Patent Description:
An additional approach to the use of processors and related components, based on CMOS technology, is the use of superconducting logic-based components and devices. Superconducting logic-based components and devices can also be used to process quantum information, such as qubits. However, such devices need to operate at cryogenic temperatures and thus require additional cooling. In some instances, the CMOS-based components and the superconducting-logic based components can be integrated as part of the same system.

<CIT> discloses a cooling assembly for circuit boards.

<CIT> discloses an apparatus for providing immersion cooling in a compact-format circuit card environment.

In one aspect, the present invention provides a system according to claim <NUM>.

In another aspect, the present invention provides a method according to claim <NUM>.

Certain more specific aspects of the invention are set out in the dependent claims.

Examples described in this disclosure relate to cryogenic systems with indium application to heat sinks and heat loads. Certain examples of cryogenic systems include computing systems having superconducting components and devices. The examples of the present disclosure relate to a computing system comprising components operating at cryogenic temperatures (i.e., at or below <NUM> Kelvin). In one example, the computing system is housed in a vacuum assembly. In this example, the superconducting system may include one or more superconducting component formed on a substrate. The superconducting component may include integrated circuit chips mounted on the substrate. The packaging of such superconducting components is challenging because such components may need to withstand large changes in the ambient temperature (e.g., from about <NUM> Kelvin to about <NUM> Kelvin or lower).

Superconducting components and devices may use Josephson junctions to implement the functionality associated with a circuit. An exemplary Josephson junction may include two superconductors coupled via a region that impedes current. The region that impedes current may be a physical narrowing of the superconductor itself, a metal region, or a thin insulating barrier. As an example, the Superconductor-Insulator-Superconductor (SIS) type of Josephson junctions may be implemented as part of the superconducting circuits. As an example, superconductors are materials that can carry a direct electrical current (DC) in the absence of an electric field. Superconductors have a critical temperature (Tc) below which they have zero resistance. Niobium, one such superconductor, has a critical temperature (Tc) of <NUM> Kelvin. At temperatures below Tc, niobium is superconductive; however, at temperatures above Tc, it behaves as a normal metal with electrical resistance. Thus, in the SIS type of Josephson junction superconductors may be niobium superconductors and insulators may be Al<NUM>O<NUM> barriers. In SIS type of junctions, the superconducting electrons are described by a quantum mechanical wave-function. A changing phase difference in time of the phase of the superconducting electron wave-function between the two superconductors corresponds to a potential difference between the two superconductors.

Various superconducting circuits including transmission lines can be formed by coupling multiple Josephson junctions by inductors or other components, as needed. Microwave pulses can travel via these transmission lines under the control of at least one clock. The microwave pulses can be positive or negative or a combination thereof. The microwave pulses may have a frequency of up to <NUM> or higher. Any circuit board or other type of structure, such as an interposer with such superconducting circuits, may be required to support not only the high-frequency microwave signals but also direct current (DC) signals. Although there are several benefits of superconductivity, including lower resistance and better bandwidth characteristics, superconducting materials need to be operated at temperatures below their critical temperature and thus require additional cooling.

<FIG> shows a diagram of a cryogenic system <NUM> comprising a housing <NUM> including a chassis for receiving blades in accordance with one example. The housing <NUM> is configured to maintain a lower pressure inside the housing than a pressure outside the housing. In one example, housing <NUM> may be configured to maintain a vacuum inside the housing. The lower pressure inside the housing may be a vacuum that corresponds to a pressure in a range between <NUM> Pa to <NUM> x <NUM>-<NUM> Pa (<NUM>-<NUM> Torr to <NUM>-<NUM> Torr). Thus, several components (e.g., processors and memory) corresponding to cryogenic system <NUM> may be located inside housing <NUM> that maintains vacuum. The use of the vacuum ensures that there is no convection and thereby advantageously allows components that are operating at very different temperatures to be housed in the same chassis or another such structure. Housing <NUM> may also maintain thermal insulation with respect to ambient temperature.

With continued reference to <FIG>, housing <NUM> includes one or more chassis for receiving blades (e.g., computing blades). As used herein, the term "chassis" includes, but is not limited to, any structure for interfacing with a blade having at least one circuit board. The term "chassis" also includes any parts that could be separately machined and installed as part of the structure for receiving the blade. In this example, housing <NUM> includes chassis <NUM>. In one example, chassis <NUM> may have blades installed with only superconducting components operable in an environment having a temperature at or below <NUM>. Alternatively, the circuit boards may include both superconducting components and semiconductor components (e.g., CMOS-based integrated circuits). The circuit boards may include components other than superconducting and non-superconductor components. As an example, the circuit boards may include components, such as passive resistors, discrete capacitors, discrete inductors, micro-electromechanical systems (MEMS), optical components, or other types of components used for computing, storage, and networking applications. Different temperature zones may be maintained in the housing depending on the types of components mounted on circuit boards inserted into the slots (e.g., slots <NUM> and <NUM>) corresponding to chassis <NUM>. This may be accomplished via a combination of thermal isolation and cooling via liquid helium or other such coolants. With respect to the components mounted on a circuit board, as used herein the phrase "operating in an environment having a temperature at or below" means that the respective circuit board is thermally linked to a chassis portion that is maintained at or below the specified temperature (e.g., a temperature of <NUM>, <NUM>, or <NUM>).

