Low-melting-point metallic thermal interface materials

Abstract

The present invention relates to a thermal interface material useful for transferring heat out of electronic components, the thermal interface material comprising at least a low-melting-point gallium alloy and a mercapto-containing silicone oil, as well as an emulsifying compound, at least one polymer, a thermally conductive powder, and a coupling compound. The present invention relates to a liquid metal thermal interface material useful for transferring heat out of electronic components, the liquid metal thermal interface material comprising a relatively high weight percent of a low-melting-point metal alloy.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Patent Application No. 18 / 523,255, filed November 29, 2023, and claims the benefit of U.S. Provisional Patent Application No. 63 / 433,608, filed December 19, 2022, both of which are incorporated by reference herein in their entireties.

[0002] FIELD OF THE INVENTION The present disclosure relates generally to thermal interface materials, and more particularly to thermal interface materials including low melting point metal alloys. [Background technology]

[0003] Thermal interface materials (TIMs) are widely used to dissipate heat from electronic components such as central processing units, video graphics arrays, servers, game consoles, smartphones, LED boards, etc. Thermal interface materials are typically used to transfer excess heat from the electronic component to a heat spreader such as a heat sink.

[0004] A practice that is becoming more common in the industry is to use TIMs that include thermal grease, phase change materials (PCMs), and / or gap fillers, among other materials. Compared to traditional TIMs (e.g., thermal greases, PCMs, gap fillers), liquid metal (LM)-based TIMs offer several advantages due to their inherently high thermal conductivity, non-toxicity, and low melting point, effectively reducing the thermal resistance between the chip and the heat dissipation unit. However, traditional LM-based TIMs may react with metal substrates and damage the metal surface, may be difficult to compress, have high surface tension and poor wettability, and / or may be flowable, making them prone to short circuits in the event of a leak. Therefore, there is a need for LM-based TIM compositions that do not exhibit such drawbacks. Summary of the Invention

[0005] The present disclosure provides a thermal interface material composition comprising a low melting point gallium alloy and a mercapto group-containing silicone oil.

[0006] The present disclosure also provides a method for applying a thermal interface material to a substrate, the method including combining a low melting point gallium alloy, a mercapto group-containing silicone oil, an emulsifying compound, at least one polymer, a thermally conductive powder, and a coupling compound to form a thermal interface material, and applying the thermal interface material to a metal substrate.

[0007] The present disclosure also provides a composition for an electronic component comprising a heat sink, an electronic chip, and a thermal interface material disposed between the heat sink and the electronic chip, the thermal interface material comprising a low-melting-point gallium alloy and a mercapto-group-containing silicone oil. [Brief explanation of the drawings]

[0008] The above and other features and advantages of the present disclosure, as well as the manner in which they are achieved, will become more apparent, and the invention itself will be better understood, by referring to the following description of embodiments of the invention in conjunction with the accompanying drawings. [Figure 1A] 1 shows a schematic representation of an electronic chip, a heat spreader, a heat sink, and first and second thermal interface materials. [Figure 1B] 1 illustrates a schematic representation of an exemplary thermal interface material disposed between an electronic chip and a heat sink. [Figure 1C] 1A and 1B illustrate schematic diagrams of exemplary thermal interface materials disposed between a heat spreader and a heat sink. [Figure 1D] 1A and 1B illustrate schematic diagrams of exemplary thermal interface materials disposed between an electronic chip and a heat spreader.

[0009] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set forth herein illustrate exemplary embodiments of the present invention, and such exemplifications should not be construed as limiting the scope of the present invention in any way. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention relates to thermal interface materials useful for transferring heat away from electronic components. In particular, the present invention relates to liquid metal thermal interface materials containing a relatively high weight percent of a low melting point metal alloy useful for transferring heat away from electronic components.

[0011] I. Thermal interface material composition: The present invention relates to a thermal interface material (TIM) useful for transferring heat away from electronic components, which solves problems associated with conventional liquid metal TIMs. The thermal interface material composition may include one or more of a low-melting point (e.g., liquid, soft, etc.) metal alloy, a functionalized silicone oil (e.g., a mercapto / thiol-functionalized silicone oil), a thermally conductive filler, a coupling agent / compound, and a surfactant / emulsifier. In some exemplary embodiments, the TIM is prepared by combining the individual components in a heated mixer and mixing the composition together. The mixed composition can then be applied directly to a substrate, such as by a stencil printing process.

[0012] A. Low melting point metal alloys: The thermal interface material composition may include a metal alloy, which may have a relatively low melting point temperature, such as less than 200°C.

[0013] In one exemplary low melting point metal alloy, the metal alloy may include gallium, bismuth, tin, indium, or any combination thereof.

[0014] In another exemplary low melting point metal alloy, the metal alloy may include gallium or a gallium alloy that may be combined with other metallic elements.

