High-thermal-conductivity low-interface-thermal-resistance liquid silica gel and preparation method thereof

Abstract

The application discloses a kind of high thermal conductivity low interface thermal resistance liquid silica gel and preparation method thereof, belong to liquid silica gel material technical field.The liquid silica gel adopts two-component design, includes A component and B component.A component includes vinyl silicone oil 100 parts, surface modification boron nitride 30~100 parts, surface modification spherical alumina 20~80 parts, inhibitor 0.05~0.1 parts and platinum catalyst 0.5~0.8 parts;B component includes vinyl silicone oil 110 parts, modified hydrogen-containing silicone oil 2~5 parts and surface modification spherical alumina 20~80 parts.The modified hydrogen-containing silicone oil is the product of N-(3-butenyl)-fluorophthalimide and alkenyl-containing alkoxysilane and hydrogen-containing silicone oil carry out silicohydride addition reaction, realizes the double modification to the interface of silicone oil matrix and heat-conducting filler.The liquid silica gel of the application has high thermal conductivity, low interface thermal resistance, low viscosity and excellent dielectric properties and long-term reliability, especially suitable for AI chip, GPU and other high-power electronic devices packaging and heat dissipation.

Description

Technical Field

[0001] This invention relates to the field of liquid silicone technology, specifically to a liquid silicone with high thermal conductivity and low interfacial thermal resistance and its preparation method. Background Technology

[0002] With the continuous improvement of computing power density of artificial intelligence chips, the packaging and heat dissipation of high-power electronic components face severe challenges. At present, the heat flux density of advanced process AI chips can reach the level of 500W / cm², and the operating temperature often exceeds 150℃. With the demand for high-frequency signal transmission, multi-dimensional performance requirements are put forward for packaging materials: (1) Thermal expansion coefficient matching: the CTE of silicon chips is about 3ppm / ℃, while the CTE of traditional epoxy resin encapsulation layer is usually 50~80ppm / ℃. The two generate significant CTE mismatch stress in the thermal cycle from -40℃ to 150℃, which easily leads to interface delamination and microcracks; (2) High-frequency dielectric properties: the dielectric loss tangent of traditional organic encapsulation materials in the frequency band above 10GHz is usually greater than 0.01, causing signal delay and energy loss; (3) Heat dissipation efficiency: the intrinsic thermal conductivity of unmodified liquid silicone rubber is only about 0.2W / (m·K), which is difficult to meet the heat dissipation requirements of high-power chips.

[0003] Among many alternative materials, liquid silicone rubber has attracted much attention due to its unique advantages: (1) Low viscosity potting: The viscosity of unfilled liquid silicone rubber can be as low as 500~5000 mPa·s, which can fill micro gaps below 0.1mm; (2) Low stress curing: The curing shrinkage rate of silicone rubber is less than 0.1%, and although the bulk CTE (about 150~300ppm / ℃) is higher than that of silicon chips, it can be moderately controlled by the type and amount of filler. Compared with epoxy resin, it has better flexibility and thermal shock resistance; (3) Excellent dielectric properties: The polysiloxane main chain has low polarity, and the intrinsic dielectric loss tangent is less than 0.001 in a wide frequency range, which is suitable for high frequency signal transmission scenarios.

[0004] However, the following technical bottlenecks still exist when liquid silicone rubber is used for high-power chip packaging: (1) The contradiction between thermal conductivity and interfacial thermal resistance: In order to improve thermal conductivity, high thermal conductivity fillers such as boron nitride and alumina need to be added to the silicone oil matrix. However, the poor intrinsic interfacial compatibility between the filler and the silicone oil matrix leads to filler agglomeration and debonding of the matrix-filler interface, which increases the interfacial thermal resistance and makes the overall thermal conductivity much lower than the theoretical value.

[0005] (2) The contradiction between high filling and low viscosity: In order to achieve a higher thermal conductivity, the filling amount of filler often needs to be increased. At this time, the viscosity of the system rises sharply to more than 20,000 mPa·s, the potting and dispensing processing performance is severely degraded, and it is difficult to fill the fine gap between the chip and the heat sink.

[0006] (3) The contradiction between interfacial adhesion and long-term reliability: Unmodified silicone rubber has weak physical adsorption to metal surfaces such as copper and aluminum, and is prone to interfacial debonding under long-term thermal cycling and humid heat aging conditions, leading to encapsulation failure. Existing technologies improve adhesion by adding tackifiers or primers, but often sacrifice thermal conductivity or dielectric properties.

[0007] (4) Difficulty in achieving both dielectric and thermal conductivity: High thermal conductivity fillers (such as boron nitride and alumina) have high dielectric constants, and the polarization of the filler-matrix interface will further increase dielectric loss; at the same time, the injection and accumulation of space charge under high frequency and high electric field can easily cause partial discharge, reducing insulation reliability. Existing technologies cannot achieve high thermal conductivity while maintaining low dielectric constant, dielectric loss and excellent charge tolerance.

[0008] Therefore, developing a liquid silicone material that combines high thermal conductivity, low interfacial thermal resistance, low viscosity, excellent dielectric properties, and long-term thermal cycling reliability is of significant technical value and has broad application prospects for solving the heat dissipation problem of high-power electronic devices. Summary of the Invention

[0009] The purpose of this invention is to provide a liquid silicone rubber with high thermal conductivity and low interfacial thermal resistance and its preparation method, so as to solve the technical problems of low thermal conductivity, high interfacial thermal resistance, viscosity surge under high filling and insufficient long-term reliability of liquid silicone rubber in the prior art.

