A thermal interface material with low dispense viscosity, minimal vertical flow after dispensing, and low thermal impedance after curing.

Abstract

Provided is a thermal interface material comprising: divinylpolydimethylsiloxane; a chain extender; a crosslinker; 80 volume percent or more of a thermally conductive filler; a treating composition; a platinum hydrosilylation catalyst; and up to 0.2 weight percent of a hydrosilylation inhibitor, wherein the weight percent values ​​are based on the weight of the thermal interface material composition and the volume percent values ​​are based on the volume of the thermal interface material composition; wherein the thermal interface material composition has a molar ratio of silyl hydride groups to vinyl groups that is greater than or equal to 0.4 and less than or equal to 1.0; and wherein the molar ratio of silyl hydride functional groups from the chain extender to silyl hydride functional groups from the crosslinker is greater than or equal to 13 and less than or equal to 70.

Description

[Technical Field]

[0001] The present invention relates to polysiloxane-based thermal interface materials, methods of applying such thermal interface materials, and articles containing such thermal interface materials.

[0002] Introduction Thermal interface materials (TIMs) provide a thermally conductive bond between two components and are often used in electronic devices to draw heat from a heat source to a heat sink. The effectiveness of a TIM material can be measured by the thermal impedance of the TIM between substrates:

number

[0003] One way to reduce the thermal impedance of a TIM is to reduce the bondline thickness of the TIM. The BLT corresponds to the thickness of the TIM between substrates. Typically, a TIM material is applied to a substrate at a thickness that may be 1 millimeter thick, and then another substrate is applied, compressing the TIM between the substrates. Reducing the BLT is desirable to reduce thermal impedance and to facilitate the manufacture of smaller devices. A thinner BLT allows for thinner electronic components, which is desirable as consumers demand smaller cell phones and other electronic devices. It is desirable for the TIM to be compressible to a BLT of less than 30 micrometers between substrates.

[0004] Thermal conductivity is also important for TIMs. Increasing thermal conductivity helps reduce thermal impedance and promotes efficient heat transfer through the TIM between substrates. Increasing thermal conductivity is important as electronic devices become more powerful and generate more heat concomitantly. It is even more beneficial if the TIM has a thermal conductivity of 6.0 watts per meter*Kelvin (W / m*K) or greater.

[0005] While it is desirable to achieve low thermal impedance with the TIM alone, it is even more desirable to do so while providing a TIM that has a low dispensable viscosity (120 Pascal*seconds (Pa*s) or less) to allow easy application by printing onto a substrate, and a low-shear viscosity high enough to remain in its original position during a vertical drop test without expanding, slipping, or showing evidence of void formation. A challenge with TIM materials is "pump-out" or void formation, which typically arises from a heat source and heat sink having different thermal expansion coefficients and / or non-uniformities in the TIM material. Passing the vertical drop test indicates minimal or no pump-out of the TIM and no void formation. While attempts are sometimes made to pass the vertical drop test by simply increasing the viscosity of the TIM, such an approach can hinder the ability to dispense the TIM. Thus, while a lower dispensable viscosity of 120 Pa*s or less is desirable, it is difficult to achieve while still passing the vertical drop test.

[0006] One approach to achieving low dispensable viscosity while attempting to improve performance in the vertical drop test is to blend an organic solvent with a high-viscosity TIM formulation. The solvent first reduces the viscosity to enable dispensability, but then evaporates, resulting in a higher viscosity TIM composition after dispensing. However, such formulations require the use of organic solvents, which evaporate and undesirably contribute to the release of volatile organic compounds (VOCs). Therefore, it is desirable to provide a TIM that has a low dispensable viscosity and passes the vertical drop test without the need for an organic solvent. Summary of the Invention

[0007] The present invention provides a composition that is sufficiently compressible to achieve a bond line thickness (BLT) of 30 micrometers or less when tested at 80°C for 15 minutes under a pressure of 276 kilopascals (kPa) (40 pounds per square inch) in accordance with ASTM D-5470, while having a dispensable viscosity of 120 Pa*s or less (when tested in accordance with ASTM D4440-15 using a TA Instruments RES-G2 rotational rheometer with 25 millimeter parallel plates at 0.01 to 300% strain and a frequency of 10 rad / sec), and a low thermal impedance (0.1°C*cm 2 This invention provides a solution to the problem of obtaining a thermal interface material (TIM) that provides a thermal conductivity of less than 1 W / m*K and passes the Vertical Drop Test described herein below. Desirably, the TIM possesses all of these characteristics while being free of organic solvents. Even more desirably, the TIM of the present invention also has a thermal conductivity of 6.0 W / m*K or greater, preferably 6.5 W / m*K or greater, as determined by the Thermal Conductivity Test Method described herein below.

