APPARATUS AND METHODS FOR COOLING OF AN INTEGRATED CIRCUIT

Systems and methods for cooling an Integrated Circuit (IC) are provided. In one embodiment, the system includes a vessel for holding a coolant in a liquid phase, where the IC is at least in part thermally coupled to the coolant via a heat transfer surface to transfer heat generated by the IC to the coolant. The heat transfer surface has a porous surface exhibiting a gradient of porosity and/or particle size along at least one direction of the heat transfer surface.

FIELD OF THE INVENTION

The invention generally relates to cooling of integrated circuits and more particularly to apparatus and methods for cooling of an integrated circuit by use of a liquid coolant.

BACKGROUND

The amount of power an integrated circuit (IC) produces fluctuates based on computational workload of the IC. In general, an increase in power results in an increase in temperature of the IC and in particular an increase in the transistors junction temperature. As the junction temperature increases so does the probability of getting logic errors in the IC and after a certain temperature the IC can no longer be expected to function properly. Thus, when there is a high computational workload of an IC, there is a desire to ensure that the IC functions properly by controlling the temperature of the IC.

One conventional method for controlling the temperature of an IC includes monitoring the IC's temperature with a thermal sensor and adjusting the speed of a fan directed to a heat sink coupled to the IC accordingly. Another conventional method for controlling the temperature of an IC includes monitoring the IC's temperature and lowering the clock frequency of the IC accordingly when the temperature increases.

However, the computing power of ICs is generally limited by thermal management issues and as such when it is desirable for an IC to be processing at a high computational workload, conventional methods for controlling the temperature of ICs may not allow for adequate temperature control that ensure that the IC functions properly while still meeting the desired high computational workload.

In light of the above, there is a need for improving the way that the temperature of ICs is managed and/or the manner in which ICs are cooled.

SUMMARY

In accordance with one embodiment there is provided a system for cooling an integrated circuit (IC). The system comprises a closed vessel for holding a coolant in a liquid phase, the vessel being delimited at least in part by a heat transfer region, the heat transfer region being thermally-coupled with at least one surface of the IC. The system also comprises a heat-releasing element. The heat transfer region comprises a porous layer, the porous layer exhibiting a gradient of at least one of a porosity and a pore size distribution along at least one dimension of the heat transfer region.

In accordance with another embodiment there is provided a system for cooling an integrated circuit (IC). The system comprises a closed vessel for holding a coolant in a liquid phase and a heat-releasing element. The heat transfer from the IC to the liquid coolant occurs via at least one heat transfer region having a thermal resistance, the heat transfer region being integral with the IC.

In accordance with another embodiment there is provided a system for cooling an integrated circuit (IC). The system comprises a closed vessel for holding a coolant in a liquid phase, the vessel being delimited at least in part by a heat exchange surface, the heat exchange surface being thermally-coupled with at least one surface of the IC, The system also comprises a heat-releasing element. The heat exchange surface has a thermal resistance of no more than about 0.4 degree Celsius per watt for an IC power of about 45 watts.

In accordance with another embodiment there is provided a system for cooling an integrated circuit (IC). The system comprises a closed vessel for holding a coolant in a liquid phase, the vessel being delimited at least in part by a heat exchange surface, the heat exchange surface being thermally-coupled with at least one surface of the IC, The system also comprises a heat-releasing element. The heat exchange surface has a thermal resistance of no more than about 0.36 degree Celsius per watt for an IC power of about 67 watts.

In accordance with another embodiment there is provided a system for cooling an integrated circuit (IC). The system comprises a closed vessel for holding a coolant in a liquid phase, the vessel being delimited at least in part by a heat exchange surface, the heat exchange surface being thermally-coupled with at least one surface of the IC, The system also comprises a heat-releasing element. The heat exchange surface has a thermal resistance of no more than about 0.33 degree Celsius per watt for an IC power of about 88 watts.

In accordance with another embodiment there is provided a system for cooling an integrated circuit (IC). The system comprises a closed vessel for holding a coolant in a liquid phase, the vessel being delimited at least in part by a heat exchange surface, the heat exchange surface being thermally-coupled with at least one surface of the IC. The system also comprises a heat-releasing element. The heat exchange surface has a thermal resistance of no more than about 0.29 degree Celsius per watt for an IC power of about 110 watts.

In accordance with another embodiment there is provided a system for cooling an integrated circuit (IC). The system comprises a closed vessel for holding a coolant in a liquid phase, the vessel being delimited at least in part by a heat transfer region, the heat transfer region being thermally-coupled with at least one surface of the IC. The vessel comprises at least one valve. The system also comprises a heat-releasing element comprising at least one fan. The system also comprises a controller configured for operating the IC at a first IC parameter and deactivating the least one fan. The controller is also configured to control a pressure within the vessel such that the pressure within the vessel is within a first pressure P1and a second pressure P2. The system is also configured to operate the IC at a second IC parameter and activating the least one fan. The system is also configured to turn the IC off when the pressure within the vessel reaches a third pressure P3

It is to be expressly understood that the description and drawings are only for the purpose of illustrating certain embodiments of the invention and are an aid for understanding. They are not intended to be a definition of the limits of the invention.

DETAILED DESCRIPTION

In general, a cooling system is provided for cooling an integrated circuit that is at least in part thermally coupled to a liquid coolant that is held in a vessel. A method for cooling an integrated circuit using the cooling system is also provided. Examples of implementation are illustrated in the annexed drawings and further described below.

According to one non-limiting embodiment, the cooling system includes a sealed vessel extending between an integrated circuit and a heat sink. A liquid coolant is provided within the vessel, the coolant having specific thermal properties that cause the coolant to absorb latent heat that is generated by the integrated circuit and evaporate from a liquid to a vapor at a surface in contact with the integrated circuit during its operation. The properties of the coolant also cause the coolant to condense from the vapor back to the liquid when the vapor contacts the heat sink, thus releasing the latent heat from the vapor to the heat sink.

In the following description, specific exemplary embodiments in which the disclosure may be practiced are described in sufficient detail to enable those skilled in the art to practice the disclosed embodiments. For example, specific details such as specific, structures, elements, and connections have been presented herein. However, it is to be understood that the specific details presented need not be utilized to practice embodiments of the present disclosure. It is also to be understood that other embodiments may be utilized and that logical, architectural, programmatic, mechanical, electrical and other changes may be made without departing from general scope of the disclosure.

Cooling System

FIG.1shows a cooling system100for cooling an integrated circuit (IC)102in accordance with a first non-limiting embodiment. The cooling system100notably comprises a vessel104for holding a liquid coolant108, a heat sink112, a controller106and an optional sensor110. The vessel104is in thermal communication with the IC102as well as the heat sink112, as further described below.

The IC102may be implemented using any suitable hardware components for implementing a central processing unit (CPU) including a microcontroller, field-programmable gate array (FPGA), application-specific integrated circuit (ASIC), digital signal processor (DSP), graphics processing unit (GPU), any other suitable semiconductor device, or any other suitable device. The IC102may be configured such that when it is running (e.g., powered on and in operation) it may process various data. The IC102may be suitable for a server, such as in servers running in data centers. When the IC102is running, it produces heat based on a number of factors including the voltage level, the clock/frequency speed/rate, and/or the workload of the IC102. As such, when the IC102is running, the temperature of the IC102is based at least in part on the heat produced by the IC102. As the temperature of the IC102increases, a critical temperature may be reached, at which the IC102must be shut down or throttled down to prevent it from overheating. With further reference toFIG.2, in some non-limiting examples, the IC102may be packaged in a module. The module may include the IC102, a substrate202, as well as other structural elements (e.g., solder joints, underfill material, etc.), the module being itself attached to an electronic device204, such as a motherboard via a socket (not illustrated). As such, the IC102may be associated with various electronic components external to the IC102and connected via the electronic device204.

In this first embodiment, the vessel104comprises a heat absorbing surface1041, a heat releasing surface1042and a plurality of walls150i, as further described below. In terms of its composition, the vessel104may be made of any suitable material, or combination of materials, as it will be readily appreciated that the heat absorbing surface1041, the heat releasing surface1042and the plurality of walls150imay be made of the same material or they may be made of different materials. For example, the heat absorbing surface1041and the heat releasing surface1042may be made of a material that generally facilitates and/or improves heat transfer, while the plurality of walls may be made of a separate material that impedes, rather than facilitates, heat transfer. In one non-limiting example, the vessel104may be made of a first material, the first material being a metallic material that generally isolates the IC102from external electromagnetic interferences, such as but not limited to stainless steel. In another non-limiting example, the first material may be a composite material along with a suitable electromagnetic shielding, such as copper meshing. Taken together, the heat absorbing surface1041, the heat releasing surface1042and the plurality of walls1051define an inner compartment that is sealed during use, that is the inner compartment of the vessel104has a fixed volume such that the coolant108is prevented from escaping the vessel104when the coolant108is in a gaseous phase. A pressure within the vessel104once the vessel has been loaded with the liquid coolant108and the vessel104has been sealed may be less than atmospheric pressure and it will be appreciated that the pressure within the vessel104will vary at least in part based on the particular coolant being used and the operational parameters of the system (i.e., coolant temperature, etc.). In some non-limiting examples the pressure within the vessel104may be less than about 30 psia, in some cases less than about 27.5 psia, in some cases less than about 25 psia, in some cases less than about 22.5 psia, in some cases less than about 20 psia, in some cases less than about 17.5 psia, in some cases less than about 15 psia, in some cases less than about 12.5 psia, in some cases less than about 10 psia, in some cases less than about 8.5 psia and in some cases even less. It will be readily appreciated that, in use, given that the vessel104defines a sealed inner compartment having a fixed volume, the pressure within the vessel104will vary according to the operational parameters (i.e., load, temperature, etc.) of the IC102. It will also be readily appreciated that the pressure within the vessel104will directly impact the boiling point of the coolant108used, as further described below. The vessel104may also include at least one pressure valve (not shown)—the pressure valve may be configured to be opened manually or automatically. The pressure valve can notably be used to release some gas from the vessel104after the vessel has been sealed and set for operation, as further described below, and can therefore be used to modulate a pressure within the vessel104.