[0010] Specifically, the technical problems to be solved by the present invention include: (1) the thermal conductivity of existing liquid silicone is insufficient, which makes it difficult to meet the heat dissipation requirements of high-power devices such as AI chips; (2) the interface compatibility between thermally conductive filler and silicone oil matrix is ​​poor, which leads to increased interface thermal resistance and reduced thermal conductivity; (3) when the filling amount of high thermal conductivity filler is high, the viscosity of the system increases sharply, making potting processing difficult; (4) the interfacial bonding reliability of existing materials under long-term thermal cycling and humid heat environment is insufficient.

[0011] To achieve the above objectives, the present invention provides a liquid silicone with high thermal conductivity and low interfacial thermal resistance, which adopts a two-component design, comprising component A and component B, wherein the mass ratio of component A to component B is 1:(1~1.5).

[0012] Component A, by weight, comprises: 100 parts vinyl silicone oil, 30-100 parts surface-modified boron nitride, 20-80 parts surface-modified spherical alumina, 0.05-0.1 parts inhibitor, and 0.5-0.8 parts platinum catalyst.

[0013] Component B, by weight, comprises: 110 parts vinyl silicone oil, 2-5 parts modified hydrogen-containing silicone oil, and 20-80 parts surface-modified spherical alumina.

[0014] The modified hydrogen-containing silicone oil is the product of a hydrosilylation reaction between N-(3-butenyl)-fluorophthalimide and an alkenyl-containing alkoxysilane and the hydrogen-containing silicone oil.

[0015] The method for preparing the N-(3-butenyl)-fluorophthalimide is as follows: fluorophthalic anhydride and 3-buten-1-amine are subjected to an imidization reaction in an aprotic organic solvent in the presence of an imidization catalyst to obtain N-(3-butenyl)-fluorophthalimide.

[0016] The preferred molar ratio of the fluorophthalic anhydride to 3-buten-1-amine is 1:(1.0~1.1); the fluorophthalic anhydride is selected from one or more of 3-fluorophthalic anhydride, 4-fluorophthalic anhydride, and 5-fluorophthalic anhydride; the preferred imidization catalyst is 4-dimethylaminopyridine (DMAP), used in an amount of 10~20 mol% of the molar amount of the fluorophthalic anhydride; the preferred aprotic organic solvent is anhydrous toluene; the imidization reaction is carried out in two steps: the first step is a pre-reaction at room temperature for 2~4 h to form an amide acid intermediate; the second step is a heating to 80~110 °C for a dehydration and ring-closure reaction for 8~16 h.

[0017] The modified hydrogen-containing silicone oil is prepared by reacting N-(3-butenyl)-fluorophthalimide and alkenyl-containing alkoxysilane with hydrogen-containing silicone oil in the presence of a platinum catalyst via a hydrosilylation reaction.

[0018] The platinum catalyst is a Karstedt platinum catalyst with a platinum content of 5-20 ppm; the reaction temperature is 60-90℃ and the reaction time is 4-8 h; the molar ratio of Si-H in the N-(3-butenyl)-fluorophthalimide, alkenyl-containing alkoxysilane, and hydrogen-containing silicone oil is (0.15-0.3):(0.10-0.20):1; the hydrogen content of the hydrogen-containing silicone oil is 0.8-1.6 wt%; the alkenyl-containing alkoxysilane is selected from one or more of vinyltriethoxysilane and allyltriethoxysilane.

[0019] The vinyl silicone oil comprises a compound system of high-viscosity vinyl-terminated polydimethylsiloxane and low-viscosity vinyl-terminated polydimethylsiloxane. The high-viscosity vinyl-terminated polydimethylsiloxane has a viscosity of 5000~20000 mPa·s and a vinyl content of 0.25~0.5 mol%; the low-viscosity vinyl-terminated polydimethylsiloxane has a viscosity of 200~1000 mPa·s and a vinyl content of 0.8~1.9 mol%. The preferred mass ratio of the high-viscosity to low-viscosity vinyl-terminated polydimethylsiloxane is (3:1)~(6:1). By compounding the high- and low-viscosity vinyl silicone oils, sufficient fluidity of the system can be ensured while maintaining the mechanical strength and resilience of the cured silicone rubber.

[0020] The surface-modified boron nitride is obtained by treating boron nitride with a fluorosilane containing a fluorinated alkyl carbon chain length of C3-C6. The boron nitride is preferably plate-like hexagonal boron nitride (h-BN) with a D50 particle size of 5-10 μm and a D90 particle size of 10-30 μm. The fluorosilane is selected from one or more of 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, (1H,1H,2H,2H-perfluorohexyl)trimethoxysilane, and (1H,1H,2H,2H-perfluorohexyl)triethoxysilane, with the amount of fluorosilane used being 1-3 wt% of the boron nitride mass. After surface modification with fluorosilane, the surface of the boron nitride changes from hydrophilic to oleophobic to hydrophobic and oleophilic, significantly improving its compatibility with the silicone oil matrix. Simultaneously, the introduction of fluorine further reduces the surface energy and dielectric constant of the material.