[0008] The present invention provides a polysiloxane matrix composition having a specific silyl hydride to vinyl ratio (SiH:vinyl ratio) in combination with a specific blend of a linear polysiloxane having two terminally located silyl hydride functional groups (di-SiH polysiloxane) and a polysiloxane having more than two silyl hydride functional groups (multi-SiH polysiloxane) that crosslinks sufficiently to prevent dripping, but not so extensively as to prevent compression to a BLT of 30 micrometers or less, and has a crosslinking strength of 0.1°C*cm. 2This finding indicates that it is possible to achieve a TIM that achieves a thermal impedance of less than 1 / W. It has been found that when the SiH:Vi ratio is 0.4 or greater and 1.0 or less, and the molar ratio of SiH functional groups from the di-SiH polysiloxane to SiH functional groups from the multi-SiH polysiloxane is 13 or greater and 70 or less, the TIM formulation can be compressed to a BLT of less than 30 micrometers, even when crosslinked. When the SiH / Vi ratio is greater than 1.0 and / or the ratio of di-SiH polysiloxane SiH functional groups to multi-SiH polysiloxane functional groups is less than 13, the cured TIM tends to be too crosslinked to compress to a BLT of less than 30 micrometers. When the SiH / Vi ratio is less than 0.4 and / or the ratio of di-SiH polysiloxane functional groups to multi-SiH polysiloxane functional groups is greater than 70, pump-out may occur due to unreacted polymer.

[0009] The present inventors have further surprisingly found that, in addition to the aforementioned properties, the compositions of the present invention can achieve thermal conductivities of 6.0 W / m*K or greater when the compositions include a thermally conductive filler composition having boron nitride in an amount of 0.5 to 12 weight percent (wt %) based on the weight of the composition.

[0010] In a first aspect, the present invention provides a treating agent comprising: (a) a divinylpolydimethylsiloxane having a viscosity of 30 to 200 millipascals*seconds; (b) a chain extender that is a linear polysiloxane having two terminal silylhydride functional groups, one on each end of the molecule; (c) a crosslinker that is a polysiloxane having more than two silylhydride functional groups; (d) 80 volume percent or more of a thermally conductive filler; and (e) an alkyltrialkoxysilane and a mono-trialkoxysiloxy- and trimethylsiloxy-terminated dimethylpolysiloxane having a degree of polymerization of 20 to 120. (f) a platinum hydrosilylation catalyst; and (g) up to 0.2 weight percent of a hydrosilylation inhibitor, wherein the weight percent values ​​are based on the weight of the thermal interface material composition and the volume percent values ​​are based on the volume of the thermal interface material composition, wherein the thermal interface material composition has a molar ratio of silyl hydride groups to vinyl groups that is greater than or equal to 0.4 and less than or equal to 1.0, and a molar ratio of silyl hydride functional groups from the chain extender to silyl hydride functional groups from the crosslinker that is greater than or equal to 13 and less than or equal to 70.

[0011] In a second aspect, the invention is a method of applying a composition of the first aspect onto a substrate, the method comprising dispensing a composition of the first aspect onto the substrate.

[0012] In a third aspect, the invention is an article comprising the composition of the first aspect in cured form in contact with a substrate. DETAILED DESCRIPTION OF THE INVENTION

[0013] Test methods, unless a date is given with the test method number, refer to the test method most recent as of the priority date of this document. Reference to a test method includes both a reference to the testing society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International methods, EN refers to European Norm, DIN refers to Deutsches Institut für Normung, ISO refers to the International Organization for Standards, and UL refers to the Underwriters Laboratory.

[0014] Products identified by trade names refer to compositions available under those trade names as of the priority date of this document.

[0015] "Plurality" means two or more. "And / or" means "and, or alternatively." All ranges are inclusive of endpoints unless otherwise indicated. All weight percent (wt%) values ​​are by weight of the composition and all volume percent (vol%) values ​​are by volume of the composition unless otherwise specified.

[0016] "Viscosity," unless otherwise specified, refers to (a) for TIM compositions, including those for measuring dispensable viscosity: dynamic viscosity as measured according to ASTM D4440-15 using a TA Instruments RES-G2 rotational rheometer with 25 millimeter parallel plates using 0.01 to 300% strain and a frequency of 10 rad / sec; and (b) for individual polysiloxanes: viscosity according to ASTM D 445 using a glass capillary Cannon-Fenske viscometer at 25°C.

[0017] Unless otherwise specified, all characteristics of the thermal interface material composition are determined in the uncured state.

[0018] Polysiloxanes are composed of a plurality of siloxane units selected from M, D, T, and Q type siloxane units, each having the following chemical composition:

number

[0019] The present invention is a thermal interface material (TIM) composition, i.e., a composition suitable for use as a TIM. The TIM composition is curable, meaning that it can be cured by undergoing a crosslinking reaction. Curing occurs through a hydrosilylation chemical reaction between vinyl groups and silyl hydride (SiH) groups. In this regard, the TIM composition includes a vinyl-functional polysiloxane and a silyl hydride-functional polysiloxane. Desirably, none of the polysiloxanes has both vinyl and silyl hydride functional groups.

