Low-dielectric adhesive and preparation method thereof

Abstract

The invention discloses a low-dielectric adhesive and a preparation method thereof, and relates to the field of adhesives, the preparation method comprises the following steps: carrying out chemical modification on the surface of a silica filler a to obtain a silica filler b with an organic molecular layer on the surface; wherein the surface of the silicon dioxide filler b is hydrophobic and has an amino functional group; mixing a resin matrix, a curing agent and a silicon dioxide filler b at a high temperature to obtain slurry, adding a functional additive into the slurry, and mixing at a low temperature to obtain a glue solution; and performing stage curing on the glue solution to obtain the low-dielectric adhesive with the gradient interface structure. The gradient interface structure is used as a stress buffering and transferring layer, stress can be effectively absorbed and dispersed through a transition area with continuously-changed modulus under the action of external force, crack propagation is inhibited, the fracture toughness, impact resistance and layering resistance of the material are improved, and finally on the premise that excellent low dielectric performance is kept, the performance of the material is improved. The synergistic enhancement of the toughness and the reliability of the adhesive layer is realized.

Description

Technical Field

[0001] This invention relates to the field of adhesives, and more particularly to a low-dielectric adhesive and its preparation method. Background Technology

[0002] With the rapid development of advanced electronic technologies such as 5G communication and high-performance computing, increasingly stringent requirements have been placed on the dielectric properties of packaging materials. Low dielectric constant (Dk) and low dielectric loss (Df) have become key indicators. To reduce the dielectric constant, the industry generally adopts the technical route of introducing porous or hollow inorganic fillers into the organic resin matrix, utilizing the low dielectric properties of air to achieve a decrease in the overall dielectric constant.

[0003] While traditional methods for reducing the dielectric properties of adhesives can achieve excellent dielectric performance, they inevitably introduce a large number of structural defects and fragile interfaces. This results in extremely brittle adhesive layers after curing, with significantly deteriorated impact and bending resistance. For example, in practical applications of chip packaging, the package continuously undergoes temperature cycling and unavoidable mechanical stress impacts. This inherent brittleness makes it easier for microcracks to develop and propagate inside the adhesive layer or at the interface, ultimately leading to catastrophic cracking and delamination failures, seriously threatening the long-term reliability of electronic devices.

[0004] Therefore, a low-dielectric adhesive and its preparation method are proposed to solve the problems of high brittleness and poor impact and bending resistance of the cured adhesive layer. Summary of the Invention

[0005] The purpose of this invention is to provide a low dielectric adhesive and its preparation method, which solves the problems of high brittleness and poor impact and bending resistance of the cured adhesive layer.

[0006] To achieve this objective, the present invention adopts the following technical solution: A method for preparing a low-dielectric adhesive, the method comprising the following steps: Step S1: Chemically modify the surface of silica filler a to obtain silica filler b with an organic molecular layer on the surface; wherein, the surface of silica filler b is hydrophobic and has amino functional groups. Step S2: Mix the resin matrix, curing agent and silica filler b at high temperature to obtain a slurry, then add functional additives to the slurry and mix at low temperature to obtain an adhesive. Step S3: Perform staged curing of the adhesive to obtain a low-dielectric adhesive with a gradient interface structure.

[0007] Step S1 specifically includes the following steps: Step S11: First, the silane coupling agent is controlled to hydrolyze in a mixed system of anhydrous ethanol and deionized water to generate a hydrolysate rich in silanol groups. Step S12: The hydrolysate and silica filler a are thoroughly mixed and subjected to a condensation reaction under heating conditions to obtain a mixture. The mixture is then subjected to vacuum heat treatment, and silica filler b is obtained after the treatment is completed.

[0008] In step S11, the silane coupling agent is γ-aminopropyltriethoxysilane, the mass ratio of the silane coupling agent to anhydrous ethanol is 1:(8-10), the mass of deionized water in the mixed system is 4-6% of the mass of the silane coupling agent, and the stirring time of the hydrolysis process is 25-35 min. In step S12, the silica filler a is a spherical molten silica filler with an average particle size of 1-2 μm; the heating conditions are a temperature of 65-75℃, a stirring time of 1.5-2.5h, and a stirring speed of 150-250rpm; the vacuum heat treatment is a temperature of 110-125℃ and a time of 3.5-4.5h.

[0009] The slurry is obtained according to the following steps: The resin matrix, curing agent and silica filler b are added to a planetary mixing tank and stirred and mixed under the first temperature condition. After the stirring and mixing is completed, a slurry is obtained.

[0010] The resin matrix is ​​hydrogenated bisphenol A epoxy resin, the curing agent is methylhexahydrophthalic anhydride, and the weight ratio of the resin matrix, curing agent and silica filler b is 100:(66-70):(30-50). The temperature under the first temperature condition is 48-52℃, the vacuum degree is ≤ -0.095 MPa, the stirring time is 50-70 min, and the stirring speed is 500-1000 rpm.

[0011] The adhesive solution is obtained according to the following steps: The slurry is stirred and mixed under the second temperature condition. Then, functional additives a, b and c are added to the slurry in sequence. After the mixing is completed, the adhesive solution is obtained.