[0021] The surface-modified spherical alumina is obtained by treating spherical alumina with an alkyl silane having an alkyl carbon chain length of C3-C6. The D50 particle size of the spherical alumina is 1.5-2.5 μm. The alkyl silane with an alkyl carbon chain length of C3-C6 is selected from any one of propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, or hexyltriethoxysilane, and the amount of alkyl silane used is 1-5 wt% of the mass of the spherical alumina. After surface modification with alkyl silane, the dispersibility of the spherical alumina in the silicone oil matrix is ​​significantly improved, and it can form a synergistic interfacial effect with the alkoxysilane groups in the modified hydrogen-containing silicone oil, further reducing the interfacial thermal resistance.

[0022] The inhibitor is selected from at least one of 1-ethynylcyclohexanol, 3-methyl-1-butyn-3-ol, and 3,7,11-trimethyldodecyn-3-ol, and is used to inhibit premature crosslinking at room temperature and extend the storage period of component A. The platinum catalyst is a Karstedt platinum catalyst, used to catalyze the hydrosilylation reaction between vinyl groups and Si-H groups to achieve the curing and crosslinking of silicone rubber.

[0023] This invention also provides a method for preparing the above-mentioned high thermal conductivity and low interfacial thermal resistance liquid silicone, comprising the following steps: (1) Preparation of component A: Vinyl silicone oil, surface-modified boron nitride, and surface-modified spherical alumina are added to a planetary mixer and stirred evenly at room temperature. The mixture is heated to 75~85℃ for vacuum degassing, cooled to below 40℃, and platinum catalyst and inhibitor are added. The mixture is stirred under vacuum at low speed, and the product is discharged, sealed, and packaged to obtain component A. (2) Preparation of component B: Add vinyl silicone oil and surface-modified spherical alumina to a planetary mixer, stir evenly at room temperature, heat to 75~85℃ for vacuum degassing, cool to below 40℃, add modified hydrogen-containing silicone oil, stir at low speed, vacuum degas, discharge and seal packaging to obtain component B.

[0024] Before use, mix component A and component B at a mass ratio of 1:(1~1.5) until homogeneous. After vacuum degassing, inject into the mold or dispense onto the chip-heat sink interface. Cure at 80℃ for 30 min to obtain a high thermal conductivity, low interfacial thermal resistance liquid silicone rubber cured product.

[0025] Beneficial effects

[0026] This invention provides a high thermal conductivity, low interfacial thermal resistance liquid silicone. Through the synergistic interfacial design of modified hydrogen-containing silicone oil and surface-modified fillers, the cured silicone rubber obtained after crosslinking exhibits both high thermal conductivity and low interfacial thermal resistance while maintaining an appropriate filler content. The fluorinated phthalimide groups in the modified hydrogen-containing silicone oil improve the wettability with boron nitride and alumina filler surfaces through strong polar interactions, reducing phonon scattering at the filler-matrix interface. Simultaneously, the fluorinated groups form a physical adsorption layer with the metal heat sink surface, reducing the thermal resistance at the contact interface and thus improving the heat dissipation efficiency of the encapsulation. Furthermore, by blending high and low viscosity vinyl silicone oils with fluorosilane / alkylsilane surface-modified fillers, the system viscosity is controlled within a range suitable for potting and dispensing processes even at high filler contents. Surface modification changes the filler surface from hydrophilic to hydrophobic-oleophilic, significantly reducing the tendency of filler agglomeration in the silicone oil matrix, thereby maintaining a low system viscosity at high filler contents and meeting the processing requirements for filling micro-gaps.

[0027] The silicone rubber cured product of this invention has a low dielectric constant and dielectric loss tangent, meeting the packaging requirements for high-frequency signal transmission. More importantly, the introduced N-substituted fluorinated phthalimide group endows the silicone rubber cured product with deep charge trapping properties: the imide ring, as the electron deep trap center, can capture injected charge carriers and homogenize the internal electric field distribution, suppressing local electric field distortion and the formation of conductive channels; the strong electronegativity of fluorine further enhances the electron affinity of the imide ring, increasing the deep trapping cross section, while reducing the electronic polarizability of the molecular chain, reducing conductivity loss and interface polarization loss at high frequencies; and the alkoxysilane group mainly contributes to the chemical bonding of the inorganic interface and long-term hydrolytic stability. Therefore, the liquid silicone rubber cured product of this invention can effectively suppress space charge accumulation and partial discharge initiation in high-frequency, high-electric-field packaging scenarios, extending insulation life, and can be widely used in the packaging and heat dissipation of high-power electronic devices such as AI chips, GPUs, and power semiconductors. Attached Figure Description