[0015] In one exemplary low melting point metal alloy, the metal alloy may include a bismuth alloy, which may be combined with other metal elements.

[0016] Some low melting alloys, for example, those having a melting point of 0 to 25°C include GaInSnZn alloy, GaInSn alloy, GaInZn alloy, and GaIn alloy; those having a melting point of 25 to 60°C include Ga, BiPbInSnCd alloy, BiInSn alloy, and InBiCd alloy; and those having a melting point of 60 to 120°C include GaInBi alloy, BiInSn alloy, InBiCd alloy, BiPbInSnCd alloy, BiPbSnCd alloy, BiPbInSn alloy, and InB Examples of alloys having a melting point of 120 to 200°C include BiSnZn alloy, BiSn alloy, BiPb alloy, InSnPb alloy, BiPbSn alloy, InAg alloy, InPbAg alloy, InBi alloy, SnPbIn alloy, SnPbBi alloy, SnPbBi alloy, SnBi alloy, InPb alloy, SnPbAg alloy, SnPb alloy, SnZn alloy, SnPbSb alloy, PbIn alloy, and SnAg alloy.

[0017] For example, the metal alloy may have a melting point temperature at, near, or below room / ambient temperature (e.g., 50°F to 85°F, preferably below 60°F). This relatively low melting point makes the metal alloy a liquid, or at least a softened solid, at ambient temperatures. In this case, the metal alloy may be based on one or a combination of various metal alloying materials that are liquid at or near room temperature, such as gallium. For example, a low melting point metal alloy may be based on Ga 62.5 In 21.5 Sn 16 , Ga 75 In 25 , Ga 68.5 In 21.5 Sn 10The low melting point metal alloy may be an alloy containing gallium (Ga), indium (In), and / or tin (Sn), such as LM TIM. The inclusion of a low melting point metal alloy within the TIM results in a "liquid metal" (e.g., a metal alloy that can flow or at least soften at ambient conditions) thermal interface material (LM TIM) that exhibits improved thermal conductivity and heat dissipation.

[0018] Conventionally, liquid metals used in TIMs are reactive with metal substrates, difficult to compress, have high surface tension and poor wetting properties, and are flowable such that electrical components may short out if an electrical leak occurs. To avoid the aforementioned characteristics of conventional liquid metal TIMs, the liquid metal may be combined with one or more other compounds, such as functionalized silicone oils, as described in more detail herein, where the liquid metal has a coupling effect with one or more of the components of the thermal interface material (e.g., the thiol-functional silicone oils described herein) such that the aforementioned characteristics are mitigated.

[0019] Thermal interface materials provided by the present disclosure can include a relatively high weight percent of a low melting point metal alloy (e.g., a gallium-based alloy), such as from any of 80 wt%, 85 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, and / or 97 wt%, or within any range using any two of the foregoing as endpoints, where the weight percent is based on the total weight of the thermal interface material. For example, the low melting point metal alloy can constitute 80 wt% to 97 wt%, 85 wt% to 96 wt%, 89 wt% to 95 wt%, 90 wt% to 94 wt%, and / or 91 wt% to 93 wt% of the total weight of the thermal interface material.

[0020] B. Functionalized Silicone Oil The thermal interface material composition may include a functionalized silicone oil. In this case, the silicone oil may be functionalized with any one or combination of thiol / mercapto functional groups, halogen functional groups (e.g., chlorine, fluorine, etc.), hydroxyl groups (e.g., alcohol), and / or amine functional groups. The functionalization of the silicone oil reduces the surface tension and improves the overall wetting and compressibility of the low-melting-point metal alloy-based TIM formulation. Traditionally, the use of non-functionalized silicone oil in low-melting-point TIMs results in instability during printing. In this case, the silicone oil is functionalized with mercapto / thiol functional groups to provide a mercapto-functional silicone oil, which, when combined with a low-melting-point metal alloy, avoids the instability issue during printing due to the coupling effect of the mercapto-functional silicone oil with the low-melting-point metal alloy.

[0021] In some exemplary functional silicone oil compositions, the silicone oil may contain at least one mercapto group. The thiol functional group may comprise mercaptoalkyl-terminated poly(alkyl)(alkyl)siloxane, mercaptoalkyl-terminated poly(alkyl)(alkoxyl)siloxane, poly(mercaptoalkyl)alkylsiloxane, poly(mercaptoalkyl)(alkoxyl)siloxane, or copolymers thereof.

