A near-zero thermal expansion coefficient heat-conducting adhesive, a preparation method and application thereof

Abstract

The application provides a near-zero thermal expansion coefficient heat-conducting adhesive and a preparation method and application thereof, and belongs to the technical field of thermal interface materials. The application solves the triangular contradiction of heat-conducting performance, thermal expansion coefficient and bonding performance by designing a core-shell adhesive material. The core layer is a liquid metal modified low-expansion coefficient inorganic filler, which plays a role of heat conduction and low thermal expansion. The shell layer is an ultrathin polymer network, which plays a role of bonding. The core-shell structure adhesive material can be prepared by a coaxial core-shell structure needle head extrusion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal interface materials, and relates to an adhesive material and a preparation method and application thereof, in particular to a near-zero thermal expansion coefficient heat-conducting adhesive and a preparation method and application thereof. BACKGROUND

[0002] With the wide application of advanced optoelectronic systems such as high-energy lasers, high-power microwaves, high-computing artificial intelligence and high-density core particle integration in many fields, a large amount of heat is generated during system operation, which seriously affects the performance stability, operation efficiency and service life of the system. Therefore, developing a material with excellent thermal conductivity and low thermal expansion coefficient has become the focus of current research.

[0003] Especially in precision optoelectronic devices, thermal stress caused by thermal expansion mismatch between heterogeneous materials may lead to reliability problems such as interface contact failure and optical path deviation. Therefore, it is urgent to develop an adhesive with high thermal conductivity and low thermal expansion to meet the long-term stable application requirements of optoelectronic systems under harsh working conditions.

[0004] In the field of heat-conducting adhesives, for example, CN118617776A discloses a heat-conducting composite material suitable for thermal management of optoelectronic devices. By modifying the inorganic heat-conducting filler in the polymer matrix, the thermal conductivity of the material is significantly improved.

[0005] Although various techniques have been reported to improve the thermal conductivity and thermal resistance of adhesives, the problem of high thermal expansion coefficient of heat-conducting adhesives has not been solved. Even though some strategies can reduce the thermal expansion coefficient of heat-conducting adhesives, they are still far from the near-zero thermal expansion coefficient. The difficulty lies in the fact that the control of thermal conductivity and thermal expansion coefficient depends on the addition of a large amount of different inorganic fillers, and the total amount of fillers is limited. Therefore, high thermal conductivity and low thermal expansion are contradictory. SUMMARY

[0006] In view of the lack of heat-conducting adhesives with near-zero thermal expansion coefficient in the prior art, the present application provides a heat-conducting adhesive with near-zero thermal expansion coefficient and a preparation method and application thereof. The present application solves the triangular contradiction of thermal conductivity, thermal expansion coefficient and bonding performance by designing a core-shell adhesive material. The core layer is a low-expansion inorganic filler modified by a liquid metal, which plays a role in heat conduction and low thermal expansion. The shell layer is an ultrathin polymer network, which plays a role in bonding. This core-shell structure adhesive material can be prepared by a coaxial needle head extrusion.

[0007] The technical scheme of the present application is as follows:

[0008] The heat-conducting adhesive with near-zero thermal expansion coefficient described in the present application is a core-shell adhesive:

[0009] The core layer is a liquid metal modified inorganic powder material with heat conduction and expansion inhibition functions, and is realized by a unique mechanochemical modification treatment method.

[0010] The shell layer is a polymer solution material with bonding function, which is obtained by mixing a polymer matrix with a solvent and an additive according to a specified ratio, and the mixing conditions are vacuum, mixing time of 1-30 min, mixing rate of 1000 rpm, and mixing equipment of a stirred tank or a homogenizer.

[0011] The core-shell structure adhesive provided by the application has the following characteristics:

[0012] The core layer is a liquid metal modified inorganic powder filler, the content of liquid metal is low, and the thickness is 50-1000 μm.

[0013] The shell layer is a polymer layer, and the thickness is 0.01-1 μm.

[0014] In particular, theoretically, the core-shell structure adhesive will be blocked in the heat conduction path due to the low thermal conductivity and high thickness of the pure polymer shell layer, and the thermal conductivity will be greatly reduced.

