JP7728565B2 - Bonding method and bonded body using micro-sized particles - Google Patents

Description

The present invention relates to a bonding method using micro-sized silver particles, and more specifically to a bonding method that can produce a bonded joint that has excellent thermal conductivity and electrical conductivity as well as high heat resistance, and to a bonded body obtained by this bonding method.

Conventionally, solder, conductive adhesives, silver paste, anisotropic conductive films, etc. have been used to mechanically and/or electrically and/or thermally bond metal parts to one another. These conductive adhesives, silver pastes, anisotropic conductive films, etc. are sometimes used not only to bond metal parts, but also to bond ceramic parts, resin parts, etc. Examples include bonding light-emitting elements such as LEDs to substrates, bonding semiconductor chips to substrates, and further bonding these substrates to heat dissipation members.

In particular, adhesives, pastes, and films containing solder and conductive fillers made of metal are used to join parts that require electrical connection. Furthermore, because metals generally have high thermal conductivity, adhesives, pastes, and films containing solder and conductive fillers are sometimes used to improve heat dissipation.

On the other hand, when, for example, high-brightness lighting devices or light-emitting devices are made using light-emitting elements such as LEDs, or when semiconductor devices are made using semiconductor elements known as power devices that operate efficiently at high temperatures, the amount of heat generated tends to increase. Attempts have been made to reduce heat generation by improving the efficiency of devices and elements, but to date, sufficient results have not been achieved, and the operating temperatures of devices and elements are actually rising.

Furthermore, from the perspective of preventing damage to devices during bonding, there is a demand for bonding materials that can ensure sufficient bonding strength at low bonding temperatures (for example, 350°C or below). Therefore, bonding materials for bonding devices, elements, etc. are required to have heat resistance that allows them to withstand lower bonding temperatures and maintain sufficient bonding strength even when the operating temperature rises due to device operation after bonding, but conventional bonding materials are often unable to meet this requirement. For example, solder bonds components together through a process (reflow process) in which the metal is heated above its melting point, but because the melting point is generally specific to the composition, attempts to increase the heat resistance temperature also result in an increase in the heating (bonding) temperature.

Furthermore, when using solder to join multiple layers of elements or substrates, a heating process is required for each layer to be joined. To prevent melting of already joined parts, the melting point (joining temperature) of the solder used for the next joining must be lowered. Also, different solder compositions are required for each layer to be joined, making handling cumbersome.

In light of these circumstances, bonding materials using metal nanoparticles, primarily made of precious metals such as silver and gold, have been developed in recent years as an alternative to high-temperature solder (see, for example, Patent Document 1: JP 2012-046779 A). However, not only are metal nanoparticles expensive, but the bonding layer obtained by sintering metal nanoparticles also leaves behind residual organic matter used as a dispersant or solvent for the metal nanoparticles. Furthermore, the proportion of crystal grain boundaries in the bonding layer obtained by sintering metal nanoparticles is high, which can cause reduced thermal and electrical conductivity. Additionally, when metal nanoparticles are used for bonding, there is the problem of significant volume change during bonding due to the evaporation of organic matter.

In response to this, the inventors have proposed an inexpensive bonding method that uses chestnut-shaped micro-sized silver particles to reduce residual organic components and crystal grain boundaries in the bonding layer, thereby achieving a bond with excellent thermal and electrical conductivity. Specifically, Patent Document 2 (JP 2015-57291 A) discloses a bonding method characterized by using a bonding composition containing a conductive powder that includes radially extending protrusions and recesses between the protrusions, and a nucleus material for crystal growth of silver as a conductive material, the nucleus material containing silver containing metal-based particles or ceramic-based particles, and an average particle size of the nucleus material being 1 to 10 μm; and then interposing the bonding composition between two members to be bonded, heating the members to 150 to 350°C and applying pressure to the members.

In the bonding method described in Patent Document 2, the use of micro-sized silver particles with an average particle size of 1 to 10 μm reduces the amount of organic matter used to ensure dispersibility, significantly reducing residual organic components in the bonding layer and the volume change of the bonding layer during the bonding process. Furthermore, compared to nano-sized metal particles, the proportion of crystal grain boundaries in the bonding layer can be reduced, resulting in a bonded portion with excellent thermal and electrical conductivity. Furthermore, micro-sized silver particles can be produced more inexpensively than general metal nanoparticles, reducing bonding costs. Furthermore, the fine protrusions of micro-sized silver particles ensure low-temperature sintering, enabling bonding at low temperatures of 150 to 350°C.

JP 2012-046779 A JP 2015-57291 A

In recent years, the use of SiC, GaN, and other materials has been considered as semiconductor materials inside various power devices. Some of these materials exhibit high performance at high temperatures of 300°C or higher, so high heat resistance is also required for the bonding layer that bonds the semiconductor chip to the substrate.

In contrast, the bonding layer obtained by the bonding method described in Patent Document 2 can reduce the proportion of crystal grain boundaries within the bonding layer compared to nano-sized metal particles, resulting in a bonded portion with excellent thermal and electrical conductivity, but does not fully consider heat resistance. It has also been reported that bonding layers obtained by sintering metal particles undergo structural changes when exposed to high temperatures.

In light of the above circumstances, the object of the present invention is to provide an inexpensive and simple low-temperature bonding method that can reduce residual organic components and grain boundaries in the bonding layer and produce a bonded joint that has high thermal conductivity, electrical conductivity, and excellent heat resistance, as well as a bonded body obtained by this bonding method.

The inventors conducted extensive research into the composition of bonding compositions to achieve the above-mentioned objectives, and discovered that uniformly dispersing aluminum nitride particles, which impart excellent heat resistance to the bonding layer, using the voids formed by the convex and concave portions of chestnut-shaped micro-sized silver particles is extremely effective in achieving the above-mentioned objectives, leading to the development of the present invention.

That is, the present invention provides:
a conductive powder having radially extending projections and recesses between the projections, and containing a core material for growing silver crystals as a conductive material therein, the core material containing silver containing metal particles or ceramic particles, and an average particle size of the core material being 1 to 10 μm;
a bonding composition containing aluminum nitride particles having an average particle size of 10 to 100 nm, and a step of placing the bonding composition between two members to be bonded, and then heating the members to 150 to 350°C and applying pressure thereto;
The present invention provides a joining method characterized by the above.

In the bonding method of the present invention, by uniformly dispersing aluminum nitride particles with an average particle size of 10 to 100 nm in the bonding layer, it is possible to impart good high-temperature stability to the bonding layer formed by sintering the conductive powder. Furthermore, aluminum nitride is compatible with the silver sintered layer in terms of thermal conductivity and linear expansion coefficient, which reduces the adverse effects of dispersing a different material in the silver sintered layer.

