Thermal interface materials

Abstract

A thermal interface material includes a matrix material; and a thermally conductive filler dispersed in the matrix material, the thermally conductive filler constituting 50 vol% to 90 vol% of the thermal interface material; wherein the thermally conductive filler includes first particles, each of the first particles including a mineral mixture having a first component and a second component different from the first component, the first component including at least one aluminum-containing compound selected from aluminum oxide, aluminum hydroxide, and aluminum trihydrate; wherein an average weight percentage of the first component in each the first particles ranges from 20 wt.% to 95 wt.%; and the first particles contain less than 14 wt.% iron oxide.

Description

2025P00021THERMAL INTERFACE MATERIALSFIELD

[0001] Provided herein are thermal interface materials generally, and more particularly dispensable thermal interface materials and methods for manufacturing such thermally conductive constructs.BACKGROUND

[0002] Thermally conductive interface materials are widely employed for the purpose of dissipating heat from heat-generating components such as semiconductor elements, power transistors, integrated circuits, and battery elements. Thermally conductive greases, gels, pastes, and sheets have been used as interfaces between the heat-generating components and heat-dissipating elements such as plates and fins. Numerous designs and materials for such thermal interfaces have been implemented, with the highest performance being achieved when gaps between the thermal interface and the respective heat transfer surfaces are substantially avoided to promote conductive heat transfer from the electronic component to the heat dissipater. The thermal interface materials therefore preferably mechanically conform to the somewhat uneven heat transfer surfaces of the respective components. Therefore, important physical characteristics of high-performance thermal interface materials can include flexibility, dispensability, and low hardness.

[0003] In the case of dispensable materials, it is additionally important that the thermal interface is capable of wetting the heat transfer surface, and that the material provides suitable adhesive and cohesive strength to avoid delamination and to maintain the form and function of the interface over the anticipated working lifetime. Dispensable thermal interface materials therefore may be designed with a yield stress to avoid significant spreading after dispensation, or without a yield stress to maximally flow and penetrate surfaces. For thermal gap fillers, there is a demand for high dispensability to minimize process time in high volume applications. However, high dispense rates are often contrary to other important characteristics such as storage stability, limiting shelf life, and stability after dispensing.2025P00021

[0004] Thermal conductivity is an important property of thermal interface materials used for various applications, such as semiconductor elements, power transistors, integrated circuits, and battery elements. To promote increased thermal conductivity values, particulate fillers have been added to thermal interface materials. While these particulate fillers can increase thermal conductivity, high thermal conductivity particulate fillers are expensive and can adversely affect flowability / dispensability and / or mechanical characteristics. Further, conventional, high thermal conductivity particulate fillers are generally formed by extensive refinement processes, increasing the cost and carbon footprint of the overall thermal interface material. For example, extensive refinement processes to form substantially pure aluminum oxide can require chemical reactions with sodium hydroxide, filtering, precipitation, and calcination. It is an object of the present disclosure to provide thermal interface materials using a thermally conductive filler exhibiting a reduced carbon footprint, while promoting desirable thermal conductivity and / or dispensability characteristics.SUMMARY

[0005] According to one aspect, a thermal interface material includes a matrix material; and a thermally conductive filler dispersed in the matrix material, the thermally conductive filler constituting 50 vol% to 90 vol% of the thermal interface material; wherein the thermally conductive filler includes first particles, each of the first particles including a mineral mixture having a first component and a second component different from the first component, the first component including at least one aluminum-containing compound selected from aluminum oxide, aluminum hydroxide, and aluminum trihydrate; wherein an average weight percentage of the first component in each the first particles ranges from 20 wt.% to 95 wt.%; and the first particles contain less than 14 wt.% iron oxide.

[0006] According to another aspect, a thermal interface material includes a matrix material; and a thermally conductive filler dispersed in the matrix material and including first particles, the first particles including at least one of sintered bauxite and calcined bauxite, wherein the first particles have a first mean particle size (dso) of less than 752025P00021 pm, wherein the thermal interface material exhibits a thermal conductivity of at least 0.5 W / m*K.

[0007] According to another aspect, a thermally conductive curable composition includes a first resin including an epoxy resin; a second resin; and a thermally conductive filler including first particles, each of the first particles including a mineral mixture having a first component and a second component, the first component including at least one aluminum-containing compound selected from aluminum oxide, aluminum hydroxide, and aluminum trihydrate; where an average weight percentage of the first component in the first particles ranges from 20 wt.% to 95 wt.% of a total weight of the first particles, wherein a concentration of the first particles to total parts of the first resin and the second resin ranges from about 300 parts per hundred resin (phr) to about 1500 parts per hundred resin (phr).BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 illustrates voltage breakdown performance over time, comparing aluminum trihydrate (ATH) particulate filler to bauxite particulate filler in thermal interface materials, according to some embodiments.

[0009] FIG. 2 illustrates lap shear strength over time, comparing aluminum trihydrate (ATH) particulate filler to bauxite particulate filler in thermal interface materials, according to some embodiments.DETAILED DESCRIPTION

[0010] Embodiments of the present disclosure provide thermal interface materials and methods of forming these thermal interface materials. Thermal interface materials can be utilized for various heat dissipation applications, such as for central processing units (CPUs), graphics processing units (GPUs), and multichip modules. The thermal interface materials of the present disclosure generally include a matrix material and a thermally conductive filler. Thermal interface materials of the present disclosure utilize a thermally conductive filler having a reduced carbon and / or energy footprint compared to conventional thermally conductive fillers, while promoting a desirable overall thermal conductivity to the thermal interface material. Thermally conductive fillers of the present2025P00021 disclosure can include minimally processed thermally conductive filler particles (e.g., processing to form desirable particle sizes), reducing or replacing the use of conventional thermally conductive fillers formed using extensive refinement processes, such as processes requiring chemical reactions and precipitation.

[0011] Matrix materials can include polymers that may be blended with one or more components of the present disclosure to form the thermal interface material. The matrix material may act as a binder to hold the composition together and to prevent outflow in operation. In one example, the matrix material includes a material capable of holding and / or at least partially surrounding a dispersed material (e.g., thermally conductive filler). The matrix material can include an organic material.