[0015] The purpose of the application is achieved by the following technical solutions:

[0016] A near-zero thermal expansion coefficient heat-conducting adhesive is a core-shell structure adhesive, which comprises an adhesive skin layer and an adhesive core layer.

[0017] The adhesive skin layer includes a polymer matrix, solvent, and additives;

[0018] The thickness of the adhesive skin layer is 0.01 μm to 1 μm; the solid content of the adhesive skin layer, i.e., the ratio of the polymer matrix, is 0.01 wt% to 5 wt%.

[0019] The thickness of the adhesive core layer is 1 μm to 1000 μm; the adhesive core layer comprises liquid metal and inorganic filler; by mass fraction, the liquid metal accounts for 0.01 wt% to 6 wt% of the total mass of the adhesive core layer.

[0020] The physicochemical properties of the near-zero thermal expansion coefficient thermally conductive adhesive include:

[0021] The thermal conductivity is 2.4 W / (m·K)~4.0 W / (m·K);

[0022] Thermal resistance is 27 K mm² W -1 ~40K mm² W -1 ;

[0023] The coefficient of thermal expansion is 4×10 -6 K -1 ~8×10 -6 K -1 ;

[0024] The shear strength is 5.0 MPa to 9.9 MPa.

[0025] Furthermore, the polymer matrix is ​​at least one of epoxy resin, acrylic resin, silicone resin, polyimide resin, and polysilazane resin; the solvent is at least one of water, ethanol, acetone, N-methylpyrrolidone, ethyl acetate, cyclohexanone, and xylene; and the additives are crosslinking agents and initiators required for the corresponding polymer matrix.

[0026] Furthermore, the liquid metal is at least one of mercury, bismuth, gallium, tin, indium, rubidium, and cesium; the inorganic filler is at least one of low expansion coefficient fillers or negative expansion coefficient fillers such as tungsten zirconium phosphate, zirconium tungstate, fused silica, glass fiber, and bismuth nickel iron oxide.

[0027] Furthermore, the adhesive skin has a porous and ultra-thin structure after curing.

[0028] This invention also relates to a method for preparing a near-zero thermal expansion coefficient thermally conductive adhesive, comprising the following steps: preparing raw materials for the adhesive core layer, preparing raw materials for the adhesive skin layer, and co-extruding the adhesive skin layer and the core layer via a syringe.

[0029] S1, the raw material for preparing the adhesive core layer:

[0030] The raw material for preparing the adhesive core layer is obtained by coating the surface of the inorganic filler with liquid metal and then performing mechanochemical treatment;

[0031] The working condition parameters of the mechanochemical treatment include: using a treatment device under the conditions of a temperature of 10-200 DEG C, a pressure of 0.1-10 MPa, and a time of 1-60 min;

[0032] S2, the raw material for preparing the adhesive skin layer:

[0033] The polymer matrix, solvent and additives are mixed according to the set proportion, the mixing condition is vacuum, the mixing time is 1-30 min, and the mixing rate is 100-4000 rpm;

[0034] S3, the adhesive skin layer and the core layer are compounded through a double-layer coaxial needle tube:

[0035] The raw material of the adhesive skin layer is fed into the outer layer of the double-layer coaxial needle tube, and the raw material of the adhesive core layer is fed into the inner layer of the double-layer coaxial needle tube, and the needle tube simultaneously extrudes the two kinds of raw materials to obtain the adhesive with core-shell structure;

[0036] The double-layer coaxial needle tube has a structure of extremely thin skin layer and extremely thick core layer, the inner diameter of the inner ring of the needle tube core layer is 50-1000 μm, and the inner diameter of the inner ring of the skin layer is 50.01-1000.01 μm, that is, the thickness (0.01-1 μm) of the skin layer is less than 1 / 500 of the thickness (50-1000 μm) of the core layer.

[0037] Further, the treatment device in S1 is at least one of a flat press, a ball mill and a grinder.

[0038] Further, the mixing in S2 is using a stirred tank or a homogenizer.

[0039] Further, the shape of the double-layer coaxial needle tube in S3 is one of circular, square, triangular or special-shaped. The application also relates to the application of the above-mentioned near-zero thermal expansion coefficient thermal conductive adhesive, which is used for packaging optoelectronic devices, and the performance of the optoelectronic devices is very stable.

