Dispensable thermally conductive materials

Abstract

A thermally conductive interface material includes a matrix material; a thermally conductive filler dispersed in the matrix material; a first rheology modifier, the first rheology modifier including a metal oxide-containing component having a specific surface area of greater than about 50 m2 / g; and a second rheology modifier, the second rheology modifier including a plurality of second rheology modifier particles having an aspect ratio of between 0.8 -1.2, and a first mean particle size (d50) of less than about 1 μm, wherein the plurality of second rheology modifier particles includes at least one of silica-containing particles and alumina-containing particles.

Description

2023P00377DISPENSABLE THERMALLY CONDUCTIVE MATERIALSFIELD

[0001] Disclosed herein are thermally conductive materials and, in particular, thermally conductive interface materials. Methods for manufacturing such thermally conductive materials are also disclosed.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 are 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. Remixing the material is challenging due to the typical2023P00377 presence of thermally conductive fillers and the potential to entrap air. Accordingly, embodiments of the present disclosure provide thermally conductive materials with excellent dispensability, mechanical characteristics, and storage stability.SUMMARY

[0004] According to one aspect, a thermally conductive interface material includes a matrix material; a thermally conductive filler dispersed in the matrix material; a first rheology modifier, the first rheology modifier including a metal oxide-containing component having a specific surface area of greater than about 50 m2 / g; and a second rheology modifier, the second rheology modifier including a plurality of second rheology modifier particles having an aspect ratio of between 0.8 - 1.2, and a first mean particle size (dso) of less than about 1 pm, wherein the plurality of second rheology modifier particles includes at least one of silica-containing particles and alumina-containing particles.

[0005] According to another aspect, a dispensable thermally conductive interface material includes an organopolysiloxane matrix material; a thermally conductive particulate filler dispersed in the organopolysiloxane matrix material, wherein the thermally conductive particulate filler includes a plurality of particulate filler particles including a fine constituent having a first mean particle size (dso) of less than about 10 pm; a first rheology modifier, the first rheology modifier including a hydrophilic fumed metal oxide-containing component; and a second rheology modifier, the second rheology modifier including a plurality of second rheology modifier particles having an aspect ratio of between 0.8 - 1 .2 and having a second mean particle size (dso) of less than about 1 pm.

[0006] According to another aspect, a thermally conductive curable composition includes a first polymeric resin having a first viscosity; a second polymeric resin having a second viscosity, wherein the first viscosity is less than the second viscosity; a thermally conductive filler; a first rheology modifier, the first rheology modifier including a component having a specific surface area of greater than about 50 m2 / g; and a second rheology modifier, the second rheology modifier including a plurality of second rheology modifier particles having an aspect ratio of between 0.8 - 1.2 and having a2023P00377 second mean particle size (dso) of less than about 1 pm, wherein a concentration of the second rheology modifier to total parts of the first polymeric resin and the second polymeric resin ranges from about 2 parts per hundred resin (phr) to about 50 phr.BRIEF DESCRIPTION OF THE DRAWING

[0007] FIG. 1 illustrates apparatus 100 including thermally conductive interface material 130, according to some embodiments.DETAILED DESCRIPTION

[0008] Embodiments of the present disclosure provide novel thermal interface material compositions. Often, thermal interface materials transfer heat from a heat generating component to a heat dissipating component. These thermal interface materials can be used for applications such as semiconductor elements, power transistors, integrated circuits, and battery elements. While conventional thermal interface materials have been used for transferring heat between various materials, these conventional thermal interface materials can suffer from one or more of poor thermal conductivity, poor electrical insulation, inadequate dispensability, and poor stability, such as storage stability. The compositions of the present disclosure exhibit excellent storage stability and dispensability while maintaining excellent thermal conductivity and electrical insulation (resisting the flow of electric current).

[0009] Thermal interface materials of the present disclosure include thermally conductive interface materials. The thermally conductive interface material can include at least one of a matrix material, a thermally conductive filler, a first rheology modifier, a second rheology modifier, a third rheology modifier, and additives. The thermally conductive filler can be dispersed in the matrix material and can enhance the heat dissipation properties of the thermally conductive interface material. This thermally conductive filler generally includes thermally conductive and electrically insulating particulate fillers.

[0010] Thermally conductive interface materials of the present disclosure generally include a matrix material. The matrix material can be non-polar. In one example, the matrix material includes a matrix material that has been chemically crosslinked. For2023P00377 example, the matrix material can include a polymer matrix (such as including an organopolysiloxane matrix material). In one non-limiting example, the matrix material includes a cured silicone material. The matrix material can be formed from at least a curable component and a chemical cure activator. Preferably, a cure reaction is 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.

