JP2017157329A - Copper paste and manufacturing method of sintered body of copper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper paste having a high bond strength with an article to be joined.SOLUTION: A copper paste contains a copper powder and a liquid medium. The liquid medium is a polymer compound having an ether bond and can develop a reduction action at a temperature when sintering the copper paste. Copper particles constituting the copper powder have an average particle size of primary particles thereof of 0.03 μm or larger and 1.0 μm or smaller, and have a crystallite size of a (111) plane of 50 nm or smaller. The liquid medium preferably has a boiling temperature higher than the temperature where the reduction action is developed.SELECTED DRAWING: None

Description

  The present invention relates to a copper paste. Moreover, this invention relates to the manufacturing method of the sintered compact of copper using this copper paste.

  Various pastes containing metal powder or metal oxide powder and an organic solvent are known. For example, Patent Document 1 describes a conductive paste containing silver particles having an average particle diameter of 0.1 μm to 15 μm and alcohol. As the alcohol, a lower alcohol is used, or a lower alcohol having one or more substituents selected from the group consisting of lower alkoxy, amino and halogen. This document describes that this conductive paste has a low electric resistance without using an adhesive.

  A paste containing metal powder or metal oxide powder may be used not only as a conductive material but also as an alternative material for solder. For example, in recent years, semiconductor devices called power devices have been actively used as power conversion / control devices such as inverters. Unlike an integrated circuit such as a memory or a microprocessor, a power device is for controlling a high current, so that the amount of heat generated during operation becomes very large. Therefore, heat resistance is required for the solder used for mounting the power device. However, lead-free solder, which is widely used nowadays, has a drawback of low heat resistance. In view of this, various techniques have been proposed for producing sintered films by using metal particles instead of solder and applying them to an object by various coating means. For example, Patent Document 2 proposes a method of manufacturing a metallic copper film by forming a liquid composition containing copper oxide particles on a substrate and heating the composition while supplying formic acid gas.

JP 2009-170277 A JP 2011-238737 A

  Pastes that have been proposed so far as solder substitute joint materials have higher heat resistance than solder, but still have room for improvement in terms of joint strength with objects to be joined. In the case of solder, there is a possibility of remelting when exposed to a high temperature after joining. Accordingly, an object of the present invention is to provide a paste having a high bonding strength with an object to be bonded.

The present invention is a copper paste containing copper powder and a liquid medium,
The liquid medium is a polymer compound having an ether bond, and can exhibit a reducing action at a temperature at which the copper paste is sintered.
The copper particles constituting the copper powder provide a copper paste having an average primary particle size of 0.03 μm or more and 1.0 μm or less and a crystallite size of (111) plane of 50 nm or less. is there.

  Moreover, this invention provides the manufacturing method of the sintered compact of copper which has the process of attaching | subjecting the said copper paste to the baking process heated at the temperature of 100 degreeC or more and 350 degrees C or less, and forming a copper sintered compact. Is.

  According to the present invention, a copper paste having high bonding strength with an object to be bonded is provided. Therefore, this copper paste is suitable as a substitute material for solder.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The copper paste of the present invention contains copper powder and a liquid medium as its constituent components. In this specification, copper powder includes both pure copper powder and copper-based alloy powder. The copper powder contained in the copper paste may be pure copper powder, copper-based alloy powder, or a mixed powder of pure copper powder and copper-based alloy powder. The copper powder contained in the copper paste may be a mixed powder of two or more kinds of copper powders having different characteristics. Examples of the copper powder having different characteristics include two or more types of copper powders having different particle shapes, and two or more types of copper powders having the same shape but different average particle diameters. Furthermore, the copper paste may contain a small amount of metal powder other than copper powder within the range not impairing the effects of the present invention.

  The copper powder contained in the copper paste preferably has a particle size in the submicron order range of 0.03 μm to 1.0 μm. By setting the particle size of the particles to 1.0 μm or less, when the copper paste of the present invention is sintered, the bonding strength between the sintered body and the bonded body is easily improved. Moreover, it is hard to produce a space | gap between particle | grains and can reduce the specific resistance of a sintered compact. On the other hand, by setting the particle size of the particles to 0.03 μm or more, the particles can be prevented from shrinking when the copper paste of the present invention is fired. From these viewpoints, the particle size is more preferably 0.05 μm or more and 0.75 μm or less, and further preferably 0.075 μm or more and 0.5 μm or less. In the present invention, the particle size of the copper powder is the average particle size of the primary particles. Specifically, the ferret diameters of a plurality of particles measured using an observation image by a scanning electron microscope are expressed in a sphere. It is the volume average particle diameter converted. The specific value can be measured by the measurement method described in Examples described later.

