Method for manufacturing a substrate with conductive pillars and metal paste for forming conductive pillars

Abstract

The present invention provides a conductive pillar substrate having conductive pillars in which the occurrence of cracks and voids is sufficiently suppressed, while also significantly reducing resist residue, as well as a method for manufacturing the same and a metal paste. [Solution] The method comprises the steps of: preparing a substrate with a resist layer; providing a metal paste portion so as to cover the surface of the pores in the resist layer; heating the metal paste portion to remove part of the volatile solvent; removing part of the metal paste portion to form a conductive pillar precursor having a flattened exposed surface; firing the conductive pillar precursor in a reducing atmosphere at 200°C or less; and removing the resist layer. The metal particles include first copper particles with a volume average particle size of 0.8 μm or more and second copper particles with a volume average particle size of 0.5 μm or less. The concentration of metal particles in the provided metal paste portion is 95.0% by mass or more, and the content of second copper particles in the provided metal paste portion is 50% by mass or less based on the total amount of metal particles.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a substrate with conductive pillars and a metal paste for forming conductive pillars. [Background technology]

[0002] One known method for manufacturing a conductive pillar-equipped substrate is to fill the openings in a photoresist with copper nanopaste and sinter the copper without applying pressure to produce copper pillars (see Non-Patent Document 1 below). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] T. Aoki, E. Nakamura, et al, “Plating-free Bumping by Cu Nanopaste and Injection Molded Solder (IMS) for Fine Pitch Flip Chip Joining”, 2020 IEEE 70th Electronic Components and Technology Conference (ECTC), 2020, p.742-748. [Overview of the project] [Problems that the invention aims to solve]

[0004] In the method described above, it is necessary to sinter copper particles to form copper pillars and then peel off the photoresist layer. However, the photoresist layer that has undergone the sintering process is difficult to remove by a normal wet process, and resist residue tends to be generated. Furthermore, when the outer diameter and pitch of the conductive pillars to be formed are at the micro level, it becomes even more difficult to sufficiently reduce the resist residue, and it also becomes difficult to form a sintered body with sufficiently few cracks and voids.

[0005] Therefore, the present invention aims to provide a method for manufacturing a conductive pillar substrate, a metal paste that can be used therefor, and a conductive pillar substrate, which can be obtained in which conductive pillars have sufficiently suppressed crack and void formation while resist residue is sufficiently reduced. [Means for solving the problem]

[0006] One aspect of the present invention relates to the following method for manufacturing a conductive pillar-equipped substrate. [1] A resist-layered substrate is prepared, comprising a substrate and a resist layer having holes leading to the substrate; a step a is to prepare a metal paste portion containing metal particles and a volatile solvent so as to fill the inside of the holes and cover at least the surface of the resist layer around the holes; b is to heat the metal paste portion to remove a portion of the volatile solvent; and a step b is to remove a portion of the heated metal paste portion so as to expose the surface to form a conductive pillar precursor containing the metal particles and the remainder of the volatile solvent, having a flattened exposed surface, inside the holes. A method for manufacturing a substrate with conductive pillars, comprising: step c; step d of firing the conductive pillar precursor in a reducing atmosphere at 200°C or below; and step e of removing the resist layer after step d, wherein the metal particles include first copper particles having a volume average particle size of 0.8 μm or more and second copper particles having a volume average particle size of 0.5 μm or less, the concentration of the metal particles in the metal paste portion provided in step a is 95.0% by mass or more, and the content of the second copper particles in the metal paste portion provided in step a is 50% by mass or less based on the total amount of metal particles.

[0007] According to the above manufacturing method, in step a, a metal paste portion containing a volatile solvent and having the above-mentioned specific metal particle composition is provided, and then by going through steps b and c, it is possible to achieve both good filling of the inside of the pores and the formation of a conductive pillar precursor that does not shrink in volume by firing, and in step d, firing at 200°C or below, a conductive pillar can be formed in which the occurrence of cracks and voids is sufficiently suppressed, and in step e, the resist residue can be sufficiently reduced.

[0008] [2] The method for manufacturing a conductive pillar substrate according to [1], wherein the first copper particles are flake-shaped copper particles. [3] A method for manufacturing a conductive pillar substrate according to [1] or [2], wherein in step d, the conductive pillar precursor is fired in an atmosphere containing formic acid at 150°C or less. [4] The method for manufacturing a conductive pillar substrate according to [1] or [2], wherein the resist layer is of the positive type.

[0009] Another aspect of the present invention relates to the following metal paste. [5] A metal paste used for forming conductive pillars on a substrate, comprising metal particles and a volatile solvent, wherein the metal particles comprise first copper particles having a volume average particle size of 0.8 μm or more and second copper particles having a volume average particle size of 0.5 μm or less, the concentration of the metal particles being 95.0% by mass or more, and the content of the second copper particles being 50% by mass or less based on the total amount of the metal particles. [6] The metal paste for forming conductive pillars according to [5], wherein the first copper particles are flake-shaped copper particles.

[0010] The above-mentioned metal paste provides sufficient printability, and the metal paste portion can be efficiently formed in the above-mentioned method for manufacturing a conductive pillar-equipped substrate.

[0011] Another aspect of the present invention relates to the following conductive pillar-equipped substrate. [7] A substrate with conductive pillars, comprising a substrate and conductive pillars provided on the substrate, wherein the conductive pillars are made of a sintered body of the conductive pillar-forming metal paste described in [5] or [6]. [Effects of the Invention]

[0012] According to the present invention, there are provided a method for manufacturing a substrate with conductive pillars, a metal paste that can be used therein, and a substrate with conductive pillars, which can obtain a substrate with conductive pillars having sufficiently suppressed generation of cracks and voids and sufficiently reduced resist residue.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic diagram showing an example of a method for manufacturing a substrate with conductive pillars according to the present embodiment. [Figure 2] It is a schematic diagram showing an example of a method for manufacturing a substrate with conductive pillars according to the present embodiment. [Figure 3] It is a schematic diagram showing an example of a method for manufacturing a substrate with conductive pillars according to the present embodiment. [Figure 4] It is a schematic diagram showing an example of a method for manufacturing a substrate with conductive pillars according to the present embodiment. [Figure 5] It is a schematic diagram showing an example of a method for manufacturing a substrate with conductive pillars according to the present embodiment. [Figure 6] It is a schematic diagram showing an example of a substrate with conductive pillars according to the present embodiment. [Figure 7] It is a schematic diagram showing an example of a step of forming a solder bump.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0015] <Metal Paste> The metal paste of the present embodiment contains metal particles and a volatile solvent, and the content of the metal particles is 95.0% by mass or more based on the total amount of the metal paste. The metal paste of the present embodiment can be used for forming the metal paste portion in the method for manufacturing a substrate with conductive pillars described later, and can form conductive pillars.

[0016] The metal particle content in the metal paste of this embodiment may be 95.2% by mass or more, 95.5% by mass or more, 95.7% by mass or more, or 96% by mass or more, based on the total amount of metal paste, and may be 98% by mass or less, 97% by mass or less, or 96.5% by mass or less, and may be 95.0 to 98% by mass, 95.2 to 97% by mass, or 95.7 to 96.5% by mass.

[0017] [Metal particles] Examples of metal particles include nickel, silver, copper, gold, palladium, platinum, and solder. When the metal paste contains copper particles, it becomes easy to obtain a conductor that has sufficient conductivity and whose resistance does not easily increase even when subjected to temperature changes, and a substrate that has sufficient conductivity and through electrodes with excellent connection reliability. In this embodiment, the metal particles include first copper particles with a volume average particle size of 0.8 μm or more and second copper particles with a volume average particle size of 0.5 μm or less, from the viewpoint of reducing resistance, ensuring resistance to io-migration, and facilitating wiring formation.

[0018] In this specification, the volume-average particle size (hereinafter sometimes referred to as "average particle size") refers to the 50% volume-average particle size (D50). When determining the volume-average particle size of metal particles, it can be determined by dispersing the raw metal particles in a dispersion medium such as water or alcohol and measuring the result using a laser diffraction / scattering particle size distribution analyzer.

[0019] (First copper particle) The average particle size of the first copper particles may be 0.8 μm or more, 1.0 μm or more, 2.0 μm or more, or 3.0 μm or more, from the viewpoint of improving the sintering density in the pores of the resist layer corresponding to the shape of the conductive pillars and suppressing the occurrence of voids and cracks in the pores. For example, from the viewpoint of suppressing particle clogging in micropores with an inner diameter of 100 μm or less (pores for forming conductive pillars with an outer diameter of 100 μm or less) and improving packing performance, it may be 10 μm or less, 8.0 μm or less, 5.0 μm or less, or 4.0 μm or less. From the viewpoint of suppressing voids and cracks and suppressing particle clogging in micropores, it may also be 0.8 μm to 4.0 μm, 1.0 μm to 3.5 μm, or 1.2 μm to 3.0 μm. The ratio (DC1 / DH) of the average particle size DC1 of the first copper particles to the inner diameter DH of the pores may be 0.01 or greater, 0.03 or greater, or 0.04 or greater, from the viewpoint of suppressing particle clogging in micropores and improving packing performance. From the viewpoint of suppressing voids and cracks by reducing shrinkage due to firing, it may be 0.15 or less, 0.1 or less, or 0.05 or less. Furthermore, from the above viewpoint, the ratio (DC1 / DH) may be between 0.01 and 0.15, or between 0.03 and 0.1.

[0020] The shape of the first copper particles may be, for example, spherical, lumpy, needle-shaped, flattened (flake-shaped), or substantially spherical. The first copper particles may also be aggregates of copper particles having these shapes. In this embodiment, the metal paste may include spherical copper particles as the first copper particles, from the viewpoint of reducing the step difference between the central and end portions of the conductive pillar formed and suppressing fluctuations in connection resistance even after reliability tests (e.g., temperature cycle tests).

[0021] The first copper particles may contain 60% by mass or more, 80% by mass or more, or 100% by mass of particles with an aspect ratio of 2 or less, such as spherical particles, from the viewpoint of improving the printability of the metal paste. The aspect ratio (major axis / minor axis) of the particles can be determined, for example, by observing an SEM image of the particles and measuring the major axis and minor axis (e.g., thickness).

