Bonding paste

Abstract

The present invention provides a bonding paste that exhibits excellent dispersibility of copper nanoparticles in organic solvents and enables superior bonding, achieving high bonding strength even at low bonding temperatures of 250°C or below. [Solution] A bonding paste comprising composite copper nanoparticles in which the surface of copper nanoparticles is modified with alkoxysilane, the surface of which at least a portion of the surface layer is a coating containing cuprous oxide and copper carbonate, a reducing agent, and a solvent, wherein the mass oxygen concentration per unit surface area of ​​the composite copper nanoparticles is 0.10%·g / m² 2 More than 0.50% g / m 2 The following is the bonding paste.

Description

[Technical Field]

[0001] The present invention relates to a bonding paste, and more particularly to a bonding paste comprising composite copper nanoparticles in which the surface of the copper nanoparticles is modified with alkoxysilane, and a reducing agent. [Background technology]

[0002] It is known that inks or pastes containing copper nanoparticles dispersed in an organic solvent are used as bonding materials for various electronic components. It is known that coating the surface of the copper nanoparticles with a polymer film such as a dispersant improves their dispersibility in the organic solvent. Furthermore, it is known that adding a reducing agent to an ink or paste containing copper nanoparticles allows for sintering of the copper nanoparticles at low temperatures.

[0003] Patent Document 1 describes a sintered paste comprising a sintered powder containing copper particles coated with a capping agent (reducing agent) such as triethanolamine, an activator such as a dicarboxylic acid, a dispersant such as a surfactant, an organic solvent, and optionally a binder (resin). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-169512 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in the example described in Patent Document 1, the total amount of organic matter decomposed in the copper sintering process is large, with approximately 5% by mass of resin, 10% by mass of reducing agent, and 5% by mass of dispersant relative to the copper nanoparticles. Therefore, there are concerns that sufficient dispersibility of the copper nanoparticles in organic solvents may not be achieved, or that sufficient bonding strength may not be obtained at low bonding temperatures of 250°C or less due to the remaining organic matter.

[0006] In view of the above problems, the present invention aims to provide a bonding paste that exhibits excellent dispersibility of copper nanoparticles in organic solvents and enables superior bonding that can achieve high bonding strength even at low bonding temperatures of 250°C or less. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors conducted diligent research and found that in a bonding paste containing composite copper nanoparticles in which alkoxysilane is coated on the surface of copper nanoparticles and a reducing agent, by setting the mass oxygen concentration per unit surface area of ​​the composite copper nanoparticles within a predetermined range, the dispersibility of the composite copper nanoparticles in organic solvents is excellent, and sintering and diffusion bonding of the composite copper nanoparticles proceed sufficiently even at low temperatures, resulting in high bonding strength.

[0008] Based on the above findings, the gist of the present invention is as follows. [1] A bonding paste comprising: composite copper nanoparticles whose surface is modified with alkoxysilane, the surface of which is a coating containing cuprous oxide and copper carbonate on at least a portion of the surface layer; a reducing agent; and a solvent. The mass oxygen concentration per unit surface area of ​​the composite copper nanoparticles is 0.10%·g / m². 2 More than 0.50% g / m 2 The following is the bonding paste.

[0009] [2] The bonding paste according to [1], wherein the alkoxysilane comprises an alkylsilane in which an alkyl group having 3 to 18 carbon atoms is bonded to Si.

[0010] [3] The reducing agent comprises one or more selected from the group consisting of glycols, alkanolamines, and organic acids. The bonding paste according to [1] or [2] above, wherein the content of the reducing agent is 3% by mass or more and 9% by mass or less with respect to the composite copper nanoparticles.

[0011] [4] The bonding paste according to any one of the above [1] to [3], wherein the average particle size of the copper nanoparticles is 70 nm or more and 300 nm or less. [Effects of the Invention]

[0012] The bonding paste of the present invention exhibits excellent dispersibility of copper nanoparticles in organic solvents and enables superior bonding that yields high bonding strength even at low bonding temperatures of 250°C or below. [Modes for carrying out the invention]

[0013] [Bonding paste] A bonding paste according to one embodiment of the present invention comprises composite copper nanoparticles in which the surface of the copper nanoparticles is modified with an alkoxysilane, a reducing agent, and a solvent.