Housing <NUM> may further include multiple thermal shields that may be configured to thermally isolate portions of each of the circuit boards inserted into the slots corresponding to chassis <NUM>. In one example, the thermal shields may be formed using copper or aluminum and may further be wrapped in multi-layer insulation. <FIG> shows an example thermal shield <NUM> that may be cooled via liquid nitrogen or liquid helium flowing through each of the pipes <NUM> and <NUM> shown in <FIG>. Pipes <NUM> and <NUM> carrying liquid nitrogen or liquid helium may be brazed to, or otherwise attached, to cold plates associated with the appropriate thermal environment. As an example, aluminum or copper sidewalls may be mounted adjacent to superconducting components. Aluminum or copper sidewalls may also be cooled via liquid nitrogen or liquid helium flowing through pipes (e.g., pipes <NUM> and <NUM> in <FIG>.

Still referring to <FIG>, a thermosiphon (or a similar system) may be used as part of the cooling system. As part of the thermosiphon, natural convection driven by gravity with the colder fluid (e.g., liquid helium or liquid nitrogen) flowing downhill and the warmer fluid flowing back up may be used to cool the cold plates and other components associated with the cooling system. The thermosiphon may include liquid flowing down and vapor flowing back. It is to be recognized that the temperature ranges referred to herein relate to the temperature of the heat transfer elements (e.g., the heat spreaders or the chassis) to which these components are coupled and not the temperature of the components themselves. Thus, references such as the components are "operating at" or "maintained at" refer to the temperature of the heat transfer elements to which these components are coupled for heat transfer purposes. Although <FIG> shows a certain arrangement of components, substrates, and other component, these could be arranged in a different manner. In addition, fewer or additional components, substrates, and other components may be present.

<FIG> shows a diagram of a blade <NUM> for use in chassis <NUM> of <FIG>. Blade <NUM> comprises a first circuit board <NUM> and a second circuit board <NUM>. As used herein, the term "blade" includes, but is not limited to, computing blades, storage blades, communication blades, or a combination of any computing, storage, or communication functionality. In addition, the term "blade" includes any shapes or sizes of structures for mounting at least one circuit board into a chassis. Each of the circuit boards may have several integrated circuits mounted on it. In addition, each of the circuit boards may be bonded to respective heat spreaders. In this example, blade <NUM> includes a heat spreader <NUM> bonded to a circuit board <NUM> having a substrate <NUM> with superconducting components <NUM>, <NUM>, <NUM>, and <NUM> mounted on it. In this example, superconducting components <NUM>, <NUM>, <NUM>, and <NUM> may be configured to operate in an environment having a temperature at or below <NUM>. Superconducting components <NUM>, <NUM>, <NUM>, and <NUM> may be packaged and formed in many different configurations. As an example, the superconducting components may be configured as multi-chip modules, ball-grid array (BGA) packages, system-in-packages (SIPs), or package-on-packages (POPs). Blade <NUM> further includes another heat spreader <NUM> bonded to another circuit board <NUM>. Although not shown in <FIG>, circuit board <NUM> may also have a substrate with superconducting components mounted on it. In one example, superconducting components may include Central-Processing Units (CPUs), Graphics-Processing Units (GPUs), Artificial Intelligence Processors, Field-Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application-Specific Standard Products (ASSPs), System-on-a-Chip systems (SOCs), or Complex Programmable Logic Devices (CPLDs).