[0020] The TIM composition includes divinyl polydimethylsiloxane (PDMS). The divinyl PDMS has a viscosity of 30 milliPascal*seconds (mPa*s) or greater, preferably 45 mPa*s or greater, or 60 mPa*s or greater, and can have a viscosity of 90 mPa*s or greater, 100 mPa*s or greater, 120 mPa*s or greater, 140 mPa*s or greater, 160 mPa*s or greater, or even 180 mPa*s or greater, while having a viscosity of 200 mPa*s or less, 180 mPa*s or less, or even 160 mPa*s or less, 140 mPa*s or less, 120 mPa*s or less, 100 mPa*s or less, 80 mPa*s or less, or even 60 mPa*s or less. If the viscosity is too high, the TIM composition becomes too viscous to incorporate 80 volume percent or more of a thermally conductive filler. If the viscosity is too low, the TIM viscosity will be too low, resulting in poor mechanical properties and possible chalking.

[0021] Desirably, the divinyl PDMS has terminal vinyl groups and has the following general chemical structure (I): [ka] where "Vi" refers to a vinyl group (-CH=CH2) and n refers to the average number of dimethylsiloxane units, which is the degree of polymerization (DP) of the PDMS. n is selected to achieve a desired viscosity for the divinyl PDMS. Typically, n is 25 or greater, and can be 30 or greater, 35 or greater, 40 or greater, 45 or greater, 50 or greater, 60 or greater, 70 or greater, 80 or greater, or even 90 or greater, while typically n is 200 or less, 190 or less, 180 or less, 170 or less, 160 or less, 150 or less, 140 or less, 130 or less, 120 or less, 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, or even 50 or less.

[0022] The concentration of divinyl PDMS in the TIM composition is desirably 2 weight percent (wt%) or more, and can be 3 wt% or more, or even 4 wt% or more, based on the weight of the TIM composition, while typically being 10 wt% or less, 8 wt% or less, 6 wt% or less, or even 4 wt% or less. Too much divinyl PDMS results in high viscosity, which reduces the amount of thermally conductive filler that can be included. Too little divinyl PDMS requires so much filler that the TIM composition loses its dispensability.

[0023] Suitable divinyl PDMS materials can be made by ring-opening polymerization of cyclosiloxanes using vinyl endblockers for termination, as taught in US Pat. No. 5,883,215(A).

[0024] The TIM composition includes a chain extender that is a linear polysiloxane having two terminal silylhydride functional groups, one at each end of the molecule. The linear polysiloxane contains primarily M- and D-type siloxane units, but may also contain T- and / or Q-type siloxane units in a total concentration of up to 5 mole percent (mol%), preferably up to 4 mol%, up to 3 mol%, up to 2 mol%, or up to 1 mol%, and most preferably no T- or Q-type siloxane units, the mol% of T- and Q-type siloxane units being relative to the total number of siloxane units in the linear polysiloxane. The linear polysiloxane chain extender has terminal M groups that each contain a SiH functional group.

[0025] The chain extender desirably has a viscosity of 5 mPa*s or greater, and can have a viscosity of 7 mPa*s or greater, 10 mPa*s or greater, 20 mPa*s or greater, or even 30 mPa*s or greater, while generally having a viscosity of 100 mPa*s or less, and can have a viscosity of 75 mPa*s or less, 50 mPa*s or less, 25 mPa*s or less, 20 mPa*s or less, 15 mPa*s or less, or even 10 mPa*s or less. If the viscosity is too high, the TIM composition will be too viscous to incorporate 80 volume percent or more of thermally conductive filler. If the viscosity is too low, the TIM viscosity will be too low, resulting in poor mechanical properties and possible chalking.

[0026] Desirably, the chain extender is a PDMS having a SiH functional group at each end (silylhydride terminated PDMS). Such a PDMS may have the following general chemical structure (II): [ka] The value of subscript m is selected to achieve a desired viscosity, such as those already taught above for the chain extender. Desirably, subscript m has an average value of 10 or greater, 11 or greater, 12 or greater, 13 or greater, or even 14 or greater, while typically being 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, or even 15 or less. An example of one suitable chain extender is hydride-terminated PDMS (commercially available as ACM83817714 from Alfa Chemistry and DMS-V21 from Gelest) containing 1.25 wt. % vinyl, having a viscosity of 7-10 mPa*s.

