promote the formation of and/or release of vapor bubbles on the interior surface of the channels. In some embodiments, the protrusion is formed by three-dimensional printing on the interior surface. In some embodiments, the protrusion is formed by etching or machine material to leave the protrusion remaining.

The BESF described herein may be combined in any manner. In some embodiments, the protrusion is located on a recess surface in the recess. In some embodiments, the protrusion has a BEC located thereon. In some embodiments, the recess has a BEC positioned therein.

In some embodiments, a method of manufacturing a wicking heat spreader includes obtaining a frame of a wicking structure and forming at least one boiling enhancement surface feature positioned on at least one interior surface of the frame. In some embodiments, the frame includes at least one horizontal channel and at least one vertical channel that intersect and allow fluid flow therethrough.

In some embodiments, obtaining a frame includes machining the frame from a billet. In some embodiments, obtaining a frame includes three-dimensional printing of the frame. In some embodiments, obtaining a frame includes casting the frame. In some embodiments, obtaining a frame includes sintering of the frame. In some embodiments, obtaining a frame includes injection molding of the frame. In some embodiments, obtaining a frame includes a combination of machining, three-dimensional printing, casting, sintering, and injection molding. In some embodiments, obtaining a frame includes obtaining a first portion of the frame by any method described herein and subsequently additively manufacturing a second portion of the frame onto the first portion of the frame. For example, the first portion of the frame may have a BEC deposited thereon, and the second portion of the frame is additively manufactured over the first portion, thereby allowing an interior surface of the frame to have a BEC that would otherwise be inaccessible for some deposition techniques.

In some embodiments, forming at least one BESF on an interior surface of the frame includes depositing or etching a BEC on the interior surface. In some embodiments, forming at least one BESF on an interior surface of the frame includes forming a recess in the interior surface. In some embodiments, the recess is formed by etching. In some embodiments, the recess is formed by machining. In some embodiments, the recess is formed during three-dimensional printing of the frame. In some embodiments, forming at least one BESF on an interior surface of the frame includes forming a protrusion on the interior surface. In some embodiments, the protrusion is printed on the interior surface. In some embodiments, the protrusion is deposited on the interior surface. In at least one embodiment, the protrusion is formed in a recess of the interior surface.

A vapor bubble may form in a recess of the interior surface of the frame. In some embodiments, the recess includes protrusions. Liquid phase flow through the channels of the wicking heat spreader promotes the release of the vapor bubbles. In some embodiments, refilling of the vacated volume and/or release of the vapor bubble from the frame can be increased by the use of a porous frame. For example, a porous frame may allow the liquid phase of the working fluid to enter the wicking heat spreader more easily and/or create a fluid pressure behind the vapor bubble to aid in releasing the vapor bubble.

In some embodiments, working fluid (either two-phase or single-phase working fluid) can be directed adjacent to and/or directly contacting a die in a heat-generating component. In some embodiments, a stacked die processor (e.g., a heat-generating component) includes a first die and a second die with a microfluidic volume therebetween. In some embodiments, the microfluidic volume allows flow of a liquid phase of a working fluid through the microfluidic volume and around a plurality of pin fins positioned between and connected to the first die and the second die. In some embodiments, the pin fins are integrally formed with one or both of the first die and the second die to allow direct on-chip cooling of the first die and the second die.

In some embodiments, the working fluid is a single-phase working fluid, and the liquid phase of the working fluid flows through the microfluidic volume from a first lateral side of the stacked-die processor to a second lateral side of the stacked die processor. In some embodiments, the first lateral side and second lateral side are opposite one another. In some embodiments, the lateral side and second lateral side are abutting one another at a corner of the stacked-die processor, such as allowing a 90° turn to the flow of working fluid through the microfluidic volume. In some embodiments, the top surface of the first die and the bottom surface of the second die are planar and parallel to one another such that a height of the microfluidic volume is constant through the microfluidic volume.

The pin fins connect the first die and the second die to one another and may provide thermal conductivity therebetween, such as conducting heat from the first die and the second die into the pin fins to assist in transferring the heat into the liquid phase of the working fluid. In some embodiments, at least one of the pin fins has a through-silicon via (TSV) positioned therein to provide electrically connection and communication through the pin fins between the electronic components and circuitry of the first die and the second die. In some embodiments, the TSV is vulnerable to thermal damage, and efficient removal of heat from the pin fin may increase the performance and/or operational lifetime of the TSVs and/or the stacked-die processor.

