Dispensable thermally conductive gap filler

Abstract

A thermal interface material includes a matrix material; a filler dispersed in the matrix material, wherein the filler includes a plurality of particles having a maximum particle size of less than or equal to about 100 μm, wherein the plurality of particles includes first particles having a first mean particle size (d50) of between 5 and 80 µm, second particles having a second mean particle size (d50) of between 200 nm and 5 µm, and wherein a weight ratio of the first particles to the second particles is greater than 1:1; and a coupling agent capable of promoting adhesion between the matrix material and the plurality of particles, the coupling agent present in the thermal interface material in a range of between about 0.1 wt.% and about 2 wt.% of the filler.

Description

2024P00085 DISPENSABLE THERMALLY CONDUCTIVE GAP FILLER FIELD

[0001] The subject matter disclosed herein relates generally to thermally conductive materials and, in particular, to dispensable thermally conductive gap fillers. The present invention further relates to methods for manufacturing such thermally conductive constructs. BACKGROUND

[0002] Thermally conductive interface materials are widely employed for the purpose of dissipating heat from heat-generating components such as semiconductor elements, power transistors, integrated circuits, and battery elements. Thermally conductive greases, gels, pastes, and sheets have been used as interfaces between the heat-generating components and heat-dissipating elements such as plates and fins. Numerous designs and materials for such thermal interfaces have been implemented, with the highest performance being achieved when gaps between the thermal interface and the respective heat transfer surfaces are substantially avoided to promote conductive heat transfer from the electronic component to the heat dissipater. The thermal interface materials therefore preferably mechanically conform to the somewhat uneven heat transfer surfaces of the respective components. Therefore, important physical characteristics of high-performance thermal interface materials 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.2024P00085

[0004] However, high dispensability is often contrary to other important characteristics such as storage stability, limiting shelf life, and heat dissipation characteristics. For example, increasing the size of thermally conductive filler can improve dispensability, but larger particle sizes restrict the achievable thermal impedance of the assembled component. Further, increasing the size of the thermally conductive filler can accelerate the rate of resin separation. Accordingly, embodiments of the present disclosure provide thermally conductive materials with excellent dispensability and heat dissipation characteristics, while reducing the thermal impedance of the assembled component. SUMMARY

[0005] According to one aspect, a thermal interface material includes a matrix material; a filler dispersed in the matrix material, wherein the filler includes a plurality of particles having a maximum particle size of less than or equal to about 100 μm, wherein the plurality of particles includes first particles having a first mean particle size (d50) of between 5 and 80 µm, second particles having a second mean particle size (d50) of between 200 nm and 5 µm, and wherein a weight ratio of the first particles to the second particles is greater than 1:1; and a coupling agent capable of promoting adhesion between the matrix material and the plurality of particles, the coupling agent present in the thermal interface material in a range of between about 0.1 wt.% and about 2 wt.% of the filler.

[0006] According to another aspect, a thermal interface material includes an organopolysiloxane matrix material; a filler dispersed in the organopolysiloxane matrix material and including a plurality of particles, wherein the plurality of particles includes first particles having a first mean particle size (d50) of between 5 and 80 µm, second particles having a second mean particle size (d50) of less than 5 µm, and wherein a weight ratio of the first particles to the second particles is greater than 1:1; and a coupling agent having an affinity for the organopolysiloxane matrix material and capable of promoting adhesion between the organopolysiloxane matrix material and the plurality2024P00085 of particles, the coupling agent including at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent.

[0007] According to another aspect, a thermally conductive material includes a resin blend including a vinyl functional siloxane resin and a hydride functional siloxane resin; a thermally conductive filler dispersed in the resin blend and including a plurality of particles having a maximum particle size of less than or equal to about 100 μm, wherein the plurality of particles includes first particles and second particles; wherein the first particles have a first mean particle size (d50) of between 5 and 80 µm, and second particles having a second mean particle size (d50) of between 200 nm and 5 µm; wherein the first particles are present at a concentration of greater than 450 parts per hundred of the resin blend (phr), and the second particles are present at a concentration of greater than 300 phr; and a coupling agent including at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent. BRIEF DESCRIPTION OF THE DRAWING

[0008] FIG.1 illustrates apparatus 100 including thermally conductive interface material 130, according to some embodiments. DETAILED DESCRIPTION

[0009] 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, inadequate dispensability, poor stability, such as storage stability, and undesirable thermal impedance of the assembled component.

[0010] Thermal interface materials of the present disclosure can include at least one of a matrix material, a thermally conductive filler, a coupling agent, and additives. The thermally conductive filler can be dispersed in the matrix material and can enhance2024P00085 the heat dissipation properties of the thermally conductive interface material. This thermally conductive filler generally includes thermally conductive particles, where the thermal conductive particles can also be electrically insulating particulate fillers. The thermally conductive filler and coupling agent can be mixed with one or more resins using a speed mixer under vacuum.

[0011] 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. For 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.

[0012] 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.2024P00085

[0013] 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. An example silicone may be an organosiloxane having the structural formula: wherein “x” represents 1,000. The thermally conductive interfaceproduct of the organosiloxane together with a chain extender / cross-linker such as a hydride functional polydimethylsiloxane having the structural formula: wherein “x” and “y” between 1 and 1,000.

[0014] An component present 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. Viscosity values can be measured at about 20 °C and at a shear rate of 1 / s.

[0015] The chemical cure activator may itself be reactive with the curable component and may include a cross-linker for a hydrosilylation reaction. The chemical2024P00085 cure activator may include a dihydroxy aliphatic chain extender such as a hydride- terminated polydimethylsiloxane. The silicon-bonded hydrogen atoms may be located at terminal, pendant, or at both terminal and pendant positions. The chemical cure activator may include one or more organohydrogen polysiloxanes that may differ in at least one of molecular weight, viscosity, and molecular structure. Example commercially-available methylhydropolydimethylsiloxanes useful as a chemical cure activator that is reactive with the first reactant composition include Nusil XL-112 and XL- 7505 available from Avantor, Inc.; Gelest HMS-071, 082, and 991 available from Gelest, Inc.; and Andisil XL-1B and 1340 available from AB Specialty Silicones. For example, hydride functional PDMS crosslinkers with viscosity values ranging from about 20 mPa‧ s to about 300 mPa‧s may be utilized. Viscosity values can be measured at about 20 °C and at a shear rate of 1 / s.

[0016] 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 example, the first viscosity is less than 500 mPa‧s and the second viscosity is greater than 500 mPa‧s. Viscosity values can be measured at about 20 °C and at a shear rate of 1 / s. In one non-limiting example, both the first polymeric resin and the second polymeric resin include vinyl-terminated polydimethylsiloxane (PDMS) materials. The blend of multiple resins 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. In some embodiments, the matrix material may include an organic matrix including at least one of a thermoplastic resin and / or a thermoset resin. The matrix material can include a thermosetting polymer.

[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 some2024P00085 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 20oC and 1 bar pressure and exhibit a viscosity of less than 1000 cP at 20oC at a shear rate of 1 / s. In some embodiments, one or more of the monomers, oligomers, or resins may be in liquid form at 20oC and 1 bar pressure and exhibit a viscosity of less than 200 cP at 20oC at a shear rate of 1 / s.

[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 one example, the catalyst includes a Karstedt catalyst. For example, the Karstedt catalyst includes an organoplatinum compound derived from divinyl-containing disiloxane. Reaction catalysts used in the compositions of the present invention may be present 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.2024P00085

[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.

[0022] Thermal interface materials of the present disclosure generally include a filler. The filler generally includes thermally conductive filler and can be provided in the form of a plurality of particles. The plurality of particles can provide desired thermal conductivity properties to the interfaces of the present disclosure. For example, the plurality of particles can be a thermally conductive particulate filler useful for increasing the overall thermal conductivity of the thermal interface material. The filler may be dispersed in the matrix material. In one example, the filler includes electrically insulating particulate fillers. The composition, amount, and distribution of filler dispersed in the2024P00085 matrix material can be used to tune overall thermal conductivity and viscosity values of the thermal interface material.

[0023] The thermally conductive fillers contemplated for use in the preparations of the present invention include metals, metal oxides, ceramics, and combinations thereof. Example 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. The thermally conductive filler can include calcined alumina.

