Thermal interface materials for absorbing electromagnetic radiation

Abstract

A thermal interface material includes a matrix material; and a particulate filler dispersed in the matrix material, the particulate filler including particles that each include a first component and a second component, the first component exhibiting a native thermal conductivity value of greater than 10 W / m*K, wherein the thermal interface material exhibits a density of between about 1.5 g / cm3 to about 3 g / cm3, and an electromagnetic absorption value at 5 GHz of between -0.1 dB / mm and -100 dB / mm.

Description

2024P00132THERMAL INTERFACE MATERIALS FOR ABSORBING ELECTROMAGNETIC RADIATIONFIELD

[0001] Provided herein are thermal interface materials generally, and more particularly thermal interface materials for absorbing electromagnetic radiation. The present invention further relates to methods for manufacturing such thermal interface materials for absorbing electromagnetic radiation.BACKGROUND

[0002] Thermally conductive interface materials are widely utilized in the electronics industry for operably coupling heat-generating electronic components to heat-dissipating structures. Typically, such thermally conductive interface materials are utilized in connection with heat-generating electronic components such as integrated circuits (IC), central processing units (CPU), and other electronic components containing relatively high-densities of conductive traces and resistor elements. In particular, the thermal interface materials are often times utilized to operably couple such heat-generating electronic devices to heat sinking structures, such as finned heat sink structures. In such a manner, excess thermal energy generated by the electronic components may be expelled to the heat sinking structures via the thermal interface material.

[0003] Certain electronic devices, in addition to generating excess thermal energy, create electromagnetic radiation across various frequencies. Such radiation can have the effect of causing electromagnetic interference (EMI) and / or radio frequency interference (RFI) with other electronic devices susceptible to and / or tuned to receive electromagnetic or radio frequency wave forms. Devices sensitive to electromagnetic and radio frequency interference include, for example, cellular phones, portable radios, laptop computers, and the like.

[0004] While some conventional thermal interface materials have included thermally conductive fillers and an additional material for electromagnetic radiation shielding, the thermally conductive fillers and additional materials can require an energy intensive refinement process and continue to permit a large percentage of electromagnetic radiation to propagate through the thermal interface material.2024P00132

[0005] Accordingly it would be desirable to provide thermal interface materials with a particulate filler including particles each being capable of both improving the absorption of electromagnetic radiation and promoting the desirable thermal conductivity to the thermal interface material.SUMMARY

[0006] According to one aspect, a thermal interface material includes a matrix material; and a particulate filler dispersed in the matrix material, the particulate filler including particles that each include a first component and a second component, the first component exhibiting a native thermal conductivity value of greater than 10 W / m*K, wherein the thermal interface material exhibits a density of between about 1.5 g / cm3to about 3 g / cm3, and an electromagnetic absorption value at 5 GHz of between -0.1 dB / mm and -100 dB / mm.

[0007] According to another aspect, a thermal interface material includes a matrix material; and a particulate filler dispersed in the matrix material, the particulate filler comprising between 40 wt.% and 95 wt.% of the thermal interface material and including first particles that each include a mixture of aluminum oxide and iron (II, III) oxide.

[0008] According to another aspect, a method for attenuating electromagnetic radiation in an electronic device includes positioning a thermal interface material of the present disclosure in contact with at least a portion of a heat-generating component of the electronic device.

[0009] According to another aspect, a thermal interface material includes a matrix material; and a particulate filler dispersed in the matrix material, the particulate filler including first particles that each include a mixture of a first component and a second component, the first component exhibiting a native thermal conductivity value of greater than 10 W / m*K and the second component including an iron-containing material, wherein the thermal interface material exhibits an electromagnetic absorption value at 5 GHz of between -0.1 dB / mm and -100 dB / mm.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 illustrates electromagnetic absorbance values at 5 GHz for various materials, according to some embodiments.

[0011] FIG. 2 illustrates electromagnetic reflectance percentages at 5 GHz for various materials, according to some embodiments.2024P00132

[0012] FIG. 3 illustrates a comparison of electromagnetic absorption per length values of distinct formulations, according to some embodiments.