In some embodiments, the pin fins have BESFs on the pin surface, such as a BEC, recess, protrusion, or combinations thereof. The BESFs may be positioned on all of the pin surface contacting the working fluid, or the BESFs may be positioned on less than all of the pin surface. For example, the BESFs may increase drag on the working fluid, inhibiting flow of the working fluid through the microfluidic volume. In some embodiments, the BESFs are selectively located on the pin surface relative to the direction of flow of the working fluid to promote the formation of and/or release of vapor bubbles (e.g., of the vapor phase of the working fluid) while lessening the drag on the flow of the working fluid.

In some embodiments, a closed loop system for cooling a stacked-die heat generating component includes an inlet conduit connected to a first lateral side and an outlet conduit connected to a second lateral side. In other embodiments, the inlet conduit and outlet conduit connected to the same lateral side to circulate working fluid in the microfluidic volume.

In some embodiments, a stacked-die processor includes a first die, a second die, and a third die stacked with pin fins containing TSVs therebetween. In some embodiments, a first microfluidic volume is located between the first die and the second die, and a first set of pin fins couples the first die and the second die through the first microfluidic volume. In some embodiments, a second microfluidic volume is located between the second die and the third die, and a second set of pin fins couples the second die and the third die through the second microfluidic volume.

As described herein, the pin fins have, in some embodiments, at least one BESF position on a pin surface thereof. In some embodiments, the first set of pin fins and the second set of pin fins have the same BESF(s) thereon. For example, the first set of pin fins may have a BEC thereon and the second set of pin fins may have the same BEC thereon. In other examples, the first set of pin fins may have a plurality of recesses in a pin surface thereof, and the second set of pin fins may have a plurality of recesses in a pin surface thereof. In other examples, the first set of pin fins may have a plurality of protrusions on a pin surface thereof, and the second set of pin fins may have a plurality of protrusions on a pin surface thereof.

In some embodiments, the first set of pin fins and the second set of pin fins have different BESFs thereon. For example, the first set of pin fins may have a BEC thereon and the second set of pin fins may lack a BEC or have a different BEC thereon. In other examples, the first set of pin fins may have a plurality of recesses in a pin surface thereof, and the second set of pin fins may lack recesses in a pin surface thereof or have recesses in a different pattern or with different dimensions. In other examples, the first set of pin fins may have a plurality of protrusions on a pin surface thereof, and the second set of pin fins may lack protrusions on a pin surface thereof or have protrusions in a different pattern or with different dimensions. In some embodiments, the thermal management requires of the dies may be different, and the BESFs of the first set of pin fins and the second set of pin fins may be different to effect the different thermal management properties.

In some embodiments, the working fluid is urged through the first microfluidic volume and through the second microfluidic volume at the same flow rate. For example, a manifold connected to an inlet conduit may provide equal flow rate and/or equal fluid pressure to both the first microfluidic volume and the second microfluidic volume. In some embodiments, the flow rate is different, such as when different thermal management is required by different portions of the stacked-die processor. For example, a first inlet conduit may provide a first flow rate and/or fluid pressure to the first microfluidic volume and a second inlet conduit may provide a second flow rate and/or fluid pressure to the second microfluidic volume.

In some embodiments, the working fluid in the first microfluidic volume is the same working fluid in the second microfluidic volume. In some embodiments, the working fluid in the first microfluidic volume is shared with the second microfluidic volume. In other embodiments, a first working fluid is provided to the first microfluidic volume, and a second working fluid is provided to the second microfluidic volume. The first working fluid and second working fluid may have different boiling temperatures, different latent heat of boiling, different thermal capacities, different viscosities, or different reactivities, depending on different thermal management requirements of the different dies of the stacked-die processor.

While some embodiments described herein have a plurality of dies that are the same area, in other embodiments, at least one die of a stacked-die processor has a different shape or area than another die in the stacked-die processor. In some embodiments, a first die and second die (such as a CPU and GPU) have substantially the same area, while a third die (such as memory) has a different area. In some embodiments, different dies may have the same in-plane aspect ratio and have different areas, such as two different size squares. In some embodiments, different dies may have different in-plane aspect ratios and have the same area, such as two rectangles turned 900 relative to one another. In some embodiments, different dies may have different areas but share at least one dimension of their area, such as the second die and third die having different lengths in the direction of flow but having equal widths perpendicular to the direction of flow. In another example, the first die and the second die may have equal lengths in the direction of flow but having different widths perpendicular to the direction of flow.