With continued reference to <FIG>, heat spreader <NUM> may have at least two surfaces <NUM> and <NUM> that interface with a respective portion of a chassis (e.g., chassis <NUM> of <FIG>) configured to receive blade <NUM>. The heat spreader <NUM> is made of either aluminum or another type of metal. In one example, the aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight. In another example, the aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight. Indium may be pressed onto surfaces <NUM> and <NUM> by applying a high pressure. In one example, the pressure may be in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI). Prior to pressing the indium, surfaces <NUM> and <NUM> may be cleaned using water or alcohol. Surfaces <NUM> and <NUM> may also be treated with acid to remove oxides. By limiting the displacement of the press by using a die, the thickness of indium can be set to a pre-determined thickness as it extrudes during the pressing process. In this example, the pressure used to press indium against these surfaces results in a permanent bonding of the indium to the metal used to form heat spreader <NUM>. In this manner several objectives are achieved: (<NUM>) a good mechanical bond between indium and the heat spreader, (<NUM>) a good thermal bond between indium and the heat spreader, and (<NUM>) a flat indium surface. Advantageously, this process incudes no heating of any of the parts being bonded together. In one example, heat spreader <NUM> may be formed using pure aluminum, and indium may be permanently bonded to the appropriate surfaces of heat spreader <NUM>. In one example, the aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight. In another example, the aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight. Indium could also be used to renew surfaces of a heat spreader having preexisting indium by pressing additional indium onto such surfaces.

Still referring to <FIG>, indium may similarly be permanently bonded to certain surfaces of heat spreader <NUM> as well. Blade <NUM> may further comprise two wedge locks <NUM> and <NUM>. Once blade <NUM> is inserted into a slot, wedge locks <NUM> and <NUM> may be used to press heat spreaders in a way such that each heat spreader is tightly coupled with an opposing surface of the chassis. This process may increase gap <NUM> between heat spreader <NUM> and heat spreader <NUM>. Indium, once permanently bonded to the appropriate surfaces of the heat spreaders, may stick to these surfaces such that even when blade <NUM> is removed and reinserted into a slot associated with the chassis the indium may not fall off or otherwise be removed. Although the example in <FIG> refers to the use of aluminum, other metals may also be used. As an example, a high residual-resistance ratio (RRR) copper may also be used. In addition, instead of wedge locks other types of clamping devices may be used. Moreover, the surfaces having indium permanently bonded to are merely shown as examples. Indium, or a similar metal, may be bonded to other surfaces of the heat spreaders and the substrates associated with the circuit boards.

<FIG> shows a diagram of a blade <NUM> in accordance with one example. Blade <NUM> comprises circuit boards. Each of the circuit boards incorporated as part of blade <NUM> may have several integrated circuits mounted on it. In addition, each of the circuit boards may be bonded to respective heat spreaders. In this example, blade <NUM> includes two circuit boards <NUM> and <NUM>. Circuit boards <NUM> and <NUM> may be interconnected via a combination of rigid and flexible interconnects. Flexible interconnects <NUM> and <NUM> may be used to connect the components mounted on circuit board <NUM> with connectors <NUM> and <NUM> bonded to another circuit board <NUM>. Similarly, flexible interconnects <NUM> and <NUM> may be used to connect the components mounted on circuit board <NUM> with the connectors bonded to circuit board <NUM>. Other interconnection arrangements may also be used to allow for signals to propagate from one circuit board to the other circuit board and vice-versa.

With continued reference to <FIG>, circuit board <NUM> may include non-superconducting components (e.g., CMOS, BiCMOS, or other type of devices that are suitable for operation without requiring cryogenic temperatures). As an example, non-superconducting components may include components <NUM> and <NUM> mounted on substrate <NUM>. In this example, non-superconducting components <NUM> and <NUM> may be configured to operate in an environment having a temperature above <NUM> and up to <NUM>. In one example, the preferred temperature may be <NUM>. The temperature environment may be maintained via a combination of thermal isolation and cooling using water or some other coolant. As an example, copper sidewalls (included as part of chassis <NUM> or otherwise coupled to chassis <NUM>) may be mounted adjacent to the non-superconducting components. Copper sidewalls may also be cooled via water (or some other coolant) flowing through pipes or other means. Non-superconducting components <NUM> and <NUM> may be packaged and formed in many different configurations. As an example, the non-superconducting components may be configured as multi-chip modules, ball-grid array (BGA) packages, system-in-packages (SIPs), or package-on-packages (POPs). In this example, the non-superconducting components may comprise memory components, including any of non-volatile or volatile memory components. Volatile memory components may include any of the various types of random-access memory components, including dynamic random-access memory (DRAM) components. Non-volatile memory components may include any of various types of memory components that can store information even when they are not powered, including flash-memory components. Non-superconducting components may further include Field-Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application-Specific Standard Products (ASSPs), System-on-a-Chip systems (SOCs), or Complex Programmable Logic Devices (CPLDs). Thus, while the non-superconducting components may also include components, such as ASICs, ASSPs, SOCs, CPLDs, or other types of controllers that may coordinate communication between the superconducting components and the non-superconducting components. The non-superconducting components may be formed using various semiconductor fabrication processes, including photo-imaging, patterning, annealing, contact formation, and packaging.