By setting the average particle size of the aluminum nitride particles to 10 nm or more, it is possible to effectively suppress structural changes that occur when the bonding layer is maintained at high temperatures. Furthermore, by setting the average particle size of the aluminum nitride particles to 100 nm or less, it is possible to suppress a decrease in the density and strength of the bonding layer due to the dispersion of the aluminum nitride particles. Here, the average particle size of the aluminum nitride particles is preferably 15 to 80 nm, and more preferably 20 to 60 nm.

Normally, it is extremely difficult to uniformly disperse fine ceramic particles in a bonding composition. However, the bonding method of the present invention achieves uniform dispersion of aluminum nitride particles by using so-called chestnut-shaped microparticles as metal particles, which have radially extending convex portions and concave portions in the gaps between the convex portions. Specifically, the convex portions and concave portions form sufficient and uniform spaces suitable for the dispersion of the aluminum nitride particles. Furthermore, the conductive powder with convex portions and concave portions is micro-sized (1 to 10 μm), which prevents the dispersion from becoming uneven due to aggregation, as is the case with general metal nanoparticles.

In addition, by using micro-sized silver particles with an average particle size of 1 to 10 μm, it is possible to reduce the amount of organic matter used to ensure dispersibility, and significantly reduce residual organic components in the bonding layer and volume changes in the bonding layer during the bonding process. Furthermore, since the proportion of crystal grain boundaries in the bonding layer can be reduced compared to nano-sized metal particles, a bonded joint with excellent thermal and electrical conductivity can be obtained. Furthermore, micro-sized silver particles can be produced more inexpensively than general metal nanoparticles, reducing bonding costs. Here, the fine protrusions of micro-sized silver particles ensure low-temperature sintering, making bonding possible at low temperatures of 150 to 350°C.

Furthermore, in the joining method of the present invention, the pressure applied in the above process can be reduced to approximately 10 MPa, and it is possible to perform the process under the pressure of the members' own weight.

In the bonding method of the present invention, the content of the aluminum nitride particles in the bonding composition is preferably 0.4 to 1.8 mass %. By setting the content of aluminum nitride particles to 0.4 mass % or more, a sufficient number of aluminum nitride particles can be dispersed to impart high-temperature stability to the bonding layer. Furthermore, by setting the content of aluminum nitride particles to 1.8 mass % or less, it is possible to suppress a decrease in the density and strength of the bonding layer due to the dispersion of aluminum nitride particles, and to impart application properties to the bonding composition that are practically acceptable. Here, the content of aluminum nitride particles is preferably 0.7 to 1.3 mass %, and more preferably 0.9 to 1.1 mass %.

In the bonding method of the present invention, it is preferable that the shape of the convex portions is at least one shape selected from the group consisting of needle-shaped, rod-shaped, and petal-shaped. It is also preferable to use the bonding composition that contains all of the conductive powder whose convex portions are needle-shaped, the conductive powder whose convex portions are rod-shaped, and the conductive powder whose convex portions are petal-shaped. When the convex portions have these shapes, microspaces into which aluminum nitride particles can penetrate (disperse) are efficiently and uniformly formed, allowing the aluminum nitride particles to be uniformly dispersed in the final bonding layer.

Furthermore, in the bonding method of the present invention, the bonding composition preferably contains 0.001 to 0.1 mass% spherical ceramic particles having an average particle size of 10 to 100 μm. The spherical ceramic particles having an average particle size of 10 to 100 μm function as spacers, and the presence of a small amount of spherical ceramic particles in the thickness direction of the bonding layer allows for the reproducible formation of a bonding layer of any desired thickness. The average particle size of the spherical ceramic particles is preferably 20 to 90 μm, and more preferably 30 to 80 μm. The content of the spherical ceramic particles is more preferably 0.002 to 0.01 mass%. For example, silica particles can be used as the spherical ceramic particles.

The present invention also provides
A joined body in which one member to be joined and another member to be joined are joined,
the one member to be joined and the other member to be joined are metallurgically joined via a joining layer,
the bonding layer includes metal particles and aluminum nitride particles,
the metal particles are silver particles containing a core material for growing silver crystals as a conductive material therein, the core material being a metal-based particle or a ceramic-based particle;
The aluminum nitride particles have an average particle size of 10 to 100 nm,
the content of the aluminum nitride particles in the bonding layer is 0.4 to 1.8 mass %;
Also provided is a conjugate characterized by:

In the bonded body of the present invention, aluminum nitride particles with an average particle size of 10 to 100 nm are dispersed in a bonding layer formed primarily by sintering silver particles. Even when the aluminum nitride particle content is 0.4 to 1.8 mass%, uniform dispersion is achieved, resulting in the bonding layer having excellent thermal stability.

The average particle size of the aluminum nitride particles is preferably 15 to 80 nm, and more preferably 20 to 60 nm. The content of aluminum nitride particles is preferably 0.7 to 1.3 mass%, and more preferably 0.9 to 1.1 mass%.

In addition, in the bonded body of the present invention, metal-based particles or ceramic-based particles are contained within the silver particles that primarily form the bonding layer, and these particles also contribute to improving the thermal stability of the bonding layer. This effect is particularly pronounced when ceramic-based particles are contained within the silver particles.

In the bonded structure of the present invention, it is preferable that, with regard to the size of voids measured by cross-sectional observation of the bonding layer, the proportion of voids with an area of 0.2 ^μm2 or less is 90% or more of the total number of voids. By suppressing the formation of large voids in the bonding layer, good mechanical properties and thermal stability are achieved.

In addition, in the bonded body of the present invention, the bonding layer preferably contains 0.001 to 0.1 mass% spherical ceramic particles with an average particle size of 10 to 100 μm. The spherical ceramic particles with an average particle size of 10 to 100 μm function as spacers, making the thickness of the bonding layer uniform. The average particle size of the spherical ceramic particles is preferably 20 to 90 μm, and more preferably 30 to 80 μm. The content of the spherical ceramic particles is more preferably 0.002 to 0.01 mass%. The spherical ceramic particles can be, for example, silica particles.

Furthermore, in the bonded body of the present invention, it is preferable that the porosity of the bonding layer is 10% or less, and that the porosity does not increase to 10% or more when left at a high temperature of 300°C for 500 hours. Because the bonding layer is dense and the porosity does not increase to 10% or more when held at high temperatures for a long period of time, the bonded body can be suitably used, for example, as a bonded body between a semiconductor chip and a substrate, which use semiconductor materials that exhibit high performance under high-temperature conditions of 300°C or higher.

