Method for manufacturing bonding compositions

Abstract

The present invention is a method for producing a bonding composition comprising copper particles and a second solvent. In the production method, a dispersion of copper particles is prepared by producing the copper particles in a first solvent by a wet reduction method. Then, while maintaining a wet state for the dispersion, the first solvent in the dispersion is replaced ultimately with a second solvent. Replacing the first solvent with another solvent at least once and using the second solvent for the final replacement is also preferred. Carrying out solvent replacement at below 100°C is also preferred. The use as the second solvent of at least one selected from water, alcohols, ketones, esters, ethers, and hydrocarbons is also preferred.

Description

Technical Field

[0001] The present invention relates to a method for producing a composition for bonding.

Background Art

[0002] With the miniaturization and high performance of electronic devices, in the formation of electronic circuits in electronic devices, improvement of various performances such as dimensional stability, conductivity, and adhesion to members is required. In order to achieve these requirements, for example, a conductive paste containing metal powder with less aggregation of particles is desired.

[0003] Patent Document 1 discloses a method for producing a conductive paste, which includes a step of depositing metal powder by a wet reduction method and a step of adding a water-soluble organic solvent to the metal powder in a state where moisture adheres thereto to replace the moisture with the water-soluble organic solvent. Patent Document 2 discloses a method for producing a metal powder for a conductive paste, in which washing of metal powder with water or an organic solvent is performed together with pulverization. Each of the above patent documents also discloses that the dispersibility of metal powder can be improved.

[0004] Further, Patent Document 3 discloses a method for producing a silver-containing powder, in which a dispersion liquid of silver-containing particles and a surfactant is vacuum freeze-dried. Furthermore, Patent Document 4 discloses silver powder obtained by making silver particles obtained by a wet reduction method into a wet cake having a predetermined water content and adding a dispersant to the wet cake and pulverizing it. These patent documents also disclose that, similar to Patent Documents 1 and 2, the dispersibility of metal powder can be improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] While the technologies described in Patent Documents 1 to 4 all examine the dispersibility of metal particles, they do not examine the adhesion to other components when the resulting metal powder or conductive paste containing the metal powder is subjected to sintering.

[0007] The present invention aims to provide a method for manufacturing a bonding composition that exhibits excellent adhesion to other components during sintering.

[0008] The present invention involves generating copper particles in a first liquid medium by a wet reduction method, preparing a dispersion of said copper particles, and then, The present invention provides a method for producing a bonding composition, which involves maintaining the wet state of the dispersion while ultimately replacing the first liquid medium of the dispersion with a second liquid medium to obtain a bonding composition containing the copper particles and the second liquid medium. [Brief explanation of the drawing]

[0009] [Figure 1] Figures 1(a) and (b) are ultrasonic images of sintered bodies obtained by firing the bonding compositions of the examples and comparative examples together with the objects to be bonded. [Modes for carrying out the invention]

[0010] The present invention will be described below based on its preferred embodiments. The method of the present invention relates to the production of a bonding composition comprising copper particles and a second liquid medium. The bonding composition is suitably used, for example, as a conductive paste or conductive ink for bonding two objects to be bonded together. In this case, the bonding composition is preferably a dispersion comprising copper particles as a conductive filler and a second liquid medium.

[0011] The manufacturing method of the present invention is broadly divided into two steps: a step of generating copper particles in a first liquid medium by a wet reduction method to prepare a dispersion of copper particles, and a step of replacing the first liquid medium of the dispersion with a second liquid medium while maintaining the wet state of the dispersion. In this context, "wet state" refers to a state in which the copper particles are not dried by, for example, heat treatment, and the surface of the copper particles is wet, preventing direct contact between the gas phase and the copper particles. More specifically, it refers to a state in which the solid content concentration of the liquid dispersion of copper particles is maintained at 95% by mass or less.