[0012] The temperature under the second temperature condition is 28-32℃. The weight ratio of the resin matrix, functional additive a, functional additive b and functional additive c is 100:(5-12):(2-10):(0.5-1.5). Functional additive a is an epoxy-polydimethylsiloxane-epoxy triblock copolymer. The stirring speed when adding functional additive a is 180-220 rpm and the stirring time is 18-25 min. Functional additive b is a core-shell elastomer particle. The stirring speed when adding functional additive b is 130-170 rpm and the stirring time is 12-18 min. Functional additive c is microencapsulated imidazole. The stirring speed when adding functional additive c is 80-120 rpm and the stirring time is 5-10 min.

[0013] Step S3 specifically includes the following steps: Step S31: After coating or dispensing the adhesive, perform a preliminary heat treatment to obtain a gel. Step S32: The gel is subjected to heat treatment again to obtain a low dielectric adhesive.

[0014] In step S31, the initial heat treatment has a heating rate of 2-3℃ / min, a temperature of 105-115℃, and a time of 80-100min. In step S32, the heating rate of the second heat treatment is 2-3℃ / min, the temperature is 138-142℃, and the time is 170-190min.

[0015] A low-dielectric adhesive, wherein the low-dielectric adhesive is prepared by the preparation method described above.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a low-dielectric adhesive and its preparation method. A covalently bonded amino-functionalized layer is constructed on the surface of silica filler through chemical modification with a silane coupling agent, enhancing the interfacial bonding between the filler and the organic resin and preventing early delamination failure caused by weak interfaces. Subsequently, a gradient mixing process of high temperature and high shear followed by low temperature and low shear is employed to achieve highly uniform dispersion of the filler while preserving the structural integrity of key functional components such as block copolymers, core-shell particles, and microcapsules, laying a uniform material basis for structural self-assembly during the subsequent curing process. Finally, through two-stage curing, the block copolymer is first thermodynamically migrated to the filler interface at a lower temperature. The flexible pre-interface layer is formed by migration and enrichment, while the system undergoes initial gelation to fix this structure. Then, a latent catalyst is triggered at a higher temperature to initiate full and rapid curing, covalently anchoring the physically adsorbed flexible pre-interface layer onto a three-dimensional network through chemical reaction. This creates a chemically bonded gradient interface structure in situ between the filler and the matrix. This unique gradient interface acts as a stress buffer and transfer layer, effectively absorbing and dispersing stress under external forces through its continuously changing modulus transition zone. This inhibits crack propagation and improves the material's fracture toughness, impact resistance, and anti-delamination ability. Ultimately, while maintaining excellent low dielectric properties, the toughness and reliability of the adhesive layer are synergistically enhanced. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0019] Figure 1 This is a flowchart of the preparation method in this invention. Detailed Implementation

[0020] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0022] Example 1: Please see Figure 1 This embodiment discloses a low-dielectric adhesive and its preparation method, the preparation method comprising the following steps: Step S1: Chemically modify the surface of silica filler a to obtain silica filler b with an organic molecular layer on the surface; wherein, the surface of silica filler b is hydrophobic and has amino functional groups. Step S2: Mix the resin matrix, curing agent and silica filler b at high temperature to obtain a slurry, then add functional additives to the slurry and mix at low temperature to obtain an adhesive. Step S3: Perform staged curing of the adhesive to obtain a low-dielectric adhesive with a gradient interface structure.

[0023] Specifically, in step S1, the surface of silica filler a is chemically modified to obtain silica filler b with an organic molecular layer on its surface; wherein, the surface of silica filler b is hydrophobic and has amino functional groups. Step S1 specifically includes the following steps: Step S11: First, the silane coupling agent is controlled to hydrolyze in a mixed system of anhydrous ethanol and deionized water to generate a hydrolysate rich in silanol groups. In step S11, the silane coupling agent is γ-aminopropyltriethoxysilane, the mass ratio of the silane coupling agent to anhydrous ethanol is 1:(8-10), the mass of deionized water in the mixed system is 4-6% of the mass of the silane coupling agent, and the stirring time of the hydrolysis process is 25-35 min. Step S12: The hydrolysate and silica filler a are thoroughly mixed and subjected to a condensation reaction under heating conditions to obtain a mixture. The mixture is then subjected to vacuum heat treatment, and silica filler b is obtained after the treatment is completed.

[0024] It should be noted that in step S1, the silane coupling agent is first subjected to controlled hydrolysis in a mixture of anhydrous ethanol and water to generate a hydrolysate rich in silanol groups. This hydrolysate is then thoroughly mixed with silica filler a and reacted under heating conditions, causing the silanol groups of the silane to condense with the silanol groups on the surface of silica filler a, forming an organic-inorganic interface linked by covalent bonds. Finally, the solvent is removed by vacuum heat treatment, which further promotes the condensation between the silane layers, resulting in silica filler b with a uniformly coated surface of aminosilane molecules. During this process, the ethoxy groups at the ends of the silane coupling agent molecules are hydrolyzed by water molecules, transforming into highly reactive silanol groups. These silanol groups are further reacted by the energy provided by heating and stirring, and by collisions. Under certain conditions, the silane molecules undergo a dehydration condensation reaction with the inherent silanol groups on the surface of the spherical fused silica filler a, forming strong Si-O-Si covalent bonds. This chemically anchors the silane molecules to the filler surface in the form of monolayers or oligolayers. Simultaneously, the remaining silanol groups between the silane molecules also condense with each other, forming a cross-linked organic network on the surface of the spherical fused silica filler a. The surface of the spherical fused silica filler a transforms from a hydrophilic, easily agglomerated powder into a functional powder that can be stably dispersed in organic solvents and resins and has a surface rich in amino reaction sites. Under the action of the above method, through the coupling reaction in interfacial chemistry, the filler and resin are connected by covalent bonds, thus resolving the contradiction of poor compatibility and weak bonding between the two in advance.