[0011] 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 some embodiments, the matrix material may include an organic matrix including at least one of a thermoplastic resin and / or a thermoset resin.

[0012] 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 hydride2023P00377 functional silicone resins. An example silicone may be an organosiloxane having the structural formula:wherein “x” represents an integer ranging from between 1 and 1 ,000. 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 having the structural formula:wherein “x” and “y” each represent an integer having a value of between 1 and 1 ,000.

[0013] 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.

[0014] The chemical cure activator may itself be reactive with the curable component and may include a cross-linker for a hydrosilylation reaction. The chemical 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. Example2023P00377 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-1 B and 1340 available from AB Specialty Silicones.

[0015] The matrix material may be formed from multiple resin materials as curable components. The curable component can include a first polymeric resin and a second polymeric resin. For example, the first polymeric resin can have a first viscosity, and the second polymeric resin can have a second viscosity, wherein the first viscosity is less than the second viscosity. In one non-limiting example, both the first polymeric resin and the second polymeric resin include vinyl-terminated polydimethylsiloxane (PDMS) materials. In one example, the first viscosity is less than 700 mPa -s, and the second viscosity is greater than 700 mPa-s. In another example, the first viscosity is less than 600 mPa -s, and the second viscosity is greater than 800 mPa -s. The first viscosity can range from about 300 mPa-s to about 600 mPa -s. The second viscosity can range from about 850 mPa-s to about 1200 mPa -s. In one example, the second viscosity is at least 20% greater than the first viscosity. In another example, the second viscosity is at least 30% greater than the first viscosity. In yet another example, the second viscosity is at least 40% greater than the first viscosity. Viscosity values of the present disclosure can be determined at various temperatures, such as at about 25 °C or at about 20 °C. The blend of multiple resins, with distinct viscosity values of the present disclosure, can reduce or prevent excessive bleed and settling issues in the thermally conductive interface material. Further, this blend of multiple resins can improve dispensability and stability of the thermally conductive interface material.

[0016] As discussed, an example cure reaction suitable for the curable systems of the present invention is hydrosilylation from vinyl and hydride functional silicone resins. In one example, the molar ratio of hydride crosslinkers to vinyl silicone resin ranges from about 0.2:1 to about 1 :1. In another example, the molar ratio of hydride crosslinkers to vinyl silicone resin ranges from about 0.3:1 to about 0.7:1 . In yet another example, the molar ratio of hydride crosslinkers to vinyl silicone resin ranges from about 0.3:1 to about 0.5:1 . For example, the molar ratio of hydride crosslinkers to vinyl silicone resin can be about 0.4:1 .2023P00377

[0017] 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.

[0018] Other example curing reactions contemplated for the curable component and cure activator include a urethane reaction from hydroxyl and isocyanate functional monomers, oligomers, or resins, epoxy polymerization from epoxide and at least one of amino, mercapto, and anhydride functional monomers, oligomers, or resins, and radical polymerization of vinyl or vinylidene functional monomers, oligomers, or resins. Accordingly, matrix materials of the present disclosure can include fluoro, epoxy, polyurethane, or polyacrylate-based polymeric materials. Acrylates may include reaction products of acrylic acid. In one example, acrylates include one or more of methacrylates, cyanoacrylates, and silicone acrylates. Further examples of acrylates include acrylic acrylates, polyester acrylates, urethane acrylates, and polyether acrylates. In some embodiments, one or more of the monomers, oligomers, or resins may be in liquid form at 20 °C and 1 bar pressure and exhibit a viscosity of less than 1000 cP at 20 °C at a shear rate of 1 s-1. In some embodiments, one or more of the monomers, oligomers, or resins may be in liquid form at 20 °C and 1 bar pressure and exhibit a viscosity of less than 200 cP at 20 °C at a shear rate of 1 s'1.

[0019] 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 one2023P00377 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 in 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.

[0020] 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.

[0021] 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. Dispersants can be added as an additive to the thermal interface material or precursors thereof to improve separation of particles and / or to improve the viscosity. These dispersants can improve dispersion and / or stabilization of particles in the thermal interface material. In one example, the2023P00377 dispersant may include a Polydimethylsiloxane (PDMS)-soluble wetting agent. In another example, the dispersant includes titanate.