[0012] Furthermore, "ultimately replacing the first liquid medium with the second liquid medium" encompasses both cases: one in which the first liquid medium is directly replaced with the second liquid medium to obtain a dispersion containing the second liquid medium, which is the final target product; and another in which the first liquid medium is replaced with one or more other liquid mediums (excluding the first and second liquid mediums), and in the final liquid medium replacement step, the other liquid mediums (excluding the first and second liquid mediums) are replaced with the second liquid medium to obtain a dispersion containing the second liquid medium, which is the final target product.

[0013] First, copper particles are generated in a liquid medium by a wet reduction method. In the wet reduction method, for example, a copper compound, which is a copper source, and a reducing compound are mixed in a first liquid medium to prepare a reaction solution, and the copper compound in the reaction solution is reduced to obtain the desired copper particles. By producing copper particles by a wet reduction method, it is easy to control the particle size and spherical particles can be easily obtained. Copper particles can also be produced by the method described in, for example, Japanese Patent Application Publication No. 2015-168878.

[0014] There are no particular restrictions on the order or method of adding the copper compound and the reducing compound when preparing a reaction solution containing a copper compound and a reducing compound. For example, the reaction solution may be prepared by adding a solid copper compound and a solid reducing compound simultaneously. Alternatively, at least one of the copper compound and the reducing compound may be dispersed or dissolved in a liquid medium beforehand, and then one may be added to the other to prepare the reaction solution. When adding one of the copper compound and the reducing compound to the other, it may be added all at once, or it may be added continuously or intermittently, for example, by dropwise addition.

[0015] As the copper compound, it is preferable to use a compound that dissolves in a liquid medium. Examples of such copper compounds include water-soluble copper(II) salts such as copper chloride, copper acetate, and copper sulfate. These copper compounds may be anhydrous or hydrated. These copper compounds can be used individually or in combination.

[0016] The copper compound is mixed so that, when converted to the copper element content in the reaction solution, it is preferably 0.001 mol / L to 1 mol / L, and more preferably 0.1 mol / L to 0.5 mol / L. By using such a copper compound content, copper particles with a small particle size can be obtained with high productivity.

[0017] Reducing compounds reduce copper ions in a copper source. Examples of reducing compounds include hydrazine compounds such as hydrazine, hydrazine hydrochloride, hydrazine sulfate, and hydrazine hydrate, as well as sodium borohydride, sodium sulfite, sodium bisulfite, sodium thiosulfate, sodium nitrite, sodium hyponitrite, phosphorous acid, sodium phosphite, hypophosphorous acid, and sodium hypophosphite. These reducing compounds may be anhydrous or hydrated. These reducing compounds can be used individually or in combination of two or more. In particular, hydrazine is especially suitable because it generates few impurities after reduction and produces few impurities in the resulting copper particles. From the viewpoint of having strong reducing power and suppressing the inclusion of impurities in the particles, it is even more preferable to use only anhydrous or hydrated hydrazine as the reducing compound.

[0018] The content of the reducing compound in the reaction solution is preferably mixed so as to be 0.5 mol or more and 50 mol or less, more preferably 1 mol or more and 10 mol or less, and still more preferably 2 mol or more and 5 mol or less, per 1 mol of copper element. By setting the content of the reducing compound at such a ratio, copper particles with a small particle size can be easily obtained. The reduction of the copper compound by the reducing compound may be carried out only once, or may be carried out a plurality of times as necessary. The content of the reducing compound described above is a value in terms of anhydride.

[0019] The reaction conditions of the reaction solution may be reacted without heating or under heating conditions from the start point of mixing to the end point of the reaction. Also, from the viewpoint of uniformly generating the reduction reaction and obtaining copper particles with little variation in particle size, it is also preferable to continue stirring the reaction solution throughout the entire time from the start point of mixing to the end point of the reaction.

[0020] From the viewpoint of achieving both sufficient progress of the reduction reaction for the formation of copper particles and reduction of the production cost, it is preferable to carry out the reaction so as to maintain a temperature of 0°C or higher and 80°C or lower from the start point of mixing to the end point of the reaction. The time from the start point of mixing to the end point of the reaction can be appropriately changed depending on the particle size of the target copper particles, but is preferably 0.5 hours or more and 4 hours or less, and still more preferably 1 hour or more and 3 hours or less. When the reduction treatment of the copper compound by the reducing compound is carried out a plurality of times, the above time is the total of the times from the start point of mixing to the end point of the reaction for each time.