[0028] Figure 1 A schematic diagram of the synthetic route for modified hydrogen-containing silicone oil; Figure 2 Infrared spectra of hydrogen-containing silicone oil and modified hydrogen-containing silicone oil 1. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0031] The raw materials used in the examples and comparative examples are described below: High viscosity vinyl-terminated polydimethylsiloxane: viscosity 5000 mPa·s, vinyl content 0.45 mol%, Guangdong Shengfeng New Material Technology Co., Ltd. Low viscosity vinyl-terminated polydimethylsiloxane: viscosity 500 mPa·s, vinyl content 1.2 mol%, Guangdong Shengfeng New Material Technology Co., Ltd. Hydrogen-containing silicone oil: hydrogen content 1.0wt%, XHG-202-10, Xin'an Chemical; N-(3-Butenyl)-4-fluorophthalimide: Prepared in-house, the preparation method is as follows: In a dry 250 mL three-necked flask, 0.1 mol of 4-fluorophthalic anhydride and 100 mL of anhydrous toluene were added. The mixture was purged with nitrogen three times. Under nitrogen protection, 0.01 mol of 4-dimethylaminopyridine (DMAP) was added, and the mixture was stirred at room temperature for 10 min until completely dissolved. 20 mL of anhydrous toluene solution of 0.105 mol of 3-buten-1-amine was slowly added dropwise through a constant-pressure dropping funnel. After the addition was complete, the mixture was stirred at room temperature (25 °C) for 4 h. A water separator was connected, and the reaction system was heated to 110 °C and refluxed for 12 h. The generated water was continuously removed through the water separator. TLC monitoring (evolving solvent: petroleum ether / ethyl acetate = 3:1) continued until the starting anhydride point (Rf≈0.6) disappeared and the product point (Rf≈0.4) was single and stable. Cool to room temperature, pour the reaction solution into 200 mL of saturated saline solution, and extract three times with 50 mL of toluene. Combine the organic phases and wash successively with 50 mL of 1 M dilute hydrochloric acid, 50 mL of saturated sodium bicarbonate solution, and 50 mL of saturated saline solution. Dry the organic phase with anhydrous sodium sulfate for 4 h and filter. Concentrate under reduced pressure (rotary evaporator, 40 °C, -0.09 MPa) to remove toluene, giving a pale yellow crude product. Purify by silica gel column chromatography (200-300 mesh) using a gradient elution of petroleum ether / ethyl acetate = 5:1 → 3:1. The product fraction was collected and concentrated under reduced pressure to obtain a white to pale yellow crystalline solid, namely N-(3-butenyl)-4-fluorophthalimide, with a yield of 82.3%. The structure of the product was confirmed by ¹H NMR (400 MHz, CDCl3): δ 7.82 (dd, 1H, Ar-H), 7.68~7.52 (m, 2H, Ar-H), 5.75 (m, 1H, =CH-), 5.12 (m, 2H, =CH2), 3.97 (t, 2H, N-CH2, J=7.2 Hz), 2.42 (m, 2H, CH2-CH=CH2).

[0032] Modified hydrogen-containing silicone oil 1: self-made, preparation method is as follows: In a dry 250 mL three-necked flask, add 100 g of hydrogen-containing silicone oil and 100 mL of anhydrous toluene, and stir to dissolve. Through a constant-pressure dropping funnel, add 20 mL of anhydrous toluene solution of N-(3-butenyl)-4-fluorophthalimide (calculated at a molar ratio of alkenyl:Si-H = 0.2:1) and 20 mL of anhydrous toluene solution of allyltriethoxysilane (calculated at a molar ratio of alkenyl:Si-H = 0.15:1). The system is protected under nitrogen purging, with three purgings. Under nitrogen protection, add 0.4 g of Karstedt platinum catalyst and pre-stir at room temperature for 10 min. Heat to 80 °C and react under nitrogen protection for 6 h. After the reaction is complete, cool to room temperature. Add 2 g of activated carbon, stir at 60 °C for 1 h to adsorb, and filter to remove the platinum complex. The filtrate was dried with anhydrous sodium sulfate for 4 h, filtered, and concentrated under reduced pressure (rotary evaporator, 50℃, -0.09 MPa) to remove toluene, yielding a pale yellow to colorless transparent viscous liquid, i.e., modified hydrogen-containing silicone oil. The reaction process is as follows: Figure 1 As shown, the obtained hydrogen-containing silicone oil and modified hydrogen-containing silicone oil were tested using Fourier transform infrared spectroscopy (FTIR), with a scanning range of 4000–500 cm⁻¹. -1 Compared to hydrogen-containing silicone oil feedstock, the product has a higher viscosity at 2160 cm⁻¹. -1 The absorption peak intensity of the Si-H stretching vibration at 1750 cm⁻¹ decreased significantly, indicating that some Si-H bonds participated in the hydrosilylation reaction; meanwhile, at 1750 cm⁻¹... -1 1598cm -1 1380 cm -1 and 1220 cm -1 A new characteristic absorption peak appears at 2950-2860 cm⁻¹. -1 The CH stretching vibration in the region is significantly enhanced, indicating the introduction of allyltriethoxysilane; 1750 cm -1 The absorption peak at 1598 cm⁻¹ is attributed to the stretching vibration of the carbonyl group (C=O) on the N-substituted fluorinated phthalimide ring; -1 The absorption peak at 1380 cm⁻¹ is attributed to the C=C skeletal stretching vibration of the ortho-disubstituted benzene ring. -1 The absorption peak at 1200-1230 cm⁻¹ is attributed to the stretching vibration of the CN bond in the imide ring. -1 The presence of a shoulder peak in the range is attributed to the CF stretching vibration. The aforementioned infrared spectral changes indicate that N-(3-butenyl)-fluorophthalimide and allyltriethoxysilane have been successfully grafted into the hydrogen-containing silicone oil molecular chain via hydrosilylation, and the product molecule still retains unreacted Si-H groups.

[0033] Modified hydrogen-containing silicone oil 2: Compared with modified hydrogen-containing silicone oil 1, the difference is that the amount of N-(3-butenyl)-4-fluorophthalimide added is modified to be calculated by molar ratio of alkenyl:Si-H = 0.15:1, and the amount of allyltriethoxysilane added is modified to be calculated by molar ratio of alkenyl:Si-H = 0.2:1.

