Method for manufacturing copper paste, copper sintered body, and copper sintered body

Abstract

The present invention provides a copper paste capable of sintering at low temperatures and reducing the volume resistivity of the copper after sintering, a method for manufacturing a copper sintered body, and a copper sintered body. [Solution] A copper paste comprising copper particles and a copper complex, wherein the copper particles include first copper particles with a number average particle diameter D1 of 0.2 μm to 50 μm and second copper particles with a number average particle diameter D2 of 0.1 μm to 5 μm, the number average particle diameters of the first copper particles and the second copper particles being D1 > D2, the mass ratio of the first copper particles to the second copper particles being 95:5 to 5:95, and the mass ratio of the second copper particles to the copper complex being 95:5 to 5:95.

Description

[Technical Field]

[0001] The present invention relates to a copper paste, a method for producing a copper sintered body, and a copper sintered body. [Background Art]

[0002] For bonding next-generation semiconductor chips such as SiC, which have been increasing in number in recent years, the use of sintered materials that are superior in bonding durability to conventional high-temperature solders is considered promising. A sintered material is a material that is obtained by mixing fine metal powder with an organic component, forming a paste, printing the paste on a substrate, and then heat-sintering the paste to achieve bonding.

[0003] Studies on Ag sintered materials have progressed earlier in the market, but for the purpose of reducing the risk of Ag migration and lowering costs, studies on pastes for Cu sintered materials that can be sintered at low temperatures (Cu pastes) are also ongoing.

[0004] For example, Non-Patent Document 1 explores the possibility of bonding Cu paste at low temperatures, and finds that the behavior in the initial stage of sintering such as the progress of necking of Cu powder during the temperature rising process can be grasped from the decrease in volume resistivity with respect to the heating temperature.

[0005] In addition, Non-Patent Document 2 clarifies that sintering of coarse copper powder can be promoted by combining relatively coarse spherical copper powder with fine copper particles. [Prior Art Documents] [Non-Patent Documents]

[0006] [Non-Patent Document 1] "Exploration on the Possibility of Low-Temperature Bonding of Cu Paste", The 87th Annual Meeting of The Society of Chemical Engineers, Japan, O322 (March 2022) [Non-Patent Document 2] "Exploration on the Possibility of Low-Temperature Bonding of Cu Paste - Second Report", The 88th Annual Meeting of The Society of Chemical Engineers, Japan, I215 (March 2023) [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] Ideally, a sintering material should be sintered at a low temperature to prevent degradation or performance reduction of the substrate or other material to be printed on due to high-temperature sintering. Furthermore, it is preferable that the sintering material has excellent conductivity so as not to impair the performance of the substrate or other material; specifically, a low volume resistivity is ideal.

[0008] In view of these circumstances, the present invention aims to provide a copper paste, a method for manufacturing a copper sintered body, and a copper sintered body that can be sintered at a low temperature and have a low volume resistivity of copper after sintering. [Means for solving the problem]

[0009] To solve the above problems, the copper paste of the present invention comprises copper particles and a copper complex, wherein the copper particles include first copper particles with a number average particle diameter D1 of 0.2 μm to 50 μm and second copper particles with a number average particle diameter D2 of 0.1 μm to 5 μm, the number average particle diameters of the first copper particles and the second copper particles being D1 > D2, the mass ratio of the first copper particles to the second copper particles being 95:5 to 5:95, and the mass ratio of the second copper particles to the copper complex being 95:5 to 5:95.

[0010] The copper particles may include at least one of spherical particles or branched particles.

[0011] The copper particles may include particles whose surfaces are coated with an organic film.

[0012] The copper complex may include a complex represented by Cu(HCOO)2(2MAE)2, where 2MAE is 2-(methylamino)ethanol.

[0013] The copper paste of the present invention may have a shear viscosity of 1.0 Pa·s to 1000.0 Pa·s at a shear rate of 0.1 / s, and a shear viscosity of 1.0 Pa·s to 100.0 Pa·s at a shear rate of 10 / s.

[0014] Further, in order to solve the above problem, the method for producing a copper sintered body according to the present invention includes a sintering step of heating the copper paste of the present invention to sinter said copper paste.

[0015] The sintering step may be a step of performing said heating at 180°C to 250°C to sinter said copper paste.