[0013] FIG. 4 illustrates the increase in electromagnetic absorption per length values between distinct formulations, according to some embodiments.DETAILED DESCRIPTION

[0014] As noted above, provided herein are 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. These thermal interface materials are capable of absorbing electromagnetic radiation, sufficient to suppress the propagation of the electromagnetic radiation through the thermal interface material. Accordingly, the thermal interface material can be used in devices sensitive to electromagnetic interference. It is desirable to provide thermally conductive interface materials having electromagnetic absorbing properties to suppress the propagation of electromagnetic radiation while reducing material costs, lowering material density, and improving product sustainability.

[0015] For the purposes hereof, the terms “electromagnetic radiation” and “electromagnetic interference” are intended to mean radiation that is capable of interfering with the normal operation of electronic components, such as processors, transmitters, receivers, and the like. Such radiation can include frequencies in the radio spectrum, and such radiation may typically be in the range of 1-20 GHz, such as in the range of 1-10 GHz. Electromagnetic radiation and electromagnetic interference may be used interchangeably with the terms “radio frequency radiation” and “radio frequency interference”, respectively.

[0016] The thermal interface materials of the present disclosure generally include a matrix material and a particulate filler. 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. The matrix material can include an organic material. In one example, the matrix material can include at least one of a polymeric material and a non-polymeric material. Accordingly, the matrix material can include polymers, oligomers,2024P00132 oils, or greases. Examples of suitable polymeric materials used for the matrix material include at least one of silicone materials, perfluoropolyether materials, and polyphenyl ether materials.Examples of non-polymeric materials include aromatic ethers and esters. The matrix material can include a silicone-based matrix material or an epoxy-based matrix material.

[0017] 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). 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.

[0018] 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.

[0019] 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. In one non-limiting example, the thermal interface material can be formed by mixing at least the vinyl and hydride functional2024P00132 silicone resins with an inhibitor, a catalyst, and the particulate filler of the present disclosure. The formulation can be subsequently cured.

[0020] 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 cP to about 1000 cP may be utilized.

[0021] 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. 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- IB and 1340 available from AB Specialty Silicones. Hydride functional PDMS crosslinkers may be utilized, such as about 500 cP hydride functional PDMS crosslinkers.

[0022] 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.2024P00132

[0023] 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. 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 600 cP at 20 °C at a shear rate of 1 s'1.

[0024] 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. In one non-limiting example, the catalyst includes a platinum-divinyltetramethylsiloxane complex. 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 include in the range of 0.0001 up to 0.5 percent by weight reaction catalyst.

[0025] 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 include in the range of 0.012024P00132 up to 0.3 wt% water. In some embodiments, the compositions include in the range of 0.01 up to 0.2 wt% water.

[0026] The weight percentage of the matrix material in the thermal interface material may be greater than 3 wt.%. In one example, the weight percentage of the matrix material in the thermal interface material is greater than 10 wt.%. The thermally conductive interface material may further include one or more of a reaction inhibitor(s), pigment(s), plasticizer(s), coupling agent(s), and rheology modifier(s). 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 is a silicone inhibitor. In one non-limiting example, the reaction inhibitor includes methylvinyl cyclic inhibitors. Plasticizers can be added to alter the viscosity of the formulations, and coupling agents can be added to improve interaction or bonding between the matrix material and filler(s). A rheology modifier can be added to alter the thixotropic properties of the formulation.

[0027] In order to provide desired thermal conductivity properties to the interfaces of the present invention, thermally conductive particulate filler is preferably dispersed in the matrix material. In another example, the thermally conductive particulate filler is dispersed / mixed with one or more components used for a cure reaction. Importantly, the particulate filler of the present disclosure is capable of absorbing electromagnetic radiation to promote an overall electromagnetic absorption to the thermal interface material. This absorption suppresses the propagation of electromagnetic radiation through the thermal interface material, reducing electromagnetic interference to an electronic device in contact with, or adjacent to, the thermal interface material. The particulate filler generally includes first particles. In some embodiments, first particles can include a mineral material. First particles can each include a first component and a second component. Accordingly, each particle of the first particles can include a mixture of the first component and the second component. In one non-limiting example, the first particles each include an intimate mixture of the first component and the second component.