[0034] Modified hydrogen-containing silicone oil 3: Compared with modified hydrogen-containing silicone oil 1, the difference is that the amount of N-(3-butenyl)-4-fluorophthalimide added is modified to be calculated by molar ratio of alkenyl:Si-H = 0.3:1, and the amount of allyltriethoxysilane added is modified to be calculated by molar ratio of alkenyl:Si-H = 0.1:1.

[0035] Modified hydrogen-containing silicone oil 4: Compared with modified hydrogen-containing silicone oil 1, the difference is that the amount of N-(3-butenyl)-4-fluorophthalimide added is modified to be calculated by molar ratio of alkenyl:Si-H = 0.3:1, and allyltriethoxysilane is not added.

[0036] Modified hydrogen-containing silicone oil 5: Compared with modified hydrogen-containing silicone oil 1, the difference is that N-(3-butenyl)-4-fluorophthalimide is not added, and the amount of allyltriethoxysilane added is modified to be calculated by molar ratio of alkenyl:Si-H = 0.2:1.

[0037] Spherical alumina: DAW-01, D50 is 1.9μm, Denka; Surface-modified spherical alumina 1: Spherical alumina was placed in a vacuum drying oven and dried at 120℃ and -0.09 MPa for 4 h to remove physically adsorbed water from the surface. The pre-dried spherical alumina was added to a mixture of anhydrous ethanol and deionized water (95:5, volume ratio), with a solid content of 30%. The mixture was ultrasonically dispersed at 200W for 30 min to obtain a uniform suspension. Butyltrimethoxysilane (1.0 part by mass) was added to the suspension and stirred for 10 min until completely dispersed. Glacial acetic acid was added dropwise to adjust the pH of the system to 4.5~5.0. The temperature was raised to 60℃ and the reaction was stirred for 2 h under nitrogen protection. After the reaction was completed, the suspension was vacuum filtered, and the filter cake was washed three times with anhydrous ethanol (50 mL each time) to remove unreacted free silanes and hydrolysis byproducts (methanol, oligomeric siloxanes). The washing was continued until the pH of the filtrate was neutral. The washed filter cake was placed in a vacuum drying oven and dried at 120 °C and -0.09 MPa for 4 h to obtain spherical alumina modified with butylsilane. The product was sealed and stored.

[0038] Surface-modified spherical alumina 2: Compared with surface-modified spherical alumina 1, the difference is that butyltrimethoxysilane is replaced with decyltrimethoxysilane.

[0039] Boron nitride: D50 is 5~8μm, D90 is 10~20, CFP 007HS, 3M; Surface-modified boron nitride 1: Flaky hexagonal boron nitride (h-BN) was dispersed in an ethanol / water mixture (95:5 v / v) with a solid content of 30%. 3,3,3-trifluoropropyltrimethoxysilane was added, with the amount of silane being 1.5 wt% of the mass of h-BN. The pH was adjusted to 4.5-5.0 with acetic acid. The mixture was stirred at 60°C for 2 h under nitrogen protection, filtered, washed three times with ethanol, dried under vacuum at 120°C for 4 h, and pulverized through a 200-mesh sieve to obtain trifluoropropyltrimethoxysilane-modified boron nitride for later use.

[0040] Surface-modified boron nitride 2: Compared with surface-modified boron nitride 1, the difference is that trifluoropropanetrimethoxysilane is replaced with perfluorodecyltriethoxysilane.

[0041] Inhibitor: 1-ethynylcyclohexanol, commercially available.

[0042] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0043] Example 1

[0044] A liquid silica gel with high thermal conductivity and low interfacial thermal resistance, comprising component A and component B, is prepared as follows: Component A: Add 100 parts by weight of vinyl silicone oil (including 80 parts by weight of high-viscosity end-vinyl polydimethylsiloxane and 20 parts by weight of low-viscosity end-vinyl polydimethylsiloxane) and 40 parts by weight of surface-modified boron nitride 1 and 40 parts by weight of surface-modified spherical alumina 1 to a planetary mixer, stir at room temperature for 30 min, heat to 80℃ and degas under vacuum for 30 min, vacuum degree ≤ -0.095 MPa, cool to below 40℃, add 0.5 parts by weight of Karstedt platinum catalyst and 0.08 parts by weight of inhibitor, stir at 100 rpm under vacuum for 20 min, discharge, seal and package, and store in a cool, dark place (<25℃).

[0045] Component B: 110 parts by weight of vinyl silicone oil (including 90 parts by weight of high-viscosity end-vinyl polydimethylsiloxane and 20 parts by weight of low-viscosity end-vinyl polydimethylsiloxane) and 40 parts by weight of surface-modified spherical alumina 1 were added to a planetary mixer and stirred at room temperature for 30 min. The mixture was then heated to 80°C and vacuum degassed for 30 min. After cooling to below 40°C, 4.2 parts by weight of modified hydrogen-containing silicone oil 1 were added, and the mixture was stirred at low speed for 20 min. Vacuum degassed for 10 min, and the mixture was discharged, sealed, and packaged to obtain Component B.

[0046] Before use, mix component A and component B at a mass ratio of 1:1.3, stir evenly in a planetary mixer, and degas under vacuum for 5 minutes. Inject the mixture into a mold or dispensing it onto the chip-heat sink interface, and cure at 80°C for 30 minutes to obtain a high thermal conductivity, low interfacial thermal resistance liquid silicone rubber cured product.

[0047] Example 2

[0048] Compared with Example 1, the difference is that modified hydrogen-containing silicone oil 1 is replaced with modified hydrogen-containing silicone oil 2.

