Apparatuses and methods for modifying surfaces of microelectronic devices to promote boiling of a coolant liquid

Abstract

Apparatuses and methods are disclosed herein to modify one or more surfaces of a microelectronic device by incorporating microstructures that promote boiling of a coolant liquid in a two-phase immersion cooling system. In one example, modifications are made directly to the surface(s) of a lid thermally coupled to a semiconductor die of the microelectronic device. In another example, modifications are made to the surface(s) of a boiler plate, which is thermally coupled to the lid. The modifications may be made using various subtractive, forming, and additive approaches. These approaches may generate less heat than conventional processes, resulting in less or, in some instances, no thermal damage to the microelectronic device. Accordingly, modifications may be made to the surface(s) of a microelectronic device while the device is mounted to a printed circuit board assembly (PCBA) of a computing system, thus simplifying testing and validation.

Description

APPARATUSES AND METHODS FOR MODII VI NG SURFACES OF MICROELECTRONIC DEVICES TO PROMOTE BOILING OF A COOLANT LIQUIDCROSS-REFERENCE TO RELATED APPLICATION(S)[000.1] This application claims the priority benefit, under 35 U.S.C. 119(e), of U.S. Application No. 63 / 552,799, filed February 13, 2024 and entitled, “APPARATUSES AND METHODS FOR MODIFYING SURFACES OF PROCESSORS TO PROMOTE BOILING OF A COOLANT LIQUID,” and U.S. Application No. 63 / 513,828, filed July 14, 2023 and entitled, “GRINDING APPARATUSES AND METHODS FOR MECHANICALLY MODIFYING SURFACES OF PROCESSORS TO PROMOTE BOILING OF A COOLANT LIQUID.” Each of the aforementioned applications is incorporated herein by reference in its entirety.BACKGROUND[0002| Two-phase immersion cooling is a liquid cooling technique that utilizes a liquid-to-gas phase transition to remove heat from a heat-generating component, such as a processor or, more generally, a microelectronic device or component of a computing system. This is typically accomplished using a tank to submerge the heat-generating component in a pool of coolant liquid where the coolant liquid is a dielectric with a relatively low boiling point (e.g., 50°C). During operation, the coolant liquid in direct contact with the heat-generating component vaporizes (i.e., boils), producing coolant vapor that rises upwards within the tank. The coolant vapor thereafter transfers heat to a heat exchanger disposed above the coolant liquid, thus causing the coolant vapor to condense back to a liquid and thereafter fall into the pool of coolant liquid below. A two-phase immersion cooling system may be used to cool high density computing systems, such as an array of servers in a data center.SUMMARY

[0003] The Inventors have recognized and appreciated the cooling rate of a heat-generating component, such as a microelectronic device (e.g., a processor), in a two-phase immersion cooling system depends, in part, on the heat-generating component providing nucleation sites for bubbles of coolant vapor to form. However, conventional microelectronic devices, such as a central processing unit (CPU), a graphics processing unit (GPU), a data processing unit (DPU), a field- programmable gate array (FPGA), or an application-specific integrated circuit (ASIC), typicallyinclude a lid (also referred to as a “heat spreader” or “integrated heat spreader”) that is relatively smooth with few nucleation sites. To increase the number of nucleation sites available and, thus, promote boiling of the coolant liquid, a boiler plate (also referred to as a “boiling plate,” a “heat spreader,” or a “heat-dissipative element”) is often attached to the lid of the microelectronic device. The boiler plate includes a block of copper or a vapor chamber with a wick structure mounted or formed thereon that provides nucleation sites to facilitate bubble formation and, hence, boiling of the coolant liquid.|0004| Although a boiler plate provides a way to increase the number of nucleation sites, it also increases the thermal resistance between the heat-generating portion of a microelectronic, e.g., a processor chip (also referred to more generally as a “die” or a “semiconductor die”), and the surfaces at which heat is dissipated to the coolant liquid, e.g., the surfaces of the boiler plate. For example, a processor chip is thermally coupled to the lid with a first layer of thermal interface material. The lid, in turn, is thermally coupled to the boiler plate with a second layer of thermal interface material. Each additional interface increases the thermal resistance between the processor chip and the exterior surfaces of the boiler plate.[0005 j The Inventors have thus recognized structurally modifying the lid itself to include more nucleation sites can provide a way to appreciably reduce thermal resistance while still promoting boiling of the coolant liquid. However, the Inventors have also recognized there are several challenges with modifying a lid of a microelectronic device.J 0006 j Conventional processes for modifying a lid, such as an electron beam machining system, or certain laser cutting systems, often generate appreciably high heat fluxes, which can delaminate and / or degrade the thermal interface material between the lid and the processor chip and thus detrimentally affect the thermal coupling between the lid and the processor chip. Additionally, exposing the surfaces of the lid to a high heat flux can cause the surfaces of the lid to oxidize, thus degrading its thermal properties, e.g., by reducing the thermal conductivity of the lid. Conventional processes that use a chemical (e.g., an etchant) to etch the surface of the lid can damage other components of the microelectronic device or a printed circuit board (PCB) supporting the microelectronic device if the chemical is not properly contained. For example, if the chemical spills onto the PCB, wire traces and / or other electronic components on the PCB may be damaged. To reduce the risk of a chemical spill damaging the microelectronic device and / or the PCB, themicroelectronic device and the PCB may be covered with a masking material. However, careful application of masking material is often a time consuming and laborious process.

[0007] As a result, the foregoing conventional processes are typically applied only to a relatively small portion of the lid and only for the purposes of applying a pattern onto the lid, such as a logo of a company or information on the microelectronic device (e.g., model number, manufacture date). In other words, these conventional processes are not suitable to modify a relatively large portion of a surface or, in some instances, an entire surface of the lid for the purpose of promoting boiling of a coolant liquid.

[0008] The Inventors recognize the conventional processes described above may be applied to the lid A) by removing the lid from an assembled microelectronic device, modifying the lid, and thereafter remounting the lid, or B) before the microelectronic device is assembled (e.g., before the lid is mounted to the processor chip and / or a PCB supporting the processor chip). However, both of these approaches have significant limitations. The approach of removing and remounting the lid is time-consuming and labor-intensive and is thus not scalable for larger systems that may have hundreds or thousands of microelectronic devices. Additionally, removing the lid increases the risk of the processor chip getting damaged. Moreover, it is challenging to remount the lid with the same tolerance as it was originally assembled. The approach of modifying a lid before the microelectronic device is assembled is not applicable to off-the-shelf processors and expensive to implement for custom microelectronic devices.Additionally, for some computing systems, the computing system itself or each constituent computing subsystem (e.g., a PCB assembly (PCBA) with a CPU, memory, and a network card, a PCBA with multiple GPUs) may be required to undergo one or more tests to ensure the computing system / subsystem is operating correctly before installation into a two-phase immersion cooling system. Once the computing system / subsystem is validated based on the outcome of the tests, it should not be disassembled. Thus, any modifications to the lid to promote boiling of a coolant liquid are performed before the microelectronic device is mounted to a PCBA to form a computing system / subsystem and, hence, before tests are performed on the computing system / subsystem. As a result, the tests are typically performed using a coolant liquid to cool the microelectronic device since the modifications to the lid render other types of cooling systems (e.g., a cold plate, an aircooled heat sink) unsuitable to adequately cool the microelectronic device. The use of a coolantliquid makes the tests more expensive and cumbersome to perform particularly since the quality of the coolant liquid can change over time.[001.0] In view of the foregoing limitations, the present disclosure is directed to various inventive implementations of apparatuses and methods for modifying one or more surfaces of a microelectronic device by introducing microstructures that promote boiling of a coolant liquid, such as the coolant liquid of a two-phase immersion cooling system. In one aspect, the apparatuses and methods disclosed herein may be applied to directly modify one or more surfaces of a lid of a microelectronic device (e.g., a processor) in order to promote boiling without increasing the thermal resistance between a semiconductor device of the microelectronic device and the coolant liquid.(OOH | In another aspect, the apparatuses and methods disclosed herein may be applied to a microelectronic device already mounted to a computing system (e g., a PCBA with a processor mounted thereto). In particular, the lid of the microelectronic device may be modified even after the computing system has undergone validation testing, thus appreciably simplifying the process of assembling a computer system for installation into a two-phase immersion cooling system. Accordingly, the present disclosure is also directed to various inventive implementations of a microelectronic device and / or a computing system with a lid modified using the apparatuses and / or methods disclosed herein.

[0012] In some implementations, the modifications may be made using a subtractive process, where material is directly removed from the modified component (e.g., the lid). Various subtractive processes are disclosed herein. In one example, microstructures may be formed by mechanical grinding. A grinding apparatus may be used to mechanically modify, for example, a lid of a processor. For example, the grinding apparatus may form a plurality of grooves onto the lid of the processor with the grooves providing nucleation sites for bubbles to form.

[0013] The grinding apparatuses disclosed herein are configured to modify a surface of a lid or any other component of a microelectronic device in a purely mechanical manner. For example, the grinding apparatus may include one or more cutting tools (e.g., a cutting disk and / or a scribing tip) to mechanically cut the plurality of grooves on the surface. In some implementations, the surface may further be cooled, for example, via forced convection (e.g., by flowing air across the surface). For example, the grinding apparatus may be paired with a particulate removal system that removesparticulates generated by the grinding process from the surface. The particulates may be removed, for example, by vacuum suctioning the particles or by blowing air onto the surface to displace and remove the particles. The flow of air produced by the particulate removal system may also cool the surface.

[0014] Compared to conventional processes that generate a high heat flux, the mechanical approach produces appreciably less heat and has appreciably less risk of damaging other components of the microelectronic device and / or the PCBA supporting the microelectronic device. This is due, in part, to the surface being convectively cooled, e.g., by the particulate removal system and the relatively small amount of material removed from the surface to form the grooves. The less heat generated by the grinding apparatus may, in turn, allow the grinding apparatus to modify the surface(s) of a microelectronic device without damaging any components of the microelectronic device (e.g., the thermal interface material, the semiconductor die) or the PCBA. For example, the lid of a microelectronic device may be modified while the lid remains attached to a semiconductor die. Additionally, the microelectronic device may be modified while the microelectronic device remains attached to a PCB supporting the microelectronic device.[0015| In some implementations, the grinding apparatus may modify a microelectronic device after the microelectronic device is mounted to a PCBA (e.g., to form a computing system). This, in turn, may make the process of validating and testing the computing system appreciably simpler, faster, and cheaper. For example, an off-the-shelf processor may be mounted to a PCBA to form a computing system. The computing system may then undergo one or more tests (e.g., a power-on test) using a testing apparatus. At this stage, the processor remains unmodified, which means a simpler cooling system (e.g., cooling systems that do not include a coolant liquid) may be used to cool the processor, such as a cold plate or an air-cooled heat sink (e.g., a heat sink with a fan to provide forced convection, a heat sink cooled via natural convection). After the computing system is validated, the lid of the processor may then be modified using the grinding apparatus without disassembling the computing system (e.g., while the processor remains mounted to the PCBA). The modification of the lid does not affect the validation of the computing system. Thus, once the modification to the lid is complete, the computing system may be installed into the two-phase immersion cooling system.[0016} Other example implementations of subtractive processes to modify one or more surfaces of a microelectronic device are disclosed herein. For example, an electrical discharge machining (EDM) apparatus is disclosed that selectively removes material from the surface of the microelectronic device (e.g., a processor lid) by creating an electrical discharge between the surface and a cathode. The material may be removed in a manner that roughens the surface, thus providing nucleation sites to promote boiling of a coolant liquid. In another example, a laser surfacing apparatus is disclosed that utilizes a laser to remove material from the surface of the microelectronic device (e.g., a processor lid). Unlike conventional laser cutting systems, the laser surfacing apparatus disclosed herein may use a nanosecond laser, a femtosecond laser, or even a picosecond laser to emit a series of pulses to facilitate melting and / or ablation of a portion of the microelectronic device without appreciably heating the microelectronic device itself. In another example, a fluid jet apparatus is disclosed that generates a jet of dielectric fluid at a sufficiently high pressure to remove material from the surface of the microelectronic device without penetrating, for example, the lid. In other words, the material removal rate is sufficiently low that the surface of the microelectronic device is roughened as the fluid jet moves across the surface.

[0017] In some implementations, the modifications may be made using a forming process. A forming process may involve reshaping a component of the microelectronic device (e.g., the lid) to form structural features that provide nucleation sites without any appreciable removal of material from the component. For example, a skiving apparatus is disclosed that cuts fins from the surface of the microelectronic device using a skiving tool to form a plurality of structures (e.g., fins) that act as nucleation sites. In another example, a pin fin structure may be formed (e g., via cold forging) to provide the nucleation sites.

[0018] In some implementations, the modifications may be made using an additive process. In an additive process, nucleation sites may be formed by adding materials and / or structures directly to the surface(s) of the microelectronic device. In one example implementation, a plurality of particles may be deposited onto the surface of the microelectronic device (e.g., the surface of a lid). The particles provide nucleation sites to promote boiling. The particles may be initially coated with a fusible metal (e.g., a solder material) before deposition onto the microelectronic device. Once the particles are deposited, the particles may be heated to a temperature sufficient to melt the fusible metal, thereby causing the fusible metal to spread onto the surface(s) of the microelectronic device, thus adhering the particles to the microelectronic device. In another exampleimplementation, a prefabricated wick structure may be directly attached to the microelectronic device via welding. The wick structure may be formed from metal using a 3D printing process. In some implementations, the wick structure may include one or more mesh structures coupled to one another via, for example, a plurality of nanotubes or nanofibers. During assembly, the wick structure may be placed directly onto the microelectronic device and an electrical resistance welder may be used to weld the wick structure directly to the microelectronic device. In yet another example implementation, the surface(s) of a microelectronic device may be conformally coated with a layer of resin. Before the resin cures (e.g., hardens), a tool (e.g., a stamp) with patterning features (e.g., an array of spikes) may be applied to the resin. The resin may then be cured while the tool is applied. Thereafter, the tool may be removed, thus leaving behind a layer of resin with imprinted features corresponding to the patterned features. These imprinted features provide nucleation sites to promote boiling.

[0019] It should be appreciated that while various apparatuses and / or methods disclosed herein are applied to directly modify the surface(s) of a lid in a microelectronic device, the apparatuses and / or methods may generally be applied to any surface of a microelectronic device. For example, any of the apparatuses and / or methods disclosed herein may also be used to incorporate microstructures onto the surface(s) of a boiler plate. Although the addition of a boiler plate may increase the thermal resistance between the semiconductor die of a microelectronic device and the coolant liquid and, hence, adversely affect cooling performance, the apparatuses and / or methods disclosed herein may nevertheless provide several advantages over conventional approaches to fabricate boiler plates and, in particular, boiling enhancement coatings on the boiler plates. For example, the approaches disclosed herein may use less energy, exhibit lower costs, and achieve higher throughput compared to conventional approaches.

[0020] In one example implementation, a system includes: a two-phase immersion cooling system, including: a tank defining a tank volume configured to contain a coolant liquid; and a computing system disposed within the tank volume and configured for submersion in the coolant liquid, the computing system including: a microelectronic device, including: a semiconductor die; and a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die, the lid including: a surface configured for exposure to the coolant liquid; and a plurality of grooves formed on the surface to provide a plurality of nucleation sites configured to promote boiling of the coolant liquid.[00211 The system may further include the coolant liquid disposed in the tank volume of the tank. The plurality of grooves may include one or more straight grooves. The plurality of grooves may include one or more curved grooves. The one or more curved grooves may include at least one of a sinusoidal groove or an arcuate groove. The plurality of grooves may include one or more zigzag grooves. The plurality of grooves may include one or more grooves having an enclosed shape. The enclosed shape may be at least one of a circle or an ellipse. Each groove of the plurality of grooves may have a profile that is at least one of a triangle, a square, a semi-circle, or a semi-ellipse. The plurality of grooves may be randomly arranged on the surface of the lid. Each groove of the plurality of grooves may be parallel to all other grooves in the plurality of grooves. The plurality of grooves may be oriented along an axis parallel to the surface of the lid where the axis is parallel to an edge of the lid. The surface of the lid may be vertical and the plurality of grooves may be arranged such that a longitudinal axis associated with each groove of the plurality of grooves is vertical. The plurality of grooves may cover all of the surface. The plurality of grooves may cover only a portion of the surface.]0022| During operation, one or more first portions of the semiconductor die may be at a higher temperature than one or more second portions of the semiconductor die; and the plurality of grooves may be formed only on portions of the surface of the lid that overlaps with the one or more first portions of the semiconductor die. The plurality of grooves may include: a first plurality of grooves oriented along a first axis parallel to the surface of the lid; and a second plurality of grooves oriented along a second axis parallel to the surface of the lid. The first axis may be perpendicular to the second axis. The first axis may be at an acute angle with respect to the second axis. At least one of a width, a pitch, or a depth of the first plurality of grooves may be different from the second plurality of grooves. The plurality of grooves may include: a first plurality of grooves formed on a first portion of the surface of the lid; and a second plurality of grooves formed on a second portion of the surface of the lid, the second plurality of grooves having a different number of grooves per unit area than the first plurality of grooves.10023] Each groove of the plurality of grooves may have a width ranging from about 20 pm to about 40 pm. Each groove of the plurality of grooves may be separated from at least one other groove of the plurality of grooves by a pitch ranging from about 40 pm to about 100 pm. Each groove of the plurality of grooves may have a depth ranging from about 10 pm to about 70 pm.[0024} The lid may include: a bulk portion; and a layer portion, disposed on the bulk portion, having a hardness value greater than the bulk portion; and the surface of the lid is formed on the layer portion. The plurality of grooves may extend into both the layer portion and the bulk portion of the lid. The lid may be formed from at least one of copper or nickel-plated copper. The plurality of grooves may be configured to produce a boiling curve with inversion. The semiconductor die includes at least one of a central processing unit (CPU), a graphics processing unit (GPU), a data processing unit (DPU), a voltage regulator (VR), high bandwidth memory (HBM), a digital signal processor (DSP), a field-programmable gate array (FPGA), or an application-specific integrated circuit (ASIC).[0025} In another example implementation, a system includes: a two-phase immersion cooling system, including: a tank defining a tank volume configured to contain a coolant liquid; and a computing system disposed within the tank volume and configured for submersion in the coolant liquid, the computing system including: a microelectronic device, including: a semiconductor die; a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die; and a boiler plate, thermally coupled to the lid, configured to dissipate the heat to the coolant liquid, the boiler plate including: a surface configured for exposure to the coolant liquid; and a plurality of grooves formed on the surface to provide a plurality of nucleation sites configured to promote boiling of the coolant liquid.[0026} The system may further include the coolant liquid disposed in the tank volume of the tank. The plurality of grooves may include one or more straight grooves. Each groove of the plurality of grooves may be parallel to all other grooves in the plurality of grooves. The surface of the boiler plate may be vertical and the plurality of grooves may be arranged such that a longitudinal axis associated with each groove of the plurality of grooves is vertical. The plurality of grooves may cover all of the surface. During operation, one or more first portions of the semiconductor die may be at a higher temperature than one or more second portions of the semiconductor die; and the plurality of grooves may be formed only on portions of the surface of the boiler plate that overlaps with the one or more first portions of the semiconductor die. Each groove of the plurality of grooves may have a width ranging from about 20 pm to about 40 pm. Each groove of the plurality of grooves may be separated from at least one other groove of the plurality of grooves by a pitch ranging from about 40 pm to about 100 pm. Each groove of the plurality of grooves may have adepth ranging from about 10 pm to about 70 pm. The plurality of grooves may be configured to produce a boiling curve with inversion.

