A highly conductive and thermally conductive composite copper solder paste, its preparation method and application

Abstract

The present invention provides a highly conductive and thermally conductive composite copper solder paste, a preparation method thereof and an application. The copper solder paste comprises the following components: nano copper particles, micro copper particles and three-dimensional graphene with a nano copper substrate. By adding three-dimensional graphene with a nano copper substrate to the copper solder paste, the present invention improves the problem of poor affinity between graphene and copper, and can effectively reduce the agglomeration and stacking of graphene layers caused by the action of van der Waals forces, so that graphene is uniformly dispersed in the copper solder paste, and the thermal conductivity, electrical conductivity and mechanical properties of the copper solder paste are improved. The preparation method of the copper solder paste of the present invention omits the processes of vacuum drying and copper particle grinding. After the copper particles are cleaned and surface modified, they are mixed with a multi-component organic solvent system, which can effectively inhibit the agglomeration and oxidation of the copper particles and improve the low-temperature sintering performance and antioxidant performance of the copper solder paste.

Description

Technical Field

[0001] The present invention relates to the technical field of power device packaging interconnection, and particularly to a highly conductive and thermally conductive composite copper solder paste, its preparation method and application. Background Art

[0002] With the development of third-generation semiconductor materials, the working temperature of semiconductor chips has increased significantly, and power devices are more widely used in high-temperature, high-frequency, and high-power fields such as new energy vehicles and smart grids. Using traditional tin-based lead-free solder for chip interconnection packaging cannot meet the requirements for long-term service of power devices in this scenario. The nano-metal particle sintering connection technology mainly based on nano-silver solder paste and nano-copper solder paste has the characteristics of low-temperature connection and high-temperature service, showing great development potential and being a research hotspot in recent years. Among them, nano-copper sintering connection not only has excellent electrothermal performance, but also has a lower price and better electromigration resistance compared with nano-silver sintering connection, becoming one of the important development directions in the field of power device packaging interconnection technology. However, the nano-copper sintering connection layer inevitably has pores, and its thermal and electrical conductivity is much lower than that of bulk materials.

[0003] Graphene is a two-dimensional conjugated honeycomb carbon structure with excellent strength, high electron mobility, high thermal conductivity, excellent mechanical elasticity and large specific surface area. Introducing graphene into copper solder paste can establish a thermally and electrically conductive network in the copper sintering connection layer, further improving its thermal and electrical conductivity and mechanical properties. However, due to the action of van der Waals forces, the graphene sheets doped in the copper solder paste are prone to stacking and agglomeration. Moreover, the copper-graphene interface has non-wetting characteristics, with an equilibrium contact angle of about 140°, poor affinity, and poor interface bonding effect at low temperature and low pressure. Graphene oxide is easy to functionalize, but due to the large number of oxygen-containing functional groups in its structure, it has the ability to spontaneously undergo redox reactions with copper. Graphene oxide is reduced to reduced graphene, and copper is oxidized to cuprous oxide. The presence of cuprous oxide has a negative impact on the quality of nano-copper sintering connection joints. It is difficult to control the oxygen content of graphene after reduction of reduced graphene oxide. Hydrogen bonds are generated between the oxygen-containing functional groups on the surface, and the hydrogen bonds interact with each other, making the sheets prone to overlapping.

[0004] The prior art CN 110814575 B provides a solder paste and a preparation method thereof. The components of the solder paste include: nano copper particles, nano nickel particles and / or nano silver particles, graphene oxide, ascorbic acid, a dispersant, a thickener and a thixotropic agent; the mass percentage of the metal nano particles is 75 to 85, the mass percentage of the graphene oxide is 5 to 10, the mass percentage of the ascorbic acid is 3 to 8, the mass percentage of the dispersant is 2 to 8, the mass percentage of the thickener is 2 to 8, and the mass percentage of the thixotropic agent is 2 to 8. It is difficult to control the oxygen content of the reduced graphene oxide after reduction. The nano copper substrate three-dimensional graphene material composite copper solder paste of the present invention effectively avoids the negative impact on the copper sintering connection layer caused by the residual oxygen content brought by the use of reduced graphene oxide, and avoids the problem that the sheets are easily stacked on each other.