[0022] Thermally conductive interface materials of the present disclosure can include a thermally conductive filler. Thermally conductive filler can provide desired thermal conductivity properties to the interfaces of the present disclosure. For example, the thermally conductive filler can be a thermally conductive particulate filler. The thermally conductive filler may be dispersed in the matrix material. In one example, the thermally conductive filler includes electrically insulating particulate fillers. The thermally conductive filler concentration with respect to the resin in the curable component can range from about 500 phr to about 1500 phr. In one example, the thermally conductive filler concentration with respect to the resin in the curable component can range from about 700 phr to about 1000 phr.

[0023] The thermally conductive fillers contemplated for use in the preparations of the present invention include metals, metal oxides, ceramics, and combinations thereof. Example conductive fillers 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. Example electrically insulating and thermally conductive fillers include boron nitride, aluminum nitride, alumina, and alumina trihydrate.

[0024] The thermally conductive fillers may be of various shapes and size, and typically have a mean particle size (dso) in a range of between 0.1 and 200 pm. In some embodiments, the thermally conductive fillers have a mean particle size (dso) in a range of between 1 and 100 pm. In some embodiments, the distribution of thermally conductive filler particles is not a mono dispersion, but rather a particle size distribution. In some embodiments, the particle size distribution is multi-modal, including a mixture of2023P00377 relatively small particles and relatively large particles, within the size ranges described above. 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, as determined by laser light diffraction. 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.

[0025] The thermally conductive filler can include a plurality of particulate filler particles including a coarse constituent and / or a fine constituent. The coarse constituent may provide the primary mechanism for heat transfer. The coarse constituent can include thermally conductive filler materials of the present disclosure, such as alumina. In one example, about 40 vol% to about 80 vol% of the total particulate filler includes the coarse constituent. In another example, about 40 vol% to about 70 vol% of the total particulate filler includes the coarse constituent. In another example, about 50 vol% to about 70 vol% of the total particulate filler includes the coarse constituent.

[0026] In one example, the coarse constituent has a mean particle size (dso) of greater than about 5 pm. In another example, the coarse constituent has a mean particle size (dso) of greater than about 10 pm. In another example, the coarse constituent has a mean particle size (dso) of greater than about 20 pm. In one example, the coarse constituent has a mean particle size (dso) of between about 10 pm and about 100 pm. In another example, the coarse constituent has a mean particle size (dso) of between about 10 pm and about 50 pm. In one example, the coarse constituent includes particles having an aspect ratio ranging from about 0.8 to about 1.2. In another example, the coarse constituent includes particles having an aspect ratio ranging from about 0.9 to about 1.1.

[0027] The fine constituent can include thermally conductive filler materials of the present disclosure, such as alumina. In one example, the fine constituent includes calcined alumina having an alkylsilane surface treatment. In one example, about 10 vol% to about 60 vol% of the total particulate filler includes the fine constituent. In another example, about 10 vol% to about 40 vol% of the total particulate filler includes2023P00377 the fine constituent. In yet another example, about 10 vol% to about 25 vol% of the total particulate filler includes the fine constituent.

[0028] The fine constituent can have a mean particle size (dso) of less than about 10 pm. In one example, the fine constituent can have a mean particle size (dso) of less than about 5 pm. In another example, the fine constituent can have a mean particle size (dso) of less than about 3 pm. In one example, the fine constituent has a mean particle size (dso) of between about 1 pm and about 10 pm. In another example, the fine constituent has a mean particle size (dso) of between about 1 pm and about 5 pm. In one example, the majority of the fine constituent includes aspherical or irregular shaped particles.

[0029] The concentration of the coarse constituent and the fine constituent with respect to the curable component can range from about 300 phr to 700 phr, and 100 phr to 500 phr, respectively. In one example, the concentration of the coarse constituent and the fine constituent with respect to the curable component can range from about 400 phr to 600 phr, and 200 phr to 400 phr, respectively. In another example, the concentration of the coarse constituent and the fine constituent with respect to the curable component can range from about 450 phr to 500 phr, and 300 phr to 350 phr, respectively.

[0030] In addition to enhancing the thermal conductivity properties of the thermal interface material, thermally conductive fillers of the present disclosure can improve shear thinning properties of the thermal interface material. The specific combination of particle sizes and compositions of at least the coarse constituent and the fine constituent of the present disclosure can tune shear thinning properties of the thermal interface material. For example, thermal interface materials including the coarse constituent and the fine constituent can exhibit desired viscosity values under shear strain. These tuned shear thinning properties can assist with enhancing dispensability during the application process.

