JP7651832B2 - Copper paste for forming sintered copper pillars and method for producing joint body - Google Patents

Description

The present invention relates to a copper paste for forming sintered copper pillars and a method for manufacturing a joint body.

Solder joints are generally used for electrical connections in electronic devices. For example, in flip-chip connections of microdevices, solder balls or solder paste are used to connect the microdevice to the electrode pads on the substrate.

In recent years, as the pitch of terminals in flip-chip bonding becomes narrower, a method has been used in which metal pillars are formed on microdevices and then soldered to electrode pads on a substrate. However, solder bonding has problems such as (1) Kirkendall voids occurring between the solder and the electrode pads and between the solder and the metal pillars, (2) when a reflow process is performed again after bonding, the solder melts and causes bonding defects, and (3) signal reflections occur due to impedance mismatch at the interface between different metals.

In response to this, methods of bonding using metals other than solder are being considered. For example, the following Patent Document 1 proposes a method of bonding between copper pillars provided on a microdevice and copper pads on a substrate using a bonding agent (copper paste) that is a mixture of copper microparticles and copper nanoparticles.

US Patent Application Publication No. 2016/0351529

The method of Patent Document 1 requires the formation of copper pillars on the device in advance, but the mainstream method of forming copper pillars using electrolytic plating has the problem that it takes time to form the pillars. Another problem is that increasing the plating speed results in greater variation in height.

The inventors have therefore investigated a method for forming a sintered copper pillar and joining the joining members by forming a pillar precursor between the joining members using a copper paste containing copper particles and an organic dispersion medium and sintering the pillar precursor. This method makes it possible to form a sintered copper pillar efficiently and accurately. The copper paste used to form such a sintered copper pillar (copper paste for forming a sintered copper pillar) is required to have excellent bonding properties and excellent sintering properties.

Therefore, one object of the present invention is to provide a copper paste for forming sintered copper pillars that has excellent sinterability and bonding properties.

The present inventors have found that the sinterability and bondability of copper paste are improved by using a high-boiling organic dispersion medium with a boiling point above a specific temperature as the organic dispersant contained in the copper paste. In addition, since copper paste is usually printed at room temperature (e.g., 25°C), it was thought that the physical properties (e.g., solidification point) of the organic dispersion medium used in the copper paste at temperatures lower than room temperature would not affect the sinterability and bondability of the sintered copper pillar. However, as a result of the inventors' investigations, they surprisingly found that when a high-boiling organic dispersion medium such as the above is used, the physical properties at temperatures below room temperature affect the sinterability and bondability of the copper paste, and thus completed the present invention.

One aspect of the present invention relates to a copper paste for forming a sintered copper pillar that joins members together, the copper paste containing metal particles and an organic dispersion medium, the metal particles containing copper particles, the organic dispersion medium containing a high-boiling-point dispersion medium having a boiling point of 280°C or higher in a proportion of more than 99 mass% based on the total mass of the organic dispersion medium, and containing a low-freezing-point dispersion medium having a freezing point of 20°C or lower.

The copper paste for forming the sintered copper pillar of the above aspect has excellent sinterability and bonding properties. That is, the copper paste for forming the sintered copper pillar of the above aspect can suppress the occurrence of voids and cracks in the sintered copper pillar while suppressing the occurrence of peeling at the interface between the sintered copper pillar and the bonding member. The reason why the above effect is obtained is unclear, but it is presumed that the above effect is obtained due to the fact that the proportion of the high-boiling point dispersion medium in the organic dispersion medium is more than 99 mass %, which suppresses the rapid evaporation of the solvent during sintering, and the low-freezing point dispersion medium suppresses the solidification of the copper paste at room temperature, stabilizing the viscosity of the copper paste, and improving the printability of the copper paste.

In one embodiment, the content of the organic dispersion medium may be 1 to 20 mass % based on the total mass of the copper paste.

In one embodiment, the content of the low-freezing point dispersion medium may be 50% by mass or more based on the total mass of the organic dispersion medium.

In one embodiment, the metal particles may contain sub-micro copper particles having a volume average particle size of 0.01 μm or more and less than 0.8 μm in a proportion of 30 to 100 mass % based on the total mass of the metal particles.

In one embodiment, the metal particles may contain micro copper particles having a volume average particle size of 0.8 μm or more and 50 μm or less in a proportion of more than 0 mass% and not more than 70 mass% based on the total mass of the metal particles.

In one embodiment, the low-freezing point dispersion medium may include an organic dispersion medium with a freezing point of 10 to 20°C.

In one embodiment, the organic dispersion medium may contain at least one selected from the group consisting of 2-ethylhexyl stearate, isotridecyl stearate, isobornylcyclohexanol, and octyl octanoate.

One aspect of the present invention relates to a method for manufacturing a joint comprising a first member, a second member, and a sintered copper pillar that joins the first member and the second member, the method comprising the steps of forming the copper paste of the side surface into a pillar shape on the first member, 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.

The manufacturing method of the bonded body described above makes it possible to obtain a bonded body in which peeling at the interface between the sintered copper pillar and the bonding member is reduced while suppressing the occurrence of voids, cracks, etc. in the sintered copper pillar.

The present invention provides a copper paste for forming sintered copper pillars that has excellent sinterability and bonding properties.

1 is a schematic cross-sectional view showing one embodiment of a bonded body according to the present invention. 1 is a schematic cross-sectional view illustrating one embodiment of a method for producing a bonded body according to the present invention. 1 is a schematic cross-sectional view illustrating one embodiment of a method for producing a bonded body according to the present invention. FIG. 4 is a schematic cross-sectional view showing another embodiment of a bonded body according to the present invention.

The following describes in detail the form for carrying out the present invention. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified, or considered to be obviously essential in principle. The same applies to numerical values and their ranges, and they do not limit the present invention.

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 the purpose of the process is achieved. In this specification, a numerical range indicated using "~" indicates a range that includes the numerical values before and after "~" as the minimum and maximum values, respectively. In this specification, the content of each component in a composition means the total amount of the multiple substances present in the composition, unless otherwise specified, when multiple substances corresponding to each component are present in the composition. In this specification, "boiling point" and "freezing point" mean the boiling point and freezing point at 1 atmosphere.

<Copper paste>
The copper paste of one embodiment contains metal particles and an organic dispersion medium. The metal particles include copper particles. The organic dispersion medium contains an organic dispersion medium having a boiling point of 280° C. or higher (high boiling point dispersion medium) at a ratio of more than 99 mass% based on the total mass of the organic dispersion medium, and also contains an organic dispersion medium having a freezing point of 20° C. or lower (low freezing point dispersion medium).

The copper paste is a copper paste for forming a sintered copper pillar that joins components together, and is specifically used to manufacture a joint that includes a first component, a second component, and a sintered copper pillar that joins the first component and the second component.

