Non-curable thermally conductive viscous silicone material

Abstract

A non-curable thermal conductive material, comprising: (a) a matrix material, the matrix material comprising: (i) 90 wt% to 98 wt% of a non-functional non-crosslinked organosiloxane fluid having a dynamic viscosity of 50 centistokes to 350 centistokes; and (ii) 2 wt% to less than 10 wt% of a crosslinked hydrosilylation reaction product of an alkenyl-terminated polydiorganosiloxane having a degree of polymerization greater than 300 and an organohydrogensiloxane crosslinker having 2 or more SiH groups per molecule, wherein the molar ratio of SiH groups to alkenyl groups is 0.5 to 2.0; (b) greater than 80 wt% to less than 95 wt% of a thermal conductive filler dispersed throughout the matrix material; and (c) a treating agent, the treating agent being dispersed in the matrix material, the treating agent being selected from: alkyltrialkoxysilanes, wherein the alkyl contains 1 to 14 carbon atoms; and mono-trialkoxy-terminated diorganopolysiloxanes, the mono-trialkoxy-terminated diorganopolysiloxanes having a degree of polymerization of 20 to 110, and the alkoxy groups each containing 1 to 12 carbon atoms.

Description

Technical Field

[0001] The present invention relates to a thermal interface material (TIM), which is a non-curable thermally conductive viscous silicone material. Background Art

[0002] A thermal interface material (TIM) is a thermally conductive material that can be used to enhance the thermal coupling between two components in a device, such as an electronic device. Including a TIM, for example, between a heat source and a heat sink can improve the heat transfer efficiency from the heat source to the heat sink compared to contacting the heat source and the heat sink without a TIM between them.

[0003] The TIM can be a non-curable grease or a curable composition. Non-curable greases are easier to implement because these non-curable greases do not require special storage conditions and do not require curing after application. Generally, non-curable greases are applied to one component by methods such as stencil printing or screen printing, and then the other component is pressed against the thermal grease to thermally couple the two components through the TIM grease. Non-curable greases are convenient to apply, but remain flowable in the device and this can lead to undesirable pump-out, especially when the two components coupled by the TIM grease have different coefficients of thermal expansion, causing them to move to different extents during thermal cycling. When the components coupled by the TIM grease move repeatedly, for example, during a power cycle, and they move to different extents, the movable TIM grease can be extruded from between the two components, which is called pump-out. Additionally or alternatively, the matrix material can be preferentially extruded relative to the thermally conductive filler, resulting in phase separation. In either case, the thermal coupling of the TIM grease is undesirably reduced. Thus, TIM greases are typically used in applications where the heat source and the heat sink are thermally coupled indirectly, usually through some kind of enclosure (or "integrated heat sink") around the heat source. Then, the temperature difference can be alleviated to some extent, the encapsulation can be hardened, and the coefficients of thermal expansion can be more closely matched between the coupled components.

[0004] For bare die coupling - i.e., directly coupling a heat source to a heat sink without going through an enclosure intermediary - curable TIMs are desirable. A curable TIM is placed between two components to thermally couple them and then cured to reduce TIM mobility and generally enhance adhesion to the components. Once cured, the TIM is less likely to experience pump-out or phase separation compared to non-curable TIMs. However, curable TIMs require an additional step in device manufacturing - curing of the TIM. In addition, curable TIMs need to be handled carefully during storage prior to use to prevent premature curing. Thus, they are typically supplied in two-component systems that need to be mixed just prior to use. One-component curable systems require special storage conditions, such as storage in a freezer, to inhibit premature curing. Further, assembling thermally coupled parts using curable TIMs must be done immediately and completely in the same location because once the TIM is cured, further handling and mating with the TIM is not feasible, especially at a typical TIM bondline thickness of 0.2 mm to 0.3 mm. From a supply chain and manufacturing perspective, this inhibits flexibility. Non-curable TIM greases avoid all of these challenges.

[0005] There is a desire to identify TIMs that are non-curable greases for ease of storage and device manufacturing and that can also be applied to bare die applications without concern for pump-out or phase separation. Specifically, there is a desire to identify non-curable TIM greases that have a thermal conductivity greater than 1 watt per meter kelvin (W / m*K), preferably 2 W / m*K or higher, and even more preferably 5 W / m*K or higher, while having a viscosity less than 150 pascal seconds (Pa*s) to have desirable printability, while having excellent pump-out resistance as determined by forming less than 5% void space on the chip surface after 5000 thermal cycles in a pump-out resistance test (defined below). SUMMARY OF THE INVENTION

[0006] The present invention provides a TIM that is a non-curable grease for ease of device manufacturing and that can also be applied to bare die applications without concern for pump-out or phase separation. Specifically, the present invention provides a non-curable TIM grease that has a thermal conductivity greater than 1 watt per meter kelvin (W / m*K), preferably 2 W / m*K or higher, and even more preferably 5 W / m*K or higher, while having a viscosity less than 150 pascal seconds (Pa*s) to have desirable printability, while having excellent pump-out resistance as determined by forming less than 5% void space on the chip surface after 5000 thermal cycles in a pump-out resistance test (defined below).

