Thermal interface materials comprising functionalized liquid metal droplets, circuit assemblies formed therefrom, and methods of manufacture thereof

Abstract

Thermal interface materials comprising functionalized liquid metal droplets, circuit assemblies formed therefrom, and method of manufacture thereof are provided. The thermal interface material comprises a polymer component and liquid metal droplets dispersed throughout the polymer component. At least a portion of the liquid metal droplets comprise an exterior surface comprising a metal oxide. The thermal interface material comprises a functionalizing component is bonded to at least a portion of the metal oxide by an acid.

Description

THERMAL INTERFACE MATERIALS COMPRISING FUNCTIONALIZED LIQUID METAL DROPLETS, CIRCUIT ASSEMBLIES FORMED THEREFROM, AND METHODS OF MANUFACTURE THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 489,016, which was filed on March 8, 2023, the contents of which is hereby incorporated by reference into this specification.FIELD

[0002] The present disclosure relates to thermal interface materials comprising functionalized liquid metal droplets, circuit assemblies formed therefrom, and method of manufacture thereof.BACKGROUND

[0003] A thermal interface material (TIM) can be used to thermally connect two or more layers together. For example, TIMs are often used in CPU packages to thermally connect the integrated heat spreader (IHS) of a CPU package to a heat sink. There are various types of TIMs that can be used. However, current TIMs present challenges.SUMMARY

[0004] In one general aspect, the present disclosure is directed a thermal interface material comprising a polymer component and liquid metal droplets dispersed throughout the polymer component. The liquid metal droplets can comprise a melting point no greater than 30 degrees Celsius, a D90 in a range of 1 micron to 300 microns, and / or at least one of gallium, a gallium alloy, indium, an indium alloy, tin, a tin alloy, mercury, and a mercury alloy. At least a portion of the liquid metal droplets comprise an exterior surface comprising a metal oxide, such as, for example, at least one of gallium oxide, indium oxide, tin oxide, iron oxide, and mercury oxide. The thermal interface material comprises a functionalizing component (e.g., a coupling agent, a polymer chain) bonded to at least a portion the metal oxide by an acid, such as, for example, at least one of sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, and carboxylic acid. In various examples, a concentration of the functionalizing component on a surface of the liquid metal droplets is ina range of lx 10'6to 5 units / nm2. In various examples, the thermal interface material comprises an additional component, such as, for example, at least one of a catalyst, rigid particles, a coupling agent, and fumed silica.

[0005] In another general aspect, the present disclosure is directed to an assembly comprising a first layer, a second layer, and the thermal interface material according to the present disclosure disposed in contact with and between the first layer and the second layer.

[0006] In another general aspect, the present disclosure is directed to a method comprising applying the thermal interface material according to the present disclosure on a first layer of an assembly, such that the thermal interface material is in contact with and between the first layer and a second layer of the assembly. The method comprises compressing the assembly thereby deforming the liquid metal droplets. A D90 of the liquid metal droplets in the thermal interface material prior to applying is greater than a bondline thickness formed between the first layer and the second layer.

[0007] In another general aspect, the present disclosure is directed a method of manufacture of a thermal interface material. The method comprises combining a polymer component and liquid metal to form an intermediate mixture. The method comprises dispersing the liquid metal throughout the polymer component in the intermediate mixture, thereby forming liquid metal droplets having an exterior surface comprising a metal oxide. The method comprises forming a functionalizing component bonded to at least a portion of the metal oxide by contacting the metal oxide with an acid.

[0008] The present invention can provide both a low contact resistance at the material interfaces and a low thermal resistance through the TIM. The low contact resistance can be enabled by the application of the polymer in a conformable state so that the polymer and liquid metal droplets can adapt to the surface of the layer to achieve a desired contact resistance. The low thermal resistance through the TIM can be enabled by liquid metal droplets, including the size and / or shape of the liquid metal droplets. Additionally, the methods described herein can achieve a desired homogeneity of the liquid metal droplets within the TIM, a desired distribution of the liquid metal droplets on the circuit assembly, and / or desired shape of the liquid metal droplets within the TIM, thereby enhancing the effective thermal conductivity of the TIM. These and other benefits realizable from various embodiments of the present invention will be apparent from the description that follows.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The features and advantages of various examples of the present invention, and the manner of attaining them, will become more apparent, and the examples will be better understood by reference to the following description of examples taken in conjunction with the accompanying drawing, wherein:

[0010] FIG. l is a perspective view of an assembly according to the present disclosure after deposition of the thermal interface material; and

[0011] FIG. 2 is a side view of an assembly formed by compressing the first and second layer of FIG. 1.

[0012] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate certain examples, in one form, and such exemplifications are not to be construed as limiting the scope of the examples in any manner.DETAILED DESCRIPTION

[0013] Certain exemplary aspects of the present invention will now be described to provide an overall understanding of the principles of the composition, function, manufacture, and use of the compositions and methods disclosed herein. An example or examples of these aspects are illustrated in the accompanying drawing. Those of ordinary skill in the art will understand that the compositions, articles, and methods specifically described herein and illustrated in the accompanying drawing are non-limiting exemplary aspects and that the scope of the various examples of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary aspect may be combined with the features of other aspects. Such modifications and variations are intended to be included within the scope of the present invention.

[0014] Properly formulating a thermal interface material (TIM) that is applied to a circuit assembly between an integrated heat spreader (IHS) and a heat sink can require balancing the thermal resistance through the TIM and the contact resistance at the material interfaces. For example, a polymeric material may have a low contact resistance at the material interfaces but a high thermal resistance through the material. A solid metal may have a low thermalresistance through the material but a high contact resistance at the material interfaces. Additionally, some solid materials (polymeric or metal) may require a large pressure during installation to achieve a desired contact resistance. Further, when utilizing a TIM with liquid metal droplets, the current inventors have determined there are challenges with achieving a desired distribution of the liquid metal droplets on the circuit assembly, a desired stability of the liquid metal droplet and polymer component emulsion within the TIM, a desired shape of the liquid metal droplets on the circuit assembly, and homogeneity of the liquid metal within the TIM, which can affect the effective thermal conductivity through the TIM.

[0015] Thus, the present inventors provide, in various examples, a thermal interface material comprising a polymer component and liquid metal droplets dispersed throughout the polymer component. At least a portion of the liquid metal droplets comprise an exterior surface comprising a metal oxide. The thermal interface material comprises a functionalizing component bonded to at least a portion of the metal oxide by an acid. The thermal interface material according to the present disclosure can enhance the liquid metal droplets resistance to movement through the polymer component; enhance the liquid metal droplets affinity towards the polymer component; enable the liquid metal droplets to be crosslinked into the polymer component; and / or enhance surface wetability of the liquid metal droplets. Thus, the thermal interface material according to the present disclosure can achieve a desired distribution of the liquid metal droplets on the circuit assembly, a desired stability of the liquid metal droplet and polymer component emulsion within the TIM, a desired shape of the liquid metal droplets on the circuit assembly, homogeneity of the liquid metal within the TIM, and / or an enhanced effective thermal conductivity.

[0016] As used in this specification, particularly in connection with layers, films, or materials, the terms “on,” “onto,” “over,” and variants thereof (e.g., “applied on,” “formed on,” “deposited on,” “provided on,” “located on,” and the like) mean applied, formed, deposited, provided, or otherwise located over a surface of a substrate but not necessarily in contact with the surface of the substrate. For example, a TIM “deposited on” a substrate or “deposited between” two elements does not preclude the presence of another layer or other layers of the same or different composition located between the applied TIM and the substrate or layers. Likewise, a second layer “deposited on” a first layer does not preclude the presence of another layer or other layers of the same or different composition located between the deposited second layer and the deposited TIM.