Still referring to <FIG>, circuit board <NUM> may include superconducting components <NUM>, <NUM>, <NUM>, and <NUM> mounted on a substrate <NUM>. In this example, superconducting components <NUM>, <NUM>, <NUM>, and <NUM> may be configured to operate in an environment having a temperature at or below <NUM>. The temperature environment may be maintained as described in <FIG>. Superconducting components <NUM>, <NUM>, <NUM>, and <NUM> may be packaged and formed in many different configurations. As an example, the superconducting components may be configured as multi-chip modules, ball-grid array (BGA) packages, system-in-packages (SIPs), or package-on-packages (POPs). In one example, superconducting components may include Central-Processing Units (CPUs), Graphics-Processing Units (GPUs), Artificial Intelligence Processors, Field-Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application-Specific Standard Products (ASSPs), System-on-a-Chip systems (SOCs), or Complex Programmable Logic Devices (CPLDs).

Each of the superconducting components may include a stack of superconducting layers and dielectric layers formed on a substrate. In one example, the superconducting components may be formed to support signals ranging from DC to signals having a frequency that is greater than <NUM>. In this example, the superconducting components may be fabricated over large silicon substrates such as <NUM> wafers, <NUM> wafers or even larger wafers, which may be separated into multiple dies. In one example, the substrate could be made from silicon or any other thermally insulating or conducting material. Also, in this example, signal traces and ground planes may be formed by sputtering niobium, or a similar superconducting material. As an example, compounds of niobium such as niobium nitride (NbN) or niobium titanium nitride (NbTiN) may also be used. Other physical vapor deposition (PVD) methods, such as molecular beam epitaxy (MBE), may also be used. Depending on the type of the material used for the traces, sputtering processes, chemical vapor deposition (CVD) processes, plasma enhanced chemical vapor deposition (PECVD) process, evaporation processes, or atomic layer deposition (ALD) processes may also be used. Thus, for example, the niobium compounds such as NbN and NbTiN may be formed using a CVD process.

Superconducting components may include a dielectric layer formed over a substrate. The dielectric layer may be formed by depositing a dielectric (e.g., liquid crystal polymer (LCP)) on the chip substrate. A superconducting layer may be formed over the dielectric layer. The superconducting layer may be formed using any of the deposition techniques, such as CVD or PECVD, and then patterning the deposited material using photolithography. The layout for the superconducting structures may be created using a place and route design tool that is used to create the layout for the superconducting wires or other elements. As an example, photo-resist may be patterned to protect only those areas of the superconducting layer that will be formed as superconducting wires or other structures as defined by the layout of the particular layer, such as a metal layer. Other superconducting metals or metal alloys may also be used as part of this step. In one example, the vias and the traces may be formed by conformal deposition of niobium in the same deposition step as the one used for forming the traces. The via wells could be patterned directly in a photo-imageable polyimide or etched in a separate step. The metal traces and vias may be defined in the same subtractive etch step. The pad connections may be configured to support Ti/Au or Ti/Al pads for a variety of wire bond or flip chip bump and wire bond technologies, such as Indium solder bump, Tin-Silver (Snag) solder bump, Gold stud bump, Copper pillar bump, or other electrical interconnect bump types.

With continued reference to <FIG>, a heat spreader <NUM> is bonded to substrate <NUM> of circuit board <NUM>. Heat spreader <NUM> may have at least two surfaces (e.g., similar to surfaces <NUM> and <NUM> of heat spreader <NUM> in <FIG>) that interface with a respective portion of a chassis (e.g., chassis <NUM> of <FIG>) configured to receive blade <NUM>. This way heat spreader <NUM> may allow transfer of heat from non-superconducting components (e.g., non-superconducting components <NUM> and <NUM>) to a cooling system associated with a system comprising blade <NUM>. Another heat spreader <NUM> may be bonded to a substrate of a circuit board mounted on an opposite side of circuit board <NUM>. Similarly, a heat spreader <NUM> is bonded to substrate <NUM> of circuit board <NUM>. Heat spreader <NUM> may have at least two surfaces (e.g., similar to surfaces <NUM> and <NUM> of heat spreader <NUM> in <FIG>) that interface with a respective portion of a chassis (e.g., chassis <NUM> of <FIG>) configured to receive blade <NUM>. This way heat spreader <NUM> may allow transfer of heat from superconducting components (e.g., superconducting components <NUM>, <NUM>, <NUM> and <NUM>) to a cooling system associated with a system comprising blade <NUM>. Another heat spreader <NUM> may be bonded to a substrate of a circuit board mounted on an opposite side of circuit board <NUM>. As explained earlier, components mounted on circuit boards <NUM> and <NUM> may be interconnected via flexible interconnects, which in turn may be coupled to circuit board <NUM>. A heat spreader <NUM> may be bonded to circuit board <NUM>. Heat spreader <NUM> may have at least two surfaces (e.g., similar to surfaces <NUM> and <NUM> of heat spreader <NUM> in <FIG>) that interface with a respective portion of a chassis (e.g., chassis <NUM> of <FIG>) configured to receive blade <NUM>. This way heat spreader <NUM> may allow transfer of heat from the flexible interconnects and circuit board <NUM> to a cooling system associated with a system comprising blade <NUM>. Another heat spreader <NUM> may be bonded to the other side of circuit board <NUM>.