[0024] The thermally conductive filler may be of various shapes and size, and typically have a mean particle size (d50) in a range of between 0.1 and 200 µm. In some embodiments, the thermally conductive fillers have a mean particle size (d50) in a range of between 1 and 100 µm. 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 (d50) 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] As discussed, the thermal interface material can be in contact with, and positioned between, a heat generating component and a heat dissipating component,2024P00085 sufficient to efficiently transfer heat from the heat generating component to the heat dissipating component. The thermally conductive filler can include a plurality of particulate filler particles having a maximum particle size (D100) of less than or equal to about 100 μm. In one example, the plurality of particulate filler particles has a maximum particle size (D100) of less than or equal to about 80 μm. The plurality of particulate filler particles can exhibit a particle size (D90) of less than or equal to about 80 μm, where 90% of the total particles are less than or equal to 80 μm. In another example, the plurality of particulate filler particles has a maximum particle size (D100) of less than or equal to about 60 μm. In yet another example, the plurality of particulate filler particles has a maximum particle size (D100) of less than or equal to about 50 μm. The plurality of particulate filler particles can exhibit a particle size (D90) of less than or equal to about 50 μm, where 90% of the total particles are less than or equal to 50 μm.

[0026] Often, conventional materials utilize large filler particles (such as particles having maximum particle sizes (d100) above 80 μm or 100 μm) to maximize bulk thermal conductivity and enhance dispensability of thermal interface materials. However, thermal interface materials formed using this approach suffer from resin separation and an increase in assembled bondline thickness between the heat generating component and the heat dissipating component. The increase in assembled bondline thickness restricts the achievable thermal impedance of the installed thermal interface material. Accordingly, for conventional materials, the restriction of achievable thermal impedance reduces the overall heat transfer efficiency of the material.

[0027] Compared to conventional materials, particle sizes of the present disclosure (such as a maximum particle size D100or particle size D90) enable a decreased, assembled bondline thickness between the heat generating component and the heat dissipating component, minimizing thermal impedance of the thermal interface material. Decreasing or minimizing the thermal impedance of the thermal interface material promotes increased heat transfer efficiency, and the thermal interface material exhibits excellent heat generating component temperature control at high power densities. Additionally, particle sizes of the present disclosure (such as a maximum particle size D100or particle size D90) enable a desirable balance of assembled bondline thickness and dispensability of the thermal interface material.2024P00085

[0028] The thermally conductive filler can include a plurality of particulate filler particles including first particles and / or second particles. The first particles may provide the primary mechanism for heat transfer. In one example, the first particles include a thermally conductive material having a thermal conductivity value greater than about 20 W / m*K, greater than about 500 W / m*K, or greater than about 100 W / m*K. The first particles can include one or more thermally conductive fillers of the present disclosure. For example, the first particles can include one or more metal oxides. In one example, the first particles include at least one of aluminum nitride and alumina.

[0029] In one example, the first particles have a first mean particle size (d50) of greater than about 5 μm. In another example, the first particles have a first mean particle size (d50) of greater than about 8 μm. In another example, the first particles have a first mean particle size (d50) of greater than about 10 μm. In one example, the first particles have a first mean particle size (d50) of between about 5 μm and about 100 μm. In another example, the first particles have a first mean particle size (d50) of between about 5 μm and about 80 μm. In yet another example, the first particles have a first mean particle size (d50) of between about 5 μm and about 50 μm, or 5 μm and about 30 μm. In one non-limiting example, the first particles have a first mean particle size (d50) of less than 100 μm or less than 50 μm. In another non-limiting example, the first particles have a first mean particle size (d50) of less than 80 μm. The first mean particle size (d50) can be the largest mean particle size of all particles within the filler component. For example, first mean particle sizes (d50), such as a first mean particle size (d50) of between about 5 μm and about 80 μm, promote a desirable thermal conductivity value and thermal impedance to the thermal interface material while providing an efficient balance of dispensability and low shear viscosity (discussed in further detail herein). Compared to materials only having filler exhibiting particle sizes below about 5 μm, the present materials exhibit greater thermal conductivity values and improved dispensability.

[0030] The concentration of the first particles with respect to resin used to form the matrix material can range from about 200 parts per hundred resin (phr) to about 1600 phr. In one example, the concentration of the first particles with respect to resin used to form the matrix material ranges from about 450 phr to about 1600 phr. In another2024P00085 example, the concentration of the first particles with respect to resin used to form the matrix material ranges from about 450 phr to about 1100 phr. The concentration of the first particles with respect to resin used to form the matrix material can be greater than about 450 phr. The concentration of the first particles with respect to resin used to form the matrix material can be greater than about 500 phr. Concentration values of the first particles can promote a desirable thermal conductivity value to the thermal interface material while providing an efficient balance of dispensability and low shear viscosity.

[0031] The second particles can include one or more thermally conductive filler materials of the present disclosure. For example, the second particles can include calcined alumina. In one example, the second particles include at least one of aluminum nitride and alumina. The second particles can have a second mean particle size (d50) of greater than about 200 nm. In another example, the second particles have a second mean particle size (d50) of greater than about 800 nm. In another example, the second particles have a second mean particle size (d50) of greater than about 1 μm. In one example, the second particles have a second mean particle size (d50) of between about 200 nm and about 5 μm. In another example, the second particles have a second mean particle size (d50) of between about 200 nm and about 2 μm. In yet another example, the second particles have a second mean particle size (d50) of between about 1 μm and about 2 μm. In one non-limiting example, the second particles have a second mean particle size (d50) of less than 5 μm or less than 3 μm. In another non-limiting example, the second particles have a second mean particle size (d50) of less than the first mean particle size (d50).

[0032] The concentration of the second particles with respect to resin used to form the matrix material can range from about 100 parts per hundred resin (phr) to about 1000 phr. In one example, the concentration of the second particles with respect to resin used to form the matrix material ranges from about 100 phr to about 600 phr. In another example, the concentration of the second particles with respect to resin used to form the matrix material ranges from about 200 phr to about 450 phr. The concentration of the second particles with respect to resin used to form the matrix material can be less than about 600 phr. The concentration of the second particles with respect to resin used to form the matrix material can be less than about 450 phr. The concentration of the2024P00085 second particles with respect to resin used to form the matrix material can be greater than about 300 phr.

[0033] The weight ratio of the first particles to the second particles can be greater than 1:1. In one example, a weight ratio of the first particles to the second particles is greater than 1.2:1. In another example, a weight ratio of the first particles to the second particles is greater than 1.4:1. The weight ratio of the first particles to the second particles can range from about 1:1 to about 4:1. In one example, the weight ratio of the first particles to the second particles can range from about 1.4:1 to about 4:1. In another example, the weight ratio of the first particles to the second particles can range from about 1.4:1 to about 3:1. In another example, the weight ratio of the first particles to the second particles can range from about 1:1 to about 2:1.

[0034] 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 of at least the first particles and the second particles of the present disclosure can tune shear thinning properties of the thermal interface material. Further, the weight ratios of the first particles and second particles can tune the shear thinning properties. In one non-limiting example, compared to a material having a weight ratio of the first particles to the second particles of less than 1:1, weight ratios of the first particles to the second particles of greater than 1:1 can promote desirable viscosity values to the thermal interface material at both low and high shear rates, improving the shear thinning properties. For example, thermal interface materials including the first particles and the second particles can exhibit desired viscosity values under shear strain. These tuned shear thinning properties can assist with enhancing dispensability during the application process. In another non-limiting example, compared to a material having a weight ratio of the first particles to the second particles of greater than 4:1, weight ratios of the first particles to the second particles of between 1:1 and 4:1 can prevent or reduce resin separation, improving the stability of the thermal interface material.

[0035] The particulate filler may include third particles. The third particles can include fillers of the present disclosure, such as alumina. In one example, the third2024P00085 particles have a third mean particle size (d50) of less than about 1 µm. In another example, the third particles have a third mean particle size (d50) of less than about 800 nm. In another example, the third particles have a third mean particle size (d50) of less than about 500 nm. In yet another example, the third particles have a third mean particle size (d50) of between about 100 nm and about 300 nm. The third particles can have a third mean particle size (d50) of less than the second mean particle size (d50).

[0036] The total volume percentage of particulate filler in the thermal interface material may range from about 70 vol% to about 90 vol%. In one example, the total volume percentage of particulate filler in the thermal interface material may range from about 75 vol% to about 85 vol%. In another example, the total volume percentage of particulate filler in the thermal interface material may be greater than about 75 vol%. Volume percentages of the particulate filler can promote a balance between overall thermal conductivity and dispensability of the thermal interface material.