[0017] As used in this specification, the terms “polymer” and “polymeric” means prepolymers, oligomers, and both homopolymers and copolymers. As used in this specification, “prepolymer” means a polymer precursor capable of further reactions or polymerization by a reactive group or reactive groups to form a higher molecular mass or cross-linked state.

[0018] The polymer can be at least one of a polymeric binder, a thermosetting polymer, and a thermoplastic polymer. As used herein, the term “thermosetting” refers to polymers that “set” irreversibly upon curing or cross-linking, where the polymer chains of the polymeric components are joined together by covalent bonds, which is often induced, for example, by heat or radiation. In various examples, curing or a cross-linking reaction can be carried out under ambient conditions. Once cured or cross-linked, a thermosetting polymer may not flow upon the application of heat, may otherwise irreversibly increase in viscosity, and / or can be insoluble in conventional solvents. As used herein, the term “thermoplastic” refers to polymers that include polymeric components in which the constituent polymer chains are not joined (e.g., crosslinked) by covalent bonds and thereby can undergo liquid flow upon heating and are soluble in conventional solvents. In certain embodiments, the polymer can be elastomeric (e.g., rubbery, soft, stretchy) or rigid (e.g., glassy). For example, the polymer can be elastomeric.

[0019] Thermosetting polymers may include at least one of a cross-linking agent that may comprise, for example, aminoplasts, polyisocyanates (including blocked isocyanates), polyepoxides, beta-hydroxyalkylamides, polyacids, anhydrides, organometallic acidfunctional materials, polyamines, polyvinyls, polysilicon hydrides, polyalcohols, polyacid chlorides, polyhalides, and polyamides. A polymer may have functional groups that are reactive with the cross-linking agent.

[0020] The polymer in the TIMs described herein may be selected from any of a variety of polymers well known in the art. For example, the thermosetting polymer may comprise at least one of an acrylic polymer, an acrylate polymer, a vinyl polymer, a polyester polymer, a polyurethane polymer, polybutadiene, a polyamide polymer, a polyether polymer, a polysiloxane polymer (e.g., poly(dimethylsiloxone)), a silicon hydride polymer, a fluoropolymer, a polyisoprene polymer (e.g., rubber), and a copolymer of two or more thereof. The functional groups on a thermosetting polymer may be selected from any of a variety of reactive functional groups, including, for example, at least one of a carboxylic acidgroup, an amine group, an epoxide group, a hydroxyl group, a thiol group, a carbamate group, an amide group, a urea group, an isocyanate groups (including a blocked isocyanate group), a vinyl group, a silicon hydride group, an acid chloride group, an acrylate group, a halide group, and a mercaptan group.

[0021] The thermoplastic polymer can comprise at least one of propylene-ethylene copolymer, styrene-butadiene- styrene, and styrene ethylene butylene styrene. The polymer can comprise a melting point of at least 100 degrees Celsius, such as, for example, at least 120 degrees Celsius, at least 150 degrees Celsius, or at least 200 degrees Celsius.

[0022] The polymeric binder can be a polyether binder.

[0023] The liquid metal droplets for the TIM can comprise at least one of gallium, a gallium alloy, indium, an indium alloy, tin, a tin alloy, mercury, and a mercury alloy. The liquid metal droplets can comprise a melting point of no greater than 30 degrees Celsius, such as, for example, no greater than 25 degrees Celsius, no greater than 20 degrees Celsius, no greater than 15 degrees Celsius, no greater than 10 degrees Celsius, no greater than 5 degrees Celsius, no greater than 0 degrees Celsius, or no greater than -10 degrees Celsius. The liquid metal droplets can comprise a melting point of at least -40 degrees Celsius, such as, for example, at least -20 degrees Celsius, at least -19 degrees Celsius, at least -10 degrees Celsius, at least 0 degrees Celsius, at least 5 degrees Celsius, at least 10 degrees Celsius, at least 15 degrees Celsius, at least 20 degrees Celsius, or at least 25 degrees Celsius. The liquid metal droplets can comprise a melting point in a range of -40 degrees Celsius to 30 degrees Celsius, such as, for example, -20 degrees Celsius to 30 degrees Celsius, -19 degrees Celsius to 30 degrees Celsius, or -19 degrees Celsius to 25 degrees Celsius. The determination of the melting point can be made at a pressure of 1 atmosphere absolute. In certain embodiments, the TIM can comprise Gallium Indium Tin (Galinstan) and a melting point of -19 degrees Celsius.

[0024] At least a portion of the liquid metal droplets comprise an exterior surface comprising a metal oxide. For example, at least 5% of the surface area of the exterior surface can be covered by a film of a metal oxide, such as, for example, at least 10%, at least 20%, at least 30%, at least 40%, at least 60%, at least 70%, or at least 80% of the surface area of the exterior surface can be covered by a film of a metal oxide.

[0025] The metal oxide can comprise a transition metal oxide. The metal oxide can comprise at least one of gallium oxide, indium oxide, tin oxide, iron oxide, mercury oxide, aluminum oxide, nickel oxide, zinc oxide, copper oxide, and other metal oxides. For example, in examples when the liquid metal droplets comprises gallium or a gallium alloy, a film of gallium oxide may be formed on the liquid metal droplets by oxidation due to exposure to water and / or air. In various examples, a film of a metal oxide can be formed by inclusion of metal oxide particles (e.g., aluminum oxide, zinc oxide) into the polymeric binder or into the liquid metal droplets.

[0026] A functionalizing component can be bonded to at least a portion of the metal oxide by an acid. For example, the functionalizing component can be bonded (e.g., covalent bond, ionic bond) to at least a portion of the metal oxide. The functionalizing component can comprise a coupling agent, a polymer chain, or a combination thereof. The polymer chain can comprise a molecular weight of at least 400 g / mol as measured by gel permeation chromatography (GPC), such as, for example, at least 500 g / mol, at least 1,000 g / mol, at least 2,000 g / mol, or at least 5,000 g / mol, all as measured by GPC. In various examples, the polymer chain can comprises at least one of an acrylic polymer, an acrylate polymer, a vinyl polymer, a polyester polymer, a polyurethane polymer, a polybutadiene polymer, a polyamide polymer, a polyether polymer, a polysiloxane polymer, a silicon hydride polymer, a fluoropolymer, a polyisoprene polymer, polystyrene polymer, polyepoxide polymer, and a copolymer of any two or more thereof. In certain examples the functionalizing component comprises an acid functionalized polymer.

[0027] The acid may be a Bronsted-Lowry acid. The acid can comprise at least one of an acid comprising a sulfate group, an acid comprising a nitrate group, an acid comprising a phosphate group, an acid comprising a chloride group, an acid comprising a bromide group, an acid comprising an iodide group, a carboxylic acid, and an acid comprising a sulfonic group. For example, the acid can comprise at least one of sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, and carboxylic acid. The acid can be a monoprotic acid or a polyprotic acid.

[0028] The amount of functionalizing component bonded to at least a portion of the metal oxide can be sufficient to achieve an enhanced resistance of the liquid metal droplets to move through the polymer component by at least one of steric hindrances and charge repulsion compared to liquid metal droplets not bonded to the functionalizing component; enhancedaffinity of the liquid metal droplets towards the polymer component compared to liquid metal droplets not bonded to the functionalized component; enable crosslinking of the liquid metal droplets into the polymer component; and / or enhanced surface wetability of the liquid metal droplets compared to liquid metal droplets not bonded to the functionalized component.

