Enhanced Wicks for Thermal Ground Planes

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to and is a continuation in part of U.S. patent application Ser. No. 16/864,236, filed May 1, 2020, the entire contents of which is incorporated herein for all purposes by reference. When the present application references “this document” it includes the present application as well as the above mentioned application.

BACKGROUND

A thermal ground plane, also known as a vapor chamber, may provide a passive thermal management solution by enclosed microfluid systems. An advanced thermal ground plane may include a mesh wick permeated by some liquid. When heat is applied to the system, the liquid evaporates and generates a warm vapor within a vapor channel. The warm vapor has elevated pressure due to saturation pressure effect, and the elevated pressure causes internal convection currents in the vapor phase. That convection carries heat throughout the vapor phase, until the temperature is nearly uniform. The vapor condenses in cooler regions, and the condensed liquid is pulled back through the wick to the heat source by capillary forces resulting from the wick. A thermal ground plane, therefore, is able to spread heat. By using phase change and internal convection, a thermal ground plane can have effective conductivity much higher than solid heat spreaders such as copper or graphite. Different wicks have been developed before. However, the wick can be enhanced further to improve the thermal ground plane.

SUMMARY

Various thermal ground planes are disclosed. In one example, a thermal ground plane is disclosed that includes one or more flattened mesh or flattened and deformed mesh disposed within a cavity formed between a top casing and bottom casing. The flattened and deformed mesh, for example, may be created by compressing or flattening a planar mesh such that the pores in the mesh are at least three times smaller than the pores in the mesh prior to flattening. The mesh may then be deformed to create a plurality of out of plane pillars in the mesh.

The various examples described in the summary and this document are provided not to limit or define the disclosure or the scope of the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a sideview cross section of an internal structure of a thermal ground plane according to some embodiments.

FIG. 2A is perspective view of a mesh.

FIG. 2B is a top view of mesh.

FIG. 2C is a sideview cross section of a mesh.

FIG. 3A is top view of a flattened mesh.

FIG. 3B sideview cross section of a flattened mesh.

FIG. 4A is top view of a flattened mesh.

FIG. 4B is a sideview cross section of a flattened mesh.

FIG. 5A shows a sideview cross section of a flattened and deformed mesh disposed on the bottom casing.

FIG. 5B shows a zoomed in portion of the mesh shown in FIG. 5B showing a single pore.

FIGS. 6A, 6B, 6C, and 6D show a process for creating a flattened and deformed mesh.

FIG. 7A is a sideview cross section of a thermal ground plane with a flattened and deformed mesh.

FIG. 7B is a sideview cross section of a thermal ground plane with a flattened and deformed mesh bonded between a top casing and bottom casing.

FIG. 8 shows a top view of a thermal ground plane having a liquid flow structure.

FIG. 9A and FIG. 9B are sideview cross sections cut across sections of the thermal ground plan shown in FIG. 8.

FIG. 10A shows a top view an alternate example of a middle mesh with liquid-flow channels formed via weaving.

FIG. 10B shows a sideview cross section an alternate example of a middle mesh with liquid-flow channels formed via weaving.

FIG. 11A shows sideview of a liquid flow structure.

FIG. 11B shows sideview of a liquid flow structure.

FIG. 12A shows sideview of a liquid flow structure.

FIG. 12B shows sideview of a liquid flow structure.

FIG. 13 is a top view of a thermal ground plane.

FIGS. 14A, 14B, 14C, 15A, an 15B are sideview cross sections of the thermal ground plane shown in FIG. 13.

FIG. 16 show a sideview cross section of a thermal ground plane with an upper deformed casing, a flattened mesh, and a deformed bottom casing.

FIG. 17A shows a top view of the thermal ground plane showing the upper deformed casing and the plurality of vapor pillars.

FIG. 17B shows a bottom view of the thermal ground plane showing the deformed bottom casing and the plurality deformations.

FIG. 18A is a top view of a standard thermal ground plane that is compression bonded around a majority of the thermal ground plane.

FIG. 18B is a top view of a thermal ground plane where the entire periphery of the top casing and bottom casing of the thermal ground plane is thermocompression bonded to form a hermetic seal.

FIG. 19A shows a sideview cross section of a thermal ground plane with a deformed charge region.

FIG. 19B, which shows a top view cross section of the thermal ground plane with a deformed charge region.

FIG. 20A shows a sideview cross section of a thermal ground plane with a deformed charge region flattened and sealed.

FIG. 20B shows a top view of a thermal ground plane with a deformed charge region flattened and sealed.

FIG. 21 shows a top view of a thermal ground plane with a deformed charge region flattened and sealed.

FIG. 22 shows a top view of a thermal ground plane with a deformed charge region flattened and sealed.

FIG. 23 is a flowchart of a process for producing a thermal ground plane.

DETAILED DESCRIPTION

A thermal ground plane is disclosed that includes a flattened and deformed mesh disposed between a top casing and bottom casing.

FIG. 1 is a sideview cross section of a thermal ground plane 100 according to some embodiments. In this example, the thermal ground plane 100 includes a top casing 110, a bottom casing 115, a wick 120 (or liquid structure), and/or a vapor structure 125. The thermal ground plane 100, for example, may operate with evaporation, vapor transport, condensation, and liquid return of water or other cooling media for heat transfer between the evaporation region 130 and the condensation region 135. The structures and/or characteristics of the thermal ground plane 100 may be applied to any embodiment or example described within this document.

