High-thermal-conductivity low-temperature-curing high-latency conductive adhesive and preparation method thereof

Abstract

This invention discloses a high thermal conductivity, low-temperature curing, high latency conductive adhesive and its preparation method. The high thermal conductivity, low-temperature curing, high latency conductive adhesive comprises the following components in parts by weight: 3-7 parts tetrafunctional amine-curing epoxy resin; 1-5 parts toughened epoxy resin; 5-9 parts trifunctional high-activity epoxy resin; 3-7 parts core-shell microcapsules; 80-90 parts flake silver powder; 0.05-0.2 parts silane coupling agent; and 0.05-0.2 parts dispersant. The conductive adhesive provided by this invention exhibits long latency, rapid low-temperature curing, and high heat resistance, while also possessing excellent electrical and thermal conductivity as well as mechanical properties. It can precisely meet the multifunctional requirements of high-end electronic devices such as 800G / 1.6T optical modules, and has broad prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of conductive adhesive materials technology, specifically to a high thermal conductivity, low-temperature curing, high latency conductive adhesive and its preparation method. Background Technology

[0002] As optical modules evolve towards 800G, 1.6T, and even higher speeds, their applications in cutting-edge fields such as AI computing clusters, 5G / 6G base stations, and ultra-long-distance transmission using hollow-core optical fibers are becoming increasingly widespread. However, with the increase in the electrical interface speed of optical modules to the 224G and 448G levels, the sensitivity of device parasitic parameters and the demand for thermal conductivity have increased simultaneously. Furthermore, temperature-sensitive chips place higher demands on the low-temperature curing performance of single-component conductive adhesives. At the same time, the mismatch in the coefficient of thermal expansion caused by the increase in power density further exacerbates the stringency of chip-level reliability testing.

[0003] Currently, most mainstream conductive adhesive products (such as EPOTECH-H20E / H37) are epoxy resin systems combined with latent amine curing agents, using silver powder as a filler. These conductive adhesives are widely used in IC chip bonding, microelectronic devices, optoelectronic chip packaging, and point-to-point interconnection of PCB circuits, providing stable, weather-resistant bonding performance and electrical and thermal conductivity. However, for some temperature-sensitive electronic devices, in process scenarios ≤80℃, there are technical defects such as low low-temperature reaction rates and insufficient thermal conductivity after curing, making it difficult to meet the performance requirements of high-end optical module applications.

[0004] CN113265210A discloses a high electrical and thermal conductivity adhesive. This adhesive uses epoxy resin as a matrix and incorporates silver powder with specific tap density and particle size as a conductive filler. By compounding silver powder with different particle sizes to increase the filler packing density, a thermal conductivity greater than 10 W / m•K and a volume resistivity less than 9 × 10⁻⁶ are achieved. -5 The electrical and thermal conductivity of Ω•cm solves the technical problem that the thermal conductivity of traditional conductive adhesives is generally below 5W / m•k. However, this technical solution still has obvious limitations. The system requires the addition of solvents to adjust the viscosity, and the curing process relies on high-temperature sintering, which cannot meet the low-temperature curing requirements of temperature-sensitive chips in 800G / 1.6T optical modules. At the same time, the adhesive is not designed with a latent curing system, has poor room temperature storage stability, and its mechanical properties and temperature resistance reliability are difficult to match the long-term service requirements of high-end optical modules, and cannot meet the multi-functional application requirements brought about by the high frequency and miniaturization of optical module electrical interfaces.

