Nanosilver film, preparation method thereof and power device packaging structure

Abstract

The present application relates to the technical field of electronic packaging, and particularly relates to a nano-silver film, a preparation method thereof and a power device packaging structure. The preparation method of the nano-silver film comprises the following steps: mixing a silver source solution containing a coating agent with a reducing agent solution to obtain a nano-silver wire suspension; performing suction filtration or filtration on the nano-silver wire suspension to make the nano-silver wire adhere to a filter membrane to form a nano-silver wire layer; and applying an adhesive to the nano-silver wire layer to obtain the nano-silver film after drying. In the power device packaging structure, a chip is fixed to a substrate by the nano-silver film through a hot-press sintering process, the shear strength of the chip after being fixed to the substrate is 65-110 MPa, the resistivity of a sintered body of the nano-silver film is 5*10 ‑8 -20*10 ‑8 Ω*m, and the porosity is 1.5%-5%. The nano-silver film prepared from in-situ nano-silver wires has high shear strength and excellent conductive performance, and can be used for packaging of high-power devices.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging technology, and in particular to a nano silver film, its preparation method, and a power device packaging structure. Background Technology

[0002] In modern electronics, interconnect materials play a crucial role in achieving electrical connections and signal transmission between electronic components, directly impacting the performance, reliability, and stability of the entire electronic device. In high-power electronic devices, the interconnections between chips and between chips and the packaging substrate must withstand the extreme conditions of high temperature and high current generated during high-power operation, while ensuring high-speed, accurate, and stable signal transmission. Traditional interconnect materials have gradually revealed numerous limitations in the face of these new challenges. Traditional soft soldering materials have low melting points and are prone to softening and melting in the high-temperature environment of high-power devices, leading to connection failure. Although high-temperature solders based on Pb, Au, Bi, and Zn have higher melting points, solders containing heavy metals such as Pb pose environmental pollution or high cost issues. Nano-silver solder paste typically consists of nano-silver particles, organic carriers, and additives, forming good electrical connections during low-temperature sintering. However, the relatively high organic carrier content in nano-silver solder paste can lead to porosity formation during high-temperature sintering, increasing the porosity of the interconnect structure and affecting the density and reliability of the connection. Furthermore, nano-silver solder paste also suffers from issues such as significant batch-to-batch performance variations during large-scale production and increased costs due to multiple preparation steps. Additionally, nano-silver paste is difficult to apply over large areas and exhibits problems with extrusion and collapse after printing.

[0003] Currently, pre-fabricated conductive films are receiving widespread attention as a replacement for nano-silver paste. For example, CN108847395A discloses a method for preparing and encapsulating a pre-sintered nano-network silver film for low-temperature rapid bonding. This method involves mixing coated nano-silver particles with organic solvents, dispersants, and binders to obtain nano-silver paste, which is then printed into a film to obtain a pre-fabricated nano-silver film. Another example is CN110289120A, which discloses a method for preparing and encapsulating a composite sintered silver preform. This method involves mixing nano-silver particles, sintering aids, and an organic carrier to obtain nano-silver paste, which is then formed into a film using spin coating, casting, or screen printing, and finally baked and dried to obtain a preform. Both of these technologies involve forming nano-silver paste into films for easy use, but they suffer from poor film strength and weak resistance to tensile forces. Summary of the Invention

[0004] The purpose of this invention is to provide a silver nanofilm and its preparation method. The silver nanofilm prepared by in-situ silver nanowires has high shear strength and excellent electrical conductivity.

[0005] Another objective of this invention is to provide a power device packaging structure that uses the aforementioned nano-silver film as the interconnect material, which can be used for packaging high-power devices.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] A method for preparing a silver nanofilm includes the following steps:

[0008] (1) The silver source solution containing the coating agent is mixed with the reducing agent solution to obtain a silver nanowire suspension;

[0009] (2) The silver nanowire suspension is filtered or vacuum filtered to allow the silver nanowires to adhere to the filter membrane and form a silver nanowire layer.

[0010] (3) Apply an adhesive to the silver nanowire layer and dry it to obtain a silver nanofilm.

[0011] Furthermore, in step (1), after mixing the silver source solution containing the coating agent with the reducing agent solution, the mixture is heated to 100-300°C and stirred continuously for 10-300 min at a stirring speed of 100-1000 r / min.

