A high thermal conductivity, low stress acrylic chip mounting adhesive

Abstract

This application relates to a high thermal conductivity, low stress acrylic chip mounting adhesive, belonging to the field of semiconductor chip mounting adhesive technology. The high thermal conductivity, low stress acrylic chip mounting adhesive of this application comprises: an acrylic copolymer matrix modified with polyether segments, containing alkenyl imidazole ionic liquid copolymer units; a composite thermally conductive filler surface-grafted with acryloyloxysilane, constructing a three-level hierarchical thermally conductive topology of island-bridge-network through a coupling agent; an intrinsically flame-retardant polymer, whose flame-retardant functional units are covalently integrated into the acrylic block copolymer, forming a ternary soft-segment-rigid structure system with the polyether segments and ionic liquid; and hyperbranched crosslinking monomers and star-shaped polymer functional additives; the chip mounting adhesive employs a UV-thermal dual-gradient curing system. This application exhibits excellent effects such as high thermal conductivity, low elastic modulus, UL94V-0 intrinsic flame retardancy, and antistatic properties.

Description

Technical Field

[0001] This application relates to the field of semiconductor chip mounting adhesive technology, and in particular to a high thermal conductivity, low stress acrylate chip mounting adhesive. Background Technology

[0002] With the rapid development of emerging technologies such as artificial intelligence, high-performance computing, 5G communication, and autonomous driving, semiconductor devices are rapidly evolving towards higher integration, higher power density, smaller size, and heterogeneous integration. Advanced packaging technology has become a key path to continue Moore's Law. Against this backdrop, traditional epoxy or solder-based chip mounting materials face severe challenges in terms of thermal management, mechanical reliability, and process compatibility.

[0003] On the one hand, the heat generated by high-power chips increases dramatically, requiring mounting materials to have excellent thermal conductivity;

[0004] On the other hand, the significant mismatch in the coefficient of thermal expansion between large-size chips and organic substrates can easily lead to high internal stress during temperature cycling, resulting in warping, delamination, or even solder joint breakage, which seriously threatens the long-term reliability of the device.

[0005] Regarding the aforementioned technologies, current acrylate systems are widely used in the field of electronic adhesives due to their advantages such as fast curing speed, high bonding strength, and good weather resistance. However, traditional acrylate materials generally suffer from problems such as high modulus, poor toughness, and low thermal conductivity, making it difficult to meet the dual performance requirements of high thermal conductivity and low stress for advanced packaging. In addition, existing products have shortcomings in terms of filler dispersion, ion purity, process adaptability, and reworkability, making it difficult to pass automotive-grade certification.

[0006] Therefore, developing a new type of acrylic chip mounting adhesive that combines high thermal conductivity, low elastic modulus, high purity, and excellent process adaptability has become an urgent technical problem to be solved. Summary of the Invention

[0008] The purpose of this application is to provide a high thermal conductivity, low stress acrylate chip mounting adhesive to solve the problems mentioned in the background art.

[0009] This application provides a high thermal conductivity, low stress acrylic chip mounting adhesive, which employs the following technical solution and comprises the following components:

[0010] An acrylate copolymer matrix modified with polyether segments, wherein the copolymer contains alkenyl imidazole ionic liquid copolymer units; the alkenyl imidazole ionic liquid copolymer units and polyether segments synergistically construct a flexible network, and the elastic modulus is precisely controlled by the crosslinking density;

[0011] A composite thermally conductive filler dispersed in the acrylate copolymer matrix, wherein the filler is modified by grafting acryloyloxysilane onto the surface, and the acryloyloxy end of the acryloyloxysilane participates in the free radical polymerization of the acrylate copolymer, thereby anchoring the thermally conductive filler in the copolymer matrix through covalent bonds.

[0012] The intrinsic flame-retardant polymer has flame-retardant functional units covalently integrated into an acrylate block copolymer. The block copolymer comprises an A block and a B block. The A block is composed of a flame-retardant monomer containing dynamic covalent bonds, and the B block is composed of a flame-retardant monomer containing a catalytic ceramization unit. The A block and the B block form an ordered structure through reversible addition-fragmentation chain transfer polymerization. This AB block copolymer utilizes the difference in solubility parameters between the two blocks to cause microphase separation during the curing process, allowing the B block to spontaneously migrate to the material surface to form a gradient barrier layer. This achieves a dual flame-retardant mechanism of dynamic char formation and ceramization reinforcement within the temperature range of 300-550℃.

[0013] An oligomer modifier containing olefinically unsaturated end groups, wherein the oligomer forms a covalently bonded flexible region with the acrylate copolymer matrix;

[0014] Functional additives containing reactive hyperbranched crosslinking monomers with polymerizable functional groups and star-shaped polymer structures;

[0015] The chip mounting adhesive employs a UV-thermal dual-gradient curing system. During curing, UV pre-positioning forms a first network, and thermal curing forms a second network. The two networks interpenetrate to form an interpenetrating polymer network structure, controlling the curing shrinkage rate to <1%.

[0016] The chip mounting adhesive has a thermal conductivity ≥3 W / (m·K), an elastic modulus <500 MPa, and a flame retardant rating of UL94V-0 after curing.

[0017] By adopting the above technical solutions, the synergistic effect of polyether segments and ionic liquids significantly reduces the elastic modulus; the composite thermally conductive filler is grafted with silane and covalently bonded to the resin to form an efficient thermally conductive pathway; the intrinsically flame-retardant block copolymer achieves efficient flame retardancy through dynamic borate ester crosslinking and metal-catalyzed ceramicization; UV-thermal dual curing takes into account both rapid positioning and deep crosslinking, and the synergistic effect of each component enables the chip mounting adhesive to simultaneously possess excellent properties such as high thermal conductivity, low modulus, intrinsic flame retardancy, high purity, and low shrinkage.

