Thermal interface material with low partition viscosity, low vertical flow after partitioning, and low thermal resistance after curing.

Abstract

This invention provides a thermal interface material comprising divinyl polydimethylsiloxane, a chain extender, a crosslinking agent, 80 vol% or more of a thermally conductive filler, a treatment agent composition, a platinum hydride silanization catalyst, and up to 0.2 wt% of a hydride silanization inhibitor; wherein the wt% values ​​are relative to the weight of the thermal interface material composition, the vol% values ​​are relative to the volume of the thermal interface material composition, the molar ratio of silane-based hydride groups to vinyl groups in the thermal interface material composition is 0.4 or greater and simultaneously 1.0 or less, and the molar ratio of silane-based hydride functional groups from the chain extender to silane-based hydride functional groups from the crosslinking agent is 13 or greater and simultaneously 70 or less.

Description

Technical Field

[0001] This invention relates to polysiloxane-based thermal interface materials, methods for applying such thermal interface materials, and articles containing such thermal interface materials. Background Technology

[0002] Thermal interface materials (TIMs) provide a thermally conductive bond between two components and are commonly 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 resistance between the TIM and the substrate.

[0003] Θ=(d / κ)+R contact

[0004] Where Θ is the thermal resistance of the TIM, d is the bond line thickness (BLT), κ is the thermal conductivity of the TIM, and R contact This is the sum of the contact resistance values ​​between the TIM and the adjacent substrate. Reducing the thermal resistance corresponds to increased heat dissipation efficiency through the TIM. Ideally, the thermal resistance should be less than 0.1 degrees Celsius per square centimeter per watt (°C / cm²). 2 The value of / W).

[0005] One way to reduce the thermal resistance of TIM is to reduce the thickness of the TIM's bonding line. BLT corresponds to the thickness of the TIM between the substrates. Typically, TIM material is applied to one substrate to a thickness that can be one millimeter thick, and then another substrate is applied, compressing the TIM between the substrates. It is desirable to reduce the BLT to lower thermal resistance and also to facilitate the manufacture of smaller devices. Thinner BLTs allow for thinner electronic components, which is desirable as consumers seek smaller cellular phones and other electronic devices. It is desirable that TIM can be compressed between substrates to a BLT of less than 30 micrometers.

[0006] Thermal conductivity is also important in TIM. Increasing thermal conductivity reduces thermal resistance and facilitates efficient heat transfer through the TIM between substrates. As electronic devices become more powerful and generate more heat, increasing thermal conductivity is crucial. It would be further beneficial if the TIM had a thermal conductivity of 6.0 watts per meter (W / m*K) or higher.

[0007] Achieving low thermal resistance solely in TIM is desirable, but it is even more desirable to do so while providing TIM with a low distributable viscosity (120 Pa*s or less) to allow for easy application by printing onto a substrate, while having a sufficiently high low shear viscosity to remain in its original position without swelling, slipping, or showing signs of void formation during vertical drop testing. A challenge with TIM materials is “pumping out” or void formation, which is often caused by heat sources and radiators with different coefficients of thermal expansion and / or non-uniformity within the TIM material. Vertical drop testing indicates that the TIM will have minimal or no pumping out and no void formation. While one could simply attempt to pass the vertical drop test by increasing the viscosity of the TIM, this approach may inhibit the TIM’s ability to be dispensed. Therefore, a lower distributable viscosity of 120 Pa*s or less is desirable, but achieving this lower distributable viscosity through vertical drop testing is challenging.

[0008] One approach to achieving low dispensable viscosity while attempting to improve vertical drop test performance is to blend an organic solvent with a high-viscosity TIM formulation. The solvent initially reduces viscosity to allow dispensability, but then evaporates after dispensing to produce a higher-viscosity TIM composition. However, such formulations require the use of an organic solvent, which evaporates and undesirably leads to the emission of volatile organic compounds (VOCs). Therefore, it is desirable to provide a TIM with low dispensable viscosity that passes the vertical drop test without requiring an organic solvent. Summary of the Invention

[0009] This invention provides a solution to the challenge of obtaining thermal interface materials (TIMs) that offer low thermal resistance (less than 0.1 °C * cm). 2 The TIM is fully 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 kPa (40 psi) according to ASTM D-5470, and simultaneously possesses a distributable viscosity of 120 Pa*s or less (when tested according to ASTM D4440-15 using a RES-G2 rotational rheometer from TA Instruments equipped with a 25 mm parallel plate, at a strain of 0.01% to 300% and a frequency of 10 radians / second), and is tested by vertical drop testing, as described below. Desiredly, this TIM possesses all these properties 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 higher, preferably 6.5 W / m*K or higher, as determined by the thermal conductivity testing method described below.