[0022] Furthermore, the metal paste of this embodiment may contain flake-shaped copper particles as the first copper particles, from the viewpoint of suppressing voids and cracks by reducing shrinkage due to firing. It may also contain spherical copper particles and flake-shaped copper particles, from the viewpoint of lowering the viscosity of the metal paste, improving its ability to fill micropores, and suppressing voids and cracks by reducing shrinkage due to firing. When spherical copper particles and flake-shaped copper particles are used in combination, their mass ratio (spherical copper particles) / (flake-shaped copper particles) may be 1 to 9, 1.2 to 2.5, or 1.4 to 4.

[0023] The flake-shaped copper particles may have an aspect ratio of 1.5 or higher, 2 or higher, or 3 or higher.

[0024] The first copper particles may be produced by chemical reduction, atomization, electrolysis, pulverization, plasma rotation electrode method, homogeneous liquid spraying method, heat treatment method, etc., and may be wet copper powder or atomized copper powder from the viewpoint of easily obtaining a uniform diameter and improving the dispersibility of the metal paste.

[0025] The first copper particles may include wet copper powder. In this case, conductive pillars with excellent conductivity are more easily obtained. This effect is thought to be obtained because the wet copper powder has the property of readily bonding with the copper particles blended as the second metal. The wet copper powder may have a D90 / D50 ratio of 1.5 or less.

[0026] Furthermore, the copper particles can contain both wet copper powder and atomized copper powder. In this case, it becomes easier to improve the printability of the metal paste and reduce the step difference between the center and the ends of the conductive pillars formed, thereby suppressing fluctuations in connection resistance even after reliability tests (e.g., temperature cycling tests). The reason for these effects is presumed to be as follows: That is, the coexistence of wet copper powder, which readily bonds with the second copper particles and has a uniform particle size, and atomized copper powder, which has a wide particle size distribution, allows the wet copper powder to bond with the atomized copper powder while also bonding with the second copper particles, resulting in the formation of a strong sintered body with a close-packed structure and suppression of voids and cracks due to reduced shrinkage during sintering. The atomized copper powder may have a D90 / D50 of 1.6 or higher, 1.7 or higher, or 1.8 or higher.

[0027] When the first copper particles contain wet copper powder and atomized copper powder, the proportion of wet copper powder may be more than 0 parts by mass and less than 100 parts by mass, or 20 to 80 parts by mass, based on 100 parts by mass of the total amount of wet copper powder and atomized copper powder.

[0028] Commercially available copper particles can be used as the first copper particles. Examples of commercially available first copper particles include 1050Y (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 0.81 μm, D90: 1.1 μm, spherical, wet copper powder), 1100Y (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 1.1 μm, D90: 1.6 μm, spherical, wet copper powder), 1200Y (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 2.1 μm, D90: 3.1 μm, spherical, wet copper powder), 1300Y (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 3.5 μm, D90: 5 μm, spherical, wet copper powder), and 1100YP (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): Examples include 1.4μm, D90:2.3μm, flattened, wet-processed copper powder), 1200YP (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50):3.1μm, D90:5.3μm, flattened, wet-processed copper powder), MA-C02K (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50):1.8μm, D90:3.6μm, spherical, atomized copper powder), MA-C025K (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50):2.4μm, D90:5.2μm, spherical, atomized copper powder), and MA-C03K (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50):3.4μm, D90:6.3μm, spherical, atomized copper powder).

[0029] The first copper particles may be treated with a surface treatment agent from the viewpoints of dispersion stability and oxidation resistance. The surface treatment agent may be one that is removed during the formation of the conductive pillar (sintering of the copper particles). Examples of such surface treatment agents include aliphatic carboxylic acids such as palmitic acid, stearic acid, arachidic acid, and oleic acid; aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, and o-phenoxybenzoic acid; aliphatic alcohols such as cetyl alcohol, stearyl alcohol, isobornyl cyclohexanol, and tetraethylene glycol; aromatic alcohols such as p-phenylphenol; alkylamines such as octylamine, dodecylamine, and stearylamine; aliphatic nitriles such as stearonitrile and decanenitrile; silane coupling agents such as alkylalkoxysilane; and polymer treatment agents such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and silicone oligomer. The surface treatment agent may be used alone or in combination of two or more kinds.

[0030] The treatment amount of the surface treatment agent may be an amount of one molecular layer or more on the particle surface. Such a treatment amount of the surface treatment agent varies depending on the specific surface area of the first copper particles, the molecular weight of the surface treatment agent, and the minimum coating area of the surface treatment agent. The treatment amount of the surface treatment agent is usually 0.001 mass% or more.

[0031] The treatment amount of the surface treatment agent is related to the number of molecular layers (n) adhered to the surface of the first copper particles, the specific surface area (A p )(unit m 2 / g) of the first copper particles, the molecular weight (M s )(unit g / mol) of the surface treatment agent, the minimum coating area (S S )(unit m 2 / particle) of the surface treatment agent, and Avogadro's number (N A )(6.02×10 23 particles) and can be calculated from them. Specifically, the treatment amount of the surface treatment agent (mass%) = {(n × A p × M s ) / (S S × N A + n × A p × M sIt is calculated according to the formula )} × 100%.

[0032] The specific surface area of ​​the first copper particle can be calculated by measuring the specific surface area of ​​the dried copper particle using the BET specific surface area measurement method. The minimum coating area of ​​the surface treatment agent is 2.05 × 10⁻⁶ when the surface treatment agent is a linear saturated fatty acid. -19 m 2 It is / 1 molecule. For other surface treatment agents, it can be measured, for example, by calculation from a molecular model, or by the method described in "Chemistry and Education" (Katsuhiro Ueeda, Sumio Inafuku, Iwao Mori, 40(2), 1992, pp. 114-117). An example of a quantitative method for surface treatment agents is shown. Surface treatment agents can be identified by thermal desorption gas / gas chromatography-mass spectrometry of the dried powder obtained by removing the dispersion medium from the metal paste, thereby determining the carbon number and molecular weight of the surface treatment agent. The carbon content of the surface treatment agent can be analyzed by carbon content analysis. An example of a carbon content analysis method is high-frequency induction heating furnace combustion / infrared absorption spectroscopy. From the identified carbon number, molecular weight and carbon content of the surface treatment agent, the amount of surface treatment agent can be calculated using the above formula.

[0033] (Second copper particle) The average particle size of the second copper particles may be 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, or 0.2 μm or less from the viewpoint of sinterability, and may be 0.01 μm or more, 0.03 μm or more, 0.05 μm or more, 0.08 μm or more, or 0.1 μm or more from the viewpoint of suppressing synthesis costs, good dispersibility, and suppressing the amount of surface treatment agent used, and may be 0.1 μm to 0.3 μm, 0.12 μm to 0.28 μm, or 0.15 μm to 0.25 μm from the viewpoint of obtaining sinterability at low temperatures and good dispersibility in the paste.

[0034] The second copper particles can act as copper particles that suitably bond the first copper particles together. Furthermore, the second copper particles have superior sinterability compared to the first copper particles and can have the function of promoting the sintering of the copper particles. For example, compared to using the first copper particles alone, it becomes possible to sinter the copper particles at a lower temperature.

[0035] The second copper particles may be wet copper powder produced by a chemical reduction method.

[0036] The shape of the second copper particles may be, for example, spherical, lumpy, needle-shaped, flattened (flake-shaped), or approximately spherical. The second copper particles may also be aggregates of copper particles having these shapes. From the viewpoint of dispersibility and packing, the shape of the second copper particles may be spherical, approximately spherical, or flattened (flake-shaped), and from the viewpoint of flammability and miscibility with the first copper particles, they may be spherical or approximately spherical.

[0037] The aspect ratio of the second copper particles may be 5 or less, 4 or less, or 3 or less, from the viewpoint of dispersibility, packing, and miscibility with the first copper particles.

[0038] As the second copper particles, synthesized or commercially available particles can be used. Examples of commercially available second copper particles include CH0200L1 (manufactured by Mitsui Mining & Smelting Co., Ltd., trade name, average particle size (D50): 200 nm, spherical) and Tn-Cu100 (manufactured by Taiyo Nippon Sanso Corporation, average particle size (D50): 120 nm, spherical).

[0039] The second copper particles may be treated with a specific surface treatment agent. Examples of specific surface treatment agents include organic acids having 8 to 16 carbon atoms. Examples of organic acids having 8 to 16 carbon atoms include caprylic acid, methylheptanoic acid, ethylhexanoic acid, propylpentanoic acid, pelargonic acid, methyloctanoic acid, ethylheptanoic acid, propylhexanoic acid, capric acid, methylnonanoic acid, ethyloctanoic acid, propylheptanoic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanoic acid, lauric acid, methylundecanoic acid, ethyldecanoic acid, propylnonanoic acid, butyloctanoic acid, Saturated fatty acids such as pentylheptanoic acid, tridecanoic acid, methyldodecanoic acid, ethylundecanoic acid, propyldecanoic acid, butylnonanoic acid, pentyloctanoic acid, myristic acid, methyltridecanoic acid, ethyldodecanoic acid, propylundecanoic acid, butyldecanoic acid, pentylnonanoic acid, hexyloctanoic acid, pentadecanoic acid, methyltetradecanoic acid, ethyltridecanoic acid, propyldodecanoic acid, butylundecanoic acid, pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanoic acid, ethyltetradecanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecanoic acid, heptylnonanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, nonylcyclohexanecarboxylic acid, etc. Examples include acids, unsaturated fatty acids such as nonenic acid, methylnonenic acid, 10-hydroxy-2-decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, and sapienic acid; and aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, o-phenoxybenzoic acid, methylbenzoic acid, ethylbenzoic acid, propylbenzoic acid, butylbenzoic acid, pentylbenzoic acid, hexylbenzoic acid, heptylbenzoic acid, octylbenzoic acid, and nonylbenzoic acid. Organic acids may be used individually or in combination of two or more.By combining such organic acids with the second copper particles described above, it tends to be possible to achieve both good dispersibility of the second copper particles and good desorption of the organic acid during sintering.

[0040] The amount of surface treatment agent applied may be an amount that adheres to the surface of the second copper particles in a layer of one to three molecules. The amount of surface treatment agent applied may be 0.07% by mass or more, 0.10% by mass or more, or 0.2% by mass or more, and may be 2.1% by mass or less, 1.6% by mass or less, or 1.1% by mass or less. The amount of surface treatment applied to the second copper particles can be calculated for the first copper particles using the method described above. The same applies to the specific surface area, the molecular weight of the surface treatment agent, and the minimum coating area of ​​the surface treatment agent.