[0018] Preferably, the composite thermally conductive filler is constructed using a silane coupling agent to form a three-level hierarchical thermally conductive topology of island-bridge-network;

[0019] The heat-conducting island is composed of one or more micron-sized high thermal conductivity particles selected from spherical alumina, aluminum nitride, silicon carbide, and diamond powder.

[0020] The flexible bridge is composed of one or more thermally conductive materials selected from boron nitride nanosheets, graphene nanosheets, carbon nanotubes, and molybdenum disulfide nanosheets.

[0021] The covalently linked network is formed by in-situ polymerization of one or more coupling agents that can participate in free radical polymerization at the bridge-island interface, wherein the coupling agent is selected from at least one of acryloyloxysilane, vinylsilane, acryloyloxytitanate, and vinylaluminate.

[0022] By adopting the above technical solution, namely, using silane coupling agents to construct a three-level hierarchical thermal conductive topology of island-bridge-network, micron-sized particles serve as thermal conductive islands, nano-sized sheets / tubes serve as flexible bridges, and coupling agents are polymerized in situ to form a covalent network, a stable thermal conductivity is achieved under high filling conditions, while maintaining good rheological properties.

[0023] Preferably, the A block of the intrinsic flame retardant polymer is an intumescent dynamic crosslinking block, which is composed of an acrylate monomer containing a borate ester dynamic covalent bond and a flame retardant monomer containing a nitrogen heterocycle;

[0024] The acrylate monomer containing the dynamic covalent bond of the borate ester is at least one of 4-vinylphenylboronic acid or hydroxyethyl methacrylate ester formed by esterification with borate;

[0025] The nitrogen-containing heterocyclic flame-retardant monomer is selected from at least one of vinylimidazole, N-vinylpyrrolidone, and acrylamide.

[0026] By adopting the above technical solution, namely, the dynamic bonds of borate esters in the A block provide reversible crosslinking and expansion into char, and nitrogen-containing heterocycles synergistically foam, boric acid is released at 300-400℃ to form a boron-carbon glassy char layer, thus achieving early expansion and flame retardancy.

[0027] Preferably, the B block of the intrinsic flame retardant polymer is a catalytic ceramic block, which is composed of a metal acrylate monomer and a pyrolytically convertible monomer.

[0028] The metal-containing acrylate monomer is selected from at least one of zinc acrylate, copper methacrylate, and iron acrylate.

[0029] The pyrolytically convertible monomer is selected from at least one of methacryloyloxypropyltrimethoxysilane, vinyltriethoxysilane, and acrylate phosphate.

[0030] By adopting the above technical solution, the metal acrylate in the B block decomposes at 400-550℃ to generate metal oxide, which catalyzes the carbonization of the polymer and combines with silica or phosphate formed by the pyrolytically convertible monomers to generate a continuous and dense ceramicized composite layer in situ, thereby achieving high-temperature ceramicized barrier.

[0031] Preferably, the intrinsic flame-retardant polymer has its molecular structure constructed through the following steps:

[0032] Covalent clustering: By controlling the ratio of A-block to B-block through reversible addition-fragmentation chain transfer polymerization, the dynamic bonds of borate esters and metal coordination nodes are used to form nanoscale hybrid clusters within the molecule;

[0033] Self-assembling flame-retardant barrier: Utilizing the difference in solubility parameters between A-block and B-block, phase separation is induced during curing or heat exposure, causing B-block to spontaneously migrate to the material surface and form a gradient barrier layer;

[0034] Dynamic carbonization and ceramic enhancement: At 300-400℃, A-block borate esters release boric acid to form a boron-carbon glassy carbon layer. At 400-550℃, B-block metal coordination units decompose to generate metal oxides and combine with pyrolytically convertible monomers to form a continuous and dense ceramic composite layer in situ.

[0035] By adopting the above technical solution, namely the three-step molecular architecture, the A block and the B block work together: at low temperature, the A block expands into carbon, and at high temperature, the B block is ceramicized and strengthened, forming a double-layer gradient barrier structure of expanded carbon layer and ceramic hardened layer.

[0036] Preferably, the oligomer modifier containing olefinic unsaturated end groups, together with the polyether segment and the alkenyl imidazole ionic liquid copolymer unit, constitutes a ternary soft segment-rigid structure system of polyether-ionic liquid-oligomer.

[0037] By adopting the above technical solution, in which polyether segments, ionic liquids and oligomer modifiers form an alternating structure of soft and rigid segments through covalent bonds, the bonding strength is maintained while the elongation at break is guaranteed, thus achieving a balance between high toughness and low stress.

[0038] Preferably, the oligomer modifier in the ternary soft segment-rigid structure system is selected from one or more of polyethylene glycol diacrylate, polytetrahydrofuran diacrylate, polycaprolactone diacrylate, or isocyanate prepolymer modified acrylate oligomers.

[0039] By adopting the above technical solution, in which the oligomer modifier is selected from common difunctional acrylate or isocyanate prepolymers, and copolymerized with polyether segments and ionic liquids to form a uniform ternary network, the flexibility and impact resistance of the system are further improved.

[0040] Preferably, the precise control of the crosslinking density is achieved by adjusting the weight ratio of the hyperbranched crosslinking monomer to the oligomer modifier, wherein the functionality of the hyperbranched crosslinking monomer is 3-12, the number average molecular weight of the oligomer modifier is 500-5000, and the weight ratio of the two is (5-15):(0.5-5).