In this non-limiting embodiment, the vessel104may also have any suitable shape (e.g., the vessel104may be generally cubic, cuboidal, cylindrical and the likes), may have any suitable size and therefore may accommodate any suitable volume of the liquid coolant108, with the volume of liquid coolant within the vessel104being less than the (fixed) volume of the (sealed) compartment of the vessel104. In some non-limiting examples, the vessel104may be configured to accommodate at least about 10 mL of the liquid coolant108, in some cases at least about 20 mL of the liquid coolant108, in some cases at least about 30 mL of the liquid coolant108, in some cases at least about 40 mL of the liquid coolant108, in some cases at least about 50 mL of the liquid coolant108, in some cases at least about 60 mL of the liquid coolant108, in some cases at least about 70 mL of the liquid coolant108, in some cases at least about 80 mL of the liquid coolant108, in some cases at least about 90 mL of the liquid coolant108, in some cases at least about 100 mL of the liquid coolant108, in some cases at least about 200 mL of the liquid coolant108, in some cases at least about 300 mL of the liquid coolant108, in some cases at least about 400 mL of the liquid coolant108, in some cases at least about 500 mL of the liquid coolant108and in some cases even more. In other non-limiting examples, the vessel104may be configured to accommodate a volume of coolant per wattage of the IC102of at least about 0.1 mL/W, in some cases at least about 0.2 mL/W, in some cases at least about 0.3 mL/W, in some cases at least about 0.4 mL/W, in some cases at least about 0.5 mL/W, in some cases at least about 0.6 mL/W, in some cases at least about 0.7 mL/W, in some cases at least about 0.8 mL/W, in some cases at least about 0.9 mL/W, in some cases at least about 1 mL/W, in some cases at least about 1.1 mL/W, in some cases at least about 1.2 mL/W, in some cases at least about 1.3 mL/W, in some cases at least about 1.4 mL/W, in some cases at least about 1.5 mL/W and in some cases even more. Regardless of the specific means of constructing the vessel104and/or the size and configuration of the vessel104, the vessel104is generally designed for holding the coolant108in a liquid phase.

Still in this non-limiting embodiment, at least part of or at least one surface124of the IC102is thermally coupled to the coolant108to transfer heat generated by the IC102to the coolant108via the heat absorbing surface1041. As such, the at least part of or at least one surface124may be considered a heat releasing surface of the IC102. More specifically, the heat absorbing surface1041of the vessel104may be a surface of the vessel104that is formed and/or delimited by an integrated heat spreader (IHS)122of the IC102, the IHS122generally representing a material that is present on (a top surface of) the IC102to dissipate heat generated by the various components present in the IC102during use. The IHS122is therefore the region of the IC102at which a significant amount of heat dissipation occurs during operation of the IC102. The inner compartment of the vessel104in which the liquid coolant108is present is therefore defined at least in part by the IHS122. There is accordingly no direct contact between the IC102and the liquid coolant108in this non-limiting embodiment and the IC102is thermally coupled to the coolant108via the IHS122. It will be readily appreciated that, with reference toFIG.1, while only the external casing of the IC102is shown the IC102may in fact have any suitable external (i.e., shape, size, etc.) as well as internal configuration (i.e., number of CPUs, etc.) and heat may in fact be released via a number of distinct surfaces of the IC102(i.e., there may be more than one surface124).

In this non-limiting embodiment, the vessel104may accordingly be made of a second material which corresponds to a material of the IHS122. The second material may be the same as the first material, or it may be different and subjected to a variety of surface treatments to increase and/or facilitate heat transfer from the IC102to the liquid coolant108, as further described below.

Still in this non-limiting embodiment, the cooling system100also comprises a heat sink112which is thermally coupled to the coolant108to absorb heat from the coolant108in a gaseous and/or liquid phase, as further described below. The heat releasing surface1042of the vessel104may therefore be defined by the heat sink112, which may notably take the form of a base plate105comprising a first plurality of extensions105agenerally protruding from the base plate105towards the internal compartment of the vessel104, thereby increasing the overall surface of the heat releasing surface1042. Upon contact between the coolant108and the first plurality of extensions105a, the heat sink112absorbs heat which is then expelled from the cooling system100via, in one non-limiting example, a second plurality of extensions105bthat generally protrude from the base plate105away from the internal compartment of the vessel104. The second plurality of extensions105bis in direct contact, and increases the surface of contact, with another fluid such as air that is flowing between the second plurality of extensions105b. Heat is therefore transferred from the second plurality of extensions105bto air such that heat is effectively expelled from the cooling system100.

While inFIG.2Athe first plurality of extensions105aand the second plurality of extensions105bare mirror image from each other, they need not be in other non-limiting examples. That is, the first plurality of extensions105aand the second plurality of extensions105bmay each have any suitable form (e.g., fins), dimensions (e.g., length, diameter) and may each be present in any suitable number so as to effectively increase the contact surface between (i) the coolant108and the first plurality of extensions105a(i.e., the heat releasing surface104) and (ii) the second plurality of extensions105band air. To further facilitate and/or increase heat transfer from the second plurality of extensions105bto air, a fan109may be installed on top of the second plurality of extensions105bto facilitate and/or increase air circulation between the second plurality of extensions105b. Any suitable fan, as well as any suitable number of fans, may be used, such as but not limited to a fan with an air flow velocity of at least about 30 cubic feet per minute (CFM), in some cases at least about 40 CFM, in some cases at least about 50 CFM, in some cases at least about 60 CFM, in some cases at least about 70 CFM and in some cases even more. In yet further non-limiting examples, the heat sink112may be modified such that another fluid (e.g., a cooling liquid) circulates between the second plurality of extensions105b.

The first plurality of extensions105acan be configured such that, in use, the liquid coolant108is not in direct contact with the first plurality of extensions105aand heat transfer from the coolant108to the first plurality of extensions105acan therefore only occur through the gaseous phase of the coolant108. It will be readily appreciated that the configuration of the first plurality of extensions105a, as discussed above, notably includes the shape, orientation and size of the first plurality of extensions105a, and such configuration should be considered in the context of the overall shape and size of the vessel104as well as the volume of liquid coolant108that is present within the vessel104during use. In other non-limiting examples, the first plurality of extensions105acan also be configured such that, in use, the liquid coolant108is in direct contact with the first plurality of extensions105asuch that heat transfer from the coolant108to the first plurality of extensions105atherefore occurs through both the liquid and gaseous phases of the coolant108. In this example, the configuration of the first plurality of extensions105a, the vessel104and the volume of liquid coolant108can be chosen such that the first plurality of extensions105aare at least 10% (per volume or per surface or per length of the first plurality of extensions105a) immersed in the liquid coolant108, in some cases at least about 20% immersed in the liquid coolant108, in some cases at least about 30% immersed in the liquid coolant108, in some cases at least about 40% immersed in the liquid coolant108, in some cases at least about 50% immersed in the liquid coolant108, in some cases at least about 60% immersed in the liquid coolant108and in some cases even more.

Because in this embodiment the heat releasing surface1042is defined by the heat sink112, the inner compartment of the vessel104is also delimited by the heat sink112. As such, the vessel104may also be made of a third material which corresponds to a material of the heat sink112. The third material may be the same as the first material and/or the second material, or it may be different. The heat sink112, including the first plurality of extensions105aand the second plurality of extensions105b, may be made of any suitable material, for example a metallic materiel such as but not limited to aluminum, copper and the likes]. In further non-limiting examples, the first plurality of extensions105amay be further electroplated with a coating to facilitate and/or improve condensation of the coolant108in a gaseous phase on the first plurality of extensions105a, the coating notably comprising any one of a copper coating, ceramic coating and the likes. Alternatively, the first plurality of extensions105amay also be coated with a hydrophobic material or channels and/or grooves may be mechanically etched onto at least a portion of the first plurality of extensions105ato further increase the contact surface between the coolant108and the first plurality of extensions105a.

In another non-limiting embodiment, the heat sink112may also be entirely substituted for a condenser300that is configured to condense the coolant108in a gaseous phase back to a liquid phase. The condenser300may be directly integrated within a plate that defines the heat releasing surface1042and in this embodiment there are no extensions105agenerally protruding away from the plate towards the inner compartment of the vessel104. Various types and configurations of condensers may be used and the condenser configuration may also be chosen to as to accommodate at least one fan. In one non-limiting example, with further reference toFIGS.2B and2C, the condenser300may be integrated with the vessel104, and therefore in fluid communication with the inner compartment defined by the vessel104, via an upper region of the vessel104. In this example, the condenser300is secured to the vessel104via two securing members3021,3022and four threaded fasteners303xthat engage an outer and upper surface304of the vessel104. To ensure fluid communication between the vessel104and the condenser300, there is an opening124in the upper region of the vessel104that engages an inlet306of the condenser300.

While in the example ofFIGS.2B and2Cthe condenser300is positioned generally at non-nil angle relative to a generally vertical axis, this needs not be the case in other embodiments. Similarly, the condenser300may also be secured to, integrated with or otherwise connected to, the vessel104in any suitable manner as long as there is fluid communication between the inner compartment defined by the vessel104and the condenser300. The condenser300may have any suitable internal volume, that is the internal volume of the condenser300may be between about 250 mL and about 500 mL, in some cases between about 300 mL and about 450 mL, in some case between about 350 mL and about 400 mL. The condenser300may also have any suitable size and any suitable condensing capacity—for example the condenser300could be sized to accommodate a 2U (8.9 cm) or a 4U (17.8 cm) server rack system and the likes. The condenser300may also be fitted with a fan109to facilitate and/or increase air circulation around the condenser300. Any suitable fan109, as well as any suitable number of fans109, may be used, such as but not limited to a fan with an air flow velocity of at least about 30 CFM, in some cases at least about 40 CFM, in some cases at least about 50 CFM, in some cases at least about 60 CFM, in some cases at least about 70 CFM, in some cases at least about 80 CFM, in some cases at least about 90 CFM, in some cases at least about 100 CFM, in some cases at least about 110 CFM, in some cases at least about 120 CFM, in some cases at least about 130 CFM, in some cases at least about 140 CFM, in some cases at least about 150 CFM and in some cases even more. Non-limiting examples of condensers that may be used include crossflow heat exchangers with inner grooved tubes, printed circuit heat exchangers and the likes.

