Thermal interface materials

Abstract

A thermal interface member includes a first layer including a resin matrix, a thermally conductive filler dispersed in the resin matrix, and a wax component dispersed in the resin matrix at a concentration of between 5 and 25 phr of the resin in the first layer, the wax component having a melting point temperature of between 25 oC and 80 oC; and a second layer having an inner surface adhered to the first layer, the second layer having a modulus of elasticity value of greater than about 50 MPa.

Description

THERMAL INTERFACE MATERIALSTECHNICAL FIELD

[0001] The subject matter disclosed herein relates to thermal interface materials generally and, in particular, to thermal interface materials for plug-in electronic devices. 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 heatdissipating 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 conform to the somewhat uneven heat transfer surfaces of the respective components.

[0003] In the case of plug-in devices, these plug-in devices offer great convenience in data centers and automotive applications, in that the plug-in data transferring or computing units can be easily removed or replaced for updates or maintenance. With the increasing demand for fast data transfer and high computing power, said devices can generate enormous amounts of heat during operation. If the heat is not transferred away quickly and efficiently, these devices can suffer from poor performance or failure. Accordingly, thermal interface materials can be used to facilitate heat transfer from the plug-in device to a cooling unit. Unfortunately, during the typical installation or insertion process, a compression force and an insertion force is applied to the device, causing significant shear deformation to the thermal interface material. This shear deformation can cause structural damage to the thermal interface material and / or can dislocate the thermal interface material due to poor adhesion between the thermal interface material and the heat generating device. Thermal interface materials of the present disclosure are capable ofwithstanding stresses during the insertion process, and these materials exhibit excellent heat dissipation performance at typical device operating temperatures.SUMMARY

[0004] According to one aspect, a thermal interface member includes a first layer including a resin matrix, a thermally conductive filler dispersed in the resin matrix, and a wax component dispersed in the resin matrix at a concentration of between 5 and 25 phr of the resin in the first layer, the wax component having a melting point temperature of between 25 °C and 80 °C; and a second layer having an inner surface adhered to the first layer, the second layer having a modulus of elasticity value of greater than about 50 MPa.

[0005] According to another aspect, a thermal interface member includes a first layer including a resin matrix and having a first hardness value at a first temperature and a second hardness value at a second temperature, wherein an average thermal conductivity of the first layer is greater than about 1 W / mK; and a second layer having an inner surface adhered to the first layer, tiie second layer including at least one of a polymeric material and a metallic material, wherein the first hardness value is greater than 60 Shore oo and the first temperature is about 22 °C, and wherein the second hardness value is at least 15% less than the first hardness value, and the second temperature is about 60 °C.

[0006] According to another aspect, a plug-in device includes a first component including a heat generating component, a first layer including a resin matrix and having a first hardness value at a first temperature and a second hardness value at a second temperature, wherein an average thermal conductivity of the first layer is greater than about 1 W / mK, wherein the first hardness value is greater than 60 Shore oo and the first temperature is about 22 °C, and wherein the second hardness value is at least 15% less than the first hardness value, and the second temperature is about 60 °C, and a second layer having an inner surface and an outer surface, the inner surface adhered to the first layer; and a second component including a heat dissipating component, at least a portion of the second component being engageable with the outer surface of the second layer, wherein a work of adhesion between the inner surface of the second layer and the first layer is greater than a work of adhesion between the outer surface of the secondlayer and the second component when at least a portion of the second component is in contact with the outer surface of the second layer.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 illustrates thermal interface member 100, according to some embodiments.

[0008] FIG. 2A illustrates plug-in device 200 prior to installation, according to some embodiments.

[0009] FIG. 2B illustrates plug-in device 200 after installation, according to some embodiments.

[0010] FIG. 3 illustrates conventional thermal pad damage or dislocation caused by compression and insertion forces during installation of plug-in devices, according to some embodiments.

[0011] FIG. 4 illustrates a shear resistance test, according to some embodiments.

[0012] FIG. 5 illustrates compressive stress vs. strain for various thermal interface materials, according to some embodiments.

[0013] FIG. 6 illustrates thermal resistance at various contact pressures for various thermal interface materials, according to some embodiments.DETAILED DESCRIPTION

[0014] Embodiments of the present disclosure provide novel thermal interface member compositions. These thermal interface members can be used in various heat dissipation applications, such as for plug-in devices. Many conventional thermal interface materials used for plug-in devices are either soft thermal pads, which can be damaged in the repeated insertion and removal cycles, or more rigid thermal pads, which can resist abrasion wear, but tend to exhibit higher thermal impedance due to non-conformity to uneven surfaces, resulting in decreased thermal performance. Therefore, it is desirable to utilize a thermal interface member for a plug-in device with high strength at typical insertion temperatures, conformability at device operating temperatures, and tuned adhesion properties for device installation and removal.