[0041] By adopting the above technical solution, namely by adjusting the weight ratio of hyperbranched crosslinking monomers to oligomer modifiers, the crosslinking density can be precisely controlled, thereby reducing the elastic modulus while maintaining excellent bonding strength.

[0042] Preferably, the composite thermally conductive filler is functionalized in situ with acryloyloxysilane and achieves high filling capacity and high thermal conductivity through a multi-scale compounding method;

[0043] The multi-scale compounding specifically refers to the composite thermally conductive filler comprising nano-sized boron nitride and micron-sized spherical alumina, with a mass ratio of 1:(2-4), forming a tightly packed thermally conductive network through the multi-scale compounding.

[0044] The nanoscale thermally conductive filler is composed of one or more of boron nitride nanosheets, graphene nanosheets, carbon nanotubes, and molybdenum disulfide nanosheets.

[0045] The micron-sized thermally conductive filler is composed of one or more of spherical alumina, aluminum nitride, silicon carbide, and diamond powder.

[0046] By adopting the above technical solution, namely, multi-scale compounding of nano-sized boron nitride and micron-sized spherical alumina in a mass ratio to form a tightly packed thermally conductive network, combined with in-situ functionalization of silane, good rheological properties and thermal conductivity are maintained even under high filling conditions.

[0047] In addition, this application also provides a method for preparing a high thermal conductivity, low stress acrylate chip mounting adhesive, comprising the following steps:

[0048] S1. Resin Synthesis: Polyether-modified acrylate monomers, alkenyl imidazole ionic liquids, oligomer modifiers containing olefinic unsaturated end groups, hyperbranched crosslinking monomers, star-shaped polymer functional additives, phenyl ethane compounds, and free radical initiators are subjected to living radical polymerization in a benzene-free solvent system to obtain narrow-distribution acrylate copolymers.

[0049] S2. Preparation of intrinsic flame-retardant block copolymers: Block A and block B were prepared by reversible addition-fragmentation chain transfer polymerization. Block A was composed of a borate ester dynamic covalent bond acrylate monomer and a nitrogen-containing heterocyclic flame-retardant monomer, while block B was composed of a metal-containing acrylate monomer and a pyrolytically convertible monomer. The prepared blocks A and B were chain extended by reversible addition-fragmentation chain transfer polymerization to obtain AB-type intrinsic flame-retardant block copolymers.

[0050] S3. Filler modification: Nanoscale thermally conductive fillers and micron-scale thermally conductive fillers are mixed in proportion, and a coupling agent is added for surface grafting modification to obtain a modified composite filler with an island-bridge-network structure.

[0051] S4. Adhesive preparation and post-treatment: Mix the copolymer obtained in step S1, the intrinsic flame-retardant block copolymer obtained in step S2, and the modified composite filler obtained in step S3, disperse them evenly, and degas them under vacuum to obtain the chip mounting adhesive.

[0052] By adopting the above technical solution, namely, step S1 uses a composite initiation system composed of phenyl ethane compounds and free radical initiators to utilize chain transfer and controlled termination mechanisms to significantly reduce the molecular weight distribution (Đ) to 1.2-1.5, constructing a narrow-distribution, low-modulus ternary soft-segment-rigid structure matrix, providing excellent stress buffering capacity for the adhesive and increasing its bonding strength by 25%, while its high-temperature resistance jumps from 80℃ to 120℃; S2 prepares AB-type intrinsically flame-retardant block copolymers through reversible addition-fracture chain transfer polymerization, achieving halogen-free, droplet-free UL94 V-0 flame retardancy at ultra-low addition levels, and improving peel strength to ≥15 N / 25mm; S3 modifies the surface of the nano-micro multi-scale thermally conductive filler by grafting with a coupling agent to construct a three-level hierarchical thermally conductive topology of island-bridge-network; S4 integrates the above three components through covalent bonds and interpenetrating networks, and combines UV-thermal dual gradient curing and semiconductor-grade cleanroom control to obtain a high-reliability chip mounting adhesive that simultaneously meets the requirements of high thermal conductivity, low stress, high flame retardancy, high purity and low shrinkage.

[0053] In summary, this application includes at least one of the following beneficial technical effects:

[0054] 1. This application copolymerizes polyether segments with alkenyl imidazole ionic liquids and controls the crosslinking density by adjusting the ratio of hyperbranched crosslinking monomers to oligomer modifiers to form a polyether-ionic liquid-oligomer ternary soft segment-rigid structure system. This structure maintains the bonding strength while allowing the elastic modulus to be precisely reduced, and at the same time improves the elongation at break, significantly alleviating the internal stress caused by mismatch between the chip and the substrate, and effectively suppressing packaging warpage and interface delamination.

[0055] 2. This application modifies the surface of micron-sized spherical alumina and nano-sized boron nitride by acryloyloxysilane to construct a three-level hierarchical thermal conductivity topology of island-bridge-network. Specifically, micron-sized alumina serves as the thermal conductivity island, nano-sized boron nitride serves as the flexible bridge, and a covalently bonded network is formed by in-situ polymerization of silane coupling agent. This achieves high thermal conductivity at high filling rate while maintaining good rheological properties, thus resolving the contradiction between high filling rate and low viscosity.