[0040] Further, the packaging interface of the optoelectronic device involves one of the interface between silicon-based materials and metal materials, the interface between carbon-based materials and metal materials, and the interface between silicon-based materials.

[0041] Further, the encapsulation interface of the photoelectric device is cured by heating / illumination combined with pressure using the above-mentioned near-zero thermal expansion coefficient heat-conducting adhesive, on the one hand, the solvent in the surface layer of the polymer of the adhesive is fully volatilized and fully cured, on the other hand, the thickness of the skin layer of the adhesive is further reduced by removing the solvent in the skin layer of the adhesive and applying external pressure, so that the core layer of the adhesive infiltrates the porous structure of the skin layer of the adhesive, and the liquid metal and inorganic filler can penetrate through the entire adhesive layer, thereby maximizing the thermal conductivity and reducing the thermal expansion.

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] 1. The near-zero thermal expansion coefficient heat-conducting adhesive provided by the present application is a core-shell adhesive, the surface polymer layer has an extremely thin and porous structure, and the extremely thin and porous structure of the surface layer enables the adhesive to achieve good surface bonding strength at a very low content of polymer material, while the core layer is filled with 100% content of liquid metal modified negative expansion coefficient filler, thereby achieving extremely high thermal conductivity and extremely low thermal expansion coefficient. This structure can break the contradiction between low thermal resistance (27K mm² W -1 ~40K mm² W -1 ), low thermal expansion performance (4×10 -6 K -1 ~8×10 -6 K -1 ) and high bonding performance (i.e. shear strength of 5.0MPa~9.9MPa) of the heat interface material heat-conducting adhesive in the past.

[0044] 2. The preparation method of the near-zero thermal expansion coefficient heat-conducting adhesive provided by the present application is different from the simple blending preparation method of traditional single-component adhesive and two-component adhesive, but is inspired by the coaxial spinning technology, and a coaxial needle double-layer co-extrusion core-shell adhesive preparation technology is developed. This technology is simple to operate and easy to produce continuously, and can simply and quickly produce a large amount of core-shell structure adhesive. More particularly, the core-shell structure has an extremely thin and porous surface layer, so the amount of polymer is extremely low, the amount of functional filler is extremely large, and the functionality (heat conduction and thermal expansion inhibition) of the adhesive is very prominent.

[0045] 3. The photoelectric device encapsulated by the near-zero thermal expansion heat-conducting adhesive provided by the present application not only has the advantages of high-efficiency heat dissipation brought by the heat-conducting adhesive of the prior art, but also has an additional ultra-low thermal expansion coefficient (4×10 -6 K -1 ~8×10 -6 K -1 ), which can greatly reduce thermal stress and structural deformation and ensure long-term stability of the photoelectric device under wide temperature variation. BRIEF DESCRIPTION OF DRAWINGS

[0046] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of the specification, illustrate embodiments of the application and are used to explain the application, but are not to be considered limiting of the application.

[0047] Figure 1 Process flow chart of the preparation method of the near-zero thermal expansion coefficient heat-conducting adhesive according to the application;

[0048] Figure 2 Preparation principle and structural schematic diagram of the near-zero thermal expansion heat-conducting adhesive prepared in Example 1 of the application;

[0049] Figure 3 Device application and performance schematic diagram of the near-zero thermal expansion heat-conducting adhesive prepared in Example 1 of the application. DETAILED DESCRIPTION

[0050] The application will be described in further detail through examples. It is necessary to point out here that the examples are only used to further illustrate the application and cannot be understood as limiting the scope of the application. Those skilled in the art can make some non-essential improvements and adjustments according to the content of the application.

[0051] In the embodiments of the application, the near-zero thermal expansion coefficient heat-conducting adhesive is an adhesive with a core-shell structure: the core layer is a liquid metal modified inorganic powder material with heat-conducting and expansion inhibiting functions, which is realized through a unique mechanical-chemical modification treatment method. In the embodiments of the application, the working condition parameters of the mechanical-chemical treatment include: using a treatment device to perform treatment under the conditions of a temperature of 10 ℃ to 200 ℃, a pressure of 0.1 MPa to 10 MPa, and a time of 1 min to 60 min; the treatment device is at least one of a flat plate press, a ball mill, and a grinder. In particular, the inorganic powder filler with a negative (low) thermal expansion coefficient is treated in the core layer.