[0031] Thermally conductive interface materials of the present disclosure can include a first rheology modifier. The first rheology modifier can be dispersed in the matrix material. The first rheology modifier can include a metal oxide-containing component. For example, the metal oxide-containing component can include at least2023P00377 one of silica and alumina. The metal-oxide containing component can include a fumed metal oxide. The fumed metal-oxide can include a hydrophobic fumed-metal oxide. In one non-limiting example, the fumed metal-oxide includes hydrophobic fumed silica. A fumed metal-oxide can be produced using heat or a flame. For example, fumed silica can be formed by burning volatile silanes, such as silicon tetrachloride, in an oxygenhydrogen flame. The fumed metal-oxide can include a hydrophilic fumed-metal oxide. In one non-limiting example, the fumed metal-oxide includes hydrophilic fumed alumina. The hydrophilic fumed metal-oxide can exhibit excellent capability for inter-particle interactions. The inclusion of a hydrophilic fumed metal-oxide can improve the shear thinning and dispense rate of the thermal interface material, at least in part due to the capability of the hydrophilic fumed metal-oxide for inter-particle interactions.

[0032] The metal oxide-containing component can have a specific surface area of greater than about 40 m2 / g. In one example, the metal oxide-containing component has a specific surface area of greater than about 50 m2 / g. In another example, the metal oxide-containing component has a specific surface area of greater than about 100 m2 / g. In another example, the metal oxide-containing component has a specific surface area ranging from about 50 m2 / g to about 250 m2 / g. In another example, the metal oxide- containing component has a specific surface area ranging from about 100 m2 / g to about 250 m2 / g. In yet another example, the metal oxide-containing component has a specific surface area ranging from about 75 m2 / g to about 200 m2 / g. Importantly, the inclusion of metal oxide-containing components with specific surface areas of the present disclosure can increase the low shear viscosity and decrease the particle settling rate of the thermal interface material. By increasing the low shear viscosity and decreasing the particle setting rate, the stability can be improved, and shelf-life can be increased.

[0033] The concentration of the first rheology modifier to total parts resin in the curable component can range from about 0.1 parts per hundred resin (phr) to about 20 phr. In one example, the concentration of the first rheology modifier to total parts resin in the curable component can range from about 0.5 phr to about 20 phr. In another example, the concentration of the first rheology modifier to total parts resin in the curable component can range from about 0.5 phr to about 10 phr. In yet another example, the concentration of the first rheology modifier to total parts resin in the2023P00377 curable component can range from about 1 phr to about 15 phr. The concentration of the first rheology modifier to total parts resin in the curable component can be less than 10 phr. For example, if the first rheology modifier includes hydrophilic fumed alumina having a specific surface area of the present disclosure, a concentration of the first rheology modifier to total parts resin in the curable component of between about 2 phr and 10 phr can enable a high shear thinning index while maintaining desired dispense rates and viscosity values.

[0034] Thermally conductive interface materials of the present disclosure can include a second rheology modifier. The second rheology modifier can include a plurality of second rheology modifier particles. In one example, the plurality of second rheology modifier particles is dispersed in the matrix material. In another example, the plurality of second rheology modifier particles includes at least one of silica-containing particles and alumina-containing particles. For example, the plurality of second rheology modifier particles can include substantially spherical silica-containing particles.

[0035] In one example, the plurality of second rheology modifier particles is substantially spherical. In another example, the plurality of second rheology modifier particles has an aspect ratio of between about 0.8 to about 1.2. In another example, the plurality of second rheology modifier particles has an aspect ratio of between about 0.85 to about 1.15. In another example, the plurality of second rheology modifier particles has an aspect ratio of between about 0.9 to about 1.1. In yet another example, the plurality of second rheology modifier particles has an aspect ratio of about 1 .0.Importantly, the inclusion of second rheology modifier particles having aspect ratios of the present disclosure can significantly increase the low shear viscosity while maintaining desirable dispense rates.

[0036] The plurality of second rheology modifier particles can have a mean particle size (dso) of less than about 2 pm. The plurality of second rheology modifier particles can have a mean particle size (dso) of less than about 1 pm. In one example, the plurality of second rheology modifier particles has a mean particle size (dso) of less than about 800 nm. In another example, the plurality of second rheology modifier particles has a mean particle size (dso) of between about 50 nm and about 800 nm. In another example, the plurality of second rheology modifier particles has a mean particle size2023P00377(dso) of between about 100 nm and about 600 nm. In yet another example, the plurality of second rheology modifier particles has a mean particle size (dso) of between about 200 nm and about 400 nm. Importantly, specific particle sizes and aspect ratios of the second rheology modifier of the present disclosure can enhance the degree of shear thinning of the thermal interface material, increasing the dispense rate.