[0037] Thermal interface materials of the present disclosure can include a coupling agent. The coupling agent can be capable of at least partially coating the plurality of particulate filler particles. By at least partially coating the plurality of particulate filler particles, the coupling agent can reduce frictional contacts between individual particles. The coupling agent can be capable of promoting adhesion between the matrix material and the plurality of particles. In one example, the matrix material includes an organopolysiloxane, and the coupling agent exhibits an affinity for the organopolysiloxane, promoting adhesion between the organopolysiloxane and the filler. The affinity for the organopolysiloxane ensures that the coupling agent can chemically bridge the organopolysiloxane and the filler. Importantly, the coupling agent can improve flowability of the filler - promoting the reduction of installed bond-line thickness (BLT) between a heat generating component and a heat dissipating component.

[0038] In one example, the coupling agent includes at least one functional group preferring to adsorb or react on a surface of the thermally conductive filler, such as a metal-oxide filler. The coupling agent can include at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent. An example of a suitable alkylthiol coupling agent includes octadecyl mercaptan. The fatty acid coupling agent can include a branched fatty acid. Examples of suitable fatty acid coupling agents2024P00085 include at least one oleic acid, stearic acid, a titanate coupling agent, and a zirconate coupling agent. For example, the titanate coupling agent can include a monoalkoxy titanate coupling agent. Monoalkoxy titanate coupling agents can include a branched fatty acid, having compatibility with the matrix material and coordinating with the filler.

[0039] Examples of monoalkoxy titanate coupling agents include Titanium IV 2- propanolato, tris isooctadecanoato-O; Titanium IV bis 2-methyl-2-propenoato-O, isooctadecanoato-O 2-propanolato; and Titanium IV 2-propanolato, tris(dioctyl)phosphato-O. Examples of zirconate coupling agents include Zirconium IV 2,2(bis-2-propenolatomethyl)butanolato, tris neodecanolato-O; and Zirconium IV 2,2(bis-2-propenolato)butanolato, tris 2-propenoato-O. In some embodiments, the coupling agent is selected from titanate coupling agents, aliphatic coupling agents, and silane coupling agents. In one non-limiting example, the coupling agent includes Titanium IV 2-propanolato, tris isooctadecanoato-O. The coupling agent can include a trimethoxyterminated siloxane. Additional examples of coupling agents include alkyl- trimethoxysilanes and siloxane-trimethoxysilanes.

[0040] The coupling agent can be present in the thermal interface material in a range of between about 0.01 wt.% and about 3 wt.% of the filler and / or between about 0.01 wt.% and about 3 wt.% of the thermal interface material. In one example, the coupling agent is present in the thermal interface material in a range of between about 0.1 wt.% and about 2 wt.% of the filler. In another example, the coupling agent is present in the thermal interface material in a range of between about 0.1 wt.% and about 1 wt.% of the filler. In one example, the coupling agent is present in the thermal interface material at greater than 0.01 wt.% of the filler. In one example, the coupling agent is present in the thermal interface material at greater than 0.1 wt.% of the filler. In another example, the coupling agent is present in the thermal interface material at less than 2 wt.% of the filler. In one non-limiting example, a coupling agent present in the thermal interface material at greater than 2 wt.% of the filler can increase the amount of volatiles present in the system and / or can negatively impact mechanical properties of the thermal interface material.

[0041] The combination of the coupling agent having weight percentages of the present disclosure with the weight ratio and mean particle sizes of the first particles and2024P00085 second particles promotes desirable flow characteristics, such as shear thinning behavior, to the thermal interface material. Improving the shear thinning behavior can improve at least one of dispensability and reducing the assembly force to reach the desired bondline thickness. Further, this combination exhibits desirable thermal conductivity while minimizing the assembled bondline thickness of the thermal interface material, reducing the thermal impedance of the thermal interface material. The shear thinning behavior of the thermal interface material can reduce the force to reach this minimized bondline.

[0042] Thermal interface materials of the present disclosure may include one or more additives. The additive may be utilized to improve at least one of slump resistance, stability of the thermal interface material, and dispensability. In one example, the additive includes a fumed metal-oxide. Examples of suitable fumed metal-oxides include fumed alumina and fumed silica. Additionally, or alternatively, the additive may include a silicone oil. Examples of suitable silicone oils include silicone oils having a viscosity of less than about 100 mPa‧s at a temperature of 20 °C and a shear rate of 1 / s. In one example, the silicone oil exhibits a viscosity of less than 20 mPa‧s at a temperature of 20 °C and a shear rate of 1 / s.

[0043] In one example, the overall thermal conductivity of the thermal interface material is greater than about 3 W / m*K. In another example, the overall thermal conductivity of the thermal interface material is greater than about 5 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 9 W / m*K. Thermal conductivity can be measured according to ASTM D 5470. The dispense rate of the thermal interface material may be greater than 5 g / min. The dispense rate of the thermal interface material may be greater than 10 g / min. For example, the dispense rate of the thermal interface material may be greater than 50 g / min. Dispense rate can be measured using a pressure-driven flow through a 0.254 cm nozzle at 6 bar.

[0044] The low shear viscosity of the thermal interface material can be greater than 300 Pa‧s. The low shear viscosity of the thermal interface material can be less than2024P00085 1200 Pa‧s. Low shear viscosity can be measured using a 25 mm parallel plate at 11 / s. Viscosity values can be measured at 20 °C. The high shear viscosity of the thermal interface material can be less than 100 Pa‧s. The high shear viscosity of the thermal interface material can be less than 60 Pa‧s. High shear viscosity can be measured on a capillary rheometer, at 45001 / s. Viscosity values can be measured at 20 °C. The low shear viscosity values of the present disclosure enable the thermal interface material to be stable under low shear, while the high shear viscosity ensures that the material flows at a desirable rate for dispensable applications. As discussed, the specific combination of the particle sizes and weight ratio of at least the first particles and the second particles of the present disclosure in combination with the coupling agent can tune shear thinning properties of the thermal interface material.

[0045] A ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (d50) of the first particles can be greater than, or equal to, 8 W / mm2K, 9 W / mm2K, 10 W / mm2K, or 11 W / mm2K. In one example, a ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (d50) of the first particles is greater than, or equal to, 12 W / mm2K. In another example, a ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (d50) of the first particles is greater than, or equal to, 15 W / mm2K. In yet another example, a ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (d50) of the first particles is between about 10 W / mm2K and 30 W / mm2K. In yet another example, a ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (d50) of the first particles is between about 12 W / mm2K and 20 W / mm2K.

[0046] FIG.1 illustrates apparatus 100 including thermally conductive interface material 130, according to some embodiments. Apparatus 100 may include a heat- generating 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 thermal interface material 130. Thermal interface material 130 includes thermal interface materials of the present disclosure. As shown, the thermal interface material 130 is in contact with at least a2024P00085 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 thermal interface material 130 to be electrically insulating. In another example, heat dissipating component 120 includes a metal heat dissipating component, optionally including one or more fins for enhanced heat dissipation. Accordingly, thermal interface material 130 transfers heat from the heat producing component 110 to the heat dissipating component 120.

[0047] The assembled bondline thickness 132 of thermal interface material 130 can be less than about 200 μm. In one example, the assembled bondline thickness 132 of thermal interface material 130 is less than about 160 μm. In another example, the assembled bondline thickness 132 of thermal interface material 130 is less than about 100 μm. In one non-limiting example, bondline measurements can be performed at about room temperature (e.g., 20 °C). In another non-limiting example, bondline measurements can be performed using a screw fixture. In another non-limiting example, bondline measurements can be performed using a pressure of about 1 MPa. Further, the thermal interface material 130 exhibits desirable thermal conductivity while minimizing the installed bondline thickness of the thermal interface material, reducing the thermal impedance of the thermal interface material. EXAMPLES Example 1

[0048] Thermal conductivity was measured according to ASTM D 5470. Dispense rate was measured using a pressure-driven flow through a 0.254 cm nozzle at 6 bar. Low shear viscosity was measured using a 25 mm parallel plate at 11 / s and about 20 °C. High shear viscosity was measured on a capillary rheometer, at 45001 / s and about 20 °C. The liquid components included a PDMS blend containing 500 cP vinyl terminated PDMS and 100 cP hydride functional PDMS crosslinker, a 2% platinum Karstedt catalyst, and a methylvinylcyclic inhibitor.