The copper paste has excellent sinterability and bondability. In other words, the copper paste can suppress the occurrence of voids and cracks in the sintered copper pillar while suppressing the occurrence of peeling at the interface between the sintered copper pillar and the joining member (first member and/or second member).

(Metal Particles)
The metal particles include copper particles. The copper particles refer to particles containing copper as a main component, for example, particles having a copper content of 80% by mass or more. The copper content of the copper particles may be 85% by mass or more, 90% by mass, 95% by mass or more, or 99% by mass. The metal particles may further include metal particles other than copper particles (hereinafter also referred to as "other metal particles") as necessary.

Examples of copper particles include submicro copper particles and micro copper particles. Submicro copper particles refer to copper particles having a particle size of 0.01 μm or more and less than 0.8 μm. Micro copper particles refer to copper particles having a particle size of 0.8 μm or more and 50 μm or less.

The metal particles preferably contain sub-micro copper particles from the viewpoint of easily ensuring sufficient bonding strength and connection reliability. From the viewpoint of further reducing volumetric shrinkage and void generation when sintering the pillar precursor formed from the copper paste, and from the viewpoint of more easily ensuring sufficient bonding strength, the metal particles may contain sub-micro copper particles and micro copper particles. In particular, when the metal particles contain sub-micro copper particles and micro copper particle paste and the bonding member is a micro device, the micro device tends to exhibit good die shear strength and connection reliability.

[Submicron copper particles]
As the submicro copper particles, for example, copper particles having sinterability in a temperature range of 150 ° C. or more and 300 ° C. or less can be used. As the submicro copper particles, for example, submicro copper particles having a volume average particle size of 0.01 μm or more and less than 0.8 μm can be used. If the volume average particle size of the submicro copper particles is 0.01 μm or more, effects such as suppression of the synthesis cost of the submicro copper particles, good dispersibility, and suppression of the amount of the surface treatment agent used can be easily obtained. If the volume average particle size of the submicro copper particles is less than 0.8 μm, better sinterability can be easily obtained. From the viewpoint of further achieving the above effect, the volume average particle size of the submicro copper particles may be 0.6 μm or less, 0.5 μm or less, or 0.4 μm or less. The volume average particle size of the submicro copper particles may be 0.02 μm or more, 0.05 μm or more, or 0.1 μm or more. The volume average particle size of the sub-micro copper particles may be, for example, 0.01 μm or more and 0.5 μm or less, 0.12 μm or more and less than 0.8 μm, 0.15 μm or more and less than 0.8 μm, 0.15 μm or more and 0.6 μm or less, 0.2 μm or more and 0.5 μm or less, or 0.3 μm or more and 0.45 μm or less.

In this specification, the volume average particle size means the 50% volume average particle size. The volume average particle size of copper particles can be determined by, for example, dispersing raw copper particles or dried copper particles obtained by removing volatile components from copper paste in a dispersion medium using a dispersant, and measuring the resulting dispersion medium with a light scattering particle size distribution measuring device (for example, Shimadzu nanoparticle size distribution measuring device (SALD-7500nano, manufactured by Shimadzu Corporation)). When using a light scattering particle size distribution measuring device, hexane, toluene, α-terpineol, 4-methyl-1,3-dioxolan-2-one, etc. can be used as the dispersion medium.

The shape of the sub-micro copper particles is not particularly limited. Examples of the shape of the sub-micro copper particles include spherical, clumpy, needle-like, columnar, flake-like, nearly spherical, and aggregates thereof. From the viewpoint of dispersibility and packing property, the shape of the sub-micro copper particles may be spherical, nearly spherical, or flake-like, and from the viewpoint of combustibility, dispersibility, mixability with flake-like microparticles, etc., the shape of the sub-micro copper particles may be spherical or nearly spherical. In this specification, "flake-like" includes flat shapes such as plate-like and scale-like.

The aspect ratio of the sub-micro copper particles may be 5 or less, or may be 3 or less, from the viewpoints of dispersibility, packing property, and mixability with flake-shaped microparticles. In this specification, the "aspect ratio of a particle" refers to the long side/thickness of a particle. The long side and thickness of a particle can be measured, for example, from an SEM image of the particle.

The submicron copper particles may be treated with a specific surface treatment agent. Examples of specific surface treatment agents include organic acids having 2 to 18 carbon atoms (e.g., organic acids having an alkyl group having 1 to 17 carbon atoms). Examples of organic acids having 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, 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 cyclohexane carboxylic acid, propyl tridecanoic acid, butyl dodecanoic acid, pentyl undecanoic acid, hexyl decanoic acid, heptyl nonanoic acid, heptadecanoic acid, octadecanoic acid, methyl cyclohexane carboxylic acid, ethyl cyclohexane carboxylic acid, propyl cyclohexane carboxylic acid, butyl cyclohexane carboxylic acid, pentyl cyclohexane carboxylic acid, hexyl cyclohexane carboxylic acid, heptyl cyclohexane carboxylic acid, octyl cyclohexane carboxylic acid, and nonyl cyclohexane carboxylic acid; octenoic acid, nonenoic acid, etc. , methylnonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, sapienic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, and other unsaturated fatty acids; 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. The organic acid may be used alone or in combination of two or more. By combining such an organic acid with the submicro copper particles, it tends to be possible to achieve both the dispersibility of the submicro copper particles and the detachment of the organic acid during sintering.

The amount of the surface treatment agent 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.

Submicron copper particles can be commercially available. Examples of commercially available products include CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.36 μm), HT-14 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.41 μm), CT-500 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.72 μm), Tn-Cu100 (manufactured by Taiyo Nippon Sanso Co., Ltd., volume average particle size 0.12 μm), and Cu-C-40 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 0.2 μm).

The content of the sub-micro copper particles may be 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more, and 100% by mass or less, 95% by mass or less, 90% by mass or less, or 80% by mass or less, based on the total mass of the metal particles, from the viewpoint of easily ensuring sufficient bonding strength. From the above viewpoint, the content of the sub-micro copper particles may be 30 to 100% by mass, 40 to 95% by mass, 40 to 90% by mass, 50 to 95% by mass, 50 to 90% by mass, 50 to 80% by mass, 60 to 90% by mass, or 60 to 80% by mass, based on the total mass of the metal particles. When the content of the sub-micro copper particles is within the above range and the bonding member is a micro device, the micro device tends to exhibit good die shear strength and connection reliability.

The content of the sub-micro copper particles may be 20 to 95% by mass, 30 to 85% by mass, or 40 to 75% by mass based on the total mass of the copper paste, from the viewpoints of promoting sintering, achieving good connection between the first and second components, and exhibiting low-temperature sintering properties.

