Metal paste and method for manufacturing joined body

Abstract

To provide a metal paste capable of efficiently providing a joined body having reliability high in electrical and mechanical strength even when narrowed in pitch, and to provide a method for manufacturing the joined body.SOLUTION: A metal paste comprises metal particles and a solvent, and has a shear viscosity of 1 to 100 Pa_s, measured at a shear rate of 10 s-1 at 25°C, wherein a value (TI value) obtained by log-transforming a ratio of a shear viscosity measured at a shear rate of 0.1 s-1 and a shear viscosity measured at a shear rate of 1 s-1 is 0.7 to 1.0.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a metal paste and a method for producing a joint. [Background technology]

[0002] Solder joints are generally used for electrical connections in electronic devices, and in particular, the flip-chip method is widely used for electrical connections between semiconductor chips and semiconductor packages.

[0003] In recent years, with the increasing integration density of chips, flip chip technology using metal pillars has also been attracting attention. In such technology, for example, metal pillars are formed on a semiconductor chip, and the tips of the metal pillars are soldered to electrodes of a semiconductor package to connect the electrodes (for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Jonas Zurcher1 et al., "Nanoparticle Assembly and Sintering Towards All-Copper Flip Chip Interconnect", 2015 Electronic Components & Technology Conference, 2015, p.1115-1121 Summary of the Invention [Problem to be solved by the invention]

[0005] However, recently, with the miniaturization and high integration of chips, the pitch between metal pillars has been narrowing (hereinafter sometimes simply referred to as "narrow pitch"), making it difficult to ensure high reliability in terms of electrical and mechanical strength in electronic devices.

[0006] In particular, the narrower the pitch, the more likely it is that solder bridges will occur between metal pillars. Solder bridges can cause short circuits (electrical failures) between electrodes, and so need to be suppressed. On the other hand, if the viscosity of the metal paste applied to the metal pillar is increased or the amount applied (transferred amount) is reduced in order to suppress solder bridging, this can lead to poor transfer of the metal paste to the metal pillar (reduced transfer rate) and poor connection between the electrodes (poor electrical and / or mechanical strength connection).

[0007] In other words, there is a trade-off between the problem of electrode short-circuiting due to solder bridging that accompanies narrower pitches and the problems of poor transfer of metal paste and poor connection between electrodes. In particular, when the metal pillar spacing is narrowed to, for example, 40 μm or less, the above-mentioned problems become more pronounced, and it has been extremely difficult to efficiently obtain a bonded body having high reliability in terms of electrical and mechanical strength and with a high manufacturing yield.

[0008] Therefore, in order to achieve narrower pitches (metal pillar spacing of, for example, 40 μm or less), there is a demand for a metal paste and a method for producing a bonded body that can efficiently obtain a bonded body that has high reliability in terms of electrical and mechanical strength. In particular, there is a demand for a metal paste that can achieve both a high transfer rate and an appropriate amount of transfer in order to efficiently obtain a bonded body that has high reliability in terms of electrical and mechanical strength.

[0009] An object of the present disclosure is to provide a metal paste and a method for producing a bonded body, which can efficiently obtain a bonded body having high reliability in terms of electrical and mechanical strength, even when the pitch is narrowed. [Means for solving the problem]

[0010] The present disclosure includes the following aspects. [1] A metal paste comprising metal particles and a solvent, Shear rate 10 s at 25°C -1The shear viscosity measured is 1 to 100 Pa s. Shear rate 0.1s -1 Shear viscosity measured at 1s and shear rate -1 The metal paste has a logarithmic TI value (a ratio of the shear viscosity measured in the above step) of 0.7 to 1.0. [2] Step 1 of applying a metal paste onto a substrate to prepare a transfer film; A step 2 of contacting a metal pillar of a first bonded body having a metal pillar with the transfer film to transfer the metal paste to at least one surface of the metal pillar; A step 3 of contacting the metal paste transferred to the metal pillar with a second object to be joined; A method for producing a bonded body, comprising: The surface of the transfer film has a surface roughness Ra of 0.1 to 5 μm and a surface roughness Rz of 0.5 to 10 μm; A method for producing a bonded body, wherein the ratio (t / h) of the thickness (t) of the transferred film to the height (h) of the metal pillar is 0.4 to 0.7. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a metal paste and a method for producing a bonded body, which can efficiently obtain a bonded body having high reliability in terms of electrical and mechanical strength, even when the pitch is narrowed. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating an example of step 1 in the method for producing a bonded body. [Diagram 2] FIG. 2 is a schematic cross-sectional view illustrating an example of step 2 in the method for producing a bonded body. [Diagram 3] FIG. 3 is a schematic cross-sectional view illustrating an example of step 3 in the method for producing a bonded body. [Figure 4] FIG. 4 is a schematic cross-sectional view illustrating one example of a bonded body obtained by the method for producing a bonded body. As shown in FIG. [Diagram 5]FIG. 5 is an image obtained when checking the transfer rate in Example 7. [Figure 6] FIG. 6 shows an image obtained when checking the transfer rate in Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, one embodiment of the present disclosure will be described in detail, but the scope of the present disclosure is not limited to the embodiment described here, and various modifications can be made within the scope of the present disclosure. Each aspect disclosed in this specification can be combined with any other features disclosed in this specification. In this disclosure, a combination of preferred aspects is a more preferred aspect. In addition, when multiple upper and lower limit values ​​are described for a specific parameter, any upper and lower limit values ​​among these upper and lower limit values ​​can be combined to form a suitable numerical range. In addition, the lower and / or upper limit values ​​of the numerical range described in this disclosure are numerical values ​​within the numerical range and may be replaced with numerical values ​​shown in the examples. The expression "X to Y" indicating a numerical range means "X or more and Y or less". When a specific description described for one embodiment is also applicable to other embodiments, the description may be omitted in other embodiments.

[0014] [Metal paste] The metal paste of the present disclosure contains metal particles and a solvent, and is melt-melted at a shear rate of 10 s at 25° C. -1 The shear viscosity measured at a shear rate of 1 to 100 Pa s is -1 Shear viscosity measured at 1s and shear rate -1 The logarithmic ratio of the shear viscosity measured at 200° C. to the shear viscosity measured at 200° C. (TI value) is 0.7 to 1.0.

[0015] The above-mentioned configuration makes it possible to obtain a transfer film having excellent surface smoothness and a metal paste that can suppress sagging of the metal paste even after transfer. With such a metal paste, it is believed that it is possible to realize both a high transfer rate and an appropriate transfer amount, and to efficiently obtain a bonded body having high reliability in terms of electrical and mechanical strength.

[0016] The reason why the metal paste of the present disclosure exhibits the above-mentioned effects is not clear, but one possible reason is as follows.

[0017] Conventional metal pastes had a problem where if a large amount was transferred onto the metal pillar (transfer amount), sagging (the phenomenon in which the metal paste does not maintain its shape on the metal pillar and drips down the side of the metal pillar to the base) occurred. The problem of sagging becomes more serious as the pitch becomes narrower (for example, when the distance between metal pillars is 40 μm or less), and was one of the causes of solder bridging. In order to suppress such sagging, conventional methods have been devised, such as increasing the viscosity of the metal paste or reducing the amount transferred. However, in these cases, there have been problems with a decrease in the transfer rate of the metal paste to the metal pillar or an excessively small amount of transfer, which can lead to poor connection between the electrodes (poor electrical and / or mechanical strength connection).

[0018] In consideration of the above problems, the present inventors have investigated ways to improve the transfer rate while optimizing the amount of metal paste transferred. As a result, they newly discovered that the transfer rate of the metal paste can be improved by increasing the surface smoothness of the transferred film. Therefore, the inventors of the present invention further investigated a metal paste that can obtain a transfer film with excellent surface smoothness and can suppress the sagging of the metal paste even after transfer. As a result, they found that the viscosity of the metal paste can be adjusted under a predetermined condition (shear rate of 10 s at 25° C.). -1 The shear viscosity measured at a shear rate of 1 to 100 Pa s is -1 Shear viscosity measured at 1s and shear rate -1It has been found that this can be achieved by controlling the logarithmic ratio of the shear viscosity measured by the thermal expansion coefficient (TI value) to 0.7 to 1.0.

[0019] That is, since the metal paste of the present disclosure has a predetermined viscosity characteristic, a transfer film having excellent surface smoothness can be obtained, and sagging of the metal paste can be suppressed even after transfer. Therefore, when such a metal paste is used as a transfer film, it is possible to realize both a high transfer rate and an appropriate transfer amount, and it is considered that a bonded body having high reliability in terms of electrical and mechanical strength can be efficiently obtained.

[0020] Each component will be described in detail below.

[0021] (metal particles) The metal paste of the present disclosure includes metal particles.

[0022] The metal particles used in the present disclosure may be any metal particles that have electrical conductivity after sintering, and may be, for example, gold, silver, copper, nickel, palladium, tin, aluminum, or alloys thereof, or oxides thereof (copper oxide (Cu 2 Among them, from the viewpoint of obtaining a sintered body having high electrical conductivity, the metal particles are preferably one or more selected from the group consisting of copper particles, silver particles, and particles of oxides thereof, more preferably one or more selected from the group consisting of copper particles and silver particles, and even more preferably copper particles.