While in this embodiment condensation of the coolant108from a gaseous phase back to a liquid phase occurs directly within the internal compartment of the vessel104(for example, when the heat sink112or the condenser300delimits the inner compartment of the vessel104), this needs not be the case in other embodiments as the condenser300may also be remotely positioned from the vessel104, in which case the coolant108may be circulated via thermosiphoning between the vessel104and the condenser300. It will be readily appreciated that in this case the condenser may also act as condenser for a plurality of cooling systems100, effectively centralizing the heat removal step for a plurality of cooling systems100and/or a plurality of electronic devices204.

The cooling system100also comprises connection means114configured to secure the cooling system100onto the electronic device204. Specifically, the connection means114create a mechanical link between the electronic device204and the cooling system110, and may enable the regulation of the amount of pressure that is exerted by the cooling system100(i.e., the vessel104) onto the electronic device204when the cooling system100is attached onto the electronic device204. In other words, the mechanical link established between the electronic device204and the cooling system110(via the connection means114) seals the inner compartment of the vessel104when the cooling system is secured to the electronic device204, the IHS122of the IC102delimiting at least in part the internal compartment of the vessel104. To this end, the connection means114may notably include a frame and a plurality of fasteners (e.g., threaded fasteners such as screws, bolts, rivets and the likes) configured to secure the frame to the electronic device204. The connection means114may be configured to fit any suitable socket, including a CPU socket such as but not limited to a LGA2011 socket, a LGA2066 socket, a LGA 3647 socket, a GPU socket as well as any other type of socket. The connection means114may also include at least one electrostatic isolator to create a further dielectric barrier between the coolant108and the IC102/electronic device204when the cooling system100is in use. Using the connection means114, the cooling system100can be fitted onto any commercially-available IC102/electronic device204. Any other suitable connection means114may be used in other non-limiting embodiments.

The cooling system100may therefore be provided as a kit comprising at least the vessel104(exclusive of the heat absorbing surface1041), the heat sink112and the connection means114—in this case the heat absorbing surface1041of the cooling system100will be defined by the IHS122when the cooling system100is mounted onto the IC102. In other embodiments, the kit may also comprise the IHS122and means to secure the IHS122to the IC102prior to mounting the cooling system100onto the IC102.

It will be readily appreciated that the cooling system100is generally configured to be mounted directly onto the electronic device204, and may be mounted onto the electronic device204in a localized manner such that the cooling system100engages only one particular IC102for cooling of the particular IC102. As such, a plurality of cooling systems100could be used to cool various ICs102of a single electronic device204. Even though the cooling system100uses a liquid coolant108to cool the IC102, as further described below, the configuration of the cooling system100notably with its vessel104and connection mean114ensures that there is no contact between the liquid coolant108and the electronic device204. Further, in one non-limiting embodiment there is also no contact between the liquid coolant108and the IC102since the IC102is thermally connected to the coolant108via the IHS122. Given that during operation the pressure within the vessel104will change, this ensures that the cooling system100does not exert any additional pressure on the IC102/the electronic device124in use.

Coolant

The coolant108may be a liquid coolant, specifically a dielectric coolant to avoid short-circuiting the electrical connections between the IC102and the various associated electronic components. The liquid coolant108can be engineered with a specific boiling point at a temperature selected according to cooling requirements. Since the phase transition from liquid to vapor takes-up a significant amount of energy, the boiling point may be selected to be lower than the maximal operational temperature of the IC102. In other words, if the temperature of the IC102progressively increases, the coolant108should start boiling before the point at which the critical temperature is reached and the IC102must be shut down or throttled down to prevent it from overheating. The temperature differential, which is the difference between the IC's102critical temperature, which is considered to be the upper limit of its operational temperature range and the liquid boiling temperature (e.g., the boiling point), may be determined according to the specifications of the IC102and of the coolant108. It is however preferred that the boiling point of the coolant108be below the IC's102critical temperature. As such, the coolant108has at least one boiling point. The boiling point of the coolant108may be relatively low when compared to other liquids. For example, the coolant108when compared with water may have a lower boiling point. More specifically, in some embodiments, the maximum boiling point of the coolant is no greater than 90 degree Celsius, in some cases no greater than 80 degree Celsius, in some cases no greater than 70 degree Celsius, in some cases no greater than 60 degree Celsius, in some cases no greater than 50 degree Celsius, in some cases no greater than 40 degree Celsius, in some cases no greater than 30 degree Celsius and in some cases even less. The chemicals sold by 3M™ under the trademark Novec™ are examples of coolant108that may be used, such as but not limited to Novec™ 649, Novec™ 7000, Novec™ 7100 and the likes. The chemicals sold by 3M™ under the trademark Fluorinert™ are also examples of coolant108that may be used, such as but not limited to FC-3284, FC-72, FC-84 and the likes. The chemical sold by Dupont™ under the trademark Vertrel© are yet further examples of coolant108that may be used, such as but not limited to Dupont™ Vertrel© XF and the likes. Alternatively, any other liquid, even non-dielectric liquid, with a boiling temperature less than about 50° C. at 1 atm could also be used as the coolant108.

Coolants with multiple boiling points may also be used, as notably described in International Publication No. WO 2014/040182. In a specific example, this can be achieved by mixing liquids having different boiling points. The family of Novec products referred to earlier can be engineered to provide a range of boiling points so it is a matter of selecting the proper liquid composition to provide the desired phase transition temperatures. Coolants with multiple boiling points may provide a more gradual thermal energy absorption than a liquid having a single boiling point. A single boiling point invokes a significant heat take-up mechanism and it is not a gradual process. It is rather a step process. With multiple boiling points the mechanism is more progressive. Albeit it still has a step-like nature, there are multiple steps so it is possible to operate between steps. In one non-limiting example, the liquid coolant108can be a mixture of two liquids of the Novec family having boiling points A and B respectively, where A is lower than B. As the temperature of the IC102increases, the liquid with boiling point A will undergo phase change and will provide an enhanced cooling action. The additional cooling may thus suffice to stabilize the temperature of the IC102. Should increased cooling be further required, the fraction of the coolant with boiling point B will start changing phase. At that point, both coolant fractions will be boiling.

In another non-limiting example, the boiling points can be selected such as to straddle the operational temperature of the IC102. In other words, during steady state operation, the IC102is at a temperature that exceeds the boiling point A (which is assumed to the lowest) and that coolant fraction is boiling. The fraction having boiling point B (which is the highest) starts to change phase when a higher temperature is reached. As with the previous example, the boiling point B is at or slightly below the critical temperature such as to provide additional cooling before the temperature reaches a point where the IC102has to be shut down.

In another non-limiting example, using coolant engineered with multiple boiling points fraction of the coolant that is still liquid may help condensate at least in part the gaseous fraction. Since the difference of temperature between the boiling points can be significant, for example in the order of 10 degrees Celsius or more, the bubbles of the evaporating fraction have to travel through the liquid medium to reach the surface of the coolant body. That liquid medium has the ability to take up more heat, as its boiling point is higher. The cooling effect provided by the coolant that is still liquid on the vapor component may, in certain circumstances, suffice to completely condensate the vapor. Thus, little or no bubbles will break the surface.

The fractions having different boiling points may have the same density, in which case they will likely mix uniformly or different densities. Different density cooling fractions may also be used when they have similar boiling points. In this situation, the body of coolant108in the vessel104may be stratified and there is a lower density fraction on top with a higher density fraction below. Assuming that the higher density fraction starts to boil first, the vapor will travel through the lighter density fraction and assuming this fraction is sufficiently cool, it will condensate at least in part the vapors.

In this embodiment, the liquid coolant108is substantially free from non-condensable gas when the liquid coolant108is within the internal (and sealed) compartment of the vessel104. Within the context of the present disclosure, non-condensable gas is understood to refer to any gas that cannot be condensed in the operating conditions of the cooling system100, such as but not limited to air, nitrogen, hydrogen, oxygen, carbon dioxide, carbon monoxide or hydrogen sulphide. In some non-limiting examples, in use within the cooling system100(i.e., after a degassing protocol such as the process700ofFIG.7has been performed, as further described below), a mass fraction of non-condensable gas relative to the liquid coolant in a gaseous phase in the system100is no more than 5%, in some cases no more than 4%, in some cases no more than 3%, in some cases no more than 2%, in some cases no more than 1.5%, in some cases no more than 1% and in some cases even less.

Controller and Sensor

The controller106is configured for controlling various parameters of the cooling system100. More specifically, the controller106is configured for providing control algorithms for adjusting the heat transfer capabilities of the cooling system100. The control algorithms for adjusting the heat transfer capabilities of the cooling system100may include controlling one or more control parameters of the cooling system100and/or controlling one or more operational parameters of the IC102in order to adjust the temperature of the IC102. In other non-limiting examples, the control algorithms may also include controlling one or more parameters for any controllable element of the cooling system100, as further described below. The various aspects that the controller106is configured to control are discussed further throughout this document.

In the embodiment ofFIG.1, the controller106is external to the IC102. In such cases, the controller106may be configured as shown inFIG.3A. The controller106includes a processor292, which is different from the IC102, a computer readable memory290and input/output circuitry294. The processor292, the computer readable memory290and the input/output circuitry294may communicate with each other via one or more suitable data communication buses and the controller106communicates via one or more suitable data communication buses with the IC102.FIG.3Bis a variant ofFIG.3Ain which the controller106communicates with the IC102and at least one control component296, as further described below. In the specific and non-limiting examples ofFIGS.3A and3Bthe processor292is different from the IC102; however, in other non-limiting examples the processor292needs not be and in fact the IC102can include the processor292, for example as shown inFIG.3C. Although inFIG.3Cthe computer readable memory290and the input/output circuitry294are shown as external to the IC102, in other embodiments the computer readable memory290and the input/output circuitry294may also be included in the IC102and as such the controller106may also be implemented on the IC102(i.e., the controller106is internal to the IC102) in these non-limiting examples. The input/output circuitry294also communicates via one or more suitable data communication buses with at least one control component296. In one non-limiting example, the control component can be any controllable element of the system, such as but not limited to the fan109, a pressure valve and the likes.