[0012] Furthermore, in step (1), the molar ratio of the coating agent, the silver source, and the reducing agent is (1.5-5):1:(1.5-10).

[0013] Furthermore, in step (1), the silver source is any one or more of silver acetate, silver carbonate, silver oxide, silver benzoate, silver oxalate, silver phenolate, and silver acetate.

[0014] The coating agent is any one or more of PVP, sodium citrate, polyoxyethylene ether, polyvinyl alcohol, cetyltrimethylammonium bromide, polyacrylonitrile, and oleylamine;

[0015] The reducing agent is any one or more of ascorbic acid, citric acid, glucose, phenylhydrazine, and hydrazine hydrate;

[0016] The silver source solution containing the coating agent and the reducing agent solution are respectively dissolved in ethylene glycol, ethanol, water, ethylene glycol butyl ether, glycerol, polyethylene glycol, acetone, toluene, ethyl acetate and diethyl ether.

[0017] Furthermore, in step (1), the cross-sectional diameter of the silver nanowires in the silver nanowire suspension is 10-200 nm, and the length of the silver nanowires is 1-50 μm.

[0018] Furthermore, in step (3), the adhesive is any one of polyvinyl butyral, polyacrylic acid, polyurethane, epoxy resin and phenolic resin.

[0019] Furthermore, in step (3), the nano-silver wire layer with the adhesive is dried by vacuum drying at a temperature of 50-80°C for 3-5 hours.

[0020] Furthermore, the thickness of the silver nanofilm obtained in step (3) is 2–200 μm, and the areal density is 80–400 g / m³. 2 Its density is 0.4–4.0 g / cm³. 3 .

[0021] A nanosilver film is prepared using the above-described method for preparing a nanosilver film from in-situ nanosilver wires.

[0022] A power device packaging structure includes a substrate and a plurality of chips, wherein the chips are fixed to the substrate by a hot-pressing sintering process using the aforementioned nano-silver film, and a nano-silver film sintered body is formed between the chips and the substrate;

[0023] The shear strength of the chip after it is fixed to the substrate is 65–110 MPa, and the resistivity of the sintered silver nanofilm is 5 × 10⁻⁶ MPa. -8 ~20×10 -8 The porosity of the sintered nanosilver film is 1.5% to 5%, with an Ω·m.

[0024] The technical solution provided by this invention may include the following beneficial effects:

[0025] In this invention, silver nanowires are prepared through a redox reaction. The resulting silver nanofilm, obtained by attaching an adhesive to the silver nanowires, exhibits high shear strength, providing excellent cutability and ease of storage and transportation. Furthermore, only a small amount of adhesive is needed to form the silver nanowire film, resulting in a low organic content in the film, which reduces porosity after sintering and improves conductivity. Moreover, the preparation steps for the silver nanofilm in this invention are simple, significantly shortening the process and saving costs. Large-scale production yields products with good consistency and high stability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a chip packaging operation according to an embodiment of the present invention. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention.

[0028] A method for preparing a nano-silver film according to an embodiment of the present invention includes the following steps:

[0029] (1) The silver source solution containing the coating agent is mixed with the reducing agent solution to obtain a silver nanowire suspension;

[0030] (2) The silver nanowire suspension is filtered or vacuum filtered to allow the silver nanowires to adhere to the filter membrane and form a silver nanowire layer.

[0031] (3) Apply an adhesive to the silver nanowire layer and dry it to obtain a silver nanofilm.

[0032] In this invention, silver nanowires are prepared through a redox reaction. The resulting silver nanofilm, obtained by attaching an adhesive to the silver nanowires, exhibits high shear strength, providing excellent cutability and ease of storage and transportation. Furthermore, only a small amount of adhesive is needed to form the silver nanowire film, resulting in a low organic content in the film, which reduces porosity after sintering and improves conductivity. Moreover, the preparation steps for the silver nanofilm in this invention are simple, significantly shortening the process and saving costs. Large-scale production yields products with good consistency and high stability.