[0027] The concentration of the chain extender can be 0.5 wt. % or more, 0.75 wt. % or more, 1.0 wt. % or more, or even 1.25 wt. % or more, based on the weight of the TIM composition, while generally being 2.0 wt. % or less, 1.75 wt. % or less, 1.5 wt. % or less, 1.25 wt. % or less, or even 1.0 wt. % or less. This concentration range is most suitable for achieving the desired SiH / Vi ratio and molar ratio of silyl hydride functional groups from the chain extender to silyl hydride functional groups from the crosslinker needed to achieve the crosslink density and final hardness of the TIM composition.

[0028] Suitable chain extenders include hydride-terminated PDMS commercially available as DMS-H11 from Gelest.

[0029] The TIM composition includes a crosslinker that is a polysiloxane having more than two silyl hydride functional groups, preferably three or more. Desirably, the crosslinker has a viscosity of 10 mPa*s or more, 12 mPa*s or more, 14 mPa*s or more, 15 mPa*s or more, 16 mPa*s or more, 18 mPa*s or more, or even 19 mPa*s or more, while typically having a viscosity of 30 mPa*s or less, 25 mPa*s or less, 20 mPa*s or less, or even 19 mPa*s or less. These viscosity ranges are desirable to achieve an appropriate TIM composition viscosity at a particular component concentration.

[0030] Preferably, the crosslinker is a linear polysiloxane. Preferably, the crosslinker is a linear polysiloxane terminated at both ends with trimethyl groups. The crosslinker has the average chemical structure (III): [ka] wherein A is as previously described for the siloxane unit, but desirably is selected from methyl and phenyl in each occurrence, and most preferably is methyl in each occurrence; the average value of y is 3 or greater, and simultaneously 10 or less, 8 or less, 6 or less, or even 4 or less; and x is selected to achieve a desired viscosity for the overall crosslinker.

[0031] The crosslinker may be present in a concentration of 0.005 wt.% or more, 0.01 wt.% or more, 0.02 wt.% or more, 0.03 wt.% or more, or even 0.04 wt.% or more, based on the weight of the TIM composition, and is typically present in a concentration of 1.5 wt.% or less, 1.25 wt.% or less, 1.0 wt.% or less, 0.75 wt.% or less, 0.50 wt.% or less, 0.25 wt.% or less, 0.010 wt.% or less, 0.075 wt.% or less, 0.06 wt.% or less, or even 0.05 wt.% or less, which concentration range is most suitable for achieving the desired SiH / Vi ratio and molar ratio of silyl hydride functional groups from the chain extender to silyl hydride functional groups from the crosslinker needed to achieve the crosslink density and final hardness of the TIM composition.

[0032] Suitable crosslinkers include materials commercially available from Gelest under the designation DMS-071 and DMS-301, and from Dow, Inc. under the designation DOWSIL™ 6-3570 (DOWSIL is a trademark of The Dow Chemical Company).

[0033] The molar ratio of silyl hydride to vinyl groups in the TIM composition can be 0.1 or greater, 0.2 or greater, 0.3 or greater, 0.4 or greater, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.8 or greater, or even 0.9 or greater, and can be 1.0 or less, 0.9 or less, or even 0.8 or less. If the molar ratio exceeds 1.0, the composition may be too hard to compress to a bondline thickness of 30 micrometers or less. If the molar ratio is less than 0.1, there is a risk of failure in the vertical drop test due to insufficient crosslinking.

[0034] The TIM composition has a molar ratio of silyl hydride functional groups from the chain extender alone to silyl hydride functional groups from the crosslinker of 13 or more, 15 or more, 16 or more, 18 or more, 20 or more, 22 or more, 24 or more, 26 or more, 28 or more, 30 or more, 35 or more, 40 or more, 45 or more, or even 50 or more, while typically 70 or less, 65 or less, 60 or less, 55 or less, 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, or even 25 or less. If the molar ratio exceeds 70, there is a risk that the composition will be too hard and unable to compress to a bondline thickness of 30 micrometers or less. If the molar ratio is less than 13, there is a risk that the composition will fail the vertical drop test.

[0035] The TIM composition comprises 80 volume percent (vol%) or more, typically 98 vol% or less, and preferably 95 vol% or less of a thermally conductive filler, and can contain 94 vol% or less, 93 vol% or less, 92 vol% or less, 91 vol% or less, 90 vol% or less, 89 vol% or less, 88 vol% or less, 87 vol% or less, 86 vol% or less, 85 vol% or less, 84 vol% or less, 83 vol% or less, or even 82 vol% or less, or 81 vol% or less of a thermally conductive filler.

[0036] The thermally conductive filler can be any one or any combination of more than one thermally conductive filler known for use in TIM compositions, such as any one or any combination of more than one selected from aluminum, silver, copper, aluminum nitride, aluminum oxide, zinc oxide, aluminum nitride, boron nitride, silver-coated aluminum, carbon fiber, and graphite. Desirably, the thermally conductive filler is any one or any combination of more than one selected from the group consisting of zinc oxide, aluminum, and boron nitride.