[0056] 3. This application prepares AB-type intrinsic flame-retardant block copolymers via reversible addition-fragmentation chain transfer polymerization. Block A contains dynamic covalent bonds of borate esters and nitrogen-containing heterocycles, while block B contains metal acrylates and pyrolytically convertible monomers. Specifically, at 300-400℃, block A releases boric acid to form a boron-carbon glassy expanded char layer, and at 400-550℃, block B generates metal oxides and forms a continuous ceramicized composite layer with silane pyrolysis products. This achieves UL94V-0 flame retardancy rating and improves limiting oxygen index and char formation rate, while completely avoiding the damage to interfacial properties caused by physically blending flame retardants.

[0057] 4. This application adopts a UV-thermal dual gradient curing system, that is, firstly, ultraviolet light is used for rapid pre-positioning, and then heating is used for deep cross-linking to form an interpenetrating polymer network structure, which reduces curing shrinkage and warpage. At the same time, it is combined with benzene-free process and semiconductor-grade cleanroom control to meet the requirements of advanced packaging for high precision, high reliability and green manufacturing.

[0058] 5. This application utilizes alkenyl imidazole ionic liquids to participate in the in-situ copolymerization of acrylates, forming a continuous ionic conductive network in the resin matrix, reducing the surface resistivity of the colloid, and effectively suppressing electrostatic adsorption problems during the handling and mounting of micron-sized chips. Attached Figure Description

[0059] Figure 1 This is a comparison chart of the performance indicators of the embodiments of this application and the comparative benchmark. Detailed Implementation

[0060] The following is in conjunction with the appendix Figure 1 This application will be described in further detail below.

[0061] Example 1:

[0062] This embodiment provides a high thermal conductivity, low stress acrylate chip mounting adhesive, the preparation method of which includes the following steps:

[0063] S1, Resin Synthesis

[0064] Under nitrogen protection, add the following monomers and additives—by weight—to a three-necked flask equipped with a stirrer, condenser, and thermometer:

[0065] PPG400 diacrylate - 43.5 parts;

[0066] 1-Vinyl-3-ethylimidazolium tetrafluoroborate - 8.7 parts;

[0067] Polyethylene glycol diacrylate - 6.5 parts;

[0068] Hyperbranched crosslinked monomer - 4.3 parts, with acryloyloxy end groups;

[0069] Star-shaped polyacrylate - 2.2 parts, 4 arms;

[0070] 1,1-Diphenylethylene - 0.9 parts;

[0071] Azobisisobutyronitrile - 0.4 parts.

[0072] The above components were dissolved in benzene-free solvent, namely ethyl acetate, and reacted at 60-70℃ for 6 hours to obtain an acrylate copolymer matrix, which was designated as component A.

[0073] This step uses an integrated initiation-transfer-termination composite initiation system composed of 1,1-diphenylethylene and azobisisobutyronitrile. Through chain transfer and controlled termination mechanisms, the molecular weight distribution of the polymer is significantly narrowed. The core performance comparison is as follows.

[0074] Performance indicators Composite initiation system Comparative Example 1: Single AIBN Increase Molecular weight distribution (Đ) 1.35 2.8 52% reduction Bond strength (MPa) 28.0 22.4 Increase by 25% Thermal decomposition temperature (Td, 5%, °C) ≥120 80 Increase by 40%

[0075] In the table above, the narrow molecular weight distribution achieved through the composite initiation system enables the chip mounting adhesive to maintain a high bonding strength of ≥25MPa while its high temperature resistance jumps from 80℃ to over 120℃. This breakthrough directly meets the stringent requirements of AI / HPC chips for thermal stability under high power conditions, avoids the bonding failure caused by high temperature degradation of traditional adhesives, and provides a fundamental guarantee for the long-term reliable operation of the chip.

[0076] S2. Preparation of intrinsic flame-retardant block copolymers

[0077] A-block and B-block were prepared by reversible addition-fragmentation chain transfer polymerization:

[0078] Block A: 1.9 parts of 4-vinylphenylboronic acid, 0.9 parts of N-vinylpyrrolidone, 0.04 parts of benzyl dithiobenzoate reagent, and 0.01 parts of azobisisobutyronitrile were polymerized at 60-70℃ for 8 hours to obtain an expanded dynamic crosslinked block containing borate ester dynamic covalent bonds and nitrogen-containing heterocycles.

[0079] Block B: 1.5 parts of zinc acrylate, 2.3 parts of methacryloyloxypropyltrimethoxysilane, 0.04 parts of benzyl dithiobenzoate reagent and 0.01 parts of azobisisobutyronitrile were polymerized at 60-70℃ for 8 hours to obtain a catalytic ceramic block containing metal acrylate and a pyrolytically convertible monomer.

[0080] The above A block and B block were mixed at a mass ratio of 1:1, and 0.01 parts of initiator azobisisobutyronitrile were added. The mixture was then subjected to chain extension polymerization at 65-70℃ for 4 hours to obtain an AB type intrinsic flame retardant block copolymer, which was designated as component B.

[0081] Performance indicators A / B block copolymer Comparative Example 2: Phosphorus monomer only Increase Flame retardant rating (1.0mm) V - 0, no molten droplets V - 2, with molten droplets — Limiting oxygen index (%) 36.2 26.0 Increased by 39% Carbonization rate at 800℃ (%) 47 28 Increased by 68%

[0082] This embodiment overcomes the shortcomings of traditional physical blending of flame retardants, which easily leads to interface weakening. By chemically bonding flame retardant elements to the main chain of block copolymers through covalent bonds, it achieves intrinsic flame retardancy of UL94V-0 level and limiting oxygen index ≥36%. Compared with traditional phosphorus-containing flame retardants, it completely avoids interface weakening and mechanical property degradation caused by physical blending. At the same time, it endows the material with high-temperature ceramic self-healing ability. In addition, the boronic acid ester dynamic bond of the A block provides reversible cross-linking and expansion charring ability, while the metal acrylate of the B block decomposes at high temperature to generate metal oxides, which combine with silica or phosphate formed by pyrolytically convertible monomers to generate a continuous and dense ceramic composite layer in situ, realizing a performance leap from charring self-extinguishing to ceramic barrier.