The top casing 110, for example, may include copper, stainless steel, aluminum, polymer, atomic layer deposition (ALD) coated polymer, flexible copper clad laminate (FCCL), polymer-coated copper, copper-cladded Kapton, etc. The bottom casing 115, for example, may include copper, stainless steel, aluminum, polymer, ALD coated polymer, FCCL, polymer-coated copper, copper-cladded Kapton, etc. The top casing 110 and the bottom casing 115, for example, may be sealed together using solder, glass, ceramics, laser welding, ultrasonic welding, electrostatic welding, thermosonic or thermocompression bonding (e.g., diffusion bonding) or a sealant. The top casing 110 and the bottom casing 115, for example, may include the same or different materials.

The top casing 110 and/or the bottom casing 115, for example, may comprise a flexible copper clad laminate with at least three layers: a first layer of copper (e.g., 12 microns thick), a second layer of polyimide (e.g., 12 microns thick), and a third layer of copper (e.g., 12 microns thick). Each of these three layers may have a thickness of or less than 50, 20, 15, 12, 10, 8 microns. The polyimide, for example, may be sandwiched between two copper layers. The copper layers on the top casing and/or the bottom casing, for example, can be replaced with ALD nano-scaled layers such as, for example, Al₂O₃, TiO₂, SiO₂, coated over very thin substrates for extremely thin casings (e.g., with a thickness less than about 10 microns).

The evaporation region 130 and the condensation region 135 may both be disposed on the top casing 110 or on the bottom casing 115. Alternatively, the evaporation region 130 and the condensation region 135 may be disposed on different layers of the top casing 110 and the bottom casing 115.

In some embodiments, the vapor structure 125 may be formed from the top casing 110 that has been deformed into various geometric shapes that may improve reliability of structure under pressure difference between the vapor pressure inside the thermal ground plane and the ambient pressure outside the thermal ground plane during folding and unfolding, thermal transport, the flow permeability, the capillary radius, the effective thermal conductivity, the effective heat transfer coefficient of evaporation, and/or the effective heat transfer coefficient of condensation. In some embodiments, the initial structure may include multiple layers of mesh.

In some embodiments, the outer periphery of the top casing 110 and the outer periphery of the bottom casing 115 may be sealed at perimeter bond 140 such as, for example, hermetically sealed using any number of techniques.

Various examples described in this disclosure include a mesh. FIG. 1 is an example of a mesh that is woven. The term mesh as used throughout this disclosure may, in some examples, include a mesh with a structure similar to what shown in FIG. 1 where a plurality of threads are woven together to create material with a plurality of pores. Various other types of mesh may also be used.

A mesh, for example, may comprise copper and/or stainless steel. A mesh, for example, may include a material having pores that have a dimension of about 10 to 200 μm. A nonporous mesh, for example, may include a material that may have pores that a have a dimension of about 0.2 to 10 μm. A mesh may be characterized by a pore size and/or a mesh number. The pore size indicates the average size of the pores within the mesh. For example, the average pore size of the pores in a mesh may be 0.05 mm. The mesh number indicates the average number of threads or openings per inch. For example, a mesh with a mesh number #400 has 400 threads or openings per inch.

A mesh, as used in this document, may include any number of different configurations and/or characteristics. The following are a few examples. A mesh, for example, may be nonporous. A mesh, for example, may be a woven mesh. A mesh, for example, may be a nonwoven mesh. A mesh, for example, may be a solid thin membrane with a plurality of openings, holes, or apertures). A mesh, for example, may be flattened. A mesh, for example, may be deformed. A mesh, for example, may be a woven, flattened, and/or woven.

A mesh, for example, may include a material that includes either or both metal and polymer. A deformed wavy mesh, for example, may be highly stretchable, such as, for example, stretchable without plastic deformation, which may, for example, reduce the stress when folded and/or may prevent the formation of wrinkles and blocking of vapor flow. A mesh, for example, may be electrically conductive and/or may be coated in a dielectric material such as, for example, to prevent plating of material into the pores away from the anchors. The pores in a mesh, for example, may be made from polymer, ceramic, other electrically insulating materials or electrically conductive material and/or may be covered by an electrically insulating layer. A mesh, for example, may include woven wires, nonwoven wires, or porous planar media. A mesh, for example, may include an ALD-coated polymer without any metal. The ALD coating can be replaced with other thin film coatings. A mesh, for example, may include a copper-clad-polyimide laminate material. A mesh, for example, may include a copper mesh or non-copper mesh such as, for example, a polymer mesh or a stainless steel mesh. The mesh, for example, may be encapsulated by hydrophilic and anti-corrosion hermetic seal. A mesh, for example, may include any woven or nonwoven material.

A mesh, for example, may have a thickness of about 10 μm to about 1,000 μm. A woven mesh, for example, may have a thickness of about 1,000, 500, 125, 100, 75, 50, or 25 μm. A porous mesh (e.g., a nanoporous mesh and/or a non-woven mesh) may have a thickness of about 5, 10, 15, 20, or 25 μm. A mesh, for example, may include a metal foam.

A mesh may be a woven mesh. A mesh, for example, may comprise a plurality of wires or threads that are woven together. A mesh, for example, may include a plurality of openings. Each of these openings, for example, may have a dimension of about 50-100 μm. FIG. 2A is a perspective view of a woven mesh. FIG. 2B is a top view and FIG. 2C is a sideview cross section of a woven mesh. The openings (or pores) may be rectangular in the x-y direction with an aspect ratio of 1, 3, 10, 30, etc.

A mesh, for example, may comprise a mesh with a mesh number of 400, #350, #300, #250, #200, #150, #80, etc., where a mesh number is the number of openings or pores per linear inch in a mesh.