[0037] Desirably, the thermally conductive filler is a combination of fillers of two or three different sizes selected from small (D50 less than 1 micrometer), medium (D50 between 1 and 5 micrometers), and large (D50 greater than 5 micrometers, preferably 8 micrometers or greater, but less than 200 micrometers). The reported number average particle size is used to determine the D50 of the thermally conductive filler using a laser diffraction particle size analyzer (e.g., a CILAA920 Particle Size Analyzer or a Beckman Coulter LS 13 320 SW) operated according to the operating software.

[0038] One desirable thermally conductive filler comprises a zinc oxide filler having a D50 of less than 1 micrometer, an aluminum filler having a D50 of 1 to 20 micrometers, and, optionally, at least one boron nitride flake having a particle size of 8 to 30 micrometers. Surprisingly, it has been found that when the boron nitride flake is present in a concentration of 1 wt. % or more, preferably 1.5 wt. % or more, more preferably 2.0 wt. % or more, 2.5 wt. % or more, or even 3.0 wt. % or more, of the weight of the TIM composition, but 10 wt. % or less, preferably 8 wt. % or less, 7 wt. % or less, 6 wt. % or less, 5 wt. % or less, 4 wt. % or less, or even 3 wt. % or less, the thermal conductivity of the TIM composition is particularly high, even greater than 6.0 wt. per meter Kelvin (W / m*K). A particularly desirable combination of thermally conductive fillers resulting in a thermal conductivity of 6.5 W / m*K includes, in weight percent based on the weight of the TIM composition, 44-48.6 wt. % aluminum filler having a D50 of 9 micrometers, 25-26 wt. % aluminum filler having a D50 of 2 micrometers, 17-18 wt. % zinc oxide having a D50 of 0.2 micrometers, 3-4 wt. % boron nitride flakes having an average size of 30 micrometers, and up to 1.6 wt. % or even up to 2.0 wt. % boron nitride flakes having an average size of 8 micrometers.

[0039] The TIM composition includes a treating composition. The treating composition includes an alkyltrialkoxysilane and a mono-trialkoxysiloxy- and trimethylsiloxy-terminated dimethylpolysiloxane. The alkyltrialkoxysilane is desirably a C6-C12 alkyltrimethoxysilane, preferably a C8-C12 alkyltrimethoxysilane, and may be n-decyltrimethethoxysilane. Suitable alkyltrialkoxysilanes include n-decyltrimethethoxysilane, available from Dow, Inc. as DOWSIL™ Z-6210 silane (DOWSIL is a trademark of The Dow Chemical Company).

[0040] The mono-trialkoxysilane-terminated and trimethylsiloxy-terminated dimethylpolysiloxanes desirably have a degree of polymerization of 20 or greater, and can be 30 or greater, 40 or greater, 50 or greater, 60 or greater, 70 or greater, 80 or greater, or even 90 or greater, while typically being 150 or less, 140 or less, 130 or less, 120 or less, 110 or less, 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, or even 30 or less. Longer chain lengths (degree of polymerization of 20 or greater) are desirable because they have greater stability than shorter chains. However, shorter chain lengths are more effective at reducing viscosity than longer chain lengths, so it is desirable to keep the degree of polymerization below 150.

[0041] Examples of suitable mono-trialkoxysiloxy-terminated and trimethylsiloxy-terminated dimethylpolysiloxanes have the chemical structure (IV): [ka] where the subscript a has a value equal to the degree of polymerization as described above for the mono-trialkoxysiloxy-terminated dimethylpolysiloxane.

[0042] Suitable mono-trialkoxysiloxy- and trimethylsiloxy-terminated dimethylpolysiloxanes can be synthesized according to the teachings of US Patent Application Publication No. 2006 / 0100336.

[0043] Desirably, the alkyltrialkoxysilane is typically present in a concentration, based on the weight of the TIM composition, of 1.8 wt. % or more, 2.0 wt. % or more, 2.5 wt. % or more, 3.0 wt. % or more, or even 3.5 wt. % or more, while typically present in a concentration of 4.0 wt. % or less, 3.5 wt. % or less, or even 3.0 wt. % or less.

[0044] Desirably, the mono-trialkoxysiloxy- and trimethylsiloxy-terminated dimethylpolysiloxanes are present in a concentration of 0.05 wt.% or more, 0.1 wt.% or more, 0.2 wt.% or more, 0.3 wt.% or more, or even 0.4 wt.% or more based on the weight of the TIM composition, while typically present in a concentration of 0.5 wt.% or less, 0.4 wt.% or less, 0.3 wt.% or less, or 0.2 wt.% or less.

