Patent Description:
A power semiconductor using silicon carbide (SiC) is smaller in size than a semiconductor using silicon of the related art, has a feature of reducing energy loss, and can operate even at a high temperature of <NUM> or higher.

In a case of operating a SiC power semiconductor at a high temperature, solder of the related art having a heat-resistant temperature of approximately <NUM> in an operating environment is not suitable as a joining material. As an alternative joining material, a paste (metal fine particle paste) in which metal fine particles are dispersed in a solvent and which is excellent in heat resistance and electrical conductivity is being studied.

However, in a case where a substrate and a chip are joined at a high temperature using the metal fine particle paste, there is a problem in that the solvent volatilizes at the time of joining and large pores (voids) are generated at a joined portion, or a position of the chip is shifted in the obtained joined body.

On the other hand, in order to suppress the formation of large pores in the joined portion, a method for producing a joining material by molding silver particles while pressurizing and joining base materials by using this joining material is known (see Patent Document <NUM>). Patent documents <NUM>-<NUM> and non-patent literature <NUM> disclose joining material for bonding chips to substrates.

However, in a case where a substrate and a chip are joined at a high temperature using the joining material described in Patent Document <NUM>, there is a problem in that the joining strength of the obtained joined body is not sufficient.

Therefore, an object of the present invention is to provide a joining material capable of producing a joined body having excellent joining strength compared with that of the related art, a method for producing the joining material, and a joined body using the joining material.

In order to solve the aforementioned problems, the present invention has adopted the following configuration.

That is, according to a first aspect of the present invention, a joining material is provided according to claim <NUM>.

According to a second aspect of the present invention, a method for producing a joining material is provided according to claim <NUM>.

According to a third aspect of the present invention, a method for producing a joining material is provided according to claim <NUM>.

According to a fourth aspect of the present invention, a use according to claim <NUM> of a joining material to form a joined body is provided.

In the method for producing a joining material according to the third aspect, it is preferable that the silver powder further contain a third silver particle group having an average particle diameter of <NUM> or more and less than <NUM>.

In the method for producing a joining material according to the second or third aspect, it is preferable that, in the step of obtaining the sintered body, the coating film be heated while applying a pressure of <NUM> MPa or less to the coating film.

According to the invention, the method for producing a joining material according to the second or third aspect further includes a step of performing plating with one or more selected from the group consisting of silver, copper, tin, gold, and nickel on the surface of the sintered body.

According to a fourth aspect of the present invention, a use is provided according to. claim <NUM> to form a joined body.

According to the present invention, it is possible to provide a joining material capable of producing a joined body having excellent joining strength compared with that of the related art, a method for producing the joining material, and a joined body using the joining material.

<FIG> is a cross-sectional view showing an embodiment of a joined body according to the present invention.

A joined body <NUM> shown in <FIG> is a laminate in which a conductor <NUM> and a substrate <NUM> are joined by a joining material <NUM>.

The joined body <NUM> of the present embodiment is characterized by the joining material <NUM>, and various well-known joined bodies can be suitably applied to other configurations.

The joining material of the present embodiment contains a sintered body formed by sintering silver powder, a porosity of the sintered body is <NUM>% to <NUM>%, and a surface roughness Ra of a joining surface is <NUM> or more and <NUM> or less.

In the present specification, the joining material contains a material for joining two objects, and typically contains a material for joining a conductor and a substrate by being interposed therebetween.

The porosity of the sintered body contained in the joining material of the present embodiment is <NUM>% to <NUM>%, preferably <NUM>% to <NUM>%, and more preferably <NUM>% to <NUM>%.

When the porosity of the sintered body is within the range described above, for example, it can be said that a joining strength between the conductor and the substrate (shear strength of the joined body) is excellent.

Here, the shear strength means a strength measured by a method based on JIS Z <NUM>-<NUM>:<NUM>. A specific measurement method will be described later in the examples.

In the present specification, the porosity of the sintered body is measured as follows.

First, the sintered body is immersed in water to measure a volume of the sintered body, and a mass of the sintered body is measured. In addition, the volume in a case where the sintered body does not have pores corresponding to the mass thereof is calculated based on a theoretical density. The porosity of the sintered body is calculated from the measured volume and the theoretical volume in a case where there are no pores.

As a method for controlling the porosity of the sintered body contained in the joining material of the present embodiment within the range described above, for example, a method for suitably selecting the kind or the particle diameter of silver powder, a method for suitably setting a pressure condition at the time of sintering, a method for adjusting the amount of a solvent of a dispersion liquid in a case of producing the joining material by using the dispersion liquid of the silver powder, and the like are exemplary examples.

The joining material of the present embodiment may contain a substance other than the sintered body formed from the silver powder, as long as the shear strength of the joined body is sufficient.

A shape of the joining material of the present embodiment is not particularly limited, and a flat plate shape such as a disk, a rectangular plate, and the like; a rod shape such as a cylindrical shape, a columnar shape, a polygonal cylindrical shape, a polygonal columnar shape, and the like, and a spherical shape are exemplary examples.

In addition, the joining material of the present embodiment may have a thick portion having a thickness of <NUM> or less, in order to facilitate joining.

A size of the joining material is not particularly limited, and may be suitably adjusted according to specifications of the substrate and the conductor. In a case where the shape of the joining material is a disk shape, a diameter of the disk is preferably <NUM> to <NUM> and more preferably <NUM> to <NUM>. In a case where the shape of the joining material is a rectangular plate shape, a length of a long side is preferably <NUM> to <NUM> and more preferably <NUM> to <NUM>.