[0027] In another example implementation, a system includes: a two-phase immersion cooling system, including: a tank defining a tank volume configured to contain a coolant liquid; and a computing system disposed within the tank volume and configured for submersion in the coolant liquid, the computing system including: a microelectronic device, including: a semiconductor die; and a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die, the lid including: a surface configured for exposure to the coolant liquid; and a plurality of pin fins formed on the surface to provide a plurality of nucleation sites configured to promote boiling of the coolant liquid.(0028| The system may further include the coolant liquid disposed in the tank volume of the tank. The plurality of pin fins may be arranged as an in-line array. The plurality of pin fins may be arranged as a staggered array. Each pin fin of the plurality of pin fins may have a circular cross section. Each pin fin of the plurality of pin fins may have a square cross section. Each pin fin of the plurality of pin fins may have a rectangular cross section. Each pin fin of the plurality of pin fins may have a height ranging from about 0.5 mm to about 5 mm. Each pin fin of the plurality of pin fins may have a width ranging from about 0.5 mm to about 2.5 mm. Each pin fin of the plurality of pin fins may be separated from at least one other pin fin of the plurality of pin fins by a pitch ranging from about 0.5 mm to about 2.5 mm. The lid may be formed from at least one of copper or nickel-plated copper.

[0029] The lid may further include a powder coating covering the surface and the plurality of pin fins. The powder coating may be formed from copper. The powder coating may include a plurality of particles. Each particle of the plurality of particles may have a diameter ranging from about 50 pm to about 200 pm. Each particle of the plurality of particles may have a diameter ranging from about 150 pm to about 200 pm. Each particle of the plurality of particles may have a diameter ranging from about 75 pm to about 100 pm.

[0030] The lid may further include a plurality of grooves formed on at least one of the surface or the plurality of pin fins. The plurality of pin fins may be configured to produce a boiling curve with inversion. The semiconductor die may include at least one of a central processing unit (CPU), a graphics processing unit (GPU), a data processing unit (DPU), a voltage regulator (VR), highbandwidth memory (HBM), a digital signal processor (DSP), a field -programmable gate array (FPGA), or an application-specific integrated circuit (ASIC).[003.1] In another example implementation, a system includes: a two-phase immersion cooling system, including: a tank defining a tank volume configured to contain a coolant liquid; and a computing system disposed within the tank volume and configured for submersion in the coolant liquid, the computing system including: a microelectronic device, including: a semiconductor die; a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die; and a boiler plate, thermally coupled to the lid, configured to dissipate the heat to the coolant liquid, the boiler plate including: a surface configured for exposure to the coolant liquid; and a plurality of pin fins formed on the surface to provide a plurality of nucleation sites configured to promote boiling of the coolant liquid.

[0032] The system may further include the coolant liquid disposed in the tank volume of the tank. Each pin fin of the plurality of pin fins may have a height ranging from about 0.5 mm to about 5 mm. Each pin fin of the plurality of pin fins may have a width ranging from about 0.5 mm to about 2.5 mm. Each pin fin of the plurality of pin fins may be separated from at least one other pin fin of the plurality of pin fins by a pitch ranging from about 40 pm to about 100 pm. The lid may be formed from at least one of copper or nickel-plated copper. The lid further may include a powder coating covering the surface and the plurality of pin fins. The powder coating may be formed from copper. The powder coating may include a plurality of particles. Each particle of the plurality of particles may have a diameter ranging from about 50 pm to about 200 pm. The plurality of pin fins may be configured to produce a boiling curve with inversion.

[0033] In another example implementation, a method for preparing a computing system for installation into a two-phase immersion cooling system includes: assembling the computing system, the computing system including: a microelectronic device, including: a semiconductor die; and a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die, the lid including a surface configured for exposure to a coolant liquid of the two-phase immersion cooling system; and forming, by a laser, a plurality of grooves on the surface of the lid, the plurality of grooves providing a plurality of nucleation sites configured to promote boiling of the coolant liquid.[0034} The method may further include: installing the computing system into a tank of the two- phase immersion cooling system. The method may further include: fdling the tank with the coolant liquid such that the computing system is submerged in the coolant liquid.10035] The method may further include, before forming the plurality of grooves on the surface of the lid: mounting the computing system to a testing apparatus; and performing, by the testing apparatus, one or more tests on the computing system. The testing apparatus may include a cooling system; mounting the computing system to the testing apparatus includes: thermally coupling the cooling system to the microelectronic device; and the method further includes, while performing the one or more tests on the computing system includes: dissipating, by the cooling system, heat generated by the microelectronic device during the one or more tests. The cooling system may include at least one of a cold plate or an air-cooled heat sink. The cooling system may not include a liquid that directly contacts the microelectronic device to dissipate heat from the microelectronic device. Performing the one or more tests on the computing system may include: performing a power on test for the computing system.

[0036] The laser may be one of a nanosecond pulsed laser or a femtosecond pulsed laser. The laser may have a wavelength ranging from about 780 nm to about 1 mm. Forming the plurality of grooves on the surface of the lid may include: moving the laser relative to the surface at a speed ranging from about 20 mm / sec to about 400 mm / sec. Forming the plurality of grooves on the surface of the lid may include: illuminating, by the laser, the surface with an average laser power ranging from about 1 W to about 20 W. The method may further include: while forming the plurality of grooves on the surface of the lid, dissipating, via natural convection, heat from the lid. Each groove of the plurality of grooves may be parallel to all other grooves in the plurality of grooves. The method may further include: installing the computing system into a tank of the two- phase immersion cooling system such that the surface of the lid is vertical and a longitudinal axis associated with each groove of the plurality of grooves is vertical.

[0037] Each groove of the plurality of grooves may have a width ranging from about 20 pm to about 40 pm. Each groove of the plurality of grooves may be separated from at least one other groove of the plurality of grooves by a pitch ranging from about 40 pm to about 100 pm. Each groove of the plurality of grooves may have a depth ranging from about 10 pm to about 70 pm. The lid may be formed from at least one of copper or nickel-plated copper.

[0038] In another example implementation, a processor includes: a printed circuit board (PCB); a processor chip coupled to the PCB; a thermal interface material disposed on a portion of the processor chip; and a lid, coupled to the PCB and in physical contact with the thermal interface material, to dissipate heat generated by the processor chip, the lid having a plurality of grooves formed on a surface of the lid that provide nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid.

[0039] Each groove of the plurality of grooves may have a width less than or equal to about 500 microns. The width of each groove of the plurality of grooves may be less than or equal to about 100 microns. The width of each groove of the plurality of grooves may be less than or equal to about 50 microns. The plurality of grooves may include: a first plurality of grooves oriented along a first axis parallel to the surface of the lid; and a second plurality of grooves oriented along a second axis parallel to the surface of the lid. The first axis may be perpendicular to the second axis. The first axis may be at an acute angle with respect to the second axis.

[0040] During operation, one or more first portions of the processor chip may be at a higher temperature than one or more second portions of the processor chip; and the plurality of grooves may be formed only on portions of the surface of the lid that overlap with the one or more first portions of the processor chip. The plurality of grooves may include: a first plurality of grooves formed on a first portion of the surface of the lid; and a second plurality of grooves formed on a second portion of the surface of the lid, the second plurality of grooves having a higher density than the first plurality of grooves. The lid may include: a bulk portion; and a layer portion, formed along the surface of at least one groove of the plurality of grooves, having a hardness value greater than the bulk portion. The lid may be formed from at least one of copper, or nickel-plated copper.

[0041] In another example implementation, a grinding apparatus for grinding a lid of a processor to form a plurality of grooves on a surface of the lid, where the plurality of grooves provide nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, includes: a frame; a plurality of cutting tools slidably coupled to the frame, each cutting tool of the plurality of cutting tools having a width less than or equal to about 500 microns and being separate from another cutting of the plurality of cutting tools by a pitch less than or equal to about 500 microns; and a motor operably coupled to the plurality of cutting tools and configured to slidablymove the plurality of cutting tools with respect to the frame to form the plurality of grooves on the surface of the lid. 0042] The width of each cutting tool of the plurality of cutting tools may be less than or equal to about 100 microns; and the pitch separating one cutting tool of the plurality of cutting tools from another cutting tool of the plurality of cutting tools may be less than or equal to about 100 microns. The width of each cutting tool of the plurality of cutting tools may be less than or equal to about 50 microns; and the pitch separating one cutting tool of the plurality of cutting tools from another cutting tool of the plurality of cutting tools may be less than or equal to about 50 microns. The motor may be a first motor; and the plurality of cutting tools may include: a spindle slidably and rotatably coupled to the frame; a plurality of cutting disks rigidly mounted to the spindle; and a second motor operably coupled to the spindle and configured to rotate the spindle and the plurality of cutting disks so as to form the plurality of grooves on the surface of the lid. The plurality of cutting tools may include: a slider slidably coupled to the frame; and a plurality of scribing tips rigidly mounted to the slider and configured to form the plurality of grooves when the motor slidably moves the plurality of scribing tips across the surface of the lid.

[0043] A system may include: the apparatus; and a particulate removal system configured to remove particulates generated from the surface of the lid when the apparatus grinds the lid. The particulate removal system may generate vacuum suction near the surface of the lid to remove the particulates. The particulate removal system may blow air onto the surface of the lid to remove the particulates.

[0044] In another example implementation, a method for forming a plurality of nucleation sites on a lid of a processor where the nucleation sites facilitate boiling of a liquid heated by and in contact with the lid of the processor, comprises: A) mounting the processor to a PCB A to form a computing system; and B) grinding the lid of the processor to form the plurality of nucleation sites on a surface of the lid while the processor is mounted to the PCBA.

[0045] The step of grinding the lid of the processor to form the plurality of nucleation sites on the surface of the lid may comprise: cutting, by one or more cutting tools, a plurality of grooves onto the surface of the lid. The one or more cutting tools may include at least one of a cutting disk or a scribing tip. The plurality of grooves may be formed only on portions of the surface of the lid that overlap with portions of a processor chip of the processor that is at a higher temperature than otherportions of the processor chip. Each groove of the plurality of grooves may have a width less than or equal to about 500 microns. The plurality of grooves may include a first plurality of grooves formed on a first portion of the surface of the lid and a second plurality of grooves formed on a second portion of the surface of the lid and the first plurality of grooves may have a higher density than the second plurality of grooves. The method may further comprise, while grinding the lid of the processor to form the plurality of nucleation sites on the surface of the lid: removing particulates from the computing system where the particulates are generated from the surface of the lid in response to grinding the lid. The step of removing the particulates may comprise providing vacuum suction near the surface of the lid. The step of removing the particulates may comprise blowing air onto the surface of the lid. The method may further comprise: before grinding the lid of the processor, covering at least a portion of the computing system with a sheet to prevent particulates from covering that portion of the computing system while grinding the lid, the particulates being generated from the surface of the lid in response to grinding the lid; and after grinding the lid of the processor, removing the sheet from the computing system. The step of grinding the lid of the processor to form the plurality of nucleation sites on the surface of the lid may not include the use of a chemical etchant, a laser, or an electron beam.

[0046] In another example implementation, a method for preparing a computing system for installation into a two-phase immersion cooling system includes: A) mounting a processor to a PCBA to form the computing system; B) mounting the computing system to a testing apparatus; C) performing, by the testing apparatus, one or more tests on the computing system; D) removing the computing system from the testing apparatus; and E) grinding a lid of the processor to form a plurality of nucleation sites on a surface of the lid while the processor is mounted to the PCBA, the plurality of nucleation sites facilitating boiling of a liquid in the two-phase immersion cooling system heated by and in contact with the lid of the processor.

[0047] The method may further comprise installing the computing system into a two-phase immersion cooling system. The testing apparatus may include a cooling system, the step of mounting the computing system to the testing apparatus may comprise thermally coupling the cooling system to the processor, and the method may further comprise, while performing the one or more tests on the computing system comprises, dissipating, by the cooling system, heat generated by the processor during the one or more tests. The cooling system may include at least one of a cold plate or an air-cooled heat sink. The cooling system may not include a liquid thatdirectly contacts the processor to dissipate heat from the processor. The step of performing the one or more tests on the computing system may comprise performing a power on test for the computing system. The step of grinding the lid of the processor to form the plurality of nucleation sites on the surface of the lid may comprise cutting, by one or more cutting tools, a plurality of grooves onto the surface of the lid. The plurality of grooves may only be formed on portions of the surface of the lid that overlap portions of a processor chip of the processor that is at a higher temperature than other portions of the processor chip (e.g., hotspots).|0048| In another example implementation, an electrical discharge machining (EDM) apparatus configured to modify a lid of a processor by forming a plurality of features on a surface of the lid, where the plurality of features provide nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, includes: a tank defining a cavity; a dielectric fluid disposed in the cavity of the tank; a fixture coupled to and disposed in the cavity of the tank, the fixture being submerged in the dielectric fluid and configured to support the processor; a frame disposed above the tank; an electrode, movably coupled to the frame, having a tip submerged in the dielectric fluid and disposed above the fixture; and an electrical power supply electrically coupled to the electrode and configured to be electrically coupled to the lid of the processor, wherein during operation of the apparatus, when the tip of the electrode is sufficiently close to the surface of the lid, the electrode generates an electrical discharge to remove a portion of the lid of the processor thereby forming at least one feature of the plurality of features.}(H)49| In another example implementation, a fluid jet apparatus configured to modify a lid of a processor by forming a plurality of features on a surface of the lid, where the plurality of features provides nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, includes: a fixture configured to support the processor; a frame disposed above the fixture; a fluid source to supply a dielectric fluid; a pump, fluidically coupled to the fluid source, to generate a flow of the dielectric fluid; and a nozzle, fluidically coupled to the pump and supported by the frame, to generate a fluid jet from the flow of the dielectric fluid, wherein during operation of the apparatus, when the nozzle is disposed above the surface of the lid, the nozzle sprays the fluid jet at a sufficiently high pressure to remove a portion of the lid of the processor thereby forming at least one feature of the plurality of features.[0050| In another example implementation, a laser surfacing apparatus configured to modify a lid of a processor by forming a plurality of features on a surface of the lid, where the plurality of features provides nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, includes: a fixture configured to support the processor; a frame disposed above the fixture; and a laser, supported by the frame, to emit a plurality of pulses, wherein during operation of the apparatus, when the laser is disposed above the surface of the lid, the plurality of pulses emitted by the laser irradiates the lid and removes a portion of the lid of the processor via ablation thereby forming at least one feature of the plurality of features.

[0051] In another example implementation, a skiving apparatus configured to modify a lid of a processor by forming a plurality of features on a surface of the lid, where the plurality of features provides nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, includes: a fixture configured to support the processor; a frame; a skiving tool movably coupled to the frame; and a motor coupled to the skiving tool, wherein during operation of the apparatus, the motor is configured to move the skiving tool across the surface of the lid in a reciprocating manner to cut and deform a portion of the lid of the processor thereby forming at least one feature of the plurality of features.

[0052] In another example implementation, a method for forming a plurality of nucleation sites on a lid of a processor, where the plurality of nucleation sites facilitate boiling of a liquid heated by and in contact with the lid of the processor, includes: depositing a plurality of particles onto a surface of the lid, the plurality of particles providing the plurality of nucleation sites, each particle of the plurality of particles being coated with a fusible metal; and heating the plurality of particles to cause the fusible metal to melt thereby adhering the plurality of particles to the surface of the lid.

[0053] In another example implementation, a method for forming a plurality of nucleation sites on a lid of a processor, where the plurality of nucleation sites facilitating boiling of a liquid heated by and in contact with the lid of the processor, includes: fabricating, using a 3D printer, a metallic wick structure including one or more mesh structures, each mesh structure of the one or more of mesh structures providing the plurality of nucleation sites; placing the metallic wick structure onto a surface of the lid; and welding, via an electrical resistance welder, one or more portions of the metallic wick structure to the surface of the lid.[0054| In another example implementation, a method for forming a plurality of nucleation sites on a lid of a processor, where the plurality of nucleation sites facilitating boiling of a liquid heated by and in contact with the lid of the processor, includes: depositing a conformal layer of a resin onto a surface of the lid, the layer having a thickness less than or equal to about 5 microns; before curing the resin, patterning the layer of the resin by applying a tool with a plurality of patterning features directly onto the resin; curing the layer of the resin; and removing the tool from the layer of the resin thereby leaving imprints of the plurality of patterning features in the layer of the resin, the imprints providing the plurality of nucleation sites.

[0055] It should be appreciated that the tests and modifications described above may also be performed on a computing subsystem. Herein, a computing subsystem refers to an assembly of computing components that form part of a larger computing system (i.e., a computing system that comprises multiple computing subsystems). For example, the GPUs of a GPU baseboard assembly, which form part of a GPU server, may be tested and modified by the grinding apparatus disclosed herein.

[0056] It should also be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter disclosed herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e g., functionally similar and / or structurally similar elements).

[0058] FIG. 1 A shows an example processor with a lid and a printed circuit board (PCB).[0059| FIG. IB shows a cross-sectional view of the processor of FIG. 1 A.[0060 FIG. 2A shows a top view of an example processor before the lid is modified to include a plurality of grooves.[006.1] FIG. 2B shows a top view of the processor of FIG. 2A after the plurality of grooves are formed on the lid.

[0062] FIG. 2C shows a magnified view of the plurality of grooves corresponding to Inset A of FIG. 2B.

[0063] FIG. 2D shows a cross-sectional view of the plurality of grooves of FIG. 2C.

[0064] FIG. 3A shows a top view of another example processor with a plurality of vertically aligned grooves formed by the laser surfacing system of FIG. 3 A.

[0065] FIG. 3B shows a cross-sectional view of the plurality of grooves of FIG. 3A.

[0066] FIG. 4A shows a top view of another example processor before the lid is modified to include a plurality of grooves. Multiple example hotspots are shown.

[0067] FIG. 4B shows a top view of the processor of FIG. 4A after the plurality of grooves are selectively formed on portions of the lid where the hotspots shown in FIG. 4A occur.

[0068] FIG. 5A shows a top view of another example processor with a plurality of grooves that includes two subsets of grooves formed at an acute angle with respect to each other and at different depths.

[0069] FIG. 5B shows a cross-sectional view of the plurality of grooves of FIG. 5 A.

[0070] FIG. 6A shows a side view of an example grinding apparatus with cutting disks.

[0071] FIG. 6B shows a top view of the grinding apparatus of FIG. 6A.

[0072] FIG. 7A shows a front view of the grinding apparatus of FIG. 6A applied to the surface of a lid with a particulate removal system configured to vacuum suction particulates generated from the surface of the lid by the grinding apparatus.

[0073] FIG. 7B shows a front view of the grinding apparatus of FIG. 6A applied to the surface of a lid with a particulate removal system configured to blow air to remove particulates generated from the surface of the lid by the grinding apparatus.[0074| FIG. 7C shows a front view of the grinding apparatus of FIG. 6A applied to the surface of a lid where the surface of the lid is covered by a polymer coating.