Furthermore, in the bonded structure of the present invention, it is preferable that the shear strength of the bonding layer is 40 MPa or more, and that the shear strength of the bonding layer after being left at a high temperature of 300°C for 500 hours is 30 MPa or more. Since the bonding layer has these shear strengths and maintains high shear strength even after being held at high temperatures for a long period of time, it can be suitably used, for example, as a bonded structure between a semiconductor chip and a substrate that uses a semiconductor material that exhibits high performance under high-temperature conditions of 300°C or more.

The present invention provides an inexpensive and simple low-temperature bonding method that can reduce residual organic components and grain boundaries in the bonding layer, resulting in a bonded joint that has high thermal conductivity, electrical conductivity, and excellent heat resistance, as well as a bonded article obtained by this bonding method.

FIG. 1 is a schematic diagram illustrating the mechanism by which aluminum nitride particles are uniformly dispersed in the present invention. 1 is a SEM photograph of micro-sized silver particles used in the examples. 1 is a SEM photograph of aluminum nitride particles used in the examples. 1 is an optical microscope photograph of silica particles used in the examples. FIG. 1 is a schematic diagram of a bonded test piece used in the examples. 1 is a SEM photograph of a cross section of a bonding layer of a bonded body obtained in an example. 10 is a SEM photograph of a cross section of a bonding layer of a bonded body obtained in a comparative example. 1 is a histogram showing the area distribution of voids formed in the bonding layer of an example bonded body. 10 is a histogram showing the area distribution of voids formed in the bonding layer of a comparative bonded body. 1 shows an SEM observation image and Al element mapping of a cross section of a bonding layer of an example bonded body obtained in Example 1. 1 shows a TEM observation image and element mapping of the bonding layer of the exemplified bonded body obtained in Example 1. 1 is a graph showing the relationship between the shear strength and the aluminum nitride particle content of each example bonded body obtained in Example 2. 10 is a graph showing the bonding strength of the bonded body obtained in Comparative Example 2 and the bonded body after exposure to high temperatures.

A preferred embodiment of the joining method and joined body of the present invention will be described in detail below. Note that the following description merely illustrates one embodiment of the present invention and does not limit the present invention. Furthermore, redundant explanations may be omitted.

1. Bonding Method (1) Bonding Composition The bonding composition of this embodiment is characterized by being a mixture of chestnut-shaped conductive powder (microsized silver particles) having an average particle size of 1 to 10 μm as metal particles, aluminum nitride particles having an average particle size of 10 to 100 nm, an organic solvent, etc., and optionally containing a dispersant, etc. Each of these components will be described below.

(1-1) Conductive powder (micro-sized silver particles)
The metal particles in the bonding composition of this embodiment preferably use chestnut-shaped conductive powder with an average particle size of 1 to 10 μm. By setting the average particle size to micro-size, dispersibility and stability are improved compared to nano-sized particles, and the amount of organic material required to ensure dispersibility and stability can be significantly reduced. In addition, by setting the average particle size to less than 10 μm, sufficient surface area can be obtained to ensure contact points between metal particles. The average particle size of the conductive powder can be measured using a laser particle counter, or it can be measured from electron microscope photographs, or it can be calculated from the electron microscope photographs using an image processing device.

Preferred metal particles for the bonding composition of this embodiment are conductive powders that have (a) irregularities (i.e., convex portions (sometimes called protrusions) extending radially from the center of the particle, and concave portions (sometimes called depressions) in the gaps between the convex portions), and (b) a nucleus material for growing silver crystals as a conductive material inside, the nucleus material containing silver comprising metal-based particles or ceramic-based particles, and an average particle size of the nucleus material being 1 to 10 μm. The radially extending convex portions and the radially extending convex portions and the concave portions in the gaps between the convex portions are in good contact with each other, and sintering effectively progresses from the contact points by maintaining the powder at a low temperature (150 to 350°C).

As mentioned above, it is preferable that the shape of the convex portions of the conductive powder be at least one shape selected from the group consisting of needle-shaped (or fibrous), rod-shaped, and petal-shaped. Furthermore, it is preferable that the bonding composition contain all of conductive powder whose convex portions are needle-shaped, conductive powder whose convex portions are rod-shaped, and conductive powder whose convex portions are petal-shaped.

By combining silver powder with needle-shaped protrusions, silver powder with rod-shaped protrusions, and silver powder with petal-shaped protrusions, contact formation becomes easier and low-temperature sintering properties are further improved. More specifically, when the total amount of conductive powder is taken as 100% by weight, it is preferable to mix and use an appropriate amount within the range of 10-50% by weight of silver powder with needle-shaped protrusions, 15-50% by weight of silver powder with rod-shaped protrusions, and 20-50% by weight of silver powder with petal-shaped protrusions.

The length of the convex portion is preferably more than 40% of the average radius of the sphere formed by the closed curved surface that contacts and surrounds the tip of the convex portion. The reason for this is that such a convex portion will have an appropriate size, which will ensure a more reliable engagement with the concave portion and improve the mechanical stability of the mating portion.

The recesses are hollows formed between the protrusions, and when viewed from the side in the cross-sectional direction, they should have a shape that allows the protrusions to fit into them (ideally, a shape that allows the protrusions to fit into the recesses). This is because such a configuration allows the protrusions and recesses to easily fit into each other between adjacent conductive powder particles. The depth (size) of the recesses can be expressed as the volume of the recesses in the conductive powder, i.e., the porosity of the recesses. Specifically, when the volume of a sphere formed by a closed curve surrounding the tip of each protrusion is taken as 100 volume %, the porosity of the recesses is preferably 40 volume % or greater. This is because if the porosity of the recesses is less than 40 volume %, the fit between the protrusions and recesses may be insufficient. On the other hand, if the porosity of the recesses is excessively large, the mechanical strength of the conductive powder may be significantly reduced and agglomerated regions of aluminum nitride particles may form. Therefore, it is more preferable to set the porosity of the recesses to a value within the range of 42 to 70% by volume, and even more preferable to set it to a value within the range of 45 to 60% by volume.

The core material is preferably metal particles or ceramic particles (inorganic particles). This is because the use of metal particles not only makes it easier to adjust the specific gravity and particle size, but also makes it easier to adjust the shape retention and electrical resistivity. Furthermore, the use of ceramic particles not only makes it easier to adjust the specific gravity and particle size, but also further improves properties such as shape retention and heat resistance.