[0010] This invention results in the discovery of polysiloxane-based compositions comprising a specific blend of linear polysiloxanes (di-SiH polysiloxanes) having two terminally positioned silyl hydride functional groups (SiH:Vi ratio) and two end-positioned silyl hydride functional groups (poly-SiH polysiloxanes). These polysiloxane-based compositions achieve a TIM (transformed intracellular matrix) that is sufficiently crosslinked to prevent dripping, but not so extensively crosslinked to prevent compression to a BLT (bulk depth) of 30 micrometers or less, and achieves a thickness of less than 0.1 °C / cm². 2 Thermal resistance / 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 di-SiH polysiloxanes to SiH functional groups from poly-SiH polysiloxanes is 13 or greater and 70 or less, TIM formulations can be compressed to a BLT of less than 30 micrometers, even when crosslinked. If the SiH / Vi ratio is greater than 1.0 and / or the ratio of di-SiH polysiloxane SiH functional groups to poly-SiH polysiloxane functional groups is less than 13, the cured TIM tends to become too crosslinked to be compressible to a BLT of less than 30 micrometers. When the SiH / Vi ratio is less than 0.4, and / or when the ratio of di-SiH polysiloxane functional groups to poly-SiH polysiloxane functional groups is greater than 70, pumping out may occur due to unreacted polymers.

[0011] The inventors have also surprisingly discovered that, in addition to the aforementioned properties, the compositions of the present invention can achieve a thermal conductivity of 6.0 W / m*K or higher when the composition contains a thermally conductive filler composition of boron nitride at a weight relative to the composition weight of the composition.

[0012] In a first aspect, the present invention is a composition comprising: (a) a divinyl polydimethylsiloxane having a viscosity of 30 mPa·s to 200 mPa·s; (b) a chain extender being a linear polysiloxane having two terminal silyl hydride functional groups, one terminal silyl hydride functional group at each end of the molecule; (c) a crosslinking agent being a polysiloxane having more than two silyl hydride functional groups; (d) 80 vol% or more of a thermally conductive filler; and (e) a treatment agent composition comprising an alkyltrialkoxysilane and having a viscosity of 20 to 120%. (f) a monotrialkoxysiloxy-terminated and trimethylsiloxy-terminated dimethylpolysiloxane with a degree of polymerization; (g) a platinum hydrosilylation catalyst; and (g) up to 0.2% by weight of a hydrosilylation inhibitor; wherein the weight percentage is relative to the weight of the thermal interface material composition, the volume percentage is relative to the volume of the thermal interface material composition, the molar ratio of silane hydride groups to vinyl groups in the thermal interface material composition is 0.4 or greater and simultaneously 1.0 or less, and the molar ratio of silane hydride functional groups from the chain extender to silane hydride functional groups from the crosslinking agent is 13 or greater and simultaneously 70 or less.

[0013] In a second aspect, the present invention is a method of applying the composition of the first aspect to a substrate, the method comprising dispensing the composition of the first aspect onto the substrate.

[0014] In a third aspect, the present invention is an article comprising a composition of the first aspect in a cured form in contact with a substrate. Detailed Implementation

[0015] When a date is not indicated by a test method number, the test method refers to the most recent test method as of the priority date of this document. References to test methods include references to both the testing association and the test method number. The following test method abbreviations and designations apply to this document: ASTM refers to ASTM International Society Methods; EN refers to European Standards; DIN refers to the German Institute for Standardization; ISO refers to the International Organization for Standardization; and UL refers to Underwriters Laboratories.

[0016] Products identified by their trade names refer to compositions available under those trade names as of the priority date of this document.

[0017] "Multiple" means two or more. "And / or" means "and, or as an alternative." Unless otherwise specified, all ranges include end values. Unless otherwise specified, all weight percentage (wt%) values ​​are relative to the weight of the composition, and all volume percentage (volume%) values ​​are relative to the volume of the composition.