[0007] The present invention is the result of discovering that an uncureable thermal grease having a mucous property can be prepared by dispersing a thermal conductive filler in a carrier matrix, the carrier matrix comprising from 2 weight percent (wt%) to less than 10 wt% of a crosslinked polysiloxane and greater than 90 wt% to 98 wt% of a different non-functional non-crosslinkable polysiloxane, where the wt% is based on the weight of the carrier matrix. When used as a TIM in a bare die application, a small amount of the crosslinked polysiloxane creates the mucous property and inhibits the matrix from suffering from pump-out or phase separation. The crosslinked component in the carrier matrix is sufficient to stabilize the composition against pump-out and support the dispersed thermal conductive filler, but surprisingly, it is not high enough to inhibit the composition from being stencil printed or printed onto a component. Further, the resulting composition is stable against curing and does not require special storage or handling, nor does it require curing after being applied to a component.

[0008] In a first aspect, the present invention is an uncureable thermal conductive material comprising: (a) a matrix material comprising: (i) greater than 90 weight percent and at the same time 98 weight percent or less of a non-functional non-crosslinkable organosiloxane fluid, based on the weight of the matrix material, the non-functional non-crosslinkable organosiloxane fluid having a kinematic viscosity in the range of 50 centistokes to 350 centistokes; and (ii) from 2 weight percent to less than 10 weight percent of a crosslinked hydrosilylation reaction product of an alkenyl-terminated polydiorganosiloxane having a degree of polymerization greater than 300 and a hydrosiloxane crosslinker comprising on average 2 or more SiH groups per molecule, where the ratio of the alkenyl-terminated polydiorganosiloxane and the hydrosiloxane is such that the molar ratio of SiH groups to alkenyl groups is in the range of 0.5 to 2.0; (b) greater than 80 weight percent and at the same time less than 95 wt% of a thermal conductive filler, based on the weight of the uncureable thermal conductive material, the thermal conductive filler being dispersed throughout the matrix material; and (c) treating agents dispersed in the matrix material, the treating agents selected from: alkyltrialkoxysilanes, where the alkyl contains from 1 to 14 carbon atoms; and mono-trialkoxy-terminated diorganopolysiloxanes, the mono-trialkoxy-terminated diorganopolysiloxanes having a degree of polymerization in the range of 20 to 110, and the alkoxy groups each containing from 1 to 12 carbon atoms.

[0009] In a second aspect, the present invention is a method comprising applying the uncureable thermal conductive material of the first aspect to an object such as a bare die or a heat sink.

[0010] In a third aspect, the present invention is an article comprising the uncureable thermal conductive material of the first aspect in thermal contact with at least two objects such as a bare die and a heat sink.

[0011] The non-curable thermal conductive material of the present invention can be used as a non-curable TIM grease in electronic applications, especially for directly thermally coupling a bare chip to a heat sink. Detailed Description

[0012] When a test method is not identified by a test method number, the test method refers to the latest test method as of the priority date of this document. References to test methods include references to both the test society and the test method number. The following test method abbreviations and designations apply herein: ASTM refers to the ASTM International Society method; EN refers to the European standard; DIN refers to the German Institute for Standardization; ISO refers to the International Organization for Standardization; and UL refers to Underwriters Laboratories, Inc.

[0013] A product identified by a trade name of the product refers to a composition that was available under those trade names as of the priority date of this document.

[0014] "Plurality" means two or more. "And / or" means "and, or as an alternative". Unless otherwise specified, all ranges include the end values. Unless otherwise indicated, all weight percentage (wt%) values are based on the weight of the composition, and all volume percentage (vol%) values are based on the volume of the composition.

[0015] "Bare chip" refers to an exposed integrated circuit on silicon without an integrated heat sink.

[0016] Unless otherwise indicated, the "kinematic viscosity" of a silicone is determined by ASTM D 445 using a glass capillary Cannon-Fenske type viscometer at 25 degrees Celsius (°C).

[0017] "Viscosity at swelling" refers to the viscosity of the material at the swelling strain (swelling point), which is measured in the form of dynamic viscosity using ASTM D4440-15 and a TA Instruments ARES-G2 device equipped with 25 mm parallel plates (serrated steel). The test conditions are based on a strain sweep at 25 degrees Celsius (°C), where the strain is 0.01% - 300% and the frequency is 10 radians per second. The dynamic viscosity at the swelling strain (swelling point) is recorded as the viscosity at swelling.

[0018] By standard 1 H, 13 C and 29 Si nuclear magnetic resonance (NMR) analysis is used to determine the chemical structure of the silicone. The average particle size of the filler particles is determined as the median particle size (D50) according to the operating software using a laser diffraction particle size analyzer (CILAS 920 particle size analyzer or Beckman Coulter LS 13 320SW).

[0019] In one aspect, the present invention is a non-curable thermally conductive material that comprises a matrix material, a thermally conductive filler, and a treating agent.

[0020] "Non-curable" means that the matrix material of the composition does not contain a combination of functional groups necessary for chemical crosslinking by hydrosilylation or condensation, and preferably the composition does not contain functional groups that crosslink by any chemical reaction induced by heat or chemistry. In this regard, the matrix material desirably does not contain a combination of alkenyl and silyl hydride (SiH) functional groups, nor does it contain alkoxy functional groups. Desirably, the matrix material of the organosiloxane material only contains alkyl and / or aryl groups at its ends and attached to its sides.

[0021] "Thermally conductive" means that the non-curable thermally conductive material has a thermal conductivity greater than 1 watt per meter kelvin (W / m*K), preferably 2 W / m*K or higher, and even more preferably 5 W / m*K or higher. The thermal conductivity of the non-curable thermally conductive material is determined as described in the Examples section below.