[0045] The TIM composition includes a platinum hydrosilylation catalyst. Examples of platinum hydrosilylation catalysts include Speier's catalyst (HPtCl) and Karstedt's catalyst (platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex). The catalyst may be encapsulated or unencapsulated. An encapsulated catalyst is typically a catalyst encapsulated in a phenyl resin.

[0046] The platinum hydrosilylation catalyst is typically present in a concentration of 0.1 wt % or more, 0.2 wt % or more, and can be 0.3 wt % or more, based on the weight of the TIM composition, while typically present in a concentration of 0.5 wt % or less, 0.4 wt % or less, or even 0.3 wt % or less.

[0047] The TIM composition may include a hydrosilylation inhibitor at a concentration of up to 0.2 wt. % of the weight of the TIM composition. The hydrosilylation inhibitor may be, for example, methyl(tris(1,1-dimethyl-2-propynyloxy))silane. Desirably, the inhibitor is present and delivered in vinyldimethyl-terminated PDMS.

[0048] Desirably, the TIM composition does not contain organic solvents, and even more desirably does not contain any solvents.

[0049] The TIM composition of the present invention is particularly useful in the process of dispensing the TIM composition onto a substrate. In particular, the TIM composition of the present invention can be printed onto a substrate in a specific pattern by a process that includes dispensing the TIM composition onto a substrate by printing the TIM composition onto the substrate. Even more advantageous is the fact that after being dispensed onto the substrate, a second substrate can be applied onto the TIM composition and pressed against the TIM composition to form a TIM composition having a bondline thickness of 30 micrometers or less between the two substrates.

[0050] The present invention further includes an article comprising a TIM composition dispensed onto a substrate, preferably positioned between two substrates. The present invention includes the following aspects. Section 1. 1. A thermal interface material composition comprising: a. Divinyl polydimethyl siloxane having a viscosity of 30 to 200 millipascals per second; b. a chain extender which is a linear polysiloxane having two terminal silyl hydride functional groups, one at each end of the molecule; c. a crosslinker that is a polysiloxane having more than two silyl hydride functional groups; d. 80 volume percent or more of a thermally conductive filler; e. a treatment composition containing an alkyltrialkoxysilane and a mono-trialkoxysiloxy-terminated and trimethylsiloxy-terminated dimethylpolysiloxane having a degree of polymerization of 20 to 120; f. a platinum hydrosilylation catalyst; g. up to 0.2 weight percent of a hydrosilylation inhibitor; Including, wherein the weight percent values ​​are based on the weight of the thermal interface material composition and the volume percent values ​​are based on the volume of the thermal interface material composition, wherein the molar ratio of silyl hydride groups to vinyl groups in the thermal interface material composition is greater than or equal to 0.4 and less than or equal to 1.0, and wherein the molar ratio of silyl hydride functional groups from the chain extender to silyl hydride functional groups from the crosslinker is greater than or equal to 13 and less than or equal to 70. Section 2. a. the divinylpolydimethylsiloxane is present in a concentration of 2 to 4 weight percent; b. the chain extender is present at a concentration of 0.5 to 1.5 weight percent; c. the cross-linking agent is present at a concentration of 0.005 to 0.05 weight percent; d. the alkyltrialkoxysilane is present in a concentration of 1.8 to 4 weight percent and the monotrialkoxy-terminated dimethylpolysiloxane is present in a concentration of 0.05 to 0.5 weight percent; Item 10. The composition of item 1, wherein the weight percent values ​​are based on the weight of the thermal interface material composition. Section 3. Item 3. The thermal interface material composition of item 1 or 2, wherein the thermally conductive filler comprises zinc oxide particles having an average size of less than 1 micrometer, aluminum filler having an average particle size of 1 to 20 micrometers, and optionally boron nitride flakes having a particle size of 8 to 30 micrometers. Section 4. Item 4. The thermal interface material composition of item 3, wherein the boron nitride particles are present in a concentration of 1 to 10 weight percent, based on the weight of the thermal interface material composition. Section 5. 5. The thermal interface material composition of claim 3 or 4, wherein the thermally conductive fillers comprise, in weight percent based on the weight of the TIM composition, 44-48.6 wt. % aluminum filler having a D50 of 9 micrometers, 25-26 wt. % aluminum filler having a D50 of 2 micrometers, 17-18 wt. % zinc oxide having a D50 of 0.2 micrometers, 3-4 wt. % boron nitride flakes having an average size of 30 micrometers, and up to 1.6 wt. % or even up to 2.0 wt. % boron nitride flakes having an average size of 8 micrometers. Section 6. Item 6. The thermal interface material composition according to any one of items 1 to 5, wherein the chain extender is a silyl hydride-terminated polydimethylsiloxane. Section 7. The crosslinker has the following average chemical structure: (CH3)3SiO-[H(CH3)SiO] y -[(CH3)2SiO] x -Si(CH3)3 Item 8. The thermal interface material composition of item 7, wherein the average value of y is 3 or more, and the value of x is such that the crosslinker has a viscosity of 10 to 25 mPa*sec. Section 8. Item 8. The thermal interface material composition according to any one of items 1 to 7, which does not contain an organic solvent. Section 9. Item 9. A process comprising dispensing the thermal interface material composition of any one of items 1 to 8 onto a substrate. Section 10. Item 9. An article comprising the thermal interface material composition according to any one of items 1 to 8, disposed on a substrate. [Example]

[0051] Materials. Materials for use in sample preparation are listed in Table 1. [Table 1] DOWSIL is a trademark of The Dow Chemical Company. Polartherm is a trademark of Momentive Performance Materials Inc.