[0012] In one example, the matrix material includes a matrix material that has been chemically crosslinked. For example, the matrix material can include a polymer matrix (such as including an organopolysiloxane matrix material). The matrix material can be formed from at least a curable component and a chemical cure activator. A cure reaction can initiated with exposure between the curable component and the cure activator, in some cases when in the presence of an environmental cure reaction facilitator, such as water, heat, pressure, electromagnetic radiation, and the like. For the purposes hereof, the presence of an environmental cure reaction facilitator is assumed if necessary to the cure reaction initiated with exposure between the curable component and the cure activator. The cure activator therefore promotes a cure reaction involving the curable component.

[0013] In some embodiments, the curable component may include a monomer, oligomer, or a polymer that is capable of undergoing a cross-linking reaction to form a network. The chemical cure activator is preferably an agent that is initially separated from the curable component to avoid a cure reaction, and subsequently introduced to the curable component when the cure reaction is desired. In some embodiments, the cure activator includes a cross-linking agent. The cure activator may also or instead include a monomer, an oligomer, a polymer, a reaction initiator, a catalyst, and combinations thereof. The curable component may include a first resin, and the cure activator may include a second resin that is reactive with the first resin. In some2025P00021 embodiments, the matrix material may include an organic matrix including at least one of a thermoplastic resin and / or a thermoset resin.

[0014] The curable system of the curable component and the chemical cure activator may be selected from a wide variety of monomers, oligomers, and resins, wherein the term “resin” may include any natural or synthetic organic compound or mixture that is convertible into a polymer. An example cure reaction suitable for the curable systems of the present invention is hydrosilylation from vinyl and hydride functional silicone resins. The vinyl silicone resin can include vinyl dimethicone or vinyl phenyl methyl dimethicone, linear and / or branched, and can contain mono, dual, or multi-vinyl functionalities. An example silicone may be an organosiloxane having the structural formula:CH3CH3CH3wherein “x” represents an integer ranging from between 1 and 1,000. An example vinyl silicone resin is shown having the structural formula:CH, CH,CH, - CH - Si — f-0 - Si-) — f- O - Si -) - [-0 - Si-) — O - Si - CH CH-where n, m, and p are 1 or greater. In one example, in the vinyl silicone resin, the phenyl content can be less than about 25 mol%. In another example, for the vinyl silicone resin, the viscosity is less than about 1000 mPa-s, where viscosity values can be calculated at about 20 °C and at a shear rate of 1 / s. In another example, for the vinyl silicone resin, the viscosity is less than about 800 mPa-s, where viscosity values can be calculated at about 20 °C and at a shear rate of 1 / s.

[0015] The thermally conductive interface material may be prepared as a reaction product of the organosiloxane together with a chain extender / cross-linker such as a hydride functional polydimethylsiloxane. The hydride functional polydimethylsiloxane can be a Hydride Dimethicone or Hydride Phenyl Methyl Dimethicone, linear and / or2025P00021 branched, and can contain Mono, Dual or multi-Hydride functionalities. An example of a hydride functional polydimethylsiloxane has the structural formula:CH3( H, “ CH, ' CH-Si-O- — Si —I CH3CH.3 IIX y CHwherein “x” and “y” each represent an integer having a value of between 1 and 1 ,000. An example hydride silicone resin is shown having the structural formula:CH3CH3CH3CH3H - Si — O - Si -J — f- O - Si — O - Si - HI I n I ni Iwhere n and m are 1 or greater. In one example, in the hydride silicone resin, the phenyl content can be less than about 25 mol%. In another example, for the hydride silicone resin, the viscosity is less than about 1000 mPa-s, where viscosity values can be calculated at about 20 °C and at a shear rate of 1 / s. In another example, for the hydride silicone resin, the viscosity is less than about 800 mPa-s, where viscosity values can be calculated at about 20 °C and at a shear rate of 1 / s.

[0016] An example curable component of the present invention includes polydiorganosiloxanes, such as various vinyl or siloxy-terminated polydimethylsiloxanes (PDMS). Example commercially available PDMS materials include Nusil PLY-7500 and 7905 available from Avantor, Inc.; Evonik VS 100, 200, 500, 10000, 20000, and 65000 available from Evonik Industries AG; and Gelest DMS-V21, V22, V41, V42, and V43 available from Gelest, Inc. The curable component may include one or more polymers that differ in, for example, molecular weight, viscosity, and molecular structure. For example, vinyl-terminated PDMS with viscosity values ranging from about 50 mPa-s to about 1000 mPa-s may be utilized. These viscosity values can be calculated at about 20 °C. Viscosity values may be measured at a shear rate of 1 / s.

[0017] The chemical cure activator may itself be reactive with the curable component and may include a cross-linker for a hydrosilylation reaction. The chemical2025P00021 cure activator may include a dihydroxy aliphatic chain extender such as a hydride- terminated polydimethylsiloxane. The silicon-bonded hydrogen atoms may be located at terminal, pendant, or at both terminal and pendant positions. The chemical cure activator may include one or more organohydrogen polysiloxanes that may differ in at least one of molecular weight, viscosity, and molecular structure. Example commercially available methylhydropolydimethylsiloxanes useful as a chemical cure activator that is reactive with the first reactant composition include Nusil XL-112 and XL-7505 available from Avantor, Inc.; Gelest HMS-071, 082, and 991 available from Gelest, Inc.; and Andisil XL-1B and 1340 available from AB Specialty Silicones.

[0018] A variety of silane or silanol terminated resins may be employed in the matrices of the present invention. Condensation-curable silane- or silanol-terminated resins participate in a hydrolysis-condensation cure pathway, preferably at and above ambient temperatures. In some embodiments, the resins are non-silicone, wherein no more than a trace amount of silicone is contained in the composition. In some embodiments, no silicone is contained in the composition. Example resins suitable for the curable component of the present disclosure include reactive polymer resins with at least one silyl-reactive functional group, including at least one bond that may be activated with water. Example silyl-reactive functional groups include alkoxy silane, acetoxy silane, and ketoxime silane.