[0033] Specifically, the principle of wire formation in step (1) of this invention is driven by a redox reaction. The possible principle for generating silver nanowires during the reaction is as follows: the reducing agent reduces silver ions in the silver source to silver atoms. When the silver atoms are generated to a certain extent, crystal nuclei will form in the mixed solution. Once these crystal nuclei are formed, they will become the center for the continued deposition and growth of silver atoms. Silver atoms are continuously deposited on the surface of the crystal nuclei, causing the crystal nuclei to gradually increase in size. At this time, the added coating agent will selectively adsorb on the surface of the silver crystal nuclei or the growing silver particles. However, the coating agent molecules have a stronger adsorption capacity on certain crystal faces of the crystal nuclei, thereby inhibiting the deposition and growth of silver atoms on these crystal faces. In the direction of the crystal face with weaker adsorption, the deposition of silver atoms is relatively easier. This guides the silver crystal nuclei or particles to grow in a specific direction (i.e., along the direction of the crystal face with weaker adsorption), gradually forming a one-dimensional silver wire structure. The silver wire structure, i.e., the silver nanowire, gives the nanosilver film after film formation a large tensile strength, reaching 1-20 MPa.

[0034] In step (2), the purpose of vacuum filtration or filtration is to aggregate the silver nanowires into a membrane. The filtration device used can be any one of a positive pressure filter, a vacuum drum filter, a plate and frame filter press, a centrifugal filter, a cross-flow filter, and a bag filter. The vacuum filtration device used can be any one of a glass core vacuum filtration device, a ceramic membrane vacuum filtration device, an organic microporous membrane vacuum filtration device, a stainless steel sintered mesh vacuum filtration device, and a vacuum filtration box. When using a filtration device, the filter paper with the wet membrane layer can be directly removed, and then an adhesive solution can be evenly dripped or sprayed onto the surface of the wet membrane layer. When using a vacuum filtration device, the wet membrane layer on the surface of the filter membrane can be removed and then an adhesive solution can be evenly dripped or sprayed onto it. It should be noted that it is preferable to spray the adhesive solution onto the wet membrane layer, and the same type of solvent as the silver source solution and the reducing agent solution should be used to make it easier for the adhesive to penetrate into the wet membrane layer.

[0035] Furthermore, in step (1), after mixing the silver source solution containing the coating agent with the reducing agent solution, the mixture is heated to 100–300°C and continuously stirred for 10–300 min at a stirring speed of 100–1000 r / min. Heating and stirring promote the redox reaction, and stirring at an appropriate speed allows the generated silver nanoparticles to extend in a specific direction without agglomeration, thereby obtaining a silver nanoparticle suspension. If the stirring speed is too high, the nanoparticles will be too short, affecting the tensile strength of the silver nanoparticle film; if the stirring speed is too low, the agglomeration of silver nanoparticles will be too large, failing to produce silver nanoparticles, resulting in uneven thickness and low tensile strength of the silver nanoparticle film. Furthermore, in step (1), the cross-sectional diameter of the silver nanoparticles in the silver nanoparticle suspension is 10–200 nm, and the length of the silver nanoparticles is 1–50 μm. The larger diameter and length of the silver nanoparticles form a stronger overall framework structure when interconnected, which improves the shear strength of the silver nanoparticle film. Small-diameter and short-length silver wires tend to generate high porosity within the membrane because the connections between the fine silver wires may not be tight enough, resulting in more voids in the structure. Thicker and longer silver wires help form a more efficient conductive network, thereby reducing resistivity. In this invention, sufficiently large diameter and length silver nanowires are obtained by limiting the oxidation-reduction temperature, time, and stirring rate.

[0036] Furthermore, in step (1), the molar ratio of the coating agent, silver source, and reducing agent is (1.5–5):1:(1.5–10) to ensure the smooth progress of the redox reaction. By limiting the ratio of the coating agent, silver source, and reducing agent, and by adjusting the concentrations of the coating agent, silver source, and reducing agent, the concentration of silver nanowires in the suspension is made to be 0.5–4.5 g / L, which is beneficial for obtaining a uniformly thick silver nanofilm.