[0022] The matrix material includes and may consist of a non-functional non-crosslinked organosiloxane fluid ("carrier fluid") and a crosslinked hydrosilylation reaction product.

[0023] The non-functional non-crosslinked organosiloxane fluid ("carrier fluid") is a fluid, which means it has a kinematic viscosity of 50 centistokes (cSt) or greater, 75 cSt or greater, 100 cSt, 125 cSt or greater, 150 cSt or greater, 175 cSt or greater, 200 cSt or greater, 250 cSt or greater, or even 300 cSt or greater, while desirably having a kinematic viscosity of 350 cSt or less, 300 cSt or less, 250 cSt or less, 200 cSt or less, 150 cSt or less, or even 100 cSt or less. "Non-functional" means that the organosiloxane fluid does not contain alkenyl groups, silyl hydride groups, silanol groups, and alkoxy groups. Desirably, the carrier fluid is a fluidic polyorganosiloxane that only has alkyl and / or aryl end and attached groups. "Non-crosslinked" means that the organosiloxane fluid does not contain multiple chemical bonds connecting any two polymer chains.

[0024] The carrier fluid is desirably a linear organopolysiloxane. The linear organopolysiloxane mainly, preferably completely, contains R3SiO 1 / 2 siloxane units and R2SiO 1 / 2Siloxane units, where each R is independently selected from alkyl groups and / or aryl groups. Relative to all the siloxane units in the linear organopolysiloxane, the linear organopolysiloxane can contain up to 3 mole percent (mol%), preferably 2 mol% or less, 1 mol% or less and can be free of RSiO 3 / 2 and SiO 4 / 2 siloxane units. The carrier fluid can be polydimethylsiloxane (PDMS) or preferably PDMS where the methyl groups on some of the R2SiO 1 / 2 siloxane units are replaced by phenyl groups (thereby forming a phenylmethylsiloxane-dimethylsiloxane copolymer). The phenylmethylsiloxane-dimethylsiloxane copolymer can contain, relative to all the siloxane units in the copolymer, 5 mol% or more, 7 mol% or more, even 9 mol% or more, and at the same time generally contains 15 mol% or less, 14 mol% or less, 13 mol% or less, even 12 mol% of phenylmethylsiloxane units.

[0025] An example of a suitable carrier fluid is a phenylmethylsiloxane-dimethylsiloxane copolymer available as PMM-1021 from Gelest, which has a kinematic viscosity of 100 centistokes and contains 9 mol% - 12 mol% phenylmethylsiloxane units.

[0026] The carrier fluid constitutes the majority of the matrix material and is present at a concentration greater than 90 weight percent (wt%), or greater, 91 wt% or greater, 92 wt% or greater, 94 wt% or greater, even 96 wt% or greater, while 98 wt% or less, even 96 wt% or less or 94 wt% or less of the weight of the matrix material.

[0027] The crosslinked hydrosilylation reaction product is the crosslinked hydrosilylation reaction product of an alkenyl-terminated polydiorganosiloxane and an organohydrogensiloxane crosslinker.

[0028] The alkenyl-terminated polydiorganosiloxane (PDOS) can be a single PDOS with an alkenyl termination, or it can be an extended polymer of multiple PDOS chains with alkenyl terminations. Thus, the alkenyl-terminated PD PDOS MS has the following general chemical structure (I):

[0029] ViR2SiO-[R2SiO] x -{R’-[R2SiO] y -R2Si-R’-[R2SiO] z -} α -SiR2Vi (I)

[0030] The components in “{}” are produced by hydrosilylation chain extension to connect multiple PDOS chains. The chain extension occurs through a hydrosilylation reaction between a PDOS with vinyl end groups and a PDOS with silyl hydride end groups. If the vinyl-capped PDOS is an unextended single PDOS chain, the subscript α is 0.

[0031] In chemical structure (I):

[0032] Vi is a vinyl group;

[0033] R, each occurrence being independent, is independently selected from alkyl groups and aryl groups, preferably alkyl groups and aryl groups having 1 to 8 carbon atoms, and most preferably being methyl each occurrence;

[0034] R’ is a divalent alkylene group having 2 or more, and can have 3 or more, 4 or more, even 6 or more carbon atoms, and generally having 10 or fewer, 8 or fewer, 6 or fewer, even 4 or fewer carbon atoms;

[0035] The subscript α desirably has an average value of 0, but can have a value of 0 or greater, and can be 1 or greater, even 2 or greater, and at the same time generally being 10 or smaller, 9 or smaller, 8 or smaller, 7 or smaller, 6 or smaller, 5 or smaller, 4 or smaller, 3 or smaller, and can be 2 or smaller, even 1 or smaller;

[0036] The subscripts x, y, and z each independently have a value of 10 or higher, 20 or m higher or 30 or higher, 40 or higher, 50 or higher, 75 or higher, 100 or higher, 150 or higher, 200 or higher, 250 or higher, 300 or higher, 350 or higher, 400 or higher, 450 or higher, 500 or higher, 550 or higher, 600 or higher, 650 or higher, 700 or higher, 750 or higher, 800 or higher, even 850 or higher, while desirably being 900 or smaller, 850 or smaller, 800 or smaller, 750 or smaller, 700 or smaller, 650 or smaller, 600 or smaller, 550 or smaller, 500 or smaller, even 450 or smaller; where the value of (x + y + z) corresponds to the degree of polymerization (DP) of the vinyl-terminated PDMS and has a value of 300 or higher, preferably 350 or higher, 400 or higher, 450 or higher, 500 or higher, 550 or higher, 600 or higher, 650 or higher, 700 or higher, 750 or higher, 800 or higher, even 850 or higher, while desirably being 900 or smaller, 850 or smaller, 800 or smaller, 750 or smaller, 700 or smaller, 650 or smaller, 600 or smaller, 550 or smaller, 500 or smaller, even 450 or smaller.