[0015] The thermal interface members of the present disclosure can include a layered structure suitable for coupling with plug-in devices and capable of withstanding stresses during device installation, operation, and removal. Further, these thermal interface members also exhibitexcellent thermal conductivity and conformability at device operating temperatures. FIG. 1 illustrates thermal interface member 100, according to some embodiments. Thermal interface member 100 can include a first layer 110 and a second layer 120. First layer 110 can be adherable to second layer 120. The first layer 110 of the present disclosure can include one or more of a resin matrix, thermally conductive filler, and a wax component.

[0016] In one example, the resin matrix includes a matrix material that has been chemically crosslinked. For example, the resin matrix can include a polymer matrix (such as including an organopolysiloxane). In one non-limiting example, the resin matrix includes a cured silicone material. The resin matrix 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.

[0017] In some embodiments, the curable component may include a monomer, oligomer, or a polymer that is capable of undergoing a cross-linking reaction to form a network. The chemical cure activator is preferably an agent that is initially separated from the curable component to avoid a cure reaction, and subsequently introduced to the curable component when the cure reaction is desired. In some embodiments, the cure activator includes a cross-linking agent. The cure activator may also or instead include a monomer, an oligomer, a polymer, a reaction initiator, a catalyst, and combinations thereof. The curable component may include a first resin, and the cure activator may include a second resin that is reactive with the first resin. In some embodiments, the resin matrix may comprise an organic matrix including at least one of a thermoplastic resin and / or a thermoset resin.

[0018] 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.

[0019] An example curable component of the present invention includes polydiorganosiloxanes, such as various vinyl or siloxy-terminated polydimethylsiloxanes (PDMS). Example commercially available PDMS materials include Nusil PLY-7500 and 7905 available from Avantor, Inc.; Evonik VS 100, 200, 500, 10000, 20000, and 65000 available from Evonik Industries AG; and Gelest DMS-V21, V22, V41, V42, and V43 available from Gelest, Inc. The curable component may include one or more polymers that differ in, for example, molecular weight, viscosity, and molecular structure. For example, vinyl-terminated PDMS with viscosity values ranging from about 50 cP to about 1000 cP may be used.

[0020] The chemical cure activator may itself be reactive with the curable component and may include a cross-linker for a hydrosilylation reaction. The chemical cure activator may include a dihydroxy aliphatic chain extender such as a hydride-terminated polydimethylsiloxane. The silicon-bonded hydrogen atoms may be located at terminal, pendant, or at both terminal and pendant positions. The chemical cure activator may include one or more organohydrogen poly siloxanes 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 fromGelest, Inc.; and Andisil XL-1B and 1340 available from AB Specialty Silicones. Hydride functional PDMS crosslinkers may be used, such as about 100 cP hydride functional PDMS crosslinkers.

[0021] As discussed, an example cure reaction suitable for the curable systems of the present invention is hydrosilylation from vinyl and hydride functional silicone resins. In one example, the molar ratio of vinyl silicone resin to hydride crosslinkers ranges from about 0.5:1 to about 3:1. In another example, the molar ratio of vinyl silicone resin to hydride crosslinkers ranges from about 0.8:1 to about 2: 1. In yet another example, the molar ratio of vinyl silicone resin to hydride crosslinkers ranges from about 0.8:1 to about 1.5:1. In yet another example, the molar ratio of vinyl silicone resin to hydride crosslinkers ranges from about 0.8 : 1 to about 1.2:1. The molar ratio of vinyl silicone resin to hydride crosslinkers may be less than 1.5:1. The molar ratio of vinyl silicone resin to hydride crosslinkers may be greater than 0.8:1. Since the base hardness of a cured silicone can be dictated by the crosslinked polymer network, the base hardness of a cured silicone can be tuned according to the vinyl-to-hydride ratio.

[0022] A variety of silane or silanol terminated resins may be employed in the matrices of the present invention. Condensation-curable silane- or silanol-terminated resins participate in a hydrolysis-condensation cure pathway, preferably at and above ambient temperatures. In some embodiments, the resins are non-silicone, wherein no more than a trace amount of silicone is contained in the composition. In some embodiments, no silicone is contained in the composition. Example resins suitable for the curable component of the present disclosure include reactive polymer resins with at least one silyl-reactive functional group, including at least one bond that may be activated with water. Example silyl-reactive functional groups include alkoxy silane, acetoxy silane, and ketoxime silane.

[0023] Other example curing reactions contemplated for the curable component and cure activator include a urethane reaction from hydroxyl and isocyanate functional monomers, oligomers, or resins, epoxy polymerization from epoxide and at least one of amino, mercapto, and anhydride functional monomers, oligomers, or resins, and radical polymerization of vinyl or vinylidene functional monomers, oligomers, or resins. In some embodiments, one or more of the monomers, oligomers, or resins may be in liquid form at 20 °C and 1 bar pressure and exhibit a viscosity of less than 1000 cP at 20 °C at a shear rate of 1 s-1. In some embodiments, one or moreof the monomers, oligomers, or resins may be in liquid form at 20 °C and 1 bar pressure and exhibit a viscosity of less than 200 cP at 20 °C at a shear rate of 1 s-1.