A surface roughness Ra of the joining surface in the joining material of the present embodiment is <NUM> or more, and even more preferably <NUM> or more.

In addition, the surface roughness Ra of the joining surface in the joining material of the present embodiment is <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less, and even more preferably <NUM> or less.

An upper limit value and a lower limit value of the surface roughness Ra of the joining surface in the joining material of the present embodiment may be arbitrarily combined.

The combination of the upper limit value and the lower limit value of the surface roughness Ra is <NUM> or more and <NUM> or less, and even more preferably <NUM> or more and <NUM> or less.

As will be described later in the examples, in a case where the surface roughness Ra of the joining surface is within the range described above, the shear strength of the joined body can be excellent.

In the joining material of the present embodiment, the numerical ranges of the porosity of the sintered body and the surface roughness Ra of the joining surface defined above may be arbitrarily combined.

The combination of the porosity of the sintered body and the surface roughness Ra of the joining surface is a porosity of <NUM>% to <NUM>% and a surface roughness Ra of <NUM> or more and <NUM> or less, more preferably a porosity of <NUM>% to <NUM>% and a surface roughness Ra of <NUM> or more and <NUM> or less, and even more preferably a porosity of <NUM>% to <NUM>%, and a surface roughness Ra of <NUM> or more and <NUM> or less.

The surface roughness of the joining surface of the joining material can be measured as follows. The surface roughness is measured for five arbitrary points of the surface of the joining material by using an ultra-depth color 3D shape-measuring microscope (KEYENCE, VK-<NUM>), and an average value is calculated.

According to the invention, the method for controlling the surface roughness Ra of the joining surface of the joining material within the range described above is achieved by plating the surface of the sintered body.

According to the invention, the plating is performed with one or more metal selected from the group consisting of silver, copper, tin, gold, nickel. For the plating, overlapping plating of two or more layers having different compositions may be used.

In an embodiment not forming part of the invention, in a case where the surface of the sintered body is polished, the surface roughness Ra of the joining surface of the joining material is <NUM> or more, preferably <NUM> or more, more preferably <NUM> or more, and even more preferably <NUM> or more.

In the joining material of the present embodiment, in a case where the surface of the sintered body is polished, the surface roughness Ra of the joining surface of the joining material is <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less, and even more preferably <NUM> or less.

The upper limit value and the lower limit value of the surface roughness Ra of the joining surface in the joining material may be arbitrarily combined.

In the joining material of the present embodiment, in a case where the surface of the sintered body is polished, the combination of the upper limit value and the lower limit value of the surface roughness Ra of the joining surface of the joining material is <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, and even more preferably <NUM> or more and <NUM> or less.

In the joining material of the present embodiment, in a case where the surface of the sintered body is polished, the numerical ranges of the porosity of the sintered body and the surface roughness Ra of the joining surface defined above may be arbitrarily combined.

In the joining material of the present embodiment, in a case where the surface of the sintered body is polished, the combination of the porosity of the sintered body and the surface roughness Ra of the joining surface is a porosity of <NUM>% to <NUM>% and a surface roughness Ra of <NUM> or more and <NUM> or less, preferably a porosity of <NUM>% to <NUM>% and a surface roughness Ra of <NUM> or more and <NUM> or less, more preferably a porosity of <NUM>% to <NUM>% and a surface roughness Ra of <NUM> or more and <NUM> or less, and even more preferably a porosity of <NUM>% to <NUM>%, and a surface roughness Ra of <NUM> or more and <NUM> or less.

According to the invention, the surface of the sintered body is plated and the surface roughness Ra of the joining surface of the joining material is <NUM> or more, and even more preferably <NUM> or more.

In the joining material according to the invention, the surface of the sintered body is plated and the surface roughness Ra of the joining surface of the joining material is <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less, and even more preferably <NUM> or less.

In the joining material of the present embodiment, in a case where the surface of the sintered body is plated, the combination of the upper limit value and the lower limit value of the surface roughness Ra of the joining surface of the joining material is <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, and even more preferably <NUM> or more and <NUM> or less.

In the joining material of the present embodiment, in a case where the surface of the sintered body is plated, the numerical ranges of the porosity of the sintered body and the surface roughness Ra of the joining surface defined above may be arbitrarily combined.

In the joining material of the present embodiment, in a case where the surface of the sintered body is plated, the combination of the porosity of the sintered body and the surface roughness Ra of the joining surface is a porosity of <NUM>% to <NUM>% and a surface roughness Ra of <NUM> or more and <NUM> or less, preferably a porosity of <NUM>% to <NUM>% and a surface roughness Ra of <NUM> or more and <NUM> or less, more preferably a porosity of <NUM>% to <NUM>% and a surface roughness Ra of <NUM> or more and <NUM> or less, and even more preferably a porosity of <NUM>% to <NUM>%, and a surface roughness Ra of <NUM> or more and <NUM> or less.

The joining material of the present embodiment described above contains a sintered body of silver powder having a porosity of the sintered body of <NUM>% to <NUM>%, and a surface roughness Ra of the joining surface of <NUM> or more and <NUM> or less. As described above, since the sintered body of silver powder having the surface roughness Ra of the joining surface in the specific range and the specific porosity is adopted, according to the joining material of the present embodiment, a joined body having excellent joining strength compared with that of the related art can be produced.

