Copper paste, copper particles, and joining members using them.

Abstract

The present invention provides a copper paste that contains a high concentration of copper particles, has relatively low viscosity, and exhibits minimal changes in properties even after a certain period of time has elapsed since manufacturing. [Solution] A copper paste comprising copper particles, a polymer dispersant, a branched carboxylic acid or its salt, and a paste solvent, wherein the copper particles have an average particle diameter of 170 nm to 600 nm as measured by a scanning electron microscope, the polymer dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or its salt has 8 to 20 carbon atoms.

Description

Technical Field

[0001] The present invention relates to a copper paste, copper particles, and a joining member using them.

Background Art

[0002] Conventionally, for example, solder has been used as a joining member for joining a semiconductor element and a lead frame or the like. With the miniaturization, high performance, and expanded applications of recent devices and systems, the semiconductors used are also required to be miniaturized and have high performance. Particularly in power semiconductors, as the operating temperature increases with the use of wide-gap semiconductor materials and high integration, it has become difficult to cope with conventional joining members using solder. Therefore, as a joining member to replace solder, pastes containing metal particles such as copper particles and silver particles have been studied.

[0003] Currently, silver particles are beginning to be put into practical use as a joining member. However, silver particles have problems such as high price and easy occurrence of ion migration. As a means to solve such problems, research and development for practical use of a joining member using copper particles are also being advanced.

[0004] Patent Document 1 discloses a copper paste composition including copper powder, copper core particles having a smaller particle diameter than the copper powder, and coated copper particles containing a plurality of aliphatic carboxylic acid molecules adsorbed at a density of 2.5 to 5.2 molecules per 1 nm on the surface of the copper core particles, a plurality of polar organic low molecules having a hydrophilic group and a hydrophobic group and interacting with the plurality of aliphatic carboxylic acid molecules of the coated copper particles, and a medium, wherein the copper core particles and the aliphatic carboxylic acid molecules are thermal decomposition products of a copper aliphatic carboxylic acid complex. Further, in Example 1, a copper paste composition is described in which coated copper particles (CuP1), first copper powder having an average particle diameter of 2.0 μm, second copper powder having an average particle diameter of 0.8 μm, a polyacrylic acid-based polymer dispersant, a polymethacrylic acid-based polymer thickener, a polar organic low molecule, and a medium are blended.

[0005] ​​ Patent Document 2 discloses a conductive paste for bonding containing 100 parts by weight of metal powder, 5 to 20 parts by weight of solvent, and 0.07 to 3 parts by weight of branched higher fatty acids. Furthermore, Example 1 describes a conductive paste in which silver powder is dispersed in a texanol solution containing 13.1 parts by weight of organic solvent and 0.3 parts by weight of ethylcellulose, to which isostearic acid has been pre-added.

[0006] Patent Document 3 discloses metal colloid particles composed of metal nanoparticles and a protective colloid coating the metal nanoparticles, wherein the protective colloid is composed of an organic compound having a carboxyl group and a polymeric dispersant, and a dispersion containing the metal colloid particles and a solvent. Furthermore, Example 2 describes a silver colloid particle paste with a silver concentration of 80%, prepared by adding ethylene glycol to silver colloid particles in which silver nanoparticles with a number-average particle diameter of 20 nm are protected by a protective colloid.

[0007] Patent Document 4 discloses a copper nanoparticle dispersion containing copper nanoparticles, a carboxylic acid, an alkylamine, a polymeric dispersant, and a solvent, wherein the polymeric dispersant has an amine value and an acid value of 30 to 160 mgKOH / g, and the other amine value and acid value of 0 to 160 mgKOH / g, and the volume-average particle size measured by dynamic light scattering is 500 nm or less. Furthermore, Example 1(2) describes obtaining copper nanoparticle dispersion 1 by mixing copper nanoparticles with an average primary particle size of 39 nm coated with nonanoic acid and hexylamine, Solspers 41000, and PGME (propylene glycol monomethyl ether). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-090725 [Patent Document 2] Japanese Patent Publication No. 2019-087553 [Patent Document 3] Japanese Patent Publication No. 2009-74171 [Patent Document 4] Japanese Patent Publication No. 2015-210973 [Overview of the project] [Problems that the invention aims to solve]

[0009] In joining methods using a paste-like joining material containing copper particles, the joining material is generally applied to a substrate, and the material to be joined is placed on the side of the joining material opposite the substrate to obtain a laminate. The laminate is then heated, and the copper particles are sintered and transformed into a joining layer, thereby joining the substrate and the material to be joined through this joining layer. The joining material can be applied to the substrate by various application methods. The properties required of the paste-like joining material differ depending on the application method, but one property that is commonly considered important is viscosity.

[0010] In particular, when low-viscosity bonding components are required, low-viscosity pastes are achieved by increasing the proportion of solvent in the copper particle-containing paste or decreasing the proportion of copper particles, i.e., by lowering the concentration of copper particles. On the other hand, in such low-concentration copper pastes, because the proportion of copper particles to the entire paste is small, defects in the bonding layer are likely to occur due to the evaporation of the solvent in the paste during heating and sintering. Defects in the bonding layer are one of the causes of a decrease in bonding strength, conductivity, thermal conductivity, dimensional accuracy, etc. (hereinafter, these may be collectively referred to as "bonding characteristics"). There are broadly two types of bonding methods: non-pressure bonding and pressure bonding, and the pressure applied in pressure bonding varies, but this tendency for a decrease in bonding characteristics is more pronounced in non-pressure bonding and when the pressure applied during bonding is small. In addition, extra energy is required for the evaporation of the solvent, and the evaporated organic solvent poses problems from an environmental and safety / health perspective.

[0011] In contrast, with copper paste containing a high concentration of copper particles, it is generally difficult to reduce viscosity, and the copper particles tend to aggregate in the paste solvent, making it difficult to highly disperse them. In such paste-like bonding materials with aggregated copper particles, the application position, application amount, and uniformity of the coating film (hereinafter collectively referred to as "applicability") vary, making it impossible to perform the aforementioned application stably. Furthermore, deterioration in applicability and aggregation of copper particles lead to localized variations in the sintering state of the copper particles during heating, causing a decrease in bonding characteristics. This decrease in bonding characteristics is particularly pronounced when sintering copper particles at relatively low temperatures.

[0012] Furthermore, when using a paste containing copper particles as a bonding material, it is common for a considerable amount of time to pass between the manufacture of the copper paste and its actual use as a bonding material. Therefore, it is required that the copper paste maintain a stable viscosity for a certain period after manufacture, and that no changes in paste properties such as aggregation of copper particles or separation of solid and liquid phases are observed; in other words, it must have high storage stability. In particular, copper pastes using copper particles as metal particles tend to exhibit more aggregation of copper particles over time and an increase in viscosity compared to those using silver particles. Moreover, the higher the concentration of copper particles in the paste, the more likely it is that aggregation of copper particles will occur over time and the viscosity of the copper paste will increase. In addition, if such a copper paste with low storage stability is used as a bonding material after a certain period has elapsed since manufacture, sufficient bonding characteristics cannot be obtained.

[0013] It was confirmed that the copper paste composition described in Patent Document 1 increased in viscosity after a certain period of time had elapsed since its manufacture. In other words, it was found to have problems in terms of the storage stability of the paste. Furthermore, even when bonding was performed using this paste, sufficient bonding strength could not be obtained.

[0014] In the example described in Patent Document 2, silver nanoparticles are used. When this technology is applied to a paste containing copper particles, the viscosity is high immediately after manufacturing, and sufficient bonding strength cannot be obtained.

[0015] In the example described in Patent Document 3, silver nanoparticles are used as silver colloid particles protected by a protective colloid, and the paste concentration is 80% by mass. Applying this technology to a paste containing copper particles does not allow for the production of a high-concentration, low-viscosity paste, nor does it provide sufficient bonding strength. Furthermore, increasing the copper concentration in the paste leads to storage stability problems.

[0016] The copper nanoparticle dispersion described in Patent Document 4 has small copper particle size and low copper particle concentration. Furthermore, while it is suitable for applications where copper nanoparticles are sintered in a thin film state exposed to the atmosphere to form a conductive film, it does not provide sufficient bonding characteristics when used in a relatively thick film state confined between components, such as in bonding.

[0017] This invention has been made in view of the above problems, and aims to provide a copper paste that contains a high concentration of copper particles, has relatively low viscosity, and exhibits little change in properties even after a certain period of time has elapsed since manufacturing. Furthermore, it aims to provide a copper paste that can achieve excellent bonding characteristics when used as a bonding material. Moreover, it aims to provide a copper paste that can achieve excellent bonding characteristics even after a certain period of time has elapsed since manufacturing. [Means for solving the problem]

[0018] The inventors investigated the causes of deterioration in paste properties, such as increased viscosity, and the decrease in bonding characteristics when used as a bonding material, over time in copper paste. As a result, they confirmed that the formation of copper oxide due to oxidation of copper particles over time, and the generation of copper microparticles due to the elution and re-reduction of copper ions are influential factors. They found that including a certain amount or more of carboxylic acids in the paste is effective in suppressing these phenomena caused by the oxidation of copper particles. However, simply including a large amount of carboxylic acids made it difficult to achieve both low viscosity and other paste properties, as well as bonding characteristics such as bonding strength and low-temperature sinterability. The inventors diligently studied this problem and found that the above problem could be solved by creating a paste in which the average particle size of copper particles is within a specific range and a specific polymer dispersant and a specific branched carboxylic acid are blended, thus completing the present invention.

[0019] In other words, the present invention is (1) A copper paste comprising copper particles, a polymeric dispersant, a branched carboxylic acid or its salt, and a paste solvent, wherein the copper particles have an average particle size of 170 nm to 600 nm as measured by a scanning electron microscope, the polymeric dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or its salt has 8 to 20 carbon atoms. (2) The copper paste according to (1), wherein the copper particle content is 85% by mass or more and 96% by mass or less, the polymer dispersant content is 0.01% by mass or more and 2% by mass or less, and the branched carboxylic acid or its salt content is 0.1% by mass or more and 5% by mass or less. (3) The copper paste according to (1) or (2), further comprising a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof, (4) A copper paste according to any one of (1) to (3), wherein the copper particle content is 85% by mass or more and 96% by mass or less, and the viscosity at 25°C measured with a rotational rheometer is 0.1 Pa·s or more and 100 Pa·s or less. (5) The copper particles are a copper paste according to any one of (1) to (4), wherein a polymer dispersant is present on its surface. (6) The copper particles are the copper paste according to any one of (1) to (4), wherein a polymer dispersant and a branched carboxylic acid or its salt are present on the surface thereof. (7) The copper particles are the copper paste according to (3) or (4), wherein the polymer dispersant, the branched carboxylic acid or its salt, and a linear carboxylic acid and / or an aromatic carboxylic acid or their salts are present on the surface thereof. (8) The copper paste according to any one of (1) to (7), wherein the polymer dispersant has a polyoxyethylene chain in its structure. (9) The copper paste according to any one of (1) to (8), wherein the number average molecular weight of the polymer dispersant is 1500 or less. (10) The copper paste according to any one of (1) to (9), wherein the polymer dispersant is an anionic polymer dispersant. (11) The copper paste according to any one of (1) to (10), wherein the branched carboxylic acid or its salt is at least one selected from 2-ethylcaproic acid, isopalmitic acid, isostearic acid, and their salts. (12) Surface-treated copper particles having a polymer dispersant and a branched carboxylic acid or its salt on the surface of the copper particles, wherein the copper particles have an average particle diameter measured by a scanning electron microscope of 170 nm or more and 600 nm or less, the polymer dispersant has an acid value of 60 mgKOH / g or more, and the branched carboxylic acid or its salt has 8 to 20 carbon atoms. (13) Composite copper particles having a polymer dispersant, a branched carboxylic acid or its salt, and a linear carboxylic acid and / or an aromatic carboxylic acid or their salts on the surface of the copper particles, wherein the copper particles have an average particle diameter measured by a scanning electron microscope of 170 nm or more and 600 nm or less, the polymer dispersant has an acid value of 60 mgKOH / g or more, and the branched carboxylic acid or its salt has 8 to 20 carbon atoms. (14) A method for producing a copper paste, comprising mixing copper particles, a polymeric dispersant, a branched carboxylic acid or a salt thereof, and a paste solvent, wherein the copper particles have an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope, the polymeric dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or a salt thereof has 8 or more and 20 or less carbon atoms. (15) A method for producing copper paste comprising the following steps (A) to (B) in this order: (A) a step of mixing copper particles, a polymer dispersant, and a solvent to obtain coated copper particles; (B) a step of mixing the coated copper particles obtained in step (A), a branched carboxylic acid or a salt thereof, and a paste solvent to obtain copper paste, wherein the copper particles have an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope, the polymer dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or a salt thereof has 8 or more and 20 or less carbon atoms. (16) A method for producing copper paste comprising the following steps (A) to (B) in this order: (A) a step of mixing copper particles, a polymer dispersant, a branched carboxylic acid or a salt thereof, and a solvent to obtain surface-treated copper particles; (B) a step of mixing the surface-treated copper particles obtained in step (A) with a paste solvent to obtain copper paste, wherein the copper particles have an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope, the polymer dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or a salt thereof has 8 or more and 20 or less carbon atoms. (17) A method for producing copper paste comprising the following steps (A) to (C) in this order: (A) a step of mixing copper particles, a polymer dispersant, and a solvent to obtain coated copper particles; (B) a step of mixing the coated copper particles obtained in step (A) with a branched carboxylic acid to obtain surface-treated copper particles; (C) a step of mixing the surface-treated copper particles obtained in step (B) with a paste solvent to obtain copper paste, wherein the copper particles have an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope, the polymer dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or its salt has 8 or more and 20 or less carbon atoms. (18) A joining member comprising the copper paste described in any of (1) to (11), (19) A method for manufacturing a joined body, comprising the step of joining a base material and a material to be joined using a copper paste described in any of (1) to (11) or a joining member described in (18), (20) A method for manufacturing a bonded body according to (19), wherein the bonding surface of the base material is gold, silver, or copper, and the bonding surface of the material to be bonded is gold, silver, or copper. (21) The method for manufacturing a joined body according to (20), wherein the joining surface of the base material is copper and the joining surface of the material to be joined is gold. And so on. [Effects of the Invention]

[0020] According to the present invention, a copper paste can be obtained that contains a high concentration of copper particles, has relatively low viscosity, and exhibits minimal change in properties even after a certain period of time has elapsed since manufacturing. Furthermore, when the copper paste of the present invention is used as a bonding material, sufficient bonding characteristics can be achieved. Moreover, sufficient bonding characteristics can be achieved even after a certain period of time has elapsed since manufacturing. [Modes for carrying out the invention]

[0021] The copper paste of the present invention is a copper paste comprising copper particles, a polymeric dispersant, a branched carboxylic acid or a salt thereof, and a paste solvent, wherein the copper particles have an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope, the polymeric dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or a salt thereof has 8 or more and 20 or less carbon atoms.

[0022] This configuration allows for the production of a copper paste that contains a high concentration of copper particles, has relatively low viscosity, and exhibits minimal changes in properties even after a certain period of time has elapsed since manufacturing. Furthermore, using this paste as a bonding material enables the realization of sufficient bonding characteristics. Specifically, the bonding strength of the bonded body, as measured by the method described later, can be 20 MPa or higher, 25 MPa or higher, and even 27 MPa or higher. Moreover, sufficient bonding characteristics can be achieved even after a certain period of time has elapsed since manufacturing. For example, the bonding strength after being stored at room temperature for one week after manufacturing can be 20 MPa or higher, and even 25 MPa or higher.

[0023] As mentioned above, bonding methods using a paste-like bonding member containing copper particles include a step of heating the laminate to sinter the copper particles. The higher the heating temperature, the easier it is for the copper particles to sinter, and the better the bonding characteristics tend to be. However, from the viewpoint of the heat resistance limits of the materials to be bonded, such as semiconductor chips and substrates, and the need to reduce the energy input, it is also required that the heating temperature not be too high, for example, around 300°C or lower. Therefore, there is a need for a bonding member that can obtain sufficient bonding characteristics even at low temperatures of 300°C or lower. According to the copper paste of the present invention, sufficient bonding characteristics can be obtained even when heated at low temperatures of 300°C or lower. By adjusting the paste formulation, sufficient bonding characteristics can also be obtained when heated at temperatures of 275°C or lower, or even 250°C or lower.