[0021] Through the above steps, copper particles are generated. Since the copper particles are obtained by the wet reduction method, they are in the state of a dispersion of copper particles dispersed in the first liquid medium which is the liquid medium of the reaction solution.

[0022] The generated copper particles have a volume cumulative particle size D at a cumulative volume of 50% measured by image analysis of scanning electron microscope observation , SEM50 , SEM50 represented by, preferably 100 nm or more and 300 nm or less, more preferably 100 nm or more and 250 nm or less. D SEM50This indicates the particle size of primary particles, which are the smallest units of matter recognized from their external geometric form. By setting the copper particles within this particle size range, the bonding composition exhibits good filling and sinterability, high adhesion to other components such as the objects to be bonded, and is advantageous for forming thin coating films. The particle size of the copper particles can be appropriately adjusted, for example, by adjusting the molar ratio of the copper compound to the reducing compound or by adjusting the time of the reduction reaction.

[0023] D SEM50 This can be measured, for example, by the following method. First, using Mac-View software from Mountec, image data of copper particles obtained by observing them from directly above with a scanning electron microscope is read. Then, 50 or more copper particles are randomly selected from the data, and the particle size (Heywood diameter) of each particle is measured. Next, the volume is calculated from the obtained Heywood diameter assuming that the particles are perfectly spherical, and the volume-cumulative particle size at 50% of the cumulative volume is calculated as D SEM50 Let's assume that.

[0024] Next, while maintaining the wet state of the copper particle dispersion, the first liquid medium in the dispersion is replaced with the second liquid medium. One of the features of this step is that, in order to obtain the desired bonding composition, the first liquid medium in the dispersion is replaced with the second liquid medium, which is the liquid medium ultimately included in the bonding composition, while maintaining the wet state of the dispersion.

[0025] In the preparation of bonding compositions such as conductive pastes and conductive inks containing copper particles as a conductive filler, dried copper powder is typically used, obtained by drying the copper particles. This method allows for easy preparation of pastes and inks with desired filler concentrations by appropriately increasing or decreasing the copper particle content. However, when preparing bonding compositions using dried copper powder, the copper particles in the powder may aggregate or become prone to aggregation, making redispersion complicated or even impossible. As a result, the coating obtained by applying the bonding composition is often not smooth and exhibits poor adhesion to other components. Furthermore, the surface of the copper particles may be altered by oxidation during drying, preventing the desired properties such as adhesion and conductivity from being achieved. In particular, when using copper particles with a suitable particle size for inks and pastes in a dry state, the difficulty of redispersion and the deterioration of the particles due to oxidation, etc., were significant issues.

[0026] In order to solve this problem, the inventors investigated and found that by subjecting the obtained copper particles to subsequent processes while maintaining a wet state without drying them, contact between the copper particles and oxygen in the atmosphere is reduced. Furthermore, the dispersibility of the copper particles when preparing the bonding composition is improved, which suppresses the generation of excessive stress during film formation and sintering. As a result, it was found that the bonding composition of the present invention exhibits excellent adhesion to other members during sintering and can suppress delamination from other members caused by excessive volume shrinkage during sintering.

[0027] The substitution from the first liquid medium to the second liquid medium may be performed directly (hereinafter also referred to as "direct substitution"), or it may be performed by substituting the first liquid medium with another liquid medium (excluding the second liquid medium) one or more times before finally substituting with the second liquid medium (hereinafter also referred to as "indirect substitution"). The dispersions maintaining a wet state may independently take the form of, for example, a slurry or a wet cake.

[0028] The method of replacing the liquid medium is not particularly limited, regardless of whether it is direct or indirect replacement, as long as the wet state of the dispersion can be maintained. For example, repulping, decantation, rotary filtration, or filtration can be employed. Furthermore, the liquid medium replacement may be performed only once or multiple times as necessary.