In addition, the sintered body does not melt even at a temperature higher than a melting point of the silver powder. Further, by using the joining material containing this sintered body, it is possible to perform joining at a temperature lower than the melting point of the bulk.

The method for producing the joining material of the present embodiment includes a step of heating a coating film formed by using a dispersion liquid of a solvent and silver powder to obtain a sintered body.

The dispersion liquid of the present embodiment is obtained by dispersing the silver powder in a solvent.

As the solvent used herein, water, an alcohol-based solvent, a glycol ether-based solvent, terpineols, and the like are exemplary examples.

As alcohol-based solvents, isopropyl alcohol, <NUM>,<NUM>-butanediol, isobomyl cyclohexanol, <NUM>,<NUM>-diethyl-<NUM>,<NUM>-pentanediol, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-propanediol, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-hexanediol, <NUM>,<NUM>-dimethyl-<NUM>-hexyne-<NUM>,<NUM>-diol, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-butanediol, <NUM>,<NUM>,<NUM>-tris (hydroxymethyl) ethane, <NUM>-ethyl-<NUM>-hydroxymethyl-<NUM>,<NUM>-propanediol, <NUM>,<NUM>'-oxybis (methylene) bis (<NUM>-ethyl-<NUM>,<NUM>-propanediol), <NUM>,<NUM>-bis (hydroxymethyl)-<NUM>,<NUM>-propanediol, <NUM>,<NUM>,<NUM>-trihydroxyhexane, bis [<NUM>,<NUM>,<NUM>-tris (hydroxymethyl) ethyl] ether, <NUM>-ethynyl-<NUM>-cyclohexanol, <NUM>,<NUM>-cyclohexanediol, <NUM>,<NUM>-cyclohexanedimethanol, erythritol, threitol, guaiacol glycerol ether, <NUM>,<NUM>-dimethyl-<NUM>-octyne-<NUM>,<NUM>-diol, <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-decyne-<NUM>,<NUM>-diol, and the like are exemplary examples.

As the glycol ether-based solvent, diethylene glycol mono-<NUM>-ethylhexyl ether, ethylene glycol monophenyl ether, <NUM>-methylpentane-<NUM>,<NUM>-diol, diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, and triethylene glycol monobutyl ether, and the like are exemplary examples.

According to the third aspect of the invention, a combination of silver particle groups having different average particle diameters is used.

By using silver particle groups having different average particle diameters in combination, a joining material having a specific porosity (<NUM>% to <NUM>%) can be easily produced.

For the average particle diameter of the silver particle group, a value of a median diameter D50 is adopted. In the present invention, the median diameter D50 of each silver powder means a diameter measured by a laser diffraction method (volume-average particle diameter) using SALD-<NUM> (manufactured by Shimadzu Corporation).

A combination of silver particle groups having different average particle diameters, a combination of a nano-order silver particle group and a micro-order silver particle group is used.

According to the invention, the average particle diameter of the first silver particle group be <NUM> or more and less than <NUM>, and the average particle diameter of the second silver particle group be <NUM> or more and less than <NUM>.

The average particle diameter is preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less.

The average particle diameter of the second silver particle group is preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less.

By using the first silver particle group and the second silver particle group in combination, a joining material having a specific porosity (<NUM>% to <NUM>%) can be easily produced, and a joined body having an increased joining strength can be easily obtained.

A shape of the silver particle of the first silver particle group is not particularly limited, and may be any of a spherical or non-spherical shape. As the non-spherical shape, a flake shape, a needle shape, a horn shape, a branch shape, a granular shape, an irregular shape, a teardrop shape, a plate shape, an ultrathin plate shape, a hexagonal plate shape, a columnar shape, a rod shape, a porous shape, a fibrous shape, a lump shape, a sponge shape, an inclined shape, a round shape, and the like are exemplary examples. Among such shapes, the spherical and columnar shapes are preferable.

The second silver particle group preferably contains flake-shaped silver particles. In this case, the second silver particle group may be such that the majority of the silver particles are recognized as the flake shape (shape of thin pieces or chips) under a microscope. Typically, it means that <NUM>% by mass or more of the particles (primary particles) constituting the second silver particle group have a flake (thin pieces or chips) shape. Here, particles having the flake shape (shape of thin pieces or chips) mean particles having an aspect ratio (ratio of longest major axis/shortest minor axis) of <NUM> to <NUM>.

The silver powder may further contain a third silver particle group having an average particle diameter of <NUM> or more and less than <NUM>.

The average particle diameter of the third silver particle group is <NUM> or more and less than <NUM>, preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less.

By further using the third silver particle group in addition to the first silver particle group and the second silver particle group in combination, a joining material having a specific porosity (<NUM>% to <NUM>%) can be produced more stably.

A shape of the silver particle of the third silver particle group is not particularly limited, and may be any of a spherical or non-spherical shape. As the non-spherical shape, a flake shape, a needle shape, a horn shape, a branch shape, a granular shape, an irregular shape, a teardrop shape, a plate shape, an ultrathin plate shape, a hexagonal plate shape, a columnar shape, a rod shape, a porous shape, a fibrous shape, a lump shape, a sponge shape, an inclined shape, a round shape, and the like are exemplary examples. Among such shapes, the spherical and columnar shapes are preferable.