[0041] The content of the second metal particles in the metal paste is 50% by mass or less based on the total amount of metal particles, from the viewpoint of connection reliability. However, from the viewpoint of lowering the sintering temperature and improving adhesion with the underlying metal layer, and from the viewpoint of reducing the porosity of the sintered body, suppressing shrinkage during sintering, and suppressing crack occurrence, it may be 10 to 50% by mass or 20 to 40% by mass.

[0042] The total content of the first copper particles and the second copper particles in the metal paste may be 100 parts by mass, 85 to 99.5 parts by mass, 90 to 99 parts by mass, or 95 to 98 parts by mass, when the total mass of the metal particles is 100 parts by mass.

[0043] The content of the first copper particles and the second copper particles may be 50 to 90 parts by mass and 50 to 10 parts by mass, 55 to 85 parts by mass and 45 to 15 parts by mass, or 60 to 80 parts by mass and 40 to 20 parts by mass, respectively, based on 100 parts by mass of the total of the first and second copper particles.

[0044] The metal paste of this embodiment may contain copper particles and metal particles other than copper particles (hereinafter also referred to as "other metal particles"). In this case, the other metal particles may be nickel particles, silver particles, gold particles, palladium particles, platinum particles, or solder particles. One or more of these may be included. The average particle size of the other metal particles may be 0.01 μm or more, 0.03 μm or more, or 0.05 μm or more, and may be 5 μm or less, 3.0 μm or less, or 2.0 μm or less. The average particle size of the solder particles may be 1.0 μm or more, 1.5 μm or more, 2.0 μm or more, 3.0 μm or more, or 4.0 μm or more, and may be 15 μm or less, 10 μm or less, 8.0 μm or less, or 5.0 μm or less.

[0045] The content of other metal particles may be 5 parts by mass or less, 3 parts by mass or less, 1 part by mass or less, or 0.8 parts by mass or less, when the total mass of copper particles is 100 parts by mass. The metal paste of this embodiment may not contain solder particles as other metal particles.

[0046] [Volatile solvents] Examples of volatile solvents include monohydric and polyhydric alcohols such as pentanol, hexanol, heptanol, octanol, decanol, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol (1,3-butanediol, etc.), α-terpineol, and isobornylcyclohexanol (MTPH); ethylene glycol butyl ether, ethylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether (ethyl carbitol), diethylene glycol butyl ether (diethylene glycol mono-n-butyl ether, etc.), diethylene glycol isobutyl ether, diethylene glycol hexyl ether, triethylene glycol methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol butyl methyl ether, diethylene glycol isopropyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, and propylene glycol propyl ether. Examples include ethers such as dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, dipropylene glycol dimethyl ether, tripropylene glycol methyl ether, and tripropylene glycol dimethyl ether; esters such as dimethyl phthalate, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, propylene glycol diacetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether acetate (DPMA), ethyl lactate, butyl lactate, γ-butyrolactone, and propylene carbonate; acid amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; aliphatic hydrocarbons such as cyclohexane, octane, nonane, decane, and undecane; aromatic hydrocarbons such as benzene, toluene, and xylene; mercaptans having alkyl groups with 1 to 18 carbon atoms; and mercaptans having cycloalkyl groups with 5 to 7 carbon atoms.Examples of mercaptans having an alkyl group with 1 to 18 carbon atoms include ethyl mercaptan, n-propyl mercaptan, i-propyl mercaptan, n-butyl mercaptan, i-butyl mercaptan, t-butyl mercaptan, pentyl mercaptan, hexyl mercaptan, and dodecyl mercaptan. Examples of mercaptans having a cycloalkyl group with 5 to 7 carbon atoms include cyclopentyl mercaptan, cyclohexyl mercaptan, and cycloheptyl mercaptan. The volatile solvent may be used alone or in combination of two or more types.

[0047] The metal paste of this embodiment may contain a volatile solvent having a vapor pressure of 4 Pa ​​or more and 30 Pa or less at 20°C (hereinafter also referred to as "high vapor pressure solvent"), from the viewpoint of printability and suppressing volume shrinkage before and after firing the conductive pillar precursor (for example, between step c, which forms the conductive pillar precursor, and step d, which fires the conductive pillar precursor), thereby suppressing voids and cracks. One type of high vapor pressure solvent may be used alone, or two or more types may be used in combination.

[0048] Examples of high vapor pressure solvents include α-terpineol, 1,3-butanediol, ethyl carbitol, and propylene glycol diacetate.

[0049] The metal paste of this embodiment may contain a volatile solvent with a vapor pressure of less than 4 Pa ​​at 20°C (hereinafter also referred to as "low vapor pressure solvent") as a volatile solvent, in order to suppress powdering due to drying caused by solvent evaporation during printing or paste preparation. The low vapor pressure solvent may be used alone or in combination of two or more types.

[0050] Examples of low vapor pressure solvents include isobornylcyclohexanol (MTPH), dimethyl phthalate, and diethylene glycol mono-n-butyl ether.

[0051] From the perspective of achieving both good printability and suppression of volume shrinkage before and after firing the conductive pillar precursor (for example, between step c of forming the conductive pillar precursor and step d of firing the conductive pillar precursor), thereby suppressing voids and cracks, the metal paste of this embodiment may contain a high vapor pressure solvent and a low vapor pressure solvent. In this case, each of the high vapor pressure solvent and the low vapor pressure solvent may be used alone as one type, or may be used in combination of two or more types. The content ratio of the high vapor pressure solvent and the low vapor pressure solvent may be such that the mass ratio [high vapor pressure solvent / low vapor pressure solvent] is 20 / 80 to 80 / 20, or may be 30 / 70 to 70 / 30.

[0052] The content of the volatile solvent in the metal paste of this embodiment may be 2% by mass or more, 3% by mass or more, or 3.5% by mass or more, based on the total mass of the metal paste, and may be 5% by mass or less, 4.8% by mass or less, 4.5% by mass or less, 4.3% by mass or less, or 4% by mass or less, and may be 2 to 5% by mass, 3 to 4.8% by mass, or 3.5 to 4.5% by mass.

[0053] The metal paste of this embodiment may contain a resin component such as an epoxy resin. The content of the resin component in the metal paste of this embodiment may be 10% by mass or less, may be 5% by mass or less, or may not contain a resin component.

[0054] The metal paste can be prepared by mixing metal particles such as the copper particles described above and any components (additives, etc.) into the volatile solvent described above. After mixing each component, a stirring process may be performed. The maximum diameter of the dispersion may be adjusted by a classification operation. Also, for mixing each component, means such as a three-roll mill, kneader, planetary mixer, etc. can be used.

[0055] If the metal paste contains the first copper particles and the second particles described above, the second copper particles, a surface treatment agent, and a dispersion medium may be mixed in advance and dispersed to prepare a dispersion of the second copper particles. This dispersion may then be further mixed with the first copper particles, other metal particles as needed, and any additives. This procedure improves the dispersibility of the second copper particles and improves their mixability with the first copper particles, thereby further improving the performance of the metal paste. Aggregates may be removed by subjecting the dispersion of the second copper particles to a classification operation.

[0056] From the viewpoint of printability, the metal paste of this embodiment may have a viscosity of 100 to 600 Pa·s or 150 to 400 Pa·s at 25°C. The viscosity of the metal paste is measured using a micro-spiral viscometer PCU-02V (manufactured by Malcolm Corporation, product name) under the conditions of rotation speed: 10 rpm and temperature: 25°C.

[0057] <Manufacturing method for conductive pillar-attached substrates> The manufacturing method of the conductive pillar substrate of this embodiment includes: preparing a resist layer substrate comprising a substrate and a resist layer having holes (also called openings) leading to the substrate; providing a metal paste portion containing metal particles and a volatile solvent so as to fill the inside of the holes and cover at least the surface around the holes of the resist layer; heating the metal paste portion to remove a portion of the volatile solvent; removing a portion of the heated metal paste portion so as to expose the surface to form a conductive pillar precursor containing the remaining metal particles and volatile solvent with a flattened exposed surface inside the holes; firing the conductive pillar precursor in a reducing atmosphere at 200°C or less; and removing the resist layer after step d. In the method for manufacturing a conductive pillar substrate of this embodiment, the metal particles include first copper particles having a volume average particle size of 0.8 μm or more and second copper particles having a volume average particle size of 0.5 μm or less, the concentration of metal particles in the metal paste portion provided in step a is 95.0% by mass or more, and the content of the second copper particles in the metal paste portion provided in step a is 50% by mass or less based on the total amount of metal particles.

[0058] Figures 1 to 6 are schematic diagrams showing an example of a method for manufacturing a conductive pillar-equipped substrate according to this embodiment. Figure 1 shows an example of a substrate used in the method for manufacturing a conductive pillar-equipped substrate. The method for manufacturing a conductive pillar-equipped substrate according to this embodiment will be described below with reference to these figures.

[0059] [Step a] Examples of substrates for the resist layer prepared in this process include silicon substrates, glass substrates, ceramic substrates, printed circuit boards, and semiconductor package substrates. In this embodiment, for example, as shown in Figure 1, a silicon substrate 10 having a silicon wafer 1 and a metal film 2 provided on the surface of the silicon wafer 1 can be prepared. The following explanation will describe the case in which conductive pillars are provided on this silicon substrate 10, but the silicon wafer may be replaced with other insulating substrates in the following explanation.

[0060] The thickness of the silicon wafer 1 may be 100 μm or more, 200 μm or more, or 300 μm or more from the viewpoint of suppressing warping of the substrate after sintering, and may be 800 μm or less, 300 μm or less, 200 μm or less, or 100 μm or less from the viewpoint of reducing the weight and density of the substrate.

[0061] The metal coating 2 may be provided on both main surfaces of the silicon wafer 1, on at least one main surface of the silicon wafer 1, or not provided at all. In the embodiment shown in Figure 1, the silicon substrate 10 has the metal coating 2 on one main surface of the silicon wafer 1.

