Metal component joint

Abstract

To provide a method for bonding metal members together with high strength via a conductive bonding part.SOLUTION: A metal member-bonded body is formed by bonding a first metal member and a second metal member via metallic silver, wherein: either or both of the first and second metal members are made of copper and form a composite with a non-metal member; when the first member is made of copper, the metal member-bonded body has, from the first member side to the metallic silver side, in this order, a layer whose main constituent element is silver and a layer whose main constituent elements are copper and oxygen; when the second member is made of copper, the metal member-bonded body has, from the second member side to the metallic silver side, in this order, a layer whose main constituent element is silver and a layer whose main constituent elements are copper and oxygen; and the non-metal member is a semiconductor wafer, a semiconductor chip, an organic insulating base material, an inorganic insulating base material, or an organic-inorganic composite insulating base material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for joining metal members, a joined metal member structure, and a circuit board. [Background technology]

[0002] Traditionally, solder has been widely used for joining metal components, such as connecting electronic components to circuit boards or connecting circuits. However, because solder has a relatively low melting point, when a module manufactured using solder mounting is further mounted onto an electronic circuit board, the solder remelts during reflow at a temperature of around 260°C, causing misalignment of the mounting position. Furthermore, power semiconductor modules can operate at high temperatures exceeding 200°C. Therefore, power semiconductor modules obtained using solder mounting also faced similar problems.

[0003] One solution to the problems caused by the remelting of solder is a conductive adhesive containing metallic silver and a binder, which is a resin component. However, because conductive adhesives contain a binder, it is unavoidable that the electrical resistivity of the joint formed by the conductive adhesive will be high (usually 100 μΩ·cm or more), and there was also the problem that the heat resistance of this joint was insufficient.

[0004] On the other hand, a silver ink composition containing β-ketocarboxylate silver has been disclosed as a material that exhibits excellent conductivity upon heat treatment (see Patent Document 1). This silver ink composition is a material that forms metallic silver from β-ketocarboxylate silver upon heat treatment, and can form metallic silver with an extremely low volume resistivity of 10 μΩ·cm or less. Furthermore, the formed metallic silver does not remelt even when exposed to high temperatures of 200°C or higher thereafter. Therefore, the problems caused by the remelting of solder as described above can be solved. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-193991 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, since the silver ink composition does not contain a binder, when this silver ink composition is used to join metal members together, there is a problem in that it is difficult to increase the strength of the structure in which the metal members are joined via metallic silver, i.e., the joint strength.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a method for joining metal members that can join metal members together with high strength via a conductive joint. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides a method for joining metal members, comprising the steps of: obtaining a heated silver ink composition by heating a silver ink composition attached to the surface of either one or both of a first metal member and a second metal member at a temperature of 60°C or higher without solidifying it; and joining the first member and the second member with metallic silver by firing the heated silver ink composition while pressing the first member and the second member together with the heated silver ink composition interposed therebetween, wherein the silver ink composition is a mixture of silver carboxylate having a group represented by the formula "-COOAg", an amine compound, and formic acid, and the silver ink composition is a material for forming metallic silver by firing. In the method for joining metal members of the present invention, it is preferable that the silver ink composition, before heating without solidifying at a temperature of 60°C or higher, contains metallic silver particles produced from the silver carboxylate, and that the crystallite size of the metallic silver particles is less than 20 nm. In the method for joining a metal member of the present invention, it is preferable that the silver carboxylate is silver β-ketocarboxylate represented by the following general formula (1).

[0009]

Chemical formula

[0010] Furthermore, the present invention provides a metal member joint obtained by the above-mentioned method for joining metal members, wherein the die shear strength of the metal member joint is 15 MPa or more. Furthermore, the present invention provides a circuit board in which the metal member assembly is provided on an organic substrate, and the metal member is a metal electrode. Furthermore, the present invention provides a metal member joint, wherein the metal member joint is composed of a first metal member and a second metal member joined together via metallic silver, and either or both of the first and second members are made of copper; if the first member is made of copper, the metal member joint has, between the first member and the metallic silver, a layer with silver as the main constituent element and a layer with copper and oxygen as the main constituent elements, in that order, from the first member side toward the metallic silver side; if the second member is made of copper, the metal member joint has, between the second member and the metallic silver, a layer with silver as the main constituent element and a layer with copper and oxygen as the main constituent elements, in that order, from the second member side toward the metallic silver side; and the die shear strength of the metal member joint is 15 MPa or more. [Effects of the Invention]

[0011] According to the present invention, a method for joining metal members is provided that can join metal members together with high strength via a conductive joint. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic cross-sectional view illustrating an example of a method for joining metal members according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view illustrating another example of a method for joining metal members according to one embodiment of the present invention. [Figure 3] This is a schematic cross-sectional view illustrating yet another example of a method for joining metal members according to one embodiment of the present invention. [Figure 4] This is a schematic cross-sectional view illustrating yet another example of a method for joining metal members according to one embodiment of the present invention. [Figure 5] This is a schematic cross-sectional view illustrating yet another example of a method for joining metal members according to one embodiment of the present invention. [Figure 6] This is a schematic cross-sectional view illustrating another example of the joining process in a method for joining metal members according to one embodiment of the present invention. [Figure 7] This is a schematic cross-sectional view illustrating yet another example of a joining process in a method for joining metal members according to one embodiment of the present invention. [Figure 8] This is a schematic cross-sectional view illustrating yet another example of a joining process in a method for joining metal members according to one embodiment of the present invention. [Figure 9] This is imaging data obtained when observing the cross-section of the metal member joint obtained in Example 1 using a transmission electron microscope. [Figure 10] This is imaging data obtained when silver element was detected, when the cross-section of the metal member joint obtained in Example 1 was observed by energy-dispersive X-ray spectroscopy. [Figure 11] This is imaging data obtained when copper element was detected, when the cross-section of the metal member joint obtained in Example 1 was observed by energy-dispersive X-ray spectroscopy. [Figure 12] This is imaging data obtained when oxygen element was detected, when the cross-section of the metal member joint obtained in Example 1 was observed by energy-dispersive X-ray spectroscopy. [Modes for carrying out the invention]

[0013] <<Method for joining metal components>> A method for joining metal members according to one embodiment of the present invention is a method for joining metal members together, comprising: a step of obtaining a heated silver ink composition (sometimes referred to as a "preheating step") by heating a silver ink composition attached to the surface of one or both of a first metal member (sometimes referred to as a "first member" in this specification) and a second metal member (sometimes referred to as a "second member" in this specification) at a temperature of 60°C or higher without solidifying it; and a step of joining the first member and the second member with metallic silver (sometimes referred to as a "joining step") by firing the heated silver ink composition while pressing the first member and the second member together with the heated silver ink composition interposed therebetween. The silver ink composition comprises a silver carboxylate having a group represented by the formula "-COOAg" (sometimes referred to as a "silver carboxylate" in this specification), an amine compound, and formic acid, and the silver ink composition is a material for forming metallic silver by firing.

[0014] According to this embodiment, by performing the preheating step and the joining step using the silver ink composition within the specified range described above, a metal member joint is obtained in which the first member and the second member are joined with high bonding strength via metallic silver. The method for joining metal members in this embodiment will be described in detail below.

[0015] <Preheating process> In the preheating step, the silver ink composition adhering to the surface of either one or both of the first member and the second member is heated at a temperature of 60°C or higher without solidifying, thereby obtaining a heated silver ink composition. The silver ink composition used in this process is a material for forming metallic silver, and is composed of the aforementioned silver carboxylate, an amine compound, and formic acid.

[0016] In this process, before heating is initiated to obtain the heated material, that is, before heating at a temperature of 60°C or higher without solidification, the silver ink composition typically contains particles of metallic silver produced from the silver carboxylate. This is because the formic acid promotes the formation of metallic silver from the silver carboxylate.

[0017] In this embodiment, the crystallite size of the metallic silver particles is preferably less than 20 nm, more preferably 19 nm or less, and even more preferably 17 nm or less. By having a crystallite size less than (or less than) the upper limit, a metal member joint with higher bonding strength can be obtained.

[0018] The lower limit of the crystallite size of the metallic silver particles is not particularly limited. For example, it is preferable that the crystallite size be 3 nm or larger, as this makes it easier to prepare a silver ink composition containing such metallic silver particles.

[0019] The crystallite size of the metallic silver particles can be appropriately adjusted within a range set by arbitrarily combining any of the upper and lower limits mentioned above. For example, in one embodiment, the crystallite size of the metallic silver particles may be 3 nm or more and less than 20 nm, 3 to 19 nm, or 3 to 17 nm. However, these are just examples of crystallite sizes for the metallic silver particles.

[0020] The crystallite size of metallic silver particles can be determined by known methods. For example, metallic silver particles can be subjected to X-ray diffraction measurements, and the crystallite size can be calculated using Scherrer's equation "D = kλ / βcosθ (wherein D is the crystallite size (nm); k is a constant (0.9 is used here); λ is the wavelength of the X-ray (CuKα line) of 0.154 nm; β is the peak width at half maximum (rad); and θ is the angle half the measurement angle)" with respect to the peak with the strongest intensity in the obtained X-ray diffraction profile.

[0021] The first member is made of metal, and the metal constituting it may be either a single metal or an alloy. Preferred metals include, for example, copper, silver, gold, palladium, nickel, and alloys containing one or more metals selected from the group consisting of copper, silver, gold, palladium, and nickel. Among these, the metal is more preferably copper, silver, gold, palladium, or nickel, and even more preferably copper or silver.

[0022] In the preheating step, a metal component with an additional metal layer provided on its surface may be used as the component including the first component. The metal layer can be formed on the surface of the metal component by known methods such as vapor deposition or plating.

[0023] In a metal member having such a metal layer on its surface, the area to which the silver ink composition for forming the conductive joint described later is attached becomes the first member. For example, if the silver ink composition is attached only to the metal layer, the metal layer becomes the first member. If the silver ink composition is attached to both the metal member and the metal layer, both the metal member and the metal layer become the first members. If the silver ink composition is attached only to the metal member, the metal member becomes the first member.

[0024] A preferred example of a metal component having such a metal layer on its surface is a copper component having a silver layer on its surface, but this is just one example.

[0025] In the preheating process, a composite of a metal member and a non-metal member may be used as the member including the first member. Examples of the non-metallic components include semiconductor wafers, semiconductor chips, organic insulating substrates, inorganic insulating substrates, organic-inorganic composite insulating substrates, and these may be known materials.

[0026] Examples of the semiconductor wafer or semiconductor chip include wafers or chips whose constituent materials are semiconductors such as silicon, silicon carbide, or gallium nitride. Examples of the organic insulating substrates include polytetrafluoroethylene (PTFE) substrates, polyimide substrates, liquid crystal polymer substrates, and cycloolefin polymer substrates. Examples of the inorganic insulating substrate include ceramic substrates. The aforementioned organic-inorganic composite insulating substrate is a substrate that comprises both organic and inorganic materials, and examples of such substrates include glass epoxy resin substrates.

[0027] The composite can be manufactured, regardless of the type of non-metallic component, by, for example, forming a metal component on the target area of ​​the non-metallic component by vapor deposition, plating, sputtering, or printing, or by joining a metal component by brazing or bonding with an adhesive.

[0028] Up to this point, we have mainly described metal components that are provided on semiconductor wafers, semiconductor chips, organic insulating substrates, inorganic insulating substrates, or organic-inorganic composite insulating substrates, but as metal components, metal plates not provided on these (for example, heat sinks) are also suitable.

[0029] The shape of the first member is not particularly limited and may be any of the following: sheet-like, plate-like, prismatic, pyramidal, cylindrical, conical, spherical, oblong spherical, rod-like, a combination or fusion of two or more types selected from the group consisting of these nine types (i.e., sheet-like, plate-like, prismatic, pyramidal, cylindrical, conical, spherical, oblong spherical, and rod-like), or an irregular shape.

[0030] The size of the first member is not particularly limited.

[0031] The shape and size of the first component can be appropriately selected depending on the intended use of the first component. For example, if the first member is plate-shaped or rod-shaped, the length of one side of the joining surface (first surface, described later) of the first member may be any of 0.01 to 30 mm, 0.02 to 24 mm, or 0.03 to 18 mm, and the thickness of the first member may be any of 0.01 to 5 mm, 0.02 to 3 mm, or 0.03 to 1.5 mm. However, these are just examples of the shape and size of the first member. First members of these shapes and sizes are suitable, for example, as electrodes that constitute a circuit. If the shape of the first member is neither plate-shaped nor rod-shaped, for example, the size of the first member can be adjusted so that the area of ​​the joining surface is equal to the area of ​​the joining surface calculated from the length of one side as described above.

[0032] The second member is also made of metal. Examples of metals that can be used to make up the second component include those that can be used to make up the first component as described above. The shape of the second component may be the same as that of the first component. The size of the second member may be the same as the size of the first member.

[0033] The second member can also be used as a member including the second member, similar to the case of the first member. And the member including the second member can be used in the same way as the member including the first member described above.

[0034] The first and second members may be identical to each other, or they may be different from each other. For example, the first and second members to be joined in the joining process described later may be identical or different in terms of material, shape, and size.

[0035] In this embodiment, preferred first and second members include, for example, electrodes that constitute a circuit.

[0036] In the preheating step, either or both of the first member and the second member are used with the silver ink composition attached to their surfaces. Specifically, in the preheating step, one of the following combinations is used: (A1) a first member with the silver ink composition attached to its surface and a second member without the silver ink composition attached to its surface (referred to as "combination (A1)" in this specification), (A2) a first member without the silver ink composition attached to its surface and a second member with the silver ink composition attached to its surface (referred to as "combination (A2)" in this specification), or (A3) a first member with the silver ink composition attached to its surface and a second member with the silver ink composition attached to its surface (referred to as "combination (A3)" in this specification).