[0075] FIG. 8A shows a side view of another example grinding apparatus with scribing tips.

[0076] FIG. 8B shows a front view of the grinding apparatus of FIG. 8 A.|0077] FIG. 9 shows a flow chart for an example method of preparing a computing system for installation into a two-phase immersion cooling system.

[0078] FIG. 10A shows a diagram of an example EDM system for modifying a surface of a processor lid to promote boiling of a coolant liquid.]0079{ FIG. 10B shows an inset view of the EDM system of FIG. 10A where a portion of the processor lid is removed via an electrical discharge.]0080] FIG. 11 A shows an example electrode for the EDM system of FIG. 10A with a wide end.] 0081] FIG. 1 IB shows another example electrode for the EDM system of FIG. 10A with a narrow end.

[0082] FIG. 11C shows another example electrode for the EDM system of FIG. 10A with multiple narrow ends.

[0083] FIG. 12A shows a diagram of an example fluid jet system to modify a surface of a processor lid to promote boiling of a coolant liquid.

[0084] FIG. 12B shows an inset view of the fluid jet system of FIG. 12A where a portion of the processor lid is removed via a fluid jet.

[0085] FIG. 13 A shows a diagram of an example laser surfacing system to modify the surface of a processor lid to promote boiling of a coolant liquid.]0086] FIG. 13B shows an inset view of the laser surfacing system of FIG. 13 A where a portion of the processor lid is removed via a laser.

[0087] FIG. 14 shows experimental boiling curve data for a copper substrate with a plurality of vertically aligned grooves formed via laser surfacing.

[0088] FIG. 15A shows a diagram of a skiving system to modify a surface of a processor lid to promote boiling of a coolant liquid.

[0089] FIG. 15B shows an inset view of the skiving system of FIG. 15A where the processor lid is modified to form a wick structure.

[0090] FIG. 16A shows an example processor lid with a plurality of pin fins.[009.1] FIG. 16B shows the pin fins arranged in an in-line array.|0092] FIG. 16C shows the pin fins arranged in a staggered array.

[0093] FIG. 16D shows another example processor lid with a plurality of pin fins and a powder coating.

[0094] FIG. 17 shows a perspective view of another example processor lid with a plurality of pin fins and a powder coating.

[0095] FIG. 18 shows experimental boiling curve data for a bare copper substrate and copper substrates with a mesh or a plurality of pin fins in combination with different sized powders coatings.

[0096] FIG. 19A shows a diagram of an example process for depositing particles coated with a fusible metal onto a processor lid.

[0097] FIG. 19B shows an inset view of the processor lid of FIG. 19A with several particles.

[0098] FIG. 19C shows a diagram of an example process for curing the particles on the processor lid in FIG. 19A.

[0099] FIG. 19D shows an inset view of the processor lid of FIG. 19C with several cured particles.

[0100] FIG. 20A shows a diagram of an example process for spot welding a wick structure to a processor lid.

[0101] FIG. 20B shows an inset view of the processor lid of FIG. 20A with the wick structure welded directly to the processor lid.

[0102] FIG. 21 A shows a diagram of a processor lid coated with a resin.

[0103] FIG. 2 IB shows an inset view of the processor lid of FIG. 21 A coated with a layer of resin.

[0104] FIG. 21C shows a diagram of an example process for transferring a pattern onto the resin of FIG. 21A via a stamp.

[0105] FIG. 21D shows an inset view of the processor lid of FIG. 21 C with the stamp applied to the layer of resin. 0106] FIG. 2 IE shows a diagram of the processor lid of FIG. 21C with a patterned layer of resin after the stamp is removed.[01071 FIG. 21F shows an inset view of the processor lid of FIG. 21E with the patterned layer of resin.

[0108] FIG. 22 shows an example processor lid with a boiler plate where a surface of the boiler plate is patterned according to any one of the approaches disclosed in the present application.

[0109] FIG. 23 shows an example two-phase immersion cooling system with a tank containing a computing system.DETAILED DESCRIPTION

[0110] Following below are more detailed descriptions of various concepts related to, and implementations of, apparatuses and methods for modifying components of a microelectronic device (e.g., the lid of a processor, a boiler plate) by introducing microstructures that promote boiling of a coolant liquid in a two-phase immersion cooling system, methods for preparing the microelectronic device or, more generally, a computing system containing the microelectronic device for installation into the two-phase immersion cooling system (e.g., by executing one or more tests), and example microelectronic devices with lids modified by the apparatuses and methods disclosed herein. Various approaches are contemplated herein to incorporate microstructures onto one or more surfaces of the microelectronic device including, but not limited to, mechanical grinding, electrical discharge machining (EDM), fluid jet machining, laser surfacing, skiving, forming pin fins, particle deposition, attachment of a prefabricated wick structure, and patterning a resin layer. The apparatuses and methods may generally be applied to various microelectronic devices including, but not limited to, a central processing unit (CPU), a graphics processing unit (GPU), a data processing unit (DPU), a voltage regulator (VR), high bandwidth memory (HBM), a digital signal processor (DSP), a field-programmable gate array (FPGA), and an application-specific integrated circuit (ASIC). It should be appreciated that various concepts introduced above and discussed in greater detail below may be implemented in multiple ways. Examples of specific implementations and applications are provided primarily forillustrative purposes so as to enable those skilled in the art to practice the implementations and alternatives apparent to those skilled in the art.[011.1] The figures and example implementations described below are not meant to limit the scope of the present implementations to a single embodiment. Other implementations are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the disclosed example implementations may be partially or fully implemented using known components, in some instances only those portions of such known components that are necessary for an understanding of the present implementations are described, and detailed descriptions of other portions of such known components are omitted so as not to obscure the present implementations.(0112) In the discussion below, various examples of apparatuses and methods for modifying a surface of a microelectronic device (e.g., a processor lid, a boiler plate) to promote boiling of a coolant liquid and microelectronic devices with modified surfaces are provided, wherein a given example or set of examples showcases features of a grinding apparatus (e.g., a cutting tool such as a cutting disk, or a scribing tip, a particulate removal system), a laser surfacing apparatus (e.g., a laser), an electrical discharge machining apparatus (e.g., a cathode, a tank, dielectric fluid), a skiving apparatus (e.g., a skiving tool), pin fins, particles coated with fusible metal, a wick structure, a resin material, and an arrangement of structural features formed on the surface(s) of the microelectronic device. It should be appreciated that one or more features discussed in connection with a given example of an apparatus, a method, or a modified microelectronic device may be employed in other examples of apparatuses, methods, or modified microelectronic devices, respectively, according to the present disclosure, such that the various features disclosed herein may be readily combined in a given apparatus, method, or modified microelectronic device according to the present disclosure (provided that respective properties are not mutually inconsistent).

[0113] Certain dimensions and features of the apparatuses disclosed herein and / or the microelectronic devices with a modified surface are disclosed herein using the terms “approximately,” “about,” “substantially,” and / or “similar.” As used herein, the terms “approximately,” “about,” “substantially,” and / or “similar” indicates that each of the described dimensions or features is not a strict boundary or parameter and does not exclude functionally similar variations therefrom. Unless context or the description indicates otherwise, the use of theterms “approximately,” “about,” “substantially,” and / or “similar” in connection with a numerical parameter indicates that the numerical parameter includes variations that, using mathematical and industrial principles accepted in the art (e.g., rounding, measurement or other systematic errors, manufacturing tolerances, etc.), would not vary the least significant digit.1. An Example of a Conventional Microelectronic Device with a Lid[0114| Conventional microelectronic devices often include a semiconductor die and a lid to enclose and protect the semiconductor die. The lid is also used to dissipate heat generated by the semiconductor die during operation. The lid is typically mounted onto a printed circuit board (PCB) supporting the semiconductor die and thermally coupled to the semiconductor die via a layer of thermal interface material. Thus, the lid and the thermal interface material provide a thermal pathway to conduct heat away from the semiconductor die. Examples of conventional microelectronic devices with lids include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), a data processing unit (DPU), a voltage regulator (VR), high bandwidth memory (HBM), a digital signal processor (DSP), a field-programmable gate array (FPGA), and an application-specific integrated circuit (ASIC).[0115| As an illustrative example, FIGS. 1A and IB show a processor 10. The processor 10 is an example of a microelectronic device contemplated herein (e.g., a CPU, a GPU, a DPU, and / or the like). As shown, the processor 10 includes a printed circuit board (PCB) 14 and a processor chip 16 (more generally referred to as a semiconductor die) mounted to the PCB 14 via a ball grid array 20. An underfill material 22 is typically included to bond the processor chip 16 to the PCB 14 and protect the electrical connections formed by the ball grid array 20. A thermal interface material 18 is applied to a surface of the processor chip 16 opposite to the ball grid array 20. A lid 12 is mounted to the PCB 14 such that a portion of the lid 12 is in physical contact with the thermal interface material 18, thus thermally coupling the lid 12 to the processor chip 16. The lid 12 is typically mounted to the PCB 14 via an adhesive or a solder joint. The PCB 14 provides an electrical interface to couple the processor 10 to another PCB, such as a motherboard or, more generally, a PCB assembly (PCBA). For example, FIG. IB shows the PCB 14 may be electrically coupled to a PCBA 26 with another ball grid array 24. However, it should be appreciated that in other example processors, a pin grid array or a land grid array may be used to electrically couple the processor 10 to the PCB 26.[0116} During operation, an appreciable portion of the heat generated by the processor chip 16 is conducted to the lid 12 through the thermal interface material 18. The thermally conductive properties of the lid 12, in turn, may facilitate heat conduction laterally across the lid 12, thus spreading the heat across a larger volume and, in turn, providing a way to more effectively remove the heat from a larger surface of the processor 10 (e.g., the surface 13 of the lid 12 shown in FIG. IB).[0117| Herein, the heat may be removed from the processor 10 and, in particular, the surface 13 of the lid 12 by submerging the processor 10 and the PCBA 26 in a coolant liquid of a two-phase immersion cooling system. Compared to computing systems that include a boiler plate mounted to the lid 12, the coolant liquid may directly contact the surface 13 of the lid 12. As heat is transferred from the processor chip 16 to the lid 12, the temperature of the lid 12 increases. If the temperature of the surface 13 exceeds the liquid-vapor phase transition temperature of the coolant liquid, the coolant liquid that directly contacts the surface 13 may vaporize (e.g., by forming a bubble) so long as a nucleation site to facilitate bubble formation is present on the surface 13. In this manner, the coolant liquid dissipates heat from the lid 12, in part, by absorbing the heat to vaporize the coolant liquid.

[0118] The rate at which heat is removed from the lid 12 by boiling a coolant liquid may be appreciably increased by increasing the number of nucleation sites on the surface 13 available for bubbles to form. This may be accomplished by structurally modifying one or more surfaces of the lid 12 to incorporate microstructures that provide nucleation sites to promote boiling of the coolant liquid. Accordingly, various approaches are disclosed herein to structurally modify the surface 13 to provide microstructures that promote boiling of a coolant liquid. These approaches may involve one or more subtractive processes (e.g., mechanical grinding, EDM, fluid jet machining, or laser surfacing), forming processes (e.g., skiving, forging), and / or additive processes (e.g., particle deposition, attachment of prefabricated wick structures, patterning a deposited resin layer). In some implementations, the microstructures formed by the various approaches disclosed herein may even produce a boiling curve with inversion where a wall superheat temperature remains constant and / or decreases as the heat flux at the boiling surface increases (see Sections 2.5 and 3.2 for further details).[0119| Additionally, the various approaches disclosed herein may form microstructures on the surface(s) of the lid while generating appreciably less heat compared to conventional systems, such as an electron beam machining system, or certain laser cutting systems. In some implementations, the reduction in heat generation may allow modifications to be made to the lid while the lid remains attached to the PCB and the semiconductor die of the microelectronic device without damaging any component of the microelectronic device (e.g., the thermal interface material between a lid and a processor chip). In some implementations, modifications to the lid may even be made after the microelectronic device is mounted to another PCBA (e g., the processor 10 mounted to the PCBA 26), which appreciably simplifies the process of testing and validating a microelectronic device and / or a computing system with the microelectronic device mounted to a PCBA (see Section 5 for further details).

[0120] Although direct modifications of the lid may be preferable to achieve a lower thermal resistance between the semiconductor die and the coolant liquid, it should be appreciated that the various approaches described herein to incorporate microstructures onto a surface may be applied to the surfaces of other components in the microelectronic device or, more generally, the computing system. For example, the same microstructures may be readily incorporated onto one or more surfaces of a boiler plate, which is mounted to the lid. Even though the addition of a boiler plate may increase the thermal resistance between the semiconductor die and the coolant liquid, the approaches described herein may nevertheless provide improvements over conventional approaches of implementing boiling enhancement structures onto the surfaces of a boiler plate, such as lower energy consumption, lower cost of operation, and / or higher fabrication throughput.

[0121] Following below are several non-limiting examples of apparatuses and methods for incorporating microstructures onto one or more surfaces of a lid of a microelectronic device. It should be appreciated that while each inventive apparatus and / or method may individually be suitable for forming microstructures that provide nucleation sites to promote boiling, it is also possible to use multiple apparatuses and / or methods in combination to form more complex microstructures. Accordingly, any structural features disclosed herein may be combined together. For example, the microstructures may include an array of pin fins with grooves formed thereon via a laser surfacing apparatus.2. Example Subtractive Processes[0122 In some implementations, the structural modifications to the surface(s) of a microelectronic device may be achieved using one or more subtractive processes. A subtractive process involves the removal of material from the surface of the modified component. For example, a subtractive process applied to the lid of a microelectronic device involves removing material from the lid itself.2.1 Example Microstructures

[0123] Following below are several non-limiting examples of microstructures that may be incorporated onto one or more surfaces of a microelectronic device using a subtractive process.2.1.1. An Example of Crosshatch Grooves

[0124] In some implementations, the microstructures formed on the surfaces of the microelectronic device by the subtractive processes disclosed herein may include an array of grooves. A groove may be a depression formed by removing material along a path. The path may extend across the entirety of the surface or span only a portion of the surface. Each groove may provide one or more nucleation sites along its length to promote boiling of a coolant liquid in a two-phase immersion cooling system.

[0125] For example, FIGS. 2A-2D show an array of grooves 120’ formed on a surface 1 13’ of a lid 112’ with a crosshatch pattern. For reference, FIG. 2A shows a processor 100a with a lid 112 before modifications are made by the various approaches disclosed herein. The lid 112 encapsulates a processor chip 190 and is thermally coupled to the processor chip 190 via a thermal interface material (not shown). For reference, the processor chip 190, which is not visible due to the lid 112, is shown using a dotted line to indicate its location relative to the lid 112. It should be appreciated the processor 100a is a non-limiting example and that, more generally, the array of grooves 120’ may be applied to any microelectronic device with a semiconductor die and a lid.[0.1 6] The lid 112 may be larger in size than the processor chip 190 and provide a surface 113 to dissipate heat away from the processor 100a (e.g., via a coolant liquid). Initially, the surface 1 13 may be substantially flat as shown in FIG. 2A, which is typical for off-the-shelf processors. The lid 112 may be formed from a thermally conductive material, such as copper, a copper alloy, aluminum, or the like. It should be appreciated that the thermally conductive material forming thelid 112 may be coated with another material, for example, to reduce or, in some instances, prevent corrosion. For example, a lid 112 formed of copper may be coated or plated with nickel.

[0127] FIG. 2B shows the processor 100a after being modified by the approaches disclosed herein (hereafter referred to as the processor 100a’). The processor 100a’ includes a lid 112’ with a surface 113’ modified to include the grooves 120’. As shown, the grooves 120’ may include a subset of grooves 120a’ aligned longitudinally along a first axis, n, and a subset of grooves 120b’ aligned longitudinally along a second axis, . Each of the subsets of grooves 120a’ and 120b’ may be a parallel array of grooves. Specifically, the grooves 120’ in each subset may be straight with a longitudinal axis that is aligned parallel to respective longitudinal axes of all other grooves 120’ in that same subset. FIG. 2C further shows the grooves 120a’ may be uniformly distributed along the first axis, n, where each groove 120a’ has a width wi and is separated from an adjacent groove 120a’ by a pitch pi. The grooves 120b’ may be uniformly distributed along the second axis, , where each groove 120b’ has a width W2 and is separated from an adjacent groove 120b’ by a pitch p2. The width of the grooves 120a’ (wi) and the grooves 120b’ (w2) may be the same or different. The pitch of the grooves 120a’ (pi) and the grooves 120b’ (p2) may be the same or different. FIG. 2D further shows the grooves 120a’ may have a depth di. The grooves 120b’ may also have the same depth di.10128] The dimensions and geometry of the grooves 120’ and the composition of the coolant liquid may affect the generation rate of bubbles, e g., when the lid 112’ is at an elevated temperature and in contact with the coolant liquid. For example, the dimensions and the geometry may affect the wettability of the coolant liquid to the surface of the groove 120’ which, in turn, affects the formation of a bubble on a groove 120’ . The coolant liquids typically used in two-phase immersion cooling systems are fluorocarbon-based coolants, such as fluoroketone. For most fluorocarbon- based coolants, the characteristic dimensions of the grooves 120’ should preferably be on the order of hundreds of microns or less to facilitate bubble formation and the angle between the surfaces of the grooves 120’ should be an acute angle to facilitate wicking of coolant liquid into the groove and to discharge vapor bubbles as they are formed in the groove. In some implementations, the grooves 120’ may provide a heat flux greater than or equal to 15 W / cm2.

[0129] In some implementations, the width of the grooves 120a’ (wi) and / or the grooves 120b’ (w2) is less than or equal to about 500 pm, including all values and sub-ranges in between. Morepreferably, the width of the grooves 120a’ (ivy) and / or the grooves 120b’ (u’y) is less than or equal to about 100 pm, including all values and sub-ranges in between. Even more preferably, the width of the grooves 120a’ (wy) and / or the grooves 120b’ (wi) is less than or equal to about 50 pm, including all values and sub-ranges in between. In some implementations, the width of the grooves 120a’ (wy) and / or the grooves 120b’ (w ) may range from about 20 pm to about 40 pm, including all values and sub-ranges in between.

[0130] In some implementations, the depth of the grooves 120a’ (di) and / or the grooves 120b’ (t / y) is less than or equal to about 500 pm, including all values and sub-ranges in between. More preferably, the depth of the grooves 120a’ (< / y) and / or the grooves 120b’ ( / ) is less than or equal to about 100 pm, including all values and sub-ranges in between. Even more preferably, the depth of the grooves 120a’ (t / y) and / or the grooves 120b’ (di) is less than or equal to about 50 pm, including all values and sub-ranges in between. In some implementations, the depth of the grooves 120a’ (<7y) and / or the grooves 120b’ (di) may range from about 10 pm to about 70 pm, including all values and sub-ranges in between.(01311 The pitch of the grooves 120a’ (pi) and the grooves 120b’ (pi) affect the overall density of the grooves 120’ on the surface 113’. Herein, the density of grooves may be defined as the number of grooves per unit area. In some implementations, the pitch of the grooves 120a’ (pi) and the grooves 120b’ (pi) may be equal to the width of the grooves 120a’ (wy) and the grooves 120b’ (rry), respectively. In some implementations, the pitch of the grooves 120a’ (pi) and / or the grooves 120b’ (pi) may range from about 0 pm to about 1000 pm, including all values and sub-ranges in between. In some implementations, the pitch of the grooves 120a’ (pi) and / or the grooves 120b’ (pi) may range from about 40 pm to about 100 pm, including all values and sub-ranges in between.