[0016] Further, in order to solve the above problem, the copper sintered body according to the present invention has a film thickness of 1 μm to 2 mm, and an initial volume resistivity R0 of 5 to 200 μΩ·cm.

Effects of the Invention

[0017] According to the present invention, there can be provided a copper paste, a method for producing a copper sintered body, and a copper sintered body that can be sintered at low temperature and achieve a low volume resistivity of copper after sintering.

Brief Description of Drawings

[0018] [Figure 1] External appearance of a copper complex ink and structural formula of a copper complex. [Figure 2] A graph showing measurement results of volume resistivity in a preliminary test. [Figure 3] A graph showing measurement results of volume resistivity in Comparative Examples 1 and 2.

Mode for Carrying Out the Invention

[0019] Hereinafter, an embodiment of the copper paste, the method for producing a copper sintered body, and the copper sintered body according to the present invention will be described.

[0020] [Copper Paste] The copper paste according to the present invention includes copper particles described below and a copper complex.

[0021] <Copper Particles> When the copper paste contains copper particles together with a copper complex, a copper sintered body obtained by firing the copper paste can form a copper sintered body such as a thick metal wiring having a thickness of several μm or more or a die attach material.

[0022] For example, by including copper particles in the copper paste, a thick copper sintered body with a thickness of several micrometers or more can be formed on a substrate or other coating surface in a single application using screen printing or similar methods. This is possible because copper reduced from the copper complex precipitates on the surface of the copper particles, creating a good conductive path for the copper.

[0023] Specifically, the copper sintered body formed by the copper paste of the present invention can exhibit good volume resistivity due to the conductive paths provided by the copper.

[0024] On the other hand, in the case of copper complex inks that do not contain copper particles, it is not possible to form a copper sintered body of sufficient thickness with a single application, and multiple applications are required to obtain sufficient thickness. However, when attempting to form a fine copper sintered body by screen printing, the method of repeatedly applying multiple coats can cause misalignment of the copper sintered body after printing, making it difficult to form a copper sintered body with a uniform shape.

[0025] The copper particles consist of first-order copper particles with a number-average particle diameter (D1) of 0.2 μm to 50 μm, and second-order copper particles with a number-average particle diameter (D2) of 0.1 μm to 5 μm, where D1 > D2. By using particles with different particle diameters, the packing density can be adjusted, and by appropriately mixing these copper particles, the packing density of the mixture can be maximized. Furthermore, by using first-order copper particles with a larger number-average particle diameter, sufficient thickness can be ensured for the copper sintered body.

[0026] In particular, for metal sintered films used for die attachment, a high density of metal portions is desirable for both strength and heat dissipation characteristics. However, under no-pressure conditions, interparticle sintering is limited to necking growth; therefore, a high filler packing density is desirable during the pre-drying stage before sintering. For this reason, multiple types (two or more) of copper particles with different number-average particle sizes and shapes can be combined. The maximum copper particle size used and the corresponding ratio of small-particle powder can be appropriately changed according to the required sintered film thickness.

[0027] The mass ratio of the first copper particles to the second copper particles is not particularly limited, but can be set to, for example, 95:5 to 5:95. Considering the volume resistivity of the copper sintered body, the mass ratio can be set to 68:32 to 40:60.

[0028] The shape of the copper particles is not particularly limited for either the first or second copper particles. For example, spherical particles and branched particles can be used.

[0029] Furthermore, the surface condition of the copper particles is not particularly limited for either the first or second copper particles. For example, copper particles with an untreated surface may be used, or copper particles with an organic film coating on the surface may be used, and at least one of these can be used.

[0030] <Copper complex> The copper complex is not particularly limited, but for example, the general formula is Cu(HCOO)2(L) m The complex represented by can be used. In the general formula, L is at least one selected from 2-amino-2-methyl-1-propanol, 1-amino-2-propanol, 2-amino-1-butanol, 2-(methylamino)ethanol, and 2-aminoethanol, and m is a natural number from 2 to 6.