[Micro copper particles]
As the micro copper particles, for example, micro copper particles having a volume average particle size of 0.8 μm to 50 μm can be used. From the viewpoint of easily obtaining the above-mentioned effects by combining with the sub-micro copper particles, the volume average particle size of the micro copper particles may be 0.8 μm to 20 μm, 0.8 μm to 10 μm, 2 μm to 20 μm, 2 μm to 10 μm, 3 μm to 20 μm, or 3 μm to 10 μm.

The shape of the micro copper particles is not particularly limited, but examples include spheres, chunks, needles, flakes, roughly spherical shapes, and aggregates of these.

When sub-micro copper particles and micro copper particles are used in combination, the micro copper particles may include flake-shaped micro copper particles. In this case, the flake-shaped micro copper particles are oriented approximately parallel to the joining surface within the pillar precursor, thereby suppressing the volumetric shrinkage of the pillar precursor in the joining surface direction during sintering, making it easier to ensure sufficient joining strength. In particular, when the joining member is a micro device, the micro device tends to exhibit good die shear strength and connection reliability. From the viewpoint of making the above effect prominent, the aspect ratio of the flake-shaped micro copper particles is preferably 3 or more, more preferably 4 or more, and even more preferably 6 or more.

From the viewpoint of suppressing the variation in height of the pillar precursor while making it easier to obtain the above-mentioned effects, the content of the flake-shaped micro copper particles may be more than 0 mass% and not more than 70 mass%, may be 5 mass% or more and not more than 50 mass%, may be 10 mass% or more and not more than 40 mass%, or may be 20 mass% or more and not more than 40 mass%, based on the total mass of the metal particles.

In the micro copper particles, the presence or absence of treatment with a surface treatment agent is not particularly limited. From the viewpoint of dispersion stability and oxidation resistance, the micro copper particles may be treated with a surface treatment agent. The surface treatment agent may be one that is 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 decanenitrile; silane coupling agents such as alkylalkoxysilanes; and polymer treatment agents such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and silicone oligomers. The surface treatment agent may be used alone or in combination of two or more types.

Commercially available micro copper particles can be used. Commercially available spherical or nearly spherical micro copper particles include, for example, 1050Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.81 μm), 1100Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 1.1 μm), 1200Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 2.1 μm), 1300Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 4.6 μm), 1400Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 5.5 μm), 1200YM (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 1.9 μm), 1300YM (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 3.4 μm), 1400YM (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 4.2 μm), Cu-HWQ 1.5 μm (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 1.5 μm), Cu-HWQ 1.5 μm (manufactured by Fukuda Metal Foil Powder Industrial Co., Ltd., volume average particle size 1.4 μm), Cu-HWQ 3.0 μm (manufactured by Fukuda Metal Foil Powder Industrial Co., Ltd., volume average particle size 3.0 μm), Cu-HWQ 5.0 μm (manufactured by Fukuda Metal Foil Powder Industrial Co., Ltd., volume average particle size 4.1 μm) and Cu-HWQ 10 μm (manufactured by Fukuda Metal Foil Powder Industrial Co., Ltd., volume average particle size 9.4 μm). Commercially available flake-shaped micro copper particles include, for example, MA-C025KFD (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 7.5 μm), 4L3N (manufactured by Fukuda Metal Foil Powder Industrial Co., Ltd., volume average particle size 3.0 μm), 3L3N (manufactured by Fukuda Metal Foil Powder Industrial Co., Ltd., volume average particle size 5.7 μm), 3L3 (manufactured by Fukuda Metal Foil Powder Industrial Co., Ltd., volume average particle size 8.0 μm), 2L3N (manufactured by Fukuda Metal Foil Powder Industrial Co., Ltd., 9.9 μm), 1110F (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 3.8 μm), 1050YP (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.94 μm), 1100YP (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 1.2 μm), 1200YP (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 3.4 μm), and 1400YP (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 5.2 μm).

The content of the micro copper particles may be more than 0 mass% or more than 5 mass% or more than 10 mass% or more than 20 mass% and may be 70 mass% or less, 50 mass% or less, or 40 mass% or less, based on the total mass of the metal particles, from the viewpoint that the above-mentioned effect is easily obtained by combining with the sub-micro copper particles. From the above viewpoint, the content of the micro copper particles may be more than 0 mass% or less than 70 mass%, may be 5 mass% or more and 50 mass% or less, may be 10 mass% or more and 40 mass% or less, or may be 20 mass% or more and 40 mass% or less, based on the total mass of the metal particles.

The copper particles may contain copper nanoparticles to the extent that the effects of the microcopper particles and submicrocopper particles described above are not impaired. Copper nanoparticles refer to copper particles having a particle size of less than 0.01 μm. From the viewpoint of making the sintered copper pillars denser and increasing the copper content, the content of the copper nanoparticles is preferably 30% by mass or less, more preferably 15% by mass or less, and even more preferably 0% by mass (i.e., no copper nanoparticles) based on the total mass of the metal particles.

[Metal particles other than copper particles]
Examples of metal particles (other metal particles) other than copper particles include zinc, nickel, silver, gold, palladium, platinum, and the like. The volume average particle size of the other metal particles may be 0.01 μm or more and 10 μm or less, 0.01 μm or more and 5 μm or less, or 0.05 μm or more and 3 μm or less. From the viewpoint of obtaining sufficient bonding properties, the content of the other metal particles may be less than 20 mass%, 10 mass% or less, 5 mass% or less, or 0 mass% (i.e., not including copper nanoparticles) based on the total mass of the metal particles. The shape of the other metal particles is not particularly limited.

When the metal particles contain other metal particles, particularly when they contain metal particles having a metal species with a low freezing point, the sintering temperature can be lowered. Furthermore, since a sintered body in which multiple types of metals are dissolved or dispersed can be obtained, the mechanical properties of the sintered body, such as the yield stress and fatigue strength, can be improved, and the connection reliability can be improved. Furthermore, by adding multiple types of metal particles, the sintered body can have sufficient bonding strength to a specific adherend. In particular, when the joining member is a microdevice, the die shear strength and connection reliability of the microdevice can be improved.

(Organic Dispersion Medium)
The organic dispersion medium contains an organic dispersion medium (high boiling dispersion medium) having a boiling point of 280° C. or more at a ratio of more than 99% by mass based on the total mass of the organic dispersion medium. In other words, the content of an organic dispersion medium (low boiling dispersion medium) having a boiling point of less than 280° C. in the organic dispersion medium is less than 1% by mass based on the total mass of the organic dispersion medium. The organic dispersion medium may be composed of only a high boiling dispersion medium. The high boiling dispersion medium may be used alone or in combination.