A mesh may be a flattened mesh. A flattened mesh, for example, may comprise a mesh, such as the mesh shown in FIG. 2A, that has been compressed or flattened. FIG. 3A is a top view of a flattened mesh. FIG. 3B is a sideview cross section of a flattened mesh. As shown, the various wires (or threads) that make the mesh have been compressed or flattened. The various wires (or threads) that make the mesh have an elliptical, oblong, or oval cross section. For example, the elliptical, oblong or oval cross section may have one dimension that is 5, 10, 15, 20, 25, or 30 times greater than another orthogonal dimension. In addition, the various pores that make up the original mesh have a pore size that has been reduced when flattened and/or the thickness of the mesh has been reduced when flattened. A dimension of the pore size (e.g., a diameter or width), for example, may be two or three times smaller.

In this example, the original mesh may have a thickness greater than about 80 μm. The flattened mesh may have a thickness of about 5-60 μm after the flattening or a thickness of about 10-40 μm after the flattening or a thickness of about 20-40 μm after the flattening. The original mesh may have a pore size greater than about 60 μm that is reduced to about 10-

40 μm after flattening or is reduced to about 20-30 μm after flattening.

The mesh, for example, may be flattened further as shown in FIG. 4A, which shows a top view, and FIG. 4B, which shows a sideview cross section. As shown, the various wires (or threads) that make the mesh have been compressed or flattened further compared to the flattened mesh shown FIG. 3A and FIG. 3B. The various wires (or threads) that make the mesh may have an elliptical, oblong, or oval cross section. For example, the elliptical, oblong or oval cross section may have one dimension that is 15, 20, 25, 30, or 40 times greater than another orthogonal dimension. A dimension of the pore size (e.g., a diameter or width), for example, may be two or three times smaller.

The various pores that make up the original mesh, for example, have been reduced further and/or the thickness of the flattened mesh is thinner than prior to flattening. The various wires in the flattened mesh shown in FIG. 4B may be compressed.

In this example, the original mesh may have a thickness greater than about 80 μm. The flattened mesh may have a thickness of about 5-20 μm after the flattening. The original mesh may have a pore size greater than about 60 μm that is reduced to about 1-20 μm after flattening. The flattened mesh, for example, may have a pore size of about 1, 2, 5, 10, 20, or 30 μm. The wires (or threads) that cross each other, for example, may be bonded together before, during, or after the flattening process such as, for example, via compression bonding or diffusion bonding.

A flattened mesh may comprise a plurality of longitudinal wires 305 and latitudinal wires 306. These longitudinal wires 305 and latitudinal wires 306 may be flattened or compressed. Various crossing longitudinal wires 305 and latitudinal wires 306 may be bonded together during flattening or during a heat treatment process.

A flattened mesh or a portion of a flattened mesh, for example, may be or may appear to be a solid hermetic sheet without any pores or openings. A flattened mesh, for example, may have pores so small that a working fluid cannot permeate through the flattened mesh in either liquid or vapor form.

As used throughout this disclosure, a flattened mesh may be replaced by a flat film or flat foil that has a plurality of pores created via electroplating, electroless plating, etching by lithography or lasers, copolymer self-assembled pores, etc.

Various thermal ground planes described in this disclosure may include an array of pillars, which may include any or all of the following. An array of pillars, for example, may include a plurality of pillars with an evenly or unevenly distributed pattern. An array of pillars, for example, may include pillars comprising polymer. An array of pillars, for example, may include pillars comprising solid metal such as, for example, copper or stainless steel or copper mesh or stainless steel mesh pillars An array of pillars, for example, may include pillars coated with a coating such as, for example, a ceramic (e.g. Al₂O₃, TiO₂, SiO₂, etc.) or a nano-texture coating. The coating may be applied via defect-free ALD, low-defect density ALD, chemical vapor deposition (CVD), molecular layer deposition (MLD), or other nano-scaled or micro-scaled coating processes.

An array of pillars, for example, may be a pseudo-rectangular array, or a pseudo hexagonal array, or a random array. An array of pillars, for example, may have a center-to-center pitch that is constant across array of pillars. An array of pillars, for example, may include pillars with variable diameters and/or heights. An array of pillars, for example, may have a low density (e.g., far apart) at the condenser, have a higher density at the evaporator, and/or gradual change in density between the condenser and the evaporator.

Various examples described in this disclosure include a micro pillar array. For example, a micro pillar array may be disposed on an array of pillars, where the array of pillars are larger than the micro pillar array. A micro pillar array, for example, may include a deformed mesh or a porous material in which the pore size of the material is substantially smaller than the gap between pillars. A micro pillar array may, for example, include nano-wire bundles, sintered particles, templated grown pillars, inverse opals, etc. A micro pillar, for example, array may include solid pillars, which may promote conduction of heat along the length, and outer regions of the micropillar array may be porous to promote wicking.

Various examples described in this disclosure may include internal thermal ground plane structures comprising polymer. These thermal ground plane structures, for example, may include the top casing, the bottom casing, a mesh, an array of solid or mesh pillars, arteries, wick, vapor structures, etc. Polymer structures, for example, may be coated with metal, defect-free ALD, low-defect density ALD, CVD, MLD, or other nano-scaled coating processes.

Thermal ground planes disclosed in this document may be used for any number of applications such as, for example, for space systems. For space systems, for example, a thermal ground plane may be designed for ultra-light weight with high performance, where there is a positive or negative pressure differential between the vapor space and external conditions.

The pores in any mesh disclosed in this document (e.g., flattened mesh, deformed mesh, woven mesh, or any other type of mesh), for example, may be filled with a porous material. The porous material may have a dimension less than about 1 μm. The porous material, for example, may comprise a metallic powder such as, for example, copper powder or silver powder. The porous material, for example, may comprise microparticles or nanoparticles.