[0024] Furthermore, since copper particles easily form an oxide film on their surface, heating and sintering bonding components using copper particles required heating in a reducing atmosphere to remove the surface oxide film. However, heating in a reducing atmosphere incurs additional costs, such as the introduction of specialized equipment for atmosphere control. Therefore, there is a need for bonding components that can be used in non-reducing atmospheres, such as inert atmospheres. The copper paste of the present invention provides sufficient bonding characteristics even when heated in a non-reducing atmosphere.

[0025] As mentioned above, there are two main types of joining methods: non-pressure joining and pressure joining. Pressure joining involves heating a laminate, which is formed by stacking a base material and materials to be joined via a joining member, while applying a load exceeding 0.01 MPa. This sintersects the copper particles, transforming them into a bonding layer, and then joining the base material and materials to be joined through this bonding layer. In contrast, non-pressure joining involves heating a laminate, which is formed by stacking a base material and materials to be joined via a joining member, while the laminate is positioned in a direction where the weight of the base material acts upon it, or while applying a load of 0.01 MPa or less. This sintersects the copper particles, transforming them into a bonding layer, and then joining the base material and materials to be joined through this bonding layer. Of these, non-pressure joining does not require pressurizing the materials to be joined during joining, thus improving production efficiency. It also reduces damage to the materials to be joined (such as semiconductors) during joining. However, non-pressure joining has the drawback of not being able to achieve sufficient bonding strength. Therefore, there is a need for a joining component that can produce a sintered body with sufficient joining strength using a pressureless joining method. According to the copper paste of the present invention, sufficient joining characteristics can be obtained even when a pressureless joining method is employed.

[0026] <Copper particles> The copper paste of the present invention contains copper particles, the copper particles having an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope.

[0027] By creating a paste using copper particles with an average particle size within the aforementioned range, a specific polymer dispersant, and a branched carboxylic acid or its salt, a copper paste can be obtained that contains a high concentration of copper particles while having relatively low viscosity and exhibiting minimal changes in properties even after a certain period of time has elapsed since manufacturing. Furthermore, when this paste is used as a bonding material, sufficient bonding characteristics can be achieved. Moreover, sufficient bonding characteristics can be achieved even after a certain period of time has elapsed since manufacturing. In addition, sufficient bonding characteristics can be achieved using a non-pressure bonding method even under an inert atmosphere and with low-temperature heating below 300°C.

[0028] Generally, when metal particles are used for sintering, particles with a size of nano-order (less than 100 nm) are used in anticipation of a melting point depression due to the size effect. However, in this invention, the problem can be solved by using copper particles with the above average particle size in combination with the above polymer dispersant and branched carboxylic acid or a salt thereof.

[0029] In particular, if the average particle size of the copper particles is within the aforementioned range, oxidation of the copper particles is relatively slow, thus contributing to improved storage stability of the copper paste. Furthermore, even if the concentration of copper particles in the paste is increased, the copper particles disperse easily, reducing the degree of increase in the viscosity of the paste.

[0030] The average particle diameter of copper particles is determined by imaging copper particles using a scanning electron microscope (hereinafter sometimes referred to as "SEM"), measuring the maximum Ferret diameter (hereinafter simply referred to as Ferret diameter) of 50 primary particles within the SEM field of view, and taking the arithmetic mean of these values ​​as the average particle diameter.

[0031] The average particle size of the copper particles is preferably between 180 nm and 500 nm. Within this range, a better balance can be achieved between the viscosity reduction and storage stability of the copper paste and the bonding characteristics when used as a bonding material. The average particle size is more preferably between 200 nm and 400 nm.

[0032] The shape of the copper particles is not particularly limited, and any shape can be used, such as spherical, polyhedral, spindle-shaped, plate-shaped, rod-shaped, needle-shaped, or irregularly shaped.

[0033] Copper particles may contain substances other than metallic copper to an extent that is acceptable depending on the application. These other substances include unavoidable impurities and alloying components. Oxides such as copper oxide, cuprous oxide, and trace amounts of copper oxide may be present on their surface. Raw materials, reaction products, and auxiliary materials used in the manufacturing process may also remain.

[0034] The copper paste of the present invention may contain copper particles other than the copper particles described above. Specifically, it may contain micro-copper particles with an average particle diameter of 1 μm to 50 μm, or nano-copper particles with an average particle diameter of 100 nm or less. The shape of the micro-copper particles and nano-copper particles is not particularly limited and can be any shape such as spherical, lumpy, needle-shaped, flake-shaped, substantially spherical, irregularly shaped, polyhedral, spindle-shaped, or flattened, as well as aggregates of these shapes. The average particle diameter of the micro-copper particles and nano-copper particles can be measured in the same way as the average particle diameter of the copper particles described above.

[0035] In the copper paste of the present invention, there are no restrictions on the copper particle content, and any copper concentration may be set. The copper paste of the present invention has low viscosity and high storage stability even at high copper concentrations. Therefore, the copper particle content can be 85% by mass or more, 88% by mass or more, or 90% by mass or more of the total paste. There are also no upper limits on the copper concentration, and although it depends on the balance with other components, for example, the copper particle content may be 96% by mass or less, 95% by mass or less, or 94% by mass or less of the total paste. The copper particle content in the copper paste can be confirmed, for example, by thermogravimetric analysis.

[0036] <Polymer dispersant> The copper paste of the present invention contains a polymeric dispersant, the polymeric dispersant having an acid value of 60 mgKOH / g or more.

[0037] By using a polymer dispersant with an acid value within the aforementioned range, copper particles with an average particle size within a specific range, and a branched carboxylic acid or its salt to create a paste, a copper paste can be obtained that contains a high concentration of copper particles, has relatively low viscosity, and exhibits minimal changes in properties even after a certain period of time has elapsed since manufacturing. Furthermore, when this paste is used as a bonding material, sufficient bonding characteristics can be achieved. Moreover, sufficient bonding characteristics can be achieved even after a certain period of time has elapsed since manufacturing. In addition, sufficient bonding characteristics can be achieved using a no-pressure bonding method even under an inert atmosphere and with low-temperature heating below 300°C.

[0038] In particular, by setting the acid value of the polymer dispersant within the aforementioned range, it is believed that the polymer dispersant becomes more readily available to act on copper particles, thereby improving the dispersibility of copper particles in the paste. As a result, even when the concentration of copper particles in the paste is increased, the degree of increase in viscosity of the paste can be reduced. Furthermore, it is understood that the acid groups have an effect of removing oxide films, allowing the paste to be suitably used as a bonding material even in a non-reducing atmosphere, and even pastes that have been aged for a certain period after manufacturing can be suitably used as a bonding material.

[0039] If the polymer dispersant is a commercially available product, refer to the catalog value for its acid value. If the polymer dispersant is manufactured in-house, the acid value can be measured using the following method. The acid value of the polymer dispersant is measured by non-aqueous titration using an automatic titrator (GT-310BRT (manufactured by Nitto Analytech Co., Ltd.)). A 0.1 ml / L potassium hydroxide-ethanol solution (manufactured by Nacalai Tesque Co., Ltd.) is used as the titration solution, and the titration sample is prepared by dissolving 0.5 g of the polymer dispersant in 100 mL of ethanol.

[0040] The acid value of the polymeric dispersant is preferably 60 mgKOH / g or higher, and more preferably 70 mgKOH / g or higher, as this improves the dispersibility of copper particles in the paste and reduces the degree of viscosity increase of the paste. There is no particular upper limit to the acid value of the polymeric dispersant, but it is preferable that it is 200 mgKOH / g or lower, as this improves the balance between the dispersibility and bonding properties of copper particles in the paste. It is even more preferable that the acid value of the polymeric dispersant is between 70 mgKOH / g and 200 mgKOH / g.

[0041] In the copper paste of the present invention, there are no restrictions on the content of the polymer dispersant, and any polymer dispersant concentration may be set. It is preferable to set the polymer dispersant content to 0.01% by mass or more relative to the total paste, as this can further improve the dispersibility of copper particles in the copper paste, and it is more preferable to set it to 0.02% by mass or more. It is preferable to set the polymer dispersant content to 2% by mass or less relative to the total paste, as this makes it less likely for defects to occur in the bonding layer during heating and further improves the bonding characteristics, and it is more preferable to set it to 1% by mass or less.

[0042] The polymeric dispersant only needs to be present in the copper paste, and there are no restrictions on its state of existence. For example, the polymeric dispersant may be adsorbed onto copper particles, or it may be free in the paste. Furthermore, the polymeric dispersant may be directly adsorbed onto the surface of the copper particles, or it may be adsorbed via other additives adsorbed onto the surface of the copper particles.

[0043] The polymeric dispersant may have an amine value, and its amine value is not particularly limited. For example, the amine value of the polymeric dispersant may be 45 mgKOH / g or less, preferably 20 mgKOH / g or less, and more preferably 5 mgKOH / g or less. It is even more preferable to use a polymeric dispersant that does not have an amine value. When the amine value of the polymeric dispersant is within the above range, the reaction between acidic components such as branched carboxylic acids contained in the copper paste and components derived from the amine value can be effectively avoided, and the dispersibility of copper particles in the paste is further improved. As a result, even if the concentration of copper particles in the paste is increased, the degree of increase in the viscosity of the paste can be reduced.

[0044] The polymeric dispersant in the copper paste of the present invention is not particularly limited as long as its acid value is 60 mgKOH / g or higher. Examples of polymeric dispersants include anionic, cationic, and nonionic types. Anionic polymeric dispersants are preferred because they easily improve the balance between the dispersibility and bonding properties of copper particles in the paste. Anionic dispersants include carboxylic acid type, sulfonic acid type, sulfate ester type, and phosphate ester type. Among these, the carboxylic acid type is particularly preferred.

[0045] Polymer dispersants have polyoxyethylene chains ((OCH2CH2) in their structure. n It may have O). Having such a structure is preferable because it makes the copper particles in the copper paste easier to sinter and improves bonding properties. In addition, the thermal decomposition properties of the polymer dispersant are improved, and the polymer dispersant or its residual components are more likely to volatilize when heated and are less likely to remain in the bonding layer, thereby reducing defects in the bonding layer caused by them. As a result, it is preferable because it can achieve higher bonding properties. The presence of polyoxyethylene chains can be confirmed by detecting the molecular weight in increments of 44, which is the repeating structure of the ethylene glycol chain, using liquid chromatography / mass spectrometry (LC-MS).

[0046] The number-average molecular weight of the polymer dispersant in the copper paste of the present invention is not particularly limited. For example, if the number-average molecular weight is 1500 or less, the polymer dispersant or its residual components are more likely to volatilize during heating and are less likely to remain in the bonding layer, thus reducing defects in the bonding layer caused by them. As a result, higher bonding characteristics can be achieved, which is preferable. A number-average molecular weight of 1200 or less is more preferable, and 1000 or less is even more preferable.

[0047] Furthermore, a number-average molecular weight of 300 or more is preferable because it improves the dispersibility of copper fine particles in the paste, 350 or more is more preferable, and 400 or more is even more preferable.

[0048] Therefore, the number-average molecular weight is preferably 300 to 1500, more preferably 350 to 1200, and even more preferably 400 to 1000.

[0049] The number-average molecular weight of polymeric dispersants can be measured by gel permeation chromatography (GPC). Specifically, the polymeric dispersant is dissolved in tetrahydrofuran (THF), and GPC analysis is performed.

[0050] Furthermore, the polymeric dispersant may have a carboxyl group in its structure. Polymeric dispersants having a carboxyl group are preferable because they readily act on copper particles in particular via the carboxyl group, thereby further improving the dispersibility of copper particles in the paste. They are also preferable because they can further reduce the increase in viscosity of the paste even when the concentration of copper particles in the paste is increased. The presence of a carboxyl group can be confirmed by the presence of an absorption peak in infrared spectroscopy.

[0051] The number of carboxyl groups in the polymeric dispersant in the copper paste of the present invention is not particularly limited. For example, the molecule may have one carboxyl group or two or more carboxyl groups. Having one carboxyl group in the polymeric dispersant molecule is preferable as it makes it easier to achieve both good dispersibility and bonding properties for the copper particles in the paste.

[0052] The number of carboxyl groups in a polymeric dispersant can also be calculated from its number-average molecular weight and acid value. The number of carboxyl groups calculated from the number-average molecular weight is preferably 0.5 to 1.2 per molecule, and more preferably 0.5 to 1.1.

[0053] The exothermic peak temperature due to the thermal decomposition of the polymer dispersant (hereinafter sometimes referred to as the decomposition exothermic peak temperature) is not particularly limited. For example, the decomposition exothermic peak temperature of the polymer dispersant in air is preferably 300°C or lower, more preferably 290°C, and even more preferably 280°C or lower.

[0054] If the peak exothermic temperature of the polymer dispersant's decomposition is below the aforementioned value, the polymer dispersant is more easily thermally decomposed even at low temperatures, and when heated, the polymer dispersant or its residual components are more likely to volatilize and less likely to remain in the bonding layer, thereby reducing defects in the bonding layer caused by them. As a result, higher bonding characteristics can be achieved, which is preferable.

[0055] The exothermic peak temperature of the decomposition of polymer dispersants is measured by thermogravimetric differential thermal analysis (TG-DTA). Specifically, the polymer dispersant is heated from 25°C to 1000°C in air at a heating rate of 10°C / min, and the exothermic peak temperature is confirmed. If multiple exothermic peaks are observed, the temperature of the exothermic peak observed at the highest temperature is adopted.

[0056] The polymeric dispersant may be a commercially available product or may be manufactured by a known manufacturing method. Examples of commercially available polymeric dispersants include BYK-LP C 24365 and BYK-LP C 22552 (both manufactured by BYK-Chemie). The polymeric dispersant may be used alone or in combination of two or more types.

[0057] <branched carboxylic acid> The copper paste of the present invention contains a branched carboxylic acid or a salt thereof, wherein the number of carbon atoms is between 8 and 20. (Hereafter, "branched carboxylic acid" or "branched carboxylic acid, etc." may be used. In such cases, unless otherwise specified, this includes not only branched carboxylic acids but also salts of branched carboxylic acids.)

[0058] In this invention, a branched carboxylic acid or a salt thereof refers to a branched hydrocarbon chain in which at least one carboxyl group is bonded to any carbon atom.

[0059] In this invention, the number of carbon atoms in a branched carboxylic acid or its salt refers to all carbon atoms in the compound, including the carbon atoms of the carboxyl group (COOH). The same applies when any functional group containing carbon atoms is bonded to the compound.

[0060] By using a paste made in combination with a branched carboxylic acid or its salt having a carbon number within the aforementioned range, a polymeric dispersant having an acid value within a specific range, and copper particles with an average particle size within a specific range, a copper paste can be obtained that contains copper particles at a high concentration, has relatively low viscosity, and exhibits little change in properties even after a certain period of time has elapsed since manufacturing. Furthermore, when this paste is used as a bonding material, sufficient bonding characteristics can be achieved. Moreover, sufficient bonding characteristics can be achieved even after a certain period of time has elapsed since manufacturing. In addition, sufficient bonding characteristics can be achieved by a non-pressure bonding method even when heated at low temperatures of 300°C or less under an inert atmosphere.

[0061] In particular, using a branched carboxylic acid or its salt with a carbon number within the aforementioned range in the copper paste of the present invention does not inhibit the dispersion function of copper particles by the polymer dispersant, the viscosity of the copper paste can be kept low, and changes in the properties of the copper paste after being stored for a certain period after manufacturing can also be reduced. Furthermore, it is understood that heating exhibits an oxide film removal effect, which can promote the sintering of copper particles and improve bonding characteristics.

[0062] The number of carboxyl groups in the branched carboxylic acid or its salt in the copper paste of the present invention is not particularly limited. For example, the branched carboxylic acid or its salt may have one carboxyl group in the molecule, or it may have two or more carboxyl groups in the molecule. When used in joining members at relatively low temperatures, it is preferable to have one carboxyl group in the branched carboxylic acid or its salt molecule, as this facilitates the reduction of defects in the joining layer.