In addition, as the first silver particle group, the second silver particle group, and the third silver particle group, two or more kinds having different average particle diameters may be used as each silver particle group.

It is preferable to use two or more kinds having different average particle diameters as the second silver particle group. For example, as the second silver particle group, it is preferable to use the silver particle group having an average particle diameter of <NUM> or more and less than <NUM> and the silver particle group having an average particle diameter of <NUM> or more and less than <NUM> in combination.

In a case where the silver particle groups having different average particle diameters are used in combination as the silver powder of the present embodiment, a percentage of the first silver particle group is preferably <NUM> to <NUM>% by mass, more preferably <NUM> to <NUM>% by mass, and even more preferably <NUM> to <NUM>% by mass with respect to a total mass (<NUM>% by mass) of the silver powder.

A percentage of the second silver particle group is preferably <NUM> to <NUM>% by mass, more preferably <NUM> to <NUM>% by mass, and even more preferably <NUM> to <NUM>% by mass with respect to the total mass (<NUM>% by mass) of the silver powder.

In a case of further using the third silver particle group in combination, a percentage of the third silver particle group is preferably <NUM> to <NUM>% by mass, more preferably <NUM> to <NUM>% by mass, and even more preferably <NUM> to <NUM>% by mass with respect to a total mass (<NUM>% by mass) of the silver powder. However, a sum of the percentages of the first silver particle group, the second silver particle group, and the third silver particle group does not exceed <NUM>% by mass.

According to the second aspect of the invention, in the dispersion liquid of the solvent and the silver powder, a content of the solvent in the dispersion liquid is <NUM>% by mass or more and <NUM>% by mass or less, more preferably <NUM>% by mass or more and <NUM>% by mass or less, even more preferably <NUM>% by mass or more and <NUM>% by mass or less, and particularly preferably <NUM>% by mass or more and <NUM>% by mass or less.

By setting the content of the solvent in the dispersion liquid to <NUM>% by mass or more and <NUM>% by mass or less, a sintered body having a porosity of <NUM>% to <NUM>% can be easily obtained.

When the dispersion liquid is sintered, the solvent in the dispersion liquid is volatilized and the pores are formed in the sintered body. By setting the content of the solvent in the dispersion liquid within the range described above, the porosity of the sintered body can be set to <NUM>% to <NUM>%.

Next, the method for producing the joining material of the present embodiment will be described in detail.

In the step of obtaining the sintered body of the present embodiment, a coating film formed by using a dispersion liquid of a solvent and silver powder is heated to obtain a sintered body.

First, the dispersion liquid described above is applied onto a base to form a coating film. The method for coating is not particularly limited, and dispensing coating, print coating, spray coating, brush coating, injection, and the like are exemplary examples.

As a material of the base, glass, quartz, silicon, metal, and the like are exemplary examples, but there is no limitation thereto. As will be described later in the examples, for example, brass can be used as the metal, but the metal is not limited thereto.

When using a metal base, if a lubricating mold release agent is applied to the base in advance, the sintered body can be easily peeled off from the base.

Next, the coating film is heated to obtain the sintered body. A heating temperature can be suitably set, as long as it is a temperature at which the sintered body can be obtained, and is, for example, preferably <NUM> or higher and <NUM> or lower and more preferably <NUM> or higher and <NUM> or lower.

The time for heating the coating film can be suitably set, as long as it is the time during which the sintered body can be obtained, and is, for example, preferably <NUM> minutes or longer and <NUM> minutes or shorter and more preferably <NUM> minutes or longer and <NUM> minutes or shorter.

In the step of obtaining the sintered body in the present embodiment, a pressure applied to the coating film can be preferably suppressed to <NUM> MPa or less, can be suppressed to <NUM> MPa or less, and particularly can also be no pressurization.

Next, the obtained sintered body may be cut according to the specifications of the substrate and the conductor. A tool used for cutting the sintered body is not particularly limited, and scissors, a diamond knife, a paper cutter, and the like are exemplary examples. In the present specification, the cut sintered body described above may be simply referred to as the sintered body.

More specifically, the following examples, not forming part of the invention, may be used as the method for producing the joining material described above.

Embodiment (i): A method for producing a joining material, the method including a step of heating a coating film formed by using a dispersion liquid of a solvent and silver powder to obtain a sintered body, in which a content of the solvent in the dispersion liquid is <NUM>% by mass or more and <NUM>% by mass or less.

According to the embodiment (i), by setting the content of the solvent in the dispersion liquid to a specific ratio, a joining material containing a sintered body having a porosity of <NUM>% to <NUM>% can be easily produced.

Embodiment (ii): A method for producing a joining material, the method including a step of heating a coating film formed by using a dispersion liquid of a solvent and silver powder to obtain a sintered body, in which a content of the solvent in the dispersion liquid is <NUM>% by mass or more and <NUM>% by mass or less, the silver powder consists of a first silver particle group and a second silver particle group having different average particle diameters, an average particle diameter of the first silver particle group is <NUM> or more and less than <NUM>, and an average particle diameter of the second silver particle group is <NUM> or more and less than <NUM>.

In the silver powder, for example, a percentage of the first silver particle group may be <NUM> to <NUM>% by mass, and a percentage of the second silver particle group may be <NUM> to <NUM>% by mass.