[0037] In some embodiments of the present invention, in step (1), the silver source is any one or more of silver acetate, silver carbonate, silver oxide, silver benzoate, silver oxalate, silver phenolate, and silver acetate;

[0038] The coating agent is any one or more of PVP, sodium citrate, polyoxyethylene ether, polyvinyl alcohol, cetyltrimethylammonium bromide, polyacrylonitrile, and oleylamine;

[0039] The reducing agent is any one or more of ascorbic acid, citric acid, glucose, phenylhydrazine, and hydrazine hydrate;

[0040] The silver source solution containing the coating agent and the reducing agent solution are respectively dissolved in ethylene glycol, ethanol, water, ethylene glycol butyl ether, glycerol, polyethylene glycol, acetone, toluene, ethyl acetate and diethyl ether.

[0041] In one embodiment of the present invention, in step (3), the adhesive is any one of polyvinyl butyral, polyacrylic acid, polyurethane, epoxy resin and phenolic resin.

[0042] In order to ensure that the silver nanofilm is completely dry and has sufficient strength and excellent conductivity, in step (3), the silver nanowire layer with adhesive is dried by vacuum drying at a temperature of 50-80°C for 3-5 hours.

[0043] In this embodiment of the invention, the thickness of the silver nanofilm obtained in step (3) is 2–200 μm, and the areal density is 80–400 g / m³. 2 Its density is 0.4–4.0 g / cm³. 3 This satisfies the requirements for power device packaging on the substrate. Furthermore, the thickness of the silver nanofilm in the embodiments of the present invention fluctuates by 0.3–4.0%, the density fluctuates by 0.2–4.5%, the tensile strength is 1–20 MPa, and the impurity content is 0.01–0.2%. It can be seen that the silver nanofilm prepared by the method of the present invention has excellent performance and good product consistency.

[0044] Accordingly, the present invention also provides a silver nanofilm, which is prepared by the above-described method of preparing a silver nanofilm using in-situ silver nanowires. This silver nanofilm is used in the packaging of high-power devices. Correspondingly, the present invention also provides a power device packaging structure, including a substrate and several chips, wherein the chips are fixed to the substrate by a hot-pressing sintering process using the above-described silver nanofilm, and a silver nanofilm sintered body is formed between the chips and the substrate.

[0045] The shear strength of the chip after it is fixed to the substrate is 65–110 MPa, and the resistivity of the sintered silver nanofilm is 5 × 10⁻⁶ MPa. -8 ~20×10 -8The porosity of the sintered nanosilver film is 1.5% to 5%, with an Ω·m.

[0046] Therefore, the sintered nano-silver film of this invention exhibits very low porosity and low resistivity, making it suitable for packaging high-power devices. It generates less heat under high current conditions, and its high shear strength after chip bonding allows the interconnects between the chip and the packaging substrate, as well as the interconnects between chips, to withstand the extreme conditions of high temperature and high current generated during high-power operation. Specifically, the chip packaging operation ( Figure 1 The process involves attaching a nano-silver film to a substrate, then covering the nano-silver film with a chip, followed by a hot-pressing sintering process. The hot-pressing sintering temperature is 100–300℃, and the pressure is 0–20MPa.

[0047] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to conventional methods and conditions or according to the product instructions. Unless otherwise specified, the reagents are commercially available; and the performance of products from different sources does not have a significant impact.

[0048] Example 1

[0049] The preparation and application of the silver nanofilm in this embodiment are as follows:

[0050] (1) Silver acetate, PVP and ethylene glycol solution were mixed and stirred to dissolve to obtain silver salt solution; ascorbic acid and ethylene glycol solution were mixed and dissolved to obtain reducing agent solution; the silver salt solution and reducing agent solution were reacted at 160℃ for 4h with a stirring rate of 200r / min to obtain silver nanowire suspension; wherein, the concentration of silver nanowires in the silver nanowire suspension was 4.5g / L, the cross-sectional diameter of the silver nanowires was 200nm, and the length of the silver nanowires was 45μm; the molar ratio of polyvinylpyrrolidone (PVP), silver acetate and ascorbic acid was 1.5:1:1.5;

[0051] (2) Then the nano-silver suspension was transferred to a positive pressure filter for filtration until no liquid dripped out;

[0052] (3) After filtration, the wet membrane layer attached to the filter paper is removed. An adhesive solution is obtained by mixing epoxy resin adhesive with ethylene glycol solution. The adhesive solution is then evenly sprayed onto the surface of the wet membrane layer. The membrane layer is then dried in an oven to cure the adhesive and give it adhesion, resulting in a complete nano-silver membrane. The vacuum drying temperature is 60℃ and the drying time is 3h. The nano-silver membrane has a thickness of 5μm and a surface density of 85g / m³. 2 Its density is 0.4 g / cm³. 3The silver nanofilm has a thickness fluctuation of 0.3%, a density fluctuation of 0.2%, a tensile strength of 20 MPa, and an impurity content of 0.02%.