[0052] Characterization Methods. Characterize the samples according to the following methods:

[0053] Dispenseable Viscosity. Dispenseable viscosity is a measure of the ability of a TIM formulation to be deposited onto a substrate by printing. If the viscosity is too high, it is difficult to print the TIM formulation precisely and accurately. The present invention achieves a dispenseable viscosity of 120 Pa*s or less. Dispenseable viscosity is determined using the dynamic viscosity test method of ASTM D4440-15, using a TA Instruments ARES-G2 rheometer with 25 millimeter parallel plates. Test conditions are based on a strain sweep at 25°C, 0.1 to 300% strain, and a frequency of 10 rad / sec.

[0054] Bondline Thickness and Thermal Impedance. The bondline thickness (BLT) and thermal impedance of the TIM formulations are determined according to ASTM D-5470 using a LongWin Model LW 9389 TIM Thermal Interface Materials Tester. The pressure applied to the TIM material samples is 275.9 kilonewtons per square meter (40 pounds per square inch). The test time for each sample is 15 minutes, and the temperature is 80°C.

[0055] Vertical Drop Test: 0.2 grams of TIM formulation is applied to a piece of aluminum panel. Two 0.2-millimeter plastic shims are placed on either side of the sample, and a 1-millimeter-thick cover glass slide is placed on top of the TIM formulation and pressed against the formulation, resulting in a 0.2-millimeter-thick film of TIM formulation between the cover glass slide and the aluminum panel. The cover glass and aluminum panel are clamped together with clips to hold them in place, and the assembly is placed vertically in a temperature cycling chamber (ESPEC Corp. PSL-2J). The temperature is cycled from -40°C to 125°C with 15 minutes between each temperature limit, and each limit is held for 15 minutes. After 500 cycles, the sample is evaluated. A TIM formulation "passes" the vertical drop test if there is no evidence of TIM formulation expanding or sliding between the cover glass slide and the aluminum panel, little or no void formation, and little or no pumping of the TIM formulation is observed.

[0056] Thermal Conductivity. Measure the thermal conductivity of the TIM formulation using a Hot Disk Instrument TPS 2500 S manufactured by Hot Disk AB (Goteborg, Sweden) according to the ISO 22007-2:2015 test method. Use a C5501 sensor, a heating time of 2 to 5 seconds, and a power of 500 milliwatts. Fill two cups with the TIM formulation and place the flat sensor inside. Use a fine-tuned analysis with temperature drift compensation and time correction selected between 50 and 150 points.

[0057] Sample TIM formulation Formulation Preparation. Sample formulations are prepared by combining the ingredients in a 100 milliliter (mL) speed mixer cup. The treating agent, silicone oil with vinyl PDMS, chain extender, and crosslinker are added to the 100 mL speed mixer cup. The small and medium thermally conductive fillers are then added and mixed for 20 seconds at 100 revolutions per minute (RPM) using a FlackTek speed mixer. The large thermally conductive fillers are added in two portions, mixing for 20 seconds at 1000 RPM and 20 seconds at 1500 RPM after each addition. If applicable, BN fillers are added and mixed for 20 seconds at 1000 RPM, then 20 seconds at 1500 RPM to obtain a flowable metal-polyorganosiloxane mixture. The catalyst is added and mixed twice for 20 seconds at 800 RPM. Viscosity, thermal conductivity, and vertical drop test performance are determined. The formulation is cured in an oven at 100° C. for 1 hour and then tested for bondline thickness and thermal impedance.

[0058] All sample formulations were organic solvent free.

[0059] Out-of-range SiH / Vi ratios and molar ratios of SiH functional groups from the chain extender to SiH functional groups from the crosslinker. Samples 1-7 represent TIM formulations with SiH / Vi ratios greater than 1.0 or molar ratios of SiH functional groups from the chain extender to SiH functional groups from the crosslinker less than 13. The results show that in any of these situations, the formulations cannot be compressed to a BLT of 30 micrometers or less. Notably, all of these formulations have dispensable viscosities of 120 Pa*s or less.