Here, metal particles include silver particles, gold particles, copper particles, aluminum particles, zinc particles, solder particles, tin particles, nickel particles, etc., either singly or in combination, with silver particles being preferred. Furthermore, ceramic particles include silica particles (white carbon), titanium oxide particles, zirconium oxide particles, aluminum oxide particles, zinc oxide particles, tin oxide particles, niobium oxide particles, etc., either singly or in combination. Among these particles, silica particles (white carbon) and titanium oxide particles are particularly preferred core materials, as they not only facilitate adjustment of specific gravity, particle size, and electrical resistivity, but also significantly improve properties such as shape retention.

Furthermore, with regard to the type of core material, it is preferable that it be porous or an agglomerated particle. The reason for this is that it is possible to uniformly form radial projections extending from the porous or agglomerated particle core material as the center, thereby obtaining a conductive powder with a narrower particle size distribution and excellent shape retention. Therefore, for core materials consisting of porous or agglomerated particles, it is preferable to set the BET surface area to a value within the range of 0.01 to 500 m ² /g. Whether a core material is porous or an agglomerated particle can be easily confirmed by observation with an electron microscope.

The amount of core material added is preferably within the range of 0.01 to 30% by weight of the total amount. The reason for this is that if the amount of core material added is less than 0.01% by weight, it may be difficult to uniformly form convex portions extending radially from the core material center. On the other hand, if the amount of core material added exceeds 30% by weight, the electrical resistivity of the conductive powder may increase significantly. Therefore, it is more preferable to set the amount of core material added within the range of 0.1 to 20% by weight of the total amount, and even more preferably within the range of 0.5 to 10% by weight. Note that if the amount of core material added is a predetermined amount or more, for example, 1% by weight or more, it can be measured using an electron probe microanalyzer (EPMA), for example.

The metal particles in the bonding composition of this embodiment are not particularly limited as long as they are conductive powder (micro-sized silver particles) with the characteristics described above, but for example, conductive powder manufactured by Kaken Tech Co., Ltd. can be suitably used.

(1-2) Aluminum Nitride Particles The bonding composition of this embodiment contains aluminum nitride particles having an average particle size of 10 to 100 nm. By uniformly dispersing aluminum nitride particles having an average particle size of 10 to 100 nm in the bonding layer, it is possible to impart good high-temperature stability to the bonding layer formed by sintering the conductive powder. Furthermore, aluminum nitride is compatible with the silver sintered layer in terms of thermal conductivity and linear expansion coefficient, and the adverse effects of dispersing aluminum nitride in the silver sintered layer can be reduced. The method for measuring the average particle size of aluminum nitride particles is not particularly limited, and various conventionally known measurement methods can be used. For example, it may be determined from images observed using a scanning electron microscope or a transmission electron microscope, or it may be determined using small-angle X-ray scattering or the like.

By setting the average particle size of the aluminum nitride particles to 10 nm or more, it is possible to effectively suppress structural changes that occur when the bonding layer is maintained at high temperatures. Furthermore, by setting the average particle size of the aluminum nitride particles to 100 nm or less, it is possible to suppress a decrease in the density and strength of the bonding layer due to the dispersion of the aluminum nitride particles. Here, the average particle size of the aluminum nitride particles is preferably 15 to 80 nm, and more preferably 20 to 60 nm.

It is also preferable that the aluminum nitride particle content be 0.4 to 1.8 mass%. By setting the aluminum nitride particle content to 0.4 mass% or more, a sufficient number of aluminum nitride particles can be dispersed to provide high-temperature stability to the bonding layer. Furthermore, by setting the aluminum nitride particle content to 1.8 mass% or less, it is possible to prevent a decrease in the density and strength of the bonding layer due to the dispersion of aluminum nitride particles. Here, the aluminum nitride particle content is preferably 0.7 to 1.3 mass%, and more preferably 0.9 to 1.1 mass%.

(1-3) Spherical ceramic particles (spacer particles)
If necessary, the thickness of the bonding layer can be easily controlled by adding spherical ceramic particles. The average particle size of the spherical ceramic particles is preferably 10 to 100 μm, more preferably 20 to 90 μm, and most preferably 30 to 80 μm. The content of the spherical ceramic particles is preferably 0.001 to 0.1 mass%, more preferably 0.002 to 0.01 mass%. For example, silica particles can be used as the spherical ceramic particles.

(1-4) Others Various organic solvents can be used in the bonding composition of this embodiment as long as the effects of the present invention are not impaired. Examples of organic solvents include terpene-based solvents, ketone-based solvents, alcohol-based solvents, ester-based solvents, ether-based solvents, aliphatic hydrocarbon-based solvents, aromatic hydrocarbon-based solvents, cellosolve-based solvents, and carbitol-based solvents. More specifically, organic solvents such as terpineol, methyl ethyl ketone, acetone, isopropanol, butyl carbitol, decane, undecane, tetradecane, benzene, toluene, hexane, diethyl ether, and kerosene can be used.

In addition to the components described above, the bonding composition of this embodiment may contain optional components such as a dispersion medium, an oligomer component that acts as a binder, a resin component, an organic solvent (which may dissolve or disperse part of the solid content), a surfactant, a thickener, or a surface tension adjuster, to impart appropriate viscosity, adhesion, drying properties, printability, or other properties depending on the intended use, provided the effects of the present invention are not impaired. There are no particular limitations on such optional components.

A variety of optional dispersion media can be used as long as they do not impair the effects of the present invention, including, for example, hydrocarbons and alcohols.

Hydrocarbons include aliphatic hydrocarbons, cyclic hydrocarbons, and alicyclic hydrocarbons, each of which may be used alone or in combination of two or more.

Examples of aliphatic hydrocarbons include saturated or unsaturated aliphatic hydrocarbons such as tetradecane, octadecane, heptamethylnonane, tetramethylpentadecane, hexane, heptane, octane, nonane, decane, tridecane, methylpentane, normal paraffin, and isoparaffin.

Examples of cyclic hydrocarbons include toluene and xylene.

Further examples of alicyclic hydrocarbons include limonene, dipentene, terpinene, terpinene (also called terpinene), nesol, sinene, orange flavor, terpinolene, terpinolene (also called terpinolene), phellandrene, menthadiene, terebene, dihydrocymene, mosulene, isoterpinene, isoterpinene (also called isoterpinene), chrytomene, cautusine, cajeptene, eulimene, pinene, turpentine, menthane, pinane, terpene, cyclohexane, etc.