[0014] (Composite copper nanoparticles) In this embodiment, the composite copper nanoparticles are formed by modifying the surface of the copper nanoparticles with alkoxysilane. Here, "modification of the surface of the copper nanoparticles with alkoxysilane" means that the hydroxyl groups present on the surface of the copper nanoparticles and the alkoxy groups of the alkoxysilane undergo a dehydration condensation reaction, and silanols are bonded to the surface of the copper nanoparticles. Alternatively, even if hydroxyl groups are not present, the alkoxy groups of the alkoxysilane are hydrolyzed by electrostatic interactions, forming silanol groups that are adsorbed onto the surface of the copper nanoparticles. Subsequent dehydration condensation between the alkoxysilanes then forms a monolayer on the surface of the copper nanoparticles.

[0015] <Copper nanoparticles> Copper nanoparticles are defined as having a coating on their surface containing cuprous oxide (copper(I) oxide, chemical formula: Cu2O) and copper carbonate, at least in part. Generally, when copper nanoparticles oxidize, a coating containing cuprous oxide inevitably forms on at least part of the surface. The inclusion of copper carbonate in addition to the cuprous oxide coating helps to keep the sintering temperature of the copper nanoparticles low. The thickness of the coating is not particularly limited, but for copper nanoparticles of a typical size, the coating thickness is about a few nanometers (2-5 nm).

[0016] The shape (form) of the copper nanoparticles is not particularly limited. Examples of the shape of the copper particles include spherical (sphere), elliptical (ellipsoid), plate-like, etc. Among these, spherical and elliptical shapes are preferred, and a spherical shape is more preferred.

[0017] When the size of the copper nanoparticles is too small, the surface energy increases as the specific surface area of the copper nanoparticles increases. Therefore, it becomes difficult to disperse the copper nanoparticles in an organic solvent with a very small amount of alkoxysilane, and it is difficult to obtain a dense bonding layer. For this reason, the average particle diameter of the copper nanoparticles is preferably 70 nm or more, and more preferably 100 nm or more. On the other hand, when the size of the copper nanoparticles is too large, the sintering of the copper nanoparticles hardly progresses, and it is difficult to obtain a high bonding strength. For this reason, the average particle diameter of the copper nanoparticles is preferably 300 nm or less, and more preferably 200 nm or less.

[0018] The average particle diameter of the copper nanoparticles can be calculated based on the following formula. The specific surface area of the copper nanoparticles in the formula can be measured using a BET adsorption apparatus for nitrogen gas (for example, "MACSORB HM-1201" manufactured by Mountech Co., Ltd.).

Number

[0019] Examples of such copper nanoparticles include metal ultrafine powders obtained by the production method described in Japanese Patent No. 4304221 and copper fine particles obtained by the production method (dry method by reducing flame) described in Japanese Patent No. 6130616. Also, when copper nanoparticles are commercially available, they may be used. Copper nanoparticles produced by a dry method are not limited to the above production methods. For example, copper nanoparticles can also be obtained by a method of reducing a copper compound gas with a reducing gas or a method of cooling copper vaporized by plasma.

[0020] <Alkoxysilane> The alkoxysilane is not particularly limited as long as it can chemically bond to or adsorb onto the surface of copper nanoparticles and improve dispersibility in the solvent. The alkoxysilane has the general formula XSi(R'). n (OR) 3-n The organosilicon compound is represented by (where n is 0 to 2), where X is an alkyl group or a reactive functional group, R' is an alkyl group, and R in OR, which is a hydrolyzable group, is an alkyl group. When n=0, it is a trialkoxysilane of general formula XSi(OR)3, when n=1, it is a dialkoxysilane of general formula XSi(R')1(OR)2, and when n=2, it is a monoalkoxysilane of general formula XSi(R')2(OR)1. Considering the ease of adsorption to the surface of copper nanoparticles, the alkoxysilane preferably contains (or consists of) one or both of dialkoxysilane and trialkoxysilane, and more preferably contains (or consists of) trialkoxysilane.

[0021] R is preferably an alkyl group having 1 to 5 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and most preferably an alkyl group having 1 or 2 carbon atoms (i.e., a methyl group or an ethyl group).

