Method for manufacturing copper paste and bonded body for forming sintered copper pillars

Abstract

The copper paste for forming sintered copper pillars contains copper particles and an organic dispersion medium. The copper particles comprise first submicron copper particles having a volume-average particle diameter of 0.05-0.35 µm, second submicron copper particles having a volume-average particle diameter of 0.5-1.5 µm, and spherical micron copper particles having a volume-average particle diameter of 2-5 µm. The content of the first submicron copper particles is 40-70 mass% based on the total mass of the copper particles. The content of the second submicron copper particles is 10-40 mass% based on the total mass of the copper particles. The content of the spherical micron copper particles is 15-45 mass% based on the total mass of the copper particles.

Description

[Technical Field]

[0001] The present invention relates to a copper paste for forming sintered copper pillars and a method for manufacturing a bonded body. [Background technology]

[0002] Soldering is generally used for electrical connections in electronic devices. For example, in flip-chip bonding of microdevices, solder balls or solder paste are used to connect the microdevice to electrode pads on the substrate.

[0003] In recent years, with the narrowing of terminal pitches in flip-chip bonding, a method has been adopted in which metal pillars are formed on the microdevice and soldered to the electrode pads on the substrate. However, solder bonding has several problems, including (1) the generation of Kirkendal voids between the solder and the electrode pads, and between the solder and the metal pillars, (2) the melting of the solder and resulting in poor bonding when a reflow process is performed again after bonding, and (3) signal reflection due to impedance mismatch at dissimilar metal interfaces.

[0004] In response to this, methods for joining using metals other than solder are being considered. For example, Patent Document 1 below proposes a method for joining copper pillars provided on a microdevice and copper pads on a substrate using a bonding agent (copper paste) which is a mixture of copper microparticles and copper nanoparticles.

[0005] However, the method described in Patent Document 1 requires the pre-formation of copper pillars on the device, and the electrolytic plating method, which is the mainstream method for forming copper pillars, has the problem of being time-consuming. In addition, increasing the plating speed leads to a large variation in height, which is also a problem.

[0006] Therefore, the present inventors have been studying a method of forming a pillar precursor between joining members using a copper paste containing copper particles and an organic dispersion medium, and sintering the pillar precursor to form a sintered copper pillar and join the joining members together (see Patent Document 2). According to this method, a sintered copper pillar can be formed efficiently and with high precision.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] As a result of further studies by the present inventors, it has been found that voids and cracks may occur in the sintered copper pillar formed using the above copper paste, and peeling may occur at the interface between the sintered copper pillar and the joining member. From the viewpoint of the long-term reliability of the joined body, such voids, cracks, and peeling are preferably as few as possible.

[0009] Therefore, the main object of the present invention is to provide a copper paste for forming a sintered copper pillar that can reduce voids and cracks in the sintered copper pillar and peeling at the interface between the sintered copper pillar and the joining member.

Means for Solving the Problems

[0010] In order to solve the above problems, the present inventors studied using a plurality of types of copper particles having different volume average particle diameters as the copper particles contained in the copper paste. As a result, they found that the above problems can be solved by using spherical copper particles as micro copper particles while blending copper particles having a specific volume average particle diameter at a specific ratio, and completed the present invention.

[0011] One aspect of the present invention is a copper paste for forming a sintered copper pillar containing copper particles and an organic dispersion medium. As the copper particles, there are first sub-micro copper particles having a volume average particle diameter of 0.05 to 0.35 μm, second sub-micro copper particles having a volume average particle diameter of 0.5 to 1.5 μm, and spherical micro copper particles having a volume average particle diameter of 2 to 5 μm. The content of the first sub-micro copper particles is 40 to 70% by mass based on the total mass of the copper particles, the content of the second sub-micro copper particles is 10 to 40% by mass based on the total mass of the copper particles, and the content of the spherical micro copper particles is 15 to 45% by mass based on the total mass of the copper particles. It relates to a copper paste for forming a sintered copper pillar.

[0012] According to the copper paste of the above aspect, voids and cracks in the sintered copper pillar and peeling at the interface between the sintered copper pillar and the joining member can be reduced.

[0013] In one embodiment, the first sub-micro copper particles may be spherical and the second sub-micro copper particles may be flaky. In this case, there is a tendency to further reduce peeling at the interface between the sintered copper pillar and the joining member.

[0014] In one embodiment, the mass ratio of the content of the spherical micro copper particles to the total content of the first sub-micro copper particles and the second sub-micro copper particles may be 0.20 to 0.50. In this case, there is a tendency to further reduce voids and cracks in the sintered copper pillar and peeling at the interface between the sintered copper pillar and the joining member.

[0015] In one embodiment, the mass ratio of the content of the second sub-micro copper particles to the content of the first sub-micro copper particles may be 0.15 to 0.45. In this case, there is a tendency to further reduce voids and cracks in the sintered copper pillar and peeling at the interface between the sintered copper pillar and the joining member.

[0016] In one embodiment, the content of the organic dispersion medium may be 5 to 70% by mass, based on the total mass of the copper paste. In this case, it becomes easier to achieve both excellent printability and excellent sinterability of the copper paste.

[0017] Another aspect of the present invention relates to a method for manufacturing a joined body comprising a first member, a second member, and a sintered copper pillar for joining the first member and the second member, the method comprising the steps of: forming a pillar shape from the copper paste on the side surface onto the first member, then mounting the second member, providing a pillar precursor between the first member and the second member; and forming a sintered copper pillar by sintering the pillar precursor.

[0018] According to the above-described method for manufacturing the side surface, the occurrence of voids and cracks in the sintered copper pillar of the joint, as well as delamination at the interface between the sintered copper pillar and the joint member, can be reduced. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a copper paste for forming sintered copper pillars that reduces the occurrence of voids and cracks in sintered copper pillars, as well as delamination at the interface between the sintered copper pillar and the joining member. [Brief explanation of the drawing]

[0020] [Figure 1] Figure 1 is a schematic cross-sectional view showing a joint of one embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view illustrating the manufacturing method of the joint shown in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view illustrating the manufacturing method of the joint shown in Figure 1. [Figure 4] Figure 4 is a schematic cross-sectional view showing a joint of another embodiment. [Figure 5] Figure 5 shows cross-sectional SEM images of the joints prepared in Experimental Examples 1-3. [Figure 6] Figure 6 shows a cross-sectional SEM image of the joint fabricated in Experimental Example 3. [Figure 7] Figure 7 shows cross-sectional SEM images of the joints prepared in experimental examples 4-7. [Modes for carrying out the invention]

[0021] The embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including elemental steps, etc.) are not essential unless they are clearly essential in principle, as specifically indicated. The same applies to numerical values ​​and their ranges, and they do not limit the present invention.

[0022] In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their objective is achieved. In this specification, numerical ranges indicated using "~" indicate a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in one stage may be replaced with the upper or lower limit of a numerical range in another stage. Also, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples. Furthermore, the upper and lower limits described individually can be combined in any way. In this specification, the content of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if multiple substances corresponding to each component exist in the composition. In this specification, "boiling point" means the boiling point at 1 atmosphere.