[0028] The first component can at least promote overall thermal conductivity to the thermal interface material. The first component generally exhibits a native thermal conductivity of greater than about 5 W / m*K. For example, the native thermal conductivity of the first2024P00132 component is the average thermal conductivity of the material(s) forming the first component if isolated and in the substantially pure form, typically distinct from the overall thermal conductivity of the blended particle including the first component and the second component. In one example, if the first component is aluminum oxide, the native thermal conductivity of the first component can range from about 29 W / m*K to about 35 W / m*K. For example, native thermal conductivity of certain ceramics can be tested using ASTM C408. Native thermal conductivity can be measured by steady-state methods such as cut bar comparative techniques, heat flow meter techniques, guarded hot-plate / heater / hot-wire techniques, and calorimetry techniques. It can also be determined by transient techniques (hot wire and flash diffusivity).

[0029] In one example, the first component exhibits a native thermal conductivity of greater than about 10 W / m*K. In another example, the first component exhibits a native thermal conductivity of greater than about 20 W / m*K. The first component can exhibit a native thermal conductivity of greater than about 15 W / m*K, 18 W / m*K, 21 W / m*K, 24 W / m*K, 27 W / m*K, 30 W / m*K, or values therebetween. Utilizing a first component exhibiting a native thermal conductivity of the present disclosure ensures that the first particles promote the desirable thermal conductivity properties to the formed thermal interface material. The first component can exhibit a native thermal conductivity ranging from about 5 W / m*K to about 350 W / m*K.The first component can exhibit a native thermal conductivity ranging from about 5 W / m*K to about 100 W / m*K.

[0030] The first component can include metals, metal oxides, ceramics, and combinations thereof. In one example, the first component includes at least one of 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.

[0031] In one example, the first component includes at least one of boron nitride, aluminum nitride, alumina, and alumina trihydrate. In some embodiments, the first component is2024P00132 considered electrically insulative. In one non-limiting example, the first component is alumina. In one example, the average weight percentage of the first component in the first particles is greater than about 25 wt.%. In another example, the average weight percentage of the first component in the first particles is greater than about 40 wt.%. In yet another example, the average weight percentage of the first component in the first particles ranges from about 25 wt.% to about 75 wt.%. For example, the average weight percentage of the first component in the first particles can range from about 40 wt.% to about 75 wt.%. Average weight percentages of the first component in the first particles of the present disclosure (such as greater than about 25 wt.% or greater than about 40 wt.%) can ensure that the first particles are capable of promoting a desirable thermal conductivity to the thermal interface material.

[0032] The second component of the first particles can at least promote the overall electromagnetic absorption of the thermal interface material. The second component generally includes a material capable of absorbing electromagnetic radiation, such as electromagnetic radiation at a frequency in the range of 1-10 GHz. The second component can include an iron- containing material. The iron-containing material can include one or more ferrites. Examples of ferrites include trevorite, jacobsite, magnetite, and franklinite. In one non-limiting example, the iron-containing material is iron(II, III) oxide. In other embodiments, the second component can include at least one of a ferrite, magnetic metal, nickel coated carbon, nickel coated graphite, ceramic, carbonyl iron, and iron silicide. The first particles can include a blend of alumina and an iron-containing compound, such as iron(II, III) oxide. In one non-limiting example, an example of first particles including a mixture of alumina and iron(II, III) oxide is emery particles. Emery can include alumina, iron (II, III) oxide, silicon dioxide, and titanium dioxide. Accordingly, first particles may further include silicon dioxide and / or titanium dioxide, and optionally other trace compounds. The first component and the second component may be substantially homogenously distributed throughout each first particle.

[0033] The average weight percentage of the second component in the first particles can be greater than 15 wt.%. In one example, the average weight percentage of the second component in the first particles is greater than about 20 wt.%. In another example, the average weight percentage of the second component in the first particles is greater than about 25 wt.%. The average weight percentage of the second component in the first particles can range from about 15 wt.% to about 75 wt.%. In one example, the average weight percentage of the second component2024P00132 in the first particles ranges from about 25 wt.% to about 75 wt.%. For example, weight percentages of the second component of the present disclosure (such as between about 25 wt.% to about 75 wt.%) ensure that the first particles can not only promote a desirable overall thermal conductivity to the thermal interface material, but that the first particles absorb desirable levels of electromagnetic radiation at various frequencies, such as at frequencies in the range of 1-10 GHz. Absorbing desirable levels of electromagnetic radiation at various frequencies can reduce the electromagnetic interference in electronic devices.