[0019] The matrix material can be formed using at least one of a first resin and a second resin. The first resin can include an epoxy resin. The first resin generally has a viscosity of less than 100000 mPa*s at 25°C and 1 s'1. In one example, the first resin has a viscosity of less than 10000 mPa*s at 25°C and 1 s'1. In another example, the first resin includes a diglycidyl ether of bisphenol F resin. The second resin can include a dimer diamine. The second resin generally has a viscosity of less than 100000 mPa*s at 25°C and 1 s-1. In one example, the second resin has a viscosity of less than 10000 mPa*s at 25°C and 1 s'1. A diglycidyl ether of bisphenol F resin and a dimer diamine can form an amine cured matrix material. In one non-limiting example, the diglycidyl ether of bisphenol F resin and a dimer diamine can be cured without the addition of a catalyst. In one non-limiting example, performing curing without the need for a catalyst can be a beneficial combination with thermally conductive fillers of the present2025P00021 disclosure, since certain fillers may cause catalyst deactivation. In one example, the first resin includes EPON™ Resin 862. In another example, the second resin includes Priamine™ 1074.

[0020] The first resin can include a polyepoxide resin. The polyepoxide resin can have a viscosity of less than 1000 mPa*s at 25 °C, using ASTM D445. The polyepoxide resin can have a viscosity of less than 600 mPa*s at 25 °C, using ASTM D445. The second resin can include an aromatic monoepoxide, such as a o-cresyl glycidyl ether resin. The o-cresyl glycidyl ether resin can have a viscosity of less than 100 mPa*s at 25°C, using ASTM D445. The o-cresyl glycidyl ether resin can have a viscosity of less than 20 mPa*s at 25°C, using ASTM D445. A weight ratio of the polyepoxide resin to the o-cresyl glycidyl ether resin can range from about 2:1 to about 6:1. In one example, the weight ratio of the polyepoxide resin to the o-cresyl glycidyl ether resin ranges from about 3:1 to about 5:1. In another example, the weight ratio of the polyepoxide resin to the o-cresyl glycidyl ether resin is about 4:1. The first resin and second resin can be mixed with a phenalkamine curing agent. The first resin and second resin can be mixed without a dispersant.

[0021] The matrix material can include one or more silyl modified polymers (SMP). Silyl modified polymers, also referred to as silane modified polymer or silyl terminated polymer, include a polymer backbone which is terminated by silane groups. The silane groups can be independent or supported by urethane groups. Silyl modified polymers can combine one or more properties of silicones and one or more properties of polyurethanes. One example of a silyl modified polymer is silyl terminated polyether.

[0022] In some embodiments, the cure activator may include a catalyst, such as a reaction catalyst. A reaction catalyst may, for example, be employed to further facilitate the hydrosilylation reactions described above. Example reaction catalysts useful in the compositions of the present invention include platinum compounds, and organotin and organo-zinc and organo-titanium compounds (together referred to herein as “organo-metal catalyst”) that facilitate moisture cure of the silyl-modified reactive resins. In one example, the catalyst includes a Karstedt catalyst. For example, the Karstedt catalyst includes an organoplatinum compound derived from divinyl-containing disiloxane.Reaction catalysts used in the compositions of the present invention may be present in2025P00021 the range of 0 up to 0.5 percent by weight. In some embodiments, the compositions comprise in the range of 0.01 up to 0.5 percent by weight reaction catalyst.

[0023] The curable component of the present disclosure may be curable in the presence of water (moisture curable) at ambient temperature. Depending upon the application, the moisture may be available from the ambient environment or from water released from the object(s) to which the composition is applied. In some embodiments, the compositions of the invention are curable without addition of environmental moisture. In some embodiments, water may be included as an ingredient in a non-resin part of the multiple part curable composition, for mixture with the reactive constituents in situ. Preferably, however, the amount of water required in the composition itself is minor so as not to interfere with functional properties of the thermal material. In some embodiments, water is present in the compositions of the invention in the range of 0 up to 0.5 wt.%. In some embodiments, the compositions comprise in the range of 0.01 up to 0.3 wt.% water. In some embodiments, the compositions comprise in the range of 0.01 up to 0.2 wt.% water.

[0024] The thermal interface material, or pre-cured material, can include additives such as a reaction inhibitor. Reaction inhibitors can include substances that adjust the rate of a chemical reaction or stop the chemical reaction. In one example, the reaction inhibitor of the present disclosure can adjust cure rate of vinyl and hydride functional silicone systems that cure via hydrosilylation. Various reaction inhibitors may be utilized for the thermal interface materials of the present disclosure. In one example, the reaction inhibitor includes silicon. In one non-limiting example, the reaction inhibitor includes methylvinyl cyclic inhibitors. For example, the reaction inhibitor can include 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl-cyclotetrasiloxane. The thermal interface material may further include antioxidants.

[0025] In order to provide desired thermal conductivity properties to the interfaces of the present invention, thermally conductive filler is preferably dispersed in the matrix material to form the thermal interface material. The matrix material can be formed by curing one or more resins. In another example, the thermally conductive filler is dispersed / mixed with one or more components used for a cure reaction. The thermally2025P00021 conductive filler can include a plurality of particulate filler particles including first particles, second particles, and / or third particles.

[0026] The first particles may provide the primary mechanism for heat transfer. In one example, the first particles include a thermally conductive material having a thermal conductivity value greater than about 2 W / m*K, greater than about 2.5 W / m*K, or greater than about 2.7 W / m*K. In one example, compared to quartz (~1 W / m*K) and calcium carbonate (~ 2.5 W / m*K), the first particles can include a thermally conductive material having a thermal conductivity of greater than about 2.7 W / m*K, promoting desirable overall thermal conductivity to the thermal interface material. In another example, the first particles include a thermally conductive material having a thermal conductivity value greater than about 3 W / m*K, greater than about 5 W / m*K, or greater than about 10 W / m*K.

[0027] Each of the first particles includes a mineral mixture. The mineral mixture includes a naturally occurring, inorganic solid having a mixture of multiple components (e.g., elements and / or compounds). The mineral mixture includes a first component and a second component different from the first component. The first component includes at least one aluminum-containing compound. The at least one aluminum-containing compound can be selected from aluminum oxide, aluminum hydroxide, aluminum oxide hydroxide, and aluminum trihydrate. In one example, the first component includes two or more of aluminum oxide, aluminum hydroxide, and aluminum trihydrate. In another example, the first component is aluminum oxide (e.g., AI2O3).