[0023] The shape of the metal particles is not particularly limited, and may be, for example, spherical, ellipsoidal, flake-like (flat), fibrous, or amorphous. Among these, from the viewpoint of coatability and storage stability of the metal paste, the metal particles are preferably spherical or flake-like.

[0024] The volume average particle size of the metal particles is not particularly limited, but is preferably 1 nm to 100 μm, more preferably 10 nm to 50 μm, even more preferably 30 nm to 35 μm, still more preferably 50 nm to 10 μm, and even more preferably 70 nm to 1 μm. The volume average particle diameter of the above metal particles is the average particle diameter at 50% cumulative frequency in the volume-based particle size distribution (median diameter, D50), and can be measured by the method described in the Examples section of the present disclosure or a method that will be understood by those skilled in the art to be equivalent thereto.

[0025] The metal particles may be synthetic or commercially available. The metal particles may be used alone or, if necessary, in the form of a mixture of two or more types of metal particles having different compositions, shapes, or volume average particle sizes.

[0026] The metal particles may be a combination of two or more types of metal particles having different volume average particle diameters, such as nano-sized particles having a volume average particle diameter of preferably 1 nm or more and less than 300 nm, more preferably 1 to 200 nm, and even more preferably 1 to 150 nm; sub-nano-sized particles having a volume average particle diameter of preferably 0.30 μm or more and less than 1.00 μm, more preferably 0.40 to 0.95 μm, and even more preferably 0.50 to 0.90 μm; or micro-sized particles having a volume average particle diameter of preferably 1.0 to 100 μm, more preferably 1.5 to 50 μm, even more preferably 2.0 to 35 μm, still more preferably 2.5 to 10 μm, and even more preferably 3.0 to 10 μm.

[0027] When metal particles having different volume average particle sizes are used in combination, the mass ratio of the nano-sized particles to the total metal particles (nano-sized particles / total metal particles) is preferably 0.05 to 0.90, more preferably 0.10 to 0.85, and even more preferably 0.15 to 0.80.

[0028] When two or more types of metal particles having different compositions are used in combination, the mass ratio of copper particles to all metal particles (copper particles / all metal particles) is preferably 0.35 to 0.90, more preferably 0.40 to 0.87, and even more preferably 0.45 to 0.84.

[0029] The content of the above metal particles in the metal paste of the present disclosure (the total content when two or more types of metal particles differing in composition, shape, and volume average particle diameter are contained) is preferably 70 to 99 mass%, more preferably 72 to 95 mass%, even more preferably 74 to 93 mass%, still more preferably 76 to 95 mass%, and even more preferably 78 to 93 mass%.

[0030] (solvent) The metal paste of the present disclosure includes a solvent.

[0031] The solvent in the metal paste of the present disclosure serves as a dispersion medium and a sintering aid.

[0032] The solvent used in the present disclosure is not particularly limited, and a wide variety of components that are generally used as a dispersion medium for metal pastes can be used, but preferably contains formic acid and a basic compound.

[0033] <Formic acid> In the present disclosure, formic acid is compatible with a basic compound described below to serve as a dispersion medium for metal particles, and also reduces the oxide film on the surface of the metal particles to promote sintering of the metal particles.

[0034] For the formic acid used in the present disclosure, formic acid or a mixed solution containing formic acid can be used. Among them, a mixed solution containing 50 mass% or more of formic acid is preferred from the viewpoint of ease of handling, and a formic acid-triethylamine azeotropic composition (e.g., formic acid:triethylamine=5:2 (molar ratio)), a 98% aqueous solution of formic acid, an 88% aqueous solution of formic acid, etc. are more preferred.

[0035] <Basic compounds> The basic compound in the present disclosure increases the temperature at which formic acid volatilizes in the metal paste, makes the compatible material a good dispersion medium, and inhibits corrosion of the metal particle surfaces by formic acid.

[0036] The basic compound used in the present disclosure is preferably a nitrogen-containing compound represented by the following formula (1). TIFF2025086076000002.tif26170 (in formula (1), R a ~R c are the same or different and each represents a hydrogen atom or a hydrocarbon group which may have a substituent. The substituent is the same or different and is at least one group selected from an amino group, an N-substituted amino group, an N,N-substituted amino group, an imino group, an N-substituted imino group, and a hydroxyl group. a ~R c are not hydrogen atoms at the same time. A double line including a dashed line represents a single bond or a double bond. If it is a double bond, R c does not exist. R a ~R c Any two of may be bonded to each other to form a ring together with the adjacent nitrogen atom.

[0037] R a ~R c Examples of the hydrocarbon group include an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. Among these, an aliphatic hydrocarbon group and an alicyclic hydrocarbon group are preferred, and an aliphatic hydrocarbon group is more preferred.

[0038] Examples of the aliphatic hydrocarbon group include linear or branched alkyl groups, linear or branched alkenyl groups, linear or branched alkynyl groups, and linear or branched alkylidene groups, and among these, linear or branched alkyl groups are preferred.

[0039] The linear or branched alkyl group is preferably a linear alkyl group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms, or a branched alkyl group having preferably 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, and even more preferably 3 to 6 carbon atoms. Examples of the linear or branched alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a decyl group, a dodecyl group, a tetradecyl group, an octadecyl group, an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, and a 2-ethylhexyl group.

[0040] The linear or branched alkenyl group is preferably a linear alkenyl group having 2 to 12 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms, or a branched alkenyl group having preferably 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, and even more preferably 3 to 6 carbon atoms. Examples of the linear or branched alkenyl group include a vinyl group, a 1-propenyl group, a 2-propenyl group, a 1-butenyl group, a 2-butenyl group, a 3-butenyl group, a 1-pentenyl group, a 2-pentenyl group, a 3-pentenyl group, a 4-pentenyl group, a 1-hexenyl group, a 3-hexenyl group, a 5-hexenyl group, a 1-heptenyl group, a 1-octenyl group, a 1-nonenyl group, a 1-decenyl group, an isopropenyl group, a 2-methyl-1-propenyl group, a methallyl group, a 3-methyl-2-butenyl group, and a 4-methyl-3-pentenyl group.

[0041] The linear or branched alkynyl group is preferably a linear alkynyl group having 2 to 12 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms, or a branched alkynyl group having 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, and even more preferably 3 to 6 carbon atoms. Examples of the linear or branched alkynyl group include an ethynyl group, a 1-propynyl group, a 2-propynyl group, a 1-butynyl group, a 2-butynyl group, a 3-butynyl group, a 1-pentynyl group, a 2-pentynyl group, a 3-pentynyl group, a 4-pentynyl group, a 1-hexynyl group, a 2-hexynyl group, a 3-hexynyl group, a 4-hexynyl group, a 5-hexynyl group, a 1-heptynyl group, a 1-octynyl group, a 1-nonynyl group, a 1-decynyl group, a trimethylsilylethynyl group, and a triethylsilylethynyl group.

[0042] The linear or branched alkylidene group is preferably a linear alkylidene group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms, or a branched alkylidene group having preferably 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, and even more preferably 3 to 6 carbon atoms. Examples of the linear or branched alkylidene group include a methylidene group, a propylidene group, an isopropylidene group, a butylidene group, an isobutylidene group, a sec-butylidene group, a pentylidene group, an isopentylidene group, an octylidene group, and an isooctylidene group.

[0043] Examples of the alicyclic hydrocarbon group include a cycloalkyl group and a cycloalkenyl group. The cycloalkyl group is preferably a cycloalkyl group having 3 to 12 carbon atoms, more preferably 4 to 10 carbon atoms, and further preferably 5 to 8 carbon atoms, and examples thereof include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, and a cyclodecyl group. The cycloalkenyl group is preferably a cycloalkenyl group having 3 to 12 carbon atoms, more preferably 4 to 10 carbon atoms, and even more preferably 5 to 8 carbon atoms, and examples thereof include a cyclopentenyl group and a cyclohexenyl group.

[0044] The aromatic hydrocarbon group is preferably an aryl group having 6 to 18 carbon atoms, more preferably 6 to 18 carbon atoms, and even more preferably 6 to 10 carbon atoms, and examples thereof include a phenyl group and a naphthyl group.

[0045] In formula (1), the double line including the dashed line represents a single bond or a double bond. When the double line including the dashed line is a double bond, R c does not exist, and R in formula (1) a and R b The nitrogen atom to which is attached represents an imino group or an N-substituted imino group.

[0046] R a ~R cThe total number of amino groups, N-substituted amino groups and N,N-substituted amino groups that may be contained in the alkyl group is preferably 0 to 6, more preferably 1 to 4, and even more preferably 1 to 2. R a ~R c The total number of imino groups and N-substituted imino groups that may be contained is preferably 0 to 4, more preferably 1 to 3, and further preferably 1 or 2. R a ~R c The total number of hydroxyl groups that may be possessed by the alkyl group is preferably 0 to 6, more preferably 1 to 4, and even more preferably 1 to 2.

[0047] The substituents of the above-mentioned N-substituted amino group, N,N-substituted amino group, and N-substituted imino group are the same as those of the above-mentioned R a ~R c The hydrocarbon groups are the same as those described above.