[0005] The prior art CN 112238310 A provides a copper solder paste, a copper solder paste preparation method and a chip. The copper solder paste comprises the following components in mass percentage: composite copper paste: 95% to 99.8%; electrically and thermally conductive carbon-based material: 0.2% to 5%. The electrically and thermally conductive carbon-based material is selected from one or a mixture of several of carboxylated multi-walled carbon nanotubes, amino-functionalized multi-walled carbon nanotubes, fluorinated carbon nanotubes, nitrogen-doped multi-walled carbon nanotubes, nickel-coated multi-walled carbon nanotubes, graphene oxide, carboxylated graphene, amino-functionalized graphene, mercapto-functionalized graphene to mix with copper powder to prepare a composite copper paste; adding the electrically and thermally conductive carbon-based material into the composite copper paste to prepare a copper solder paste. The carbon-based material used in the nano copper substrate three-dimensional graphene material composite copper solder paste of the present invention is nano copper substrate three-dimensional graphene, effectively avoiding the stacking and agglomeration phenomenon, and making the carbon nano material and copper have higher compatibility, and achieving a better bonding effect under low temperature and low pressure sintering.

[0006] The prior art CN 111554445 B provides a surface metallized carbon nano material composite nano silver paste and a preparation method thereof, realizing the surface metallization of the carbon nano material and the uniform mixing with the nano silver particles. The nano copper substrate three-dimensional graphene material composite copper solder paste of the present invention has excellent thermal and electrical conductivity and reliability, and at the same time has more excellent anti-electrochemical migration performance and a lower price.

[0007] The traditional process for preparing copper solder paste is to clean copper particles and then put them into a vacuum drying oven. After drying, the copper particles are taken out, and finally, organic solvents with a specific ratio are added and mechanically stirred until they are evenly mixed. However, the cleaned copper particles are more likely to agglomerate. Therefore, after being placed in the vacuum drying oven for a long time, the taken-out copper particles show obvious caking phenomenon and usually need to be ground in a mortar before being used to mix with organic solvents. Even after grinding, it will still cause an increase in the particle size of copper particles, and there may be re-oxidation of copper particles during the grinding process. During the stirring and mixing process, if the time is too short, the organic solvents cannot be completely mixed evenly with the copper particles; if the time is too long, the organic matter that decomposes at low temperature will volatilize, and the viscosity of the copper solder paste will change.

[0008] Therefore, based on the problems existing in the current preparation and application of copper solder paste in sintering connection technology, it is necessary to make improvements. Summary of the Invention

[0009] The purpose of the present invention is to provide a highly conductive and thermally conductive composite copper solder paste, its preparation method and application, and this composite copper solder paste can solve the problems raised in the above background technology.

[0010] In the first aspect of the present invention, a highly conductive and thermally conductive composite copper solder paste is provided, which includes the following components: nano copper particles, micro copper particles, and three-dimensional graphene on a nano copper substrate.

[0011] Preferably, the mass ratio of the nano copper particles, micro copper particles, and three-dimensional graphene on a nano copper substrate is (70 - 90):(10 - 30):(0.2 - 1.5).

[0012] Preferably, the shape of the nano copper particles includes one or more of spherical, flaky, dendritic; the particle size range of the nano copper particles is 10 - 800 nm; more preferably, the particle size of the nano copper particles is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm.

[0013] Preferably, the shape of the micro copper particles includes one or more of spherical, flaky, dendritic; the particle size range of the micro copper particles is 1 - 8 μm; more preferably, the particle size of the micro copper particles is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm.

[0014] Preferably, the highly conductive and thermally conductive composite copper solder paste further includes the following component: a multi-component organic solvent system.

[0015] Preferably, the multi-component organic solvent system includes: a dispersant, a binder, a reducing agent, and a diluent.

[0016] Preferably, the mass ratio of the dispersant, binder, reducing agent, and diluent can be adjusted according to the specific type of organic matter selected. For example: 1:1:1:1, 2:1:3:1, etc.

[0017] Preferably, the dispersant includes one or more of polyvinylpyrrolidone, isopropanolamine, trinitroacetic acid, capric acid, decylamine, aminoisopropanol, stearic acid, cetyltrimethylammonium bromide; more preferably, the dispersant is isopropanolamine; the dispersant is used to prevent particle agglomeration during the preparation and printing of the composite copper solder paste.