[0053] (4) The hot pressing sintering temperature of the obtained silver nanofilm when it is used for chip and substrate interconnection is 220℃ and the pressure is 5MPa.

[0054] Example 2

[0055] The preparation and application of the silver nanofilm in this embodiment are as follows:

[0056] (1) Silver oxide, sodium citrate and ethanol solution were mixed and stirred to dissolve to obtain silver salt solution; glucose and ethanol solution were mixed and dissolved to obtain reducing agent solution; the silver salt solution and reducing agent solution were reacted at 140℃ for 3h with a stirring rate of 300r / min to obtain silver nanowire suspension; wherein, the concentration of silver nanowires in the silver nanowire suspension was 3.75g / L, the cross-sectional diameter of the silver nanowires was 128nm, and the length of the silver nanowires was 27.5μm; the molar ratio of sodium citrate, silver oxide and glucose was 2.5:1:2.5;

[0057] (2) Then the prepared silver nanowire suspension was placed in a glass core filtration device and filtered under vacuum conditions.

[0058] (3) After solvent filtration, the wet membrane layer on the filter membrane surface is removed. A phenolic resin binder is mixed with an ethanol solution to form a binder solution, which is then uniformly sprayed onto the surface of the wet membrane layer. The membrane is then dried in an oven to cure the binder and give it adhesiveness, finally obtaining a complete nano-silver membrane. The vacuum drying temperature is 70℃, and the drying time is 3.5h. The nano-silver membrane has a thickness of 75μm and a surface density of 250g / m³. 2 Its density is 2.5 g / cm³. 3 The nano-silver film has a thickness fluctuation of 2.5%, a density fluctuation of 2.5%, a tensile strength of 15 MPa, and an impurity content of 0.15%.

[0059] (4) The hot pressing sintering temperature of the obtained silver nanofilm when it is used for chip and substrate interconnection is 240℃ and the pressure is 6MPa.

[0060] Example 3

[0061] The preparation and application of the silver nanofilm in this embodiment are as follows:

[0062] (1) A silver salt solution was obtained by mixing silver carbonate, polyoxyethylene ether and glycerol solution and stirring to dissolve the mixture; a reducing agent solution was obtained by mixing citric acid and glycerol solution and stirring to dissolve the mixture; the silver salt solution and the reducing agent solution were reacted at 150℃ for 3.5h with a stirring rate of 500r / min to obtain a silver nanowire suspension; wherein, the concentration of silver nanowires in the silver nanowire suspension was 2.25g / L, the cross-sectional diameter of the silver nanowires was 87.5nm, and the length of the silver nanowires was 35.4μm; the molar ratio of polyoxyethylene ether, silver carbonate and citric acid was 1.25:1:1.25;

[0063] (2) Then the prepared silver nanowire suspension is transferred to a positive pressure filter for filtration until no liquid drips out;

[0064] (3) After filtration, the wet membrane layer attached to the filter paper is removed. A polyurethane adhesive is mixed with a glycerol solution to form an adhesive solution, which is then sprayed evenly onto the surface of the wet membrane layer. The membrane is then dried in an oven to cure the adhesive and give it adhesion, resulting in a complete nano-silver membrane. The vacuum drying temperature is 65℃, and the drying time is 4 hours. The nano-silver membrane has a thickness of 155μm and an areal density of 165g / m³. 2 Its density is 1.45 g / cm³. 3 The silver nanofilm has a thickness fluctuation of 1.3%, a density fluctuation of 1.2%, a tensile strength of 18.5 MPa, and an impurity content of 0.08%.

[0065] (4) The hot pressing sintering temperature of the obtained silver nanofilm when it is used for chip and substrate interconnection is 230℃ and the pressure is 5.5MPa.