  The copper powder contained in the copper paste is a polycrystal composed of a collection of fine crystals in addition to the particle size of the particles being in the submicron order as described above, and the copper paste containing the copper powder. Is preferable because the bonding strength between the sintered body and the joined body is easily improved. The degree of crystallinity of the copper particles can be evaluated using the crystallite size as a scale. Specifically, the crystallite size of the copper particles constituting the copper powder is preferably such that the (111) -plane crystallite size is 50 nm or less, more preferably 45 nm or less, and 40 nm or less. Even more preferred. The lower limit of the crystallite size is preferably 10 nm. By setting the crystallite size within this range, it is possible to easily improve the bonding strength between the sintered body and the bonded body when the copper paste containing the copper powder is sintered. The crystallite size of the copper powder is measured by performing X-ray diffraction measurement of the copper powder using, for example, Ultimate IV manufactured by Rigaku Corporation. The crystallite size (nm) is calculated by the Scherrer method using the (111) peak obtained by the measurement.

  The copper particles constituting the copper powder contained in the copper paste may be provided with an organic surface treatment agent on the surface thereof. An organic surface treating agent is an agent for suppressing aggregation between copper particles. What is suitably used in the present invention as an agent for suppressing aggregation between copper particles is, for example, various fatty acids, aliphatic amines, and complexes having adsorptivity to copper. In particular, it is preferable to use a saturated or unsaturated fatty acid or aliphatic amine having 6 to 18 carbon atoms, particularly 10 to 18 carbon atoms, from the viewpoint of improving the bonding strength. Specific examples of such fatty acids or aliphatic amines include benzoic acid, pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, oleic acid, stearic acid, pentylamine, hexylamine, Examples include octylamine, decylamine, laurylamine, oleylamine, stearylamine and the like. Examples of the complex having an adsorptivity to copper include amino acids such as glycine and dimethylglyoxime. These fatty acids, aliphatic amines, and complexes can be used singly or in combination of two or more.

When carrying out organic surface treatment, it can give to the particle | grain surface by mixing copper powder and this organic surface treating agent in the post process of copper powder manufacture, for example. The amount of the organic surface treatment agent applied is such that the ratio of the organic surface treatment agent to the powder in the state where the organic surface treatment agent has been applied is 0.1 mass% or more and 5.50 mass% or less in terms of carbon atoms It is preferable that By setting the ratio of the organic surface treatment agent to 0.1% by mass or more in terms of carbon atoms, the bonding strength can be significantly improved. Moreover, by setting it as 5.50 mass% or less, joining strength can be improved, avoiding extreme shrinkage. From the viewpoint of making these effects more remarkable, the ratio of the organic surface treatment agent is more preferably 0.1% by mass or more and 5.50% by mass or less in terms of carbon atoms, and more preferably 0.15% by mass or more. It is more preferable to set it as 5.00 mass% or less, and it is still more preferable that it is 0.2 mass% or more and 4.50 mass% or less. The ratio of the organic surface treating agent applied to the surface of the copper particles can be measured as follows. Heating 0.5 g of copper powder in an oxygen stream with a carbon / sulfur analyzer (Horiba, EMIA-320V) to decompose the carbon content of the powder into CO or CO ₂ and quantify the amount. Can be measured.

  The copper particles constituting the copper powder can take various shapes depending on the method for producing the copper powder. The copper particles can be spherical, for example. Alternatively, it may be a polyhedron such as a hexahedron or an octahedron. Furthermore, it may be flaky (plate-like). Copper powder may be comprised only from the particle | grains of 1 type of these shapes, or may be comprised from the combination of the particle | grains of 2 or more types of shapes. For example, copper powder can be comprised from the mixture of the copper powder A comprised from spherical particle | grains, and the copper powder B comprised from flake shaped particle | grains. Alternatively, copper powder is composed of copper powder A composed of spherical particles having an average primary particle diameter A and copper powder composed of spherical particles having an average primary particle diameter B (A ≠ B). It can consist of a mixture with B. In any case, (i) both the copper powder A and the copper powder B may have the above-described particle diameter and the above-described crystallite size, or (b) copper. Only one of the powder A and the copper powder B may have the particle size described above and the crystallite size described above. In the case of (b), the ratio of the copper powder having the above-mentioned particle size and the above-mentioned crystallite size in the entire copper powder is preferably 1% by mass or more and 99% by mass or less, and 10% by mass. % To 90% by mass, more preferably 30% to 70% by mass.