[0052] The shell layer is a polymer solution material with a bonding effect, which is obtained by mixing a high molecular matrix, a solvent, and an additive according to a specified proportion, the mixing conditions are vacuum, a mixing time of 1 min to 30 min, a mixing rate of 1000 rpm, and a mixing device of a stirred tank or a homogenizer; the high molecular matrix is at least one of an epoxy resin, an acrylic resin, a silicone resin, a polyimide resin, and a polysilazane resin; the additive is a crosslinking agent and an initiator required for the corresponding high molecular matrix, and the solvent is at least one of water, ethanol, acetone, tetrahydrofuran, N-methyl pyrrolidone, ethyl acetate, cyclohexanone, and dimethylbenzene.

[0053] In the embodiments of the application, the structure of the core-shell structure adhesive provided has the following characteristics:

[0054] Core layer: Liquid metal modified inorganic powder filler, low liquid metal content, thickness: 50μm ~1000μm;

[0055] Shell: Polymer layer, thickness: 0.01μm~1μm.

[0056] The thermal conductivity and thermal resistance of adhesive thermal interface materials were measured using an LW-9389 TIM thermal resistance and thermal conductivity measuring instrument according to ASTM D-5470 standard. The test was conducted at a temperature of 80 °C and a pressure of 40 psi.

[0057] The thermal expansion properties of the cured adhesive material were tested using the Discovery TMA 450 from TA Instruments, with the test direction being the coefficient of thermal expansion along the z-axis.

[0058] The adhesive properties of the adhesive materials were tested using an INSTRON 5967 universal testing machine. Before testing, the adhesive was bonded to the interface of two metal plates, and the load cell was set to 500 N. To ensure the reliability of the data, at least five samples were tested in each experiment.

[0059] Example 1:

[0060] A method for preparing a thermally conductive adhesive with a near-zero coefficient of thermal expansion includes the following three steps, the preparation process of which is as follows: Figure 1 As shown:

[0061] S1. Raw materials for preparing the adhesive core layer:

[0062] 0.1g of liquid gallium metal and 9.9g of tungsten zirconium phosphate powder (D50 particle size 1.5μm) were placed together in a ball mill and milled at 1000rpm for 50min at room temperature. The product was then placed in a flat hot press and pressed for 10min at room temperature and 10MPa to obtain the raw material for the adhesive core layer.

[0063] S2. Raw materials for preparing the adhesive skin layer:

[0064] 10g of acrylic-modified photocurable silicone resin, 9.9g of acetone, 0.001g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 0.001g of triethanolamine were placed in a mixer, vacuum was applied, the mixing rate was 3600rpm, the mixing mode was rotation combined with revolution, and the mixing time was 3min to obtain the raw material for the adhesive skin layer.

[0065] S3. The adhesive skin layer and core layer are bonded together via a double-layer coaxial needle tube:

[0066] Figure 2 The preparation principle and structural diagram of the near-zero thermal expansion heat-conducting adhesive prepared in Example 1 are shown in FIG. 1. Figure 2 As shown in FIG. 1, the raw material of the adhesive skin layer is fed into the outer layer of the double-layer coaxial needle tube, and the raw material of the adhesive core layer is fed into the inner layer of the double-layer coaxial needle tube. The needle tube extrudes the two kinds of raw materials at the same time to obtain the adhesive with a core-shell structure. The material of the double-layer coaxial needle tube is stainless steel, which has the structural characteristics of extremely thin skin layer and extremely thick core layer. The inner diameter of the inner ring of the needle tube core layer is 100 μm, and the inner diameter of the inner ring of the skin layer is 102 μm, that is, the thickness (2 μm) of the skin layer is 1 / 50 of the thickness (100 μm) of the core layer.

[0067] The application of the above-mentioned near-zero thermal expansion coefficient heat-conducting adhesive is to use the near-zero thermal expansion coefficient heat-conducting adhesive to bond the interface of the hetero-materials of the optoelectronic device.