In this example, each of the heat spreaders associated with blade <NUM> may be made of either aluminum or another type of metal. In one example, the aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight. In another example, the aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight. Indium may be pressed onto relevant surfaces of the heat spreaders by applying a high pressure. In one example, the pressure may be in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI). Prior to pressing the indium, the appropriate surfaces may be cleaned using water or alcohol. These surfaces may also be treated with acid to remove surface oxide. By limiting the displacement of the press by using a die, the thickness of indium can be set to a pre-determined thickness as it extrudes during the pressing process. In this example, the pressure used to press indium against these surfaces results in a permanent bonding of the indium to the metal used to form the heat spreaders. In one example, the heat spreaders (e.g., heat spreaders <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>) may be formed using pure aluminum, and indium may be permanently bonded to the appropriate surfaces of the respective heat spreaders. In one example, the aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight. In another example, the aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight. Blade <NUM> may further comprise several wedge locks (e.g., wedge locks <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>), which may function in a similar manner as the wedge locks described earlier with respect to <FIG>. Indium, once permanently bonded to the appropriate surfaces of the heat spreaders, may stick to these surfaces such that even when blade <NUM> is removed and reinserted into a slot associated with the chassis the indium may not fall off or otherwise removed. Although the example in <FIG> refers to the use of aluminum, other metals may also be used. As an example, a high residual-resistance ratio (RRR) copper may also be used. In addition, instead of wedge locks other types of clamping devices may be used. Moreover, the surfaces having indium permanently bonded to are merely shown as examples. Indium, or a similar metal, may be bonded to other surfaces of the heat spreaders and the substrates associated with the circuit boards.

With respect to each of the circuit boards described with respect to blade <NUM> of <FIG> and blade <NUM> of <FIG>, superconducting components or non-superconducting components may communicate with each other using circuit traces formed on the top or the bottom surface of each of the substrates (e.g., substrates <NUM> and <NUM>). The circuit traces may be formed using a suitable manufacturing process, including, but not limited to, selective laser sintering, fused deposition modeling, direct metal laser sintering, stereolithography, cladding, electron beam melting, electron beam direct manufacturing, aerosol jetting, ink jetting, semi-solid freeform fabrication, digital light processing, <NUM> photon polymerization, laminated object manufacturing, 3D printing, or other similar manufacturing processes. In one example, the circuit traces may be made of niobium (or another suitable superconducting material) in a region of the substrate that includes superconducting components. This region may exclude any normal metal, e.g., copper metal. In the other region the circuit traces may be made of both niobium and copper (or another suitable metal or metal alloy comprising a superconducting metal and a normal metal) that includes the non-superconducting components.

<FIG> shows a view <NUM> of blade <NUM> of <FIG> partially inserted into a portion of chassis <NUM> of <FIG> in accordance with one example. In this example, a portion <NUM> of the chassis may include several surfaces that interface with the surfaces of the heat spreaders having indium pressed into them. In this example, surface <NUM> of the top heat spreader is shown as interfacing with surface <NUM> of portion <NUM> of the chassis. In addition, surface <NUM> of the top heat spreader is shown as interfacing with surface <NUM> of the chassis. Another portion of the bottom heat spreader is shown as interfacing with surface <NUM> of portion <NUM> of the chassis. As explained earlier wedge locks <NUM> and <NUM> may be used to increase the pressure between the surfaces having indium pressed into them to improve heat transfer. Although <FIG> shows a certain arrangement of components, these could be arranged in a different manner. In addition, fewer or additional components, heat spreaders, and other circuit boards may be present.