[0062] Examples of metal coating 2 include titanium, nickel, chromium, copper, aluminum, palladium, platinum, and gold. From the viewpoint of adhesion, it is preferable that metal coating 2 is a coating in which titanium, nickel, and copper are layered in that order. Adhesion is improved by oxidizing the surface of the silicon wafer 1 to silicon oxide and forming a titanium layer on top of the silicon oxide. Furthermore, by providing a nickel layer on top of the titanium layer and then a copper layer on top of that, the diffusion of copper into the silicon wafer 1 can be suppressed compared to the case where the copper layer is directly provided on top of the titanium layer. In addition, by providing a copper layer on the surface, the adhesion between the copper layer and the copper particles in the metal paste is improved, and reliability is improved.

[0063] The resist layer of the substrate with a resist layer may be positive or negative, and from the viewpoint of reducing the amount of residue left behind after peeling of the resist layer, it may be positive.

[0064] The resist layer can be formed, for example, by forming a positive or negative photosensitive layer on a metal film 2 of the substrate 10, exposing the photosensitive layer in a predetermined pattern, and developing it. This makes it possible to obtain a substrate 20 with a resist layer, as shown in Figure 2, which comprises a substrate 10 and a resist layer 3 having holes (openings) 30 that lead to the substrate 10.

[0065] The photosensitive layer can be formed by applying a photosensitive composition or laminating a photosensitive film.

[0066] Positive-type photosensitive compositions may include commercially available products such as positive-type resist AH-3000 (manufactured by Resonaq Corporation, product name), positive-type resist AR-5100 (manufactured by Resonaq Corporation, product name), and positive-type resist OFPR-8600 (manufactured by Tokyo Ohka Kogyo Co., Ltd., product name). Negative-type photosensitive compositions may include commercially available products such as negative-type resist TER-20HF (manufactured by Taiyo Ink Manufacturing Co., Ltd., product name) and negative-type resist TMMR NA1000PM (manufactured by Tokyo Ohka Kogyo Co., Ltd., product name). Negative photosensitive films may be commercially available products such as negative resist HM-4035 (manufactured by Resonaq Corporation, product name), negative resist HM-4056 (manufactured by Resonaq Corporation, product name), negative resist TMMF NA1000 (manufactured by Tokyo Ohka Kogyo Co., Ltd., product name), or negative resist PSR-800AUSSR-1 (manufactured by Taiyo Ink Manufacturing Co., Ltd., product name).

[0067] Examples of active light sources used for exposure include light from a g-line stepper; ultraviolet light from low-pressure mercury lamps, high-pressure mercury lamps, metal halide lamps, i-line steppers, etc.; electron beams; and laser light. The exposure amount is appropriately selected depending on the light source used, the thickness of the photosensitive layer, etc.

[0068] The developer used for exposure may be an alkaline developer, for example, an alkaline aqueous solution prepared by dissolving an alkaline compound such as sodium carbonate, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, or choline in water to a concentration of about 1 to 10% by mass, or an alkaline aqueous solution such as ammonia water. Development methods include shower development, spray development, immersion development, and paddle development.

[0069] The thickness of the resist layer can be appropriately set according to the length (height) of the conductive pillar to be formed, and may be, for example, 5 to 200 μm, 10 to 100 μm, or 10 to 60 μm.

[0070] The size and number of holes (openings) 30 can be appropriately set according to the shape and number of conductive pillars to be formed. The inner diameter of the holes (corresponding to the outer diameter of the conductive pillars) may be 5 μm or more, 10 μm or more, or 20 μm or more from the viewpoint of suppressing the occurrence of cracks and voids, and may be 500 μm or less, 200 μm or less, or 100 μm or less from the viewpoint of increasing the density of the resulting semiconductor device. From the above viewpoint, the inner diameter of the holes may be 5 to 500 μm, 10 to 200 μm, or 20 to 100 μm.

[0071] The metal paste portion can be formed, for example, by creating a metal particle film 40 on a support film 7 by providing a metal particle-containing layer 4p made of the metal paste of this embodiment described above, as shown in Figures 3(a) and 3(b), and then pressing this metal particle film 40 onto the resist-layer-attached substrate 20.

[0072] Examples of the support film 7 include polyimide film, polyethylene naphthalate film, and polyethylene terephthalate film. The thickness of the support film may be 20 to 200 μm, 25 to 175 μm, or 30 to 150 μm, from the viewpoint of workability for forming the metal particle-containing layer by coating.

[0073] The composition of the metal particles and volatile solvent in the metal particle-containing layer can be appropriately set so as to satisfy the conditions for the metal paste of this embodiment described above. The thickness of the metal particle-containing layer may be 100 μm or less. From the viewpoint of ensuring sufficient filling of the pores (openings) in the resist layer, the thickness of the metal particle-containing layer may be 30 μm or more, 40 μm or more, or 50 μm or more.

[0074] From the viewpoint of suppressing the generation of voids within the pores (openings) of the resist layer, the metal particle-containing layer may have a waviness (height difference) of 20 μm or less on the surface opposite to the support film, or it may have a waviness (height difference) of 10 μm or less. By reducing the waviness (height difference), when the metal particle film is pressed and the metal particle composition is filled into the pores of the substrate, it becomes easier to simultaneously fill multiple pores (opening patterns) provided in the resist layer, making it easier to reduce pores that are not completely filled or pores that partially generate voids. The waviness (height difference) can be evaluated by a non-contact method using a laser displacement meter or the like.

[0075] The metal particle film described above can be produced by applying the metal paste of this embodiment described above onto a support film to form a metal particle-containing layer with a metal particle concentration of 95.0% by mass or more, or by applying a metal paste with an increased volatile solvent content (for example, increased to an amount such that the metal particle concentration is less than 94.0% by mass), and drying the coated film to form a metal particle-containing layer with a metal particle concentration of 95.0% by mass or more.

[0076] Methods for applying metal paste include, for example, screen printing, transfer printing, offset printing, jet printing, dispensers, jet dispensers, needle dispensers, comma coaters, slit coaters, die coaters, gravure coaters, slit coats, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, bar coating, applicators, particle deposition methods, spray coaters, spin coaters, dip coaters, and the like.

[0077] From the viewpoint of ease of application and uniformity of the applied film thickness, metal paste can be applied onto a support film by screen printing.

[0078] The thickness of the coating film may be 1 μm or more, 2 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more, and may be 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, 120 μm or less, 100 μm or less, 80 μm or less, or 50 μm or less.

[0079] The step of drying the coating film to form a metal particle-containing layer can be carried out at room temperature or at a temperature of room temperature to 100°C or lower, and the atmosphere may be air or nitrogen.

[0080] In step a, the metal particle film described above is pressed onto the resist-layered substrate 20 so that the metal particle-containing layer 4p of the metal particle film is in contact with the resist-layered substrate 20, thereby filling the holes 30 of the resist-layered substrate 20 with metal paste (Figure 3(b)). In this case, for example, the metal particle film and the resist-layered substrate 20 can be pressed together from above and below using a pressure jig. The pressure jig is not particularly limited, but may be a commercially available one, or it may be made using a metal member having a flat portion. For example, a pressure jig having two or more of the above-mentioned metal members can press the metal particle film against the resist-layered substrate by sandwiching the metal particle film and the resist-layered substrate between metal members arranged so that their flat portions face each other. The pressure jig may have a mechanism to adjust the pressure applied to the metal particle film and the resist-layered substrate. A spring or the like can be used as a pressure adjustment means.

[0081] The pressing conditions can be, for example, room temperature to 50°C or below, and the atmosphere may be a vacuum, air, or nitrogen. To reduce voids, the metal particle film may be pressed onto the resist-coated substrate after maintaining a vacuum of 1000 Pa or less, or 200 Pa or less. The pressure of the pressing jig when pressing the metal particle film onto the resist-coated substrate should be within a range that does not cause the resist-coated substrate to crack, for example, 0.01 MPa or more, 0.1 MPa or more, or 1 MPa or more.

[0082] The metal paste portion only needs to fill the inside of the hole and cover at least the surface of the resist layer around the hole on the substrate. As shown in Figure 4(a), the metal paste portion 4a may fill the inside of the hole 30 and cover the entire resist layer.

[0083] [Step b] In this process, the metal paste is heated to remove some of the volatile solvent; in other words, the metal paste is heated so that some of the volatile solvent remains. If the above-mentioned metal particle film is used, the metal paste can be heated after the support film has been removed.

[0084] For heating, for example, a hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far infrared heating furnace, microwave heating device, laser heating device, electromagnetic heating device, heater heating device, steam heating furnace, hot plate press device, etc. can be used.

[0085] The heating atmosphere may be air, an oxygen-free atmosphere such as nitrogen and noble gases, or a reducing atmosphere such as hydrogen and formic acid. In the case of air, copper particles tend to oxidize when the heating temperature exceeds 100°C. However, if the metal paste contains the high vapor pressure solvents mentioned above as volatile solvents, some of the volatile solvents can be removed at temperatures below 100°C, 95°C or below, or 90°C or below. If the metal paste does not contain high vapor pressure solvents as volatile solvents, for example, if it contains only the low vapor pressure solvents mentioned above, heating at 110°C or above, 130°C or above, or 150°C or above in an oxygen-free or reducing atmosphere can suppress the oxidation of copper particles while removing some of the volatile solvents.

[0086] If the metal paste contains a high vapor pressure solvent, the heating temperature may be 70°C or higher but less than 100°C, or 80°C or higher but 95°C, from the viewpoint of suppressing oxidation of copper particles, and the heating time may be 5 to 60 minutes, or 10 to 30 minutes, from the viewpoint of suppressing oxidation of copper particles.

[0087] Furthermore, in order to suppress volume shrinkage before and after firing the conductive pillar precursor (for example, between step c, which forms the conductive pillar precursor, and step d, which fires the conductive pillar precursor), and to suppress voids and cracks, the metal paste portion may be heated to a concentration of metal particles of 96% by mass or more, 97.5% by mass or more, and 98% by mass or more.

[0088] [Process c] In this step, as shown in Figure 4(b) and Figure 5(a), the heated metal paste portion 4a obtained in step b is flattened (or smoothed) while removing the metal paste covering the surface of the resist layer and filling the pores with metal paste. This allows a conductive pillar precursor 4b having a flattened exposed surface VP1 and containing the metal particles and the remainder of the volatile solvent to be formed inside the pore (opening) 30.