[0024] In some embodiments, the cure activator may include a catalyst, such as a reaction catalyst. A reaction catalyst may, for example, be employed to further facilitate the hydrosilylation reactions described above. Example reaction catalysts useful in the compositions of the present invention include platinum compounds, and organotin and organo-zinc and organo-titanium compounds (together referred to herein as “organo-metal catalyst”) that facilitate moisture cure of the silyl-modified reactive resins. In one example, the catalyst includes a Karstedt catalyst. For example, the Karstedt catalyst includes an organoplatinum compound derived from divinyl-containing disiloxane. 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.

[0025] The curable component of the present disclosure may be curable in the presence of water (moisture curable) at ambient temperature. Depending upon the application, the moisture may be available from the ambient environment or from water released from the object(s) to which the composition is applied. In some embodiments, the compositions of the invention are curable without addition of environmental moisture. In some embodiments, water may be included as an ingredient in a non-resin part of the multiple part curable composition, for mixture with the reactive constituents in situ. Preferably, however, the amount of water required in the composition itself is minor so as not to interfere with functional properties of the thermal material. In some embodiments, water is present in the compositions of the invention in the range of 0 up to 0.5 wt%. In some embodiments, the compositions 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.

[0026] In order to provide desired thermal conductivity properties to the interfaces of the present invention, thermally conductive filler is preferably dispersed in the resin matrix. In another example, the thermally conductive filler is dispersed / mixed with one or more components used for a cure reaction. The thermally conductive fillers contemplated for use in the preparations of the present invention include metals, metal oxides, ceramics, and combinations thereof. Example conductive fillers include calcium carbonate, boron nitride, aluminum nitride,alumina, alumina trihydrate, silicon, silicon carbide, graphite, diamond, magnesium oxide, magnesium hydroxide, zinc oxide, gold, silver, copper, platinum, palladium, nickel, aluminum, indium, alloy of nickel (e.g., alloy 42), alloy of zinc, alloy of iron, alloy of indium, silver-plated copper, silver-plated aluminum, bismuth, tin, bismuth-tin alloy, silver-plated fiber, silver-plated graphite, silver-plated silicon carbide, silver-plated boron nitride, silver-plated diamond, silver- plated alumina, silver-plated alloy 42, graphene, silver-plated graphene, silver-coated polymer, cadmium and alloys of cadmium, lead and alloys of lead, antimony and alloys of antimony, and the like, as well as mixtures of any two or more thereof.

[0027] In some embodiments, the thermally conductive filler is electrically insulating in order to promote an overall electrical resistivity to the first layer 110. Example electrically insulating and thermally conductive fillers include boron nitride, aluminum nitride, alumina, and alumina trihydrate. In some embodiments, the thermally conductive filler is alumina. The thermally conductive fillers may be of various shapes and size, and typically has 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. Spherical thermally conductive filler may have an aspect ratio of between 0.8- 1.2.

[0028] The weight percentage of the thermally conductive filler in the first layer 110 may be varied according to desired characteristics, such as the desired overall thermal conductivity of the first layer 110. In one example, the weight percentage of thermally conductive filler in the first layer 110 is greater than about 75 wt.%. In another example, the weight percentage of thermally conductive filler in the first layer 110 is greater than about 85 wt.%. In yet another example, the weight percentage of thermally conductive filler in the first layer 110 is greater than about 90 wt.%. In one example, the weight percentage of thermally conductive filler in the firstlayer 110 ranges from about 75 wt.% to about 98 wt.%. In one example, the weight percentage of thermally conductive filler in the first layer 110 ranges from about 85 wt.% to about 98 wt.%.

[0029] The concentration of thermally conductive filler in parts per hundred resin in first layer 110 may range from about 500 phr to about 2000 phr. In one example, the concentration of thermally conductive filler in parts per hundred resin in first layer 110 ranges from about 1000 phr to about 2000 phr. In another example, the concentration of thermally conductive filler in parts per hundred resin in first layer 110 ranges from about 1200 phr to about 2000 phr. In yet another example, the concentration of thermally conductive filler in parts per hundred resin in first layer 110 ranges from about 1200 phr to about 1700 phr. The concentration of thermally conductive filler in parts per hundred resin in first layer 110 may be greater than 500 phr, greater than 1000 phr, or greater than 1200 phr.

[0030] The first layer 110 may further include one or more of a reaction inhibitor(s), dispersant(s), coupling agent(s), and rheology modifier(s). Reaction inhibitors can include substances that adjust the rate of a chemical reaction or stop the chemical reaction. In one example, the reaction inhibitor of the present disclosure can adjust cure rate of vinyl and hydride functional silicone systems that cure via hydrosilylation. Various reaction inhibitors may be used 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 methyl vinyl cyclic inhibitors.