[0029] Whether by direct or indirect substitution, the liquid medium substitution is carried out by setting the temperature of the liquid medium to preferably less than 100°C, more preferably 80°C or lower, and even more preferably 60°C or lower. By setting the temperature to such a level, evaporation of the liquid medium during substitution is suppressed, and a bonding composition with excellent adhesion to other components can be obtained while maintaining a wet state and high dispersibility of copper particles.

[0030] In the process of ultimately replacing the first liquid medium with the second liquid medium, it is preferable to efficiently remove components originating from the first liquid medium that may cause impurities, and to improve the workability of replacing it with the second liquid medium contained in the target bonding composition. This is achieved by replacing the first liquid medium contained in the copper particle dispersion obtained by the wet reduction method with another liquid medium (excluding the first and second liquid media) at least once, and using the second liquid medium for the final replacement. In other words, it is preferable to employ indirect replacement in this manufacturing method.

[0031] Furthermore, even when the first liquid medium is replaced multiple times with other liquid mediums (excluding the second liquid medium), it is preferable to maintain the wet state of the dispersion during each step of the replacement: the replacement from the first liquid medium to the first other liquid medium, the replacement between other liquid mediums when two or more types of other liquid mediums are used, and the replacement from the last other liquid medium to the second liquid medium. When the first liquid medium is replaced with another liquid medium one or more times, the solid content concentration in each replacement step may be the same or different, independently of each other. By maintaining the wet state of the copper particles and replacing the liquid medium, it is possible to efficiently remove components originating from the first liquid medium that may cause impurities, while obtaining copper particles that have high redispersibility and minimal deterioration. Therefore, when the bonding composition containing these copper particles is sintered, it is possible to achieve even better adhesion with other components.

[0032] One embodiment of a method for replacing the first liquid medium with another liquid medium once or more is, for example, a method in which a dispersion of copper particles in the first liquid medium obtained by a wet reduction method is washed with another liquid medium such as water. When performing a washing process, methods such as repulping, decantation, rotary filtration, and filtration can be employed. When performing a washing process, it is preferable that the copper particles after washing be subjected to subsequent processes in a dispersed state that maintains a moist condition.

[0033] When washing copper particles using the decantation method, for example, another liquid medium is added and washing is carried out until the conductivity of the dispersion is preferably 5 mS or less. When water is used as the other liquid medium, the washing temperature is preferably less than 100°C, and more preferably between 15°C and 30°C. By performing the washing under these conditions, impurities contained in the copper particles are reduced, and the particles remain uniformly dispersed, allowing them to be used for subsequent processes. After that, the liquid dispersion of washed copper particles is subjected to a final substitution using a second liquid medium while maintaining a wet state.

[0034] Another embodiment of the method for replacing the first liquid medium with another liquid medium one or more times is the method described in the examples below, but as long as the effects of the present invention are achieved, there are no particular restrictions on the number of replacements or the type of liquid medium used. Thereafter, the liquid dispersion of copper particles is subjected to a final replacement using the second liquid medium while maintaining a wet state.

[0035] Through the above process, a bonding composition containing copper particles and a second liquid medium can be obtained. According to this manufacturing method, the dispersion treatment of copper particles when preparing the bonding composition is simplified, and aggregation of copper particles is reduced, so a highly smooth coating film can be efficiently formed. In addition, surface deterioration of the copper particles can be reduced. As a result, when the coating film formed by the bonding composition is sintered, the melting properties of the copper particles are increased, improving the melting properties of the copper particles and increasing the contact area between the molten particles and other components. As a result, a sintered body can be obtained that is less prone to cracking and peeling and has excellent adhesion to other components.

[0036] As the first liquid medium used in this manufacturing method, one or more of water, alcohol, ketone, ester, and ether are preferred from the viewpoint of efficiently carrying out the reduction of copper by the wet reduction method, and one or more of water and alcohol are even more preferred from the viewpoint of improving compatibility with copper salts and improving the efficiency of copper particle production in the production of copper particles by the wet reduction method.