[0068] Figure 3 The device application and performance diagram of the near-zero thermal expansion heat-conducting adhesive prepared in Example 1 are shown in FIG. 2. Figure 3 As shown in FIG. 2, the adhesive with a core-shell structure is extruded to the interface between the diamond and the microcrystalline glass of the optoelectronic device. A UV lamp with a power of 125 W and a wavelength of 365 nm-405 nm is used for irradiation for 10 s for curing. Then, the bonded device is subjected to external use of a flat press to apply a pressure of 0.1 MPa and heated to 150 ℃ for 3 min to make it fully cured and bonded to the interface of the hetero-materials. The amount of the adhesive depends on the area and thickness of the interface. The optoelectronic device is operated for 30 days to observe the changes in the light path deviation and the stability of the performance of the optoelectronic device.

[0069] Example 2

[0070] A preparation method of a near-zero thermal expansion coefficient heat-conducting adhesive, which is different from Example 1 in that the inner diameter of the inner ring of the needle tube core layer is 100 μm, and the inner diameter of the inner ring of the skin layer is 100.5 μm, that is, the thickness (0.5 μm) of the skin layer is 1 / 500 of the thickness (100 μm) of the core layer, and the remaining conditions and parameters are unchanged.

[0071] Example 3

[0072] A preparation method of a near-zero thermal expansion coefficient heat-conducting adhesive, which is different from Example 2 in that the content of the liquid metal is increased when the raw material of the adhesive core layer is prepared in step S1. The ratio of the liquid metal to the powder is adjusted to 0.5 g of liquid metal gallium and 9.5 g of tungsten-zirconium phosphate powder (D50 particle size 1.5 μm) together in a ball mill for grinding. The remaining conditions and parameters are unchanged.

[0073] Example 4

[0074] A preparation method of a near-zero thermal expansion coefficient heat-conducting adhesive, which is different from example 3 in that the type of liquid metal in the raw material for preparing the adhesive core layer in step S1 is changed from liquid metal gallium to liquid metal gallium indium tin, and the remaining conditions and parameters are unchanged.

[0075] Example 5:

[0076] A preparation method of a near-zero thermal expansion coefficient heat-conducting adhesive, which is different from example 4 in that the raw material for preparing the adhesive skin layer in step S2 is changed: 10 g of urethane group modified epoxy resin, 9.9 g of tetrahydrofuran, 0.001 g of phthalic anhydride, and 0.001 g of 2-methyl imidazole are placed in a mixing machine, vacuum is drawn, the mixing rate is 3600 rpm, the mixing mode is self-rotation combined with revolution, and the mixing time is 3 min to obtain the raw material for the adhesive skin layer, and the remaining conditions and parameters are unchanged.

[0077] Comparative example 1:

[0078] A preparation method of an adhesive without core-shell structure and filler, which is different from example 1 in that no filler is introduced: 10 g of acrylic acid modified photocurable silicone resin, 9.9 g of acetone, 0.001 g of 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, and 0.001 g of triethanolamine are directly placed in a mixing machine, vacuum is drawn, the mixing rate is 3600 rpm, the mixing mode is self-rotation combined with revolution, and the mixing time is 3 min to obtain the adhesive, and the remaining conditions and parameters are unchanged.

[0079] Comparative example 2:

[0080] A preparation method of a heat-conducting and low-thermal expansion adhesive without core-shell structure, which is different from example 1 in that the liquid metal modified inorganic powder filler is directly physically blended with the adhesive without forming a core-shell structure: 0.1 g of liquid metal gallium and 9.9 g of tungsten-zirconium phosphate powder (D50 particle size 1.5 μm), 10 g of acrylic acid modified photocurable silicone resin, 9.9 g of acetone, 0.001 g of 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, and 0.001 g of triethanolamine are placed together in a mixing machine, vacuum is drawn, the mixing rate is 3600 rpm, the mixing mode is self-rotation combined with revolution, and the mixing time is 3 min to obtain the adhesive, and the remaining conditions and parameters are unchanged.