The boiling point of the high-boiling dispersion medium is preferably 290°C or higher, and more preferably 300°C or higher. A dispersion medium having such a boiling point is likely to remain in the pillar precursor up to the firing temperature of 150°C to 300°C, so that adhesion and flexibility are more easily maintained. In addition, by using a dispersion medium having such a boiling point, it tends to be possible to extend the standing time (the time from the formation of the pillar precursor to the mounting of the joining member) during which stable formation of a joint by the sintered copper pillar is possible. On the other hand, the boiling point of the high-boiling dispersion medium is preferably 450°C or lower, and more preferably 400°C or lower. The dispersion medium is volatilized and removed by its vapor pressure even at temperatures below its boiling point, but when an organic dispersion medium with a boiling point of 450°C or lower is used, the volatilization rate does not become too slow at the sintering temperature of 150°C to 300°C, and sintering inhibition due to the remaining dispersion medium is less likely to occur.

In order to improve the dispersibility of the metal particles (e.g., copper particles such as submicro copper particles and micro copper particles) contained therein, it is preferable to select a high-boiling-point dispersion medium with a structure having a high affinity with the metal particle surface. For example, when the metal particles are surface-treated with a surface treatment agent containing an alkyl group, it is preferable to select a dispersion medium having an alkyl group. As a combination of the surface treatment agent for the metal particles and the high-boiling-point dispersion medium, it is preferable that the surface treatment agent is an organic acid containing an alkyl group having 1 to 17 carbon atoms, and the high-boiling-point dispersion medium is a dispersion medium containing an alkyl group having 1 to 17 carbon atoms, more preferably the surface treatment agent is an organic acid containing an alkyl group having 5 to 17 carbon atoms, and the high-boiling-point dispersion medium is a dispersion medium containing an alkyl group having 5 to 17 carbon atoms, and even more preferably the surface treatment agent is an organic acid containing an alkyl group having 10 to 17 carbon atoms, and the high-boiling-point dispersion medium is a dispersion medium containing an alkyl group having 10 to 17 carbon atoms. According to the above combination, the metal particles can be dispersed well even when the content of the high-boiling-point dispersion medium is increased.

Specific high-boiling point dispersion media include isobornylcyclohexanol (MTPH, manufactured by Nippon Terpene Co., Ltd.), butyl stearate, Exepar BS (manufactured by Kao Corporation), stearyl stearate, Exepar SS (manufactured by Kao Corporation), 2-ethylhexyl stearate, Exepar EH-S (manufactured by Kao Corporation), isotridecyl stearate, Exepar TD-S (manufactured by Kao Corporation), isooctadecanol, Fine Oxocol 180 (manufactured by Nissan Chemical Industries, Ltd.), Fine Oxocol 180T (manufactured by Nissan Chemical Industries, Ltd.), 2-hexyldecanol, Fine Oxocol 1600 (manufactured by Nissan Chemical Industries, Ltd.), tributyrin, tetraethylene glycol, heptadecane, octadecane, nonadecane, eicosane, heneicosane, docosane, methylheptadecanol, , tridecylcyclohexane, 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, heptadecylnitrile, benzyl benzoate, cinmethylin, etc.

The organic dispersion medium includes an organic dispersion medium having a freezing point of 20°C or less (low freezing point dispersion medium). The low freezing point dispersion medium may be a high boiling point dispersion medium. That is, the boiling point of the low freezing point dispersion medium may be 280°C or more. From the viewpoint of improving printability and providing better sinterability and bondability, the freezing point of the low freezing point dispersion medium may be 15°C or less, 10°C or less, 5°C or less, or 0°C or less. The freezing point of the low freezing point dispersion medium may be -10°C or more, -5°C or more, 0°C or more, 5°C or more, or 10°C or more. The low freezing point dispersion medium may be used alone or in combination of multiple types.

When the organic dispersion medium contains an organic dispersion medium with a freezing point of 10 to 20°C as a low-freezing point dispersion medium, the printability, sinterability, and bondability tend to be superior. From the viewpoint of obtaining such effects more significantly, the organic dispersion medium may contain two or more organic dispersion mediums with a freezing point of 10 to 20°C, and may contain an organic dispersion medium with a freezing point of 10 to 20°C and an organic dispersion medium with a freezing point of 15°C or lower (for example, an organic dispersion medium with a freezing point of 0°C or lower).

Examples of low-freezing point dispersion media include 2-ethylhexyl stearate, isotridecyl stearate, isobornylcyclohexanol, octyl octanoate, 4-n-octylaniline, benzhydrylamine, isostearyl alcohol, isooctadecanol, 2-hexyldecanol, tetradecyl mercaptan, phenyl p-trisulfide, tributyrin, methyl myristate, ethyl myristate, methyl linoleate, triethylene glycol bis(2-ethylhexanoic acid), tributyl citrate, dibutyl sebacate, benzyl benzoate, dibutyl adipate, linoleate, Examples of suitable esters include methyl phthalate, dibutyl phthalate, bis(2-methoxyethyl) phthalate, ethoxycarbonylmethylethyl phthalate, tributyl O-acetylcitrate, dioctyl sebacate, dioctyl phthalate, tetrabutyltin, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, octadecane, tridecylbenzene, 2-methylheptadecane, 1-heptadecene, 1-phenylpentadecane, squalane, 4-bromodiphenyl ether, 1-iodonaphthalene, 1-bromo-4-methylnaphthalene, cresyldiphenyl phosphate, triphenyl phosphite, etc. Among these, from the viewpoint of excellent printability, sinterability, and bondability, at least one selected from the group consisting of 2-ethylhexyl stearate, isotridecyl stearate, isobornylcyclohexanol, and octyl octanoate is preferably used.

From the viewpoint of achieving better printability, sinterability, and bondability, the organic dispersion medium may contain isotridecyl stearate and at least one selected from the group consisting of 2-ethylhexyl stearate, octyl octanoate, and isobornylcyclohexanol. In this case, the content of isotridecyl stearate may be 30% by mass or more, 40% by mass or more, or 50% by mass or more, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total mass of the organic dispersion medium.

From the viewpoint of achieving superior printability, sinterability, and bondability, the organic dispersion medium may contain 2-ethylhexyl stearate and at least one selected from the group consisting of octyl octanoate, isotridecyl stearate, and isobornylcyclohexanol. In this case, the content of 2-ethylhexyl stearate may be 30% by mass or more, 40% by mass or more, or 50% by mass or more, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total mass of the organic dispersion medium.

From the viewpoint of achieving superior printability, sinterability, and bondability, the organic dispersion medium may contain isobornylcyclohexanol and at least one selected from the group consisting of octyl octanoate, 2-ethylhexyl stearate, and isotridecyl stearate. In this case, the content of isobornylcyclohexanol may be 30% by mass or more, 40% by mass or more, or 50% by mass or more, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total mass of the organic dispersion medium.