[0018] Preferably, the binder includes one or more of polyvinyl alcohol, polyvinyl butyral, ethyl cellulose; more preferably, the binder is ethyl cellulose or polyvinyl alcohol; the binder is used to prevent cracks from occurring during the sintering of the composite copper solder paste.

[0019] Preferably, the reducing agent includes one or more of lactic acid, ascorbic acid, citric acid, malic acid, glutaric acid, succinic acid; more preferably, the reducing agent is ascorbic acid or glutaric acid; the reducing agent is used to remove the oxide on the surface of the copper particles and inhibit the formation of oxides in the subsequent process of the composite copper solder paste.

[0020] Preferably, the diluent includes one or more of ethylene glycol, terpineol, 1-decanol, butanol, n-methyl-2-pyrrolidone, diethylene glycol, triethylene glycol, polyethylene glycol, allyl alcohol; more preferably, the diluent is polyethylene glycol or n-methyl-2-pyrrolidone and terpineol; the diluent is used to adjust the viscosity of the composite copper solder paste.

[0021] In the second aspect of the present invention, a method for preparing a highly conductive and thermally conductive composite copper solder paste is provided, including the following steps:

[0022] S1. Mix the nano copper particles and micro copper particles, use dilute acid to ultrasonically oscillate and process the mixed copper particles, centrifuge, pour off the supernatant after solid-liquid separation, add deionized water for ultrasonic cleaning, centrifuge, pour off the supernatant after solid-liquid separation, add absolute ethanol for ultrasonic cleaning, centrifuge, and pour off the supernatant after solid-liquid separation to obtain the mixed-size copper particles after acid washing.

[0023] Preferably, in step S1, the dilute acid includes one or more of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid; more preferably, the dilute acid is dilute sulfuric acid; the mass ratio of the mixed copper particles to the dilute acid is 1:2 to 1:4; more preferably, the mass ratio of the mixed copper particles to the dilute acid is 1:2, 1:3, 1:4.

[0024] S2. Add the mixed-size copper particles after pickling in step S1 into the mixed solution of carboxylic acid and absolute ethanol, ultrasonically vibrate, centrifuge, pour off the supernatant after solid-liquid separation, add absolute ethanol for ultrasonic cleaning, centrifuge, and pour off the supernatant after solid-liquid separation to obtain the surface-modified mixed-size copper particles.

[0025] Preferably, in step S2, the carboxylic acid includes one or more of formic acid, lactic acid, oxalic acid, phosphoric acid, and oxalic acid; more preferably, the carboxylic acid is formic acid or lactic acid; the mass ratio of the carboxylic acid to absolute ethanol is 1:1 to 1:5; more preferably, the mass ratio of the carboxylic acid to absolute ethanol is 1:1, 1:2, 1:3, 1:4, 1:5.

[0026] Preferably, step S2 further includes the following steps: disperse the surface-modified mixed-size copper particles in an ethanol solution, add a coating agent, mix and ultrasonically disperse, and then centrifuge to obtain the coated surface-modified copper particles. Coating can inhibit oxidation and slow down sedimentation; preferably, the coating agent is polyvinylpyrrolidone (PVP).

[0027] S3. Use magnetic stirring to uniformly mix the dispersant, binder, reducing agent, and diluent in proportion to obtain a multi-component organic solvent system.

[0028] Preferably, in step S3, the mass ratio of the dispersant, binder, reducing agent, and diluent can be adjusted according to the specific types of organic substances selected, for example: 1:1:1:1, 2:1:3:1, etc.

[0029] Preferably, the dispersant includes one or more of polyvinylpyrrolidone, isopropanolamine, trinitroacetic acid, capric acid, decylamine, aminoisopropanol, stearic acid, and cetyltrimethylammonium bromide; more preferably, the dispersant is isopropanolamine; the dispersant is used to prevent particle agglomeration during the preparation and printing of the composite copper solder paste.

[0030] Preferably, the binder includes one or more of polyvinyl alcohol, polyvinyl butyral, and ethyl cellulose; more preferably, the binder is ethyl cellulose, polyvinyl alcohol; the binder is used to prevent cracks from occurring during the sintering of the composite copper solder paste.