  The copper powder contained in the copper paste should have less residual organic matter inside the copper powder. When there is a large amount of residual organic matter inside the copper powder, the sintering may not proceed easily, or the bonding strength may be lowered due to gas generation after sintering. The amount of residual organic matter inside the copper powder can be measured by the following method. Copper powder is heated from room temperature to 1000 ° C. in a He atmosphere using TG-MS (TG-DTA Rigaku Thermoplus TG8120, MS Shimadzu GCMS-QP2010Plus). The amount of residual organic matter can be measured by measuring the amount of gas generated in a high temperature region such as 650 ° C. In the copper powder used in the present invention, the peak top intensity derived from the compound ion gas consisting of carbon atoms, oxygen atoms, hydrogen atoms, nitrogen atoms, etc. generated from 1 mg of the sample at 650 ° C. or higher is the maximum peak in the spectrum. It is desirable that it is 10% or less of the top strength. The peak top intensity is the intensity (peak height) when the baseline is 0.

  The copper powder contained in the copper paste is preferably produced by the method described below. That is, in this production method, in the reduction of wet copper ions using hydrazine as a reducing agent, water or an organic solvent that is compatible with water and can reduce the surface tension of water is used. . Specifically, in this production method, a reaction liquid containing water and the organic solvent as a medium and containing a monovalent or divalent copper source is mixed with hydrazine, and the copper source is reduced to obtain copper particles. Is generated.

  Examples of the organic solvent include monohydric alcohols, polyhydric alcohols, polyhydric alcohol esters, ketones, ethers, and the like. As the monohydric alcohol, those having 1 to 5 carbon atoms, particularly 1 to 4 carbon atoms are preferable. Specific examples include methanol, ethanol, n-propanol, isopropanol, t-butanol and the like.

  Examples of the polyhydric alcohol include diols such as ethylene glycol, 1,2-propylene glycol and 1,3-propylene glycol, and triols such as glycerin.

  Examples of the ester of the polyhydric alcohol include the fatty acid ester of the polyhydric alcohol described above. As the fatty acid, for example, a monovalent fatty acid having 1 to 8 carbon atoms, particularly 1 to 5 carbon atoms is preferable. The ester of the polyhydric alcohol preferably has at least one hydroxyl group.

  As the ketone, an alkyl group bonded to a carbonyl group having 1 to 6 carbon atoms, particularly 1 to 4 carbon atoms is preferable. Specific examples of the ketone include methyl ethyl ketone and acetone.

  Examples of the ether include dimethyl ether, ethyl methyl ether, diethyl ether, cyclic compounds such as octacene, tetrahydrofuran, and tetrahydropyran, and polyethers such as polyethylene glycol and polypropylene glycol.

  Of the various organic solvents described above, it is preferable to use a monohydric alcohol from the viewpoints of economy and safety.

  In the medium, the ratio of the mass of the organic solvent to the mass of water (the mass of the organic solvent / the mass of water) is preferably from 1/99 to 90/10, and more preferably from 1.5 / 98.5. 90/10. When the ratio of water and organic solvent is within this range, the surface tension of water during wet reduction can be reduced moderately, and copper powder having a particle size and crystallite size suitable for the present invention can be easily obtained. be able to. The medium preferably consists only of the organic solvent and water.

  In this production method, a reaction solution is prepared by dissolving or dispersing a copper source in the medium. Examples of the method for preparing the reaction solution include a method in which a medium and a copper source are mixed and stirred. In the reaction solution, the ratio of the medium to the copper source is such that the mass of the liquid medium is preferably 2 g or more and 2000 g or less, more preferably 4 g or more and 1000 g or less with respect to 1 g of the copper source. It is preferable for the ratio of the medium to the copper source to be within this range because the productivity of copper powder synthesis is high.