[0023] <Copper paste> One embodiment of the copper paste contains copper particles and an organic dispersion medium. The copper paste is a copper paste for forming sintered copper pillars that join members together (copper paste for forming sintered copper pillars), and is specifically used to manufacture a joined body comprising a first member, a second member, and a sintered copper pillar that joins the first member and the second member. The copper paste of this embodiment is suitably used in a method of joining members together by sintering without pressure.

[0024] The above copper paste contains, as copper particles, first submicro copper particles with a volume average particle size of 0.05 to 0.35 μm, second submicro copper particles with a volume average particle size of 0.5 to 1.5 μm, and spherical micro copper particles with a volume average particle size of 2 to 5 μm. The content of the first submicro copper particles is 40 to 70% by mass based on the total mass of copper particles, the content of the second submicro copper particles is 10 to 40% by mass based on the total mass of copper particles, and the content of spherical micro copper particles is 15 to 45% by mass based on the total mass of copper particles.

[0025] The above-mentioned copper paste can reduce the occurrence of voids and cracks in the sintered copper pillar, as well as delamination at the interface between the sintered copper pillar and the joining member (first member and / or second member).

[0026] (Copper particles) Copper particles refer to particles that contain copper as their main component, for example, particles in which the copper content is 80% by mass or more. The copper content in copper particles may be 85% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more.

[0027] The copper paste of this embodiment contains, as copper particles, first submicro copper particles, second submicro copper particles, and spherical micro copper particles.

[0028] [First submicro copper particle] The first submicro copper particles are copper particles having a volume-average particle size of 0.05 to 0.35 μm. As the first submicro copper particles, for example, copper particles that are sinterable in a temperature range of 150°C to 300°C can be used.

[0029] The volume-average particle size of the first submicro copper particles may be 0.1 μm or more or 0.2 μm or more, from the viewpoint of obtaining better dispersibility and further reducing voids and cracks in the sintered copper pillar, as well as delamination at the interface between the sintered copper pillar and the joining member. The volume-average particle size of the first submicro copper particles may be 0.3 μm or less, 0.2 μm or less, or 0.1 μm or less, from the viewpoint of further reducing voids and cracks in the sintered copper pillar. From these viewpoints, the volume-average particle size of the first submicro copper particles may be, for example, 0.05 to 0.3 μm, 0.1 to 0.3 μm, 0.1 to 0.2 μm, 0.05 to 0.1 μm, or 0.2 to 0.3 μm.

[0030] In this specification, volume-average particle size refers to the 50% volume-average particle size. To determine the volume-average particle size of copper particles, dry copper particles obtained by removing volatile components from raw copper particles or copper paste are dispersed in a dispersion medium using a dispersant, and the particle size can be determined by measuring the dispersed particles using a light scattering particle size distribution analyzer (for example, the Shimadzu Nanoparticle Size Distribution Analyzer (SALD-7500nano, manufactured by Shimadzu Corporation)). When using a light scattering particle size distribution analyzer, hexane, toluene, α-terpineol, 4-methyl-1,3-dioxolan-2-one, etc., can be used as the dispersion medium.

[0031] The shape of the first sub-micro copper particles is not particularly limited. Examples of the shape of the first sub-micro copper particles include spherical, massive, needle-like, columnar, flaky, and aggregates thereof. From the viewpoints of dispersibility and filling property, the shape of the first sub-micro copper particles may be spherical or flaky, and from the viewpoints of combustibility, dispersibility, miscibility with other copper particles (e.g., flaky copper particles), etc., the shape may be spherical. In this specification, "spherical" means a sphere having an aspect ratio (long side / short side of the particle) of 2 or less. The measurement of the long side and short side of the particle can be obtained, for example, from the SEM image of the particle. In this specification, "flaky" includes flat plate-like shapes such as plate-like and scaly shapes.

[0032] From the viewpoints of improving dispersibility, filling property, miscibility with other copper particles (e.g., flaky copper particles), and printability of the copper paste, the aspect ratio of the first sub-micro copper particles may be 2 or less, and may also be 1.5 or less.

[0033] The specific surface area of the first sub-micro copper particles may be 1 m 2 / g or more, 2 m 2 / g or more, or 4 m 2 / g or more from the viewpoint of the dispersibility of the paste. From the viewpoints of improving the electrical conductivity and heat dissipation of the sintered copper pillar, the specific surface area of the first sub-micro copper particles may be 10 m 2 / g or less, 8 m 2 / g or less, or 5 m 2 / g or less. From these viewpoints, the specific surface area of the first sub-micro copper particles may be 1 to 10 m 2 / g, 2 to 8 m 2 / g, or 4 to 5 m 2 / g.

[0034] The first submicro copper particles may be treated with a surface treatment agent. Examples of surface treatment agents include organic acids having 2 to 18 carbon atoms (e.g., organic acids having alkyl groups with 1 to 17 carbon atoms).Examples of organic acids with 2 to 18 carbon atoms include acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, 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, and propyl Nonanoic acid, butyl octanoic acid, pentyl heptanoic acid, tridecanoic acid, methyl dodecanoic acid, ethyl undecanoic acid, propyl decanoic acid, butyl nonanoic acid, pentyl octanoic acid, myristic acid, methyl tridecanoic acid, ethyl dodecanoic acid, propyl undecanoic acid, butyl decanoic acid, pentyl nonanoic acid, hexyl octanoic acid, pentadecanoic acid, methyl tetradecanoic acid, ethyl tridecanoic acid, propyl dodecanoic acid, butyl undecanoic acid, pentyl decanoic acid, hexyl nonanoic acid, palmitic acid, methyl pentadecanoic acid, ethyl tetradecanoic acid Saturated fatty acids such as octenoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecanoic acid, heptylnonanoic acid, heptadecanoic acid, octadecanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, nonylcyclohexanecarboxylic acid, etc.; octenoic acid, nonenic acid Examples include unsaturated fatty acids such as methylnonenic acid, 10-hydroxy-2-decenoic acid, un10-hydroxy-2-decenoic acid, do10-hydroxy-2-decenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, sapienic acid, oleic acid, vaccenoic acid, linoleic acid, and linolenic 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.By combining such an organic acid with the first submicro copper particles described above, it tends to be possible to achieve both the dispersibility of the first submicro copper particles and the desorption of the organic acid during sintering. The organic acid may be used alone or in combination of two or more types.

[0035] The amount of surface treatment agent applied may be 0.07% by mass or more and 2.1% by mass or less, 0.10% by mass or more and 1.6% by mass or less, or 0.2% by mass or more and 1.1% by mass or less.

[0036] Commercially available submicro copper particles can be used as the first submicro copper particles. Examples of commercially available products include CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.26 μm), CuC-40 (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., volume average particle size 0.30 μm), and Cp-250 (manufactured by Techno Alpha Co., Ltd., volume average particle size 0.25 μm).