[0037] When using combination (A3), the silver ink composition attached to the surface of the first member and the silver ink composition attached to the surface of the second member may be the same as or different from each other.

[0038] A silver ink composition can be attached to the surface of the first or second member by known methods such as printing or coating.

[0039] Examples of the aforementioned printing methods include screen printing, flexographic printing, offset printing, dip printing, inkjet printing, dispenser printing, jet dispenser printing, gravure printing, gravure offset printing, and pad printing.

[0040] Examples of the coating methods include methods using various coaters such as spin coaters, air knife coaters, curtain coaters, die coaters, blade coaters, roll coaters, gate roll coaters, bar coaters, rod coaters, and gravure coaters; methods using wire bars; methods using coating equipment such as slot dies; and spray methods.

[0041] It is preferable to perform a cleaning treatment to remove impurities from the areas on the surface of the first or second member where the silver ink composition is applied, before applying the silver ink composition. By doing so, a metal member joint with higher bonding strength can be obtained.

[0042] The aforementioned cleaning treatment can be carried out by known methods, and may include, for example, chemical treatment of the surface with an agent or physical treatment by surface processing. Examples of the aforementioned chemicals include acids such as nitric acid, phosphoric acid, sulfuric acid, and hydrochloric acid; and organic solvents such as acetone. Chemical treatment with acid is useful for removing impurities in general. When using acid, it is preferable to further wash the acid-treated surface of the first or second component with water. Chemical treatment with organic solvents is useful for removing highly lipid-soluble impurities. Examples of the aforementioned surface treatment include polishing using abrasive materials such as files.

[0043] The reason for using a silver ink composition comprising silver carboxylate, an amine compound, and formic acid in the preheating process is that it offers the following advantages. In other words, the silver ink composition is advantageous for increasing the amount of silver carboxylate compared to other silver ink compositions containing silver carboxylate. In this case, because the silver ink composition has a high content of silver carboxylate-derived components (e.g., silver carboxylate, metallic silver derived from silver carboxylate, etc.) per unit amount, it can form more of the heated material on the surfaces of the first and second members in a single application. Furthermore, because the silver ink composition has a high viscosity, it is easy to increase the amount of silver ink composition that adheres to the surfaces of the first and second members. Therefore, in this respect as well, the silver ink composition can form more of the heated material on the surfaces of the first and second members in a single application. Thus, the silver ink composition is advantageous in that it can easily increase the amount of heated material formed on the surfaces of the first and second members.

[0044] Furthermore, the first and second members to which the silver ink composition is applied are made of metal, and metal oxides are easily formed on their surfaces by oxidation reactions. When such metal oxides are formed, either in film form or as a non-film form, not only does the resistivity of the metal member joint increase, but the bonding strength of the metal member joint also decreases. In contrast, the formic acid contained in the silver ink composition has a reducing effect, and the silver ink composition itself has good reducing properties. Therefore, the silver ink composition is advantageous in that it can reduce the amount of metal oxides on the surfaces of the first and second members.

[0045] Furthermore, compounds containing a formyl group exhibit a more activated reducing action under basic conditions. The silver ink composition is basic due to the influence of the blended amine compound, and the reducing action of the formic acid containing the formyl group is further activated. Therefore, the silver ink composition is advantageous in that it exhibits a greater effect due to the use of the aforementioned formic acid.

[0046] The amount of silver ink composition adhering to the surface of the first or second member is not particularly limited and may be set appropriately considering the desired thickness of the conductive joint.

[0047] The thickness of the heated silver ink composition on the surface of the first or second member is preferably 100 μm or more, more preferably 200 μm or more, and even more preferably 250 μm or more. By having a thickness of the heated material equal to or greater than the lower limit, a metal member joint with higher bonding strength can be obtained.

[0048] There is no particular upper limit to the thickness of the heated silver ink composition on the surface of the first or second member. In order to avoid excessive thickness, the thickness of the heated material is preferably 1000 μm or less.

[0049] The thickness of the heated object can be appropriately adjusted within a range set by arbitrarily combining any of the lower and upper limits described above. For example, in one embodiment, the thickness of the heated object may be any of 100 to 1000 μm, 200 to 1000 μm, or 250 to 1000 μm. However, these are just examples of the thickness of the heated object.

[0050] In the preheating step, the heated silver ink composition may consist of one layer or two or more layers. If there are two or more layers, their combination and ratio can be arbitrarily adjusted according to the purpose. If the silver ink composition has two or more heating layers, it is preferable to ensure that the total thickness of each layer equals the preferred thickness of the heating layer as described above.

[0051] For example, depending on the type of silver ink composition and the method of applying it, the amount of silver ink composition applied may not be the desired amount after only one application. In such cases, it is necessary to repeat the application process two or more times. In this case, the final heated material may consist of one layer, or it may consist of two or more layers. Furthermore, for example, depending on the purpose, it may be necessary to form a conductive junction composed of two or more layers with different compositions. In such cases, it is necessary to perform the operation of applying different types of silver ink compositions a total of two or more times. In this case, the final heated material will consist of two or more layers. In this embodiment, the heated material having two or more layers can be treated in the same way as the heated material having one layer, regardless of its type.

[0052] In the method described above, the operation of attaching the silver ink composition to either the first member or the second member is repeated two or more times. However, as explained earlier, even when using a combination of a first member with the silver ink composition attached to its surface and a second member with the silver ink composition attached to its surface (i.e., the combination (A3)), a similar conductive joint composed of two or more layers can ultimately be formed.

[0053] In the preheating process, it is preferable to directly heat the areas of both the first component to which the silver ink composition is attached and the second component to which the silver ink composition is attached that do not have the silver ink composition attached. Doing so further enhances the effect of suppressing unintended deterioration of the silver ink composition.

[0054] In the preheating step, the silver ink composition can be heated by known methods such as heating in an electric furnace, heating with a heat-sensitive heating head, heating by far-infrared irradiation, heating by blowing high-temperature gas, heating by high-frequency irradiation, and dielectric heating.

[0055] In the preheating step, in all of the above combinations (A1) to (A3), the silver ink composition adhering to the surface of the first member and the silver ink composition adhering to the surface of the second member are heated to a temperature of 60°C or higher. However, the silver ink composition being heated at this time should not be allowed to solidify. In this process, the heated silver ink composition obtained without solidification maintains its fluidity.

[0056] In the preheating process, the temperature at which the silver ink composition starts heating may be, for example, room temperature. In this specification, "room temperature" means a temperature that is neither cooled nor heated, i.e., a normal temperature, such as 15-25°C.

[0057] The heating temperature of the silver ink composition in the preheating step may be, for example, 70°C or higher, 80°C or higher, or 90°C or higher.

[0058] The upper limit of the heating temperature of the silver ink composition in the preheating step is not particularly limited. For example, in order to easily avoid solidification of the silver ink composition, the heating temperature is preferably 120°C or lower.

[0059] The heating temperature of the silver ink composition in the preheating step can be appropriately adjusted within a range set by arbitrarily combining any of the lower and upper limits described above. For example, in one embodiment, the heating temperature may be 60-120°C, 70-120°C, 80-120°C, or 90-120°C. However, these are just examples of the heating temperatures.

[0060] In the preheating step, the rate at which the silver ink composition heats up is not particularly limited, but is preferably 5 to 50°C / min, more preferably 5 to 30°C / min, and even more preferably 5 to 16°C / min.

[0061] In the preheating step, the heating time of the silver ink composition is not particularly limited, but is preferably 1 minute to 12 hours, more preferably 2 minutes to 6 hours, and even more preferably 4 minutes to 1 hour.

[0062] The preheating process may be carried out under atmospheric pressure, reduced pressure, or pressurized pressure. Furthermore, the preheating process may be carried out, for example, under an atmospheric environment or under an inert gas atmosphere. Examples of the inert gas include nitrogen gas, argon gas, and helium gas. The preheating step is preferably carried out under reduced pressure or an inert gas atmosphere when conditions are met to suppress the oxidation reaction of the first component, the second component, the silver ink composition, and the heated material. For example, the preheating step is preferably carried out under an inert gas atmosphere because it has a high effect in suppressing oxidation reactions, and preferably under reduced pressure because it is low-cost.

[0063] In the preheating process, the temperature of the silver ink composition may be consistently increased until its completion (in other words, it is not necessary to keep it constant or decrease it), or a period of constant temperature may be provided, or a period of decreasing temperature may be provided. In particular, in order to obtain a metal component joint with higher bonding strength, it is preferable to always raise or keep the temperature of the silver ink composition constant (in other words, not let it decrease at all) from the start to the end of the preheating process. For example, the temperature of the silver ink composition may be consistently raised from the start of the preheating process, and then the highest temperature reached may be held for a certain period of time until the end of the preheating process. In that case, the time for which the temperature of the silver ink composition is held is preferably 0.5 to 10 minutes, more preferably 0.5 to 6 minutes, and even more preferably 0.5 to 3 minutes.

[0064] During the preheating process, foaming is typically observed in the silver ink composition until the heated product is obtained. This is because the components of the silver ink composition react, generating gas, which then escapes. Typically, by the end of this process, this foaming disappears and gas generation almost or completely stops. Because foaming occurs in the silver ink composition in this way, the mass of the heated silver ink composition at the end of this process is less than the mass of the silver ink composition at the start of this process. In other words, a decrease in the mass of the silver ink composition is observed in this process.

[0065] In this embodiment, (B1) after the preheating step is completed, the first member and the second member may be brought into contact via the heated object (the first member, the heated object, and the second member may be stacked) (this may be referred to as "preheating method (B1)" in this specification), (B2) the first member and the second member may be brought into contact via the silver ink composition (the first member, the silver ink composition, and the second member may be stacked) before the preheating step is performed (this may be referred to as "preheating method (B2)" in this specification), and (B3) the first member and the second member may be brought into contact via the heated silver ink composition during the preheating step (the first member, the heated silver ink composition, and the second member may be stacked) (this may be referred to as "preheating method (B3)" in this specification), and the timing of stacking (laminating) the first member and the second member can be arbitrarily selected.

[0066] Among these methods, it is preferable to use preheating method (B1) or (B3) in order to obtain a metal member joint with higher bonding strength, and it is more preferable to use preheating method (B1).

[0067] In the preheating step, if combination (A1) is selected, the second member is brought into contact with the silver ink composition attached to the surface of the first member before heating, the silver ink composition during heating, or the silver ink composition after heating (i.e., the heated material). In the preheating step, if combination (A2) is selected, the first member is brought into contact with the silver ink composition attached to the surface of the second member before heating, the silver ink composition during heating, or the silver ink composition after heating (i.e., the heated material). In the preheating step, if combination (A3) is selected, the silver ink composition before heating, the silver ink composition during heating, or the silver ink composition after heating (i.e., the heated material) adhering to the surface of the first member is brought into contact with the silver ink composition before heating, the silver ink composition during heating, or the silver ink composition after heating (i.e., the heated material) adhering to the surface of the second member. In either case, the silver ink composition adhering to the first or second member forms a conductive joint that connects the first and second members in a later step.

[0068] In this embodiment, the bonding strength of the conductive joint is significantly increased by forming the heated material in the preheating step. The reason for this excellent effect is not entirely clear, but it is presumed that by heating the silver ink composition without solidifying it, the resulting heated material is fluid, unlike when it is solidified, and this improves the adhesion between the heated material and the first member, and between the heated material and the second member. Furthermore, as explained above, foaming is typically observed in the silver ink composition until the heated material is obtained, but this foaming disappears by the end of this step. Moreover, because the heated material is not solidified, the surface roughness of the heated material caused by foaming is reduced, and it is presumed that this increases the contact area between the heated material and the first member, and between the heated material and the second member.

[0069] The heated material obtained in the preheating process typically does not have the luster characteristic of metallic silver, and is, for example, dark green in color. These external characteristics also indicate that the heated material does not primarily consist of high-purity metallic silver.

[0070] <Joining process> After the preheating step, in the joining step, the first member and the second member are joined by metallic silver by interposing a heated silver ink composition between them and firing the heated composition while pressing the two members together. The aforementioned silver ink composition is a material for forming metallic silver, and in this process, it solidifies by firing to ultimately form metallic silver, which is then used to join the first member and the second member.

[0071] In the joining process, the first member and the second member can be pressed together by applying either or both of the following pressures to the composite material, which is formed by stacking the first member, the heated material, and the second member in this order: pressure in the direction from the first member to the second member, and pressure in the direction from the second member to the first member.

[0072] When applying pressure to the composite material in the direction from the first member to the second member, it is preferable to apply the pressure while the second member is fixed in this direction. When applying pressure to the composite material in the direction from the second member toward the first member, it is preferable to apply the pressure while the first member is fixed in this direction.

[0073] The two pressures mentioned above can be applied using known methods. For example, if pressure is to be applied in only one of the two directions described above, the composite can be fixed on a horizontal plane with one surface of the first member or the second member facing downward in the vertical direction, and a weight placed on the other surface of the first member or the second member facing upward in the vertical direction, thereby applying pressure to the composite from only one direction. Here, we have described a case where pressure is applied to either the first member or the second member by placing a weight on it, but pressure may also be applied by other pressing means. Furthermore, although this description has focused on the case where the surfaces of the first and second members are oriented vertically, the composite material may also be oriented in other directions, such as horizontally.

[0074] In the joining process, the pressure applied when the first member and the second member are pressed together with the heated material interposed between them (sometimes abbreviated as "pressure pressure" in this specification) is not particularly limited, but is preferably 0.2 MPa or higher, more preferably 0.4 MPa or higher, and even more preferably 0.6 MPa or higher. By setting the pressure to be equal to or above the lower limit, a metal member joint with higher bonding strength can be obtained.