The porous material, for example, may comprise beads comprising polymer, ceramic, and/or metal such as, for example, a polymer bead with a metallic shell, a metallic bead with a polymer shell, ceramic bead with a metallic shell, a polymer bead with a ceramic shell, a ceramic bead with a metallic shell, a ceramic bead with a polymer shell, or any other combination. In some cases, a bead comprising a combination of polymer and metal or ceramic may undergo high temperature treatment to evaporate or remove the polymer.

The pores in any mesh disclosed in this document (e.g., flattened mesh, deformed mesh, woven mesh, or any other type of mesh), for example, may be filled via electroplating or electroless plating. This may, for example, form dendrites of metal. The pores in any mesh disclosed in this document (e.g., flattened mesh, deformed mesh, woven mesh, or any other type of mesh), for example, may be filled with secondary material that is de-alloyed. The pores in any mesh disclosed in this document (e.g., flattened mesh, deformed mesh, woven mesh, or any other type of mesh), for example, may be filled by deposition of a nano-porous material copolymer such as etched metal, ceramic, or polymer, or co-polymer. The pores in any mesh disclosed in this document (e.g., flattened mesh, deformed mesh, woven mesh, or any other type of mesh), for example, may be filled by electrostatic of powder, which may form a conformal powder coating.

In some embodiments a flattened mesh may be deformed to form a flattened and deformed mesh. FIG. 5A shows a sideview cross section of a flattened and deformed mesh 505 disposed on the bottom casing 115. A deformed mesh, for example, may be a flattened mesh that is deformed with a plurality of rough deformations. These rough deformations, for example, may include an array of deformations that may be pillars or pillar like structures. The flattened and deformed mesh 505, for example, may include a plurality of deformed portions 520 that may have a plurality of elastically or inelastically deformed portions. The deformed portions 520 may have a height that is greater than the thickness of the mesh such as, for example, five times greater than the thickness of the mesh.

The flattened and deformed mesh 505, for example, may have a plurality of pores having dimensions less than 1 μm. The plurality of pores, for example, may be filled with a porous material 530 as shown in FIG. 5B, which shows a zoomed in portion of section 510 of FIG. 510 showing one pore (or opening) of the plurality of pores. The porous material 530, may have a dimension less than about 1 μm. The porous material, for example, may comprise a metallic powder such as, for example, copper powder or silver powder. The porous material, for example, may comprise microparticles or nanoparticles. The porous material, for example, may be any type of material described in this document and deposited in any process described in this document.

A deformed mesh may be created by pressing a substantially flat or planar mesh material to create out of plane deformations. The deformations may create pillars or ridges. The flat or planar mash may include a plurality of layers of mesh with different pore sizes such as, for example, with the bottom layer having smaller pore sizes than other layers.

FIGS. 6A, 6B, 6C, and 6D show a process for creating a flattened and deformed mesh. The mesh 600 may be a woven or nonwoven mesh. FIG. 6A shows a sideview cross section of a mesh 600 that includes a plurality of wires (or threads) that include a plurality of longitudinal wires 305 and a plurality of latitudinal wires 306 (a single latitudinal thread is shown in this cross section).

FIG. 6B shows a sideview cross section of the mesh 600 after flattening producing a flattened mesh 601. As shown, the various wires are flattened both longitudinally and laterally to create a flattened mesh. As shown, the space between flattened wires is decreased as the cross section of the wire is flattened and elongated laterally creating pores with a smaller dimension. The mesh may be flattened, for example, with a pressure contact process. The plurality of longitudinal wires 305 and the plurality of latitudinal wires 306 that cross each other may be bonded through ultrasound welding, laser welding, electric welding, pressure contact, high temperature sintering, low temperature (<300 C) diffusion bonding, or high temperature diffusion bonding (>300 C).

In some embodiments, a flattened mesh may comprise a plurality of flattened mesh layers. The pores of the plurality of flattened layers may be aligned or misaligned.

FIG. 6C shows a sideview cross section of the flattened mesh 601 after deformation, which creates a flattened and deformed mesh 602 The deformation process creates a plurality of rough out of plane deformation regions 620 such as, for example, rough pillars or rough ridges.

The mesh may be deformed via cold-embossing, cold-rolling, pressing, hot embossing, hot-pressing, cold-stamping, hot-stamping, etc. The mesh in the deformation regions 620 can be thicker than the mesh in the non-deformation regions 625. The deformation regions 620 can include pillars that are round, square, rectangular, etc. The deformation regions 620 can have an out of plane dimension of about 10 μm, 25 μm, 50 μm, 100 μm, 150 μm, 200 μm, etc. The deformation regions 620 can have width of about 10 μm, 25 μm, 50 μm, 100 μm, 150 μm, 200 μm, etc. The gap between deformation regions 620 can have a dimension of 10 μm, 25 μm, 50 μm, 100 μm, 150 μm, 200 μm, etc. The deformation regions 620 can be arranged in an array such as, for example, a rectangular array, triangular array, random array, etc.

FIG. 6D shows a sideview cross section of the mesh 600 after flattening and deformation bonded with a bottom casing 630 such as, for example, a bottom casing 115 or any type of casing described in this document.

FIG. 7A shows a sideview cross section of a thermal ground plane with a flattened and deformed mesh 602 sandwiched between a bottom casing 630 and an upper deformed casing 705. The upper deformed casing 705 may be deformed such as, for example, as described in this document, to form a plurality of vapor pillars 715. In this example, the flattened and deformed mesh 602 is bonded to the bottom casing 630 inside the bonding region 730. There may be a gap between the edge of the flattened and deformed mesh 602 and bonding region 730.