[0022] In some exemplary thiol / mercapto-functional silicone oil compositions, the mercaptoalkyl-terminated poly(alkyl)(alkyl)siloxanes include (HS) n1 -R1-Si(CH3)2-[O-Si(CH3)2] n3 -R2-(SH) n2 , (HS) n1 -R1-Si(CH3)(C4H9)-[O-Si(CH3)(C4H9)] n3 -R2-(SH) n2 , (HS) n1 -R1-Si(CH3)2-[O-Si(CH3)2] n3 -[O-Si(CH3)(C4H9)] n4 -R2-(SH) n2 , (HS) n1-R1-Si(CH3)2-[O-Si(CH3)2] n3 -[O-Si(CH3)(C2H5)] n4 -[O-Si(CH3)(CH 17 )] n5 -R2-(SH) n2 wherein n1, n2, n3, n4, n5 are integers such that n1+n2≧1, and R1 and R2 are organic groups.

[0023] In some exemplary thiol / mercapto-functional silicone oil compositions, the mercaptoalkyl-terminated poly(alkyl)(alkoxyl)siloxanes include (HS) n1 -R1-Si(CH3)(OCH3)-[O-Si(CH3)(OCH3)] n3 -R2-(SH) n2 , (HS) n1 -R1-Si(CH3)(C4H9)-[O-Si(CH3)(OCH3)] n3 -[O-Si(CH3)2] n4 -R2-(SH) n2 , (HS) n1 -R1-Si(CH3)2)-[O-Si(CH3)(OCH3)] n3 -[O-Si(CH3)2] n4 -[O-Si(CH3)(C4H9)] n5 -R2-(SH) n2 wherein n1, n2, n3, n4, n5 are integers such that n1+n2≧1, and R1 and R2 are organic groups.

[0024] In some exemplary thiol / mercapto-functional silicone oil compositions, the poly(mercaptoalkyl)alkylsiloxane contains the group —{O—Si—(R1)[—R2—(SH) n1 ]} n2 -, wherein n1 and n2 are integers of 1 or greater, and R1 and R2 are organic groups.

[0025] In some exemplary thiol / mercapto-functional silicone oil compositions, the poly(mercaptoalkyl)(alkoxyl)siloxane contains a group -{O-Si-(O-R1)[-R2-(SH) n1 ]} n2 -, wherein n1 and n2 are integers of 1 or greater, and R1 and R2 are organic groups.

[0026] In some exemplary thiol / mercapto-functional silicone oil compositions, the silicone oil is

[0027] [ka] It is possible that.

[0028] In one exemplary thiol / mercapto-functional silicone oil composition, the average molecular weight (Mw) of the composition can be 200 or greater, preferably 500 or greater, more preferably 1000 or greater, and even more preferably 2000 or greater.

[0029] In one exemplary thiol / mercapto-functional silicone oil composition, the average molecular weight (Mw) of the composition can be as low as 200, 300, 500, 800, 1000, 2000, to as high as 3000, 5000, 10000, 20000, 50000, 100000, 500000, 1000000, 5000000.

[0030] Thermal interface material compositions provided by the present disclosure can include a weight percentage of functionalized silicone oil (e.g., thiol / mercapto-functionalized silicone oil) from, for example, 0.1 wt%, 0.4 wt%, 0.8 wt%, 1.2 wt%, 1.6 wt%, 2 wt%, 2.4 wt%, 2.8 wt%, 3 wt%, 5 wt%, and / or 7 wt%, or any range using any two of the foregoing as endpoints, where the weight percentage is based on the total weight of the thermal interface material composition. For example, the thermal interface material can include 0.1 wt% to 7 wt%, 0.1 wt% to 5 wt%, and / or 0.1 wt% to 3 wt% of the total weight of the thermal interface material composition.

[0031] In one exemplary functional silicone oil, thiol / mercapto functional silicone oil composition is prepared by thiol-ene chemical reaction process.For example, the synthesis of linear thiol silicone oil is achieved by reacting polythiol (polymeric mercapto group-containing thiol) with carbon-carbon unsaturated bond functional silicone oil in a molar ratio of 0.1:1 to 1:0.1, preferably 2:1, 1:1 or 1:2.

[0032] In one exemplary thiol functionalization reaction, the polythiol contains at least two mercapto groups and has the general formula R—(SH) nwherein R is an organic moiety having a valence n, where n is at least 2, such as 1,2-ethanedithiol, 1,3-propanedithiol, 1,8-octanedithiol, 2,3-butanedithiol, 1,9-nonanedithiol, 2,2'-(1,2-ethanediylperoxy)bisethanethiol, pentaerythritol tetrakis(3-mercaptopropionate), mercaptosilicone oil, pentaerythritol tetrakis(3-mercaptobutyrate), and the like. The thiol-functional silicone oil composition provided by the present disclosure can include, for example, a weight percent of polymeric mercapto group-containing thiol within any range from 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, or 60 wt%, or any range using any two of the foregoing as endpoints, where the weight percent is based on the total weight of the thiol-functional silicone oil. For example, the polymeric mercapto group-containing thiol can constitute 15 wt% to 60 wt%, 20 wt% to 55 wt%, and / or 25 wt% to 50 wt% of the total weight of the thiol-functional silicone oil.