[0132] The term “about,” when used to describe the dimensions of the grooves 120’, is intended to cover manufacturing tolerances. For example, “about 100 pm” may correspond to the following dimensional ranges: 99 to 101 pm (+ / - 1% tolerance), 99.2 to 100.8 pm (+ / - 0.8% tolerance), 99.4 to 100.6 pm (+ / - 0.6% tolerance), 99.6 to 100.4 pm (+ / - 0.4% tolerance), 99.8 to 100.2 pm (+ / - 0.2% tolerance), including all values and sub-ranges in between.

[0133] It should be appreciated that the dimensions of the grooves 120’ or, more generally, the microstructures formed on the surface(s) of the microelectronic device may be chosen based on the particular coolant liquid used in the two-phase immersion cooling system. Generally, thedimensions of the microstructures may be affected by various properties of the coolant liquid including, but not limited to, surface tension, latent heat of vaporization, boiling point, viscosity, density, and the like. In some implementations, the dimensions of the microstructures may be chosen such that the coolant liquid readily wets the surfaces of the microstructures and the bubbles generated from these surfaces are sufficiently large to avoid being pinned to the microstructures, thus appreciably reducing the likelihood of dry out (i.e., when the heat flux reaches the critical heat flux).|0134| FIG. 2D further shows the grooves 120a’ may have a triangular profile when formed on the surface 113’ of the lid 112’ . It should be appreciated that this profile is a non-limiting example. More generally, the profile of the grooves formed on the surface of the lid may have various geometries including, but not limited to, a triangle, a square, a rectangle, a semi-circle, a semiellipse, and any combinations of the foregoing.|O135] For the processor 100a’, the axis, n, may be aligned to a first edge 114’ of the surface 113’ and the axis, , may be aligned to a second edge 115’ of the surface 113’ as shown in FIG. 2B. In some implementations, the first and second edges 114’ and 115’ may be orthogonal (i.e., perpendicular) and thus the axes n and may also be orthogonal (i.e., perpendicular). As a result, the grooves 120a’ and 120b’ may form a crosshatch pattern. Additionally, the grooves 120a’ and 120b’ may extend to the edges of the surface 113’, as shown in FIG. 2B. Thus, the grooves 120’ may introduce nucleation sites across the entirety of the surface 113’.[O136| It should be appreciated that the lid 112’ shown in FIGS. 2B-2D with the grooves 120’ forming a crosshatch pattern is a non-limiting example. More generally, various arrangements of grooves are contemplated herein that may be formed onto the surface of a lid.|0137] The grooves may include one or multiple subsets of grooves aligned longitudinally along one or more axes. In some implementations, the grooves may be aligned longitudinally along only a single axis (e g., ry, , or another axis with any orientation along the surface 113’). For example, FIGS. 3 A and 3B show a processor 100d’ that includes an array of linear grooves 120’. As shown, the grooves 120’ may be arranged as a parallel array. Specifically, each groove 120’ may be straight with a longitudinal axis that is aligned parallel to respective longitudinal axes of all other grooves 120’. The grooves 120’ may further be aligned parallel to an axis r. The grooves 120’ may extend to the edges 114’ and 116’ of the lid 112’. The grooves 120’ may further be distributed tospan the length of the edges 114’ and 116’, thus covering the surface 113’. As shown in FIG. 3B, the grooves 120’ may each have a width wi and a depth di. The grooves 120’ may further be evenly separated by a pitch, pi. The width, depth, and pitch of the grooves 120’ may correspond to the dimensional values recited above for the processor 100a’. In some implementations, the grooves 120’ may be arranged such that when the processor 100d’ is installed into a two-phase immersion cooling system, the grooves 120’ are oriented vertically (i.e., the axis r is vertical).

[0138] In some implementations, the grooves may include subsets of grooves that are aligned longitudinally along three or more axes. For example, the grooves 120’ on the lid 112’ of the processor 100a’ may include a third subset of grooves aligned along an axis that is oriented 45 degrees with respect to the axes n and ri.

[0139] Additionally, the axes along which the different subsets of grooves are aligned may also be oriented in various ways. In the example processor 100a’, the axes n and are orthogonal and aligned to edges 114’ and 115’, respectively, as shown in FIG. 2B. More generally, the axes n and r2 may not be aligned to any edge of the surface 113’. In some implementations, the axes ri and r? may each be oriented such that an angle between the axis n and the edge 114’ and / or an angle between the axis and the edge 115’ range from about 0 degrees to about 90 degrees, including all values and sub-ranges in between. For example, the angle between the axis n and the edge 114’ and / or the angle between the axis and the edge 115’ may be about 0 degrees, about 5 degrees, about 10 degrees, about 15 degrees, about 20 degrees, about 25 degrees, about 30 degrees, about 35 degrees, about 40 degrees, about 45 degrees, about 50 degrees, about 55 degrees, about 60 degrees, about 65 degrees, about 70 degrees, about 75 degrees, about 80 degrees, about 85 degrees, or about 90 degrees. Furthermore, the axes ri and r may be oriented such that an angle between the axes n and r2 is greater than 0 degrees and less than or equal to about 90 degrees (see, for example, the processor 100c’ in FIG. 5 A). For example, the angle between the axes n and may be about 5 degrees, about 10 degrees, about 15 degrees, about 20 degrees, about 25 degrees, about 30 degrees, about 35 degrees, about 40 degrees, about 45 degrees, about 50 degrees, about 55 degrees, about 60 degrees, about 65 degrees, about 70 degrees, about 75 degrees, about 80 degrees, about 85 degrees, or about 90 degrees. The foregoing ranges may apply to any pair of axes along which subsets of grooves are aligned, e.g., processors with lids having grooves aligned along two or more axes.[0140) The term “about,” when used to describe the orientation of the axes n, r2, or any axis along which a subset of grooves is aligned, is intended to cover manufacturing tolerances. For example, “about 90 degrees” may correspond to the following ranges: 89.1 degrees to 90.9 degrees (+ / - 1% variation), 88.2 degrees to 91.8 degrees (+ / - 2% variation), 87.3 degrees to 92.7 degrees (+ / - 3% variation), 86.4 degrees to 93.6 degrees (+ / - 4% variation), 85.5 degrees to 94.5 degrees (+ / - 5% variation), including all values and sub-ranges in between.

[0141] It should also be appreciated that the foregoing examples of grooves 120’ are non-limiting examples. More generally, at least a subset of the grooves formed on the surface of the lid may not be straight or aligned longitudinally to a particular axis. For example, the grooves may be curved (e.g., a sinusoidal groove, an arcuate groove). In another example, the grooves may form an enclosed shape (e.g., a circular groove, an elliptical groove). In yet another example, the grooves may be formed as a series of segments where each segment is aligned at a different angle to an adjoining segment (e.g., a zigzag curve). In yet another example, the grooves may be arranged in a random manner on the surface of the lid with no order or pattern. In yet another example, the grooves formed on the surface of the lid may be a combination of any of the grooves described above.

[0142] In the example processor 100a’, the grooves 120’ are shown covering the entirety of the surface 113’. In some implementations, the grooves may cover only a portion of the surface of the lid. For example, the crosshatch pattern of grooves 120’ shown in FIG. 2B may only cover a central portion of the surface 113’ that experiences the largest temperature increase in the processor 100a’ due to the heat generated by the processor chip 190 leaving a peripheral portion that includes the edges 114’ and 115’ unmodified. By modifying a smaller area of the surface 113’, the process time to modify the surface 113’ may be reduced.

[0143] In another example, one or more portions of the processor chip 190 may generate more heat than other portions of the processor chip 190, thus creating hotspots on the processor chip 190. Herein, a hotspot may generally be a region of the processor chip 190 that has a higher temperature than another region of the processor chip 190. In some implementations, a hotspot may correspond to regions of the processor chip 190 that have an elevated tempreature greater than or equal to an operating temperature threshold. If portions of the processor chip 190 exceed the operating temperature threshold, the processor chip 190 may become appreciably more susceptibleto reliability issues and performance errors. In some implementations, the operating temperature threshold may correspond to a maximum operating temperature set by the manufacturer of the microelectronic device. For example, the operating temperature threshold may be about 100°C. Accordingly, the grooves may only be formed on portions of the surface 113’ where hotspots occur to facilitate increased boiling and, hence, cooling of the lid 112 in those portions (see, for example, the processor 100b’ in Section 2.1.2).

[0144] It should also be appreciated that, in some implementations, the grooves 120a’, the grooves 120b’, or any subset of grooves aligned along a particular axis may have a variable width, depth, and / or pitch along its corresponding axis. For example, the surface of the lid may include one or more portions (e.g., portions of the lid that overlap with portions of the processor chip where hotspots occur during operation) where the grooves 120a’ have a relatively smaller width and / or a relatively smaller pitch, thus resulting in a higher density of grooves. The remaining portions of the surface may include a relatively larger width and / or a relatively larger pitch resulting in a lower density of grooves. In some implementations, the remaining portions of the surface may include no grooves (e.g., the remaining portions may be unmodified). In another example, the grooves 120a’ may include different subsets of grooves formed with different depths (see, for example, the processor 100c’ in FIG. 5B). By varying the depth of the grooves, smaller feature details may be formed on the surface 113’ of the lid 112’, further improving boiling of the coolant liquid.

[0145] In some implementations, the surface 113’ of the lid 1 12’ may be work hardened (also sometimes referred to as "strain harden”) as modifications are made to the surface 113’. For example, a grinding apparatus may work harden the surface 113’ of the lid 112’ by plastically deforming the surface 113’ as the grooves 120’ are formed. As a result, the lid 112’ may form a layer of material (also referred to herein as a “layer portion”) along the surface 113’ coinciding with the grooves 120’ with a relatively higher yield strength and hardness and a lower ductility compared to the bulk of the lid 112’ (also referred to herein as a “bulk portion”).

[0146] The extent to which the lid 112’ is work hardened may be evaluated in several ways. For example, a hardness test (e.g., a Vickers hardness test, a Knoop hardness test) may be performed on the lid 112’ before and after modification by the grinding apparatus. The measurement of a higher hardness value after modification indicates the lid 112 is work hardened. In another example, a cross sectional image of the lid 112’ near the surface 113’ may be acquired using amicroscope (e g., an optical microscope, a scanning electron microscope). A portion of the lid 112’ may be cut to expose the cross section for imaging. In this example, work hardening may be detected by evaluating the grain structure of the lid 112’ along its cross section. If the lid 112’ is work hardened, a thin layer may be formed along the surface 113’ with a different grain structure than the bulk of the lid 112’. For instance, if the lid 112’ is formed of copper, the thin layer may have relatively smaller grains compared to the bulk copper.2.1.2 An Example of Selectively Placed Grooves

[0147] As described above in Section 2.1.1, it may be preferable in some applications to selectively form grooves only on certain portions of the surface of a lid. FIGS. 4A and 4B show one non-limiting example of a processor 100b’ with a lid 112’ that is modified to include grooves on portions of the surface 113’ where hotspots occur on the processor chip 190. Specifically, FIG. 4A shows a processor 100b before modifications are made to a lid 112. As shown, the lid 112 includes a surface 113 to facilitate cooling as described above. FIG. 4 A further shows the processor chip 190 includes regions 192 and 194 where hotspots 199a and 199b, respectively, occur during operation of the processor 100b.[0148 FIG. 4B shows the processor 100b after the surface 113 is modified by the approaches described herein (hereafter referred to as the processor 100b’). As shown, the surface 113’ of the lid 112’ includes a first set of grooves 122a’ located in the region 192 of the processor chip 190 and a second set of grooves 122b’ located in the region 194 of the processor chip 190. The remaining portions of the surface 113’ are shown unmodified. In this manner, when the processor 100b’ is immersed in a coolant liquid of a two-phase immersion cooling system, the coolant liquid may boil at an appreciably higher rate in the regions 192 and 194 of the lid 112’ where the hotspots 199a and 199b occurred for the unmodified processor 100b.

[0149] In some implementations, the dimensions of the grooves 122a’ and 122b’ (e.g., the width, the depth, the pitch) may be the same or different. For example, if the hotspot 199a exhibits a higher temperature than the hotspot 199b, a higher density of grooves 122a’ may be formed to provide more nucleation sites per unit area for the portion of the lid 112 collocated with the region 192 compared to the region 194. This, in turn, may facilitate a higher cooling rate at or near the region 192 compared to the region 194.[0150| In some cases, the formation of higher density grooves may have a longer processing time compared to lower density grooves. For example, a grinding apparatus may cut the same region of the surface of the lid multiple times to increase the number of grooves within that region. By altering the density of grooves for different regions of the lid, the desired cooling rate for each region (e.g., via boiling of a coolant liquid) may be obtained while reducing the overall processing time to modify the surface of the lid. However, it should be appreciated that, in some implementations, the processing time to form the grooves may be sufficiently short such that the same density of grooves may be formed on different regions of the lid (e.g., the grooves 122a’ and 122b’) without appreciably increasing the overall processing time.2.1.3 An Example of Grooves with a Variable Depth and an Acute Orientation[0151 | FIGS. A and 5B show a non-limiting example of a processor 100c’ that is modified to include grooves 124a’ and 124b’ on the surface 113’ of the lid 112’. FIG. 5A shows the grooves 124a’ and 124b’ may be oriented at an acute angle, 0, with respect to each other. The grooves 124a’ and 124b’ may further intersect one another on a portion of the surface 113’ that overlaps with a processor chip 190. FIG. 5B further shows the grooves 124a’ may be formed at a depth, di, and the grooves 124b’ may be formed at a depth, d2, less than di. In FIG. 5B, the groove 124b’ is shown with dotted lines to indicate the groove 124b’ is located at a different plane from the cross- sectional plane of FIG. 5B.2.2 Example Grinding Apparatuses[01521 In one non-limiting example, a grinding apparatus is disclosed herein that removes material from the surface(s) of a microelectronic device (e.g., the lid) by mechanically cutting the surface(s). Specifically, the grinding apparatus may include one or more cutting tools to selectively remove material from the surface. In this manner, microstructures (e.g., grooves) may be formed on the surface(s), thus providing nucleation sites to facilitate boiling of a coolant liquid in a two- phase immersion cooling system. Following below are several non-limiting examples of grinding apparatuses configured to remove material from the lid of a microelectronic device to form, for example, the microstructures discussed in Section 2.1.2.2.1 An Example Grinding Apparatus with Cutting Disks[0153 In one illustrative example, FIGS. 6A and 6B show a grinding apparatus 200a with multiple cutting disks 230 configured to form multiple grooves on one or surfaces of a microelectronic device (e.g., the surface of a lid). As shown, the cutting disks 230 may be rigidly mounted to a spindle 242, which, in turn, may be rotatably coupled to a pair of sliders 240, e.g., via corresponding bearings (not shown). The sliders 240 may slidably couple the cutting disks 230 and the spindle 242 to a frame 220 to facilitate movement of the cutting disks 230 along the surface of the lid when forming the grooves. Specifically, the sliders 240 may be slidably coupled to corresponding channels 222 on the frame 220. In some implementations, each channel 222 may include a protruding rail portion 223 that meshes with a recessed portion 244 on the corresponding slider 240 to constrain and guide movement of the cutting disks 230 and the spindle 242 along the channels 222.

[0154] The rotation of the cutting disks 230 and the movement of the cutting disks 230 and the spindle 242 along the channels 222 of the frame may be facilitated, in part, by one or more motors. For example, the apparatus 200a may include a motor 210 directly coupled to the spindle 242 to rotate the spindle 242 and the cutting disks 230. The apparatus 200a may further include a motor 212 coupled to the motor 210 to actuate and move the motor 210, the cutting disks 230, and the spindle 242 along the channels 222 of the frame 220 via a rod 214. In some implementations, the motor 210 may be a direct current (DC) brushless motor. In some implementations, the motor 212 may be a ball screw drive and the rod 214 may include helical threads. During operation, the rod 214 may be constrained to the motor 212 such that rotational motion of the rod 214 induces translational motion and, in turn, movement of the motor 210, the cutting disks 230, and the spindle 242 relative to the motor 212 and the frame 220. In some implementations, the motor 210 may also be slidably mounted to a track 216 to guide the movement of the motor 210 with respect the motor 212.