[0025] It is understood that by imparting uniform and robust amino functional groups to the surface of spherical fused silica filler a, the chemical activation and interface preparation effects of spherical fused silica filler a are achieved. Specifically, through chemical activation, the originally inert surface of spherical fused silica filler a is transformed into an active surface capable of undergoing ring-opening addition reactions with epoxy resin. Through interface preparation, the hydrophobic surface energy of spherical fused silica filler b provides an interface environment with good affinity for subsequently added functional additives. Under the action of chemical activation and interface preparation, a basic strong interfacial bonding foundation is constructed for the material system, ensuring that loads and stresses can be efficiently transferred from the resin matrix to the rigid filler through chemical bonds, rather than debonding failure at the interface due to weak bonding, thereby ensuring the long-term reliability and durability of the low-dielectric adhesive.

[0026] Understandably, through covalent bonding, the interfacial bonding energy between the spherical fused silica filler b and the resin is significantly enhanced, with the bonding strength far exceeding that of physical forces. This makes it difficult for cracks to initiate and propagate at the interface under impact or cyclic stress, thus eliminating the risk of early failure due to weak interfaces. Simultaneously, the uniform aminosilane layer on the spherical fused silica filler b provides a stable and consistent interfacial chemical environment, creating conditions for the preferential and controllable adsorption of functional additives in subsequent steps. This is a prerequisite and spatial positioning basis for the subsequent construction of gradient interfacial structures. The above method effectively solves the problem of bonding strength, avoiding the occurrence of delamination due to physical adsorption or weak bonding. More importantly, by pre-constructing a rigid anchoring layer with Si-O-Si covalent bonds at its core between the inorganic filler and the organic resin, the risk of traditional low-dielectric adhesives becoming a preferred path for crack initiation and propagation due to weak interfacial bonding is eliminated. This lays the most fundamental chemical bonding guarantee for the excellent anti-delamination reliability of the final adhesive layer.

[0027] It is worth noting that the above method ensures that silane molecules react with the surface of the spherical molten silica filler a in an optimal active state, forming a dense and uniform monolayer. The silane concentration aims to balance reaction efficiency and economy; too low a concentration results in insufficient coverage, while too high a concentration may lead to multilayer physical adsorption rather than chemical bonding. Furthermore, the water volume used in hydrolysis avoids incomplete hydrolysis due to insufficient water, resulting in a low number of active silanol groups; while excessive water may promote excessive self-polymerization of silanes, forming precipitation and hindering effective grafting. The corresponding temperature of 65-75℃ during hydrolysis also provides sufficient kinetic energy to overcome the reaction barrier. The rapid condensation reaction, while avoiding excessive temperature that could lead to excessive evaporation of the solvent ethanol or decomposition of silane, and the prolonged vacuum drying in the subsequent processing, effectively removes physically adsorbed solvents and small molecules, and further promotes the condensation and cross-linking of the silane layer itself, transforming it from a loose physically adsorbed state to a dense and stable chemically bonded state, thus forming a strong and hydrolysis-resistant barrier. Under the above-mentioned effects, the spherical molten silica filler b is ensured to have high reactivity, high stability and excellent redispersibility, providing a raw material basis with constant quality and reliable performance for the successful implementation of all subsequent steps.

[0028] Specifically, in step S2, the resin matrix, curing agent and silica filler b are mixed at high temperature to obtain a slurry, and then functional additives are added to the slurry and mixed at low temperature to obtain an adhesive. The slurry is obtained according to the following steps: The resin matrix, curing agent and silica filler b are added to a planetary mixing tank and stirred and mixed under the first temperature condition. After the stirring and mixing is completed, a slurry is obtained.

[0029] The resin matrix is ​​hydrogenated bisphenol A epoxy resin, the curing agent is methylhexahydrophthalic anhydride, and the weight ratio of the resin matrix, curing agent and silica filler b is 100:(66-70):(30-50). The temperature under the first temperature condition is 48-52℃, the vacuum degree is ≤ -0.095 MPa, the stirring time is 50-70 min, and the stirring speed is 500-1000 rpm.

[0030] The adhesive solution is obtained according to the following steps: The slurry is stirred and mixed under the second temperature condition. Then, functional additives a, b and c are added to the slurry in sequence. After the mixing is completed, the adhesive solution is obtained.