<FIG> shows a view <NUM> of blade <NUM> of <FIG> partially inserted into a portions of chassis <NUM> of <FIG> in accordance with one example. In this example, portions <NUM>, <NUM>, and <NUM> of the chassis may include several surfaces that interface with the surfaces of the heat spreaders having indium pressed into them. In this example, surface <NUM> of the top heat spreader is shown as interfacing with surface <NUM> of portion <NUM> of the chassis. In addition, surface <NUM> of the top heat spreader is shown as interfacing with surface <NUM> of the chassis. As explained earlier wedge locks <NUM> and <NUM> may be used to tighten the coupling between the surfaces having indium pressed into them to improve heat transfer. Other heat spreaders may also have indium pressed into similar surfaces to allow for better thermal coupling between the heat spreaders and the respective portions of the chassis. In this example, portion <NUM> of the chassis may be associated with the circuit board having semiconductor components <NUM> and <NUM> mounted on it. Portion <NUM> of the chassis may be associated with the circuit board having connectors <NUM> and <NUM>. Portion <NUM> of the chassis may be associated with the circuit board having superconducting components <NUM>, <NUM>, <NUM>, and <NUM>. Each portion of the chassis may be maintained at a different temperature by cooling the portion via heat transfer. Although <FIG> shows a certain arrangement of components, these could be arranged in a different manner. In addition, fewer or additional components, heat spreaders, and other circuit boards may be present.

<FIG> is a view <NUM> having additional details of a blade in accordance with one example. As shown in view <NUM>, heat spreaders <NUM> and <NUM> may be spread apart from each other using wedge lock <NUM> to improve thermal contact between heat spreaders <NUM> and <NUM> and the chassis (or another heat transfer element). In this example, two circuit boards <NUM> and <NUM> are shown. A surface of circuit board <NUM> is bonded to a surface of heat spreader <NUM> and a surface of circuit board <NUM> is bonded to a surface of heat spreader <NUM>. The thermal interface between the circuit boards and the heat spreaders may be flat. The efficient heat transfer via the interfaces (at the edges of the blade) between the heat spreader's surfaces and the chassis (as shown in <FIG> and earlier in <FIG> and <FIG>) may reduce the stress introduced by the coefficient of thermal expansion (CTE) mismatch between the material used to form the substrate and the metal used to form the heat spreader.

<FIG> shows a flow chart <NUM> of a method for assembling a computing system comprising at least one blade. Step <NUM> includes forming a first heat spreader configured to transfer heat from the first circuit board to a cooling system associated with the computing system. The first heat spreader may be any of the heat spreaders described earlier. Step <NUM> includes forming a second heat spreader configured to transfer heat from the second circuit board to a cooling system associated with the computing system. Each of the first heat spreader and the second heat spreaders may be any of the heat spreaders described earlier with respect to blade <NUM> of <FIG> and blade <NUM> of <FIG>. Similarly, each of the first circuit boards and the second circuit boards may be any of the circuit boards described earlier with respect to blade <NUM> of <FIG> and blade <NUM> of <FIG>. In this example, forming the first heat spreader may include machining a first block of aluminum, and forming the second heat spreader may include machining a second block of aluminum. Each of the first block of aluminum and the second block of aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight. In another example, the aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight.

Step <NUM> includes permanently bonding indium to a first selected surface of the first heat spreader, where the first selected surface is part of a first heat transfer path from the first circuit board to the cooling system. Step <NUM> includes permanently bonding indium to a second selected surface of the second heat spreader, where the second selected surface is part of a second heat transfer path from the second circuit board to the cooling system. Prior to permanently bonding the indium, respective surfaces may be cleaned using water or alcohol. In one example, permanently bonding indium to the first selected surface of the first heat spreader may include extruding indium on to the first selected surface of the first heat spreader and pressing indium onto the first selected surface using a pressure in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI). Similarly, permanently bonding indium to the second selected surface of the second heat spreader may include extruding indium on to the second selected surface of the second heat spreader and pressing indium onto the second selected surface using a pressure in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI). Advantageously, no heat may be applied to any of the heat spreaders during the permanent bonding of indium to respective surfaces. By limiting the displacement of the press by using a die, the thickness of indium can be set to a pre-determined thickness as it extrudes during the pressing process. In this example, the pressure used to press indium against these surfaces results in a permanent bonding of the indium to the metal used to form the heat spreaders. In this manner several objects are achieved: (<NUM>) a good mechanical bond between indium and the heat spreader, (<NUM>) a good thermal bond between indium and the heat spreader, and (<NUM>) a flat indium surface.

Step <NUM> includes installing the first circuit board and the second circuit board in a chassis associated with the computing system. As an example, the circuit boards may be installed as part of blades described earlier into the chassis (e.g., chassis <NUM> of <FIG>). Although flow chart <NUM> describes the steps being performed in a certain order, the steps need not be performed in this order. In addition, fewer or more steps may be performed as part of the method described with respect to flow chart <NUM> of <FIG>.