[0063] Examples of branched carboxylic acids in the copper paste of the present invention include isopalmitic acids such as 2-ethylcaproic acid (main chain 6, side chain 2), 2-methylheptanoic acid (main chain 7, side chain 1), 4-methyln-octanoic acid (main chain 8, side chain 1), 4-methylnonanoic acid (main chain 9, side chain 1), isopalmitic acids such as 2-hexyldecanoic acid (main chain 10, side chain 6) and 14-methylpentadecanoic acid (main chain 15, side chain 1), and isostearic acid such as 2,2,4,8,10,10-hexamethylundecane-5-carboxylic acid (multi-branched), 2-heptylundecanoic acid (main chain 11, side chain 7), and 16-methylheptadecanoic acid (main chain 17, side chain 1).

[0064] Examples of salts of the branched carboxylic acid include alkali metal salts such as sodium salts and potassium salts of the branched carboxylic acid, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, and amine salts.

[0065] The branched carboxylic acid or its salt is preferably at least one selected from 2-ethylcaproic acid, isopalmitic acid, and isostearic acid, and their salts. These branched carboxylic acids are preferred because they are inexpensive (compared to other branched carboxylic acids) and can reduce the manufacturing cost of the copper paste of the present invention. Furthermore, isopalmitic acid and isostearic acid are preferred because they have high boiling points and remain even after the solvent evaporates during the sintering process, effectively suppressing the aggregation of copper particles and enabling uniform sintering.

[0066] In the copper paste of the present invention, there are no restrictions on the branched carboxylic acid content, and any branched carboxylic acid concentration may be set. It is preferable to set the branched carboxylic acid content to 0.1% by mass or more relative to the total paste, as this sufficiently reduces the aggregation of copper particles in the copper paste during storage, further reducing the increase in viscosity, and also promotes the sintering of copper particles, thereby further improving bonding properties. It is more preferable to set it to 0.2% by mass or more relative to the total paste. It is preferable to set the branched carboxylic acid content to 5% by mass or less relative to the total paste, as this makes it less likely for defects to occur in the bonding layer during heating, and makes it easier to obtain sufficient bonding properties. It is more preferable to set it to 3% by mass or less.

[0067] The branched carboxylic acid or its salt may be present in the copper paste, and there are no restrictions on its state of existence. For example, the branched carboxylic acid or its salt may be adsorbed onto copper particles, or it may be present free in the paste. Alternatively, the branched carboxylic acid or its salt may be directly adsorbed onto the surface of the copper particles, or it may be adsorbed via other additives adsorbed onto the surface of the copper particles.

[0068] In the copper paste of the present invention, only one type of branched carboxylic acid or its salt may be used, or two or more types may be used in combination. A branched carboxylic acid and a branched carboxylate salt may also be used in combination. When joining in a non-reducing atmosphere or when joining easily oxidizable members, using two or more types in combination is preferable because it makes it easier to adjust the temperature range and rate of the sintering reaction of the joining members. When using two or more types in combination in this way, both the branched carboxylic acid and the branched carboxylate salt may have 8 to 20 carbon atoms, or only one type may have 8 to 20 carbon atoms. It is preferable to use both of them having 8 to 20 carbon atoms, and it is more preferable to use a combination of one with 8 or more carbon atoms and less than 12 carbon atoms and one with 12 or more carbon atoms and 20 or less carbon atoms.

[0069] <Solvent for paste> The copper paste of the present invention contains a paste solvent.

[0070] The solvent for the paste is not particularly limited, and any organic solvent can be used. For example, protic polar solvents and aprotic solvents can be used, and multiple solvent types can be used in appropriate combinations.

[0071] In the present invention, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, and ester-based solvents can be suitably used because they have high affinity for polymer dispersants and carboxylic acids that have an acid value.

[0072] Examples of alcoholic solvents include aliphatic alcohols and denatured alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, pentanol, hexanol, heptanol, octanol, nonanol, and decanol, or aromatic alcohols such as benzyl alcohol, menthol, and terpineol (α, β, γ, δ).

[0073] Examples of glycol-based solvents include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, polypropylene glycol, and butanediol.

[0074] Glycol ether solvents include ethylene-based glycol ethers and propylene-based glycol ethers.

[0075] Examples of ethylene glycol ethers include ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether (ethyl carbitol), diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether (hexyl carbitol), triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, triethylene glycol monohexyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, ethylene glycol diacetate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate, and ethylene glycol phenyl ether.

[0076] Examples of propylene glycol ethers include propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monohexyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, tripropylene glycol monohexyl ether, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol diacetate, propylene glycol monobutyl ether acetate, dipropylene glycol monobutyl ether acetate, and propylene glycol phenyl ether.

[0077] Examples of ester solvents include methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, and n-propyl acetate.

[0078] In the copper paste of the present invention, only one type of paste solvent may be used, or two or more types may be used. The type and mixing ratio may be arbitrarily set considering the desired properties of the copper paste, the desired properties of the bonding member, compatibility with other compounding components, and bonding conditions (heating temperature, heating time, heating rate, presence or absence of pressure, etc.). Examples of combinations of multiple paste solvents include a combination of hexyl carbitol and dipropylene glycol, a combination of hexyl carbitol, dipropylene glycol, α-terpineol and tripropylene glycol, α-terpineol, tripropylene glycol, 1,3-propanediol and ethyl carbitol, and a combination of hexyl carbitol, dipropylene glycol and α-terpineol.

[0079] The copper paste of the present invention may contain various additives as needed. Examples of additives include various commonly used reducing agents, dispersants, emulsifiers, antifreezes, pH adjusters, thickeners, defoaming agents, film-forming aids, and the like.

[0080] In the copper paste of the present invention, it is preferable that the copper particle content is 85% to 96% by mass, the polymer dispersant content is 0.01% to 2% by mass, and the branched carboxylic acid content is 0.1% to 5% by mass. By using a paste with such a composition, a copper paste can be obtained that contains a high concentration of copper particles, has relatively low viscosity, and exhibits less change in properties even after a certain period of time has elapsed since manufacturing. Furthermore, when this paste is used as a bonding member, more sufficient bonding characteristics can be achieved. Moreover, even after a certain period of time has elapsed since manufacturing, more sufficient bonding characteristics can be achieved. In addition, sufficient bonding characteristics can be achieved by a no-pressure bonding method even when heated at low temperatures of 300°C or less under an inert atmosphere. It is more preferable that the copper particle content is 88% to 94% by mass, the polymer dispersant content is 0.02% to 1% by mass, and the branched carboxylic acid content is 0.2% to 3% by mass.

[0081] The content of the paste solvent in the copper paste of the present invention can be appropriately adjusted according to the content of other substances.

[0082] The copper paste of the present invention may have a copper particle content of 85% to 96% by mass relative to the total copper paste, and a viscosity of 0.1 Pa·s to 100 Pa·s, more preferably 0.5 Pa·s to 75 Pa·s. The viscosity is measured at 25°C using a rotational rheometer by the method described in the examples below. Furthermore, unless otherwise specified, the value is given at a shear rate of 10s. -1 This refers to the viscosity at that time.

[0083] The copper paste of the present invention achieves low viscosity despite its high copper particle content, thereby improving the applicability of the paste. Therefore, when used as a bonding component, it is less prone to defects in the bonding layer due to solvent evaporation and aggregation of copper particles during heating and sintering, resulting in excellent bonding characteristics. In particular, it can achieve sufficient bonding characteristics in pressureless bonding.

[0084] The viscosity can be adjusted by controlling the content of copper particles, polymer dispersants, and branched carboxylic acids, as well as the amount of paste solvent. It can also be adjusted by adding additives such as thickeners. The copper paste of this invention has the advantage of having a low basic viscosity, thus expanding the range of viscosity adjustment, and can be used in a wide range of applications.

[0085] The copper paste of the present invention exhibits minimal changes in properties such as viscosity even after a certain period has elapsed since manufacturing, and has high applicability. For example, the change in viscosity after storage at 25°C for one week in an inert atmosphere can be kept below 20 Pa·s. Storage conditions and measurement of viscosity after storage are performed by the methods described in the examples below.

[0086] The copper paste of the present invention may further contain linear carboxylic acids and / or aromatic carboxylic acids or salts thereof. In this application, when "linear carboxylic acids, etc." refers to "linear carboxylic acids and / or aromatic carboxylic acids or salts thereof," that is, "at least one selected from linear carboxylic acids, aromatic carboxylic acids, salts of linear carboxylic acids, and salts of aromatic carboxylic acids," unless otherwise specified, and when "linear carboxylic acids" and "aromatic carboxylic acids" refer to salts of linear carboxylic acids and salts of aromatic carboxylic acids, respectively.

[0087] In the copper paste of the present invention, the storage stability of the copper paste is specifically achieved by using a polymeric dispersant with a specific acid value and a branched carboxylic acid with a specific number of carbon atoms in combination with copper particles of a specific particle size. Furthermore, the storage stability of the copper paste can be further enhanced by including a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof in the copper paste.

[0088] Examples of the linear carboxylic acid include acetic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid. Lauric acid, palmitic acid, and capric acid are particularly preferred. The inclusion of these linear carboxylic acids is preferable because it is expected to improve the sinterability and storage stability of the copper paste.

[0089] Examples of salts of the linear carboxylic acid include alkali metal salts such as sodium salts and potassium salts of the linear carboxylic acid mentioned above, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, and amine salts.

[0090] The above-mentioned linear carboxylic acid or its salt may be used alone, or two or more may be used in combination.

[0091] Examples of the aforementioned aromatic carboxylic acids include benzoic acid, salicylic acid, naphthalene carboxylic acid, 1-hydroxy-2-naphthalene carboxylic acid, and phthalic acid.

[0092] Examples of salts of the aromatic carboxylic acid include alkali metal salts such as sodium salts and potassium salts of the aromatic carboxylic acid mentioned above, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, and amine salts.

[0093] The above-mentioned aromatic carboxylic acid or its salt may be used alone, or two or more may be used in combination.

[0094] The linear carboxylic acids and aromatic carboxylic acids or their salts may be used individually or in any combination.

[0095] When using linear carboxylic acids and / or aromatic carboxylic acids, there are no restrictions on their content, and any concentration may be set. It is preferable to set the content of linear carboxylic acids and / or aromatic carboxylic acids to 0.005% by mass or more relative to the total copper paste, as this can further improve the storage stability of the copper paste, and it is more preferable to set it to 0.01% by mass or more. It is preferable to set the content of linear carboxylic acids and / or aromatic carboxylic acids to 0.4% by mass or less relative to the total paste, as this makes it possible to adjust the viscosity of the copper paste to a low level, and also makes it less likely for defects to occur in the bonding layer during heating, resulting in sufficient bonding characteristics, and it is more preferable to set it to 0.2% by mass or less.

[0096] The linear carboxylic acids and aromatic carboxylic acids or their salts mentioned above only need to be present in the copper paste, and there are no restrictions on their state of existence. For example, the linear carboxylic acids and aromatic carboxylic acids or their salts may be adsorbed onto copper particles, or they may be present free in the paste. Furthermore, the linear carboxylic acids and aromatic carboxylic acids or their salts may be directly adsorbed onto the surface of the copper particles, or they may be adsorbed via other additives adsorbed onto the surface of the copper particles.

[0097] In the copper paste of the present invention, it is preferable that the copper particle content is 85% to 96% by mass, the polymer dispersant content is 0.01% to 2% by mass, the branched carboxylic acid content is 0.1% to 5% by mass, and the linear carboxylic acid and / or aromatic carboxylic acid content is 0.005% to 0.4% by mass. By using a paste with such a composition, a copper paste can be obtained that contains a high concentration of copper particles, has relatively low viscosity, and exhibits less change in properties even after a certain period of time has elapsed since manufacturing. Furthermore, when this paste is used as a bonding member, sufficient bonding characteristics can be achieved. Moreover, the bonding characteristics can be further improved after a certain period of time has elapsed since manufacturing. In addition, sufficient bonding characteristics can be achieved by a non-pressure bonding method even when heating at low temperatures of 300°C or less under an inert atmosphere. It is particularly suitable when bonding in a non-reducing atmosphere or when bonding easily oxidizable members. It is more preferable that the copper particle content is 88% to 94% by mass, the polymer dispersant content is 0.02% to 1% by mass, the branched carboxylic acid content is 0.2% to 3% by mass, and the linear carboxylic acid and / or aromatic carboxylic acid content is 0.01% to 0.2% by mass. It is preferable that the polymer dispersant is present in excess of the linear carboxylic acid, etc., as the polymer dispersant is more likely to cover the surface of the copper particles, thereby improving the dispersibility of the copper particles.

[0098] In the copper paste of the present invention, it is preferable that the total amount of polymer dispersant, branched carboxylic acid, linear carboxylic acid, and / or aromatic carboxylic acid contained in the copper paste is 0.3% by mass or more and 5% by mass or less, as this allows for better bonding characteristics while maintaining a low viscosity of the copper paste. It is even more preferable that the amount is 0.5% by mass or more and 4% by mass or less.

[0099] In one embodiment of the present invention, the copper particles in the copper paste of the present invention may have a polymeric dispersant on their surface and a branched carboxylic acid may be dissolved or dispersed in the paste solvent. In other words, the copper paste may contain copper particles with a polymeric dispersant on their surface (hereinafter sometimes referred to as "coated copper particles"), a branched carboxylic acid, and a paste solvent.

[0100] By placing a polymeric dispersant on the surface of the copper particles, the dispersibility of the copper particles in the paste can be efficiently improved even with a smaller amount of polymeric dispersant compared to when the polymeric dispersant is separately included in the paste. This allows for a greater reduction in the increase in viscosity of the paste, even when the concentration of copper particles in the paste is increased. Furthermore, the sintering of the copper particles during heating is promoted, making it easier to obtain superior bonding properties, or to obtain sufficient bonding properties even at lower heating temperatures, which is preferable. In addition, there is a manufacturing benefit in that the mixing of copper particles and paste solvents during copper paste production can be carried out with low load.

[0101] In this invention, "a polymeric dispersant is present on the surface" means that the polymeric dispersant is interacting with the surface of the copper particles in some way, regardless of whether it is chemical bonding, chemiadsorption, or physiadsorption. Furthermore, "coated copper particles" include not only states in which the polymeric dispersant directly interacts with the copper particle surface, but also states in which other additives (e.g., linear carboxylic acids and / or aromatic carboxylic acids or their salts) are present on the copper particle surface, and the polymeric dispersant interacts with the copper particles via these additives. In this case, the polymeric dispersant is preferably present in an amount of 0.01% to 2% by mass relative to the total amount of coated copper particles, and more preferably in an amount of 0.02% to 1% by mass. The amount of polymeric dispersant in coated copper particles can be measured by thermogravimetric analysis, pyrolysis gas chromatography, liquid chromatography, etc.

[0102] The polymer dispersant may exist in any state, either uniformly covering the surface of the copper particles, or partially present on the surface of the copper particles, appearing as islands.

[0103] Furthermore, this embodiment includes not only copper pastes containing coated copper particles, branched carboxylic acid, and a paste solvent, but also copper pastes containing coated copper particles, a polymer dispersant, a branched carboxylic acid, and a paste solvent.

[0104] Furthermore, the coated copper particles may be coated with linear carboxylic acids and / or aromatic carboxylic acids or salts thereof. The state of presence of the polymeric dispersant and linear carboxylic acids, etc., is not particularly limited; it is sufficient that the polymeric dispersant and linear carboxylic acids, etc., cover at least a portion of the copper particle surface. The order, proportion, and state of each component covering the copper particles are not particularly limited. For example, the polymeric dispersant may be present in a layer or partially on the copper particle surface, with linear carboxylic acids, etc., present in a layer or partially on top of that. Alternatively, linear carboxylic acids, etc., may be present in a layer or partially on the copper particle surface, with the polymeric dispersant present in a layer or partially on top of that. Alternatively, the polymeric dispersant and linear carboxylic acids, etc., may be present in a mixed state in a layer or partially on the copper particle surface, with linear carboxylic acids, etc., or the polymeric dispersant present in a layer or partially on top of that. Alternatively, linear carboxylic acids, etc., or the polymeric dispersant may be present in a layer or partially on the copper particle surface, with the polymeric dispersant and linear carboxylic acids, etc., present in a mixed state in a layer or partially on top of that. Alternatively, copper particles loosely coated with a polymeric dispersant or a linear carboxylic acid, etc., may have an island-like coating state where the other component is scattered and coating all or part of the exposed copper portion. A linear carboxylic acid, etc. and / or a polymeric dispersant may be further present on top of this. In this case, the polymeric dispersant, linear carboxylic acid, etc. are preferably present in an amount of 0.05% to 6% by mass, more preferably in an amount of 0.3% to 5% by mass, and even more preferably in an amount of 0.4% to 4% by mass, based on the total amount of the coated copper particles. The amount of organic matter in the coated copper particles can be measured by thermogravimetric analysis, pyrolysis gas chromatography, liquid chromatography, etc.