[0037] The content of the first submicro copper particles is 40 to 70% by mass, based on the total mass of the copper particles. From the viewpoint of further reducing voids and cracks in the sintered copper pillar, the content of the first submicro copper particles may be 45% or more by mass, or 50% or more by mass, based on the total mass of the copper particles. From the viewpoint of further reducing delamination at the interface between the sintered copper pillar and the joining member, the content of the first submicro copper particles may be 65% or less by mass, or 55% or less by mass, based on the total mass of the copper particles. From these viewpoints, the content of the first submicro copper particles may be 45 to 65% by mass, 45 to 55% by mass, or 50 to 55% by mass, based on the total mass of the copper particles. In this embodiment, the content of the first submicro copper particles, based on the total mass of the first submicro copper particles, the second submicro copper particles, and the spherical microcopper particles, may be within the above range.

[0038] [Second submicro copper particle] The second submicro copper particles are copper particles having a volume-average particle size of 0.5 to 1.5 μm. As the second submicro copper particles, for example, copper particles that are sinterable in a temperature range of 150°C to 300°C can be used.

[0039] The volume-average particle size of the second sub-micro copper particles may be 0.8 μm or larger or 1.0 μm or larger, from the viewpoint of obtaining better dispersibility and further reducing voids and cracks in the sintered copper pillar, as well as delamination at the interface between the sintered copper pillar and the bonding member. The volume-average particle size of the second sub-micro copper particles may be 1.3 μm or smaller, 1.2 μm or smaller, 0.9 μm or smaller, or 0.6 μm or smaller, from the viewpoint of further reducing voids and cracks in the sintered copper pillar. From these viewpoints, the volume-average particle size of the second sub-micro copper particles may be 0.8 to 1.3 μm, 1.0 to 1.2 μm, 0.5 to 0.9 μm, or 0.5 to 0.6 μm.

[0040] The shape of the second submicro copper particles is not particularly limited. Examples of the shapes of the second submicro copper particles include spherical, lumpy, needle-shaped, columnar, flake-shaped, and aggregates thereof. From the viewpoint of dispersibility and packing, the shape of the second submicro copper particles may be spherical or flake-shaped. When the first submicro copper particles are spherical, the second submicro copper particles may be flake-shaped. In this case, the flake-shaped second submicro copper particles are oriented substantially parallel to the bonding surface within the pillar precursor, which tends to suppress volume shrinkage of the pillar precursor in the direction of the bonding surface during sintering, and further reduce delamination at the interface between the sintered copper pillar and the bonding member. In particular, when the bonding member is a microdevice, the microdevice tends to exhibit good die-shear strength and connection reliability. From the viewpoint of achieving the above effect significantly, the aspect ratio of the flake-shaped second submicro copper particles may be 2 to 10.

[0041] The specific surface area of ​​the second sub-micro copper particle is, from the viewpoint of paste dispersibility, 1 m². 2 / g or more, 2m 2 / g or more, 3m2 / g or more or 4m 2 It may be 10 m² or more. The specific surface area of ​​the second submicro copper particle is 10 m² from the viewpoint of improving the electrical conductivity and heat dissipation of the sintered copper pillar. 2 / g or less, 8m 2 / g or less, 5m 2 / g or less or 4m 2 It may be less than / g. From these perspectives, the specific surface area of ​​the second submicro copper particle is 1 to 10 m². 2 / g, 2-8m 2 / g, 3-4m 2 / g or 4-5m 2 / g is also acceptable.

[0042] The second submicro copper particles may be treated with a surface treatment agent. Examples of surface treatment agents include the organic acids exemplified as surface treatment agents for the first submicro copper particles. The organic acids may be used individually or in combination of two or more. The amount of surface treatment agent applied may be the same as that applied to the first submicro copper particles.

[0043] As the second sub-micro copper particles, commercially available ones can be used. Examples of commercially available products include CT-500 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.51 μm), EFC-20 (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., volume average particle size 0.56 μm), EFC-09 (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., volume average particle size 1.26 μm), FMC-SB (manufactured by Furukawa Chemicals Co., Ltd., volume average particle size 0.8 μm), and CP-1500 (manufactured by Techno Alpha Co., Ltd., volume average particle size 1.5 μm).

[0044] The content of the second submicro copper particles is 10 to 40% by mass, based on the total mass of the copper particles. From the viewpoint of further reducing delamination at the interface between the sintered copper pillar and the joining member, the content of the second submicro copper particles may be 15% or more by mass, or 20% or more by mass, based on the total mass of the copper particles. From the viewpoint of further reducing voids and cracks in the sintered copper pillar, the content of the second submicro copper particles may be 35% or less by mass, or 30% or less by mass, based on the total mass of the copper particles. From these viewpoints, the content of the second submicro copper particles may be 20 to 40% by mass, 15 to 35% by mass, or 20 to 30% by mass, based on the total mass of the copper particles. In this embodiment, the content of the second submicro copper particles, based on the total mass of the first submicro copper particles, the second submicro copper particles, and the spherical microcopper particles, may be within the above range.

[0045] The mass ratio of the content of the second submicro copper particles to the content of the first submicro copper particles ([content of the second submicro copper particles] / [content of the first submicro copper particles]) may be 0.15 or more, 0.20 or more, 0.22 or more, or 0.25 or more, from the viewpoint of further reducing delamination at the interface between the sintered copper pillar and the joining member. The mass ratio of the content of the second submicro copper particles to the content of the first submicro copper particles may be 0.45 or less, 0.40 or less, or 0.35 or less, from the viewpoint of further reducing voids and cracks in the sintered copper pillar. From these viewpoints, the mass ratio of the content of the second submicro copper particles to the content of the first submicro copper particles may be 0.15 to 0.45, 0.20 to 0.45, 0.20 to 0.40, 0.22 to 0.40, or 0.25 to 0.35.

[0046] [Spherical microcopper particles] Spherical microcopper particles are spherical copper particles with a volume-average particle size of 2 to 5 μm.

[0047] The volume-average particle size of the spherical microcopper particles may be 2.5 μm or more or 3 μm or more, from the viewpoint of suppressing cracks generated in the pillars during bonding and improving the electrical conductivity and heat dissipation of the sintered copper pillars. The volume-average particle size of the spherical microcopper particles may be 4.5 μm or less, 3.5 μm or less, or 3 μm or less, from the viewpoint of improving dispersibility and printability. From these viewpoints, the volume-average particle size of the spherical microcopper particles may be 2 to 3 μm, 2.5 to 4.5 μm, or 3 to 3.5 μm.

[0048] The specific surface area of ​​spherical microcopper particles is 0.1 m², from the viewpoint of paste dispersibility. 2 / g or more, 0.4m 2 / g or more, 1m 2 / g or more, 2m 2 / g or more or 4m 2 It may be 10 m² or more. The specific surface area of ​​the spherical microcopper particles is 10 m² from the viewpoint of improving the electrical conductivity and heat dissipation of the sintered copper pillar. 2 / g or less, 8m 2 / g or less, 5m 2 / g or less, 1m 2 / g or less or 0.5m 2 It may be less than / g. From these perspectives, the specific surface area of ​​spherical microcopper particles is 1 to 10 m². 2 / g, 2-8m 2 / g, 4-5m 2 / g, 0.1~1m 2 / g or 0.4~0.5m 2 / g is also acceptable.