[0083] S3, Filler Modification and Compounding

[0084] Nanoscale thermally conductive filler: Boron nitride nanosheets - 8.7 parts;

[0085] Micron-sized thermally conductive filler: 26.1 parts of spherical alumina.

[0086] The two were mixed at a mass ratio of 1:3, and 2.2 parts of acryloyloxysilane and 1.3 parts of vinyltriethoxysilane were added. The mixture was stirred and reacted in a mixed solvent of ethanol and water at 50-60℃ for 2 hours. After drying, a modified composite filler with a three-level hierarchical structure of island-bridge-network was obtained and denoted as component C.

[0087] In this process, micron-sized spherical alumina serves as a heat-conducting island, providing heat flow buffers and lateral diffusion nodes; nano-sized boron nitride acts as a flexible bridge, overlapping adjacent alumina islands along the thickness direction to form directional heat-conducting channels; silane coupling agents are polymerized in situ at the bridge-island interface to form a covalently bonded network, fixing the topology and suppressing interfacial phonon scattering. This step involves surface grafting modification of the filler with acryloyloxysilane to achieve in-situ functionalization of the filler, ensuring that the thermally conductive filler can form covalent bonds with the resin matrix under high filling rates, thus constructing an efficient heat-conducting pathway while maintaining good rheological properties.

[0088] S4, Rubber Mixing and Post-processing

[0089] Mix the following components in a dual planetary mixer:

[0090] Resin obtained from component A-S1: 42.9 parts;

[0091] Flame-retardant block copolymer obtained from component B-S2: 4.2 parts;

[0092] Modified composite filler obtained from component C-S3: 51.5 parts;

[0093] Photoinitiator: 0.9 parts;

[0094] Thermal initiator: 0.4 parts;

[0095] The above materials are mixed in a double planetary mixer and vacuum degassed for 30 minutes to obtain chip mounting adhesive.

[0096] Curing Process: This embodiment adopts a UV-thermal dual gradient curing process. First, pre-positioning curing is performed by UV irradiation for rapid positioning. The UV wavelength is 350-380nm, the light intensity is 100-300mW / cm², and the irradiation time is 10-60 seconds. Second, deep cross-linking curing is performed by heating. The thermal curing temperature is 100-150℃, and the time is 10-60 minutes. During the curing process, microphase separation occurs between the A block and the B block. The B block spontaneously migrates to the material surface to form a 10-20nm gradient barrier layer. At the same time, the first polyacrylate network formed by UV curing and the second polyacrylate network formed by thermal curing interpenetrate with each other to form an interpenetrating polymer network structure, which effectively suppresses warping deformation after chip mounting.

[0097] Purity and Environmental Protection: No benzene solvents were used in the entire preparation process in this embodiment. The ethyl acetate used in S1 is a low-toxicity and environmentally friendly solvent, and it can be fully removed by vacuum degassing after the gel is prepared. The use of benzene solvents is eliminated from the polymerization source, ensuring that the product is suitable for cleanroom environments.

[0098] Antistatic performance description: Due to the participation of alkenyl imidazole ionic liquid in S1 in the in-situ copolymerization of acrylate, a continuous ionic conductive network is formed in the resin matrix, reducing the surface resistivity of the colloidal material to ≤10. 8 Ω effectively suppresses electrostatic adsorption during the handling and mounting of micron-sized chips, effectively inhibiting the interference of electrostatic adsorption on the handling and mounting of micron-sized chips; at the same time, the bonding strength reaches ≥25MPa, and the temperature resistance is simultaneously improved to 120℃, comprehensively exceeding the performance boundaries of traditional materials.

[0099] The performance test results for Example 1 are shown in the table below:

[0100] Performance indicators Example 1 Test methods thermal conductivity 3.8 W / (m·K) ASTM D5470 elastic modulus 320 MPa DMA Bond strength 28 MPa Chip push cutter Elongation at break 18 % ASTM D638 Curing shrinkage 0.7 % Density method Flame retardant rating V - 0 (1.0mm, no dripping) UL94 Limiting oxygen index 36.2 % GB / T 2406 Carbonization rate (800℃) 47 % TGA Surface resistivity <![CDATA[6×10 7 Oh]]> GB / T 1410 Total metal ion content Na⁺<0.2, K⁺<0.1, Cl⁻<0.5 ppm ICP - MS Viscosity (25℃, 10rpm) 38 Pa·s Rotational viscometer

[0101] As can be seen from the above performance data, Example 1 achieved a narrow molecular weight distribution by introducing a composite initiation system composed of 1,1-diphenylethylene and azobisisobutyronitrile during the resin synthesis stage, thereby increasing the bonding strength to 28 MPa and the temperature resistance to 120°C. The A / B block intrinsic flame-retardant copolymer prepared by reversible addition-fragmentation chain transfer polymerization achieved a UL94V-0 flame retardant rating, a limiting oxygen index of 36.2%, and a char rate of 47% at ultra-low addition levels. Through a three-level hierarchical thermally conductive topology of island-bridge-network, good processability was achieved with a thermal conductivity of 3.8 W / (m·K) and a viscosity of 38 Pa·s at a 65 vol% filler content. Combined with UV-thermal dual curing to form an interpenetrating polymer network, the curing shrinkage rate was controlled at 0.7%. Furthermore, the total metal ion content was <1 ppm and the surface resistivity was 6 × 10⁻⁶. 7 Ω fully meets the comprehensive requirements of semiconductor packaging for high thermal conductivity, low stress, intrinsic flame retardancy, high purity and low shrinkage.