From the viewpoint of achieving superior printability, sinterability, and bondability, the organic dispersion medium may contain at least one selected from the group consisting of isobornylcyclohexanol, 2-ethylhexyl stearate, and isotridecyl stearate, or may contain octyl octanoate and at least one selected from the group consisting of isobornylcyclohexanol, 2-ethylhexyl stearate, and isotridecyl stearate. In this case, the content of octyl octanoate may be 30% by mass or more, 40% by mass or more, or 50% by mass or more, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total mass of the organic dispersion medium.

From the viewpoint of achieving superior printability, sinterability, and bondability, the content of the low-freezing point dispersion medium is preferably more than 50 mass%, more preferably 60 mass% or more, and even more preferably 70 mass% or more, based on the total mass of the organic dispersion medium. The content of the low-freezing point dispersion medium may be 100 mass% or less, 90 mass% or less, or 80 mass% or less, based on the total mass of the organic dispersion medium.

The content of the organic dispersion medium may be 1 mass% or more, 2 mass% or more, 3 mass% or more, or 4 mass% or more based on the total mass of the copper paste, from the viewpoint of adjusting the viscosity of the copper paste to a more appropriate value. The content of the organic dispersion medium may be 20 mass% or less, 10 mass% or less, or 5 mass% or less based on the total mass of the copper paste, from the viewpoint of further improving the sinterability of the copper particles.

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 gas and TOF-SIMS. As another analytical method, the supernatant obtained by separating the particle components by centrifugation can be identified by conventional organic analysis, for example, FT-IR, NMR, liquid chromatography, or a combination of these. The ratio of types of organic dispersion medium can be quantified by liquid chromatography, NMR, etc.

(Components other than metal particles and organic dispersion medium)
The copper paste may further contain components other than the metal particles and the organic dispersion medium, such as a flexibility-imparting component such as a thermally decomposable resin, a filler, a dispersant, and a flux.

As the thermally decomposable resin, a non-crystalline polymer capable of exhibiting adhesiveness or tackiness is preferred for the purpose of temporarily fixing the pillar precursor to the joining member, which is the adherend, from after the pillar precursor is formed until it is fired. In addition, it is preferable that the thermally decomposable resin has thermal decomposition properties that allow it to decompose at the sintering temperature without leaving any residue.

The thermal decomposition temperature of the thermally decomposable resin is preferably 300°C or lower, and more preferably 250°C or lower. The thermal decomposition temperature of the thermally decomposable resin is the temperature at which the thermally decomposable resin starts to decompose, and is the temperature at which the resin loses 5% weight in TG/DTA measurement. However, this temperature does not mean the decomposition start temperature in an oxidizing atmosphere such as air, but in a reducing gas atmosphere containing hydrogen or formic acid, or in an inert gas atmosphere from which oxygen has been removed.

The less residue there is after the thermal decomposition of the thermally decomposable resin, the better, as it will prevent the sintering of the copper particles. Usually, the amount of residue at the sintering temperature is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, based on the mass of the resin before thermal decomposition. The amount of residue after thermal decomposition of the thermally decomposable resin can be measured by TG/DTA of the thermally decomposable resin in an inert gas (nitrogen or argon) containing 3 to 5% by mass of hydrogen, as the weight change after holding the resin at the sintering temperature for the sintering time. Note that TG/DTA measurement in air is not preferred, as oxidative decomposition proceeds and the amount of residue is less than that in a reducing gas atmosphere.

The thermally decomposable resin has, for example, solubility in the organic dispersion medium described above. Examples of thermally decomposable resins that have solubility in organic dispersion media and the desired properties described above include polycarbonate, polymethacrylic acid, polymethacrylic acid ester, and polyester.

The content of the thermally decomposable resin may be 25% by mass or less, 15% by mass or less, 5% by mass or less, or 3% by mass or less, based on the total mass of the copper paste. If the purpose is to form sintered copper pillars, it is not necessary to add a thermally decomposable resin. On the other hand, from the viewpoint of increasing the proportion of the flexibility-imparting component contained in the entire dispersion medium and reducing the progress of drying, the content of the thermally decomposable resin may be 5% by mass or more, based on the total mass of the copper paste.

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

The thixotropy index (hereinafter also referred to as "TI value") of the copper paste may be 2.0 or more and 20 or less, 3.0 or more and 15 or less, or 4.0 or more and 10 or less. When the TI value of the copper paste is within this range, the viscosity of the copper paste is reduced by shear force, so that the copper paste is easily printed by stirring it manually or with a stirring device (for example, a rotation-revolution type stirring device (Planetary Vacuum Mixer ARV-310, manufactured by Thinky Corporation) before printing. In addition, since the viscosity of the copper paste is restored by leaving it still after it is attached to the joining member, excessive wetting and spreading of the printed matter can be suppressed. The TI value of the copper paste is a value calculated by the following formula when the viscosity measured by an E-type viscometer at 25 ° C. and a rotation speed of 0.5 rpm is μ _0.5 , and the viscosity measured by an E-type viscometer at 25 ° C. and a rotation speed of 5 rpm is μ ₅ .
TI value = μ _0.5 / μ ₅

<Method of preparing copper paste>
The copper paste can be prepared by mixing the above-mentioned metal particles, the organic dispersion medium, and, if necessary, any component such as a flexibility-imparting component. Specifically, for example, the copper paste may be prepared by adding sub-micro copper particles, micro copper particles, and, if necessary, other metal particles and any additives to a mixed liquid (solution) of the flexibility-imparting component and the organic dispersion medium, and performing a dispersion treatment. In addition, for example, the copper paste may be prepared by mixing a mixed liquid (solution) of the flexibility-imparting component and the organic dispersion medium, a mixed liquid (dispersion) of copper particles and the organic dispersion medium, and, if necessary, other metal particles and any additives.

When the copper particles include submicro copper particles and micro copper particles, first, the submicro copper particles and, if necessary, a dispersant may be added to an organic dispersion medium or a component that imparts flexibility, and then the mixture may be dispersed. Then, micro copper particles and, if necessary, other metal particles may be added and dispersed. The dispersion method and conditions suitable for dispersion may differ between submicro copper particles and micro copper particles. Generally, submicro copper particles require a stronger dispersion than micro copper particles, while micro copper particles are easily dispersed and a weaker dispersion is sufficient, and strong dispersion may cause deformation of the micro copper particles. By following the above procedure, the dispersibility is improved, and the performance of the copper paste can be further improved. The dispersion may be classified to remove aggregates.

In this preparation method, a stirring process may be performed after mixing the components. The maximum particle size of the dispersion of the copper paste may be adjusted by a classification operation. In this case, the maximum particle size of the dispersion can be set to 20 μm or less, or can be set to 10 μm or less.

Dispersion processing can be carried out using a disperser or agitator. Examples include Ishikawa type agitators, Silverson agitators, cavitation agitators, rotation-revolution type agitators, ultra-thin film high-speed rotary dispersers, ultrasonic dispersers, Raikai machines, twin-screw kneaders, bead mills, ball mills, triple-roll mills, homomixers, planetary mixers, ultra-high pressure dispersers, thin layer shear dispersers, etc.