[0075] In the joining process, the upper limit of the crimping pressure is not particularly limited. However, in terms of facilitating easier crimping, the crimping pressure is preferably 3 MPa or less.

[0076] In the joining process, the crimping pressure can be appropriately adjusted within a range set by arbitrarily combining any of the lower and upper limits described above. For example, in one embodiment, the crimping pressure may be any of 0.2 to 3 MPa, 0.4 to 3 MPa, or 0.6 to 3 MPa. However, these are just examples of the crimping pressure.

[0077] In the joining process, the crimping pressure may or may not be kept constant from the start of crimping to the end of crimping. If the crimping pressure is not kept constant, the crimping pressure may be consistently increased (in other words, it is not necessary to keep it constant or decrease it), or there may be periods when the pressure is kept constant or periods when it is decreased. In particular, it is preferable that the crimping pressure is always increased or kept constant (in other words, not decreased at all).

[0078] In the joining process, metallic silver is formed by firing the heated material. The firing of the heated material in the joining process can be carried out by further heating of the heated material. This heating can be carried out in the same manner as the heating of the silver ink composition in the preheating process.

[0079] In the joining process, the temperature at the start of firing the heated material may be lower than the temperature at the end of the preheating process, such as room temperature, but it is preferable that it be at or above the temperature at the end of the preheating process.

[0080] The firing temperature of the heated material in the joining process may be, for example, 170°C or higher, 220°C or higher, or 270°C or higher.

[0081] The upper limit of the firing temperature of the heated material in the joining process is not particularly limited. For example, in order to shorten the process time and avoid excessively high temperatures, the firing temperature is preferably 350°C or lower, and more preferably 320°C or lower. The reason why the firing temperature can be kept relatively low is that the silver ink composition uses components within a relatively limited range.

[0082] The firing temperature of the heated material in the joining process can be appropriately adjusted within a range set by arbitrarily combining any of the lower and upper limits described above. For example, in one embodiment, the firing temperature may be any of 170-350°C, 220-350°C, or 270-350°C. In one embodiment, the firing temperature may be any of 170-320°C, 220-320°C, or 270-320°C. However, these are just examples of the firing temperatures mentioned above.

[0083] In the joining process, the heating rate during firing of the heated material is not particularly limited, but is preferably 5 to 50°C / min, more preferably 5 to 45°C / min, and even more preferably 5 to 40°C / min.

[0084] In the joining process, the firing time of the heated material is not particularly limited, but is preferably 1 minute to 24 hours, more preferably 5 minutes to 12 hours, and even more preferably 10 minutes to 2 hours.

[0085] In the joining process, the firing temperature of the heated material may be consistently increased until its completion (in other words, it is not necessary to keep it constant or decrease it), or a period of time may be set for keeping it constant, or a period of time may be set for decreasing the temperature. In particular, it is preferable to increase or keep the firing temperature of the heated material constant (in other words, not decrease it at all) from the start to the end of the joining process. For example, the firing temperature of the heated material may be consistently increased from the start of the joining process, and then the highest temperature reached may be maintained for a certain period of time until the end of the joining process. In this case, the time for which the firing temperature of the heated material is maintained is preferably 5 to 60 minutes, more preferably 10 to 50 minutes, and even more preferably 15 to 40 minutes.

[0086] The joining process may be carried out under normal pressure, reduced pressure, or increased pressure. Furthermore, the joining process may be carried out in either an atmospheric environment or an inert gas atmosphere. Examples of the inert gas include nitrogen gas, argon gas, and helium gas. When the joining process is carried out under conditions that can suppress the oxidation reaction of the first member, the second member, and the fired product (i.e., metallic silver), it is preferable to carry it out under reduced pressure or in an inert gas atmosphere. For example, the joining process is preferable to carry out under an inert gas atmosphere because it has a high effect in suppressing the oxidation reaction, and preferable to carry it out under reduced pressure because it is low cost.

[0087] The thickness of the conductive joint (in other words, metallic silver) formed by firing the heated material is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 25 μm or more. A thickness of the conductive joint equal to or greater than the lower limit increases the bonding strength of the metal member joint. Furthermore, a conductive joint with a thickness of 20 μm or more is easier to form. In this specification, "thickness of the conductive joint" means "the thickness of the conductive joint in the direction of joining the first member and the second member."

[0088] The upper limit of the thickness of the conductive joint is not particularly limited. To avoid excessive thickness, the thickness of the conductive joint is preferably 100 μm or less.

[0089] The thickness of the conductive joint can be appropriately adjusted within a range set by arbitrarily combining any of the lower and upper limits described above. For example, in one embodiment, the thickness of the conductive joint may be 10 to 100 μm, 20 to 100 μm, or 25 to 100 μm. However, these are just examples of the thickness of the conductive joint.

[0090] The thickness of the conductive joint is determined, for example, by the thickness of the heated material before firing. Typically, the thickness of the conductive joint can be preferably 4-16%, more preferably 6-14%, and even more preferably 8-12% of the thickness of the heated material before firing. However, these are just examples of the relationship between the thickness of the conductive joint and the thickness of the heated material before firing.

[0091] In this embodiment, (C1) the firing of the heated material may be started after the pressing of the first member and the second member has begun (this may be referred to as the "pressure firing method (C1)" in this specification), (C2) the pressing of the first member and the second member may be started after the firing of the heated material has begun (this may be referred to as the "pressure firing method (C2)" in this specification), or (C3) the pressing of the first member and the second member and the firing of the heated material may be started simultaneously (this may be referred to as the "pressure firing method (C3)" in this specification), and the timing of starting the pressing and firing as described above can be arbitrarily selected.

[0092] Among these methods, the pressure firing method (C1) or (C3) is preferable, and the pressure firing method (C1) is more preferable, as it provides a metal member joint with higher bonding strength.

[0093] In the joining process, the bonding strength of the conductive joint is significantly increased by the compression between the first and second members with the heated material interposed between them. Unlike conventional methods, it is quite surprising that such an increase in bonding strength occurs in a conductive joint that does not contain resin components such as binders. The reason for this excellent effect is not entirely clear, but it is speculated that the laminated structure of the first member, the heated material during firing, and the second member are compressed against each other in the thickness direction, which reduces the volume of voids in the heated material during firing and increases its density, resulting in improved strength of the fired product (conductive joint).

[0094] The strength of the conductive joint in the metal member joint obtained in this embodiment can be evaluated, for example, by measuring the die shear strength. Die shear strength can be measured in accordance with JIS C62137-1-2:2010 (lateral shear strength test, IEC 62137-1-2:2007). Specifically, in a metal member joint, one of the first member and the second member, which are joined by a conductive joint, is fixed, and a force is applied to the other member in a direction perpendicular to the lamination direction of the first member, the conductive joint, and the second member (in other words, a direction parallel to their lamination surfaces). The force applied when this laminated structure (first member, conductive joint, and second member) breaks is adopted as the die shear strength.

[0095] In this embodiment, the die shear strength of the metal member joint is preferably 15 MPa or higher, and may be, for example, 22.5 MPa or higher, 27.5 MPa or higher, or 32.5 MPa or higher.

[0096] In this embodiment, the upper limit of the die shear strength of the metal member joint is not particularly limited. For example, in terms of ease of manufacturing the metal member joint, the die shear strength is preferably 50 MPa or less.

[0097] The die share intensity can be appropriately adjusted within a range set by arbitrarily combining any of the lower and upper limits described above. For example, in one embodiment, the die shear strength may be any of 15-50 MPa, 22.5-50 MPa, 27.5-50 MPa, or 32.5-50 MPa. However, these are just examples of die shear strengths.

[0098] <Other processes> The method for joining metal members in this embodiment may include other steps that do not fall under either the preheating step or the joining step, as long as they do not impair the effects of the present invention. The aforementioned other steps are not particularly limited and can be arbitrarily selected depending on the purpose. The timing of the other processes can also be arbitrarily selected according to the purpose, and may be, for example, before the preheating process, between the preheating process and the joining process, or after the joining process.

[0099] <Examples of methods for joining metal components> Figure 1 is a schematic cross-sectional view illustrating an example of a method for joining metal members according to one embodiment of the present invention. Please note that the diagrams used in the following explanation may be enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may not be the same as in reality.

[0100] Figure 1 is a schematic cross-sectional view illustrating the joining method of metal members (sometimes referred to as "joining method (1-1)" in this specification) when a combination (A1) and preheating method (B1) are selected. In other words, in the preheating step of joining method (1-1), as shown in Figure 1(a), a combination of a first member 11 with the silver ink composition 130 attached to its surface and a second member 12 without the silver ink composition attached to its surface is used. The silver ink composition 130 is attached to one surface (sometimes referred to as the "first surface" in this specification) 11a of the first member 11.

[0101] In the preheating step of joining method (1-1), the silver ink composition 130 adhering to the first surface 11a of the first member 11 is heated at a temperature of 60°C or higher without solidifying, thereby obtaining a heated silver ink composition 130' as shown in Figure 1(b).

[0102] Next, in the joining step of joining method (1-1), as shown in Figure 1(c), the heated silver ink composition 130' is interposed, and the first member 11 and the second member 12 are pressed together while the heated silver ink composition 130' is fired. At this time, the force applied to press together the laminated structure of the first member 11, the heated silver ink composition 130', and the second member 12 can be either force P1 or force P2, or both. At this time, the surface of the second member 12 on the first member 11 side (sometimes referred to as the "first surface" in this specification) 12a comes into contact with the heated silver ink composition 130'.

[0103] By performing the preheating and joining processes in this manner, a metal member assembly 1 is obtained in which the first member 11 and the second member 12 are joined via metallic silver (in other words, a conductive joint) 13, as shown in Figure 1(d).

[0104] Figure 2 is a schematic cross-sectional view illustrating another example of a method for joining metal members according to one embodiment of the present invention. In Figures 2 and beyond, components identical to those shown in previously explained figures are denoted by the same reference numerals, and their detailed explanations are omitted.

[0105] Figure 2 is a schematic cross-sectional view illustrating the joining method of metal members (sometimes referred to as "joining method (2-1)" in this specification) when a combination (A2) and preheating method (B1) are selected. In other words, in the preheating step of joining method (2-1), as shown in Figure 2(a), a combination of a first member 11 on which no silver ink composition is attached to the surface and a second member 12 on which the silver ink composition 130 is attached to the surface is used. The silver ink composition 130 is attached to the first surface 12a of the second member 12.

[0106] In the preheating step of the joining method (2-1), the silver ink composition 130 adhering to the first surface 12a of the second member 12 is heated at a temperature of 60°C or higher without solidifying, thereby obtaining a heated silver ink composition 130' as shown in Figure 2(b).

[0107] Next, in the joining process of joining method (2-1), as shown in Figure 2(c), the heated silver ink composition 130' is interposed, and the first member 11 and the second member 12 are pressed together while the heated silver ink composition 130' is fired. At this time, the surface of the first member 11 that faces the second member 12, i.e., the first surface 11a, comes into contact with the heated silver ink composition 130'. After forming the laminated structure of the first member 11, the heated object 130', and the second member 12, this process can be carried out in the same manner as in the joining method (1-1) described with reference to Figure 1.

[0108] By performing the preheating and joining processes in this manner, a metal member assembly 1 is obtained in which the first member 11 and the second member 12 are joined via metallic silver (in other words, a conductive joint) 13, as shown in Figure 2(d).

[0109] Figure 3 is a schematic cross-sectional view illustrating yet another example of a method for joining metal members according to one embodiment of the present invention. Figure 3 is a schematic cross-sectional view illustrating the joining method of metal members (sometimes referred to as "joining method (3-1)" in this specification) when a combination (A3) and preheating method (B1) are selected. In other words, in the preheating step of joining method (3-1), as shown in Figure 3(a), a combination of a first member 11 with a silver ink composition 130 attached to its surface and a second member 12 with a silver ink composition 130 attached to its surface is used. The silver ink composition 130 is attached to both the first surface 11a of the first member 11 and the first surface 12a of the second member 12. These silver ink compositions 130, 130 may be the same or different.

[0110] In the preheating step of the joining method (3-1), the silver ink composition 130 adhering to the first surface 11a of the first member 11 and the silver ink composition 130 adhering to the first surface 12a of the second member 12 are both heated to a temperature of 60°C or higher without solidifying, thereby obtaining heated silver ink composition 130' as shown in Figure 3(b).

[0111] Next, in the joining process of joining method (3-1), as shown in Figure 3(c), the first member 11 and the second member 12 are pressed together with heated silver ink compositions 130', 130' interposed, and the heated silver ink compositions 130', 130' are fired. At this time, the heated silver ink composition 130' on the first surface 11a of the first member 11 and the heated silver ink composition 130' on the first surface 12a of the second member 12 come into contact. This process can be carried out in the same manner as the joining method (1-1) described with reference to Figure 1, except that the object to be pressed is this laminated structure, after forming the laminated structure with reference to Figure 1.

[0112] By performing the preheating and joining processes in this manner, a metal member assembly 2 is obtained in which the first member 11 and the second member 12 are joined via two layers of metallic silver (layers) 13, or in other words, conductive joints 23, as shown in Figure 3(d).

[0113] Here, for convenience, the conductive joint 23 in the metal member joint 2 is shown as being composed of two layers. In the joining method (3-1), if the silver ink composition 130 initially attached to the first member 11 and the silver ink composition 130 initially attached to the second member 12 are of different types, the conductive joint 23 will be composed of such two layers. On the other hand, if the silver ink composition 130 initially attached to the first member 11 and the silver ink composition 130 initially attached to the second member 12 are of the same type, the conductive joint 23 may be composed of such two layers, or it may be a single-layer conductive joint (for example, a conductive joint similar to the conductive joint 13 shown in Figures 1 and 2).