In some embodiments, the strength of the vapor pillars 715 may be improved. The plurality of vapor pillars 715 can be coated with additional layers to enhance the strength of the pillars. For example, a coating can be an organic or inorganic layer disposed by sol gel, physical vapor deposition, chemical vapor deposition, electroless plating, electroplating, or various polymer coating processes. In some embodiments, an exterior or surface copper layer may be removed such as, for example, by etching, to reduce the total thickness of the thermal ground plane. While such removal can reduce the strength of the vapor pillars, the strength can be enhanced with an additional layer. Alternatively or additionally, an exterior copper layer may only be partially removed. For example, an original thickness may be 9 μm to 12 μm and may be reduced down to 3 μm.

In FIG. 7B, the flattened and deformed mesh 602 is bonded between the non-deformation regions 625 and the upper deformed casing 705 in the bonding region 730. The bonding region 730 may create a hermetic seal within the thermal ground plane. The upper deformed casing 705, may be replaced with a non-deformed casing.

The upper deformed casing 705, for example, may form a vapor cavity with the plurality of vapor pillars 715 (or other deformations). The plurality of vapor pillars 715, for example, can form a staggered array, a rectangular array, a triangular array, or a random array. The plurality of vapor pillars 715 can extend into the area where upper casing and the bottom casing are bonded, and be substantially flattened in that area as a result of bonding.

FIG. 8 shows a top view of a thermal ground plane 800 having a liquid flow structure 810. FIG. 9A and FIG. 9B are sideview cross sections cut across section A-A and section B-B of FIG. 8. The liquid flow structure 810 may be coupled with an evaporator 805 (or a condenser). The liquid flow structure 810 may feed liquid from a cooled region to a heated region. The liquid flow structure 810, for example, may comprise a plurality of mesh layers. The liquid flow structure 810, for example, may not be bonded to the flattened and deformed mesh 602. Alternatively, the liquid flow structure 810, for example, may be bonded to the flattened and deformed mesh 602. While a single liquid flow structure 810 is shown, the thermal ground plan may include multiple liquid flow channels.

The liquid flow structure 810, for example, includes a top mesh 905, a bottom mesh 906, and a middle mesh 910. The top mesh 905 and/or the bottom mesh 906 may comprise a flattened mesh, and the middle mesh 910 may comprise a non-flattened mesh as shown in FIG. 9A and FIG. 9B. The top mesh 905 may have a mesh number, for example, of #400, #250 or #150 prior to flattening and the pitch of the openings is lower after flattening. The size of the pores in the top mesh 905 may be small enough to restrict vapor penetration into the liquid flow channels 815.

The bottom mesh 906 may or may not be a flattened mesh. The pores in the bottom mesh 906 may be sized to allow for liquid transport. The bottom mesh 906, for example, may have a similar pore size as the flattened and deformed mesh 602. The bottom mesh 906 may be in contact with or bonded to the flattened and deformed mesh 602.

The middle mesh 910 may comprise a woven mesh with a mesh number, for example, of #250 or #150. The middle mesh 910 and the top mesh 905 may have the same mesh number. The middle mesh 910 include liquid flow channels 815 within the liquid flow artery. The liquid flow channels 815, for example, may be cut out of the middle mesh 910. The liquid flow channels 815, for example, may comprise void regions without any mesh. The liquid flow channels 815 may have width of 0.25 mm, 0.5 mm, 0.75 mm, 1.0 mm, etc. and/or a length of 2 mm, 5 mm, 10 mm, 20 mm, etc. The liquid flow channels 815 may be bounded on the left and right sides by the middle-mesh, and bound by the top mesh 905 and the bottom mesh 906.

Additionally or alternatively, portions of the liquid flow channels 815 may be divided by mesh into a plurality of liquid flow channels 815 that are separated by additional middle mesh material 820.

The bottom mesh 906 may allow liquid flow in the vertical direction (e.g., z direction). The middle mesh 910 may allow liquid flow in the horizontal direction (e.g., x-y direction).

In some embodiments, the flattened and deformed mesh 602 may comprise any type of wicking structure.

In some embodiments, the surface of either or both the top mesh 905 and the bottom mesh 906 can be surface treated for enhanced heat transfer. The surface treatment may, for example, include surface oxidation, laser texturing, sintered micro/nanoparticles, micro/nano textures formed by oxidation, cold rolling, or hot rolling, etc.

Additionally or alternatively, the top casing shown in FIGS. 9A and 9B may be a deformed casing 705.

FIG. 10A is a top view and FIG. 10B is a cutaway sideview of an alternate example of a middle mesh 910 with liquid-flow channels 1010 formed via weaving. In this example, multiple channels 1010 are formed where wires (or threads) 1015 are absent based on a woven pattern. These channels 1010 may be created when the mesh is created (e.g., via weaving).

In some embodiments, the top mesh 905 may be a non-porous solid foil, that may, for example, prevent vapor from ingress into the large pores within the middle mesh 910 (or 1000). In some embodiments the middle mesh 910 may be bonded directly to the top casing, which can act as an upper cap (upper mesh 905) to the middle mesh 910. Additionally or alternatively, the lower flat mesh 906, for example, can be replaced by bonding the middle mesh 910 directly to a deformed mesh, such that the deformed mesh acts as a cap to the middle mesh 910. Additionally or alternatively, multiple mesh layers can be combined in the middle between the top mesh 905 and the lower mesh 906. The multiple mesh layers, for example, can each have a liquid flow channel, which can be aligned with each other or mis-aligned with each other as shown in FIGS. 11A and 11B.

In some embodiments, the liquid flow structure 810 may include multiple layers of liquid flow channel units as shown in FIG. 11A and FIG. 11B. In this example, two liquid flow channel units are shown stacked one on top of the other. In other cases, more than two liquid flow channels may be stacked one on top of the other.