[0031] Dispersants can be added to the thermal interface material or precursors thereof to improve separation of particles and / or to improve the viscosity. These dispersants can improve dispersion and / or stabilization of particles in the thermal interface material. In one example, the dispersant may include a polydimethylsiloxane (PDMS)-soluble wetting agent. In another example, the dispersant includes titanate. Coupling agents can be added to the thermal interface material or precursors thereof to enhance / create bonds between materials. For example, coupling agents can be used as an adhesion promoter. In one example, coupling agents of the present disclosure include silane coupling agents. In another example, coupling agents of the present disclosure include vinyl trimethoxy silane (VTMO).

[0032] The first layer 110 may be formed by mixing two or more of a curable component, cure activator component, catalyst, reaction inhibitor, dispersant, coupling agent, and rheology modifier. For example, mixing may include using a mixer under vacuum. Each of these possiblecomponents may be added and mixed in various orders, and each of these components may be added in the liquid form. In one non-limiting example, a mixture may be formed using two unique vinyl-terminated PDMS components with distinct viscosity values, such as viscosity values ranging from about 50 to about 1000 cP. The thermally conductive filler may be added during or after this mixing process. Alternatively, the thermally conductive filler may be present in one of the liquid components prior to mixing. For example, materials may be provided in a two-part composition, wherein the thermally conductive filler is dispersed within one or both of the parts. These two parts may be initially separate. Thermal interface materials of the present disclosure may be sold as a kit, wherein the kit includes at least two separate components to be mixed for curing to form the first layer 110.

[0033] The first layer 110 may include a wax component. The wax component can be dispersed in the resin matrix. In one example, the wax component includes one or more of an alkylated silicone wax and a paraffin wax. Examples of suitable alkylated silicone waxes include cerotyl dimethicone wax and stearyl dimethicone wax. In one example, cerotyl dimethicone wax has a melting point temperature of about 43 °C. In another example, stearyl dimethicone wax has a melting point temperature of about 28 °C. The paraffin wax may include one or more components following the formula CnH2n+2. For example, n may range from 20 to 40. The wax component may be added with the resin and / or crosslinking components in various forms, such as in the form of particles or beads. In one non-limiting example, chemical compatibility and miscibility of the wax component are important for many applications. For example, if a silicone resin is used for the resin matrix, an alkylated silicone wax can be used in the wax component for desirable chemical compatibility.

[0034] In one example, the wax component has a melting point temperature of above about 25 °C. In another example, the wax component has a melting point temperature of above about 35 °C. In yet another example, the wax component has a melting point temperature of below about 85 °C. In one example, the wax component has a melting point temperature of between 25 °C and 80 °C. In yet another example, the wax component has a melting point temperature of between 25 °C and 60 °C. In yet another example, the wax component has a melting point temperature of between 25 °C and 65 °C. In yet another example, the wax component has a melting point temperature of between 25 °C and 50 °C. In one non-limiting example, the wax component has a melting point below about 85 °C. In this non-limiting example, utilizing a waxcomponent with a melting point below about 85 °C is desirable for enhanced conformability and heat transfer properties at typical device operating temperatures.

[0035] The wax component can include a first group and a second group, wherein the first group has a first average melting point temperature that is lower than a second average melting point temperature of the second group. The first group and the second group include wax components of the present disclosure, such as alkylated silicone waxes. The first group and the second group can exhibit melting point temperatures of the present disclosure. In one example, the first group has a melting point temperature below about 35 °C, and the second group has a melting point temperature above about 35 °C. In another example, the first group has a melting point temperature below about 40 °C, and the second group has a melting point temperature above about 40 °C. The first average melting point temperature can be at least 10 °C less than the second average melting point temperature. The first average melting point temperature can be at least 20 °C less than the second average melting point temperature.

[0036] The wax component can be dispersed in the first layer 110 at a concentration above about 2 phr (parts per hundred resin) of the resin in the first layer 110. In one example, the wax component is dispersed in the first layer 110 at a concentration above about 5 phr of the resin in the first layer 110. In one example, the wax component is dispersed in the first layer 110 at a concentration between 5 phr and 25 phr of the resin in the first layer 110. In another example, the wax component is dispersed in the first layer 110 at a concentration between 5 phr and 20 phr of the resin in the first layer 110. In yet another example, the wax component is dispersed in the first layer 110 at a concentration between 5 phr and 15 phr of the resin in the first layer 110. The wax component may be dispersed in the first layer 110 at a concentration below 25 phr. In one non-limiting example, a concentration of the wax component below 25 phr may be desirable to prevent or reduce the wax component from leeching out of the resin matrix.