[0033] In one exemplary thiol functionalization reaction, the ene (carbon-carbon unsaturated bond) composition can include a silicone oil having a -C(R1)=C(R2)- group, where R1 and R2 are independently H or an organic group.

[0034] In one exemplary thiol functionalization reaction, the ene (carbon-carbon unsaturated bond) composition can include a silicone oil having vinyl groups, acetylene groups, acrylic groups, methacrylic groups, or combinations thereof.

[0035] In one exemplary ene (carbon-carbon unsaturated bond) composition, vinyl, acetylenic, or acrylic groups are singly terminated, diterminated, or grafted onto a silicone oil.

[0036] In one exemplary ene (carbon-carbon unsaturated bond) composition, the average molecular weight (Mw) of the silicone oil having —C(R1)═C(R2)— groups can be 100 or greater, preferably 500 or greater, more preferably 1000 or greater, and even more preferably 2000 or greater.

[0037] In one exemplary ene (carbon-carbon unsaturated bond) composition, the average molecular weight (Mw) of the silicone oil having -C(R1)=C(R2)- groups can be as low as 200, 300, 500, 800, 1000, 2000, to as high as 3000, 5000, 10000, 20000, 50000, 100000, 500000, 1000000, 5000000, 5000000.

[0038] In the case of thiol functionalization, the thiol-functional silicone oil can be made by mixing a polymeric mercapto group-containing thiol, an acrylic-containing silicone oil, and a photoinitiator. The thiol-functional silicone oil can be prepared according to the following reaction mechanism:

[0039] [ka]

[0040] In one exemplary thiol-functional silicone oil composition, pentaerythritol tetra(3-mercaptopropionate) is mixed with a methacrylic or acryl-containing chemical. In one exemplary thiol-functional silicone oil composition, pentaerythritol tetra(3-mercaptopropionate) is mixed with a polysiloxane containing a methacrylic or acryl group on a single-end or multi-end functional modified silicone oil in a 1:1 molar ratio, and a photoinitiator is further added at 0.5% by weight of the solution. The components of the composition are mixed and exposed to UV light for 30 minutes to obtain a thiol-functional silicone oil.

[0041] Exemplary acrylic-containing silicone oils can be selected from any number of long-chain silicone oils (e.g., methacrylic-functionalized silicone oils) containing one or more acrylic functional groups, including: (A1) n1-R1-Si(R11)(R12)-[O-Si(R13)(R14)] n3 -R2-(A2) n2 In the formula, n1, n2, and n3 are integers such that n1+n2≧1; R1 and R2 are independently organic groups; R11, R12, R13, and R14 are independently organic groups (e.g., alkyl groups, alkoxyl groups); and A1 and A2 are independently acrylic or methacrylic groups.

[0042] In one exemplary ene (carbon-carbon unsaturated bond) composition, the vinyl-containing silicone oil is (CH=CH) n1 -R1-Si(R11)(R12)-[O-Si(R13)(R14)] n3 -R2-(CH=CH2) n2 wherein n1, n2, and n3 are integers such that n1+n2≧1; R1 and R2 are independently organic groups; and R11, R12, R13, and R14 are independently organic groups (e.g., alkyl groups, alkoxy groups).

[0043] Exemplary ene (carbon-carbon unsaturated bond) compositions include:

[0044] [ka] Monovinyl silicone oils such as the following can be mentioned.

[0045] Exemplary ene (carbon-carbon unsaturated bond) compositions include:

[0046] [ka]

[0047] [ka] Monoacrylic silicone oils such as the above are included.

[0048] Exemplary ene (carbon-carbon unsaturated bond) compositions include:

[0049] [ka] and the like.

[0050] Vinyl silicone oil is a polysiloxane containing only one vinyl. The vinyl may be, for example, at the end or on either side of the silica backbone. The thiol-functional silicone oil composition provided by the present disclosure may contain, for example, an acrylic-containing silicone oil in a weight percent range from 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, and / or 60 wt%, or any range using any two of the foregoing as endpoints, where the weight percent is based on the total weight of the thiol-functional silicone oil. For example, the acrylic-containing silicone oil may constitute 15 wt% to 60 wt%, 20 wt% to 55 wt%, and / or 25 wt% to 50 wt% of the total weight of the thiol-functional silicone oil.