[0089] For example, the metal paste portion can be removed using a rubber squeegee 42, as shown in Figure 4(b). This allows for the removal of a portion of the metal paste (the metal paste covering the surface of the resist layer and the metal paste protruding from the holes) so that the surface of the resist layer and the exposed surface VP1 of the conductive pillar precursor 4b are on the same plane. Another method involves removal using a metal squeegee made of SUS or similar material.

[0090] [Step d] In this step, the conductive pillar precursor 4b formed in step c is fired. This allows for the formation of a conductive pillar 4c made of a metal body. The metal body may include a copper sintered body having a porous structure. The porosity of the conductive pillar may be 7% or less, 1.0 to 6.5%, or 1.5 to 5.0%, from the viewpoint of suppressing the penetration of chemicals into the copper sintered body when immersed in chemicals such as resist stripping solution or pre-plating treatment in subsequent processes, and improving reliability. If the conductive pillar is made of a copper sintered body, the porosity of the copper sintered body may be within the above range. The porosity can be determined by the following method.

[0091] (Porosity of conductive pillars) A conductive pillar-equipped substrate that had undergone mechanical polishing was cut in the thickness direction, and the cross-section of the central part of the conductive pillar was exposed using a focused ion beam and observed. When observing the cross-section of the central part of the conductive pillar, the observation range was ±5 μm from the center of the conductive pillar in the direction in which the conductive pillar extends and ±5 μm in the direction perpendicular to the direction in which the conductive pillar extends. A focused ion beam processing observation device (Hitachi High-Technologies Corporation, product name: MI4050) was used. For observation, a scanning electron microscope (Hitachi High-Technologies Corporation, product name: S-3700N) was used at a magnification of 5000x, and a cross-sectional image of the conductor (approximately 10 μm square) was captured. Five observation points were used. The obtained cross-sectional images were binarized using image analysis software (Adobe Photoshop® Elements) so that the sintered copper portion and the porous (vacancy) portion were separated. For each of the five observation points, the ratio of the porous (empty) area to the total area of ​​the conductive pillar cross-section was calculated and defined as the porosity. The average of the porosities from the five observation points was used as the porosity of the conductive pillar.

[0092] Firing can be carried out by heat treatment. For heat treatment, heating means such as a hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far infrared heating furnace, microwave heating device, laser heating device, electromagnetic heating device, heater heating device, steam heating furnace, etc. can be used.

[0093] The atmosphere during firing may be an oxygen-free atmosphere from the viewpoint of suppressing oxidation of the copper sintered body, or a reducing atmosphere from the viewpoint of removing surface oxides from the copper particles in the conductive pillar precursor. Examples of an oxygen-free atmosphere include the introduction of oxygen-free gases such as nitrogen or noble gases, or under vacuum. Examples of a reducing atmosphere include pure hydrogen gas, a mixed gas of hydrogen and nitrogen represented by foaming gas, nitrogen containing formic acid gas, a mixed gas of hydrogen and noble gases, or a noble gas containing formic acid gas. When sintering the conductive pillar precursor by heating without pressurization, a nitrogen atmosphere containing formic acid gas or a noble gas containing formic acid gas is preferable, and a mixed gas of formic acid and nitrogen is preferable. Heating in an atmosphere containing formic acid makes it possible to lower the sintering temperature of the copper particles. The concentration of formic acid may be 1 to 10 volume percent, or 2 to 5 volume percent.

[0094] The maximum temperature reached during the heat treatment may be 100°C or higher, or 150°C or higher, and may be 300°C or lower, 200°C or lower, or 150°C or lower, from the viewpoint of reducing thermal damage to each component and improving yield. If the maximum temperature reached is 100°C or higher, sintering tends to proceed sufficiently when the maximum temperature is held for 60 minutes or less. The maximum temperature is held for 1 minute or more, and may be 60 minutes or less, 40 minutes or less, or 30 minutes or less, from the viewpoint of completely evaporating the volatile solvent and improving yield.

[0095] In this embodiment, by using the metal paste of this embodiment, sintering can be performed at a low temperature of 300°C or less, 200°C or less, or 150°C or less in an atmosphere containing formic acid gas, and firing may also be performed at 100-300°C, 100-200°C, or 100-150°C. Even in this case, conductive vias with excellent conductivity and connection reliability can be formed.

[0096] The calcination of the conductive pillar precursor may be carried out under no pressure or under pressure. In the latter case, under an atmosphere containing formic acid, the pressure may be 0.05 MPa or higher, 0.1 MPa or higher, or 0.3 MPa or higher, and 20 MPa or lower, 15 MPa or lower, or 10 MPa or lower. Under an atmosphere containing pure hydrogen gas, the pressure may be 0.05 MPa or higher, 0.1 MPa or higher, or 0.3 MPa or higher, and 20 MPa or lower, 15 MPa or lower, or 10 MPa or lower. Also, under an atmosphere containing nitrogen gas, the pressure may be 1 MPa or higher, or 3 MPa or higher, and 20 MPa or lower, 15 MPa or lower, or 10 MPa or lower.

[0097] By setting the pressure to 0.05 MPa or higher when using a gas containing formic acid, 0.05 MPa or higher when using pure hydrogen gas, and 1 MPa or higher when using nitrogen gas, it becomes easier to suppress the generation of voids in the conductive pillars formed in the center of the pores 30 of the resist layer, making it easier to obtain conductive pillars with good conductivity. Furthermore, by setting the pressure to above the lower limit mentioned above, if the substrate 10 has a metal film 2, it becomes easier to improve the bonding strength between the metal film 2 and the conductive pillars.

[0098] Furthermore, if the pressure applied during firing is within the above range, a special pressurizing device is not required, thus reducing voids, improving bonding strength, and connection reliability without compromising yield. Methods for applying pressure to the conductive pillar precursors formed in the pores of the resist layer include, for example, placing weights on them, using a pressurizing device to apply pressure, and using a fixing jig for applying pressure.

[0099] The copper sintered body contained in the metal body may have a copper element ratio of 95% by mass or more, 97% by mass or more, 98% by mass or more, or 100% by mass among the constituent elements excluding light elements. If the above ratio of copper elements in the copper sintered body is within the above range, the formation of intermetallic compounds or the precipitation of dissimilar elements at the grain boundaries of the metallic copper crystal can be suppressed, the properties of the metallic copper constituting the copper sintered body tend to become stronger, and even better connection reliability can be obtained.

[0100] In step d, the conductive pillar precursor has a flat exposed surface VP1 with a sufficiently small step difference from the resist layer surface, and also has a composition that is less susceptible to volume shrinkage during firing, thus enabling the production of pillars with high in-plane uniformity.

[0101] [Process e] In step e, the resist layer 3 is removed from the conductive pillar substrate 50 having a resist layer, which was obtained in step d.

[0102] Methods for removing the resist layer 3 include wet processes using alkaline aqueous solutions or organic solvent-based chemicals such as organic amines like TMAH and ketones like acetone.

[0103] In the case of a wet process, for example, an aqueous solution with an even stronger alkalinity than the alkaline developer used for developing the resist layer may be used. Methods for removing the resist layer include immersion, spraying, and paddle methods.

[0104] By step e described above, a conductive pillar-equipped substrate 100 as shown in Figure 6 can be obtained. The conductive pillar-equipped substrate 100 has conductive pillars 4c in which the occurrence of cracks and voids is sufficiently suppressed, and even when the spacing between conductive pillars 4c is narrow (especially 100 μm or less, or 70 μm or less), the surface S of the substrate 10 is maintained. 10 The amount of residual peeling of the resist layer is sufficiently reduced.

[0105] In the method described above, solder bumps may be provided on the tips of the conductive pillars. If solder bumps are provided on the tips of the conductive pillars before step e, for example, solder bumps may be provided on the surface VP2 of the conductive pillar-equipped substrate 50 having a resist layer, obtained in step d, by reflow soldering using solder balls or by flow soldering.

[0106] If solder bumps are to be provided on the tips of the conductive pillars after step e, for example, the following method for forming solder bumps may be used.

[0107] A method for forming solder bumps comprises the steps of: applying solder paste to the area of ​​a conductive pillar-equipped substrate where the conductive pillars are located (application step); heating the conductive pillar-equipped substrate and solder paste at a temperature T1 below the melting point of the solder (the melting point of the solder constituting the solder particles) to volatilize the dispersion medium in the solder paste and form a solder particle-containing layer on the conductive pillar-equipped substrate (drying step); heating the conductive pillar-equipped substrate and the solder particle-containing layer at a temperature T2 above the melting point of the solder to melt the solder particles in the solder particle-containing layer and form solder bumps on the conductive pillars of the conductive pillar-equipped substrate (reflow step); and removing any remaining solder particle-containing layer residue between adjacent solder bumps by washing (washing step).

[0108] In the method of this embodiment, the conductive pillar substrate may be further provided with an insulating resin coating 5 that covers the areas where the conductive pillars 4c are not provided. The following describes a method for forming solder bumps on a member on which the resin coating 5 is provided on the conductive pillar substrate 100.

[0109] (Coating process) In the coating process, as shown in Figure 7(a), a solder paste containing solder particles 62 is applied to the area of ​​the member 66 where the conductive pillars 4c are located, forming a solder paste layer 64 on the member 66. This results in a solder paste-coated substrate 110.

[0110] The solder paste can contain solder particles, flux, and a volatile dispersion medium.

[0111] Solder particles contain tin. Solder particles may contain pure tin or tin alloys. Examples of tin alloys include In-Sn, In-Sn-Ag, Sn-Bi, Sn-Bi-Ag, Sn-Ag-Cu, and Sn-Cu alloys. Solder particles may be used individually or in combination of two or more types.

[0112] Specific examples of tin alloys are shown below. In-Sn (In: 52% by mass, Sn: 48% by mass, melting point: 118°C) In-Sn-Ag (In: 20% by mass, Sn: 77.2% by mass, Ag: 2.8% by mass, melting point: 175°C) • Sn-Bi (Sn: 42% by mass, Bi: 58% by mass, melting point: 138°C) Sn-Bi-Ag (Sn: 42% by mass, Bi: 57% by mass, Ag: 1% by mass, melting point: 139°C) ·Sn-Ag-Cu (Sn: 96.5% by mass, Ag: 3% by mass, Cu: 0.5% by mass, melting point: 217℃) • Sn-Cu (Sn: 99.3% by mass, Cu: 0.7% by mass, melting point: 227°C)

[0113] The tin content in the solder particles may be, for example, 40% by mass or more, 60% by mass or more, or 80% by mass or more, and may be 99.5% by mass or less, 80% by mass or less, or 60% by mass or less.