[0022] When the alkoxysilane is a monoalkoxysilane or a dialkoxysilane, R' is preferably an alkyl group having 1 to 5 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and most preferably an alkyl group having 1 or 2 carbon atoms (i.e., a methyl group or an ethyl group).

[0023] When X is an alkyl group, the alkoxysilane is also an alkylsilane. From the viewpoint of surface modification of copper nanoparticles, it is preferable that the alkoxysilane is an alkylsilane. By using an alkylsilane, the amount of carbon contained in the composite copper nanoparticles can be reduced without impairing the dispersibility of the composite copper nanoparticles in organic solvents. In this case, it is preferable that X is an alkyl group with 3 to 18 carbon atoms. If the alkyl group has 3 or more carbon atoms, the alkyl group can exert steric effects by adhering to the surface of the copper nanoparticles, resulting in excellent dispersibility in organic solvents and making it easier to obtain a dense bonding layer. On the other hand, if the alkyl group is longer than necessary, when the composite copper nanoparticles are sintered and applied to bonding applications, carbon residue increases, decomposition gases increase, and this can cause voids and cracks in the bonding layer. Therefore, it is preferable that the alkyl group has 18 or fewer carbon atoms. The alkylsilane may be one or more selected from the group consisting of n-propyltrimethoxysilane, n-propyltriethoxysilane, n-octyltrimethoxysilane, n-octyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, octadecyltrimethoxysilane, and octadecyltriethoxysilane. In particular, n-octyltrimethoxysilane is preferred.

[0024] When X is a reactive functional group, an alkoxysilane is a so-called silane coupling agent. X may be a group comprising one or more selected from the group consisting of an amino group, an epoxy group, a methacrylic group, a vinyl group, and a mercapto group. Examples of silane coupling agents include acroyloxyalkylsilanes, aminoalkylsilanes, and glycidyloxyalkylsilanes. Examples of acroyloxyalkylsilanes include 3-(methacryloyloxy)propyltrimethoxysilane, triethoxy(3-methacryloyloxypropyl)silane, 3-(acrylooxy)propyltrimethoxysilane, and (triethoxysilyl)methyl methacrylate. Examples of aminoalkylsilanes include 3-aminopropyltrimethoxysilane and 3-(2-aminoethylamino)propyltrimethoxysilane. Examples of glycidyloxyalkylsilanes include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyl(dimethoxy)methylsilane, and triethoxy(3-glycidyloxypropyl)silane.

[0025] <Oxygen concentration per unit surface area of ​​composite copper nanoparticles> In this embodiment, the mass oxygen concentration per unit surface area of ​​the composite copper nanoparticles is 0.10%·g / m². 2 More than 0.50% g / m 2It is important that the "mass oxygen concentration per specific surface area of the composite copper nanoparticles" is a value obtained by dividing the mass ratio of oxygen (mass %) to the total mass of the composite copper nanoparticles by the specific surface area of the composite copper nanoparticles. The mass oxygen concentration of the composite copper nanoparticles is the total value of the oxygen concentration of the copper nanoparticles before modification with alkoxysilane and the oxygen concentration derived from alkoxysilane. That is, the "mass oxygen concentration per specific surface area of the composite copper nanoparticles" is the total value of the mass oxygen concentration per specific surface area derived from the copper nanoparticles and the mass oxygen concentration per specific surface area derived from the alkylsilane. When the mass oxygen concentration per specific surface area of the composite copper nanoparticles is too small, the effect of oxidation occurs, so that the dispersibility of the copper nanoparticles in an organic solvent cannot be sufficiently obtained, and the bonding strength cannot be sufficiently obtained at a low bonding temperature of 250 °C or lower. From this viewpoint, the mass oxygen concentration per specific surface area of the composite copper nanoparticles is 0.10%·g / m 2 or more, and preferably 0.20%·g / m 2 or more. On the other hand, when the mass oxygen concentration per specific surface area of the composite copper nanoparticles is too large, when the composite copper nanoparticles are fired, the oxygen derived from the copper nanoparticles and alkoxysilane cannot be sufficiently reduced by the reducing agent, and the bonding strength cannot be sufficiently obtained at a low bonding temperature of 250 °C or lower. From this viewpoint, the mass oxygen concentration of the composite copper nanoparticles is 0.50%·g / m 2 or less, preferably 0.45%·g / m 2 or less, more preferably 0.40%·g / m 2 or less, and most preferably 0.35%·g / m 2 or less.