[0018] Unless otherwise stated, “viscosity” means: (a) for TIM compositions, including the dynamic viscosity used to measure distributable viscosity, as measured according to ASTM D4440-15 using a RES-G2 rotational rheometer equipped with a 25 mm parallel plate from TA Instruments, with strains from 0.01% to 300% and a frequency of 10 radians / second; and (b) for individual polysiloxanes: the viscosity determined by ASTM D 445 using a glass capillary Cannon-Fenske type viscometer at 25 degrees Celsius (°C).

[0019] Unless otherwise stated, all characterizations of the thermal interface material composition in its uncured state are determined.

[0020] Polysiloxanes comprise multiple siloxane units. These siloxane units are selected from M-type, D-type, T-type, and Q-type siloxane units. The siloxane units have the following chemical composition:

[0021] M-type siloxane unit = (A3SiO) 1 / 2 )

[0022] D-type siloxane unit = (A2SiO) 2 / 2 )

[0023] T-type siloxane unit = (ASiO) 3 / 2 )

[0024] Q-type siloxane unit = (SiO) 4 / 2 )

[0025] Wherein: A can be hydrogen, a hydrocarbon group or a substituted hydrocarbon group, or any other group such as hydroxyl, alkoxy, or halogen; and where oxygen represents oxygen shared with other siloxane units, thus half of each oxygen atom is associated with the stated siloxane unit. For example, "O 1 / 2 "Corresponds to an oxygen shared with another siloxane unit, and "O 3 / 2 "Corresponding to the three oxygen atoms shared with other siloxane units. The average number of siloxane units in a molecule is usually determined in the chemical structure by the subscript associated with the siloxane unit. Through..." 1 H, 13 C and 29 Si nuclear magnetic resonance (NME) spectroscopy is used to determine the composition of polysiloxanes. It is noteworthy that the siloxane units within the polysiloxane can be random, block, partially random, and partially block, unless otherwise stated herein.

[0026] This invention relates to thermal interface material (TIM) compositions. Specifically, compositions suitable for use as TIMs. The TIM compositions are curable, meaning they can be cured by undergoing a crosslinking reaction. This curing is carried out via a hydrosilylation chemistry between vinyl groups and silane hydride (SiH) groups. In this respect, the TIM compositions comprise vinyl-functionalized polysiloxanes and silane hydride-functionalized polysiloxanes. Desiredly, no single polysiloxane possesses both vinyl and silane hydride functional groups.

[0027] The TIM composition comprises divinyl polydimethylsiloxane (PDMS). The divinyl PDMS has a viscosity of 30 mPa*s or higher, preferably 45 mPa*s or higher, 60 mPa*s or higher, and may have viscosities of 90 mPa*s or higher, 100 mPa*s or higher, 120 mPa*s or higher, 140 mPa*s or higher, 160 mPa*s or higher, or even 180 mPa*s or higher, while having viscosities of 200 mPa*s or lower, 180 mPa*s or lower, or even 160 mPa*s or lower, 140 mPa*s or lower, 120 mPa*s or lower, 100 mPa*s or lower, 80 mPa*s or lower, or even 60 mPa*s or lower. If the viscosity is too high, the TIM composition will be too high to contain 80% by volume or more of thermally conductive filler. If the viscosity is too low, the TIM viscosity may be too low, resulting in poor mechanical properties and potential pulverization.

[0028] Desiredly, divinyl PDMS has terminal vinyl groups and the following general chemical structure (I):

[0029] Vi(CH3)2SiO-[(CH3)2SiO] n -Si(CH3)2Vi(I)

[0030] Wherein, "Vi" refers to the vinyl group (-CH=CH2), and n refers to the average number of dimethylsiloxane units, which is the degree of polymerization (DP) of PDMS. n is chosen to achieve the desired viscosity of the divinyl PDMS. Typically, n is a value of 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 it 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.

[0031] The concentration of divinylPDMS in the TIM composition is desirablely 2% by weight (wt%) or greater, and can be 3% by weight or greater, even 4% by weight or greater, while typically 10% by weight or less, and can be 8% by weight or less, 6% by weight or less, or even 4% by weight or less, where wt% is based on the weight of the TIM composition. Excessive divinylPDMS reduces the amount of thermally conductive filler that can be included due to its high viscosity. Insufficient divinylPDMS results in the TIM composition requiring so much filler that the composition loses its dispensability.