[0034] The weight percentage of the first particles in the thermal interface material can be greater than about 25 wt.%. In one example, the weight percentage of the first particles in the thermal interface material is greater than about 30 wt.%. The weight percentage of the first particles in the thermal interface material can range from about 30 wt.% to about 95 wt.%. The volume percentage of the first particles in the thermal interface material can be greater than about 25 vol%. The volume percentage of the first particles in the thermal interface material can be greater than about 30 vol%. In one example, the volume percentage of the first particles in the thermal interface material can be greater than about 40 vol%. Weight percentages and / or volume percentages of the first particles in the thermal interface material listed in the present disclosure promote the desirable thermal conductivity and electromagnetic absorption to the thermal interface material.

[0035] The first particles may be of various shapes and size, and typically have a mean particle size (dso) of less than 500 pm. The first particles can have a mean particle size (dso) of less than 250 pm. In some embodiments, the first particles have a mean particle size (dso) in a range of between 0.1 and 500 pm. In some embodiments, the first particles have a mean particle size (dso) in a range of between 1 and 250 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 of 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. Example2024P00132 aspherical shapes include blocky, flake-like, plate-like, rod-like, and so on. Spherical thermally conductive filler may have an aspect ratio of between 0.8-1.2.

[0036] Since each of the first particles includes a mixture of the first component and the second component, these particles promote a desirable overall thermal conductivity to the thermal interface material and attenuate electromagnetic interference in an electronic device. Compared to conventional thermal interface materials that utilize a thermally conductive filler and a separate additive for electromagnetic interference management, often requiring highly refined materials, by utilizing first particles that, within each individual particle includes a mixture of the first component and the second component, the density of the thermal interface material (such as in the uncured form) can be decreased and the flow rate can be increased. Decreasing the density of the material can decrease transportation cost, and increasing the flow rate promotes efficient coating, injection, and / or dispensing of the thermal interface material.

[0037] Often, the conventional materials include separate electrically conductive shielding materials, as opposed to electromagnetic radiation absorbing materials. Further compared to conventional materials, the present first particles can promote at least the same overall thermal conductivity as conventional thermal interface materials while improving electromagnetic absorption. Importantly, thermal interface materials of the present disclosure improve sustainability by including first particles capable of both promoting a desirable overall thermal conductivity and attenuating electromagnetic interference in an electronic device, where the first particles require less pre-processing compared to conventional filler materials.

[0038] The particulate filler may further include second particles. The second particles can be used to increase the overall electromagnetic absorption of the thermal interface material. In one example, the second particles include an iron- containing material. In another example, the second particles include at least one ferrite, magnetite, a soft magnetic metal (such as Ni or sendust), nickel coated carbon, nickel coated graphite, silicon carbide, carbonyl iron, and iron silicide. Examples of suitable ferrites include trevorite, jacobsite, magnetite, and franklinite. In one non-limiting example, the second particles include manganese-zinc ferrite.

[0039] The second particles may include particles having a mean particle size (dso) ranging from about 1 pm to about 50 pm. In one example, the second particles include particles having a mean particle size (dso) ranging from about 2 pm to about 20 pm. The average surface area of the second particles can range from about 1.2 m2 / g to about 1.8 m2 / g. The weight percentage of the2024P00132 second particles in thermal interface material can be greater than 25 wt.%. In one example, the weight percentage of the second particles in thermal interface material is greater than 30 wt.%. In another example, the weight percentage of the second particles in thermal interface material is greater than 40 wt.%. The weight percentage of the second particles can be used to tune the overall balance of electromagnetic absorption and thermal conductivity of the thermal interface material.

[0040] The weight percentage of the total particulate filler in the thermal interface material can be greater than 40 wt.%. In one example, the weight percentage of the total particulate filler in the thermal interface material can be greater than 50 wt.%. In another example, the weight percentage of the total particulate filler in the thermal interface material can be greater than 60 wt.%. The weight percentage of the total particulate filler in the thermal interface material can range from about 40 wt.% to about 95 wt.%. In one example, the weight percentage of the total particulate filler in the thermal interface material can range from about 70 wt.% to about 95 wt.%. The volume percentage of the total particulate filler in the thermal interface material can be greater than 40 vol.%. In one example, the volume percentage of the total particulate filler in the thermal interface material is greater than 50 vol.%. Weight and volume percentages of the total particulate filler in the thermal interface material listed in the present disclosure are useful for promoting the desirable thermal conductivity and electromagnetic absorption to the thermal interface material.