Although the controller106is illustrated and discussed in this document as a digital controller, the controller106may be implemented as an analog controller in other embodiments. The analog controller may include various electronic components that typically would not include the processor292and the computer readable memory290. In other words, the controller106may be implemented to perform analog signal processing which is conducted on continuous analog signals by some analog means (as opposed to the discrete digital signal processing where the signal processing is carried out by a digital process). It is appreciated that the controller106may include both analog and digital components in various implementations of the controller106. For ease of readability of the rest of this document, unless specified otherwise, reference to the cooling system100is to be understood to be reference to the controller106regardless of whether the controller106is implemented external to the IC102or on the IC102.

Turning now to the structure of the controller106, the computer readable memory290may be any type of non-volatile memory (e.g., flash memory, read-only memory (ROM), magnetic computer storage devices or any other suitable type of memory) or semi-permanent memory (e.g., random access memory (RAM) or any other suitable type of memory). Although only a single computer readable memory290is illustrated, the controller106may have more than one computer readable memory module. The computer readable memory290stores program code and/or instructions, which may be executed by the processor292. The program code and/or instructions executable by the processor292may include software implementing control algorithms for adjusting the heat transfer capabilities of the cooling system100(e.g., increasing and/or decreasing the heat flux supplied by the IC102to the coolant108). The computer readable memory290may also include one or more databases for the storage of data.

The processor292may be implemented using any suitable hardware component for implementing a central processing unit (CPU) including a microcontroller, field-programmable gate array (FPGA), application-specific integrated circuit (ASIC), digital signal processor (DSP), integrated circuit (IC), graphics processing unit (GPU) or any other suitable device. The processor292is in communication with the computer readable memory290, such that the processor292is configured to read data obtained from the computer readable memory290such as information pertaining to the control algorithms and execute instructions stored in the computer readable memory290such as defined by the control algorithms for adjusting the heat transfer capabilities of the cooling system100. Although only a single processor292is illustrated, it is appreciated that more than one processor may be used.

The controller106may runs an operating system stored in the computer readable memory290such as Android, iOS, Windows 7, Windows 8, Linux and Unix operating systems, to name a few non-limiting possibilities. The processor292may execute instructions stored in the computer readable memory290to run the operating system such that the control algorithms for adjusting the heat transfer capabilities of the cooling system100can then be executed. It is appreciated that the controller106may be adapted to run on operating systems that may be developed in the future.

The input/output circuitry294may be used to communicate with the IC102and/or the at least one control component296. That is, the controller106may transmit or receive signals via the input/output circuitry294to or from the IC102. The transmitted signals from the controller106to the IC102may be one or more control signals that include control information for controlling at least one operational parameter (e.g., clock frequency, supply voltage, number of active cores, etc.) of the IC102that controls a rate of heat energy produced by the IC102and more specifically for increasing and/or decreasing the heat flux supplied by the IC102to the coolant108. In other words, the control signal from the controller106to the IC102may be used to control at least one operational parameter of the IC102in order to control the temperature of the IC102. The input/output circuitry294may also be used to communicate with the sensor110. That is, the controller106may transmit or receive signals via the input/output circuitry294to or from the sensor110. The received signals at the controller106from the sensor110may include information pertaining to measurements taken by the sensor110or a status of the sensor110(e.g., operational or not, etc.). The sensor110may be any one of a variety of sensors and may include one or more optical, acoustic, temperature, pressure, conductivity sensors and/or any other suitable sensors.

The sensor110may be a temperature sensor. The temperature sensor may be positioned at various locations, for example the temperature sensor may be located on the IC102for measuring the temperature of the IC102, in the vessel104for measuring the temperature of the coolant108(for example, using a thermocouple), or at the level of the IHS122for measuring the temperature of the IHS22. For example, the temperature sensor may be positioned near the heat absorbing surface1041and used to measure the surface temperature of the IC102or the temperature of the coolant108near the heat absorbing surface1041. Multiple temperature sensors may also be present concurrently at various locations of the cooling system100.

In another non-limiting embodiment, the sensor110may also be used to measure a state and/or phase change such as a state of the coolant108or various properties of the coolant108at the heat absorbing surface1041and/or on the surface of the IC102. For example, the sensor110may monitor the boiling of the coolant108near the heat absorbing surface1041. In particular, the sensor110observes the state of phase change of the coolant108from liquid to gas, by determining the morphology of the bubbles generated at the surface of the IC102. This could include measuring the bubble density, such as the mean number of bubbles per unit area or the area of the IC surface that is occupied by bubbles. In other words, the sensor110may be a boiling monitor. A first example of a boiling monitor includes having a light source on one side of the surface of the IC102, where a detector measures the amount of light from the light source being transmitted through the boiling liquid. The light source could be a LED, a LED collimated with a lens, or a laser. A second example of a boiling monitor includes having a camera with a lens assembly to image the surface of the IC102. Image processing software measures the density of bubbles or the area of bubbles on the IC102. The lens assembly could have a relatively shallow focal depth so that bubbles that have detached from the surface of the IC102do not appear sharply in the image. A third example of a boiling monitor is having an ultrasound emitter sending a pulse into the liquid and an ultrasound receiver measures the amplitude or time of arrival of the pulse. The pulse could propagate at a grazing angle to the surface of the IC102or it could come at a substantially sharper angle and be reflected by the surface.

The sensor110may also be a pressure sensor for measuring the pressure of the coolant108within the vessel104. Given that the vessel104is closed/sealed during use, it will be readily appreciated that the pressure within the vessel104will change (and build up) as the temperature of the coolant108increases during operation of the cooling system100.

Irrespective of its specific implementation, the sensor110is configured to sense either one of a temperature (of the IC102, the IHS122or within the vessel104), a pressure (within the vessel104) and/or a state of phase change of the coolant108and to generate a signal, which is transmitted to the controller106indicative of the state of phase change of the coolant108. The received signal from the sensor110to the controller106, is then processed by the controller106to generate the control signal to the IC102for regulating the transfer of thermal energy between the IC102and the coolant108.

The cooling system100may also include other components such as mechanisms for inducing a liquid flow within the vessel104and/or near the surface of the IHS122and/or mechanism for vibrating the IC102in the vessel104. Such mechanism

The input/output circuitry294may be also used to communicate with the at least one control component296. That is, the controller106may transmit or receive signals via the input/output circuitry294to or from the at least one control component296. The at least one control component296may be used to adjust at least one operational parameter of the cooling system100that controls, among others, the temperature of the IC102, the rate of heat energy absorbed by the coolant108, the operational status of the fan109of the pressure valve and the likes. As such, the transmitted signals from the controller106to the control components296may include control information for controlling at least one operational parameter of the cooling system100that controls that controls, among others, the temperature of the IC102, the rate of heat energy absorbed by the coolant108, the operational status of the fan109of the pressure valve and the likes. In one non-limiting example, the at least one control component296can be the fan109in which case the signals transmitted between the controller106and the fan109may be used to activate or deactivate the fan109, increase or decrease the RPM of the fan109as well as provide information to the controller106regarding the operational status of the fan109(i.e., an on/off state) as well as its RPM. In another non-limiting example, the at least one control component296can be a pressure valve in which case the signals transmitted between the controller106and the pressure valve may be used to open/close the valve as well as to provide information to the controller106regarding the status of the fan109(i.e., its open/closed state, etc.).

It is further appreciated that the cooling system100may be implemented in various other forms and that the examples given above are only some examples of implementation of the cooling system100.

It will be readily appreciated that, at the time the liquid coolant108is added to the vessel104, the addition is performed in an open vessel at atmospheric pressure. In other words, the coolant108will be in contact at least with air during the addition the vessel104and the coolant108will not be substantially free of non-condensable gas once added to the vessel104. Because of such contact with air, it is also not possible to degas the coolant108prior to the coolant108being added to the vessel104. After the vessel104is sealed, loaded with the coolant108and essentially ready to be operated, the coolant108needs to be degassed so as to maximize heat transfer efficiency during the operation of the cooling system108.

In accordance with one embodiment, the cooling system100is configured to degas the coolant108directly within the vessel104—more specifically, the cooling system100is configured to use at least the IC102as a heat source to perform a degassing protocol directly within the vessel104. In a preferred embodiment, the degassing protocol is therefore performed before the first operation of the cooling system100and no further degassing should be required for as long as the cooling system100remains a closed system (e.g., no pressure valve is opened, the cooling system100retains its gas seal integrity such that there is no fluid communication at any time between the inner compartment of the vessel104and the ambient air, etc.).

With further reference toFIG.7is shown a non-limiting embodiment of a process700for performing a degassing protocol within the vessel104. As such, the vessel104is sealed, loaded with the coolant108and considered essentially ready to be operated prior to the beginning of the process700. It will be readily appreciated that the various operational parameters of the process700herein described will be reliant upon a variety of factors, such as but not limited to the IC type and its rated power, the configuration and size of the vessel104, the type and size of the heat sink112or condenser300used, the type and number of fans109used, the type and volume of coolant108used, etc. As such, any numerical value provided therein is not meant to be limiting, but rather illustrative of a specific example, and it will be well within the grasp of the person of ordinary skills in the art to determine what these numeral values ought to be for a particular configuration of the cooling system100.

In a first step710the IC102is operated at a prescribed percentage of its rated power value (referred to as X % at step710, the power referring to the power being consumed by the IC102during use, the rated power of the IC102referring to the maximum power at which the IC102ought to be operated) and the fan is turned off. In some examples, at step710the IC is operated at less than 100% of its rated power value, for example at no more than 70% of its rated power value, in some cases at no more than 60% of its rated power value, in some cases at no more than 50% of its rated power value, in some cases at no more than 40% of its rated power value and in some cases even less. For clarity, the person skilled in the art will appreciate that the prescribed percentage of the rated power value of the IC102is a power in watts (W—e.g., 50% of a rated power value of 100 W corresponds to 50 W) and that such power can generally be considered an average power over a prescribed period of time.

In order to do so, and with further reference toFIG.8, the controller106implements a process800to determine whether an action is needed in terms of sending control signals to the IC102to modulate the power of the IC102. In a first step810the controller106receives IC information from the IC102and protocol information from the memory290. In some non-limiting examples, the IC information may notably include an IC identifier, a rated power for the IC102as well as an actual power (i.e., the power effectively consumed by the IC102at a prescribed point in time—this can be provided in the form of a percentage of the rated power of the IC102or in any other suitable form), a temperature of the IC102(in which case the IC information is derived at least in part from sensor information from a temperature sensor110located on the IC102) and the likes.