[0105] In one embodiment of the present invention, the copper particles in the copper paste of the present invention may be dispersed in a paste solvent with a polymer dispersant and a branched carboxylic acid present on their surface. In other words, the copper paste may contain copper particles with a polymer dispersion and a branched carboxylic acid on their surface (hereinafter sometimes referred to as "surface-treated copper particles") and a paste solvent.

[0106] By placing polymeric dispersants and branched carboxylic acids on the surface of copper particles, the dispersibility of copper particles in the paste can be efficiently improved even with smaller amounts compared to when they are released into the paste. This allows for a greater reduction in the increase in viscosity of the paste, even when the concentration of copper particles in the paste is increased. Furthermore, the sintering of copper particles during heating is promoted, making it easier to obtain superior bonding properties, or to obtain sufficient bonding properties even at lower heating temperatures, which is preferable. In addition, there is a manufacturing benefit in that the mixing of copper particles and paste solvents during copper paste production can be carried out with low load. ru.

[0107] In the present invention, "the presence of polymer dispersion and branched carboxylic acid on the surface" means, as described above, that the polymer dispersant and branched carboxylic acid are interacting with the surface of the copper particles in some way, and the state of chemical bonding, chemiadsorption, or physiadsorption is irrelevant.

[0108] The state in which the polymeric dispersant and branched carboxylic acid exist is such that at least a portion of the copper particle surface is covered by the polymeric dispersant and branched carboxylic acid, and the order, proportion, and state of each component covering the copper particle are not particularly limited. For example, the polymeric dispersant may be present in a layer or partially on the copper particle surface, and the branched carboxylic acid may be present in a layer or partially on top of that. Alternatively, the branched carboxylic acid may be present in a layer or partially on the copper particle surface, and the polymeric dispersant may be present in a layer or partially on top of that. Alternatively, the polymeric dispersant and branched carboxylic acid may be present in a mixed state in a layer or partially on the copper particle surface, and the branched carboxylic acid or polymeric dispersant may be present in a layer or partially on top of that. Alternatively, the branched carboxylic acid or polymeric dispersant may be present in a layer or partially on the copper particle surface, and the polymeric dispersant and branched carboxylic acid may be present in a mixed state in a layer or partially on top of that. Alternatively, in copper particles loosely coated with the polymeric dispersant or branched carboxylic acid, the other component may be scattered and cover all or part of the exposed copper portion, resulting in an island-like coating state. Further branched carboxylic acid and / or polymeric dispersant may be present on top of that. In this case, the polymeric dispersant and the branched carboxylic acid are preferably present in amounts of 0.05% to 6% by mass, more preferably in amounts of 0.3% to 5% by mass, and even more preferably in amounts of 0.4% to 4% by mass, relative to the total amount of coated copper particles. The amount of organic matter in the coated copper particles can be measured by thermogravimetric analysis, pyrolysis gas chromatography, liquid chromatography, etc.

[0109] Furthermore, this embodiment includes not only copper pastes containing surface-treated copper particles and a paste solvent, but also copper pastes containing surface-treated copper particles, a polymer dispersant, a branched carboxylic acid and a paste solvent, and copper pastes containing surface-treated copper particles, a polymer dispersant and a paste solvent.

[0110] In one embodiment of the present invention, the copper particles in the copper paste of the present invention may be dispersed in the paste solvent with a polymer dispersant and a branched carboxylic acid, as well as a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof, on their surface. In other words, it refers to a copper paste containing a paste solvent and copper particles (hereinafter sometimes referred to as "composite copper particles") on which a polymer dispersion, a branched carboxylic acid, and a linear carboxylic acid, etc., are present on their surface.

[0111] By placing polymer dispersants, branched carboxylic acids, and linear carboxylic acids on the surface of copper particles, the same effects as those obtained with coated copper particles or surface-treated copper particles can be achieved.

[0112] In the present invention, "a polymer dispersion and branched carboxylic acid, as well as a linear carboxylic acid and / or aromatic carboxylic acid or a salt thereof, are present on the surface" means, as described above, that the polymer dispersant, branched carboxylic acid, and linear carboxylic acid are interacting with the surface of the copper particles in some way, regardless of whether it is chemical bonding, chemiadsorption, or physiadsorption.

[0113] The polymeric dispersant, branched carboxylic acid, linear carboxylic acid, etc., should be present in such a way that they cover at least a portion of the copper particle surface. The order, proportion, and state of each component covering the copper particle are not particularly limited. They may be present individually and / or in a mixture, in layers or partially, as a single layer or in a stacked state; the state is arbitrary. In this case, the polymeric dispersant, branched carboxylic acid, linear carboxylic acid, etc., are preferably present in an amount of 0.05% to 6% by mass, more preferably in an amount of 0.3% to 5% by mass, and even more preferably in an amount of 0.4% to 4% by mass, relative to the total amount of coated copper particles. The amount of organic matter in the coated copper particles can be measured by thermogravimetric analysis, pyrolysis gas chromatography, liquid chromatography, etc.

[0114] The polymeric dispersant and branched carboxylic acids, linear carboxylic acids, etc., mentioned above only need to be present in the copper paste, and there are no restrictions on their state of existence. Furthermore, it is acceptable for carboxylic acids, etc., that are pre-coated on the copper particles to remain partially or entirely on the surface. For example, the polymeric dispersant and branched carboxylic acids, linear carboxylic acids, etc., may cover the carboxylic acids, etc., that are pre-coated on the surface of the copper particles, or the carboxylic acids, etc., that are pre-coated on the surface of the copper particles may be partially or entirely replaced by the polymeric dispersant and branched carboxylic acids, linear carboxylic acids, etc.

[0115] Furthermore, this embodiment includes not only copper pastes containing composite copper particles and a paste solvent, but also copper pastes containing composite copper particles, a polymer dispersant and a paste solvent, copper pastes containing composite copper particles, a branched carboxylic acid and a paste solvent, copper pastes containing composite copper particles, a linear carboxylic acid, etc. and a paste solvent, copper pastes containing composite copper particles, a polymer dispersant and a branched carboxylic acid and a paste solvent, copper pastes containing composite copper particles, a polymer dispersant and a linear carboxylic acid, etc. and a paste solvent, copper pastes containing composite copper particles, a branched carboxylic acid and a linear carboxylic acid, etc. and a paste solvent, and copper pastes containing composite copper particles, a polymer dispersant and a branched carboxylic acid and a linear carboxylic acid, etc. and a paste solvent.

[0116] The copper particles in the paste may be dispersed as primary particles, or as secondary particles formed by the aggregation of primary particles. The aforementioned states of existence of polymer dispersants, branched carboxylic acids, linear carboxylic acids, etc., encompass the states of existence on either the surface of the primary or secondary copper particles.

[0117] <Method for manufacturing copper paste> The present invention provides a method for producing copper paste, comprising mixing copper particles, a polymer dispersant, a branched carboxylic acid or its salt, and a paste solvent, wherein the copper particles have an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope, the polymer dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or its salt has 8 or more and 20 or less carbon atoms.

[0118] Another embodiment of the present invention is a method for producing copper paste, comprising mixing copper particles, a polymer dispersant, a branched carboxylic acid or a salt thereof, a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof, and a paste solvent, wherein the copper particles have an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope, the polymer dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or a salt thereof has 8 or more and 20 or less carbon atoms.

[0119] The copper paste of the present invention may contain the aforementioned additives as needed.

[0120] The copper particles may be in the form of a dry powder, or they may be in the form of a cake, slurry, or dispersion containing copper particles and a solvent.

[0121] The polymer dispersant, branched carboxylic acid or its salt, linear carboxylic acid and / or aromatic carboxylic acid or its salt may be used as is, or dissolved or dispersed in a solvent.

[0122] The solvent may be any solvent, and may be the same as or different from the solvent used for the paste. It may be a single solvent or a mixture of two or more solvents.

[0123] The mixing may involve mixing all materials simultaneously, or in any order; the order of mixing does not matter as long as all materials are included in the final copper paste. Other steps may also be included in the process.

[0124] In the aforementioned mixing process, known mixers can be used. Examples include twin-screw mixers, three-roll mixers, sand mills, and planetary mixers, which are commonly used in industry. On a laboratory scale, agitators, hybrid mixers, homogenizers, and paint shakers can be used. The materials may also be mixed without using a mixer. Mixing includes contact and coexistence between materials.

[0125] When performing the aforementioned mixing step, a grinding media may be used as appropriate. Examples of grinding media include those composed of glass, alumina, zirconia, zirconium silicate, etc.

[0126] Degassing may be performed during or after the mixing process as necessary.

[0127] The atmosphere during the mixing process can be air, an inert gas, or a vacuum. From the viewpoint of suppressing performance degradation due to oxidation of copper particles, an inert gas or vacuum atmosphere is preferred for this process.

[0128] The copper particles are not particularly limited as long as their average particle diameter is between 170 nm and 600 nm. For example, commercially available copper particles may be purchased, or copper particles manufactured by known methods may be used. They can also be manufactured by the method described below.

[0129] (Example of copper particle manufacturing) The following is an example of a method for manufacturing copper particles (steps A and B).

[0130] (Process A) This process involves mixing a copper compound, a carboxylic acid or its salt, an amine compound, and a solvent. This process yields a mixed solution containing the copper compound.

[0131] The copper compound is not particularly limited as long as it contains copper atoms. The copper compound used in step A may be just one type or two or more types.

[0132] Examples of the aforementioned copper compounds include copper(I) carboxylates such as copper(I) formate, copper(I) acetate, copper(I) propionate, copper(I) butyrate, copper(I) valerate, copper(I) caproate, copper(I) caprylate, copper(I) caprate, copper(II) formate, copper(II) acetate, copper(II) propionate, copper(II) butyrate, copper(II) valerate, copper(II) caproate, copper(II) caprylate, copper(II) caprate, copper(II) citrate, copper(II) citrate, copper(II) oxide, copper(II) oxide, copper(I) oxide, copper(II) hydroxide, copper(I) hydroxide, copper nitride, and the like.

[0133] Among the copper compounds mentioned above, copper(II) oxide is preferred from the viewpoint of reducing manufacturing costs.

[0134] The amount of the copper compound added is not particularly limited. For example, it is preferable that the amount is 1 part by mass or more and 100 parts by mass or less relative to the solvent.

[0135] If the amount of copper compound is 1 part by mass or more relative to the solvent, it is preferable because it effectively avoids a decrease in the amount of copper particles produced by step B described later. If the amount of copper compound is 100 parts by mass or less relative to the solvent, it is preferable because it effectively avoids a heterogeneous reaction due to viscosity increase when the solvent and the copper compound are mixed in this step.

[0136] The chemical structure of the molecule of the carboxylic acid or its salt is not particularly limited, and it is sufficient that it has a hydrocarbon group portion and a carboxyl group portion in its structure.

[0137] The hydrocarbon group portion is not particularly limited as long as it yields copper particles according to the present invention. For example, it may consist only of single bonds, or it may have multiple bonds in the middle or at the end. Furthermore, heteroatoms may be included at any point in the hydrocarbon group.

[0138] The carboxyl group portion is not particularly limited as long as the copper particles according to the present invention are obtained. For example, the molecule of the carboxylic acid or its salt may have one carboxyl group, or it may have two or more carboxyl groups. In particular, it is preferable that the molecule of the carboxylic acid or its salt has one carboxyl group.

[0139] The number of carbon atoms in the molecule of the carboxylic acid or its salt is not particularly limited, as long as copper particles according to the present invention are obtained. For example, it is preferably 2 to 20, more preferably 4 to 18, and even more preferably 6 to 16.

[0140] Examples of the carboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, enanthic acid, pelargonic acid, capric acid, lauric acid, oleic acid, stearic acid, isostearic acid, 2-ethylcaproic acid, isopalmitic acid, and the like.

[0141] Examples of salts of the carboxylic acid include alkali metal salts such as sodium salts and potassium salts of the carboxylic acid mentioned above, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, and amine salts.

[0142] The carboxylic acid or its salt may be of one type or two or more types. Among the carboxylic acid or its salt, it is more preferable to include acetic acid, caproic acid, caprylic acid, capric acid, or 2-ethylcaproic acid. Using such a carboxylic acid or its salt is preferable because it efficiently results in copper particles with the desired average particle size obtained in step B.

[0143] The amount of carboxylic acid or its salt added is not particularly limited, but is preferably 0.01 ml to 2 ml per 1 ml of copper compound. This range is preferable because it allows the copper particles obtained in step B to efficiently achieve the desired average particle size.

[0144] The amine compound used in step A is not particularly limited and only needs to have an amino group and a hydroxyl group in its structure.

[0145] The amine compound is preferably an amino alcohol. Using an amino alcohol preferably suppresses foaming of the copper compound-containing mixture in step A.

[0146] Examples of the amino alcohols include methanolamine, monoethanolamine (2-aminoethanol), diethanolamine, triethanolamine, 3-amino-1-propanol, 1-dimethylamino-2-propanol, 3-(dimethylamino)-1-propanol, 4-ethylamino-1-butanol, N-methylethanolamine, 2-diethylethanolamine, 2-aminodibutanol, heptaminol, isoethanoline, sphingosine, 3-dimethylamino-1,2-propanediol, 3-diethyl Examples include 1,2-propanediol, 3-methylamino-1,2-propanediol, 3-(dimethylamino)-1,2-propanediol, 2-amino-2-methyl-1,3-propanediol, 3-(diethylamino)-1,2-propanediol, 2-amino-2-ethyl-1,3-propanediol, 3-amino-1,2-propanediol, 2-amino-2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol, and 2-amino-1,3-propanediol.

[0147] Among the aforementioned amine compounds, it is more preferable that monoethanolamine be included. Monoethanolamine decomposes at low temperatures. Therefore, monoethanolamine is less likely to remain even during sintering (at low temperatures), and a decrease in sinterability due to residual components can be effectively avoided, which is preferable.

[0148] The amount of the amine compound added is not particularly limited, but it is preferably 0.25 ml to 2 ml per 1 ml of the carboxylic acid.

[0149] If the amount of amine compound added is within the aforementioned range, it is preferable because it effectively avoids thickening of the mixture containing the copper compound.

[0150] The time for adding the amine compound is not particularly limited, but is preferably between 10 seconds and 30 minutes. This preferably suppresses the rapid exothermic reaction of the mixed solution containing the copper compound in step A.

[0151] The solvent used in step A is not particularly limited, as long as it does not react with other raw materials to inhibit the formation of copper particles.

[0152] Alcohols can be suitably used as the solvent. Examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, butanol, pentanol, hexanol, heptanol, octanol, decanol, and the like. These may be used alone or in combination of two or more. These alcohols are preferred because they exhibit high compatibility with the carboxylic acid or its salt and with the amine compound.

[0153] The mixing order of the aforementioned raw materials is not particularly limited. For example, all raw materials may be mixed at once, or the solvent and other raw materials may be mixed one by one in any order. In particular, it is preferable to mix the solvent, copper compound and carboxylic acid or its salt first, and then further mix with the amine compound.

[0154] In the mixing step, known agitators can be used. Examples include vane-type agitators, disperser mixers, homomixers, and the like.

[0155] The mixing conditions in the aforementioned mixing process can be set as appropriate. For example, the stirring time should be 5 minutes or more, and the rotation speed should be 50 rpm or more. Under these mixing conditions, each raw material can be thoroughly mixed.

[0156] (Process B) This step involves intermittently or continuously adding a reducing agent to a mixed solution containing a copper compound obtained in step A, wherein the temperature of the mixed solution at the time of adding the reducing agent is between 40°C and 95°C. This step allows for obtaining a dispersion containing copper particles.

[0157] The reducing agent can be any agent that reduces copper compounds, and more preferably has a boiling point of 70°C or higher, and more preferably a boiling point higher than or equal to the heating temperature in the heating step. Using such a reducing agent is preferable because it efficiently reduces copper compounds even when the liquid temperature of the mixture is between 40°C and 95°C. The reducing agent may be used by itself or by using two or more types.