[0028] An average weight percentage of the first component in each the first particles is generally greater than about 20 wt.%. In one example, the average weight percentage of the first component in each the first particles is greater than about 22 wt.%. In another example, the average weight percentage of the first component in each the first particles is greater than about 25 wt.%. In another example, the average weight percentage of the first component in each the first particles is greater than about 30 wt.%. In another example, the average weight percentage of the first component in each the first particles is greater than about 23 wt.%, greater than about 27 wt.%, greater than about 40 wt.%, greater than about 50 wt.%, greater than about 60 wt.%, greater than about 70 wt.%, or values therebetween.2025P00021

[0029] An average weight percentage of the first component in each the first particles is generally less than about 99 wt.%. In one example, the average weight percentage of the first component in each the first particles is less than about 95 wt.%. In another example, the average weight percentage of the first component in each the first particles is less than about 90 wt.%. In another example, the average weight percentage of the first component in each the first particles is less than about 85 wt.%. In another example, the average weight percentage of the first component in each the first particles is less than about 98 wt.%, less than about 96 wt.%, less than about 94 wt.%, less than about 92 wt.%, less than about 88 wt.%, less than about 86 wt.%, or values therebetween.

[0030] An average weight percentage of the first component in each the first particles can range from about 15 wt.% to 99 wt.%. In one example, an average weight percentage of the first component in each the first particles ranges from about 20 wt.% to 99 wt.%. In another example, an average weight percentage of the first component in each the first particles ranges from about 20 wt.% to 95 wt.%. In another example, an average weight percentage of the first component in each the first particles ranges from about 25 wt.% to 95 wt.%. In another example, an average weight percentage of the first component in each the first particles ranges from about 30 wt.% to 90 wt.%. In another example, an average weight percentage of the first component in each the first particles ranges from about 50 wt.% to 90 wt.%.

[0031] The first particles can include at least 12 wt.% aluminum, based on elemental analysis. An average weight percentage of aluminum oxide in each the first particles can be greater than about 20 wt.%. In one example, the average weight percentage of aluminum oxide in each the first particles is greater than about 25 wt.%. In another example, the average weight percentage of aluminum oxide in each the first particles is greater than about 30 wt.%. In another example, the average weight percentage of aluminum oxide in each the first particles is greater than about 50 wt.%. In another example, the average weight percentage of aluminum oxide in each the first particles is greater than about 60 wt.%, greater than about 70 wt.%, greater than about 80 wt.%, greater than about 85 wt.%, or values therebetween. For example, and in comparison, compared to a particulate filler having less than 20 wt.% aluminum oxide2025P00021 (e.g., granite powder or basalt powder) or no aluminum oxide (such as calcium carbonate or silica), the first particles of the present disclosure promote a desirable overall thermal conductivity of the thermal interface material.

[0032] An average weight percentage of aluminum oxide in each the first particles can range from about 20 wt.% to 95 wt.%. In one example, an average weight percentage of aluminum oxide in each the first particles ranges from about 25 wt.% to 90 wt.%. In another example, an average weight percentage of aluminum oxide in each the first particles ranges from about 30 wt.% to 90 wt.%. In another example, an average weight percentage of aluminum oxide in each the first particles ranges from about 50 wt.% to 90 wt.%. For example, and in comparison, a refined aluminum oxide particulate filler typically contains at least 99 wt.%, at least 99.25 wt.%, or at least 99.5 wt.% aluminum oxide. The first particles of the present disclosure including the mineral mixture can promote desirable thermal conductivity to the thermal interface material, without requiring the extensive processing or refining of a conventional, refined aluminum oxide or aluminum trihydrate particulate filler.

[0033] In one example, the first particles have a first mean particle size (dso) of greater than about 0.1 pm. For the purposes hereof, the term “mean particle size” refers to a cumulative weight average value (dso) in which 50% of the particles are larger than the value, and 50% of the particles are smaller than the value, such as determined by laser light diffraction. In another example, the first particles have a first mean particle size (dso) of greater than about 1 pm. In another example, the first particles have a first mean particle size (dso) of greater than about 2 pm. In one example, the first particles have a first mean particle size (dso) of between about 2 pm and about 100 pm. In another example, the first particles have a first mean particle size (dso) of between about 5 pm and about 80 pm. In yet another example, the first particles have a first mean particle size (dso) of between about 5 pm and about 60 pm, or 5 pm and about 30 pm. In one non-limiting example, the first particles have a first mean particle size (dso) of less than 500 pm or less than 100 pm. In another non-limiting example, the first particles have a first mean particle size (dso) of less than 75 pm. Utilizing a first mean particle size (dso) of less than 75 pm can decrease the overall bondline thickness of the2025P00021 assembled component, promoting desirable thermal impedance and overall heat transfer efficiency of the assembled component.

[0034] The first mean particle size (dso) can be the largest mean particle size of all particles within the filler component. For example, first mean particle sizes (dso), such as a first mean particle size (dso) of between about 5 pm and about 75 pm, promotes a desirable thermal conductivity value to the thermal interface material while providing an efficient balance of dispensability and dispersion viscosity. Compared to materials only having fillers exhibiting particle sizes below about 5 pm, the present materials exhibit greater thermal conductivity values and improved dispensability.

[0035] The concentration of the first particles with respect to resin used to form the matrix material can be greater than about 250 phr. In one example, the concentration of the first particles with respect to resin used to form the matrix material is greater than about 300 phr. For example, and in comparison, using a concentration of first particles of less than 300 phr may decrease the overall thermal conductivity of the thermal interface material to undesirable values, such as less than 1 W / m*K. Concentration values of the first particles can promote a desirable thermal conductivity value to the thermal interface material while providing an efficient balance of dispensability and low shear viscosity.

[0036] The concentration of the first particles with respect to resin used to form the matrix material can range from about 200 parts per hundred resin (phr) to about 2000 phr. In one example, the concentration of the first particles with respect to resin used to form the matrix material ranges from about 300 phr to about 1500 phr. In one nonlimiting example, utilizing a concentration of the first particles with respect to resin used to form the matrix of less than 1500 phr promotes an efficient balance of dispensability and viscosity. In another example, the concentration of the first particles with respect to resin used to form the matrix material ranges from about 300 phr to about 1100 phr.