[0029] The surface wettability of the liquid metal droplets can be determined by measuring a contact angle of the liquid metal droplets. The liquid metal droplets according to the present disclosure can comprise a contact angle of no greater than 120 degrees, such as, for example, no greater than 100 degrees or no greater than 75 degrees. The liquid metal droplets according to the present disclosure can comprise a contact angle of at least 30 degrees, such as, for example, at least 40 degrees. In various examples, the liquid metal droplets according to the present disclosure can comprise a contact angle in a range of 30 degrees to 120 degrees, such as, for example, 30 degrees to 100 degrees. Some conventional liquid metal droplets without the functionalizing component can comprise a contact angle of greater than 150 degrees. The reduced contact angle of the liquid metal droplets according to the present disclosure can be a result of a reduced surface energy on the liquid metal droplets that is correlated with a surface density of the functionalizing component. For example, a concentration of the functionalizing component on a surface of the liquid metal droplets can be in a range of lx 10'6to 5 molecules / nm2of the exterior surface of the liquid metal droplet. The contact angle can be measured by placing a drop of liquid metal on a glass slide and using optical microscopy to measure an angle formed by the drop where the liquid-vapor interface of the drop meets the glass slide.

[0030] Adding a functionalizing component that increases a size of the liquid metal droplets can cause enhanced steric hindrances, which may inhibit movement of the liquid metal droplets in the polymer component. Adding a functionalizing component that has a similar charge to the polymer component can inhibit movement of the liquid metal droplets in the polymer component by charge repulsion.

[0031] Adding a functionalizing component to the liquid metal droplets that shares a similar composition to the polymer matrix and / or an opposing charge to a charge of the polymer component (e.g., charge attraction) can enhance affinity of the liquid metal droplets towards the polymer component compared to liquid metal droplets not bonded to the functionalized component.

[0032] In various examples, the functionalizing component can be configured to be crosslinked into the polymer component. For example, the functionalizing component can participate in a polymerization reaction with the polymer component and be chemically bond to the polymer component.

[0033] In various examples, the metal oxide comprises gallium oxide, the liquid metal droplets comprise gallium or a gallium alloy, the acid is a carboxylic acid, the functionalizing component comprises a polymer chain covalently bonded to the carboxylic acid.

[0034] The TIM can be manufactured by combining the polymer component and liquid metal to form an intermediate mixture. The method can further comprise dispersing the liquid metal throughout the polymer component in the intermediate mixture, thereby forming liquid metal droplets having an exterior surface comprising a metal oxide. For example, the polymer and bulk liquid metal can be mixed together with at least one of a high shear mixer, a centrifugal mixer, by shaking in a container, a mortar and pestle, and sonication to form an emulsion. More details about exemplary ways to form an emulsion of the polymer and the liquid metal droplets are described in (1) published PCT WO / 2019 / 136252, entitled “Method of Synthesizing a Thermally Conductive and Stretchable Polymer Composite”, (2) published U.S. application US 2017 / 0218167, entitled “Polymer Composite with Liquid Phase Metal Inclusions,” (3) U.S. Patent No. 10,777,483, entitled “Method, apparatus, and assembly for thermally connecting layers”, (4) U.S. Provisional Patent No. 63 / 268,134, entitled “Thermal interface material, an integrated circuit assembly, and a method for thermally connecting layers”, (5) published PCT WO 2022 / 204689 entitled “A method, apparatus, and assembly for thermally connecting layers with thermal interface materials comprising rigid particles”, and (6) U.S. provisional application 63 / 479,879, entitled “A method of Manufacture of a Thermal Interface Material, a Thermal Interface Material Formed Therefrom, and an Integrated Circuit Formed Therefrom”, all of which are incorporated herein by reference in their entirety.

[0035] The method of manufacture of the TIM can comprise forming a functionalizing component bonded to at least a portion of the metal oxide by contacting the metal oxide with an acid. For example, the acid and / or acid functionalized polymer can react with the metal oxide after dispersing the liquid metal throughout the polymer component and / or prior to combining the polymer component and the liquid metal. In certain examples, the functionalizing component can be added to the emulsion after dispersing the liquid metalthroughout the polymer. In various examples, the functionalizing component can be added to the polymer component prior to combining the polymer component with the liquid metal. In certain examples, the functionalizing component can be added to the liquid metal prior to combining the polymer component with the liquid metal.

[0036] The composition and / or mixing techniques can be chosen such that the viscosity of the TIM is less than 850,000 cP (centipoise), such as, for example, less than 750,000 cP, less than 500,000 cp, less than 250,000 cP, 200,000 cP, less than 150,000 cP, less than 100,000 cP, less than 50,000 cP, less than 15,000 cP, less than 14,000 cP, less than 13,000 cP, less than 12,000 cP, less than 11,000 cP, or less than 10,000 cP. For example, the composition and / or mixing techniques can be chosen such that the viscosity of the TIM is at least 1,000 cP, such as, for example, at least 2,000 cP, at least 5,000 cP, or at least 10,000 cP. The composition and / or mixing techniques can be chosen such that the viscosity of the TIM is in a range of 1,000 cP to 850,000 cP, such as, for example, 2,000 cP to 750,000 cP, or 2,000 cP to 500,000 cP. The viscosity of the TIM emulsion can be measured by a parallel plate (40mm) rheometer at 25 degrees Celsius, a frequency of 10 radians per second, and a strain of 5%. Selecting the viscosity can require a balance of installation pressure, which may increase with a high viscosity and an ability to resist undesirably fast spreading during application of the TIM and pump out during operation.

[0037] The TIM can comprise at least 1% liquid metal droplets by total volume of the TIM, such as, for example, at least 5% liquid metal droplets, at least 10% liquid metal droplets, at least 20% liquid metal droplets, at least 30% liquid metal droplets, at least 40% liquid metal droplets, at least 50% liquid metal droplets, at least 60% liquid metal droplets, at least 70% liquid metal droplets, at least 80% liquid metal droplets, or at least 90% liquid metal droplets, all based on the total volume of the liquid metal droplets. The TIM can comprise no greater than 95% liquid metal droplets by total volume of the TIM, such as, for example, no greater than 93% liquid metal droplets, no greater than 90% liquid metal droplets, no greater than 80% liquid metal droplets, no greater than 70% liquid metal droplets, no greater than 60% liquid metal droplets, no greater than 50% liquid metal droplets, no greater than 40% liquid metal droplets, no greater than 30% liquid metal droplets, no greater than 20% liquid metal droplets, or no greater than 10% liquid metal droplets, all based on the total volume of the TIM. The TIM can comprise a range of 1% to 95% liquid metal droplets by total volume of the TIM, such as, for example, 5% to 93% liquid metal droplets, 50% to 93% liquid metaldroplets, 60% to 93% liquid metal droplets, 70% to 95% liquid metal droplets, or 70% to 93% liquid metal droplets, all based on the total volume of the TIM. The amount of liquid metal droplets can be selected while balancing a desired elasticity and a desired effective thermal conductivity of the TIM.

[0038] The composition and / or mixing techniques can be selected to achieve a desired Dso and / or D90 of the liquid metal droplets in the TIM prior to compressing. The D50 of the liquid metal droplets can be at least 1 micron prior to compressing, such as, for example, at least 5 microns, at least 10 microns, at least 15 microns, at least 20 microns, at least 30 microns, at least 35 microns, at least 40 microns, at least 50 microns, at least 60 microns, at least 70 microns, at least 80 microns, at least 90 microns, at least 100 microns, at least 120 microns, at least 150 microns, or at least 200 microns, all prior to compressing. The D50 of the liquid metal droplets can be no greater than 300 micron, such as, for example, no greater than 250 microns, no greater than 200 microns, no greater than 150 microns, no greater than 120 microns, no greater than 100 microns, no greater than 90 microns, no greater than 80 microns, no greater than 70 microns, no greater than 60 microns, no greater than 50 microns, no greater than 40 microns, no greater than 35 microns, no greater than 30 microns, no greater than 20 microns, no greater than 10 microns, or no greater than 5 microns, all prior to compressing. For example, the D50 of the liquid metal droplets can be in a range of 1 microns to 300 microns, such as, for example, 5 microns to 300 microns, 150 microns to 250 microns, 5 microns to 150 microns, 15 to 150 microns, 35 microns to 150 microns, 35 microns to 70 microns, or 5 microns to 100 microns, all measured prior to compressing.