[0037] The organohydrogensiloxane crosslinker contains an average of 2 or more SiH groups per molecule. The organohydrogensiloxane crosslinker can have the chemical structure (II):

[0038] R3SiO-[R2SiO] a -[HRSiO] b -SiR3 (II)

[0039] where each R is independently selected, at each occurrence, from alkyl groups and aryl groups, preferably alkyl groups and aryl groups having from 1 to 8 carbon atoms; the subscript a has an average value of 3 or greater, 5 or greater, 10 or greater, 14 or greater, 20 or greater, 25 or greater, 50 or greater, even 75 or greater, while having an average value of 100 or less, 75 or less, 50 or less, 25 or less, 20 or less, even 15 or less; and the subscript b has an average value of 2 or greater, 5 or greater, 10 or greater, 15 or greater, even 20 or greater, while having an average value of 30 or less, 25 or less, 20 or less, even 15 or less. Desirably, R is methyl (-CH3) at each occurrence.

[0040] The crosslinked hydrosilylation reaction product is the result of reacting an alkenyl-terminated polydiorganosiloxane and an organohydrogensiloxane crosslinker in the presence of a hydrosilylation catalyst such that the molar ratio of SiH groups to alkenyl groups is 0.5 or higher, 1.0 or higher, even 1.5 or higher and at the same time 2.0 or lower and can be 1.5 or lower. Generally, the hydrosilylation catalyst is a platinum catalyst such as Karstedt catalyst and / or Speier catalyst (H2PtCl6). The Karstedt catalyst is an organoplatinum compound derived from a divinyl-containing disiloxane (1,1,3,3,-tetramethyl, 1,3-divinyldisiloxane). The hydrosilylation catalyst can (and usually does) remain in the matrix material of the non-curable thermally conductive material of the present invention, or the catalyst can be removed after the formation of the crosslinked hydrosilylation reaction product and is not present in the matrix material. Based on the matrix weight, the catalyst is usually present in the matrix material at a platinum metal concentration of 0.5 parts per million by weight (ppm) or greater, 1.0 ppm or greater, 2.0 ppm or greater, 3.0 ppm or greater, 4.0 ppm or greater, 5.0 ppm or greater, 10 ppm or greater, 15 ppm or greater, 20 ppm or greater, 30 ppm or greater, even 40 ppm or greater, while usually being present at a concentration of 50 ppm or less, 40 ppm or less, 30 ppm or less, 20 ppm or less, 10 ppm or less, 5 ppm or less, 4 ppm or less, 3 ppm or less, 2 ppm or less, even 1 ppm or less.

[0041] The crosslinked hydrosilylation reaction product is usually present in the matrix material at a concentration of 2 wt% or higher, 3 wt% or higher, 4 wt% or higher, 5 wt% or higher, 6 wt% or higher, 7 wt% or higher, 8 wt% or higher, even 9 wt% or higher, while less than 10 wt%, and can be 9 wt% or lower, 8 wt% or lower, 7 wt% or lower, 6 wt% or lower, 5 wt% or lower, 4 wt% or lower, even 3 wt% or lower, where wt% is based on the weight of the matrix material.

[0042] The crosslinked hydrosilylation reaction product and the carrier fluid are desirably mixed to form a single composition, preferably a homogeneous composition, which forms a matrix in which other components of the non-curable thermally conductive material are dispersed. In fact, the vinyl-terminated polydiorganosiloxane and the organohydrogensiloxane crosslinker can be mixed with the non-functional non-crosslinked organosiloxane before the reaction so that they undergo hydrosilylation crosslinking in the carrier fluid. In this way, once the hydrosilylation crosslinking reaction is complete, the crosslinked hydrosilylation reaction product has been mixed with the carrier fluid to form the matrix material without having to blend the crosslinked material into another fluid.

[0043] The non-curable thermally conductive material also contains thermally conductive fillers dispersed throughout the matrix material. The thermally conductive fillers can be any fillers that can be used in TIM materials. For example, the thermally conductive fillers can be any combination of any one or more thermally conductive fillers selected from alumina, aluminum, zinc oxide, boron nitride, aluminum nitride, and aluminum trihydrate. Desirably, the thermally conductive fillers are any combination of any one or more selected from the group consisting of: alumina, aluminum, and zinc oxide. Even more desirably, the thermally conductive fillers are any one or any combination or more than one filler selected from: spherical aluminum particles having an average size of 8 to 10 microns, spherical aluminum particles having an average particle size of 1 to 3 microns, zinc oxide particles having an average particle size of 0.10 to 0.15 microns, alumina particles having an average particle size of 10 to 20 microns, and spherical alumina particles having an average particle size of 1 to 5 microns. The average particle size of the filler particles is determined as the median particle size (D50) according to the operating software using a laser diffraction particle size analyzer (CILAS 920 particle size analyzer or Beckman Coulter LS 13 320SW).

[0044] The amount of the heat-conductive filler is greater than 80 wt%, preferably 85 wt% or more, 90 wt% or more, 91 wt% or more, 92 wt% or more, even 93 wt% or more, and usually 95 wt% or less, 94 wt% or less, even 93 wt% or less, 92 wt% or less, 91 wt% or less, or 90 wt% or less, where wt% is based on the weight of the non-curable heat-conductive material.