The protocol information, which can be stored directly at the level of the controller106or even remotely in other embodiments, includes various degassing process parameters such as, but not limited to, the number of process steps and a step identifier, for each step a prescribed pressure and/or temperature (including ranges of pressure and/or temperature) within the vessel104, a prescribed percentage of rated power for the IC102, a prescribed temperature for the IC102, a status for the fan109, a number of times the pressure valve should be opened and/or closed, a prescribed time, where applicable, and the likes.

At step820the controller106implements a decision logic on the basis of the IC information and the protocol information received at step810to determine whether a modification of the IC power102is needed. This may involve a comparison between the prescribed percentage of the rated power of the IC102from the protocol information and the (actual) percentage of the rated power of the IC102from the IC information. Alternatively, this may also involve a comparison between the prescribed temperature of the IC102from the protocol information and the (actual) temperature of the IC102from the IC information. If a discrepancy is found between both values, the controller106determines that a modification to the power of the IC102is needed and then proceeds to step830. If conversely no discrepancy is found then the process800ends.

At step830, the controller106generates control signals at least in part based on a magnitude of the discrepancy between the prescribed percentage of the rated power of the IC102from the protocol information and the (actual) percentage of the rated power of the IC102from the IC information9or the magnitude of the discrepancy between the prescribed temperature of the IC102from the protocol information and the (actual) temperature of the IC102from the IC information). For example, if according to the protocol information at the first step of the degassing process the IC102should run at 50% of its rated power, and if according to the IC information the IC102currently runs at 100% of its rated power, then the controller106generates control signals and communicates the control signals to the IC102to instruct the IC102to reduce its power by 50%.

As such, it will readily be appreciated that, given that the temperature of the IC102can be correlated to the power consumed by the IC102, and that as such the rated power of the IC102can be correlated to a maximum temperature of the IC102, step710can be entirely performed by the controller106by relying on temperature data versus power data—for example, the IC102may also be operated at step710at a prescribed percentage of its maximum temperature, in which case such temperature data may be obtained via at least one temperature sensor110located on the IC102.

With further reference toFIG.9, the controller109also implements a process900to determine whether an action is needed in terms of sending control signals to the fan109to modulate the activity of the fan. In a first step910the controller106receives fan information from the fan109and protocol information from the memory290. In some non-limiting examples, the fan information may notably include a fan status (i.e., on/off) and the likes. At step920the controller106implements decision logic on the basis of the fan information and the protocol information received at step910to determine whether a modification of the fan109activity is needed. For example, if according to the protocol information at the first step of the degassing process the fan109should be turned off, and if according to the fan information the fan109is currently on, then the controller106generates control signals and communicates the control signals the fan109to turn the fan109off.

As such, it will be readily appreciated that at step710the controller106may send control signals via the input/output circuitry294to the IC102and/or the fan109, as needed, based on the IC and protocol information that has been received by the controller106as regards the operational status of the IC102and the fan109. At the end of step710the cooling system100has been set in the operational conditions conforming to those of a first step of the degassing process. As such, processes800and900are each only performed once at step710and up and until the controller106determines that the first step of the degassing process has been completed (at the end of step720, as further described below), the controller106does not return to processes800and900.

At step720, the controller106then maintains a pressure within the vessel104between a first pressure value P1and a second pressure value P2. The range of pressure defined between P1and P2may be any suitable range. For example, P1may be no less than about 10 psia, in some cases no less than about 12 psia, in some cases no less than about 14 psia, in some cases no less than about 16 psia, in some cases no less than about 18, in some cases no less than about 20 psia and in some cases even more. P2may also be no more than about 24 psia, in some cases no more than about 22 psia, in some cases no more than about 20 psia, in some cases no more than about 18 psia, in some cases no more than about 16 psia and in some cases even less.

In order to do so, and with reference toFIG.10, the controller106implements a process1000for maintaining the pressure within the vessel104between P1and P2. In a first step1010the controller106receives vessel information and protocol information. In some non-limiting examples, the vessel information notably includes a pressure within the vessel104(in which case the vessel information is derived at least in part from sensor information from a pressure sensor110), a status of a pressure valve (i.e., open/closed), a number of times the pressure valve has been opened and the likes and it may also be stored in the memory290. At step1020the controller106implements decision logic to determine whether a modification of the pressure within the vessel104is needed such that the pressure remains between P1and P2. This involves a comparison between the pressure within the vessel104and P1/P2—for example, considering P1as the lower pressure of the two, for the controller106to determine that a modification of the pressure within the vessel104is needed the pressure within the vessel104needs to be less than P1or more than P2. In the event the controller106determines that a modification to the pressure of the vessel104is needed at step1020, the controller then proceeds to step1030where the controller106generates and communicate control signals to the valve to trigger an action.

For example, in the instance where a temperature and a pressure within the vessel104increase as the power of the IC102is maintained at its rated power (i.e., at its maximum power consumption/highest temperature)—which necessarily requires the pressure valve to be in a closed state—and therefore when the pressure within the vessel106reaches P2, the controller106will instruct the cooling system100to decrease the pressure within the vessel104to maintain the pressure between P1and P2. To this end, the control signals generated are communicated by the controller106at step1030to the pressure valve and instruct the pressure valve to open so as to release gas from, and therefore decrease the pressure within, the vessel104. Conversely, in the instance where the pressure valve is opened and the temperature and pressure within the vessel104decrease, when the pressure within the vessel104reaches P1the controller will instruct the cooling system100to increase the pressure within the vessel104to maintain the pressure between P1and P2. To this end, the control signals generated are communicated by the controller106at step1030to the pressure valve and instruct the pressure valve to close so as to stop the release gas of from, and therefore the decrease of the pressure within, the vessel104. It will be readily appreciated that step1030may also include some validation by the controller106to the effect that prior to sending the control signals to open the pressure valve the pressure valve is in a closed state (for example, as per the vessel information). This will ensure that no redundant control signals are sent by the controller106to the pressure valve.

Upon completion of step1030or following a determination at step1020that no modification to the pressure within the vessel104is needed, the controller106then proceeds to step1040where a determination is made as to whether process1000should end. This determination may be made in a number of ways. For example, at each iteration the controller106can update the vessel information stored in the memory290to specify a number of times the pressure valve has been opened (e.g., at each iteration the number is increased by 1) and then compares this number to the prescribed value from the protocol information (e.g., according to the protocol the pressure valve should be opened 8 times). As long as there is no match between the two values then the controller106reverts to step1010and the process1000starts over. Alternatively, the controller106may also monitor a time since when the process1000originally started and compare this value to the prescribed time from the protocol information—this can be useful in the instances where such time can be correlated to the number of times the pressure valve should be opened. The controller106may also consider in its determination at step1040the state of the pressure valve (i.e., whether the pressure valve is opened or closed). For example, the controller106may be configured to not allow the ending of the process1000when the pressure valve is opened, but only to allow the ending of the process1000when the pressure valve is closed. It will be readily appreciated that, via step1040, the controller106is continuously, or substantially continuously, running through the process1000for as long as no determination has been made to the effect that the process1000should end. The higher the frequency at which the controller106is performing the assessment and control operations described above in the context of the process1000, the more granular and precise the regulation implemented by the controller106is.

When the controller106determines that the process1000should end then the controller106reverts to step730ofFIG.7in which the IC102is operated at another prescribed percentage of its rated power value (called Y % at step730) and the fan is turned on by the controller106. Generally, Y≤X and in some examples at step730the IC102is operated at no more than about 10% of its rated power value, in some cases at no more than about 9% of its rated power value, in some cases at no more than about 8% of its rated power value, in some cases at no more than about 7% of its rated power value, in some cases at no more than about 6% of its rated power value, in some cases at no more than about 5% of its rated power value and in some cases even less. Much like what was described above in connection with step710ofFIG.7, the controller106also runs once through processes800and900to determine whether an action is needed in terms of sending control signals to the IC102to modulate the power consumed by the IC102(or the temperature of the IC102, as described above) and/or in terms of sending control signals to the fan109to modulate the activity of the fan109. At the end of step730the cooling system100has been set in the operational conditions conforming to those of a second step of the degassing process.

At step740, the controller106then monitors the pressure within the vessel104until the pressure within the vessel104goes below a third pressure value P3. Generally, P3≤P1and P3≤P2. For example, P3may be no more than about 10 psia, in some cases no more than about 9 psia, in some cases no more than about 8 psia, in some cases no more than about 7 psia, in some cases no more than about 6 psia, in some cases no more than about 5 psia and in some cases even less. In this case, and contrary to what was described in the context ofFIG.10above, the controller106monitors the pressure within the vessel104but does not actively regulate the pressure within the vessel104.

At step750, that is after the pressure within the vessel reaches the third pressure value P3, the controller106then turns off the IC102via the process800ofFIG.8, the fan109remaining on. This effectively sets the operational conditions conforming to those of a third and last step of the degassing process. From a perspective of the process700, in some examples the process700ends as soon as the IC102has been turned off by the controller106at step740. More broadly however, the degassing process may practically continue longer up and until the cooling system100has reached thermodynamic equilibrium, at which point the pressure within the vessel104will be lower than the atmospheric pressure and the liquid coolant108substantially free of non-condensable gas, as described above. As such, in other non-limiting examples, the controller106may also optionally implement a delay function that will prevent the IC102from being turned on for a prescribed period of time (which can, for example, be stored in the protocol information) after the IC102has been turned off by the controller106at step740—this will practically ensure that the cooling system100will reach equilibrium, and therefore that the degassing process is complete, prior to the IC102being turned on again. Any suitable period of time may be defined by the controller106, such as but not limited to at least about 10 minutes, in some cases at least about 15 mins, in some cases at least about 20 mins, in some cases at least about 30 mins, in some cases at least about 40 mins and in some cases even more.