  As the copper source, various monovalent or divalent copper compounds can be used. In particular, it is preferable to use copper chloride, copper acetate, copper hydroxide, copper sulfate, copper oxide, or cuprous oxide. When these copper compounds are used as a copper source, a copper powder having a particle size suitable for the present invention can be easily obtained. Moreover, copper powder with few impurities can be obtained.

  Next, the reaction solution and hydrazine are mixed. The amount of hydrazine added is preferably 0.5 to 50 mol, more preferably 1 to 20 mol with respect to 1 mol of copper. When the amount of hydrazine added is within this range, a copper powder having a particle size and crystallite size suitable for the present invention can be easily obtained. For the same reason, the temperature of the reaction solution is preferably maintained at 30 ° C. or higher and 90 ° C. or lower, particularly 40 ° C. or higher and 70 ° C. or lower, from the mixing start point to the end point. Furthermore, for the same reason, it is preferable to continue stirring of the reaction solution from the start of mixing to the end of reaction.

The reaction solution and hydrazine are preferably mixed as in any of the following (a) and (b). By doing so, it is possible to effectively prevent inconvenience caused by a rapid reaction.
(A) Hydrazine is added to the reaction solution a plurality of times at intervals.
(B) Hydrazine is continuously added to the reaction solution over a predetermined time.
In the case of (a), the plurality of times is preferably about 2 times or more and 9 times or less. The interval between the additions of hydrazine is preferably about 5 minutes to 90 minutes.
In the case of (b), the predetermined time is preferably about 1 minute to 180 minutes. The reaction solution is preferably aged by continuing stirring even after mixing with hydrazine is completed. By doing so, it is easy to obtain a copper powder having a particle size suitable for the present invention.

  In this production method, it is preferable to use only hydrazine as the reducing agent because copper powder with less impurities can be obtained.

  The copper powder thus obtained (that is, the copper powder before the surface treatment) can be subjected to a surface treatment with an organic surface treatment agent after washing by a decantation method or the like. The surface treatment can be performed as follows, for example. That is, an organic solvent compatible with water in a 5.0 to 50.0 mass% copper powder water slurry having a conductivity of 2.0 mS or less, heated to the melting point of the organic surface treatment agent or higher (for example, 25 to 70 ° C). Surface treatment can be performed by instantly adding the surface treatment agent dissolved in and then stirring for 1 hour. By setting the slurry conductivity to 2.0 mS or less, the surface treatment can be performed while the copper powder in the slurry is uniformly dispersed without agglomeration. In addition, by increasing the temperature during the treatment above the melting point of the surface treatment agent and adding the organic surface treatment agent instantly, it becomes possible to uniformly treat the surface while preventing the organic surface treatment agent from solidifying. . By passing through the above process, the adsorption amount to the copper powder can be controlled.

  Next, the liquid medium used with the copper powder described so far will be described. The liquid medium used in the present invention can exhibit a reducing action at the temperature at which the copper paste of the present invention is sintered. By using a liquid medium that can exhibit a reducing action, it is possible to improve the bonding strength between the sintered body generated by sintering the copper paste and the bonded portion. Whether or not the liquid medium has developed a reducing action can be confirmed by the following method. That is, a paste made of cuprous oxide and the liquid medium is applied to a glass substrate and subjected to heat treatment. The mass% of copper in the entire cuprous oxide used in the paste before the heat treatment and the mass% of copper in the mass of the entire coating film after the heat treatment are measured, and the mass of the copper before the heat treatment. If the mass% of copper after the heat treatment is larger than%, it is determined that the liquid medium has developed a reducing action at the heating temperature. The mass% of copper can be calculated based on measurement results such as fluorescent X-ray and ICP emission spectroscopic analysis. The proportion of cuprous oxide contained in the paste used here is 80% by mass, and the proportion of the liquid medium is 20% by mass.

  In particular, the liquid medium preferably has a boiling point higher than the temperature at which the reducing action is exhibited. This makes it possible to give a reducing action to the copper powder while the liquid medium remains in a liquid state. In relation to this, it is preferable that the liquid medium is capable of exhibiting a reducing action at 100 ° C. or higher and 300 ° C. or lower, particularly 125 ° C. or higher and 290 ° C. or lower, especially 150 ° C. or higher and 280 ° C. or lower. It is preferable that it can be expressed. This temperature range correlates with a preferable sintering temperature range of the copper paste of the present invention. The liquid medium is preferably one that can exhibit a reducing action at a temperature lower than the temperature at which the copper paste is actually sintered.