[0037] The first particles may have an aspect ratio ranging from about 0.5 to about 1.5. The aspect ratio may be defined as the ratio of the length to the width of the individual particle. In one example, the first particles include substantially spherical particles. Substantially spherical first particles may have an aspect ratio of between 0.8 - 1.2. Utilizing substantially spherical first particles can enable a higher loading of2025P00021 thermally conductive filler while maintaining the viscosity at a desirable value. Utilizing a higher loading of thermally conductive filler promotes a higher thermal conductivity of the overall thermal interface material. The shape of the thermally conductive filler may be spherical, aspherical, and combinations thereof. Example aspherical shapes include flake-like, plate-like, rod-like, and so on.

[0038] The second component is different from the first component. For example, the second component can include one or more compounds with a distinct chemical structure / formula compared to the first component. The second component may exhibit different properties, such as variation in thermal conductivity from the first component. The second component can include at least one of: one or more aluminum minerals (e.g., AIO(OH)), one or more iron oxides (e.g., FezOa, FeO(OH)), one or more silicon compounds (e.g., SiOz), one or more titanium compounds (e.g., TiOz), and one or more calcium compounds (CaCC ). In one example, the second component includes at least one of iron oxide FezCh, silicon dioxide SiOz, and titanium oxide TiOz. In another example, the second component includes two or more of iron oxide FezC , silicon dioxide SiOz, and titanium oxide TiOz. The weight percentage of iron oxide FezC in the first particles can be less than 14 wt.% (e.g., 0 wt.% to 13.9 wt.%). The weight percentage of iron oxide FezC in the first particles can be less than about 5 wt.%. The weight percentage of iron oxide FezC in the first particles can be less than about 2 wt.%. The weight percentage of silicon dioxide SiOz in the first particles can be less than 14 wt.%. The weight percentage of silicon dioxide SiOz in the first particles can be less than about 10 wt.%.

[0039] The mineral mixture can include at least one of bauxite and gibbsite. In one example, the mineral mixture includes bauxite. Bauxite can include at least one of raw ground bauxite, sintered bauxite, and calcined bauxite. Raw ground bauxite can include bauxite-containing particles that have been lightly refined to decrease particle size. Sintered bauxite can be formed by utilizing heat and / or pressure sufficient to form a solid mass of material from bauxite ore, typically without melting the material. Calcined bauxite can be formed by heating bauxite-containing materials to high temperatures (e.g., greater than 1500 °C) sufficient to reduce impurities. Calcined bauxite can be produced using rotary kilns or shaft kilns. Bauxite of the present disclosure (such as2025P00021 sintered and calcined bauxite) can include aluminum oxide (AI2O3), iron oxide (Fe2O3), and silicon dioxide (SiC ). In one example, bauxite of the present disclosure includes aluminum oxide (AI2O3) at 60 wt.% to 95 wt.%, iron oxide (Fe2Os) at 0.5 wt.% to 14 wt.%, and silicon dioxide (SiC ) at 3 wt.% to 14 wt.%. In another example, first particles of the present disclosure can be substantially free of iron oxide. The bauxite can include refinery grade bauxite. Highly refined aluminum oxide has been used as thermally conductive fillers for thermal interface materials. For example, extensive refinement processes to form substantially pure aluminum oxide can require chemical reactions with sodium hydroxide, filtering, precipitation, and calcination. Importantly, the mineral mixture of the present disclosure can be utilized to efficiently reduce, or replace, the use of highly refined aluminum oxide to reduce cost and the carbon footprint of the thermal interface material, while maintaining desirable thermal conductivity and dispensability of the overall thermal interface material.

[0040] The second particles can include one or more thermally conductive filler materials of the present disclosure. The thermally conductive fillers contemplated for use as second particles include metals, metal oxides, carbon, ceramics, and combinations thereof. Example conductive fillers used in / as second particles include calcium carbonate, boron nitride, aluminum nitride, alumina, alumina trihydrate, silicon, silicon carbide, graphite, diamond, magnesium oxide, magnesium hydroxide, zinc oxide, gold, silver, copper, platinum, palladium, nickel, aluminum, indium, alloy of nickel (e.g., alloy 42), alloy of zinc, alloy of iron, alloy of indium, silver-plated copper, silver-plated aluminum, bismuth, tin, bismuth-tin alloy, silver-plated fiber, silver-plated graphite, silver-plated silicon carbide, silver-plated boron nitride, silver-plated diamond, silver-plated alumina, silver-plated alloy 42, graphene, silver-plated graphene, silver-coated polymer, cadmium and alloys of cadmium, lead and alloys of lead, antimony and alloys of antimony, and the like, as well as mixtures of any two or more thereof.

[0041] The second particles can include one or more components used for the first particles. Each of the second particles can include a mineral mixture of the present disclosure having a first component of the present disclosure and a second component of the present disclosure. In one example, the second particles include bauxite. In2025P00021 another example, the second particles include at least one of calcined aluminum oxide and aluminum trihydrate.

[0042] The second particles can have a second mean particle size (dso) of greater than about 0.05 pm. In another example, the second particles have a second mean particle size (dso) of greater than about 1 pm. In another example, the second particles have a second mean particle size (dso) of greater than about 2 pm. In one example, the second particles have a second mean particle size (dso) of between about 3 pm and about 20 pm. In another example, the second particles have a second mean particle size (dso) of between about 5 pm and about 12 pm. In yet another example, the second particles have a second mean particle size (dso) of between about 7 pm and about 12 pm. In one non-limiting example, the second particles have a second mean particle size (dso) of less than 20 pm or less than 15 pm. In another non-limiting example, the second particles have a second mean particle size (dso) of less than the first mean particle size (dso).

[0043] The second particles may have an aspect ratio ranging from about 0.5 to about 1.5. The aspect ratio may be defined as the ratio of the length to the width of the individual particle. In one example, the second particles include substantially spherical particles. Spherical thermally conductive filler may have an aspect ratio of between 0.8-1.2. Spherical thermally conductive filler can be useful for greater thermally conductive filler loading and overall thermal conductivity while minimizing the increase in viscosity. Minimizing the increase of viscosity can be particularly important for dispensable materials. The shape of the thermally conductive filler may be spherical, aspherical, and combinations thereof. Example aspherical shapes include flake-like, plate-like, rod-like, and so on.