[0049] Example 3

[0050] Compared with Example 1, the difference is that 4.2 parts by weight of modified hydrogen-containing silicone oil 1 is replaced with 4.5 parts by weight of modified hydrogen-containing silicone oil 3.

[0051] Example 4

[0052] Compared with Example 1, the difference is that surface-modified boron nitride 1 is replaced with surface-modified boron nitride 2, and surface-modified spherical alumina 1 is replaced with surface-modified spherical alumina 2.

[0053] Comparative Example 1 Compared with Example 1, the difference is that 4.2 parts by weight of modified hydrogen-containing silicone oil 1 is replaced with 2.73 parts by weight of hydrogen-containing silicone oil.

[0054] Comparative Example 2 Compared with Example 1, the difference is that the surface-modified boron nitride 1 is replaced with boron nitride, that is, the boron nitride is not modified.

[0055] Comparative Example 3 Compared with Example 1, the difference is that the surface-modified spherical alumina 1 is replaced with spherical alumina, that is, the spherical alumina is not modified.

[0056] Comparative Example 4 Compared with Example 1, the difference is that 4.2 parts by weight of modified hydrogen-containing silicone oil 1 is replaced with 3.9 parts by weight of modified hydrogen-containing silicone oil 4.

[0057] Comparative Example 5 Compared with Example 1, the difference is that 4.2 parts by weight of modified hydrogen-containing silicone oil 1 is replaced with 3.4 parts by weight of modified hydrogen-containing silicone oil 5.

[0058] The high thermal conductivity and low interfacial thermal resistance liquid silicone and its cured silicone rubber prepared in the examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 1.

[0059] (1) Viscosity: The viscosity of components A and B was measured using a rheometer. Based on the approximate viscosity range of liquid silica gel, a PP-25 flat plate rotor was selected for testing. The amount of sample added at one time was about 2 ml, the temperature was set to 25℃, the number of test segments was 1, the number of test points was 31, and the shear rate was 0.1~10 rad / s and showed a logarithmic change.

[0060] (2) Thermal conductivity / interfacial thermal resistance: Samples were prepared according to ASTM D5470. The size of the cured silicone rubber was Φ25.4mm. Three different thicknesses (1 mm, 2 mm, 3 mm) of circular pieces were prepared. The upper and lower surfaces were polished to parallelism ≤0.05 mm. The steady-state heat flow method was used, and a pressure of 0.1~1.0 MPa was applied. The thermal resistance-thickness data were recorded. The thermal conductivity was calculated by the slope of the linear fitting. The linear fitting was extrapolated to zero thickness, and the y-intercept was the interfacial thermal resistance (2Re).

[0061] (3) Dielectric constant / dielectric loss tangent: The sample was prepared according to ASTM D150. The size of the cured silicone rubber was Φ50 mm×(1~2) mm. The upper and lower surfaces were flat, smooth and parallel. The contact electrode was used. The dielectric constant and dielectric loss tangent were tested in the 1 kHz~1 MHz frequency band using a wideband LCR tester under the conditions of 23±2℃ and 50±5%RH.

[0062] (4) Peel strength test: Prepare samples according to ASTM D1876 and test the T-type peel strength between the cured silicone rubber and the copper foil.

[0063] (5) Thermal cycling reliability test: The cured silicone rubber was clamped between the aluminum-aluminum interface and subjected to thermal cycling test from -40℃ to 150℃. The change rate of interface thermal resistance and the peel strength retention rate were recorded after 1000 cycles.

[0064] Table 1 Test results of the examples and comparative examples

[0065] As shown in Table 1, Example 1 uses hydrogen-containing silicone oil synergistically modified with N-(3-butenyl)-fluorophthalimide and allyltriethoxysilane bifunctional groups, combined with trifluoropropyl-modified boron nitride and butyl-modified spherical alumina. The cured silicone rubber exhibits a thermal conductivity of 2.6 W / (m·K), an interfacial thermal resistance of 18.5 mm²·K / W, a viscosity of component A of 8200 mPa·s, a dielectric constant of 3.2, and a peel strength to copper foil of 5.2 N / mm. The fluorophthalimide groups improve the dispersibility of boron nitride and alumina in the silicone oil and reduce phonon scattering at the filler-matrix interface through strong polarity, while forming a physical adsorption layer on the surface of the metal heat sink to reduce contact thermal resistance. During the curing process, the alkoxysilane groups form Si-O-Metal chemical bonds with the metal oxide layer, and the two work synergistically to achieve a balance between low interfacial thermal resistance and high adhesive strength.

[0066] Compared to Example 1, Example 2 increased the proportion of alkoxysilanes and decreased the proportion of imides. Due to the decreased density of imide groups, the polar interactions on the filler surface weakened, and the boron nitride dispersibility was slightly worse than in Example 1. This resulted in a decrease in thermal conductivity to 2.4 W / (m·K), an increase in interfacial thermal resistance to 20.0 mm²·K / W, and an increase in the viscosity of component A to 8500 mPa·s. Simultaneously, the number of physical anchoring sites on the metal surface decreased, and the peel strength decreased to 4.8 N / mm. This indicates that the contribution of imide groups to filler dispersion and interfacial adsorption is dose-dependent.