[0005] CN102391472A discloses a latent curing agent for epoxy resin microcapsules synthesized from acrylic acid modified resin. By preparing microcapsules using imidazole and synthetic resin adducts as core materials and ethyl cellulose as wall materials, the latent curing agent is regulated. The adhesive formulated with epoxy resin has a shelf life of more than 15 days at 40°C and a bonding strength of more than 10 MPa, which improves to some extent the problems of short shelf life and high brittleness of traditional latent curing agents. However, this technical solution still has many shortcomings in adapting to high-end optical module applications: First, the curing trigger temperature of the microcapsule curing agent is 110-120℃, which is far higher than the low-temperature curing process requirement of ≤80℃ for temperature-sensitive chips in 800G / 1.6T optical modules, and cannot meet the core requirement of low-temperature rapid curing; Second, its curing system is only based on the design of a single imidazole component, without combining the synergistic effect of multiple types of curing agents. The thermal conductivity, heat resistance and mechanical reliability of the cured adhesive have not been specifically optimized, making it difficult to match the thermal conductivity and long-term service requirements of high-power density optical modules; Third, the microcapsule uses ethyl cellulose as the wall material, which has a simple wall structure. The rupture and release efficiency of active components in the low-temperature range are low, and the active sites of the curing agent are not chemically modified and shielded. The improvement of latency relies only on physical encapsulation. There is still a problem of slow leakage of active components when stored at room temperature, which cannot meet the industrial production line storage requirements of single-component conductive adhesives.

[0006] Therefore, there is an urgent need to develop a conductive adhesive that combines low-temperature rapid curing, long latency, high thermal conductivity, high heat resistance, and excellent mechanical reliability to precisely meet the multifunctional requirements of high-end electronic devices such as 800G / 1.6T optical modules. Summary of the Invention

[0007] Therefore, embodiments of the present invention provide a high thermal conductivity, low-temperature curing, high latency conductive adhesive and its preparation method.

[0008] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0009] According to a first aspect of the present invention, the present invention provides a high thermal conductivity, low-temperature curing, high latency conductive adhesive, comprising the following components in parts by weight:

[0010] 3-7 parts of tetrafunctional amine-cured epoxy resin;

[0011] 1-5 parts of toughening epoxy resin;

[0012] 5-9 parts of trifunctional, highly reactive epoxy resin;

[0013] 3-7 portions of core-shell microcapsules;

[0014] 80-90 parts of flake silver powder;

[0015] 0.05-0.2 parts of silane coupling agent;

[0016] Dispersant 0.05-0.2 parts.

[0017] Furthermore, it includes the following components in parts by weight:

[0018] Five parts of tetrafunctional amine-cured epoxy resin;

[0019] 3 parts toughening epoxy resin;

[0020] 7 parts of trifunctional, highly reactive epoxy resin;

[0021] Five portions of core-shell microcapsules;

[0022] 85 parts of flake silver powder;

[0023] 0.1 parts of silane coupling agent;

[0024] 0.1 parts of dispersant.

[0025] Furthermore, the preparation method of the core-shell microcapsules includes the following steps:

[0026] (1) 1-Methylimidazolium reacts with polyethylene glycol diglycidyl ether to give the first product I-PEG;

[0027] (2) 4-Isopropylphenyl isocyanate reacts with dimethylamine to give the second product U-BH;

[0028] (3) Dicyandiamide reacted with 1,3-bis(4'-glycidyl ether phenyl)adamantane in the presence of potassium carbonate to give the third product Ad-dicy;

[0029] (4) I-PEG, U-BH, and Ad-dicy were dissolved in butyl acetate, and polyurea shells were formed by in-situ polymerization of 4-diisocyanate and tripentaerythritol to obtain shells with a thickness of 80-120 nm and a particle size D 50 Core-shell microcapsules with a diameter of 1.5-2 µm.

[0030] Further, in step (1), the mass ratio of 1-methylimidazole to polyethylene glycol diglycidyl ether is 70:1000, and the reaction conditions are: temperature 90℃, time 4h;

[0031] In step (2), the mass ratio of 4-isopropylphenyl isocyanate to dimethylamine is 160:46, and the reaction conditions are: stirring at 0-5℃ for 1 h, and then stirring at 22-25℃ for 2 h.

[0032] In step (3), the mass ratio of dicyandiamide, 1,3-bis(4'-glycidyl ether phenyl)adamantane, and potassium carbonate is 85:210:7, and the reaction conditions are: temperature 110℃, time 6h;

[0033] In step (4), the mass ratio of I-PEG, U-BH and Ad-dicy is 4.5-5.5:1.5-2.5:0.5-1.5.