[0048] R a ~R c Any two of may be bonded to each other to form a ring together with the adjacent nitrogen atom. Examples of the ring formed include a pyrrolidine ring, a pyrroline ring, a piperidine ring, a pyrrole ring, an imidazolidine ring, an imidazole ring, a piperazine ring, an imidazolidine ring, a pyridine ring, a diazine ring, and a triazine ring.

[0049] R a ~R cThe hydrocarbon group may have a substituent other than an amino group, an N-substituted amino group, an N,N-substituted amino group, an imino group, an N-substituted imino group, or a hydroxyl group. Examples of such a substituent include a halogen atom (a fluorine atom, a chlorine atom, a bromine atom, an iodine atom), an oxo group, a substituted oxy group (an alkoxy group having 1 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aryloxy group having 6 to 10 carbon atoms, an aralkyloxy group having 7 to 16 carbon atoms, an acyloxy group having 1 to 4 carbon atoms, etc.), a carboxyl group, a substituted oxycarbonyl group (an alkoxycarbonyl group having 1 to 4 carbon atoms, an aryloxycarbonyl group having 6 to 10 carbon atoms, an aralkyloxycarbonyl group having 7 to 16 carbon atoms, etc.), a cyano group, a nitro group, a sulfo group, a mercapto group, a heterocyclic group, etc.

[0050] Specific examples of the basic compound represented by formula (1) include, for example, a ~R c at least one of R is a straight-chain or branched-chain alkyl group; a , R b is a hydrogen atom, and R c is a linear or branched alkyl group having one hydroxyl group; R in formula (1) a is a hydrogen atom, and R b and R c are the same or different and are linear or branched alkyl groups having one hydroxyl group; R in formula (1) a ~R c are the same or different and are linear or branched alkyl groups having one hydroxyl group; R in formula (1) a , R b are the same or different and are a hydrogen atom or a linear or branched alkyl group; R c is a linear or branched alkyl group having two hydroxyl groups; a ~R c A diamine having a total of one amino group; R in formula (1) a ~R c A triamine having a total of 2 amino groups; R in formula (1) a~R c R in formula (1) is a diaminoalkanol having a total of one amino group and a total of one hydroxyl group; a ~R c An imidazole compound in which a ring is formed by incorporating nitrogen atoms of the imino groups, the total number of which is one; a , R b is bonded to an imino group, and a ring is formed containing the imino group (such as a pyridine compound, a diazine compound, or a triazine compound).

[0051] Examples of the alkylamine include methylamine, ethylamine, propylamine, butylamine, pentylamine, dimethylamine, N,N-dimethyldodecylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, piperidine, trimethylamine, triethylamine, 4-dimethylaminopyridine, 2-aminopyrazine, 2-aminopyrimidine, 3-aminopyridazine, 2-aminotriazine, diazabicyclononene, and diazabicycloundecene.

[0052] Examples of the monoalkanolamine include 2-aminoethanol, 3-aminopropanol, 1-amino-2-propanol, 1-amino-2-methyl-2-propanol, 2-amino-2-methyl-1-propanol, 4-amino-1-butanol, 6-amino-1-hexanol, 10-amino-1-decanol, 12-amino-1-dodecanol, N-methyl-2-aminoethanol, N-ethyl-2-aminoethanol, N-propyl-2-aminoethanol, 2-dimethylaminoethanol, 6-diethylaminohexanol, 1-(2-hydroxyethyl)pyrrolidine, 2-(hydroxymethyl)pyrrolidine, 2-(2-hydroxyethyl)-1-methylpyrrolidine, 1-piperidineethanol, and 1-ethanol-4-propanolpiperidine.

[0053] Examples of the dialkanolamine include diethanolamine, N-methyldiethanolamine, di-n-propanolamine, diisopropanolamine, di-n-butanolamine, and diisobutanolamine.

[0054] Examples of the trialkanolamine include triethanolamine, tri-n-propanolamine, triisopropanolamine, tri-n-butanolamine, and triisobutanolamine.

[0055] Examples of the aminoalkanediol include 1-amino-2,3-propanediol, 4-amino-1,2-butanediol, 4-amino-1,3-butanediol, 2-amino-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol, 1-methylamino-2,3-propanediol, 1-ethylamino-2,3-propanediol, 1-propylamino-2,3-propanediol, 1-butylamino-2,3-propanediol, 3-dimethylamino-1,2-propanediol, and 2-diethylamino-1,3-propanediol.

[0056] Examples of the diamine include 1,3-propanediamine, 2,2-dimethyl-1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,5-diamino-2-methylpentane, N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N'-dimethyl-1,3-propanediamine, N,N'-diethyl-1,3-propanediamine, N,N'-dimethyl-1,4-butanediamine, N,N'-diethyl-1,4-butanediamine, N,N'-di Examples of the methyl-1,6-hexanediamine include N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-diethyl-1,3-propanediamine (=diethylaminopropylamine), N,N-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, 1,2-cyclohexanediamine, 1,4-cyclohexanediamine, piperazine, N-methylpiperazine, N-ethylpiperazine, N,N'-dimethylpiperazine, and homopiperazine.

[0057] Examples of the triamine include diethylenetriamine, N,N,N',N",N"-pentamethyldiethylenetriamine (=pentamethyldiethylenetriamine), N,N,N',N",N"-pentakis(2-hydroxypropyl)diethylenetriamine, 3,3'-diaminodipropylamine, N-(3-aminopropyl)-N-methyl-1,3-propanediamine, N'-[3-(dimethylamino)propyl]-N,N-dimethyl-1,3-propanediamine, 2,6,10-trimethyl-2,6,10-triazaundecane, N-(2-aminoethyl)piperazine, 1,4,7-triazacyclononane, N,N,N',N",N"-pentakis(2-hydroxypropyl)diethylenetriamine, 1-(2-aminoethyl)-4-methylpiperazine, and 1-(2-dimethylaminoethyl)-4-methylpiperazine.

[0058] Examples of the diaminoalkanol include 1,3-diaminopropan-2-ol, 2-(2-aminoethylamino)ethanol, 2-(2-aminopropylamino)ethanol, 2-(2-aminoethylmethylamino)ethanol, 1-(2-hydroxyethyl)piperazine, 4-methylpiperazine-1-ethanol, and 1,4-bis(2-hydroxyethyl)piperazine.

[0059] Examples of the imidazole compound include imidazole, 2-methylimidazole, 2-propylimidazole, N-methylimidazole (=1-methylimidazole), N-propylimidazole, N-butylimidazole, 1-(2-hydroxyethyl)imidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1-acetylimidazole, and 2-hydroxybenzimidazole.

[0060] Examples of the nitrogen-containing aromatic compound include pyridine, α-picoline, β-picoline, γ-picoline, 2,6-lutidine, 2,3-lutidine, pyrazine, 2-hydroxypyrazine, pyrimidine, 2-hydroxypyrimidine, 4-hydroxypyrimidine, pyridazine, 3-hydroxypyridazine, 4-hydroxypyridazine, triazine, and 2-hydroxytriazine.

[0061] The above basic compounds may be used alone or in combination of two or more kinds, if necessary. The basic compound may be either liquid or solid at room temperature and normal pressure (eg, 25° C. and 1 atm).

[0062] The solvent is preferably a mixture containing the formic acid and the basic compound, and is liquid or solid at room temperature and normal pressure, but it is more preferable that the solvent is an organic substance that becomes liquid when mixed with the metal particles and can disperse the metal particles into a paste-like form.

[0063] The molar ratio (basic group / formic acid) of the number of moles of the basic group related to the basic compound in the solvent to the number of moles of the formic acid is preferably 0.50 to 1.20, more preferably 0.55 to 1.15, and even more preferably 0.60 to 1.10. When the molar ratio is within the above range, the storage stability of the metal paste is improved, and it becomes easier to obtain a sintered body with excellent conductivity. The number of moles of the basic group related to the basic compound is the number of moles of the basic compound multiplied by the number of basic groups that the basic compound has, and the basic group in the imidazole compound is the one attached to the nitrogen atom at the 1st position.

[0064] In addition, the solvent may contain water, an organic solvent other than formic acid and the basic compound, or a basic compound other than the basic compound, as necessary. Examples of organic solvents other than formic acid and basic compounds include organic acids other than formic acid (acetic acid, propionic acid, n-octanoic acid, etc.); ester-based solvents such as acetates (ethyl acetate, butyl acetate, etc.); ether-based solvents such as dioxane and tetrahydrofuran; ketone-based solvents such as acetone; aromatic solvents such as toluene and xylene; halogen-based solvents such as dichloromethane and chloroform; alcohol-based solvents such as methanol, ethanol, isopropanol, and butanol; and nitrile-based solvents such as acetonitrile and benzonitrile. Examples of basic compounds other than the basic compounds include inorganic bases (sodium hydroxide, potassium hydroxide, ammonia, etc.).

[0065] The content of the solvent in the metal paste of the present disclosure is preferably 10.0 to 30.0 mass %, more preferably 15.0 to 25.0 mass %, and even more preferably 17.0 to 22.0 mass %.