[0039] As used herein, Dxcan be measured using microscopy (e.g., optical microscopy or electron microscopy). The size can be the diameter of spherical particles or the length along the largest dimension if ellipsoidal or otherwise irregularly shaped particle. As used herein, “Dx” of particles refers to the diameter at which X% of the volume of the particles have a smaller diameter.

[0040] The D90 of the liquid metal droplets can be at least 1 micron, such as, for example, at least 5 microns, at least 10 microns, at least 15 microns, at least 20 microns, at least 30 microns, at least 35 microns, at least 40 microns, at least 50 microns, at least 60 microns, at least 70 microns, at least 80 microns, at least 90 microns, at least 100 microns, at least 120 microns, at least 150 microns, or at least 200 microns, all prior to compressing. The D90 of the liquid metal droplets can be no greater than 300 micron, such as, for example, no greaterthan 250 microns, no greater than 200 microns, no greater than 150 microns, no greater than 120 microns, no greater than 100 microns, no greater than 90 microns, no greater than 80 microns, no greater than 70 microns, or no greater than 50 microns, all prior to compressing. For example, the D90 of the liquid metal droplets can be in a range of 1 microns to 300 microns, such as, for example, 5 microns to 300 microns, 150 microns to 250 microns, 10 microns to 200 microns, 15 to 150 microns, 35 microns to 150 microns, 35 microns to 120 microns, or 50 microns to 100 microns, all measured prior to compressing.

[0041] The TIM can optionally comprise other components such as, for example, rigid particles, a catalyst, fumed silica, and coupling agents. The rigid particles can comprise at least one of iron, an iron alloy (e.g., steel), vanadium, a vanadium alloy, niobium, a niobium alloy, titanium, a titanium alloy, copper, a copper alloy (e.g., bronze), a rigid polymer, a glass, and a ceramic. The rigid particles can be resistant to deformation and / or corrosion by the liquid metal droplets. For example, the rigid particles can comprise a Young’s modulus of at least 100 MPa (megapascals), such as, for example, at least 110 MPa, at least 150 MPa, at least 200 MPa, at least 250 MPa, at least 500 MPa, at least 750 MPa, at least 1 GPa (gigapascals), or at least 2 GPa. Young’s Modulus can be measured according to ASTM El 11-17. The TIM can comprise a range of 0.1% to 30% rigid particles by total volume of the TIM, such as, for example, 0.1% to 10% rigid particles, 0.1% to 5% rigid particles, 1% to 10% rigid particles, or 1% to 5% rigid particles, all based on the total volume of the TIM.

[0042] In various examples, the polymer component can comprise 0.1% by to 0.5% by weight of a coupling agent based on a total weight of the polymer component. For example, the coupling agent can comprise at least one of 3-Glycidoxypropyltrimethoxysilane, 3- Glycidoxypropyltriethoxysilane, 3 -Aminopropyltrimethoxy silane, and Bis(3- trimethoxysilylpropyl)amine.

[0043] In various examples, the polymer component can comprise 0.1% by to 0.5% by weight of a coupling agent based on a total weight of the polymer component. For example, the coupling agent can comprise at least one of 3-Glycidoxypropyltrimethoxysilane, 3- Glycidoxypropyltriethoxysilane, 3 -Aminopropyltrimethoxy silane, and Bis(3- trimethoxysilylpropyl)amine.

[0044] In certain examples, the polymer component can comprises 0.1% by weight to 5% by weight of a fumed silica based on a total weight of the polymer component.

[0045] The Dso of the rigid particles in the TIM can be selected to achieve a desired bondline thickness in the assembly. The average particle size of the rigid particles can be at least 1 micron, such as, for example, at least 5 microns, at least 10 microns, at least 20 microns, at least 30 microns, at least 35 microns, at least 40 microns, at least 50 microns, at least 60 microns, at least 70 microns, at least 80 microns, at least 90 microns, at least 100 microns, at least 120 microns, or at least 125 microns. The D50 of the rigid particles can be no greater than 150 microns, such as, for example, no greater than 125 microns, no greater than 120 microns, no greater than 100 microns, no greater than 90 microns, no greater than 80 microns, no greater than 70 microns, no greater than 60 microns, no greater than 50 microns, no greater than 40 microns, no greater than 35 microns, no greater than 30 microns, no greater than 20 microns, no greater than 10 microns, or no greater than 5 microns. For example, the D50 of the rigid particles can be in a range of 1 microns to 150 microns, such as, for example, 15 to 150 microns, 5 microns to 125 microns, 35 microns to 125 microns, 35 microns to 70 microns, or 50 microns to 70 microns.

[0046] The TIM can be applied to various layers and devices and it is described below with reference to FIGs. 1-2 with reference to a circuit assembly but is not limited to only a circuit assembly and could be applied to other devices. Referring to FIG. 1, the method according to the present disclosure comprises depositing a TIM 104 according to the present disclosure between a first layer 106 of an assembly 102 and a second layer 108 of the assembly 102. The thickness of the TIM can be selected based on the desired application.

[0047] Depositing the TIM 104 can comprise, for example, at least one of dispensing, extruding (e.g., through a nozzle, such as, a circular nozzle, a fan nozzle, or other nozzle shape), applying with a utensil (e.g., brush, spatula), stencil printing, 3D printing, and screen printing. The TIM 104 can be deposited in a conformable state such that the TIM 104 can adapt to the surfaces of the first layer 106 and the second layer 108 to achieve a desired level of surface contact therebetween. In various examples, the TIM 104 can be applied directly to the first layer 106 and, thereafter, the second layer 108 can be applied directly to the TIM 104. In various other examples, the TIM 104 can be applied directly to the second layer 108 and, thereafter, the first layer 106 can be applied directly to the TIM 104. In certain examples, the TIM 104 can be applied to both the first layer 106 and the second layer 108 and then the first layer 106 and the second layer 108 can be applied together. In various examples, after deposition of the TIM 104 and compression of the assembly 102, the TIM104 can be in direct contact with the first layer 106 and the second layer 108. In certain examples, the application of the TIM 104 may be limited to the surfaces of the first layer 106 such that the TIM 104 can be efficiently used.

[0048] The TIM 104 can be dispensed from a container and applied to a layer in a conformable state. The TIM 104 can be stored in a container prior to use. The TIM 104 can be in a conformable state in the container. The container can comprise at least one of a pillow pack, a syringe, a beaker, a jar, a bottle, and a drum. In various examples, the container can be a ready to use dispensing device, such as, for example, a pillow pack or a syringe. In certain examples, the TIM 104 may not be stored and can be used after creation of the emulsion without storage.

[0049] The TIM 104 can be applied to at least 1% of a surface area of an exposed side 106a of the first layer 106 prior to compressing the assembly 102, such as, for example, at least 2%, at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, or at least 50%, all of the surface area of the exposed side 106a of the first layer 106. For example, the TIM 104 can be applied to a range of 1% to 100% of the surface area of an exposed side 106a of the first layer 106 prior to compressing the assembly 102, such as, for example 2% to 100%, 5% to 90%, or 5% to 80%, all of the surface area of the exposed side 106a of the first layer 106.