[0034] Furthermore, the tetrafunctional amine-cured epoxy resin is tetraglycidyldiaminodiphenylmethane;

[0035] The toughening epoxy resin is a rubber elastomer toughening epoxy resin, such as a polymer of polybutadiene rubber and bisphenol A epoxy resin.

[0036] The trifunctional high-activity epoxy resin is a trifunctional glycidyl amine epoxy resin, such as an aromatic amine skeleton at the molecular center, with three glycidyl groups directly connected to nitrogen atoms.

[0037] The D of the flake-shaped silver powder 50 =2-4µm, specific surface area is 0.5-0.8m² 2 / g;

[0038] The silane coupling agent is KH-560;

[0039] The dispersant is a polymeric nonionic dispersant.

[0040] In some preferred embodiments, the polymeric nonionic dispersant has an AB block or comb-like structure, and its molecular chain contains anchoring groups such as carboxyl groups; it also contains polyether segments as solvation chains, achieving homogeneous dispersion and stable suspension of the powder in the polymer system through steric hindrance. As an example, Nippon Oil Co., Ltd.'s NOPCALL 5200 can be used. The dispersant of the present invention can form a strong adsorption layer on the powder surface, and achieve homogeneous dispersion and stable suspension of the powder in the polymer system through steric hindrance and solvation.

[0041] According to a second aspect of the present invention, the present invention provides a method for preparing a high thermal conductivity, low-temperature curing, high latency conductive adhesive as described above, the method comprising:

[0042] A tetrafunctional amine-cured epoxy resin, a toughened epoxy resin, a trifunctional high-activity epoxy resin, and core-shell microcapsules are mixed and dispersed at high speed. A silane coupling agent and a dispersant are added and mixed evenly. Then, flake silver powder is added and dispersed at high speed. After high-speed dispersion, the mixture is dispersed by three-roll milling and vacuum degassing to obtain the high thermal conductivity, low-temperature curing, high latency conductive adhesive.

[0043] Furthermore, the high-speed dispersion rotation speed is 800-1200 rpm / min.

[0044] Furthermore, the conditions for the three-roll milling and dispersion are: a rotation speed of 280 rpm, and roller gaps of 60 μm, 40 μm, 20 μm, and 10 μm sequentially, with each gap group being dispersed twice. This invention achieves gradual refinement through a gradient reduction in gap size. The initial 60 μm gap breaks down large agglomerates, and subsequently, the gaps are successively reduced to 40, 20, and 10 μm to disperse smaller agglomerates, avoiding particle morphology damage caused by a single high-pressure operation. Dispersing twice per gap group ensures sufficient dispersion, allowing the silver powder to be evenly distributed in the carrier. This operation effectively improves the dispersion uniformity of the raw materials, thereby ensuring the stability and uniformity of the prepared conductive adhesive.

[0045] Furthermore, the vacuum degassing conditions are: 1000 rpm rotation speed, 0.5 kPa pressure, and 1.5 minutes. This invention utilizes the centrifugal force generated by the 1000 rpm rotation speed, combined with a low-pressure environment of 0.5 kPa, to efficiently remove air bubbles from the adhesive (air bubbles are the main source of voids after curing, reducing thermal / electrical conductivity). The 1.5-minute degassing time is set to balance degassing efficiency and process stability (too short a time may result in incomplete bubble removal, while too long a time may lead to evaporation of the adhesive mixture or sedimentation of fillers). This operation thoroughly removes air bubbles from the adhesive, reduces the porosity of the cured product, and improves the tightness and reliability of the interfacial bonding.

[0046] The embodiments of the present invention have the following advantages:

[0047] This invention constructs a ternary curing system using imidazole (curing initiator), organic urea (curing initiator), and dicyandiamide (curing agent). The system is temporarily deactivated through covalent grafting and spatial shielding mechanisms, and then encapsulated to form latent microcapsules with a core-shell structure. These microcapsules, as a latent curing system, effectively solve the problems of poor latency, slow low-temperature curing rate, and insufficient heat resistance found in existing conductive adhesives.