[0066] In order to facilitate the production of a sintered body exhibiting good electrical conductivity, the content of formic acid, the content of the basic compound, and the mass ratio (basic compound / formic acid) in the metal paste of the present disclosure preferably satisfy the following ranges at the same time: The content of formic acid is preferably 4.0 to 12.0 mass%, more preferably 6.0 to 10.0 mass%, and even more preferably 8.0 to 9.0 mass%, the content of the basic compound (total content when two or more types are used in combination) is preferably 5.0 to 20.0 mass%, more preferably 7.0 to 16.0 mass%, and even more preferably 9.0 to 13.0 mass%, and the weight ratio of the basic compound to formic acid (basic compound / formic acid) is preferably 0.50 to 3.00, more preferably 0.70 to 2.00, and even more preferably 1.00 to 1.50.

[0067] When the metal paste of the present disclosure contains one or more selected from the group consisting of water, organic solvents other than the formic acid and the basic compound, and basic compounds other than the basic compounds, the total content of water, acid, organic solvents other than the basic compound, and basic compounds other than the basic compounds in the metal paste is preferably 10 mass% or less, more preferably 5 mass% or less, even more preferably 1 mass% or less, and still more preferably 0.5 mass% or less.

[0068] The vapor pressure of the solvent at 25° C. is preferably 3.0×10 -7 Within the above range, evaporation of the solvent from the transferred film can be effectively suppressed, and changes in the thickness and surface roughness of the transferred film can be suppressed. The vapor pressure of the above-mentioned solvent at 25° C. can be calculated using computer software “Aspen Plus V12 (registered trademark)” (manufactured by Aspen Tech).

[0069] <Other ingredients> The metal paste of the present disclosure may further contain components other than metal particles and a solvent in order to adjust the fluidity (viscosity) and operability. Other components include resin components (e.g., polymeric compounds having a number average molecular weight of 10,000 or more, such as ethyl cellulose resin, alkyl cellulose resin, polyvinyl acetal resin, and acrylic resin), and additives (surface conditioners (leveling agents), defoamers, dispersants, thixotropy-imparting agents, etc.).

[0070] When the metal paste of the present disclosure contains other components, the content of these components in the metal paste is preferably 10 mass % or less, more preferably 5 mass % or less, even more preferably 1 mass % or less, and even more preferably 0.5 mass % or less.

[0071] The metal paste of the present disclosure has an appropriate viscosity and does not need to contain a resin component. However, from the viewpoint of making it easier to adjust the fluidity (viscosity) of the metal paste to a desired range, it is preferable that the metal paste of the present disclosure further contains a resin component. When the metal paste of the present disclosure contains a resin component, the content of the resin component in the metal paste is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. If the content of the resin component exceeds the above range, the ash derived from the resin component generated by firing tends to cause a decrease in electrical conductivity, which is not preferable.

[0072] When the metal paste of the present disclosure contains an additive, the content of the additive in the metal paste is preferably 10 mass % or less, more preferably 5 mass % or less, even more preferably 1 mass % or less, and even more preferably 0.5 mass % or less.

[0073] (Metal paste viscosity characteristics) The metal paste of the present disclosure has a shear rate of 10 s at 25 °C. -1 The shear viscosity measured by is 1 to 100 Pa·s. By being in the above range, a transfer film having excellent surface smoothness can be obtained, and dripping of the metal paste can be suppressed even after transfer. If the viscosity is less than 1 Pa·s, the metal paste after transfer tends to sag. On the other hand, if the viscosity is more than 100 Pa·s, a transferred film with excellent surface smoothness tends not to be obtained. From the viewpoint of improving the surface smoothness of the transferred film and effectively suppressing sagging of the metal paste after transfer, the viscosity is preferably 1 to 70 Pa·s, more preferably 5 to 50 Pa·s, and even more preferably 5 to 30 Pa·s. At 25°C, shear rate is 10 s -1 The shear viscosity measured at 100° C. can be measured by the method described in the Examples section of this disclosure or by a method understood by one of ordinary skill in the art to be equivalent thereto. At 25°C, shear rate is 10 s -1 Examples of a method for adjusting the shear viscosity measured in the above to 1 to 100 Pa s include a method for adjusting the type and amount of each component described above, and a method for adjusting the shear viscosity by adding an additive such as a thixotropy-imparting agent as necessary.

[0074] The metal paste of the present disclosure has a shear rate of 0.1 s at 25°C. -1 Shear viscosity measured at 1s and shear rate -1 The logarithmic value (TI value) of the ratio of the shear viscosity measured by the above method is 0.7 to 1.0. When the TI value is within the above range, a transfer film having excellent surface smoothness can be obtained, and dripping of the metal paste can be suppressed even after transfer. The TI value can be calculated by the following formula (I). TI value=Log(η(0.1) / η(1)) / Log(1 / 0.1) ···(I) In the above formula (1), η(0.1) is the shear rate of 0.1 s -1 is the shear viscosity measured at a shear rate of 1 s -1 The shear viscosity is measured at . If the TI value is less than 0.7, the metal paste after transfer tends to sag. On the other hand, if the TI value is more than 1.0, a transferred film with excellent surface smoothness tends not to be obtained. From the viewpoint of improving the surface smoothness of the transferred film and effectively suppressing sagging of the metal paste after transfer, the TI value is preferably 0.70 to 1.00, more preferably 0.75 to 0.95. At 25°C, shear rate 0.1 s -1 Shear viscosity measured at 1s and shear rate -1 The shear viscosity measured at 100° C. can be measured by the method described in the Examples section of this disclosure or by a method understood by one of ordinary skill in the art to be equivalent thereto. Examples of methods for adjusting the TI value to 0.7 to 1.0 include adjusting the amount of resin or thixotropy-imparting agent added, adjusting the SP value of the solvent, adjusting the particle size of copper particles, adjusting the content of copper particles, etc. For example, the TI value can be increased by increasing the amount of thixotropy-imparting agent added, or by reducing the particle size of copper particles and narrowing the particle size distribution. The TI value can also be decreased by decreasing the amount of thixotropy-imparting agent added, or by decreasing the content of copper particles.

[0075] The method for controlling the copper paste of the present disclosure to have the above-mentioned predetermined viscosity characteristics is not particularly limited, and can be adjusted by a known viscosity adjustment method. Specifically, for example, the type and amount of each of the above-mentioned components can be adjusted according to the desired viscosity, and additives such as a thixotropic agent can be added as necessary.

[0076] (Metal Paste Manufacturing Method) The metal paste of the present disclosure can be produced through a process of mixing metal particles with the solvent. Preferably, the metal paste of the present disclosure can be produced through a process of mixing metal particles with the formic acid and basic compound, and further with other components as necessary.

[0077] The temperature during mixing is preferably not higher than 100°C. The mixture may be cooled to room temperature (eg, 25° C.) or below after mixing, and may be gradually cooled at room temperature or rapidly cooled by ice cooling or the like.

[0078] The mixing can be carried out using equipment known to those skilled in the art, such as an ultrasonic disperser, a disperser, a mixer, a planetary mixer, a two- or three-roll mill, a ball mill, a bead mill, a tumbler, a pressure kneader, a self-rotating mixer, or a high-pressure homogenizer.

[0079] The mixture of formic acid and a basic compound contained in the metal paste of the present disclosure quickly volatilizes during firing, and furthermore, the formic acid reduces the surface oxidation of the metal particles, making it possible to fire the metal paste at low temperatures (preferably 120 to 320°C, more preferably 150 to 290°C, and even more preferably 180 to 260°C) without being in a reducing atmosphere.

[0080] (Metal paste applications) The metal paste of the present disclosure combines the above-mentioned characteristics, and therefore can form a good coating film on the surface of a substrate (e.g., a ceramic substrate, a green sheet, etc.) by casting or the like. In addition, it is possible to form a uniform transfer film with small surface roughness while preventing the sedimentation and local aggregation of metal particles and stably maintaining a uniformly highly dispersed state. Such a transfer film can improve the transfer yield (transfer rate). In addition, since it has good sinterability, it is possible to form a joint with excellent conductivity with high precision.

[0081] Moreover, the conductive paste of the present disclosure can be selectively discharged at desired positions on the surface of a substrate provided with electrodes, circuits, etc., for example, by screen printing, dispense printing, etc., and then the electronic components, etc. can be attached and fired to electrically connect the substrate and the electronic components, etc. Furthermore, since firing can be performed at a low temperature, mounting can be performed at a lower temperature than mounting using solder, and it can be used for mounting electronic components, etc. that have poor heat resistance.

[0082] Therefore, the conductive paste of the present disclosure is particularly useful for producing, for example, printed wiring boards such as multilayer printed wiring boards, capacitors such as multilayer ceramic capacitors, inductors, varistors, thermistors, transistors, speakers, actuators, antennas, solid oxide fuel cells (SOFCs), hybrid ICs, and the like, in particular, multilayer ceramic capacitors.

[0083] [Method of manufacturing the bonded body] The method for producing a bonded body according to the present disclosure includes: Step 1 of applying a metal paste onto a substrate to prepare a transfer film; A step 2 of contacting a metal pillar of a first bonded body having a metal pillar with the transfer film to transfer the metal paste to at least one surface of the metal pillar; A step 3 of contacting the metal paste transferred to the metal pillar with a second object to be joined; having The surface of the transfer film has a surface roughness Ra of 0.1 to 5 μm and a surface roughness Rz of 0.5 to 10 μm; The ratio (t / h) of the thickness (t) of the transferred film to the height (h) of the metal pillar is 0.4 to 0.7.