[0032] Suitable divinyl PDMS materials can be prepared by ring-opening polymerization of cyclosiloxanes with vinyl end-capping agents for end-capping, as taught in US 5883215A.

[0033] The TIM composition comprises a chain extender, which is a linear polysiloxane having two terminal silane hydride functional groups, one terminal silane hydride functional group at each end of the molecule. The linear polysiloxane primarily comprises M-type and D-type siloxane units, but may include T-type and / or Q-type siloxane units, at a combined concentration of up to 5 mol%, preferably up to 4 mol%, up to 3 mol%, up to 2 mol%, up to 1 mol%, and most preferably free of T- and Q-type siloxane units, wherein the mol% of T- and Q-type siloxane units is relative to the total number of siloxane units in the linear polysiloxane. The linear polysiloxane chain extender has terminal M groups, each comprising a SiH functional group.

[0034] Chain extenders ideally have a viscosity of 5 mPa*s or higher, and can have viscosities of 7 mPa*s or higher, 10 mPa*s or higher, 20 mPa*s or higher, or even 30 mPa*s or higher, while typically having a viscosity of 100 mPa*s or lower, and can have viscosities of 75 mPa*s or lower, 50 mPa*s or lower, 25 mPa*s or lower, 20 mPa*s or lower, 15 mPa*s or lower, or even 10 mPa*s or lower. If the viscosity is too high, the TIM composition will be too high to contain 80% by volume or more of thermally conductive filler. If the viscosity is too low, the TIM viscosity may be too low, resulting in poor mechanical properties and potential pulverization.

[0035] Desiredly, the chain extender is PDMS (silicon-hydride-terminated PDMS) with SiH functional groups at each end. Such PDMS can have the following general chemical structure (II):

[0036] H(CH3)2SiO-[(CH3)2SiO] m-Si(CH3)2H(II)

[0037] Choose a value for the subscript m to achieve the desired viscosity, such as the viscosity taught above for chain extenders. Desirably, the 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 it is an average of 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, or even 15 or less. An example of a suitable chain extender is PDMS with a viscosity of 7 mPa*s to 10 mPa*s and containing 1.25 wt% vinyl hydride-terminated (available commercially from Alfa Chemistry as ACM83817714 and from Gelest as DMS-V21).

[0038] Based on the weight of the TIM composition, 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, while typically it is 2.0 wt% or less, 1.75 wt% or less, 1.5 wt% or less, and can be 1.25 wt% or less, or even 1.0 wt% or less. This concentration range is optimal for achieving the desired SiH / Vi ratio and the molar ratio of silane-based hydride functional groups from the chain extender to the silane-based hydride functional groups from the crosslinking agent, which is necessary to achieve the crosslinking density and final hardness of the TIM composition.

[0039] Suitable chain extenders include hydride-terminated PDMS, which can be commercially available from Gellért.

[0040] The TIM composition comprises a crosslinking agent, which is a polysiloxane having more than two silane hydride functional groups, preferably three or more. Desiredly, the crosslinking agent has a viscosity of 10 mPa*s or higher, 12 mPa*s or higher, 14 mPa*s or higher, 15 mPa*s or higher, 16 mPa*s or higher, 18 mPa*s or higher, or even 19 mPa*s or higher, while typically 30 mPa*s or lower, 25 mPa*s or lower, 20 mPa*s or lower, or even 19 mPa*s or lower. These viscosity ranges are desirable for achieving appropriate TIM composition viscosities at specified component concentrations.

[0041] Desiredly, the crosslinking agent is a linear polysiloxane. Desiredly, the crosslinking agent is a linear polysiloxane with both ends capped with trimethyl groups. The crosslinking agent may have an average chemical structure (III):

[0042] (CH3)3SiO-[(CH3)HSiO] y-[(CH3)2SiO] x -Si(CH3)3(III)

[0043] Wherein A is as previously described for the siloxane unit, but preferably selected from methyl and phenyl in each occurrence, and most preferably methyl in each occurrence; and wherein 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 the desired viscosity of the entire crosslinking agent.

[0044] The crosslinking agent can be present at concentrations of 0.005 wt% or greater, 0.01 wt% or greater, 0.02 wt% or greater, 0.03 wt% or greater, or even 0.04 wt% or greater relative to the weight of the TIM composition, while typically present at concentrations 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. This concentration range is optimal for achieving the desired SiH / Vi ratio and the molar ratio of silane-based hydride functional groups from the chain extender to the silane-based hydride functional groups from the crosslinking agent, which is necessary to achieve the crosslinking density and final hardness of the TIM composition.