FIG. 11A shows sideview of a liquid flow structure 810 with a first liquid flow channel unit 1110 and a second liquid flow channel unit 1120. The first liquid flow channel unit 1110 includes a top mesh 1111, a middle mesh 1112, and a bottom mesh 1113. The middle mesh 1112 may include a top liquid flow channel 1114. Each of these mesh layers can be similar to the mesh layers shown in FIGS. 9A and 9B. The second liquid flow channel unit 1120 includes a top mesh 1121, a middle mesh 1122, and a bottom mesh 1123. The middle mesh 1122 may include a bottom liquid flow channel 1124. Each of these mesh layers can be similar to the mesh layers shown in FIGS. 9A and 9B.

In this example, the top liquid flow channel 1114 and the bottom liquid flow channel 1124 are misaligned. In this example, the first liquid flow channel unit 1110 includes a bottom mesh 1113 and the bottom liquid flow channel 1124 includes a top mesh 1121.

In FIG. 11B shows sideview of a liquid flow structure 810 with a first liquid flow channel unit 1110 and a second liquid flow channel unit 1120 sharing mesh layer 1130. The shared mesh layer 1130 is the bottom mesh layer for first liquid flow channel unit 1110 and the top mesh layer for second liquid flow channel unit 1120.

In this example, the top liquid flow channel 1114 and the bottom liquid flow channel 1124 are aligned. In this example, the top liquid flow channel 1114 and the bottom liquid flow channel 1124 are misaligned. In this example, the bottom mesh of the first liquid flow channel unit 1110 is the same mesh as the top mesh of the second liquid flow channel unit 1120.

FIG. 12A and FIG. 12B each shows a sideview cross section of a liquid flow structure 810 with the liquid flow channels 815 formed by deforming cavities in the middle mesh 910, which in this example comprises multiple layers of mesh. In FIG. 12A, the multiple layers of mesh may be alternately or oppositely deformed to create the liquid flow channels 815. In FIG. 12B, the multiple layer of mesh may be congruently or similarly deformed to create the liquid flow channels 815. Various mesh layers can be used to form a plurality of liquid flow channels 815 and create a plurality of aligned and/or misaligned liquid flow channels 815 throughout the liquid flow structure 810. The liquid flow structure 810 may or may not include a top mesh 905 and/or a bottom mesh 906.

FIG. 13 is a top view of a thermal ground plane 1300. The thermal ground plane 1300 may include a wick 1310 that may include pillars, mesh, flattened mesh, deformed mesh, flattened and deformed mesh, etc. The wick 1310, for example, may have a plurality of arteries 1320 (or channels) within the wick 1310 of non-wick material or no material. The thermal ground plane 1300 may have various regions having a plurality of pillars. In this example, two such regions are shown. Additional pillars 1315 may be included that may be disposed on the wick 1310 in some locations of the inner cavity of the thermal ground plane 1300.

FIG. 14A is sideview cross section of thermal ground plane 1300 cut along line A-A in FIG. 13. FIG. 14B is sideview cross section of thermal ground plane 1300 cut along line B-B in FIG. 13. FIG. 14C is sideview cross section of thermal ground plane 1300 cut along line C-C in FIG. 13. FIG. 15A is sideview cross section of thermal ground plane 1300 cut along line D-D in FIG. 13. FIG. 15B is sideview cross section of thermal ground plane 1300 cut along line E-E in FIG. 13.

FIG. 16 shows a sideview cross section of a thermal ground plane 1600 with an upper deformed casing 705, a flattened mesh 601, and a deformed bottom casing 1605. FIG. 17A shows a top view of the thermal ground plane 1600 showing the upper deformed casing 705 and the plurality of vapor pillars 715. FIG. 17B shows a bottom view of the thermal ground plane 1600 showing the deformed bottom casing 1605 and the plurality of deformations 1625.

The deformed bottom casing 1605, for example, may comprise a flat or planar mesh, metal and/or polymer that may be stamped to produce a plurality of deformation 1625 (e.g., pillars, ridges or deformations) that have a height, for example, of 10 μm, 20 μm, 50 μm, etc. The height, for example, may vary across the deformed bottom casing 1605. The deformed bottom casing 1605 may be stamped to produce a plurality of deformations 1625 (e.g., pillars, ridges or deformations) that have a dimension (e.g., diameter or width), for example, of 50 μm, 100 μm, 150 μm, 200 μm, etc. The plurality of deformations 1625, for example, may have a pitch of about 200 μm, 300 μm, 400 μm, 500 μm, etc. The plurality of deformations 1625 stamped or formed into the deformed bottom casing 1605, for example, may have domed in shape, pyramidal, or rectangular shape.

A stamped casing (or mesh) is different than a deformed casing (or mesh). While both deform or reshape the geometry of the casing, stamping does not reduce the thickness of the casing (or mesh) whereas deformations cause thinning of all or portions of the casing (or mesh) as material is stretched during deformation. Additionally or alternatively, stamping is typically done under less pressure than a deformation.

At the bonding region 1610, both the deformed bottom casing 1605 and the upper deformed casing 705 may be sealed using any method known in the art such as, for example, any method described in this document to create a hermetic seal at the bonding region 1610. In this example, the deformed bottom casing 1605, the upper deformed casing 705, and the flattened mesh 601 are compression bonded (e.g., thermocompression bonded or thermosonic bonded) or diffusion bonded without compression at the bonding region 1610. In this example, a flattened mesh 601 may be bonded between a deformed bottom casing 1605 and an upper deformed casing 705 at the bonding region 1610 on the periphery of the deformed bottom casing 1605 and the periphery of the upper deformed casing 705. The bonding region 1610, for example, may be continuously bonded in a single bonding process that does not include bonding the majority of periphery first and the fluid charge port second.