[0051] In the case of a thiol functionalization reaction, an initiator may further be included. The initiator may include, for example, a photoinitiator or a heat-sensitive initiator, or a mixture thereof. Exemplary photoinitiators may include a number of commercially available radical photoinitiators from companies such as Ciba Specialties (trade names Irgacure and Darocure), Lamberti (Esacure), BASF (Lucirin), Sartomer (Lambson), and many others. Radical photoinitiators are widely used in UV-curable adhesives, coatings, or inks. Common examples of photoinitiators include, but are not limited to, benzoin methyl ether, benzophenone (BP), bis(4,4'-dimethylamino)benzophenone, thioxanthone (such as the 2-isopropyl derivative, ITX), 9,10-anthraquinone, camphorquinone, 3-ketocoumarin, 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylphenylpropan-1-one (photoinitiator 1173), alpha-hydroxyacetophenone, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-(4-propylphenyl)-phosphine oxide, and mixtures thereof. Examples of heat-sensitive radical initiators include, but are not limited to, azobisisobutyronitrile, azobisisoheptonitrile, azobiscyanovaleric acid, dimethyl azobisisobutyrate, 2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), benzoyl peroxide, potassium persulfate, or ammonium persulfate. The thiol-functional silicone oil composition provided by the present disclosure can include, for example, a weight percent of photoinitiator within any range from 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt%, 1 wt%, or 2 wt%, or any range using any two of the foregoing as endpoints, where the weight percent is based on the total weight of the thiol-functional silicone oil. For example, the photoinitiator can comprise 0.1 wt% to 2 wt%, 0.1 wt% to 1.5 wt%, and / or 0.1 wt% to 1 wt% of the total weight of the thiol-functional silicone oil.

[0052] C. Thermally conductive filler The thermal interface material composition can include one or more thermally conductive fillers, which can increase the thermal conductivity of the thermal interface material while reducing any settling when forming the LM TIM composition.

[0053] Exemplary thermally conductive fillers may include any one of, or combinations of, metals, alloys, non-metals, metal oxides, and / or ceramics. Metals may include, but are not limited to, aluminum, copper, silver, zinc, nickel, tin, indium, and lead. Non-metals may include, but are not limited to, carbon, graphite, carbon nanotubes, carbon fiber, graphene, boron nitride, and silicon nitride. Metal oxides or ceramics include, but are not limited to, alumina (aluminum oxide), aluminum nitride, boron nitride, zinc oxide, and tin oxide. In one exemplary embodiment, the filler is aluminum nitride.

[0054] Thermal interface material compositions provided by the present disclosure can include one or more thermally conductive fillers in weight percents within any range from, for example, 0 wt%, 0.1 wt%, 1 wt%, 5 wt%, 8 wt%, or 10 wt%, or using any two of the foregoing as endpoints, where the weight percent is based on the total weight of the TIM composition. For example, the thermally conductive fillers can comprise 0 wt% to 10 wt%, 0.1 wt% to 8 wt%, and / or 1 wt% to 5 wt%.

[0055] The thermally conductive filler can be selected based on its average particle size. For example, a smaller particle size can be selected based on a desired higher packing density, resulting in better coating performance for the LM TIM composition. In this case, the thermally conductive filler can have an average particle size of at least 0.1 micron, 1 micron, or 10 microns, or as much as 50 microns, 75 microns, or 100 microns, or any range defined between any two of the foregoing values.

[0056] D. Coupling Agent Thermal interface material compositions provided by the present disclosure may include one or more coupling agents. Exemplary coupling agents include silane coupling agents having the general formula Y-(CH)-Si-X, where Y is an organic functional group and X is a hydrolyzable group. The organic functional group Y can include alkyl, glycidoxy, acryloxyl, methylacryloxyl, amine, or a combination thereof. The hydrolyzable group X can include alkyloxy or acetoxy. In some exemplary embodiments, the silane coupling agent can include an alkyltrialkoxysilane. Exemplary alkyltrialkoxysilanes include decyltrimethoxysilane, undecyltrimethoxysilane, hexadecyltrimethoxysilane, octadecyltrimethoxysilane, or dodecyltrimethyloxysilane. In one exemplary embodiment, the LM TIM includes dodecyltrimethyloxysilane as a coupling agent, as shown in the following formula:

[0057] [ka]

[0058] The coupling agent can increase the dispersibility and wetting of the LM TIM composition.

[0059] Thermal interface material compositions provided by the present disclosure can include one or more coupling agents in a weight percent range from, for example, 0 wt%, 0.2 wt%, 0.23 wt%, 0.25 wt%, 0.27 wt%, 0.3 wt%, or 0.33 wt%, 0.35 wt%, 0.37 wt%, 0.4 wt%, 0.45 wt%, or 0.5 wt%, or any range using any two of the foregoing as endpoints, where the weight percent is based on the total weight of the TIM composition. For example, the one or more coupling agents can constitute 0 wt% to 0.5 wt%, 0.2 wt% to 0.45 wt%, 0.23 wt% to 0.4 wt%, 0.25 wt% to 0.37 wt%, 0.27 wt% to 0.35 wt%, or 0.3 wt% to 0.33 wt% of the total weight of the TIM composition.

[0060] E. Emulsifiers / Surfactants The thermal interface material compositions provided by the present disclosure may include one or more surfactants that can act as emulsifiers. The emulsifiers / surfactants may include cationic surfactants, anionic surfactants, nonionic surfactants, or mixtures thereof.