In the silver powder, for example, the percentage of the first silver particle group may be <NUM> to <NUM>% by mass, and the percentage of the second silver particle group may be <NUM> to <NUM>% by mass.

The percentage of the first silver particle group and the second silver particle group is the percentage with respect to the total mass (<NUM>% by mass) of the silver powder. In addition, a sum of the percentages of the first silver particle group and the second silver particle group does not exceed <NUM>% by mass.

According to the embodiment (ii), by using the silver particle groups having specific average particle diameters in combination, a joining material containing a sintered body having a porosity of <NUM>% to <NUM>% can be easily produced.

Embodiment (iii): A method for producing a joining material, the method including a step of heating a coating film formed by using a dispersion liquid of a solvent and silver powder to obtain a sintered body, in which a content of the solvent in the dispersion liquid is <NUM>% by mass or more and <NUM>% by mass or less, the silver powder consists of a first silver particle group, a second silver particle group, a third silver particle group having different average particle diameters, an average particle diameter of the first silver particle group is <NUM> or more and less than <NUM>, an average particle diameter of the second silver particle group is <NUM> or more and less than <NUM>, and an average particle diameter of the third silver particle group is <NUM> or more and less than <NUM>.

In the silver powder, for example, a percentage of the first silver particle group may be <NUM> to <NUM>% by mass, a percentage of the second silver particle group may be <NUM> to <NUM>% by mass, and a percentage of the third silver particle group may be <NUM> to <NUM>% by mass.

In the silver powder, for example, the percentage of the first silver particle group may be <NUM> to <NUM>% by mass, the percentage of the second silver particle group may be <NUM> to <NUM>% by mass, and the percentage of the third silver particle group may be <NUM> to <NUM>% by mass.

The percentage of the first silver particle group, the second silver particle group, and the third silver particle group is the percentage with respect to the total mass (<NUM>% by mass) of the silver powder. However, a sum of the percentages of the first silver particle group, the second silver particle group, and the third silver particle group does not exceed <NUM>% by mass.

According to the embodiment (iii), by using the silver particle groups having specific average particle diameters in combination, a joining material containing a sintered body having a porosity of <NUM>% to <NUM>% can be easily produced.

The method for producing a joining material of the present invention includes other steps in addition to the step of obtaining a sintered body.

In order to control the roughness of the surface of the obtained sintered body, the method further includes a step of performing plating with one or more selected from the group consisting of silver, copper, tin, gold, and nickel on the surface of the sintered body, on the subsequent stage side of the step of obtaining the sintered body.

In a case, not forming part of the invention, where the method for producing the joining material of the present embodiment includes the step of performing the plating, the surface roughness Ra of the joining surface in the joining material obtained by the step of polishing or the step of performing the plating is <NUM> or more, and even more preferably <NUM> or more.

On the other hand, the upper limit of the surface roughness Ra of the joining surface of the joining material obtained by the step of performing the plating is <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less, and even more preferably <NUM> or less.

The upper limit value and the lower limit value of the surface roughness Ra of the joining surface in the joining material obtained by the step of polishing or the step of performing the plating may be arbitrarily combined.

The combination of the upper limit value and the lower limit value of the surface roughness Ra of the joining surface of the joining material obtained by the step of polishing or the step of performing the plating is <NUM> or more and <NUM> or less, and even more preferably <NUM> or more and <NUM> or less.

The method for polishing the surface of the sintered body is not particularly limited, and chemical polishing, electrolytic polishing, mechanical polishing, and the like are exemplary examples. As will be described later in the examples, by polishing the surface of the sintered body with abrasive paper No. <NUM>, a joining material capable of producing a joined body having sufficient joining strength can be obtained.

In a case, not forming part of the invention, where the method for producing the joining material of the present embodiment includes the step of polishing the surface of the sintered body, the surface roughness Ra of the joining surface in the joining material obtained by the step of polishing is <NUM> or more, preferably <NUM> or more, more preferably <NUM> or more, and even more preferably <NUM> or more.

On the other hand, the surface roughness Ra of the joining surface of the joining material obtained by the step of polishing is <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less, and even more preferably <NUM> or less.

The upper limit value and the lower limit value of the surface roughness Ra of the joining surface in the joining material obtained by the step of polishing may be arbitrarily combined.

The combination of the upper limit value and the lower limit value of the surface roughness Ra of the joining surface of the joining material obtained by the step of polishing is <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, and even more preferably <NUM> or more and <NUM> or less.

The method for plating the surface of the sintered body is not particularly limited, and electroplating, electroless plating, vacuum plating, and the like are exemplary examples. The plating is performed with one or more selected from the group consisting of silver, copper, tin, gold, and nickel.

The step of performing the plating may be plating by overlapping two or more layers of plating having different compositions.

For example, in a case where one of the objects to be joined is a copper substrate, the surface of the sintered body may be copper-plated. Accordingly, the affinity between the joining material and the copper substrate is strengthened, and the joining strength is likely to be increased.

In a case where the method for producing the joining material of the present embodiment includes the step of performing the plating of the surface of the sintered body, the surface roughness Ra of the joining surface in the joining material obtained by the step of performing the plating is <NUM> or more, and even more preferably <NUM> or more.

On the other hand, the surface roughness Ra of the joining surface of the joining material obtained by the step of performing the plating is <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less, and even more preferably <NUM> or less.