[0031] This copper complex can be described as a state in which at least one of the following ligands is coordinated to copper formate (Cu(HCOO)2) by 2 to 6 molecules: (CH3)2C(NH2)CH2OH (2-amino-2-methyl-1-propanol, sometimes referred to as "AMP"), CH3C(OH)CH2NH2 (1-amino-2-propanol, sometimes referred to as "APol"), CH3C(NH2)CH2OH (2-amino-1-butanol, sometimes referred to as "ABol"), CH3NHCH2CH2OH (2-(methylamino)ethanol, sometimes referred to as "2MAE"), and NH2CH2CH2OH (2-aminoethanol, sometimes referred to as "AEol").

[0032] Below, (HCOO)2Cu((CH3)2C(NH2)CH2OH) 2~6 The copper complex represented by (HCOO)2Cu((CH3)2C(NH2)CH2OH) is called "Cu-AMP". 2~6 The copper complex represented by (HCOO)2Cu(CH3C(OH)CH2NH2) is called "Cu-AMP". 2~6 The copper complex represented by (HCOO)2Cu(CH3C(NH2)CH2OH) is called "Cu-APol". 2~6 The copper complex shown is called "Cu-ABol" (HCOO)2Cu(CH3NHCH2CH2OH) 2~6 The copper complex shown is called "Cu-2MAE" and (HCOO)2Cu(NH2CH2CH2OH) 2~6 The copper complex shown is sometimes referred to as "Cu-AEol".

[0033] By including the above-mentioned copper complex along with copper particles in the copper paste, it is possible to form a copper sintered body with low volume resistivity as a copper sintered body obtained by firing the copper paste.

[0034] In other words, because the copper paste contains a copper complex, reduced copper from the complex can be deposited on the surface of the copper particles, thus forming a good conductive path of copper. Since the unoxidized copper, immediately after reduction from the copper complex, is deposited on the surface of the copper particles, the electrical properties of the conductive path are good.

[0035] Specifically, the copper sintered body formed by the copper paste of the present invention can exhibit good volume resistivity due to conductive paths formed by the deposition of reduced copper on copper particles.

[0036] The mass ratio of the second copper particles to the copper complex is not particularly limited, but can be appropriately selected depending on the application of the copper sintered body. For example, the mass ratio can be set to 95:5 to 5:95.

[0037] (Other ingredients) The copper paste of the present invention may contain an organic solvent. The organic solvent is not particularly limited, but examples include hydrocarbon solvents, alcohol solvents, ketone solvents, ester solvents, ether solvents, glycol solvents, glyme solvents, halogen solvents, aromatic solvents, and heterocyclic solvents. More specifically, as alcohols, methanol, ethanol, propanol, butanol, pentanol, etc. can be used, and as glycols and ethers, ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, diethylene glycol, dipropylene glycol, triethylene glycol, diethylene glycol monoethyl ether, dipropylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol dimethyl ether, diethylene glycol monobutyl ether, etc. can be used. In addition, glycerin, diethylene glycol monobutyl acetate, dimethylacetamide, diacetone alcohol, etc. can be used.

[0038] Furthermore, additives such as adhesion promoters, surface modifiers, defoamers, rheology control agents, and reducing agents such as ascorbic acid, formic acid, and oxalic acid can be included in the copper paste.

[0039] <Viscosity of copper paste>

[0040] The copper paste of the present invention may have a shear viscosity of 1.0 Pa·s to 1000.0 Pa·s at a shear rate of 0.1 / s, and may have a shear viscosity of 1.0 Pa·s to 100.0 Pa·s or 5.0 Pa·s to 70.0 Pa·s at a shear rate of 10 / s.

[0041] These values ​​serve as a guideline for the printing characteristics of copper paste intended for screen printing. When screen printing with copper paste, i.e., when the shear rate is high, it is important that the copper paste exhibits excellent fluidity like a liquid, which improves screen penetration. After the copper paste has penetrated the screen and the shear rate is slow, it is important that it exhibits solid-like behavior to maintain the printed shape. The above numerical ranges can satisfy these characteristics.

[0042] <Method for manufacturing copper paste> The method for producing the copper paste of the present invention is not particularly limited, but for example, the copper paste can be produced by the following method.