[0037] Furthermore, as the second liquid medium used in this manufacturing method, from the viewpoint of increasing productivity by allowing the bonding composition to be used directly as a conductive paste or conductive ink, one or more of water, alcohol, ketone, ester, ether, and hydrocarbon are preferred, and the use of alcohol and hydrocarbons is even more preferred. The first and second liquid media described above may be the same or different.

[0038] From the viewpoint of achieving both a reduction in the residual amount of the first liquid medium and ease of replacement with the second liquid medium, when using other liquid mediums (excluding the first and second liquid mediums), it is preferable to use one or more of water, alcohols, ketones, esters, ethers, and hydrocarbons as the other liquid medium, and it is even more preferable to use one or more of water and alcohols.

[0039] Examples of alcohols that can be used include monohydric alcohols such as methanol, ethanol, n-propanol, 2-propanol, and n-butanol; diols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, butylene glycol, pentylene glycol, and hexylene glycol; triols such as glycerin; and polyols such as polyethylene glycol and polypropylene glycol.

[0040] Examples of esters include fatty acid esters of the polyhydric alcohols mentioned above. The fatty acids are, for example, monohydric fatty acids with a carbon atom number of 1 to 8, more preferably 1 to 5. The polyhydric alcohol esters preferably have at least one hydroxyl group.

[0041] As for the ketone, those in which the alkyl group bonded to the carbonyl group has 1 to 6 carbon atoms, and more preferably 1 to 4 carbon atoms, are preferred. Specific examples of ketones include methyl ethyl ketone and acetone.

[0042] Examples of ethers include linear ethers such as dimethyl ether, ethyl methyl ether, and diethyl ether, as well as cyclic ethers such as oxacene, tetrahydrofuran, and tetrahydropyran.

[0043] Examples of hydrocarbons include aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, and hexadecane.

[0044] In the case of direct substitution, it is even more preferable that the first and second liquid media used are mutually miscible under conditions of 1 atmosphere and 25°C. Miscibility refers to the phenomenon in which two or more liquid components in a fluid containing two or more liquid components mix with each other and form a single phase. By using a compatible liquid medium, the copper particle dispersion in the first liquid medium can be replaced with the second liquid medium while maintaining the dispersibility of the particles. In addition, since the copper particles can be replaced with the second liquid medium while reducing the alteration of the copper particles, when the resulting bonding composition is sintered, the meltableness of the copper particles can be increased, and the contact area between the molten particles and the surface of other components can be increased. As a result, a sintered body with high adhesion to other components and low impurity can be obtained.

[0045] Furthermore, in the case of indirect substitution, when the first liquid medium is substituted with another liquid medium once or more times, it is preferable that the combinations of the first liquid medium and the first other liquid medium, the other liquid media that are consecutive in the process when substitution is performed two or more times using the other liquid medium, and the combinations of the last other liquid medium and the second liquid medium are all mutually compatible, and it is more preferable that they are mutually compatible under conditions of 1 atmosphere and 25°C. Furthermore, in the case of indirect substitution, the first liquid medium and the second liquid medium may be mutually compatible under the conditions of 1 atmosphere and 25°C, or they may be incompatible under the same conditions. By using mutually compatible fluids during the substitution of each fluid, components originating from the first fluid and other fluids that could cause impurities can be efficiently removed. As a result, a sintered body with high adhesion to other components and low impurity content can be obtained.

[0046] Furthermore, as one aspect of indirect substitution, the impurities in the dispersion can be reduced by substituting the first liquid medium with another liquid medium having a lower viscosity (excluding the first and second liquid media), and then finally substituting it with a second liquid medium having a higher viscosity than the other liquid medium (excluding the first and second liquid media). The viscosity of the liquid medium can be measured, for example, by a vibrating viscometer or a rotational viscometer.