[0031] The temperature under the second temperature condition is 28-32℃. The weight ratio of the resin matrix, functional additive a, functional additive b and functional additive c is 100:(5-12):(2-10):(0.5-1.5). Functional additive a is an epoxy-polydimethylsiloxane-epoxy triblock copolymer. The stirring speed when adding functional additive a is 180-220 rpm and the stirring time is 18-25 min. Functional additive b is a core-shell elastomer particle. The stirring speed when adding functional additive b is 130-170 rpm and the stirring time is 12-18 min. Functional additive c is microencapsulated imidazole. The stirring speed when adding functional additive c is 80-120 rpm and the stirring time is 5-10 min.

[0032] It should be noted that the hydrogenated bisphenol A epoxy resin matrix, methyl hexahydrophthalic anhydride curing agent, and silica filler b are mixed for a long time under heating, vacuum, and high shear conditions to achieve uniform dispersion and initial wetting of the filler without agglomeration. Subsequently, the resulting high-viscosity slurry is actively cooled to reduce its viscosity and internal shear stress. Under these conditions, epoxy-polydimethylsiloxane-epoxy triblock copolymer and core-shell elastomer particles are added slowly and gently stirred to achieve uniform dispersion and avoid structural damage. Finally, with the addition of a microencapsulated imidazole latent catalyst, the integration of all materials is completed, resulting in a homogeneous colloid that can be stored at low temperatures. During this process, when the materials are in the high-shear mixing stage, the strong mechanical shear force and vacuum degassing jointly overcome the van der Waals forces between silica filler b particles, breaking down their agglomerates. The process disperses the low-viscosity resin matrix and curing agent mixture, fully wetting and coating each filler particle to form a stable suspension system with the filler as the dispersed phase and the resin mixture as the continuous phase. Upon cooling and entering a low-shear stage, the epoxy-polydimethylsiloxane-epoxy triblock copolymer is dispersed as tiny droplets. Due to the thermodynamic incompatibility between its PDMS segments and the epoxy resin matrix, these droplets are in a metastable state and possess the potential to migrate towards the interface. Furthermore, the complete spherical structure of the core-shell elastomer particles is preserved, and the epoxy grafted shell on its surface has good compatibility with the resin matrix. Additionally, the polymer shell of the microencapsulated imidazole remains intact under mild shear, and the internal liquid catalyst is completely encapsulated. During this process, the adhesive solution transforms from an initial multiphase heterogeneous state into a uniform, fine, viscous adhesive solution free of visible particles or bubbles.

[0033] It should also be noted that the epoxy-polydimethylsiloxane-epoxy triblock copolymer, which is functional additive a, has a polydimethylsiloxane segment molecular weight of 2000 and an epoxy equivalent (EEW) of 1500 g / eq at both ends of the epoxy group. This ensures that the copolymer has sufficient thermodynamic driving force to migrate to the interface. At the same time, the reactivity of its end epoxy group is relatively low compared with the resin matrix, thereby achieving a delayed reaction effect of physical enrichment followed by chemical anchoring. The core-shell elastomer particles, which are functional additive b, have a core of cross-linked polybutyl acrylate elastomer and a shell of polymethyl methacrylate and epoxy resin graft copolymer with an average particle size of 0.2 μm. This core-shell structure ensures good compatibility and interfacial bonding between the particles and the epoxy matrix, enabling them to effectively dissipate energy through cavitation mechanism when under stress, thus ensuring bulk toughening.

[0034] It is understood that differentiated shear mixing achieves the effect of constructing a uniform matrix and preserving functional structures. Specifically, high-shear mixing forms a basic resin-filler composite matrix with extremely uniform filler dispersion and no potential defects, which provides a fundamental guarantee for the material to obtain consistent and predictable mechanical and dielectric properties. Subsequent low-shear mixing preserves the molecular chain integrity of the epoxy-polydimethylsiloxane-epoxy triblock copolymer, the spherical core-shell structure of the core-shell elastomer particles, and the sealing properties of the microencapsulated imidazole. The preservation of these functional structures is used to achieve the predetermined interface segregation toughening, particle cavitation toughening, and latent curing triggering, so as to lay the physical basis for the expected material properties in the final curing stage after the subsequent curing reaction.

[0035] Understandably, the problems of high brittleness and uneven performance are synergistically solved through highly uniform dispersion and structural preservation. Specifically, the uniform dispersion of the filler eliminates the risk of brittle fracture directly caused by agglomerates acting as stress concentration points, while the uniform distribution of core-shell elastomer particles means that energy dissipation points exist with equal probability throughout the entire domain, which can universally induce crazes and shear bands, thereby significantly and stably improving the toughness of the matrix. Furthermore, the uniform initial distribution of the epoxy-polydimethylsiloxane-epoxy triblock copolymer is key to ensuring that it can migrate evenly to the surface of each filler particle during subsequent heating, thus ensuring that the gradient interface structure can be formed reproducibly over a large area throughout the entire material, rather than just existing in a localized area. The complete preservation of microencapsulated imidazole ensures the precise triggering of the curing reaction, avoiding storage failure due to premature rupture or internal stress caused by localized overly rapid curing. More importantly, the above method ensures that the filler, functional additive a, and functional additive b are uniformly distributed in the resin matrix, thereby eliminating the possibility of brittle fracture directly induced by local stress peaks caused by filler agglomeration. This allows elastic particles to act as uniformly distributed energy dissipation points, comprehensively improving the toughness of the matrix. It ensures that each filler particle has an equal opportunity to be coated by the flexible interface layer, achieving a consistent and repeatable gradient interface toughening effect. This overcomes the defects of traditional low-dielectric adhesives, such as large performance fluctuations and unpredictable brittle fracture caused by structural inhomogeneity.