[0043] (Manufacturing of copper complex inks) As raw materials for copper complex inks, powdered Cu(HCOO)2·4H2O and liquid 2MAE can be used. Since 2MAE coordinates to Cu(HCOO)2 in two molecules, the molar ratio when mixing them is preferably Cu(HCOO)2·4H2O:2MAE = 1:2, and this molar ratio is acceptable in the range of 1:1.8 to 2.2. The powdered Cu(HCOO)2·4H2O and 2MAE can be stirred in the following stirring step.

[0044] (Grinding process) Cu(HCOO)2·4H2O can absorb moisture from the atmosphere, increasing in weight and sometimes agglomerating to form lumps. Therefore, to facilitate the mixing of raw materials by crushing these lumps, a crushing step of crushing the Cu(HCOO)2·4H2O powder may be included before the stirring step described later.

[0045] (Agitation process) Liquid 2MAE is placed in a container and stirred with a hot stirrer at 40°C and 500 rpm. Cu(HCOO)2·4H2O after the grinding process is then added and stirring is continued. After stirring for 24 hours, the stirring conditions are changed to 25°C and 100 rpm and stirred for a total of 96 hours to produce Cu-MAE as a copper complex. Alternatively, ethylene glycol or the like may be used as a solvent, and additives such as surfactants like amines may be used to stabilize the polyoxyethylene(2)alkyl(C14-C18)amine-based complex colloid.

[0046] Furthermore, when producing copper complexes, the mixing equipment and mixing conditions in the stirring process can be set as appropriate.

[0047] Copper complex inks are exemplified by those containing a colloid formed by the aggregation of micelles of a copper complex represented by (HCOO)2Cu(2MAE)2, and ethylene glycol in which the colloid is dispersed. Immediately after synthesis, copper complex inks consist of micelles (i.e., colloidal particles), and multiple micelles aggregate via water molecules to form a large colloid, which may then be dispersed in ethylene glycol. The micelles of the colloid dispersed in ethylene glycol can be reduced in size and stabilized by the use of a surfactant.

[0048] It is preferable to add a dehydration step after the stirring step to the copper complex ink, in which the resulting mixture is dehydrated under reduced heat. However, the dehydration step may also be added during the weighing and stirring of each component before the stirring step, in which the mixture is dehydrated under reduced heat. This yields a copper amine formate complex ink with excellent wettability with SiC crystals. Alternatively, by pre-mixing ethanol, which is compatible with water, with copper formate hydrate, the ethanol and water can be removed by azeotropic distillation.

[0049] The method of dehydration is not particularly limited, but a specific method involves transferring about 10 ml of the mixture into a round-bottom flask, heating and stirring the flask portion with 40°C warm water using an evaporator, and then placing it under reduced pressure in an aspirator for about 30 minutes to azeotropically dehydrate the alcohol and obtain a copper complex ink.

[0050] (Manufacturing of copper paste) For example, copper paste can be produced by placing the manufactured copper complex ink, copper particles, and ethylene glycol into a container and mixing them using a rotary mixer or the like. The amounts of copper particles and organic solvents can be adjusted as needed.

[0051] Furthermore, copper paste can be manufactured using the same procedure even when ligands other than 2MAE are coordinated to copper to form a complex.

[0052] [Method for manufacturing copper sintered bodies] The method for producing a copper sintered body according to the present invention includes a sintering step of heating the copper paste of the present invention to sinter the copper paste.

[0053] <Sintering process> The purpose of the sintering process is to volatilize ligands such as formic acid and 2MAE from the copper complex, and water if it is inevitably present in the paste, thereby sintering the copper particles. For example, one possible processing condition is to heat the copper paste to 180°C to 250°C. Sintering may also be performed by holding the heating within this temperature range for 5 to 30 minutes. Furthermore, the heating conditions from room temperature to 180°C to 250°C can be arbitrarily selected, for example, by setting it to 0.5°C to 20°C / minute. In addition, after heating, the sintered film may be cooled to room temperature by air cooling or other means.

[0054] Furthermore, since a lower heating temperature reduces the impact on the substrate being processed, it is preferable to be able to sinter at a lower temperature.

[0055] To prevent the film before and after sintering from being affected by oxygen in the air during the heating, warming, and cooling processes, heating, warming, and cooling may be carried out in an inert atmosphere such as argon gas or nitrogen gas (oxygen concentration of, for example, 50 ppm), or in a mixed gas atmosphere of nitrogen gas mixed with 3% to 5% hydrogen gas.