[0114] Up to this point, we have described the method of joining metal components when preheating method (B1) is selected in the preheating process. However, in the above manufacturing method, preheating method (B2) or (B3) can also be selected.

[0115] Figure 4 is a schematic cross-sectional view illustrating the joining method of metal members (sometimes referred to as "joining method (1-2)" in this specification) when a combination (A1) and preheating method (B2) are selected. In other words, in the preheating step of joining method (1-2), as in joining method (1-1), a combination of a first member 11 with the silver ink composition 130 attached to its surface and a second member 12 without the silver ink composition attached to its surface is used, as shown in Figure 1(a).

[0116] In the preheating step of joining method (1-2), the first member 11 and the second member 12 are then brought into contact via the silver ink composition 130 adhering to the first surface 11a of the first member 11, as shown in Figure 4(b). After stacking the first member 11, the silver ink composition 130, and the second member 12 in this manner, the silver ink composition 130 is heated at a temperature of 60°C or higher without solidifying it, thereby obtaining a heated silver ink composition 130', as shown in Figure 4(c). This results in a laminated structure of the first member 11, the heated silver ink composition 130', and the second member 12, in the same state as shown in Figure 1(c).

[0117] Next, in the joining process of joining method (1-2), as shown in Figure 4(c), the heated silver ink composition 130' is interposed and the first member 11 and the second member 12 are pressed together while the heated silver ink composition 130' is fired, in the same manner as in joining method (1-1).

[0118] By performing the preheating and joining processes in this manner, a metal member assembly 1 is obtained in which the first member 11 and the second member 12 are joined via metallic silver (in other words, a conductive joint) 13, as shown in Figure 4(d).

[0119] Figure 5 is a schematic cross-sectional view illustrating the joining method of metal members (sometimes referred to as "joining method (1-3)" in this specification) when a combination (A1) and preheating method (B3) are selected. In other words, in the preheating step of joining method (1-3), as in the case of joining method (1-1), a combination of a first member 11 with the silver ink composition 130 attached to its surface and a second member 12 without the silver ink composition attached to its surface is used, as shown in Figure 5(a).

[0120] In the preheating step of joining method (1-3), heating is started as shown in Figure 5(b) so as not to solidify the silver ink composition 130 adhering to the first surface 11a of the first member 11 at a temperature of 60°C or higher. Here, the silver ink composition at an intermediate stage of heating, before becoming the heated object 130', is denoted by reference numeral 1301.

[0121] Next, in the preheating step of joining method (1-3), as shown in Figure 5(c), the first member 11 and the second member 12 are brought into contact via the heated silver ink composition 1301 during this step. The temperature of the heated silver ink composition 1301 when it is brought into contact in this way may be less than 60°C or 60°C or higher.

[0122] Next, in the preheating step of joining method (1-3), the silver ink composition 1301 adhering to the first member 11 and the second member 12 is further heated to a temperature of 60°C or higher without solidifying, thereby obtaining a heated silver ink composition 130' as shown in Figure 5(d).

[0123] Next, in the joining step of joining method (1-3), as shown in Figure 5(e), the heated silver ink composition 130' is interposed and the first member 11 and the second member 12 are pressed together while the heated silver ink composition 130' is fired, in the same manner as in joining method (1-1).

[0124] By performing the preheating and joining processes in this manner, a metal member assembly 1 is obtained in which the first member 11 and the second member 12 are joined via metallic silver (in other words, a conductive joint) 13, as shown in Figure 5(f).

[0125] Up to this point, we have explained the joining method for metal components when a combination (A1) and preheating method (B1) to (B3) are selected. However, it is also possible to select a combination (A2) or (A3) and a preheating method (B1), (B2), or (B3).

[0126] Up to this point, the joining methods described with reference to Figures 1 to 5 have not specifically described the sequence of events between the start of pressing the first member and the second member together with the heated silver ink composition interposed in the joining process, and the start of firing the heated material. In this embodiment, these sequences can be arbitrarily selected, as previously described in the pressing and firing methods (C1) to (C3).

[0127] The following will provide a more detailed explanation using the joining method (1-1) described in Figure 1 as an example. Figure 6 is a schematic cross-sectional view illustrating the joining process in a method for joining metal members (sometimes referred to as "joining method (1-1-1)" in this specification) when a combination (A1), a preheating method (B1), and a pressure firing method (C1) are selected.

[0128] In the joining process of joining method (1-1-1), a laminated structure is obtained consisting of the first member 11, the heated object 130', and the second member 12, as shown in Figure 6(a), similar to the one shown in Figure 1(c). Next, as shown in Figure 6(b), the crimping of this laminated structure is started.

[0129] Next, in the joining process of joining method (1-1-1), firing of the heated material 130' is started as shown in Figure 6(c). Here, the heated material at an intermediate stage of firing (including the start of firing) before it becomes the conductive joint 13 is denoted by reference numeral 1301'.

[0130] By performing the joining process in this manner, a metal member assembly 1 is obtained in which the first member 11 and the second member 12 are joined via the conductive joint 13, as shown in Figure 6(d), similar to the one shown in Figure 1(d).

[0131] Figure 7 is a schematic cross-sectional view illustrating the joining process in a method for joining metal members (sometimes referred to as "joining method (1-1-2)" in this specification) when a combination (A1), a preheating method (B1), and a pressure firing method (C2) are selected.

[0132] In the joining process of joining method (1-1-2), a laminated structure is obtained consisting of the first member 11, the heated object 130', and the second member 12, as shown in Figure 7(a), similar to the one shown in Figure 1(c). Next, as shown in Figure 7(b), firing of the heated object 130' is started. Here again, the heated object at an intermediate stage of firing (including the start of firing) before it becomes the conductive joint 13 is denoted by reference numeral 1301'.

[0133] Next, in the joining process of joining method (1-1-2), as shown in Figure 7(c), the bonding of the laminated structure consisting of the first member 11, the heated material 1301' in the intermediate stage of firing, and the second member 12 is initiated.

[0134] By performing the joining process in this manner, a metal member assembly 1 is obtained in which the first member 11 and the second member 12 are joined via the conductive joint 13, as shown in Figure 7(d), similar to the one shown in Figure 1(d).

[0135] Figure 8 is a schematic cross-sectional view illustrating the joining process in a method for joining metal members (sometimes referred to as "joining method (1-1-3)" in this specification) when a combination (A1), a preheating method (B1), and a pressure firing method (C3) are selected.

[0136] In the joining process of joining method (1-1-3), a laminated structure is obtained consisting of the first member 11, the heated object 130', and the second member 12, similar to that shown in Figure 1(c) and as shown in Figure 8(a). Next, as shown in Figure 8(b), the firing of the heated object 130' and the compression of the laminated structure are started simultaneously. Here, the force applied at the start of compression of the laminated structure is denoted by the symbol P. 11and the symbol P 21 The label is added, and the heated material at the start of firing is given the label 1302'.

[0137] By performing the joining process in this manner, a metal member assembly 1 is obtained in which the first member 11 and the second member 12 are joined via the conductive joint 13, as shown in Figure 8(c) and similar to that shown in Figure 1(d).

[0138] Up to this point, we have explained the joining method for metal components when a combination (A1), preheating method (B1), and pressure firing method (C1) to (C3) is selected. However, it is also possible to select a combination (A2) or (A3), a preheating method (B1), (B2), or (B3), and a pressure firing method (C1), (C2), or (C3).

[0139] Up to this point, the method for joining metal members in this embodiment has been described in which one first member and one second member are joined with one metallic silver (conductive joint). However, in the method for joining metal members in this embodiment, one first member and one second member may be joined with two or more metallic silver (conductive joints). Furthermore, in the method for joining metal members according to this embodiment, one first member and two or more second members may be joined with a single metallic silver (conductive joint). In this case, the two or more second members may all be the same, all be different, or only partially different. Furthermore, in the method for joining metal members of this embodiment, one first member and two or more second members may be joined with two or more metallic silver (conductive joints). In this case, the number of second members and the number of metallic silver (conductive joints) may be the same or different. Also, the two or more second members may all be the same, all be different, or only some be different. The number of first and second components exemplified here may be reversed. Next, the silver ink composition used in this embodiment will be described in detail.

[0140] <Silver ink composition> The silver ink composition comprises the silver carboxylate, the amine compound, and formic acid. The silver ink composition preferably does not contain resin components such as binders, and more preferably the silver carboxylate is uniformly dispersed during formulation.

[0141] By using the aforementioned silver carboxylate, metallic silver is generated, and a conductive joint containing this metallic silver as the main component is formed. In this case, by preferably not using the aforementioned resin component, the proportion of metallic silver can be made sufficiently high so that the conductive joint can appear to consist solely of metallic silver. In this case, for example, the ratio of the total mass of metallic silver in the conductive joint to the total mass of the conductive joint can be, for example, 97% by mass or more, 98% by mass or more, and 99% by mass or more. The upper limit of the ratio can be, for example, 100% by mass, 99.9% by mass, 99.8% by mass, 99.7% by mass, 99.6% by mass, 99.5% by mass, 99.4% by mass, 99.3% by mass, 99.2% by mass, and 99.1% by mass, but these are just examples.

[0142] [Silver Carboxylate] The silver carboxylate is a silver salt of a carboxylic acid and has a group represented by the formula "-COOAg". The silver carboxylate is not particularly limited as long as it has a group represented by the formula "-COOAg". For example, there may be only one group represented by the formula "-COOAg" in one molecule of silver carboxylate, or there may be two or more. Furthermore, the position of the group represented by the formula "-COOAg" in the silver carboxylate is not particularly limited.

[0143] In this embodiment, the silver carboxylate may be used alone or in combination of two or more types, and when two or more types are used in combination, the combination and ratio thereof can be adjusted arbitrarily.

[0144] The silver carboxylate is preferably one or more selected from the group consisting of β-ketocarboxylate silver represented by the following general formula (1) (hereinafter sometimes abbreviated as "β-ketocarboxylate silver (1)") and silver carboxylate silver represented by the following general formula (4) (hereinafter sometimes abbreviated as "silver carboxylate (4)"). In this specification, unless otherwise specified, the term "silver carboxylate" refers not only to "β-silver ketocarboxylate (1)" and "silver carboxylate (4)," but also to "silver carboxylate having a group represented by the formula "-COOAg," encompassing both of these.

[0145] [ka] (wherein R is a carbon-1 to carbon-20 aliphatic hydrocarbon group or phenyl group, hydroxyl group, amino group, or general formula "R 1 -CY 1 2-", CY 1 3-", "R 1 -CHY 1 -", "R 2 O-", "R 5 R 4 N-", (R 3 O)2CY 1 -" or "R 6 -C(=O)-CY 1 It is a base represented by "2-"; Y 1 Each of these is independently a fluorine atom, a chlorine atom, a bromine atom, or a hydrogen atom; R 1 R is an aliphatic hydrocarbon group or phenyl group having 1 to 19 carbon atoms; 2 R is an aliphatic hydrocarbon group having 1 to 20 carbon atoms; 3 R is an aliphatic hydrocarbon group having 1 to 16 carbon atoms; 4 and R 5 Each of these is independently an aliphatic hydrocarbon group having 1 to 18 carbon atoms; R 6 This refers to an aliphatic hydrocarbon group having 1 to 19 carbon atoms, a hydroxyl group, or a group represented by the formula "AgO-"; X 1Each of these independently consists of a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, a halogen atom, a phenyl group or benzyl group in which one or more hydrogen atoms may be substituted with substituents, a cyano group, an N-phthaloyl-3-aminopropyl group, a 2-ethoxyvinyl group, or the general formula "R 7 O-", "R 7 S-", "R 7 -C(=O)-" or "R 7 It is a base represented as -C(=O)-O-; R 7 This is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a thienyl group, or a phenyl or diphenyl group in which one or more hydrogen atoms may be substituted with substituents.

[0146] [ka] (In the formula, R 8 (This refers to an aliphatic hydrocarbon group having 1 to 19 carbon atoms, a carboxyl group, or a group represented by the formula "-C(=O)-OAg". If the aliphatic hydrocarbon group has a methylene group, one or more of these methylene groups may be substituted with carbonyl groups.)

[0147] (β-silver ketocarboxylate (1)) Silver β-ketocarboxylate (1) is represented by the general formula (1) above. In the formula, R is a carbon-1 to carbon-20 aliphatic hydrocarbon group or phenyl group, hydroxyl group, amino group, or general formula "R 1 -CY 1 2-", CY 1 3-", "R 1 -CHY 1 -", "R 2 O-", "R 5 R 4 N-", (R 3 O)2CY 1 -" or "R 6 -C(=O)-CY 1 It is a base represented by "2-".

[0148] The aliphatic hydrocarbon group having 1 to 20 carbon atoms in R may be linear, branched, or cyclic (aliphatic cyclic group), and if cyclic, it may be monocyclic or polycyclic. Furthermore, the aliphatic hydrocarbon group may be either a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. The number of carbon atoms in the aliphatic hydrocarbon group is preferably 1 to 10, and more preferably 1 to 6. Examples of preferred aliphatic hydrocarbon groups in R include alkyl groups, alkenyl groups, and alkynyl groups.