[0066] Example 4

[0067] The preparation and application of the silver nanofilm in this embodiment are as follows:

[0068] (1) Silver acetate, polyvinyl alcohol, and ethylene glycol butyl ether solution were mixed and stirred to dissolve to obtain a silver salt solution; hydrazine hydrate was mixed and dissolved to obtain a reducing agent solution; the silver salt solution and the reducing agent solution were reacted at 200℃ for 2.5h with a stirring rate of 600r / min to obtain a silver nanowire suspension; wherein, the concentration of silver nanowires in the silver nanowire suspension was 3g / L, the cross-sectional diameter of the silver nanowires was 57nm, and the length of the silver nanowires was 15μm; the molar ratio of polyvinyl alcohol, silver acetate, and hydrazine hydrate was 2:1:2;

[0069] (2) Then the prepared silver nanowire suspension was placed in a ceramic membrane filtration device and filtered under vacuum conditions.

[0070] (3) After solvent filtration, the wet membrane layer on the filter membrane surface is removed. A binder solution is formed by mixing polyacrylic acid binder with ethylene glycol butyl ether solution. The binder is then evenly sprayed onto the surface of the wet membrane layer. The membrane is then dried in an oven to cure the binder and give it adhesiveness, finally obtaining a complete nano-silver membrane. The vacuum drying temperature is 50℃ and the drying time is 4.5h. The nano-silver membrane has a thickness of 20μm and an areal density of 80g / m³. 2 Its density is 1.5 g / cm³. 3 The silver nanofilm has a thickness fluctuation of 3.5%, a density fluctuation of 3.2%, a tensile strength of 8 MPa, and an impurity content of 0.08%.

[0071] (4) The hot pressing sintering temperature of the obtained silver nanofilm when it is used for chip and substrate interconnection is 250℃ and the pressure is 7MPa.

[0072] Example 5

[0073] The preparation and application of the silver nanofilm in this embodiment are as follows:

[0074] (1) Silver oxalate, polyacrylonitrile, and acetone solution were mixed and stirred to dissolve to obtain a silver salt solution; citric acid and acetone solution were mixed and dissolved to obtain a reducing agent solution; the silver salt solution and reducing agent solution were reacted at 100℃ for 5h with a stirring rate of 100r / min to obtain a silver nanowire suspension; wherein, the cross-sectional diameter of the silver nanowire was 185nm and the length of the silver nanowire was 50μm; the molar ratio of polyacrylonitrile, silver oxalate, and citric acid was 1.5:1:2;

[0075] (2) Then the prepared silver nanowire suspension was placed in a ceramic membrane filtration device and filtered under vacuum conditions.

[0076] (3) After solvent filtration, the wet membrane layer on the filter membrane surface is removed. A binder solution is formed by mixing polyacrylic acid binder with acetone, and the binder is evenly sprayed onto the surface of the wet membrane layer. The membrane is then dried in an oven to cure the binder and give it adhesiveness, finally obtaining a complete nano-silver membrane. The vacuum drying temperature is 80℃ and the drying time is 5h. The nano-silver membrane has a thickness of 2μm and an areal density of 100g / m³. 2 Its density is 400 g / cm³ 3 The silver nanofilm has a thickness fluctuation of 3.5%, a density fluctuation of 3.2%, a tensile strength of 14 MPa, and an impurity content of 0.09%.

[0077] (4) The hot pressing sintering temperature of the obtained silver nanofilm when it is used for chip and substrate interconnection is 100℃ and the pressure is 20MPa.

[0078] Example 6

[0079] The preparation and application of the silver nanofilm in this embodiment are as follows:

[0080] (1) Silver benzoate, polyvinyl alcohol and ethylene glycol butyl ether solution were mixed and stirred to dissolve to obtain silver salt solution; hydrazine hydrate and ethylene glycol butyl ether solution were mixed and dissolved to obtain reducing agent solution; the silver salt solution and reducing agent solution were reacted at 300℃ for 10 min with a stirring rate of 1000 r / min to obtain silver nanowire suspension; wherein, the cross-sectional diameter of the silver nanowire was 10 nm and the length of the silver nanowire was 1 μm; the molar ratio of polyvinyl alcohol, silver benzoate and hydrazine hydrate was 5:1:10;

[0081] (2) Then the prepared silver nanowire suspension was placed in a ceramic membrane filtration device and filtered under vacuum conditions.