[0044] The thermally conductive filler can include third particles. The third particles can include one or more thermally conductive fillers of the present disclosure. The third particles can have a third mean particle size (dso) of greater than about 0.01 pm. In another example, the third particles have a third mean particle size (dso) of greater than about 0.05 pm. In another example, the third particles have a third mean particle size (dso) of greater than about 1 pm. In one example, the third particles have a third mean particle size (dso) of between about 0.1 pm and about 5 pm. In another example, the2025P00021 third particles have a third mean particle size (dso) of between about 0.1 pm and about 3 pm. In yet another example, the third particles have a third mean particle size (dso) of between about 1 pm and about 3 pm. In one non-limiting example, the third particles have a third mean particle size (dso) of less than 5 pm or less than 3 pm. In another non-limiting example, the third particles have a third mean particle size (dso) of less than the second mean particle size (dso).

[0045] The thermally conductive filler can include a bimodal distribution of first particles and second particles, or a trimodal distribution of first particles, second particles, and third particles. Accordingly, the thermally conductive filler can include a trimodal distribution of bauxite-containing particles. In one non-limiting example, the thermally conductive filler can include bauxite-containing particles having a first mean particle size (dso) between 20 pm and 75 pm, a second mean particle size (dso) between 5 pm and 20 pm, and a third mean particle size (dso) between 0.5 pm and 5 pm. The particles in each set of particle sizes can be independently selected forms of bauxite, such as sintered bauxite and calcined bauxite. For example, utilizing a trimodal distribution can allow for utilization of a greater amount of thermally conductive filler while maintaining a desirable dispersion viscosity.

[0046] The thermally conductive filler can constitute 50 vol% to 90 vol% of the thermal interface material. For example, the total volume percentage of thermally conductive filler in the thermal interface material may range from about 55 vol% to about 90 vol%. In one example, the total volume percentage of thermally conductive filler in the thermal interface material may range from about 60 vol% to about 85 vol%. In another example, the total volume percentage of thermally conductive filler in the thermal interface material may be greater than about 75 vol%. Volume percentages of the particulate filler can promote a balance between overall thermal conductivity and dispensability of the thermal interface material.

[0047] The weight percentage of the thermally conductive filler in the thermal interface material may be varied according to desired characteristics, such as the desired overall thermal conductivity of the thermal interface material. In one example, the weight percentage of thermally conductive filler in the thermal interface material is greater than about 75 wt.%. In another example, the weight percentage of thermally2025P00021 conductive filler in the thermal interface material is greater than about 80 wt.%. In yet another example, the weight percentage of thermally conductive filler in the thermal interface material is greater than about 90 wt.%. The weight percentage of thermally conductive filler in the thermal interface material can be greater than 90 wt.%, greater than 92 wt.%, greater than 94 wt.%, greater than 95 wt.%, or values therebetween. In one example, the weight percentage of thermally conductive filler in the thermal interface material ranges from about 80 wt.% to about 98 wt.%.

[0048] The thermal interface material can exhibit a thermal conductivity of greater than 1 W / m*K. The thermal interface material can exhibit a thermal conductivity of greater than 2 W / m*K. The thermal interface material can exhibit a thermal conductivity between 0.5 W / m*K and 4 W / m*K. The thermal interface material can exhibit a thermal conductivity between 0.75 W / m*K and 3 W / nTK. Thermal conductivity can be measured according to ASTM D 5470. The thermal interface material can exhibit a density between 1.5 g / cm3and 4 g / cm3. The thermal interface material can exhibit a density between 2 g / cm3and 3.5 g / cm3. Density can be measured using ASTM D792. The thermal interface material can have a dispense rate of greater than 1 cm3 / s. The thermal interface material can have a dispense rate of between 1 cm3 / s and 10 cm3 / s. The thermal interface material can have a dispense rate of between 3 cm3 / s and 7 cm3 / s. Dispense rate can be measured using a pressure-driven flowthrough a nozzle (e.g., 0.254 cm) at about 6.2 bar.

[0049] The thermal interface material can exhibit an adhesive strength of greater than 10 bar. The thermal interface material can exhibit an adhesive strength ranging from 10 bar to 100 bar. The thermal interface material can exhibit an adhesive strength ranging from 20 bar to 60 bar. Adhesive strength can be measured at 22 °C and a relative humidity of 40%. Adhesive strength can be measured according to ASTM D1002. Even after harsh conditions, the thermal interface material exhibits excellent adhesive strength. For example, the thermal interface material can exhibit an adhesive strength ranging from 10 bar to 100 bar after aging. For example, aging can include sustaining at least 85 °C and 85% relative humidity for at least 20 hours. The thermal interface material can exhibit an adhesive strength ranging from 40 bar to 80 bar after aging. Adhesive strength after aging can be measured according to ASTM D1002.2025P00021

[0050] The thermal interface material can exhibit a voltage breakdown strength of greater than 1 kV / mm. The thermal interface material can exhibit a voltage breakdown strength ranging from 1 kV / mm to 20 kV / mm. The thermal interface material can exhibit a voltage breakdown strength ranging from 2 kV / mm to 16 kV / mm. Voltage breakdown strength can be measured at 22 °C and a relative humidity of 40%. Voltage breakdown strength can be measured according to ASTM D149. Even after harsh conditions, the thermal interface material exhibits excellent voltage breakdown strength. For example, the thermal interface material can exhibit a voltage breakdown strength ranging from 1 kV / mm to 10 kV / mm after aging. For example, aging can include sustaining at least 85 °C and 85% relative humidity for at least 20 hours. The thermal interface material can exhibit a voltage breakdown strength ranging from 2 kV / mm to 6 kV / mm after aging. Voltage breakdown strength after aging can be measured according to ASTM 0149.