[0045] The non-curable heat-conductive material further contains a treating agent. The treating agent can be used to assist in dispersing and stabilizing the dispersion of the filler particles in the matrix material. Desirably, the conductive material is one or more materials selected from alkyltrialkoxysilanes and mono-trialkoxy-capped diorganopolysiloxanes. Preferably, the alkyl group of the alkyltrialkoxysilane contains one or more, and can contain 2 or more, 4 or more, 6 or more, 8 or more, 10 or more, even 12 or more carbon atoms, and usually contains 14 or fewer, even 12 or fewer, 10 or fewer carbon atoms at the same time. Each alkoxy group of the alkyltrialkoxysilane desirably contains one or more and 6 or fewer, 4 or fewer, even 2 or fewer carbon atoms at the same time. A desired alkyltrialkoxysilane is n-decyltrimethoxysilane. The mono-trialkoxy-capped diorganopolysiloxane desirably has the chemical structure (III):

[0046] R'3SiO[R'2SiO] m Si(OR')3.(III)

[0047] where each R' is independently selected from alkyl groups having 1 to 12 carbon atoms each time it appears, and the subscript m corresponds to the degree of polymerization of the material, and has a value of 20 or greater, 30 or greater, 40 or greater, 60 or greater, 80 or greater, even 100 or greater and desirably 110 or less. Desirably, R' is methyl (-CH3) each time it appears, and more desirably, the average value of a is also in the range of 30 to 110. Desirably, the treating agent is a combination of n-decyltrimethoxysilane and mono-trimethoxy-capped dimethylpolysiloxane with an average degree of polymerization of 110.

[0048] Based on the weight of the non-curable heat-conductive material, the amount of the treating agent in the non-curable heat-conductive material is desirably 0.1 wt% or more, 0.5 wt% or more, 1.0 wt% or more, 1.5 wt% or more, even 2.0 wt% or more, and usually 3.0 wt% or less, 2.5 wt% or less, 2.0 wt% or less, even 1.0 wt% or less.

[0049] Desirably, the non-curable thermally conductive material has a viscosity expansion of less than 150 Pascal-seconds (Pa*s) in order to have a desired printability. The viscosity expansion of the non-curable thermally conductive material is generally 150 Pa*s or less, and can be 125 Pa*s or less, 120 Pa*s or less, 110 Pa*s or less, 100 Pa*s or less, 75 Pa*s or less, 50 Pa*s or less, or even 40 Pa*s or less, while generally being 30 Pa*s or more, 40 Pa*s or more, and can be 50 Pa*s or more, 75 Pa*s or more, or even 100 Pa*s or more.

[0050] Surprisingly and beneficially, the non-curable thermally conductive material has a thermal conductivity greater than 1 watt per meter-kelvin (W / m*K), preferably 2 W / m*K or greater, and even more preferably 5 W / m*K. At the same time, the non-curable thermally conductive material has a viscosity at expansion of less than 150 Pa*s and exhibits "good" printability in the printability tests described below herein. The non-curable thermally conductive material exhibits excellent anti-pumping properties by forming less than 5% void space on the chip surface after 5000 thermal cycles in the pumping-out test (defined below).

[0051] Without being bound by theory, one hypothesis regarding the non-curable thermally conductive material of the present invention is that the carrier fluid swells the crosslinked hydrosilylation reaction product to form a mucous fluid, which stabilizes the dispersion of the thermally conductive filler particles without separating from the non-curable material and also inhibits the pumping-out behavior of the matrix material. Nevertheless, the non-curable thermally conductive material still has a low enough viscosity to be printable and thus easy to apply to a substrate.

[0052] The non-curable thermally conductive material is prepared by: (a) combining the reactants for preparing the crosslinked hydrosilylation reaction product (i.e., the vinyl-terminated polydiorganosiloxane and the organohydrogensiloxane crosslinker) with a hydrosilylation catalyst, a non-functional non-crosslinking organosiloxane fluid, a treatment agent, and optionally any or all of the thermally conductive fillers; (b) crosslinking these reactants in the presence of the treatment agent and optionally the thermally conductive filler to prepare the crosslinked hydrosilylation reaction product; and (c) mixing the thermally conductive filler to a concentration greater than 80% by weight and simultaneously less than 95 wt% based on the weight of the combined materials, if not already at that concentration. The thermally conductive filler can be added during any one step or any combination of steps (a)-(c). However, it is important that the non-functional non-crosslinking organosiloxane fluid and the treatment agent are present during the hydrosilylation reaction for forming the crosslinked hydrosilylation reaction product of the matrix material, such that the crosslinked hydrosilylation reaction product is swollen by the non-functional non-crosslinking organosiloxane fluid.

[0053] The non-curable thermal conductive material can be part of a device, where the non-curable thermal conductive material is located between two objects and thermally couples the two objects. The non-curable thermal conductive material is particularly suitable as a thermal interface material (TIM) for thermally coupling two objects, especially when one of these objects is a bare chip and the other component is a heat sink. This is a particularly challenging coupling to maintain because the bare chip tends to cycle over a large temperature and size range during use and can cause pumping out of the TIM. However, the non-curable thermal conductive material of the present invention is suitable for such applications.