[0155] Each cutting disk 230 may have a width, wa, and may further be separated from adjacent cutting disks 230 by a pitch, pa. In some implementations, the width of the cutting disk 230 may be dimensioned to be the same as the desired width of the groove (e.g., the width wa is equal to the width wi or wj). In some implementations, the cutting disk 230 may include a relatively large width and a tapered edge. The width of the groove formed on the surface of the lid may becontrollably adjusted based on, for example, the depth at which the tapered edge of the cutting disk 230 cuts into the surface of the lid. For example, if the cutting disk 230 cuts into the surface of the lid with a relatively shallow depth, a relatively narrow groove may be formed. In another example, if the cutting disk 230 cuts into the surface of the lid with a relatively deep depth, a relatively wide groove may be formed.[(I156| In some implementations, the pitch of the cutting disks 230 may correspond to the desired pitch of the grooves (e.g., the pitch pa is equal to the pitch pi or p ). It should be appreciated, however, that grooves with a smaller pitch (e.g., pi or p2 less than pd) may be formed by using the cutting disks 230 to form multiple sets of grooves within the same region of the surface of the lid. For example, the cutting disks 230 may form a first set of grooves on the surface of the lid with a pitch pd. The first set of grooves may be aligned longitudinally along a first axis. Thereafter, the cutting disks 230 may be offset by a distance equal to half the pitch pd along a second axis orthogonal to the first axis and thereafter applied again to form a second set of grooves that are also aligned longitudinally along the first axis. The first and second sets of grooves together may form a set of grooves having a pitch equal to half the pitch pd.[(Il 57| The cutting disks 230 may generally be formed of a material having a hardness greater than the material of the lid 112 (e.g., copper, nickel). For example, the cutting disks 230 may be formed of various ceramic materials including, but not limited to, a carbide material (e.g., tungsten carbide), a nitride material (e.g., boron nitride), and diamond coated steel.[(Il 58| The process of modifying a lid of a processor may begin by securing the processor and / or the PCBA with the processor mounted thereto to a sample holder (not shown). Thereafter, the grinding apparatus 200a may be placed onto the sample holder such that the cutting disks 230 are aligned to the surface of the lid (e.g., the surface 113 of the lid 112). The cutting disks 230 may thereafter begin rotating (e.g., via the motor 210) and brought into contact with the surface to begin removing material and forming a portion of the grooves. The cutting disks 230 may then be moved (e.g., via the motor 212 along an axis defined by the channels 222) to form the remaining portion of the grooves across the surface of the lid. In some implementations, the initial placement of the cutting disks 230 on the surface of the lid and the range of movement of the cutting disks 230 along the channels 222 may be adjusted to selectively form grooves on a desired portion of the lid.[0159| The depth at which the grooves are formed may be controlled in several ways. In one example, the apparatus 200a may be placed such that the cutting disks 230 are positioned a desired distance above the surface of the lid. Thereafter, the grinding apparatus 200a may be lowered (e.g., via a servo actuator) by a predetermined distance to form grooves at a desired depth into the surface of the lid. In another example, the sample holder supporting the processor and / or the PCBA may be raised (e.g., via servo actuator) to bring the surface of the lid into contact with the cutting disks 230. In some implementations, the servo actuator may apply a force onto the grinding apparatus 200a or the sample holder such that the cutting disks 230 and the surface of the lid are pressed against one another to facilitate removal of material.[0l60| As material is removed from the surface of the lid via the grinding apparatus 200a, particulates may be generated and discharged in the air around the processor and / or the PCBA where they may then deposit onto various surfaces including the lid, the PCB of the processor, and / or the PCBA supporting the processor. If not removed, the particulates may damage the processor and / or the PCBA, e.g., by creating a short circuit between various electrical connections or circuit elements.(01611 Thus, the grinding apparatus 200a may operate together with a particulate removal system. For example, FIG. 7A shows a particulate removal system 300a that includes a duct 310 positioned above the grinding apparatus 200a and the lid 112. The duct 310 may be operably coupled to a vacuum pump (not shown) to generate vacuum suction at the duct 310. Thus, as particulates are generated and discharged into the air by the grinding apparatus 200a from the surface 113 of the lid 112, the particulates may be suctioned and removed from the vicinity of the apparatus 200a, the processor, the PCBA, and the sample holder. In another example, FIG. 7B shows a particulate removal system 300b that again includes a duct 310 positioned above the grinding apparatus 200a and the lid 112. The duct 310 may be operably coupled to a pump (not shown) to generate a flow of air directed towards the apparatus 200a, the processor, the PCBA, and the sample holder. In this example, the particulates may be blown away from the apparatus 200a, the processor, the PCBA, and the sample holder by the particulate removal system 300b. For both particulate removal systems 300a and 300b, a flow of air may pass along the surface 113 of the lid 112. In addition to facilitating removal of particulates, this flow of air may also convectively cool the surface 113.[0162| In some implementations, a portion of the processor and / or the PCBA may be covered before the grinding apparatus 200a begins removing material from the surface of the lid. For example, FIG. 7C shows a side portion of the lid 112 and a peripheral portion of the surface 113 may be covered with a sheet 320 while a central portion of the surface 113 is left exposed for the apparatus 200a to remove material. In some implementations, the sheet 320 may merely be placed onto the surfaces of the lid, other components of the processor, and / or the PCBA without being directly attached to the foregoing surfaces. In some implementations, the sheet 320 may adhere to the surfaces of the lid, other components of the processor, and / or the PCBA. For example, the sheet 320 may be attached via static cling (e.g., a static cling vinyl fdm) or a removable adhesive. As grooves are formed on the surface 113 of the lid 112, the sheet 320 provides a barrier to prevent particulates from depositing directly onto surfaces of the processor and / or the PCBA. After the grooves are formed, the sheet 320 may be removed. The sheet 320 may be used in combination with the particulate removal systems 300a or 300b described above to reduce or, in some instances, eliminate undesirable deposition of particulates on the processor and / or the PCBA.[0163} It should be appreciated that after the lid is modified by the grinding apparatus 200a, the processor and / or the PCBA with the processor mounted thereto may be washed to remove any remaining particulates. For example, the PCBA may be washed using isopropyl alcohol. In another example, the PCBA may be washed with deionized water followed by isopropyl alcohol.2.2.2 An Example Grinding Apparatus with Scribing Tips[0164} In another illustrative example, FIGS. 8A and 8B show a grinding apparatus 200b with multiple scribing tips 250 configured to form multiple grooves on the surface of a lid. The apparatus 200b may include several of the same features and / or components as the grinding apparatus 200a described in Section 2.2.1. The apparatus 200b may further operate in combination with the particulate removal systems 300a and 300b. Additionally, the apparatus 200b may modify a surface of a lid where a portion of the lid, the other components of the processor, and / or the PCBA supporting the processor are coated with the sheet 320. For brevity, repeated discussions of these features are not provided below unless indicated otherwise.|0165j As shown, the scribing tips 250 may be mounted to a rod 243, which in turn is rigidly coupled to a pair of sliders 240. The sliders 240 may slidably couple the scribing tips 250 and the rod 243 to corresponding channels 222 of a frame 220. The rod 243 may further be coupled to abase mount 252, which slidably moves together with the rod 243 and the scribing tips 250. The base mount 252 may be coupled to a motor 212 via a rod 214. The motor 212 may thus actuate and move the base mount 252, the rod 243, and the scribing tips 250 along the channels 222 of the frame 220 via the rod 214.

[0166] Each scribing tip 250 may have a width, wt, and may further be separated from adjacent scribing tips 250 by a pitch, pt. In some implementations, the width of the scribing tip 250 may be dimensioned to be the same as the desired width of the groove (e.g., the width wt is equal to the width wi or j). In some implementations, the scribing tip 250 may include a relatively large width and a tapered tip. The width of the groove formed on the surface of the lid may be controllably adjusted based on, for example, the depth at which the tapered tip of the scribing tip 250 cuts into the surface of the lid.

[0167] In some implementations, the pitch of the scribing tips 250 may correspond to the desired pitch of the grooves (e.g., the pitch pa is equal to the pitch pi or p2). It should be appreciated, however, that grooves with a smaller pitch (e.g., pi or p less than p ) may be formed by using the scribing tips 250 to form multiple sets of grooves within the same region of the surface of the lid.

[0168] The scribing tips 250 may include a tip formed of a material having a hardness greater than the material of the lid 112 (e.g., copper, nickel). For example, the scribing tips 250 may be formed of various ceramic materials including, but not limited to, a carbide material (e.g., tungsten carbide), a nitride material (e.g., boron nitride), and diamond.

[0169] The grinding apparatus 200b may be used in a similar manner as the grinding apparatus 200a. For example, the process of modifying a lid of a processor may begin by securing the processor and / or the PCBA with the processor mounted thereto to a sample holder (not shown). Thereafter, the grinding apparatus 200b may be placed onto the sample holder such that the scribing tips 250 are aligned to the surface of the lid (e.g., the surface 113 of the lid 112). The scribing tips 250 may thereafter be brought into contact with the surface. The scribing tips 250 may then be moved across the surface of the lid to form a set of grooves. In some implementations, the initial placement of the scribing tips 250 on the surface of the lid and the range of movement of the scribing tips 250 along the channels 222 may be adjusted to selectively form grooves on a desired portion of the lid.2.3 An Example Electrical Discharge Machining Apparatus[0170 In another non-limiting example, electrical discharge machining (EDM) may be used to remove material from one or more surfaces of a microelectronic device (e.g., a surface of a processor lid) in order to roughen the surface and, thus, create nucleation sites to promote boiling of a coolant liquid. EDM is a fabrication process that utilizes a series of electrical discharges (e.g., sparks) to remove material from a workpiece to obtain a desired shape. Typically, the electrical discharges are generated directly between an electrode and a workpiece. Further, the electrode and the workpiece are immersed in dielectric fluid, which provides a medium that allows more precise control over the material removal rate.

[0171] FIGS. 10A and 10B show an example EDM apparatus 500a. As shown, the apparatus 500a includes a tank 504 that defines a cavity 503 to contain therein a fixture 502 supporting a PCBA 101 and a dielectric fluid 501 to immerse the fixture 502 and the PCBA 101. The PCBA 101 further includes a processor with a processor lid 112. More generally, the apparatus 500a may be applied to any surface of a microelectronic device (e.g., the lid enclosing a semiconductor die).

[0172] The apparatus 500a includes a frame 518 disposed above the tank 504, a motion stage 516 movably coupled to the frame 518, and an electrode 520 securely coupled to the motion stage 516. The motion stage 516 may controllably move the electrode 520 along one or more axes of motion (collectively shown as x) with respect to the lid 112. For example, the motion stage 516 may provide three translational degrees of freedom to move the electrode 520 across the surface of the lid 112 and adjust the gap distance between the electrode 520 and the lid 112 and / or three rotational degrees of freedom to adjust the end 522 of the electrode 520 with respect to the surface of the lid 112. As shown in FIG. 10B, the electrode 520 is partially submerged in the dielectric fluid 501 with an end 522 disposed in close proximity to the lid 112. The electrode 520 is further electrically coupled to a power supply 506 via an electrical connection 508a. The PCBA 101 is also electrically coupled to the power supply 506 via an electrical connection 508b coupled to the fixture 502. Thus, in some implementations, the fixture 502 may provide an electrical connection (e.g., an integrated wire) that electrically connects the PCBA 101 to the electrical connection 508b.|0173] During operation, the electrode 520 and the processor lid 112 function as two electrodes separated by a dielectric fluid. When the electrode 520 and the processor lid 112 are sufficiently close and the voltage between the electrode 520 and the processor lid 112 is sufficiently large, thedielectric fluid may undergo dielectric breakdown. This, in turn, creates a temporary pathway for current to flow between the electrode 520 and the processor lid 112 resulting in an electrical discharge 521. As shown in FIG. 10B, the electrical discharge 521 removes material from the surface of the lid 112, resulting in a crater 126. As the electrode 520 moves across the surface of the lid 112, multiple craters 126 are created resulting in a roughened surface.[(1174| The apparatus 500a may be configured to create craters 126 that do not penetrate through the lid 112. For example, the depth of the craters 126 may be less than or equal to about 50 microns, including all values and sub-ranges in between. In another example, the depth of the crater 126 may range from about 10 pm to about 70 pm, including all values and sub-ranges in between. This may be accomplished, in part, by adjusting various operating parameters that affect the material removal rate of EDM including, but not limited to, the gap distance between the electrode 520 and the surface of the lid 112, the current between the electrode 520 and the surface of the lid 112 when dielectric breakdown of the dielectric fluid 501 occurs, and the voltage between the electrode 520 and the surface of the lid 112 when dielectric breakdown of the dielectric fluid 501 occurs. At least some of these parameters may further depend on the dielectric breakdown voltage of the fluid 501. In one illustrative example, the breakdown voltage across an interelectrode gap (IEG) may be about 200 V. The power supply 506 may further include a RC circuit with a capacitance of about 50 pF.[0175| The material removed from the lid 1 12 is typically dispersed in the dielectric fluid 501 as contaminants. The contaminants may subsequently deposit onto various surfaces of the PCBA 101, thus damaging the PCBA 101. To reduce the likelihood of contaminants depositing onto the PCBA 101 and / or other surfaces of the tank 504 and / or fixture 502, the apparatus 500a may include a filtration system. For example, FIG. 10A shows the apparatus 500a includes a pump 512 and a filter 514 fluidically coupled to the tank 504 via a fluid conduit 510. During operation, the pump 512 may pull in dielectric fluid 501 from the tank 504 and pass the dielectric fluid 501 through the filter 514 to remove contaminants from the dielectric fluid 501. It should be appreciated that the filtration system of FIG. 10A is a non-limiting example. In another example, the dielectric fluid 501 may be periodically replaced (e.g., by draining the tank 504 of contaminated dielectric fluid 501 and adding in uncontaminated dielectric fluid 501).[0176| The manner in which material is removed from the surface of the lid 112 may also be influenced by the geometry of the end 522 of the electrode 520. For example, FIG. 11 A shows an electrode 520a with an end 522a that is relatively wide and flat. This geometry may facilitate the generation of electrical discharges covering a larger area (e.g., to form larger-sized craters 126) and / or multiple electrical discharges distributed over a larger area (e.g., to form multiple craters 126 across a portion of the lid 112 without moving the electrode 520). In another example, FIG. 1 IB shows an electrode 520b with an end 522b that is relatively narrow and sharp. This geometry may facilitate the generation of electrical discharges localized at the end 522b and covering a relatively smaller area (e.g., to form craters 126 at precise, discrete locations on the surface of the lid 112). In yet another example, FIG. 11C shows an electrode 520c with multiple ends 522b to generate multiple electrical discharges simultaneously at precise locations on the surface of the lid 112.

[0177] In some implementations, the electrode 520 may include multiple ends 522a and / or 522b of varying size and shape. Furthermore, one or more of the ends may be chosen at a time and used simultaneously, thus providing a way to dynamically change the size, number, and / or pattern of craters 126 formed on the surface of the lid 112. The selection of different end(s) to use may be accomplished, for example, by rotating the electrode 520 such that the desired end(s) face the surface of the lid 112.

[0178] The electrode 520 may be formed from various electrically conductive materials including, but not limited to, graphite, brass, and copper. In some implementations, the dielectric fluid 501 may be any dielectric fluid commonly used for EDM including, but not limited to, a dielectric oil (e.g., kerosene) and deionized water.2.4 An Example Fluid Jet Apparatus

[0179] In some implementations, a fluid jet may be used to remove material from the surface(s) of a microelectronic device (e.g., the surface of a processor lid) in order to roughen the surface and, thus, create nucleation sites to promote boiling of a coolant liquid. A fluid jet is a relatively narrow, high-pressure stream of fluid capable of removing material from a workpiece via ablation.[0.180] FIGS. 12A and 12B show an example fluid jet apparatus 500b. As shown, the apparatus 500b includes a fixture 530 to support the PCBA 101 with a processor having a lid 112. More generally, the apparatus 500b may be applied to any surface of a microelectronic device (e.g., thelid enclosing a semiconductor die). The apparatus 500b further includes a frame 534 disposed above the fixture 530, a motion stage 532 movably coupled to the frame 534, and a nozzle 540 securely coupled to the motion stage 532. The motion stage 532 may controllably move the nozzle 540 along one or more axes of motion (collectively shown as x) with respect to the lid 112. For example, the motion stage 532 may provide three translational degrees of freedom to move the nozzle 540 across the surface of the lid 112 and adjust the distance between the nozzle 540 and the lid 112 and / or three rotational degrees of freedom to adjust the orientation of the nozzle 540 and, hence, the fluid jet 541 with respect to the surface of the lid 112. The nozzle 540 is fluidically coupled to a pump 538 and a fluid supply 536 via a fluid conduit 539. In this example, the fluid supply 536 may provide a supply of dielectric fluid as the working fluid for the fluid jet.]0181] During operation, the pump 538 may generate a flow of dielectric fluid through the fluid conduit 539. The nozzle 540, in turn, may generate a fluid jet 541 from the flow of dielectric fluid. As shown in FIG. 12B, the nozzle 540 may be positioned near the surface of the lid 112. The fluid jet 541, in turn, may remove material from the lid 112, thus forming a recess 127 in the shape of the fluid jet. As the nozzle 540 moves across the surface of the lid 112, a continuous recess 127 may form along the path traversed by the fluid jet 541 across the surface if the fluid jet 541 is continuously sprayed.10182 ] The depth of the recess 127 at one location may generally increase over time if the fluid jet is stationary at that location. The rate at which the depth increases also depends on the pressure of the fluid jet. Accordingly, the depth of the recesses 127 formed along the surface of the lid 112 may be controlled, in part, by the pressure of the fluid jet and the velocity of the nozzle 540 as it moves along the surface of the lid 112. Generally, the pressure of the fluid jet 541 and / or the velocity of the nozzle 540 may be selected to remove material from the lid 112 without penetrating through the lid 112. For example, the velocity of the fluid jet may be about 800 m / sec. In some implementations, the depth of the recesses 127 may be less than or equal to about 50 microns, including all values and sub-ranges in between. In some implementations, the depth of the recesses 127 may range from about 10 pm to about 70 pm, including all values and sub-ranges in between.

[0183] As described above, the fluid jet 541 comprises a dielectric fluid supplied from the fluid supply 536. Various dielectric fluids may be used including, but not limited to, deionized water. In some implementations, the dielectric fluid may further contain abrasive particles (e.g., silicaparticles) to increase the material removal rate. The abrasive particles may be formed from various materials including, but not limited to, silicon carbide, aluminum oxide, sand, and garnet.2.5 An Example Laser Surfacing Apparatus 0184] In some implementations, a laser may be used to remove material from one or more surfaces of a microelectronic device (e.g., the surface of a processor lid) in order to roughen the surface and, thus, create nucleation sites to promote boiling of a coolant liquid. To reduce or, in some instances, mitigate heating of the microelectronic device, a nanosecond pulsed laser, a femtosecond pulsed laser, or a picosecond pulsed laser may be used. For example, the laser may also be configured to remove a relatively small amount of material from the surface of the processor lid, further reducing heating of the bulk of the processor lid.

[0185] FIGS. 13 A and 13B show an example laser surfacing apparatus 500c. As shown, the apparatus 500c includes a fixture 551 to support the PCBA 101 with a processor having a lid 112. More generally, the apparatus 500c may be applied to any surface of a microelectronic device (e.g., the lid enclosing a semiconductor die). The apparatus 500c further includes a frame 553 disposed above the fixture 551, a motion stage 552 movably coupled to the frame 553, and a laser 550 securely coupled to the motion stage 552. The motion stage 552 may controllably move the laser 550 along one or more axes of motion (collectively shown as x) with respect to the surface of the lid 112. For example, the motion stage 552 may provide three translational degrees of freedom to move the laser 550 across the surface of the lid 112 and adjust the distance between the laser 550 and the lid 112 and / or three rotational degrees of freedom to adjust the orientation of the laser 550 and, hence, the direction of the pulse(s) 554 generated by the laser 550 with respect to the surface of the lid 112.

[0186] During operation, the laser 550 may directly irradiate the surface of the lid 112 with a series of pulses 554. The pulse(s) 554 provides sufficient energy to remove material from the surface of the lid 112 to form a recess 127. For example, the pulse(s) 554 may transfer sufficient energy to a portion of the lid 112 to facilitate melting and / or ablation. The laser 550 may be configured to remove material from components formed from various metals including, but not limited to, copper, copper alloys, aluminum, and the like.|OI87] In some implementations, the laser 550 may emit pulse(s) 554 at various wavelengths including, but not limited to, 515 nm, 1070 nm, 1030 nm, and 1035 nm. More generally, the laser550 may emit pulse(s) at one or more wavelengths ranging from about 500 nm to about 1050 nm, including all values and sub-ranges in between. In some implementations, the laser 550 may emit pulse(s) in the infrared spectrum at wavelengths ranging from about 780 nm to about 1 mm, including all values and sub-ranges in between.

[0188] The motion stage 552 may move the laser 550 at a speed (also referred to as a “raster speed”) ranging from about 20 mm / sec to about 400 mm / sec, including all values and sub-ranges in between. The average power of the pulse(s) emitted by the laser 550 and illuminating the surface of the microelectronic device may range from about 1 W to about 20 W, including all values and sub-ranges in between.

[0189] The pulse(s) 554 may remove a relatively small amount of material from the lid 112, thus reducing or, in some instances, mitigating any adverse effects of the lid 112 being heated. For example, the pulses(s) 554 may form a recess 127 having a depth that is less than or equal to about 50 microns, including all values and sub-ranges in between. In another example, the pulses(s) 554 may form a recess 127 having a depth that ranges from about 10 pm to about 70 pm, including all values and sub-ranges in between. In some implementations, any heat transferred and / or accumulated in the lid 112 may be readily dissipated via natural convection to the surrounding air. However, it should be appreciated that, in some implementations, the apparatus 500c may include a forced convection cooling system (e.g., a fan).