[0026] The mass oxygen concentration of the composite copper nanoparticles can be measured using an oxygen-nitrogen analyzer (for example, "TC600" manufactured by LECO). The specific surface area of the composite copper nanoparticles is equivalent to the specific surface area of the copper nanoparticles before modification with alkoxysilane, and can be measured using a BET adsorption apparatus for nitrogen gas (for example, "MACSORB HM-1201" manufactured by Mount Tech Co., Ltd.). The mass oxygen concentration per specific surface area of the composite copper nanoparticles can be obtained by dividing the mass oxygen concentration of the composite copper nanoparticles obtained by measurement by the specific surface area.

[0027] The mass oxygen concentration per specific surface area of ​​composite copper nanoparticles can be controlled by controlling either or both of the oxygen concentration per specific surface area derived from the copper nanoparticles before modification with alkoxysilane, and the oxygen concentration per specific surface area derived from the alkoxysilane. However, the oxygen concentration per specific surface area derived from the copper nanoparticles before modification with alkoxysilane is a value that is uniquely determined depending on the manufacturing method and conditions of the copper nanoparticles. Therefore, it is easier to control the mass oxygen concentration per specific surface area of ​​composite copper nanoparticles by controlling the oxygen concentration per specific surface area derived from the alkoxysilane. The oxygen concentration per specific surface area derived from the alkoxysilane can be controlled by adjusting the amount of alkoxysilane added and the reaction conditions between the copper nanoparticles and the alkoxysilane during the manufacturing process of the composite copper nanoparticles.

[0028] In this invention, it is important that the mass oxygen concentration per unit surface area of ​​the composite copper nanoparticles is within a predetermined range, and the individual values ​​of the oxygen concentration per unit surface area derived from the copper nanoparticles before modification with alkoxysilane and the oxygen concentration per unit surface area derived from the alkoxysilane are not particularly limited. However, the oxygen concentration per unit surface area derived from the copper nanoparticles before modification with alkoxysilane is 0.07%·g / m². 2 More than 0.47% g / m 2 The following is preferable. Furthermore, the oxygen concentration per unit surface area derived from the alkoxysilane is 0.03%·g / m². 2 More than 0.43% g / m 2 The following is preferable:

[0029] The oxygen concentration per unit surface area derived from copper nanoparticles before modification with alkoxysilane can be determined by measuring the mass oxygen concentration and specific surface area of ​​the raw material copper nanoparticles before reaction with alkoxysilane. The oxygen concentration per unit surface area derived from alkoxysilane can be determined by subtracting the mass oxygen concentration per unit surface area derived from the raw material copper nanoparticles from the mass oxygen concentration per unit surface area of ​​the composite copper nanoparticles.

[0030] (Reducing agent) The reducing agent is a compound that reduces cuprous oxide and cuprous carbonate present in the surface film of copper nanoparticles during sintering. During sintering, the reduction of cuprous oxide and cuprous carbonate by the reducing agent causes the copper nanoparticles (pure copper) to come into contact with each other, promoting sintering and diffusion bonding. In this embodiment, the reducing agent also functions as a dispersant to improve dispersibility in organic solvents.

[0031] The reducing agent is not particularly limited as long as it can interact with the surface of the composite copper nanoparticles, adsorb or chemically bond to the surface of the composite copper nanoparticles, improve dispersibility in the solvent, and act as a reducing agent. Examples of such reducing agents include one or more selected from the group consisting of glycols, alkanolamines, and organic acids.

[0032] Examples of glycols include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, glycerin, and tetraethylene glycol.

[0033] Examples of alkanolamines include monoethanolamine, diethanolamine, and triethanolamine.

[0034] Examples of organic acids include formic acid, acetic acid, propionic acid, butyric acid, pentanoic acid, hexanoic acid, lactic acid, citric acid, malonic acid, and malic acid.

[0035] In this embodiment, the reducing agent content is preferably 3% by mass or more and 9% by mass or less relative to the composite copper nanoparticles. If the reducing agent content is 3 parts by mass or more per 100 parts by mass of composite copper nanoparticles, there will be no shortage of reducing agent, and higher bonding strength can be obtained without uneven sintering of the copper nanoparticles. Furthermore, if the reducing agent content is 9 parts by mass or less per 100 parts by mass of composite copper nanoparticles, the reducing agent will not leach out during bonding.