The stirring process can be carried out using a stirrer. Examples include an Ishikawa stirrer, a rotation-revolution type stirrer, a Raikai mixer, a twin-shaft kneader, a three-roll mill, a planetary mixer, etc.

Classification can be performed, for example, by filtration, natural sedimentation, centrifugation, etc. Examples of filters for filtration include water combs, metal mesh, metal filters, nylon mesh, etc.

<Joint>
1, a bonded body 10 of one embodiment includes a first member 1, a second member 2, and a sintered copper pillar 3 that bonds the first member 1 and the second member 2. The sintered copper pillar 3 is made of, for example, a sintered body of the copper paste.

The lower and upper surfaces of the sintered copper pillar form the bonding surface with the first member and the bonding surface with the second member, respectively, and the two are bonded by a metallic bond. By forming such a metallic bond, the bonded body can have low electrical resistance and be firmly bonded.

The first member 1 and the second member 2 may be an active or passive electronic device, a wiring board on which an electronic device is mounted, or a package having an electronic device and a redistribution layer provided on the electronic device.

Electronic devices include coils, capacitors, SAW filters, power ICs, logic chips, memory chips, sensors, piezoelectric elements, transistors, diodes, etc.

Examples of wiring boards include mounting substrates, 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 rewiring layers.

One of the first member 1 and the second member 2 may be an active or passive electronic device, and the other may be a wiring board on which an electronic device is mounted. In this case, highly reliable electronic device mounting is possible.

In addition, both the first member 1 and the second member 2 may be packages having an electronic device and a redistribution layer provided on the electronic device. In this case, highly reliable package-on-package mounting is possible.

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 on the bonding 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 bonding surface contains these metals, it is possible to reduce and remove the oxide film on the surface at a sintering temperature of 300°C or less in a reducing gas atmosphere such as hydrogen or formic acid. Therefore, the bonded body 10 can have high bonding strength due to the metal bond between the exposed metal surface of the member and the sintered copper pillar.

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). Note that the above carbon, oxygen, and nitrogen are components that may be unintentionally contained in the sintered copper pillar due to the filling of an underfill or a sealing material during mounting.

A sintered copper pillar with a copper content within the above range can be easily formed by printing and sintering the copper paste described above. Furthermore, if the copper content in the sintered copper pillar is within the above range, it is advantageous in terms of ensuring bonding strength and suppressing electromigration. Furthermore, when the bonding surfaces contain copper, bonding is performed using the same metal, making it easier to suppress the occurrence of Kirkendall voids, and a bonded body with even better connection reliability can be obtained.

From the viewpoint of thermal conductivity and electrical conductivity, the volume ratio of copper in the sintered copper pillar 3 is preferably 50 volume % or more, more preferably 60 volume % or more, and even more preferably 70 volume % or more. The greater the volume ratio of copper in the sintered copper pillar 3, the higher the thermal conductivity and electrical conductivity of the sintered copper pillar 3. The volume ratio of copper in the sintered copper pillar 3 can be determined from an 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 expressed as voids. When a resin component such as a filler or underfill is contained in the void, the volume of the component is also included in the volume of the void.

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 bonding surface of the sintered copper pillar 3 with the first member 1 and the bonding surface with the second member 2.

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 of the sintered copper pillar 3 (the direction in which the pillar extends).

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

The height H and width W can be determined from a SEM image of the cross section of the sintered copper pillar.

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.

The shear strength can be calculated, for example, by using a bonding strength testing device to push the sintered copper pillar horizontally at a constant speed with the device's tool, and dividing the maximum strength at which the bonded surface between the sintered copper pillar and the component peels off by the cross-sectional area of the pillar.

The manufacturing method of the bonded body 10 described above includes a step of forming the copper paste into a pillar shape on the first member 1, 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 a step of 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.

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

Printing methods for copper paste that can be used include, for example, screen printing, transfer printing, offset printing, jet printing, dispenser, jet dispenser, needle dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, bar coat, applicator, particle deposition method, spray coater, spin coater, dip coater, and electrocoating.

From the viewpoints of simple manufacturing process, easy maintenance of shape stability, and ease of thick film printing, it is preferable to form the copper paste into a pillar shape by screen printing or stencil printing. In screen printing and stencil printing, for example, first, a metal mask 4 is placed on the first member 1 (FIG. 2(a)). Next, copper paste 3a is placed on the first member 1 and the metal mask 4 (FIG. 2(b)). Next, the copper paste 3a is spread using a squeegee 5, and the copper paste 3a is filled into the holes in the metal mask 4 (FIG. 2(c)). In this way, the copper paste 3b formed into a pillar shape is formed on the first member 1 (FIG. 3(a)).

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 may be 50 μm or more and 100 μm or less. The arrangement of the holes may be in a lattice pattern. The pitch interval may be 1 μm or more and 500 μm or less. The squeegee angle may be 10° or more and 90° or less, or may be 45° or more and 70° or less.

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

Next, as shown in FIG. 3, for example, the second member 2 is mounted on the first member (on the copper paste 3b formed into a pillar shape), and a pillar precursor 3c is provided between the first member 1 and the second member 2. Specifically, as shown in FIG. 3(b), for example, the second member 2 is pushed in from above the copper paste 3b formed into a pillar shape, so that the second member 2 is mounted on the first member. In this way, a pillar precursor 3c is provided between the first member 1 and the second member 2.

The method of mounting the second member 2 is not particularly limited, but for example, when the first member 1 and the second member 2 are a microdevice and a substrate, a method using, for example, a chip mounter, a flip chip bonder, or a carbon or ceramic positioning jig may be used.

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 taking into consideration the height of the sintered copper pillar or pillar precursor to be formed.

(Second step)
In the second step, the pillar precursor 3c disposed between the first member 1 and the second member 2 is sintered. As a result, the sintered copper pillar 3 is formed, and the first member 1 and the second member 2 are joined by the sintered copper pillar 3, thereby obtaining a joined body 10 shown in FIG. 3(c).

The pillar precursor 3c may be dried appropriately from the viewpoint of suppressing flow and generation of voids during sintering. The gas atmosphere during drying may be air, an oxygen-free atmosphere such as nitrogen or a rare gas, or a reducing gas atmosphere such as hydrogen or formic acid. The drying method may be drying by leaving at room temperature, heating, or drying under reduced pressure. For example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, a hot plate pressing device, etc. may be used for heating and drying or drying under reduced pressure. The drying temperature and time may be appropriately adjusted according to the type and amount of the organic dispersion medium and the flexibility-imparting component used. The drying temperature and time may be, for example, 50°C or higher and 180°C or lower, and 30 seconds to 120 minutes or less.