[0149] Examples of linear or branched alkyl groups in R include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1-methylbutyl group, 2-methylbutyl group, n-hexyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 4-methylpentyl group, 1,1-dimethylbutyl group, 2,2-dimethylbutyl group, 3,3-dimethylbutyl group, 2, 3-dimethylbutyl group, 1-ethylbutyl group, 2-ethylbutyl group, 3-ethylbutyl group, 1-ethyl-1-methylpropyl group, n-heptyl group, 1-methylhexyl group, 2-methylhexyl group, 3-methylhexyl group, 4-methylhexyl group, 5-methylhexyl group, 1,1-dimethylpentyl group, 2,2-dimethylpentyl group, 2,3-dimethylpentyl group, 2,4-dimethylpentyl group, 3,3-dimethylpentyl group, 4,4-dimethylpentyl group, 1-ethylpentyl group, 2-ethylpentyl group, 3-ethylpentyl group, 4-ethylpentyl group, 2,2,3-trimethylbutyl group, 1-propylbutyl group, n-octyl group, isooctyl group, 1-methylheptyl group, 2-methylheptyl group, 3-methylheptyl group, 4-methylheptyl group, 5-methylheptyl group, 1-ethylhexyl group, 2-ethylhexyl group, 3-ethylhexyl group, 4-ethylhexyl group, 5-ethylhexyl group, 1,1-dimethylhexyl group, 2,2-dimethylhexyl group, 3,3-dimethylhexyl group, 4,4-dimethylhexyl group, 5,5-dimethylhexyl group, 1,2, 3-trimethylpentyl group, 1,2,4-trimethylpentyl group, 2,3,4-trimethylpentyl group, 2,4,4-trimethylpentyl group, 1,4,4-trimethylpentyl group, 3,4,4-trimethylpentyl group, 1,1,2-trimethylpentyl group, 1,1,3-trimethylpentyl group, 1,1,4-trimethylpentyl group, 1,2,2-trimethylpentyl group, 2,2,3-trimethylpentyl group, 2,2,4-trimethylpentyl group, 1,3,3-trimethylpentyl group, 2,3,3-trimethylpentyl group, 3,3,Examples include 4-trimethylpentyl group, 1-propylpentyl group, 2-propylpentyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, and eicosyl group. Examples of the cyclic alkyl group in R include cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group, norbornyl group, isobornyl group, 1-adamantyl group, 2-adamantyl group, tricyclodecyl group, and the like.

[0150] Examples of the alkenyl group in R include a group in which one single bond (CC) between carbon atoms of the alkyl group in R is replaced with a double bond (C=C). Examples of such alkenyl groups include vinyl group (ethenyl group, -CH=CH2), allyl group (2-propenyl group, -CH2-CH=CH2), 1-propenyl group (-CH=CH-CH3), isopropenyl group (-C(CH3)=CH2), 1-butenyl group (-CH=CH-CH2-CH3), 2-butenyl group (-CH2-CH=CH-CH3), 3-butenyl group (-CH2-CH2-CH=CH2), cyclohexenyl group, cyclopentenyl group, and the like.

[0151] Examples of the alkynyl group in R include a group in which one single bond (CC) between carbon atoms of the alkyl group in R is replaced with a triple bond (C≡C). Examples of such alkynyl groups include ethynyl groups (-C≡CH) and propargyl groups (-CH2-C≡CH).

[0152] The aliphatic hydrocarbon group having 1 to 20 carbon atoms in R may have one or more hydrogen atoms substituted with substituents. Preferred substituents include, for example, fluorine atoms, chlorine atoms, and bromine atoms. Furthermore, the number and position of the substituents on the aliphatic hydrocarbon group are not particularly limited. When there are multiple substituents, these substituents may be identical or different from one another. That is, all substituents may be identical, all substituents may be different, or only some substituents may be different.

[0153] The phenyl group in R may have one or more hydrogen atoms substituted by substituents. Preferred substituents include, for example, a saturated or unsaturated monovalent aliphatic hydrocarbon group having 1 to 16 carbon atoms, a monovalent group formed by bonding the aliphatic hydrocarbon group to an oxygen atom, a fluorine atom, a chlorine atom, a bromine atom, a hydroxyl group (-OH), a cyano group (-C≡N), a phenoxy group (-O-C6H5), and the like. In the phenyl group having substituents, the number and position of the substituents are not particularly limited. Furthermore, if there are multiple substituents, these substituents may be identical or different from one another. Examples of the aliphatic hydrocarbon group that is a substituent include those that are the same as the aliphatic hydrocarbon group in R, except that they have 1 to 16 carbon atoms.

[0154] Y in R 1 These are, independently, a fluorine atom, a chlorine atom, a bromine atom, or a hydrogen atom. And the general formula is "R 1 -CY 1 2-", CY 1 3-" and "R 6 -C(=O)-CY 1 In "2-", each has multiple Y 1 They may be the same or different from one another.

[0155] R in R 1 R is an aliphatic hydrocarbon group or a phenyl group (C6H5-) having 1 to 19 carbon atoms. 1Examples of the aliphatic hydrocarbon group in R include those similar to the aliphatic hydrocarbon group in R, except that they have 1 to 19 carbon atoms. R in R 2 This is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, and examples include those similar to the aliphatic hydrocarbon group in R. R in R 3 R is an aliphatic hydrocarbon group having 1 to 16 carbon atoms. 3 Examples of the aliphatic hydrocarbon group in R include those similar to the aliphatic hydrocarbon group in R, except that they have 1 to 16 carbon atoms. R in R 4 and R 5 These are, independently, aliphatic hydrocarbon groups having 1 to 18 carbon atoms. That is, R 4 and R 5 They may be the same or different from each other, R 4 and R 5 Examples of the aliphatic hydrocarbon group in R include those similar to the aliphatic hydrocarbon group in R, except that they have 1 to 18 carbon atoms. R in R 6 R is an aliphatic hydrocarbon group having 1 to 19 carbon atoms, a hydroxyl group, or a group represented by the formula "AgO-". 6 Examples of the aliphatic hydrocarbon group in R include those similar to the aliphatic hydrocarbon group in R, except that they have 1 to 19 carbon atoms.

[0156] R is a linear or branched alkyl group among the above, with the general formula "R 6 -C(=O)-CY 1 The group represented by "2-" is preferably a hydroxyl group or a phenyl group. 6 It is preferable that this is a linear or branched alkyl group, a hydroxyl group, or a group represented by the formula "AgO-".

[0157] In general formula (1), X 1is independently a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, a halogen atom, a phenyl group or a benzyl group (C6H5-CH2-) in which one or more hydrogen atoms may be substituted with a substituent, a cyano group, an N-phthaloyl-3-aminopropyl group, a 2-ethoxyvinyl group (C2H5-O-CH=CH-), or a group represented by the general formula "R 7 O-", "R 7 S-", "R 7 -C(=O)-", or "R 7 -C(=O)-O-". X 1 Examples of the aliphatic hydrocarbon group having 1 to 20 carbon atoms in include the same ones as the aliphatic hydrocarbon group in R.

[0158] X 1 Examples of the halogen atom in include, for example, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. X 1 The phenyl group and the benzyl group in may have one or more hydrogen atoms substituted with a substituent. Preferred examples of the substituent include, for example, a halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom), a nitro group (-NO2), etc. In the phenyl group and the benzyl group having a substituent, the number and position of the substituent are not particularly limited. And when the number of substituents is plural, these plural substituents may be the same as or different from each other.

[0159] X 1 R 7 in is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a thienyl group (C4H3S-), or a phenyl group or a diphenyl group (biphenyl group, C6H5-C6H4-) in which one or more hydrogen atoms may be substituted with a substituent. Examples of the aliphatic hydrocarbon group in R 7 include the same ones as the aliphatic hydrocarbon group in R, except that the number of carbon atoms is 1 to 10. Also, R 7Examples of substituents on the phenyl and diphenyl groups include halogen atoms (fluorine, chlorine, bromine, and iodine atoms). The number and position of substituents on the phenyl and diphenyl groups are not particularly limited. If there are multiple substituents, these substituents may be identical or different from one another. R 7 If X is a thienyl group or a diphenyl group, then X 1 The bonding position with adjacent groups or atoms (oxygen atom, sulfur atom, carbonyl group, carbonyloxy group) is not particularly limited. For example, the thienyl group may be either a 2-thienyl group or a 3-thienyl group.

[0160] In general formula (1), two X 1 X may be bonded as a single group via a double bond to a carbon atom sandwiched between two carbonyl groups. 1 Examples include the group represented by the formula "=CH-C6H4-NO2".

[0161] X 1 Among the above, this includes a hydrogen atom, a linear or branched alkyl group, a benzyl group, or the general formula "R 7 It is preferable that the group is represented by -C(=O)- and at least one X 1 Preferably, it is a hydrogen atom.

[0162] β-Ketocarboxylate silver (1) is 2-methylacetoacetate silver (CH3-C(=O)-CH(CH3)-C(=O)-OAg), acetoacetate silver (CH3-C(=O)-CH2-C(=O)-OAg), 2-ethylacetoacetate silver (CH3-C(=O)-CH(CH2CH3)-C(=O)-OAg), propionylacetate silver (CH3CH2-C(=O)-CH2-C(=O)-OAg), isobutyl Silver lylacetate ((CH3)2CH-C(=O)-CH2-C(=O)-OAg), silver pivaloylacetate ((CH3)3C-C(=O)-CH2-C(=O)-OAg), silver caproylacetate (CH3(CH2)3CH2-C(=O)-CH2-C(=O)-OAg), silver 2-n-butylacetoacetate (CH3-C(=O)-CH(CH2CH2CH2CH3)-C(=O)-OAg), 2-benzyl Silver acetoacetate (CH3-C(=O)-CH(CH2C6H5)-C(=O)-OAg), silver benzoylacetate (C6H5-C(=O)-CH2-C(=O)-OAg), silver pivaloylacetoacetate ((CH3)3C-C(=O)-CH2-C(=O)-CH2-C(=O)-OAg), silver isobutyrylacetoacetate ((CH3)2CH-C(=O)-CH2-C(=O)-CH2-C(=O)-O It is preferable that the silver acetate is Ag), 2-acetylpivaloyl acetate ((CH3)3C-C(=O)-CH(-C(=O)-CH3)-C(=O)-OAg), 2-acetylisobutyryl acetate ((CH3)2CH-C(=O)-CH(-C(=O)-CH3)-C(=O)-OAg), or acetone dicarboxylate (AgO-C(=O)-CH2-C(=O)-CH2-C(=O)-OAg).

[0163] In a conductor (metallic silver) formed by solidification treatment such as drying or heating (calcination) of a silver ink composition using β-silver ketocarboxylate (1), the concentration of residual raw materials and impurities can be further reduced. In such a conductor, the fewer raw materials and impurities there are, for example, better contact between the formed metallic silver particles, making conductivity easier and reducing resistivity.

[0164] As described later, β-ketocarboxylate silver (1) can decompose at a low temperature, preferably 60 to 210°C, more preferably 60 to 200°C, to form metallic silver, even without using reducing agents known in the field. Furthermore, when β-ketocarboxylate silver (1) is used in combination with a reducing agent, it decomposes at an even lower temperature to form metallic silver.

[0165] In the present invention, β-silver ketocarboxylate (1) may be used alone or in combination of two or more types, and when two or more types are used in combination, the combination and ratio thereof can be arbitrarily adjusted.

[0166] (Silver Carboxylate (4)) Silver carboxylate (4) is represented by the general formula (4) above. In the formula, R 8 This refers to an aliphatic hydrocarbon group having 1 to 19 carbon atoms, a carboxyl group (-COOH), or a group represented by the formula "-C(=O)-OAg". R 8 The aliphatic hydrocarbon group in is the same as the aliphatic hydrocarbon group in R, except that it has 1 to 19 carbon atoms. However, R 8 The aliphatic hydrocarbon group in the above is preferably having 1 to 15 carbon atoms, and more preferably 1 to 10 carbon atoms.

[0167] R 8 If the aliphatic hydrocarbon group in has a methylene group (-CH2-), one or more of the methylene groups may be substituted with carbonyl groups. The number and position of methylene groups that may be substituted with carbonyl groups are not particularly limited, and all methylene groups may be substituted with carbonyl groups. Here, "methylene group" includes not only a single group represented by the formula "-CH2-", but also a single group represented by the formula "-CH2-" in an alkylene group which is formed by a chain of multiple groups represented by the formula "-CH2-".

[0168] The silver carboxylate (4) is preferably silver pyruvate (CH3-C(=O)-C(=O)-OAg), silver acetate (CH3-C(=O)-OAg), silver butyrate (CH3-(CH2)2-C(=O)-OAg), silver isobutyrate ((CH3)2CH-C(=O)-OAg), silver 2-ethylhexanoate (CH3-(CH2)3-CH(CH2CH3)-C(=O)-OAg), silver neodecanoate, silver oxalate (AgO-C(=O)-C(=O)-OAg), or silver malonate (AgO-C(=O)-CH2-C(=O)-OAg). Furthermore, of the two groups represented by the formula "-COOAg" in silver oxalate (AgO-C(=O)-C(=O)-OAg) and silver malonate (AgO-C(=O)-CH2-C(=O)-OAg), those in which one group is represented by the formula "-COOH" (HO-C(=O)-C(=O)-OAg, HO-C(=O)-CH2-C(=O)-OAg) are also preferred.

[0169] When using silver carboxylate (4), similar to when using β-ketosilver carboxylate (1), the concentration of residual raw materials and impurities in the conductor (metallic silver) formed by solidification treatments such as drying and heating (calcination) of the silver ink composition can be further reduced. Furthermore, when used in combination with a reducing agent, silver carboxylate (4) decomposes at a lower temperature to form metallic silver.

[0170] In the present invention, silver(4) carboxylate may be used alone or in combination of two or more types. When two or more types are used in combination, the combination and ratio of these types can be adjusted as desired.