[0061] Exemplary surfactants may include non-ionic surfactants, such as glycerin esters (e.g., monoglycerides, diglycerides), polyethylene glycol esters, sorbitan esters (e.g., sorbitan trioleate, sorbitan monooleate), polyoxyethylene sorbitan esters (e.g., polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan monooleate), polysorbates (e.g., polysorbate 40, polysorbate 80), or mixtures thereof.

[0062] Exemplary surfactants include Span-85, Span-80, Span-60, Span C12 and 1ATC9, tween-85, tween-60, dopamine, dopamine hydrochloride, 3-mercapto N-propionamide, and polyvinylpyrrolidone, 1-dodecanethiol, cetrimonium bromide, poly(4-vinyl 1-methyl-pyridinium bromide), lysozyme, and trithiocarbonate-functionalized brushed polyethylene glycol, 3-chloropropyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltriethoxysilane, and mixtures thereof. Surfactants and emulsifying agents can improve the stability of the liquid metal between the dispersed alloy phase and the organic phase.

[0063] Thermal interface materials provided by the present disclosure can include one or more surfactants or emulsifiers in weight percents within any range from, for example, 0%, 0.1%, 0.3%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 2%, and / or 3%, or any range using any two of the foregoing as endpoints, where the weight percentages are based on the total weight of the thermal interface material composition. For example, the surfactant can constitute 0% to 3%, 0.1% to 2%, 0.3% to 1.5%, 0.5% to 1.4%, 0.6% to 1.3%, 0.7% to 1.2%, 0.8% to 1.1%, and / or 0.9% to 1% of the total weight of the thermal interface material.

[0064] II. Properties of low-melting-point Ga-based thermal interface materials: The thermal interface materials of the present disclosure can exhibit relatively high thermal conductivities. For example, gallium-based thermal interface materials provided by the present disclosure can include, for example, a thermal conductivity, as determined according to ASTM D5470, of 2 W / (m·k), 3 W / (m·k), 4 W / (m·k), 5 W / (m·k), 6 W / (m·k), 7 W / (m·k), 8 W / (m·k), 9 W / (m·k), 10 W / (m·k), 11 W / (m·k), or 12 W / (m·k), or any range using any two of the foregoing as endpoints. For example, thermal conductivities can include 2 W / (m·k) to 12 W / (m·k), 3 W / (m·k) to 11 W / (m·k), and 4 W / (m·k) to 10 W / (m·k). In one exemplary embodiment, the thermal interface material exhibits a thermal conductivity of 8 W / (m·k) as determined according to ASTM D5470.

[0065] Thermal impedance (TI) testing characterizes the ability of a composition to spread heat from one electrical component to the rest of an electrical device. Gallium-based thermal interface materials provided by the present disclosure may include, for example, a TI within the range of 0.01 or 0.06 C°C·cm2 / W, as determined according to ASTM D5470. In one exemplary embodiment, the thermal interface material exhibits a thermal impedance of 0.01 to 0.05 C°C·cm2 / W, as measured by ASTM D5470.

[0066] III. Applications using thermal interface materials The thermal interface material compositions provided by the present disclosure can be used as thermal interface materials in a variety of electronic component contexts.

[0067] For example, FIG. 1A schematically illustrates an electronic chip 34, a heat spreader 36, and a heat sink 32, with a first thermal interface material (TIM) 10A connecting the heat sink 32 and the heat spreader 36, and a second thermal interface material 10B connecting the heat spreader 36 and the electronic chip 34. One or both of the thermal interface materials 10A and / or 10B may include the low melting point thermal interface material compositions described above. FIG. 1B illustrates an exemplary thermal interface material 10 as a thermal interface layer, designated as a TIM, disposed between the electronic chip 34 and the heat sink 32, such that a first surface of the TIM 10 contacts the surface of the electronic chip 34 and a second surface of the TIM 10 contacts the surface of the heat sink 32. As in FIG. 1A, the TIM 10 may include the low melting point thermal interface material compositions described above. FIG. 1C illustrates an exemplary thermal interface material 10 as a thermal interface material disposed between a heat spreader 36 and a heat sink 32, such that a first surface of the TIM 10 contacts the surface of the heat spreader 36 and a second surface of the TIM 10 contacts the surface of the heat sink 32. Similar to FIGS. 1A and 1B, the TIM 10 may include the low melting point thermal interface material composition described above. FIG. 1D illustrates an exemplary thermal interface material 10 as a thermal interface material disposed between an electronic chip 34 and a heat spreader 36, such that a first surface of the TIM 10 contacts the surface of the electronic chip 34 and a second surface of the TIM 10 contacts the surface of the heat spreader 36. Similar to FIGS. 1A, 1B, and 1C, the TIM 10 may include the low melting point thermal interface material composition described above.