[0041] The thermal interface material may have a density of less than about 3 g / cm3. In one example, the thermal interface material has a density of less than about 2.5 g / cm3. The thermal interface material may have a density of greater than about 1.5 g / cm3. In one example, the thermal interface material has a density of greater than about 2 g / cm3. The thermal interface material may have a density ranging from about 1.5 g / cm3to about 3 g / cm3. In one example, the thermal interface material has a density ranging from about 1.5 g / cm3to about 2.5 g / cm3. In another example, the thermal interface material has a density ranging from about 2 g / cm3to about 2.5 g / cm3. Densities of the present disclosure can be attained by at least using the first particles of the present disclosure in conjunction with the matrix material. The first particles are both thermally conductive and capable of absorbing electromagnetic radiation while decreasing the density of the thermal interface material compared to conventional thermal materials that use separate thermally conductive filler particles and additives for electromagnetic interference.2024P00132Decreasing the overall density of the thermal interface material can decrease the weight of the product, decreasing the product transportation cost. Moreover, thermally conductive filler particles of decreased density can improve storage stability by reducing settling of the particles.

[0042] The thermal interface material may exhibit a thermal conductivity of greater than 0.5 W / m*K. In one example, the thermal interface material exhibits a thermal conductivity of greater than 1 W / m*K. In another example, the thermal interface material exhibits a thermal conductivity of greater than 2 W / m*K. The thermal interface material may exhibit a thermal conductivity ranging from about 0.5 W / m*K to about 10 W / m*K. In one example, the thermal interface material exhibits a thermal conductivity ranging from about 1 W / m* to about 8 W / m*K. In another example, the thermal interface material exhibits a thermal conductivity ranging from about 1 W / m*K to about 5 W / m*K. For example, thermal conductivity values can be derived from ASTM D5470. Thermal conductivity values of the thermal interface material of the present disclosure are useful for dissipating heat from heat generating devices to maintain the heat generating devices at desirable temperatures.

[0043] The thermal interface material can absorb at least 0.1 dB / mm of electromagnetic radiation at 5GHz. In one example, the thermal interface material can absorb at least 0.5 dB / mm of electromagnetic radiation at 5 GHz. The thermal interface material can exhibit an electromagnetic absorption value at 5 GHz of between -0.1 dB / mm and -100 dB / mm. In one example, the thermal interface material can exhibit an electromagnetic absorption value at 5 GHz of between -0.1 dB / mm and -50 dB / mm. In one non-limiting example, the thermal interface material can exhibit an electromagnetic absorption value at 5 GHz of between -0.5 dB / mm and - 10 dB / mm. Electromagnetic absorption values can be measured using ASTM D5568. By absorbing, in addition to reflecting, electromagnetic radiation (such as absorbing at least 0.1 or 0.5 dB / mm of electromagnetic radiation at 5GHz), thermal interface materials of the present disclosure can reduce electromagnetic interference to electronic components.

[0044] The thermal interface material can exhibit an absorption percentage (for electromagnetic radiation at 5 GHz) of at least 15 %. The thermal interface material can exhibit an absorption percentage (for electromagnetic radiation at 5 GHz) of at least 20 %. The thermal interface material can exhibit a reflectance percentage (for electromagnetic radiation at 5 GHz) of at least 30 %. The thermal interface material can exhibit a reflectance percentage (for electromagnetic radiation at 5 GHz) of at least 40 %. Accordingly, the thermal interface material2024P00132 can also reflect or shield one or more electronic components from electromagnetic radiation, reducing or preventing electromagnetic interference. Importantly, compared to conventional thermal interface materials with electromagnetic-shielding only materials, the first particles are capable of both absorbing and reflecting electromagnetic radiation.

[0045] The thermal interface material can absorb at least 0.5 dB / mm of electromagnetic radiation at 15GHz. In one example, the thermal interface material can absorb at least 1 dB / mm of electromagnetic radiation at 15GHz. The thermal interface material can exhibit an electromagnetic absorption value at 15 GHz of between -0.1 dB / mm and -100 dB / mm. In one example, the thermal interface material can exhibit an electromagnetic absorption value at 51 GHz of between -0.1 dB / mm and -50 dB / mm. In one non-limiting example, the thermal interface material can exhibit an electromagnetic absorption value at 15 GHz of between -0.5 dB / mm and -10 dB / mm. Electromagnetic absorption values can be measured using ASTM D5568. Thermal interface materials exhibiting electromagnetic absorption values of the present disclosure can be attained using at least the first particles to promote overall electromagnetic absorption of the thermal interface material.