[0037] The plurality of second rheology modifier particles can have a specific surface area of less than about 70 m2 / g. The plurality of second rheology modifier particles can have a specific surface area of less than about 50 m2 / g. In one example, the plurality of second rheology modifier particles has a specific surface area of between about 10 m2 / g and about 50 m2 / g. In another example, the plurality of second rheology modifier particles has a specific surface area of between about 10 m2 / g and about 40 m2 / g. In yet another example, the plurality of second rheology modifier particles has a specific surface area of between about 15 m2 / g and about 30 m2 / g. In one non-limiting example, the plurality of second rheology modifier particles can include silica-containing particles having a mean particle size (dso) of less than about 1 pm, having an aspect ratio of between about 0.9 to about 1.1 , and having a specific surface area ranging from about 10 m2 / g and about 50 m2 / g.

[0038] The concentration of the second rheology modifier to total parts resin in the curable component can range from about 1 part per hundred resin (phr) to about 60 phr. In one example, the concentration of the second rheology modifier to total parts resin in the curable component can range from about 5 phr to about 50 phr. In another example, the concentration of the second rheology modifier to total parts resin in the curable component can range from about 5 phr to about 40 phr. In another example, the concentration of the second rheology modifier to total parts resin in the curable component can range from about 5 phr to about 15 phr. The concentration of the second rheology modifier to total parts resin in the curable component can be greater than 5 phr. The concentration of the second rheology modifier to total parts resin in the curable component can be less than 50 phr.

[0039] The combination of the first rheology modifier and the second rheology modifier can enhance stability of the thermal interface material and / or curable components used to form the thermal interface material. For example, this combination2023P00377 can decrease the settling rate of particles in the thermal interface material. Further, this combination can improve shear thinning and dispense rate, while maintaining desired low shear viscosity properties. Accordingly, the combination of the first rheology modifier (such as a fumed metal oxide having a specific surface area of greater than about 50 m2 / g) and the second rheology modifier (such as particles having a mean particle size (dso) of less than about 1 pm and having an aspect ratio of between about 0.8 to about 1.2) can improve stability, dispensability, and shelf-life of the thermal interface material. In contrast to only using a higher viscosity suspending fluid to increase the viscosity and improve stability, which directly decreases dispense rate, the first rheology modifier and the second rheology modifier can improve stability while maintaining desirable dispense rates. In contrast to only decreasing the density difference between the suspending fluid and the thermally conductive filler particles, involving significant tradeoffs in cost, thermal conductivity, or viscosity impact, the first rheology modifier and the second rheology modifier can improve stability for systems using thermally conductive fillers with a wide range of densities.

[0040] Thermally conductive interface materials of the present disclosure can include a third rheology modifier. The third rheology modifier can include active surface functionalities for promoting hydrogen bonding. For example, the third rheology modifier can include an organically modified clay component. In contrast to adding watercontaining chemical additives, which can have significant issues with silicones due to consumption of the crosslinking agent, the third rheology modifier can promote hydrogen bonding without negatively impacting the matrix material. In one example, the third rheology modifier exhibits particles having an aspherical shape. Due at least in part to the active surface functionality and shape of the third rheology modifier, the third rheology modifier can increase the low shear viscosity of the thermal interface material without decreasing the overall shear thinning.

[0041] The concentration of the third rheology modifier to total parts resin in the curable component can range from about 0.1 part per hundred resin (phr) to about 10 phr. In one example, the concentration of the third rheology modifier to total parts resin in the curable component can range from about 1 phr to about 5 phr. In another example, the concentration of the third rheology modifier to total parts resin in the2023P00377 curable component can range from about 1 phr to about 3 phr. The concentration of the third rheology modifier to total parts resin in the curable component can be greater than 1 phr. The concentration of the third rheology modifier to total parts resin in the curable component can be less than 5 phr.

[0042] In one example, the overall thermal conductivity of the thermal interface material is greater than about 2 W / m*K. In another example, the overall thermal conductivity of the thermal interface material is greater than about 4 W / m*K. In yet another example, the overall thermal conductivity of the thermal interface material is greater than about 6 W / m*K. In one non-limiting example, the overall thermal conductivity of the thermal interface material ranges from about 3 W / m*K to about 7 W / m*K. In one example, the electrical resistivity of the thermal interface material is at least 1010Q*m. In another example, the electrical resistivity of the thermal interface material is at least 1011Q*m. In yet another example, the electrical resistivity of the thermal interface material is at least 1012Q*m.