[0050] The first layer 106 can be a heat-generating electronic component (e.g., a battery, memory, a data storage unit, a power inverter, a thermoelectric generator, a motor winding, an integrated circuit) and / or thermally connected to the heat-generating electronic component. The integrated circuit can comprise a processor (e.g., central processing unit(CPU), tensor processing unit (TPU), graphics processing unit (GPU), artificial intelligence focused processor, an ASIC, and / or a system-on-a-chip (SOC)). The second layer 108 can be an upper layer that can be thermally conductive. The first layer 106 and the second layer 108, individually, can be at least one of a battery, a processor, a heat sink (e.g., fins, fan, liquid cooling, cold plate, heat sink, heat wick, heat pipe), an integrated heat spreader, and packaging. In various examples, the first layer 106 can comprise a processor and the second layer 108 can comprise at least one of a heat sink, an integrated heat spreader, and packaging. In certain examples, the first layer 106 can comprise an integrated heat spreader and the second layer 108 can comprise at least one of a heat sink, an integrated heat spreader, and packaging. In various examples, the first layer 106 can comprise a battery andthe second layer 108 can comprise at least one of a heat sink, an integrated heat spreader, and packaging.

[0051] After deposition of the TIM 104, the method comprises compressing the assembly 102, thereby deforming the liquid metal droplets 112 and forming an assembly 202. For example, referring to the detailed views in FIGs. 1-2, the first layer 106 and the second layer 108 can be urged together. For example, compressing the assembly 102 can comprise applying a pressure to the first layer 106 and the second layer 108 of at least 1 psi, such as, for example, at least 5 psi, at least 10 psi, at least 15 psi, or at least 20 psi. Compressing the assembly 102 can comprise applying a pressure to the first layer 106 and the second layer 108 of no greater than 50 psi. In various examples, compressing the assembly 102 comprises a first compression process based on displacement where a pressure is applied to the first layer 106 and the second layer 108 until the TIM 104 is compressed to a desired bondline thickness, tni.

[0052] In various examples, the relative liquid metal surface area coverage between the TIM 104, and the first layer 106 and the second layer 108 can be increased by compression. For example, the relative liquid metal surface area coverage after compression can be in a range of 1% to 100%, such as, for example, 1% to 5%, 5% to 10%, 10% to 30%, 30% to 50%, or increasing until the liquid metal surface area coverage achieves 100%. As used herein, “relative liquid metal area coverage” is the surface area covered by the liquid metal normalized by the total contact surface area between the TIM 104 and the first layer 106 and second layer 108. Relative liquid metal area coverage can be measured using crosssectioning followed by optical imaging using a ZEISS Axio Zoom.V16 or confocal scanning acoustic microscopy using a Hitachi FineSAT III for CSAM.

[0053] After compression, the bondline thickness, tm, of the assembly 102 can be no greater than 300 microns, such as, for example, no greater than 250 microns, no greater than 200 microns, no greater than 150 microns, no greater than 145 microns, no greater than 140 microns, no greater than 125 microns, no greater than 100 microns, no greater than 80 microns, no greater than 70 microns, no greater than 50 microns, no greater than 40 microns, no greater than 35 microns, or no greater than 30 microns. The bondline thickness, tm, of the assembly 102 can be at least 1 microns, such as, for example, at least 10 microns, at least 15 microns, at least 30 microns, at least 35 microns, at least 40 microns, at least 50 microns, at least 70 microns, at least 75 microns, at least 80 microns, at least 100 microns, at least 120microns, at least 140 microns, at least 145 microns, or at least 200 microns. The bondline thickness, tBL, of the assembly 102 can be in a range of 1 micron to 300 microns, such as, for example, 1 microns to 250 microns, 10 microns to 300 microns, 10 microns to 250 microns, 1 micron to 200 microns, 15 microns to 200 microns, 15 microns to 150 microns, 30 microns to 150 microns, 50 microns to 120 microns, 75 microns to 125 microns, or 15 microns to 100 microns.

[0054] The D90 of the liquid metal droplets 112 in the TIM 104 prior to applying can be greater than the bondline thickness, tm. For example, the D90 of the liquid metal droplets 312 prior to applying and / or a compressing process can be greater than the bondline thickness, tm, such as, for example, 1% greater than the bondline thickness, tm, 2% greater than the bondline thickness, tm, 5% greater than the bondline thickness, tm, 10% greater than the bondline thickness, tm, 15% greater than the bondline thickness, tm, 20% greater than the bondline thickness, tm, 30% greater than the bondline thickness, tm, 40% greater than the bondline thickness, tm, 50% greater than the bondline thickness, tm, or 75% greater than the bondline thickness, tm. The D90 of the liquid metal droplets 112 prior to applying and / or a compressing process can be no more than 100% greater than the bondline thickness, tm, such as, for example, no more than 75% greater than the bondline thickness, tm, no more than 50% greater than the bondline thickness, tm, no more than 40% greater than the bondline thickness, tm, no more than 30% greater than the bondline thickness, tm, no more than 20% greater than the bondline thickness, tm, no more than 15% greater than the bondline thickness, tm, no more than 10% greater than the bondline thickness, tm, no more than 5% greater than the bondline thickness, tm, or no more than 2% greater than the bondline thickness, tm. The D90 of the liquid metal droplets 112 prior to applying and / or a compressing process can be in a range of 1% to 100% greater than the bondline thickness, tm, such as, for example, 1% to 50% greater than the bondline thickness, tm, 1% to 30% greater than the bondline thickness, tm, 2% to 30% greater than the bondline thickness, tm, or 5% to 20% greater than the bondline thickness, tm,.

[0055] The TIM can cover at least 90% of a surface area of an exposed side 106a of the first layer 106 after compressing the circuit assembly, such as, for example, at least 95% of the surface area of the exposed side 106a.

[0056] Compressing the assembly 102 can apply a force to the TIM 104 and can deform the liquid metal droplets 112 dispersed within the polymer component 110 of the TIM 104. Because the polymer component 110 is still conformable and moveable, the compressingforce can deform the liquid metal droplets 112. The liquid metal droplets 112 can be in the liquid phase during deformation such that a lower pressure is required for the compression and a desired deformation can be achieved. For example, the liquid metal droplets 112 can be generally spherical as shown in FIG. 1 and thereafter can be generally ellipsoidal as shown in FIG. 2. In various examples, the liquid metal droplets 112 prior to compressing can have a first average aspect ratio and after compressing the liquid metal droplets 112 can have a second average aspect ratio. The second average aspect ratio can be different that the first average aspect ratio. For example, the second average aspect ratio can be greater than the first average aspect ratio. The average aspect ratio can be a mean ratios of the width of the liquid metal droplets 112 to the height of the liquid metal droplets 112. In various examples, the first aspect ratio can be 1 and the second aspect ratio can be greater than 1. In certain examples, the first aspect ratio can be in a range of 1 to 1.5. In certain examples, the second aspect ratio can be at least 0.5 greater than the first aspect ratio, such as, for example, at least1 greater than the first aspect ratio, at least 2 greater than the first aspect ratio, or at least 5 greater than the first aspect ratio. In certain examples, the second aspect ratio can be at least2 after compressing the assembly 102, such as, for example, at least 3, or at least 4 after compressing the assembly 102.

[0057] The width (e.g., longest dimension) of the liquid metal droplets 112 can be substantially aligned with the longitudinal plane of the TIM 104 in the assembly 102 and the height of the liquid metal droplets 112 can be substantially aligned with the thickness of the TIM 104 (e.g., the bondline thickness, dni). The width of the liquid metal droplets 112 can increase upon compression of the assembly 102. For example, in certain examples, the diameter of liquid metal droplets 112 prior to compressing can be 200 pm (with a first aspect ratio of 1) and after compression to a bondline thickness of 100 pm, the liquid metal drop can be deformed to an ellipsoidal shape with a 400 pm width (e.g., second aspect ratio of 4).