[0158] Examples of the reducing agent include hydrazine or its derivatives. Examples of hydrazine derivatives include hydrazine monohydrate, hydrazine hydrate, methylhydrazine, ethylhydrazine, n-propylhydrazine, i-propylhydrazine, n-butylhydrazine, i-butylhydrazine, sec-butylhydrazine, t-butylhydrazine, n-pentylhydrazine, i-pentylhydrazine, neo-pentylhydrazine, t-pentylhydrazine, n-hexylhydrazine, i-hexylhydrazine, n-heptylhydrazine, n-o Examples include cultylhydrazine, n-nonylhydrazine, n-decylhydrazine, n-undecylhydrazine, n-dodecylhydrazine, cyclohexylhydrazine, phenylhydrazine, 4-methylphenylhydrazine, benzylhydrazine, 2-phenylethylhydrazine, 2-hydrazinoethanol, acetohydrazine, adipic acid dihydrazide, sebacate dihydrazide, dodecanedihydrazide, isophthalic acid dihydrazide, salicylic acid hydrazide, and the like.

[0159] When adding the reducing agent to the mixed solution containing the copper compound obtained in step A, it should not be added all at once in a short time, but rather intermittently or continuously. The addition time for the reducing agent is preferably 50 minutes to 6 hours, and more preferably 60 minutes to 6 hours.

[0160] In this application, "adding intermittently or continuously" means adding small amounts over time. Furthermore, the reducing agent may be added in multiple separate additions.

[0161] In this application, "addition time" means the time required from the time the copper compound is added to the mixture containing the reducing agent until the entire amount of the reducing agent is added to the mixture (hereinafter, this may also be referred to as "time required to add the entire amount of the reducing agent").

[0162] By adding the reducing agent intermittently or continuously, the heat generated during reduction is suppressed, and the average particle size of the copper particles obtained by this process can be brought within a desired range.

[0163] The amount of reducing agent added is preferably 1.0 mol to 4.0 mol per 1.0 mol of copper compound. An amount of 1.0 mol or more is preferable because it allows for sufficient reduction of the copper compound. An amount of 4.0 mol or less is preferable because it reduces the load during washing of solids containing copper particles.

[0164] When adding the reducing agent, the temperature of the mixed solution containing the copper compound is preferably 40°C to 95°C, and more preferably 45°C to 90°C.

[0165] By keeping the temperature of the mixed solution containing the copper compound within the aforementioned range, copper particles having a desired average particle size can be obtained.

[0166] The temperature of the mixture containing the copper compound may be adjusted before adding the reducing agent, or during the addition of the reducing agent. Preferably, the temperature of the mixture containing the copper compound is adjusted to the aforementioned range before adding the reducing agent.

[0167] In this process, known mixing equipment such as stirrers, mixers, homogenizers, and agitators can be used as needed. The rotational speed is not limited, but it should be 50 rpm or higher.

[0168] The dispersion containing copper particles obtained in this process may be aged if necessary.

[0169] The maturation conditions can be set as appropriate. For example, the maturation temperature is preferably 40°C to 120°C, and more preferably 60°C to 100°C. The maturation time is preferably 1 minute to 2 hours. Furthermore, during maturation, stirring may be performed using the known mixer mentioned above. The rotation speed is not limited, but it should be 50 rpm or higher.

[0170] The dispersion containing copper particles obtained in this process may be subjected to solid-liquid separation if necessary.

[0171] Known methods can be used for solid-liquid separation. For example, commonly used industrial presses, such as rotary presses and filter presses, vacuum filters such as Nutche filters and Moore filters, and centrifugal separators can be used. Decantation may also be performed as appropriate.

[0172] The solid content obtained by the solid-liquid separation may be washed by known methods.

[0173] The solids obtained by the solid-liquid separation may be dried by known methods. For example, heating equipment such as dryers, ovens, and electric furnaces, or a desiccator controlled to a predetermined temperature, a vacuum dryer, or a reduced-pressure dryer can be used.

[0174] When a desiccator is used in the drying process, the solids can be dried by controlling the temperature inside the desiccator to a predetermined level and creating a vacuum atmosphere. A vacuum pump may be used to create a vacuum atmosphere inside the desiccator. For example, a G-20DA manufactured by ULVAC, Inc. can be used as a vacuum pump.

[0175] Drying conditions can be set as appropriate. For example, the drying temperature is preferably 20°C to 120°C, the drying time is preferably 0.5 hours to 10 hours, and from the viewpoint of suppressing oxidation of copper particles, the drying atmosphere is preferably under an inert gas stream such as nitrogen or argon, or under a vacuum atmosphere.

[0176] By the manufacturing method including steps A and B described above, copper particles with an average particle diameter of 170 nm to 600 nm can be obtained, and these copper particles are used as raw materials when manufacturing the copper paste of the present invention.

[0177] Another embodiment of the present invention's method for producing copper paste is a method for producing copper paste consisting of the following steps (A) to (B). Step (A) A step of mixing copper particles, a polymer dispersant, and a solvent to obtain coated copper particles. Step (B) is a step of obtaining a copper paste by mixing the coated copper particles obtained in step (A) with a branched carboxylic acid or a salt thereof and a paste solvent.

[0178] Step (A) is a step of producing coated copper particles by a method that includes mixing copper particles, a polymer dispersant, and a solvent.

[0179] (Preparation process of coated copper particles) In preparing coated copper particles, the copper particles can be those described in paragraphs

[0026] to

[0034] above. Alternatively, copper particles manufactured by the method described above may be used. When manufactured by the method described above, the copper particles may be in the form of a cake, slurry, or dispersion containing the copper particles and solvent after solid-liquid separation, or they may be in the form of a powder after a drying process.

[0180] The polymer dispersant can be any of the polymer dispersants described in paragraphs

[0036] to

[0056] above.

[0181] The solvent is not particularly limited as long as it has high compatibility with the polymer dispersant and does not react with it. Examples of such solvents include methanol, ethanol, 1-propanol, 2-propanol, acetone, methyl ethyl ketone, and the like.

[0182] The mixing order of the aforementioned raw materials is not particularly limited. For example, all raw materials may be mixed at once, or the solvent and other raw materials may be mixed one by one in any order. Alternatively, a solution may be prepared by mixing the solvent with at least one raw material, and this solution may be mixed in any order. Specifically, a processing solution may be prepared by mixing the solvent with a polymer dispersant, and the copper particles may be mixed with the processing solution prepared by mixing the solvent with a polymer dispersant.

[0183] Step (A) is a process for producing coated copper particles by a method that includes mixing a processing solution containing a polymer dispersant and a solvent with copper particles, because it allows the polymer dispersant to be efficiently present on the surface of the copper particles.

[0184] (Preparation process of the treatment solution) In the method for producing coated copper particles of the present invention, the treatment solution is prepared by a method that includes the step of mixing a polymer dispersant with a solvent.

[0185] The amount of polymer dispersant in the processing solution is not particularly limited, as long as it can process the copper particles with a predetermined amount of organic components. For example, the amount of polymer dispersant in the processing solution is preferably 0.01% by mass or more and 10% by mass or less of the total processing solution, more preferably 0.05% by mass or more and 8% by mass or less, and even more preferably 0.1% by mass or more and 6% by mass or less.

[0186] If the composition of the processing solution is within the aforementioned range, it is preferable because a predetermined amount of polymer dispersant can be applied to the copper particles.

[0187] In the preparation step of the processing liquid, when mixing the processing liquid, a known stirrer may be used for stirring. Examples of such stirrers include a rotary-orbit mixer, a blade-type stirrer, a disperser mixer, a homomixer, and an ultrasonic disperser.

[0188] In the aforementioned stirring step, the stirring conditions, such as stirring time and stirring speed, are not particularly limited as long as the raw materials are thoroughly mixed. For example, the stirring time may be 1 minute or more, and the stirring speed may be 50 rpm or more.

[0189] (Coating process) The step of mixing the copper particles and the processing liquid can be performed using a known agitator. Examples include a rotary-orbit mixer, a blade-type agitator, a disperser mixer, a homomixer, an ultrasonic disperser, etc. The materials may also be mixed without using a mixer. Mixing includes contact and coexistence between materials. Examples include immersing the copper particles in the processing liquid or permeating the copper particles with the processing liquid.

[0190] The stirring time and stirring speed are not particularly limited, as long as the aforementioned raw materials are thoroughly mixed. For example, the stirring time can be 1 minute or more, and the stirring speed can be 50 rpm or more. In the case of immersion or impregnation, 10 minutes or more is sufficient.

[0191] After the coating process described above, solid-liquid separation may be performed as needed. Known filtration methods can be used for solid-liquid separation. For example, pressure filtration devices such as rotary presses and filter presses, vacuum filtration devices such as Nutche filters and Moore filters, and centrifuges can be used. Decantation may also be performed as appropriate.

[0192] After the coating process, the recovered solids may be washed if necessary. Known washing methods can be used to wash the solids. The solvent used for washing is not particularly limited. In this way, the coated copper particles of the present invention are obtained.

[0193] (drying process) The coated copper particles of the present invention may be dried into a powder by a method that includes a drying step from a cake containing the coated copper particles and a solvent after solid-liquid separation.

[0194] The conditions in the drying process, such as drying temperature, drying time, and drying atmosphere, can be set as appropriate. For example, the drying temperature is preferably 20°C to 120°C, the drying time is preferably 0.5 hours to 10 hours, and the drying atmosphere is preferably under an inert gas such as nitrogen or argon, or under vacuum.

[0195] In the drying process, known drying equipment may be used. For example, heating equipment such as dryers, ovens, and electric furnaces, or desiccators controlled to a predetermined temperature, vacuum dryers, and reduced-pressure dryers can be used.

[0196] When using a desiccator in the drying process, the mixture of copper particles and the treatment liquid can be dried by controlling the temperature inside the desiccator to a predetermined level and creating a vacuum atmosphere.

[0197] A vacuum pump may be used to create a vacuum atmosphere inside the desiccator. For example, a G-20DA manufactured by ULVAC, Inc. can be used as a vacuum pump.

[0198] After the drying process, the composite copper particles may be crushed or pulverized as needed to adjust the particle size. Known crushers, classifiers, etc., can be used for crushing or pulverizing.

[0199] (Paste-making process) Next, step (B) is a step of mixing the coated copper particles obtained in step (A) with a branched carboxylic acid or a salt thereof and a paste solvent to obtain a copper paste.

[0200] The coated copper particles may be in the form of a dry powder, or they may be in the form of a cake, slurry, or dispersion containing the coated copper particles and a solvent.

[0201] The branched carboxylic acid or its salt can be one of those described in paragraphs "0057" to "0068" above. It may also be used dissolved or dispersed in a solvent, or used as is. The solvent may be any solvent, and may be the same as or different from the solvent for the paste. It may be one type, or two or more types may be mixed and used.

[0202] The solvent for the paste can be one of those described in paragraphs "0069" to "0078" above.

[0203] In the mixing process, known mixers can be used. Examples include twin-screw mixers, three-roll mixers, sand mills, and planetary mixers, which are commonly used in industry. On a laboratory scale, agitators, orbital agitators, hybrid mixers, homogenizers, and paint shakers can be used.

[0204] When performing the aforementioned mixing step, a grinding media may be used as appropriate. Examples of grinding media include those composed of glass, alumina, zirconia, zirconium silicate, etc.

[0205] During or after the mixing process, degassing or vacuum drying may be performed as needed. This allows for the evaporation of solvents other than the paste solvent, such as the solvent contained in the cake or a solvent in which a branched carboxylic acid or its salt is dissolved.

[0206] The atmosphere during the mixing process can be air, an inert gas, or a vacuum. From the viewpoint of performance degradation due to oxidation of copper particles, an inert gas or a vacuum is preferred.

[0207] The copper paste of the present invention may optionally contain the aforementioned additives. It may also contain polymer dispersants, linear carboxylic acids and / or aromatic carboxylic acids, or salts thereof. These additives may be included in one of the raw materials before the paste formation process, mixed simultaneously with the raw materials during the paste formation process, or mixed separately into the copper paste after the copper paste is produced.

[0208] Another embodiment of the present invention's method for producing copper paste is a method for producing copper paste consisting of the following steps (A) to (B). Step (A) A step of mixing copper particles, a polymer dispersant, a branched carboxylic acid or its salt, and a solvent to obtain surface-treated copper particles. Step (B) A step of mixing the surface-treated copper particles obtained in step (A) with a paste solvent to obtain a copper paste.

[0209] (Preparation process for surface-treated copper particles) Step (A) is a step of producing surface-treated copper particles by a method that includes mixing copper particles, a branched carboxylic acid or a salt thereof, a polymer dispersant, and a solvent.

[0210] In the preparation of surface-treated copper particles, the copper particles, polymer dispersant, and solvent used can be the same as those used in the preparation of coated copper particles described above. The branched carboxylic acid or its salt can be the same as those used in the paste-forming step of coated copper particles described above.

[0211] The mixing order of the aforementioned raw materials is not particularly limited. For example, all raw materials may be mixed at once, or the solvent and other raw materials may be mixed one by one in any order. Alternatively, a solution may be prepared by mixing the solvent with at least one raw material, and this solution may be mixed in any order. Specifically, a processing solution may be prepared by mixing the solvent, a polymer dispersant, and a branched carboxylic acid or a salt thereof, and the copper particles may be mixed with this processing solution. Alternatively, a dispersion containing copper particles, which is a mixture of the solvent and copper particles, may be mixed with a processing solution that is a mixture of the solvent, a polymer dispersant, and a branched carboxylic acid or a salt thereof.

[0212] Step (A) is a preferred method for producing surface-treated copper particles, which includes a step of mixing a treatment solution containing a polymer dispersant, a branched carboxylic acid or its salt, and a solvent with copper particles, because it allows the polymer dispersant and the branched carboxylic acid or its salt to be efficiently present on the surface of the copper particles.

[0213] (Preparation process of the treatment solution) In the method for producing surface-treated copper particles of the present invention, the treatment solution is prepared by a method comprising the step of mixing a branched carboxylic acid or a salt thereof, a polymer dispersant, and a solvent.

[0214] In the preparation step of the processing solution, the order in which each raw material is added is not particularly limited. For example, all raw materials may be mixed at once, or the solvent and other raw materials may be mixed one by one in any order.

[0215] In the preparation step of the processing solution, the same apparatus as in the preparation step of the processing solution for the preparation of coated copper particles described above can be used, and the same setting conditions can be adopted.

[0216] The total amount of branched carboxylic acid or its salt and polymer dispersant in the treatment solution is not particularly limited, as long as it can treat the copper particles with a predetermined amount of organic components. For example, the total amount of branched carboxylic acid or its salt and polymer dispersant in the treatment solution is preferably 1.0% by mass or more and 30% by mass or less, more preferably 1.5% by mass or more and 25% by mass or less, and even more preferably 2.0% by mass or more and 20% by mass or less, relative to the total amount of the treatment solution.

[0217] The content of branched carboxylic acid or its salt in the treatment solution is not particularly limited. For example, the content of carboxylic acid or its salt in the treatment solution is preferably 0.7% by mass or more and 25% by mass or less, more preferably 1.5% by mass or more and 18% by mass or less, and even more preferably 2.0% by mass or more and 16% by mass or less, relative to the total amount of the treatment solution.

[0218] The content of the polymer dispersant in the processing liquid is not particularly limited. For example, the content of the polymer dispersant in the processing liquid is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 8% by mass or less, and even more preferably 0.1% by mass or more and 6% by mass or less, relative to the total amount of the processing liquid.

[0219] If the composition of the treatment solution is within the aforementioned range, it is preferable because the copper particles can be treated with a predetermined amount of branched carboxylic acid or its salt and a polymeric dispersant.

[0220] Each step of preparing surface-treated copper particles by mixing the copper particles and the treatment solution, washing, separating the solid and liquid, and drying and adjusting the particle size as necessary, can be carried out using the same methods, apparatus, conditions, and auxiliary materials as described above for coated copper particles.

[0221] (Paste-making process) Next, step (B) is a step of mixing the surface-treated copper particles obtained in step (A) with a paste solvent to obtain a copper paste.