[0084] With the above-mentioned configuration, even when the pitch is narrowed, a bonded body having high reliability in terms of electrical and mechanical strength can be efficiently obtained. The reason why the method for producing a bonded body according to the present disclosure exhibits the above-mentioned effects is not clear, but one possible reason is as follows.

[0085] By controlling the surface roughness of the transfer film within a predetermined range (surface roughness Ra of 0.1 to 5 μm and surface roughness Rz of 0.5 to 10 μm) and controlling the ratio (t / h) of the thickness (t) of the transfer film to the height (h) of the metal pillar within a predetermined range (0.4 to 0.7), an appropriate amount of metal paste can be efficiently attached to the metal pillar in step 2, where the metal pillar is brought into contact with the transfer film, improving the transfer rate and optimizing the transfer amount. As a result, it is believed that even when the pitch between the metal pillars is narrowed, a bonded body having high reliability in terms of electrical and mechanical strength can be efficiently obtained.

[0086] Hereinafter, the manufacturing method of the bonded body according to the present disclosure will be described in detail with reference to the drawings.

[0087] (Process 1) In step 1, a metal paste 2 is applied onto a substrate 11 to prepare a transfer film 20 (FIG. 1). FIG. 1 is a schematic cross-sectional view showing an example of step 1.

[0088] The substrate 11 is not particularly limited, and may be, for example, a transfer film production jig 11 having a groove 11H of a predetermined size and depth as shown in FIG. 1(a). For example, the transfer film preparation jig 11 may be a Si wafer having a groove of a predetermined size and depth formed on the surface thereof. A wide variety of commonly available Si wafers can be used as the Si wafer, and a wafer having a predetermined size and thickness can be selected according to the size and depth of the grooves to be formed.

[0089] When using a transfer film forming jig 11, a metal paste 2 is applied to a groove 11H of the transfer film forming jig, and the metal paste 2 is filled into the groove 11H using a metal squeegee 13 (Figure 1(b)), thereby forming a transfer film 20 (Figure 1(c)). In this method, the depth of the groove 11H corresponds to the thickness (t) of the transfer film, and therefore the thickness (t) of the transfer film can be adjusted by changing the depth of the groove.

[0090] The metal paste 2 is not particularly limited as long as it can control the surface roughness of the surface 20S of the transfer film 20 within a predetermined range. However, it is preferable to use the metal paste disclosed above, since it results in a transfer film having a smooth surface and the metal paste is less likely to drip after transfer.

[0091] The transfer film 20 used in the present disclosure has a predetermined surface roughness. That is, the surface roughness Ra of the surface 20S of the transfer film 20 is 0.1 to 5 μm, and the surface roughness Rz is 0.5 to 10 μm. By controlling the surface roughness to a predetermined range together with the ratio (t / h) described later, an appropriate amount of metal paste can be efficiently attached to the metal pillar, the transfer rate can be improved, and the transfer amount can be optimized. As a result, even if the pitch between the metal pillars is narrowed, a bonded body having high reliability in terms of electrical and mechanical strength can be efficiently obtained. From this viewpoint, the surface roughness Ra is preferably 0.1 to 4 μm, more preferably 0.1 to 3 μm, and the surface roughness Ra is preferably 0.5 to 7 μm, more preferably 0.1 to 5 μm. Methods for controlling the surface roughness on the surface 20S of the transfer film 20 within the above-mentioned specified range include, for example, adjusting the viscosity of the metal paste, adjusting the surface roughness of the surface of the metal squeegee 13 used when forming the transfer film 20 that comes into contact with the metal paste, and adjusting the application speed when applying the metal paste with the metal squeegee 13.

[0092] Furthermore, the thickness (t) of the transfer film 20 used in the present disclosure is controlled so that the ratio (t / h) of the thickness (t) to the height (h) of the metal pillar 30 of the first bonded body 3 to be contacted in step 2 described later is in the range of 0.4 to 0.7. By controlling the above ratio (t / h) within a predetermined range together with the surface roughness of the surface 20S of the transfer film 20 described above, an appropriate amount of metal paste can be efficiently attached to the metal pillar, the transfer rate can be improved, and the transfer amount can be optimized. As a result, even if the pitch between the metal pillars is narrowed, a bonded body having high reliability in terms of electrical and mechanical strength can be efficiently obtained. From this viewpoint, the above ratio (t / h) is preferably 0.4 to 0.6, more preferably 0.45 to 0.55. The thickness (t) of the transfer film 20 is not particularly limited, but is, for example, 1 to 50 μm, preferably 5 to 20 μm, and more preferably 7 to 15 μm.

[0093] (Process 2) In step 2, the metal pillar 30 of the first bonded body 3 having the metal pillar 30 is brought into contact with the transfer film 20, and the metal paste 2 is transferred to at least one surface 30S of the metal pillar 30 (FIG. 2). FIG. 2 is a schematic cross-sectional view showing an example of step 2.

[0094] The first object to be joined 3 is not particularly limited as long as it has the metal pillar 30, and any generally available object can be used. The first bonded object 3 may include, for example, a metal pillar 30 and a substrate (first substrate) 31 having the metal pillar 30 provided on one surface thereof. Specifically, the first bonded object 3 may be a microdevice such as a logic, analog IC, or power IC.

[0095] The metal pillars 30 are provided, for example, in multiple numbers on one surface of the first substrate 31, and are arranged on the first substrate 31 so that when the first bonded object 3 and the second bonded object 4 are arranged opposite each other, each of the multiple metal pillars 30 faces an electrode pad 40 on the second bonded object 4 (see FIG. 3).

[0096] The material of the metal pillar 30 is not particularly limited. When an oxide film is formed on the bonding surface of the metal pillar 30 (surface 30S on which the metal paste 2 is disposed), from the viewpoint of facilitating removal of the oxide film in step 4 described below, it is preferable that at least the bonding surface of the metal pillar 30 is made of a material (metal or alloy) containing one or more selected from the group consisting of gold, platinum, silver, palladium, copper, nickel, and zinc. In addition, from the viewpoint of suppressing Kirkendall voids after bonding and suppressing impedance mismatch, it is preferable that at least the bonding surface of the metal pillar 30 is made of a material containing copper, and more preferably, it is made of a material containing a certain percentage or more of copper (for example, 90 mass% or more). Among them, it is more preferable that the metal pillar is a copper pillar.

[0097] The shape of the metal pillar 30 is not particularly limited. The shape of the cross section perpendicular to the extending direction of the metal pillar 30 may be, for example, a circle, an ellipse, a rectangle, or the like. The height (h) of the metal pillar 30 may be, for example, 10 μm or more and 100 μm or less. The pillar diameter of the metal pillar 30 (maximum diameter when the cross section is other than a circle) may be, for example, 10 μm or more and 300 μm or less.

[0098] The interval between the metal pillars 30 provided on one surface of the first substrate 31 (the distance from the center of a metal pillar 30 to the center of an adjacent metal pillar 30, also referred to as the "metal pillar interval") is not particularly limited, and may be, for example, 10 μm or more and 80 μm or less. The shorter the interval between the metal pillars 30, the more likely solder bridges will occur. However, according to the manufacturing method of the bonded body of the present disclosure, solder bridges can be effectively suppressed, particularly even when the interval between the metal pillars 30 is narrowed to, for example, 40 μm or less.

[0099] In step 2, the force with which the metal pillar 30 is brought into contact with the transfer film 20 is preferably 0.6 to 2.0 N, more preferably 0.7 to 1.8 N, and even more preferably 0.8 to 1.4 N. By setting the force within the above range, an appropriate amount of metal paste can be efficiently attached to the metal pillar, improving the transfer rate and optimizing the amount of transfer. This makes it possible to efficiently obtain a bonded body that has high reliability in terms of electrical and mechanical strength.

[0100] In step 2, the time for contacting the metal pillar 30 with the transfer film 20 is preferably 500 to 2000 ms, more preferably 700 to 1500 ms, and even more preferably 800 to 12000 ms. By setting the time within the above range, an appropriate amount of metal paste can be efficiently attached to the metal pillar, improving the transfer rate and optimizing the amount of transfer. This makes it possible to efficiently obtain a bonded body having high reliability in terms of electrical and mechanical strength.

[0101] Step 2 may be performed once or twice or more, and from the viewpoint of improving the transfer rate and obtaining an appropriate amount of transfer, it is preferably performed 2 to 4 times, more preferably 2 to 3 times, whereby a bonded body having high reliability in terms of electrical and mechanical strength can be efficiently obtained. Here, when step 2 is performed two or more times, the metal paste has already been transferred to the metal pillar from the second time onwards. Therefore, step 2 from the second time onwards is step 2' in which the metal pillar 30 to which the metal paste 2 has been transferred is brought into contact with the transfer film 20, and the metal paste 2 is further transferred to at least one surface 30S of the metal pillar 30. The transfer film used in this step 2' is not particularly limited as long as its surface roughness and thickness satisfy predetermined conditions, but it is preferable to use a portion that has not yet been contacted by the metal pillar (an unused portion of the transfer film).