  The liquid medium preferably has a boiling point of 100 ° C. or higher and 350 ° C. or lower in relation to the above-described temperature at which the reducing action can be exhibited. In particular, the boiling point is preferably within this range on condition that the boiling point is higher than the temperature at which the reducing action is exhibited. As a result, it is possible to effectively give a reducing action to the copper powder, and it is possible to improve the bonding strength between the sintered body generated by the sintering and the object to be bonded. From this viewpoint, the boiling point of the liquid medium is preferably 150 ° C. or higher and 325 ° C. or lower, and more preferably 175 ° C. or higher and 300 ° C. or lower.

  Examples of the liquid medium suitably used in the present invention include alkylene glycol polymers having various molecular weights (for example, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol), and polyalkylene glycol derivatives having various molecular weights (for example, Polyethylene glycol monomethyl ether). A liquid medium can be used individually by 1 type or in combination of 2 or more types. When two or more liquid media are used, it is sufficient that at least one liquid medium exhibits a reducing action, and the other liquid media may exhibit a reducing action, or may exhibit a reducing action. It may not be expressed. The ratio of the reducing solvent in the entire liquid medium is desirably 50% by mass or more.

  In particular, the liquid medium is preferably a compound having an ether bond (—C—O—C—). Such a compound can generate carbon monoxide by heating, and the generated carbon monoxide exhibits a reducing action. The ether bond is preferably in the main chain of the compound. From the viewpoint of efficient generation of carbon monoxide, polyalkylene glycol is preferably used as the liquid medium having an ether bond. Examples of the polyalkylene glycol include polyethylene glycol and polypropylene glycol. Among these, it is preferable to use polyethylene glycol from the point of high reduction action.

  When the above-described polyethylene glycol is used as the compound having an ether bond, the number average molecular weight of this substance is preferably 90 or more and 600 or less, more preferably 120 or more and 400 or less, and more preferably 180 or more and 400 or less. More preferably. By using polyethylene glycol having a molecular weight in this range, it is possible to improve the bonding strength between the sintered body produced by sintering the copper paste and the bonded portion. The number average molecular weight of the polyethylene glycol can be determined from the hydroxyl value obtained by the neutralization titration method described in JIS K0070 7.1.

  In the copper paste of the present invention, the mass ratio of the copper powder in the paste is preferably 50% by mass or more and 99% by mass or less, more preferably 60% by mass or more and 98% by mass or less, and 70% by mass. More preferably, it is 95% or less by mass. By mix | blending copper powder and a liquid medium in this ratio, the joint strength of the sintered compact obtained by sintering of a copper paste can be improved. Moreover, the handling property of the copper paste is improved.

  In addition to the above-described copper powder and liquid medium, the copper paste of the present invention may contain other components as necessary. Examples of other components include ionic surfactants, nonionic surfactants, silane coupling agents, titanium coupling agents, aluminum coupling agents, zirconia coupling agents, silicone resins, metal alkoxides, metal chelates, A thermoplastic resin, a thermosetting resin, a glass frit, etc. are mentioned. The total mass of the other components is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass or less based on the mass of the copper powder.

  The copper paste of the present invention is interposed between two objects to be bonded, and is subjected to a firing step in which the copper paste is heated to form a copper sintered body. The body can be joined. The sintered body formed in this manner joins two joined bodies with high strength. Further, the sintered body formed in this way has a high conductivity in addition to a high bonding strength. Therefore, such a sintered body can be used as a conductive material. For example, the copper paste of the present invention can be used as a conductive bonding material when a surface-mount electronic device is mounted on a printed wiring board. Or the copper paste of this invention can be used as a wiring material of a printed wiring board.

  The temperature at which the copper paste of the present invention is heated and subjected to the firing step is preferably 100 ° C. or higher and 350 ° C. or lower, and preferably 160 ° C. or higher and 325 ° C. or lower, although it depends on the material to be joined. Is more preferable, and 180 ° C. or higher and 300 ° C. or lower is even more preferable. By carrying out sintering in this temperature range, the bonding strength of the obtained sintered body can be sufficiently increased, and the conductivity can be sufficiently increased. In this range, the damage to the member tends to be suppressed as the firing temperature is lower, while the stronger joining state tends to be obtained as the firing temperature is higher. The firing temperature is preferably selected to be higher than the lowest temperature at which the liquid medium can exhibit a reducing action. The temperature rise profile may be one in which the temperature rises linearly with respect to time, or one in which the temperature rises in multiple steps (that is, stepwise) (see Example 5 described later). ).