[0048] Specifically: 1-methylimidazole was modified by NH epoxy addition with polyethylene glycol diglycidyl ether (PEGDGE) to generate I-PEG, which shielded the active site and extended its half-life at room temperature (25℃) by about 20 times; sterically hindered urea U-BH was generated by reacting 4-isopropylphenyl isocyanate with dimethylamine, where NH was shielded by the ortho-isopropyl group, reducing the hydrogen bond donor ability by about 50%; dicyandiamide cyano group was modified by epoxy addition with 1,3-bis(4'-glycidyl ether phenyl)adamantane (ADGEB) to generate Ad-dicy, whose melting point was reduced from 209℃ to 125℃, and it could melt and participate in curing at 70℃; the three modified products were encapsulated in situ by TDI-tripentaerythritol polymerization in a specific ratio to form core-shell microcapsules.

[0049] This invention significantly extends the shelf life (>5 days) of conductive adhesives at room temperature through the physical isolation of core-shell microcapsules. The encapsulated curing agent effectively prevents contact and reaction with epoxy groups during low-temperature storage (standard room temperature storage conditions <25℃) by shielding active sites and physically isolating them. When the temperature rises to the low-temperature range of 70-80℃, the end-capped chemical bonds undergo reversible reactions or break, releasing the active sites of the highly active curing agent. Simultaneously, the microcapsule wall material softens and ruptures, releasing the active components of the curing agent. Specifically, modified imidazole and modified organic urea fully utilize their high reactivity to efficiently initiate the ring-opening reaction of epoxy resin, achieving rapid initiation of the early curing stage. Modified dicyandiamide participates in the later crosslinking reaction, forming a curing network with a gradient distribution of crosslinking density. This curing system not only completes curing rapidly in a short time but also increases the glass transition temperature (Tg) of the cured product by approximately 25℃, achieving a volume resistivity ≤7×10⁻⁶. -5 Ω·cm, thermal conductivity >6W / (mK), shear strength ≥15 MPa.

[0050] In summary, the conductive adhesive provided by this invention has long latency, rapid low-temperature curing and high heat resistance, and also has excellent electrical conductivity, thermal conductivity and mechanical properties. It can precisely match the multifunctional needs of high-end electronic devices such as 800G / 1.6T optical modules and has broad prospects for industrial application. Attached Figure Description

[0051] To more clearly illustrate the embodiments of the present invention or the technical solutions in 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 merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0052] Figure 1 The image shows a TEM image (scale bar is 2 μm) of the core-shell microcapsule provided in Example 1 of this invention. Detailed Implementation

[0053] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In the following description, the tetrafunctional amine-cured epoxy resin is Huntsman MY721 with an epoxy equivalent of 150 g / eq; the toughened epoxy resin is KaneAce MX-154 with an epoxy equivalent of 301 g / eq; the trifunctional high-activity epoxy resin is Huntsman MY0510 with an epoxy equivalent of 150 g / eq; the dispersant is WI-133 from Nippon Oil Co., Ltd.; and the flake silver powder is D. 50 =2-4µm, specific surface area is 0.5-0.8m² 2 / g, Ningxia Zhongse New Materials, Model 3B.

[0055] Example 1

[0056] Preparation method of core-shell microcapsules:

[0057] (1) 1-Methylimidazole (70g, Aladdin 99%) and PEGDGE (1000g, Aladdin Mn≈2000) were heated (90℃) in a glass flask and stirred slowly for 4h. Vacuum devolatilization was performed to obtain a pale yellow liquid, which was denoted as I-PEG.

[0058] (2) 4-Isopropylphenyl isocyanate (160g, Aladdin > 98%) and dimethylamine (115g, Aladdin 40% aqueous solution) were placed in a glass flask and stirred slowly in an ice bath (0-5℃) for 1 hour. Then the ice bath was removed and the mixture was stirred slowly at room temperature (22-25℃) for 2 hours. Finally, the entire reaction solution was poured into pure water at 0℃. The precipitated solid was filtered and dried in an oven at 40-50℃ for 6 hours to obtain a white solid powder, denoted as U-BH.