[0171] The silver carboxylate is preferably β-ketocarboxylate (1). Among these β-ketocarboxylate silver (1), 2-methylacetoacetate silver, acetoacetate silver, isobutyrylacetate silver, and pivaloylacetate silver are particularly suitable for increasing the concentration of silver ink compositions due to their excellent compatibility with nitrogen-containing compounds (especially amine compounds) described later.

[0172] The ratio of the total mass of silver derived from silver carboxylate in the silver ink composition to the total mass of the silver ink composition is preferably 5% by mass or more, and more preferably 8% by mass or more. Having this ratio within this range results in a more superior quality conductive layer (silver layer). The upper limit of this ratio is not particularly limited as long as it does not impair the effects of the present invention, but considering the handling characteristics of the silver ink composition, 25% by mass is preferred. In this specification, unless otherwise specified, "silver derived from silver carboxylate" is synonymous with the silver in the silver carboxylate blended during the manufacture of the silver ink composition, and includes the silver that continues to constitute the silver carboxylate after blending, the silver in the decomposition products generated by the decomposition of silver carboxylate after blending, and the silver itself (metallic silver) generated by the decomposition of silver carboxylate after blending.

[0173] [Amine compounds] The amine compound is preferably one with 1 to 25 carbon atoms, and may be a primary amine, a secondary amine, or a tertiary amine. The amine compound may be linear, branched, or cyclic. In this specification, "linear amine compound" means "amine compound whose main chain is linear," "branched amine compound" means "amine compound whose main chain is branched," and "cyclic amine compound" means "amine compound whose main chain is cyclic." Furthermore, "main chain" refers to the chain-like structure to which the amine moiety (for example, the amino group (-NH2) of a primary amine) is directly bonded.

[0174] The amine compound may have one nitrogen atom constituting the amine moiety (for example, the nitrogen atom constituting the amino group (-NH2) of a primary amine), or it may have two or more.

[0175] Examples of the primary amine include monoalkylamines, monoarylamines, mono(heteroaryl)amines, and diamines, in which one or more hydrogen atoms may be substituted with substituents.

[0176] The alkyl group constituting the monoalkylamine may be linear, branched, or cyclic, and examples of such alkyl groups include those similar to the alkyl group in R. The alkyl group is preferably a linear or branched alkyl group having 1 to 19 carbon atoms, or a cyclic alkyl group having 3 to 7 carbon atoms. Preferred monoalkylamines include, specifically, n-butylamine, n-hexylamine, n-octylamine, n-dodecylamine, n-octadecylamine, isobutylamine, sec-butylamine, tert-butylamine, 3-aminopentane, 3-methylbutylamine, 2-heptylamine (2-aminoheptane), 2-aminooctane, 2-ethylhexylamine, 1,2-dimethyl-n-propylamine, and the like.

[0177] Examples of aryl groups constituting the monoarylamine include phenyl groups, 1-naphthyl groups, and 2-naphthyl groups. The number of carbon atoms in the aryl group is preferably 6 to 10.

[0178] The heteroaryl group constituting the mono(heteroaryl)amine has heteroatoms as atoms constituting the aromatic ring skeleton, and examples of such heteroatoms include nitrogen atoms, sulfur atoms, oxygen atoms, boron atoms, etc. Furthermore, the number of heteroatoms constituting the aromatic ring skeleton is not particularly limited and may be one or two or more. If there are two or more, these heteroatoms may be identical or different from each other. That is, these heteroatoms may all be the same, all be different, or only some may be different. The heteroaryl group may be monocyclic or polycyclic, and its number of members (the number of atoms constituting the ring skeleton) is not particularly limited, but it is preferably a 3- to 12-membered ring.

[0179] Examples of the heteroaryl groups that are monocyclic and have 1 to 4 nitrogen atoms include pyrrolyl, pyrrolinyl, imidazolyl, pyrazolyl, pyridyl, pyrimidyl, pyrazinyl, pyridadinyl, triazolyl, tetrazolyl, pyrrolidinyl, imidazolidinyl, piperidinyl, pyrazolidinyl, and piperazinyl groups. Such heteroaryl groups are preferably 3 to 8-membered rings, and more preferably 5 to 6-membered rings. Examples of the heteroaryl group having one oxygen atom and being monocyclic include the furanyl group, and such heteroaryl groups are preferably 3- to 8-membered rings, and more preferably 5- to 6-membered rings. Examples of the heteroaryl group having one sulfur atom and being monocyclic include the thienyl group, and such heteroaryl groups are preferably 3- to 8-membered rings, and more preferably 5- to 6-membered rings. Examples of the heteroaryl group having 1 to 2 oxygen atoms and 1 to 3 nitrogen atoms in a monocyclic structure include oxazolyl, isoxazolyl, oxadiazolyl, and morpholinyl groups. Such heteroaryl groups are preferably 3 to 8-membered rings, and more preferably 5 to 6-membered rings. Examples of the heteroaryl group having 1 to 2 sulfur atoms and 1 to 3 nitrogen atoms in a monocyclic structure include thiazolyl, thiadiazolyl, and thiazolidinyl groups. Such heteroaryl groups are preferably 3 to 8-membered rings, and more preferably 5 to 6-membered rings. Examples of the heteroaryl groups that are polycyclic and have 1 to 5 nitrogen atoms include indolyl, isoindolyl, indolidine, benzimidazolyl, quinolyl, isoquinolyl, indazolyl, benzotriazolyl, tetrazolopyridyl, tetrazolopyridazinyl, and dihydrotriazolopyridazinyl groups. Such heteroaryl groups are preferably 7 to 12-membered rings, and more preferably 9 to 10-membered rings. Examples of the aforementioned heteroaryl group that is polycyclic and has 1 to 3 sulfur atoms include the dithianaphthalenyl group and the benzothiophenyl group. Such heteroaryl groups are preferably 7 to 12-membered rings, and more preferably 9 to 10-membered rings. Examples of the aforementioned heteroaryl group that is polycyclic and has 1 to 2 oxygen atoms and 1 to 3 nitrogen atoms include the benzoxazolyl group and the benzoxadiazolyl group. Such heteroaryl groups are preferably 7 to 12-membered rings, and more preferably 9 to 10-membered rings. Examples of the aforementioned heteroaryl group that is polycyclic and has 1 to 2 sulfur atoms and 1 to 3 nitrogen atoms include the benzothiazolyl group and the benzothiadiazolyl group. Such heteroaryl groups are preferably 7 to 12-membered rings, and more preferably 9 to 10-membered rings.

[0180] The diamine only needs to have two amino groups, and the relative positions of the two amino groups are not particularly limited. Preferred diamines include, for example, the monoalkylamine, monoarylamine, or mono(heteroaryl)amine in which one hydrogen atom other than the hydrogen atom constituting the amino group (-NH2) is substituted with an amino group. The number of carbon atoms in the diamine is preferably 1 to 10. More preferred diamines include, for example, ethylenediamine, 1,3-diaminopropane, and 1,4-diaminobutane.

[0181] Examples of the secondary amines include dialkylamines, diarylamines, and di(heteroaryl)amines, in which one or more hydrogen atoms may be substituted with substituents.

[0182] The alkyl group constituting the dialkylamine is the same as the alkyl group constituting the monoalkylamine, and is preferably a linear or branched alkyl group having 1 to 9 carbon atoms, or a cyclic alkyl group having 3 to 7 carbon atoms. Furthermore, the two alkyl groups in one molecule of dialkylamine may be the same or different. Preferred dialkylamines include, specifically, N-methyl-n-hexylamine, diisobutylamine, and di(2-ethylhexyl)amine.

[0183] The aryl group constituting the diarylamine is the same as the aryl group constituting the monoarylamine, and preferably has 6 to 10 carbon atoms. Furthermore, the two aryl groups in one molecule of diarylamine may be identical or different.

[0184] The heteroaryl group constituting the di(heteroaryl)amine is similar to the heteroaryl group constituting the mono(heteroaryl)amine, and is preferably a 6- to 12-membered ring. Furthermore, the two heteroaryl groups in one molecule of di(heteroaryl)amine may be identical or different.

[0185] Examples of the tertiary amine include trialkylamines and dialkylmonoarylamines, in which one or more hydrogen atoms may be substituted with substituents.

[0186] The alkyl group constituting the trialkylamine is the same as the alkyl group constituting the monoalkylamine, and is preferably a linear or branched alkyl group having 1 to 19 carbon atoms, or a cyclic alkyl group having 3 to 7 carbon atoms. Furthermore, the three alkyl groups in one trialkylamine molecule may be the same or different from each other. That is, the three alkyl groups may all be the same, all be different, or only some may be different. Preferred trialkylamines include, specifically, N,N-dimethyl-n-octadecylamine and N,N-dimethylcyclohexylamine.

[0187] The alkyl group constituting the dialkylmonoarylamine is the same as the alkyl group constituting the monoalkylamine, and is preferably a linear or branched alkyl group having 1 to 6 carbon atoms, or a cyclic alkyl group having 3 to 7 carbon atoms. Furthermore, the two alkyl groups in one molecule of dialkylmonoarylamine may be the same or different. The aryl group constituting the dialkylmonoarylamine is the same as the aryl group constituting the monoarylamine, and preferably has 6 to 10 carbon atoms.

[0188] Up to this point, we have mainly described linear amine compounds, but the amine compound may also be a heterocyclic compound in which the nitrogen atoms constituting the amine moiety are part of a ring skeleton structure (heterocyclic skeleton structure). In other words, the amine compound may be a cyclic amine. In this case, the ring structure (the ring containing the nitrogen atoms constituting the amine moiety) may be monocyclic or polycyclic, and the number of ring members (the number of atoms constituting the ring skeleton) is not particularly limited, and may be either an aliphatic ring or an aromatic ring. Examples of preferred cyclic amines include pyridine.

[0189] In the primary, secondary, and tertiary amines, "hydrogen atoms that may be substituted with substituents" refers to hydrogen atoms other than those bonded to the nitrogen atoms constituting the amine moiety. The number of substituents is not particularly limited; there may be one, two or more, and all of the hydrogen atoms may be substituted with substituents. If there are multiple substituents, these substituents may be identical or different from each other. That is, all substituents may be the same, all may be different, or only some may be different. Furthermore, the positions of the substituents are not particularly limited.

[0190] Examples of substituents in the amine compound include alkyl groups, aryl groups, halogen atoms, cyano groups, nitro groups, hydroxyl groups, and trifluoromethyl groups (-CF3). Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0191] When the alkyl group constituting the monoalkylamine has substituents, it is preferable that the alkyl group is a linear or branched alkyl group having 1 to 9 carbon atoms and having an aryl group as a substituent, or a cyclic alkyl group having 3 to 7 carbon atoms and preferably having an alkyl group having 1 to 5 carbon atoms as a substituent. Specific examples of monoalkylamines having such substituents include 2-phenylethylamine, benzylamine, and 2,3-dimethylcyclohexylamine. Furthermore, the aryl group and alkyl group, which are substituents, may have one or more hydrogen atoms substituted with halogen atoms. Examples of monoalkylamines having substituents substituted with halogen atoms include 2-bromobenzylamine. Here, examples of the halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, and the like.

[0192] When the aryl group constituting the monoarylamine has a substituent, it is preferable that the aryl group is an aryl group having 6 to 10 carbon atoms and having a halogen atom as a substituent. Specific examples of monoarylamines having such substituents include, for example, bromophenylamine. Here, examples of the halogen atom include fluorine, chlorine, bromine, and iodine atoms.

[0193] When the alkyl group constituting the dialkylamine has substituents, the alkyl group is preferably a linear or branched alkyl group having 1 to 9 carbon atoms and having a hydroxyl group or an aryl group as a substituent. Specific examples of such substituent-containing dialkylamines include diethanolamine and N-methylbenzylamine.

[0194] The amine compound is preferably n-propylamine, n-butylamine, n-hexylamine, n-octylamine, n-dodecylamine, n-octadecylamine, isobutylamine, sec-butylamine, tert-butylamine, 3-aminopentane, 3-methylbutylamine, 2-heptylamine, 2-aminooctane, 2-ethylhexylamine, 2-phenylethylamine, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, N-methyl-n-hexylamine, diisobutylamine, N-methylbenzylamine, di(2-ethylhexyl)amine, 1,2-dimethyl-n-propylamine, N,N-dimethyl-n-octadecylamine, or N,N-dimethylcyclohexylamine. Among these amine compounds, 2-ethylhexylamine stands out for its excellent compatibility with silver carboxylate, making it particularly suitable for increasing the concentration of silver ink compositions, and for being especially suitable for reducing the surface roughness of metallic silver.

[0195] In this embodiment, the amine compound is preferably linear or branched.

[0196] In this embodiment, the amine compound may be used alone or in combination of two or more, and when two or more are used in combination, the combination and ratio thereof can be adjusted arbitrarily.

[0197] In the silver ink composition, the blending amount of the amine compound is preferably 0.3 to 15 moles, more preferably 0.3 to 12 moles, particularly preferably 0.3 to 8 moles, per mole of the blending amount of the silver carboxylate. For example, it may be any of 0.3 to 5 moles, 0.3 to 3 moles, and 0.3 to 1.5 moles. When the blending amount of the amine compound is within such a range, the stability of the silver ink composition is further improved, and the quality of the metallic silver is further improved.

[0198] [Formic acid] In the silver ink composition, the blending amount of formic acid (H-C(=O)-OH) is preferably 0.04 to 3.5 moles, more preferably 0.06 to 2.5 moles, per mole of the blending amount of the silver carboxylate. For example, it may be any of 0.08 to 1.5 moles and 0.1 to 1 mole. When the blending amount of formic acid is within such a range, the silver ink composition can more easily and stably form metallic silver.