[0114] Tin in solder particles is present, for example, in bulk form (purity of 99.9% or higher). Because tin is an easily oxidized metal, solder particles typically contain tin oxide on at least a portion of their surface (e.g., on top of the bulk tin).

[0115] The melting point of the solder (the melting point of the solder constituting the solder particles) may be 250°C or lower or 220°C or lower. From the viewpoint of enabling the formation of solder bumps at low temperatures and reducing the load on the component on which the solder bumps are formed, it may be 180°C or lower, 160°C or lower, or 140°C or lower. The melting point of the solder may be, for example, 100°C or higher so that it does not melt when the dispersion medium is volatilized. Note that the melting point of the solder can also be said to be the melting point of the solder particles before oxidation.

[0116] The average particle size of solder particles may be 9.0 μm or less, 8.0 μm or less, 5.0 μm or less, 3.0 μm or less, or 2.0 μm or less, from the viewpoint of further suppressing the formation of bridges. The smaller the average particle size of solder particles, the more likely it is that the formation of bridges will be suppressed.

[0117] The average particle size of the solder particles may be 0.1 μm or larger, and may also be 0.3 μm or larger, 0.5 μm or larger, 1.0 μm or larger, or 2.0 μm or larger, from the viewpoint of enabling uniform melting of the solder particles when heated above the melting point of the solder.

[0118] The average particle size of the solder particles may be set according to the distance between adjacent conductive pillars on the conductive pillar substrate to which the solder paste is applied. Specifically, when the average particle size of the solder particles is one-third or less of the distance between adjacent conductive pillars, the occurrence of bridges tends to be further suppressed. In order to obtain this tendency more significantly, the average particle size of the solder particles may be one-quarter or one-fifth or less of the distance between adjacent conductive pillars.

[0119] The maximum diameter of the solder particles may be 1.0 μm or more, or 2.0 μm or more, and may be 10 μm or less, 9.0 μm or less, 8.0 μm or less, 5.0 μm or less, 3.0 μm or less, or 2.0 μm or less. The less variation there is in the particle size of the solder particles, the easier it is to uniformly melt the solder particles on the conductive pillars of the substrate with conductive pillars, and the better the bump shape tends to be. Also, the less variation there is in the particle size of the solder particles, the easier it is to suppress the melting of solder particles remaining between solder bumps and the formation of bridges, and the easier it is to suppress the formation of bridges caused by large solder particles. From these viewpoints, the proportion of solder particles having the above maximum diameter may be 80% by mass or more, 90% by mass or more, or 95% by mass or more.

[0120] The maximum diameter and average particle size of solder particles can be calculated from an SEM image using, for example, the following procedure: Place the solder particle powder onto a carbon tape for SEM using a spatula to create an SEM sample. Observe this SEM sample at 5000x magnification using an SEM device to obtain an SEM image. From the obtained SEM image, draw a rectangle circumscribing the solder particle using image processing software, and define the maximum diameter of the particle as the longest side of the rectangle. Perform this measurement on 50 or more solder particles using multiple SEM images, calculate the average of the maximum diameters of these solder particles, and define this as the average particle size (average maximum diameter). The maximum diameter and average particle size of solder particles in solder paste can be determined by washing with an organic solvent such as acetone, filtering, drying at room temperature (e.g., 25°C), and then using the method described above.

[0121] The shape of the solder particles may be, for example, spherical, lumpy, needle-shaped, flattened (flake-shaped), or nearly spherical. The solder particles may also be aggregates of solder particles having these shapes. Among these, when the solder particles are spherical, they tend to be uniformly dispersed on and between the conductive pillars (especially on the conductive pillars) of the substrate with conductive pillars. As a result, the solder particle-containing layer obtained by drying the solder paste is uniformly formed on and between the conductive pillars of the substrate with conductive pillars, and when this solder particle-containing layer is heated above the melting point of the solder, the solder particles located on the upper part of the conductive pillars tend to melt preferentially compared to the solder particles located between the conductive pillars due to the effect of flux. This results in effects such as further suppression of bridge formation and easier formation of solder bumps with better shapes. Here, spherical solder particles refer to particles whose aspect ratio ("long side of particle / short side of particle") is 1.3 or less, as determined from the above SEM image.

[0122] The solder particle content in the solder paste is less than 70% by mass, based on the total mass of the solder paste. The solder particle content may be 65% by mass or less, 60% by mass or less, or 50% by mass or less, from the viewpoint of making it easier to uniformly form a solder particle-containing layer on and between the conductive pillars of a substrate with conductive pillars, thereby uniformizing the bump shape on the top of the conductive pillars and making it easier to achieve uniform bump height and shape, and from the viewpoint of making it easier to uniformly disperse the solder particles between electrodes, making it more difficult for the solder particles between conductive pillars to melt, thereby further suppressing the occurrence of bridges between conductive pillars. The solder particle content in the solder paste may be 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 50% by mass or more, based on the total mass of the solder paste, from the viewpoint of suppressing the settling of solder particles in the paste and improving the uniformity of the solder paste during application.

[0123] (Flux) As the flux, those commonly used in soldering and other applications can be used. Specific examples include zinc chloride, mixtures of zinc chloride and inorganic halides, mixtures of zinc chloride and inorganic acids, molten salts, phosphoric acid, derivatives of phosphoric acid, organic halides, hydrazine, rosin, organic acids, amino acids, amines, and hydrohalides of amines. These may be used individually or in combination of two or more.

[0124] Examples of molten salts include ammonium chloride. Examples of organic acids include lactic acid, citric acid, stearic acid, glutamic acid, glutaric acid, succinic acid, adipic acid, pimelic acid, suberic acid, benzoic acid, and malic acid. Examples of pine resin include activated pine resin and inactivated pine resin. Pine resin is a type of rosin mainly composed of abietic acid. Examples of amino acids include glycine, alanine, and glutamic acid. Common amines can be used, for example, primary amines, secondary amines, and tertiary amines. Hydrohalides of amines may be combinations of amines and halogen elements.

[0125] Using an organic acid or rosin containing two or more carboxyl groups as a flux significantly improves the reliability of conductivity between conductive pillars. In particular, using an organic acid containing two or more carboxyl groups as a flux removes tin oxide from the surface of solder particles, exposing bulk tin and improving wettability with the electrodes. This prevents solder non-wetting and significantly improves the formation of well-shaped solder bumps. For example, while rosins mainly composed of abietic acid, known as flux base resins, have high re-oxidation prevention and viscosity adjustment functions, they are less effective at removing tin oxide from the surface of solder particles and promoting solder wetting to the electrode surface. On the other hand, organic acids containing two or more carboxyl groups are more effective than rosins mainly composed of abietic acid in removing tin oxide from the surface of solder particles, exposing bulk tin, and improving wettability with the electrodes. Furthermore, with organic acids having two or more carboxyl groups, the effect can be obtained with a smaller amount (for example, 5 parts by mass or less per 100 parts by mass of solder particles) compared to the rosins mentioned above, making it easy to apply them with a uniform thickness on and between conductive pillars. As a result, the shape of solder bumps can be made more uniform, and the occurrence of bridges can be further suppressed.

[0126] The flux may be a low molecular weight compound with a molecular weight of 200 or less, from the viewpoint of being easily dissolved in the dispersion medium and facilitating the application of the solder paste. The molecular weight of the flux may be 180 or less or 150 or less, from the viewpoint of obtaining the above effects more significantly. The molecular weight of the flux may be 100 or more, 150 or more, 180 or more, or 200 or more. In this embodiment, the solder paste may contain a polymer compound such as a resin (for example, a compound with a weight-average molecular weight of 300 or more) as the flux, but from the viewpoint of removing tin oxide from the surface of the solder particles to expose bulk tin and further improving wettability with the electrode, the content of the polymer compound may be 10 parts by mass or less, or even 0 parts by mass, per 100 parts by mass of solder particles.

[0127] The melting point of the flux may be 50°C or higher, 70°C or higher, or 80°C or higher, and may be 200°C or lower, 160°C or lower, 150°C or lower, or 140°C or lower. When the melting point of the flux is within the above range, the flux effect is exerted more effectively, and solder particles can be arranged on the conductive pillars more efficiently. From the viewpoint of obtaining such an effect more significantly, the melting point of the flux may be 80 to 190°C or 80 to 140°C.

[0128] Fluxes with melting points in the range of 80 to 190°C include dicarboxylic acids such as succinic acid (melting point: 186°C), glutaric acid (melting point: 96°C), adipic acid (melting point: 152°C), pimelic acid (melting point: 104°C), and suberic acid (melting point: 142°C), as well as benzoic acid (melting point: 122°C) and malic acid (melting point: 130°C).

[0129] From the viewpoint of improving cleanability in the process of removing residual solder particle-containing layers remaining between adjacent solder bumps after the process of forming solder bumps on conductive pillars, the flux content may be 10 parts by mass or less, 8 parts by mass or less, 6 parts by mass or less, or 5 parts by mass or less per 100 parts by mass of solder particles. From the viewpoint of exhibiting the flux effect more effectively, the flux content may be 0.1 parts by mass or more, 0.2 parts by mass or more, or 0.3 parts by mass or more per 100 parts by mass of solder particles. From these viewpoints, the flux content may be 0.1 to 10 parts by mass, 0.2 to 8 parts by mass, 0.3 to 6 parts by mass, or 0.3 to 5 parts by mass per 100 parts by mass of solder particles.

[0130] (dispersion medium) The dispersion medium is not particularly limited, as long as it is volatile and capable of dispersing solder particles (e.g., a liquid). The dispersion medium may be, for example, an organic compound with a vapor pressure of 0.1 to 500 Pa at 20°C. Compounds with fluxing properties are not included in the dispersion medium, nor are compounds with thermosetting properties.