[0049] A PDMS blend was mixed with alumina filler and fumed silica to make a stable mixture. As shown in Table 1, the ratio of the fillers and the fumed silica content were varied. In one example, the desirable properties of the dispersion were to2024P00085 formulate a thermal interface material having a high enough low shear viscosity to give a stable bead after dispensing that does not move, even when placed on a vertical surface, while maintaining a low enough viscosity under shear to flow at a desirable rate to be useful in applications. Table 1. Viscosity, Shear Thinning Index, and Flow rate of Formulations. 1-1 1-2 1-3 1-4PDMS blend 100 100 100 100 Calcined alumina, 2 μm 540 450 360 360 Spherical alumina, 10 μm 360 450 540 540 Fumed silica 0 4 0 5 TTS coupling agent 2 2 2 2 Viscosity, low shear (Pa.sec) 1195 1290 440 1000 Viscosity, high shear (Pa.sec) 220 90 40 55 Shear thinning index 5.4 14.3 11.0 18.2 Flow rate, 90 PSI (g / min) 58 116 205 138 Wt.% TTS of total filler 0.2 0.2 0.2 0.2

[0050] Examples 1-1, 1-2, and 1-4 exhibited high low shear viscosity and had desirable resistance to movement after dispensing, but the flow rate is relatively poor for examples 1-1 and 1-2, due to the high value of the viscosity at high shear rate. Example 1-3 exhibited an improved flow rate and also maintains a high low shear viscosity, exhibiting the desirable flow properties. For example, compared to examples 1-1 and 1- 2 where the weight ratio of first particles (Spherical alumina, 10 μm) was equal to or less than second particles (Calcined alumina, 2 μm), the weight ratio of first particles to second particles in examples 1-3 and 1-4 was greater than 1:1. In examples 1-3 and 1- 4, the weight ratio of the first particles to second particles is 1.5:1. By increasing the weight ratio to greater than 1:1, the formulations in 1-3 and 1-4 exhibited improved viscosity values at both low and high shear rates. The weight % of the TTS coupling agent was about 0.2 wt.% of the filler in the thermal interface material for Examples 1-1, 1-2, 1-3, and 1-4.2024P00085 Example 2

[0051] Table 2 shows the thermal conductivity of an aluminum nitride (AIN) filler containing coarse (d50= 10-20 μm) and fine (d50= 1-2 μm) components. In comparison to alumina, AIN provides a boost to thermal conductivity when incorporated into a matrix material. High conductivity materials can typically contain larger fillers and filler volume fractions nearing 90%. However, larger filler particles can increase the bond-line thickness and its related thermal impedance, and thermal impedance is of importance in various industries such as the auto and e-mobility industries. Table 2 shows that fillers with particle sizes of the present disclosure can be used to achieve thermal conductivities nearing 8 W / m*K and remain dispensable. The weight ratio of the first particles to the second particles in examples 2-1, 2-2, and 2-3 was above 1.5:1. The estimated bond-line of these formulations is 50 μm, advantageous for contact resistance. The weight percentage of TTS coupling agent with respect to the weight of the filler ranged from about 0.2 wt.% (Ex.2-1) to about 0.5 wt.% (Ex.2-2 and 2-3). Table 2. Volume percentages, Dispense Rate, and Thermal Conductivity. 2-1 2-2 2-3 PDMS blend 100 100 100 Aluminum nitride, d50= 10-20 μm 1022 805 723 Aluminum nitride, d50= 1-2 μm 473 522 447 TTS coupling agent 2.8 7.1 5.7 Volume % filler 81 78.5 76.5 Dispense rate (g / min) 9.3 11.5 33.4 Thermal conductivity (W / m*K) 5.8 7.8 7.1 Wt.% TTS of total filler 0.2 0.5 0.5 Example 3

[0052] The thermal interface material was demonstrated using a thermal test vehicle (TTV) based on the ASTM D 5470 method. The TTV was constructed to provide an interfacial area similar to an automotive electronics application with a space for a mechanical standoff that can be filled to simulate a fixed gap or left empty for a minimum bondline test. A hole was drilled into the top and bottom platens as near to the2024P00085 interface as possible to provide a measurement of the hot-side and cold-side temperatures, TH and TC respectively, resulting from a given power input, q. The ratio of the temperature difference to the power input defines the thermal resistance, Rθ, of the system: ^^^^^^ − ^^^^^^^^ =^^ ^^^^^^^^(1) ^^^^ For a homogeneous material,can be related to the thermal conductivity of the thermal interface material by the expression: ^^^^ ^^^^^^^^= (2) ^^^^ ^^^^ where A is the cross-sectionalthe path of heat flow (i.e., area of the platen) directly above and below the interfaces to measure temperature during the test, and a resistor was mounted above the top platen to introduce heat into the system.

[0053] The gap filler was dispensed directly on the bottom platen and the top platen was lowered using an MTS load frame to provide precise control of load and gap during assembly. Measurements taken before dispensing and after curing for 24 hours at room temperature showed no significant difference. Several formulations were evaluated with various bulk thermal conductivities and maximum particle size. In one non-limiting example, bondline measurements were performed at about room temperature (e.g., 20 °C). In another non-limiting example, bondline measurements can be performed using a screw fixture. The compositions of the materials are shown in Table 3.2024P00085 Table 3. Volume percentages, Minimum Bondline, Dispense Rate, and Thermal Conductivity. 3-1 3-2 3-3 3-4 3-5 PDMS blend 100 100 100 100 100 Aluminum nitride, 80 μm 958 984 Aluminum nitride, 50 μm 350 888 973 Alumina, 50 pm 475 Aluminum nitride, 20 μm 81 Alumina, 10 μm 300 527 Alumina, 5 μm 438 Alumina, 1-2 μm 135 Aluminum nitride, 1-2 μm 115 316 263 543 500 Alumina, 200 nm 70 100 241 74 80 TTS coupling agent 1 1 4 4 4.5 Minimum Bondline (μm) 134 192 189 161 153 Volume % filler 80 84 84 82 83 120- Dispense rate (g / min) 180 45-50 50-55 35-44 19-20 Thermal conductivity (W / m*K) 6.5 9.5 9.5 9 10 Wt.% TTS of total filler 0.1 0.1 0.2 0.3 0.3

[0054] TV measurements were taken without a spacer to simulate a minimum bondline test and with a 0.5 mm offset. The power input was 125 W and calculated power density was ~4 W / cm2. The thermal conductivity, thermal conductivity divided by the mean particle size of the larger filler particles, and temperature changes for the formulations in examples 1-4, 3-1, 3-2, 3-3, 3-4, and 3-5 are shown in Table 4.2024P00085 Table 4. Thermal Conductivity and Temperature Change of Various Formulations. κTIMκTIM / d50ΔT (W / m*K) (W / mm2K) (°C) ΔT (°C) No 0.5 mm Puck spacer shim 1-4 3 30 5.6 23.5 3-1 6.5 13 8 18.4 3-2 9.5 12 9 11 3-3 9.5 12 5.6 7 3-4 9 18 3.9 5.1 3-5 10 20 4 7.4