[0037] The weight percentage of the wax component in the first layer 110 can be tuned according to desired properties. In one example, the weight percentage of the wax component in the first layer 110 is greater than about 2 wt.%. In another example, the weight percentage of the wax component in the first layer 110 is greater than about 5 wt.%. In yet another example, the weight percentage of the wax component in the first layer 110 is less than about 20 wt.%. In one example, the weight percentage of the wax component in the first layer 110 ranges from about 5wt.% to about 25 wt.%. In another example, the weight percentage of the wax component in the first layer 110 ranges from about 5 wt.% to about 15 wt.%.

[0038] Importantly, by utilizing the low melting point wax component in the first layer 110, the thermal interface member 100 is robust at typical device insertion / desertion temperatures to resist shear stress, but conformable and compressible at elevated device operating temperatures. This prevents dislocation and / or damage to the thermal interface member 100 during plug-in device insertion or desertion. Further, due to the increased compressibility, the wax component enhances the conformability at device operating temperatures, enhancing the heat dissipation properties of the thermal interface member 100 by reducing thermal impedance at the respective thermal transfer interface. Accordingly, the wax component decreases the thermal resistance compared to conventional interface materials at typical device operating temperatures, such as above about 40 °C, above about 60 °C, or above about 80 °C.

[0039] The average thermal conductivity of the first layer 110 can be greater than about 1 W / mK. In one example, the average thermal conductivity of the first layer 110 is greater than about 2 W / mK. In another example, the average thermal conductivity of the first layer 110 is greater than about 5 W / mK. In one example, the average thermal conductivity of the first layer 110 ranges from about 1 W / mK to about 10 W / mK. In another example, the average thermal conductivity of the first layer 110 ranges from about 2 W / mK to about 8 W / mK. In yet another example, the average thermal conductivity of the first layer 110 ranges from about 3 W / mK to about 7 W / mK. The thickness of the first layer 110 may be tuned according to the desired application. In one example, the thickness of the first layer 110 is less than, or equal to, 3 mm. In another example, the thickness of the first layer 110 is less than, or equal to, 2 mm. In yet another example, the thickness of the first layer 110 is less than, or equal to, 1 mm.

[0040] The first layer 110 may have a first hardness value at a first temperature and a second hardness value at a second temperature. For example, the first hardness value can be greater than 55 Shore oo when the first temperature is less than, or equal to, about 22 °C. In one example, the first hardness value can be greater than 60 Shore oo when the first temperature is less than, or equal to, about 22 °C. In another example, the second hardness value is less than 55 Shore oo when the second temperature is greater than, or equal to, about 60 °C. In another example, the second hardness value is less than 55 Shore oo when the second temperature is greater than, or equal to, about 60 °C. In another example, the second hardness value is less than40 Shore oo when the second temperature is greater than, or equal to, about 60 °C. Based on the Shore A scale, the first hardness value can be greater than 30 Shore A when the first temperature is less than, or equal to, about 22 °C. Based on the Shore A scale, the first hardness value can be greater than 50 Shore A when the first temperature is less than, or equal to, about 22 °C. For example, Shore hardness can be measured according to ASTM D2240.

[0041] The second hardness value can be at least 15% less than the first hardness value when the first temperature is less than, or equal to 22 °C, and the second temperature is greater than, or equal to, 60 °C. The second hardness value can be at least 25% less than the first hardness value when the first temperature is less than, or equal to 22 °C, and the second temperature is greater than, or equal to, 60 °C. In one example, the second hardness value is 20% to 60% less than the first hardness value when the first temperature is less than, or equal to 22 °C, and the second temperature is greater than, or equal to, 60 °C. In another example, the second hardness value is 30% to 50% less than the first hardness value when the first temperature is less than, or equal to 22 °C, and the second temperature is greater than, or equal to, 60 °C. Dynamic hardness values of the present disclosure can be important for maintaining superior material toughness at near ambient conditions and for enhanced conformability and heat transfer at device operating temperatures.

[0042] The thermal interface member 100 may include a pressure-sensitive adhesive coating applied to various surfaces of the first layer 110 and / or the second layer 120. In some embodiments, the pressure-sensitive adhesive coating may be used to couple the first layer 110 to the second layer 120. The pressure-sensitive adhesive coating may be used to adhere and secure the first layer 110 or the second layer 120 to the heat generating device. Accordingly, the pressure-sensitive adhesive coating is contactable with both the first layer 110 and the second layer 120. Examples of pressure-sensitive adhesives include rubber-based adhesives and UV acrylic adhesives.