[0131] Examples of dispersion media include monohydric and polyhydric alcohols such as pentanol, hexanol, heptanol, octanol, decanol, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, terpineol, and isobornylcyclohexanol (MTPH); ethylene glycol butyl ether, ethylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, diethylene glycol isobutyl ether, diethylene glycol hexyl ether, triethylene glycol methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol butyl methyl ether, diethylene glycol isopropyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, propylene glycol propyl ether, and dipropylene glycol methyl ether. Examples include ethers such as ethers, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, dipropylene glycol dimethyl ether, tripropylene glycol methyl ether, and tripropylene glycol dimethyl ether; esters such as ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether acetate (DPMA), ethyl lactate, butyl lactate, γ-butyrolactone, and propylene carbonate; acid amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; aliphatic hydrocarbons such as cyclohexane, octane, nonane, decane, and undecane; aromatic hydrocarbons such as benzene, toluene, and xylene; mercaptans having alkyl groups with 1 to 18 carbon atoms; and mercaptans having cycloalkyl groups with 5 to 7 carbon atoms.Examples of mercaptans having an alkyl group with 1 to 18 carbon atoms include ethyl mercaptan, n-propyl mercaptan, i-propyl mercaptan, n-butyl mercaptan, i-butyl mercaptan, t-butyl mercaptan, pentyl mercaptan, hexyl mercaptan, and dodecyl mercaptan. Examples of mercaptans having a cycloalkyl group with 5 to 7 carbon atoms include cyclopentyl mercaptan, cyclohexyl mercaptan, and cycloheptyl mercaptan. These may be used individually or in combination of two or more.

[0132] The vapor pressure of the dispersion medium at 20°C may be 0.1 to 500 Pa, or it may be 0.2 to 100 Pa, 0.3 to 50 Pa, or 0.5 to 10 Pa. When the vapor pressure at 20°C is 0.1 Pa or higher, it is easier to achieve both coating properties and volatility. In particular, when using low-melting-point solder particles, the temperature T1 below the melting point of the solder becomes lower, so using a dispersion medium with a vapor pressure of 0.1 Pa or higher can reduce the amount of residual dispersion medium. On the other hand, when the vapor pressure at 20°C is 500 Pa or lower, volatilization of the dispersion medium is less likely to occur during coating, and the increase in solder particle concentration due to volatilization of the dispersion medium during continuous use is suppressed. Therefore, it is easier to control the coating thickness during continuous coating.

[0133] Examples of dispersion media (organic compounds) with a vapor pressure of 0.3 to 50 Pa at 20°C include 1-heptanol (vapor pressure 28 Pa), 1-octanol (vapor pressure 8.7 Pa), 1-decanol (vapor pressure 1 Pa), ethylene glycol (vapor pressure 7 Pa), diethylene glycol (vapor pressure 2.7 Pa), propylene glycol (vapor pressure 10.6 Pa), 1,3-butylene glycol (vapor pressure 8 Pa), terpineol (vapor pressure 3.1 Pa), ethylene glycol monophenyl ether (vapor pressure 0.9 Pa), diethylene glycol methyl ether (ethyl carbitol) (vapor pressure 13 Pa), and diethylene glycol monobutyl ether (vapor pressure 3 Pa). When at least one of these dispersion media is used, the volatilization of the dispersion media during coating is easily suppressed, making it easier to control the coating thickness during continuous coating, while the dispersion media can be easily volatilized at a temperature T1 below the melting point of solder.

[0134] The dispersion medium content is 30% by mass or more based on the total mass of the solder paste, and may be 35% by mass or more or 38% by mass or more from the viewpoint of further suppressing the occurrence of bridging and solder nonwetting. The dispersion medium content may be 80% by mass or less, 70% by mass or less, or 60% by mass or less based on the total mass of the solder paste, from the viewpoint of suppressing the settling of solder particles and improving uniformity after application. From these viewpoints, the dispersion medium content may be 30-80% by mass, 35-70% by mass or 38-60% by mass based on the total mass of the solder paste.

[0135] (Other ingredients) The solder paste may further contain components other than those listed above (other components). Examples of other components include thermosetting compounds (e.g., thermosetting resins). Examples of thermosetting compounds include oxetane compounds, epoxy compounds, episulfide compounds, (meth)acrylic compounds, phenol compounds, amino compounds, unsaturated polyester compounds, polyurethane compounds, silicone compounds, polyimide compounds, etc. The content of thermosetting compounds may be, for example, 0 to 10 parts by mass based on the total mass of the solder paste.

[0136] The solder paste may further contain additives such as thixotropic agents, antioxidants, fungicides, and matting agents as other components.

[0137] The solder paste is applied such that a solder paste layer 64 is formed at least on and between the conductive pillars 4c. The solder paste may be applied to the member 66 so as to cover all of the conductive pillars 4c, for example, to the entire surface of the member 66 (the entire surface on which the conductive pillars 4c are formed). Methods for applying the solder paste include, for example, screen printing, transfer printing, offset printing, jet printing, dispensers, jet dispensers, needle dispensers, comma coaters, slit coaters, die coaters, gravure coaters, slit coats, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, bar coating, applicators, particle deposition methods, spray coaters, spin coaters, dip coaters, etc.

[0138] The thickness D1 of the solder paste layer 64 can be appropriately changed depending on the thickness of the solder particle-containing layer 68 obtained after drying. For example, it may be 1 μm or more, 2 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more, and may be 120 μm or less, 100 μm or less, 80 μm or less, or 50 μm or less. The thickness D1 of the solder paste layer 64 is the length of the portion indicated by D1 in Figure 7(a), and is the shortest distance from the surface of the resin film 5 to the surface of the solder paste layer 64.

[0139] (drying process) In the drying process, as shown in Figure 7(b), the solder paste-coated substrate 110 is heated at a temperature T1 below the melting point of the solder (the melting point of the solder constituting the solder particles 62), thereby volatilizing the dispersion medium in the solder paste (solder paste layer 64) and forming a solder particle-containing layer 68 on the substrate 10. This yields a solder particle-containing layer-coated substrate 120.

[0140] The drying temperature T1 is a temperature below the melting point of the solder, for example, 30 to 120°C. From the viewpoint of oxidizing the surface of the solder particles, the drying temperature T1 may be close to the melting point of the solder, for example, 50°C or higher, 70°C or higher, or 90°C or higher.

[0141] The drying time may be adjusted as appropriate according to the type and amount of dispersion medium used. Specifically, for example, it may be 1 minute or more and 120 minutes or less.

[0142] The drying atmosphere may be an atmospheric atmosphere or a nitrogen atmosphere. Drying in an atmospheric atmosphere makes the surface of the solder particles more susceptible to oxidation. This inhibits the growth of solder particles that melt and bond together with each other during the formation of solder bumps (during the reflow process described later), and tends to further suppress the formation of bridges between conductive pillars. This effect is more easily obtained when the drying temperature T1 is close to the melting point of the solder.

[0143] The solder particle-containing layer 68 formed in the drying process contains solder particles 62 and flux. Some of the dispersion medium may remain in the solder particle-containing layer 68 without volatilizing, but the content of the dispersion medium in the solder particle-containing layer 68 may be 5% by mass or less, 1% by mass or less, or 0.1% by mass or less, based on the total mass of the solder particle-containing layer.

[0144] The thickness D2 of the solder particle-containing layer 68 may be two-thirds or less of the distance p between adjacent conductive pillars, or one-third or less, from the viewpoint of further suppressing the occurrence of bridges. Specifically, the thickness D2 of the solder particle-containing layer 68 may be, for example, 50 μm or less, 40 μm or less, 30 μm or less, or 25 μm or less. From the viewpoint of further suppressing the occurrence of solder nonwetting, the thickness D2 of the solder particle-containing layer 68 may be, for example, 3 μm or more, 5 μm or more, 10 μm or more, or 15 μm or more. Note that the thickness D2 of the solder particle-containing layer 68 is the length of the portion indicated by D2 in Figure 7(b), and is the shortest distance from the surface of the resin film 5 to the surface of the solder particle-containing layer 68.

[0145] (Reflow process) In the reflow process, as shown in Figure 7(c), the component with the solder particle-containing layer (component 66 and solder particle-containing layer 68) is heated to a temperature T2 above the melting point of the solder, melting the solder particles 62 in the solder particle-containing layer 68 and forming solder bumps 70 on the conductive pillars 4c of the component 66. At this stage, residue of the solder particle-containing layer 68 exists between the solder bumps 70 (between the conductive pillars 4c). The residue of the solder particle-containing layer 68 includes, for example, solder particles 62 and organic components 69 such as flux. The solder particles 62 include, for example, coarse particles 72 that have grown through the melting and bonding of solder particles with each other.

[0146] Heat treatment (heating to a temperature T2 above the melting point of solder) can be performed using, for example, a hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far infrared heating furnace, microwave heating device, laser heating device, electromagnetic heating device, heater heating device, steam heating furnace, hot plate press device, etc.

[0147] The heat treatment temperature T2 is a temperature above the melting point of the solder, and may be, for example, 5°C or more, 10°C or more, 20°C or more, 30°C or more, or 40°C or more higher than the melting point of the solder. When the heat treatment temperature T2 is 10°C or more higher than the melting point of the solder, the occurrence of solder nonwetting tends to be further suppressed. The difference between the heat treatment temperature T2 and the melting point of the solder may be 40°C or less, 30°C or less, or 20°C or less. When the difference between the heat treatment temperature T2 and the melting point of the solder is high, such as 40°C or less, the occurrence of bridging tends to be further suppressed. From the viewpoint of further suppressing solder nonwetting and bridging, the heat treatment temperature T2 may be 10 to 40°C higher than the melting point of the solder. The heat treatment time may be, for example, 1 minute or more, and 120 minutes or less.

[0148] The height of the solder bump can be adjusted by the composition and amount of solder paste applied, for example, to 3 to 30 μm.

[0149] (Washing process) In the cleaning process, as shown in Figure 7(d), the uncleaned solder bump member 130 obtained in the reflow process is cleaned to remove the residue of the solder particle-containing layer 68 remaining between adjacent solder bumps 70. This results in a solder bump member 200.

[0150] The cleaning may be done with water, for example, or with a solvent. Examples of cleaning solutions include water, alcohol-based solvents, terpene-based solvents, petroleum-based solvents, hydrocarbon-based solvents, and alkaline solvents. These may be used individually or in mixtures of two or more. The cleaning solution may also contain a cleaning agent (such as a surfactant). [Examples]

[0151] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0152] [Preparation of metal paste] (Preparation examples A to G) Metal pastes were prepared by mixing the raw materials listed below in the proportions shown in Table 1 using a three-roll mixing machine.