[0199] [Other components] The silver ink composition may be one in which other components that do not correspond to any of the silver carboxylate, the amine compound, and formic acid are blended. The other components are not particularly limited and can be arbitrarily selected according to the purpose. Examples of the other components include alcohols and solvents other than alcohols (which may be simply referred to as "solvents" in this specification).

[0200] In this embodiment, when using the other components, the other components may be used alone or in combination of two or more. When using two or more in combination, their combinations and ratios can be arbitrarily adjusted.

[0201] (Alcohol) The alcohol is preferably an acetylene alcohol represented by the following general formula (2) (hereinafter, may be abbreviated as "acetylene alcohol (2)").

[0202] [ka] (In the formula, R' and R'' are each independently a hydrogen atom, a C1-C20 alkyl group, or a phenyl group in which one or more hydrogen atoms may be substituted with substituents.)

[0203] • Acetylene alcohol (2) Acetylene alcohol (2) is represented by the general formula (2) above. In the formula, R' and R'' are each independently a hydrogen atom, a C1-C20 alkyl group, or a phenyl group in which one or more hydrogen atoms may be substituted with substituents. The C1-C20 alkyl groups in R' and R'' may be linear, branched, or cyclic, and if cyclic, they may be monocyclic or polycyclic. Examples of the alkyl groups in R' and R'' are the same as those in R.

[0204] Examples of substituents in which hydrogen atoms of the phenyl group in R' and R'' may be substituted include saturated or unsaturated monovalent aliphatic hydrocarbon groups having 1 to 16 carbon atoms, monovalent groups formed by the aliphatic hydrocarbon group being bonded to an oxygen atom, fluorine atoms, chlorine atoms, bromine atoms, hydroxyl groups, cyano groups, phenoxy groups, and the like. These substituents are the same as those in which hydrogen atoms of the phenyl group in R may be substituted. In the phenyl group having substituents, the number and position of the substituents are not particularly limited, and if there are multiple substituents, these substituents may be the same or different from one another.

[0205] R' and R'' are preferably a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and more preferably a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms.

[0206] Preferred acetylene alcohols (2) include, for example, 3,5-dimethyl-1-hexyn-3-ol, 3-methyl-1-butyn-3-ol, 3-methyl-1-pentin-3-ol, 2-propyne-1-ol, 4-ethyl-1-octin-3-ol, and 3-ethyl-1-heptin-3-ol.

[0207] The aforementioned alcohol may be used alone or in combination of two or more types. When using two or more types in combination, the combination and ratio of these alcohols can be adjusted as desired.

[0208] (solvent) The solvent is not particularly limited, as long as it is something other than an alcohol (i.e., one that does not have a hydroxyl group). However, the solvent is preferably one that is liquid at room temperature. Examples of the aforementioned solvents include aromatic hydrocarbons such as toluene, o-xylene, m-xylene, and p-xylene; aliphatic hydrocarbons such as pentane, hexane, cyclohexane, heptane, octane, cyclooctane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, and decahydronaphthalene; halogenated hydrocarbons such as dichloromethane and chloroform; esters such as ethyl acetate, monomethyl glutarate, and dimethyl glutarate; ethers such as diethyl ether, tetrahydrofuran (THF), and 1,2-dimethoxyethane (dimethyl cellosolve); ketones such as acetone, methyl ethyl ketone (MEK), and cyclohexanone; nitriles such as acetonitrile; and amides such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide.

[0209] The amount of the other components in the silver ink composition may be appropriately selected depending on the type of the other components.

[0210] For example, when acetylene alcohol (2) is used as the other component, the amount of acetylene alcohol (2) in the silver ink composition is preferably 0.01 to 0.7 moles per mole of β-ketocarboxylate silver (1), more preferably 0.02 to 0.5 moles, and particularly preferably 0.02 to 0.3 moles. The stability of the silver ink composition is further improved by having the amount of acetylene alcohol (2) within this range.

[0211] For example, when the solvent is used as one of the other components, the amount of the solvent can be selected according to the purpose, such as the viscosity of the silver ink composition. However, in general, the ratio of the amount of the solvent to the total amount of the components in a silver ink composition is preferably 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 10% by mass or less.

[0212] For example, when using a component other than acetylene alcohol (2) and the solvent as the other component, the ratio of the amount of the other component to the total amount of the components in the silver ink composition is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0213] Even if the ratio of the amount of the other components to the total amount of the blended components is 0 by mass, that is, even without blending the other components, the silver ink composition will still exert its full effect.

[0214] In a silver ink composition, all components may be dissolved, or some or all components may be dispersed without dissolving. However, it is preferable that all components are dissolved, and that the undissolved components are uniformly dispersed.

[0215] <Method for producing silver ink composition> The silver ink composition is obtained by blending the silver carboxylate, the amine compound, formic acid, and, if necessary, the other components. After blending each component, the obtained blend may be used as the silver ink composition as it is, or a purified product obtained by subsequently performing a known purification operation as necessary may be used as the silver ink composition. In the present embodiment, generation of impurities that reduce the conductivity of metallic silver can be suppressed when blending the above components. This tendency is particularly remarkable when β-ketocarboxylic acid silver (1) is used as the silver carboxylate. Therefore, even when using the silver ink composition without performing a purification operation, metallic silver having sufficient conductivity can be obtained.

[0216] The blending order of each component is not particularly limited. As an example of a preferable blending method of each component, there is a blending method in which the silver carboxylate is added to the amine compound, and formic acid is added to the obtained mixture.

[0217] When blending each component, all the components may be added and then mixed, or some components may be added and mixed sequentially, or all the components may be added and mixed sequentially. The mixing method is not particularly limited, and a known method such as a method of rotating a stirrer or a stirring blade to mix; a method of using a mixer, a three-roll mill, a kneader or a bead mill to mix; a method of adding ultrasonic waves to mix, etc. may be appropriately selected. In the silver ink composition, when uniformly dispersing the undissolved components, for example, it is preferable to apply a method of dispersing using the above three-roll mill, kneader or bead mill.

[0218] The temperature during blending is not particularly limited as long as each blending component does not deteriorate, but it is preferably -5 to 60°C. And the temperature during blending may be appropriately adjusted so that the mixture obtained by blending has a viscosity that is easy to stir according to the types and amounts of the blending components. Also, the blending time is not particularly limited as long as each blending component does not deteriorate, but it is preferably 10 minutes to 36 hours.

[0219] <<Metal member assembly>> A metal member joint according to one embodiment of the present invention (metal member joint of the first embodiment) is a metal member joint obtained by the metal member joining method described above, wherein the die shear strength of the metal member joint is 15 MPa or more. The metal member joint of this embodiment and its die shear strength are as described above.

[0220] The conductive joint in the metal member joint of the first embodiment (in other words, the metallic silver formed from the silver ink composition) may contain trace amounts of impurities derived from the constituent components, such as decomposition products resulting from the decomposition of any of the constituent components of the silver ink composition: the silver carboxylate, the amine compound, formic acid, and the other components; compounds resulting from the reaction of any of the constituent components of the silver carboxylate, the amine compound, formic acid, and the other components with the decomposition products; and compounds resulting from the reaction of any of the constituent components of the silver carboxylate, the amine compound, formic acid, and the other components with each other. It can be confirmed that the composition of these impurities is clearly different from that of metallic silver formed from other silver ink compositions produced by different formulations of essential components than those in the case of the silver ink composition. On the other hand, the firing temperature of the heated material of the silver ink composition in the bonding process can be relatively low. This is because the silver ink composition uses the aforementioned limited range of components (silver carboxylate, amine compound, and formic acid). In other words, the impurities in the metallic silver in the first embodiment reflect the use of the silver ink composition, which has the advantage of being able to form (i.e., calcine) metallic silver at a relatively low temperature.

[0221] A metal member joint according to one embodiment of the present invention (a metal member joint according to a second embodiment) is composed of a first metal member and a second metal member joined together via metallic silver, wherein either or both of the first and second members are made of copper, and if the first member is made of copper, the metal member joint has between the first member and the metallic silver a layer in which silver is the main constituent element, and a layer in which copper and oxygen are the main constituent elements, in that order, from the first member side toward the metallic silver side, and if the second member is made of copper, the metal member joint has between the second member and the metallic silver a layer in which silver is the main constituent element, and a layer in which copper and oxygen are the main constituent elements, in that order, from the second member side toward the metallic silver side, and the die shear strength of the metal member joint is 15 MPa or more. The metal member joint according to the second embodiment can also be obtained by the metal member joining method described above.

[0222] When the first member is made of copper, the metal member assembly of the second embodiment has a laminated structure in which the copper first member, a layer with silver as the main constituent element, a layer with copper and oxygen as the main constituent elements, and metallic silver are present in that order. When the second member is made of copper, the metal member assembly of the second embodiment has a laminated structure in which the copper second member, a layer with silver as the main constituent element, a layer with copper and oxygen as the main constituent elements, and metallic silver are present in that order. These layered structures are quite unexpected in that silver and copper elements are arranged alternately.

[0223] In the layer described above, in which copper and oxygen are the main constituent elements, oxygen may exist as a product of reaction with copper, such as copper oxide, or it may exist on its own without reacting with copper.

[0224] The aforementioned "layer with silver as its main constituent element" refers to a layer that contains silver as a constituent element to such an extent that it clearly exhibits properties resulting from its presence. For example, a layer in question may have a ratio of 50% or more of the mass of silver to the total mass of all elements. The aforementioned "layers with copper and oxygen as major constituent elements" refers to layers that contain copper and oxygen as constituent elements to such an extent that they clearly exhibit properties resulting from the presence of copper and oxygen. For example, in the layer in question, the ratio of the total mass of copper and oxygen elements to the total mass of all elements is 50% by mass or more.

[0225] Thus, in the metal member joint of the second embodiment, the reason why the copper first member and metallic silver, or the copper second member and metallic silver, do not simply come into contact with each other, but instead have the laminated structure described above, is not clear, but it can be inferred as follows. In other words, it is presumed that, by using the manufacturing method of this embodiment and performing the preheating and bonding steps with the silver ink composition having a specific range of composition, the copper first member or copper second member reacts with the silver ink composition or its heated material, resulting in either or both of the following: diffusion of metallic silver into the copper first member or copper second member, and diffusion of copper from the copper first member or copper second member into metallic silver. Furthermore, it is possible that the reducing action of formic acid, a component of the silver ink composition, is involved in such diffusion. Therefore, regardless of whether the first or second component is made of copper, it is presumed that the silver in the layer, which has silver as its main constituent element, originates from the silver ink composition or its heated product. Furthermore, regardless of whether the first or second component is made of copper, it is presumed that the copper in the layer, whose main constituent elements are copper and oxygen, originates from the first or second component, which is made of copper.

[0226] The fact that the metal member joint of the second embodiment has the above-described laminated structure is consistent with the fact that the die-shear strength of the metal member joint is sufficiently large.

[0227] The die shear strength of the metal member joint in the second embodiment is 15 MPa or more, which is the same as that of the metal member joint in the first embodiment.

[0228] The laminated structure in the metal member joint of the second embodiment can be confirmed, for example, by preparing a cross-section in the metal member joint in a direction parallel to the joining direction of the first member, metallic silver, and second member, and observing this cross-section using a transmission electron microscope (TEM) or by energy dispersive X-ray spectroscopy (EDS or EDX).

[0229] The applications of the metal member joint of this embodiment (first and second embodiment) are not particularly limited. For example, the metal member joint is useful as a joint between electrodes in a circuit board. That is, preferred examples of the metal members constituting the metal member joint, i.e., the first and second members, include metal electrodes.

[0230] <<Circuit board>> A circuit board according to one embodiment of the present invention is provided with the metal member assembly on an organic substrate, and the metal member serves as a metal electrode. As explained above, the firing temperature of the heated silver ink composition in the bonding process can be relatively low. This is because the silver ink composition uses a relatively limited range of components. Therefore, even if an organic substrate containing organic components such as resin with relatively low heat resistance is used as the substrate material, and the above-described method of joining metal components to metal electrodes on it is applied, a circuit board without quality problems can be manufactured. On the other hand, if extremely high heating temperatures are required when joining metal components, such a circuit board cannot be manufactured.

[0231] The circuit board of this embodiment can have the same configuration as a known circuit board, except that it includes the aforementioned metal member joint having a die-sheath strength of 15 MPa or more. Furthermore, it can be manufactured in the same way as a known circuit board, except that it uses the aforementioned metal member joint. [Examples]

[0232] The present invention will be described in more detail below with reference to specific examples. However, the present invention is not limited in any way to the examples shown below.

[0233] [Example 1] <<Manufacturing of Metal Component Joints>> <Manufacturing of silver ink composition> To obtain a liquid, 2-methylacetoacetate (19.0 g) was added to 2-ethylhexylamine (0.4 molar amount relative to silver 2-methylacetoacetate, described later) in a beaker, and the mixture was stirred for 15 minutes using a mechanical stirrer, so that the liquid temperature was below 50°C. Formic acid (0.7 molar amount relative to silver 2-methylacetoacetate) was added dropwise to this liquid over 30 minutes, so that the reaction solution temperature was below 50°C. After the addition of formic acid was complete, the reaction solution was stirred further at 25°C for 1.5 hours to obtain a silver ink composition.

[0234] Table 1 shows the types and proportions of each component. In Table 1, "Amine compound (molar ratio)" refers to the amount of amine compound (in moles) per mole of silver carboxylate ([moles of amine compound] / [moles of silver carboxylate]). Similarly, "Formic acid molar ratio" refers to the amount of formic acid (in moles) per mole of silver carboxylate ([moles of formic acid] / [moles of silver carboxylate]).