[0031] Preferably, the reducing agent includes one or more of lactic acid, ascorbic acid, citric acid, malic acid, glutaric acid, and succinic acid; more preferably, the reducing agent is ascorbic acid, glutaric acid; the reducing agent is used to remove the oxide on the surface of the copper particles and inhibit the formation of oxides in the subsequent process of the composite copper solder paste.

[0032] Preferably, the diluent includes one or more of ethylene glycol, terpineol, 1-decanol, butanol, n-methyl-2-pyrrolidone, diethylene glycol, triethylene glycol, polyethylene glycol, and allyl alcohol; more preferably, the diluent is polyethylene glycol, n-methyl-2-pyrrolidone, and terpineol; the diluent is used to adjust the viscosity of the composite copper solder paste.

[0033] In a specific embodiment:

[0034] S4. Mix the three-dimensional graphene of the nano-copper substrate, the surface-modified mixed-size copper particles obtained in step S2, and the multi-component organic solvent system obtained in step S3, perform ultrasonic oscillation to make them fully mixed, and perform centrifugation after mixing evenly to separate the solid and liquid phases. Discard the supernatant to obtain a highly conductive and thermally conductive composite copper solder paste.

[0035] Preferably, in step S4, the mass ratio of the three-dimensional graphene of the nano-copper substrate to the surface-modified mixed-size copper particles is 1:2 to 1:3 with respect to the mass of the multi-component organic solvent system.

[0036] Preferably, in step S4, the preparation method of the three-dimensional graphene of the nano-copper substrate includes: plasma-enhanced chemical vapor deposition (PECVD), rapid thermal annealing (RTA).

[0037] Preferably, in step S4, the carbon source used for preparing the three-dimensional graphene of the nano-copper substrate includes any one of methane, tryptophan, and sucrose.

[0038] Preferably, the preparation method of the three-dimensional graphene of the nano-copper substrate includes the following steps: Using sucrose as a reaction precursor, attaching sucrose to the surface of copper particles by doping or impregnation, using a mixed gas of hydrogen and argon as an auxiliary gas, and through a rapid thermal annealing process, at 800 °C, uniformly grow graphene on the surface of copper particles to form graphene with a network structure on the surface of copper particles.

[0039] Preferably, in step S4, mix the three-dimensional graphene of the nano-copper substrate, the surface-modified mixed-size copper particles obtained in step S2, and the multi-component organic solvent system obtained in step S3, and add malonic acid to adjust the pH value to make the mixed solution weakly acidic. Perform ultrasonic oscillation to make them fully mixed, and perform centrifugation after mixing evenly to separate the solid and liquid phases. Discard the supernatant to obtain a highly conductive and thermally conductive composite copper solder paste. The copper solder paste prepared in a weakly acidic environment has better performance.

[0040] In another specific embodiment:

[0041] S4. Mix the coated three-dimensional graphene on the nano copper substrate, the coated surface-modified copper particles obtained in step S2, and the multi-component organic solvent system obtained in step S3, perform ultrasonic oscillation to make them fully mixed, and after mixing evenly, perform centrifugation to separate the solid and liquid phases. Discard the supernatant to obtain a highly conductive and thermally conductive composite copper solder paste.

[0042] Preferably, the mass ratio of the coated three-dimensional graphene on the nano copper substrate to the coated surface-modified copper particles is 1:2 to 1:3 with respect to the mass of the multi-component organic solvent system.

[0043] Preferably, the coated three-dimensional graphene on the nano copper substrate is coated with n-propanol, and the obtained coated three-dimensional graphene on the nano copper substrate can inhibit oxidation and slow down sedimentation.

[0044] Preferably, the preparation method of the coated three-dimensional graphene on the nano copper substrate includes the following steps: Using sucrose as a reaction precursor, attach sucrose to the surface of copper particles by incorporation or impregnation. A mixed gas of hydrogen and argon is used as an auxiliary gas. Through a rapid thermal annealing process, at 800 °C, uniformly grow graphene on the surface of copper particles to form graphene with a network structure on the surface of copper particles. After dispersing the three-dimensional graphene particles on the nano copper substrate in an ethanol solution, add the coating agent n-propanol, mix and ultrasonically disperse, and then perform suction filtration under a nitrogen atmosphere to obtain the surface-coated wet three-dimensional graphene particles on the nano copper substrate. After freeze-drying, the coated three-dimensional graphene on the nano copper substrate is obtained.