[0082] (3) After solvent filtration, the wet membrane layer on the filter membrane surface is removed. A binder solution is formed by mixing polyacrylic acid binder with ethylene glycol butyl ether solution. The binder is then evenly sprayed onto the surface of the wet membrane layer. The membrane is then dried in an oven to cure the binder and give it adhesiveness, finally obtaining a complete nano-silver membrane. The vacuum drying temperature is 60℃, and the drying time is 5 hours. The nano-silver membrane has a thickness of 200 μm and an areal density of 400 g / m³. 2 Its density is 4 g / cm³ 3 The silver nanofilm has a thickness fluctuation of 3.5%, a density fluctuation of 3.2%, a tensile strength of 1 MPa, and an impurity content of 0.1%.

[0083] (4) The hot pressing sintering temperature of the obtained nano silver film when it is used for chip and substrate interconnection is 300℃ and the pressure is 0MPa.

[0084] In step (4) of Examples 1-6, the obtained silver nanofilm was used to fabricate interconnect devices. The performance of the fabricated interconnect devices was tested, and the specific test results are shown in the table below:

[0085]

[0086]

[0087] The nanosilver film, its preparation method, and other components and operations of the power device packaging structure according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here. When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. The described performance can be achieved within the proportions specified in the present invention. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art to which this invention pertains.

[0088] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a nano-silver film, characterized in that, Includes the following steps: (1) The silver source solution containing the coating agent is mixed with the reducing agent solution to obtain a suspension of silver nanowires: The silver source solution containing the coating agent is mixed with the reducing agent solution, heated to 100~300℃ and stirred continuously for 10~300min at a stirring speed of 100~1000r / min; the cross-sectional diameter of the silver nanowires in the silver nanowire suspension is 10~200nm and the length of the silver nanowires is 1~50μm. (2) The silver nanowire suspension is filtered or vacuum filtered to allow the silver nanowires to adhere to the filter membrane and form a silver nanowire layer. (3) Apply an adhesive to the silver nanowire layer and dry it to obtain a silver nanofilm; The adhesive is any one of polyvinyl butyral, polyacrylic acid, polyurethane, epoxy resin and phenolic resin; the adhesive solution is sprayed onto the wet film layer obtained in step (2), and the same type of solvent as the silver source solution and the reducing agent solution is used so that the adhesive can penetrate into the wet film layer more easily. The thickness of the silver nanofilm obtained in step (3) is 2~200 μm, and the areal density is 80~400 g / m³. 2 Its density is 0.4~4.0 g / cm³. 3 .

2. The method for preparing a nano-silver film according to claim 1, characterized in that, In step (1), the molar ratio of the coating agent, silver source and reducing agent is (1.5~5):1:(1.5~10).

3. The method for preparing the nano-silver film according to claim 1 or 2, characterized in that, In step (1), the silver source is any one or more of silver acetate, silver carbonate, silver oxide, silver benzoate, silver oxalate, silver phenolate, and silver acetate. The coating agent is any one or more of PVP, sodium citrate, polyoxyethylene ether, polyvinyl alcohol, cetyltrimethylammonium bromide, polyacrylonitrile, and oleylamine; The reducing agent is any one or more of ascorbic acid, citric acid, glucose, phenylhydrazine, and hydrazine hydrate; The silver source solution containing the coating agent and the reducing agent solution are respectively dissolved in ethylene glycol, ethanol, water, ethylene glycol butyl ether, glycerol, polyethylene glycol, acetone, toluene, ethyl acetate and diethyl ether.

4. The method for preparing a nano-silver film according to claim 1, characterized in that, In step (3), the nano-silver wire layer with adhesive is dried by vacuum drying at a temperature of 50-80°C for 3-5 hours.

5. A nano-silver film, characterized in that, It is prepared by the method of any one of claims 1 to 4.

6. A power device packaging structure, characterized in that, The device includes a substrate and several chips, wherein the chips are fixed to the substrate by a hot-pressing sintering process using a nano-silver film as described in claim 5, and a nano-silver film sintered body is formed between the chips and the substrate; The shear strength of the chip after it is fixed to the substrate is 65~110MPa, and the resistivity of the sintered nano-silver film is 5×10⁻⁶. -8 ~20×10 -8 The porosity of the sintered nanosilver film is 1.5% to 5%, with an Ω·m.

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