[0045] Suitable crosslinking agents include materials commercially available from Gallest under the names DMS-071 and DMS-301, and those under the name DOWSIL. TM 6-3570 Materials purchased from Dow, Inc. (DOWSIL is a trademark of The Dow Chemical Company).

[0046] The TIM composition has a molar ratio of silane hydride to vinyl groups that is 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, and can be 0.9 or greater, while being 1.0 or less, and can be 0.9 or less, or even 0.8 or less. If the molar ratio exceeds 1.0, there is a possibility that the composition is too stiff to be compressed to a bond line thickness of 30 micrometers or less. If the molar ratio is less than 0.1, there is a risk of failure in vertical drop tests due to insufficient crosslinking.

[0047] The TIM composition has a molar ratio of silane-based hydride functional groups solely from the chain extender to silane-based hydride functional groups from the crosslinking agent, wherein the molar ratio is 13 or greater, 15 or greater, 16 or greater, 18 or greater, 20 or greater, 22 or greater, 24 or greater, 26 or greater, 28 or greater, 30 or greater, 35 or greater, 40 or greater, 45 or greater, or even 50 or greater, 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 become too stiff to be compressed to a bond line thickness of 30 micrometers or less. If the molar ratio is less than 13, there is a risk of failure in the vertical drop test.

[0048] The TIM composition contains 80 vol% or more and typically 98 vol% or less, preferably 95 vol% or less, and may 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 thermally conductive filler.

[0049] The thermally conductive filler can be any one or any combination of more than one thermally conductive filler known for use in TIM compositions, for example, any one or a combination of more than one selected from aluminum, silver, copper, aluminum nitride, alumina, zinc oxide, aluminum nitride, boron nitride, silver-coated aluminum, carbon fiber, and graphite. Desiredly, the thermally conductive filler is any one or a combination of more than one selected from the group consisting of zinc oxide, aluminum, and boron nitride.

[0050] Ideally, the thermally conductive filler is a combination of at least two or three different sizes of fillers selected from the following: small (D50 less than 1 micrometer), medium (D50 between 1 micrometer and 5 micrometers), and large (D50 greater than 5 micrometers, preferably 8 micrometers or larger, and less than 200 micrometers). The D50 of the thermally conductive filler is determined using a laser diffraction particle size analyzer (e.g., a CILAA920 particle size analyzer or a Beckman Coulter LS 13 320SW) operated with software based on values ​​reported in number-average particle size.

[0051] An attractive thermally conductive filler comprises zinc oxide filler having a D50 of less than 1 micrometer, aluminum filler having a D50 between 1 and 20 micrometers, and optionally at least one type of boron nitride flakes having a particle size of 8 to 30 micrometers. Surprisingly, it has been found that the thermal conductivity of the TIM composition is particularly high, even greater than 6.0 W / m Kelvin (W / m*K), when the boron nitride flakes are present at 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, while simultaneously present at a concentration of 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. A particularly desirable combination of thermally conductive fillers resulting in a thermal conductivity of 6.5 W / m*K comprises 44 wt% to 48.6 wt% of aluminum filler with a D50 of 9 micrometers, 25 wt% to 26 wt% of aluminum filler with a D50 of 2 micrometers, 17 wt% to 18 wt% of zinc oxide with a D50 of 0.2 micrometers, 3 wt% to 4 wt% of boron nitride flakes with an average size of 30 micrometers, and up to 1.6 wt% or even up to 2.0 wt% of boron nitride flakes with an average size of 8 micrometers, wherein wt% is relative to the weight of the TIM composition.

[0052] The TIM composition comprises a treatment agent composition. The treatment agent composition comprises an alkyltrialkoxysilane and a monotrialkoxysiloxy-terminated and trimethylsiloxy-terminated dimethylpolysiloxane. The alkyltrialkoxysilane is preferably a 6- to 12-carbon (C6-C12) alkyltrimethoxysilane, preferably a C8-C12 alkyltrimethoxysilane, and may be n-decyltrimethethoxysilane. Suitable alkyltrialkoxysilanes include n-decyltrimethoxysilane, which may DOWSIL TM Z-6210 silane (DOWSIL is a trademark of Dow Chemical Company) was purchased from Dow Company.