[0051] Thermal interface materials of the present disclosure utilize a thermally conductive filler having a reduced carbon and / or energy footprint compared to conventional thermally conductive fillers, while promoting a desirable overall thermal conductivity to the thermal interface material. In one non-limiting example, the thermally conductive filler includes at least one of sintered bauxite and calcined bauxite. Utilizing sintered bauxite and / or calcined bauxite reduces or removes the utilization of additional thermally conductive fillers, such as highly refined aluminum oxide and aluminum trihydrate. Reducing or removing the utilization of highly refined thermally conductive fillers can reduce the cost and carbon footprint of the thermal interface material.Example 1

[0052] Thermal interface materials were formulated using an epoxy matrix in combination with various thermally conductive fillers. Table 1 shows formulations utilizing three distinct thermally conductive fillers. Specifically, an epoxy matrix was utilized with aluminum oxide unimodal particles (Formulation 1), aluminum trihydrate unimodal particles (ATH, Formulation 2), and bauxite unimodal particles (Formulation 3). The volume fraction of fillers for these materials is about 50 vol%. Specifically, the thermal interface material shown as Formula 1 includes Epon™ 862 resin, Priamine™ 1074, and aluminum oxide (AI2O3) powder. The aluminum oxide powder in Formulation2025P00021 1 has a mean particle size (dso) of about 1.6 pm. The thermal interface material shown as Formulation 2 includes Epon™ 862 resin, Priamine™ 1074, and aluminum trihydrate powder. The aluminum trihydrate powder in Formula 2 has a mean particle size (dso) of about 2 pm. The thermal interface material of Formulation 3 includes Epon™ 862 resin, Priamine™ 1074, and bauxite powder. The bauxite utilized in Formulation 3 includes a rotary kiln bauxite. The rotary kiln bauxite (RK88) of Formulation 3 includes about 87.8 wt.% AI2O3, about 4.5 wt.% SiO2, about 3.8 wt.% TiO2, and about 1.3 wt.% Fe2Os.Table 1. Formulations for Thermal Interface Materials.Material Formulation 1, Formulation 2, Formulation 3,AI2O3 ATH BauxiteEpon™ 862 resin 60 phr 60 phr 60 phrPriamine™ 1074 40 phr 40 phr 40 phrAI2O3 powder 400 phr(Martoxid® 2250)ATH powder 180 phr(Martinal® 2550)Bauxite powder 260phr(Reade RK88)

[0053] Table 2 shows thermal conductivity, viscosity, gel time, and lap shear strength for Formulation 1, Formulation 2, and Formulation 3. Thermal conductivity can be measured according to ASTM D 5470. Viscosity can be measured using a 25 mm parallel plate rheometer at 1 s-1. Gel time can be measured according to ASTM D4470. Lap shear strength and adhesive strength can be measured according to ASTM D1002. As shown, the materials using bauxite have similar or improved performance compared to the aluminum trihydrate filled thermal interface materials. While the aluminum oxide filled thermal interface materials have an improved thermal conductivity compared to the other two materials, other properties are similar, such as gel time and lap shear strength. Aluminum oxide is more refined than aluminum trihydrate and significantly more refined than bauxite, and thus involves a significantly higher carbon footprint than bauxite to produce.2025P00021 Table 2. Thermal conductivity, viscosity, gel time, and lap shear strength for Formulation 1, Formulation 2, and Formulation 3.Property Formulation Formulation 2, Formulation 3,1, AI2O3 ATH Bauxite Thermal conductivity 1.5 0.9 1.1(W / m*K)Viscosity (Pa-s, 1 1 / s) 42 1210 14Gel time (min., 80 °C) 24 26 23Lap shear strength time 0 3.7 1.9 3.6(MPa, AI / AI)

[0054] In addition to the time 0 properties above, the material properties of the aluminum trihydrate and bauxite filled thermal interface materials were evaluated over time when stored at 80 °C and 85 °C / 85% relative humidity (RH). FIG. 1 illustrates voltage breakdown performance over time, comparing aluminum trihydrate (ATH) particulate filler (Formulation 2) to bauxite particulate filler in thermal interface materials (Formulation 3), according to some embodiments. The voltage breakdown performance was tested at 0 days, 20 days, and 63 days, and the performance was tested using a thickness of about 0.5 mm. While the aluminum trihydrate containing material had slightly better voltage breakdown performance at time 0, after storage the properties of the two materials became very similar. Surprisingly, the bauxite-containing thermal interface material exhibited excellent voltage breakdown performance, even while including additional components, such as non-aluminum-containing compounds.

[0055] FIG. 2 illustrates lap shear strength over time, comparing aluminum trihydrate (ATH) particulate filler (Formulation 2) to bauxite particulate filler (Formulation 3) in thermal interface materials, according to some embodiments. The lap shear strength over time was measured at 0 days, 12 days, and 20 days. The load cell used in this test reached its maximum load at 7 MPa. Surprisingly, for the lap shear strength, the bauxite-containing thermal interface material outperformed the aluminum trihydrate containing material both at time 0 and after exposure to the referenced conditions.Example 2

[0056] Example 2 demonstrates a thermal interface material filled with a blend of aluminum trihydrate and bauxite, with a total volume percentage of thermally conductive2025P00021 filler of about 60 vol.% filler. Table 3 shows the formulation (Formulation 4) including an epoxy resin, a curing agent, aluminum trihydrate powder, and bauxite powder. The rotary kiln bauxite (RK88) of Formulation 4 includes about 87.8 wt.% AI2O3, about 4.5 wt.% SiO2, about 3.8 wt.% TiO2, and about 1.3 wt.% Fe2C>3. Table 4 shows the thermal conductivity, density, voltage breakdown strength, and dispense rate for the thermal interface material of Table 3. Thermal conductivity can be measured according to ASTM D 5470. Density was measured according to ASTM D792. Voltage breakdown strength was measured according to ASTM D149. Dispense rate can be measured using a pressure-driven flow through a nozzle (e.g., 0.254 cm) at about 6.2 bar. As shown, the thermal conductivity, density, voltage breakdown strength, and dispense rate are all in a desirable range for a 1.5 W / m*K thermal interface material, while incorporating a significant portion of a lower cost and lower embodied carbon filler.Table 3. Formulation for Thermal Interface Material including Aluminum Trihydrate and Bauxite.Formulation 4 Parts per hundredresin (phr)Epoxy resin (Epon™ 862 60resin)Curing agent (Priamine™ 401074)ATH powder (Huber SB-34) 175Bauxite powder (Reade 340RK88)Table 4. Thermal Conductivity, Density, Voltage Breakdown Strength, and Dispense Rate for Thermal Interface Material of Formulation 4.Formulation 4 ValueThermal conductivity (W / m*K) 1.6Density (g / cm3) 2.2Voltage breakdown strength 16(kV / mm)Dispense rate (cm3 / s, using 3.090psi / 6.2 bar)2025P00021 Example 3