The pillar precursor 3c can be sintered by a heat treatment. For example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, etc. can be used for the heat treatment.

The gas atmosphere during sintering may be a reducing gas atmosphere from the viewpoint of removing the copper particles contained in the pillar precursor 3c and surface oxides on the deposition surface. Examples of reducing gas atmospheres include a pure hydrogen gas atmosphere, a mixed gas atmosphere of hydrogen and nitrogen such as forming gas, a nitrogen atmosphere containing formic acid gas, a mixed gas atmosphere of hydrogen and rare gas, and a rare gas atmosphere containing formic acid gas.

When the diameter of the pillar precursor 3c is small (especially when it is 200 μm or less), the formic acid penetrates into the interior of the pillar precursor 3c, making it easier to reduce the copper particles, and the copper particles can be sufficiently sintered in a reducing gas atmosphere containing formic acid gas. In this case, it is possible to sinter using a formic acid reflow furnace, and the degree of sintering can be improved efficiently.

The maximum temperature reached during the heat treatment may be 150°C or higher and 300°C or lower, 170°C or higher and 250°C or lower, or 200°C or higher and 250°C or lower, from the viewpoint of sufficiently advancing sintering, reducing thermal damage to components such as the microdevice and the substrate, and improving yield. If the maximum temperature reached is 150°C or higher, sintering tends to proceed sufficiently even if the maximum temperature is held for 60 minutes or less.

The time for which the maximum temperature is maintained may be from 1 minute to 60 minutes, from 1 minute to less than 40 minutes, or from 1 minute to less than 30 minutes, from the viewpoint of being able to sufficiently remove the organic dispersion medium and the flexibility-imparting components, allowing sintering to proceed sufficiently, and improving the yield.

Although one embodiment of the bonded body and its manufacturing method have been described above, the present invention is not limited to the above embodiment.

For example, the method for manufacturing the bonded body may further include a step of filling the periphery of the sintered copper pillar with resin. In this case, as shown in FIG. 4, a bonded body 20 is obtained in which a sealing material 6 is provided between the first member 1 and the second member 2.

As the sealing material, from the viewpoint of protecting the joint area from heat, moisture and impact and further improving the connection reliability, a compression molding sealing material, a liquid sealing material, a transfer molding sealing material, an underfill sealing material, etc. can be used.

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

Example 1
The copper paste was prepared, a bonded body was produced and evaluated, and a bonding member with pillars was produced and evaluated by the following methods.

[Preparation of copper paste]
0.07 g of octyl octanoate (organic dispersion medium, manufactured by Sigma-Aldrich Japan G.K., boiling point: 307°C, freezing point: 18°C), 0.07 g of 2-ethylhexyl stearate (organic dispersion medium, manufactured by Kao Corporation, boiling point: 340°C, freezing point: 9°C), and previously prepared CH-0200 (submicro copper particles, manufactured by Mitsui Kinzoku Co., Ltd., product name, 50% volume average particle size: 0.36 μm, surface treatment agent: lauric acid) and octyl octanoate (dispersion medium, manufactured by Sigma-Aldrich Japan G.K., boiling point: 307°C, freezing point: 18°C) were mixed together. A slurry mixture (16.18 g of CH-200: octyl octanoate: 2-ethylhexyl stearate = 90: 5: 5, mass ratio) of CH-200 (manufactured by G.K.) and 2-ethylhexyl stearate (organic dispersion medium, manufactured by Kao Corporation) and 3.52 g of MA-025KFD (flake-shaped micro copper particles, product name, manufactured by Fukuda Metal Foil & Powder Co., Ltd., 50% volume average particle size: 5.9 μm) were kneaded in an agate mortar until no dry powder remained, and the mixed liquid was transferred to a plastic bottle.

The sealed plastic bottle was stirred for 2 minutes at 2000 min ⁻¹ (2000 revolutions/minute) using a planetary vacuum mixer (Planetary Vacuum Mixer ARV-310, manufactured by Thinky Corporation). Thus, a copper paste was obtained.

[Printability evaluation]
First, a stainless steel metal mask (thickness: 70 microns) with circular openings was placed on a silicon wafer (size: 6 inches), and copper paste was applied by stencil printing using a metal squeegee. In this way, pillars (pillar-shaped copper paste) were arranged on the silicon wafer. The opening diameter of the metal mask was 150 microns. Next, the number of pillars arranged on the silicon wafer was confirmed using a digital microscope (VHX-6000, manufactured by Keyence Corporation). The printability was evaluated according to the following criteria. The results are shown in Tables 1 and 2.
◯: The ratio of the number of pillars formed to the total (mask numerical aperture) is 80% or more and 100% or less. △: The ratio of the number of pillars formed to the total (mask numerical aperture) is 50% or more and less than 80%. ×: The ratio of the number of pillars formed to the total (mask numerical aperture) is 0% or more and less than 50%.

[Preparation of Joint]
The copper paste obtained above was used to form a bonded body by the following method. A stainless steel metal mask (thickness: 70 μm) with φ150 μm openings arranged in a grid pattern with a pitch of 500 μm was placed on a copper plate (size: 15 mm × 20 mm, thickness: 3 mm) as the first member, and the copper paste was applied by stencil printing using a metal squeegee. After applying the copper paste, a Cu-plated Si chip (size: 3 mm × 3 mm, thickness: 0.15 mm) as the second member was mounted on the pillar-shaped copper paste provided on the substrate using a flip chip bonder (T-3000-TC-3, manufactured by Dr. Tresky). Then, these laminates (copper plate / pillar precursor / Si chip) were placed in a sintering furnace (reducing gas atmosphere of 10% hydrogen / 90% nitrogen), heated to 225 ° C. over 30 minutes, and held at 225 ° C. for 60 minutes. Thereafter, the assembly was cooled to 50° C. or less by water cooling to obtain a bonded assembly.