[0081] Comparative example 3:

[0082] A preparation method of an adhesive with a core-shell structure, which is different from example 1 in that when the adhesive skin layer and the core layer are compounded through a double-layer coaxial needle tube in step S3, they do not have the structural characteristics of an extremely thin skin layer and an extremely thick core layer:

[0083] The raw material of the adhesive skin layer is fed into the outer layer of the double-layer coaxial needle tube, and the raw material of the adhesive core layer is fed into the inner layer of the double-layer coaxial needle tube, and the needle tube extrudes the two kinds of raw materials at the same time to obtain the adhesive with core-shell structure. The material of the double-layer coaxial needle tube is stainless steel, which has the structural characteristics of extremely thin skin layer and extremely thick core layer. The inner diameter of the inner ring of the core layer of the needle tube is 100 μm, and the inner diameter of the inner ring of the skin layer is 200 μm, that is, the thickness of the skin layer (100 μm) is consistent with the core layer (100 μm), and the remaining conditions and parameters are unchanged.

[0084] Results and discussion:

[0085] The properties of Examples 1-6 and Comparative Examples 1-3 are shown in Table 1:

[0086] Table 1: Material thermal conductivity, material thermal resistance, material thermal expansion coefficient, interface bonding strength, and performance stability of optoelectronic devices

[0087]

[0088] 1. As can be seen from the comparison of Example 1 and Comparative Example 1 in Table 1, after introducing the liquid metal modified inorganic powder filler into the polymer matrix of the adhesive in Example 1, the thermal conductivity of the material is significantly increased, from 0.3 W m -1 K -1 of Comparative Example 1 to 2.4 W m -1 K -1 , an increase of nearly 7 times; the thermal resistance is significantly reduced, from 120 mm 2 KW -1 of Comparative Example 1 to 40 mm 2 KW -1 of Example 1, the thermal expansion coefficient is reduced from 152 mm 2 KW -1 to 6 mm 2 KW -1 , a decrease of 4%; the improvement of comprehensive thermal performance significantly improves the performance stability of the optoelectronic device, and the stability of the optical path and structure is improved from unstable to stable.

[0089] 2. As can be seen from the comparison of Example 1 and Comparative Example 2, the core-shell structure of Example 1 has more outstanding thermal performance than the simple mixed and uniformly dispersed structure of Comparative Example 2, with an increase of 71% in thermal conductivity, a decrease of 44% in thermal resistance, a decrease of 47% in thermal expansion coefficient, and an increase of 100% in bonding strength. The stability of the optoelectronic device is improved from relatively stable to stable, which shows that the special core-shell structure design of the present application can better break through the limits of the thermal conductivity, thermal expansion performance and bonding performance of the adhesive material, and achieve the balance of the three and the improvement of the reliability of the device performance.

[0090] 3、By comparing example 1 with comparative example 3, it can be seen that the core-shell structure adhesive of example 1 has more outstanding thermal performance than that of comparative example 3, the thermal conductivity is increased by 71%, the thermal resistance is reduced by 44%, the thermal expansion coefficient is reduced by 94%, and the stability of the optoelectronic device is improved from unstable to stable, which shows that the special thin-porous core-shell structure design of the skin layer can improve the thermal conductivity and thermal expansion performance of the adhesive material compared with the ordinary core-shell structure with balanced core-shell thickness, which is beneficial to the improvement of the performance reliability of the optoelectronic device.

[0091] 4、By comparing example 5 with examples 1-4, it can be seen that after optimizing the shell thickness, liquid metal content, liquid metal type and shell polymer material type of the adhesive core-shell structure, the thermal performance and bonding performance can be further improved, the thermal conductivity of example 1 is increased from 2.4 W m -1 K -1 to 4.0 W m -1 K -1 of example 5, the thermal resistance of example 1 is reduced from 40 mm 2 KW -1 to 27 mm 2 KW -1 of example 5, the thermal expansion coefficient is basically unchanged, the interfacial bonding strength is increased from 6.6 MPa of example 1 to 9.9 MPa of example 5, and the performance stability of the optoelectronic device is improved from stable to very stable.

[0092] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, and the person skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be combined appropriately to form other embodiments that can be understood by the person skilled in the art.