[0049] Spherical microcopper particles may be treated with a surface treatment agent from the viewpoint of dispersion stability and oxidation resistance. The surface treatment agent may be removed during bonding. Examples of such surface treatment agents include aliphatic carboxylic acids such as dodecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, arachidic acid, linoleic acid, linolenic 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, isobornylcyclohexanol, and tetraethylene glycol; aromatic alcohols such as p-phenylphenol; alkylamines such as octylamine, dodecylamine, and stearylamine; aliphatic nitriles such as stearonitrile and decanonitrile; silane coupling agents such as alkylalkoxysilanes; and polymeric treatment agents such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and silicone oligomers. One type of surface treatment agent may be used alone, or two or more types may be used in combination.

[0050] Commercially available spherical microcopper particles can be used. Examples of commercially available spherical microcopper particles include MA-C025K (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., volume average particle size 2.65 μm) and CP-2500 (manufactured by Techno Alpha Co., Ltd., volume average particle size 2.5 μm).

[0051] The content of spherical microcopper particles is 15 to 45% by mass, based on the total mass of copper particles. From the viewpoint of further reducing delamination at the interface between the sintered copper pillar and the joining member and improving the electrical conductivity and heat dissipation of the sintered copper pillar, the content of spherical microcopper particles may be 20% or more by mass or 25% or more by mass, based on the total mass of copper particles. From the viewpoint of further reducing voids and cracks in the sintered copper pillar and improving the printability of the copper paste, the content of spherical microcopper particles may be 40% or less by mass or 35% or less by mass, based on the total mass of copper particles. From these viewpoints, the content of spherical microcopper particles may be 20 to 40% by mass or 25 to 35% by mass, based on the total mass of copper particles. In this embodiment, the content of spherical microcopper particles based on the total mass of the first sub-microcopper particles, the second sub-microcopper particles and the spherical microcopper particles may be within the above range.

[0052] The mass ratio of the content of spherical microcopper particles to the sum of the content of first submicrocopper particles and second submicrocopper particles ([content of spherical microcopper particles] / [sum of content of first submicrocopper particles and second submicrocopper particles]) may be 0.20 or more, 0.25 or more, or 0.30 or more, from the viewpoint of further reducing delamination at the interface between the sintered copper pillar and the joining member and improving the electrical conductivity and heat dissipation of the sintered copper pillar. The mass ratio of the content of spherical microcopper particles to the sum of the content of first submicrocopper particles and second submicrocopper particles may be 0.50 or less, 0.48 or less, or 0.45 or less, from the viewpoint of further reducing voids and cracks in the sintered copper pillar and improving the printability of the copper paste. From these perspectives, the mass ratio of the spherical microcopper particle content to the sum of the first submicrocopper particle content and the second submicrocopper particle content may be 0.20-0.50, 0.25-0.48, or 0.30-0.45.

[0053] The copper paste of this embodiment may contain only first submicro copper particles, second submicro copper particles, and spherical microcopper particles as copper particles, or it may further contain copper particles other than the first submicro copper particles, second submicro copper particles, and spherical microcopper particles. The total content of the first submicro copper particles, second submicro copper particles, and spherical microcopper particles may be 90% by mass or more, 95% by mass or more, or 99% by mass or more, based on the total mass of the copper paste.

[0054] (Organic dispersion medium) The organic dispersion medium includes organic dispersion mediums having a boiling point below 300°C and / or organic dispersion mediums having a boiling point of 300°C or higher.

[0055] Examples of organic dispersion media having a boiling point below 300°C include α-terpineol, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, 4-methyl-1,3-dioxolan-2-one, and diethylene glycol monobutyl ether. Organic dispersion media having a boiling point below 300°C can be easily removed in the drying or heating process before sintering the pillar precursor. Organic dispersion media having a boiling point below 300°C can be used individually or in combination of multiple types.

[0056] The content of the organic dispersion medium having a boiling point below 300°C may be 0-50% by mass, 10-40% by mass, or 20-30% by mass, based on the total mass of the organic dispersion medium, from the viewpoint of promoting the sintering of copper particles.

[0057] For organic dispersion media having a boiling point of 300°C or higher, it is preferable to select a structure with high affinity to the copper particle surface in order to improve the dispersibility of copper particles. If the copper particles have been surface-treated with a surface treatment agent containing alkyl groups, it is preferable to select an organic dispersion media containing alkyl groups. Examples of organic dispersion media having a boiling point of 300°C or higher include isobornylcyclohexanol (MTPH, manufactured by Nippon Terpene Co., Ltd.), butyl stearate, Excepal BS (manufactured by Kao Corporation), stearyl stearate, Excepal SS (manufactured by Kao Corporation), 2-ethylhexyl stearate, Excepal EH-S (manufactured by Kao Corporation), isotridecyl stearate, Excepal TD-S (manufactured by Kao Corporation), isooctadecanol, Fineoxocol 180 (manufactured by Nissan Chemical Corporation), Fineoxocol 180T (manufactured by Nissan Chemical Corporation), 2-hexyldecanol, Fineoxocol 1600 (manufactured by Nissan Chemical Corporation), tributylin, tetraethylene glycol, heptadecane, octadecane, nonadecane, eicosane, heneicosane, docosane, methylheptadecane, tridecane Examples include silcyclohexane, tetradecylcyclohexane, pentadecylcyclohexane, hexadecylcyclohexane, undecylbenzene, dodecylbenzene, tetradecylbenzene, tridecylbenzene, pentadecylbenzene, hexadecylbenzene, heptadecylbenzene, nonylnaphthalene, diphenylpropane, octyl octanoate, methyl myristate, ethyl myristate, methyl linoleate, methyl stearate, triethylene glycol bis(2-ethylhexanoic acid), tributyl citrate, pentylphenol, dibutyl sebacate, oleyl alcohol, cetyl alcohol, methoxyphenethyl alcohol, benzylphenol, hexadecanenitrile, heptadecanenitrile, benzyl benzoate, and scinmethyline. Organic dispersion media having a boiling point of 300°C or higher can be used individually or in combination of multiple types.

[0058] As an organic dispersion medium having a boiling point of 300°C or higher, an organic dispersion medium with a boiling point of 310°C or higher is more preferable. Such a dispersion medium remains in the pillar precursor until the firing temperature of 150°C to 300°C, contributing to the maintenance of adhesion and flexibility. On the other hand, as an organic dispersion medium having a boiling point of 300°C or higher, an organic dispersion medium with a boiling point of 450°C or lower is preferable, and an organic dispersion medium with a boiling point of 400°C or lower is more preferable. Although the organic dispersion medium is removed by volatilization due to its vapor pressure even at temperatures below its boiling point, when using an organic dispersion medium with a boiling point of 450°C or lower, the volatilization rate does not become too slow at the sintering temperature of 150°C to 300°C, and sintering inhibition by residual dispersion medium is less likely to occur.