[0047] In the steps of generating copper particles by the wet reduction method described above, and the substitution from the first liquid medium to the second liquid medium, and optionally the substitution from the first liquid medium to another liquid medium, and the substitution from another liquid medium to the second liquid medium, it is preferable to carry out these steps in the absence of organic polymers, and it is even more preferable to carry out all steps of the manufacturing method of the present invention in the absence of organic polymers. In this manufacturing method, in order to ensure that organic polymers are not present in the reaction system, for example, organic polymers and raw materials containing organic polymers should not be used in each step of the reductive wet reaction and the liquid medium substitution process. By performing each step in the absence of organic polymers, it is possible to maintain a low degree of copper particle aggregation while allowing sufficient sintering of the copper particles when the bonding composition is sintered. In addition, since the content of residual organic matter, which is one of the impurities and can inhibit sintering, can be reduced, the resulting product is of higher density and has even better adhesion to other components.

[0048] The organic polymers mentioned above include natural and synthetic polymers used as dispersants and surface treatment agents in the relevant technical field. Specifically, examples of natural polymers include proteins such as gelatin, gum arabic, casein, sodium caseate, ammonium caseate, starch, dextrin, agar, and sodium alginate. Examples of synthetic polymers include cellulosic compounds such as hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, polyvinyl compounds such as polyvinyl alcohol, and polyacrylic acid compounds such as sodium polyacrylate and ammonium polyacrylate.

[0049] The bonding composition obtained through the above process is a dispersion containing copper particles and a second liquid medium. The bonding composition may contain only the second liquid medium as the liquid medium constituting the composition, or it may inevitably contain the liquid medium used for the previous liquid medium replacement in addition to the second liquid medium. In either case, it is preferable that the second liquid medium is present in the largest mass proportion of the total liquid medium constituting the bonding composition.

[0050] The bonding composition can be used as is, or, if necessary, by further adding at least one of the following: metal particles other than copper particles contained in the bonding composition, a liquid medium, a binder resin, etc., in the form of a conductive paste or conductive ink. That is, the present invention also includes a method for producing a conductive paste, which comprises at least the bonding composition obtained through the above-described process, and further mixing the composition with, if necessary, at least one of the following: metal particles other than copper particles contained in the bonding composition, a liquid medium, and a binder resin.

[0051] Examples of metal particles that can be further added to the bonding composition include particles containing metals such as copper, silver, and gold. As a liquid medium that can be further added to the bonding composition, for example, one similar to those exemplified in the descriptions of the first and second liquid media above, and which has good compatibility with the binder resin, can be used. Examples of binder resins that can be further added to the bonding composition include one or more of the following: acrylic resin, epoxy resin, polyester resin, polycarbonate resin, and cellulose resin.

[0052] The bonding composition can be applied between any two materials to be bonded by a predetermined means, thereby bonding the two materials together to form a bonded structure. In other words, the present invention also includes a method for bonding materials by applying a bonding composition between them, as well as a method for manufacturing a bonded structure. The materials to be bonded can be independently substrates, semiconductor elements, and the like. As a specific embodiment, for example, it can be used as a bonding agent when surface mounting electronic devices on a printed circuit board, or as a via-filling material in a printed circuit board. Furthermore, it can also be used to form wiring circuits on a printed circuit board or to form electrodes for chip components.

[0053] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, copper particles obtained by a wet reduction method do not necessarily exclude the unavoidable presence of trace amounts of other elements or the unavoidable slight oxidation of the copper particle surface, as long as the effects of the present invention are achieved. [Examples]

[0054] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples.

[0055] [Example 1] In this example, the bonding composition was manufactured in the absence of organic polymers in all steps. (1) Generation of copper particles by wet reduction method In a 36-liter stainless steel tank, a mixture of 5.0 liters of warm pure water and 5.0 liters of methanol was added as the first liquid medium, along with 2.5 kg of copper acetate as the copper source. The mixture was stirred at 40°C for 30 minutes to dissolve the copper acetate. Next, 150 g of hydrazine was added to the liquid medium all at once, and stirring was continued at 40°C for 30 minutes to generate cuprous oxide particles in the liquid medium. After 30 minutes, another 1400 g of hydrazine was added to the liquid medium all at once, and stirring was continued at 40°C for 60 minutes to reduce the cuprous oxide particles to metallic copper particles. In this way, a dispersion of copper particles was obtained in the first liquid medium. This dispersion remained wet. The particle size D of the obtained copper particles SEM50 The wavelength was 155 nm.