[0059] (3) Dicyandiamide (85g, Dyhard 100S), 1,3-bis(4'-glycidylphenyl)adamantane (210g, Aladdin 97%), and anhydrous potassium carbonate (7g, Aladdin > 99%) were heated (110℃) in a glass container for 6 hours. The mixture was filtered within 5 minutes, and the filtrate was collected. The filtrate was recrystallized from ethyl acetate at 0-5℃ and dried in an oven at 40-50℃ for 2 hours to obtain white crystals, denoted as Ag-dicy.

[0060] (4) Preparation of core-shell microcapsules

[0061] ① In a beaker, dissolve I-PEG (32.5g), U-BH (13g), Ad-dicy (6.5g) and TDI (133g, BASF 99.9%) in butyl acetate (431g, Aladdin ≥99.5%) and stir until completely dissolved.

[0062] ② In a 5L reactor, add deionized water (2800g), tripentaerythritol (40g, Aladdin-industrial grade), and emulsifier (42g, PVA-217) in sequence. Stir at 60℃ until completely dissolved, and cool to room temperature (25℃).

[0063] ③ Slowly add the liquid obtained in ① to the liquid obtained in ②, and use a homogenizer to stir and emulsify at 8000 rpm for 20 minutes.

[0064] ④ After emulsification, heat to 60℃ and stir slowly (200 rpm) for 4 hours. Cool to room temperature (25℃) and filter using a stainless steel filter with a 5μm pore size. Then wash the filter cake three times with a mixed solvent of deionized water and ethanol (volume ratio 1:1), each time using approximately twice the volume of the filter cake. Finally, transfer the washed wet filter cake to a vacuum drying oven and dry at 40-45℃ and -0.01 MPa or higher vacuum for at least 12 hours until constant weight is achieved, yielding a shell thickness of 80-120 nm and a particle size D. 50 Core-shell microcapsules with a diameter of 1.5-2 µm.

[0065] Example 2

[0066] This embodiment provides a high thermal conductivity, low-temperature curing, high latency conductive adhesive, the raw materials of which are:

[0067] Five parts of tetrafunctional amine-cured epoxy resin, three parts of toughened epoxy resin, seven parts of trifunctional high-activity epoxy resin, five parts of core-shell microcapsules, eighty-five parts of flake silver powder, 0.1 parts of silane coupling agent, and 0.1 parts of dispersant.

[0068] The preparation method of the above-mentioned high thermal conductivity, low-temperature curing, high latency conductive adhesive includes:

[0069] (1) Add tetrafunctional amine-cured epoxy resin, toughened epoxy resin, trifunctional high-activity epoxy resin and core-shell microcapsules in sequence according to the mass fraction of each material to obtain a resin curing agent system; disperse the mixture system at high speed using a planetary mixer, set to 1000 rpm and 5 min, to obtain the primary carrier L.

[0070] (2) Add silane coupling agent and dispersant according to the mass fraction of each material, and stir manually to obtain the additive system mixture J.

[0071] (3) Add the additive system J to the primary carrier L, then add the flake silver powder, and disperse the resulting mixture at high speed using a planetary mixer. Set the speed to 1000 rpm and the time to 5 min to obtain the silver paste premix X.

[0072] (4) The silver paste premix X is dispersed by three-roll milling. The specific operation steps include: three-roll milling and dispersion, with the roller gap starting from an initial 60μm and a milling speed of 280rpm; after each round of milling, the roller gap is reduced, with the milling gaps successively being 60μm, 40μm, 20μm, and 10μm, and each set of gaps is dispersed twice. The dispersion gap limit shall not be lower than the maximum particle size of the silver powder system, to obtain the milled and dispersed paste X.

[0073] (5) The rubber compound X is degassed and homogenized in a vacuum degassed equipment. The specific operation steps include: degassed for 1.5 minutes at a speed of 1000 rpm and a pressure of 0.5 kPa.