  The atmosphere when the copper paste of the present invention is heated and subjected to the firing step may be an oxidizing atmosphere or a non-oxidizing atmosphere. Since the copper paste of the present invention contains a liquid medium that can exhibit a reducing action, sintering proceeds even in an oxidizing atmosphere. However, it is advantageous to use a non-oxidizing atmosphere from the viewpoint of further improving the bonding strength of the sintered body and further improving the conductivity. As the non-oxidizing atmosphere, for example, an inert atmosphere such as nitrogen, a reducing atmosphere such as formic acid or hydrogen, or a vacuum atmosphere can be used. Of these various non-oxidizing atmospheres, use of formic acid, hydrogen, or the like is preferable because the bonding strength of the sintered body is further improved and the conductivity is further improved. On the other hand, using an inert atmosphere such as nitrogen as the non-oxidizing atmosphere is advantageous from an industrial viewpoint such as economy and safety.

  Conventionally known metal paste-based bonding materials generally use a reducing atmosphere such as formic acid or hydrogen at the time of sintering, and exhibit sufficient bonding force unless a pressure of 10 MPa or more is applied. There wasn't. It was not easy to join even under an inert atmosphere such as nitrogen. On the other hand, when the copper paste of the present invention is used, not only in a reducing atmosphere but also in an inert atmosphere such as nitrogen, a relatively low pressure, for example, 0.4 MPa or less (including 0 MPa). Adequate bonding force is generated by pressure. Therefore, when a reducing atmosphere such as formic acid or hydrogen is used, sintering can be performed at a lower pressure than before. On the other hand, when an inert atmosphere such as nitrogen is used, bonding can be performed even under pressure conditions that could not be bonded so far. This is also advantageous in the design of the joining device.

  The joined body made of the sintered body thus formed has a joining strength of preferably 10 MPa or more, more preferably 15 MPa or more, and further preferably 18 MPa or more. The term “joint strength” as used herein refers to shear strength, and the measurement method thereof will be described in detail in Examples described later.

  Power devices that make use of the high-temperature characteristics of wide band gap semiconductors such as SiC are expected to become more efficient, smaller, and lighter in the future. Power supplies for automobiles, industrial power devices, and all next-generation power supplies It is expected to contribute to higher efficiency. The copper paste of the present invention greatly contributes to widely spreading these next-generation power devices throughout society.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
(1) Production of copper powder 5.0 liters of hot pure water and 5.0 liters of methanol were placed in a 36 liter stainless steel tank, and 2.5 kg of copper acetate was placed therein. The mixture was stirred at a liquid temperature of 40.0 ° C. for 30 minutes to dissolve copper acetate. Next, 150.0 g of hydrazine was added all at once in the liquid, and then stirring was continued for 30 minutes to produce cuprous oxide fine particles in the liquid. After 30 minutes, 1400.0 g of hydrazine was added all at once to the liquid, and stirring was continued for 60 minutes to reduce the cuprous oxide fine particles to copper fine particles. The aqueous copper fine particle slurry thus obtained was washed with a rotary filter until the conductivity reached 1.0 mS. The obtained copper powder 20% aqueous slurry was heated to 50 ° C., and a methanol solution in which 32 g of lauric acid was dissolved was added instantaneously and stirred for 1 hour. Thereafter, solid-liquid separation was performed by filtration. The obtained copper powder was vacuum dried to obtain an organic surface-treated copper powder. The average particle diameter and crystallite size of the primary particles of the obtained copper powder were measured by the method described above. The results are shown in Table 1 below.
(2) Preparation of copper paste The copper powder thus obtained was mixed with polyethylene glycol having a molecular weight of 300 and a boiling point of about 250 ° C. (hereinafter also referred to as “PEG”) to prepare a paste. . The blending ratio of both was as shown in Table 1. This polyethylene glycol exhibited a reducing action at 200 ° C.
(3) Production of sintered body A copper plate was used as the base material. The paste was applied on the substrate with an area of 16 cm ² and a thickness of 0.1 mm. The top was covered with another copper plate, and a pressure of 0.4 MPa was applied to the whole. Sintering was performed at 300 ° C. for 60 minutes in a nitrogen atmosphere. The shear strength of the obtained joined body was measured. The results are shown in Table 1 below. The shear strength was measured by the following method.