In conclusion, in one aspect of the present disclosure a system including a housing configured to maintain a lower pressure inside the housing than a pressure outside the housing is provided. The system further includes a chassis, arranged inside the housing. The chassis comprises at least one slot for receiving a blade. The blade includes a circuit board having a plurality of components mounted on a substrate. The chassis is coupled to a cooling system to maintain at least a subset of the plurality of components operating in an environment having a temperature at or below <NUM> Kelvin. The blade, arranged in a slot of the chassis, includes a first heat spreader comprising a metal. The first heat spreader including metal is arranged to transfer heat from the first circuit board to the cooling system via a first interface between a first surface of the first heat spreader and a second surface of the chassis, and where indium is permanently bonded to either the first surface of the first heat spreader, or the second surface of the chassis, or both the first surface of the first heat spreader and the second surface of the chassis.

Indium may be permanently bonded to either the first surface of the first heat spreader, or the second surface of the chassis, or both the first surface of the first heat spreader and the second surface of the chassis by pressing indium onto a respective surface using a pressure in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI).

The blade further includes a second circuit board, mounted on an opposite side of the first circuit board, having a second plurality of components mounted on a second substrate and a second heat spreader comprising a metal, where the second heat spreader is arranged to transfer heat from the second circuit board to the cooling system via a second interface between a third surface of the second heat spreader and a fourth surface of the chassis, and where indium is permanently bonded to either the third surface of the second heat spreader, or the fourth surface of the chassis, or both the third surface of the second heat spreader and the fourth surface of the chassis. Indium may be permanently bonded to either the third surface of the second heat spreader, or the fourth surface of the chassis, or both the third surface of the second heat spreader and the fourth surface of the chassis by pressing indium onto a respective surface using a pressure in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI).

The blade may comprise a first wedge lock and a second wedge lock configured to spread the first heat spreader from the second heat spreader further apart to improve a thermal contact between the first heat spreader and the chassis and to improve a thermal contact between the second heat spreader and the chassis. The metal may be high purity aluminum having at least <NUM> percent aluminum by weight. The lower pressure inside the housing may correspond to a pressure in a range between <NUM> Pa to <NUM> x <NUM>-<NUM> Pa (<NUM>-<NUM> Torr to <NUM>-<NUM> Torr).

In another aspect the present disclosure relates to a method for assembling a computing system comprising at least one blade including a first circuit board and a second circuit board, where at least one of the first circuit board or the second circuit board includes superconducting components configured to operate in an environment having a temperature at or below <NUM> Kelvin. The method includes forming a first heat spreader configured to transfer heat from the first circuit board to a cooling system associated with the computing system. The method further includes forming a second heat spreader configured to transfer heat from the second circuit board to a cooling system associated with the computing system. The method further includes permanently bonding indium to a first selected surface of the first heat spreader, where the first selected surface is part of a first heat transfer path from the first circuit board to the cooling system. The method further includes permanently bonding indium to a second selected surface of the second heat spreader, where the second selected surface is part of a second heat transfer path from the second circuit board to the cooling system. The method further includes installing the first circuit board and the second circuit board in a chassis associated with the computing system.

As part of this method, forming the first heat spreader may comprise machining a first block of aluminum, and forming the second heat spreader may comprise machining a second block of aluminum, where each of the first block of aluminum and the second block of aluminum may be high purity aluminum having at least <NUM> percent aluminum by weight.

In addition, permanently bonding indium to the first selected surface of the first heat spreader may comprise extruding indium on to the first selected surface of the first heat spreader and pressing indium onto the first selected surface using a pressure in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI). No heat may be applied to the first heat spreader during permanently bonding indium to the first selected surface of the first heat spreader.

Moreover, permanently bonding indium to the second selected surface of the second heat spreader may comprise extruding indium on to the second selected surface of the second heat spreader and pressing indium onto the second selected surface using a pressure in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI). No heat may be applied the second heat spreader during permanently bonding indium to the second selected surface of the second heat spreader. Finally, prior to installing the first circuit board and the second circuit board in the chassis associated with the computing system, the method may include combining the first circuit board, the second circuit board, the first heat spreader, and the second heat spreader into a computing blade.