[0059] The content of the organic dispersion medium having a boiling point of 300°C or higher may be 50-100% by mass, 55-95% by mass, or 60-90% by mass, based on the total mass of the organic dispersion medium, from the viewpoint of improving the printability of the copper paste and suppressing cracking and peeling of the pillars during sintering.

[0060] From the viewpoint of adjusting the viscosity of the copper paste to a more appropriate level, the content of the organic dispersion medium may be 1% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more, based on the total mass of the copper paste. From the viewpoint of further improving the sinterability of the copper particles, the content of the organic dispersion medium may be 70% by mass or less, 65% by mass or less, or 60% by mass or less, 50% by mass or less, 20% by mass or less, or 10% by mass or less, based on the total mass of the copper paste. From these viewpoints, the content of the organic dispersion medium may be 1 to 70% by mass, 5 to 70% by mass, 5 to 65% by mass, 10 to 60% by mass, 15 to 50% by mass, 1 to 20% by mass, or 1 to 10% by mass, based on the total mass of the copper paste.

[0061] The type of organic dispersion medium contained in the copper paste can be analyzed, for example, by gas chromatography-mass spectrometry of high-temperature desorbed gases and TOF-SIMS. Alternatively, the supernatant obtained by separating particulate components by centrifugation may be identified using conventional organic analysis methods, such as FT-IR, NMR, liquid chromatography, or a combination thereof. The ratio of the types of organic dispersion mediums can be quantified using liquid chromatography, NMR, etc.

[0062] (Other ingredients) The copper paste may further contain components other than copper particles and an organic dispersion medium. Examples of components other than copper particles and an organic dispersion medium include metal particles other than copper particles, flexibility-imparting components such as pyrolytic resins, fillers, dispersants, fluxes, and the like.

[0063] The viscosity of the copper paste may be suitable for printing and coating methods for forming pillar precursors. From the viewpoint of facilitating the formation of pillar precursors by the various printing methods described later, the viscosity of the copper paste at 25°C may be 50 Pa·s to 2000 Pa·s, 100 Pa·s to 1750 Pa·s, or 200 Pa·s to 1500 Pa·s. Note that the viscosity of the copper paste refers to the value measured by an E-type viscometer at 25°C with a rotation speed of 0.5 rpm. As an E-type viscometer, for example, a VISCOMETER-TV33 viscometer manufactured by Toki Sangyo Co., Ltd. can be used. As a measuring jig for the cone rotor, for example, a 3°×R14, SPP can be applied.

[0064] The thixotropy index (hereinafter also referred to as "TI value") of the copper paste may be between 2.0 and 20, between 3.0 and 15, or between 4.0 and 10. When the TI value of the copper paste is within this range, the viscosity of the copper paste decreases due to shear force, making it easier to print by stirring the copper paste manually or with a stirring device (for example, a planetary vacuum mixer (ARV-310, manufactured by Thinky Co., Ltd.)) before printing. Furthermore, since the viscosity recovers after the copper paste adheres to the bonding material, excessive wetting and spreading of the printed material can be suppressed. The TI value of the copper paste is measured using an E-type viscometer at 25°C and a rotation speed of 0.5 rpm, with the viscosity measured in μm. 0.5 Assuming that μ5 is the viscosity measured by an E-type viscometer at 25°C and a rotation speed of 5 rpm, the value is calculated by the following formula. TI value = μ 0.5 / μ5

[0065] <Method for preparing copper paste> The copper paste of the above embodiment can be prepared by mixing first submicro copper particles, second submicro copper particles, spherical micro copper particles, an organic dispersion medium, and optional components (such as flexibility-imparting components) as needed. The copper paste may be prepared by mixing these components simultaneously, or by mixing them in multiple stages. For example, an intermediate slurry may be prepared by mixing the organic dispersion medium, the first submicro copper particles, and the optional component, and then the copper paste may be prepared by mixing the intermediate slurry, the second submicro copper particles, the spherical micro copper particles, the organic dispersion medium, and the optional component. Dispersion treatment may be performed during mixing. Furthermore, stirring treatment may be performed after mixing each component.

[0066] Dispersion processing can be carried out using a disperser or agitator. Examples include Ishikawa-type agitators, Silverson agitators, cavitation agitators, rotational agitators, ultra-thin film high-speed rotary dispersers, ultrasonic dispersers, Raikai machines, twin-screw kneaders, bead mills, ball mills, three-roll mills, homomixers, planetary mixers, ultra-high-pressure dispersers, thin-layer shear dispersers, and the like.

[0067] The stirring process can be carried out using a stirrer. Examples include the Ishikawa type stirrer, a self-rotating and revolving type stirrer, a raikai machine, a twin-shaft kneader, a three-roll mill, and a planetary mixer.

[0068] In this preparation method, aggregates may be removed by classification. The maximum particle size of copper particles may also be adjusted by classification. Classification can be performed using methods such as filtration, natural sedimentation, or centrifugation. Examples of filters for filtration include water combs, metal meshes, metal filters, and nylon meshes.

[0069] <zygote> A joint manufactured using the copper paste of the above embodiment and a method for manufacturing the joint will be described below.

[0070] Figure 1 is a schematic cross-sectional view showing a joint according to one embodiment. The joint 10 shown in Figure 1 comprises a first member 1, a second member 2, and a sintered copper pillar 3 that joins the first member 1 and the second member 2. The sintered copper pillar 3 is made of a sintered body of copper paste according to the above embodiment.

[0071] The lower and upper surfaces of the sintered copper pillar form the joint surfaces with the first member and the second member, respectively, and the two are joined by a metallic bond. Because such a metallic bond is formed, the joined body can be strongly bonded with low electrical resistance.

[0072] Examples of the first component 1 and the second component 2 include active or passive electronic devices, a wiring board on which electronic devices are mounted, and a package having an electronic device and a rewiring layer provided on the electronic device.

[0073] Examples of electronic devices include coils, capacitors, SAW filters, power ICs, logic chips, memory chips, sensors, piezoelectric elements, transistors, and diodes.

[0074] Examples of printed circuit boards include mounting boards, lead frames such as copper lead frames, ceramic substrates, resin molded products with printed metal wiring such as MIDs (Molded Interconnect Devices), and packages with redistribution layers.

[0075] The first component 1 and the second component 2 may be either an active or passive electronic device, or the other may be a wiring board on which the electronic device is mounted. In this case, highly reliable electronic device mounting becomes possible.

[0076] Furthermore, both the first component 1 and the second component 2 may be a package having an electronic device and a redistribution layer provided on the electronic device. In this case, highly reliable package-on-package mounting becomes possible.

[0077] The first member 1 and / or the second member 2 may contain one or more metals selected from the group consisting of copper, nickel, silver, platinum, gold, and palladium at the joint surface with the sintered copper pillar 3. Specifically, for example, a metal film or sintered metal layer containing one or more metals selected from the group consisting of copper, nickel, silver, platinum, gold, and palladium may be provided on the first member 1 and / or the second member 2. When the joint surface contains these metals, the oxide film on the surface can be reduced and removed under a reducing gas atmosphere such as hydrogen or formic acid at a sintering temperature of 300°C or lower. Therefore, the joint 10 can have high joint strength due to the metallic bond between the exposed metal surface of the member and the sintered copper pillar.