Alcohols are compounds containing one or more OH groups in their molecular structure, and include aliphatic alcohols, cyclic alcohols, and alicyclic alcohols. They may be used alone or in combination of two or more. Some of the OH groups may be derivatized to acetoxy groups, etc., as long as the effects of the present invention are not impaired.

Examples of the aliphatic alcohol include saturated or unsaturated C6-30 aliphatic alcohols such as heptanol, octanol (1-octanol, 2-octanol, 3-octanol, etc.), decanol (1-decanol, etc.), lauryl alcohol, tetradecyl alcohol, cetyl alcohol, 2-ethyl-1-hexanol, octadecyl alcohol, _hexadecenol , and oleyl alcohol.

Examples of cyclic alcohols include cresol and eugenol.

Further examples of alicyclic alcohols include cycloalkanols such as cyclohexanol, terpineol (including α-, β-, and γ-isomers, or any mixture thereof), terpene alcohols (e.g., monoterpene alcohols) such as dihydroterpineol, dihydroterpineol, myrtenol, sobrerol, menthol, carveol, perillyl alcohol, pinocarveol, sobrerol, and verbenol.

When a dispersion medium is included in the bonding composition of this embodiment, its content can be adjusted depending on the desired properties, such as viscosity. The content of the dispersion medium in the bonding composition is preferably 1 to 30% by mass. If the content of the dispersion medium is 1 to 30% by mass, the effect of adjusting the viscosity to a range that is easy to use as a bonding composition can be obtained. The content of the dispersion medium is more preferably 1 to 20% by mass, and even more preferably 1 to 15% by mass.

Examples of resin components include polyester resins, polyurethane resins such as blocked isocyanates, polyacrylate resins, polyacrylamide resins, polyether resins, melamine resins, and terpene resins. These may be used alone or in combination of two or more.

In addition to the above-mentioned dispersion media, examples of organic solvents include methyl alcohol, ethyl alcohol, n-propyl alcohol, 2-propyl alcohol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,2,6-hexanetriol, 1-ethoxy-2-propanol, 2-butoxyethanol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol having a weight-average molecular weight of 200 to 1,000, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol having a weight-average molecular weight of 300 to 1,000, N,N-dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, glycerin, and acetone. These may be used alone or in combination of two or more.

Examples of thickeners include clay minerals such as clay, bentonite, and hectorite; emulsions such as polyester emulsion resins, acrylic emulsion resins, polyurethane emulsion resins, and blocked isocyanates; cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropylmethyl cellulose; and polysaccharides such as xanthan gum and guar gum. These may be used alone or in combination of two or more.

A surfactant different from the organic component may also be added. In multi-component solvent-based metal colloid dispersions, differences in evaporation rate during drying can easily cause roughness on the coating surface and uneven solid content. By adding a surfactant to the bonding composition of this embodiment, these disadvantages can be suppressed, resulting in a bonding composition that can form a uniform conductive coating.

The surfactant that can be used in this embodiment is not particularly limited, and any of anionic surfactants, cationic surfactants, and nonionic surfactants can be used, such as alkylbenzene sulfonates and quaternary ammonium salts. Fluorine-based surfactants are preferred, as they are effective even when added in small amounts.

The easiest way to adjust the amount of organic components within a specified range is to heat them. Alternatively, this can be done by adjusting the amount of organic components added when preparing the conductive powder. Heating can be done in an oven or evaporator, and may be done under reduced pressure. When heating under normal pressure, it can be done in either air or an inert atmosphere. Furthermore, amines (and carboxylic acids) can be added later to fine-tune the amount of organic components.

The viscosity of the bonding composition of this embodiment can be adjusted as needed so long as the solids concentration does not impair the effects of the present invention. For example, the viscosity range is 0.01 to 5000 Pa·S, with a viscosity range of 0.1 to 1000 Pa·S being more preferable, and a viscosity range of 1 to 100 Pa·S being particularly preferable. By setting the viscosity within this range, a wide range of methods can be used to apply the bonding composition to the materials to be joined.

Viscosity can be adjusted by adjusting the particle size of the conductive powder, the amount of organic matter contained, the amount of dispersion medium and other components added, the blending ratio of each component, adding a thickener, etc. The viscosity of the metal bonding composition can be measured, for example, using a cone-plate viscometer (e.g., an Anton Paar MCR301 rheometer).

The bonding composition used in the bonding method of the present invention can be obtained by uniformly mixing the above-mentioned conductive powder, aluminum nitride particles, organic solvent, etc. using any of a variety of conventionally known methods. The mixing method may be dry mixing, or wet mixing using a solvent, etc.

(2) Bonding Method The use of the bonding composition of this embodiment allows for high bonding strength to be achieved when bonding members together using heat. Specifically, the bonding method includes a bonding composition application step in which the bonding composition is applied between a first member to be bonded and a second member to be bonded, and a bonding step in which the bonding composition applied between the first member to be bonded and the second member to be bonded is baked at a desired temperature (e.g., 350°C or less, preferably 150 to 300°C) to bond the members. Furthermore, the baking temperature can be increased or decreased in stages. It is also possible to apply a surfactant or surface activator to the surfaces of the members to be bonded in advance.

After extensive research, the inventors have discovered that using the bonding composition of the present embodiment described above as the bonding composition in the bonding composition application step not only makes it possible to more reliably bond the first and second members to be bonded with high bonding strength (obtaining a bonded body), but also imparts high thermal stability to the bonding layer obtained after bonding.

Here, the term "application" of the bonding composition of this embodiment refers to both planar application of the bonding composition and linear application (drawing). The shape of the coating film made of the bonding composition after application and before firing by heating can be formed into any desired shape. Therefore, in the bonded body of this embodiment after firing by heating, the bonding composition refers to both planar and linear bonding layers, and these planar and linear bonding layers may be continuous or discontinuous, and may include both continuous and discontinuous portions.

The first and second bonded members that can be used in this embodiment are not particularly limited as long as they can be bonded by applying a bonding composition and baking it with heat, but it is preferable that they are heat-resistant enough to not be damaged by the temperatures used during bonding.

Examples of materials that can be used to form such bonded members include polyamide (PA), polyimide (PI), polyamideimide (PAI), polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), polycarbonate (PC), polyethersulfone (PES), vinyl resin, fluororesin, liquid crystal polymer, ceramics, glass, and metal, but metal bonded members are preferred. Metal bonded members are preferred because they have excellent heat resistance and excellent affinity with the bonding composition of the present invention, whose inorganic particles are metal.