[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.2024P00085 CLAIMS: 1. A thermal interface material comprising: a matrix material; a filler dispersed in the matrix material, wherein the filler includes a plurality of particles having a maximum particle size of less than or equal to about 100 μm, wherein the plurality of particles includes first particles having a first mean particle size (d50) of between 5 and 80 µm, second particles having a second mean particle size (d50) of between 200 nm and 5 µm, and wherein a weight ratio of the first particles to the second particles is greater than 1:1; and a coupling agent capable of promoting adhesion between the matrix material and the plurality of particles, the coupling agent present in the thermal interface material in a range of between about 0.1 wt.% and about 2 wt.% of the filler. 2. The thermal interface material of claim 1, wherein a ratio of an overall thermal conductivity value of the thermal interface material to the first mean particle size is greater than 12 W / mm2K. 3. The thermal interface material of claim 1, wherein the matrix material includes an organopolysiloxane. 4. The thermal interface material of claim 1, wherein the weight ratio of the first particles to the second particles ranges from 1.4:1 to 4:1. 5. The thermal interface material of claim 1, wherein the weight ratio of the first particles to the second particles ranges from 1.4:1 to 3:1.2024P00085 6. The thermal interface material of claim 1, wherein the first particles include at least one of aluminum nitride and alumina. 7. The thermal interface material of claim 6, wherein the second particles include aluminum nitride. 8. The thermal interface material of claim 1, wherein the first mean particle size (d50) ranges from 5 µm to 50 µm. 9. The thermal interface material of claim 1, wherein the plurality of particles further includes third particles having a third mean particle size (d50) that is less than the second mean particle size (d50). 10. The thermal interface material of claim 1, wherein a total volume percentage of the filler in the thermal interface material ranges from 75 vol% to 85 vol%. 11. The thermal interface material of claim 1, wherein the coupling agent includes a titanate coupling agent. 12. The thermal interface material of claim 11, wherein the titanate coupling agent includes a monoalkoxy titanate coupling agent. 13. A thermal interface material comprising: an organopolysiloxane matrix material; a filler dispersed in the organopolysiloxane matrix material and including a plurality of particles, wherein the plurality of particles includes first particles having a first mean particle size (d50) of between 5 and 80 µm, second particles having a second mean particle size (d50) of less than 5 µm, and wherein a weight ratio of the first particles to the second particles is greater than 1:1; and2024P00085 a coupling agent having an affinity for the organopolysiloxane matrix material and capable of promoting adhesion between the organopolysiloxane matrix material and the plurality of particles, the coupling agent including at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent. 14. The thermal interface material of claim 13, wherein a ratio of an overall thermal conductivity of the thermal interface material to a mean particle size (d50) of the first particles is greater than, or equal to, 12 W / mm2K. 15. The thermal interface material of claim 13, wherein the first particles include at least one of aluminum nitride and alumina. 16. The thermal interface material of claim 13, wherein the alkylthiol coupling agent includes octadecyl mercaptan. 17. The thermal interface material of claim 13, wherein the fatty acid coupling agent includes at least one oleic acid, stearic acid, a titanate coupling agent, and a zirconate coupling agent. 18. The thermal interface material of claim 13, wherein the fatty acid coupling agent includes a titanate coupling agent. 19. A thermally conductive material, the thermally conductive material comprising: a resin blend including a vinyl functional siloxane resin and a hydride functional siloxane resin; a thermally conductive filler dispersed in the resin blend and including a plurality of particles having a maximum particle size of less than or equal to about 100 μm, wherein the plurality of particles includes first particles and second particles;2024P00085 wherein the first particles have a first mean particle size (d50) of between 5 and 80 µm, and second particles having a second mean particle size (d50) of between 200 nm and 5 µm; wherein the first particles are present at a concentration of greater than 450 parts per hundred of the resin blend (phr), and the second particles are present at a concentration of greater than 300 phr; and a coupling agent including at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent. 20. The thermally conductive material of claim 19 exhibiting a viscosity of greater than 300 Pa‧s at 1 / s and 20 °C. 21. The thermally conductive material of claim 19 exhibiting a viscosity of less than 100 Pa‧s at 45001 / s and 20 °C. 22. The thermally conductive material of claim 19, wherein a weight ratio of the first particles to the second particles is greater than 1:1. 23. The thermally conductive material of claim 19, wherein the fatty acid coupling agent includes a titanate coupling agent.2024P00085 ABSTRACT A thermal interface material includes a matrix material; a filler dispersed in the matrix material, wherein the filler includes a plurality of particles having a maximum particle size of less than or equal to about 100 μm, wherein the plurality of particles includes first particles having a first mean particle size (d50) of between 5 and 80 µm, second particles having a second mean particle size (d50) of between 200 nm and 5 µm, and wherein a weight ratio of the first particles to the second particles is greater than 1:1; and a coupling agent capable of promoting adhesion between the matrix material and the plurality of particles, the coupling agent present in the thermal interface material in a range of between about 0.1 wt.% and about 2 wt.% of the filler.2024P00085

[0004] However, high dispensability is often contrary to other important characteristics such as storage stability, limiting shelf life, and heat dissipation characteristics. For example, increasing the size of thermally conductive filler can improve dispensability, but larger particle sizes restrict the achievable thermal impedance of the assembled component. Further, increasing the size of the thermally conductive filler can accelerate the rate of resin separation. Accordingly, embodiments of the present disclosure provide thermally conductive materials with excellent dispensability and heat dissipation characteristics, while reducing the thermal impedance of the assembled component.SUMMARY

[0005] According to one aspect, a thermal interface material includes a matrix material; a filler dispersed in the matrix material, wherein the filler includes a plurality of particles having a maximum particle size of less than or equal to about 100 pm, wherein the plurality of particles includes first particles having a first mean particle size (dso) of between 5 and 80 pm, second particles having a second mean particle size (dso) of between 200 nm and 5 pm, and wherein a weight ratio of the first particles to the second particles is greater than 1 :1 ; and a coupling agent capable of promoting adhesion between the matrix material and the plurality of particles, the coupling agent present in the thermal interface material in a range of between about 0.1 wt.% and about 2 wt.% of the filler.

[0006] According to another aspect, a thermal interface material includes an organopolysiloxane matrix material; a filler dispersed in the organopolysiloxane matrix material and including a plurality of particles, wherein the plurality of particles includes first particles having a first mean particle size (dso) of between 5 and 80 pm, second particles having a second mean particle size (dso) of less than 5 pm, and wherein a weight ratio of the first particles to the second particles is greater than 1 :1 ; and a coupling agent having an affinity for the organopolysiloxane matrix material and capable of promoting adhesion between the organopolysiloxane matrix material and the plurality2024P00085 of particles, the coupling agent including at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent.

[0007] According to another aspect, a thermally conductive material includes a resin blend including a vinyl functional siloxane resin and a hydride functional siloxane resin; a thermally conductive filler dispersed in the resin blend and including a plurality of particles having a maximum particle size of less than or equal to about 100 pm, wherein the plurality of particles includes first particles and second particles; wherein the first particles have a first mean particle size (dso) of between 5 and 80 pm, and second particles having a second mean particle size (dso) of between 200 nm and 5 pm; wherein the first particles are present at a concentration of greater than 450 parts per hundred of the resin blend (phr), and the second particles are present at a concentration of greater than 300 phr; and a coupling agent including at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent.BRIEF DESCRIPTION OF THE DRAWING

[0008] FIG. 1 illustrates apparatus 100 including thermally conductive interface material 130, according to some embodiments.DETAILED DESCRIPTION

[0009] 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, inadequate dispensability, poor stability, such as storage stability, and undesirable thermal impedance of the assembled component.

[0010] Thermal interface materials of the present disclosure can include at least one of a matrix material, a thermally conductive filler, a coupling agent, and additives. The thermally conductive filler can be dispersed in the matrix material and can enhance2024P00085 the heat dissipation properties of the thermally conductive interface material. This thermally conductive filler generally includes thermally conductive particles, where the thermal conductive particles can also be electrically insulating particulate fillers. The thermally conductive filler and coupling agent can be mixed with one or more resins using a speed mixer under vacuum.

[0011] 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. For 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.

[0012] 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.2024P00085

[0013] 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. 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.

[0014] 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 antor, 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 m Pa-s to about 1000 mPa-s may be utilized. Viscosity values can be measured at about 20 °C and at a shear rate of 1 / s.

[0015] The chemical cure activator may itself be reactive with the curable component and may include a cross-linker for a hydrosilylation reaction. The chemical2024P00085 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-1 B and 1340 available from AB Specialty Silicones. For example, hydride functional PDMS crosslinkers with viscosity values ranging from about 20 mPa- s to about 300 mPa-s may be utilized. Viscosity values can be measured at about 20 °C and at a shear rate of 1 / s.

[0016] 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 example, the first viscosity is less than 500 mPa-s and the second viscosity is greater than 500 mPa-s. Viscosity values can be measured at about 20 °C and at a shear rate of 1 / s. In one non-limiting example, both the first polymeric resin and the second polymeric resin include vinyl-terminated polydimethylsiloxane (PDMS) materials. The blend of multiple resins 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. In some embodiments, the matrix material may include an organic matrix including at least one of a thermoplastic resin and / or a thermoset resin. The matrix material can include a thermosetting polymer.

[0017] A variety of silane or silanol terminated resins may be employed in the matrices of the present invention. Condensation-curable silane- or silanol-term inated 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 some2024P00085 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. 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.

[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 one example, the catalyst includes a Karstedt catalyst. For example, the Karstedt catalyst includes an organoplatinum compound derived from divinyl-containing disiloxane. Reaction catalysts used in the compositions of the present invention may be present 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.2024P00085

[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 che ical 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-tetramethy ,3,5,7-tetravinyl-cyclotetrasiloxane.

[0022] Thermal interface materials of the present disclosure generally include a filler. The filler generally includes thermally conductive filler and can be provided in the form of a plurality of particles. The plurality of particles can provide desired thermal conductivity properties to the interfaces of the present disclosure. For example, the plurality of particles can be a thermally conductive particulate filler useful for increasing the overall thermal conductivity of the thermal interface material. The filler may be dispersed in the matrix material. In one example, the filler includes electrically insulating particulate fillers. The composition, amount, and distribution of filler dispersed in the2024P00085 matrix material can be used to tune overall thermal conductivity and viscosity values of the thermal interface material.

[0023] The thermally conductive fillers contemplated for use in the preparations of the present invention include metals, metal oxides, ceramics, and combinations thereof. Example 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. The thermally conductive filler can include calcined alumina.

[0024] The thermally conductive filler 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 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. Example aspherical shapes include flake-like, plate-like, rod-like, and so on.