[0036] (solvent) The type of solvent is not particularly limited, and one or more solvents selected from the group consisting of terpene solvents such as terpineol, dihydroterpineol, dihydroterpinyl acetate, and dihydroterpinyl methyl ether, alcohols such as 1-propanol, 2-propanol, butanol, pentanol, hexanol, and octanol, ketones such as acetone and methyl ethyl ketone, and aromatic solvents such as toluene can be used.

[0037] The concentration of composite copper nanoparticles in the bonding paste is preferably 60% by mass or more and 90% by mass or less. If the concentration of composite copper nanoparticles in the bonding paste is 60% by mass or more, the coating film is less likely to run after paste application, making it easy to adjust the coating film. If the solvent concentration in the bonding paste is 90% by mass or less, the paste printability is excellent, and it is easy to obtain a good coating film.

[0038] [Method for manufacturing bonding paste] A preferred method for manufacturing a bonding paste according to one embodiment of the present invention is described.

[0039] First, copper nanoparticles are manufactured or prepared by the method described above, in which at least a portion of the surface layer is a coating containing cuprous oxide and copper carbonate.

[0040] Subsequently, composite copper nanoparticles are produced by modifying the surface of the copper nanoparticles with alkoxysilane.

[0041] First, as a mixing and dispersion step, a mixture obtained by mixing copper nanoparticles, an organic solvent, and an alkoxysilane is subjected to a dispersion treatment to produce a dispersion liquid. One method for dispersing copper nanoparticles is to pressurize the above mixture and feed it into a narrow channel, thereby applying shear force to the mixture. In this case, for example, wet jet mills such as the "NanoVeta B-ED" manufactured by Yoshida Machinery Industry Co., Ltd. or the "JN1000" manufactured by Joko Co., Ltd. can be used. The method for dispersing copper nanoparticles is not limited to the above method, and other methods such as using a self-rotating mixer or using blades or rolls can also be used.

[0042] The organic solvent is not particularly limited as long as it is capable of dissolving alkoxysilanes and dispersing copper nanoparticles. Examples of organic solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and terpineol; polyols such as ethylene glycol, dimethylene glycol, and triethylene glycol; ethers such as diethylene glycol monobutyl ether; and polar solvents such as N,N-dimethylformamide and N-methylpyrrolidone.

[0043] Next, in the reaction step, the dispersion is heated and stirred to chemically bond the alkoxysilane to the surface of the copper nanoparticles. At this time, the oxygen concentration per unit surface area of ​​the resulting composite copper nanoparticles can be controlled mainly by adjusting the amount of alkoxysilane added.

[0044] Next, the dispersion, after the reaction process is complete, is washed by adding an organic solvent and stirring. A stirrer, ultrasonic bath, or shaker can be used for stirring. This washing step can be omitted.

[0045] Next, the dispersion after the reaction or washing step is dried to remove the organic solvent by methods such as filtration drying, vacuum drying, forced air drying, or spray drying, thereby obtaining a composite copper nanoparticle powder.

[0046] Subsequently, the composite copper nanoparticles, reducing agent, and solvent are mixed to obtain a mixture, and the mixture is subjected to a dispersion treatment to obtain the bonding paste according to this embodiment. The dispersion method is not particularly limited, but one or more selected from a self-rotating mixer, a high-pressure wet disperser, an ultrasonic homogenizer, and an ultrasonic bath can be used. [Examples]

[0047] [Manufacturing of bonding paste] The bonding pastes for Test Examples No. 1 to 27 shown in Table 1 were manufactured using the following procedure.

[0048] First, copper nanoparticles with various average particle sizes and specific surface areas, as shown in Table 1, were prepared using the dry method with a reducing flame described in Japanese Patent Publication No. 6130616. A coating containing cuprous oxide and copper carbonate was formed on the surface of the manufactured copper nanoparticles. The oxygen concentration of the copper nanoparticles was measured using the method described above, and the "oxygen concentration per specific surface area derived from the copper nanoparticles" was determined by dividing it by the specific surface area, and is shown in Table 1.