The members to be joined may have various shapes, such as plate or strip shapes, and may be rigid or flexible. The thickness of the substrate may also be selected appropriately. To improve adhesion or adhesion or for other purposes, members with a surface layer formed thereon or members that have undergone surface treatment such as hydrophilization may also be used.

A variety of methods can be used in the process of applying the bonding composition to the members to be bonded. As mentioned above, an appropriate method can be selected from the following: dipping, screen printing, spraying, bar coating, spin coating, inkjet printing, dispenser printing, pin transfer, brush coating, casting, flexography, gravure printing, syringe printing, etc.

After application as described above, the coating film is baked by heating to a temperature of, for example, 350°C or less within a range that does not damage the members to be joined, thereby obtaining the bonded body of this embodiment. As described above, in this embodiment, the use of the bonding composition of this embodiment results in a bonding layer with excellent adhesion to the members to be joined, and strong bonding strength can be obtained more reliably.

In this embodiment, if the bonding composition contains a binder component, the binder component will also be sintered from the perspective of improving the strength of the bonding layer and the bonding strength between the bonded members. However, in some cases, the firing conditions may be controlled to remove the binder component entirely, with the main purpose of the binder component being to adjust the viscosity of the bonding composition for application to various printing methods.

The method for carrying out the baking is not particularly limited, and for example, the bonding can be achieved by baking the bonding composition applied or drawn on the bonded members using a conventional oven or the like so that the temperature is, for example, 350°C or lower. The lower limit of the baking temperature is not necessarily limited, and it is preferable that the temperature be within a range that allows the bonded members to be bonded together and does not impair the effects of the present invention. Here, in order to obtain as high a bonding strength as possible, it is preferable that the amount of organic matter remaining in the bonding composition after the baking is as small as possible, but it is acceptable for some organic matter to remain as long as it does not impair the effects of the present invention.

The bonding composition used in the bonding method of the present invention contains an organic substance. However, unlike conventional methods that utilize heat curing, such as epoxy resins, the bonding strength after firing is not achieved through the action of the organic substance; rather, sufficient bonding strength is achieved through the fusion of the fused conductive powder, as described above. Therefore, even if the remaining organic substance deteriorates or decomposes or disappears after bonding due to the use in an environment that is higher than the bonding temperature, there is no risk of a decrease in bonding strength, and therefore the method has excellent heat resistance.

The bonding composition used in the bonding method of the present invention can achieve a bond with a bonding layer that exhibits high conductivity even when fired at low temperatures, such as around 150 to 250°C, making it possible to bond relatively heat-sensitive bonded members together. Furthermore, there are no particular restrictions on the firing time, and it can be set to any firing time that allows bonding to be achieved, depending on the firing temperature.

In this embodiment, the surfaces of the members to be joined may be treated to further enhance adhesion between the members to be joined and the joining layer. Examples of such surface treatment methods include dry treatments such as corona treatment, plasma treatment, UV treatment, and electron beam treatment, as well as methods in which a primer layer or a conductive paste-receiving layer is provided on the substrate in advance.

The atmosphere in which the bonding process is carried out is not particularly limited, and it can be carried out in air, in an inert gas atmosphere, under reduced pressure, etc.

2. Bonded Body The bonded body of the present invention is a bonded body in which one bonded member and another bonded member are bonded together, wherein the one bonded member and the other bonded member are metallurgically bonded together via a bonding layer, the bonding layer containing metal particles and aluminum nitride particles, the metal particles being nuclei for causing crystal growth of silver as a conductive material therein, the nuclei being silver particles containing metal-based particles or ceramic-based particles, the aluminum nitride particles having an average particle size of 10 to 100 nm, and the bonding layer containing 0.4 to 1.8 mass % of aluminum nitride particles.

The bonding layer, formed primarily by sintering silver particles, contains dispersed aluminum nitride particles with an average particle size of 10 to 100 nm. Because uniform dispersion is achieved even when the aluminum nitride particle content is 0.4 to 1.8 mass%, the bonding layer has excellent thermal stability. While it is difficult to directly and quantitatively define the state in which aluminum nitride particles are uniformly dispersed, this can be confirmed, for example, by observing that the porosity in the bonding layer does not increase to 10% or more after being left at a high temperature of 300°C for 500 hours.

The average particle size of the aluminum nitride particles is preferably 15 to 80 nm, and more preferably 20 to 60 nm. The content of aluminum nitride particles is preferably 0.7 to 1.3 mass%, and more preferably 0.9 to 1.1 mass%.

Figure 1 schematically shows the mechanism by which aluminum nitride particles are uniformly dispersed in the bonding composition and bonded body of the present invention, resulting in a bonding layer with excellent thermal stability. The conductive powder, which accounts for the majority of the bonding composition, is made up of microparticles with convex and concave portions on their surfaces. Fine aluminum nitride particles measuring 10 to 100 nm are trapped in the concave portions of the conductive powder, thereby achieving uniform dispersion extremely efficiently. Furthermore, while sintering (densification) progresses primarily through contact between the convex portions of the conductive powder, the dispersion of the aluminum nitride particles prevents contact between the bodies of the conductive powder. This suppresses mass transfer at high temperatures, resulting in good thermal stability.

In addition, the silver particles that primarily form the bonding layer contain metal-based particles or ceramic-based particles inside, and these particles also contribute to improving the thermal stability of the bonding layer. This effect is particularly pronounced when ceramic-based particles are contained inside the silver particles.

Furthermore, in the bonded structure, it is preferable that the proportion of voids with an area of 0.2 ^μm2 or less relative to the total number of voids measured by cross-sectional observation of the bonding layer be 90% or more. By suppressing the formation of large voids in the bonding layer, good mechanical properties and thermal stability are achieved. Here, the proportion of voids with each area can be easily determined, for example, by image analysis of a cross-sectional SEM observation image.

The bonding layer preferably contains 0.001 to 0.1 mass% spherical ceramic particles with an average particle size of 10 to 100 μm. The spherical ceramic particles with an average particle size of 10 to 100 μm function as spacers, allowing for a uniform thickness of the bonding layer. The average particle size of the spherical ceramic particles is preferably 20 to 90 μm, and more preferably 30 to 80 μm. The content of the spherical ceramic particles is more preferably 0.002 to 0.01 mass%. The spherical ceramic particles can be, for example, silica particles.

Furthermore, it is preferable that the porosity of the bonding layer is 10% or less, and that the porosity does not increase to 10% or more when left at a high temperature of 300°C for 500 hours. Because the bonding layer is dense and the porosity does not increase to 10% or more when kept at high temperatures for a long period of time, it can be suitably used, for example, as a bonded body between a semiconductor chip and a substrate that uses a semiconductor material that exhibits high performance under high-temperature conditions of 300°C or more.