[0068] The low melting point TIM of the present disclosure can be applied to a substrate using various printing processes, including stencil printing processes. Using a stencil can provide greater control and / or efficiency in applying the TIM to an electrical component. For example, using a stencil, the LM TIM can be repeatedly applied in the same pattern on many components. Stencils can be made in a variety of shapes, allowing the LM TIM to be applied to a variety of electrical components. The TIM can be printed on a substrate, which can be a conductive metal substrate, such as a copper substrate or an aluminum substrate. In some cases, the conductive substrate can be a nickel-coated substrate, such as a nickel-coated copper substrate or a nickel-coated aluminum substrate.

[0069] For example, the components of the low melting point TIM composition provided by the present disclosure can be combined into a paste. The paste can be printed onto a coated metal substrate, such as a nickel-coated copper substrate or a nickel-coated aluminum substrate, by a squeegee and stencil process, for example. The upper portion of the substrate can be covered with a stencil, which includes both a thickness (t) and a plurality of openings arranged as a mesh. The openings can be based on various geometries, including hexagonal geometries, and the geometry of each opening includes a length (l) (or diameter). The distance (a) between each of the openings around the mesh can be based on the thickness (t) of the stencil, with the distance (a) being proportional to (t). For example, if the stencil includes a relatively large thickness (t), the distance (a) between the openings can be relatively large; conversely, if the thickness (t) is relatively small, the distance (a) between the openings can also be relatively small. The distance (a) between the openings may also be proportional to the length (l) of the openings, such that the distance (a) between the openings may also be relatively large for openings with larger length (l) values. Each of at least the variables (a), (l), and (t) may be adjusted alone or in combination to deposit a desired thickness of low melting point TIM paste onto the coated metal substrate.

[0070] For example, a pattern can be cut into a steel substrate using a laser or other process that results in clean edges in the stencil geometry. Some processes, such as traditional steel stamping, can be avoided because they may not fit the stencil flush or may leave rounded edges or sharp features that could scratch the heat sink surface. The feature size of the stencil can be small enough to avoid the straightness of the scraper edge affecting the paste thickness (i.e., wide openings should be avoided). A honeycomb pattern can be used because it provides a uniform distribution and can be easily identified on a drawing using two dimensions. A scraper can be used to press the paste into the stencil features, and the use of the pattern allows the scraper to remain parallel to the heat sink at all points. The pattern remains on the surface until the module is pressed down and temperature cycled, at which point the paste flows and fills the voids. The shape, size, and spacing of the holes, along with the stencil thickness, determine the resulting paste thickness after the module is attached.

[0071] For example, if the length of the pattern (e.g., honeycomb orientation) cut into the steel sheet is 2.0 mm and the spacing between individual pattern cutouts is 0.5 mm, the resulting thickness of the past may be approximately 0.08 mm. In another example, if the length of the honeycomb pattern is 3.0 mm and the spacing between individual pattern cutouts is 0.75 mm, the resulting thickness of the past may be approximately 0.1 mm. In yet a further example, if the length of the honeycomb pattern is 4.0 mm and the spacing between individual pattern cutouts is either 1 mm or 2 mm, the resulting thickness of the past may be approximately 0.12 mm and in the range of 0.15 mm to 0.2 mm, respectively. [Example]

[0072] Example 1 A thiol-functional organopolysiloxane oil was prepared according to the formulation provided in Table 1.

[0073] [Table 1]

[0074] Thermal interface materials were prepared according to the formulations provided in Table 2.

[0075] [Table 2]

[0076] Materials 1, 2, 3, 4, 5 were added according to their mass ratios and mixed using a SpeedMixer at 2000 rpm for 5 minutes, then scraped and stirred manually.

[0077] Materials 6 and 7 were added to the mixture and mixed for 2 minutes at 2000 rpm using a SpeedMixer. The resulting composition was then manually scraped together and stirred again and mixed for 1 minute at 2000 rpm using a SpeedMixer.

[0078] The composition was then subjected to vacuum with stirring at 1000 rpm for 2 minutes.

[0079] The resulting composition comprises a liquid metal coated with a polymer and aluminum nitride.

[0080] The resulting low-melting-point TIM has a thermal conductivity of 4–10 W / (m·k) using the method of ASTM 5470 (TIM tester) and a thermal impedance of 0.01–0.05 C°C·cm2 / W using the method of ASTM D5470 (cut bar apparatus).

[0081] Example 2 A thiol-functional organopolysiloxane oil was prepared according to the formulation provided in Table 1.

[0082] A second embodiment of the thermal interface material was prepared according to the formulation provided in Table 3.

[0083] [Table 3]

[0084] The compositions from Tables 1 and 3 were mixed according to the method described in paragraphs

[0069] to

[0071] .

[0085] The resulting composition comprises a liquid metal coated with a polymer and aluminum nitride.