In some embodiments, and with further reference toFIG.11, the controller106may also be configured to further implement a process1100to determine whether the gas seal integrity of the cooling system100has been compromised (i.e., whether the cooling system100suffers from any leak). In some non-limiting examples, this can be achieved using the vessel information which, as described above, can notably include the pressure within the vessel104and the status of the pressure valve. At step1110, using both the pressure within the vessel104and the status of the pressure valve the controller106can determine whether a decrease in pressure within the vessel104when the valve is not opened is or is not associated with a reduction of the power of the IC102or of a temperature of the IC102. In other words, when the pressure valve is closed and no gas escapes the vessel104via the pressure valve, a decrease in the pressure within the vessel104while the power/temperature of the IC102is constant or increases can only be indicative of a leak in the cooling system100, and therefore of an absence of gas seal integrity. Since this would have a negative effect on the performance and the overall efficacy of the process700, the process1100can be run by the controller106continuously, or substantially continuously, and concurrently with the process700described above, up and until the IC102is turned off. When gas seal integrity is found at step1110, the process1100repeats itself up and until the IC102is turned off. When an absence of gas seal integrity is found at step1110, the controller106then proceeds to step1120where an action is taken by the controller106before repeating the process1100. A variety of actions may be performed—these notably include, but are not limited to, throttling or turning off the IC102, terminating the process700and the likes.

It will be readily appreciated that the protocol700should only be performed once on a given cooling system100for as long as the gas seal integrity of the cooling system100is maintained, i.e. for as long as the vessel104remains a sealed compartment post-degassing. In other words, it is not necessary for the controller106to perform the process700each and every time the IC102is turned on. To this end, and with further reference toFIG.12, the controller106is further configured to implement a process1200for self-degassing of the cooling system100. In a first step1210, and prior to running the process700, when the IC102is turned on the controller106first determines whether the process700has already been run on the IC102. This can be done in a number of ways, for example the controller106may consult the vessel information stored in the memory290to determine whether the number of times the pressure valve has been opened is non-nil, consult any record generated by the controller106and stored in the memory294to the effect that process700has been performed once, etc.

Heat Flow from IC to Coolant

As at least part or at least one surface of the IC102is thermally coupled to the coolant108, heat flows from the IC102to coolant108, when the IC102is running. This flow of heat from the IC102to the coolant108constitutes the heat flux, which is the rate of heat energy transferred through a given surface per unit time. Of relevance, the heat energy transits through at least one element that exhibits some thermal resistance in the system, namely the IHS122, as further described below.

The heat flow mechanics from the IC102to the coolant108will now be described by reference toFIGS.4A to4DandFIG.5.FIGS.4A to4Dillustrate specific and non-limiting examples of the coolant108in various states of phase change as heat flows from the IC102to the coolant108, via the IHS122.FIG.5illustrates a specific and non-limiting example of a heat flux curve for the heat transfer from the IC102to the coolant108. Heat flux is the rate of heat energy transfer through a given surface per unit time, in this example the heat flux is the rate of heat energy transferred through the surface of the IC102per unit time. The x-axis of the graph inFIG.5is the excess temperature, Tw-Tsat′(in Celsius), where Twis the surface temperature of the IC102and Tsat′is saturated fluid temperature of the coolant108, and the y-axis of the graph is the heat flux, qw″ (W/m2). The excess temperature corresponds to a difference between the surface temperature of the IC102in relation to a saturated fluid temperature of the coolant108.FIG.5shows four regions1,2,3and4, where in the first region1natural heat convection occurs, which is illustrated inFIG.4A. Then in region2, nucleate boiling occurs. Nucleate boiling is a type of boiling that takes place when the surface temperature of the IC102is hotter than the saturated fluid temperature of the coolant108by a certain amount. At first isolated bubbles212occur, as shown inFIG.4B, and then as the excess temperature increases columns and slugs214occur, as shown inFIG.4C. Then at the burnout point, qmax″ the bubbles collapse into a substantially continuous dry film216, leading to a dry IC102, which is shown inFIG.4D. In region3, transition boiling occurs which may include unstable film and partial nucleate boiling and then in region4, film boiling occurs.

ConsideringFIGS.4A to4DandFIG.5in further detail, thermal energy is directed from the IC102to the adjoining liquid coolant108(via the IHS122) and defines the heat flux from the IC102into the coolant108. At first, thermal energy that is directed from the IC102to the adjoining liquid coolant108, which has the effect of elevating the temperature of the liquid coolant108via convection heat transfer.FIG.4Aillustrates an example where convection heat transfer from the IC102to the coolant108is occurring. When heat flows from the IC102to the coolant108, the temperature of the coolant108increases, to the point where vapor bubbles212nucleate at the surface of the IC102, as shown inFIG.4B. As such, a phase change occurs that takes up the thermal energy from the IC102. In other words, when the temperature of the IC102exceeds the boiling point of the liquid coolant108, it causes the liquid coolant108to evaporate. The latent heat of vaporization associated with this phase transition helps increase the magnitude of the heat flow from the IC102to the liquid coolant108beyond the heat flow due to convection. This process is most efficient when the bubbles212nucleate easily, and when they also detach easily. After detachment, the bubbles212generally rise in the liquid coolant108(due to buoyancy forces), and therefore contribute to transporting heat away from the IC102. A number of regimes can thus be observed in the cooling process: (i) at low IC surface temperatures, bubbles do not form, and heat is transported by convection in the liquid coolant108(e.g., as inFIG.4A); (ii) as the IC surface temperature increases, bubbles nucleate and detach at an increasing rate, leading to efficient heat transfer (e.g., as inFIG.4B); (iii) the density of bubbles on the IC surface becomes large at higher IC surface temperatures (e.g., as inFIG.4C), and the bubbles collapse to form a continuous film (e.g., as inFIG.4D), leading to a dry IC surface and less efficient heat transfer; (iv) at very high temperatures, conduction and radiation heat transfer through the vapor film eventually lead to high heat fluxes again. The maximum heat flux at the end of regime (iii) is called the “critical heat flux” (CHF), indicated by qmax″ inFIG.5. Passed that operational point, the heat flux decreases as the excess temperature increases. It is essentially a thermal runaway condition where heat is no longer efficiently removed from the IC surface, which can damage the IC.

The specific critical heat flux value for the setup shown inFIG.1may be for instance defined by the setup parameters of the cooling system100, such as but not limited to the physical properties of the coolant108, the characteristics of the heat exchanging surface1041, the characteristic of the IHS122and the pressure among others.

The CHF shown inFIG.5by qmax″ corresponds to heat flux measured in a steady-state situation, where power has been applied to the IC102for a long enough time for the heat flux to have stabilized. In transient conditions, heat transfer inertia between the heat input of the IC102and the response of the liquid coolant108exists. This heat transfer inertia defines a window of time during which the heat flux can exceed the steady-state CHF value without creating a burnout. In other words, during that window the coolant108is able to absorb the heat flux, which exceeds the steady-state CHF value for the particular setup, but without the bubbles collapsing to form a dry surface. As such, one aspect of some embodiments described herein is to periodically increase the heat output produced by the IC102in order to temporarily produce a heat flux above the steady-state CHF value. The heat output of the IC102is then lowered, but before a burn out occurs. The process can be repeated indefinitely.

The heat flux is a value that cannot be readily measured. However, the heat flux can be correlated to the temperature of the IC102surface. For a given setup, the heat flux can be computed and the temperature at which the CHF occurs, determined. Then by monitoring the temperature of the IC102surface, one can determine the operational point relative to the CHF. With reference to regions1and2inFIG.5, as the temperature of the IC102increases the steady-state heat flux of the IC102into the coolant108also increases until a maximum is reached; thereafter, as the temperature of the IC102increases the steady-state heat flux of the IC102into the coolant108decreases, as shown in region3inFIG.5. As such, an aspect of some embodiments described herein is to monitor the surface temperature of the IC102and manage the operational parameters of the IC102based on the identified surface temperature of the IC102at which CHF is reached.

The IHS122thermally couples the IC102to the liquid coolant108within the vessel104, the IHS122thereby defining at least one region having a thermal resistance between the IC102and the coolant108. To this end, the IHS122is attached onto the at least part or at least one surface124of the IC102. Any suitable connection mean may be used, such as but not limited to thermal paste, indium soldering and the likes. To ensure the gas seal integrity of the vessel104, the IHS122is also sealed to the vessel104, specifically to the neighboring portions of respective ones of the plurality of walls150iusing any suitable sealing mean. It will be readily appreciated that, contrary to the heat sink112, the IHS122does not itself retain a significant amount of heat, but rather distributes or conducts heat generated by the IC102towards the coolant108. This transfer of heat energy from the IC102to the coolant108can be facilitated and/or improved in a number of ways, as further described below.

In this non-limiting embodiment, the IHS122has horizontal (i.e., x and y) and vertical (i.e., z) dimensions. That is, in the non-limiting example in which the IHS122has the general shape of a cuboid, the IHS122has a length, a width and a depth. The characterization of IHS122may be made according to the geometrical configuration and the composition of the IHS122, as well as to the (heat transfer) properties of the IHS122, as further described below.

In one non-limiting example, the IHS122may have a homogeneous composition and be made of any suitable material, such as but not limited to a metallic material such as copper, nickel and the likes, a composite material or any other suitable material. In other non-limiting examples, the composition of the IHS122may be heterogeneous and the IHS122may be made of at least two different materials, such as but not limited to two different metallic materials, a metallic material and a ceramic material, and the likes. In some non-limiting examples, the heterogeneous composition of the IHS122may be obtained by electroplating a first metallic material with a second metallic material, such as but not limited to copper electroplated with nickel, nickel electroplated with copper and the likes. It will be readily appreciated that electroplating may also be used to produce IHS122with homogeneous compositions, for example nickel electroplated with nickel or copper electroplated with copper, although these homogeneous compositions may also exhibit properties that are different from the ones of the IHS122with the same metallic composition but without any electroplating, as further described below. Beyond electroplating, other surface treatment processes may also be used, alone or in combination with other surface treatment processes, and which also result in the IHS122having a heterogeneous composition, such as but not limited to various coatings, including coating with microporous metallic boiling enhancement (BEC) sold by 3M, electroplating, the soldering of a metallic porous surface onto the IHS122, the machining of small fin on the IHS122and the likes. The various methods described above may be performed directly on the IHS122which overlays the IC102(i.e., the IHS122is electroplated as it overlays the IC102, which would be the case for a variety of IC102that are commercially available with the IHS122), or they may also be performed on various layers and/or films of metallic material which are then secured to the IC102using any suitable securing method such as brazing and the likes.