[0049] Next, in each test example, composite copper nanoparticles were produced by modifying the surface of the copper nanoparticles shown in Table 1 with the alkylsilanes shown in Table 1. Specifically, using the "NanoVeta B-ED" manufactured by Yoshida Machinery Industry Co., Ltd., a mixture of copper nanoparticles, ethanol, and alkylsilane was pressurized and sent into a narrow channel, where shear force was applied to the mixture to obtain a dispersion. By stirring this dispersion while heating, the alkoxysilane was chemically bonded to the surface of the copper nanoparticles. Subsequently, a washing treatment was performed by adding ethanol to the dispersion and stirring, and the ethanol was dried and removed to obtain composite copper nanoparticle powder. The oxygen concentration per specific surface area of ​​the obtained composite copper nanoparticles and the oxygen concentration per specific surface area derived from the alkylsilane were measured by the method described above and are shown in Table 1. The oxygen concentration per specific surface area derived from the alkylsilane was controlled by adjusting the amount of alkoxysilane added in the composite copper nanoparticle manufacturing process described above.

[0050] In each test example, 40 g of the prepared composite copper nanoparticles were mixed with the reducing agent and solvent shown in Table 1, and dispersed using a self-rotating mixer to obtain a bonding paste. The total amount of reducing agent and solvent was fixed at 17.14 g, so that the concentration of composite copper nanoparticles was 70% by mass. The content of the reducing agent relative to the composite copper nanoparticles was then adjusted to the values ​​shown in Table 1.

[0051] [Evaluation of paste dispersibility] The prepared bonding paste was applied to a glass substrate in a 1 cm square area using a bar coater and dried to create a 20 μm thick dried film. The surface roughness Rz of the dried film was measured for 10 fields of view using a laser microscope (Keyence "VK-110"), and the average value was used as an evaluation index for paste dispersibility. A result of less than 2.0 μm for the average Rz was judged as "excellent," and a result of 2.0 μm or more was judged as "poor." The average Rz value and the judgment result for each test example are shown in Table 1.

[0052] [Joint evaluation] The prepared bonding paste was applied to an oxygen-free copper plate C1020 (20 mm square, 2 mm thick) using a mask, in a 7 mm square, 100 μm thick layer, and pre-dried at 100°C for 30 minutes. Then, a 5 mm square, 350 μm thick SiC sheet was mounted onto the dried film, and bonding was performed using a pressure bonding apparatus under the following conditions: bonding temperature 250°C, pressure 10 MPa, bonding time 5 minutes, and under a nitrogen atmosphere. The shear strength of the resulting bonded product was measured using a destructive testing apparatus. A shear strength of 50 MPa or higher was judged as "excellent," 35 MPa or higher but less than 50 MPa as "good," and less than 35 MPa as "poor." Table 1 shows the shear strength and judgment results for each test example.

[0053] [Evaluation of liquid (reducing agent) seepage in the bonding layer] In each test example, the outer periphery of the SiC in the bonded product was observed at 20x magnification using a microscope (HOZAN Corporation, L-KIT504) to check for the presence or absence of liquid seepage around the outer periphery of the SiC, as shown in Table 1.

[0054] [Table 1] [Industrial applicability]

[0055] The bonding paste of the present invention has potential applications in bonding electronic components, more specifically, in high-temperature environments where bonding materials such as solder are difficult to use, such as inside electronic devices called power devices, for bonding components such as substrates and elements.

Claims

1. A bonding paste comprising: composite copper nanoparticles whose surface is modified with alkoxysilane, the surface of which is a coating containing cuprous oxide and copper carbonate on at least a portion of the surface layer of the copper nanoparticles; a reducing agent; and a solvent. The mass oxygen concentration per unit surface area of ​​the composite copper nanoparticles is 0.10% g / m². ２ More than 0.50%・g / m ２ The following is the bonding paste.

2. The bonding paste according to claim 1, wherein the alkoxysilane includes an alkylsilane in which an alkyl group having 3 to 18 carbon atoms is bonded to Si.

3. The reducing agent comprises one or more selected from the group consisting of glycols, alkanolamines, and organic acids. The bonding paste according to claim 1 or 2, wherein the content of the reducing agent is 3% by mass or more and 9% by mass or less with respect to the composite copper nanoparticles.

4. The bonding paste according to claim 1 or 2, wherein the average particle size of the copper nanoparticles is 70 nm or more and 300 nm or less.

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