[0190] In some implementations, the apparatus 500c may form hierarchical structures on the portion of the surface of the lid 112 where material is removed by the laser 550. The hierarchical structure may comprise both microstructures (i.e., structures with a characteristic length greater than or equal to 1 pm) and nanostructures (i.e., structures with a characteristic length less than 1 pm). For example, the hierarchical structure may include micron-sized and nano-sized bumps and / or recesses along the surface. In another example, the hierarchical structure may include micron-sized grooves with nano-sized bumps and / or recesses. In some applications, the hierarchical structures may be used to identify whether a microstructure is formed by laser surfacing or another approach. For example, conventional machining (e.g., computer numerical control (CNC) machining) may only produce micron-sized structural features. Accordingly, if inspection of the surface of a lid reveals both micron-sized and nano-sized structural features (i.e.,a hierarchical structure), that may provide evidence indicating laser surfacing was used to form those features. Inspection may be performed using a microscope or a profilometer.

[0191] In one example method, the apparatus 500c may be used to form microstructures on a surface of a lid in a microelectronic device as follows. The method may begin by assembling a computing system that comprises a microelectronic device having a semiconductor die and a lid thermally coupled to the semiconductor die to dissipate heat generated by the semiconductor die. The lid may comprise a surface configured for exposure to a coolant liquid of the two-phase immersion cooling system. The next step may be forming, by the laser 550, a plurality of grooves on the surface of the lid where the plurality of grooves provides a plurality of nucleation sites configured to promote boiling of the coolant liquid. For example, an array of linear grooves may be formed that are oriented vertically when the computing system is installed in the tank of a two- phase immersion cooling system. In this step, the plurality of grooves may be formed by using a particular combination of a laser wavelength, raster speed, and average power. The relevant dimensions of the grooves (e.g., width, pitch, depth) may also be predetermined. If any oxides are present on the surface of the lid, the cooling performance of the lid may be adversely affected due to the low thermal conductivity associated with the oxides. Accordingly, the next step may be removing the oxides via a chemical etchant (e.g., a mild acid sonication). Otherwise, if no oxides are present, the next step may be cleaning the surface of the lid by sonicating the microelectronic device in a mixture of ethanol and isopropanol for about 15 minutes to about 30 minutes. Thereafter, the microelectronic device with the modified lid may be ready for deployment. It should be appreciated the foregoing method may be applied to any surface of the microelectronic device including, for example, one or more surfaces of a boiler plate attached to the lid.101921 As an example demonstration, a nanosecond pulsed laser was used to form an array of linear grooves on a surface of a copper substrate. The substrate, in turn, was placed into a container of coolant liquid (e.g., fluoroketone) such that the array of grooves was oriented vertically. Experimental measurements were then performed to evaluate the boiling curve of the modified copper substrate in the coolant liquid.

[0193] FIG. 14 shows the data acquired from these experimental measurements. Specifically, FIG. 14 shows the measured wall superheat temperature and the measured heat flux at the surface of the copper substrate. The wall superheat temperature refers to the difference between the surfacetemperature and the boiling point of the coolant liquid where the surface temperature is greater than the boiling point. As shown, at least a portion of the boiling curve exhibits isothermal -like behavior where the wall superheat temperature remains approximately the same between about 6°C and 6.4°C as the heat flux increases from 11 W / cm2to 18 W / cm2. In practice, this means the temperature of a semiconductor die may remain approximately constant even as the amount of heat generated by the semiconductor die varies (e.g., due to variations in processing load).

[0194] This can be attributed to the grooves inducing an inversion in the boiling curve. In a typical boiling curve, the heat flux increases as the wall superheat temperature increases until the heat flux reaches the critical heat flux. An inversion occurs when the wall superheat temperature either remains constant or decreases with increasing heat flux. This phenomena is also referred to as secondary pool boiling effects and can occur due to an appreciable increase in the heat transfer coefficient at wall superheat temperatures near the critical heat flux.3. Example Forming Processes10195] In some implementations, the structural modifications to the surface(s) of a microelectronic device may be achieved using one or more forming processes. In a forming process, the surface of a component may be reshaped and / or deformed to form structural features that provide nucleation sites to promote boiling. Thus, a forming process may not remove material from a component unlike the subtractive processes described in Section 2. Following below are examples of forming processes that may be used to form microstructures on one or more surfaces of a microelectronic device.3.1 An Example Skiving Apparatus](H96] In some implementations, the surface(s) of a microelectronic device (e.g., the surface of a processor lid) may be modified by skiving (also sometimes referred to as “scarfing”). Skiving is the process of cutting a material, such as a metal, into thin slices. The slices may thereafter be deformed into a desired shape. For example, skiving is often used to form fins on a heat sink. Herein, skiving may be used to form one or more fins along the surface(s) of the microelectronic device for purposes of creating structural features that act as nucleation sites to promote boiling.

[0197] FIGS. 15A and 15B show an example skiving apparatus 500d. As shown, the apparatus 500d includes a fixture 560 to support the PCBA 101 with a processor having a lid 112. Moregenerally, the apparatus 500d may be applied to any surface of a microelectronic device (e.g., the lid enclosing a semiconductor die). The apparatus 500d further includes a frame 561 disposed above the fixture 560, a motion stage 564 movably coupled to the frame 561, and a skiving tool 562 securely coupled to the motion stage 564. The motion stage 564 may controllably move the skiving tool 562 along one or more axes of motion (collectively shown as x) with respect to the lid 112. For example, the motion stage 564 may provide three translational degrees of freedom to move the skiving tool 562 across the surface of the lid 112 and adjust the distance between the skiving tool 562 and the lid 112 and / or three rotational degrees of freedom to adjust the orientation of the skiving tool 562 with respect to the surface of the lid 112.

[0198] In particular, the angle of the skiving tool 562 relative to the surface of the lid 1 12 may influence whether the tool 562 is able to cut a thin slice of material from the lid 112. For example, FIG. 15B shows the skiving tool 562 may have a surface 563 oriented at an oblique angle with respect to the surface of the lid 112. The angle may be chosen to facilitate shearing of the lid 112. Additionally, the velocity of the tool 562 relative to the lid 112 may also influence the ability of the tool 562 to cut the lid 112. For example, skiving may occur when the relative velocity is above a threshold velocity of about 10 m / min. It should be appreciated that the threshold velocity may depend, in part, on particular materials used to form the tool 562 and / or the lid 112. Additionally, the threshold velocity may be lowered by vibrating the tool 562 during operation. In some implementations, the apparatus 500d may be configured to form one fin every 3 to 5 seconds. However, it should be appreciated that the duration of time to form a fin may vary depending on the dimensions of the fin and the ductility of the material being cut.|OI99[ As shown, as the tool 562 moves across the surface of the lid 112, a fin 128a may be formed. The fin 128a may thereafter be bent, for example, into a vertical upright orientation. As shown in FIG. 15B, multiple fins 128b may be formed by the skiving tool 562 as it moves across the surface of the lid 112. This may be accomplished, for example, by the skiving tool 562 moving in a reciprocating manner to repeatedly cut and form fins 128b on the lid 112 as the skiving tool 562 moves from one side of the lid 112 to an opposite side of the lid 112. The fins 128b in this example are structural features that provide nucleation sites.

[0200] Generally, the skiving apparatus 500d may form the fins 128b along the surface of the lid 112 without penetrating through the lid 112. Accordingly, the dimensions of the fins 128b may berelatively thin and / or short in height. For example, the fins 128b may have a height, h, less than or equal to about 50 microns, including all values and sub-ranges in between. In another example, the fins 128b may have a thickness, z, less than or equal to about 50 microns, including all values and sub-ranges in between.

[0201] The skiving tool 562 may generally be formed of a material that has a hardness greater than the surface hardness of the material used to form the lid 112. For example, the lid 112 is often formed of copper or a copper alloy. Accordingly, the skiving tool 562 may be formed from materials with a relatively higher hardness including, but not limited to, a tool steel (e.g., an ironbased alloy with carbide-forming metals).3.2 An Example Pin Fin Structure[ 202| In some implementations, the surface(s) of a microelectronic device (e.g., the surface of a processor lid) may be modified by incorporating one or more pin fins onto the surface(s). The pin fins may be formed, for example, via a cold forging process. Herein, one or more pin fins may be formed on the surface(s) of the microelectronic device for purposes of creating structural features that act as nucleation sites to promote boiling.

[0203] FIG. 16A shows an example pin fin structure 130a formed on a surface 113 of a lid 112. As shown, the pin fin structure 130a may include an array of pin fins 132 distributed across the surface 1 13. The array of pin fins 132 may be distributed in several ways.

[0204] In one example, FIG. 16B shows the pin fins 132 may be arranged as an in-line array. Generally, an in-line array may be formed when the pin fin structure 130a only includes identical rows 133 of pin fins 132, each row 133 contains two or more pin fins 132, and the respective pin fins 132 in each row 133 are aligned to a corresponding pin fin 132 in every other row 133. For instance, FIG. 16B shows the pin fin structure 130a may include multiple rows 133 of pin fins 132 oriented along an x axis and distributed along ay axis. The pin fins 132 in each row 133 may be located at the same positions along the x axis as the pin fins 132 in every other row 133. For example, FIG. 16B shows each row 133 may include one pin fin 132 at the position xi along the x axis. FIG. 16B further shows the pitch, pi, between each adjacent pair of pin fins 132 in each row 133 may be equal. More generally, the pitch, / ?;, between different adjacent pairs of pin fins 132 in each row 133 may be different. Similarly, FIG. 16B also shows the pitch, / 2, between each adjacent rows 133 of pin fins 132 may be equal. In some implementations, the pitch, pi, may beequal to the pitch, / ?;. More generally, the pitch, / ??, between different adjacent rows 133 of pin fins 132 may be different.

[0205] In another example, FIG. 16C shows the pin fins 132 may be arranged as a staggered array. As shown, a staggered array may be formed when the pin fin structure 130a includes alternating rows of pin fins 132 that are offset in position along an axis relative to one another. For instance, FIG. 16C shows the pin fin structure 130a includes rows 133a and 133b arranged in an alternating manner along they axis. The pin fins 132 in each row 133a are located at the same positions along the x axis as the pin fins 132 in every other row 133a. For example, each row 133a includes a pin fin 132 located at the position xi along the x axis. Similarly, the pin fins 132 in each row 133b are located at the same positions along the x axis as the pin fins 132 in every other row 133b. For example, each row 133b includes a pin fin 132 located at the position X2 along the x axis. Additionally, the pitch, / ?;, between adjacent pairs of pin fins 132 in rows 133a and 133b may be equal. However, the pin fins 132 in the rows 133a are offset in position along the x axis by an offset distance, si, with respect to the pin fins 132 in the rows 133b. In some implementations, the offset distance, si, may be equal to half the pitch, pi. More generally, the offset distance, si, may be greater than 0 and less than the pitch, pi.

[0206] The pin fin structure 130a may include pin fins 132 with a uniaxial geometry. The pin fins 132 may have various cross-sectional geometries including, but not limited to, a circle, an ellipse, a square, a rectangle, a polygon, and any combinations of the foregoing. The pin fins 132 may each have a height, h, ranging from about 0.5 mm to about 5 mm, including all values and subranges in between. The pin fins 132 may each have a width, w, (or a diameter for a circular cross section) ranging from about 0.5 mm to about 2.5 mm, including all values and sub-ranges in between. The pin fins 132 may each be separated from at least one other pin fin 132 by a pitch, / ?, ranging from about 0.5 mm to about 2.5 mm, including all values and sub-ranges in between.[0207| The pin fin structure 130a may generally be formed from the same material as the component from which its formed on. For example, the pin fin structure 130a may be formed from the same material as the lid 112. In another example, the pin fin structure 130a may be formed from the same material as a boiler plate. The materials used to form the pin fin structure 130a include, but are not limited to, copper, a copper alloy (e.g., nickel-plated copper), aluminum, and the like.[0208} In some implementations, the pin fin structure may be further augmented by a powder coating applied to the surfaces of the pin fins and / or the surface of the component from which the pin fins are formed. Thus, the application of the powder coating may be viewed as an additive process (see Section 4 for additional examples of additive processes). The powder coating may provide additional structural features (e.g., a wick structure) with nucleation sites to promote boiling of the coolant liquid.[0209| For example, FIG. 16D shows a lid 112 with a pin fin structure 130b that includes an array of pin fins 132 and a powder coating 134 disposed on the surfaces of the pin fins 132 and the surface 113. The powder coating 134 may be formed from particles that are sintered directly onto the pin fins 132 and / or the surface 1 13. The particles may be formed from various materials including, but not limited to, copper, a copper alloy, aluminum, and the like. The particles may have a diameter that ranges from about 50 pm to about 200 pm, including all values and subranges in between. In some implementations, the particles may have a diameter that ranges from about 150 pm to about 200 pm, including all values and sub-ranges in between. In some implementations, the particles may have a diameter that ranges from about 75 pm to about 100 pm, including all values and sub-ranges in between.

[0210] In one example demonstration, FIG. 17 shows a pin fin structure 130c formed on a copper substrate where the pin fin structure 130c includes a staggered array of pin fins 132 and a powder coating 134. The powder coating 134 is also formed from copper. It should be appreciated that the powder coating 134 may be applied to any surface and / or microstructure formed on the surface of the microelectronic device. For example, the powder coating 134 may be applied directly to a surface without any microstructures formed thereon. In another example, the powder coating 134 may be applied to a mesh structure, which is thereafter attached to a surface of the microelectronic device (see, for example, Section 4.2).[02111 FIG. 18 shows data acquired from experimental measurements characterizing the boiling curve for the pin fin structure 130c in FIG. 17 along with other pin fin structures with a powder coating and mesh structures with a powder coating. For reference, experiments were also performed on a bare copper substrate with a polished surface (i.e., mirror surface). The samples with “big powder” included particles with a diameter ranging from 150 pm to 200 pm and the samples with “small powder” included particles with a diameter ranging from 75 pm to 100 pm.[0212} As shown, the bare copper substrate exhibits an appreciably higher wall superheat temperature for the same heat flux values compared to the samples with pin fin structures or mesh structures. The wall superheat temperature also increases appreciably from 18°C to 27°C as the heat flux increases from 11 W / cm2to 20 W / cm2.[02131 In contrast, the mesh structures exhibited a relatively smaller increase in the wall superheat temperature for a larger range of heat flux. For the mesh structure with small powder, the wall superheat temperature increased from 5°C to 9°C as the heat flux increased from 18 W / cm2to 30 W / cm2. For the mesh structure with big powder, the wall superheat temperature increased from 3°C to 5°C as the heat flux increased from 18 W / cm2to 30 W / cm2. For both mesh structure samples, the wall superheat temperature increased rapidly once the heat flux exceeded 30 W / cm2.[0214} Compared to the mesh structures, the pin fin structures exhibited a similar increase in the wall superheat temperature, but for an even larger range of heat flux. For the pin fin structure with small powder, the wall superheat temperature increased from 3 °C to 7°C as the heat flux increased from 13 W / cm2to 35 W / cm2. For the pin fin structure with big powder, the wall superheat temperature increased from 4°C to 9°C as the heat flux increased from 13 W / cm2to 37 W / cm2.[0215} These results indicate the pin fin structures and the mesh structures can appreciably enhance boiling of the coolant liquid, thus allowing appreciably lower wall superheat temperatures for a larger range of heat flux.4. Example Additive Processes102161 In some implementations, the structural modifications to the surface(s) of a microelectronic device may be achieved using one or more additive processes. In an additive process, materials may be deposited onto the surface(s) of the microelectronic device for the purposes of forming structures that act as nucleation sites to promote boiling. Following below are several example additive processes that may be used to modify one or more surfaces of a microelectronic device.4.1 Depositing Coated Particles[0217} FIGS. 19A-19D show an example additive process 600a where particles 610 are deposited onto the surface of a lid 112. As shown in FIG. 19A, the process 600a may begin by depositing particles 610 onto the surface of the lid 112 from a source 602. FIG. 19B shows the particles 610 may include a core 614 and a coating 612a. The core 614 may be formed of a thermally conductivematerial, such as copper, silver, gold, and aluminum. The core 614 of the particles 610 may further have a diameter that ranges from about 1 micron to about 100 microns, including all values and sub-ranges in between. The coating 612a may be formed of a fusible metal with a melting temperature less than the melting temperature of the core 614 and the lid 112. In some implementations, the fusible metal may be a solder material that includes, but is not limited to, tin, copper, silver, bismuth, indium, zinc, and antimony.

[0218] After the particles 610 are deposited onto the lid 112, FIG. 19C shows the particles 610 and the lid 112 may be heated by a heat source 604 to selectively melt the coating 612a to securely attach the particles 610 to the lid 112. The heat source 604 may, for example, be an atmospheric oven that exposes the microelectronic device with the processor lid 112 and the particles 610 to an environment at an elevated temperature. FIG. 19D shows the coating 612a may transform into a joint 612b that bonds the core 614 of the particles 610 to the surface of the lid 112. This may be accomplished, for example by heating the particles 610 and the lid 112 to a temperature at or slightly above the melting tempreature of the coating 612a. The cores 614 of the particles 610 thereafter provide nucleation sites to promote boiling of a coolant liquid.

[0219] The deposition of the particles 610 may be accomplished in several ways. In one example, the particles 610 may be deposited onto the lid 112 via vapor deposition. The source 602 may generate a spray of particles 610 directed towards the lid 112. In another example, the particles 610 may be deposited onto the lid 112 via solution deposition. The source 602 may deposit one or more droplets of a solution containing the particles 610 directly onto the lid 112. For example, the solution may be a mixture of the particles 610 and a surfactant. After deposition, the surfactant may evaporate leaving only the particles 610 on the lid 112.10220] In some implementations, the process 600a may deposit the particles 610 onto the lid 112 such that the lid 112 is covered or substantially covered by a monolayer of particles 610. A monolayer of particles 610 may be preferable to ensure the coolant liquid physically contacts a nucleation site in close proximity to the lid 112 where heat is dissipated from the processor. It should be appreciated, however, that the deposition of multiple layers of particles 610 may still be suitable to facilitate boiling of a coolant liquid provided the number of layers is sufficiently small and / or the overall thickness of the layers of particles 610 is sufficiently small. If multiple layers of particles 610 are deposited, the subsequent melting of respective coatings 612a may result in joints612b being formed between adjacent cores 614. In some implementations, the number of layers of particles 610 deposited onto the lid 112 may be less than or equal to 5, including all values and sub-ranges in between. In some implementations, the overall thickness of the particles 610 deposited onto the lid 112 may be less than or equal to 0.5 millimeters, including all values and sub-ranges in between.[0221 | Additional details and examples of particles and methods for attaching particles to a lid of a processor may be found in international application No. PCT / US2023 / 069853, filed on July 10, 2023, entitled, “DIRECT TO CHIP APPLICATION OF BOILING ENHANCEMENT COATING,” which is incorporated herein by reference in its entirety.4.2 Attaching a Wick Structure[02221 FIGS. 20A and 20B show another example additive process 600b where a wick structure 630 is welded directly to the surface of the lid 112. The wick structure 630 may be a metallic structure. In some implementations, the wick structure may include one or more meshes. Each mesh may include one or more capillaries to facilitate the transport of coolant liquid towards the surface of the lid 112 and pathways through the structure for coolant vapor to flow from the surface of the lid 112 as the coolant liquid evaporates. The meshes may further be connected to one another via a plurality of nanofibers or nanotubes. In this example, the wick structure 630 is fabricated beforehand and transferred onto the lid 112. The wick structure 630 may be fabricated in various ways including, but not limited to, 3d printing, and sintering.[0223| As shown in FIG. 20A, the wick structure 630 may be welded directly to the lid 112 via a welder 620. In some implementations, the welder 620 may form one or more spot welds 632 across the wick structure 630 and the lid 112 as shown in FIG. 20B. The welder 620 may be coupled to a motion stage (not shown) to controllably move the welder 620 along one or more axes of motion (collectively shown as x) with respect to the lid 112. Alternatively, multiple welders 620 may be used in parallel to form multiple spot welds 632 simultaneously at different locations along the wick structure 630 and the lid 112. In some implementations, the welder 620 may be an electrical resistance welder. 0224] As described above, the wick structure may be formed of a metal. The metal may include, but is not limited to, copper, and a copper alloy. Assuming the lid 112 is also formed from copper or a copper alloy, the spot welds 632 may be formed from a material that is compatible with copperand / or copper alloys. For example, the spot welds 632 may be formed from a copper alloy that includes, but is not limited to, copper, zinc, tin, aluminum, silicon, and nickel.