[0222] The surface-treated copper particles may be in the form of a dry powder, or they may be in the form of a cake, slurry, or dispersion containing coated copper particles and a solvent.

[0223] The solvent for the paste can be one of those described in paragraphs "0069" to "0078" above.

[0224] Each step of mixing the surface-treated copper particles with the paste solvent and degassing as necessary to obtain a copper paste can be carried out using the same methods, apparatus, conditions, and auxiliary materials as described above for the paste formation step of coated copper particles.

[0225] The copper paste of the present invention may optionally contain the various additives described above. It may also contain polymer dispersants, branched carboxylic acids, linear carboxylic acids and / or aromatic carboxylic acids or salts thereof. These various additives may be included in one of the raw materials before the paste formation process, mixed simultaneously with the raw materials during the paste formation process, or mixed into the paste after it has been formed.

[0226] Another embodiment of the present invention's method for producing copper paste is a method for producing copper paste consisting of the following steps (A) to (C). Step (A) A step of mixing copper particles, a polymer dispersant, and a solvent to obtain coated copper particles. Step (B) A step of mixing the coated copper particles obtained in step (A) with a branched carboxylic acid to obtain surface-treated copper particles. Step (C) is a step of mixing the surface-treated copper particles obtained in step (B) with a paste solvent to obtain a copper paste.

[0227] Step (A) is a process for producing coated copper particles by a method that includes mixing copper particles, a polymer dispersant, and a solvent. This step can be carried out in the same manner as the process for producing coated copper particles described above.

[0228] Step (B) is a step of producing surface-treated copper particles by a method that includes mixing the coated copper particles obtained in step (A) with a branched carboxylic acid or a salt thereof.

[0229] Branched carboxylic acids or their salts can be used in the same manner as described in the preparation of surface-treated copper particles.

[0230] There are no particular restrictions on the method of mixing the coated copper particles obtained in step (A) with the branched carboxylic acid or its salt. For example, a mixing method similar to the one described in the preparation step for surface-treated copper particles may be used.

[0231] A solvent may be used during mixing. When a solvent is used, the mixing order of each raw material is not particularly limited. For example, all raw materials may be mixed at once, or the solvent and other raw materials may be mixed one by one in any order. Alternatively, a solution may be prepared by mixing the solvent with at least one raw material, and this solution may be mixed in any order. Specifically, a processing solution may be prepared by mixing the solvent with a branched carboxylic acid or a salt thereof, and this processing solution may be mixed with the coated copper particles obtained in step (A). Alternatively, a dispersion of the coated copper particles obtained in step (A) may be mixed with the processing solution of the solvent with a branched carboxylic acid or a salt thereof.

[0232] Step (B) is a step to produce surface-treated copper particles by a method that includes mixing the coated copper particles obtained in step (A) with a treatment solution containing a branched carboxylic acid or a salt thereof and a solvent, because it allows the branched carboxylic acid or a salt thereof to be efficiently present on the surface of the coated copper particles.

[0233] A treatment solution containing a branched carboxylic acid or a salt thereof and a solvent can be prepared in the same manner as described above for the preparation of treatment solutions for coated copper particles and surface-treated copper particles.

[0234] The content of branched carboxylic acid or its salt in the treatment solution is not particularly limited. For example, the content of branched carboxylic acid or its salt in the treatment solution is preferably 0.7% by mass or more and 25% by mass or less, more preferably 1.5% by mass or more and 18% by mass or less, and even more preferably 2.0% by mass or more and 16% by mass or less, relative to the total content of the treatment solution. A composition of the treatment solution within the above range is preferable because it allows for the treatment of copper particles with a predetermined amount of branched carboxylic acid or its salt.

[0235] Each step of preparing surface-treated copper particles by mixing the coated copper particles obtained in step (A) with the treatment solution, washing, solid-liquid separation, drying and particle size adjustment as necessary, can be carried out using the same methods, apparatus, conditions, and auxiliary materials as described above for surface-treated copper particles.

[0236] (Paste-making process) Next, step (C) is a step of mixing the surface-treated copper particles obtained in step (B) with a paste solvent to obtain a copper paste. This step can also be carried out using the same methods, apparatus, conditions, and materials as the paste-forming step of the coated copper particles described above.

[0237] Another embodiment of the present invention's method for producing copper paste is a method for producing copper paste consisting of the following steps (A) to (B). Step (A) A step of mixing copper particles, a polymer dispersant, a branched carboxylic acid or a salt thereof, a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof, and a solvent to obtain composite copper particles. Step (B) is a step of mixing the composite copper particles obtained in step (A) with a paste solvent to obtain a copper paste.

[0238] (Preparation process of composite copper particles) Step (A) is a step of producing composite copper particles by a method that includes mixing copper particles, a branched carboxylic acid or a salt thereof, a polymeric dispersant, a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof, and a solvent.

[0239] In the preparation of the composite copper particles of the present invention, the copper particles, polymer dispersant, branched carboxylic acid or its salt, and solvent used can be the same as those used in the preparation of coated copper particles described above. The linear carboxylic acid and / or aromatic carboxylic acid or its salt can be those described in paragraphs "0086" to "0094" above.

[0240] The mixing order of the aforementioned raw materials is not particularly limited. For example, all raw materials may be mixed at once, or the solvent and other raw materials may be mixed one by one in any order. Alternatively, a solution may be prepared by mixing the solvent with at least one raw material, and this solution may be mixed in any order. Specifically, a processing solution may be prepared by mixing the solvent, a polymer dispersant, a branched carboxylic acid or its salt, a linear carboxylic acid and / or an aromatic carboxylic acid or its salt, and the copper particles may be mixed with the processing solution. Alternatively, a dispersion containing copper particles, obtained by mixing the solvent and copper particles, may be mixed with a processing solution obtained by mixing the solvent, a polymer dispersant, a branched carboxylic acid or its salt, a linear carboxylic acid and / or an aromatic carboxylic acid or its salt. Alternatively, the copper particles containing the solvent may be mixed sequentially with the processing solution obtained by mixing the solvent and a polymer dispersant, the processing solution obtained by mixing the solvent and a branched carboxylic acid or its salt, and the processing solution obtained by mixing the solvent and a linear carboxylic acid and / or an aromatic carboxylic acid or its salt.

[0241] Step (A) is a method for producing composite copper particles by mixing a processing solution containing a polymer dispersant, a branched carboxylic acid or its salt, a linear carboxylic acid and / or an aromatic carboxylic acid or its salt, and a solvent with copper particles. This is preferable because it allows the polymer dispersant, branched carboxylic acid or its salt, linear carboxylic acid and / or an aromatic carboxylic acid or its salt to be efficiently present on the surface of the copper particles.

[0242] (Preparation process of the treatment solution) In the method for producing composite copper particles of the present invention, the treatment solution is prepared by a method comprising the step of mixing a branched carboxylic acid or a salt thereof, a polymeric dispersant, a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof, and a solvent.

[0243] In the preparation step of the processing solution, the order in which each raw material is added is not particularly limited. For example, all raw materials may be mixed at once, or the solvent and other raw materials may be mixed one by one in any order.

[0244] In the preparation step of the treatment solution, the same apparatus as in the preparation step of the treatment solution for the coated copper particles and surface-treated copper particles described above can be used, and the same setting conditions can be adopted.

[0245] The total amount of branched carboxylic acid or its salt, polymer dispersant, and linear carboxylic acid and / or aromatic carboxylic acid or its salt in the treatment solution is not particularly limited as long as it can treat the copper particles with a predetermined amount of organic components. For example, the total amount of these branched carboxylic acid or its salt, polymer dispersant, and linear carboxylic acid and / or aromatic carboxylic acid or its salt in the treatment solution is preferably 1.0% by mass or more and 30% by mass or less, more preferably 1.5% by mass or more and 25% by mass or less, and even more preferably 2.0% by mass or more and 20% by mass or less, relative to the entire treatment solution.

[0246] The content of branched carboxylic acid or its salt in the treatment solution is not particularly limited. For example, the content of branched carboxylic acid or its salt in the treatment solution is preferably 0.7% by mass or more and 25% by mass or less, more preferably 1.5% by mass or more and 18% by mass or less, and even more preferably 2.0% by mass or more and 16% by mass or less, relative to the total amount of the treatment solution.

[0247] The content of the polymer dispersant in the processing liquid is not particularly limited. For example, the content of the polymer dispersant in the processing liquid is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 8% by mass or less, and even more preferably 0.1% by mass or more and 6% by mass or less, relative to the total amount of the processing liquid.

[0248] The content of linear carboxylic acids and / or aromatic carboxylic acids or their salts in the treatment solution is not particularly limited. For example, the content in the treatment solution is preferably 0.01% by mass or more and 1% by mass or less, more preferably 0.05% by mass or more and 0.8% by mass or less, and even more preferably 0.1% by mass or more and 0.6% by mass or less, relative to the total amount of the treatment solution.

[0249] If the composition of the treatment solution is within the aforementioned range, it is preferable because the copper particles can be treated with a predetermined amount of branched carboxylic acid or its salt, a polymeric dispersant, and a linear carboxylic acid and / or aromatic carboxylic acid or its salt.

[0250] Each step of preparing composite copper particles by mixing the copper particles and the processing solution, washing, separating the solid and liquid, and drying and adjusting the particle size as necessary, can be carried out using the same methods, apparatus, conditions, and auxiliary materials as those used for preparing coated copper particles and surface-treated copper particles.

[0251] (Paste-making process) Next, step (B) is a step of mixing the composite copper particles obtained in step (A) with a paste solvent to obtain a copper paste. This step can also be carried out using the same methods, apparatus, conditions, and materials as the paste formation steps for the coated copper particles and surface-treated copper particles described above.

[0252] <Joining components> The copper paste of the present invention can be used as a bonding component and can effectively bond a substrate and a material to be bonded. It can also be used for bonding three-dimensional stacked integrated circuits (3D-ICs).

[0253] The aforementioned joining member may contain additives as appropriate, depending on its application. Examples of such additives include the various additives mentioned above.

[0254] The base material and the material to be joined may be made of the same material or of different materials. The material to be joined is not particularly limited. Examples include various metal materials, semiconductor materials, ceramic materials, or resin materials.

[0255] The surfaces of the substrate and the material to be joined may be polished as needed.

[0256] For metal materials, polishing methods include grinding, lapping, buffing, barrel polishing, and electrolytic polishing. The abrasives and grains used can be any known material as appropriate. Examples of abrasive grains include diamond, alumina, silicon carbide, and cubic boron nitride.

[0257] In semiconductor materials, chemical mechanical polishing (CMP) is one such method. Examples of abrasive grains include inorganic metal oxides such as cerium oxide and silicon oxide.

[0258] For ceramic and resin materials, mechanochemical polishing is one possible method.

[0259] The surfaces of the substrate and the material to be joined may be plated as needed.

[0260] The type of metal to be plated can be selected appropriately depending on the application. Examples include gold plating, silver plating, copper plating, nickel plating, chromium plating, and various metal alloy platings. When alloy plating is performed, the composition of the plating can also be adjusted appropriately according to the application.

[0261] Known methods can be used for plating. Examples include dry plating such as physical vapor deposition plating and chemical vapor deposition plating, and wet plating such as displacement plating, electroplating, and electroless plating.

[0262] Specific examples of the aforementioned substrates include semiconductor substrates such as silicon substrates, metal substrates such as copper substrates, lead frames, metal-bonded ceramic substrates (e.g., Direct Bonded Copper: DBC), substrates for mounting semiconductor elements such as LED (Light-Emitting Diode) packages, copper ribbons, metal blocks, power supply components such as terminals, heat sinks, water cooling plates, and the like.

[0263] Methods for applying bonding materials to a substrate include screen printing, transfer printing, offset printing, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, jet printing, dispenser printing, comma coating, slit coating, die coating, gravure coating, bar coating, spray coating, spin coating, and electrodeposition coating.

[0264] The substrate coated with the bonding material may be dried as needed. The drying conditions can be set as appropriate. By drying the substrate before sintering, it is possible to suppress the flow of the bonding material and the occurrence of defects in the bonding layer during sintering.

[0265] As for the drying conditions, for example, the drying atmosphere may be an atmospheric atmosphere, an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere. The drying pressure may be atmospheric pressure or reduced pressure. The drying temperature is not particularly limited as long as the composite copper particles contained in the joining member do not sinter.

[0266] <Method for manufacturing a jointed body> The method for manufacturing a joined body of the present invention includes a step of joining a base material and a material to be joined using the copper paste or joining member.

[0267] In the method for manufacturing the bonded body of the present invention, the above-described base material and the material to be bonded can be used. Among them, the manufacturing method of the present invention can be preferably used when the bonding surface of the base material is gold, silver or copper, and the bonding surface of the material to be bonded is gold, silver or copper. In this case, the types of metals on the bonding surfaces of the base material and the material to be bonded may be the same or different. The case where the bonding surface of the base material is copper and the bonding surface of the material to be bonded is gold is more preferable. The reasons suitable for using these metals on the bonding surface are understood as follows. When using a base material and a substrate having the above metal as the bonding surface, it is necessary to bond at a relatively high temperature. The copper paste of the present invention contains branched carboxylic acids having relatively long chains (specifically, 8 to 20 carbon atoms), and these carboxylic acids have a higher decomposition temperature (compared to carboxylic acids having 1 to 7 carbon atoms). Therefore, even when bonding at a relatively high temperature, the branched carboxylic acids remain even after the paste solvent has volatilized, thereby preventing the aggregation of copper particles, and thus the adhesion to the bonding surface is improved.

[0268] The copper paste and the bonding member of the present invention can be preferably used in the non-pressure bonding method because a bonded body having a high bonding strength can be manufactured only by sintering by heating.

[0269] In the present application, the "non-pressure bonding method" refers to a method in which when heating a laminate in which a base material and a material to be bonded are laminated via a bonding member, the bonding member and the material to be bonded are arranged in the direction in which the self-weight of the base material acts, or in a state where a load of 0.01 MPa or less is applied, and the laminate is heated and bonded.

[0270] The heating atmosphere of the laminate in the non-pressure bonding method may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere, but from the viewpoint of the manufacturing cost of the bonded body, an inert atmosphere is more preferable.

[0271] Preheating may be performed before completely sintering the laminate in the non-pressure bonding method. The preheating temperature is preferably 150°C or lower, more preferably 140°C or lower. From the viewpoint of the evaporation rate of the solvent, it is even more preferably 130°C or lower. Further, preheating can also be omitted by setting the heating rate applied to the laminate to 10°C / min or lower. The copper particles may or may not sinter during preheating. The preheating conditions may be appropriately set according to the desired bonding characteristics.

[0272] The heating temperature of the laminate in the non-pressure bonding method is preferably 100°C or higher and 400°C or lower, and more preferably 150°C or higher and 300°C or lower. If the sintering temperature is 300°C or lower, it can be said that the bonding member of the present invention can be sufficiently sintered at a low temperature.

[0273] The heating time including preheating of the laminate in the non-pressure bonding method is preferably 1 minute or longer and 120 minutes or shorter from the viewpoints of sufficiently volatilizing the solvent contained in the bonding member and sufficiently progressing the sintering of the metal particles contained in the bonding member.

[0274] The bonding strength of the bonded body obtained by the non-pressure bonding method is measured by the method described in the examples.

[0275] The bonding strength of the bonded body obtained by the non-pressure bonding method is preferably 20 MPa or higher, more preferably 25 MPa or higher, and even more preferably 27 MPa or higher. If the bonded body has such a bonding strength, it can be judged that it is sufficiently bonded, and it can be confirmed that the bonding member of the present invention can be suitably used as a non-pressure bonding paste.

[0276] The copper particle content of a suitable paste in the non-pressure bonding method is preferably 85% by mass or more and 96% by mass or less, preferably 88% by mass or more and 95% by mass or less, and more preferably 90% by mass or more and 94% by mass or less from the viewpoint of reducing defects in the bonding layer due to solvent evaporation.

[0277] The viscosity of the paste suitable for the no-pressure bonding method is determined by the copper particle content of the paste, from the viewpoint of dispersibility, at a shear rate of 10s. -1 The viscosity at this time is 0.1 Pa·s or more and 100 Pa·s or less, more preferably 0.5 Pa·s or more and 75 Pa·s.

[0278] The application of the joining member of the present invention to a non-pressure joining method has been described above, but the joining member of the present invention can also be suitably used in a pressure joining method. In that case, the composition and joining conditions can be appropriately adjusted according to the desired properties.