[0067] Compared to Example 1, Example 3 increased the imide ratio and decreased the alkoxy ratio. The high-density fluorinated phthalimide rings resulted in optimal boron nitride dispersibility, minimal filler agglomeration, and the most unobstructed phonon transport paths, thus leading to the highest thermal conductivity, lowest interfacial thermal resistance, and lowest viscosity of component A. The imide rings exhibited the strongest polar adsorption to the metal surface. However, the reduced alkoxy ratio weakened the contribution of chemical bonding, and the increase in interfacial thermal resistance after long-term thermal cycling was similar to that of Example 1, maintaining excellent reliability.

[0068] Example 4 uses perfluorodecyl-modified boron nitride and decyl-modified spherical alumina (C10 long chain), which has the highest fluorine atom density, resulting in the lowest dielectric constant and dielectric loss. However, the steric hindrance of the long-chain fluoroalkyl and decyl groups and the flexible spacer layer weaken the tight contact between the filler and the matrix, increasing the phonon transport interface thermal resistance, resulting in slightly worse thermal conductivity and interface thermal resistance than in Example 1. At the same time, the long-chain molecular entanglement increases the viscosity of component A to 9000 mPa·s, the highest among the examples.

[0069] Comparative Example 1 used unmodified hydrogen-containing silicone oil instead of modified hydrogen-containing silicone oil. When combined with modified fillers, the silicone oil-filler interface compatibility was insufficient, boron nitride easily agglomerated, the viscosity of component A reached as high as 12000 mPa·s, the thermal conductivity was only 2.2 W / (m·K), and the interfacial thermal resistance was 28.0 mm²·K / W. Due to the lack of imide polar adsorption and alkoxy chemical bonding, the peel strength with copper foil was only 2.1 N / mm, and severe debonding occurred at the interface after thermal cycling, significantly deteriorating reliability. This demonstrates that multifunctional modification of hydrogen-containing silicone oil is a necessary condition for reducing interfacial thermal resistance and improving adhesion strength.

[0070] Comparative Example 2: Boron nitride, without fluorosilane modification, exhibits a hydrophilic and oleophobic surface. It severely agglomerates in the silicone oil, forming a hydrogen bond network, resulting in a viscosity of component A reaching 15000 mPa·s, rendering it unusable for practical processing. Filler agglomeration leads to a dramatic increase in phonon scattering at the interface, reducing the thermal conductivity to 2.0 W / (m·K) and increasing the interfacial thermal resistance to 32.0 mm²·K / W. This indicates that even with modification of the base silicone oil, low viscosity and low interfacial thermal resistance cannot be achieved without matching oleophobic modification of the boron nitride surface. Comparative Example 3: Spherical alumina, without alkylsilane modification, exhibits similar characteristics to Comparative Example 2. Hydrogen bonding between hydroxyl groups on the unmodified alumina surface leads to filler agglomeration. Furthermore, the alumina particles are smaller, resulting in a larger specific surface area. The interfacial defect effect is more pronounced in the unmodified form compared to boron nitride.

[0071] Comparative Example 4 only introduced fluorinated phthalimide groups. The imide ring improved the filler dispersion and provided physical adsorption at the metal interface. The thermal conductivity and interfacial thermal resistance were improved compared to Comparative Example 1, and the peel strength was also higher than that of Comparative Example 1. However, lacking the chemical bonding of alkoxysilanes, the increase in interfacial thermal resistance and the retention rate of peel strength after long-term thermal cycling were significantly worse than those of Example 1, proving that physical adsorption alone is insufficient to resist CTE mismatch stress.

[0072] Comparative Example 5 only introduced allyltriethoxysilane. Alkoxysilane provides some chemical bonding, but lacks the strong polar adsorption and rigid anchoring of the imide ring, resulting in limited improvement in filler dispersibility. Its overall performance is inferior to that of Comparative Example 4, demonstrating that when alkoxysilane is used alone, insufficient filler dispersibility limits the improvement in thermal conductivity and interfacial properties.

[0073] In summary, this invention achieves a balance between low viscosity, low interfacial thermal resistance, moderate thermal conductivity, excellent dielectric properties, and long-term thermal cycling reliability at low filler content through a triple interface engineering design of modified hydrogen-containing silicone oil, short-chain fluorosilane-modified boron nitride, and short-chain alkylsilane-modified spherical alumina. The imide groups primarily drive filler dispersion, polar adsorption at the metal interface, and charge trap insulation enhancement, while the alkoxysilanes primarily drive chemical bonding and long-term hydrolytic stability; both are indispensable. Short-chain (C3~C6) surface modifiers are superior to long-chain (C10) modifiers in terms of thermal conductivity and interfacial thermal resistance, while long-chain modifiers are more beneficial for dielectric property optimization.

[0074] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A liquid silicone with high thermal conductivity and low interfacial thermal resistance, comprising component A and component B, characterized in that: Component A, by weight, comprises 100 parts vinyl silicone oil, 30-100 parts surface-modified boron nitride, 20-80 parts surface-modified spherical alumina, 0.05-0.1 parts inhibitor, and 0.5-0.8 parts platinum catalyst; Component B, by weight, comprises 110 parts vinyl silicone oil, 2-5 parts modified hydrogen-containing silicone oil, and 20-80 parts surface-modified spherical alumina. The modified hydrogen-containing silicone oil is the product of a hydrosilylation reaction between N-(3-butenyl)-fluorophthalimide and an alkenyl-containing alkoxysilane with the hydrogen-containing silicone oil.