[0074] Example 3

[0075] This embodiment provides a high thermal conductivity, low-temperature curing, high latency conductive adhesive, the raw materials of which are: 3 parts tetrafunctional amine-curing epoxy resin, 3 parts toughened epoxy resin, 8 parts trifunctional high-activity epoxy resin, 4 parts core-shell microcapsules, 86 parts flake silver powder, 0.1 parts silane coupling agent, and 0.15 parts dispersant. The preparation method is the same as in Example 2.

[0076] Example 4

[0077] This embodiment provides a high thermal conductivity, low-temperature curing, high latency conductive adhesive, the raw materials of which are: 7 parts tetrafunctional amine-curing epoxy resin, 1 part toughened epoxy resin, 8 parts trifunctional high-activity epoxy resin, 4 parts core-shell microcapsules, 86 parts flake silver powder, 0.1 parts silane coupling agent, and 0.1 parts dispersant. The preparation method is the same as in Example 2.

[0078] Example 5

[0079] This embodiment provides a high thermal conductivity, low-temperature curing, high latency conductive adhesive, the raw materials of which are: 4 parts tetrafunctional amine-curing epoxy resin, 5 parts toughened epoxy resin, 6 parts trifunctional high-activity epoxy resin, 6 parts core-shell microcapsules, 84 parts flake silver powder, 0.1 parts silane coupling agent, and 0.15 parts dispersant. The preparation method is the same as in Example 2.

[0080] Comparative Example 1

[0081] This comparative example provides a conductive adhesive, which differs from Example 2 only in that the core-shell microcapsules are different. The preparation method of the core-shell microcapsules used in this comparative example differs from that in Example 1 in step (4) of preparing the core-shell microcapsules, the amount of I-PEG is 52g, that is, the mass ratio of I-PEG, U-BH and Ad-dicy is 8:2:1.

[0082] Comparative Example 2

[0083] This comparative example provides a conductive adhesive, which differs from Example 2 only in the core-shell microcapsules. The core-shell microcapsules used in this comparative example do not contain any modified imidazole, organic urea, or dicyandiamide. The preparation method is as follows: core-shell microcapsules are prepared using imidazole (32.5g), unsubstituted urea isocyanate (4-isopropylphenyl isocyanate) (13g), and dicyandiamide (6.5g) as raw materials according to step (4) of Example 1.

[0084] Comparative Example 3

[0085] This comparative example provides a conductive adhesive that differs from Example 2 in that a modified curing system without a core-shell structure is used to replace the core-shell microcapsules in Example 2. Specifically, the curing system consists of I-PEG (32.5g), U-BH (13g), and Ad-dicy (6.5g).

[0086] Comparative Example 4

[0087] This comparative example provides a conductive adhesive, which differs from Example 2 in that the core-shell microcapsules are different. The preparation method of the core-shell microcapsules used in this comparative example differs from that in Example 1 in step (4) of preparing the core-shell microcapsules, the amount of I-PEG is 6.5g, the amount of U-BH is 13gg, and the amount of Ad-dicy is 32.5g, that is, the mass ratio of I-PEG, U-BH and Ad-dicy is 1:2:5.

[0088] Test Example 1

[0089] 1. Basic performance

[0090] (1) Latency (shelf life) test method

[0091] After sealing 50g of the sample, it was stored in a 25℃ constant temperature oven. Viscosity was tested periodically. If the viscosity increase was ≤20%, the storage period was considered acceptable. A Brookfield CP51 cone-plate viscometer was used for testing, with the temperature set at 25℃ and the rotation speed at 5 rpm. Initial viscosity: 12000 cP.

[0092] (2) Volume resistivity test method

[0093] A HIOKI RM3545 resistance meter was used; the method disclosed in JP 2020035721A (March 5, 2020) was used for implementation and calculation, and the unit is Ω.cm.

[0094] (3) Shear strength test method:

[0095] A 3 mm × 3 mm silver-plated nickel pillar (purchased from Fukuda SEG Electronics) was bonded to a polished pure silver sheet (Ag≥99.9%) using conductive adhesive. It was then placed in a DHG-9070A forced-air drying oven and cured at 80°C for 1.5 hours, followed by natural cooling at room temperature (25°C). The shear strength was calculated by pushing the silver-plated nickel pillar horizontally at a constant speed until it detached using a push-pull force tester.