Different size dies may have different thermal management requirements. In some embodiments, a first set of pin fins and a second set of pin fins have different BESFs thereon. For example, the first set of pin fins may have a BEC thereon and the second set of pin fins may lack a BEC or have a different BEC thereon. In other examples, the first set of pin fins may have a plurality of recesses in a pin surface thereof, and the second set of pin fins may lack recesses in a pin surface thereof or have recesses in a different pattern or with different dimensions. In other examples, the first set of pin fins may have a plurality of protrusions on a pin surface thereof, and the second set of pin fins may lack protrusions on a pin surface thereof or have protrusions in a different pattern or with different dimensions. In some embodiments, the thermal management requires of the dies may be different, and the BESFs of the first set of pin fins and the second set of pin fins may be different to effect the different thermal management properties.

In some embodiments, the working fluid is urged through the first microfluidic volume and through the second microfluidic volume at the same flow rate. For example, a manifold connected to an inlet conduit may provide equal flow rate and/or equal fluid pressure to both the first microfluidic volume and the second microfluidic volume. In some embodiments, the flow rate is different, such as when different thermal management is required by different portions of the stacked-die processor. For example, a first inlet conduit may provide a first flow rate and/or fluid pressure to the first microfluidic volume and a second inlet conduit may provide a second flow rate and/or fluid pressure to the second microfluidic volume.

In some embodiments, the working fluid in the first microfluidic volume is the same working fluid in the second microfluidic volume. In some embodiments, the working fluid in the first microfluidic volume is shared with the second microfluidic volume. In other embodiments, a first working fluid is provided to the first microfluidic volume, and a second working fluid is provided to the second microfluidic volume. The first working fluid and second working fluid may have different boiling temperatures, different latent heat of boiling, different thermal capacities, different viscosities, or different reactivities, depending on different thermal management requirements of the different dies of the stacked-die processor.

In some embodiments, the pin fin height can vary between sets of pin fins. For example, a first pin fin height of the first set of pin fins may be different from a second pin fin height of the second set of pin fins.

In some embodiments, a pin fin has a pin fin aspect ratio of the pin fin height to pin fin maximum transverse dimension. In some embodiments, a pin fin has a circular shape in transverse cross-section, and the pin fin maximum transverse dimension is a diameter of the pin fin. In some embodiments, a pin fin has a square shape in transverse cross-section, and the pin fin maximum transverse dimension is a diagonal dimension of the pin fin. In some embodiments, a pin fin has an oval shape in transverse cross-section, and the pin fin maximum transverse dimension is a major axis of the pin fin. In some embodiments, the maximum transverse dimension is no more than 100 micrometers. In some embodiments, the maximum transverse dimension is no more than 75 micrometers. In some embodiments, the maximum transverse dimension is no more than 50 micrometers.

In some embodiments, the pin fin aspect ratio is approximately 1.0. In some embodiments, the pin fin aspect ratio is greater than 1.0. In some embodiments, the pin fin aspect ratio is no more than 1.0. In some embodiments, the pin fin aspect ratio varies from one pin fin to another in a set of pin fins. For example, the pin fin aspect ratio may increase in a direction of flow of working fluid through the microfluidic volume. By decreasing the maximum transverse dimension of the pin fins in the direction of flow, there may be greater amounts of microfluidic volume between the pin fins as vapor bubble formation occupies a larger proportion of the microfluidic volume.

The pin fin aspect ratio is at least partially based on the number and diameter of TSVs in the pin fin. For example, a higher pin fin aspect ratio reduces the volume of the pin fin, allowing greater surface area-to-volume ratio and more efficient cooling by working fluid in the microfluidic volume. However, a higher pin fin aspect ratio also reduces the volume of the pin fin, limiting the quantity and/or size of the TSVs positioned therethrough, which may limit performance of the processor.

A volume ratio of the stacked-die processor is the amount of total volume of the microfluidic volume that is occupied by the pin fins. For example, a volume ratio of 1.0 means there is no microfluidic volume and the entire space between the first die and the second die is filled with silicon and/or TSVs. A volume ratio of 0.5 means that there is an equal amount of pin fins and microfluidic volume between the first die and the second die. In some embodiments, the volume ratio is no more than 0.9. In some embodiments, the volume ratio is no less than 0.5. In some embodiments, the volume ratio is approximately 0.75.

A pin fin may have any quantity of TSVs therethrough. In some embodiments, a pin fin has at least one TSV therethrough. In some embodiments, a pin fin has at least three TSVs therethrough. In some embodiments, a pin fin has at least 7 TSVs therethrough. In some embodiments, the TSVs of a pin fin are arranged in a square. In some embodiments, the TSVs of a pin fin are arranged in a hexagonal close-pack arrangement.