[0025] As discussed, the thermal interface material can be in contact with, and positioned between, a heat generating component and a heat dissipating component,2024P00085 sufficient to efficiently transfer heat from the heat generating component to the heat dissipating component. The thermally conductive filler can include a plurality of particulate filler particles having a maximum particle size (D100) of less than or equal to about 100 pm. In one example, the plurality of particulate filler particles has a maximum particle size (D100) of less than or equal to about 80 pm. The plurality of particulate filler particles can exhibit a particle size (D90) of less than or equal to about 80 pm, where 90% of the total particles are less than or equal to 80 pm. In another example, the plurality of particulate filler particles has a maximum particle size (D100) of less than or equal to about 60 pm. In yet another example, the plurality of particulate filler particles has a maximum particle size (D100) of less than or equal to about 50 pm. The plurality of particulate filler particles can exhibit a particle size (D90) of less than or equal to about 50 pm, where 90% of the total particles are less than or equal to 50 pm.

[0026] Often, conventional materials utilize large filler particles (such as particles having maximum particle sizes (dioo) above 80 pm or 100 pm) to maximize bulk thermal conductivity and enhance dispensability of thermal interface materials. However, thermal interface materials formed using this approach suffer from resin separation and an increase in assembled bondline thickness between the heat generating component and the heat dissipating component. The increase in assembled bondline thickness restricts the achievable thermal impedance of the installed thermal interface material. Accordingly, for conventional materials, the restriction of achievable thermal impedance reduces the overall heat transfer efficiency of the material.

[0027] Compared to conventional materials, particle sizes of the present disclosure (such as a maximum particle size D100 or particle size D90) enable a decreased, assembled bondline thickness between the heat generating component and the heat dissipating component, minimizing thermal impedance of the thermal interface material. Decreasing or minimizing the thermal impedance of the thermal interface material promotes increased heat transfer efficiency, and the thermal interface material exhibits excellent heat generating component temperature control at high power densities. Additionally, particle sizes of the present disclosure (such as a maximum particle size Dwo or particle size D90) enable a desirable balance of assembled bondline thickness and dispensability of the thermal interface material.102024P00085

[0028] The thermally conductive filler can include a plurality of particulate filler particles including first particles and / or second particles. The first particles may provide the primary mechanism for heat transfer. In one example, the first particles include a thermally conductive material having a thermal conductivity value greater than about 20 W / m*K, greater than about 500 W / m*K, or greater than about 100 W / m*K. The first particles can include one or more thermally conductive fillers of the present disclosure. For example, the first particles can include one or more metal oxides. In one example, the first particles include at least one of aluminum nitride and alumina.

[0029] In one example, the first particles have a first mean particle size (dso) of greater than about 5 pm. In another example, the first particles have a first mean particle size (dso) of greater than about 8 pm. n another example, the first particles have a first mean particle size (dso) of greater than about 10 pm. In one example, the first particles have a first mean particle size (dso) of between about 5 pm and about 100 pm. In another example, the first particles have a first mean particle size (dso) of between about 5 pm and about 80 pm. In yet another example, the first particles have a first mean particle size (dso) of between about 5 pm and about 50 pm, or 5 pm and about 30 pm. In one non-limiting example, the first particles have a first mean particle size (dso) of less than 100 pm or less than 50 pm. In another non-limiting example, the first particles have a first mean particle size (dso) of less than 80 pm. The first mean particle size (dso) can be the largest mean particle size of all particles within the filler component. For example, first mean particle sizes (dso), such as a first mean particle size (dso) of between about 5 pm and about 80 pm, promote a desirable thermal conductivity value and thermal impedance to the thermal interface material while providing an efficient balance of dispensability and low shear viscosity (discussed in further detail herein). Compared to materials only having filler exhibiting particle sizes below about 5 pm, the present materials exhibit greater thermal conductivity values and improved dispensability.

[0030] The concentration of the first particles with respect to resin used to form the matrix material can range from about 200 parts per hundred resin (phr) to about 1600 phr. In one example, the concentration of the first particles with respect to resin used to form the matrix material ranges from about 450 phr to about 1600 phr. In another112024P00085 example, the concentration of the first particles with respect to resin used to form the matrix material ranges from about 450 phr to about 1100 phr. The concentration of the first particles with respect to resin used to form the matrix material can be greater than about 450 phr. The concentration of the first particles with respect to resin used to form the matrix material can be greater than about 500 phr. Concentration values of the first particles can promote a desirable thermal conductivity value to the thermal interface material while providing an efficient balance of dispensability and low shear viscosity.

[0031] The second particles can include one or more thermally conductive filler materials of the present disclosure. For example, the second particles can include calcined alumina. In one example, the second particles include at least one of aluminum nitride and alumina. The second particles can have a second mean particle size (dso) of greater than about 200 nm. In another example, the second particles have a second mean particle size (dso) of greater than about 800 nm. In another example, the second particles have a second mean particle size (dso) of greater than about 1 pm. In one example, the second particles have a second mean particle size (dso) of between about 200 nm and about 5 pm. In another example, the second particles have a second mean particle size (dso) of between about 200 nm and about 2 pm. In yet another example, the second particles have a second mean particle size (dso) of between about 1 pm and about 2 pm. In one non-limiting example, the second particles have a second mean particle size (dso) of less than 5 pm or less than 3 pm. In another non-limiting example, the second particles have a second mean particle size (dso) of less than the first mean particle size (dso).

[0032] The concentration of the second particles with respect to resin used to form the matrix material can range from about 100 parts per hundred resin (phr) to about 1000 phr. In one example, the concentration of the second particles with respect to resin used to form the matrix material ranges from about 100 phr to about 600 phr. In another example, the concentration of the second particles with respect to resin used to form the matrix material ranges from about 200 phr to about 450 phr. The concentration of the second particles with respect to resin used to form the matrix material can be less than about 600 phr. The concentration of the second particles with respect to resin used to form the matrix material can be less than about 450 phr. The concentration of the122024P00085 second particles with respect to resin used to form the matrix material can be greater than about 300 phr.

[0033] The weight ratio of the first particles to the second particles can be greater than 1 :1. In one example, a weight ratio of the first particles to the second particles is greater than 1.2:1. In another example, a weight ratio of the first particles to the second particles is greater than 1.4:1. The weight ratio of the first particles to the second particles can range from about 1 : 1 to about 4:1. In one example, the weight ratio of the first particles to the second particles can range from about 1 .4:1 to about 4:1 . In another example, the weight ratio of the first particles to the second particles can range from about 1 .4:1 to about 3:1 . In another example, the weight ratio of the first particles to the second particles can range from about 1 :1 to about 2:1.

[0034] 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 of at least the first particles and the second particles of the present disclosure can tune shear thinning properties of the thermal interface material. Further, the weight ratios of the first particles and second particles can tune the shear thinning properties. In one non-limiting example, compared to a material having a weight ratio of the first particles to the second particles of less than 1 :1 , weight ratios of the first particles to the second particles of greater than 1 :1 can promote desirable viscosity values to the thermal interface material at both low and high shear rates, improving the shear thinning properties. For example, thermal interface materials including the first particles and the second particles can exhibit desired viscosity values under shear strain. These tuned shear thinning properties can assist with enhancing dispensability during the application process. In another non-limiting example, compared to a material having a weight ratio of the first particles to the second particles of greater than 4:1 , weight ratios of the first particles to the second particles of between 1 :1 and 4:1 can prevent or reduce resin separation, improving the stability of the thermal interface material.

[0035] The particulate filler may include third particles. The third particles can include fillers of the present disclosure, such as alumina. In one example, the third132024P00085 partides have a third mean partide size (dso) of less than about 1 pm. n another example, the third partides have a third mean particle size (dso) of less than about 800 nm. In another example, the third particles have a third mean particle size (dso) of less than about 500 nm. In yet another example, the third particles have a third mean particle size (dso) of between about 100 nm and about 300 nm. The third particles can have a third mean particle size (dso) of less than the second mean particle size (dso).

[0036] The total volume percentage of particulate filler in the thermal interface material may range from about 70 vol% to about 90 vol%. In one example, the total volume percentage of particulate filler in the thermal interface material may range from about 75 vol% to about 85 vol%. In another example, the total volume percentage of particulate filler in the thermal interface material may be greater than about 75 vol%. Volume percentages of the particulate filler can promote a balance between overall thermal conductivity and dispensability of the thermal interface material.