Furthermore, in the bonded structure of the present invention, it is preferable that the shear strength of the bonding layer is 40 MPa or more, and that the shear strength of the bonding layer after being left at a high temperature of 300°C for 500 hours is 30 MPa or more. Since the bonding layer has these shear strengths and maintains high shear strength even after being held at high temperatures for a long period of time, it can be suitably used, for example, as a bonded structure between a semiconductor chip and a substrate that uses a semiconductor material that exhibits high performance under high-temperature conditions of 300°C or more.

The above describes typical embodiments of the present invention, but the present invention is not limited to these. For example, in the above embodiment, only micro-sized silver particles are used as the conductive powder, but it is also possible to appropriately add nanoparticles or the like to the bonding composition.

The joining method and joined article of the present invention will be further explained in the following examples, but the present invention is not limited to these examples in any way.

Example 1
5.94 g of a silver particle paste containing 80% by mass of silver particles with fine protrusions manufactured by Kaken Tech Co., Ltd., 0.06 g of aluminum nitride particles, and an organic solvent were mixed to prepare 6.0 g of a silver paste containing 1% by mass of aluminum nitride particles. Furthermore, silica particles with a particle size of approximately 50 μm (Hipressica TS manufactured by Ube Exsymo Co., Ltd.) were added to the silver paste so that the content was approximately 0.05% by mass to prepare a bonding composition.

Figure 2 shows an SEM photograph of micro-sized silver particles, Figure 3 shows an SEM photograph of aluminum nitride particles, and Figure 4 shows an optical microscope photograph of silica particles. The average particle size of the silver particles is approximately 3 μm, and it can be seen that they have a unique shape containing tiny protrusions extending radially and a nucleus material in the center for crystal growth. The particle size of the aluminum nitride particles is less than 1 μm, with an average particle size of 60 nm. The silica particles are spherical particles with a relatively uniform size.

Figure 5 shows the shape of the oxygen-free copper bonding test pieces used in the bonding tests. The bonding test pieces were disk-shaped, with the smaller one measuring 3 mm diameter x 2 mm height, and the larger one measuring 10 mm diameter x 5 mm height. A layer of Au approximately 0.6 μm thick and a layer of Ni approximately 3 μm thick were formed on the surface of the bonding test piece, in that order. A fixed amount of bonding composition was applied to the bonding surface of the larger disk test piece, and the smaller test piece was placed on top and lightly pressed together to adjust the bonding test piece so that the bonding composition spread over the entire bonding surface. A metal mask with a thickness of 100 μm and a hole diameter of 5 mm was used to apply the bonding composition, ensuring a uniform thickness of the applied paste.

A 1 mm thick graphite sheet (PF-100, manufactured by Toyo Tanso Co., Ltd.) cut into 5 mm x 5 mm pieces was then placed on top of the bonded test pieces, and four bonded bodies were then simultaneously fabricated using a large-area pressure and heating device (RB-100D, manufactured by Ayumi Industries Co., Ltd.). The temperature was increased at a rate of 1°C/sec, and all processes involving heating were carried out in a nitrogen atmosphere. Pressurization began after the maximum temperature (bonding temperature) reached 300°C, and the applied pressure was 30 MPa. The specimens were then held at 300°C for 10 minutes to sinter the silver particles, yielding an example bonded body. After pressure and heating were completed, the bonded bodies were left in the bonding device in a nitrogen atmosphere for 30 minutes and then cooled to room temperature.

The resulting bonded assembly was subjected to a high-temperature storage test at 300°C in air using a precision thermostat (FH-360, manufactured by Toyo Seisakusho Co., Ltd.). The high-temperature storage times were 72 hours, 168 hours, 504 hours, and 1008 hours.

After leaving the bonded body at high temperature, the resin-embedded body was cut and polished, and then subjected to ion milling and coating processes to prepare a sample for cross-sectional observation. A scanning electron microscope (SEM: Hitachi High-Technologies Corporation, SU-70) was used to observe the cross section near the center of the bonded layer.

Furthermore, the observed images were analyzed using image analysis software (ImageJ) to calculate the porosity, average void size, number of voids, and void distribution of the bonding layer. Here, porosity is the area ratio of voids present in the bonding layer in the observed image, average void size is the average area of voids detected in the observed image, and the number of voids is the number of voids confirmed in the observed image. Furthermore, the observed images used for image analysis were within a range of approximately 120 μm in width, and the bonding layers of three different bonded bodies obtained under the same conditions were observed, and the most average was taken as the observation result.

Furthermore, to evaluate the bond strength of the bonded bodies, a shear test was conducted using a joint strength tester (STR-1001, manufactured by Rhesca Corporation). The bonded bodies before and after the high-temperature storage test were placed on a stage, and a shear load was applied to the top of the bonded body at a shear rate of 1.0 mm/min and a shear height of 200 μm. The maximum load at break was divided by the area of the bonded part to determine the bond strength. The bond strength of four bonded bodies was measured for each treatment condition, and the average was taken as the bond strength for that treatment condition.

Example 2
In order to confirm the effect of the aluminum nitride particle content on the properties of the bonding composition, bonding compositions were obtained in the same manner as in Example 1, except that the aluminum nitride particle content of the bonding composition was changed within the range of 0.4 to 2.0 mass %. In addition, bonded bodies were produced in the same manner as in Example 1, and the bonding strength was evaluated by a shear test.

Comparative Example 1
A comparative bonded body was obtained in the same manner as in Example 1, except that aluminum nitride particles were not added to the bonding composition. Also, a high-temperature storage test and various evaluations were carried out in the same manner as in Example 1.

Comparative Example 2
A comparative bonding composition was obtained in the same manner as in Example 1, except that silver nanoparticles were used instead of the micro-sized silver particles having fine protrusions. A comparative bonding composition was also prepared without adding aluminum nitride particles.

Next, bonded bodies were prepared in the same manner as in Example 1, and the bond strength of the resulting bonded bodies and the bonded bodies after high-temperature exposure was evaluated by shear testing in the same manner as in Example 1. The high-temperature exposure was carried out in air at 300°C, and the exposure times were 168 hours, 504 hours, and 1008 hours.

Figures 6 and 7 show cross-sectional SEM images of the working bonded structure obtained in Example 1 and the comparative bonded structure obtained in Comparative Example 1, respectively. Table 1 also shows the porosity, average void size, and number of voids in the bonding layers of the working bonded structure and the comparative bonded structure.