In some embodiments, a stacked-die processor includes a first set of pin fins with a first pin fin aspect ratio and a second set of pin fins with a second pin fin aspect ratio. In some embodiments, a stacked-die processor includes three dies with TSVs of varying sizes and aspect ratios in each set of pin fins.

In some embodiments, a flow of the liquid phase of the working fluid is controlled by a controller that is in data communication with a pump and one or more sensors, such as a flow meter, temperature gauge, or other sensors that measure operating conditions of the working fluid in the inlet conduit and/or the outlet conduit. The outlet conduit, in some embodiments, circulates the hot working fluid (which may include both liquid phase and vapor phase) to a condenser or heat exchanger.

In some embodiments, the controller is in data communication with the heat-generating component to receive operating metrics of the heat-generating component, such as clock frequency, core voltage, core temperature, power draw, etc. In some embodiments, a flow rate of the working fluid through the inlet conduit into the microfluidic volume is controlled by the controller based at least partially on the operating conditions of the working fluid in the inlet conduit and/or the outlet conduit and/or the operating metrics of the heat-generating components. The controller may adjust the flow rate of the working fluid by sending instructions to the fluid pump and/or to a valve or baffle in the conduits. In some embodiments, the flow rate of the working fluid from the fluid pump is less than 1.0 liters per minute. In some embodiments, the flow rate of the working fluid from the fluid pump is less than 0.5 liters per minute.

In some embodiments, a stacked-die processor includes a first die and a second die with a wicking heat spreader therebetween. The wicking heat spreader, such as any embodiment of a wicking heat spreader described herein, connects the first die and the second die. In some embodiments, at least a portion of the wicking heat spreader is integrally formed with silicon of one or more of the first die and the second die. In some embodiments, the wicking heat spreader is manufactured as a separate and discrete component, and the wicking heat spreader is affixed to one or both of the first die and the second die. For example, at least a portion of a vertical rail has one or more TSVs positioned therein, similar to the embodiments of pin fins described herein.

In some embodiments, a stacked-die processor has a wicking heat spreader with a plurality of BESFs positioned thereon. In some embodiments, the wicking heat spreader includes one or more BESFs located on an interior surface of the horizontal channels and vertical channels. In some embodiments, the BESFs include a BEC, a recess, a protrusion, or combinations thereof.

For example, a BEC may be deposited on an interior surface of a horizontal rail or a vertical rail of the wicking heat spreader. The BEC may be deposited by physical vapor deposition, chemical vapor deposition, sputtering, electroplating, or other coating deposition methods to create a surface roughness, texture, or chemical composition that promotes the formation of and/or release of vapor bubbles on the interior surface of the channels. In some embodiments, the BEC is etched into the interior surface of a horizontal rail or a vertical rail of the wicking heat spreader. For example, the BEC may be etched by ion etching or chemical etching to create a surface roughness or texture that promotes the formation of and/or release of vapor bubbles on the interior surface of the channels.

In some embodiments, the BESF includes or is a recess in the interior surface. The recess may include a curve or a corner. In some embodiments, the recess is positioned in the interior surface to promote the formation of a vapor bubble that is smaller than the cross-sectional area of the channel (e.g., the horizontal channel). For example, the recess may have an opening that is no more than half of the transverse dimension (such as the channel width or height) of the channel such that the vapor bubble that forms in the recess is smaller than the channel area. In other examples, the opening is no more than ⅓ of the transverse dimension of the channel.

A protrusion may be located on the interior surface to promote the promote the formation of and/or release of vapor bubbles on the interior surface of the channels. In some embodiments, the protrusion is formed by three-dimensional printing on the interior surface. In some embodiments, the protrusion is formed by etching or machine material to leave the protrusion remaining.

The BESF described herein may be combined in any manner. In some embodiments, the protrusion is located on a recess surface in the recess. In some embodiments, the protrusion has a BEC located thereon. In some embodiments, the recess has a BEC positioned therein.

In some embodiments, a stacked-die processor has a wicking heat spreader located between a first die and a second die and a set of pin fins between the second die and the third die. In some embodiments, the BESFs described herein may be used in any combination with the wicking heat spreaders and pin fins described herein. For example, the wicking heat spreader may be similar to that described herein, while the pin fins may have a BEC, a recess, a protrusion, or combinations thereof.