[0086] The resulting low-melting-point TIM has a thermal conductivity of 4–10 W / (m·k) using the method of ASTM 5470 (TIM tester) and a thermal impedance of 0.01–0.05 C°C·cm2 / W using the method of ASTM D5470 (cut bar apparatus).

[0087] Example 3 A thiol-functional organopolysiloxane oil was prepared according to the formulation provided in Table 1.

[0088] A third embodiment of the thermal interface material was prepared according to the formulation provided in Table 4.

[0089] [Table 4]

[0090] The compositions from Tables 1 and 4 were mixed according to the method described in paragraphs

[0069] to

[0071] .

[0091] The resulting composition comprises a liquid metal coated with a polymer and aluminum nitride.

[0092] The resulting low-melting-point TIM has a thermal conductivity of 8 W / (m·k) using the method of ASTM 5470 (TIM tester) and a thermal impedance of 0.01–0.05 C°C·cm2 / W using the method of ASTM D5470 (cut bar apparatus).

[0093] Example 4 A thiol-functional organopolysiloxane oil was prepared according to the formulation provided in Table 1.

[0094] A fourth embodiment of the thermal interface material was prepared according to the formulation provided in Table 5.

[0095] [Table 5]

[0096] The compositions from Tables 1 and 5 were mixed according to the method described in paragraphs

[0069] to

[0071] .

[0097] The resulting composition comprises a liquid metal coated with a polymer and aluminum nitride.

[0098] The resulting low-melting-point TIM has a thermal conductivity of 4–10 W / (m·k) using the method of ASTM 5470 (TIM tester) and a thermal impedance of 0.01–0.05 C°C·cm2 / W using the method of ASTM D5470 (cut bar apparatus).

Claims

1. 1. A thermal interface material comprising: A low-melting-point gallium alloy, and a mercapto group-containing silicone oil.

2. an emulsifying compound; at least one polymer; a thermally conductive powder; 10. The thermal interface material of claim 1, further comprising a coupling compound.

3. The thermal interface material of claim 1 , wherein the low melting point gallium alloy comprises 80% to 97% by weight of the total weight of the thermal interface material.

4. 10. The thermal interface material of claim 1, wherein the mercapto-containing silicone oil comprises 0.1% to 3% by weight of the total weight of the thermal interface material.

5. The mercapto group-containing silicone oil is a polymeric mercapto group-containing thiol; an acrylic-containing silicone oil; and a photoinitiator.

6. the polymeric mercapto group-containing thiol constitutes 25% by weight to 50% by weight of the total weight of the mercapto group-containing silicone oil; the acryl-containing silicone oil constitutes 25% by weight to 50% by weight of the total weight of the mercapto group-containing silicone oil; 6. The thermal interface material of claim 5, wherein the photoinitiator comprises 0.1% to 1% by weight of the total weight of the mercapto-containing silicone oil.

7. 3. The thermal interface material of claim 2, wherein the at least one polymer comprises a first polymer and a second polymer, the first polymer comprising a silicon-based polymer and the second polymer comprising a diol-modified polymer.

8. 8. The thermal interface material of claim 7, wherein the silicone-based polymer comprises 0% to 3% by weight of the total weight of the thermal interface material and the diol-modified polymer comprises 0% to 3% by weight of the total weight of the thermal interface material.

9. 1. A method for applying a thermal interface material to a substrate, the method comprising: combining a low melting point gallium alloy, a mercapto group-containing silicone oil, an emulsifying compound, at least one polymer, a thermally conductive powder, and a coupling compound to form the thermal interface material; applying the thermal interface material to a metal substrate.

10. 10. The method of claim 9, wherein the mercapto group-containing silicone oil comprises a polymeric mercapto group-containing thiol, an acrylic-containing silicone oil, and a photoinitiator, and the method further comprises combining each of the polymeric mercapto group-containing thiol, the acrylic-containing silicone oil, and the photoinitiator, and exposing each of the polymeric mercapto group-containing thiol, the acrylic-containing silicone oil, and the photoinitiator to ultraviolet radiation for one minute or less.

11. The method of claim 9 , wherein the metal substrate comprises a nickel-coated copper substrate or a nickel-coated aluminum substrate.

12. 10. The method of claim 9, wherein the thermal interface material is applied in a stencil printing process at a speed of 10 mm / sec or less.

13. An electronic component, A heat sink; Electronic chips and a thermal interface material disposed between the heat sink and the electronic chip, the thermal interface material comprising: low-melting-point gallium alloys, and and a thermal interface material comprising a mercapto group-containing silicone oil.

14. the thermal interface material an emulsifying compound; at least one polymer; a thermally conductive powder; The electronic component of claim 13 further comprising a coupling compound.

15. 14. The electronic component of claim 13, wherein the thermal interface material has a thermal conductivity of 4 W / (m·k) to 16 W / (m·k), as determined according to ASTM D5470.

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