[0056] (2) Replacement of liquid medium In this embodiment, the first liquid medium was replaced with other liquid mediums multiple times, and then the final replacement was with the second liquid medium. All steps were carried out while maintaining a wet state of the dispersion. In detail, pure water compatible with the first liquid medium was used as the first other liquid medium. The first liquid medium dispersion of copper particles was washed with pure water by decantation until the conductivity reached 3.5 mS, thereby obtaining a first dispersion in which copper particles were dispersed in water. This first dispersion maintained a wet state. Next, as a second liquid medium, a denatured alcohol compatible with the first liquid medium (a mixed liquid medium of 89% by mass of ethanol and 11% by mass of 2-propanol) was used. The first dispersion was washed with the denatured alcohol using a rotary filter until the water concentration in the first dispersion was 1% by mass or less, to obtain a second dispersion in which copper particles were dispersed in the denatured alcohol. This second dispersion maintained a wet state. Next, hexylene glycol, which is compatible with the second liquid medium, was used as the second liquid medium for the final substitution. After washing with hexylene glycol using a rotary filter until the denatured alcohol concentration in the second dispersion was 3% by mass or less, the hexylene glycol was separated into solid and liquid components by pressure filtration to obtain a bonding composition in which copper particles were dispersed in the second liquid medium. This bonding composition maintained a wet state with a solid content concentration of 92%.

[0057] (3) Preparation of bonding paste A bonding paste containing copper particles was prepared by mixing 7.6 parts by mass of bonding composition, 3 parts by mass of metal particles other than copper particles contained in the bonding composition (copper particles, 1200YF, manufactured by Mitsui Mining & Smelting Co., Ltd.), 0.5 parts by mass of a BIS-TRIS / hexylene glycol solution with a solid content of 50% by mass, and 0.1 parts by mass of polyethylene glycol 300, with the remainder being hexylene glycol, so that the copper particle concentration was 76% by mass.

[0058] [Comparative Example 1] Similar to Example 1, (1) copper particles were produced by a wet reduction method. The first liquid dispersion of copper particles was then washed with pure water by decantation until the conductivity was 3 mS, thereby obtaining a dispersion in which copper particles were dispersed in water. This dispersion remained wet. Next, the dispersion was heated to 50°C, and while stirring, a dimethylglyoxime / methanol solution was added so that the dimethylglyoxime content relative to the copper particle content was 0.5% by mass. The mixture was then stirred at 50°C for 1 hour to obtain a water / methanol dispersion of surface-treated copper particles. Subsequently, the surface-treated copper particles were vacuum-dried to obtain dry copper particles. No liquid medium was present in these copper particles. Finally, instead of the bonding composition, a bonding paste with the same composition and concentration as in Example 1 was prepared using dry copper particles.

[0059] [Evaluation of adhesion] The bonding pastes of the examples and comparative examples were screen printed onto the center of the surface of a copper plate (20 mm long x 20 mm wide x 2 mm thick) with dimensions of 10 mm long x 10 mm wide x 110 μm thick, and the bonding pastes were dried at 110°C for 20 minutes to obtain a dried film. Next, an alumina plate with an Ag-plated surface (5mm long x 5mm wide x 0.5mm thick) was placed on the dry film and sintered at 280°C for 20 minutes at 6 MPa under a nitrogen atmosphere with a heating rate of 120°C / min, thereby joining the copper plate and the alumina plate. After bonding, an ultrasonic flaw detector (Hitachi Power Solutions, model number: FineSATIII) with a 75MHz probe was used to observe the copper plate from the side where the alumina plate was placed, using the reflection method. The presence or absence of voids in the sintered body of the dried film and the condition of the outer periphery (unpressurized area) of the alumina plate in the sintered body of the dried film were observed. The denser the sintered structure, the darker the color observed. The results are shown in Figure 1.