[0045] Preferably, in step S4, mix the coated three-dimensional graphene on the nano copper substrate, the coated surface-modified copper particles obtained in step S2, and the multi-component organic solvent system obtained in step S3, and add malonic acid to adjust the pH value to make the mixed solution weakly acidic. Perform ultrasonic oscillation to make them fully mixed. After mixing evenly, perform centrifugation to separate the solid and liquid phases. Discard the supernatant to obtain a highly conductive and thermally conductive composite copper solder paste. The copper solder paste prepared in a weakly acidic environment has more excellent performance.

[0046] In the third aspect of the present invention, an application of the highly conductive and thermally conductive composite copper solder paste is provided. The above-mentioned highly conductive and thermally conductive composite copper solder paste or the highly conductive and thermally conductive composite copper solder paste obtained by the above-mentioned preparation method is coated on the surface of a substrate and / or a chip by screen printing. The chip and the substrate coated with the composite copper solder paste are mutually adhered to form a sandwich interconnect structure, and thermal compression sintering connection is performed under a nitrogen atmosphere.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] (1) The copper solder paste of the present invention is added with a nano-copper-based three-dimensional graphene material to establish a thermally conductive and electrically conductive interconnected network in the copper sintered connection layer, thereby improving its thermal and electrical conductivity and mechanical properties. The nano-copper-based three-dimensional graphene material has sufficient interface strength between copper and graphene, and the graphene layers in the three-dimensional graphene structure have higher stability and dispersion, with less agglomeration and stacking, which is conducive to fully utilizing the excellent properties of graphene.

[0049] (2) The copper solder paste of the present invention is mixed with copper particles of various particle sizes to form a denser stacking structure, thereby increasing the density of the sintered connection layer and obtaining a sintered joint with better electrical and thermal conductivity.

[0050] (3) The present invention's method for preparing a copper solder paste eliminates the vacuum drying and copper particle grinding steps. After cleaning and surface modification, the copper particles are immediately mixed with a multi-component organic solvent system, effectively inhibiting copper particle agglomeration and oxidation, thereby improving the low-temperature sintering performance and antioxidant properties of the copper solder paste. The copper solder paste obtained by centrifugation after sufficient contact between the copper particles and the excess solvent has a high solid content, suitable viscosity, and good wettability.

[0051] (4) The copper solder paste preparation method of the present invention uses carboxylic acid to modify the surface of copper particles, and utilizes carboxylic acid to react with surface copper oxide to generate copper carboxylate salt that can be decomposed into copper element at low temperature, thereby reducing the sintering resistance of copper particles, making the copper solder paste suitable for sintering at lower temperatures, and improving the electrical and mechanical properties of the sintered connection layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0053] Figure 1 A schematic diagram of the preparation process of the high-electrical and thermal-conductive composite copper solder paste provided by the present invention;

[0054] Figure 2 Schematic diagram of the three-dimensional graphene material on a nano-copper substrate provided by the present invention;

[0055] Figure 3 This is a schematic diagram of the sintering curve of the composite copper solder paste provided by the present invention.

[0056] Explanation of the accompanying drawings: 1. Graphene; 2. Nano-copper particles. DETAILED DESCRIPTION

[0057] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0058] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular also includes the plural. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0059] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0060] Example 1

[0061] This embodiment provides a highly conductive and thermally conductive composite copper solder paste, comprising the following components: 300 nm spherical copper particles, 1 μm flaky copper particles, nano-copper-based three-dimensional graphene particles, isopropanolamine, a 2 wt.% mixed solution of ethyl cellulose and ethanol, ascorbic acid, and polyethylene glycol.

[0062] like Figure 1 As shown, this embodiment also provides a method for preparing a high-electrical and thermal-conductive composite copper solder paste, comprising the following steps:

[0063] S1. Mix 8 g of 300 nm spherical copper particles and 1.9 g of 1 μm flaky copper particles, add 30 ml of 0.5 mol / L dilute sulfuric acid, and ultrasonically vibrate the mixture. After ultrasonication for 10 min, centrifuge at a speed of 5000 r / min for 3 min. After centrifugation, discard the supernatant, add deionized water and ultrasonically clean for 5 min, centrifuge, discard the supernatant, add anhydrous ethanol and ultrasonically clean for 5 min, centrifuge, and discard the supernatant.