[0058] In certain examples, the liquid metal droplets 112 can be aligned substantially in a monolayer as shown in FIG. 2 after compressing. The monolayer can be achieved by selecting the Dso and / or D90 of the liquid metal droplets 112 and the bondline thickness, tm. Configuring the liquid metal droplets 112 in a monolayer can reduce the thermal resistance of the TIM 104.

[0059] The D50 and / or D90 of the liquid metal droplets 112, deformation of the liquid metal droplets 112, and the method of deposition of the liquid metal droplets 112 can improve thethermal resistance value of the TIM 104. For example, the TIM 104 can comprise a thermal resistance value of at least 0.5 (°K*mm2) / W, such as, for example, at least 1 (°K*mm2) / W, at least 2 (°K*mm2) / W, at least 3 (°K*mm2) / W, at least 5 (°K*mm2) / W, or at least 10 (°K*mm2) / W. The TIM 104 can comprise a thermal resistance value of no greater than 30 (°K*mm2) / W, such as, for example, no greater than 20 (°K*mm2) / W, no greater than 15 (°K*mm2) / W, no greater than 10 (°K*mm2) / W, no greater than 9 (°K*mm2) / W, no greater than 8 (°K*mm2) / W, no greater than 7 (°K*mm2) / W, or no greater than 5(°K*mm2) / W. The TIM 104 can comprise a thermal resistance value in a range of 0.5 (°K*mm2) / W to 30 (°K*mm2) / W, such as, for example, 0.5 (°K*mm2) / W to 20 (°K*mm2) / W, 0.5 (°K*mm2) / W to 15 (°K*mm2) / W, 1 (°K*mm2) / W to 10 (°K*mm2) / W, 2 (°K*mm2) / W to 10 (°K*mm2) / W, or 2 (°K*mm2) / W to 8 (°K*mm2) / W. The thermal resistance value can be measured using a TIMA 5 instrument from NanoTest (Germany).

[0060] The composition of the TIM 104, the Dso and / or D90 of the liquid metal droplets 112, deformation of the liquid metal droplets 112, and the method of deposition of the liquid metal droplets 112 can improve the thermal conductivity value of the TIM 104. For example, the TIM 104 can comprise an effective thermal conductivity value of at least 5 W / m*K, such as, for example, at least 10 W / m*K, at least 12 W / m*K, at least 15 W / m*K, at least 17 W / m*K, or at least 20 W / m*K. The TIM can comprise an effective thermal conductivity value in a range of 5 W / m*K to 50 W / m*K, such as, for example, 10 W / m*K to 40 W / m*K or 10 W / m*K to 30 W / m*K. As used herein, the effective thermal conductivity is a thickness of the TIM divided by a thermal resistance of the TIM.

[0061] The TIM 104 can be cured or may not be cured depending on the application. For example, the TIM 104 may be cured to thicken the TIM, which may increase the viscosity of the polymer component 110. In certain examples, the TIM may be cured to a solid. In various examples, the TIM 104 is cured after compressing the first layer 106 and the second layer 108 of the assembly 102. Applying the TIM 104 at a lower viscosity can enable a more efficient installation and ability to wet surfaces of the first layer 106 and the second layer 108. Increasing the viscosity after application can enable the TIM 104 to resist pump out and enhance removal of the TIM 104. In various examples, the TIM 104 may not be cured.

[0062] In various examples, the polymer component 110 after curing is elastomeric. Curing the polymer component 110 can inhibit pump out of the liquid metal droplets 112 during thermal cycling of the assembly 102 and can provide a mechanical bond between the firstlayer 106 and the second layer 108. In various examples, curing the TIM 104 can comprise crosslinking the liquid metal droplets 114 into the polymer component 110 using the functionalizing component. For example, the functionalizing component can be bonded to the liquid metal droplets 114 via the metal oxide and the functionalizing component can chemically react and form a bond with the polymer component 110.

[0063] Curing the TIM 104 can comprise at least one of heating the TIM 104 (e.g., in examples with a thermosetting polymer), adding a catalyst to the TIM 104, exposing the TIM 104 to air, cooling the TIM 104 (e.g., in examples with a thermoplastic polymer), applying electromagnetic radiation (e.g., photo-polymerization), and applying pressure to the TIM 104. Curing the TIM 104 can increase the viscosity of the TIM emulsion. For example, the TIM 104 can comprise a viscosity after curing that is at least double of the TIM prior to curing, such as, for example, at least triple, at least quadrupole, or ten times a viscosity of the TIM prior to curing. For example, the TIM 104 can comprise a viscosity after curing of greater than 15,000 cP, such as, for example, greater than 20,000 cP, greater than 30,000 cP, greater than 50,000 cP, greater than 100,000 cP, greater than 150,000 cP, greater than 200,000 cP, greater than 250,000 cP, greater than 500,000 cP, greater than 750,000 cP, greater than 850,000 cP, greater than 1,000,000 cP, greater than 1,500,000 cP, greater than 2,500,000 cP, greater than 4,000,000 cP, or greater than 5,000,000 cP. In various examples, the TIM 104 can be an adhesive. The polymer in the TIM 104 can be selected to reduce off-gasing of the TIM 104 during curing. In certain examples, the TIM 104 can be removed with a solvent and / or scrapping.

[0064] As used in this specification, the terms “cure” and “curing” refer to the chemical cross-linking of components in an emulsion or material applied over a substrate or the increase of viscosity of the components in the emulsion or material applied over the substrate. Accordingly, the terms “cure” and “curing” do not encompass solely physical drying of an emulsion or material through solvent or carrier evaporation. In this regard, the term “cured,” as used in this specification in examples comprising a thermosetting polymer, refers to the condition of an emulsion or material in which a component of the emulsion or material has chemically reacted to form new covalent bonds in the emulsion or material e.g., new covalent bonds formed between a binder resin and a curing agent). The term “cured”, as used in this specification in examples comprising a thermoplastic polymer, refers to the condition of an emulsion or material in which the temperature of the thermoplastic polymer decreasesbelow the melting point of the thermoplastic polymer such that the viscosity of the emulsion or material increases. In examples comprises both a thermosetting polymer and a thermoplastic polymer, the term “cured” refers to one of or both of the polymers curing as described herein.

[0065] In various other examples, the TIM according to the present disclosure can be used in a system on a package. For example, a single horizontal TIM layer can be in contact with multiple dies on one side (e.g., the integrated circuit can comprise multiple dies or multiple integrated circuits can be in contact with the same side of the TIM) and an upper layer or layers on a different side.

[0066] Those skilled in the art will recognize that the herein described compositions, articles, methods, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken as limiting.

[0067] With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those that are illustrated or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise.

[0068] Although various examples have been described herein, many modifications, variations, substitutions, changes, and equivalents to those examples may be implemented and will occur to those skilled in the art. Also, where materials are disclosed for certain components, other materials may be used. It is therefore to be understood that the foregoing description and the appended claims are intended to cover all such modifications andvariations as falling within the scope of the disclosed examples. The following claims are intended to cover all such modification and variations.

[0069] Various aspects of the invention according to the present disclosure include, but are not limited to, the aspects listed in the following numbered clauses.

[0070] Clause 1. A thermal interface material comprising: a polymer component; and liquid metal droplets dispersed throughout the polymer component, wherein at least a portion of the liquid metal droplets comprise an exterior surface comprising a metal oxide; and a functionalizing component bonded to at least a portion of the metal oxide by an acid.