[0060] In Figure 1, the region where the alumina plate is located is denoted by symbol A, the region where the sintered body of the dried film is located is denoted by symbol B, and the region where the copper plate is exposed is denoted by symbol C. As shown in Figure 1(a), the sintered paste obtained using the bonding composition of Example 1 shows a darker color in region A where the alumina plate is placed, indicating the formation of a dense structure with few voids and good bonding between the alumina plate and the copper plate. Furthermore, in region B where the sintered body is located on the outer periphery of the alumina plate, the observed color is uniform, and no delamination between the sintered body and the copper plate was observed. Therefore, it can be seen that the paste using the bonding composition of Example 1 exhibits excellent adhesion to other components.

[0061] On the other hand, as shown in Figure 1(b), in the sintered paste obtained using the bonding composition of Comparative Example 1, the region A where the alumina plate is placed is observed to be darker in color, indicating that the bonding state between the alumina plate and the copper plate is good. However, in region B where the sintered body is located on the outer periphery of the alumina plate, the observed color is uneven, and a lot of delamination between the sintered body and the copper plate was observed. Therefore, it can be seen that the paste using the bonding composition of Comparative Example 1 has poor adhesion to other components. [Industrial applicability]

[0062] According to the manufacturing method of the present invention, a bonding composition with excellent adhesion to other components can be obtained during sintering.

Claims

1. A method for manufacturing a joining composition used to form a joined structure by joining by sintering, which is placed between two materials to be joined, Copper particles are generated in the first liquid medium by a wet reduction method, and a dispersion of the copper particles is prepared thereafter. While maintaining the wet state of the dispersion, the first liquid medium of the dispersion is ultimately replaced with a second liquid medium to obtain a bonding composition in which the copper particles are dispersed in the second liquid medium without drying the copper particles. A method for producing a bonding composition, wherein the copper particles are generated in the absence of an organic polymer.

2. A method for manufacturing a joining composition used to form a joined structure by joining by sintering, which is placed between two materials to be joined, A dispersion of copper particles is prepared by generating copper particles in a first liquid medium containing water using a wet reduction method, and then, While maintaining the wet state of the dispersion, the first liquid medium of the dispersion is ultimately replaced with a second liquid medium to obtain a bonding composition in which the copper particles are dispersed in the second liquid medium without drying the copper particles. A method for producing a bonding composition, wherein the copper particles are generated in the absence of an organic polymer.

3. The manufacturing method according to claim 1 or 2, wherein the liquid medium replacement is performed at a temperature of less than 100°C.

4. The manufacturing method according to any one of claims 1 to 3, wherein one or more of water, alcohol, ketone, ester, ether, and hydrocarbon are used as the second liquid medium.

5. The copper particles are measured by scanning electron microscopy, and the cumulative volume particle size D at 50% of the cumulative volume is measured. ＳＥＭ５０ The manufacturing method according to any one of claims 1 to 4, wherein the wavelength is 100 nm or more and 300 nm or less.

6. A method for producing the composition according to any one of claims 1 to 5, wherein the first liquid medium is replaced once or more with another liquid medium (excluding the first and second liquid mediums), and the second liquid medium is used for the final replacement.

7. The manufacturing method according to claim 6, wherein the first liquid medium is replaced with the other liquid medium while maintaining the wet state of the dispersion.

8. The manufacturing method according to claim 6 or 7, wherein the first liquid medium and the second liquid medium are different from each other.

9. The manufacturing method according to any one of claims 6 to 8, wherein the steps of replacing the first liquid medium with the other liquid medium and replacing the other liquid medium with the second liquid medium are carried out in the absence of an organic polymer.

10. A method for producing a conductive paste comprising a bonding composition obtained by the manufacturing method described in any one of claims 1 to 9.

11. A method for joining materials, comprising placing a joining composition obtained by the manufacturing method described in any one of claims 1 to 9 between two materials to be joined and sintering it to form a joined structure by joining by sintering.

Images