[0046] The present disclosure includes methods for attenuating electromagnetic interference in an electronic device, according to some embodiments. A thermal interface material of the present disclosure can be positioned so that at least a portion of the thermal interface material is in contact with at least a portion of a heat-generating component of the electronic device. Reducing electromagnetic interference can include absorbing electromagnetic radiation at frequencies of the present disclosure. Examples of heat-generating components include semiconductor elements, power transistors, integrated circuits, and battery elements. The heat-generating component can be an electronic chip capable of processing data in an electronic device, such as a cellular phone. The thermal interface material can also be in contact with a heat-dissipating component, such that the thermal interface material is interposed between the heat-generating component and the heat-dissipating component. Examples of heat-dissipating components include plates and fins. Accordingly, heat can be transferred through the thermal interface material, from the heat-generating component to the heat-dissipating component.2024P00132EXAMPLESExample 1

[0047] Formulations were prepared using 48 vol.% of filler in an addition-cure silicone matrix. Three filler types were tested: Crushed bauxite as an example of an unrefined alumina (aluminum oxide), ground calcined aluminum oxide as an example of a thermally conductive filler, and ground emery, which is a mixture of alumina and iron oxide. Electromagnetic absorption was tested at 5 GHz using ASTM D 5568. Each material was tested with a thickness of about 1.52 mm. FIG. 1 illustrates absorbance values at 5 GHz for various materials, according to some embodiments. As shown, the electromagnetic absorption of the emeiy-containing product was significantly more than that of the crushed bauxite and the calcined aluminum oxide. FIG. 2 illustrates reflectance percentages at 5 GHz for various materials, according to some embodiments. As shown, the incorporation of emery in the formulation also increased the electromagnetic reflection. Accordingly, first particles of the present disclosure increase the absorption and the reflection of the thermal interface material, sufficient to reduce or prevent electromagnetic interference of electronic devices coupled to the thermal interface material.Example 2

[0048] Formulations were prepared to test the thermal conductivity, density (of the uncured suspension), and dispense rate (of the uncured suspension). As shown in Table 1 below, Formulation 1 included ferrite powder and alumina. As shown in Table 2 below, Formulation 2 included ferrite powder and the first particles of the present disclosure, wherein the first particles included emery particles, having aluminum oxide and iron (II, III) oxide. While Formulations 1 and 2 utilized a vinyl-terminated polydimethyl silicone resin and a pendent hydride siloxane crosslinker, other materials such as epoxies can be used as a matrix material. The formulations also included a reaction inhibitor, catalyst, and carbon black pigment. Table 3 below lists the thermal conductivity, density, and dispense rate for Formulations 1 and 2. The thermal conductivity was tested per ASTM D5470 using a 3-layer stack and a pressure of about 6.2 bar. Dispense rate was calculated at a pressure of about 6.2 bar. Importantly, the use of the first particles in Formulation 2 decreased the density of the formulation and increased the dispense rate as compared to Formulation 1, while maintaining the desirable thermal conductivity.2024P00132Table 1. Formulation 1 Weight Percentage, Volume Percentage, and PHR of Components.Table 2. Formulation 2 Weight Percentage, Volume Percentage, and PHR of Components.Table 3. Thermal Conductivity, Density, and Dispense Rate of Formulations 1 and 2.

[0049] Sheets were prepared using Formulation 1 and Formulation 2. The sheets were then tested per ASTM D5568 to determine the absorption and electromagnetic properties at 5 GHz, 13 GHz, 15 GHz, and 17 GHz. The tested thickness of Formulation 1 was 1.42 mm, and the tested thickness of Formulation 2 was 1.15 mm. FIG. 3 illustrates a comparison of absorption per length values of distinct formulations, according to some embodiments. Specifically, FIG. 3 compares the absorption per length of Formulation 1 and Formulation 2. As shown, Formulation 1 exhibited an absorption per length at 5 GHz ranging from about - 1.06 to - 1.14 dB / mm, while Formulation 2 exhibited an absorption per length at 5 GHz ranging from about -1.26 to -1.33 dB / mm. The use of the emery first particles in Formulation 2, rather than 50 pm alumina,2024P00132 increased the absorption per length of the formulation compared to Formulation 1 at multiple frequencies.