Claims

1. A thermally conductive adhesive with a near-zero coefficient of thermal expansion, characterized in that, An adhesive with a core-shell structure includes: an adhesive skin and an adhesive core layer; The adhesive skin layer comprises a polymer matrix, a solvent, and additives; the polymer matrix is ​​at least one selected from epoxy resin, acrylic resin, silicone resin, polyimide resin, and polysilazane resin. The thickness of the adhesive skin layer is 0.01 μm to 1 μm; the solid content of the adhesive skin layer, i.e., the ratio of the polymer matrix, is 0.01 wt% to 5 wt%. The thickness of the adhesive core layer is 1 μm to 1000 μm; the adhesive core layer comprises liquid metal and inorganic filler; by mass fraction, the liquid metal accounts for 0.01 wt% to 6 wt% of the total mass of the adhesive core layer; the inorganic filler is at least one of tungsten zirconium phosphate, zirconium tungstate, fused silica, glass fiber, and bismuth nickel iron oxide low expansion coefficient filler or negative expansion coefficient filler; The method for preparing a near-zero thermal expansion coefficient thermally conductive adhesive includes the following steps: S1. Raw materials for preparing the adhesive core layer: Liquid metal is coated onto the surface of inorganic filler, followed by mechanochemical treatment to obtain the raw material for the adhesive core layer; The working conditions for the mechanochemical treatment include: processing with the equipment at a temperature of 10 ℃ to 200 ℃, a pressure of 0.1 MPa to 10 MPa, and a time of 1 min to 60 min. S2. Raw materials for preparing the adhesive skin layer: The polymer matrix, solvent, and additives are mixed in a set ratio under vacuum conditions. The mixing time is 1 min to 30 min, and the mixing rate is 100 rpm to 4000 rpm. S3. The adhesive skin layer and core layer are bonded together via a double-layer coaxial needle tube: The raw material for the adhesive skin layer is fed into the outer layer of the double-layer coaxial syringe, and the raw material for the adhesive core layer is fed into the inner layer of the double-layer coaxial syringe. The syringe extrudes both raw materials simultaneously to obtain a core-shell structured adhesive. The double-layer coaxial needle has a structure with an extremely thin outer layer and an extremely thick core layer. The inner diameter of the inner ring of the core layer is 100 μm, the inner diameter of the inner ring of the outer layer is 102 μm, and the thickness of the outer layer is 1 / 50 of the thickness of the core layer.

2. The near-zero thermal expansion coefficient thermally conductive adhesive according to claim 1, characterized in that, The solvent is at least one of water, ethanol, acetone, N-methylpyrrolidone, ethyl acetate, cyclohexanone, and xylene; the additive is a crosslinking agent and initiator required for the corresponding polymer matrix.

3. The near-zero thermal expansion coefficient thermally conductive adhesive according to claim 1, characterized in that, The liquid metal is at least one of bismuth, gallium, tin, indium, rubidium, and cesium.

4. The near-zero thermal expansion coefficient thermally conductive adhesive according to claim 1, characterized in that, The processing equipment mentioned in S1 is at least one of a flat plate press, a ball mill, and a grinding mill.

5. The near-zero thermal expansion coefficient thermally conductive adhesive according to claim 1, characterized in that, The mixing described in S2 is performed using a stirring tank or a homogenizer.

6. The near-zero thermal expansion coefficient thermally conductive adhesive according to claim 1, characterized in that, The shape of the double-layer coaxial needle tube described in S3 is one of the following: round, square, triangular, or irregular shape.

7. The application of a near-zero thermal expansion coefficient thermally conductive adhesive according to any one of claims 1-6, characterized in that, The optoelectronic device is encapsulated using a thermally conductive adhesive with a near-zero coefficient of thermal expansion.

8. The application of a near-zero thermal expansion coefficient thermally conductive adhesive according to claim 7, characterized in that, The packaging interface of the optoelectronic device is one of the following: the interface between silicon-based materials and metal materials, the interface between carbon-based materials and metal materials, and the interface between silicon-based materials.

9. The application of a near-zero thermal expansion coefficient thermally conductive adhesive according to claim 8, characterized in that, The encapsulation interface of the optoelectronic device is cured using the aforementioned thermally conductive adhesive with a near-zero coefficient of thermal expansion through a combination of heating / light irradiation and pressure.

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