[0036] It is worth noting that the above-mentioned method of high-temperature and high-shear mixing of silica filler b can reduce the viscosity of the resin matrix to break the secondary agglomeration of silica filler b. The corresponding vacuum environment can remove the encapsulated gas and prevent the formation of microscopic void defects. The subsequent active cooling of the slurry before adding functional additives is to significantly reduce the viscosity and internal shear stress of the system, so as to protect the epoxy-polydimethylsiloxane-epoxy triblock copolymer molecular chains from being excessively stretched and broken, the core-shell particle shells from being crushed, and the microencapsulated imidazole shells from being worn. In addition, the amount of epoxy-polydimethylsiloxane-epoxy triblock copolymer ensures a balance between interface coverage and avoiding excessive phase separation. The stirring time after its addition also ensures that it is initially dispersed into micro-regions of appropriate size, providing a suitable starting point for subsequent migration. The mixing parameters corresponding to the microencapsulated imidazole minimize the probability of collision with hard particles such as silica filler b, ensuring the integrity of the capsules and guaranteeing the storage stability and curing reproducibility of the adhesive.

[0037] Specifically, in step S3, the adhesive is cured in stages to obtain a low-dielectric adhesive with a gradient interface structure.

[0038] Step S3 specifically includes the following steps: Step S31: After coating or dispensing the adhesive, perform a preliminary heat treatment to obtain a gel. In step S31, the initial heat treatment has a heating rate of 2-3℃ / min, a temperature of 105-115℃, and a time of 80-100min. Step S32: The gel is subjected to heat treatment again to obtain a low dielectric adhesive.

[0039] In step S32, the heating rate of the second heat treatment is 2-3℃ / min, the temperature is 138-142℃, and the time is 170-190min.

[0040] It should be noted that heating the applied adhesive layer from room temperature to the initial heat treatment stage and maintaining it for a sufficient time during this initial heat treatment will cause the system viscosity to decrease and molecular motion to intensify. This will induce the interfacial gradient building agent to migrate and accumulate at the filler interface. Simultaneously, the resin matrix and curing agent react to gel the system, thus initially fixing the structure. Furthermore, under the subsequent second heat treatment, the temperature reaches the rupture threshold of the microencapsulated imidazole latent catalyst, causing the catalyst to release and rapidly diffuse, strongly catalyzing the epoxy-anhydride main reaction and the final dissolution of the interfacial gradient building agent. The reaction of the terminal epoxy groups allows the entire system to fully solidify, firmly anchoring the flexible segments enriched at the interface to the three-dimensional cross-linked network via covalent bonds. During this process, the initial heat input from the heat treatment causes a sharp drop in the system viscosity, providing kinetic energy for the molecular chain movement of the epoxy-polydimethylsiloxane-epoxy triblock copolymer. Simultaneously, based on the significant thermodynamic incompatibility between the PDMS (polydimethylsiloxane) segments and the epoxy resin matrix, interfacial segregation occurs, driven by a reduction in interfacial free energy. This means the copolymer segregates towards all interfaces (especially...). The process involves the migration and enrichment of a flexible pre-interface layer formed by the physical adsorption of a silica filler (b) modified with aminosilane and having an affinity for it. Simultaneously, methylhexahydrophthalic anhydride undergoes a slow ring-opening addition reaction with hydrogenated bisphenol A epoxy resin under thermal initiation, increasing the molecular weight and gradually forming a gel. This locks the flexible pre-interface layer within the interfacial region, achieving the assembly and pre-fixation of the gradient interfacial structure. Subsequently, during a second heat treatment of the gel, the temperature exceeds the rupture threshold of the microencapsulated imidazole shell, releasing the internal liquid imidazole catalyst. This catalyst, acting as a strong nucleophile, efficiently catalyzes the alternating copolymerization of acid anhydrides and epoxy, causing a sharp increase in crosslinking density and complete solidification of the system. At this point, the epoxy groups at the ends of the epoxy-polydimethylsiloxane-epoxy triblock copolymer enriched at the interface also ultimately participate in the reaction under strong catalysis, thereby covalently stitching the flexible pre-interface layer into the three-dimensional crosslinking network and transforming it into a thermodynamically stable, chemically anchored gradient interface structure. Under the action of the above mechanism, the adhesive changes from a viscous flow state to an elastic gel state, and finally transforms into a low-dielectric adhesive.

[0041] It is known that the relatively mild heating environment of the initial heat treatment guides and allows the thermodynamically driven interfacial segregation process to proceed fully, ensuring that the flexible components can be uniformly and fully enriched at each filler interface to achieve the construction of a gradient structure. Simultaneous gelation plays a shaping role, preventing the assembled structure from being disturbed and destroyed during subsequent heating. The higher temperature of the second heat treatment serves as a clear chemical signal, triggering the release of latent catalysts. By utilizing the differences in the reactivity of different epoxy groups, the cross-linking reaction is carried out sequentially or layeredly, thus achieving the final locking of performance by first forming a rigid main network framework and then chemically anchoring the in-place flexible interfacial components onto it.