The IHS122may have any suitable shape and/or dimension, for example the IHS122may be a cube or a cuboid. In the horizontal dimension, the IHS122may have any suitable surface of contact with the liquid coolant108. In one non-limiting example, in the horizontal dimension the IHS122may have a surface of contact with the liquid coolant108that is less than 150 cm2, in some cases less than 125 cm2, in some cases less than 100 cm2, in some cases less than 75 cm2, in some cases less than 50 cm2, in some cases less than 25 cm2and in some cases even less. It will be readily appreciated that, as further described below, the overall cooling capacity of the IHS122is dependent upon the surface of the IHS122, i.e. the larger the IHS122surface of contact with the liquid coolant108the greater the cooling capacity of the IHS122.

The IHS122may also have any suitable thickness. In one non-limiting example, the IHS122may have a thickness of less than 10 mm, in some cases less than 9 mm, in some cases less than 8 mm, in some cases less than 7 mm, in some cases less than 6 mm, in some cases less than 5 mm, in some cases less than 4 mm, in some cases less than 3 mm and in some cases even less. Where applicable, the thickness of the IHS122includes that of any surface treatment of the IHS122, which itself contributes to an increase in its thickness as further described below. It will be readily appreciated that the thickness of the IHS122needs not be identical along the entire surface of the IHS122. That is, in some embodiments, the IHS122may exhibit a varying thickness in at least one of the x and the y directions. For example, the IHS122may exhibit a decreasing thickness profile from a center of the IHS122towards a periphery of the IHS122in at least one of the x and y directions. In other examples, the IHS122may exhibit an increasing thickness profile from a center of the IHS122towards a periphery of the IHS122in at least one of the x and y directions.

In this embodiment, the shape of the IHS122being generally that of a cube or a cuboid, the surface of contact between the IHS122and the liquid coolant108is generally planar, that is it is substantially straight in both the x and y directions. This however needs not be the case in other embodiments in which the surface of contact between the IHS122and the liquid coolant108may have any suitable shape. For example, in the z direction the surface of contact between the IHS122and the liquid coolant108may exhibit a generally curved or Gaussian profile.

Electroplating and/or coating of the IHS122, as described above, may also facilitate the heat transfer from the IHS122to the liquid coolant108, for example by facilitating bubble formation and bubble release. More specifically, electroplating and/or coating may be used to create a porous layer on the IHS122that will increase the surface area of the IHS122/coolant108interface. In this context, the IHS122may be characterized in a number of ways, including but not limited to a porosity (which as used herein refers to a fraction of void within the porous layer) and a pore size distribution (which as used herein refers to the distribution of various pore sizes in a unit volume of the porous layer), more specifically a porosity and a pore size distribution within the region of the IHS122that constitutes the porous layer.

As regards pore size distribution, in some non-limiting examples the pores are generally dimensioned such that the average pore size is larger than the average bubble size. In this fashion, bubbles are less likely to become trapped in the porous layer. Bubble formation may induce an isolation layer due to the fact that heat transfer is less through gas than through liquid. The bubble starts small and increases in size until the point where the force of differential density is larger than the force of adhesion of the bubble surface to the surface of the IHS122. Hence the bubble should be carried away as fast as possible once created. Another feature of the porous layer is to increase the heat transfer coefficient, thereby increasing the heat flux at the IHS122/coolant108interface, as further described below. The porous layer can have a random and generally uniform pore size distribution or the pore size distribution can be controlled to create a pore-size gradient, as further described below. The pore size gradient may be such that the pore size generally increases with the distance from the surface of the IC102. In other words, the pores that are closer to the surface of the IC102are the smallest and moving further away from the IC102the pores become increasingly larger. Small pores create a larger heat exchange surface and also provide more nucleation sites for bubble formation. As bubbles are created and released from the smaller pores, they travel through larger pores which owing to their size provide a larger escape pathway to prevent bubble trapping. The pore-size gradient employed should allow for high heat transfer and ease of bubble extraction at the IHS122/coolant108interface.

As regards porosity, it may be measured in a number of ways, for example by manually processing scanning electron microscope (SEM) images of the surface of the IHS122using the ImageJ image and processing software (using a variety of thresholds set forth by the user) or automatically by processing the SEM images of the surface of the IHS122using the PorJ extension in ImageJ. In some non-limiting examples, after electroplating a porosity at a surface of the IHS122may be less 40%, in some cases less than 35%, in some cases less than 30% and in some cases even less. It will be readily appreciated that, and with further reference toFIGS.6A-6C, much like the pore-size distribution above, the porosity of the IHS122may also not be homogeneous in the horizontal and/or vertical directions. That is, the porosity of the IHS122may for example vary according to whether, in a horizontal plane, the porosity is measured at a center or around the periphery of the IHS122(in which case the porosity is always measured at a top of the porous layer) or whether, in a vertical plane, the porosity is measured at a top or at a center of the porous layer. In other words, the porous layer of the IHS122may also exhibit gradients of porosity in the horizontal (i.e., x and y) and/or vertical (i.e., z) directions, and such gradients will themselves be reliant upon the general dimensions of the IHS122in the x, y and z directions. In the examples ofFIGS.6A-6C, the porous layer exhibits a decreasing porosity profile from a center of the layer in the z direction towards a top of the layer in the z direction (see e.g.,FIGS.6A and6B). The porous layer also exhibits a decreasing porosity profile from a center of the porous layer towards a periphery of the porous layer (see, e.g.FIGS.6B and6C).

In some non-limiting examples, a porosity at a periphery of the IHS122may be 20% less than of a porosity at a center of the IHS122(the center being defined according to the general shape in the horizontal plane of the IHS122, both porosities being measured at a top of the porous layer), in some cases 17.5% less than of a porosity at a center of the IHS122, in some cases 15% less than of a porosity at a center of the IHS122, in some cases 12.5% less than of a porosity at a center of the IHS122, in some cases 10% less than of a porosity at a center of the IHS122, in some cases 7.5% less than of a porosity at a center of the IHS122and in some cases even less. That is, in these non-limiting examples, the porosity of the IHS122generally decreases away from the center of the porous layer.

In other non-limiting examples, a porosity at a top of the porous layer of the IHS122may be 30% less than of a porosity at a center of the porous layer of the IHS122(in the z direction), in some cases 25% less than of a porosity at a center of the porous layer of the IHS122, in some cases 20% less than of a porosity at a center of the porous layer of the IHS122, in some cases 15% less than of a porosity at a center of the porous layer of the IHS122, and in some cases even less. That is, in these non-limiting examples, the porosity of the IHS122generally increases away from the top of the porous layer.

In one non-limiting embodiment, the IHS122may exhibit a thermal resistance of no more than about 0.4° C./W for a power of the IC102of about 45 W, in some cases no more than about 0.38° C./W for a power of the IC102of about 45 W, in some cases no more than about 0.36° C./W for a power of the IC102of about 45 W, in some cases no more than about 0.35° C./W for a power of the IC102of about 45 W, in some cases no more than about 0.34° C./W for a power of the IC102of about 45 W and in some cases even less.

In another non-limiting embodiment, the IHS122may exhibit a thermal resistance of no more than about 0.36° C./W for a power of the IC102of about 67 W, in some cases no more than about 0.34° C./W for a power of the IC102of about 67 W, in some cases no more than about 0.32° C./W for a power of the IC102of about 67 W, in some cases no more than about 0.31° C./W for a power of the IC102of about 67 W, in some cases no more than about 0.30° C./W for a power of the IC102of about 67 W in some cases no more than about 0.29° C./W for a power of the IC102of about 67 W and in some cases even less.

In yet a further non-limiting embodiment, the IHS122may exhibit a thermal resistance of no more than about 0.33° C./W for a power of the IC102of about 88 W, in some cases no more than about 0.31° C./W for a power of the IC102of about 88 W, in some cases no more than about 0.29° C./W for a power of the IC102of about 88 W, in some cases no more than about 0.28° C./W for a power of the IC102of about 88 W, in some cases no more than about 0.27° C./W for a power of the IC102of about 88 W, in some cases no more than about 0.26° C./W for a power of the IC102of about 88 Wand in some cases even less.

In yet a further non-limiting embodiment, the IHS122may exhibit a thermal resistance of no more than about 0.29° C./W for a power of the IC102of about 110 W, in some cases no more than about 0.27° C./W for a power of the IC102of about 110 W, in some cases no more than about 0.25° C./W for a power of the IC102of about 110 W, in some cases no more than about 0.24° C./W for a power of the IC102of about 110 W, in some cases no more than about 0.23° C./W for a power of the IC102of about 110 W, in some cases no more than about 0.22° C./W for a power of the IC102of about 110 W and in some cases even less.

Example 1—Degassing Protocol

A cooling system was provided for cooling a 110 W CPU. The cooling system included a vessel having a height of about 14 cm configured to receive a volume of about 50 mL of 3M™ Novec™ 649 dielectric coolant as well as a heat sink (having a plurality of fins) with a fan installed thereon to further facilitate heat transfer. The cooling system was first filled with the dielectric coolant and was then sealed to define a fixed volume within the vessel, the vessel being loaded with about 50 mL of dielectric coolant containing non-condensable gas.

With further reference toFIG.13, the degassing protocol for the dielectric coolant was performed as follows. In a first step, the CPU was run at about 50% of its rated power, that is for a CPU of 110 W at about 50 W, and the fan is turned off. The pressure within the vessel was monitored and was kept between about 16 and 18 psia at all times (with Novec™ 649). In other words, upon running the CPU at about 50% of its rated power the pressure within the vessel increases—when the pressure reaches about 18 psia a pressure valve in the cooling system is opened to release some gas from the vessel and bring the pressure within the vessel down to about 16 psia, at which point the pressure valve is closed and pressure rises again. In this first step the sequence above is repeated 8 times.

In a second step the fan is turned on and the CPU is run at about 5% of its rated power, that is for a CPU of 110 W at about 6 W. The pressure within the vessel decreases and is left to decrease until the pressure within the vessel has reached about 6.5 psia (with Novec™ 649).

In a third step, once the pressure within the vessel has reached about 6.5 psia the CPU is shut down with the fan remaining on. Once the system has reached thermodynamic equilibrium in at least about 20 minutes, degassing is complete and the pressure within the vessel is below atmospheric pressure.