[Bondability evaluation]
Ultrasonic inspection of the bonded structure was carried out using an ultrasonic scanning device (IS-300, manufactured by Insight). The frequency of the probe was 35 MHz. In the image obtained by ultrasonic inspection, the parts where the pillars were joined and where the joining was successful are displayed in black. The number of parts where the joining was successful (joints that appear in black) in the obtained image was counted as the number of joints, and the bondability was evaluated based on the ratio of the number of joints to the total (joints) using the following criteria. The results are shown in Tables 1 and 2.
◯: The ratio of the number of joints is 80% or more and 100% or less of the total (joints) △: The ratio of the number of joints is 50% or more and less than 80% of the total (joints) ×: The ratio of the number of joints is 0% or more and less than 50% of the total (joints)

[Sinterability evaluation]
The bonded body was placed in a plastic cup, and epoxy resin (Epomount, manufactured by Refine Tech Co., Ltd.) was poured around the bonded body until it was buried, and then the cup was placed in a vacuum desiccator and decompressed for 1 minute to defoam it. Then, the epoxy resin was left at room temperature (25°C) for 10 hours to harden. Next, a Refine Saw Excel (RCB-961, manufactured by Refine Tech Co., Ltd.) with a diamond cutting wheel (11-304, manufactured by Refine Tech Co., Ltd.) was used to cut near the bonded cross section. Next, the cross section was polished with a polishing device (Refine Polisher HV, manufactured by Refine Tech Co., Ltd.) with waterproof abrasive paper (carbon paper, manufactured by Refine Tech Co., Ltd.). Then, flat milling was performed with a CP processing device (IM4000, manufactured by Hitachi, Ltd.) at an acceleration voltage of 6 kV, an argon gas flow rate of 0.07 to 0.1 cm ³ /min, and a processing time of 20 minutes. Next, platinum was sputtered to a thickness of 10 nm using a sputtering device (ION SPUTTER, manufactured by Hitachi High-Technologies Corporation) to prepare a sample for SEM observation, and the cross section of the joint body was observed at various magnifications with an applied voltage of 10 kV using an SEM device (ESEM XL30, manufactured by Philips), and the sinterability was evaluated according to the following criteria. The results are shown in Tables 1 and 2.
◯: The number of voids and cracks in the sintered copper pillar is less than 10. Δ: The number of voids and cracks in the sintered copper pillar is 10 to 50. ×: The number of voids and cracks in the sintered copper pillar is 50 or more.

Example 2
A copper paste was prepared in the same manner as in Example 1, except that the amounts of octyl octanoate and 2-ethylhexyl stearate used were adjusted so that the compounding ratio (mass ratio) of octyl octanoate to 2-ethylhexyl stearate in the copper paste and the slurry mixture was 3:7. In addition, printability, sinterability, and bondability were evaluated in the same manner as in Example 1, except that the obtained copper paste was used.

Example 3
A copper paste was prepared in the same manner as in Example 2, except that isotridecyl stearate (organic dispersion medium, manufactured by Kao Corporation, boiling point: 489.84°C, solidification point: 12°C) was used instead of 2-ethylhexyl stearate. In addition, printability, sinterability, and bondability were evaluated in the same manner as in Example 1, except that the obtained copper paste was used.

Example 4
A copper paste was prepared in the same manner as in Example 3, except that the amounts of 2-ethylhexyl stearate and isotridecyl stearate used were adjusted so that the compounding ratio (mass ratio) of 2-ethylhexyl stearate to isotridecyl stearate in the copper paste and the slurry mixture was 4:6. In addition, printability, sinterability, and bondability were evaluated in the same manner as in Example 1, except that the obtained copper paste was used.

Example 5
A copper paste was prepared in the same manner as in Example 1, except that isobornylcyclohexanol (Tersolve MTPH, manufactured by Nippon Terpene Chemical Co., Ltd., boiling point: 308°C, freezing point: -6.2°C) was used instead of octyl octanoate as the organic dispersion medium. In addition, the printability, sinterability, and bondability were evaluated in the same manner as in Example 1, except that the obtained copper paste was used.

(Example 6)
A copper paste was prepared in the same manner as in Example 5, except that isotridecyl stearate was used as the organic dispersion medium instead of 2-ethylhexyl stearate. In addition, printability, sinterability, and bondability were evaluated in the same manner as in Example 1, except that the obtained copper paste was used.

(Example 7)
A copper paste was prepared in the same manner as in Example 1, except that butyl stearate (organic dispersion medium, manufactured by Fujifilm Wako Co., Ltd., boiling point: 343°C, freezing point: 25°C) was used instead of 2-ethylhexyl stearate, and the amounts of 2-ethylhexyl stearate and isotridecyl stearate used were adjusted so that the blending ratio (mass ratio) of octyl octanoate to butyl stearate in the copper paste and the slurry mixture was 9:1. In addition, printability, sinterability, and bondability were evaluated in the same manner as in Example 1, except that the obtained copper paste was used.

(Comparative Example 1)
A copper paste was prepared in the same manner as in Example 2, except that dihydroterpineol (organic dispersion medium, manufactured by Nippon Terpene Chemical Co., Ltd., boiling point: 220° C.) was used instead of 2-ethylhexyl stearate. In addition, the printability, sinterability, and bondability were evaluated in the same manner as in Example 1, except that the obtained copper paste was used.

REFERENCE SIGNS LIST 1...first member, 2...second member, 3...sintered copper pillar, 3a...copper paste, 4...metal mask, 5...squeegee, 10, 20...joint body.

Claims (8)

A copper paste for forming a sintered copper pillar that bonds components together,
Contains metal particles and an organic dispersion medium,
the metal particles include copper particles;
The organic dispersion medium contains a high-boiling point dispersion medium having a boiling point of 280° C. or higher in an amount of more than 99% by mass based on the total mass of the organic dispersion medium, and contains a low-freezing point dispersion medium having a freezing point of 20° C. or lower;
The copper paste for forming a sintered copper pillar , wherein the low-freezing point dispersion medium includes an organic dispersion medium having a freezing point of 10 to 20°C and an organic dispersion medium having a freezing point of 15°C or lower . The copper paste according to claim 1, wherein the content of the organic dispersion medium is 1 to 20 mass % based on the total mass of the copper paste. The copper paste according to claim 1 or 2, wherein the content of the low-freezing point dispersion medium is 50 mass% or more based on the total mass of the organic dispersion medium. The copper paste according to any one of claims 1 to 3, wherein the metal particles contain sub-micro copper particles having a volume average particle size of 0.01 μm or more and less than 0.8 μm in a proportion of 30 to 100 mass % based on the total mass of the metal particles. The copper paste according to any one of claims 1 to 4, wherein the metal particles contain micro copper particles having a volume average particle size of 0.8 μm or more and 50 μm or less in a proportion of more than 0 mass% and not more than 70 mass% based on the total mass of the metal particles. The copper paste according to any one of claims 1 to 5, wherein the organic dispersion medium comprises isotridecyl stearate and at least one selected from the group consisting of 2-ethylhexyl stearate, octyl octanoate, and isobornyl cyclohexanol . The copper paste according to any one of claims 1 to 5 , wherein the organic dispersion medium comprises 2-ethylhexyl stearate and at least one selected from the group consisting of octyl octanoate, isotridecyl stearate, and isobornyl cyclohexanol . A method for manufacturing a joined body including a first member, a second member, and a sintered copper pillar joining the first member and the second member, comprising the steps of:
A step of forming the copper paste according to any one of claims 1 to 7 into a pillar shape on the first member, mounting the second member, and providing a pillar precursor between the first member and the second member;
and forming the sintered copper pillar by sintering the pillar precursor.

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