[0042] It is understandable that the chemical and structural reasons for the high toughness, impact resistance, and anti-delamination properties of low-dielectric adhesives are derived from gradient interface chemical anchoring and complete network curing. Specifically, the gradient interface, formed by the initial heat treatment and chemically locked by the subsequent heat treatment, creates a transition zone with continuously changing modulus between the filler and the resin—the gradient interface structure. Its modulus continuously changes from the rigid filler surface to the flexible PDMS layer and then to the rigid resin body, eliminating the sharp stress concentration points caused by abrupt modulus changes in traditional materials. When the adhesive is subjected to external impact or stress, the gradient interface structure can efficiently utilize the reversible extension, conformational changes, and micro-area shear deformation of its chemically bonded flexible PDMS segments to effectively resist external forces. By absorbing, dissipating, and redistributing stress, crack propagation is inhibited, and the crack propagation path is forced to deflect, branch, or even terminate, rather than propagating directly along the fragile interface. This transforms the failure mode of the adhesive from low-energy brittle fracture to high-energy toughness failure, improving the impact resistance, fracture toughness, and anti-delamination ability of the adhesive layer. At the same time, the core-shell elastomer particles, as independent toughening points uniformly dispersed in the matrix, work synergistically with the gradient interface structure to further dissipate energy through mechanisms such as cavitation and shear yielding, jointly constructing a multi-scale toughening system. The low-dielectric adhesive obtained in the above manner maintains low dielectric properties while implanting toughening genes at the interface, thus achieving a unity of low dielectric and high toughness.

[0043] It is worth noting that the initial heat treatment temperature is higher than the onset temperature of the thermally initiated reaction between the acid anhydride and epoxy to ensure gelation, and lower than the rupture temperature of the microencapsulated imidazole to prevent premature triggering of rapid curing. At the same time, it can also reduce viscosity and promote migration. The duration of the initial heat treatment provides sufficient time for the relatively slow diffusion process of thermodynamically driven interfacial segregation. The corresponding heating rate also ensures the uniformity of heating and avoids internal stress and uneven curing caused by excessive temperature difference. The temperature of the second heat treatment serves as a trigger signal. It is higher than the precise rupture temperature of the microencapsulated imidazole shell to ensure the complete and synchronous release of the catalyst and trigger explosive crosslinking. The duration of the second heat treatment ensures the complete formation of a high crosslinking density network and the full reaction of the epoxy groups at the interface, achieving the highest glass transition temperature and optimal mechanical properties.

[0044] The following is a comparison of the properties of the low-dielectric adhesive obtained according to Example 1 with those of a conventional low-dielectric adhesive, as shown in Tables 1 and 2: Table 1 Table 2 As shown in Tables 1 and 2, the low-dielectric adhesive obtained in Example 1 achieves a breakthrough improvement in comprehensive performance with a dielectric constant that is only slightly higher than that of traditional porous filler products. Its mechanical toughness, fracture toughness, and impact strength are all superior to those of traditional products. At the same time, the improved bonding strength eliminates the risk of interface delamination. In addition, thanks to its dense interface structure, the low-dielectric adhesive obtained in Example 1 also has better dielectric loss and insulation reliability than traditional products, providing an ideal adhesive material for advanced electronic packaging that combines excellent signal integrity and long-term structural reliability.

[0045] The data for the control group are the average values ​​of traditional low-dielectric adhesives after multiple tests. Traditional low-dielectric adhesives are obtained by the following method: First, porous or hollow silica fillers are conventionally soaked or sprayed with an ethanol solution of silane coupling agent. After drying, hydrophobic fillers are obtained. Then, epoxy resin, curing agent, pretreated porous / hollow fillers and other additives are added to a mixing container at one time. The mixture is then subjected to medium-high speed shear mixing using a planetary mixer at room temperature or moderate heating to ensure uniform dispersion of the fillers. Vacuum degassing is then performed. Finally, the uniformly mixed adhesive is coated and placed in an oven for a one-stage curing process to achieve complete cross-linking and molding.