[0064] S2. Add 40 ml of a solution of 30 wt.% lactic acid and anhydrous ethanol, ultrasonically shake for 10 minutes, centrifuge, discard the supernatant, add anhydrous alcohol and ultrasonically clean for 5 minutes, centrifuge, discard the supernatant, and obtain surface-modified wet mixed copper particles.

[0065] S3. Mix 13 g of isopropanolamine, 2 g of a mixed solution of 2 wt.% ethyl cellulose and ethanol, 1 g of ascorbic acid, and 8 g of polyethylene glycol, and stir magnetically for 3 h to obtain a uniformly mixed multi-component organic solvent system.

[0066] S4. Mix the above surface-modified wet mixed copper particles, 0.1 g of nano-copper substrate three-dimensional graphene, and 20 g of the multi-component organic solvent system, and perform ultrasonic oscillation for 30 min, then centrifuge at 6000 r / min for 5 min, and pour off the supernatant to obtain a copper solder paste with appropriate viscosity (preferably about 15% of the organic matter in the solder paste).

[0067] Among them, the preparation of nano-copper substrate three-dimensional graphene uses sucrose as the reaction precursor, attaches sucrose to the surface of copper particles by doping or impregnation, uses a mixed gas of hydrogen and argon as the auxiliary gas, and through a rapid thermal annealing process, uniformly grows graphene on the surface of copper particles at 800 °C, forming graphene with a network structure on the surface of copper particles (as Figure 2 shown).

[0068] This embodiment also provides the application of the highly conductive and thermally conductive composite copper solder paste sintered joint:

[0069] Coat the composite copper solder paste on the upper surface of the substrate and the lower surface of the chip by screen printing, fit the chip and the substrate together to form a sandwich interconnect structure, and perform thermocompression sintering connection. The sintering curve is as Figure 3 shown. Put the sintered joint into a sintering machine with an initial temperature of 60 °C, evacuate and then introduce a nitrogen atmosphere, heat it to 160 °C at a heating rate of 20 °C / min, keep it at 160 °C for 5 min for preheating, then apply a pressure of 5 MPa and continue to heat to the sintering temperature of 250 °C at a heating rate of 20 °C / min. After sintering for 15 min, introduce a nitrogen atmosphere for cooling, and take out the sintered joint when the temperature drops below 100 °C.

[0070] Example 2

[0071] This embodiment provides a highly conductive and thermally conductive composite copper solder paste, which includes the following components: 80 nm spherical copper particles, 300 nm spherical copper particles, 1 μm flaky copper particles, nano-copper substrate three-dimensional graphene particles, isopropanolamine, a mixed solution of 1 wt.% polyvinyl alcohol and ethanol, glutaric acid, N-methyl-2-pyrrolidone, and terpineol.

[0072] This embodiment also provides a preparation method of the highly conductive and thermally conductive composite copper solder paste, including the following steps:

[0073] S1. Mix 3 g of 80-nm spherical copper particles, 5.85 g of 300-nm spherical copper particles, and 1 g of 1-μm flaky copper particles, add 30 ml of 0.5 mol / L dilute sulfuric acid, conduct ultrasonic oscillation on it, after ultrasonic for 10 min, conduct centrifugal separation, the centrifugal speed is 5000 r / min, the centrifugal time is 3 min, after centrifugation, pour out the supernatant, add deionized water for ultrasonic cleaning for 5 min, centrifuge, pour out the supernatant, add absolute ethanol for ultrasonic cleaning for 5 min, centrifuge, pour out the supernatant.

[0074] S2. Add 30 ml of a solution mixed with 50 wt.% anhydrous formic acid and absolute ethanol, conduct ultrasonic oscillation for 10 min, centrifuge, pour out the supernatant, add absolute alcohol for ultrasonic cleaning for 5 min, centrifuge, pour out the supernatant, and obtain surface-modified wet mixed copper particles. After dispersing the surface-modified wet mixed copper particles in an ethanol solution, add the coating agent PVP, mix and conduct ultrasonic dispersion and then centrifuge.