[0102] (Step 3) Step 3 is a step of bringing the metal paste 2 transferred to the metal pillar 30 into contact with a second object to be joined 4 (FIG. 3). FIG. 3 is a schematic cross-sectional view showing an example of step 3.

[0103] The second object to be bonded 4 is not particularly limited, and any generally available object can be used. The second bonded object 4 includes, for example, an electrode pad 40 and a substrate (second substrate) 41 having the electrode pad 40 provided on one surface thereof. Specifically, the substrate may be a mounting substrate, a lead frame, a high heat dissipation mounting substrate, a silicon interposer, an epoxy wiring board, or the like.

[0104] The electrode pads 40 are provided, for example, in multiple numbers on one surface of the second substrate 41, and are arranged on the second substrate 41 so that when the first bonded object 3 and the second bonded object 4 are arranged opposite each other, each of the multiple electrode pads 40 faces a metal pillar 30 in the first bonded object 3 (FIG. 3). In step 3 shown in Figure 3, the metal paste 2 transferred to the metal pillar 30 is brought into contact with the bonding surface (surface 40S on which the metal paste 2 is to be placed) of the electrode pad 40 provided on one surface of the second bonded object 4 (Figure 3(b)).

[0105] The shape and material of the electrode pad 40 are not particularly limited. When an oxide film is formed on the bonding surface of the electrode pad 40 (the surface 40S on which the metal paste 2 is placed), from the viewpoint of facilitating removal of the oxide film in step 4 described below, it is preferable that at least the bonding surface of the electrode pad 40 is made of one or more materials (metals or alloys) selected from the group consisting of gold, platinum, silver, palladium, copper, nickel, and zinc. In addition, from the viewpoint of suppressing Kirkendall voids after bonding and suppressing impedance mismatch, it is preferable that at least the bonding surface of the electrode pad 40 is made of a material containing copper, and more preferably, it is made of a material containing a certain percentage or more of copper (for example, 90 mass% or more). The materials (metals or alloys) constituting the metal pillar 30 and the electrode pad 40 may be the same or different.

[0106] 3, the metal paste 2 forms a joint 21 between the metal pillar 30 and the electrode pad 40. In FIG. 3(b), the metal paste 2 is present only between the metal pillar 30 and the electrode pad 40, but the location of the metal paste 2 is not limited thereto. In other words, it is sufficient that the metal paste 2 is present at least between the metal pillar 30 and the electrode pad 40, and a small amount of the metal paste 2 may be present in regions other than between the metal pillar 30 and the electrode pad 40 (for example, on the side surfaces of the metal pillar 30 and the electrode pad 40) as long as no solder bridge is formed.

[0107] In step 3, the first object to be bonded 3 (e.g., a microdevice) and the second object to be bonded 4 (e.g., a substrate) may be stacked using, for example, a chip mounter, a flip chip bonder, or a carbon or ceramic positioning jig.

[0108] The metal paste 2 disposed between the first object to be joined 3 and the second object to be joined 4 (between the metal pillar 30 and the electrode pad 40) may be dried from the viewpoint of suppressing flow and generation of voids during sintering. That is, the manufacturing method of the present disclosure may further include a drying step of drying the metal paste 2 after step 3 and before step 4 described below.

[0109] Drying may be performed in the air, in an oxygen-free atmosphere such as nitrogen or a rare gas, or in a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying by leaving it at room temperature (e.g., 25°C), drying by heating, or drying under reduced pressure. For example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared ray dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, a hot plate pressing device, or the like can be used for drying by heating or drying under reduced pressure. The drying conditions (drying temperature and time) may be appropriately set according to the type and amount of volatile components (e.g., components other than metal particles such as solvents) used in the metal paste. The drying conditions (drying temperature and time) may be, for example, conditions for drying at 50°C or higher and lower than 150°C for 1 to 120 minutes.

[0110] (Step 4) The manufacturing method of the present disclosure preferably further includes a step 4 of heating the first object to be joined 3 and the second object to be joined 4 that are in contact with each other via the metal paste 2 . In step 4, a bonded body 100 is obtained, which includes the first bonded body 3, the second bonded body 4, and the sintered body (bonding portion) 22 provided on the metal pillar 30 and the electrode pad 40 (FIG. 4). FIG. 4 is a schematic cross-sectional view showing an example of a bonded body. In the bonded body 100 , the metal pillar 30 and the electrode pad 40 are electrically connected by the sintered body 22 . In step 4, the laminate of the first bonded body 3 and the second bonded body 4 obtained in step 3 (FIG. 3(b)) is heated at a bonding temperature (sintering temperature) to sinter the metal paste 2 into a sintered body 22.

[0111] For the heating treatment, for example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, or the like can be used.

[0112] The bonding temperature (sintering temperature) (maximum temperature reached during heat treatment) is, for example, 150 to 300°C, preferably 170 to 280°C, and more preferably 200 to 260°C, from the viewpoints of sufficiently advancing sintering, reducing thermal damage to the first bonded body 3 (e.g., a microdevice) and the second bonded body 4 (e.g., a substrate), and improving yield.

[0113] The heating time (the holding time at the maximum temperature reached) is, from the viewpoint of sufficiently removing volatile components (e.g., components other than metal particles such as a solvent) and sufficiently proceeding with sintering, for example, 1 to 120 minutes, and preferably 5 to 60 minutes.

[0114] The atmosphere in which the heating is performed may be a gas atmosphere having a hydrogen concentration of 45% or less, and taking into consideration the explosiveness of hydrogen gas, may be a gas atmosphere having a hydrogen concentration of 10% or less, a gas atmosphere having a hydrogen concentration of 4.5% or less, or a gas atmosphere containing no hydrogen.

[0115] Examples of the gas atmosphere include a mixed gas atmosphere containing hydrogen and a rare gas and / or nitrogen, a gas atmosphere containing formic acid gas, a mixed gas atmosphere containing formic acid gas and a rare gas and / or nitrogen, and a gas atmosphere containing a rare gas and / or nitrogen. As the gas atmosphere not containing hydrogen, a nitrogen gas atmosphere, an argon gas atmosphere, or a mixed gas atmosphere of nitrogen gas and argon gas is preferable from the viewpoint of an inert gas.

[0116] Step 4 may be performed under pressure or without pressure (a state in which the metal paste is subjected to a slight pressure of 0.01 MPa or less, either solely or in addition to the weight of the members to be joined). Examples of a method for subjecting the metal paste to a pressure of 0.01 MPa or less include a method of placing a weight on a member (e.g., second member to be joined 4) arranged vertically above, and a method of applying pressure with a spring jig. When step 4 is performed under pressure, the joining surfaces of the joined body (laminate) may be pressed with a pressure of, for example, 20 MPa or less.

[0117] As described above, according to the method for producing a bonded body of the present disclosure, it is possible to realize both a high transfer rate and an appropriate transfer amount, particularly when transferring a metal paste to a metal pillar, and it is possible to efficiently form a bonded body having high reliability in terms of electrical and mechanical strength. As a result, it is possible to obtain effects such as an improvement in production yield. In particular, the effect of the method for producing a bonded body of the present disclosure is more remarkable when the pitch between the metal pillars is narrowed to, for example, 40 μm or less.

[0118] From the viewpoint of sufficiently bonding the first and second objects to be bonded, the shear strength of the bonded body 100 is preferably 10 MPa or more. The die shear strength can be measured by the method described in the Examples section of the present disclosure or a method that will be understood by those skilled in the art to be equivalent thereto.

[0119] The manufacturing method of the bonded body of the present disclosure can be applied to flip chip bonding of microdevices and three-dimensional packages.

[0120] A non-limiting list of exemplary embodiments and combinations of exemplary embodiments of the present disclosure are disclosed below. [1] A metal paste comprising metal particles and a solvent, Shear rate 10 s at 25°C -1 The shear viscosity measured is 1 to 100 Pa s. Shear rate 0.1s -1 Shear viscosity measured at 1s and shear rate -1 The metal paste has a logarithmic TI value (a ratio of the shear viscosity measured in the above step) of 0.7 to 1.0. [2] The metal paste according to [1] above, wherein the metal particles are copper particles. [3] The metal paste according to [1] or [2] above, wherein the solvent contains formic acid and a basic compound. [4] Step 1 of applying a metal paste onto a substrate to prepare a transfer film; A step 2 of contacting a metal pillar of a first bonded body having a metal pillar with the transfer film to transfer the metal paste to at least one surface of the metal pillar; A step 3 of contacting the metal paste transferred to the metal pillar with a second object to be joined; A method for producing a bonded body, comprising: The surface of the transfer film has a surface roughness Ra of 0.1 to 5 μm and a surface roughness Rz of 0.5 to 10 μm; A method for producing a bonded body, wherein the ratio (t / h) of the thickness (t) of the transferred film to the height (h) of the metal pillar is 0.4 to 0.7. [5] The method for producing a bonded body according to the above [4], further comprising a step 4 of heating the first bonded body and the second bonded body that are in contact with each other via the metal paste. [6] The method for producing a joint body according to the above [4] or [5], wherein in step 2, a force for contacting the metal pillar with the transfer film is 0.6 to 2.0 N. [7] The method for producing a bonded body according to any one of the above [4] to [6], wherein in step 2, the metal pillar is kept in contact with the transferred film for a period of 500 to 2000 ms. [8] The method for producing a bonded body according to any one of the above [4] to [7], wherein step 2 is carried out two to four times. [9] The method for producing a bonded body according to any one of the above [4] to [8], wherein the metal paste is the metal paste according to any one of the above [1] to [3].