[0053] Dimethyl polysiloxanes with monotrialkoxysiloxy and trimethylsiloxy end-capsulation are desirable to 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 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 offer greater stability compared to shorter chains. However, it is desirable to keep the degree of polymerization below 150 because shorter chain lengths are more effective at reducing viscosity than longer chain lengths.

[0054] Examples of suitable monotrialkoxysiloxy-terminated and trimethylsiloxy-terminated dimethylpolysiloxanes have the chemical structure (IV):

[0055] (CH3)3SiO-[(CH3)2SiO] a -Si(OCH3)3 (IV)

[0056] The subscript 'a' has a value equal to the degree of polymerization described above for monotrialkoxysiloxy-terminated dimethylpolysiloxanes.

[0057] Suitable monotrialkoxysiloxy-terminated and trimethylsiloxy-terminated dimethylpolysiloxanes can be synthesized according to the teachings in US2006 / 0100336.

[0058] Desiredly, alkyltrialkoxysilanes are typically present at concentrations of 1.8 wt% or greater, 2.0 wt% or greater, 2.5 wt% or greater, 3.0 wt% or greater, or even 3.5 wt% or greater, while also typically present at concentrations of 4.0 wt% or less, 3.5 wt% or less, or even 3.0 wt% or less, where wt% is relative to the weight of the TIM composition.

[0059] Desiredly, the monotrikoxysiloxy-terminated and trimethylsiloxy-terminated dimethylpolysiloxane is present at a concentration of 0.05 wt% or greater, 0.1 wt% or greater, 0.2 wt% or greater, 0.3 wt% or greater, or even 0.4 wt% or greater, relative to the weight of the TIM composition, while typically present at a concentration of 0.5 wt% or less, 0.4 wt% or less, 0.3 wt% or less, or 0.2 wt% or less.

[0060] The TIM composition contains a platinum hydrosilylation catalyst. The platinum hydrosilylation catalyst includes Speier's catalyst (H₂PtCl₆) and Karstedt's catalyst (platinum(O)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex). The catalyst may be encapsulated or unencapsulated. Encapsulated catalysts are typically encapsulated in a phenyl resin.

[0061] The platinum hydrosilylation catalyst is typically present at a concentration of 0.1 wt% or greater, 0.2 wt% or greater, and may be 0.3 wt% or greater, while it is typically present at a concentration of 0.5 wt% or less, 0.4 wt% or less, or even 0.3 wt% or less, relative to the weight of the TIM composition.

[0062] The TIM composition may contain a concentration of up to 0.2 wt% of a hydrosilylation inhibitor by weight of the TIM composition. The hydrosilylation inhibitor may be, for example, methyl(tris(1,1-dimethyl-2-propynoxy))silane. Desiredly, the inhibitor is present and delivered in vinyldimethyl-terminated PDMS.

[0063] To be expected, the TIM composition is free of organic solvents, and even more to be expected, free of any solvents.

[0064] The TIM compositions of the present invention are particularly useful in methods of dispensing TIM compositions onto substrates. Specifically, the TIM compositions of the present invention can be printed onto a substrate in a specific pattern by a method comprising dispensing the TIM composition onto the substrate by printing the TIM composition onto the substrate. Even more advantageous is the fact that once dispensed onto the substrate, a second substrate can be applied onto and pressed against the TIM composition to form a TIM composition having an adhesive line thickness of 30 micrometers or less between the two substrates.

[0065] The present invention also includes an article comprising a TIM composition dispensed onto a substrate, preferably a TIM composition located between two substrates.

[0066] Example

[0067] Materials. Table 1 lists the materials used in the sample preparation.

[0068] Table 1

[0069]

[0070]

[0071]

[0072] DOWSIL is a trademark of Dow Chemical Company.

[0073] Polartherm is a trademark of Momentive Advanced Materials Group.

[0074] Characterization methods. The samples were characterized according to the following methods.

[0075] Distributable viscosity. Distributable viscosity is a measure of how easily a TIM formulation can be applied to a substrate via printing. If the viscosity is too high, it is difficult to print the TIM formulation accurately and precisely. This invention achieves a distributable viscosity of 120 Pa*s or lower. Distributable viscosity was determined using an ARES-G2 rheometer equipped with a 25 mm parallel plate from a TA instrument, using the dynamic viscosity test method of ASTM D4440-15. Test conditions were based on strain scans at 25°C, strains from 0.1% to approximately 300%, and a frequency of 10 radians / second.