[0043] The viscosity of the thermal interface material, or the curable composition, at 0.01 1 / s can be less than about 50000 Pa -s. In one example, the viscosity of the thermal interface material, or the curable composition, at 0.01 1 / s is less than about 30000 Pa -s. The viscosity of the thermal interface material, or the curable composition, at 0.01 1 / s can range from about 2000 Pa-s to about 40000 Pa-s. In one example, the viscosity of the thermal interface material, or the curable composition, at 0.01 1 / s ranges from about 10000 Pa -s to about 40000 Pa -s. In another example, the viscosity of the thermal interface material, or the curable composition, at 0.01 1 / s ranges from about 10000 Pa -s to about 30000 Pa -s. In yet another example, the viscosity of the thermal interface material, or the curable composition, at 0.01 1 / s ranges from about 20000 Pa- s to about 30000 Pa-s. Viscosity values can measured at various temperatures. In one non-limiting example, viscosity values can be measured at about 20 °C.

[0044] The dispense rate of the thermal interface material, or a curable composition, may be greater than 25 cc / min. In one example, the dispense rate of the thermal interface material, or the curable composition, is greater than 30 cc / min. In another example, the dispense rate of the thermal interface material, or the curable2023P00377 composition, may be greater than 40 cc / min. Dispense rates can be measured using a pressure-driven flow through a 2.54 mm nozzle at 6 bar. In one non-limiting example, the viscosity at 0.01 1 Is ranges from about 10000 Pa ■ s to about 30000 Pa ■ s and the dispense rate is greater than about 50 cc / min. The effective settling rate of the thermal interface material, or the curable composition, may be less than about 40 pm / min. In one example, the effective settling rate of the thermal interface material, or the curable composition, is less than about 20 pm / min. In another example, the effective settling rate of the thermal interface material, or the curable composition, is less than about 10 pm / min.

[0045] Embodiments of the present disclosure include thermally conductive curable compositions. These thermally conductive curable compositions can include at least one of a resin, the thermally conductive filler, the first rheology modifier, the second rheology modifier, the third rheology modifier, and additives. The resin can include a first polymeric resin and a second polymeric resin. For example, the first polymeric resin can have a first viscosity, and the second polymeric resin can have a second viscosity, wherein the first viscosity is less than the second viscosity. The resin, thermally conductive filler, first rheology modifier, second rheology modifier, third rheology modifier, and additive can include resins, thermally conductive fillers, first rheology modifiers, second rheology modifiers, third rheology modifiers, and additives of the present disclosure.

[0046] FIG. 1 illustrates apparatus 100 including thermally conductive interface material 130, according to some embodiments. Apparatus 100 may include a heatgenerating apparatus and / or an electronics apparatus. Embodiments of the present disclosure include an apparatus 100, wherein apparatus 100 includes a heat producing component 110, a heat dissipating component 120, and a thermally conductive interface material 130. Thermally conductive interface material 130 includes thermal interface materials of the present disclosure. As shown, the thermally conductive interface material 130 is in contact with at least a portion of the heat producing component 110 and at least a portion of the heat dissipating component 120. In one example, heat producing component 110 includes an electronic component or a battery. Therefore, it is useful for thermally conductive interface material 130 to be electrically insulating. In2023P00377 another example, heat dissipating component 120 includes a metal heat dissipating component, optionally including one or more fins for enhanced heat dissipation. Accordingly, thermally conductive interface material 130 transfers heat from the heat producing component 110 to the heat dissipating component 120.

[0047] Importantly, thermal interface materials and curable compositions of the present disclosure can exhibit an excellent balance of high dispense rate, high shear thinning index, and desirable viscosity. The high shear thinning index can ensure that these materials have a long shelf-life while being highly dispensable. These materials can also have a high viscosity at low shear rates, improving stability of particles.Thermal interface materials of the present disclosure can be used for improvements in heat dissipation for electrical components in automotive, industrial, and consumer electronics applications.EXAMPLESExample 1

[0048] Formulations were prepared using a speed mixer under vacuum. Thermal conductivity was measured according to ASTM D 5470. Dispense rate was measured using a pressure-driven flow through a 2.54 mm nozzle at 6 bar, and viscosity was measured using a 25 mm parallel plate. For Table 1 , a 500 mPa -s vinyl-terminated PDMS was used as the suspending fluid and a total of 900 phr of alumina was added. A 2 pm calcined alumina with an alkylsilane surface treatment was used as fine filler and various spherical alumina was used as coarse filler. The results show that increasing the diameter of the coarse filler provides for a significant reduction in viscosity and increase in dispense rate, with negligible impact on the shear thinning index. However, there is a significant increase in the estimated settling rate of the filler, which is estimated in Table 1 based on Stokes’ equation. For example, the effective settling rate herein can exclude effects of particle crowding or shear thinning.2023P00377Table 1. Impact of coarse particle size.