[0096] (4) Thermal conductivity test method

[0097] Thermal conductivity was determined using the laser scintillation method according to JIS R1611:1997 standard. Sample preparation: Conductive adhesive was uniformly filled into a cylindrical mold with a diameter of 8 mm and a thickness of 0.5-1 mm, and sintered into a dense, metal-like disk using a stepped heating method. Sintering conditions: 25-80℃, 45 minutes, heating rate 7℃ / min; 80-140℃, 30 minutes, heating rate 7℃ / min; 140-250℃, 150 minutes, heating rate 7℃ / min.

[0098] The basic performance test results of the conductive adhesives in Examples 2-5 and Comparative Examples 1-4 are shown in Table 1 below.

[0099] Table 1

[0100]

[0101] The results show that the conductive adhesives of Examples 1-4 of this invention have a shelf life of >5 days at 25°C, meeting the process requirements of single-component production lines; they can be cured in 1.5 hours at 80°C, with low energy consumption. Furthermore, the volume resistivity after curing is ≤7×10⁻⁶. -5 It exhibits excellent electrical and thermal conductivity and mechanical properties, with a thermal conductivity >6 W / (mK) and a shear strength ≥15 MPa (Al-Al or Cu-Cu). Specifically, in Comparative Example 1, using different mass ratios of I-PEG, U-BH, and Ad-dicy significantly reduced the shear strength. In Comparative Example 2, using unmodified microcapsules resulted in a substantial increase in viscosity and loss of latency. In Comparative Example 3, which only underwent end-capping modification, both exhibited shortened shelf life. In Comparative Example 4, the reduced amount of imidazole and increased amount of dicyandiamide in the core-shell microcapsules significantly decreased the shear strength and reliability, while also resulting in a substantial increase in volume resistivity.

[0102] 2. Reliability (GJB548B-2005)

[0103] (1) High temperature and high humidity test

[0104] The prepared shear strength specimens and resistance test strips were placed in a DHS-100 constant temperature and humidity chamber, with the following conditions set: temperature 85℃; humidity 85%; duration 168 hours. After standing at room temperature for 2 hours, their shear strength and resistance values ​​were tested. Based on the initial performance, the shear strength retention rate and resistance change rate were calculated.

[0105] (2) Temperature cycling test

[0106] The prepared shear strength specimens and resistance test strips were placed in an HZ-2012B(50L) three-chamber thermal shock testing machine. The conditions were set as follows: -55℃ to 150℃; temperature holding time 30 minutes; temperature switching speed 30 seconds / cycle; 1000 temperature cycles. After the cycles, the shear strength and resistance values ​​of the samples were tested. Based on the initial performance, the shear strength retention rate and resistance change rate were calculated.

[0107] (3) High Temperature Aging (HTS) Test

[0108] The samples were placed in a 150℃ forced-air drying oven for long-term heat aging. Samples were taken after 1000 hours to test their shear strength and resistivity. Based on the initial properties, the shear strength retention rate and resistivity change rate were calculated.

[0109] The reliability test results of the conductive adhesives in Examples 2-5 and Comparative Examples 1-4 are shown in Table 2 below.

[0110] Table 2

[0111]

[0112] The results showed that the reliability of the conductive adhesive in Comparative Example 4 was significantly reduced compared with Examples 2-4 and Comparative Examples 1-4.

[0113] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A high thermal conductivity, low-temperature curing, high latency conductive adhesive, characterized in that, The components include the following parts by weight: 3-7 parts of tetrafunctional amine-cured epoxy resin; 1-5 parts of toughening epoxy resin; 5-9 parts of trifunctional, highly reactive epoxy resin; 3-7 portions of core-shell microcapsules; 80-90 parts of flake silver powder; 0.05-0.2 parts of silane coupling agent; Dispersant 0.05-0.2 parts.