[0102] Example 2

[0103] The main difference between this embodiment and Embodiment 1 is that the proportions of each component in the ternary soft segment-rigid structure system are adjusted to further optimize the balance between elastic modulus and bonding strength.

[0104] S1, Resin Synthesis

[0105] Under nitrogen protection, the following monomers and additives are added to the reactor:

[0106] PPG600 diacrylate - 50.0 parts;

[0107] 1-Vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt - 6.0 parts;

[0108] Polytetrahydrofuran diacrylate - 8.0 parts;

[0109] Hyperbranched crosslinking monomer - 3.5 parts, with methacryloyloxy end group;

[0110] Star-shaped polyacrylate - 1.5 parts, 6 arms;

[0111] 1,1-Diphenylethylene - 0.8 parts;

[0112] 0.5 parts of tert-butyl peroxide.

[0113] The above components were dissolved in a mixed solvent of ethyl acetate and propylene glycol methyl ether acetate and reacted at 75°C for 5 hours to obtain an acrylate copolymer matrix, denoted as component A-2.

[0114] This embodiment further reduces the crosslinking density by lowering the ratio of hyperbranched crosslinking monomers to oligomer modifiers. At the same time, the use of higher molecular weight polyether segments and more compliant polytetrahydrofuran segments significantly improves the flexibility of the resin matrix.

[0115] S2. Preparation of intrinsic flame-retardant block copolymers

[0116] The process is basically the same as in Example 1, except that: in block A, 1.2 parts of vinylimidazole are used to replace N-vinylpyrrolidone, and in block B, 1.0 parts of copper methacrylate and 0.8 parts of iron acrylate are used to replace zinc acrylate. The rest of the operation is the same, and an AB-type intrinsic flame-retardant block copolymer is obtained, which is denoted as component B-2.

[0117] S3, Filler Modification and Compounding

[0118] The process is essentially the same as in Example 1, except that: 2.0 parts of carbon nanotubes and 6.0 parts of boron nitride nanosheets are added to the nanoscale filler; 24.0 parts of spherical alumina and 4.0 parts of diamond powder are used as the micron-scale filler; and 1.8 parts of acryloyloxytitanate and 1.0 parts of vinylsilane are used as the coupling agent. All other operations are the same, resulting in a modified composite filler, denoted as component C-2.

[0119] S4, Rubber Mixing and Post-processing

[0120] Component A-2: 45.0 parts;

[0121] Component B-2: 3.5 parts;

[0122] Component C-2: 50.0 parts;

[0123] Photoinitiator: 0.8 parts;

[0124] Thermal initiator: 0.7 parts.

[0125] The performance test results for Example 2 are shown in the table below:

[0126] Test Project Example 2 Example 1 range of change thermal conductivity 3.9 W / (m·K) 3.8W / (m·K) +0.1 W / (m·K) elastic modulus 210MPa 320MPa -34% Bond strength 24MPa 28MPa -14% Elongation at break 25 % 18 % +39% Curing shrinkage 0.6 % 0.7 % improve

[0127] As can be seen from the table above, by precisely controlling the ratio of hyperbranched crosslinking monomers to oligomer modifiers, Example 2 reduced the elastic modulus to 210 MPa, while increasing the elongation at break to 25%, and the bond strength decreased by only 14%. This balance of high toughness, extremely low stress, and maintained strength can effectively absorb thermal cycling stress, prevent interfacial fatigue delamination, and at the same time slightly improve the thermal conductivity and further improve the curing shrinkage rate.

[0128] Example 3

[0129] The main difference between this embodiment and Embodiment 1 is that the particle size distribution and surface modification process of the thermally conductive filler are optimized, and the construction effect of the island-bridge-network three-level hierarchical thermally conductive topology is highlighted.

[0130] S1, Resin Synthesis

[0131] The process is basically the same as in Example 1, except that 8.0 parts of polycaprolactone diacrylate are used to replace part of the polyethylene glycol diacrylate to enhance the interfacial compatibility with the hydrophobic filler. The remaining components and operations are the same as in Example 1, and an acrylate copolymer matrix is ​​obtained, which is denoted as component A-3.

[0132] S2. Preparation of intrinsic flame-retardant block copolymers

[0133] Similar to Example 1, component B-3 was obtained.

[0134] S3, Filler Modification and Compounding

[0135] This embodiment focuses on optimizing the three-level hierarchical structure of the thermally conductive filler:

[0136] Thermal island: It is made of three different micron-sized spherical alumina composites - 15 parts with a median particle size of 20 microns, 25 parts with a median particle size of 5 microns, and 10 parts with a median particle size of 0.5 microns, forming a densely packed system from coarse to fine, with a mass ratio of about 3:5:2.

[0137] Flexible bridge: It is made of 12 parts boron nitride nanosheets and 3 parts graphene nanosheets in a mass ratio of 4:1. The aspect ratio of the nanosheets is about 200 for boron nitride nanosheets and about 500 for graphene nanosheets, which effectively bridges the gaps between micron-sized particles.

[0138] Covalent network: A thermally conductive network formed by in-situ polymerization of 3.5 parts acryloyloxysilane and 1.5 parts vinyltriethoxysilane on the filler surface using covalent bonds.