The present disclosure also provides a system including a housing configured to maintain a lower pressure inside the housing than a pressure outside the housing. The system further includes a chassis, arranged inside the housing, where the chassis comprises at least one slot for receiving a blade, where the blade comprises a first circuit board having a plurality of superconducting components mounted on a first substrate and a second circuit board having a plurality of non-superconducting components mounted on a second substrate. The chassis is coupled to a cooling system to maintain the plurality of superconducting components operating in an environment having a temperature at or below <NUM> Kelvin. The chassis may be coupled to the cooling system to maintain the plurality of non-superconducting components operating in an environment having a temperature at or below <NUM> Kelvin. The blade, arranged in a slot of the chassis, includes a first heat spreader comprising a metal, where the first heat spreader is arranged to transfer heat from the first circuit board to the cooling system via a first interface between a first surface of the first heat spreader and a second surface of the chassis, and where indium is permanently bonded to either the first surface of the first heat spreader, or the second surface of the chassis, or both the first surface of the first heat spreader and the second surface of the chassis. The blade may further include a second heat spreader comprising a metal, where the second heat spreader is arranged to transfer heat from the second circuit board to the cooling system via a second interface between a third surface of the second heat spreader and a fourth surface of the chassis, and where indium is permanently bonded to either the third surface of the second heat spreader, or the fourth surface of the chassis, or both the third surface of the second heat spreader and the fourth surface of the chassis.

The first circuit board may be coupled via a first set of flexible interconnects to a third circuit board, the second circuit board may be coupled via a second set of flexible interconnects to the third circuit board, and the third circuit board may be maintained at a temperature equal to or below <NUM> Kelvin. The first set of flexible interconnects may be coupled to the second set of flexible interconnects to allow for exchange of signals between the plurality of superconducting components and the plurality of non-superconducting components.

Indium may be permanently bonded to either the first surface of the first heat spreader, or the second surface of the chassis, or both the first surface of the first heat spreader and the second surface of the chassis by pressing indium onto a respective surface using a pressure in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI). In addition, indium may be permanently bonded to either the third surface of the second heat spreader, or the fourth surface of the chassis, or both the third surface of the second heat spreader and the fourth surface of the chassis by pressing indium onto a respective surface using a pressure in a range between <NUM> MPa to <NUM> MPa (<NUM>,<NUM> pounds per square inch (PSI) to <NUM>,<NUM> PSI).

The blade may comprise a first wedge lock and a second wedge lock configured to spread the first heat spreader from the second heat spreader further apart to improve a thermal contact between the first heat spreader and the chassis and to improve a thermal contact between the second heat spreader and the chassis.

It is to be understood that the methods, modules, and components depicted herein are merely exemplary. For example, and without limitation, illustrative types of superconducting devices may include Field-Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application-Specific Standard Products (ASSPs), System-on-a-Chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), etc..

In addition, in an abstract, but still definite sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or inter-medial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "coupled," to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundaries between the functionality of the above-described operations are merely illustrative. The functionality of multiple operations may be combined into a single operation, and/or the functionality of a single operation may be distributed in additional operations. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.

Although the disclosure provides specific examples, various modifications and changes can be made without departing from the scope of the disclosure as set forth in the claims below. Any benefits, advantages, or solutions to problems that are described herein with regard to a specific example are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.

Claim 1:
A computing system comprising
a housing (<NUM>) ;
a chassis (<NUM>), arranged inside the housing (<NUM>); and
a blade (<NUM>) arranged in a slot (<NUM>) of the chassis (<NUM>), wherein the blade (<NUM>) comprises a first circuit board (<NUM>) having a plurality of components (<NUM>, <NUM>) mounted on a substrate (<NUM>);
wherein the chassis is coupled to a cooling system to maintain at least a subset of the plurality of components (<NUM>, <NUM>) operating in an environment having a temperature at or below <NUM> Kelvin;
wherein the blade comprises a first heat spreader (<NUM>) comprising a metal, wherein the first heat spreader (<NUM>) is arranged to transfer heat from the first circuit board (<NUM>) to the cooling system via an interface between a first surface of the first heat spreader (<NUM>) and a second surface of the chassis (<NUM>), and wherein indium is permanently bonded to either the first surface of the first heat spreader (<NUM>), or the second surface of the chassis (<NUM>), or both the first surface of the first heat spreader (<NUM>) and the second surface of the chassis (<NUM>); and
wherein
the housing (<NUM>) is configured to maintain a lower pressure inside the housing (<NUM>) than a pressure outside the housing;
the blade further comprises a second circuit board (<NUM>), mounted on an opposite side of the first circuit board (<NUM>), having a second plurality of components (<NUM>, <NUM>, <NUM>, <NUM>) mounted on a second substrate (<NUM>) and a second heat spreader (<NUM>) comprising a metal, wherein the second heat spreader (<NUM>) is arranged to transfer heat from the second circuit board (<NUM>) to the cooling system via a second interface between a third surface of the second heat spreader (<NUM>) and a fourth surface of the chassis (<NUM>), and wherein indium is permanently bonded to either the third surface of the second heat spreader (<NUM>), or the fourth surface of the chassis (<NUM>), or both the third surface of the second heat spreader (<NUM>) and the fourth surface of the chassis (<NUM>).