[0046] The data corresponding to Example 1 was obtained from Examples a and b: Example a is: Step S1: First, the silane coupling agent γ-aminopropyltriethoxysilane is mixed with anhydrous ethanol at a mass ratio of 1:8. Deionized water, equivalent to 4% of the silane coupling agent's mass, is added, and the mixture is stirred at 25°C for 25 minutes to obtain a hydrolysate. Then, this hydrolysate is mixed with 100 parts by weight of spherical molten silica filler a with an average particle size of 1.2 μm. The mixture is reacted at 65°C and 150 rpm for 1.5 hours. The resulting mixture is then subjected to vacuum heat treatment at 110°C for 3.5 hours to obtain silica filler b with a hydrophobic surface and amino functional groups. Step S2: 100 parts by weight of hydrogenated bisphenol A epoxy resin, 66 parts by weight of methylhexahydrophthalic anhydride curing agent, and 30 parts by weight of silica filler b were added to a planetary mixing tank. Under the first temperature condition of 48℃ and a vacuum degree ≤-0.095MPa, the mixture was stirred at 500 rpm for 50 min to obtain a homogeneous slurry. Subsequently, the slurry temperature was controlled under the second temperature condition of 32℃, and 5 parts by weight of epoxy-polydimethylsiloxane-epoxy triblock copolymer (functional additive a) were added sequentially and stirred at 180 rpm for 18 min. Then, 2 parts by weight of core-shell elastomer particles (functional additive a) were added. Add agent b) and stir at 130 rpm for 12 min. Finally, add 0.5 parts by weight of microencapsulated imidazole (functional additive c) and stir at 80 rpm for 10 min. After mixing evenly, obtain the adhesive solution. In step S3, after coating the obtained adhesive solution, heat it to 105℃ at a rate of 2℃ / min and perform an initial heat treatment, holding for 100 min to obtain a gel. Then, heat it to 138℃ at the same rate and perform a second heat treatment, holding for 170 min. After complete curing, the low dielectric adhesive is obtained. First, mix 10g of γ-aminopropyltriethoxysilane with 90g of... Anhydrous ethanol was mixed with 0.5 g of deionized water and stirred at 25 °C for 30 min to obtain a hydrolysate. Then, 100 g of spherical molten silica filler with an average particle size of 1.5 μm was added to the hydrolysate, and the mixture was reacted at 70 °C and 200 rpm for 2 h. After filtration, the solid was dried in a vacuum oven at 120 °C for 4 h to obtain surface-modified silica filler b. Next, 100 g of hydrogenated bisphenol A epoxy resin, 66 g of methylhexahydrophthalic anhydride, and 30 g of silica filler b were mixed in a planetary stirred tank and stirred at 50 °C and a vacuum degree ≤-0.095. The mixture was stirred at 800 rpm for 60 min at a pressure of MPa to obtain a slurry. The slurry was then cooled to 30°C, and 5 g of epoxy-polydimethylsiloxane-epoxy triblock copolymer was added and stirred at 200 rpm for 20 min. Then, 5 g of core-shell elastomer particles were added and stirred at 150 rpm for 15 min. Finally, 2.5 g of microencapsulated imidazole was added and stirred at 100 rpm for 8 min. After mixing evenly, an adhesive was obtained. Finally, the adhesive was coated and heated to 110°C at a rate of 2.5°C / min and held for 100 min. Then, the temperature was increased to 140°C at the same rate and held for 180 min to complete the curing process, thus obtaining the low-dielectric adhesive.

[0047] Example b is as follows: Step S1: First, the silane coupling agent γ-aminopropyltriethoxysilane is mixed with anhydrous ethanol at a mass ratio of 1:10. Deionized water, equivalent to 6% of the silane coupling agent's mass, is added and stirred at 25°C for 35 min to obtain a hydrolysate. Then, this hydrolysate is mixed with 100 parts by weight of spherical molten silica filler a with an average particle size of 1.8 μm. The mixture is reacted at 75°C and 250 rpm for 2.5 h, and then the resulting mixture is subjected to vacuum heat treatment at 125°C for 4.5 h to obtain silica filler b with a hydrophobic surface and amino functional groups. Step S2: 100 parts by weight of hydrogenated bisphenol A epoxy resin, 70 parts by weight of methylhexahydrophthalic anhydride curing agent, and 50 parts by weight of silica filler b were added to a planetary mixing tank. Under the first temperature condition of 52°C and a vacuum degree ≤ -0.095 MPa, the mixture was stirred at 1000 rpm for 70 minutes to obtain a homogeneous slurry. Subsequently, the slurry temperature was controlled under a second temperature condition of 28°C, and 12 parts by weight of epoxy-polydimethylsiloxane-epoxy triblock copolymer (functional additive a) were added sequentially, and the mixture was stirred at 220 rpm for 25 minutes. Finally, 10 parts by weight of core-shell elastomer particles (functional additive a) were added. Add agent b) and stir at 170 rpm for 18 min. Finally, add 1.5 parts by weight of microencapsulated imidazole (functional auxiliary agent c) and stir at 120 rpm for 5 min. After mixing evenly, obtain the adhesive solution. In step S3, after coating the obtained adhesive solution, heat it to 115°C at a rate of 3°C / min and perform an initial heat treatment, holding for 80 min to obtain a gel. Then, heat it to 142°C at the same rate and perform a second heat treatment, holding for 190 min. After complete curing, the low dielectric adhesive is obtained. First, mix 10 g of γ-aminopropyltriethoxysilane with 80 g of anhydrous ethyl acetate. Alcohols were mixed, and 0.6 g of deionized water was added. The mixture was stirred at 25 °C for 30 min to obtain a hydrolysate. Then, 100 g of spherical molten silica filler with an average particle size of 1.5 μm was added to the hydrolysate, and the mixture was stirred at 75 °C and 200 rpm for 2.5 h. After filtration, the solid was dried in a vacuum oven at 125 °C for 4.5 h to obtain surface-modified silica filler b. Next, 100 g of hydrogenated bisphenol A epoxy resin, 70 g of methylhexahydrophthalic anhydride, and 40 g of silica filler b were mixed in a planetary mixer and stirred at 52 °C under a vacuum degree ≤-0.098. The mixture was stirred at 1000 rpm for 70 min at a pressure of MPa to obtain a slurry. The slurry was then cooled to 28°C, and 10 g of epoxy-polydimethylsiloxane-epoxy triblock copolymer was added and stirred at 220 rpm for 25 min. Then, 10 g of core-shell elastomer particles were added and stirred at 170 rpm for 18 min. Finally, 3 g of microencapsulated imidazole was added and stirred at 120 rpm for 5 min. After mixing evenly, an adhesive was obtained. Finally, the adhesive was coated and heated to 115°C at a rate of 3°C / min and held for 80 min. Then, the temperature was increased to 142°C at the same rate and held for 190 min to complete the curing process, thus obtaining the low-dielectric adhesive.