[0075] S3. Mix 6 g of isopropanolamine, 3 g of a mixed solution of 1 wt.% polyvinyl alcohol and ethanol, 7 g of glutaric acid, 7 g of n-methyl-2-pyrrolidone, and 4 g of terpineol, conduct magnetic stirring for 3 h to obtain a uniformly mixed multi-component organic solvent system.

[0076] S4. Mix the above surface-modified mixed copper particles after coating, 0.15 g of three-dimensional graphene on the coated nano-copper substrate, and 30 g of the multi-component organic solvent system, and add malonic acid to adjust the pH value to make the mixed solution weakly acidic, conduct ultrasonic oscillation for 15 min, centrifuge at 3000 r / min for 5 min, pour out the supernatant, and obtain copper solder paste with appropriate viscosity.

[0077] Among them, the preparation of three-dimensional graphene on the coated nano-copper substrate uses sucrose as a reaction precursor, makes sucrose adhere to the surface of copper particles by doping or impregnation, uses a mixed gas of hydrogen and argon as an auxiliary gas, and through a rapid thermal annealing process, at 800 °C, uniformly grow graphene on the surface of copper particles, and form graphene with a network structure on the surface of copper particles. After dispersing the three-dimensional graphene particles on the nano-copper substrate in an ethanol solution, add the coating agent n-propanol, mix and conduct ultrasonic dispersion and then conduct suction filtration under a nitrogen atmosphere to obtain surface-coated wet three-dimensional graphene particles on the nano-copper substrate, and obtain three-dimensional graphene particles on the coated nano-copper substrate after freeze-drying for 12 h.

[0078] This embodiment also provides the application of the highly conductive and thermally conductive composite copper solder paste sintered joint:

[0079] The composite copper solder paste is coated on the upper surface of the substrate by screen printing. The substrate with the composite copper solder paste coated on its surface is placed in a sintering furnace with an initial temperature of 30 °C, evacuated, and then nitrogen gas is introduced into the atmosphere. It is heated to 100 °C at a heating rate of 10 °C / min, and kept at 100 °C for 5 minutes for preheating. The chip and the preheated substrate are mutually bonded to form a sandwich interconnect structure, and then hot-press sintering connection is carried out. The sintered connection joint is placed in a sintering furnace with an initial temperature of 100 °C, evacuated, and then nitrogen gas is introduced into the atmosphere. A pressure of 15 MPa is applied and the temperature is continuously increased to the sintering temperature of 250 °C at a heating rate of 20 °C / min. After sintering for 5 minutes, nitrogen gas is introduced into the atmosphere for cooling. When the temperature drops below 100 °C, the sintered connection joint is taken out.

[0080] The obtained sintered connection joints are respectively subjected to electrical conductivity and thermal conductivity tests, as shown in Table 1:

[0081] Table 1

[0082]

[0083] Control Example 1

[0084] In this control example, the step S1 in Example 1, "30 ml of 0.5 mol / L dilute sulfuric acid", is replaced with deionized water of the corresponding volume, and the rest is basically the same as in Example 1.

[0085] After testing, the copper oxide content of the copper solder paste obtained in this control example without undergoing the pickling process increases. The presence of copper oxide will hinder the sintering between copper particles and reduce the thermal and electrical conductivity. Therefore, after pickling is adopted in the present invention, less copper oxide remains, which is more conducive to the formation of sintering necks during the sintering process and is beneficial to improving the thermal and electrical conductivity of the sintered connection joint.

[0086] Control Example 2

[0087] In this control example, except for not performing step S2, the rest is basically the same as in Example 1.

[0088] After testing, the shear strength of the sintered connection joint prepared from the copper solder paste obtained in this control example without modification drops to 43.72 MPa under the same conditions. Therefore, the copper solder paste obtained after carboxylic acid modification in the present invention is more conducive to improving the mechanical properties of the sintered connection joint.

[0089] Control Example 3

[0090] In this control example, except for not adding nano-copper-based three-dimensional graphene in step S4, the rest is basically the same as in Example 2.

[0091] After testing, the results are shown in Table 1. The performance of the copper solder paste without adding nano-copper-based three-dimensional graphene particles in this comparative example is lower than that of the copper solder paste adding nano-copper-based three-dimensional graphene particles in Example 2 in terms of thermal conductivity and resistivity. Therefore, using nano-copper-based three-dimensional graphene particles to prepare copper solder paste in the present invention helps to improve its thermal and electrical conductivity performance.