[0054] The present invention includes a method that includes the step of applying a non-curable thermal conductive material to an object, such as a bare chip or a heat sink. The method can also include placing the non-curable thermal conductive material between the object and a second object by applying a second component onto the non-curable thermal conductive material and applying pressure. For example, the non-curable thermal conductive material can be applied to an object that is a bare chip or a heat sink, and the other of the bare chip or the heat sink is applied to the non-curable thermal conductive material such that both the bare chip and the heat sink are thermally coupled to the non-curable thermal conductive material.

[0055] Example

[0056] Table 1 lists the components used in the embodiments of the present invention. SILASTIC, SYLOFF, and DOWSIL are trademarks of The Dow Chemical Company.

[0057] Table 1

[0058]

[0059]

[0060]

[0061] Preparation of matrix material

[0062] MM1-MM10: According to the formulations in Table 2 (these formulations express the components in parts by weight), the matrix materials (MM) 1-10 are prepared as follows: Mix the vinyl-terminated polydiorganosiloxane (AT PDOS) and the carrier fluid 1 in a glass vial until homogeneous. Add 3.3 parts by weight of treating agent 1, 39 parts by weight of treating agent 2, and 0.07 parts by weight of the platinum catalyst and mix. Slowly add the organohydrogensiloxane crosslinking agent 1 with stirring. After the addition is complete, continue stirring at 25 °C for one day to complete the crosslinking reaction. The resulting composition is the matrix material.

[0063] MM11: MM13 was prepared in a similar manner to MM1-MM12, except that 0.05 g of platinum catalyst was used and no treatment agent was included.

[0064] Table 2

[0065]

[0066]

[0067] Preparation of non-curable thermal conductive material

[0068] I. Samples with Al-1, Al-2 and ZnO-1

[0069] Reference Sample A - A thermal conductive material with only a carrier fluid matrix. Add 5.10 grams (g) of Carrier Fluid 1, 0.17 g of Treatment Agent 1, 1.99 g of Treatment Agent 2, 50.25 g of Al-1, 25.12 g of Al-2, and 17.37 g of ZnO-1 to a 100 milliliter (mL) dental cup. Mix with a dental mixer at 1500 revolutions per minute (RPM) for 2 minutes to obtain a flowable mixture. Transfer the flowable mixture to a container and heat at 150 °C under vacuum (2.2 kilopascals; 22 torr) for one hour to obtain Reference Sample A.

[0070] Samples 1 - 10: Thermal conductive materials. Samples 1 - 10 were prepared as follows: Add 7.26 g of matrix material (see Table 3), 50.25 g of Al-1, 25.12 g of Al2, and 17.37 g of ZnO1 to a 100 mL dental cup. Mix with a dental mixer at 1500 RPM for 2 minutes to provide a flowable mixture. Transfer the mixture to a metal container and heat to 150 °C under vacuum (2.2 kilopascals; 22 torr) for one hour to provide the final samples.

[0071] Table 3

[0072]

[0073] Sample 11: Prepared in a similar manner to Sample 2, except that 13.00 g of matrix material MM2, 47.13 g of Al-1, 23.56 g of Al-2, and 16.29 g of ZnO-1 were used.

[0074] Sample 12: Prepared in a similar manner to Sample 2, except that 15.00 g of matrix material MM2, 46.06 g of Al-1, 23.02 g of Al-2, and 15.92 g of ZnO-1 were used.

[0075] II. Samples with alumina-1, alumina-2 and ZnO-1

[0076] Reference Sample B - A thermally conductive material with only a carrier fluid matrix. Add 4.25 g of Carrier Fluid 2, 1.5 g of Carrier Fluid 3, 0.2 g of Treatment Agent 1, 0.8 g of Treatment Agent 3, 53.5 g of Alumina - 1, 26.7 g of Alumina - 2, 12.8 g of ZnO - 1, 0.1 g of Stabilizer, and 0.15 g of Fumed Silica to a 100 milliliter (mL) dental cup. Mix with a dental mixer at 1500 revolutions per minute (RPM) for 2 minutes to obtain a flowable mixture. Transfer the flowable mixture to a container and heat at 150 °C under vacuum (2.2 kPa; 22 Torr) for one hour to obtain Reference Sample B.

[0077] Sample 13: A thermally conductive material with Alumina - 1 and Alumina - 2. Prepare Sample 13 as follows: Add 5.9 g of Matrix Material 11, 0.2 g of Treatment Agent 1, 0.8 g of Treatment Agent 3, 53.5 g of Alumina - 1, 26.7 g of Alumina - 2, 12.8 g of ZnO - 1, and 0.1 g of Stabilizer to a 100 mL dental cup. Mix with a dental mixer at 1500 RPM for 2 minutes to provide a flowable mixture. Transfer the mixture to a metal container and heat to 150 °C under vacuum (2.2 kPa; 22 Torr) for one hour to provide the final sample.

[0078] Samples 14 - 17: Thermally conductive materials with Alumina - 3 and Alumina - 4. These samples explore a range of thermally conductive filler loadings. The weight of each component is listed in Table 4. Add the specified amounts of MM2, Alumina - 1, and Alumina - 2 to a 100 mL dental cup. Mix with a dental mixer at 1500 RPM for 2 minutes to provide a flowable mixture. Transfer the mixture to a metal container and heat to 150 °C under vacuum (2.2 kPa; 22 Torr) for one hour to provide the final sample.