The upper limit value and the lower limit value of the surface roughness Ra of the joining surface in the joining material obtained by the step of performing the plating may be arbitrarily combined.

The surface roughness of the joining surface of the joining material obtained by the step of performing the plating is <NUM> or more and <NUM> or less, and even more preferably <NUM> or more and <NUM> or less.

In a case, not forming part of the invention, where the method for producing the joining material includes the step of polishing the surface of the sintered body or the step of performing the plating at the subsequent stage side of the embodiment (i) of the step of obtaining the sintered body, in the joining material to be obtained, the surface roughness Ra of the joining surface is in the specific range and the sintered body has the specific porosity.

In a case, not forming part of the invention, where the method for producing the joining material includes the step of polishing the surface of the sintered body or the step of performing the plating at the subsequent stage side of the embodiment (ii) of the step of obtaining the sintered body, in the joining material to be obtained, the surface roughness Ra of the joining surface is in the specific range, and for the sintered body, the sintered body of the silver powder having the specific porosity is obtained.

In a case not forming part of the invention, where the method for producing the joining material includes the step of polishing the surface of the sintered body or the step of performing the plating at the subsequent stage side of the embodiment (iii) of the step of obtaining the sintered body, in the joining material to be obtained, the surface roughness Ra of the joining surface is in the specific range, and for the sintered body, the sintered body of the silver powder having the specific porosity is obtained.

In the joined body of the present embodiment, as shown in <FIG>, the conductor and the substrate are joined by the joining material described above.

As the conductor, a chip part such as a condenser and a resistor, or a Si chip, a SiC chip, GaN, and the like obtained by forming a semiconductor element such as a resistor, a transistor, a condenser, and an integrated circuit on a wafer and cutting out a section of each semiconductor element from the wafer, and the like are exemplary examples.

As the substrate, a circuit board, a glass fiber-reinforced epoxy-based printed circuit board, a polyimide-based substrate, a ceramics substrate, a metal substrate, a Cu lead frame, and the like are exemplary examples.

A temperature at the time of joining is, for example, preferably <NUM> or higher and <NUM> or lower and more preferably <NUM> or higher and <NUM> or lower.

As the method for joining the conductor and the substrate by using the joining material described above, a well-known method can be adopted.

A pressure at the time of joining is not particularly limited, and may be, for example, <NUM> MPa or more and <NUM> MPa or less.

The atmosphere at the time of joining may be the atmosphere or nitrogen.

In the joined body of the present embodiment described above, the joining material containing the sintered body of the silver powder having a porosity of <NUM>% to <NUM>% and having the surface roughness Ra of the joining surface of <NUM> or more and <NUM> or less is applied. Therefore, such a joined body has excellent joining strength compared with that of the related art.

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to the following Examples.

Silver particle groups shown below were used as the silver powder.

The shape of the silver particles of the silver particle groups 1A, 1B, 2A, and <NUM> was a spherical shape, and the shape of the silver particles of the silver particle group 2B was a flake shape.

Ethylene glycol was used as the solvent.

For the average particle diameter described above, the value of the median diameter D50 was adopted. In the present invention, the median diameter D50 of each silver powder means a diameter measured by a laser diffraction method (volume-average diameter) using SALD-<NUM> (manufactured by Shimadzu Corporation).

The silver particle group and the solvent described above were mixed in the composition shown in Table <NUM> to prepare dispersion liquids <NUM> to <NUM>. In Table <NUM>, each value of the silver particle groups indicates the percentage (mass%) of the mass of each silver particle group with respect to the total mass of the silver powder. In addition, the percentage of the solvent indicates the percentage (mass%) of the mass of the solvent with respect to the total mass of the silver powder and the solvent.

A coating film was produced on a brass base using the dispersion liquid <NUM>.

As the brass, brass consisting of <NUM>% by mass of copper and <NUM>% by mass of zinc was used.

The produced coating film was heated at <NUM> for <NUM> minutes without pressure to obtain a sintered body. The obtained sintered body was cut into small pieces (dimension of length × width: <NUM> × <NUM>) by using scissors.

The surface of the sintered body of the obtained small piece was polished by using abrasive paper No. <NUM> (water-resistant abrasive paper sheet manufactured by Sankyo Rikagaku Co. ) to obtain a joining material.

A joining material was obtained in the same manner as in Example <NUM>, except that the sintering conditions were changed to <NUM> for <NUM> minutes.

A coating film was produced on the brass base described above using the dispersion liquid <NUM>.

The produced coating film was heated at <NUM> for <NUM> minutes without pressure to obtain a sintered body.

The obtained sintered body was immersed in a solution obtained by dissolving silver acetoacetic acid in <NUM>-ethylhexylamine and allowed to stand at <NUM> for <NUM> minutes. Then, the sintered body was taken out from the mixed solution and dried.

A joining material was obtained in the same manner as in Example <NUM>, except that the dispersion liquid used was changed to the dispersion liquid <NUM>.

The obtained sintered body was immersed in a solution obtained by dissolving copper (II) formate tetrahydrate (manufactured by Wako Pure Chemical Industries, Ltd. , model number: LKJ3210, primary average particle diameter: <NUM>) in <NUM>-ethylhexylamine in a nitrogen atmosphere, and allowed to stand at <NUM> for <NUM> minutes. Then, the sintered body was taken out from the mixed solution and dried.