[0121] Although the embodiments of the present disclosure have been described above, the configurations and combinations thereof in each embodiment are merely examples, and addition, omission, substitution, and other modifications of the configurations are possible as appropriate within the scope of the gist of the present disclosure. The present disclosure is not limited to the embodiments. Each feature disclosed herein may be combined with any other feature disclosed herein. EXAMPLES

[0122] The present disclosure will be described in more detail below by showing examples, but interpretation of the present disclosure is not limited to these examples.

[0123] <Material> First, the materials used in the examples and comparative examples are summarized below.

[0124] (metal particles) Copper particles A: manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle diameter 200 nm (measured by laser diffraction / scattering method) Copper particles B: Taiyo Nippon Sanso Corporation, volume average particle diameter 110 nm (measured by SEM observation method)

[0125] (solvent) Formic acid: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., formic acid concentration over 98% by mass, reagent MDEtA: N-methyldiethanolamine, Tokyo Chemical Industry Co., Ltd., reagent PMDTA: Pentamethyldiethylenetriamine, manufactured by Tokyo Chemical Industry Co., Ltd., reagent DMDA: N,N-Dimethyldodecylamine, manufactured by Tokyo Chemical Industry Co., Ltd., reagent 1,3-BG: 1,3-butanediol, manufactured by Daicel Corporation 1,6-HDDA: 1,6-Hexanediol diacetate, manufactured by Daicel Corporation

[0126] (resin) PVP K30: Polyvinylpyrrolidone, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. S-LEC SV12: Polyvinyl acetal resin, manufactured by Sekisui Chemical Co., Ltd. S-LEC SV26: Polyvinyl acetal resin, manufactured by Sekisui Chemical Co., Ltd. EC20: Ethyl cellulose resin, manufactured by Dow Chemical EC300: Ethyl cellulose resin, manufactured by Dow Chemical CELTOL OG-02: Manufactured by Daicel Corporation

[0127] (First conjugate) CC40: Manufactured by Waltz Corporation, 29,576 copper pillars (material: copper, pillar diameter 22 μm, height (h) 20 μm), pillar spacing 40 μm (distance from center of pillar to center of adjacent pillar) (Second transconjugant) IP40: Manufactured by Waltz Corporation, 29,576 electrode pads

[0128] [1] Preparation of copper paste Example 1 Copper particles A, formic acid, and basic compounds MDEtA, PMDTA, and DMDA were mixed to the composition shown in Table 1, and the mixture was stirred for 2 minutes using a planetary centrifugal mixer (Thinky Corporation, product name "Awatori Rentaro") to prepare a copper paste.

[0129] (Examples 2 to 5, Comparative Examples 1 and 2) A copper paste was prepared in the same manner as in Example 1, except that the materials were mixed so as to obtain the composition shown in Table 1.

[0130] <Copper paste viscosity> The copper paste prepared in [1] above was subjected to a shear rate of 0.01 s at 25 °C using a rheometer (Anton Paar "MCR302e"). -1 From 300s -1 The shear viscosity was measured when the shear stress was changed to Furthermore, from the obtained measurement data, -1 and 1s -1 The TI value was calculated by substituting the respective shear viscosity data at this time into the following formula (I). TI value=Log(η(0.1) / η(1)) / Log(1 / 0.1) ···(I) In the above formula (I), η(0.1) is the shear rate of 0.1 s -1 η(1) is the shear viscosity at a shear rate of 1s -1 is the shear viscosity at Table 1 shows the shear rate of 10 s -1 The shear viscosity and TI value at these times are shown.

[0131] <Evaluation of copper paste> The copper paste prepared in [1] above was used to carry out the following evaluations. The results are shown in Table 1.

[0132] Evaluation (1): Surface roughness of the transferred film The surface roughness of the transferred film was evaluated by the following method. First, a groove measuring 20 mm×20 mm and 10 μm deep was dug on the surface of a Si wafer (diameter 100 mm, thickness 525 μm) to prepare a transfer film preparation jig A. Next, the copper paste prepared in [1] above was filled into the grooves of the transfer film preparation jig A using a metal squeegee to prepare a transfer film. The surface roughness Ra and Rz of the obtained transferred film were measured using a laser microscope ("VK9510" manufactured by Keyence Corporation) and evaluated according to the following evaluation criteria. The smaller the surface roughness of the transfer film, the higher the transfer rate tends to be. Therefore, in this example, "2" and "3" were evaluated as passing. [Evaluation Criteria] 1: Ra is greater than 5 μm 2: Ra is 5μm or less and Rz is over 10μm 3: Ra is 5 μm or less and Rz is 10 μm or less

[0133] Rating (2): Drooping after transcription The evaluation of sagging after transfer was carried out by the following method. First, the copper pillar of the first bonded body (CC40) was brought into contact with the transfer film prepared in the above evaluation (1) and pressed against it for 1000 ms with a force of 0.98 N to transfer the copper paste to the copper pillar. Once again, the copper pillar to which the copper paste was transferred was pressed against the transfer film under the same conditions as above to obtain a first bonded body having a copper pillar to which the copper paste was transferred. The state of the copper paste transferred to the copper pillar was observed at a magnification of 200 times using a digital microscope (manufactured by Keyence Corporation, "VHX800") from a direction perpendicular to the surface on which the copper pillar of the obtained first bonded body was arranged. Furthermore, an image for analysis was taken in an arbitrarily selected observation area, and the diameter of the copper paste transferred onto the copper pillar (above 30S in FIG. 2) was measured for the copper pillar in the image. In this example, when there was one or more copper pillars in the image in which the diameter of the copper paste transferred onto the copper pillar was larger than 1.2 times the diameter (22 μm) of the copper pillar before transfer, the state was judged as "with sagging" as a state in which sagging occurred, and the other states were judged as "without sagging". In addition, since the occurrence of sagging can cause electrode shorts due to solder bridging in narrow-pitch electronic devices, it is preferable that sagging be eliminated.

[0134] [Table 1]

[0135] As shown in Table 1, at 25°C, the shear rate was 10 s -1 The shear viscosity measured at is in the range of 1 to 100 Pa s and the shear rate is 0.1 s -1 Shear viscosity measured at 1s and shear rate -1 It was confirmed that a copper paste having a logarithmic TI value (the ratio of the shear viscosity measured by the method) within the range of 0.7 to 1.0 can obtain a transfer film having a smooth surface, and further, when the transfer film is used to transfer onto a copper pillar, sagging of the copper paste after transfer can be effectively suppressed (Examples 1 to 5).

[0136] In contrast, copper paste at 25°C and a shear rate of 10 s -1 It was confirmed that when the shear viscosity measured by is not within the range of 1 to 100 Pa s (Comparative Example 1) or when the TI value is not within the range of 0.7 to 1.0, it is not possible to obtain a transfer film having a smooth surface while suppressing sagging of the copper paste after transfer.

[0137] [2] Preparation of the zygote Example 6 First, a transfer film A having a thickness (t) of 10 μm was prepared using the copper paste of Example 1 prepared in [1] above. The transfer film A was prepared in the same manner as in the above evaluation (1), and the surface roughnesses Ra and Rz were measured in the same manner. Next, the copper pillar of the first bonded body (CC40) was brought into contact with the transfer film A and pressed with a force of 0.98 N for 1000 ms to transfer the copper paste to the copper pillar, thereby obtaining a first bonded body having a copper pillar to which the copper paste was transferred. At this time, the transfer characteristics of the first bonded body having a copper pillar to which the copper paste was transferred were evaluated as described below. Next, a second bonded object (IP40) having an electrode pad was prepared, and mounted using a flip chip bonder so that the copper paste transferred to the copper pillar of the first bonded object was in contact with the electrode pad of the second bonded object. The bonded object was then heated and bonded at 250°C for 10 minutes under a nitrogen atmosphere with a load of 1.6 MPa applied, to produce a bonded object.

[0138] Example 7 In Example 7, a bonded body was obtained in the same manner as in Example 6, except that the number of times that the copper pillar of the first bonded body was brought into contact with the transfer film A was changed from once to twice.

[0139] Example 8 In Example 8, a bonded body was obtained in the same manner as in Example 6, except that the number of times that the copper pillar of the first bonded body was brought into contact with the transfer film A was changed from once to three times.

[0140] Example 9 In Example 9, a bonded body was obtained in the same manner as in Example 6, except that the number of times that the copper pillar of the first bonded body was brought into contact with the transfer film A was changed from once to four times.

[0141] Comparative Example 3 In Comparative Example 3, a bonded structure was obtained in the same manner as in Example 7, except that the transfer membrane B described below was used instead of the transfer membrane A described above. Transfer film B was prepared in the same manner as in evaluation (1) above, except that the surface of transfer film A was scratched and roughened overall using a metal squeegee with an uneven surface, and the surface roughness Ra and Rz were measured in the same manner.