[0071] Clause 2. The thermal interface material of clause 1, wherein the acid is a Bronsted- Lowry acid.

[0072] Clause 3. The thermal interface material of any of clauses 1-2, wherein the acid comprises at least one of an acid comprising a sulfate group, an acid comprising a nitrate group, an acid comprising a phosphate group, an acid comprising a chloride group, an acid comprising a bromide group, an acid comprising an iodide group, a carboxylic acid, and an acid comprising a sulfonic group.

[0073] Clause 4. The thermal interface material of any of clauses 1-3, wherein the acid comprises at least one of sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, and carboxylic acid.

[0074] Clause 5. The thermal interface material of any of clauses 1-4, wherein the acid is a monoprotic acid.

[0075] Clause 6. The thermal interface material of any of clauses 1-4, wherein the acid is a polyprotic acid.

[0076] Clause 7. The thermal interface material of any of clauses 1-6, wherein a concentration of the functionalizing component on a surface of the liquid metal droplets is in a range of lx 10'6to 5 molecules / nm2.

[0077] Clause 8. The thermal interface material of any of clauses 1-7, wherein the functionalizing component further comprises a coupling agent covalently bonded to the acid.

[0078] Clause 9. The thermal interface material of any of clauses 1-8, wherein the functionalizing component further comprises a polymer chain covalently bonded to the acid.

[0079] Clause 10. The thermal interface material of clause 9, wherein the polymer chain comprises a molecular weight of at least 400 g / mol.

[0080] Clause 11. The thermal interface material of any of clauses 9-10, wherein the polymer chain comprises at least one of an acrylic polymer, an acrylate polymer, a vinyl polymer, a polyester polymer, a polyurethane polymer, a polybutadiene polymer, a polyamide polymer, a polyether polymer, a polysiloxane polymer, a silicon hydride polymer, a fluoropolymer, a polyisoprene polymer, polystyrene polymer, polyepoxide polymer, and a copolymer of any two or more thereof.

[0081] Clause 12. The thermal interface material of any of clauses 1-11, wherein the liquid metal droplets comprise a D90 in a range of 1 micron to 300 microns.

[0082] Clause 13. The thermal interface material of any of clauses 1-12, wherein the liquid metal droplets comprise at least one of gallium, a gallium alloy, indium, an indium alloy, tin, a tin alloy, mercury, and a mercury alloy.

[0083] Clause 14. The thermal interface material of any of clauses 1-13, wherein the metal oxide comprises at least one of gallium oxide, indium oxide, tin oxide, iron oxide, mercury oxide, aluminum oxide, nickel oxide, zinc oxide, and copper oxide.

[0084] Clause 15. The thermal interface material of any of clauses 1-14, wherein the metal oxide comprises gallium oxide, the liquid metal droplets comprise gallium or a gallium alloy, the acid is a carboxylic acid, the functionalizing component further comprises a polymer chain covalently bonded to the carboxylic acid.

[0085] Clause 16. The thermal interface material of any of clauses 1-15, wherein the liquid metal droplets comprise a melting point no greater than 30 degrees Celsius.

[0086] Clause 17. The thermal interface material of any of clauses 1-16, wherein the thermal interface material comprises a first viscosity in a range of 1,000 cP to 850,000 cP measured at 25 °C.

[0087] Clause 18. The thermal interface material of any of clauses 1-17, further comprising at least one of a catalyst, rigid particles, a coupling agent, and fumed silica.

[0088] Clause 19. The thermal interface material of any of clauses 1-18, wherein the liquid metal droplets comprise a contact angle of no greater than 120 degrees.

[0089] Clause 20. A circuit assembly comprising: a first layer; a second layer; and the thermal interface material of any of clauses 1-19 disposed in contact with and between the first layer and the second layer.

[0090] Clause 21. The circuit assembly of clause 20, wherein the liquid metal droplets are generally ellipsoidal.

[0091] Clause 22. The circuit assembly of any of clauses 20-21, wherein a bondline thickness formed between the first layer and the second layer is no greater than 300 microns.

[0092] Clause 23. The circuit assembly of clause 20-22, wherein the first layer comprises at least one of a processor and an integrated heat spreader and the second layer comprises at least one of a heat sink, an integrated heat spreader, and packaging.

[0093] Clause 24. A method comprising: applying the thermal interface material of any of clauses 1-19 on a first layer of an assembly, such that the thermal interface material is in contact with and between the first layer and a second layer of the assembly; and compressing the assembly thereby deforming the liquid metal droplets, wherein a D90 of the liquid metal droplets in the thermal interface material prior to applying is greater than a bondline thickness formed between the first layer and the second layer.

[0094] Clause 25. The method of clause 24, further comprising, after compressing the assembly, curing the thermal interface material thereby forming a cured assembly.

[0095] Clause 26. The method of clause 25, wherein the curing comprises crosslinking the liquid metal droplets into the polymer component using the functionalizing component.

[0096] Clause 27. An assembly produced by the method of any of clauses 24-26.

[0097] Clause 28. A method of manufacture of a thermal interface material, the method comprising: combining a polymer component and liquid metal to form an intermediate mixture; dispersing the liquid metal throughout the polymer component in the intermediatemixture, thereby forming liquid metal droplets having an exterior surface comprising a metal oxide; and forming a functionalizing component bonded to at least a portion of the metal oxide by contacting the metal oxide with an acid.

[0098] Clause 29. The method of clause 28, wherein the acid contacted with the metal oxide after dispersing the liquid metal throughout the polymer component.

[0099] Clause 30. The method of clause 28, wherein the acid is added prior to combining the polymer component and the liquid metal.

[0100] Clause 31. The method of any of clauses 28-30, wherein the functionalizing component further comprises a polymer chain bonded to the acid.

[0101] Clause 32. A method of manufacture of the thermal interface material of any of clauses 1-19, the method comprising: combining the polymer component and liquid metal to form an intermediate mixture; dispersing the liquid metal throughout the polymer component in the intermediate mixture, thereby forming the liquid metal droplets having the exterior surface comprising the metal oxide; and forming the functionalizing component bonded to at least a portion of the metal oxide by contacting the metal oxide with an acid.

[0102] As used herein, “at least one of’ a list of elements means one of the elements or any combination of two or more of the listed elements. As an example “at least of A, B, and C” means A only; B only; C only; A and B; A and C; B and C; or A, B, and C.

[0103] Various features and characteristics are described in this specification to provide an understanding of the composition, structure, production, function, and / or operation of the invention, which includes the disclosed compositions, coatings, and methods. It is understood that the various features and characteristics of the invention described in this specification can be combined in any suitable manner, regardless of whether such features and characteristics are expressly described in combination in this specification. The Inventors and the Applicant expressly intend such combinations of features and characteristics to be included within the scope of the invention described in this specification. As such, the claims can be amended to recite, in any combination, any features and characteristics expressly or inherently described in, or otherwise expressly or inherently supported by, this specification. Furthermore, the Applicant reserves the right to amend the claims to affirmatively disclaim features and characteristics that may be present in the priorart, even if those features and characteristics are not expressly described in this specification. Therefore, any such amendments will not add new matter to the specification or claims and will comply with the written description, sufficiency of description, and added matter requirements.

[0104] Any numerical range recited in this specification describes all sub-ranges of the same numerical precision (z.e., having the same number of specified digits) subsumed within the recited range. For example, a recited range of “1.0 to 10.0” describes all sub-ranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 10.0, such as, for example, “2.4 to 7.6,” even if the range of “2.4 to 7.6” is not expressly recited in the text of the specification. Accordingly, the Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range of the same numerical precision subsumed within the ranges expressly recited in this specification. All such ranges are inherently described in this specification such that amending to expressly recite any such sub-ranges will comply with the written description, sufficiency of description, and added matter requirements.