[0076] Bond line thickness and thermal resistance. The bond line thickness (BLT) and thermal resistance of the TIM formulation were determined using a LongWin Model LW 9389 TIM thermal interface material tester according to ASTM D-5470. The pressure applied to the TIM material samples was 275.9 kN / m² (40 psi). The test time for each sample was 15 minutes, and the temperature was 80°C.

[0077] Vertical Drop Test. Apply 0.2 g of TIM formulation to an aluminum plate. Place two 0.2 mm plastic gaskets on either side of the sample, and place a 1 mm thick sliding cover glass on top of the TIM formulation, pressing it against the formulation to create a 0.2 mm thick film of TIM formulation between the sliding cover glass and the aluminum plate. Clamp the cover glass and aluminum plate together to hold them in place, and position the assembly vertically in a temperature cycling chamber (ESPEC Corp. PSL-2J). Cycle the temperature between -40°C and 125°C, with a 15-minute drop between each temperature limit and a 15-minute hold time at each temperature limit. Evaluate the sample after 500 cycles. If there is no evidence that the TIM formulation expands or slides between the sliding cover glass and the aluminum plate, and little or no void formation or pumping out of the TIM formulation is observed, the TIM formulation “passes” the vertical drop test.

[0078] Thermal conductivity. Tested according to ISO 22007-2:2015, using Hot Disk AB from Gothenburg, Sweden. The thermal conductivity of TIM formulations was measured using a Hot Disk Instrument TPS 2500S (Sweden). A C5501 sensor was used, with heating times ranging from 2 to 5 seconds and a power output of 500 milliwatts. Two cups were filled with TIM formulation, and a flat sensor was placed inside. Fine-tuning analysis with temperature drift compensation and time correction was performed using a setting selected between point 50 and point 150.

[0079] Sample TIM formulation

[0080] Formulation Preparation. The sample formulation was prepared by combining the components in a 100 mL speed mixer cup. Treatment agents, silicone oil including vinyl PDMS, chain extenders, and crosslinking agents were added to the 100 mL speed mixer cup. Small and medium-sized thermally conductive fillers were then added and mixed for 20 seconds at 100 rpm using a FlackTek speed mixer. Larger thermally conductive fillers were added in two portions, mixing for 20 seconds at 1000 RPM and 20 seconds at 1500 RPM after each addition. If applicable, BN filler was added and mixed for 20 seconds at 1000 RPM, and then for 20 seconds at 1500 RPM to obtain a flowable metal-polysiloxane mixture. The catalyst was added twice and mixed for 20 seconds at 800 RPM. Viscosity, thermal conductivity, and vertical drop test performance were determined. The formulation was cured in an oven at 100°C for one hour before testing the bond line thickness and thermal resistance.

[0081] All sample formulations are free of organic solvents.

[0082] The range of SiH / Vi ratios and the molar ratio of SiH functional groups from the chain extender to those from the crosslinking agent is exceeded. Samples 1 through 7 exhibit TIM formulations with a SiH / Vi ratio greater than 1.0 or a molar ratio of SiH functional groups from the chain extender to those from the crosslinking agent less than 13. The results indicate that in any of these cases, the formulations cannot be compressed to a BLT of 30 micrometers or less. Notably, all of these formulations exhibit a distributable viscosity of 120 Pa*s or less.

[0083] It is noteworthy that Sample 7 has a SiH / Vi ratio of 1.0 and a BLT of 320 micrometers. While this particular sample demonstrates formulations that cannot achieve a BLT of 30 micrometers or smaller, it is close to 30 micrometers compared to Samples 1 through 6. Sample 23 (see Table 3) shows that a BLT of 30 micrometers or smaller can be achieved when the SiH / Vi ratio is 1.0, provided the SiH CE / SiH crosslinker ratio is increased sufficiently.

[0084] Table 2 shows the formulations of samples 1 through 7 and the characterization of those samples. The formulations are defined by the gram-based composition used to prepare them.

[0085] Table 2

[0086]

[0087] *NM = Not measured

[0088] **Failure due to void formation and pumping out of TIM formulation.