[0225] It should also be appreciated that the process 600b is a non-limiting example method for attaching the wick structure 630 to the lid 112. In some implementations, the wick structure 630 may be attached to the lid 112 via an epoxy.4.3 Patterning a Resin Layer[02261 FIGS. 21 A-21F show yet another example additive process 600c where a layer of resin 640 is patterned by a tool 650 to create structural features that provide nucleation sites to promote boiling. As shown in FIG. 21 A, the process 600c begins by coating the surface of the lid 112 with the resin 640. In some implementations, the resin 640 may form a conformal coating on the lid 112 with a substantially uniform thickness (see FIG. 21B). This may be accomplished, for example, by spin coating the resin 640. For example, the resin 640 may be deposited as a liquid directly onto the lid 112 and the lid 112 together with the resin 640 may thereafter by spun at a predetermined speed to spread the resin 640 across the surface of the lid 112 such that a layer of resin 640 is formed at a desired thickness. The resin 640 may be formed from various materials including, but not limited to, a thermoset polymer (e.g., vinyl-ester resins).[0227| Once the layer of resin 640 is formed, but before the resin 640 cures (e.g., hardens), FIG. 21 C shows the tool 650 may be applied to directly pattern the layer of resin 640. For example, FIG. 21D shows the tool 650 may include multiple patterning features 652 (e.g., depicted as spikes in FIG. 2 ID). When the tool 650 is applied against the layer of resin 640, the patterning features 652 may be directly imprinted onto the resin 640. In some implementations, the resin 640 may thereafter be cured while the tool 650 remains in physical contact with the layer of resin 640. For example, the assembly of the lid 112, the resin 640, and the tool 650 may be heated (e.g., in an oven) to facilitate evaporation of any solvents and / or the like from the resin 640 such that it hardens and holds its shape.[0228| Thereafter, FIGS. 21E and 21F show the tool 650 may be removed with the layer of resin 640 retaining imprinted features 642 corresponding to the patterning features 652 of the tool 650. The imprinted features 642 may thus provide nucleation sites to promote boiling. In some implementations, the height, A, of the imprinted features 642 (which is determined by the thickness of the layer of the resin 640), may be less than or equal to about 50 microns, including all valuesand sub-ranges in between. In some implementations, the imprinted features 642 may have a height, h, that ranges from about 10 pm to about 70 pm, including all values and sub-ranges in between. In some implementations, the imprinted features 642 may have a width, w, that is less than or equal to about 50 microns, including all values and sub-ranges in between. In some implementations, the imprinted features 642 may have a width, w, that ranges from about 20 pm to about 40 pm, including all values and sub-ranges in between.

[0229] It should be appreciated that, in some implementations, the layer of resin 640 may be sufficiently set when the tool 650 is applied in FIG. 21C such that the resin 640 is able to retain the shape of the imprinted features 642 when the tool 650 is removed, but before the resin 640 is fully cured.

[0230] It should also be appreciated that the shape of the imprinted features 642 shown in FIGS. 21C-21F are non-limiting examples. More generally, the imprinted features 642 may have various cross-sectional geometries including, but not limited to, a circle, an ellipse, a polygon (e.g., a triangle, a square), and any combinations of the foregoing. In some implementations, the imprinted features 642 may have a uniform cross section along its height, h. In some implementations, the imprinted features 642 may have a cross section that varies in size and / or shape along its height, h (e.g., a tapered prism, a cone).|023.1] Additionally, the shape, size, and / or distribution of imprinted features 642 may vary across the surface of the lid 112. For example, some portions of the lid 112 may have a relatively higher density of imprinted features 642 than other portions of the lid 112. In another example, some portions of the lid 112 may have imprinted features 642 while other portions of the lid 112 do not have any imprinted features 642.5. An Example Method for Preparing a Computing System for Installation into a Two-Phase Immersion Cooling System

[0232] As described above, the modifications to the lid of a processor using the apparatuses and methods disclosed herein may be accomplished while the lid remains attached to the PCB and the processor chip of the processor. This, in turn, may appreciably simplify the process of testing and validating a processor or, more generally, a computing system that includes one or more processors before installation into a two-phase immersion cooling system. Specifically, an unmodified off- the-shelf processor may be tested using a conventional, easy-to-use cooling system before the lidof the processor is modified to promote boiling of a coolant liquid in a two-phase immersion cooling system. Moreover, the modifications to the lid may be performed without disassembling the lid from the processor or the processor from the PCBA.10233] FIG. 9 shows an example method 400 for preparing a computing system with a processor for installation into a two-phase immersion cooling system. The method 400 begins at step 402 by mounting a processor onto a PCBA to form a computing system. The processor may be an unmodified off-the-shelf processor. It should be appreciated that the PCBA may support multiple processors that each include a lid, which may be subsequently modified by the apparatuses and / or methods described herein. Accordingly, at step 402, the computing system is assembled to include the various hardware components that are ultimately installed in the two-phase immersion cooling system. In some implementations, the processor may be mounted to the PCBA by soldering respective electrical connections of the processor to the PCBA.

[0234] After assembly of the computing system, the computing system may then be mounted to a testing apparatus at step 404. The testing apparatus may generally provide various hardware to support operation of the computing system. For example, the testing apparatus may include a computer chassis to support the computing system, a power supply to provide electrical power to the computing system, a display screen to display information to a user regarding the tests (e.g., the progress of the tests, the test results), and a user input device (e.g., a keyboard, a mouse) to facilitate user interaction with the computing system.

[0235] The testing apparatus may also include a cooling system to cool each processor of the computing system. Because the processors remain unmodified at step 404, conventional cooling systems that don’t require a coolant liquid to physically contact the processor, such as a cold plate or an air-cooled heat sink (e.g., a heat sink with a fan to provide forced convection, a heat sink cooled via natural convection), may be used. For example, a thin layer of thermal interface material may be applied to the lid of the processor (e.g., the surface 113 of the lid 112) and a heat sink or cold plate may be attached to the thermal interface material. This makes testing appreciably simpler, cheaper, and faster compared to cooling systems that include a coolant liquid to directly cool the processor, such as an immersion cooling system, since coolant liquid is expensive and difficult to maintain.[II236| At step 406, one or more tests may be performed on the computing system using the testing apparatus. The tests performed may include, but are not limited to, a power on test, a performance test (e.g., to assess the speed / time to perform certain processes), a memory test (e.g., to assess the read / write performance of memory in the computing system), and a functional test. For example, the power on test may verify the PCBA turns on when an appropriate power input is provided. The power on test may also verify any software (e.g., a Basic Input / Output System (BIOS), an operation system (OS)) stored in memory on a memory device of the PCBA (e.g., a hard drive) is properly booted and operates as desired. In another example, the functional test may evaluate whether the power usage and operating temperature are within a desired design tolerance when performing certain processes. The functional test may also provide correction factors for power usage, operating temperature, and / or performance variation, which may be used by the computing system after the test(s) are performed to correlate the results of the test with system performance during operation. It should be appreciated that the test performed may vary depending on the processor and / or the computing system being tested. For example, a CPU and a GPU may undergo different tests. In another example, a PCBA for a GPU server and a PCBA with network cards may undergo different tests.

[0237] At step 408, the computing system may be removed from the testing apparatus. In some implementations, the lid of each processor or at least the processors that will be modified may be cleaned to remove a residual thermal interface material. Thereafter, at step 410, the computing system may be mounted to a sample holder and the respective lids of one or more processors may be modified to promote boiling of a coolant liquid. This may be accomplished, for example, using the grinding apparatuses disclosed herein (e.g., the grinding apparatuses 200a or 200b) to form a plurality of grooves onto at least a portion of the surface of the lid (e.g., see, for example, the grooves 120’, 122a’, or 122b’ shown in FIGS. 2B and 3B). It should be appreciated, however, that any of the apparatuses and methods disclosed herein may be used to modify the lid of each processor. Again, modifications to the lids of the processor(s) may be accomplished without removing the lid from the processor or removing the processor(s) from the PCBA. Moreover, modifications to the lids of the processor(s) do not affect the validation of the computing system. Once the desired modifications are complete, the computing system may then be installed into a two-phase immersion cooling system at step 412.6. An Example Boiler Plate with Microstructures[0238 In Sections 2-5, various approaches were discussed to modify the surface of a lid of a microelectronic device. It should be appreciated that these approaches are not limited in application to the surfaces of a lid. More generally, any of the approaches disclosed herein can be applied to any surface of the microelectronic device. For example, one or more surface(s) of a boiler plate may be readily modified to incorporate the microstructures described herein. The boiler plate, in turn, may be mounted onto, for example, the lid of the microelectronic device to promote boiling of a coolant liquid and, thus, enhance cooling of a semiconductor die thermally coupled to the lid.

[0239] As discussed in Section 1, even though the addition of a boiler plate may increase the thermal resistance between the semiconductor die and the coolant liquid, the approaches described herein may nevertheless provide improvements over conventional approaches of implementing boiling enhancement structures on the surfaces of a boiler plate, such as lower energy consumption, lower cost of operation, and / or higher fabrication throughput.

[0240] In one non-limiting example, FIG. 22 shows a lid 112 with a boiler plate 700a mounted thereon. As shown the boiler plate 700a may include a substrate 710 with microstructures 712 (also referred to as a boiling enhancement structure). The substrate 710 may be mounted to the surface 113 of the lid 112 via a layer of thermal interface material 720. The microstructures 712 may be formed by any of the methods disclosed in Sections 2-5.7. An Example Two-Phase Immersion Cooling System

[0241] The computing systems disclosed herein may generally be cooled via a two-phase immersion cooling system. Specifically, the computing system may be submerged in coolant liquid configured to undergo a liquid-to-vapor phase change as it is heated by the computing system. As discussed above, the various approaches described in Sections 2-6 to modify one or more surfaces of a microelectronic device are intended to provide additional nucleation sites to promote boiling of a coolant liquid in the two-phase immersion cooling system. By increasing the number of nucleation sites on surfaces of a microelectronic device exposed to the coolant liquid, the rate of bubble formation may increase, thus increasing the rate of heat removal from the microelectronic device.[0242) FIG. 23 shows an example two-phase immersion cooling system 800 that includes a computing system 99 with a microelectronic device 100. The microelectronic device 100 may include one or more surfaces modified by any of the approaches disclosed herein. Accordingly, the microelectronic device 100 may correspond, for example, to the processors 100a’, 100b’, 100c’, or 100d’. As shown, the system 800 includes a tank 811 defining a tank volume 812 to contain coolant liquid 820. The computing system 99 is fully submerged in the coolant liquid 820. The system 800 further includes a cooling distribution unit 813 with a condenser coil 814 that carries a secondary coolant. The cooling distribution unit 813 is a non-limiting example of a heat exchanger used to extract heat from the coolant vapor within the tank 811. The condenser coil 814 is partially disposed in the tank volume 812 above the coolant liquid 820.

[0243] During operation, the semiconductor die of the microelectronic device 100 generates heat, which is dissipated to the coolant liquid 820. When the coolant liquid 820 is sufficiently heated, the coolant liquid 820 vaporizes producing coolant vapor 821, which rises above into a gas space 824 within the tank volume 812 containing a mixture 823 of air and coolant vapor 821. As the coolant vapor 821 physically contacts the condenser coil 814, heat from the coolant vapor 821 is transferred to the secondary coolant carried by the condenser coil 814, thus causing the coolant vapor 821 to condense to liquid droplets 822 that falls back into the coolant liquid 820 below. The secondary coolant is circulated to the cooling distribution unit 813 where the heat is thereafter dissipated from the secondary coolant.

[0244] In some implementations, the computing system 99 may be installed into the tank 811 before the coolant liquid 820 is added. Thereafter, the tank 811 may be fdled with the coolant liquid 820.8. Conclusion

[0245] All parameters, dimensions, materials, and configurations disclosed herein are meant to be example and the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the inventive teachings is / are used. It is to be understood that the foregoing embodiments are presented primarily by way of example and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and / or method disclosed herein.[0246| In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and arrangement of respective elements of the example implementations without departing from the scope of the present disclosure. The use of a numerical range does not preclude equivalents that fall outside the range that fulfill the same function, in the same way, to produce the same result.

[0247] Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0248] All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

[0249] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0250] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0251] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionallyincluding elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0252] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e., “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0253] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0254] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall beclosed or semi-closed transitional phrases, respectively, as set forth in the United States PatentOffice Manual of Patent Examining Procedures, Section 2111.03.

Claims

CLAIMS1. A system, comprising: a two-phase immersion cooling system, comprising: a tank defining a tank volume configured to contain a coolant liquid; and a computing system disposed within the tank volume and configured for submersion in the coolant liquid, the computing system comprising: a microelectronic device, comprising: a semiconductor die; and a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die, the lid comprising: a surface configured for exposure to the coolant liquid; and a plurality of grooves formed on the surface to provide a plurality of nucleation sites configured to promote boiling of the coolant liquid.

2. The system of claim 1, further comprising: the coolant liquid disposed in the tank volume of the tank.

3. The system of claim 1, wherein the plurality of grooves comprises one or more straight grooves.

4. The system of claim 1, wherein the plurality of grooves comprises one or more curved grooves.

5. The system of claim 4, wherein the one or more curved grooves comprises at least one of a sinusoidal groove or an arcuate groove.

6. The system of claim 1, wherein the plurality of grooves comprises one or more zigzag grooves.

7. The system of claim 1, wherein the plurality of grooves comprises one or more grooves having an enclosed shape.

8. The system of claim 7, wherein the enclosed shape is at least one of a circle or an ellipse.

9. The system of claim 1, wherein each groove of the plurality of grooves has a profile that is at least one of a triangle, a square, a semi-circle, or a semi -ellipse.

10. The system of claim 1, wherein the plurality of grooves is randomly arranged on the surface of the lid.

11. The system of claim 1, wherein each groove of the plurality of grooves is parallel to all other grooves in the plurality of grooves.

12. The system of claim 11, wherein the plurality of grooves is oriented along an axis parallel to the surface of the lid, the axis being parallel to an edge of the lid.

13. The system of claim 1, wherein: the surface of the lid is vertical; and the plurality of grooves is arranged such that a longitudinal axis associated with each groove of the plurality of grooves is vertical.

14. The system of claim 1, wherein the plurality of grooves covers all of the surface.

15. The system of claim 1, wherein the plurality of grooves covers only a portion of the surface.

16. The system of claim 1, wherein: during operation, one or more first portions of the semiconductor die are at a higher temperature than one or more second portions of the semiconductor die; and the plurality of grooves is formed only on portions of the surface of the lid that overlaps with the one or more first portions of the semiconductor die.

17. The system of claim 1, wherein the plurality of grooves comprises:a first plurality of grooves oriented along a first axis parallel to the surface of the lid; and a second plurality of grooves oriented along a second axis parallel to the surface of the lid.

18. The system of claim 17, wherein the first axis is perpendicular to the second axis.

19. The system of claim 17, wherein the first axis is at an acute angle with respect to the second axis.

20. The system of claim 17, wherein at least one of a width, a pitch, or a depth of the first plurality of grooves is different from the second plurality of grooves.

21. The system of claim 1, wherein the plurality of grooves comprises: a first plurality of grooves formed on a first portion of the surface of the lid; and a second plurality of grooves formed on a second portion of the surface of the lid, the second plurality of grooves having a different number of grooves per unit area than the first plurality of grooves.

22. The system of claim 1, wherein each groove of the plurality of grooves has a width ranging from about 20 pm to about 40 pm.

23. The system of claim 1, wherein each groove of the plurality of grooves is separated from at least one other groove of the plurality of grooves by a pitch ranging from about 40 pm to about 100 pm.

24. The system of claim 1, wherein each groove of the plurality of grooves has a depth ranging from about 10 pm to about 70 pm.

25. The system of claim 1, wherein: the lid comprises: a bulk portion; anda layer portion, disposed on the bulk portion, having a hardness value greater than the bulk portion; and the surface of the lid is formed on the layer portion.

26. The system of claim 25, wherein the plurality of grooves extends into both the layer portion and the bulk portion of the lid.

27. The system of claim 1, wherein the lid is formed from at least one of copper or nickel- plated copper.

28. The system of claim 1, wherein the plurality of grooves is configured to produce a boiling curve with inversion.

29. The system of claim 1, wherein the semiconductor die comprises at least one of a central processing unit (CPU), a graphics processing unit (GPU), a data processing unit (DPU), a voltage regulator (VR), high bandwidth memory (HBM), a digital signal processor (DSP), a field-programmable gate array (FPGA), or an application-specific integrated circuit (ASIC).

30. A system, comprising: a two-phase immersion cooling system, comprising: a tank defining a tank volume configured to contain a coolant liquid; and a computing system disposed within the tank volume and configured for submersion in the coolant liquid, the computing system comprising: a microelectronic device, comprising: a semiconductor die; a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die; and a boiler plate, thermally coupled to the lid, configured to dissipate the heat to the coolant liquid, the boiler plate comprising: a surface configured for exposure to the coolant liquid; anda plurality of grooves formed on the surface to provide a plurality of nucleation sites configured to promote boiling of the coolant liquid.

31. The system of claim 30, further comprising: the coolant liquid disposed in the tank volume of the tank.

32. The system of claim 30, wherein the plurality of grooves comprises one or more straight grooves.

33. The system of claim 30, wherein each groove of the plurality of grooves is parallel to all other grooves in the plurality of grooves.

34. The system of claim 30, wherein: the surface of the boiler plate is vertical; and the plurality of grooves is arranged such that a longitudinal axis associated with each groove of the plurality of grooves is vertical.

35. The system of claim 30, wherein the plurality of grooves covers all of the surface.

36. The system of claim 30, wherein: during operation, one or more first portions of the semiconductor die are at a higher temperature than one or more second portions of the semiconductor die; and the plurality of grooves is formed only on portions of the surface of the boiler plate that overlaps with the one or more first portions of the semiconductor die.