[0048] Example 2: This embodiment provides a low-dielectric adhesive, which is prepared using the method described in Example 1.

[0049] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a low-dielectric adhesive, characterized in that, The preparation method includes the following steps: Step S1: Chemically modify the surface of silica filler a to obtain silica filler b with an organic molecular layer on the surface; wherein, the surface of silica filler b is hydrophobic and has amino functional groups. Step S2: Mix the resin matrix, curing agent and silica filler b at high temperature to obtain a slurry, then add functional additives to the slurry and mix at low temperature to obtain an adhesive. Step S3: Perform staged curing of the adhesive to obtain a low-dielectric adhesive with a gradient interface structure.

2. The method for preparing the low-dielectric adhesive according to claim 1, characterized in that, Step S1 specifically includes the following steps: Step S11: First, the silane coupling agent is controlled to hydrolyze in a mixed system of anhydrous ethanol and deionized water to generate a hydrolysate rich in silanol groups. Step S12: The hydrolysate and silica filler a are thoroughly mixed and subjected to a condensation reaction under heating conditions to obtain a mixture. The mixture is then subjected to vacuum heat treatment, and silica filler b is obtained after the treatment is completed.

3. The method for preparing the low-dielectric adhesive according to claim 2, characterized in that, In step S11, the silane coupling agent is γ-aminopropyltriethoxysilane, the mass ratio of the silane coupling agent to anhydrous ethanol is 1:(8-10), the mass of deionized water in the mixed system is 4-6% of the mass of the silane coupling agent, and the stirring time of the hydrolysis process is 25-35 min. In step S12, the silica filler a is a spherical molten silica filler with an average particle size of 1-2 μm; the heating conditions are a temperature of 65-75℃, a stirring time of 1.5-2.5h, and a stirring speed of 150-250rpm; the vacuum heat treatment is a temperature of 110-125℃ and a time of 3.5-4.5h.

4. The method for preparing the low-dielectric adhesive according to claim 1, characterized in that, The slurry is obtained according to the following steps: The resin matrix, curing agent and silica filler b are added to a planetary mixing tank and stirred and mixed under the first temperature condition. After the stirring and mixing is completed, a slurry is obtained.

5. The method for preparing the low-dielectric adhesive according to claim 4, characterized in that, The resin matrix is ​​hydrogenated bisphenol A epoxy resin, the curing agent is methylhexahydrophthalic anhydride, and the weight ratio of the resin matrix, curing agent and silica filler b is 100:(66-70):(30-50). The temperature under the first temperature condition is 48-52℃, the vacuum degree is ≤ -0.095 MPa, the stirring time is 50-70 min, and the stirring speed is 500-1000 rpm.

6. The method for preparing the low-dielectric adhesive according to claim 5, characterized in that, The adhesive solution is obtained according to the following steps: The slurry is stirred and mixed under the second temperature condition. Then, functional additives a, b and c are added to the slurry in sequence. After the mixing is completed, the adhesive solution is obtained.

7. The method for preparing the low-dielectric adhesive according to claim 6, characterized in that, The temperature under the second temperature condition is 28-32℃. The weight ratio of the resin matrix, functional additive a, functional additive b and functional additive c is 100:(5-12):(2-10):(0.5-1.5). Functional additive a is an epoxy-polydimethylsiloxane-epoxy triblock copolymer. The stirring speed when adding functional additive a is 180-220 rpm and the stirring time is 18-25 min. Functional additive b is a core-shell elastomer particle. The stirring speed when adding functional additive b is 130-170 rpm and the stirring time is 12-18 min. Functional additive c is microencapsulated imidazole. The stirring speed when adding functional additive c is 80-120 rpm and the stirring time is 5-10 min.

8. The method for preparing the low-dielectric adhesive according to claim 1, characterized in that, Step S3 specifically includes the following steps: Step S31: After coating or dispensing the adhesive, perform a preliminary heat treatment to obtain a gel. Step S32: The gel is subjected to heat treatment again to obtain a low dielectric adhesive.

9. The method for preparing the low-dielectric adhesive according to claim 8, characterized in that, In step S31, the initial heat treatment has a heating rate of 2-3℃ / min, a temperature of 105-115℃, and a time of 80-100min. In step S32, the heating rate of the second heat treatment is 2-3℃ / min, the temperature is 138-142℃, and the time is 170-190min.

10. A low-dielectric adhesive, characterized in that, The low-dielectric adhesive is prepared by the preparation method described in any one of claims 1-9.

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