[0092] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high electrical and thermal conductive composite copper solder paste, characterized in that: The invention comprises the following components: nano copper particles, micron copper particles and three-dimensional graphene on a nano copper substrate; the mass ratio of the nano copper particles, micron copper particles and three-dimensional graphene on a nano copper substrate is (70-90):(10-30):(0.2-1.5); the particle size of the nano copper particles is in the range of 10-800 nm; and the particle size of the micron copper particles is in the range of 1-8 μm.

2. The high electrical and thermal conductive composite copper solder paste according to claim 1, characterized in that: The shapes of the nano copper particles include: spherical, flake, dendritic or one or more of the following.

3. The high electrical and thermal conductive composite copper solder paste according to claim 1, characterized in that: The micron copper particles may have a shape of one or more of spherical, flake, and dendritic.

4. The method for preparing the high electrical and thermal conductive composite copper solder paste according to any one of claims 1 to 3, characterized in that: The steps include: S1. Mixing nano-copper particles and micro-copper particles, ultrasonically shaking the mixed copper particles with dilute acid, centrifuging, separating the solid and liquid, and discarding the supernatant, adding deionized water for ultrasonic cleaning, centrifuging, separating the solid and liquid, and discarding the supernatant, adding anhydrous ethanol for ultrasonic cleaning, centrifuging, separating the solid and liquid, and discarding the supernatant to obtain acid-washed mixed-size copper particles; S2. Adding a mixed solution of carboxylic acid and anhydrous ethanol to the mixed-size copper particles after pickling in step S1, ultrasonically shaking, centrifuging, and discarding the supernatant after solid-liquid separation, adding anhydrous ethanol to ultrasonically clean, centrifuging, and discarding the supernatant after solid-liquid separation to obtain surface-modified mixed-size copper particles; S3, using magnetic stirring to uniformly mix the dispersant, binder, reducing agent, and diluent in proportion to obtain a multi-component organic solvent system; S4. Mix the nano-copper-based three-dimensional graphene, the surface-modified mixed-size copper particles obtained in step S2, and the multi-organic solvent system obtained in step S3, perform ultrasonic vibration to fully mix them, centrifuge after mixing evenly to separate the solid and liquid, pour out the supernatant, and obtain a highly conductive and thermally conductive composite copper solder paste.

5. The method for preparing the high electrical and thermal conductive composite copper solder paste according to claim 4, characterized in that: In step S1, the dilute acid includes one or more of dilute sulfuric acid, dilute hydrochloric acid, and dilute nitric acid.

6. The method for preparing the high electrical and thermal conductive composite copper solder paste according to claim 4, characterized in that: In step S2, the carboxylic acid includes one or more of formic acid, lactic acid, oxalic acid, phosphoric acid, and oxalic acid.

7. The method for preparing the high electrical and thermal conductive composite copper solder paste according to claim 4, characterized in that: In step S3, the mass ratio of the dispersant, binder, reducing agent and diluent is 1:1:1:1 or 2:1:3:

1.

8. The method for preparing the high electrical and thermal conductive composite copper solder paste according to claim 4, characterized in that: In step S4, the method for preparing three-dimensional graphene on a nano-copper substrate includes the following steps: using sucrose as a reaction precursor, adhering sucrose to the surface of copper particles by incorporation or impregnation, using a mixture of hydrogen and argon as an auxiliary gas, and through a rapid thermal annealing process at 800°C, in situ growing uniform graphene on the surface of the copper particles, thereby forming graphene with a network structure on the surface of the copper particles.

9. An application of a high electrical and thermal conductive composite copper solder paste, characterized in that: The high-conductivity and thermal-conductivity composite copper solder paste described in any one of claims 1 to 3 or the high-conductivity and thermal-conductivity composite copper solder paste obtained by the preparation method according to any one of claims 4 to 8 is applied to the surface of the substrate and / or the chip by screen printing, and the chip and substrate coated with the composite copper solder paste are bonded to each other to form a sandwich interconnection structure, which are then hot-pressed and sintered in a nitrogen atmosphere.

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