A joining material was obtained in the same manner as in Comparative Example <NUM>, except that the sintering conditions were changed to <NUM> for <NUM> minutes and the sintering was performed while pressurizing at <NUM> MPa at the time of sintering.

A joining material was obtained in the same manner as in Comparative Example <NUM>, except that the sintering was performed while pressurizing at <NUM> MPa at the time of sintering.

A joining material was obtained in the same manner as in Comparative Example <NUM>, except that the sintering conditions were changed to <NUM> for <NUM> minutes.

A joining material was obtained in the same manner as in Example <NUM>, except that the dispersion liquid used was changed to the dispersion liquid <NUM> and the surface of the sintered body was not polished.

For each of the joining materials obtained in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM>, the porosity and the surface roughness were measured by the measurement method shown below.

The volume of the joining material was measured by immersing the joining material in water, and the mass of the joining material was measured. In addition, the volume in a case where the joining material did not have pores corresponding to the mass thereof was calculated based on a theoretical density. The porosity was calculated from the measured volume and the theoretical volume in a case where there were no pores.

The surface roughness was measured for five arbitrary points of the surface of the joining material by using an ultra-depth color 3D shape-measuring microscope (KEYENCE, VK-<NUM>), and an average value was calculated. A size of the measurement point was <NUM> × <NUM>.

Table <NUM> shows the sintering conditions, the porosity, and the surface roughness of each joining material obtained in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM>.

In a case where the silver powder contains silver particle group <NUM> and silver particle group <NUM> and the content of the solvent in the dispersion liquid is <NUM>% by mass or more and <NUM>% by mass or less, the porosity of the sintered body of the obtained joined body of Examples <NUM> to <NUM> was <NUM>% to <NUM>%.

After embedding the obtained sintered body with a resin, a sintered body embedded with the resin was cut using an ion milling device IM4000PLUS (manufactured by Hitachi High-Technologies Corporation) to obtain a smoothed section. The obtained section was observed using a scanning electron microscope (SEM). A microscopic image of a cross section of the joining material obtained by an SEM is shown in <FIG>.

<FIG> is a microscopic image of a cross section of the joining material of Example <NUM> obtained by the SEM. <FIG> is a microscopic image of a cross section of the joining material of Example <NUM> obtained by the SEM. <FIG> is a microscopic image of a cross section of the joining material of Comparative Example <NUM> obtained by the SEM. <FIG> is a microscopic image of a cross section of the joining material of Example <NUM> obtained by the SEM. <FIG> is a microscopic image of a cross section of the joining material of Example <NUM> obtained by the SEM.

As a result, on the cross sections of the joining materials of Examples <NUM>, <NUM>, <NUM>, and <NUM>, a larger number of pores were observed, compared to the cross section of the joining material of Comparative Example <NUM>.

As the conductor, a Si chip (dimensions of length × width: <NUM> × <NUM>) in which a Ti layer (thickness <NUM>) and an Ag layer (thickness <NUM>) were laminated by sputtering was used in order from the Si chip side. As the joining material, each of the joining materials of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> was used. The thickness of each joining material was <NUM>. A copper substrate was used as the substrate.

After stacking the substrate, the joining material, and the conductor in this order so that the polished surface of the joining material is the joining surface, joining was performed by setting the pressure to <NUM> MPa in the atmosphere and performing heat treatment at a temperature of <NUM> to obtain the joined body. Using the joining materials of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM>, joined bodies of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> were obtained.

The shear strengths of the obtained joined bodies of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> were measured by the following measurement method. The results are shown in Table <NUM>.

The shear strength of each of the joined bodies of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> was measured as follows. The measurement results are shown in Table <NUM>.

For each of the obtained joined bodies, the shear strength (MPa) between the Si chip and the substrate was measured by the method based on JIS Z <NUM>-<NUM>:<NUM> under a condition of room temperature (<NUM>) by using a universal bond tester Nordson DAGE Series <NUM> (manufactured by Nordson Corporation). Each sample was measured <NUM> times and an average value of shear strengths (MPa) was calculated.

In a case where the joining materials of Examples <NUM> to <NUM> having a porosity of <NUM>% to <NUM>% were used, the shear strengths of the joined bodies of Examples <NUM> to <NUM> were sufficient.

In a case where the joining materials of Examples <NUM> to <NUM> having a surface roughness Ra of the joining surface of <NUM> or more and <NUM> or less were used, the shear strengths of the obtained joined bodies of Examples <NUM> to <NUM> were sufficient.

In a case where the joining materials of Examples <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> to <NUM> obtained by polishing the surface of the sintered body were used, the shear strengths of the obtained joined bodies of Examples <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> to <NUM> were sufficient.

In a case where the joining materials of Examples <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> obtained by plating the surface of the sintered body were used, the shear strengths of the obtained joined bodies of Examples <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> were sufficient.

In a case where the content of the solvent in the dispersion liquid was increased within the range of <NUM>% by mass or more and <NUM>% by mass or less and the obtained joining materials of Examples <NUM> and <NUM> were used to obtain joined bodies, the shear strengths of the joined bodies of Examples <NUM> and <NUM> were sufficient.

The joining materials of Comparative Examples <NUM> to <NUM> obtained by using the dispersion liquid containing only the silver particle group 1B had a porosity of the sintered body less than <NUM>%, and shear strengths of the joined bodies of Comparative Examples <NUM> to <NUM> using these were not sufficient.