[0089] Within the range of SiH / Vi ratios and the molar ratio of SiH chain extender functional groups to SiH crosslinker functional groups, samples 8 to 23 exhibit TIM formulations with a SiH / Vi ratio of 1.0 or less and a molar ratio of chain extender SiH to crosslinker SiH functional groups of 13 or greater. The results indicate that when these ratios are met, the formulations can form BLTs smaller than 30 micrometers and achieve a temperature gradient of less than 0.1 °C*cm. 2 The samples exhibited a thermal resistance of 120 Pa*s or lower and passed the vertical drop test. Furthermore, the samples including the boron nitride thermally conductive filler had exceptionally high thermal conductivity values ​​exceeding 6.0 W / m*K. Notably, all these formulations possessed a distributable viscosity of 120 Pa*s or lower.

[0090] Table 3 presents the formulations of samples 8 through 23 and the characterization of those samples. The formulations are defined by the gram amounts of components used to prepare them. Note: “TA” = treatment agent. “TCF” = TC filler. “CE” = chain extender. “TC” = thermal conductivity. “TI” = thermal resistance.

[0091] “VDP” = Vertical Drop Test

[0092]

[0093]

Claims

1. A thermal interface material composition comprising: a. divinyl polydimethylsiloxane having a viscosity of 30 millipascal seconds to 200 millipascal seconds, determined by ASTM D 445 using a glass capillary viscometer at 25 °C; b. a chain extender, the chain extender being a linear polysiloxane having two terminal silicon hydride functional groups, one at each end of the molecule; c. a crosslinker, the crosslinker being a polysiloxane having more than two silicon hydride functional groups; d. 80 volume percent or more of a thermally conductive filler; e. a treatment agent composition comprising 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; and wherein the weight percent values are relative to the thermal interface material composition weight, the volume percent values are relative to the thermal interface material composition volume, the molar ratio of silicon hydride groups to vinyl groups in the thermal interface material composition is > 0.4 and < 1.0, and the molar ratio of silicon hydride functional groups from the chain extender to silicon hydride functional groups from the crosslinker is > 13 and < 70.

2. The thermal interface material composition of claim 1, wherein: a. the divinylpolydimethylsiloxane is present at 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; and c. the crosslinker is present at a concentration of 0.005 to 0.05 weight percent; e. the alkyltrialkoxysilane is present at a concentration of 1.8 to 4 weight percent and the mono trialkoxysiloxy terminated and trimethylsiloxy terminated dimethylpolysiloxane is present at a concentration of 0.05 to 0.5 weight percent; wherein the weight percent values are relative to the thermal interface material composition weight.

3. The thermal interface material composition of claim 1 or 2, wherein the thermally conductive filler comprises zinc oxide particles having an average size of less than 1 micron, aluminum filler having an average particle size of between 1 micron and 20 microns, and optionally boron nitride flake having a particle size of 8 to 30 microns.

4. The thermal interface material composition of claim 3, wherein the boron nitride flake is present at a concentration of 1 to 10 weight percent relative to the thermal interface material composition weight.

5. The thermal interface material composition of claim 3, wherein the thermally conductive filler comprises 44 to 48.6 wt% aluminum filler having a D50 of 9 microns, 25 to 26 wt% aluminum filler having a D50 of 2 microns, 17 to 18 wt% zinc oxide having a D50 of 0.2 microns, 3 to 4 wt% boron nitride flake having an average size of 30 microns, and up to 1.6 wt% or even up to 2.0 wt% boron nitride flake having an average size of 8 microns, wherein the wt% is relative to the thermal interface material composition weight.

6. The thermal interface material composition of claim 1, wherein the chain extender is a silicon hydride terminated polydimethylsiloxane.

7. The thermal interface material composition of claim 6, wherein the crosslinker has the following average chemical structure: (CH3)3SiO-[H(CH3)SiO] y -[(CH3)2SiO] x -Si(CH3)3, 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 millipascal seconds to 25 millipascal seconds, as determined by ASTM D 445 using a glass capillary viscometer at 25 °C.

8. The thermal interface material composition of claim 1, wherein the thermal interface material composition is free of organic solvents.

9. A method of dispensing a thermal interface material composition, the method comprising dispensing the thermal interface material composition of any one of claims 1-8 onto a substrate.

10. A thermal interface material article, the article comprising the thermal interface material composition of any one of claims 1 to 8 disposed on a substrate.

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