[0279] The copper paste of the present invention can be used not only as a joining component but also for other applications. Other applications include, for example, its use as a conductive material. Specifically, it can be used as a material for conductive materials such as conductive films, electrodes, and wiring, or as a plating nucleus when manufacturing conductive materials by plating. [Examples]

[0280] The reagents used are as follows:

[0281] (Manufacturing of copper particles) 1-Propanol (first grade) (manufactured by Kishida Chemical Co., Ltd.) Cupric oxide (manufactured by Nisshin Chemco: N-300) Acetic acid (special grade) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Capric acid (special grade) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 2-Aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) 60% hydrazine hydrate (manufactured by Mitsubishi Gas Chemical Co., Ltd.) 2-Propanol (Special Grade) (Manufactured by Nacalai Tesque)

[0282] (branched carboxylic acid) Isopalmitic acid (2-hexyldecanoic acid) (manufactured by Tokyo Chemical Industry Co., Ltd.) 2-Ethylcaproic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) Isostearic acid (2,2,4,8,10,10-hexamethylundecane-5-carboxylic acid) (manufactured by Tokyo Chemical Industry Co., Ltd.) (Linear carboxylic acid) Caprylic acid (special grade) (manufactured by FUJIFILM Wako Pure Chemical Corporation) Lauric acid (manufactured by Tokyo Chemical Industry Co., Ltd.) Palmitic acid (>97% (GC)) (manufactured by Tokyo Chemical Industry Co., Ltd.) (Aromatic carboxylic acid) Benzoic acid (special grade) (manufactured by Nacalai Tesque, Inc.) (Polymer dispersant) BYK-LP C 24365 (manufactured by BYK Chemie Japan Co., Ltd.) BYK-LP C 22552 (manufactured by BYK Chemie Japan Co., Ltd.) (Solvent for paste) Hexyl carbitol (manufactured by Tokyo Chemical Industry Co., Ltd.) Dipropylene glycol (primary grade) (manufactured by FUJIFILM Wako Pure Chemical Corporation) α-Terpineol (>95% (GC)) (manufactured by Tokyo Chemical Industry Co., Ltd.) Tripropylene glycol (>98% (GC)) (manufactured by Tokyo Chemical Industry Co., Ltd.) 1,3-Propanediol (special grade) (manufactured by FUJIFILM Wako Pure Chemical Corporation) Ethyl carbitol (manufactured by Nacalai Tesque, Inc.)

[0283] (Analysis of polymer dispersant) (Confirmation of polyoxyethylene chain) Regarding the polymer dispersant used in the present application, the presence or absence of polyoxyethylene chains in the structure of the polymer dispersant was confirmed by analyzing under the following conditions using liquid chromatography / mass spectrometry (LC / MS).

[0284] (Measuring device) Liquid chromatography / mass spectrometry (LC / MS) LC: e2695 manufactured by Waters MS: SQ Detectоr2 manufactured by Waters

[0285] (Measuring conditions) Column: SunShell C18 (2.6μm 100×2.1mm) manufactured by ChromaNik Mobile phase A: 0.1 Vol% ammonium formate aqueous solution Mobile phase B: Acetonitrile Gradient elution: 10 → 90 B% (15 min) Flow rate: 0.4mL / min Column temperature: 40℃ Detection method: Electrospray ionization (ESI) method (Pos. / Nega) Injection volume: 5μL Sample concentration: 0.1 wt% (methanol solution)

[0286] Using LC / MS, the molecular weight of the polymeric dispersant or its decomposition product was measured under the above conditions. As a result, multiple molecular weight peaks at 44-molecular-weight intervals, such as molecular weights of 574, 530, and 486, suggesting a repeating structure of ethylene glycol chains, were detected in both dispersants.

[0287] <Measurement of number-average molecular weight and weight-average molecular weight of polymer dispersants> The number-average molecular weight and weight-average molecular weight of polymer dispersants were measured using a high-speed GPC instrument (HLC-8420GPC (manufactured by Tosoh Corporation)) under the following conditions. Dedicated software, EcoSEC Elite, was used for instrument control, data acquisition, calculation, and report generation.

[0288] Column: TSKgel SuperHZM-N (4.6mm inner diameter x 15cm x 2 tubes) Eluent solvent: Tetrahydrofuran (THF) Flow rate: 0.35mL / min Column temperature: 40℃ Detector: Differential refractometer (RI detector) Sample concentration: 5 mg / 5 mL Injection volume: 10μL

[0289] <Exothermic peak temperature of polymer dispersants> Using a thermogravimetric differential thermal analyzer (Rigaku Corporation: TG-DTA8122), the exothermic peak temperatures of the polymer dispersants used in the examples and comparative examples of this application were measured under the conditions shown below.

[0290] ○Measurement conditions Measurement atmosphere: Under air Atmospheric flow rate: 100 mL / min Measurement temperature range: 25℃~1000℃ Heating rate: 10℃ / min

[0291] Table 1 shows the physical properties of the polymeric dispersant. Note that the presence of carboxyl groups and the acid value are based on manufacturer-published information. Table 1 also shows the number of acid groups per molecule of the polymeric dispersant, calculated from the number-average molecular weight.

[0292] [Table 1] *Polymer dispersant A: BYK-LP C 24365 *Polymer dispersant B: BYK-LP C 22552

[0293] (Manufacturing of copper particles) (Manufacturing Example 1) A 10L four-necked glass flask was placed in an oil bath, and 2L of 1-propanol as the solvent, 637.6g of cupric oxide as the copper source, 384.0g of acetic acid, and 329.6g of capric acid were added to obtain a mixture of raw materials. The aforementioned raw material mixture was stirred at room temperature at a rotation speed of 250 rpm, and 508.8 g of 2-aminoethanol was added dropwise over 10 minutes. The subsequent steps were also carried out while stirring at a constant rotation speed. Next, the obtained liquid was heated in an oil bath until the liquid temperature reached 90°C. Then, 996 g of 60% hydrazine hydrate was added dropwise as a reducing agent over 90 minutes. During this time, stirring was continued, and the oil bath temperature was set to 90°C. After the dropwise addition was complete, the mixture was stirred for 1 hour to obtain a dispersion of copper particles. The dispersion of copper particles was allowed to cool naturally while being stirred until the liquid temperature dropped below 50°C, and then allowed to stand for 30 minutes. After that, the supernatant was removed to obtain a slurry of copper particles. From the aforementioned copper particle slurry, a quantity of copper particle slurry containing approximately 40 g of copper particles was separated, 75 mL of 2-propanol was mixed in, and the mixture was stirred at 2000 rpm for 4 minutes using a rotary-revolving mixer (Awatori Rentaro AR-250, manufactured by Shinky Co., Ltd., the same model was used in the following examples as well). Then, solid-liquid separation was performed at 400 G for 5 minutes using a centrifuge (Beckman Coulter, Allegra X-30R, the same model was used in the following examples as well), followed by washing. After that, the washing process was repeated to obtain copper particles 1 of Production Example 1 in the form of a copper cake containing copper particles and approximately 4-5% 2-propanol.

[0294] (Manufacturing example 2) A 10L glass four-necked flask was placed in an oil bath, and 2L of 1-propanol as the solvent, 637.6g of cupric oxide as the copper source, 96.0g of acetic acid, and 82.4g of capric acid were added to obtain a raw material mixture. While stirring the aforementioned raw material mixture at room temperature, 127.2 g of 2-aminoethanol was added dropwise over 2.5 minutes. Next, the obtained liquid was heated in an oil bath until the liquid temperature reached 90°C, at which point 996 g of 60% hydrazine hydrate was added dropwise as a reducing agent over 300 minutes. After the addition was complete, the mixture was stirred for 10 minutes to obtain a dispersion of copper particles. The dispersion of copper particles was allowed to cool naturally while being stirred until the liquid temperature dropped below 50°C, and then allowed to stand for 30 minutes. After that, the supernatant was removed to obtain a slurry of copper particles. From the aforementioned copper particle slurry, a quantity of copper particle slurry containing approximately 40 g of copper particles was separated, 75 mL of 2-propanol was mixed in, and the mixture was stirred using a rotation-revolution mixer at 2000 rpm for 4 minutes. Then, solid-liquid separation was performed using a centrifuge at 400 G for 5 minutes, followed by washing. After that, the washing process was repeated to obtain copper particle 2 of Production Example 2, which was in the form of a copper cake containing copper particles and approximately 4-5% 2-propanol.

[0295] (Measurement of the average particle size of copper particles) The average particle size of copper particles was calculated using a scanning electron microscope (S-4800, manufactured by Hitachi High-Technologies Corporation). The specific procedure was as follows:

[0296] The magnification was set to 30,000x, and images of copper particles were captured. Next, 50 copper particles were randomly selected from the images, their ferret diameter was measured, and the average particle diameter was calculated based on the number of particles. Here, the average particle diameter of copper particles 1 obtained in manufacturing example 1 was 261 nm. The average particle diameter of copper particles 2 obtained in manufacturing example 2 was 360 nm.

[0297] (Processing of copper particles and manufacture of copper paste)

[0298] (Example 1) (Processing of copper particles) BYK-LP C 24365 and 2-propanol were mixed to prepare 75 mL of a treatment solution containing 2% by mass of BYK-LP C 24365. A copper cake containing approximately 40g of copper particles 1 obtained in Production Example 1 was mixed with the processing liquid and stirred at 2000 rpm for 4 minutes using a rotating / revolving mixer. Subsequently, the solid-liquid separation was performed using a centrifuge at 1200G for 15 minutes to obtain a cake of coated copper particles 1 coated with a polymer dispersant. Furthermore, a portion of the cake containing coated copper particles 1 was taken, vacuum-dried, and the amount of solids in the cake (mass of coated copper particles) was confirmed. (Manufacturing of copper paste) A paste solvent containing a branched carboxylic acid was prepared by mixing hexyl carbitol, dipropylene glycol, and isopalmitic acid in a mass ratio of 3.5:3.5:0.5. To obtain a mixed solution, the coated copper particles 1 constituted 92.5% by mass of the copper paste. The coated copper particles 1 were then mixed with the paste solvent containing the branched carboxylic acid in a cake of coated copper particles 1, and the mixture was heated to 2000 rpm for 4 minutes using a rotating / revolving mixer. The mixture was left to stand in a desiccator, and the desiccator was heated to 1.3 Pa and 25°C using a vacuum pump (ULVAC, G-20DA). Under this atmosphere, the mixture was vacuum-dried for 300 minutes to volatilize the 2-propanol and obtain copper paste 1.

[0299] (Example 2) Coated copper particles 2 and copper paste 2 were obtained in the same manner as in Example 1, except that BYK-LP C 24365 was changed to BYK-LP C 22552 during the processing of the copper particles.

[0300] (Example 3) Copper paste 3 was obtained in the same manner as in Example 1, except that the mass ratio of hexyl carbitol, dipropylene glycol, and isopalmitic acid in the paste solvent containing a branched carboxylic acid was 2.75:2.75:2.0.

[0301] (Example 4) (Processing of copper particles) BYK-LP C 24365, 2-ethyl caproic acid, and 2-propanol were mixed to prepare 75 mL of a treatment solution containing 2% by mass of BYK-LP C 24365 and 6% by mass of 2-ethyl caproic acid. A copper cake containing approximately 40g of copper particles 1 obtained in Production Example 1 was mixed with the processing liquid and stirred at 2000 rpm for 4 minutes using a rotating / revolving mixer. Subsequently, solid-liquid separation was performed using a centrifuge at 1200G for 15 minutes to obtain a cake of surface-treated copper particles 4 coated with a polymer dispersant and a branched carboxylic acid. A portion of this surface-treated copper particle 4 cake was also taken and vacuum-dried to confirm the amount of solid content (mass of surface-treated copper particles) in the cake. (Manufacturing of copper paste) A solvent for pastes containing a linear carboxylic acid was prepared by mixing hexyl carbitol, dipropylene glycol, and capric acid in a mass ratio of 3.7:3.7:0.1. To obtain a mixture, the surface-treated copper particles 4 constituted 92.5% by mass of the copper paste. The paste solvent containing the linear carboxylic acid was added to the cake of surface-treated copper particles 4, and the mixture was mixed at 2000 rpm for 4 minutes using a rotating / revolving mixer. The mixture was left to stand in a desiccator, and the desiccator was heated to 1.3 Pa and 25°C using a vacuum pump (ULVAC, G-20DA). Under this atmosphere, the mixture was vacuum-dried for 300 minutes to volatilize the 2-propanol and obtain copper paste 4.

[0302] (Example 5) (Processing of copper particles) BYK-LP C 24365, 2-ethyl caproic acid, isopalmitic acid, and 2-propanol were mixed to prepare 75 mL of a treatment solution containing 2% by mass of BYK-LP C 24365, 2% by mass of 2-ethyl caproic acid, and 8% by mass of isopalmitic acid. A copper cake containing approximately 40g of copper particles 1 obtained in Production Example 1 was mixed with the processing liquid and stirred at 2000 rpm for 4 minutes using a rotating / revolving mixer. Subsequently, solid-liquid separation was performed using a centrifuge at 1200G for 15 minutes to obtain a cake of surface-treated copper particles 5 coated with a polymer dispersant and a branched carboxylic acid. A portion of this surface-treated copper particle 5 cake was also taken and vacuum-dried to confirm the amount of solid content (mass of surface-treated copper particles) in the cake. (Manufacturing of copper paste) A paste solvent was prepared by mixing hexyl carbitol and dipropylene glycol in a mass ratio of 1.0 to 1.0. The solvent for the paste was added to the cake of surface-treated copper particles 5 so that the surface-treated copper particles 5 in the copper paste constituted 92.5% by mass, and the mixture was mixed at 2000 rpm for 4 minutes using a rotating / revolving mixer to obtain the mixture. The mixture was left to stand in a desiccator, and the desiccator was heated to 1.3 Pa and 25°C using a vacuum pump (ULVAC, G-20DA). Under this atmosphere, the mixture was vacuum-dried for 300 minutes to volatilize the 2-propanol and obtain copper paste 5.

[0303] (Example 6) (Processing of copper particles) BYK-LP C 24365, isopalmitic acid, lauric acid, and 2-propanol were mixed to prepare a 75 mL treatment solution containing 2% by mass of BYK-LP C 24365, 8% by mass of isopalmitic acid, and 0.1% by mass of lauric acid. A copper cake containing approximately 40g of copper particles 1 obtained in Production Example 1 was mixed with the processing liquid and stirred at 2000 rpm for 4 minutes using a rotating / revolving mixer. Subsequently, solid-liquid separation was performed using a centrifuge at 1200G for 15 minutes to obtain a cake of composite copper particles 6 coated with a polymer dispersant, a branched carboxylic acid, and a linear carboxylic acid. A portion of this composite copper particle 6 cake was also taken and vacuum-dried to confirm the amount of solid content (mass of composite copper particles) in the cake. (Manufacturing of copper paste) A paste solvent was prepared by mixing hexyl carbitol and dipropylene glycol in a mass ratio of 1.0 to 1.0. The solvent for the paste was added to the cake of composite copper particles 6 so that the composite copper particles 6 in the copper paste constituted 92.5% by mass, and the mixture was mixed at 2000 rpm for 4 minutes using a rotating / revolving mixer to obtain the mixture. The mixture was left to stand in a desiccator, and the desiccator was heated to 1.3 Pa and 25°C using a vacuum pump (ULVAC, G-20DA). Under this atmosphere, the mixture was vacuum-dried for 300 minutes to volatilize the 2-propanol and obtain copper paste 6.

[0304] (Example 7) (Processing of copper particles) In the treatment of copper particles in Example 5, a cake of surface-treated copper particles 7 coated with a polymer dispersant and a branched carboxylic acid was obtained in the same manner as in Example 5, except that the copper particles were changed to copper particles 2 obtained in Production Example 2. (Manufacturing of copper paste) A solvent for pastes containing linear carboxylic acids was prepared by mixing hexylcarbitol, dipropylene glycol, α-terpineol, and tripylene glycol with lauric acid in a mass ratio of 2.7:2.7:0.5:0.5:0.1. To obtain a mixture, the surface-treated copper particles 7 in the copper paste comprised 93.5% by mass. The paste solvent containing the linear carboxylic acid was added to the cake of surface-treated copper particles 7, and the mixture was mixed at 2000 rpm for 4 minutes using a rotating / revolving mixer. The mixture was left to stand in a desiccator, and the desiccator was heated to 1.3 Pa and 25°C using a vacuum pump (ULVAC, G-20DA). Under this atmosphere, the mixture was vacuum-dried for 300 minutes to volatilize the 2-propanol and obtain copper paste 7.