[0037] Thermal interface materials of the present disclosure can include a coupling agent. The coupling agent can be capable of at least partially coating the plurality of particulate filler particles. By at least partially coating the plurality of particulate filler particles, the coupling agent can reduce frictional contacts between individual particles. The coupling agent can be capable of promoting adhesion between the matrix material and the plurality of particles. In one example, the matrix material includes an organopolysiloxane, and the coupling agent exhibits an affinity for the organopolysiloxane, promoting adhesion between the organopolysiloxane and the filler. The affinity for the organopolysiloxane ensures that the coupling agent can chemically bridge the organopolysiloxane and the filler. Importantly, the coupling agent can improve flowability of the filler - promoting the reduction of installed bond-line thickness (BLT) between a heat generating component and a heat dissipating component.

[0038] In one example, the coupling agent includes at least one functional group preferring to adsorb or react on a surface of the thermally conductive filler, such as a metal-oxide filler. The coupling agent can include at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent. An example of a suitable alkylthiol coupling agent includes octadecyl mercaptan. The fatty acid coupling agent can include a branched fatty acid. Examples of suitable fatty acid coupling agents142024P00085 include at least one oleic acid, stearic acid, a titanate coupling agent, and a zirconate coupling agent. For example, the titanate coupling agent can include a monoalkoxy titanate coupling agent. Monoalkoxy titanate coupling agents can include a branched fatty acid, having compatibility with the matrix material and coordinating with the filler.

[0039] Examples of monoalkoxy titanate coupling agents include Titanium IV 2- propanolato, tris isooctadecanoato-O; Titanium IV bis 2-methyl-2-propenoato-O, isooctadecanoato-0 2-propanolato; and Titanium IV 2-propanolato, tris(dioctyl)phosphato-O. Examples of zirconate coupling agents include Zirconium IV 2,2(bis-2-propenolatomethyl)butanolato, tris neodecanolato-O; and Zirconium IV 2,2(bis-2-propenolato)butanolato, tris 2-propenoato-O. In some embodiments, the coupling agent is selected from titanate coupling agents, aliphatic coupling agents, and silane coupling agents. In one non-limiting example, the coupling agent includes Titanium IV 2-propanolato, tris isooctadecanoato-O. The coupling agent can include a trimethoxyterminated siloxane. Additional examples of coupling agents include alkyltrimethoxysilanes and siloxane-trimethoxysilanes.

[0040] The coupling agent can be present in the thermal interface material in a range of between about 0.01 wt.% and about 3 wt.% of the filler and / or between about 0.01 wt.% and about 3 wt.% of the thermal interface material. In one example, the coupling agent is present in the thermal interface material in a range of between about 0.1 wt.% and about 2 wt.% of the filler. In another example, the coupling agent is present in the thermal interface material in a range of between about 0.1 wt.% and about 1 wt.% of the filler. In one example, the coupling agent is present in the thermal interface material at greater than 0.01 wt.% of the filler. In one example, the coupling agent is present in the thermal interface material at greater than 0.1 wt.% of the filler. In another example, the coupling agent is present in the thermal interface material at less than 2 wt.% of the filler. In one non-limiting example, a coupling agent present in the thermal interface material at greater than 2 wt.% of the filler can increase the amount of volatiles present in the system and / or can negatively impact mechanical properties of the thermal interface material.

[0041] The combination of the coupling agent having weight percentages of the present disclosure with the weight ratio and mean particle sizes of the first particles and152024P00085 second particles promotes desirable flow characteristics, such as shear thinning behavior, to the thermal interface material. Improving the shear thinning behavior can improve at least one of dispensability and reducing the assembly force to reach the desired bondline thickness. Further, this combination exhibits desirable thermal conductivity while minimizing the assembled bondline thickness of the thermal interface material, reducing the thermal impedance of the thermal interface material. The shear thinning behavior of the thermal interface material can reduce the force to reach this minimized bondline.

[0042] Thermal interface materials of the present disclosure may include one or more additives. The additive may be utilized to improve at least one of slump resistance, stability of the thermal interface material, and dispensability. In one example, the additive includes a fumed metal-oxide. Examples of suitable fumed metal-oxides include fumed alumina and fumed silica. Additionally, or alternatively, the additive may include a silicone oil. Examples of suitable silicone oils include silicone oils having a viscosity of less than about 100 m Pa-s at a temperature of 20 °C and a shear rate of 1 / s. In one example, the silicone oil exhibits a viscosity of less than 20 mPa -s at a temperature of 20 °C and a shear rate of 1 / s.

[0043] In one example, the overall thermal conductivity of the thermal interface material is greater than about 3 W / m*K. In another example, the overall thermal conductivity of the thermal interface material is greater than about 5 W / m*K. In yet another example, the overall thermal conductivity of the thermal interface material is greater than about 6 W / m*K. n one non-limiting example, the overall thermal conductivity of the thermal interface material ranges from about 3 W / m*K to about 9 W / m*K. Thermal conductivity can be measured according to ASTM D 5470. The dispense rate of the thermal interface material may be greater than 5 g / min. The dispense rate of the thermal interface material may be greater than 10 g / min. For example, the dispense rate of the thermal interface material may be greater than 50 g / min. Dispense rate can be measured using a pressure-driven flow through a 0.254 cm nozzle at 6 bar.

[0044] The low shear viscosity of the thermal interface material can be greater than 300 Pa -s. The low shear viscosity of the thermal interface material can be less than162024P000851200 Pa-s. Low shear viscosity can be measured using a 25 mm parallel piate at 1 1 / s. Viscosity values can be measured at 20 °C. The high shear viscosity of the thermal interface material can be less than 100 Pa ■ s. The high shear viscosity of the thermal interface material can be less than 60 Pa-s. High shear viscosity can be measured on a capillary rheometer, at 4500 1 / s. Viscosity values can be measured at 20 °C. The low shear viscosity values of the present disclosure enable the thermal interface material to be stable under low shear, while the high shear viscosity ensures that the material flows at a desirable rate for dispensable applications. As discussed, the specific combination of the particle sizes and weight ratio of at least the first particles and the second particles of the present disclosure in combination with the coupling agent can tune shear thinning properties of the thermal interface material.

[0045] A ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (dso) of the first particles can be greater than, or equal to, 8 W / mm2K, 9 W / mm2K, 10 W / mm2K, or 11 W / mm2K. In one example, a ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (dso) of the first particles is greater than, or equal to, 12 W / mm2K, In another example, a ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (dso) of the first particles is greater than, or equal to, 15 W / mm2K. In yet another example, a ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (dso) of the first particles is between about 10 W / mm2K and 30 W / mm2K. In yet another example, a ratio of the overall thermal conductivity of the thermally conductive interface material to the first mean particle size (dso) of the first particles is between about 12 W / mm2K and 20 W / mm2K.

[0046] F G. 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 thermal interface material 130. Thermal interface material 130 includes thermal interface materials of the present disclosure. As shown, the thermal interface material 130 is in contact with at least a172024P00085 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 thermal interface material 130 to be electrically insulating. In another example, heat dissipating component 120 includes a metal heat dissipating component, optionally including one or more fins for enhanced heat dissipation. Accordingly, thermal interface material 130 transfers heat from the heat producing component 110 to the heat dissipating component 120.

[0047] The assembled bondline thickness 132 of thermal interface material 130 can be less than about 200 pm. In one example, the assembled bondline thickness 132 of thermal interface material 130 is less than about 160 pm. In another example, the assembled bondline thickness 132 of thermal interface material 130 is less than about 100 pm. In one non-limiting example, bondline measurements can be performed at about room temperature (e.g., 20 °C). In another non-limiting example, bondline measurements can be performed using a screw fixture. In another non-limiting example, bondline measurements can be performed using a pressure of about 1 MPa. Further, the thermal interface material 130 exhibits desirable thermal conductivity while minimizing the installed bondline thickness of the thermal interface material, reducing the thermal impedance of the thermal interface material.EXAMPLESExample 1

[0048] Thermal conductivity was measured according to ASTM D 5470. Dispense rate was measured using a pressure-driven flow through a 0.254 cm nozzle at 6 bar. Low shear viscosity was measured using a 25 mm parallel plate at 1 1 / s and about 20 °C. High shear viscosity was measured on a capillary rheometer, at 4500 1 / s and about 20 °C. The liquid components included a PDMS blend containing 500 cP vinyl terminated PDMS and 100 cP hydride functional PDMS crosslinker, a 2% platinum Karstedt catalyst, and a methylvinylcyclic inhibitor.

[0049] A PDMS blend was mixed with alumina filler and fumed silica to make a stable mixture. As shown in Table 1 , the ratio of the fillers and the fumed silica content were varied. In one example, the desirable properties of the dispersion were to182024P00085 formulate a thermal interface material having a high enough low shear viscosity to give a stable bead after dispensing that does not move, even when placed on a vertical surface, while maintaining a low enough viscosity under shear to flow at a desirable rate to be useful in applications.Table 1. Viscosity, Shear Thinning Index, and Flow rate of Formulations.