[0139] The above filler and coupling agent were stirred and reacted in a mixed solvent of ethanol and water at 50-60℃ for 3 hours. After drying, a modified composite filler with a complete island-bridge-network structure was obtained, denoted as component C-3.

[0140] S4, Rubber Mixing and Post-processing

[0141] Component A-3: 38.0 parts;

[0142] Component B-3: 4.0 parts;

[0143] Component C-3: 56.5 parts;

[0144] Photoinitiator: 0.8 parts;

[0145] Thermal initiator: 0.7 parts.

[0146] The performance test results for Example 3 are shown in the table below:

[0147] Test Project Example 3 Example 1 range of change thermal conductivity 4.5W / (m·K) 3.8W / (m·K) +18% elastic modulus 350MPa 320MPa +9% Bond strength 27MPa 28MPa -4% Elongation at break 15 % 18 % -17% Viscosity (25℃, 10rpm) 45 Pa·s 38Pa·s +18%

[0148] The beneficial effects of Example 3 are explained as follows: This example constructs a complete three-level hierarchical thermally conductive topology consisting of "thermal island-three-level particle size gradation alumina, flexible bridge-boron nitride nanosheets and graphene nanosheets, and covalent network-silane in-situ polymerization". Under the extreme condition that the total filling amount exceeds 70 vol%, Example 3 still achieves a high thermal conductivity of 4.5 W / (m·K), which is 18% higher than that of Example 1. It also maintains a good dispensing viscosity of 45 Pa·s and an elongation at break of 15%. At the same time, the covalently bonded island-bridge-network structure ensures thermal conductivity stability during thermal cycling and avoids performance degradation caused by filler migration. The close packing system formed by the three particle size gradations effectively reduces the voids between fillers. The synergistic effect of the flexible bridging of nanosheets and the covalent network maximizes the construction of phonon transport paths while maintaining good process rheology and mechanical properties.

[0149] The performance tests are summarized in the table below:

[0150] Test Project Example 1 Example 2 Example 3 Comparison benchmark Thermal conductivity W / (m·K) 3.8 3.9 4.5 1.8 Elastic modulus (MPa) 320 210 350 820 Bond strength (MPa) 28 24 27 22.4 Elongation at break % 18 25 15 9 Curing shrinkage rate % 0.7 0.6 0.6 3.2 Flame retardant rating 1.0 V - 0 V - 0 V - 0 V -2

[0151] From the table above and Figure 1 As can be seen from the above, this application achieves a breakthrough in comprehensive performance of high thermal conductivity, low modulus and high flame retardancy through multi-dimensional synergistic innovation, such as composite initiation system, intrinsic flame retardant block copolymer, island-bridge-network thermally conductive topology, ternary soft segment-rigid crosslinking regulation and UV-thermal dual curing. Examples 1-3 respectively verify the feasibility of the basic scheme, flexibility optimization and thermal conductivity limit exploration, which can be adjusted in a targeted manner according to different packaging scenarios.

Claims

1. A high thermal conductivity, low stress acrylic chip mounting adhesive, characterized in that, Includes the following components: An acrylate copolymer matrix modified with polyether segments, wherein the copolymer contains alkenyl imidazole ionic liquid copolymer units; the alkenyl imidazole ionic liquid copolymer units and polyether segments synergistically construct a flexible network, and the elastic modulus is precisely controlled by the crosslinking density; A composite thermally conductive filler dispersed in the acrylate copolymer matrix, wherein the filler is modified by grafting acryloyloxysilane onto the surface, and the acryloyloxy end of the acryloyloxysilane participates in the free radical polymerization of the acrylate copolymer, thereby anchoring the thermally conductive filler in the copolymer matrix through covalent bonds. Intrinsic flame-retardant polymers, wherein flame-retardant functional units are covalently integrated in acrylate block copolymers, the block copolymers comprising A blocks and B blocks, wherein A blocks are composed of flame-retardant monomers containing dynamic covalent bonds, and B blocks are composed of flame-retardant monomers containing catalytic ceramicization units, and A blocks and B blocks form an ordered structure through reversible addition-fragmentation chain transfer polymerization. An oligomer modifier containing olefinically unsaturated end groups, wherein the oligomer forms a covalently bonded flexible region with the acrylate copolymer matrix; Functional additives containing reactive hyperbranched crosslinking monomers with polymerizable functional groups and star-shaped polymer structures; The chip mounting adhesive uses a UV-thermal dual gradient curing system; The chip mounting adhesive has a thermal conductivity ≥3 W / (m·K), an elastic modulus <500 MPa, and a flame retardant rating of UL94V-0 after curing.

2. The high thermal conductivity, low stress acrylic chip mounting adhesive according to claim 1, characterized in that, The composite thermally conductive filler is constructed using a silane coupling agent to create a three-level hierarchical thermally conductive topology of island-bridge-network. The heat-conducting island is composed of one or more micron-sized high thermal conductivity particles selected from spherical alumina, aluminum nitride, silicon carbide, and diamond powder. The flexible bridge is composed of one or more thermally conductive materials selected from boron nitride nanosheets, graphene nanosheets, carbon nanotubes, and molybdenum disulfide nanosheets. The covalently linked network is formed by in-situ polymerization of one or more coupling agents that can participate in free radical polymerization at the bridge-island interface, wherein the coupling agent is selected from at least one of acryloyloxysilane, vinylsilane, acryloyloxytitanate, and vinylaluminate.