[0079] Table 4

[0080] Sample MM2 (g) Alumina-3 (g) Alumina-4 (g) Wt% filler loading 14 7.80 31.3 20.9 87 15 9.00 30.6 20.4 85 16 10.80 29.5 19.7 82 17 12.00 28.8 19.2 80

[0081] Sample evaluation

[0082] The samples were evaluated by characterizing the viscosity during expansion, thermal conductivity, and printability using the following methods:

[0083] Pump - out resistance: Pump - out resistance was evaluated in a test simulating the final application, and the amount of pump - out was evaluated after accelerated power cycling. The power cycling heated the electronic device during 5000 cycles of the power cycle and simulated a 5 - year device life at approximately 3 cycles per day. The device used for testing was an AMD Radeon TMThe GPU card from Gigabyte with RX VeEGA 64 GPU power supply. The sample material is applied to the GPU by the following steps: (1) Disassemble the GPU card to expose the radiator and the side of the chipset; (2) If necessary, carefully clean the residual TIM on both sides by using a swab or a cleaner; (3) Attach a silk screen template with a thickness of 200 microns to the radiator to symmetrically match the position of the chipset; (4) Template-print the sample material onto the chipset through the template; and (5) Remove the template and reassemble the GPU.

[0084] The following computer components are used for testing: CPU: AMD Ryzen 7 2700X 8-core; Motherboard: ASUS TUF X470-PLIS GAMING; Memory: KINSTON DDR4 266 8GB; Graphics card: Gigabyte Radeon computer graphics card (GV-RXVEGA64GAMING OC-8GD); Solid state drive: Intel SSD 760P series (256GB, M.2 80mm PCle 3.0x4, 3D2, TLC); Monitor: Del U2417H; Keyboard: Dell; Mouse: Dell; Computer case: Antec P8 ATX; Power supply: Antec NEO750W; KVM: MT-viki HK05.

[0085] The thermal cycling test is carried out by running the FurMark GPU stress test software, which can be obtained from free download at: https: / / geeks3d.com / furmark / 。The script (in AutoIt) includes steps to open and close the Furmark software and steps to vary the fan speed to control the temperature of the GPU card. The AutoIt script includes: (1) opening the Furmark program; (2) activating the Furmark stress test routine; (3) during a 200,000 millisecond heating cycle, setting the fan speed to 30% of its maximum speed; (4) stopping the stress test routine; (5) closing the Furmark program; (6) during a 200,000 millisecond cooling cycle, setting the fan speed to 90% of its maximum speed; (7) repeating the sequence. This process is used to cycle the temperature on the GPU card from 35 °C to 85 °C and back to 35 °C. After 5000 cycles, the computer is shut down. The graphics card is removed. The graphics card is opened and the heat sink and chips on the circuit board are recorded with the high-resolution camera on a Keyence VHX digital microscope. The areas (bare spots) of the heat sink and chips without sample material due to pumping out during the cycling test are measured. The quantitative area of the bare spots is calculated using readily available "sketchandcalc" software (or any equivalent software that can calculate area with a digital imager). The total bare spot area due to grease pumping out is divided by the total GPU chip area (495 square millimeters) to determine the bare spot area % on the chip. The results are classified as follows: excellent = less than 5% bare spot area on the chip; medium = 5 - 10% bare spot area on the chip; and poor = greater than 10% bare spot area on the chip.

[0086] Note: For Sample B and Sample 13, the anti-pumping-out property is evaluated using the following modified anti-pumping-out test. A component is prepared with 0.1 grams of sample material between glass and aluminum plates spaced 0.1 millimeters apart, with 0.1 millimeter thick gaskets on either side of the sample material. The component is placed in an oven and cycled between -40 °C and 125 °C at a rate of reaching one extreme to the other in 30 minutes and then holding at each extreme for 30 minutes. The cycle is for 168 hours, and then the coverage of the material on the aluminum plate under the cover glass is evaluated: excellent = less than 5% bare spot area; medium => 5% and < 10% bare spot area; poor => 10% bare spot area. The performance in this modified test is expected to correspond to the anti-pumping-out test described above.

[0087] Viscosity during swelling: Dynamic is measured using ASTM D4440 - 15 and a TA Instruments ARES - G2 type device equipped with a 25 millimeter parallel plate (serrated steel). The test conditions are based on a strain sweep conducted at 25 degrees Celsius (°C), where strain: 0.01% - 300%, and the frequency is 10 radians per second. The dynamic viscosity at the swelling strain (swelling point) is recorded as the viscosity during swelling.

[0088] Thermal conductivity: According to ISO 22007-2:2015, the thermal conductivity was measured using a Hot Disk Instrument TPS 2500S from Hot Disk AB, Gothenburg, Sweden. Sensor C5501 was used. Two cups were filled with the sample material, with the planar sensor held between the cups. The analysis conditions were: fine-tuning analysis, temperature drift compensation, and time correction, and the calculation was carried out using the selected points between point 50 and point 150.

[0089] Printability test: The sample was screen-printed using an 80-mesh metal screen to print a pattern of 25 cm by 25 cm with a thickness of 200 microns onto the heat sink. The screen was held above the heat sink and 5 g of the sample material was positioned on the top part of the screen. Using a squeegee held at a 45° angle to the screen and the heat sink moving at a constant speed and force, the thermal grease was transferred through the screen onto the heat sink. The screen printability of the sample was evaluated using the following criteria: Good: The sample could be deposited on the heat sink for full surface coverage; Medium: The sample was deposited to cover approximately 70%-80% of the printed surface area only. Additional squeegee attempts were required to deposit the sample onto the surface. Some materials might hang in the screen mesh; Poor: The sample was deposited on less than 20% of the printed surface area. The sample was too thick to have good screen printability. Most of the sample might hang in the screen mesh.