[0056] <Coating process> The method for manufacturing a copper sintered body of the present invention may include a coating step of applying the copper paste of the present invention to a substrate before the sintering step. For example, the copper paste can be printed onto a coating target such as an electronic substrate including an alumina substrate, copper substrate, polyimide film, PET film, PEN film, glass, etc., by screen printing, inkjet printing, gravure printing, gravure offset printing, dispenser, spin coating, bar coater, etc.

[0057] <Drying process> The method for manufacturing a copper sintered body of the present invention may include a step of drying the copper paste after the coating step. Performing a drying step before the sintering step can stabilize the shape of the coating film obtained by applying the copper paste. The drying conditions are not particularly limited, but for example, drying at 80°C to 120°C, which is the temperature at which the crystal water of copper formate evaporates, can be used. The drying time is not particularly limited, but depending on the amount of copper paste applied, for example, it can be about 1 to 30 minutes, and drying for 5 minutes or more is more preferable.

[0058] (Other processes) The method for producing a copper-nickel sintered film according to the present invention may include other steps in addition to the steps described above. For example, a step of processing the copper sintered body into a specific shape may be included.

[0059] [Copper sintered body] The copper sintered body of the present invention can be manufactured, for example, by the method for manufacturing the copper sintered body of the present invention described above. The copper sintered body can be used, for example, as a die attach material to bond a copper substrate to a SiC chip. In addition to transferring and dissipating the heat generated by the SiC chip during operation to the substrate, the die attach material also absorbs the difference in the coefficients of linear expansion (and the resulting strain) between the two materials caused by heating and cooling.

[0060] Furthermore, copper sintered bodies can be used in applications where conductivity is required for heat-treated films such as metal wiring, and their shape and thickness can be arbitrarily set. For example, copper sintered bodies with line widths of approximately 30 μm to 2 mm can be formed by screen printing, and line widths of 2 mm or more are also possible, allowing copper sintered bodies of any line width to be formed as copper wires.

[0061] The copper sintered body of the present invention has conductive paths formed by copper particles and copper reduced from a copper complex. By sintering a combination of first copper particles with a large average particle size and second copper particles with a smaller average particle size, the film thickness can be set to a wide range from 1 μm to 2 mm.

[0062] Furthermore, the initial volume resistivity R0 of the copper sintered body of the present invention is 5 to 200 μΩ·cm. Within this range, a sufficient current can be stably passed through the copper sintered body. However, if R as a resistance value is large, the copper sintered body itself becomes a resistor, posing a risk of overheating. To prevent this, R can be reduced by increasing the thickness of the copper sintered body to increase its cross-sectional area. However, for flexible use of the copper sintered body, there are limitations on thickness due to issues such as the strength of the copper sintered body. From this perspective as well, R0 is set within the range of 5 to 200 μΩ·cm. [Examples]

[0063] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited in any way by the examples.

[0064] [Raw materials used] Copper tetrahydrate ((HCOO)2Cu·4H2O) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 2-methylaminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.), ethanol, ethylene glycol (both manufactured by Nacalai Tesque Co., Ltd.), and polyoxyethylene (2)alkyl(C14-C18)amine (manufactured by Kao Corporation: Amito 302) were used. In addition, branched electrolytic copper powder with a number average particle size of 10 μm (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., FCC-SP-99) was used as the first copper particle, and wet-process reduced copper powder with a number average particle size of 0.45 μm (manufactured by Sumitomo Metal Mining Co., Ltd., Polyol Copper Powder UCP030) was used as the second copper particle.

[0065] [Preliminary Examination] First, a copper powder ethylene glycol mixture was produced without using a copper complex, and the performance of the volume resistivity due to the difference in the mass ratio of the first and second copper particles was verified.

[0066] <Manufacturing of copper powder ethylene glycol mixture> A total of 10 g (approximately 1.12 ml by volume) of first-order copper particles and second-order copper particles were weighed into a container, and 1.2 g (approximately 1.1 ml by volume) of ethylene glycol was added and stirred to obtain a copper powder ethylene glycol mixture. The mass ratio of first-order copper particles to second-order copper particles was set to 100:0, 70:30, 60:40, and 0:100. Although the polyol copper powder used as the second-order copper particles has excellent affinity with ethylene glycol and therefore does not require a dispersant, a dispersant may be added if other commercially available copper powders are used as the second-order copper particles. A self-rotating mixer (Sinky Co., Ltd., Self-rotating mixer ARE-310) was used as the stirrer.