[0049] In Table 2 and Table 3, the impact of hydrophobic fumed silica addition is demonstrated. For the mixture with 10 pm spherical alumina, the addition of 4 phr hydrophobic fumed silica (with a specific surface area ranging from about 150-200 m2 / g) increases the low shear viscosity by ~5x with an associated doubling of shear thinning index, but with a reduction in dispense rate. The hydrophobic fumed silica improved the settling rate for the formulation, at least in part due to the increase in low shear viscosity.Table 2. Impact of hydrophobic fumed silica as a first rheology modifier with 10 pm alumina.

[0050] As shown in Table 3, increasing the size of the coarse alumina to 30 pm results in a much higher dispense rate with 2 and 4 phr fumed silica, but there remains an associated trade-off in effective settling rate due to the high surface area of the2023P00377 fumed silica. For example, the effective setting rate in pm / min was increased when using 30 pm alumina compared to using 10 pm alumina. Accordingly, the formulations of Table 2 exhibited improved stability compared to the formulations of Table 3.Table 3. Impact of hydrophobic fumed silica as a first rheology modifier with 30 pm alumina.

[0051] In Table 4, the hydrophobic fumed silica is compared with a hydrophilic fumed alumina. For example, the hydrophilic fumed alumina can include untreated, hydrophilic fumed alumina. Both the fumed alumina and fumed silica can have similar fine primary particle size, on the order of 10-50 nanometers, and show significant flocculation and inter-particle interactions associated with the production method.However, the fumed alumina is hydrophilic and has a greater capability for inter-particle interactions. Compared to the hydrophobic fumed silica, the hydrophilic fumed alumina shows a similar viscosity at 0.01 11s, indicating a similar yield stress, but with a shear thinning index nearly 3x higher than the hydrophobic fumed silica and an improved dispense rate.2023P00377Table 4. Comparison between hydrophobic fumed silica and hydrophilic fumed alumina as first rheology modifiers.

[0052] In Table 5, an organoclay (organically modified clay) is used as a third rheology modifier to boost the shear thinning with controlled impact on dispensability. The organoclay has a pronounced impact on rheology because of its non-spherical shape, high surface area, and the presence of active surface functionalities that can promote hydrogen bonding. The addition of the organo-clay alone causes a 2x increase in viscosity at 0.01 1 / s, with a relatively minor dispense rate decrease, and no change in overall shear thinning behavior. Accordingly, due at least in part to the active surface functionality and shape of the third rheology modifier, the third rheology modifier can increase the low shear viscosity of the thermal interface material without decreasing the overall shear thinning. Increasing the amount of fumed alumina improved the shear thinning and dispense rate.2023P00377Table 5. Impact of a first rheology modifier, second rheology modifier, and third rheology modifier on rheology, dispensability, and stability.

[0053] Different loadings of fumed alumina and sub-micron spherical silica were compared for impacts on dispensability. As shown in Table 6, the mixture with fumed alumina and organo-clay alone showed a good dispense rate, high shear thinning, and high viscosity at low shear rate. The addition of the spherical colloidal silica resulted in a significant increase in low shear viscosity, indicative of a pronounced increase in yield stress, along with a minor reduction in dispense rate. Reducing the total amount of hydrophilic fumed alumina enables an excellent property balance with extremely high shear thinning index, high dispense rate, and desirable high viscosity at 0.01 1 / s.

[0054] In one example, if the first rheology modifier includes hydrophilic fumed alumina having a specific surface area of the present disclosure, a concentration of the first rheology modifier to total parts resin in the curable component of between about 2 phr and 10 phr can enable a high shear thinning index while maintaining desired dispense rates and viscosity values. In one non-limiting example, the formulations with 5 phr of hydrophilic fumed alumina (100-200 m2 / g) and 10 phr spherical silica (200 nm) exhibited improved dispense rates, shear thinning index, and desired viscosity.2023P00377Table 6. Impact of a first rheology modifier, second rheology modifier, and third rheology modifier on rheology, dispensability, and stability.