[0050] FIG. 4 illustrates the increase in absorption per length values between distinct formulations, according to some embodiments. As shown, at 5 GHz, the percentage change in dB / mm absorbed by using Formulation 2 instead of Formulation 1 ranged from about 10 % to 25 % (relative to Formulation 1). At 15 GHz, the percentage change in dB / mm absorbed by using Formulation 2 instead of Formulation 1 ranged from about 25 % to 32 %. At 17 GHz, the percentage change in dB / mm absorbed by using Formulation 2 instead of Formulation 1 ranged from about 5 % to 42 %. Accordingly, the use of the emery first particles increased the dB / mm absorbed for the thermal interface material. By increasing the dB / mm absorbed by the thermal interface material, the potential for electromagnetic interference of electronic devices is reduced.

[0051] 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

2024P00132CLAIMS:

1. A thermal interface material, comprising: a matrix material; and a particulate filler dispersed in the matrix material, the particulate filler including particles that each include a first component and a second component, the first component exhibiting a native thermal conductivity value of greater than 10 W / m*K, wherein the thermal interface material exhibits a density of between about 1.5 g / cm3to about 3 g / cm3, and an electromagnetic absorption value at 5 GHz of between -0.1 dB / mm and -100 dB / mm.

2. The thermal interface material of claim 1, wherein the matrix material includes a silicone- based matrix material or an epoxy-based matrix material.

3. The thermal interface material of claim 1, wherein the native thermal conductivity value of the first component is greater than about 20 W / m*K.

4. The thermal interface material of claim 1, wherein the first component includes aluminum oxide.

5. The thermal interface material of claim 4, wherein the second component includes an iron-containing material.

6. The thermal interface material of claim 4, wherein the second component includes iron (II, III) oxide.

7. The thermal interface material of claim 6, wherein the density of the thermal interface material ranges from 2 g / cm3to 2.5 g / cm3.

8. The thermal interface material of claim 1, wherein the thermal interface material exhibits an electromagnetic absorption value at 5 GHz of between -0.5 dB / mm and -10 dB / mm.2024P001329. The thermal interface material of claim 1 , wherein the thermal interface material exhibits a thermal conductivity value of greater than about 1 W / m*K.

10. The thermal interface material of claim 1, wherein the particulate filler further includes second particles including iron oxide.

11. The thermal interface material of claim 1 , wherein the second component includes an iron-containing material, and an average weight percentage of the second component in the particles is greater than about 25 wt.%.

12. The thermal interface material of claim 11 , wherein an average weight percentage of the first component in the particles is greater than about 50 wt.%.

13. A thermal interface material, comprising: a matrix material; and a particulate filler dispersed in the matrix material, the particulate filler comprising between 40 wt.% and 95 wt.% of the thermal interface material and including first particles that each include a mixture of aluminum oxide and iron (II, III) oxide.

14. The thermal interface material of claim 13, wherein the particulate filler includes second particles, wherein the second particles are present in the thermal interface material in a range of from about 10 vol% to about 40 vol%.

15. The thermal interface material of claim 13, wherein the thermal interface material exhibits an electromagnetic absorption value at 5 GHz of between about -0.5 dB / mm to about - 10 dB / mm.

16. A method for attenuating electromagnetic radiation in an electronic device, the method comprising: positioning the thermal interface material of Claim 13 in contact with at least a portion of a heat-generating component of the electronic device.2024P0013217. A thermal interface material, the thermal interface material comprising: a matrix material; and a particulate filler dispersed in the matrix material, the particulate filler including first particles that each include a mixture of a first component and a second component, the first component exhibiting a native thermal conductivity value of greater than 10 W / m*K and the second component including an iron-containing material, wherein the thermal interface material exhibits an electromagnetic absorption value at 5 GHz of between -0.1 dB / mm and -100 dB / mm.

18. The thermal interface material of claim 17, wherein the first component includes aluminum oxide, and the iron-containing material includes iron (II, III) oxide.

19. The thermal interface material of claim 17, wherein the thermal interface material exhibits an electromagnetic absorption value at 5 GHz of between about -0.5 dB / mm to about - 10 dB / mm.20

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