As shown in Figures 6, 7, and Table 1, the bonding layer of the example bonded body is dense and exhibits excellent thermal stability, with no increase in porosity or average pore size up to 504 hours of high-temperature exposure. On the other hand, the comparative bonded body has a dense bonding layer, but the porosity and average pore size increase significantly as the high-temperature exposure time increases.

Histograms showing the area distribution of voids formed in the bonding layers of the example bonded structure obtained in Example 1 and the comparative bonded structure obtained in Comparative Example 1 are shown in Figures 8 and 9, respectively. Each element in Figures 8 and 9 shows the proportion of the number of target voids to the total number of voids, broken down by size for every 0.2 ^μm2 of void area. For the bonding layer of the example bonded structure, the proportion of voids with an area of 0.2 ^μm2 or less was 95% of the total number of voids, which is 90% or more. On the other hand, for the bonding layer of the comparative bonded structure, this proportion was 89%. Furthermore, for the bonding layer of the example bonded structure, the proportion of voids with an area of 0.2 ^μm2 or less remained 90% or more until the high-temperature exposure time was 504 hours. However, for the bonding layer of the comparative bonded structure, this proportion significantly decreased due to high-temperature exposure, reaching less than 80% at 504 hours.

In Figure 6, the dark areas at the top and bottom are the bonded test piece (copper), the white area in the center is the bonded layer, and the dark gray area within the bonded layer corresponds to the area where aluminum nitride particles are dispersed. SEM-EDS analysis was performed on the dark gray area, confirming the presence of aluminum nitride particles in that area. The aluminum nitride particles are uniformly dispersed throughout the bonded layer without agglomerating in any particular area, and as a result, structural changes in the bonded layer during high-temperature storage tests are effectively suppressed.

Table 2 shows the bond strength (shear strength) of the working bonded body obtained in Example 1 and the comparative bonded body obtained in Comparative Example 1. The bond strength is expressed in MPa. The working bonded body has a shear strength of 40 MPa or more, and even after being left at a high temperature of 300°C for 504 hours, it maintains a shear strength of 30 MPa or more. On the other hand, the comparative bonded body also has a shear strength of 40 MPa or more, but the shear strength drops rapidly when left at a high temperature, and after being left at a high temperature for 504 hours, it is down to a value of around 10 MPa.

Figure 10 shows an SEM image of the cross section of the bonding layer of the exemplified bonded structure obtained in Example 1 and Al element mapping obtained by SEM-EDS. It can be seen that the Al originating from the aluminum nitride particles is uniformly present throughout the bonding layer, and is mainly distributed between the silver microparticles.

Using an FIB, an observation sample approximately 100 nm thick was prepared from the center of the bonded layer of the exemplified bonded body obtained in Example 1, and TEM and STEM-EDS observations were performed. The TEM observation image and the corresponding element mapping are shown in Figure 11. Aluminum nitride particles can be confirmed from the distribution of Al elements, and it can be seen that the aluminum nitride particles penetrate between the silver microparticles, suppressing contact between the silver microparticles.

Figure 12 shows the relationship between the shear strength and aluminum nitride particle content of each exemplified bonded body obtained in Example 2. Figure 12 also shows the shear strength of bonded bodies when no aluminum nitride particles were added. When the amount of aluminum nitride particles added was 1.8 mass% or less, a high shear strength of 25 MPa or more was obtained for all bonded bodies. On the other hand, when the amount of aluminum nitride particles added was increased to 2.0 mass%, the shear strength decreased. Furthermore, each bonding composition with an aluminum nitride particle content of 1.8 mass% or less had good application performance. These results demonstrate that setting the amount of aluminum nitride particles to 1.8 mass% or less ensures high shear strength of the bonded body and good application performance of the bonding composition.

Figure 13 shows the bond strength of the bonded body obtained in Comparative Example 2 and the bonded body after high-temperature exposure. When silver nanoparticles were used as the conductive material, the addition of aluminum nitride particles reduced the bond strength, and even after high-temperature exposure, the shear strength was lower than when aluminum nitride particles were added. Furthermore, as shown in Table 2, the average shear strength of the bonded body obtained in Example 1 decreased by only about 30% after 504 hours of high-temperature exposure at 300°C, whereas the shear strength of the bonded body obtained in Comparative Example 2 decreased by about 65%. These results demonstrate that high bond strength and high-temperature stability cannot be achieved simply by adding aluminum nitride particles; it is necessary to use microparticles with an appropriate shape as the conductive material and to uniformly disperse the aluminum nitride particles.

Claims (8)

a conductive powder having radially extending projections and recesses between the projections, and containing a core material for growing silver crystals as a conductive material therein, the core material containing silver containing metal particles or ceramic particles, and an average particle size of the core material being 1 to 10 μm;
and aluminum nitride particles having an average particle size of 10 to 100 nm,
a step of interposing the bonding composition between two members to be bonded, and then heating the members to 150 to 350°C and applying pressure thereto;
A joining method characterized by: The content of the aluminum nitride particles in the bonding composition is 0.4 to 1.8 mass %;
The joining method according to claim 1, characterized by: The bonding composition contains 0.001 to 0.1 mass % of spherical ceramic particles having an average particle size of 10 to 100 μm;
The joining method according to claim 1 or 2 , characterized by: A joined body in which one member to be joined and another member to be joined are joined,
the one member to be joined and the other member to be joined are metallurgically joined via a joining layer,
the bonding layer includes metal particles and aluminum nitride particles,
the metal particles are silver particles containing a core material for growing silver crystals as a conductive material therein, the core material being a metal-based particle or a ceramic-based particle;
The aluminum nitride particles have an average particle size of 10 to 100 nm,
the content of the aluminum nitride particles in the bonding layer is 0.4 to 1.8 mass %;
A conjugate characterized by: Regarding the size of the voids measured by cross-sectional observation of the bonding layer,
The ratio of the number of voids having an area of 0.2 ^μm2 or less to the number of all voids is 90% or more;
The bonded body according to claim 4 , characterized in that the bonding layer contains 0.001 to 0.1 mass % of spherical ceramic particles having an average particle size of 10 to 100 μm;
The bonded body according to claim 4 or 5 , characterized in that the porosity of the bonding layer is 10% or less, and the porosity does not increase to 10% or more when left at a high temperature of 300°C for 500 hours;
The bonded body according to any one of claims 4 to 6 , characterized in that The shear strength of the bonding layer is 40 MPa or more, and the shear strength of the bonding layer after being left at a high temperature of 300°C for 500 hours is 30 MPa or more;
The bonded body according to any one of claims 4 to 7 , characterized in that