[0078] The sintered copper pillar 3 preferably has a copper content of 96% by mass or more, more preferably 96.5% by mass or more, and even more preferably 97% by mass or more, based on the total mass of the components constituting the sintered copper pillar (excluding carbon, oxygen, and nitrogen). The above-mentioned carbon, oxygen, and nitrogen are components that may be unintentionally included in the sintered copper pillar due to the filling of underfill or sealing material during mounting.

[0079] Sintered copper pillars with a copper content within the above range can be easily formed by printing and sintering the copper paste described above. Furthermore, having a copper content within the above range in sintered copper pillars is advantageous in terms of ensuring joint strength and suppressing electromigration. In addition, when the joint surface contains copper, the joint is made of the same type of metal, making it easier to suppress the generation of Kirkendal voids, resulting in a joint with even greater connection reliability.

[0080] From the viewpoint of thermal conductivity and electrical conductivity, the sintered copper pillar 3 preferably contains 50 volume% or more copper, more preferably 60 volume% or more, and even more preferably 70 volume% or more. The higher the volume percentage of copper in the sintered copper pillar 3, the higher the thermal conductivity and electrical conductivity of the sintered copper pillar 3. The volume percentage of copper in the sintered copper pillar 3 can be determined from the SEM image of the cross-section of the sintered copper pillar. In this specification, the parts of the sintered copper pillar other than copper are represented as voids. If a resin component such as a filler or underfill is contained in the void, the volume of that component is also included in the volume of the void.

[0081] The height H of the sintered copper pillar 3 may be 5 to 200 μm, 10 to 150 μm, or 20 to 100 μm. Here, the height of the sintered copper pillar 3 refers to the shortest distance between the joint surface of the sintered copper pillar 3 with the first member 1 and the joint surface of the sintered copper pillar 3 with the second member 2.

[0082] The width (diameter) W of the sintered copper pillar 3 may be 10 to 500 μm, 25 to 300 μm, or 50 to 150 μm. Here, the width (diameter) of the sintered copper pillar 3 refers to the minimum diameter of the cross-section perpendicular to the height direction (the direction in which the pillar extends) of the sintered copper pillar 3. From the viewpoint of reducing thermal stress after joining, the width (diameter) W of the sintered copper pillar 3 may be 100 to 200 μm, 125 to 175 μm, or 140 to 160 μm.

[0083] The sintered copper pillar 3 may have a ratio of height H to width W (H / W) (sometimes referred to as the "aspect ratio of the cross-sectional area of ​​the sintered copper pillar") of 0.01 to 4.0, 0.1 to 2.5, or 0.15 to 2.0.

[0084] The above height H and width W can be determined from the SEM image of the cross-section of the sintered copper pillar.

[0085] The shear strength at the interface between the sintered copper pillar 3 and the first member and / or the second member (the shear strength between the joint surface of the sintered copper pillar 3 and the joint surface of the first member and / or the second member) can be 4 MPa or more, may be 10 MPa or more, or may be 20 MPa or more. In this case, the joint surface of the first member and / or the second member may contain the above-mentioned metal. For example, the joint surface of the first member and / or the second member may be the surface of a metal layer containing the above-mentioned metal.

[0086] Shear strength can be calculated, for example, by using a bonding strength testing apparatus, pressing a sintered copper pillar horizontally at a constant speed with the apparatus's tool, and dividing the maximum strength at which the joint surface between the sintered copper pillar and the member peels off by the cross-sectional area of ​​the pillar.

[0087] The manufacturing method for the assembled body 10 described above comprises the steps of: forming the copper paste into a pillar shape on the first member 1, then mounting the second member 2 and providing a pillar precursor between the first member 1 and the second member 2 (hereinafter also referred to as the "first step"); and forming a sintered copper pillar 3 by sintering the pillar precursor (hereinafter also referred to as the "second step"). The method will be described in detail below with reference to Figures 2 and 3.

[0088] (First step) In the first step, copper paste 3a is first formed into a pillar shape on the first member 1 by printing or the like, for example, as shown in Figure 2.

[0089] For printing copper paste, methods such as 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 electrodeposition coating can be used.

[0090] In the first step, it is preferable to form the copper paste into pillars by screen printing or stencil printing, from the viewpoint of simplicity of the manufacturing process, ease of maintaining shape stability, and ease of thick film printing. In screen printing and stencil printing, for example, first, a metal mask 4 is placed on the first member 1 (Figure 2(a)). Next, copper paste 3a is placed on the first member 1 and the metal mask 4 (Figure 2(b)). Next, the copper paste 3a is spread using a squeegee 5 and filled into the holes of the metal mask 4 (Figure 2(c)). In this way, a pillar-shaped copper paste 3b is formed on the first member 1 (Figure 3(a)).

[0091] The via diameter of the metal mask used for screen printing or stencil printing may be 30 μm or more and 200 μm or less, or 50 μm or more and 100 μm or less. The arrangement of the holes may be a grid. The pitch spacing may be 1 μm or more and 500 μm or less. The squeegee angle may be 10° or more and 90° or less, or 45° or more and 70° or less.

[0092] The print height H1 may be 5 μm or more and 500 μm or less, or 10 μm or more and 200 μm or less. In addition, the wetting spread W1 from the pillar edge after printing may be 100 μm or less or 50 μm or less.

[0093] Next, as shown in Figure 3, for example, the second member 2 is mounted on the first member (on the pillar-shaped copper paste 3b), and a pillar precursor 3c is provided between the first member 1 and the second member 2. Specifically, as shown in Figure 3(b), for example, the second member 2 is mounted on the first member by pressing the second member 2 onto the pillar-shaped copper paste 3b. In this way, a pillar precursor 3c is provided between the first member 1 and the second member 2.

[0094] The method for mounting the second component 2 is not particularly limited, but for example, if the first component 1 and the second component 2 are a microdevice and a substrate, it may be a method using, for example, a chip mounter, a flip-chip bonder, or a positioning jig made of carbon or ceramic.

[0095] The indentation depth (H1-H2) when the second member 2 is mounted may be 500 μm or less, 100 μm or less, or 50 μm or less from the top of the pillar-shaped copper paste. H2 is set considering the height of the formed sintered copper pillar or pillar precursor.

[0096] (Second step) In the second step, the pillar precursor 3c, which is placed between the first member 1 and the second member 2, is sintered. This forms a sintered copper pillar 3, and the first member 1 and the second member 2 are joined by the sintered copper pillar 3, resulting in the joined body 10 shown in Figure 3(c).