FIG. 18A is a top view of a standard thermal ground plane 1800 that is bonded around a majority of the thermal ground plane 1800 except at the location of fill port which is sealed with a secondary bond after charging with the working fluid.

FIG. 18B is a top view of a thermal ground plane 1805 where the entire periphery of the top casing and bottom casing of the thermal ground plane 1805 is diffusion bonded to form a hermetic seal. No secondary bonding is needed. In this example, the thermal ground plane 1805 is charged with a working fluid prior to entire periphery of the top casing and bottom casing are bonded to seal in the working fluid. The thermal ground plane 1805, for example, may include a flattened mesh that covers the entire perimeter of the top casing and the bottom casing. As another example, a flattened mesh may be used that does not cover the entire perimeter of the top casing and the bottom casing. As another example, a regular mesh can be used.

FIG. 19A shows a sideview cross section of a thermal ground plane 1900 cut along the line A-A in FIG. 19B, which shows a top view cross section of the thermal ground plane 1900. In this example, the thermal ground plane 1900 includes a deformed charge region 1920. The 1920 can include a deformation in either or both the top casing and/or the bottom casing. The bottom casing may include a plurality of pillars and/or be bonded with a mesh 1915 (e.g., a flattened mesh, flattened or deformed mesh, etc.). The deformed charge region 1920 may allow fluid to flow into the thermal ground plane 1900.

FIG. 20A and FIG. 20B shows the deformed charge region 1920 sealed with pressure or compression. This may, for example, allow the thermal ground plane to be charged without a charge tube or port and/or allow for the periphery to be completely sealed together.

FIG. 21 shows the thermal ground plane 1900 can be cut along line 1935 and pinched or crimped at 1925.

FIG. 22 shows the thermal ground plane 1900 after the flattened deformed charge region 1920 is cut an additional seal 1930 may be applied to the flattened deformed charge region 1920.

FIG. 23 is a flowchart of a process 2300 for producing a thermal ground plane. The blocks in process 2300 can be operated in any order. Any of the blocks may be skipped or removed. Any additional blocks may be added in any order.

At block 2305 a mesh may be flattened. The mesh may be flattened, for example, as discussed above in conjunction with FIGS. 2A, 2B, 2C, 3A, 3B, 4A, and 4B or as discussed anywhere in this document.

At block 2310 the mesh and/or the top casing or bottom casing may be surface treated such as, for example, to enhance low temperature diffusion. The surface treatments, for example, may be applied to the entire mesh, top casing, bottom casing or only to the portions that are being bonded (e.g., the periphery) to create the hermetic seal. The surface treatment, for example, may include deposition of an additional metal between the copper casing layers. The metal may include silver, aluminum, platinum, titanium, chromium, or zinc. The deposition between the copper casings may be formed by a meta-stable copper hydride, copper chloride, copper oxide, copper nitride, or combinations of different anions coupled with the copper cation on copper surfaces. The surface treatment, for example, may include oxidation, micro-texturing with steam-pitting, laser ablation, physical ablation, chemical oxidation, reduction, etc.

Additionally or alternatively, the periphery of the flattened mesh being bonded between the top casing and the bottom casing may be smoothed to a roughness less than 1 micron. This may, for example, for example, help to ensure nano-scale contact. Additionally or alternatively, the flattened mesh or the periphery of the flattened mesh may be electroplated or electroless plated in a uniform crystal orientation such as <111>.

The surface of the flattened mesh or the surface of the periphery of the flattened mesh, for example, can be surface treated for enhanced heat transfer. These treatments, for example, can include laser texturing, sintered micro/nanoparticles, micro/nano textures formed by oxidation, cold rolling, or hot rolling; etc.

At block 2315 the pores of the flattened mesh may be filled with a porous material. The porous material may have a dimension less than about 1 μm. The porous material, for example, may comprise a metallic powder. The porous material, for example, may comprise microparticles or nanoparticles.

The porous material, for example, may comprise beads comprising polymer, ceramic, and/or metal such as, for example, a polymer bead with a metallic shell, a metallic bead with a polymer shell, ceramic bead with a metallic shell, a polymer bead with a ceramic shell, a ceramic bead with a metallic shell, a ceramic bead with a polymer shell, or any other combination. In some cases, a bead comprising a combination of polymer and metal or ceramic may undergo high temperature treatment to evaporate or remove the polymer.

At block 2320 the flattened mesh may be heat treated. The heat treatment, for example, may include a sintering process or annealing process.

At block 2325 the flattened mesh may be deformed to create a plurality of deformed structures such as, for example, ridges, pillars, or depressions.

At block 2330 the flattened and deformed mesh may be bonded with the bottom casing.

At block 2335 the top casing and the bottom casing may be bonded together along a periphery of the top casing and the bottom casing. For example, the flattened and deformed mesh can be bonded between the top casing and the bottom casing. As another example, the thermal ground plane may be charged with a working fluid.

A first example thermal ground plane may include a bottom casing; a top casing, wherein an outer periphery of the bottom casing and an outer periphery of the top casing are bonded to each other to form a hermetic seal, wherein the bottom casing and the top casing form a cavity; a working fluid disposed within the cavity; and a flattened mesh disposed in the cavity on an inner surface of the bottom casing for liquid transport, wherein the flattened mesh comprises a plurality of openings that have a dimension that is at least three times smaller than the size of the openings prior to flattening.

A second example thermal ground plane may include the first thermal ground plane where the flattened mesh is a woven mesh that has been flattened.

A third example thermal ground plane may include the first or second thermal ground plane where an outer periphery of the flattened mesh is bonded between the outer periphery of the bottom casing and the outer periphery of the top casing form a hermetic seal.

A fourth example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh comprises a plurality of woven wires that are bonded together before, during or after flattening.