[0043] The second layer 120 can be contactable with the first layer 110. For example, the second layer 120 may be adhered to the first layer 110. For example, in plug-in device applications, second layer 120 can be used to prevent and / or reduce material contamination from first layer 110 to a portion of the plug-in device, such as a cooling unit. Second layer 120 can include inner surface 122 and outer surface 124. Accordingly, inner surface 122 of second layer 120 can be adhered to at least a portion of first layer 110. In one example, the second layer 120includes a polymeric material. Examples of suitable polymeric materials include at least one of polyimide (PI) and polyethylene terephthalate (PET). In another example, the second layer 120 includes at least one of a polymeric material and a metallic material. Examples of suitable metallic materials include at least one of aluminum, indium, and copper. Due to the specific tack properties of the first layer 110, in some embodiments the second layer 120 is securable to the first layer 110 without the use of an adhesive layer. For example, the first layer 110 can be coated and subsequently cured on the second layer 120, such as on inner surface 122. In other embodiments, the inner surface 122 of second layer 120 is securable to the first layer 110 using an adhesive, such as pressure sensitive adhesives of the present disclosure.

[0044] In one example, the modulus of elasticity of the second layer 120 is greater than about 50 MPa. In another example, the modulus of elasticity of the second layer 120 is greater than about 100 MPa. In yet another example, the modulus of elasticity of the second layer 120 is greater than about 500 MPa. Modulus of elasticity values of the present disclosure can be useful for toughness of the material for withstanding insertion forces. In one example, the second layer 120 has a thickness of less than 0.2 mm. In another example, the second layer 120 has a thickness of less than 0.1 mm. In yet another example, the second layer 120 has a thickness of less than 0.06 mm.

[0045] The average thermal conductivity of thermal interface member 100 can be greater than 1 W / mK. In one example, the average thermal conductivity of thermal interface member 100 is greater than 2 W / mK. In another example, the average thermal conductivity of thermal interface member 100 ranges from about 2 to 8 W / mK. In yet another example, the average thermal conductivity of thermal interface member 100 ranges from about 3 to 7 W / mK. The overall thickness of thermal interface member 100 can be less than about 4 mm. In one example, the overall thickness of thermal interface member 100 is less than about 2.2 mm.

[0046] FIG. 2A illustrates plug-in device 200 prior to installation, according to some embodiments. FIG. 2B illustrates plug-in device 200 after installation, according to some embodiments. Plug-in device 200 can be a plug-in device used in data centers and automotive applications. This plug-in device can include data transferring units or computing units that can be easily removed for updates or maintenance. Plug-in device 200 generally includes one or more components capable of being contactable or engageable with other components during the installation process. Plug-in device 200 includes first component 210 and second component220. As shown, plug-in device 200 can include thermal interface member 100. First component 210 can include a heat generating component, and second component 220 can include a heat dissipating component. Prior to installation, as shown in FIG. 2A, second component 220 is not in contact with second layer 120. After installation, as shown in FIG. 2B, at least a portion of second component 220, such as a surface, is in contact with second layer 120.

[0047] In one example, first component 210 includes an electronic device or a chip capable of transferring and / or processing data. Second component 220 can include a thermally conductive heat dissipating component, such as a metal heat dissipating component, optionally including one or more fins for enhanced heat dissipation. First component 210, first layer 110, and second layer 120 are capable of being removed from second component 220. FIGS. 2A and 2B illustrate possible layers and configurations, while it is understood that the thicknesses, orientations, and / or shapes of the various components can be changed according to the desired application. For example, second component 220 may include a channel or cavity, and in the installed position at least one of first component 210, first layer 110, and second layer 120 can be at least partially disposed in the channel or cavity.

[0048] In some embodiments, at least a portion of second component 220 is engageable and / or contactable with outer surface 124 of second layer 120. In one example, FIG. 2B illustrates the contact of a surface of first component 210 to a surface of first layer 110, the contact of a surface of first layer 110 to inner surface 122 of second layer 120, and the contact of outer surface 124 of second layer 120 to at least a portion of second component 220. As discussed, prior to plug-in device 200 installation, outer surface 124 of second layer 120 may not be in contact with second component 220. During insertion or installation, a compression force can be applied to ensure a compact thermal interface, and an insertion force can be applied to engage or push the device in. Accordingly, second layer 120 may slide along or across second component 220 during installation. Conventional plug-in devices with thermal interface materials suffer from thermal interface material damage or dislocation during installation or removal. Importantly, thermal interface members of the present disclosure are capable of withstanding insertion and removal forces, while being conformable, compressible, and thermally conductive during operation of the heat generating device.

[0049] The work of adhesion between the first layer 110 and inner surface 122 of second layer 120 is generally greater than the work of adhesion between outer surface 124 of secondlayer 120 and a surface of second component 220. In one example, the work of adhesion between outer surface 124 of second layer 120 and a surface of second component 220 is less than about 5 MPa. In another example, the work of adhesion between outer surface 124 of second layer 120 and a surface of second component 220 is less than about 1 MPa. In yet another example, the work of adhesion between outer surface 124 of second layer 120 and a surface of second component 220 is less than about 0.5 MPa. Work of adhesion values of the present disclosure can be useful for avoiding failure, avoiding second layer 120 dislocation, and / or ease of plug-in device removal.