[0055] While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

2023P00377CLAIMS:1 . A thermally conductive interface material comprising: a matrix material; a thermally conductive filler dispersed in the matrix material; a first rheology modifier including a metal oxide-containing component having a specific surface area of greater than about 50 m2 / g; and a second rheology modifier including a plurality of second rheology modifier particles having an aspect ratio of between 0.8 - 1.2, and a first mean particle size (dso) of less than about 1 pm, wherein the plurality of second rheology modifier particles includes at least one of silica-containing particles and alumina-containing particles.

2. The thermally conductive interface material of claim 1 , wherein the matrix material is non-polar.

3. The thermally conductive interface material of claim 1 , wherein the matrix material includes an organopolysiloxane.

4. The thermally conductive interface material of claim 1 , wherein the thermally conductive filler includes a plurality of particulate filler particles including a coarse constituent having a second mean particle size (dso) of greater than about 5 pm, and the plurality of particulate filler particles includes a fine constituent having a third mean particle size (dso) of less than about 5 pm.

5. The thermally conductive interface material of claim 1 , wherein the thermally conductive filler includes alumina.

6. The thermally conductive interface material of claim 1 , wherein the metal oxide- containing component has a specific surface area ranging from about 100 m2 / g to about 200 m2 / g.

7. The thermally conductive interface material of claim 1 , wherein the metal oxide- containing component includes hydrophobic fumed silica.2023P003778. The thermally conductive interface material of claim 1, wherein the metal oxidecontaining component includes hydrophilic fumed alumina.

9. The thermally conductive interface material of claim 1, wherein the plurality of second rheology modifier particles has an aspect ratio of between 0.9 - 1 .1.

10. The thermally conductive interface material of claim 1, wherein the plurality of second rheology modifier particles has a specific surface area of less than about 50 m2 / g.

11. The thermally conductive interface material of claim 1 further including a third rheology modifier including an organically modified clay component.

12. A dispensable thermally conductive interface material comprising: an organopolysiloxane matrix material; a thermally conductive particulate filler dispersed in the organopolysiloxane matrix material, wherein the thermally conductive particulate filler includes a plurality of particulate filler particles including a fine constituent having a first mean particle size (dso) of less than about 10 pm; a first rheology modifier, the first rheology modifier including a hydrophilic fumed metal oxide-containing component; and a second rheology modifier, the second rheology modifier including a plurality of second rheology modifier particles having an aspect ratio of between 0.8 - 1.2 and having a second mean particle size (dso) of less than about 1 pm.

13. The dispensable thermally conductive interface material of claim 12, wherein the plurality of second rheology modifier particles has a specific surface area ranging from about 10 m2 / g to about 40 m2 / g.

14. The dispensable thermally conductive interface material of claim 12, wherein the hydrophilic fumed metal oxide-containing component includes hydrophilic fumed alumina.2023P0037715. The dispensable thermally conductive interface material of claim 12, wherein a specific surface area of the hydrophilic fumed metal oxide-containing component ranges from about 100 m2 / g to about 200 m2 / g.

16. The dispensable thermally conductive interface material of claim 12, wherein the plurality of second rheology modifier particles includes silica particles having an aspect ratio of between 0.9 - 1 .1 .

17. The dispensable thermally conductive interface material of claim 12, wherein the hydrophilic fumed metal oxide-containing component has a specific surface area of greater than about 50 m2 / g.

18. A thermally conductive curable composition, the thermally conductive curable composition comprising: a first polymeric resin having a first viscosity; a second polymeric resin having a second viscosity, wherein the first viscosity is less than the second viscosity; a thermally conductive filler; a first rheology modifier, the first rheology modifier including a component having a specific surface area of greater than about 50 m2 / g; and a second rheology modifier, the second rheology modifier including a plurality of second rheology modifier particles having an aspect ratio of between 0.8 - 1 .2 and having a second mean particle size (dso) of less than about 1 pm, wherein a concentration of the second rheology modifier to total parts of the first polymeric resin and the second polymeric resin ranges from about 2 parts per hundred resin (phr) to about 50 phr.

19. The thermally conductive curable composition of claim 18, wherein a concentration of the first rheology modifier to total parts of the first polymeric resin and the second polymeric resin ranges from about 1 phr to about 15 phr.2023P0037720. The thermally conductive curable composition of claim 18, wherein the concentration of the second rheology modifier to total parts of the first polymeric resin and the second polymeric resin ranges from about 5 parts per hundred resin (phr) to about 30 phr.21 . The thermally conductive curable composition of claim 18, wherein the component includes hydrophilic fumed alumina.

22. The thermally conductive curable composition of claim 18, wherein the first polymeric resin and the second polymeric resin include vinyl terminated polydimethylsiloxane (PDMS).

Images