[0067] Four types of copper powder ethylene glycol mixtures were prepared and coated onto alumina substrates to a thickness of 100 μm and an area of ​​10 mm × 5 mm. These were heated in nitrogen gas (oxygen concentration 50 ppm or less) at 240°C for 1 hour to obtain calcined samples. The volume resistivity of these calcined samples was then measured using the four-terminal method. The measurement results are shown in Figure 2.

[0068] As shown in Figure 2, the calcined sample with a mass ratio of first copper particles to second copper particles of 60:40 showed the lowest volume resistivity of 120 μΩcm. This is presumed to be the result of an optimized volume ratio of first and second copper particles, where the second copper particles filled in between the first copper particles, increasing the necking amount and lowering the volume resistivity.

[0069] Based on these results, in Example 1 below, the mass ratio of copper powder was set to 60:40 for the first copper particles and 60:40 for the second copper particles. A copper complex was then added to prepare a copper complex ink, after which a calcined sample was prepared, and the calcination temperature and volume resistivity were measured.

[0070] [Example 1] <Manufacturing of copper complex ink> 5.00 g of copper tetrahydrate hexahydrate and 1.00 g of ethylene glycol were placed in a container and mixed. The mixing was performed at room temperature (25°C) using a stirrer (Sinky Co., Ltd. ARE-310 self-rotating mixer).

[0071] 4.47 g of 2-methylaminoethanol was added to the above container, and these were further mixed to synthesize (HCOO)2Cu(2MAE)2, obtaining a dispersion in which a colloid of aggregated copperamine (Aco) formate complex micelles was dispersed in ethylene glycol. Mixing was performed at room temperature (25°C) using a stirrer (Sinky Co., Ltd., self-rotating mixer ARE-310).

[0072] 2.00 g of ethanol and 0.02 g of polyoxyethylene(2)alkyl(C14-C18)amine were added to the above container to obtain an ethylene glycol dispersion. Mixing was performed at room temperature (25°C) using a stirrer (ARE-310, manufactured by Thinky Co., Ltd.).

[0073] <Dehydration process> The above dispersion was transferred from the container to a round-bottom flask, and water and ethanol were azeotropically dissolved using an evaporator. The mixture was thoroughly dehydrated until no further evaporation was observed, yielding the copper complex ink of Example 1. Figure 1 shows the appearance of the copper complex ink and the structural formula of the copper complex.

[0074] <Manufacturing of copper paste> Six g of first-order copper particles (approximately 0.67 ml by volume) and four g of second-order copper particles (approximately 0.45 ml by volume) were weighed into a container, and 1.2 g of ethylene glycol (approximately 1.1 ml by volume) was added and stirred to obtain a copper powder ethylene glycol mixture. The mass ratio of first-order copper particles to second-order copper particles was set to first-order copper particles:second-order copper particles = 60:40. A self-rotating mixer (Sinky Co., Ltd., Self-rotating mixer ARE-310) was used as the stirrer.

[0075] To the above copper powder ethylene glycol mixture, 0.33 ml of copper complex ink (approximately 60 vol% of copper amine formate complex = 0.2 ml) was added, and the mixture was further processed in a rotary mixer to obtain the copper paste of Example 1. The mass ratio of copper particles to copper complex was set to copper particles:copper complex = 20:1, and the mass ratio of second copper particles to copper complex was set to second copper particles:copper complex = 8:1.

[0076] Multiple test specimens were prepared by coating an alumina substrate with the copper paste from Example 1 to a thickness of 100 μm and an area of ​​10 mm × 5 mm. These test specimens were heated in nitrogen gas (oxygen concentration of 50 ppm or less) at 150°C, 200°C, 250°C, and 310°C for 30 minutes to obtain fired samples. The volume resistivity of these samples was measured using the four-terminal method. The measurement results are shown in Figure 3.