2. The high thermal conductivity, low interfacial thermal resistance liquid silicone as described in claim 1, characterized in that, The vinyl silicone oil comprises high-viscosity vinyl-terminated polydimethylsiloxane and low-viscosity vinyl-terminated polydimethylsiloxane. The viscosity of the vinyl-terminated polydimethylsiloxane is 5000~20000 mPa·s, and the vinyl content is 0.25~0.5 mol%. The viscosity of the low-viscosity vinyl-terminated polydimethylsiloxane is 200~1000 mPa·s, and the vinyl content is 0.8~1.9 mol%.

3. The high thermal conductivity, low interfacial thermal resistance liquid silicone as described in claim 2, characterized in that, The mass ratio of high-viscosity end-vinyl polydimethylsiloxane to low-viscosity end-vinyl polydimethylsiloxane in the vinyl silicone oil is (3:1) to (6:1).

4. The high thermal conductivity, low interfacial thermal resistance liquid silicone as described in claim 1, characterized in that, The surface-modified boron nitride is boron nitride treated with a fluorosilane containing a fluorinated alkyl carbon chain length of C3-C6. The boron nitride is plate-shaped hexagonal boron nitride with a D50 particle size of 5-10 μm and a D90 particle size of 10-30 μm. The fluorosilane is one or more of 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, (1H,1H,2H,2H-perfluorohexyl)trimethoxysilane, and (1H,1H,2H,2H-perfluorohexyl)triethoxysilane. The amount of fluorosilane used is 1-3 wt% of the mass of boron nitride.

5. The high thermal conductivity, low interfacial thermal resistance liquid silicone as described in claim 1, characterized in that, The surface-modified spherical alumina is spherical alumina treated with alkylsilanes with an alkyl carbon chain length of C3 to C6; the D50 particle size of the spherical alumina is 1.5 to 2.5 μm, and the alkylsilanes with an alkyl carbon chain length of C3 to C6 are selected from any one of propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, or hexyltriethoxysilane, and the amount of alkylsilane used is 1 to 5 wt% of the spherical alumina.

6. The high thermal conductivity, low interfacial thermal resistance liquid silicone as described in claim 1, characterized in that, The method for preparing the N-(3-butenyl)-fluorophthalimide is as follows: fluorophthalic anhydride and 3-buten-1-amine are subjected to an imidization reaction in an aprotic organic solvent in the presence of an imidization catalyst to obtain N-(3-butenyl)-fluorophthalimide.

7. The high thermal conductivity, low interfacial thermal resistance liquid silicone as described in claim 6, characterized in that, The molar ratio of the fluorophthalic anhydride to 3-buten-1-amine is 1:(1.0~1.1); the fluorophthalic anhydride is selected from one or more of 3-fluorophthalic anhydride, 4-fluorophthalic anhydride, and 5-fluorophthalic anhydride; the imidization catalyst is 4-dimethylaminopyridine, and the amount used is 10~20 mol% of the molar amount of fluorophthalic anhydride; the aprotic organic solvent is anhydrous toluene; the imidization reaction is carried out in two steps, the first step is a pre-reaction at room temperature for 2~4 h to form an amide acid intermediate; the second step is to raise the temperature to 80~110℃ and perform a dehydration and ring-closure reaction for 8~16 h to obtain N-(3-butenyl)-4-fluorophthalimide; the dehydration is achieved by azeotropic dehydration using a water separator or in-situ adsorption dehydration using molecular sieves.

8. The high thermal conductivity, low interfacial thermal resistance liquid silicone as described in claim 6, characterized in that, The modified hydrogen-containing silicone oil is prepared by reacting N-(3-butenyl)-fluorophthalimide and an alkenyl-containing alkoxysilane with hydrogen-containing silicone oil in the presence of a platinum catalyst to obtain the modified hydrogen-containing silicone oil; the platinum catalyst is a Karstedt platinum catalyst with a platinum content of 5-20 ppm; the hydrosilylation reaction temperature is 60-90℃ and the reaction time is 4-8 h; the molar ratio of Si-H in the N-(3-butenyl)-fluorophthalimide, the alkenyl-containing alkoxysilane and the hydrogen-containing silicone oil is (0.15-0.3):(0.10-0.20):1; the hydrogen content of the hydrogen-containing silicone oil is 0.8-1.6 wt%; the alkenyl-containing alkoxysilane is selected from one or more of vinyltriethoxysilane and allyltriethoxysilane.

9. The high thermal conductivity, low interfacial thermal resistance liquid silicone as described in claim 1, characterized in that, The inhibitor is at least one of 1-ethynylcyclohexanol, 3-methyl-1-butyn-3-ol, and 3,7,11-trimethyldodecyn-3-ol, and the platinum catalyst is a Karstedt platinum catalyst.

10. The method for preparing high thermal conductivity and low interfacial thermal resistance liquid silicone according to any one of claims 1 to 9, characterized in that, Includes the following steps: (1) Component A: Vinyl silicone oil, surface-modified boron nitride, and surface-modified spherical alumina are added to a planetary mixer and stirred evenly at room temperature. The mixture is then heated to 75-85°C for vacuum degassing, cooled to below 40°C, and then mixed at low speed under vacuum with platinum catalyst and inhibitor. The mixture is then discharged, sealed, and packaged to obtain component A. (2) Component B: Add vinyl silicone oil and surface-modified spherical alumina to a planetary mixer, stir evenly at room temperature, heat to 75~85℃ for vacuum degassing, cool to below 40℃, add modified hydrogen-containing silicone oil, stir at low speed, vacuum degas, discharge and seal packaging to obtain component B.

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