2. The high thermal conductivity, low-temperature curing, high latency conductive adhesive according to claim 1, characterized in that, The components include the following parts by weight: Five parts of tetrafunctional amine-cured epoxy resin; 3 parts toughening epoxy resin; 7 parts of trifunctional, highly reactive epoxy resin; Five portions of core-shell microcapsules; 85 parts of flake silver powder; 0.1 parts of silane coupling agent; 0.1 parts of dispersant.

3. The high thermal conductivity, low-temperature curing, high latency conductive adhesive according to claim 1, characterized in that, The preparation method of the core-shell microcapsules includes the following steps: (1) 1-Methylimidazole was reacted with polyethylene glycol diglycidyl ether to obtain the first product I-PEG; (2) 4-Isopropylphenyl isocyanate was reacted with dimethylamine to give the second product U-BH; (3) Dicyandiamide was reacted with 1,3-bis(4'-glycidyl ether phenyl)adamantane in the presence of potassium carbonate to give the third product Ad-dicy; (4) I-PEG, U-BH, and Ad-dicy were dissolved in butyl acetate. Using diisocyanate and pentaerythritol as wall material monomers, a polyurethane shell was formed by in-situ polymerization to obtain a shell thickness of 80-120 nm and a particle size D. 50 Core-shell microcapsules with a diameter of 1.5-2 µm.

4. The high thermal conductivity, low-temperature curing, high latency conductive adhesive according to claim 3, characterized in that, In step (1), the mass ratio of 1-methylimidazole to polyethylene glycol diglycidyl ether is 70:1000, and the reaction conditions are: temperature 90℃, time 4h; In step (2), the mass ratio of 4-isopropylphenyl isocyanate to dimethylamine is 160:46, and the reaction conditions are: stirring at 0-5℃ for 1h, then heating to 22-25℃ and stirring for another 2h. In step (3), the mass ratio of dicyandiamide, 1,3-bis(4'-glycidyl ether phenyl)adamantane, and potassium carbonate is 85:210:7, and the reaction conditions are: temperature 110℃, time 6h; In step (4), the mass ratio of I-PEG, U-BH and Ad-dicy is 4.5-5.5:1.5-2.5:0.5-1.

5.

5. The high thermal conductivity, low-temperature curing, high latency conductive adhesive according to claim 1, characterized in that, The tetrafunctional amine-cured epoxy resin is tetraglycidyl diaminodiphenylmethane; The toughening epoxy resin is a rubber elastomer toughening epoxy resin; The trifunctional high-temperature resistant active epoxy resin is a trifunctional glycidylamine epoxy resin. The D of the flake-shaped silver powder 50 =2-4µm, specific surface area is 0.5-0.8m² 2 / g; The silane coupling agent is KH-560; The dispersant is a polymeric nonionic dispersant.

6. The preparation method of the high thermal conductivity, low-temperature curing, high latency conductive adhesive according to any one of claims 1-5, characterized in that, The method includes: A tetrafunctional amine-cured epoxy resin, a toughened epoxy resin, a trifunctional high-activity epoxy resin, and core-shell microcapsules are mixed and dispersed at high speed. A silane coupling agent and a dispersant are added and mixed evenly. Then, flake silver powder is added and dispersed at high speed. After high-speed dispersion, the mixture is dispersed by three-roll milling and vacuum degassing to obtain the high thermal conductivity, low-temperature curing, high latency conductive adhesive.

7. The preparation method of the high thermal conductivity, low-temperature curing, high latency conductive adhesive according to claim 6, characterized in that, The high-speed dispersion operates at a rotation speed of 800-1200 rpm.

8. The preparation method of the high thermal conductivity, low-temperature curing, high latency conductive adhesive according to claim 6, characterized in that, The conditions for the three-roll milling and dispersion are: rotation speed 280 rpm, roller gaps of 60 μm, 40 μm, 20 μm and 10 μm respectively, and dispersion twice for each gap.

9. The preparation method of the high thermal conductivity, low-temperature curing, high latency conductive adhesive according to claim 6, characterized in that, The vacuum degassing conditions are: 1000 rpm, 0.5 kPa, and 1.5 minutes.

Images