[0090] Results: Table 5 presents the evaluation results of the samples. Based on these results, the following conclusions are obvious:

[0091] Samples 14 - 17 revealed that in order to obtain a desired thermal conductivity greater than 1 W / m*K, the loading of the thermal conductive filler must be greater than 80 wt%.

[0092] Samples A and 1 - 4 revealed that: (1) There must be a crosslinked hydrosilylation reaction product to achieve pump-out resistance; (2) The weight ratio of the carrier fluid to the crosslinked hydrosilylation reaction product must be greater than 90 / 10 to obtain sufficient printability; and (3) The degree of polymerization of the vinyl-terminated PDOS needs to be greater than 292 to achieve good printability.

[0093] Samples B and 13 further revealed the need for a crosslinked hydrosilylation reaction product to achieve pump-out resistance.

[0094]

Claims

1. An uncured thermal conductive material, the uncured thermal conductive material comprising: (a) A matrix material, the matrix material comprising: (i) Based on the weight of the substrate material, greater than 90% by weight and simultaneously 98% by weight or less of a non-functional non-crosslinked silicone fluid, the non-functional non-crosslinked silicone fluid having a dynamic viscosity in the range of 50 centistokes to 350 centistokes; and (ii) A hydrosilylation reaction product of crosslinking of an alkenyl-terminated polydiorganosiloxane having a degree of polymerization greater than 300 and an organohydrogensiloxane crosslinker containing on average 2 or more SiH groups per molecule, based on the weight of the matrix material, in an amount of 2% to less than 10% by weight, wherein the ratio of the alkenyl-terminated polydiorganosiloxane to the organohydrogensiloxane is such that the molar ratio of SiH groups to alkenyl groups is in the range of 0.5 to less than 2.0 and not 2.0; (b) A thermal conductive filler in an amount of 90 - 95% by weight, based on the weight of the uncured thermal conductive material, the thermal conductive filler being dispersed throughout the matrix material; and (c) A treating agent, the treating agent being dispersed in the matrix material, the treating agent being selected from: alkyltrialkoxysilanes, wherein the alkyl group contains from 1 to 14 carbon atoms; and mono-trialkoxy-terminated diorganopolysiloxanes, the mono-trialkoxy-terminated diorganopolysiloxanes having a degree of polymerization in the range of 20 to 110, and each of the alkoxy groups containing from 1 to 12 carbon atoms.

2. The uncured thermal conductive material according to claim 1, wherein the non-functional non-crosslinked organosiloxane fluid is a phenylmethylsiloxane-dimethylsiloxane copolymer.

3. The uncured thermal conductive material according to any one of the preceding claims, wherein the alkenyl-terminated polydiorganosiloxane has the following chemical structure (I): ViR2SiO-[R2SiO] x -SiR2Vi (I) wherein Vi is a vinyl group, and the subscript x has an average value between 400 and 900, and R is independently selected, each occurrence, from alkyl groups and aryl groups having from 1 to 8 carbon atoms.

4. The uncured thermal conductive material according to claim 1, wherein the organohydrogensiloxane crosslinker has the following chemical structure (II): R3SiO-[R2SiO] a -[HRSiO] b -SiR3 (II) wherein R is independently selected, each occurrence, from alkyl groups and aryl groups having from 1 to 8 carbon atoms; a has an average value in the range of 3 - 100; and b has an average value in the range of 2 - 30.

5. The uncured thermal conductive material according to claim 1, wherein the thermal conductive filler is any one or any combination of more than one of the following: spherical aluminum particles having an average size of 8 to 10 microns, spherical aluminum particles having an average particle size of 1 to 3 microns, zinc oxide particles having an average particle size of 0.10 to 0.15 microns, alumina particles having an average particle size of 10 to 20 microns, and spherical alumina particles having an average particle size of 1 to 5 microns.

6. The uncured thermal conductive material according to claim 1, wherein the uncured thermal conductive material comprises both an alkyltrimethoxysilane treating agent and a mono-trialkoxy-terminated diorganopolysiloxane treating agent.

7. The non-curable heat-conductive material according to claim 1, wherein the alkyltrimethoxysilane is n-decyltrimethoxysilane, and the mono-trialkoxy-terminated diorganopolysiloxane has the following chemical structure: (CH3)3Si[(CH3)2SiO]mSi(OCH3)3; where m has a value in the range of 30 to 110.

8. A method for preparing an uncured thermally conductive material according to any one of the preceding claims, the method comprising the following steps: (a) Combining the reactants for preparing the crosslinked hydrosilylation reaction product, namely, the vinyl-terminated polydiorganosiloxane and the organohydrogensiloxane crosslinking agent, with a hydrosilylation catalyst, a non-functional non-crosslinking organosiloxane fluid, a treatment agent, and optionally any or all of the heat-conductive fillers; (b) Crosslinking the reactants in the presence of the treatment agent and optionally the heat-conductive fillers to prepare the crosslinked hydrosilylation reaction product; and (c) Mixing the heat-conductive filler to a concentration of 90-95 wt% based on the weight of the combined materials, if not already at said concentration.

9. An article comprising the non-curable heat-conductive material according to any one of claims 1 to 7 in thermal contact with at least two objects.

10. The article according to claim 9, wherein one object is a bare chip and the other object is a heat sink.

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