[0305] (Example 8) Copper paste 8 was obtained in the same manner as in Example 7, except that lauric acid was replaced with benzoic acid to create a paste solvent containing an aromatic carboxylic acid.

[0306] (Example 9) Copper paste 9 was obtained in the same manner as in Example 7, except that a paste solvent containing a linear carboxylic acid was used, which was a mixture of α-terpineol, tripropylene glycol, 1,3-propanediol, and ethyl carbitol with palmitic acid in a mass ratio of 4.9:0.5:0.5:0.5:0.1.

[0307] (Example 10) (Processing of copper particles) Except for replacing copper particle 1 used in Example 5 with copper particle 2, the process was carried out in the same manner to obtain a cake of surface-treated copper particles 8. The cake of surface-treated copper particles 8 was left to stand in a desiccator, and the inside of the desiccator was set to 1.3 Pa and 25°C using a vacuum pump (ULVAC, G-20DA), and vacuum-dried in this atmosphere for 300 minutes to volatilize 2-propanol. After that, the cake was lightly crushed with a spatula in an atmosphere with an oxygen concentration of 200 ppm or less to obtain surface-treated copper particles 8. (Manufacturing of copper paste) A paste solvent containing a branched carboxylic acid was prepared by mixing hexyl carbitol, dipropylene glycol, α-terpineol, and isostearic acid in a ratio of 3:1.5:1.5:0.5. 10 g of surface-treated copper particles 8 and 0.695 g of paste solvent were mixed using a rotating / revolving mixer at 2000 rpm for 4 minutes to obtain copper paste 10.

[0308] (Example 11) (Processing of copper particles) BYK-LP C 24365, 2-ethyl caproic acid, and 2-propanol were mixed to prepare 75 mL of a treatment solution containing 0.1% by mass of BYK-LP C 24365 and 9.9% by mass of 2-ethyl caproic acid. A copper cake containing approximately 40 g of copper particles 2 obtained in Production Example 2 was mixed with the aforementioned processing solution and stirred at 2000 rpm for 4 minutes using a rotation-revolution mixer. Then, solid-liquid separation was performed using a centrifuge at 1200 G for 15 minutes to obtain a cake of surface-treated copper particles 9 coated with a polymer dispersant and a branched carboxylic acid. The cake of surface-treated copper particles 9 was left to stand in a desiccator, and the inside of the desiccator was maintained at 1.3 Pa and 25°C using a vacuum pump (ULVAC, G-20DA), and vacuum-dried for 300 minutes in this atmosphere to volatilize 2-propanol. Then, in an atmosphere with an oxygen concentration of 200 ppm or less, the cake was lightly crushed with a spatula to obtain surface-treated copper particles 9. (Manufacturing of copper paste) A paste solvent containing a branched carboxylic acid was prepared by mixing hexylcarbitol, dipropylene glycol, α-terpineol, isostearic acid, and BYK-LP C 24365 in a ratio of 2.75:1.375:1.375:0.8:0.2. 10 g of surface-treated copper particles 9 and 0.695 g of paste solvent were mixed using a rotating / revolving mixer at 2000 rpm for 4 minutes to obtain copper paste 11.

[0309] (Comparative Example 1) Copper particles 10 and copper paste 12 were obtained in the same manner as in Example 1, except that the composition of the treatment solution was changed to 2-propanol alone.

[0310] (Comparative Example 2) Copper paste 13 was obtained in the same manner as in Example 1, except that in the paste solvent containing a branched carboxylic acid of Example 1, isopalmitic acid was replaced with caprylic acid to create a paste solvent containing a straight-chain carboxylic acid but not a branched carboxylic acid.

[0311] (Comparative Example 3) Copper paste 14 was obtained in the same manner as in Example 1, except that isopalmitic acid was not mixed into the paste solvent containing the branched carboxylic acid of Example 1, resulting in a paste solvent that did not contain the branched carboxylic acid.

[0312] (Measurement of organic components present on copper particles) The amount of organic components in each copper particle prepared in the examples and comparative examples was measured using the following method. In this application, the following methods were used to analyze the organic components present on the surface of the copper particles, depending on the treatment state of the copper particles. The results are shown in Table 2.

[0313] (1. In the case of surface-treated copper particles or composite copper particles) Using copper particles obtained by vacuum drying a cake of surface-treated copper particles or composite copper particles, the organic components present on the surface of the copper particles contained in the surface-coated copper particles or composite copper particles were measured using a gas chromatograph (Nexis GC-2030 (Shimadzu Corporation)) equipped with a multi-shot pyrolizer (MODEL EGA / PY-3030D (Frontier Labs)) under the following conditions. The specific procedure is described below.

[0314] A 0.5g portion of a cake of surface-treated copper particles or composite copper particles was taken, vacuum-dried, and the remaining 2-propanol was removed to obtain copper particles. Two mg of the copper powder was taken as a measurement sample, and qualitative and quantitative analysis of the organic components present on the copper particles was performed using a gas chromatograph (Nexis GC-2030 (Shimadzu Corporation)) equipped with a multi-shot pyrolizer (MODEL EGA / PY-3030D (Frontier Labs)) under the following conditions.

[0315] Multi-shot Pyrolyzer Furnace temperature: 300℃ Sample amount: 2 mg • Gas chromatograph Column temperature: Hold at 60°C for 3 minutes, then increase the temperature and hold at 220°C for 5 minutes. Heating rate: 25℃ / min Separation column: Ultra ALLOY-1 (Manufactured by Frontier Labs, Part Number: UA-15W-5.0F) Column flow rate: Nitrogen (99.999% UP) 6 mL / min • Detector (Flame Ionization Detector: FID) Detector temperature: 320℃ Hydrogen flow rate: 30 mL / min Air flow rate: 300 mL / min

[0316] (2. In the case of coated copper particles) Using copper powder obtained by vacuum drying coated copper particles, the organic components present on the surface of the coated copper particles were measured under the following conditions using a thermogravimetric differential thermal analyzer (TG-DTA8122 (manufactured by Rigaku Corporation)).

[0317] Measurement atmosphere: Nitrogen (Purity: 99.995%) Atmospheric flow rate: 500 mL / min Measurement temperature range: 30℃~500℃ Heating rate: 10℃ / min

[0318] <Organic components present on the surface of copper particles>

[0319] [Table 2] Polymer dispersant A: BYK-LP C 24365 Polymer dispersant B: BYK-LP C 22552 Branched Carboxylic Acid C: 2-Ethyl Caproic Acid Branched Carboxylic Acid D: Isopalmitic Acid

[0320] Table 3 shows the composition of the copper paste produced in the examples and comparative examples. <Composition of copper paste>

[0321] [Table 3]

[0322] (viscosity measurement) The copper pastes obtained in the examples and comparative examples were mixed for 2 minutes at 2000 rpm using a rotation / revolution mixer before measurement. The viscosity (η) was determined using a rotational rheometer (HR-20 (TA Instruments Co., Ltd.)) under the following conditions. The viscosities listed in Table 5 are for a shear rate of 10s. -1 This is the value at that time.

[0323] Measurement temperature: 25℃ Measurement mode: Rotation mode Shear deformation measurement range: 0.1~100s -1 Number of measurement points: 31 points (each decimal number) Each measurement time: 35 seconds Gap: 1000 μm Measuring jig: 20mm parallel plate Measurement atmosphere: Under atmospheric conditions

[0324] (Fabrication of the joint) The pastes obtained in the examples and comparative examples were used as bonding materials to prepare bonded bodies for evaluating bonding strength. Before application, the pastes were mixed using a rotation / revolution mixer at 2000 rpm for 2 minutes. The method for preparing the bonded bodies was as follows. First, a copper (C1020) base material with a thickness of 5 mm, a surface roughness (Ra: arithmetic mean roughness) of 0.1 to 0.2 μm, and a diameter (hereinafter referred to as φ) of 10 mm was prepared. A metal mask with a thickness of 0.1 mm and an opening of φ5 mm was placed on top of it, and a bonding material was applied to the opening. The metal mask was removed, and a gold-plated copper piece (C1020) with a thickness of 5 mm, an Ra of 0.1 to 0.2 μm, and a diameter of φ5 mm was placed on the area coated with the bonding material to form a laminate. The surface roughness was determined by taking the average Ra value of 3 test pieces randomly selected from 100 test pieces and measuring it with a laser microscope. The laminate was placed in a jig having a 10.5 mm space on three sides, and the laminate was left standing on a hot plate heated to 100°C for 10 minutes in an atmosphere with nitrogen (99.995% purity) flowing at 100 mL / min. Next, the temperature was raised to 250°C at a heating rate of 30°C / min and held for 15 minutes. After that, heating was stopped and the laminate was allowed to cool naturally to 50°C to obtain a bonded body.

[0325] (Measurement of joint strength) The aforementioned joint was placed in a joint testing machine (JSL-1KN (manufactured by Nippon Keisoku System Co., Ltd.)), and a shear force was applied parallel to the joint surface at a rate of 1 mm / sec from the base material side. At the point when the base material and the copper piece separated, the joint strength was calculated from the applied load. Furthermore, with the equipment used in this study, the upper limit for measuring joint strength was 51 MPa, which means that the base material and the copper piece were firmly bonded without delamination.

[0326] (Storage stability test of copper paste) Storage stability tests were performed by storing copper paste for one week in a glove box (abbreviated as GB) adjusted to an oxygen atmosphere of 200 ppm, and then performing the viscosity measurement and bonding strength test on the paste. After one week of storage, the paste was stirred for 4 minutes at 2000 rpm using a rotation / revolution mixer, and then the viscosity measurement and bonding strength test were performed. Note that storage stability tests were not performed on Comparative Examples 1 and 2, which had low initial performance.

[0327] <Performance of copper paste>

[0328] [Table 4]

[0329] The copper pastes of Examples 1 to 11, which contain copper particles with an average particle size of 170 nm to 600 nm, a polymeric dispersant with an acid value of 60 mg KOH / g or higher, and a branched carboxylic acid or its salt with a C8 to 20 ratio, exhibit superior bonding characteristics and storage stability compared to Comparative Examples 1 to 3, which do not contain any of these components. Furthermore, even with a high copper particle concentration of 85 wt% or more, a low viscosity of 100 Pa·s or less can be achieved, improving coatability and obtaining high bonding strength. In addition, by including linear carboxylic acids or aromatic carboxylic acids at 0.4 wt% or less, a copper paste with excellent storage stability can be obtained without impairing the viscosity of the copper paste. [Industrial applicability]

[0330] According to the present invention, a copper paste can be obtained that contains a high concentration of copper particles, has relatively low viscosity, and exhibits minimal change in properties even after a certain period of time has elapsed since manufacturing. Furthermore, when this paste is used as a bonding material, sufficient bonding characteristics can be achieved. Moreover, sufficient bonding characteristics can be achieved even after a certain period of time has elapsed since manufacturing.

Claims

1. A copper paste comprising copper particles, a polymer dispersant, a branched carboxylic acid or its salt, and a paste solvent, The copper particles have an average particle diameter of 170 nm or more and 600 nm or less, as measured by a scanning electron microscope. The aforementioned polymer dispersant has an acid value of 60 mg KOH / g or more. The aforementioned branched carboxylic acid or its salt has 8 to 20 carbon atoms. Copper paste.

2. The copper particle content is 85% by mass or more and 96% by mass or less. The content of the polymer dispersant is 0.01% by mass or more and 2% by mass or less. The content of the branched carboxylic acid or its salt is 0.1% by mass or more and 5% by mass or less. The copper paste according to claim 1.

3. The copper paste according to claim 1 or claim 2, further comprising a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof.

4. The copper particle content is 85% by mass or more and 96% by mass or less. The copper paste according to claim 1 or claim 2, wherein the viscosity at 25°C, as measured by a rotary rheometer, is 0.1 Pa·s or more and 100 Pa·s or less.

5. The copper paste according to claim 1 or claim 2, wherein a polymer dispersant is present on the surface of the copper particles.

6. The copper paste according to claim 1 or claim 2, wherein the copper particles have a polymer dispersant and a branched carboxylic acid or a salt thereof on their surface.

7. The copper paste according to claim 1 or claim 2, wherein the copper particles have the polymer dispersant, a branched carboxylic acid or a salt thereof, and a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof on their surface.

8. The copper paste according to claim 1 or 2, wherein the polymer dispersant has a polyoxyethylene chain in its structure.

9. The copper paste according to claim 1 or claim 2, wherein the number average molecular weight of the polymer dispersant is 1500 or less.

10. The copper paste according to claim 1 or claim 2, wherein the polymer dispersant is an anionic polymer dispersant.

11. The copper paste according to claim 1 or claim 2, wherein the branched carboxylic acid or a salt thereof is at least one selected from 2-ethylcaproic acid, isopalmitic acid, isostearic acid, and salts thereof.

12. Surface-treated copper particles having a polymer dispersant and a branched carboxylic acid or a salt thereof on their surface, wherein the copper particles have an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope, the polymer dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or salt thereof has 8 or more and 20 or less carbon atoms.

13. Composite copper particles having a polymer dispersant, a branched carboxylic acid or a salt thereof, and a linear carboxylic acid and / or an aromatic carboxylic acid or a salt thereof on the surface of the copper particles, wherein the copper particles have an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope, the polymer dispersant has an acid value of 60 mg KOH / g or more, and the branched carboxylic acid or a salt thereof has 8 or more and 20 or less carbon atoms.

14. A method for producing copper paste, comprising mixing copper particles, a polymer dispersant, a branched carboxylic acid or its salt, and a paste solvent, The copper particles have an average particle diameter of 170 nm or more and 600 nm or less, as measured by a scanning electron microscope. The aforementioned polymer dispersant has an acid value of 60 mg KOH / g or more. The aforementioned branched carboxylic acid or its salt has 8 to 20 carbon atoms. A method for manufacturing copper paste.

15. A method for producing copper paste comprising the following steps (A) to (B) in this order, (A) A step of mixing copper particles, a polymer dispersant, and a solvent to obtain coated copper particles. (B) A step of mixing the coated copper particles obtained in step (A) with a branched carboxylic acid or a salt thereof and a paste solvent to obtain a copper paste. A method for producing a copper paste, comprising: the copper particles having an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope; the polymer dispersant having an acid value of 60 mg KOH / g or more; and the branched carboxylic acid or its salt having 8 or more and 20 or less carbon atoms.

16. A method for producing copper paste comprising the following steps (A) to (B) in this order, (A) A step of obtaining surface-treated copper particles by mixing copper particles, a polymer dispersant, a branched carboxylic acid or a salt thereof, and a solvent. (B) A step of mixing the surface-treated copper particles obtained in step (A) with a paste solvent to obtain a copper paste. A method for producing a copper paste, comprising: the copper particles having an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope; the polymer dispersant having an acid value of 60 mg KOH / g or more; and the branched carboxylic acid or its salt having 8 or more and 20 or less carbon atoms.

17. A method for producing copper paste comprising the following steps (A) to (C) in this order, (A) A step of mixing copper particles, a polymer dispersant, and a solvent to obtain coated copper particles. (B) A step of mixing the coated copper particles obtained in step (A) with a branched carboxylic acid to obtain surface-treated copper particles. (C) A step of mixing the surface-treated copper particles obtained in step (B) with a paste solvent to obtain a copper paste. A method for producing a copper paste, comprising: the copper particles having an average particle diameter of 170 nm or more and 600 nm or less as measured by a scanning electron microscope; the polymer dispersant having an acid value of 60 mg KOH / g or more; and the branched carboxylic acid or its salt having 8 or more and 20 or less carbon atoms.

18. A joining member comprising the copper paste described in claim 1 or 2.

19. A method for manufacturing a joined body, comprising the step of joining a base material and a material to be joined using the joining member described in claim 18.

20. The method for manufacturing a joined body according to claim 19, wherein the joining surface of the base material is gold, silver, or copper, and the joining surface of the material to be joined is gold, silver, or copper.

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