[0077] [Comparative Example 1] In Comparative Example 1, the first copper particles and copper complex were not used, and the second copper particles were used to produce a copper powder ethylene glycol mixture. A calcined sample was then prepared using this mixture, and the volume resistivity was measured in the same manner as in Example 1. The heating temperatures of the test specimens were 200°C, 250°C, and 310°C. The measurement results are shown in Figure 3.

[0078] <Manufacturing of copper powder ethylene glycol mixture> 10 g (approximately 1.1 ml by volume) of copper particles were weighed into a container, and 1.2 g (approximately 1.1 ml by volume) of ethylene glycol was added and stirred to obtain a copper powder ethylene glycol mixture. A self-rotating mixer (Sinky Co., Ltd., ARE-310) was used as the stirrer.

[0079] [Comparative Example 2] In Comparative Example 2, a copper complex was not used. Instead, a conductive paste was prepared using first and second copper particles, and a fired sample was prepared using this paste. The volume resistivity was measured in the same manner as in Example 1. The measurement results are shown in Figure 3.

[0080] <Manufacturing of copper paste> Six g (approximately 0.67 ml by volume) and four g (approximately 0.45 ml by volume) of second-order copper particles were weighed into a container, and 1.2 g (approximately 1.1 ml by volume) of ethylene glycol was added and stirred to obtain a copper powder ethylene glycol mixture. The mass ratio of first-order copper particles to second-order copper particles was set to first-order copper particles:second-order copper particles = 60:40. A self-rotating mixer (Sinky Co., Ltd., Self-rotating mixer ARE-310) was used as the stirrer.

[0081] Table 1 shows the copper paste formulations for Example 1, Comparative Examples 1 and 2, as well as the volume resistivity of the fired samples, the shear viscosity of the copper paste, and the measurement results of the fired samples.

[0082] [Table 1]

[0083] [result] Focusing on sintering sufficient for electrical conductivity, and comparing the volume resistivity measurements of Example 1 and Comparative Examples 1 and 2, particularly those in the 10⁻⁴ Ωcm range, it was found that adding a copper complex could lower the sintering temperature of the copper particles by approximately 50°C. Furthermore, comparing the volume resistivity at each firing temperature, Example 1, which used a copper complex, showed reduced volume resistivity, suggesting an improvement in the heat dissipation performance required for die attach materials.

[0084] Preliminary test results showed that the sinterability of branched electrolytic copper powder (first copper particles) could be improved by mixing it with wet-process reduced copper powder (second copper particles), which also exhibits excellent sinterability.

[0085] Furthermore, the results from Example 1 suggest that by using two types of copper particles of different sizes in combination with a copper complex, low-temperature sintering of copper sinter material becomes possible, and the present invention is expected to contribute to improving the bonding strength and heat dissipation of substrates and the like.

Claims

1. Copper particles and It contains a copper complex, The copper particles include first copper particles with a number-average particle diameter D1 of 0.2 μm to 50 μm and second copper particles with a number-average particle diameter D2 of 0.1 μm to 5 μm. The number-average particle diameters of the first copper particles and the second copper particles are D1 > D2. The mass ratio of the first copper particle to the second copper particle is 95:5 to 5:

95. A copper paste in which the mass ratio of the second copper particles to the copper complex is 95:5 to 5:

95.

2. The copper paste according to claim 1, wherein the copper particles include at least one of spherical particles and branched particles.

3. The copper paste according to claim 1, wherein the copper particles include particles whose surface is coated with an organic film.

4. The copper complex is Cu(HClO) ２ (2MAE) ２ The copper paste according to claim 1, comprising a complex represented by , wherein the 2MAE is 2-(methylamino)ethanol.

5. The copper paste according to claim 1, wherein the shear viscosity at a shear rate of 0.1 / s is 1.0 Pa·s to 1000.0 Pa·s, and the shear viscosity at a shear rate of 10 / s is 1.0 Pa·s to 100.0 Pa·s.

6. A method for producing a copper sintered body, comprising a sintering step of heating the copper paste described in claim 1 to sinter the copper paste.

7. The method for manufacturing a copper sintered body according to claim 6, wherein the sintering step is a step of sintering the copper paste by heating it at 180°C to 250°C.

8. The film thickness is 1 μm to 2 mm. Initial volume resistivity R ０ This is a copper sintered body with a resistance of 5 to 200 μΩ·cm.

Images