[0050] Plug-in device 200, and thermal interface members of the present disclosure, can include multiple layers of materials. For example, the thermal interface member 100 can include a third layer including the composition of the first layer 110 of the present disclosure. Additionally, or alternatively, the thermal interface member 100 can include a fourth layer including the composition of the second layer 120 of the present disclosure. These additional layers can be added to thermal interface member 100 in various positions. For example, plug-in device 200 can utilize first layer 110, second layer 120, the third layer in contact with the second layer, and the fourth layer in contact with the third layer (alternating orientation). Accordingly, additional compositions of the present disclosure can be used for plug-in device 200.

[0051] Importantly, at least in part from the unique composition of thermal interface member 100, plug-in devices of the present disclosure are capable of being installed or removed without damaging and / or dislocating one or more components of thermal interface member 100. Thermal interface member 100 is capable of being robust to withstand insertion stresses during plug-in device installation, while exhibiting excellent heat dissipation properties at typical device operating temperatures. By utilizing unique compositions to tune the dynamic hardness and conformability of thermal interface member 100 at typical device operating temperatures, thermal interface member 100 can efficiently conform to cooling device surfaces and transfer heat from the heat generating device to the heat dissipating device.EXAMPLESExample 1

[0052] Two-component silicone compositions were prepared according to Table 1. The vinyl-to-hydride ratio was 3.0, and the filler loading was 1700 parts per 100 parts of siliconeresin (phr) to achieve a 5-6 W / m*K bulk thermal conductivity. Two alkylated silicone wax compounds were formulated, and the melting points were 28 °C (LM) and 43 °C (HM), respectively. Individual components were mixed by speedmixer and subsequently combined through a static mixer at a 1 :1 ratio, by volume.

[0053] Shore hardness was measured according to ASTM D2240 on 6mm pucks of the cured material. The pucks were conditioned at 22 °C and 60 °C for at least 30 minutes before immediately conducting the hardness measurement. The wax in formulations E1-1 to E1-4 was significantly softened from 22 °C to 60 °C. In contrast, the control sample without wax (C1) maintained similar hardness to that measured at 22 °C. At 10 phr loading of wax, the low melting point wax (LM) showed enhanced softening, illustrating the ability to tune the amount of softening by the waxes at different melting points. Similarly, the loading of wax was used to tune the desired softening effect.Table 1.Thermal Interface Member Formulations and Corresponding Hardness Values.17Example 2

[0054] The base hardness of the cured silicone-based thermally conductive material can be tuned by the crosslinked polymer network, controlled by the vinyl-to-hydride ratio in the silicone formulation. The hydride- functional silicone crosslinker in the Part B formulation was adjusted to achieve desirable vinyl-to-hydride ratios as described in Table 2. Results of control samples (C2-1 to C2-4) show that by varying the vinyl-to-hydride ratio, the base hardness scale can vary from Shore oo to Shore A range. With lower filler loading, hardness of C2-5 and C2-6 drop slightly compared to their counterpart with higher filler loading. Nevertheless, with addition of the wax component, samples (E2-1 to E2-6) showed significant softening from 22 °C to 60 °C, compared to control samples.Table 2.Softening Effect from the Wax Component with Different Stoichiometry and Filler Loading.Example 3

[0055] FIG. 3 illustrates conventional thermal pad damage or dislocation caused by compression and insertion forces during installation of plug-in devices, according to some embodiments. As shown, the typical forces during plug-in device insertion include compressive force and insertion force. During installation, conventional plug-in devices with thermal interface materials suffer from damaged and / or dislocated thermal interface materials during or afterinsertion. In contrast, thermal interface members of the present disclosure are capable of withstanding insertion stresses to prevent or reduce dislocation and damage.

[0056] FIG. 4 illustrates a shear resistance test, according to some embodiments. Formulations C2-1, E2-1, C2-2, and E2-2 were coated on Aluminum foil (0.05 mm thickness) to fabricate the multi-layer thermal pad with a total thickness of 0.5 mm. The multi-layer pads were first tested for shear resistance. A test was conducted at room temperature to simulate the insertion and deletion process for plug-in devices with multi-layer thermal pads. A 1”x1” thermal pad was applied on an Aluminum Q-panel with the Aluminum foil side exposed. The top panel was put in contact with a bottom Q-panel with the thermal pad sandwiched between them. A normal force of 10lbf was applied onto the top panel before the top panel was pushed in for 0.5 inch and then retracted for 0.5 inch. As previously discussed, the robustness of the base polymer matrix is at least partially determined by the crosslinked network, the result is highly dependent on the vinyl-to-hydride ratio. For example, E2-2 remained in position and no damage was observed.

[0057] FIG. 5 illustrates compressive stress vs. strain for various thermal interface materials, according to some embodiments. To demonstrate the effect of wax on the conformability of thin thermal pads at operating conditions, compressive stress-strain curves were measured for multilayer pads with and without wax at elevated temperatures close to operating conditions. The test was conducted by parallel plate rheometer in compression mode at 75 °C with 8 mm contact diameter and a compression rate of 0.5 um / sec. The stress-strain curves showed samples with wax required much lower stress to achieve certain compression strain than control samples, indicating a better conformability of wax-containing thermal pads at operating conditions.