[0060] It is noteworthy that Sample 7 has a SiH / Vi ratio of 1.0, yet a BLT of 320 microns. This particular sample represents a formulation that is unable to achieve a BLT of 30 microns or less, but approaches 30 microns compared to Samples 1-6. Sample 23 (see Table 3) demonstrates that when the SiH / Vi ratio is 1.0, a BLT of 30 microns or less is achievable if the SiH CE / SiH crosslinker ratio is increased sufficiently.

[0061] Table 2 shows the formulations and characterization of Samples 1-7. The formulations identify the ingredients in grams used to prepare the formulation. [Table 2] * NM: Not measured ** It failed due to void formation and pumping out of the TIM formulation.

[0062] The SiH / Vi ratio and molar ratio of SiH chain extender functional groups to SiH crosslinker functional groups were within the ranges. Samples 8-23 represent TIM formulations with SiH / Vi ratios of 1.0 or less and molar ratios of chain extender SiH to crosslinker SiH functional groups of 13 or more. The results show that when these ratios are met, the formulations are capable of forming BLTs of less than 30 micrometers and with a BLT of 0.1°C*cm. 2 The results show that it is possible to achieve a thermal impedance of less than 100 W, a dispensable viscosity of 120 Pa*s or less, and pass the vertical drop test. Furthermore, the samples containing boron nitride thermally conductive filler have particularly high thermal conductivity values ​​of greater than 6.0 W / m*K. Notably, all of these formulations have a dispensable viscosity of 120 Pa*s or less.

[0063] Table 3 shows the formulations of Samples 8-23 and the characterization of those samples. The formulations identify the ingredients in grams used to prepare the formulation. Note: "TA" = Processing Agent. "TCF" = TC Filler. "CE" = Chain Extender. "TC" = Thermal Conductivity. "TI" = Thermal Impedance. "VDP" = Vertical Drop Test. [Table 3]

Claims

1. 1. A thermal interface material composition comprising: a. a divinylpolydimethylsiloxane having a viscosity of 30 to 200 mPa*sec; b. a chain extender which is a linear polysiloxane having two terminal silyl hydride functional groups, one at each end of the molecule; c. a crosslinker that is a polysiloxane having more than two silyl hydride functional groups; d. 80 volume percent or more of a thermally conductive filler; e. a treating composition comprising an alkyltrialkoxysilane and a mono-tri(alkoxy)siloxy-terminated and trimethylsiloxy-terminated dimethylpolysiloxane having a degree of polymerization of 20 to 120; f. a platinum hydrosilylation catalyst; g. up to 0.2 weight percent of a hydrosilylation inhibitor; Including, 1. A composition wherein the weight percent values ​​are based on the weight of the thermal interface material composition and the volume percent values ​​are based on the volume of the thermal interface material composition, wherein the molar ratio of silyl hydride groups to vinyl groups in the thermal interface material composition is greater than or equal to 0.1 and less than 1.0, and the molar ratio of silyl hydride functional groups from the chain extender to silyl hydride functional groups from the crosslinker is greater than or equal to 13 and less than or equal to 70.

2. 10. The thermal interface material composition of claim 1, wherein the thermally conductive filler comprises zinc oxide particles having an average size of less than 1 micrometer, aluminum filler having an average particle size of 1 to 20 micrometers, and optionally boron nitride flakes having a particle size of 8 to 30 micrometers.

3. 3. The thermal interface material composition of claim 2, wherein the boron nitride flakes are present in a concentration of 1 to 10 weight percent based on the weight of the thermal interface material composition.

4. 3. The thermal interface material composition of claim 2, wherein the thermally conductive fillers comprise, in weight percentages based on the weight of the thermal interface material composition, 44 to 48.6 wt. % aluminum filler having a D50 of 9 micrometers, 25 to 26 wt. % aluminum filler having a D50 of 2 micrometers, 17 to 18 wt. % zinc oxide having a D50 of 0.2 micrometers, 3 to 4 wt. % boron nitride flakes having a D50 of 30 micrometers, and up to 1.6 wt. % or even up to 2.0 wt. % boron nitride flakes having a D50 of 8 micrometers.

5. 10. The thermal interface material composition of claim 1, wherein the chain extender is a silyl hydride terminated polydimethylsiloxane.

6. The crosslinker has the following average chemical structure: (CH ３ , ３ t0.83[(t0.83) ３ )SiO] ｙ -[(CH ３ , ２ SiO] ｘ -Si(CH ３ , ３ 6. The thermal interface material composition of claim 5, having the formula: wherein the average value of y is 3 or greater, and the value of x is such that the crosslinker has a viscosity of 10 to 25 milliPascal*seconds.

7. 10. The thermal interface material composition of claim 1, which is organic solvent-free.

8. A process comprising dispensing a thermal interface material composition according to any one of claims 1 to 7 onto a substrate.

9. An article comprising the thermal interface material composition of any one of claims 1 to 7 disposed on a substrate.

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