3. The high thermal conductivity, low stress acrylic chip mounting adhesive according to claim 1, characterized in that, The A block of the intrinsic flame retardant polymer is an intumescent dynamic crosslinking block, which is composed of an acrylate monomer containing a borate ester dynamic covalent bond and a flame retardant monomer containing a nitrogen heterocycle. The acrylate monomer containing the dynamic covalent bond of the borate ester is at least one of 4-vinylphenylboronic acid or hydroxyethyl methacrylate ester formed by esterification with borate; The nitrogen-containing heterocyclic flame-retardant monomer is selected from at least one of vinylimidazole, N-vinylpyrrolidone, and acrylamide.

4. The high thermal conductivity, low stress acrylic chip mounting adhesive according to claim 1, characterized in that, The B-block of the intrinsic flame retardant polymer is a catalytic ceramic block, which is composed of a metal acrylate monomer and a pyrolytically convertible monomer. The metal-containing acrylate monomer is selected from at least one of zinc acrylate, copper methacrylate, and iron acrylate. The pyrolytically convertible monomer is selected from at least one of methacryloyloxypropyltrimethoxysilane, vinyltriethoxysilane, and acrylate phosphate.

5. The high thermal conductivity, low stress acrylic chip mounting adhesive according to claim 1, characterized in that, The intrinsic flame-retardant polymer is constructed into a molecular structure through the following steps: Covalent clustering: By controlling the ratio of A-block to B-block through reversible addition-fragmentation chain transfer polymerization, the dynamic bonds of borate esters and metal coordination nodes are used to form nanoscale hybrid clusters within the molecule; Self-assembling flame-retardant barrier: Utilizing the difference in solubility parameters between A-block and B-block, phase separation is induced during curing or heat exposure, causing B-block to spontaneously migrate to the material surface and form a gradient barrier layer; Dynamic carbonization and ceramic enhancement: At 300-400℃, A-block borate esters release boric acid to form a boron-carbon glassy carbon layer. At 400-550℃, B-block metal coordination units decompose to generate metal oxides and combine with pyrolytically convertible monomers to form a continuous and dense ceramic composite layer in situ.

6. The high thermal conductivity, low stress acrylic chip mounting adhesive according to claim 1, characterized in that, The oligomer modifier containing olefinic unsaturated end groups, together with the polyether segments and the alkenyl imidazole ionic liquid copolymerization unit, constitutes a ternary soft segment-rigid structure system of polyether-ionic liquid-oligomer.

7. The high thermal conductivity, low stress acrylic chip mounting adhesive according to claim 6, characterized in that, In the ternary soft segment-rigid structure system, the oligomer modifier is selected from one or more of polyethylene glycol diacrylate, polytetrahydrofuran diacrylate, polycaprolactone diacrylate, or isocyanate prepolymer modified acrylate oligomers.

8. The high thermal conductivity, low stress acrylic chip mounting adhesive according to claim 1, characterized in that, The precise control of the crosslinking density is achieved by adjusting the weight ratio of the hyperbranched crosslinking monomer to the oligomer modifier. The functionality of the hyperbranched crosslinking monomer is 3-12, and the number average molecular weight of the oligomer modifier is 500-5000. The weight ratio of the two is (5-15):(0.5-5).

9. The high thermal conductivity, low stress acrylic chip mounting adhesive according to claim 1, characterized in that, The composite thermally conductive filler is functionalized in situ with acryloyloxysilane and achieves high filling capacity and high thermal conductivity through multi-scale compounding. The multi-scale compounding specifically refers to the following: the composite thermally conductive filler includes nano-scale thermally conductive filler and micro-scale thermally conductive filler, with a mass ratio of 1:(2-4). Through the multi-scale compounding, a tightly packed thermally conductive network is formed. The nanoscale thermally conductive filler is composed of one or more of boron nitride nanosheets, graphene nanosheets, carbon nanotubes, and molybdenum disulfide nanosheets. The micron-sized thermally conductive filler is composed of one or more of spherical alumina, aluminum nitride, silicon carbide, and diamond powder.

10. A method for preparing a high thermal conductivity, low stress acrylate chip mounting adhesive, characterized in that, The preparation of the high thermal conductivity, low stress acrylate chip mounting adhesive according to any one of claims 1-9 comprises the following steps: S1. Resin Synthesis: Polyether-modified acrylate monomers, alkenyl imidazole ionic liquids, oligomer modifiers containing olefinic unsaturated end groups, hyperbranched crosslinking monomers, star-shaped polymer functional additives, phenyl ethane compounds, and free radical initiators are subjected to living radical polymerization in a benzene-free solvent system to obtain narrow-distribution acrylate copolymers. S2. Preparation of intrinsic flame-retardant block copolymers: Block A and block B were prepared by reversible addition-fragmentation chain transfer polymerization. Block A was composed of a borate ester dynamic covalent bond acrylate monomer and a nitrogen-containing heterocyclic flame-retardant monomer, while block B was composed of a metal-containing acrylate monomer and a pyrolytically convertible monomer. The prepared blocks A and B were chain extended by reversible addition-fragmentation chain transfer polymerization to obtain AB-type intrinsic flame-retardant block copolymers. S3. Filler modification: Nanoscale thermally conductive fillers and micron-scale thermally conductive fillers are mixed in proportion, and a coupling agent is added for surface grafting modification to obtain a modified composite filler with an island-bridge-network structure. S4. Adhesive preparation and post-treatment: Mix the copolymer obtained in step S1, the intrinsic flame-retardant block copolymer obtained in step S2, and the modified composite filler obtained in step S3, disperse them evenly, and degas them under vacuum to obtain the chip mounting adhesive.

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