[0097] The pillar precursor 3c may be dried as appropriate from the viewpoint of suppressing flow and void generation during sintering. The gas atmosphere during drying may be air, an oxygen-free atmosphere such as nitrogen or a noble gas, or a reducing gas atmosphere such as hydrogen or formic acid. The drying method may be drying at room temperature, heating, or vacuum drying. For heating or vacuum drying, 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. may be used. The drying temperature and time may be adjusted as appropriate according to the type and amount of organic dispersion medium and flexibility-imparting component used. For example, the drying temperature and time can be 50°C to 180°C for 30 seconds to 120 minutes.

[0098] The pillar precursor 3c can be sintered by heat treatment. 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, etc., can be used for heat treatment. The sintering of the pillar precursor 3c may be carried out without pressure.

[0099] The gas atmosphere during sintering may be a reducing gas atmosphere, from the viewpoint of removing copper particles contained in the pillar precursor 3c and surface oxides from the adherend. Examples of reducing gas atmospheres include a pure hydrogen gas atmosphere, a mixed gas atmosphere of hydrogen and nitrogen represented by a forming gas, a nitrogen atmosphere containing formic acid gas, a mixed gas atmosphere of hydrogen and a rare gas, and a rare gas atmosphere containing formic acid gas.

[0100] When the diameter of the pillar precursor 3c is small (especially 200 μm or less), formic acid penetrates deep into the pillar precursor 3c, making it easier to reduce the copper particles. This allows the copper particles to be thoroughly sintered in a reducing gas atmosphere containing formic acid gas. In this case, sintering can be performed using a formic acid reflow furnace, which efficiently improves the degree of sintering.

[0101] The maximum temperature achievable during the heat treatment may be 150°C to 300°C, 170°C to 250°C, or 200°C to 250°C, from the viewpoint of sufficiently advancing sintering, reducing thermal damage to components such as microdevices and substrates, and improving yield. If the maximum temperature achievable is 150°C or higher, sintering tends to proceed sufficiently even if the holding time at the maximum temperature is 60 minutes or less. From the viewpoint of sufficiently advancing sintering in a short time while further reducing delamination at the interface between the sintered copper pillar and the joining component, the maximum temperature achievable may be 180°C to 250°C, or 190°C to 225°C.

[0102] The holding time at the maximum temperature reached may be 1 minute or more and 60 minutes or 1 minute or more and 40 minutes or 1 minute or more and 30 minutes or less, from the viewpoint of sufficiently removing the organic dispersion medium and flexibility-imparting components, sufficiently advancing sintering, and improving yield. When the maximum temperature reached is 180°C or more and 250°C or 190°C or more and 225°C or less, it is preferable to hold the maximum temperature reached for 40 minutes or more and 80 minutes or less, and more preferably 50 minutes or more and 70 minutes or less, from the viewpoint of sufficiently advancing sintering while further reducing delamination at the interface between the sintered copper pillar and the joining member.

[0103] The heating time to reach the maximum temperature may be 10 minutes or less, 7 minutes or less, or 5 minutes or less, from the viewpoint of suppressing thermal stress caused by the thermal history of the joining members and further reducing delamination at the interface between the sintered copper pillar and the joining member. The heating time to reach the maximum temperature may be 1 minute or more, from the viewpoint of sufficiently removing the dispersion medium from the pillar.

[0104] Although one embodiment of a joint and its manufacturing method have been described above, the present invention is not limited to the above embodiment.

[0105] For example, the method for manufacturing the joint may further include a step of filling the area around the sintered copper pillar with resin. In this case, as shown in Figure 4, a joint 20 is obtained in which a sealing material 6 is provided between the first member 1 and the second member 2.

[0106] As a sealing material, from the viewpoint of protecting the joint from heat, moisture, and impact and further improving connection reliability, sealing materials for compression molds, liquid sealing materials, transfer mold sealing materials, underfill sealing materials, etc., can be used. [Examples]

[0107] The present invention will be described in more detail below with reference to experimental examples, but the present invention is not limited to the following experimental examples.

[0108] <Preparing the materials> The materials used in this experiment are shown below. [Copper particles] • CH-0200 (Product name, manufactured by Mitsui Mining & Smelting Co., Ltd., Shape: Spherical, Volume average particle size (D 50 particle size): 0.26μm, specific surface area: 4.1m 2 ( / g, aspect ratio: less than 2, surface treatment agent: dodecanoic acid) • CT-500 (product name, manufactured by Mitsui Mining & Smelting Co., Ltd., shape: flake-like, volume-average particle size (D 50 particle size): 0.51μm, specific surface area: 3.4m 2 / g, Aspect ratio: 3 or higher • MAC-025KFD (product name, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., shape: flake, volume average particle size (D 50 particle size): 5.90μm, specific surface area: 0.73m 2 ( / g, aspect ratio: 3 or higher) • MAC-025K (product name, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., shape: spherical, volume average particle size (D 50particle size): 2.65μm, specific surface area: 0.46m 2 ( / g, aspect ratio: less than 2) [Organic dispersion medium] • Octyl octanoate (manufactured by SAFC) • 2-Ethylhexyl Stearate (manufactured by Kao Corporation, product name: EH-S) [Joining member] • Cu plate (C1020, size: 19mm x 25mm, thickness: 3mm) • Si chip (bonding surface: Cu, size: 3mm x 3mm, thickness: 150μm)

[0109] <Experimental Examples 1-7> (Preparation of copper paste) 14.1 g of organic dispersion medium (octyl octanoate: 2-ethylhexyl stearate = 3:7) and 143 g of CH-0200 were placed in a plastic container and stirred using a planetary vacuum mixer (ARV-310, manufactured by Shinki Co., Ltd.). Specifically, the mixture was stirred at 1000 rpm for 4 minutes under normal pressure, then stirred five times at 2000 rpm for 1 minute each under reduced pressure, and finally stirred at 1000 rpm for 1 minute under normal pressure. Next, the resulting mixture was processed at 12000 rpm using a disk-type disperser (disparizer CDMX-150TH, manufactured by Shinto Kogyo Co., Ltd.) to produce an intermediate slurry.

[0110] Next, the above intermediate slurry, copper particles other than CH-0200 shown in Table 1, and an organic dispersion medium (octyl octanoate: 2-ethylhexyl stearate = 3:7 (mass ratio)) were added to a mortar and kneaded for 10 minutes. Then, the mixture was stirred for 1 minute at 2000 revolutions per minute under normal pressure using a rotation-and-revolving type agitator to prepare copper pastes for Experimental Examples 1 to 7 (copper pastes 1 to 7). The amount of copper particles was adjusted so that the content, based on the total mass of copper particles in the copper paste, was the value shown in Table 1. The amount of organic dispersion medium was adjusted so that the total mass of copper particles in the copper paste was 92% by mass.

[0111] [Table 1]

[0112] [Fabrication of the joint] The bonded structures (bonded structures 1-7) of Experimental Examples 1-7 were fabricated using the copper pastes (copper pastes 1-7) of Experimental Examples 1-7. Specifically, first, a stainless steel metal mask (thickness: 70 μm) with circular openings was placed on a Cu plate. Next, copper paste was applied to the Cu plate by stencil printing using a metal squeegee. The opening diameter of the metal mask was 150 μm, and the pitch of the openings was 500 μm. This formed pillar precursors (pillar-shaped copper paste) on the Cu plate.