[0105] Also, unless expressly specified or otherwise required by context, all numerical parameters described in this specification (such as those expressing values, ranges, amounts, percentages, and the like) may be read as if prefaced by the word “about,” even if the word “about” does not expressly appear before a number. Additionally, numerical parameters described in this specification should be construed in light of the number of reported significant digits, numerical precision, and by applying ordinary rounding techniques. It is also understood that numerical parameters described in this specification will necessarily possess the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameters.

[0106] Notwithstanding that numerical ranges and parameters setting forth the broad scope of the invention are approximations, numerical values set forth in the specific examples are reported precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in its respective testing measurements.

[0107] Reference throughout the specification to “various examples,” “some examples,” “ one example,” “an example,” or the like means that a particular feature, structure, orcharacteristic described in connection with the example is included in an example. Thus, appearances of the phrases “in various examples,” “in some examples,” “in one example,” “in an example,” or the like, in places throughout the specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in an example or examples. Thus, the particular features, structures, or characteristics illustrated or described in connection with one example may be combined, in whole or in part, with the features, structures, or characteristics of another example or other examples without limitation. Such modifications and variations are intended to be included within the scope of the present examples.

[0108] Any patent, publication, or other document identified in this specification is incorporated by reference into this specification in its entirety unless otherwise indicated but only to the extent that the incorporated material does not conflict with existing descriptions, definitions, statements, illustrations, or other disclosure material expressly set forth in this specification. As such, and to the extent necessary, the express disclosure as set forth in this specification supersedes any conflicting material incorporated by reference. Any material, or portion thereof, that is incorporated by reference into this specification, but which conflicts with existing definitions, statements, or other disclosure material set forth herein, is only incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material. Applicant reserves the right to amend this specification to expressly recite any subject matter, or portion thereof, incorporated by reference. The amendment of this specification to add such incorporated subject matter will comply with the written description, sufficiency of description, and added matter requirements.

[0109] Whereas particular examples of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

[0110] While the present disclosure provides descriptions of various specific aspects for the purpose of illustrating various aspects of the present disclosure and / or its potential applications, it is understood that variations and modifications will occur to those skilled in the art. Accordingly, the invention or inventions described herein should be understood to be at least as broad as they are claimed and not as more narrowly defined by particular illustrative aspects provided herein.

[0111] It is understood that the inventions described in this specification are not limited to the examples summarized in the Summary or Detailed Description. Various other aspects are described and exemplified herein.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A thermal interface material comprising: a polymer component; and liquid metal droplets dispersed throughout the polymer component, wherein at least a portion of the liquid metal droplets comprise an exterior surface comprising a metal oxide; and a functionalizing component bonded to at least a portion of the metal oxide by an acid.

2. The thermal interface material of claim 1, wherein the acid is a Bronsted-Lowry acid.

3. The thermal interface material of claim 1, wherein the acid comprises at least one of an acid comprising a sulfate group, an acid comprising a nitrate group, an acid comprising a phosphate group, an acid comprising a chloride group, an acid comprising a bromide group, an acid comprising an iodide group, a carboxylic acid, and an acid comprising a sulfonic group.

4. The thermal interface material of claim 1, wherein the acid comprises at least one of sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, and carboxylic acid.

5. The thermal interface material of claim 1, wherein the acid is a monoprotic acid.

6. The thermal interface material of claim 1, wherein the acid is a polyprotic acid.

7. The thermal interface material of claim 1, wherein a concentration of the functionalizing component on a surface of the liquid metal droplets is in a range of lx 10'6to 5 molecules / nm2.

8. The thermal interface material of claim 1, wherein the functionalizing component further comprises a coupling agent covalently bonded to the acid.

9. The thermal interface material of claim 1, wherein the functionalizing component further comprises a polymer chain covalently bonded to the acid.

10. The thermal interface material of claim 9, wherein the polymer chain comprises a molecular weight of at least 400 g / mol.

11. The thermal interface material of claim 9, wherein the polymer chain comprises at least one of an acrylic polymer, an acrylate polymer, a vinyl polymer, a polyester polymer, a polyurethane polymer, a polybutadiene polymer, a polyamide polymer, a polyether polymer, a polysiloxane polymer, a silicon hydride polymer, a fluoropolymer, a polyisoprene polymer, polystyrene polymer, polyepoxide polymer, and a copolymer of any two or more thereof.

12. The thermal interface material of claim 1, wherein the liquid metal droplets comprise a D90 in a range of 1 micron to 300 microns.

13. The thermal interface material of claim 1, wherein the liquid metal droplets comprise at least one of gallium, a gallium alloy, indium, an indium alloy, tin, a tin alloy, mercury, and a mercury alloy.

14. The thermal interface material of claim 1, wherein the metal oxide comprises at least one of gallium oxide, indium oxide, tin oxide, iron oxide, mercury oxide, aluminum oxide, nickel oxide, zinc oxide, and copper oxide.

15. The thermal interface material of claim 1, wherein the metal oxide comprises gallium oxide, the liquid metal droplets comprise gallium or a gallium alloy, the acid is a carboxylic acid, the functionalizing component further comprises a polymer chain covalently bonded to the carboxylic acid.

16. The thermal interface material of claim 1, wherein the liquid metal droplets comprise a melting point no greater than 30 degrees Celsius.

17. The thermal interface material of claim 1, wherein the thermal interface material comprises a first viscosity in a range of 1,000 cP to 850,000 cP measured at 25 °C.

18. The thermal interface material of claim 1, further comprising at least one of a catalyst, rigid particles, a coupling agent, and fumed silica.

19. The thermal interface material of claim 1, wherein the liquid metal droplets comprise a contact angle of no greater than 120 degrees.

20. An assembly comprising: a first layer; a second layer; and the thermal interface material of claim 1 disposed in contact with and between the first layer and the second layer.

21. The assembly of claim 20, wherein the liquid metal droplets are generally ellipsoidal.

22. The assembly of claim 20, wherein a bondline thickness formed between the first layer and the second layer is no greater than 300 microns.

23. The assembly of claim 20, wherein the first layer comprises at least one of a processor and an integrated heat spreader and the second layer comprises at least one of a heat sink, an integrated heat spreader, and packaging.

24. A method comprising: applying the thermal interface material of claim 1 on a first layer of an assembly, such that the thermal interface material is in contact with and between the first layer and a second layer of the assembly; and compressing the assembly thereby deforming the liquid metal droplets, wherein a D90 of the liquid metal droplets in the thermal interface material prior to applying is greater than a bondline thickness formed between the first layer and the second layer.

25. The method of claim 24, further comprising, after compressing the assembly, curing the thermal interface material thereby forming a cured assembly.

26. The method of claim 25, wherein the curing comprises crosslinking the liquid metal droplets into the polymer component using the functionalizing component.

27. An assembly produced by the method of claim 24.

28. A method of manufacture of a thermal interface material, the method comprising: combining a polymer component and liquid metal to form an intermediate mixture;dispersing the liquid metal throughout the polymer component in the intermediate mixture, thereby forming liquid metal droplets having an exterior surface comprising a metal oxide; and forming a functionalizing component bonded to at least a portion of the metal oxide by contacting the metal oxide with an acid.

29. The method of claim 28, wherein the acid contacted with the metal oxide after dispersing the liquid metal throughout the polymer component.

30. The method of claim 28, wherein the acid is added prior to combining the polymer component and the liquid metal.

31. The method of claim 28, wherein the functionalizing component further comprises a polymer chain bonded to the acid.

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