[Shear strength]
The shear strength of the obtained bonded body was evaluated using a universal bond tester (Dage4000 manufactured by Nordson Advanced Technology Co., Ltd.).

[Examples 2 and 3]
In Example 1, the ratio of the copper powder in the copper paste was changed as shown in Table 1. The rest was the same as in Example 1.

Example 4
In Example 1, the firing temperature was changed as shown in Table 1. The rest was the same as in Example 1.
Example 5
In Example 1, the firing profile was changed as shown in Table 1. The rest was the same as in Example 1.

Example 6
In Example 1, PEG having the molecular weight shown in Table 1 was used. The firing temperature was the temperature shown in Table 1. The rest was the same as in Example 1. This PEG expressed a reducing action at 200 ° C.

Example 7
In Example 1, the copper powder shown in Table 1 was used. The rest was the same as in Example 1. The copper powder is synthesized by the same method as in Example 7 of JP2012-117146A.

[Comparative Example 1]
In Example 1, the liquid medium shown in Table 1 was used. The ratio of the copper powder in the copper paste was set to the value shown in Table 1. The rest was the same as in Example 1. This liquid medium did not exhibit a reducing action at the sintering temperature.

[Comparative Example 2]
In Example 1, a copper powder having an average particle size and crystallite size of primary particles shown in Table 1 was used, and a PEG having a molecular weight shown in Table 1 was used. Furthermore, the firing temperature was set to the temperature shown in Table 1. The rest was the same as in Example 1. This copper powder is synthesized by the same method as in Example 3 of WO2015 / 122251.
[Comparative Example 3]
In Example 1, a copper powder having an average particle size and crystallite size of primary particles shown in Table 1 was used. The rest was the same as in Example 1. The copper powder is synthesized by the same method as in Example 4 of JP-A-2003-342621.
[Comparative Example 4]
In Example 1, a copper powder having an average particle size and crystallite size of primary particles shown in Table 1 was used. The rest was the same as in Example 1. The copper powder is synthesized by the same method as in Example 12 of JP2012-117146A.

  As is apparent from the results shown in Table 1, it can be seen that the sintered body produced using the copper paste of each example has high bonding strength. On the other hand, when the copper paste of Comparative Example 1 is used, the bonding strength is reduced because the solvent has volatilized before the copper powder is reduced and bonded due to the boiling point of the solvent being lower than the reduction temperature. It has become low. In the copper pastes of Comparative Examples 2, 3, and 4, the bonding strength was low because the copper powder in the paste was not sintered due to the large crystallite size.

Claims (11)

A copper paste containing copper powder and a liquid medium,
The liquid medium is a polymer compound having an ether bond, and can exhibit a reducing action at a temperature at which the copper paste is sintered.
The copper particles constituting the copper powder are copper pastes having an average primary particle size of 0.03 μm to 1.0 μm and a crystallite size of (111) plane of 50 nm or less.   The copper paste according to claim 1, wherein the liquid medium has a boiling point higher than a temperature at which a reducing action is exhibited.   The copper paste according to claim 1, wherein the liquid medium is capable of exhibiting a reducing action at 100 ° C. or more and 300 ° C. or less.   The copper paste according to any one of claims 1 to 3, wherein a mass ratio of the copper powder in the copper paste is 50% or more and 99% or less.   The copper paste as described in any one of Claims 1 thru | or 4 used as a joining material.   The copper paste according to any one of claims 1 to 4, which is used as a conductive material.   A copper sintered body having a step of forming a copper sintered body by subjecting the copper paste according to any one of claims 1 to 6 to a firing step of heating at a temperature of 100 ° C to 350 ° C. Manufacturing method.   The manufacturing method of Claim 7 which attaches | subjects to a baking process in non-oxidizing atmosphere.   The manufacturing method of Claim 8 which attaches | subjects to a baking process in nitrogen atmosphere or formic acid atmosphere.   The manufacturing method according to any one of claims 7 to 9, wherein the sintering is performed so that the bonding strength is 10 MPa or more.   A joined body comprising a sintered body obtained by the production method according to claim 7 and having a joining strength of 10 MPa or more.