[0113] Next, a flip-chip bonder (T-3000-FC-3, manufactured by Dr. Tresky) was used to mount Si chips onto a Cu plate (on the pillar precursor). Subsequently, the pillar precursor was sintered by heat treatment in a sintering furnace (manufactured by Shinko Seiki Co., Ltd.) to form sintered copper pillars, thereby joining the Cu plate and Si chips via the sintered copper pillars. The gas atmosphere during sintering was a formic acid atmosphere. For experimental examples 1-3, the maximum temperature reached was 225°C, the holding time at the maximum temperature was 1 hour, and the heating time to reach the maximum temperature was 20 minutes. For experimental examples 4-7, the maximum temperature reached was 200°C, the holding time at the maximum temperature was 1 hour, and the heating time to reach the maximum temperature was 5 minutes.

[0114] [Evaluation of the joint: Cross-sectional morphological observation] The joint was fixed inside a cup with a sample clip (Samplklip I, manufactured by Buehler), and epoxy casting resin (Epomount, manufactured by Refine Tech Co., Ltd.) was poured around it until the joint was completely filled. The sample was then placed in a vacuum desiccator and degassed by reducing the pressure for 1 minute. After that, the epoxy casting resin was allowed to cure at room temperature (25°C) for 10 hours. Next, the cast sample was cut near the cross-section to be observed using a Refine Saw Excel (RCB-961, manufactured by Refine Tech Co., Ltd.) equipped with a diamond cutting wheel (11-304, manufactured by Refine Tech Co., Ltd.). Next, the cross-section was polished using a polishing device (Refine Polisher Hv, manufactured by Refine Tech Co., Ltd.) equipped with waterproof abrasive paper (Carbomac Paper, manufactured by Refine Tech Co., Ltd.) to obtain a cross-section free of cracks in the Cu plate and Si chip. Finally, the excess casting resin was removed to finish the sample to a size that could be installed in a cross-section polisher (CP) processing machine. Next, the sample machined using the above method was subjected to a CP machining center (IM4000, manufactured by Hitachi, Ltd.) with an acceleration voltage of 6kV and an argon gas flow rate of 0.07~0.1cm³. 3 Flat milling was performed under the conditions of 1 / minute and a processing time of 20 minutes. Next, a sample for SEM observation was obtained by sputtering platinum using a sputtering device (ION SPUTTER, Hitachi High-Technologies Corporation) to obtain a platinum film with a thickness of 10 nm. Next, the surface on which the platinum film was formed (cross-section of the bonded body) of the sample for SEM observation was observed at various magnifications using an SEM device (ESEM XL30, Philips). The applied voltage was 10 kV. Cross-sectional SEM images of bonded bodies 1 to 7 are shown in Figures 5 to 7. Figures 5(a), (b), and (c) are cross-sectional SEM images of bonded bodies 1 to 3 (magnification: 500x), respectively. Figures 6(a) and (b) are cross-sectional SEM images of bonded body 3 (magnification: 10,000x). Figures 7(a), (b), (c), and (d) are cross-sectional SEM images (magnification: 500x) of the joints 4-7, respectively. In Figures 5-7, the Cu plate is indicated by 31, the Si chip by 32, the sintered copper pillar by 33, the MA-025KFD (flake-shaped micro copper particles) by 34, the delamination area by P, the void area by V, and the crack area by C.

[0115] As shown in Figure 5, delamination was observed at the interface between the Si chip and the sintered copper pillar in bonded bodies 1 and 2, and horizontal cracks were observed in the sintered copper pillar. In contrast, no delamination was observed at the interface between the Si chip and the sintered copper pillar in bonded body 3. From this, it was confirmed that copper paste 3 has superior bonding properties compared to copper pastes 1 and 2. However, in bonded body 3, as shown in Figures 5 and 6, voids of 1 to 10 μm in size were observed near MA-025KFD in the sintered copper pillar. It is presumed that the cause of void formation is that the increase in MA-025KFD increased the gaps between copper particles in the copper paste, resulting in a shortage of copper particles to fill the gaps.

[0116] As shown in Figure 7, no cracks were observed in the sintered copper pillars in joints 4-6. This is presumed to be because the use of CT-500, which is a sub-micro copper particle larger in size than CH-0200, suppressed excessive sintering and reduced volume shrinkage during sintering. However, delamination was observed at the interface between the Si chip and the copper pillar in joints 4 and 5, and voids were observed in the sintered copper pillar in joint 6. On the other hand, in joint 7, no delamination was observed at the interface between the Si chip and the sintered copper pillar, and no voids or cracks were observed in the sintered copper pillar. This is presumed to be because a denser sintered copper pillar was formed by using MA-025K, which is a spherical micro copper particle, instead of MA-025KFD, which is a flake-shaped micro copper particle. [Explanation of symbols]

[0117] 1...First component, 2...Second component, 3,33...Sintered copper pillar, 3a...Copper paste, 4...Metal mask, 5...Squeegee, 10,20...Joint, 31...Cu plate, 32...Si chip, P...Delamination, V...Void, C...Crack.

Claims

1. A copper paste for forming sintered copper pillars, containing copper particles and an organic dispersion medium, The copper particles include first submicro copper particles having a volume-average particle size of 0.05 to 0.35 μm, second submicro copper particles having a volume-average particle size of 0.5 to 1.5 μm, and spherical micro copper particles having a volume-average particle size of 2 to 5 μm. The content of the first submicro copper particles is 40 to 70% by mass, based on the total mass of the copper particles. The content of the second submicro copper particles is 10 to 40% by mass, based on the total mass of the copper particles. A copper paste for forming sintered copper pillars, wherein the content of the spherical micro-copper particles is 15 to 45% by mass, based on the total mass of the copper particles.

2. The copper paste for forming sintered copper pillars according to claim 1, wherein the first submicro copper particles are spherical and the second submicro copper particles are flake-shaped.

3. The copper paste for forming sintered copper pillars according to claim 1 or 2, wherein the mass ratio of the content of spherical microcopper particles to the sum of the content of the first submicrocopper particles and the content of the second submicrocopper particles is 0.20 to 0.

50.

4. The copper paste for forming sintered copper pillars according to any one of claims 1 to 3, wherein the mass ratio of the content of the second submicro copper particles to the content of the first submicro copper particles is 0.15 to 0.

45.

5. The copper paste for forming sintered copper pillars according to any one of claims 1 to 4, wherein the content of the organic dispersion medium is 5 to 70% by mass, based on the total mass of the copper paste.

6. A method for manufacturing a joined body comprising a first member, a second member, and a sintered copper pillar for joining the first member and the second member, The process involves forming a copper paste according to any one of claims 1 to 5 into a pillar shape on the first member, then mounting the second member, and providing a pillar precursor between the first member and the second member. A method for manufacturing a bonded body, comprising the step of forming the sintered copper pillar by sintering the pillar precursor.

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