[0142] Comparative Example 4 In Comparative Example 4, a bonded structure was obtained in the same manner as in Example 7, except that the transfer membrane C described below was used instead of the transfer membrane A described above. Transfer film C was prepared in the same manner as in evaluation (1) above, except that a metal squeegee with an uneven surface was used to pinpoint scratch and roughen a portion of the surface of transfer film A, and the surface roughness Ra and Rz were measured in the same manner.

[0143] Comparative Example 5 In Comparative Example 5, a bonded structure was obtained in the same manner as in Example 7, except that the transfer membrane D described below was used instead of the transfer membrane A described above. The transfer film D was prepared in the same manner as in the above evaluation (1), except that the transfer film preparation jig B described below was used instead of the transfer film preparation jig A, and the surface roughness Ra and Rz were measured in the same manner. The transfer film preparation jig B was prepared by digging a groove of 20 mm×20 mm and 5 μm deep on the surface of a Si wafer (diameter 100 mm, thickness 525 μm).

[0144] Comparative Example 6 In Comparative Example 6, a bonded structure was obtained in the same manner as in Example 7, except that the transfer film E described below was used instead of the transfer film A described above. The transfer film E was prepared in the same manner as in the above evaluation (1), except that the transfer film preparation tool C described below was used instead of the transfer film preparation tool A, and the surface roughness Ra and Rz were measured in the same manner. The transfer film preparation jig C was prepared by digging a groove of 20 mm×20 mm and 15 μm deep on the surface of a Si wafer (diameter 100 mm, thickness 525 μm).

[0145] <Transfer characteristics> As the transfer characteristics, the transfer rates were evaluated by the following method in Example 7 and Comparative Examples 3 and 4, and the transfer amounts were evaluated by the following method in Examples 6 to 9 and Comparative Examples 5 and 6. The results are shown in Table 2.

[0146] Transfer rate (%) In the above-mentioned bonded body production step [2], the first bonded body having the copper pillars to which the copper paste was transferred was observed at a magnification of 200 times using a digital microscope (manufactured by Keyence Corporation, "VHX800") before contacting with the second bonded body, and the obtained image was analyzed to determine the transfer rate (%). Specifically, an image for analysis was taken in an arbitrarily selected observation area, and the ratio (percentage) of the number of copper pillars to which the copper paste was transferred to the total number of copper pillars in the image was calculated to determine the transfer rate (%). A higher transfer rate means a better transfer yield and superior transfer characteristics. The parts where the copper paste has not been transferred cannot be bonded to the second object via the copper paste, which is thought to cause connection failures (opens). 5 and 6 show images of the surface of the first bonded body on which the copper pillars are arranged, which were used in the above observation. FIG. 5 corresponds to the first bonded body of Example 7, and FIG. 6 corresponds to the first bonded body of Comparative Example 3. Copper pillars to which the copper paste has been transferred are indicated by black dots. On the other hand, areas surrounded by squares without black dots are copper pillars to which the copper paste has not been transferred. The more copper pillars to which the copper paste has not been transferred, the lower the transfer rate.

[0147] Transfer amount In the above-mentioned [2] manufacturing process of the bonded body, the copper pillar to which the copper paste of the first bonded body was attached was visually observed before contact with the second bonded body, and evaluated according to the following evaluation criteria. In the following evaluation criteria, if the result is "2" or "3", it is considered that a bonded body with good connection can be obtained. On the other hand, if the result is "1", it is considered that a good connection with the second bonded body cannot be made, resulting in a poor connection (high resistance) or insufficient mechanical strength. Also, if the result is "4", it is considered that a solder bridge will occur, causing a poor connection (short circuit). [Evaluation Criteria] 1: Too little (only a portion of the copper pillar tip has copper paste) 2: Slightly less (the amount of copper paste is small, but the tip of the copper pillar is covered with copper paste) 3: Sufficient (the tip of the copper pillar is covered with a sufficient amount of copper paste, but the copper paste does not reach the base of the copper pillar) 4: Too much (the copper paste reaches the side of the copper pillar or the base of the copper pillar, and the copper pillar is buried in the copper paste)

[0148] <Evaluation of the conjugate> The bonded structure prepared in [2] above was subjected to the following evaluations. The results are shown in Table 2.

[0149] Rating (3): Share strength The bond strength (MPa) of the obtained bonded body was measured using a universal bond tester (Nordson DAGE's "Die Shear Tester SERIES 4000") and evaluated according to the following criteria. The measurement was performed three times, and the arithmetic average value was used as the measurement result. The larger the shear strength of the bonded body, the higher the mechanical strength of the bonded portion via the copper paste. In this example, a rating of "3" was evaluated as passing. [Evaluation Criteria] Less than 1:1MPa 2: 1MPa or more and less than 10MPa 3: 10MPa or more

[0150] Rating (4): Electrical resistance A terminal was attached to the pad of the lead wire on the substrate side of the resulting bonded body, and the electrical resistance (Ω) was measured using a tester (Fluke 27II industrial multimeter, manufactured by Fluke Corp.) and evaluated according to the following criteria. The measurement was performed three times, and the arithmetic average value was used as the measurement result. The lower the electrical resistance of the bonded body, the better the bonding via the copper paste. On the other hand, if the above measurement results in an open or short circuit, or if the resistance is high, it means that the bonding via the paste is poor. In this example, a score of "3" was evaluated as passing based on the following evaluation criteria. [Evaluation Criteria] 1: Open (no electricity flow, overrange) 2: High resistance (100Ω or more) 3: Good (less than 100 Ω) 4: Short (resistance value much lower than the theoretical value)

[0151] [Table 2]

[0152] As shown in Table 2, in the manufacturing methods of the bonded bodies of Examples 6 to 9, the surface roughness of the transferred film used satisfied the prescribed requirements (surface roughness Ra of 0.1 to 5 μm and surface roughness Rz of 0.5 to 10 μm), and furthermore, the ratio (t / h) of the thickness (t) of the transferred film to the height (h) of the copper pillar was controlled within the range of 0.4 to 0.7. As a result, it was confirmed that bonded bodies having high reliability in terms of electrical and mechanical strength were obtained.

[0153] On the other hand, in the manufacturing methods of the bonded bodies of Comparative Examples 3 to 6, the surface roughness of the transfer film used did not satisfy the predetermined requirements or the ratio (t / h) was not controlled within the range of 0.4 to 0.7, and therefore the obtained bonded bodies were confirmed to be inferior in particular in electrical reliability. [Industrial Applicability]

[0154] The metal paste of the present disclosure can obtain a transfer film with excellent surface smoothness and can effectively suppress sagging of the metal paste even after transfer, and therefore can be suitably used for fine bump bonding with narrow pitches, etc. Specifically, the metal paste has industrial applicability as a metal paste used in flip chip technology using metal pillars. In addition, the method for producing a bonded body according to the present disclosure can efficiently produce a bonded body having high reliability in terms of electrical and mechanical strength, and is therefore suitable as a method for producing a bonded body in which bumps are formed at high density. Specifically, the method has industrial applicability as a method for producing a high-density three-dimensional package, for example. [Explanation of symbols]

[0155] 11. Substrate and transfer film preparation tool 11H Groove 13 Metal Squeegee 2 Metal Paste 20 Transfer membrane Surface of 20S transfer membrane 21 Joint 22 Sintered body 3. First conjugate 30 Metal Pillar 30S At least one surface of the metal pillar 31 First substrate 4 Object to be joined 40 Electrode Pads 40S Electrode pad contact surface 41 Second board 100 zygote

Claims

1. A metal paste comprising metal particles and a solvent, At 25°C, shear rate 10 s －１ The shear viscosity measured by is 1 to 100 Pa s, Shear rate 0.1 s －１ Shear viscosity measured at shear rate 1s －１ The metal paste has a logarithmic TI value (a ratio of the shear viscosity measured by the method described above) of 0.7 to 1.

0.

2. The metal paste of claim 1 , wherein the metal particles are copper particles.

3. The metal paste according to claim 1 or 2, wherein the solvent comprises formic acid and a basic compound.

4. Step 1 of applying a metal paste onto a substrate to prepare a transfer film; A step 2 of contacting a metal pillar of a first bonded body having a metal pillar with the transfer film to transfer the metal paste to at least one surface of the metal pillar; A step 3 of contacting the metal paste transferred to the metal pillar with a second object to be joined; A method for producing a bonded body, comprising: The surface of the transfer film has a surface roughness Ra of 0.1 to 5 μm and a surface roughness Rz of 0.5 to 10 μm; a ratio (t / h) of a thickness (t) of the transferred film to a height (h) of the metal pillar is 0.4 to 0.

7.

5. 5. The method for producing a bonded body according to claim 4, further comprising a step 4 of heating the first bonded body and the second bonded body which are in contact with each other via the metal paste.

6. 6. The method for producing a joint body according to claim 4, wherein in step 2, a force for contacting the metal pillar with the transfer film is 0.6 to 2.0 N.

7. The method for producing a joint body according to claim 4 or 5, wherein in step 2, the time for which the metal pillar is in contact with the transfer film is 500 to 2000 ms.

8. The method for producing a bonded body according to claim 4 or 5, wherein the step 2 is carried out two to four times.

9. The method for producing a joint body according to claim 4 or 5, wherein the metal paste is the metal paste according to claim 1 or 2.

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