[0058] FIG. 6 illustrates thermal resistance at various contact pressures for various thermal interface materials, according to some embodiments. Thermal pads were first applied with a contact pressure of 5 psi, followed with an increase to 30 psi, then tested again at 5 psi. The initial thermal resistance at 5 psi for both control and (E) samples are very close. Once pressure is increased to 30 psi, samples with wax started to show lower thermal resistance than control samples, demonstrating better compressibility with wax. After pressure is reduced to 5 psi, the compression history plays a role and the samples with wax continued to show lower thermal resistance.

Claims

CLAIMS:

1. A thermal interface member, the thermal interface member comprising: a first layer including: a resin matrix; a thermally conductive filler dispersed in the resin matrix; and a wax component dispersed in the resin matrix at a concentration of between 5 and 25 phr of the resin in the first layer, the wax component having a melting point temperature of between 25 °C and 80 °C; and a second layer having an inner surface adhered to the first layer, the second layer having a modulus of elasticity value of greater than about 50 MPa.

2. The thermal interface member of claim 1, wherein the modulus of elasticity value of the second layer is greater than about 100 MPa.

3. The thermal interface member of claim 1, wherein a weight percentage of the thermally conductive filler in the first layer is greater than about 85 wt.%.

4. The thermal interface member of claim 1, wherein the wax component is present in the first layer at a concentration of between 5 and 15 phr of the resin in the first layer.

5. The thermal interface member of claim 1, wherein the wax component has a melting point temperature of between 25 °C and 60 °C.

6. The thermal interface member of claim 1, wherein the wax component includes a first group and a second group, wherein the first group has a first average melting point temperature that is lower than a second average melting point temperature of the second group.

7. The thermal interface member of claim 6, wherein the first average melting point temperature is at least 10 °C less than the second average melting point temperature.

8. The thermal interface member of claim 1 , wherein the wax component includes alkylated silicone wax.

9. The thermal interface member of claim 1 having an average thermal conductivity greater than about 1 W / mK.

10. The thermal interface member of claim 1, wherein a Shore oo hardness of the first layer decreases by more than 25% from 22 °C to 60 °C.

11. The thermal interface member of claim 1 , wherein a Shore oo hardness of the first layer is less than 55 Shore OO at temperatures greater than or equal to 60 °C.

12. The thermal interface member of claim 1 wherein the second layer has a thickness of less than 0.2 mm.

13. The thermal interface member of Claim 12 wherein the second layer has a thickness of less than 0.06 mm.

14. The thermal interface member of claim 12, wherein the second layer includes a polymeric material including at least one of polyimide (PI) and polyethylene terephthalate (PET), or a metallic material including at least one of aluminum, indium, and copper.

15. A thermal interface member, the thermal interface member comprising: a first layer including a resin matrix and having a first hardness value at a first temperature and a second hardness value at a second temperature, wherein an average thermal conductivity of the first layer is greater than about 1 W / mK; and a second layer having an inner surface adhered to the first layer, the second layer including at least one of a polymeric material and a metallic material, wherein the first hardness value is greater than 60 Shore oo and the first temperature is about 22 °C, and wherein the second hardness value is at least 15% less than the first hardness value, and the second temperature is about 60 °C.

16. The thermal interface member of claim 15, wherein the second hardness value is 20% to 60% less than the first hardness value.

17. The thermal interface member of claim 15, wherein the first layer includes a thermally conductive filler and a wax component.

18. The thermal interface member of claim 17, wherein the wax component has a melting point temperature of between 25 °C and 60 °C.

19. A plug-in device, the plug-in device comprising: a first component including: a heat generating component; a first layer including a resin matrix and having a first hardness value at a first temperature and a second hardness value at a second temperature, wherein an average thermal conductivity of the first layer is greater than about 1 W / mK, wherein the first hardness value is greater than 60 Shore oo and the first temperature is about 22 °C, and wherein the second hardness value is at least 15% less than the first hardness value, and the second temperature is about 60 °C; and a second layer having an inner surface and an outer surface, the inner surface adhered to the first layer; and a second component including a heat dissipating component, at least a portion of the second component being engageable with the outer surface of the second layer, wherein a work of adhesion between the inner surface of the second layer and the first layer is greater than a work of adhesion between the outer surface of the second layer and the second component when at least a portion of the second component is in contact with the outer surface of the second layer.

20. The plug-in device of claim 19, wherein the first layer includes a thermally conductive filler and a wax component, the wax component having a melting point temperature of between 25 °C and 60 °C, and wherein the work of adhesion between the outer surface of the second layer and the second component is less than about 5 MPa when at least a portion of the second component is in contact with the outer surface of the second layer.

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