The joining materials of Comparative Examples <NUM> to <NUM>, in which the dispersion liquid having the content of the solvent of <NUM>% was used, had a porosity of the sintered body greater than <NUM>%, and shear strengths of the joined bodies of Comparative Examples <NUM> to <NUM> using these joining materials were not sufficient.

In a case where the joining materials of Comparative Examples <NUM>, <NUM>, <NUM>, and <NUM> in which the surface of the sintered body was not polished and not plated were used, the shear strengths of the obtained joined bodies of Comparative Examples <NUM>, <NUM>, <NUM>, and <NUM> were not sufficient.

In addition, as described below, by comparing the joining materials of the examples and the joining materials of the comparative examples under the condition (a) and the condition (b), the following shown below became clear.

Comparison between joining material of Example <NUM> and joining material of Comparative Example <NUM>:
When producing the joining material, the dispersion liquid <NUM> was used in Example <NUM> and the dispersion liquid <NUM> was used in Comparative Example <NUM>, and the composition of the silver powder in the dispersion liquid was silver particle group 1A/silver particle group 2A/silver particle group 2B = <NUM>/<NUM>/<NUM> (% by mass) for both joining materials.

As for the sintering conditions, the temperature and time at the time of sintering were set to <NUM> for <NUM> minutes, the pressure at the time of sintering was set to no pressure, and the surface of the sintered body was polished for both joining materials.

The surface roughness (µm)/porosity (%)/shear strength (MPa) of the joined body in the joining material was as follows.

Comparison between joining material of Example <NUM> and joining material of Comparative Example <NUM>:
When producing the joining material, the dispersion liquid <NUM> was used in Example <NUM> and the dispersion liquid <NUM> was used in Comparative Example <NUM>, and the composition of the silver powder in the dispersion liquid was silver particle group 1A/silver particle group 2A/silver particle group 2B/silver particle group <NUM> = <NUM>/<NUM>/<NUM>/<NUM> (% by mass) for both joining materials.

Comparison between joining material of Example <NUM> and joining material of Comparative Example <NUM>:.

From the comparison under the conditions (a) and (b) described above, it was clear that, even if the surface roughness of the joining surface was about the same, there was a significant difference regarding each effect of the surface roughness within a specific range (<NUM> or more and <NUM> or less) and the porosity of the sintered body in and out of the numerical limitation (<NUM>% to <NUM>%), in terms of shear strength of the joined body. In addition, it was also clear that the shear strength of the joined body was significant throughout the numerical range of porosity (<NUM>% to <NUM>%).

That is, it was clear that, when "the porosity of the sintered body of <NUM>% to <NUM>%" and "the surface roughness Ra of the joining surface of <NUM> or more and <NUM> or less" were combined, the shear strength became particularly remarkable.

The conductor and the silver-plated copper plate were heat-treated to be joined in the atmosphere using the joining material of Example <NUM> at a pressure of <NUM> MPa or <NUM> MPa at temperatures of <NUM>, <NUM>, and <NUM>, to obtain a joined body.

<FIG> is a microscopic image of a cross section of a joined body obtained by joining by setting a pressure at <NUM> MPa and performing heat treatment at a temperature of <NUM> in the atmosphere by the SEM. <FIG> is a graph showing the relationship between the shear strength of the joined body and the temperature and pressure at the time of sintering.

As a result, the joining material of Example <NUM> was applied in the atmosphere, and the silver-plated copper plate and the conductor could be joined. It was clear that, as the temperature at the time of sintering was high and as the pressure at the time of sintering was high, the shear strength increased.

The conductor and the unplated copper plate (pure copper plate) were heat-treated to be joined in nitrogen using the joining material of Example <NUM> at a pressure of <NUM> MPa or <NUM> MPa at temperatures of <NUM>, <NUM>, and <NUM> to obtain a joined body.

<FIG> is SEM image data of a cross section of a joined body obtained by joining by setting a pressure at <NUM> MPa and performing heat treatment at a temperature of <NUM> in nitrogen. <FIG> is a graph showing the relationship between the shear strength of the joined body and the temperature and pressure at the time of sintering.

As a result, the joining material of Example <NUM> was applied in nitrogen, and the unplated copper plate and the conductor could be directly joined. It was clear that, as the temperature at the time of sintering was high and as the pressure at the time of sintering was high, the shear strength increased.

According to the present invention, it is possible to provide a joining material used for producing a joined body having excellent joining strength compared with that of the related art, a method for producing the joining material, and a joined body using the joining material.

Claim 1:
A joining material (<NUM>) comprising:
a sintered body formed by sintering silver powder,
wherein a porosity of the sintered body is <NUM>% to <NUM>%, wherein the surface of the sintered body is plated with one or more selected from the group consisting of silver, copper, tin, gold and nickel,
and
a surface roughness Ra of a joining surface is <NUM> or more and <NUM> or less,
wherein the surface roughness is measured for five arbitrary points of the surface of the joining material (<NUM>) by using a 3D shape-measuring microscope, and an average value is calculated;
and wherein the measurement of porosity of a sintered body comprises:
first, the sintered body is immersed in water to measure a volume of the sintered body, and a mass of the sintered body is measured; in addition, the volume in a case where the sintered body does not have pores corresponding to the mass thereof is calculated based on a theoretical density, the porosity of the sintered body is calculated from the measured volume and the theoretical volume in a case where there are no pores.