[0050] Examples 1-1 , 1 -2, and 1 -4 exhibited high low shear viscosity and had desirable resistance to movement after dispensing, but the flow rate is relatively poor for examples 1 -1 and 1 -2, due to the high value of the viscosity at high shear rate Example 1 -3 exhibited an improved flow rate and also maintains a high low shear viscosity, exhibiting the desirable flow properties. For example, compared to examples 1-1 and 1- 2 where the weight ratio of first particles (Spherical alumina, 10 pm) was equal to or less than second particles (Calcined alumina, 2 pm), the weight ratio of first particles to second particles in examples 1 -3 and 1 -4 was greater than 1 :1. In examples 1-3 and 1- 4, the weight ratio of the first particles to second particles is 1.5:1. By increasing the weight ratio to greater than 1 :1 , the formulations in 1 -3 and 1 -4 exhibited improved viscosity values at both low and high shear rates. The weight % of the TTS coupling agent was about 0.2 wt.% of the filler in the thermal interface material for Examples 1 -1 , 1 -2, 1-3, and 1 -4.192024P00085Example 2

[0051] Table 2 shows the thermal conductivity of an aluminum nitride (AIN) filler containing coarse (dso = 10-20 pm) and fine (dso = 1-2 pm) components. In comparison to alumina, AIN provides a boost to thermal conductivity when incorporated into a matrix material. High conductivity materials can typically contain larger fillers and filler volume fractions nearing 90%. However, larger filler particles can increase the bond-line thickness and its related thermal impedance, and thermal impedance is of importance in various industries such as the auto and e-mobility industries. Table 2 shows that fillers with particle sizes of the present disclosure can be used to achieve thermal conductivities nearing 8 W / m*K and remain dispensable. The weight ratio of the first particles to the second particles in examples 2-1 , 2-2, and 2-3 was above 1.5:1. The estimated bond-line of these formulations is 50 pm, advantageous for contact resistance. The weight percentage of TTS coupling agent with respect to the weight of the filler ranged from about 0.2 wt.% (Ex. 2-1 ) to about 0.5 wt.% (Ex. 2-2 and 2-3).Table 2. Volume percentages, Dispense Rate, and Thermal Conductivity.Example 3

[0052] The thermal interface material was demonstrated using a thermal test vehicle (TTV) based on the ASTM D 5470 method. The TTV was constructed to provide an interfacial area similar to an automotive electronics application with a space for a mechanical standoff that can be filled to simulate a fixed gap or left empty for a minimum bondline test. A hole was drilled into the top and bottom platens as near to the202024P00085 interface as possible to provide a measurement of the hot-side and cold-side temperatures, TH and Tc respectively, resulting from a given power input, q. The ratio of the temperature difference to the power input defines the thermal resistance, Re, of the system:For a homogeneous material, the thermal resistance can be related to the thermal conductivity of the thermal interface material by the expression:where A is the cross-sectional area perpendicular to the path of heat flow (i.e., area of the platen) directly above and below the interfaces to measure temperature during the test, and a resistor was mounted above the top platen to introduce heat into the system.

[0053] The gap filler was dispensed directly on the bottom platen and the top platen was lowered using an MTS load frame to provide precise control of load and gap during assembly. Measurements taken before dispensing and after curing for 24 hours at room temperature showed no significant difference. Several formulations were evaluated with various bulk thermal conductivities and maximum particle size. In one non-limiting example, bondline measurements were performed at about room temperature (e.g., 20 °C). In another non-limiting example, bondline measurements can be performed using a screw fixture. The compositions of the materials are shown in Table 3.2024P00085Table 3. Volume percentages, Minimum Bondline, Dispense Rate, and Thermal Conductivity.

[0054] TV measurements were taken without a spacer to simulate a minimum bondline test and with a 0.5 mm offset. The power input was 125 W and calculated power density was -4 W / cm2. The thermal conductivity, thermal conductivity divided by the mean particle size of the larger filler particles, and temperature changes for the formulations in examples 1-4, 3-1 , 3-2, 3-3, 3-4, and 3-5 are shown in Table 4.222024P00085Table 4. Thermal Conductivity and Temperature Change of Various Formulations.

[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

2024P00085CLAIMS:

1. Athermal interface material comprising: a matrix material; a filler dispersed in the matrix material, wherein the filler includes a plurality of particles having a maximum particle size of less than or equal to about 100 pm, wherein the plurality of particles includes first particles having a first mean particle size (dso) of between 5 and 80 pm, second particles having a second mean particle size (dso) of between 200 nm and 5 pm, and wherein a weight ratio of the first particles to the second particles is greater than 1 :1 ; and a coupling agent capable of promoting adhesion between the matrix material and the plurality of particles, the coupling agent present in the thermal interface material in a range of between about 0.1 wt.% and about 2 wt.% of the filler.

2. The thermal interface material of claim 1 , wherein a ratio of an overall thermal conductivity value of the thermal interface material to the first mean particle size is greater than 12 W / mm2K.

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

4. The thermal interface material of claim 1 , wherein the weight ratio of the first particles to the second particles ranges from 1 .4:1 to 4:1 .

5. The thermal interface material of claim 1 , wherein the weight ratio of the first particles to the second particles ranges from 1 .4:1 to 3:1 .2024P000856. The thermal interface material of claim 1 , wherein the first particles include at least one of aluminum nitride and alumina.

7. The thermal interface material of claim 6, wherein the second particles include aluminum nitride.

8. The thermal interface material of claim 1 , wherein the first mean particle size (dso) ranges from 5 pm to 50 pm.

9. The thermal interface material of claim 1 , wherein the plurality of particles further includes third particles having a third mean particle size (dso) that is less than the second mean particle size (dso).

10. The thermal interface material of claim 1 , wherein a total volume percentage of the filler in the thermal interface material ranges from 75 vol% to 85 vol%.11 . The thermal interface material of claim 1 , wherein the coupling agent includes a titanate coupling agent.

12. The thermal interface material of claim 11 , wherein the titanate coupling agent includes a monoalkoxy titanate coupling agent.

13. A thermal interface material comprising: an organopolysiloxane matrix material; a filler dispersed in the organopolysiloxane matrix material and including a plurality of particles, wherein the plurality of particles includes first particles having a first mean particle size (dso) of between 5 and 80 pm, second particles having a second mean particle size (dso) of less than 5 pm, and wherein a weight ratio of the first particles to the second particles is greater than 1 :1 ; and2024P00085 a coupling agent having an affinity for the organopolysiloxane matrix material and capable of promoting adhesion between the organopolysiloxane matrix material and the plurality of particles, the coupling agent including at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent.

14. The thermal interface material of claim 13, wherein a ratio of an overall thermal conductivity of the thermal interface material to a mean particle size (dso) of the first particles is greater than, or equal to, 12 W / mm2K.

15. The thermal interface material of claim 13, wherein the first particles include at least one of aluminum nitride and alumina.

16. The thermal interface material of claim 13, wherein the alkylthiol coupling agent includes octadecyl mercaptan.

17. The thermal interface material of claim 13, wherein the fatty acid coupling agent includes at least one oleic acid, stearic acid, a titanate coupling agent, and a zirconate coupling agent.

18. The thermal interface material of claim 13, wherein the fatty acid coupling agent includes a titanate coupling agent.

19. A thermally conductive material, the thermally conductive material comprising: a resin blend including a vinyl functional siloxane resin and a hydride functional siloxane resin; a thermally conductive filler dispersed in the resin blend and including a plurality of particles having a maximum particle size of less than or equal to about 100 pm, wherein the plurality of particles includes first particles and second particles;2024P00085 wherein the first particles have a first mean particle size (dso) of between 5 and 80 pm, and second particles having a second mean particle size (dso) of between 200 nm and 5 pm; wherein the first particles are present at a concentration of greater than 450 parts per hundred of the resin blend (phr), and the second particles are present at a concentration of greater than 300 phr; and a coupling agent including at least one of an alkylthiol coupling agent, an alkoxysilane coupling agent, and a fatty acid coupling agent.

20. The thermally conductive material of claim 19 exhibiting a viscosity of greater than 300 Pa- s at 1 / s and 20 °C.21 . The thermally conductive material of claim 19 exhibiting a viscosity of less than 100 Pa ■ s at 4500 1 / s and 20 °C.

22. The thermally conductive material of claim 19, wherein a weight ratio of the first particles to the second particles is greater than 1 :1.

23. The thermally conductive material of claim 19, wherein the fatty acid coupling agent includes a titanate coupling agent.

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