37. The system of claim 30, wherein each groove of the plurality of grooves has a width ranging from about 20 pm to about 40 pm.

38. The system of claim 30, wherein each groove of the plurality of grooves is separated from at least one other groove of the plurality of grooves by a pitch ranging from about 40 pm to about 100 pm.

39. The system of claim 30, wherein each groove of the plurality of grooves has a depth ranging from about 10 pm to about 70 pm.

40. The system of claim 30, wherein the plurality of grooves is configured to produce a boiling curve with inversion.

41. A system, comprising: a two-phase immersion cooling system, comprising: a tank defining a tank volume configured to contain a coolant liquid; and a computing system disposed within the tank volume and configured for submersion in the coolant liquid, the computing system comprising: a microelectronic device, comprising: a semiconductor die; and a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die, the lid comprising: a surface configured for exposure to the coolant liquid; and a plurality of pin fins formed on the surface to provide a plurality of nucleation sites configured to promote boiling of the coolant liquid.

42. The system of claim 41, further comprising: the coolant liquid disposed in the tank volume of the tank.

43. The system of claim 41, wherein the plurality of pin fins is arranged as an in-line array.

44. The system of claim 41, wherein the plurality of pin fins is arranged as a staggered array.

45. The system of claim 41, wherein each pin fin of the plurality of pin fins has a circular cross section.

46. The system of claim 41 , wherein each pin fin of the plurality of pin fins has a square cross section.

47. The system of claim 41, wherein each pin fin of the plurality of pin fins has a rectangular cross section.

48. The system of claim 41, wherein each pin fin of the plurality of pin fins has a height ranging from about 0.5 mm to about 5 mm.

49. The system of claim 41, wherein each pin fin of the plurality of pin fins has a width ranging from about 0.5 mm to about 2.5 mm.

50. The system of claim 41, wherein each pin fin of the plurality of pin fins is separated from at least one other pin fin of the plurality of pin fins by a pitch ranging from about 0.5 mm to about 2.5 mm.

51. The system of claim 41, wherein the lid is formed from at least one of copper or nickel - plated copper.

52. The system of claim 41, wherein the lid further comprises: a powder coating covering the surface and the plurality of pin fins.

53. The system of claim 52, wherein the powder coating is formed from copper.

54. The system of claim 52, wherein the powder coating comprises a plurality of particles.

55. The system of claim 54, wherein each particle of the plurality of particles has a diameter ranging from about 50 pm to about 200 pm.

56. The system of claim 54, wherein each particle of the plurality of particles has a diameter ranging from about 150 pm to about 200 pm.

57. The system of claim 54, wherein each particle of the plurality of particles has a diameter ranging from about 75 pm to about 100 pm.

58. The system of claim 41, wherein the lid further comprises: a plurality of grooves formed on at least one of the surface or the plurality of pin fins.

59. The system of claim 41, wherein the plurality of pin fins is configured to produce a boiling curve with inversion.

60. The system of claim 41, wherein the semiconductor die comprises at least one of a central processing unit (CPU), a graphics processing unit (GPU), a data processing unit (DPU), a voltage regulator (VR), high bandwidth memory (HBM), a digital signal processor (DSP), a field-programmable gate array (FPGA), or an application-specific integrated circuit (ASIC).

61. A system, comprising: a two-phase immersion cooling system, comprising: a tank defining a tank volume configured to contain a coolant liquid; and a computing system disposed within the tank volume and configured for submersion in the coolant liquid, the computing system comprising: a microelectronic device, comprising: a semiconductor die; a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die; and a boiler plate, thermally coupled to the lid, configured to dissipate the heat to the coolant liquid, the boiler plate comprising: a surface configured for exposure to the coolant liquid; and a plurality of pin fins formed on the surface to provide a plurality of nucleation sites configured to promote boiling of the coolant liquid.

62. The system of claim 61, further comprising:the coolant liquid disposed in the tank volume of the tank.

63. The system of claim 61, wherein each pin fin of the plurality of pin fins has a height ranging from about 0.5 mm to about 5 mm.

64. The system of claim 61, wherein each pin fin of the plurality of pin fins has a width ranging from about 0.5 mm to about 2.5 mm.

65. The system of claim 61, wherein each pin fin of the plurality of pin fins is separated from at least one other pin fin of the plurality of pin fins by a pitch ranging from about 40 pm to about 100 pm.

66. The system of claim 61, wherein the lid is formed from at least one of copper or nickel - plated copper.

67. The system of claim 61, wherein the lid further comprises: a powder coating covering the surface and the plurality of pin fins.

68. The system of claim 67, wherein the powder coating is formed from copper.

69. The system of claim 67, wherein the powder coating comprises a plurality of particles.

70. The system of claim 69, wherein each particle of the plurality of particles has a diameter ranging from about 50 pm to about 200 pm.

71. The system of claim 61, wherein the plurality of pin fins is configured to produce a boiling curve with inversion.

72. A method for preparing a computing system for installation into a two-phase immersion cooling system, the method comprising: assembling the computing system, the computing system comprising: a microelectronic device, comprising:a semiconductor die; and a lid, thermally coupled to the semiconductor die, to dissipate heat generated by the semiconductor die, the lid comprising a surface configured for exposure to a coolant liquid of the two-phase immersion cooling system; and forming, by a laser, a plurality of grooves on the surface of the lid, the plurality of grooves providing a plurality of nucleation sites configured to promote boiling of the coolant liquid.

73. The method of claim 72, further comprising: installing the computing system into a tank of the two-phase immersion cooling system.

74. The method of claim 73, further comprising: filling the tank with the coolant liquid such that the computing system is submerged in the coolant liquid.

75. The method of claim 72, further comprising, before forming the plurality of grooves on the surface of the lid: mounting the computing system to a testing apparatus; and performing, by the testing apparatus, one or more tests on the computing system.

76. The method of claim 75, wherein: the testing apparatus includes a cooling system; mounting the computing system to the testing apparatus comprises: thermally coupling the cooling system to the microelectronic device; and the method further comprises, while performing the one or more tests on the computing system comprises: dissipating, by the cooling system, heat generated by the microelectronic device during the one or more tests.

77. The method of claim 76, wherein the cooling system includes at least one of a cold plate or an air-cooled heat sink.

78. The method of claim 76, wherein the cooling system does not include a liquid that directly contacts the microelectronic device to dissipate heat from the microelectronic device.

79. The method of claim 75, wherein performing the one or more tests on the computing system comprises: performing a power on test for the computing system.

80. The method of claim 72, wherein the laser is one of a nanosecond pulsed laser or a femtosecond pulsed laser.

81. The method of claim 72, wherein the laser has a wavelength ranging from about 780 nm to about 1 mm.

82. The method of claim 72, wherein forming the plurality of grooves on the surface of the lid comprises: moving the laser relative to the surface at a speed ranging from about 20 mm / sec to about 400 mm / sec.

83. The method of claim 72, wherein forming the plurality of grooves on the surface of the lid comprises: illuminating, by the laser, the surface with an average laser power ranging from about 1 W to about 20 W.

84. The method of claim 72, further comprising: while forming the plurality of grooves on the surface of the lid, dissipating, via natural convection, heat from the lid.

85. The method of claim 72, wherein each groove of the plurality of grooves is parallel to all other grooves in the plurality of grooves.

86. The method of claim 85, further comprising: installing the computing system into a tank of the two-phase immersion cooling system such that the surface of the lid is vertical and a longitudinal axis associated with each groove of the plurality of grooves is vertical.

87. The method of claim 72, wherein each groove of the plurality of grooves has a width ranging from about 20 pm to about 40 pm.

88. The method of claim 72, wherein each groove of the plurality of grooves is separated from at least one other groove of the plurality of grooves by a pitch ranging from about 40 pm to about 100 pm.

89. The method of claim 72, wherein each groove of the plurality of grooves has a depth ranging from about 10 pm to about 70 pm.

90. The method of claim 72, wherein the lid is formed from at least one of copper or nickel- plated copper.

91. A processor, comprising: a printed circuit board (PCB); a processor chip coupled to the PCB; a thermal interface material disposed on a portion of the processor chip; and a lid, coupled to the PCB and in physical contact with the thermal interface material, to dissipate heat generated by the processor chip, the lid having a plurality of grooves formed on a surface of the lid that provide nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid.

92. The processor of claim 91, wherein each groove of the plurality of grooves has a width less than or equal to about 500 microns.

93. The processor of claim 92, wherein the width of each groove of the plurality of grooves is less than or equal to about 100 microns.

94. The processor of claim 93, wherein the width of each groove of the plurality of grooves is less than or equal to about 50 microns.

95. The processor of claim 91, wherein the plurality of grooves comprises: a first plurality of grooves oriented along a first axis parallel to the surface of the lid; and a second plurality of grooves oriented along a second axis parallel to the surface of the lid.

96. The processor of claim 95, wherein the first axis is perpendicular to the second axis.

97. The processor of claim 95, wherein the first axis is at an acute angle with respect to the second axis.

98. The processor of claim 91, wherein: during operation, one or more first portions of the processor chip are at a higher temperature than one or more second portions of the processor chip; and the plurality of grooves is formed only on portions of the surface of the lid that overlap with the one or more first portions of the processor chip.

99. The processor of claim 91, wherein the plurality of grooves comprises: a first plurality of grooves formed on a first portion of the surface of the lid; and a second plurality of grooves formed on a second portion of the surface of the lid, the second plurality of grooves having a higher density than the first plurality of grooves.

100. The processor of claim 91, wherein the lid comprises: a bulk portion; and a layer portion, formed along the surface of at least one groove of the plurality of grooves, having a hardness value greater than the bulk portion.

101. The processor of claim 91, wherein the lid is formed from at least one of copper, or nickel-plated copper.

102. A grinding apparatus for grinding a lid of a processor to form a plurality of grooves on a surface of the lid, the plurality of grooves providing nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, the apparatus comprising: a frame; a plurality of cutting tools slidably coupled to the frame, each cutting tool of the plurality of cutting tools having a width less than or equal to about 500 microns and being separate from another cutting of the plurality of cutting tools by a pitch less than or equal to about 500 microns; and a motor operably coupled to the plurality of cutting tools and configured to slidably move the plurality of cutting tools with respect to the frame to form the plurality of grooves on the surface of the lid.

103. The apparatus of claim 102, wherein: the width of each cutting tool of the plurality of cutting tools is less than or equal to about 100 microns; and the pitch separating one cutting tool of the plurality of cutting tools from another cutting tool of the plurality of cutting tools is less than or equal to about 100 microns.

104. The apparatus of claim 103, wherein: the width of each cutting tool of the plurality of cutting tools is less than or equal to about 50 microns; and the pitch separating one cutting tool of the plurality of cutting tools from another cutting tool of the plurality of cutting tools is less than or equal to about 50 microns.

105. The apparatus of claim 102, wherein: the motor is a first motor; and the plurality of cutting tools comprises:a spindle slidably and rotatably coupled to the frame; a plurality of cutting disks rigidly mounted to the spindle; and a second motor operably coupled to the spindle and configured to rotate the spindle and the plurality of cutting disks so as to form the plurality of grooves on the surface of the lid.

106. The apparatus of claim 102, wherein the plurality of cutting tools comprises: a slider slidably coupled to the frame; and a plurality of scribing tips rigidly mounted to the slider and configured to form the plurality of grooves when the motor slidably moves the plurality of scribing tips across the surface of the lid.

107. A system, comprising: the apparatus of claim 102; and a particulate removal system configured to remove particulates generated from the surface of the lid when the apparatus grinds the lid.

108. The system of claim 107, wherein the particulate removal system generates vacuum suction near the surface of the lid to remove the particulates.

109. The system of claim 107, wherein the particulate removal system blows air onto the surface of the lid to remove the particulates.

110. A method for forming a plurality of nucleation sites on a lid of a processor, the plurality of nucleation sites facilitating boiling of a liquid heated by and in contact with the lid of the processor, the method comprising: mounting the processor to a printed circuit board assembly (PCBA) to form a computing system; and grinding the lid of the processor to form the plurality of nucleation sites on a surface of the lid while the processor is mounted to the PCBA.

111. The method of claim 110, wherein grinding the lid of the processor to form the plurality of nucleation sites on the surface of the lid comprises: cutting, by one or more cutting tools, a plurality of grooves onto the surface of the lid.

112. The method of claim 111, wherein the one or more cutting tools includes at least one of a cutting disk or a scribing tip.

113. The method of claim 111, wherein the plurality of grooves is formed only on portions of the surface of the lid that overlap with hotspots of a processor chip of the processor.

114. The method of claim 111, wherein each groove of the plurality of grooves has a width less than or equal to about 500 microns.

115. The method of claim 111, wherein: the plurality of grooves includes a first plurality of grooves formed on a first portion of the surface of the lid and a second plurality of grooves formed on a second portion of the surface of the lid; and the first plurality of grooves has a higher density than the second plurality of grooves.

116. The method of claim 110, further comprising, while grinding the lid of the processor to form the plurality of nucleation sites on the surface of the lid: removing particulates from the computing system, the particulates being generated from the surface of the lid in response to grinding the lid.

117. The method of claim 116, wherein removing the particulates comprises: providing vacuum suction near the surface of the lid.

118. The method of claim 116, wherein removing the particulates comprises: blowing air onto the surface of the lid.

119. The method of claim 110, further comprising:before grinding the lid of the processor, covering at least a portion of the computing system with a sheet to prevent particulates from covering that portion of the computing system while grinding the lid, the particulates being generated from the surface of the lid in response to grinding the lid; and after grinding the lid of the processor, removing the sheet from the computing system.

120. The method of claim 110, wherein grinding the lid of the processor to form the plurality of nucleation sites on the surface of the lid does not include using a chemical etchant, a laser, or an electron beam.

121. A method for preparing a computing system for installation into a two-phase immersion cooling system, the method comprising: mounting a processor to a printed circuit board assembly (PCBA) to form the computing system; mounting the computing system to a testing apparatus; performing, by the testing apparatus, one or more tests on the computing system; removing the computing system from the testing apparatus; and grinding a lid of the processor to form a plurality of nucleation sites on a surface of the lid while the processor is mounted to the PCBA, the plurality of nucleation sites facilitating boiling of a liquid in the two-phase immersion cooling system heated by and in contact with the lid of the processor.

122. The method of claim 121, further comprising: installing the computing system into a two-phase immersion cooling system.

123. The method of claim 121, wherein: the testing apparatus includes a cooling system; mounting the computing system to the testing apparatus comprises: thermally coupling the cooling system to the processor; and the method further comprises, while performing the one or more tests on the computing system comprises:dissipating, by the cooling system, heat generated by the processor during the one or more tests.

124. The method of claim 123, wherein the cooling system includes at least one of a cold plate or an air-cooled heat sink.

125. The method of claim 123, wherein the cooling system does not include a liquid that directly contacts the processor to dissipate heat from the processor.

126. The method of claim 121, wherein performing the one or more tests on the computing system comprises: performing a power on test for the computing system.

127. The method of claim 121, wherein grinding the lid of the processor to form the plurality of nucleation sites on the surface of the lid comprises: cutting, by one or more cutting tools, a plurality of grooves onto the surface of the lid.

128. The method of claim 127, wherein the plurality of grooves is formed only on portions of the surface of the lid that overlap with hotspots of a processor chip of the processor.

129. An electrical discharge machining (EDM) apparatus configured to modify a lid of a processor by forming a plurality of features on a surface of the lid, the plurality of features providing nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, the apparatus comprising: a tank defining a cavity; a dielectric fluid disposed in the cavity of the tank; a fixture coupled to and disposed in the cavity of the tank, the fixture being submerged in the dielectric fluid and configured to support the processor; a frame disposed above the tank; an electrode, movably coupled to the frame, having a tip submerged in the dielectric fluid and disposed above the fixture; andan electrical power supply electrically coupled to the electrode and configured to be electrically coupled to the lid of the processor, wherein during operation of the apparatus, when the tip of the electrode is sufficiently close to the surface of the lid, the electrode generates an electrical discharge to remove a portion of the lid of the processor thereby forming at least one feature of the plurality of features.

130. A fluid jet apparatus configured to modify a lid of a processor by forming a plurality of features on a surface of the lid, the plurality of features providing nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, the apparatus comprising: a fixture configured to support the processor; a frame disposed above the fixture; a fluid source to supply a dielectric fluid; a pump, fluidically coupled to the fluid source, to generate a flow of the dielectric fluid; and a nozzle, fluidically coupled to the pump and supported by the frame, to generate a fluid jet from the flow of the dielectric fluid, wherein during operation of the apparatus, when the nozzle is disposed above the surface of the lid, the nozzle sprays the fluid jet at a sufficiently high pressure to remove a portion of the lid of the processor thereby forming at least one feature of the plurality of features.

131. A laser surfacing apparatus configured to modify a lid of a processor by forming a plurality of features on a surface of the lid, the plurality of features providing nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, the apparatus comprising: a fixture configured to support the processor; a frame disposed above the fixture; and a laser, supported by the frame, to emit a plurality of pulses, wherein during operation of the apparatus, when the laser is disposed above the surface of the lid, the plurality of pulses emitted by the laser irradiates the lid and removes a portion ofthe lid of the processor via ablation thereby forming at least one feature of the plurality of features.

132. A skiving apparatus configured to modify a lid of a processor by forming a plurality of features on a surface of the lid, the plurality of features providing nucleation sites to facilitate boiling of a liquid heated by and in contact with the lid of the processor, the apparatus comprising: a fixture configured to support the processor; a frame; a skiving tool movably coupled to the frame; and a motor coupled to the skiving tool, wherein during operation of the apparatus, the motor is configured to move the skiving tool across the surface of the lid in a reciprocating manner to cut and deform a portion of the lid of the processor thereby forming at least one feature of the plurality of features.

133. A method for forming a plurality of nucleation sites on a lid of a processor, the plurality of nucleation sites facilitating boiling of a liquid heated by and in contact with the lid of the processor, the method comprising: depositing a plurality of particles onto a surface of the lid, the plurality of particles providing the plurality of nucleation sites, each particle of the plurality of particles being coated with a fusible metal; and heating the plurality of particles to cause the fusible metal to melt thereby adhering the plurality of particles to the surface of the lid.

134. A method for forming a plurality of nucleation sites on a lid of a processor, the plurality of nucleation sites facilitating boiling of a liquid heated by and in contact with the lid of the processor, the method comprising: fabricating, using a 3D printer, a metallic wick structure comprising one or more mesh structures, each mesh structure of the one or more of mesh structures providing the plurality of nucleation sites; placing the metallic wick structure onto a surface of the lid; andwelding, via an electrical resistance welder, one or more portions of the metallic wick structure to the surface of the lid.

135. A method for forming a plurality of nucleation sites on a lid of a processor, the plurality of nucleation sites facilitating boiling of a liquid heated by and in contact with the lid of the processor, the method comprising: depositing a conformal layer of a resin onto a surface of the lid, the layer having a thickness less than or equal to about 5 microns; before curing the resin, patterning the layer of the resin by applying a tool with a plurality of patterning features directly onto the resin; curing the layer of the resin; and removing the tool from the layer of the resin thereby leaving imprints of the plurality of patterning features in the layer of the resin, the imprints providing the plurality of nucleation sites.

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