[0057] Example 3 and Table 5 demonstrate a thermal interface material prepared using a trimodal blend of two aluminum trihydrate particulates of different sizes and a sintered bauxite spherical particulate, referred to as Formulation 5. In this example, the total volume percentage of thermally conductive filler was about 70 vol%. Specifically, the thermal interface material was formed using an epoxy resin, a curing agent, a first aluminum trihydrate powder, a second aluminum trihydrate powder, and a sintered, spherical bauxite. The first aluminum trihydrate powder exhibited a mean particle size (dso) of about 40 pm. The second aluminum trihydrate powder exhibited a mean particle size (dso) of about 2 pm. The sintered, spherical bauxite exhibited a mean particle size (dso) of about 324 pm. In one example, Sintex Sinterlite® includes about 71.0 wt.% AI2O3, about 12.5 wt.% SiC , about 1.8 wt.% TiC , and about 13.0 wt.% Fe2Os.Table 5. Formulation for Thermal Interface Material including a trimodal blend of Aluminum Trihydrate and Bauxite.Formulation 5 Parts per hundredresin (phr)Epoxy resin (Heloxy™ modifier 505: 60(Heloxy™ modifier 624:1 by wt.)Curing agent (Cardolite® NX-6019) 40ATH powder 1 (Huber SB-34) ~ 40 pm 190D50ATH powder 2 (Martinal® 2550) ~ 2 pm 190D50Bauxite spherical powder (Sintex 493Sinterlite®) ~ 324 pm

[0058] Table 6 shows the thermal conductivity value and density for the thermal interface material of Formulation 5. Thermal conductivity can be measured according to ASTM D 5470. Density can be measured according to ASTM D792. As shown in Table 6, this example produced a thermal interface material with a thermal conductivity of nearly 3 W / m*K, while reducing the amount of aluminum trihydrate thermally conductive filler.2025P00021 Table 6. Thermal Conductivity Value and Density of the Thermal Interface Material of Formulation 5.Formulation 5 ValueThermal 2.8conductivity(W / m*K)Density (g / cm3) 3.3

Claims

2025P00021 CLAIMS:

1. A thermal interface material, comprising:a matrix material; anda thermally conductive filler dispersed in the matrix material, the thermally conductive filler constituting 50 vol% to 90 vol% of the thermal interface material;wherein the thermally conductive filler includes first particles, each of the first particles including a mineral mixture having a first component and a second component different from the first component, the first component including at least one aluminum-containing compound selected from aluminum oxide, aluminum hydroxide, and aluminum trihydrate; wherein an average weight percentage of the first component in each the first particles ranges from 20 wt.% to 95 wt.%; and the first particles contain less than 14 wt.% iron oxide.

2. The thermal interface material of claim 1 , wherein the matrix material includes an epoxy matrix material having a viscosity of less than 10000 mPa*s at 25°C and 1 s’1.

3. The thermal interface material of claim 1 , wherein the second component includes at least one of iron oxide, silicon dioxide, and titanium oxide.

4. The thermal interface material of claim 1 , wherein the mineral mixture includes at least one of bauxite and gibbsite.

5. The thermal interface material of claim 1 , wherein the mineral mixture includes at least one of sintered bauxite and calcined bauxite.

6. The thermal interface material of claim 1 , wherein the first component includes aluminum oxide, and an average weight percentage of aluminum oxide in each of the first particles is greater than 50 wt.%.

7. The thermal interface material of claim 1 , wherein the first particles exhibit an average thermal conductivity of at least 2.7 W / m*K.2025P00021 8. The thermal interface material of claim 1 , wherein the first particles have a first mean particle size (dso) of less than 75 pm.

9. The thermal interface material of claim 1 , wherein the first particles have an aspect ratio of between 0.8 - 1.2.

10. The thermal interface material of claim 1 , wherein the thermally conductive filler further includes second particles having a second mean particle size (dso) of less than 20 pm.

11. The thermal interface material of claim 11 , wherein the second particles include bauxite.

12. The thermal interface material of claim 11, wherein the second particles include at least one of calcined aluminum oxide and aluminum trihydrate.

13. A thermal interface material, comprising:a matrix material; anda thermally conductive filler dispersed in the matrix material and including first particles, the first particles including at least one of sintered bauxite and calcined bauxite, wherein the first particles have a first mean particle size (dso) of less than 75 pm,wherein the thermal interface material exhibits a thermal conductivity of at least 0.5 W / m*K.

14. The thermal interface material of claim 13, wherein the matrix material includes an epoxy matrix material having a viscosity of less than 10000 mPa*s at 25°C and 1 s-1.

15. The thermal interface material of claim 13, wherein the thermally conductive filler further includes second particles, the second particles including at least one of sintered bauxite and calcined bauxite, the second particles having a second mean particle size (dso) of less than 20 pm.2025P00021 16. A thermally conductive curable composition, comprising:a first resin including an epoxy resin;a second resin; anda thermally conductive filler including first particles, each of the first particles including a mineral mixture having a first component and a second component, the first component including at least one aluminum- containing compound selected from aluminum oxide, aluminum hydroxide, and aluminum trihydrate; where an average weight percentage of the first component in the first particles ranges from 20 wt.% to 95 wt.% of a total weight of the first particles,wherein a concentration of the first particles to total parts of the first resin and the second resin ranges from about 300 parts per hundred resin (phr) to about 1500 parts per hundred resin (phr).

17. The thermally conductive curable composition of claim 16, wherein the epoxy resin includes a diglycidyl ether of bisphenol F resin having a viscosity of less than 10000 mPa*s at 25°C and 1 s'1; and the second resin includes a dimer diamine resin.

18. The thermally conductive curable composition of claim 16, wherein the thermally conductive filler further includes second particles having a second mean particle size (dso) of less than 20 pm; and wherein the mineral mixture includes at least one of sintered bauxite and calcined bauxite.

19. The thermally conductive curable composition of claim 16, wherein the second component includes at least one of iron oxide, silicon dioxide, and titanium oxide.

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