A variant of the cooling system according to another embodiment of the invention is illustrated inFIG.14. The cooling system1400is designed as an independent module that can be installed on an IC, either at the time of the manufacture of the PCB or afterwards to retrofit the PCB with an upgraded cooling system.FIG.15provides an exploded view from different perspectives of the cooling system1400, illustrating its main components.

The cooling system1400has a base1402that defines a chamber for holding the cooling liquid. The chamber has a circular lower portion and a rectangular upper portion. The rectangular upper portion is an easier geometric configuration to mate with a condenser that has typically a rectangular arrangement.

The cooling system1400further includes a contact plate1404which implements the heath transfer pathway between the IC and the coolant, and in this example includes the integrated heat spreader described earlier. The contact plate1404is of generally circular configuration and mounts to the lower edge of the chamber1402. The contact plate is sealed to the chamber1402via a suitable gasket.

On the upper end of the chamber1402is mounted a condenser to perform condensation of the gaseous medium in the chamber. The condenser1406has a lower condenser plate1408, an upper condenser plate1410, an array of fluid transport channels1412and a fin block1416that meshes with the array of fluid transport channels1412to allow an efficient heath dissipation from the fluid transport channels to the atmosphere. It will be noted that the fin block is manufactured as a unit and has one pair of studs at each corner: there being one stud projecting upwardly and one stud projecting downwardly. Collectively the studs allow mounting the covers and the condenser plate to the base1402with fasteners, such as nuts when the studs are threaded.

More specifically, a lower condenser plate1418is provided to mate the condenser1406to the base1402, while allowing fluid to enter the respective channels of the condenser1406. Accordingly, the lower condenser plate1418allows the individual channels to communicate with the internal space of the chamber below such that gas can rise into the channels where it condensates and the condensed liquid will flow into the channels back to the chamber.

Note, for mass produced units the channels array1412and the fin block1416would typically be made as a single unit; the channels brazed or otherwise secured to the arrangement of fins.

A gasket1420is provided to seal the lower condenser plate to the chamber1402. An upper condenser plate1410closes the channels of the array1412at their top ends. In this specific example of implementation, the upper condenser plate1410also closes the top ends of the respective channels.

A top cover1422closes the assembly. The top cover1422is secured in place with nuts threadedly mounted on the studs on the fin block1416. The entire assembly is fastened with nuts to the upper edge portion of the chamber1402.

A fan1424is provided to force air to circulate through the fin block1416. The fan1424is mounted to the side of the fin block1416.

The chamber1402is mounted to the IC to be cooled via a socket1426that enables a mechanical connection between the IC and the cooling system.

FIG.16illustrates two possible contact plate versions that can be used depending on the socket type and the IC type. The version at the left is configured for a cooling system that is assembled and degassed at the factory and only needs to be physically coupled to the IC, such as, as a traditional 4U heath sink. In this version the contact plate is has a continuous surface that is uninterrupted to create a fluid-tight seal between the chamber1402and the IC. To mount the cooling system to the IC socket, thermal paste is applied on the upper surface of the IC and the cooling system is attached to the socket with mechanical fasteners. In this example of implementation, the thermal pathway to the cooling liquid in the chamber1402includes the contact plate and the thermal paste which objectively is undesirable as these components introduce some degree of thermal resistance.

The second version of the contact plate is shown at the right inFIG.16. It has an aperture that is designed to accommodate the IC such that the top surface of the IC is in direct contact with the liquid in the chamber1402. In this example, the cutout in the contact plate tightly matches the IC body such as to be able to create a fluid tight seal between the contact plate and the periphery of the IC. In practice, since a range of IC body sizes are available in the industry, a range of different contact plates would be made available to match the form factor of the IC to cool. All the contact plates will have different cut-out shapes and the installer will need to match the proper cut-out plate to the IC form factor.

The second version of the contact plate provides superior cooling performance since the thermal resistance between the IC and the cooling liquid is less as there is direct contact between the IC and the cooling liquid. The downside to this approach is the necessity to set-up the system as it cannot be pre-filled with cooling liquid at the factory, as is the case with the first version of the contact plate.

The specification described previously an example of implementation where the set-up of the system, which includes the degassing of the cooling liquid is done once the cooling system is mounted on the IC and the fluid tight seal between the IC and the interior of the chamber1402established. This procedure can be used in this example to set-up the system.

Alternatively, the cooling liquid can be degassed separately, outside of the cooling chamber1402, such that the cooling chamber1402can be directly filled with degassed cooling liquid after the chamber1402is mounted and sealed on the IC. To avoid the contamination of the degassed liquid with environmental gases that may be present in the chamber1402, the latter should be purged such as by pumping the gaseous medium out with a vacuum pump. Once, the chamber is so purged, the degassing cooling liquid is introduced in the chamber1402. At that point, the cooling system is ready of use.

FIGS.17and18provide an example of a set-up that can be used to degase the cooling liquid outside the chamber1402and then introduce it into the chamber1402after the latter has been mounted to sealed to the IC. The degassing apparatus has a vessel1700for holding non-degassed cooling liquid. A heat-source1702, such as an electric heating element heats the cooling liquid in the vessel1700. Pressure and temperature gages1704are provided to monitor the degassing operation. In use, the vessel1700is filled to the desired level with cooling liquid and the heat source1702actuated to heat the liquid at the desired temperature. When the desired temperature and pressure in the vessel1700are reached, the port1706is opened to release the gas pressure in the vessel1700, thus release a major component of the non-condensable gases that have been evaporated from the cooling liquid. At that point the cooling liquid is degassed and can be used in the cooling system. Specifically, as described earlier, the procedure may include purging the inside of the chamber1402with a vacuum pump and then pouring the cooling liquid in the chamber1402from the vessel1700via an exit port1708. When the chamber1402is filled to the desired level through a suitable inlet port, the latter is closed to establish a fluid tight seal and prevent contaminants to ingress the chamber1402.

Alternatively, instead of degassing the cooling liquid at the point of assembly of the cooling system to the IC, the cooling liquid can be degassed separately and made available in a container to fill the chamber1402. The container can be any suitable container, such as a plastic bag provided with an outlet port allowing to release the degassed liquid to the chamber1402without contamination from the external gaseous atmosphere. To further simplify the filling operation, the degassing liquid can be made available in pre-measured quantities and only requires that the chamber1402is purged and the pre-measured dose of degassed cooling liquid is introduced in the chamber1402by connecting the outlet of the flexible plastic bag to the inlet port of the chamber1402.

In a yet another embodiment, the degassed liquid is held in an individual container that is physically attached to the cooling system and the container is opened to fill the chamber1402after the chamber is purged, in order to fill the chamber. This avoids any external manipulation necessary to introduce the degassed liquid into the chamber1402.

FIG.34illustrates this arrangement. At the site of manufacture of the cooling system, the cooling liquid chamber1402is assembled with condenser1406, which is provided on the top plate thereof with a one-way vacuum sensitive valve2400that establishes a pathway between the condenser1406and a cooling liquid pack, such as flexible bag filled with a quantity of degassed cooling liquid pre-determined to fill the chamber1402at the desired fill level. The assembly thus arrives as a unit with the cooling liquid pack.

The cooling system is then mounted to the IC as described previously and the seal between the IC the cooling liquid chamber1402established. A vacuum pump is connected to the cooling liquid chamber1402to suck out the gaseous content and thus purge the chamber. The one-way vacuum sensitive valve is calibrated such as to open at a vacuum level corresponding to one where a sufficient level of purge is achieved. As the valve2400opens, the degassed liquid will flow into the chamber1402. The vacuum pump is then the stopped and the purge port is closed. The flexible bag2402, which is now empty can be removed from the valve2400that will close and keep the system isolated and ready for operation. The empty bag can be discarded.

In another example of implementation, the surface of the contact plate that is in contact with the cooling liquid is provided with a Multi-Scale Electroplated Porous (MuSEP) structure to enhance the boiling performance of the highly wetting cooling liquid. Multi-step electroplating with current variation at each step yields a random particle formation where small particles lay at the bottom, and the bigger particles arrange themselves on the top. This specific structure triggers the bubble formation at low power, which results in shortening the natural convection regime. The large particles on the top play two significant roles at high power; wicking the liquid toward the nucleation sites and spacing the nucleation sites to prohibit bubble merging.

With reference toFIGS.19,20and21, the analysis of particles distribution has been done using ImageJ software. The porosity was calculated 49.4% from the side view. The image also shows the small pores at the bottom, which are protected by the large particles on the top. The particles are distributed from small to large in the upward direction. Almost 50% of the particles have a size of less than 15 micrometers. The thickness of the coated layer is around 500 micrometers, and the porosity was calculated 49.4%.

FIGS.22and23illustrate a further embodiment of the invention where the top surface of the silicon die of the IC has been directly coated to form the porous structure, such as the MuSEP structure described earlier, it being understood that other porous structures can be used without departing from the spirit of the invention.

Specifically,FIG.22shows from bottom to top in cross-section the PCB arrangement and the silicon die resting on the PCB. The upper surface of the silicon die is provided with the MuSEP coating which enables boiling of the cooling liquid to occur directly at the top of the die. In this arrangement, there is a material continuum from the silicon to the cooling liquid providing an efficient heat transport pathway, free of material junctions that add thermal resistance.

The application of the MuSEP coating involves processing the silicon die as a substrate during the coating process. That is to say, the upper surface of the silicon die is exposed during the coating process such as to allow the deposition of the various layers of the coating to form the porous structure shown inFIG.22andFIGS.19,20and21, strongly bonded to the silicon material.

Certain additional elements that may be needed for operation of some embodiments have not been described or illustrated as they are assumed to be within the purview of those of ordinary skill in the art. Moreover, certain embodiments may be free of, may lack and/or may function without any element that is not specifically disclosed herein.

Any feature of any embodiment discussed herein may be combined with any feature of any other embodiment discussed herein in some examples of implementation.

The use of headings in the document is for illustrative purposes only and is not intended to be limiting.

Although various embodiments and examples have been presented, this was for the purpose of describing, but not limiting, the invention. Various modifications and enhancements will become apparent to those of ordinary skill in the art and are within the scope of the invention, which is defined by the appended claims.