[0153] <First copper particle> (Wet copper powder) Spherical copper particles W1:1050Y (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 0.81 μm, spherical shape) Spherical copper particles W2:1100Y (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 1.1 μm, spherical shape) Spherical copper particles W3: 1200Y (manufactured by Mitsui Kinzoku Co., Ltd., product name, average particle size (D50): 2.1 μm, spherical) Spherical copper particles W4:1300Y (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 3.5 μm, spherical shape) Flattened copper particles W1:1100YP (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 1.4 μm, flattened) Flattened copper particles W2:1200YP (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 3.1 μm, flattened) (Atomized copper powder) Spherical copper particles A1: MA-C02K (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 1.8 μm, spherical shape) Spherical copper particles A2: MA-C025K (manufactured by Mitsui Kinzoku Co., Ltd., product name, average particle size (D50): 2.4 μm, spherical) Spherical copper particles A3: MA-C03K (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 3.4 μm, spherical shape)

[0154] <Second copper particle> Spherical copper particles W5:CH0200L1 (manufactured by Mitsui Mining & Smelting Co., Ltd., product name, average particle size (D50): 200nm, spherical)

[0155] <Volatile solvents> (High vapor pressure solvent: vapor pressure of 4 Pa ​​or more and 30 Pa or less at 20°C) α-Terpineol: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., vapor pressure 6.5 Pa at 20°C. (Low vapor pressure solvent: vapor pressure less than 4 Pa ​​at 20°C) Diethylene glycol mono-n-butyl ether: Manufactured by Showa Chemical Co., Ltd., vapor pressure 1.3 Pa at 20°C.

[0156] [Table 1]

[0157] [Fabrication of conductive pillar-attached substrates] (Examples 1-42 and Comparative Examples 1-14) A conductive pillar-equipped substrate was fabricated using the following procedure.

[0158] <Preparing the silicon substrate> A silicon substrate was prepared with titanium, nickel, and copper layers formed on its surface in that order. The silicon substrate had a diameter of 6 inches and a thickness of 300 μm, and the titanium, nickel, and copper layers were formed sequentially by sputtering.

[0159] <Formation of the resist layer> (Positive resist layer: Examples 1-23 and Comparative Examples 1-8) Positive resist AH-3000 (manufactured by Resonaq Corporation, product name) was applied to the surface of a silicon substrate using a spin coater and cured on a hot plate at 120°C for 150 seconds. Subsequently, a photomask was placed over the substrate, and the aperture patterns of the inner diameter and pitch of the holes shown in Tables 2-4 and 7 were exposed, and the resist was developed. By heating in a nitrogen oven at 230°C for 120 minutes to cure, a silicon substrate with a resist layer having a predetermined aperture pattern and a thickness of 35 μm was obtained.

[0160] (Negative resist layer: Examples 24-42 and Comparative Examples 9-12) A negative-type dry film HM-4035 (manufactured by Resonac Co., Ltd., product name) was laminated onto the surface of a silicon substrate. Then, a photomask was placed over it, and the aperture pattern of the inner diameter and pitch of the holes shown in Tables 5-6 and 8 was exposed, followed by resist development. Furthermore, plasma etching was performed to remove the resist residue at the bottom of the holes (apertures), resulting in a silicon substrate with a resist layer having a predetermined aperture pattern and a thickness of 35 μm.

[0161] <Preparation of metal particle films> Using a screen printing machine, the metal paste prepared above was printed onto a 100 μm thick PET film in an 8-inch diameter (20 cm diameter circular shape) using a screen printing plate (wire diameter: 23 μm, mesh count: 400 lines, mesh opening: 41 μm, void ratio: 41 μm) to obtain a metal particle film with a metal particle-containing layer.

[0162] <Formation of conductive pillars> Using a bonding device VJ-35 (manufactured by Ayumi Kogyo Co., Ltd., product name), a metal particle film was bonded to the silicon substrate with the resist layer obtained above, starting from the metal particle-containing layer side. This laminate was then vacuum-pressed at room temperature and a pressure of 3 MPa to fill the vias (pores) in the resist layer with metal paste.

[0163] Next, the PET film was peeled off the laminate and dried in air at 90°C for 10 minutes. The concentration (mass%) of metal particles in the metal paste before and after drying is shown in the table.

[0164] After drying, the metal paste on the main surface of the silicon substrate with the resist layer, where the metal particle film was bonded, was removed using a rubber squeegee.

[0165] Next, the silicon substrate with a resist layer on which conductive pillar precursors were formed by the process described above was placed in a tube furnace (manufactured by AVC Co., Ltd.), and the air inside the tube furnace was replaced with argon gas by flowing argon gas at a rate of 1 L / min. Then, the temperature was raised to 150°C in 10 minutes while flowing nitrogen gas containing 5 volume% formic acid gas at a rate of 300 mL / min, and the conductive pillar precursors were sintered by performing a sintering treatment at 150°C for 60 minutes. After that, the substrate was cooled by flowing argon gas at a flow rate of 0.3 L / min, and removed into the air at a temperature of 50°C or lower to obtain a silicon substrate with conductive pillars having a resist layer.

[0166] <Removal of the resist layer> (Positive resist layer: Examples 1-23 and Comparative Examples 1-8) After fully exposing the conductive pillar-equipped silicon substrate having the positive resist layer obtained above, the resist layer was peeled off using an organic amine solvent (TMAH).

[0167] (Negative resist layer: Examples 24-42 and Comparative Examples 9-12) The silicon substrate with conductive pillars having the negative resist layer obtained above was subjected to peeling of the resist layer using an alkaline solution (aqueous solution of sodium carbonate).

[0168] [Evaluation of conductive pillar-equipped substrates] The silicon substrate with conductive pillars having the resist layer obtained above, and the silicon substrate with conductive pillars from which the resist layer has been peeled off, were evaluated for the presence or absence of cracks and voids in the conductive pillars, as well as the remaining residue of the peeled resist layer, according to the following method.

[0169] (Presence or absence of cracks in conductive pillars) In a silicon substrate with conductive pillars and a resist layer, the cross-sections of the conductive pillars were exposed by cross-sectional polishing. Thirty conductive pillars were then observed using a digital microscope (Keyence Corporation, product name: VHX-6000) to check for the presence or absence of cracks (length 10 μm or longer).

[0170] (Presence or absence of voids in conductive pillars) In a silicon substrate with conductive pillars and a resist layer, the cross-sections of the conductive pillars were exposed by cross-sectional polishing. Thirty conductive pillars were then observed using a digital microscope (Keyence Corporation, product name: VHX-6000) to check for the presence or absence of voids (diameter 5 μm or larger).

[0171] (Evaluation of residual peeling of the resist layer) The cross-section of the silicon substrate with conductive pillars, from which the resist layer has been peeled off, is exposed by cross-sectional polishing, and the spaces between the 30 conductive pillars (S in Figure 6) are examined using a digital microscope (Keyence Corporation, product name: VHX-6000). 10 For each of the following, the average thickness of the remaining resist was calculated, and the remaining peeling of the resist layer was evaluated according to the following criteria. A rating of B or higher can be considered good. (Judgment criteria) A: The average thickness of the resist residue is less than 5 μm. B: Average thickness of resist residue is 5 μm or more and less than 10 μm. C: Average thickness of resist residue is 10 μm or more and less than 15 μm. D: The average thickness of the resist residue is 15 μm or more.

[0172] [Table 2]

[0173] [Table 3]

[0174] [Table 4]

[0175] [Table 5]

[0176] [Table 6]

[0177] [Table 7]

[0178] [Table 8] [Explanation of symbols]

[0179] 1...Substrate, 2...Metal coating, 3...Resist layer, 4...Metal paste, 4a...Metal paste portion, 4b...Conductive pillar precursor, 4c...Conductive pillar, 4p...Metal particle-containing layer, 5...Resin coating, 7...Support film, 10...Substrate, 20...Substrate with resist layer, 30...Hole, 40...Metal film, 42...Rubber squeegee, 50...Substrate with conductive pillar, 62...Solder particles, 64...Solder paste layer, 66...Component, 70...Solder bump, 100...Substrate with conductive pillar, 200...Component with solder bump.

Claims

1. Step a: Prepare a substrate with a resist layer, comprising a substrate and a resist layer having holes leading to the substrate, and provide a metal paste portion containing metal particles and a volatile solvent so as to fill the inside of the holes and cover at least the surface around the holes of the resist layer. Step b involves heating the metal paste portion to remove a portion of the volatile solvent, Step c: Remove a portion of the heated metal paste so that the surface is exposed, thereby forming a conductive pillar precursor inside the hole, which contains the metal particles and the remainder of the volatile solvent, and has a flattened exposed surface. The conductive pillar precursor is fired in a reducing atmosphere at a temperature of 200°C or lower (step d), The process includes step e, which involves removing the resist layer after step d, The metal particles include a first copper particle having a volume-average particle size of 0.8 μm or more, and a second copper particle having a volume-average particle size of 0.5 μm or less. The concentration of the metal particles in the metal paste portion provided in step a is 95.0% by mass or more. A method for manufacturing a conductive pillar substrate, wherein the content of the second copper particles in the metal paste portion provided in step a is 50% by mass or less based on the total amount of metal particles.

2. The method for manufacturing a conductive pillar substrate according to claim 1, wherein the first copper particles are flake-shaped copper particles.

3. The method for manufacturing a conductive pillar substrate according to claim 1 or 2, wherein in step d, the conductive pillar precursor is fired in an atmosphere containing formic acid at a temperature of 150°C or lower.

4. The method for manufacturing a conductive pillar substrate according to claim 1 or 2, wherein the resist layer is of the positive type.

5. A metal paste used to form conductive pillars on a substrate, It contains metal particles and a volatile solvent. The metal particles include a first copper particle having a volume-average particle size of 0.8 μm or more, and a second copper particle having a volume-average particle size of 0.5 μm or less. The concentration of metal particles is 95.0% by mass or higher. A metal paste for forming conductive pillars, wherein the content of the second copper particles is 50% by mass or less based on the total amount of metal particles.

6. The metal paste for forming conductive pillars according to claim 5, wherein the first copper particles are flake-shaped copper particles.

7. It comprises a substrate and a conductive pillar provided on the substrate, A conductive pillar substrate, wherein the conductive pillar is made of a sintered body of the metal paste for forming conductive pillars described in claim 5 or 6.

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