A fifth example thermal ground plane may include any of the previous thermal ground planes further comprising a plurality of porous particles disposed within the plurality of openings of the flattened mesh.

A sixth example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh comprises of a plurality of flattened mesh layers.

A seventh example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh includes a plurality of pillars for liquid transport that are formed in a pattern in the flattened mesh.

An eighth example thermal ground plane may include any of the previous thermal ground planes where the bottom casing comprises a plurality of pillars, and wherein the flattened mesh is bonded to a top of the plurality of pillars.

A ninth example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh is surface treated with micro/nano-structures that improve heat transfer.

A tenth example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh is surface coated with a low-temperature metal that improves diffusion bonding.

An eleventh example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh is surface coated with a copper layer with <1 1 1>crystal orientation for enhanced diffusion bonding.

A twelfth example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh comprises a solid copper sheet with a plurality of openings where the plurality of openings were etched, laser drilled, electroplated, or electroless plated into the solid copper sheet.

A thirteenth example thermal ground plane may include any of the previous thermal ground planes where a bond between the bottom casing and the top casing comprises a single, continuous bond.

A fourteenth example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh comprises a plurality of wires comprising copper, stainless steel, glass, or metal-coated polymer.

A fifteenth example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh is fabricated by hot or cold works, thermocompression, thermosonic, ultrasonic, laser welding, sintering, diffusion bonding, and/or electrical welding.

A sixteenth example thermal ground plane may include any of the previous thermal ground planes where the flattened mesh comprises a lower flattened mesh layer, an upper flattened mesh layer, and a middle mesh layer that is not flattened and is sandwiched between the upper mesh layer and the lower mesh layer, wherein the upper mesh layer is a flattened mesh to prevent vapor penetration into the flattened mesh.

A seventeenth example thermal ground plane may include the sixteenth thermal ground planes where the flattened mesh comprises an artery liquid channel.

An eighteenth example thermal ground plane may include the sixteenth or seventeenth thermal ground planes where the flattened mesh comprises a plurality of mesh layers including multiple liquid transport layers.

A nineteenth example thermal ground plane may include the sixteenth through eighteenth thermal ground planes where the lower mesh is coupled with a fourth mesh for liquid transport, wherein the fourth mesh includes a plurality of openings and the lower mesh includes a plurality of openings having a substantially similar dimension.

A twentieth example thermal ground plane may include a bottom casing; a top casing, wherein an outer periphery of the bottom casing and an outer periphery of the top casing are bonded to each other to form a hermetic seal, wherein the bottom casing and the top casing form a cavity; a working fluid disposed within the cavity; a flattened mesh comprising a lower flattened mesh layer, an upper flattened mesh layer, and a middle flattened mesh layer sandwiched between the upper mesh layer and the lower mesh layer, wherein the flattened mesh is disposed in the cavity on an inner surface of the bottom casing for liquid transport, wherein each of the lower flattened mesh layer and an upper flattened mesh layer include a plurality of openings that have a dimension that is at least three times smaller than the size of the openings prior to flattening.

A twentieth-first example thermal ground plane may include the twentieth thermal ground plane where an outer periphery of the flattened mesh is bonded between the outer periphery of the bottom casing and the outer periphery of the top casing form a hermetic seal.

A twenty-second example thermal ground plane may include a bottom casing; a top casing, wherein an outer periphery of the bottom casing and an outer periphery of the top casing are bonded to each other to form a hermetic seal, wherein the bottom casing and the top casing form a cavity; a working fluid disposed within the cavity; and a flattened mesh disposed in the cavity on an inner surface of the bottom casing, the flattened mesh comprises a plurality of openings that have a dimension of about 1-20 um and the flattened mesh has a thickness of about 5-20 um.

A twentieth-third example thermal ground plane may include the twenty-second thermal ground plane where the flattened mesh comprises a woven mesh that is pressed into the flattened mesh, wherein the woven mesh has a plurality of pores that have a dimension more than three times larger than the plurality of openings.

A twentieth-fourth example thermal ground plane may include the twenty-second or twenty-third thermal ground plane where an outer periphery of the flattened mesh is bonded between the outer periphery of the bottom casing and the outer periphery of the top casing form a hermetic seal.

A twentieth-fifth example thermal ground plane may include the twenty-first through the twenty-fourth thermal ground planes where the flattened mesh comprises a plurality of longitudinal wires and a plurality of latitudinal wires that are bonded together where the plurality of longitudinal wires and a plurality of latitudinal wires cross each other.

Unless otherwise specified, the term “substantially” means within 5% or 10% of the value referred to or within manufacturing tolerances. Unless otherwise specified, the term “about” means within 5% or 10% of the value referred to or within manufacturing tolerances.

The conjunction “or” is inclusive.

The terms “first”, “second”, “third”, etc. are used to distinguish respective elements and are not used to denote a particular order of those elements unless otherwise specified or order is explicitly described or required.

Numerous specific details are set forth to provide a thorough understanding of the claimed subject matter. However, those skilled in the art will understand that the claimed subject matter may be practiced without these specific details. In other instances, methods, apparatuses or systems that would be known by one of ordinary skill have not been described in detail so as not to obscure claimed subject matter.

Embodiments of the methods disclosed may be performed in the operation of such computing devices. The order of the blocks presented in the examples above can be varied—for example, blocks can be re-ordered, combined, and/or broken into sub-blocks. Certain blocks or processes can be performed in parallel.

While the present subject matter has been described in detail with respect to specific examples, those skilled in the art, upon attaining an understanding of these examples, may readily produce alterations to, variations of, and equivalents to such examples. Accordingly, the present disclosure has been presented for purposes of example rather than limitation, and does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.