In some embodiments, the pin fins have BESFs on the pin surface, such as a BEC, recess, protrusion, or combinations thereof, such as described herein. The BESFs may be positioned on all of the pin surface contacting the working fluid, or the BESFs may be positioned on less than all of the pin surface. For example, the BESFs may increase drag on the working fluid, inhibiting flow of the working fluid through the microfluidic volume. In some embodiments, the BESFs are selectively located on the pin surface relative to the direction of flow of the working fluid to promote the formation of and/or release of vapor bubbles (e.g., of the vapor phase of the working fluid) while lessening the drag on the flow of the working fluid.

The present disclosure relates to systems and methods for cooling heat-generating components of a computer or computing device according to at least the examples provided in the sections below:

[A1] In some embodiments, a processor includes a first die, a second die connected to the first die with a microfluidic volume positioned between the first die and the second die, a wicking heat spreader positioned in the microfluidic volume; and a boiling enhancement surface feature positioned on at least one surface of the wicking heat spreader.

[A2] In some embodiments, the boiling enhancement surface feature of [A1] includes at least one protrusion on the at least one surface.

[A3] In some embodiments, the boiling enhancement surface feature of [A1] includes at least one recess positioned in the at least one surface.

[A4] In some embodiments, the at least one recess has a recess surface of [A3], and the recess surface has at least one protrusion on the recess surface.

[A5] In some embodiments, the wicking heat spreader of any of [A1] through [A4] includes at least one horizontal channel configured to allow fluid flow from a front surface of the wicking heat spreader to a rear surface of the wicking heat spreader.

[A6] In some embodiments, one or more of the at least one horizontal channels of [A5] is continuous and straight from the front surface to the rear surface.

[A7] In some embodiments, the wicking heat spreader of any of [A1] through [A6] includes at least one vertical rail configured to allow thermal conductivity from a bottom surface of the wicking heat spreader to a top surface of the wicking heat spreader.

[A8] In some embodiments, the one or more of the at least one vertical rails of [A7] is continuous and straight from the bottom surface to the top surface.

[A9] In some embodiments, a through-silicon via (TSV) is located in the vertical rail of [A8].

[A10] In some embodiments, the boiling enhancement surface feature is a boiling enhancement coating positioned on a surface of a frame of the wicking heat spreader.

[B1] In some embodiments, a processor includes a first die, a second die connected to the first die with a microfluidic volume positioned between the first die and the second die, a wicking heat spreader positioned in the microfluidic volume, at least one through-silicon via (TSV) in the wicking heat spreader providing electrical connection between the first die and the second die, and a boiling enhancement surface feature positioned on at least one surface of the wicking heat spreader.

[B2] In some embodiments, a top surface of the microfluidic volume of [B1] and a bottom surface of the microfluidic volume are planar and parallel.

[B3] In some embodiments, a vertical rail of the wicking heat spreader of [B1] or [B2] includes a plurality of TSVs therethrough.

[B4] In some embodiments, at least a portion of a frame of the wicking heat spreader of any of [B1] through [B3] is porous.

[B5] In some embodiments, at least part of the wicking heat spreader of [B1 through [B4] is integrally formed with one of the first die and the second die.

[B6] In some embodiments, the first die of any of [B1] through [B2] has a first area, and the second die has a second area different from the first area.

[C1] In some embodiments, a system for cooling a processor includes a first die, a second die connected to the first die with a microfluidic volume positioned between the first die and the second die, a wicking heat spreader positioned in the microfluidic volume, at least one through-silicon via (TSV) in the wicking heat spreader providing electrical connection between the first die and the second die, a boiling enhancement surface feature positioned on at least one surface of the wicking heat spreader, and a fluid pump configured to provide a working fluid to the wicking heat spreader in the microfluidic volume.

[C2] In some embodiments, the fluid pump of [C1] provides the working fluid to the microfluidic volume with a flow rate of less than 1.0 liters per minute.

[C3] In some embodiments, the system of [C1] or [C2] includes a third die connected to the second die with a second microfluidic volume positioned between the second die and the third die, a second wicking heat spreader positioned in the second microfluidic volume, and at least one TSV in the second wicking heat spreader providing electrical connection between the second die and the third die.

[C4] In some embodiments, the working fluid in the microfluidic volume of [C3] has a first flow rate, and a second flow rate of working fluid through the second microfluidic volume is different from the first flow rate.

The articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements in the preceding descriptions. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about”, “substantially”, or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value.

A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims.

It should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “front” and “back” or “top” and “bottom” or “left” and “right” are merely descriptive of the relative position or movement of the related elements.

The present disclosure may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. Changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.