[0235] <Manufacturing of metal component joints> As the first or second component, a copper plate measuring 12 mm × 8 mm × 0.8 mm and a copper chip measuring 4 mm × 4 mm × 0.8 mm were prepared. Then, these (i.e., the copper plate and the copper chip) were polished using water-soaked waterproof abrasive paper (grit 2000) (manufactured by Sankyo Rikagaku Co., Ltd.) to clean their surfaces. Next, a metal mask with a thickness of 0.3 mm, into which two 4 mm x 4 mm square areas were cut out side by side, was placed over the cleaned copper plate, and the silver ink composition obtained above was solid-printed onto the copper plate covered with this mask using a screen printing method. Based on the above, two parallel printed layers of a rectangular parallelepiped-shaped silver ink composition, each approximately 4 mm x 4 mm x 0.3 mm in size, were formed on the surface of the copper plate.

[0236] Next, under normal pressure and in an atmospheric environment, the copper plate with the printed layer was heated using a hot plate, starting from the side without the printed layer. The temperature of the copper plate and the printed layer was raised to 100°C over 5 minutes, and then held at 100°C for 1 minute (preheating step). During this time, the printed layer (i.e., the silver ink composition) did not solidify and maintained its fluidity. After the temperature reached 100°C, foaming was observed. This foaming disappeared before the 1 minute of holding the copper plate and printed layer at 100°C was completed. Thus, a heated silver ink composition was obtained. The resulting heated material did not have the characteristic luster of metallic silver and was dark green in color.

[0237] Two such first laminates, each consisting of a heated silver ink composition on a copper plate, were fabricated. Then, these two first stacks were placed in parallel, with their longitudinal directions aligned.

[0238] Next, under normal pressure and in an atmospheric environment, the copper chips were immediately placed on the surface of the heated object containing the silver ink composition (printing layer) in the first laminate, and a 5 kg weight was placed on the surface of the copper chips. At this time, one copper chip was placed on each heated object, and the positions of the outer periphery of the heated object and the copper chip were aligned when viewed from above. Furthermore, one weight was placed so as to span all four copper chips, and the position of the weight was adjusted so that the pressure was applied evenly to all four copper chips by this single weight. Based on the above, a second laminate was fabricated by aligning and stacking the heating element, copper chips, and weight on the surface of a copper plate. The second laminate consisted of two copper plates, four heating elements, four copper chips, and one weight. At this time, the pressure applied to one copper tip by the weight was 0.8 MPa.

[0239] Next, under normal pressure and in an atmospheric environment, the temperature of the second laminate in this state was raised to 300°C over 5 minutes, and then the temperature was maintained at 300°C for 30 minutes (bonding process). In other words, in this process, the copper plate and copper chip were bonded together with metallic silver by firing the heated material while pressing the heated material against the copper plate and copper chip. Next, by removing the weight, two metal member joints were obtained, each consisting of a copper plate and a copper chip joined together with metallic silver. In these joints, the conductive joint portion, which was made of the fired material from the heated material, i.e., metallic silver, was a rectangular parallelepiped with dimensions of approximately 4 mm × 4 mm × 0.03 mm. As described above, in this embodiment, the combination (A1), the preheating method (B1), and the pressure firing method (C1) were adopted.

[0240] <<Evaluation of Silver Ink Composition>> <Measurement of viscosity of silver ink composition> The viscosity of the silver ink composition obtained above was measured at a shear rate of 1000 / s at 25°C using a rheometer (Anton Paar "MCR301"). The results are shown in Table 1.

[0241] <Calculation of crystallite size of metallic silver particles in silver ink composition> Using an X-ray diffractometer (Bruker AXS, D8 DISCOVER with GADDS), the silver ink composition obtained above was filled into its sample holder, and X-ray diffraction measurements were performed on the metallic silver particles in the silver ink composition under the following measurement conditions. Next, the crystallite size was calculated using the peak of the crystal plane with the strongest intensity (2θ = 38.1°) from the obtained X-ray diffraction profile, based on Scherrer's formula described above. The results are shown in Table 1. (Measurement conditions) ·Incidence side optical system X-ray source: CuK (wavelength 1.542Å) Output: 50kV, 100mA Monochromator: Multilayer mirror Beam size: 10mm (H) x 1.0mm (W) ·Receiving side optical system Resolution of parallel solar slits: 0.12° Detector: Scintillation counter Camera distance: 15cm • Scanning conditions Scanning method: -2 (Locked Coupled) Scanning speed: 3dig / min Increment: 0.02°

[0242] <<Evaluation of Metal Member Joints>> <Measurement of die shear strength> The die shear strength of the two metal member joints obtained above was measured using a testing machine (Dage Bond Tester 4000) in accordance with JIS C62137-1-2:2010 (lateral shear strength test, IEC 62137-1-2:2007). This measurement was performed for each of the four copper chips, and the average of the four measurements was ultimately adopted as the die shear strength of the metal component joint. The results are shown in Table 2.

[0243] <Analysis of the bonding state> Using a focused ion beam (FIB) device, one of the two metal component assemblies obtained above was cut to expose its cross-section. The cross-section was observed using a transmission electron microscope (TEM). The image data obtained at this time is shown in Figure 9. At this time, the cross-section was further observed using energy-dispersive X-ray spectroscopy (EDS, EDX). Of the imaging data acquired at this time, the imaging data when silver was detected is shown in Figure 10, the imaging data when copper was detected is shown in Figure 11, and the imaging data when oxygen was detected is shown in Figure 12.

[0244] [Example 2] <<Manufacturing of Metal Component Joints>> <Manufacturing of silver ink composition> A silver ink composition was prepared using the same method as in Example 1.

[0245] <Manufacturing of metal component joints> Using the same copper plate and copper chip as in Example 1, and in the same manner as in Example 1, two parallel printed layers of a rectangular parallelepiped-shaped silver ink composition, approximately 4 mm × 4 mm × 0.3 mm in size, were formed on the surface of the copper plate.

[0246] Next, under normal pressure and in an atmospheric environment, the copper chip was placed on the surface of the printing layer (silver ink composition) so that when viewed from above, the positions of the printing layer and the outer periphery of the copper chip coincided. Next, under normal pressure and in an atmospheric environment, the copper plate with the printed layer was heated using a hot plate, starting from the side without the printed layer. The temperature of the copper plate, the printed layer, and the copper chip was raised to 100°C over 5 minutes, and then held at 100°C for 1 minute (preheating step). During this time, the printed layer (i.e., the silver ink composition) did not solidify and maintained its fluidity. After the temperature reached 100°C, foaming was observed. This foaming disappeared before the 1 minute of holding the copper plate and printed layer at 100°C was completed. Thus, a heated silver ink composition was obtained. The resulting heated material did not have the characteristic luster of metallic silver and was dark green in color.

[0247] Next, under normal pressure and in an atmospheric environment, a 5 kg weight was immediately placed on the surface of each copper chip. At this time, one weight was placed on each copper chip, and the positions of the centers of the copper chips and the weights were aligned when viewed from above. Based on the above, two laminates were formed on the surface of the copper plate by aligning and stacking the heated material, copper chips, and weights. At this time, the pressure applied to one copper tip by the weight was 0.8 MPa.

[0248] Next, the joining process was carried out in the same manner as in Example 1, and the copper plate and copper chip were joined with metallic silver by firing the heated material while pressing the heated material against the copper plate and copper chip with the heated material. As a result, a metal component assembly was obtained in which a copper plate and copper chips were joined together with metallic silver. In this assembly, the joint made of the fired material from the heated material, i.e., metallic silver, was a rectangular parallelepiped with dimensions of approximately 4 mm × 4 mm × 0.03 mm. Furthermore, another identical metal component assembly was manufactured using the same method, resulting in a total of two metal component assembly units being produced. As described above, in this embodiment, the combination (A1), the preheating method (B2), and the pressure firing method (C1) were adopted.

[0249] <<Evaluation of Silver Ink Composition>> The viscosity of the silver ink composition was measured and the crystallite size of the metallic silver particles in the silver ink composition was calculated using the same method as in Example 1. The results are shown in Table 1.

[0250] <<Evaluation of Metal Member Joints>> <Measurement of die shear strength> The die shear strength of the metal member joint was measured using the same method as in Example 1, except that the two metal member joints obtained above were used. The results are shown in Table 2.

[0251] <<Manufacturing and Evaluation of Metal Component Joints>> [Example 3] In the joining process described above, instead of raising the temperature of the copper plate and the laminate to 300°C over 5 minutes and then holding the temperature at 300°C for 30 minutes, the temperature of the copper plate and the laminate was raised to 250°C over 5 minutes and then held at 250°C for 30 minutes. Except for this difference, the metal member joint was manufactured and evaluated in the same manner as in Example 1. In Example 3, the joint portion of the resulting metal member joint, which was made of the fired material from the heated material, i.e., metallic silver, was a rectangular parallelepiped with dimensions of approximately 4 mm × 4 mm × 0.03 mm. The results are shown in Table 2.

[0252] [Example 4] In the joining process described above, instead of raising the temperature of the copper plate and the laminate to 300°C over 5 minutes and then holding the temperature at 300°C for 30 minutes, the temperature of the copper plate and the laminate was raised to 200°C over 5 minutes and then held at 200°C for 30 minutes. Except for this difference, the metal member joint was manufactured and evaluated in the same manner as in Example 1. In Example 4, the joint portion of the resulting metal member joint, which was made of the fired material from the heated material, i.e., metallic silver, was a rectangular parallelepiped with dimensions of approximately 4 mm × 4 mm × 0.03 mm. The results are shown in Table 2.

[0253] [Comparative Example 1] In the aforementioned preheating step, the time for maintaining the temperature at 100°C after raising the temperature of the copper plate and the printed layer to 100°C was changed from 1 minute to 5 minutes (hereinafter, this step may be referred to as the "comparative preheating step"), and after the aforementioned preheating step, the heated material was fired without placing a 5 kg weight on the surface of the copper chip (hereinafter, this step may be referred to as the "comparative joining step"), except that the manufacturing and evaluation of the metal component joint was carried out in the same manner as in Example 1. Specifically, in Comparative Example 1, immediately after the comparative preheating step, the copper chip was placed on the surface of the heated object of the silver ink composition (printing layer), thereby forming two comparative laminates on the surface of the copper plate in an aligned position. Next, the temperature of the copper plate and the comparative laminate in this state was raised to 300°C over 5 minutes, and the temperature was maintained at 300°C for 30 minutes. Thereafter, the copper plate and copper chip were joined with metallic silver in the same manner as in Example 1. However, in Comparative Example 1, the copper plate and copper chip could not be joined with metallic silver, and the desired metal member joint could not be obtained. In Comparative Example 1, the printed layer (i.e., the silver ink composition) had solidified and lost its fluidity by the end of the comparative preheating process. This solidified material did not have the characteristic luster of metallic silver and was dark green in color. After the temperature reached 100°C, foaming was observed in the printed layer. In the final product obtained, the fired portion of the heated material, i.e., the portion composed of metallic silver, was a rectangular parallelepiped approximately 4 mm × 4 mm × 0.03 mm in size. The results are shown in Table 2.

[0254] [Comparative Example 2] In the aforementioned preheating step, the metal member joint was manufactured and evaluated in the same manner as in Example 1, except that the time for maintaining the temperature at 100°C after raising the temperature of the copper plate and the printed layer to 100°C was changed from 1 minute to 5 minutes (i.e., a comparative preheating step was performed). In Comparative Example 2, at the end of the comparative preheating process, the printed layer (i.e., the silver ink composition) had solidified and lost its fluidity. This solidified material did not have the characteristic luster of metallic silver and was dark green in color. After the temperature reached 100°C, foaming was observed in the printed layer. In the resulting metal component joint, the fired product of the heated material, i.e., the joint made of metallic silver, was a rectangular parallelepiped approximately 4 mm × 4 mm × 0.03 mm in size. The results are shown in Table 2.

[0255] [Table 1]

[0256] [Table 2]

[0257] As is clear from the results above, in Examples 1 to 4, the die shear strength of the metal member joint was 17.5 MPa or higher (17.5 to 35 MPa) by performing the preheating and joining processes, indicating sufficiently high joint strength. In particular, the results from Examples 1 and 2 confirmed that the joint strength was further increased by placing the copper chips after the preheating process (i.e., by adopting the preheating method (B1)).

[0258] In Examples 1-4, the silver ink composition did not solidify during the preheating process and maintained its fluidity. This was evident from the observation of foaming in the silver ink composition. In Example 2, the main surface of the silver ink composition (printing layer) was covered with copper chips during the preheating process and was not exposed, so foaming of the silver ink composition could not be directly observed. However, slight fluctuations were observed in the copper chips, which indirectly confirmed that foaming was occurring in the silver ink composition. Furthermore, in all of Examples 1 to 4, the foaming of the silver ink composition disappeared by the end of the preheating process, suggesting that gas generation from the silver ink composition had almost completely ceased at this stage.

[0259] In contrast, in Comparative Example 1, a metal member joint could not be obtained. This was because the silver ink composition had solidified at the end of the comparative preheating process, and the copper plate and copper chip were not pressed together during the firing of the heated material in the comparative joining process. In Comparative Example 1, foaming was initially observed after the silver ink composition reached a temperature of 100°C. However, before this foaming disappeared, the silver ink composition solidified, and the surface of the heated silver ink composition was rougher than in Examples 1-4 due to the foaming.

[0260] In Comparative Example 2, the die shear strength of the metal component joint was 3 MPa, indicating low joint strength. This was due to the silver ink composition solidifying at the end of the comparative preheating process. In Comparative Example 2, as in Comparative Example 1, foaming was initially observed after the silver ink composition reached a temperature of 100°C. However, before this foaming disappeared, the silver ink composition solidified, and the surface of the heated silver ink composition was rougher than in Examples 1-4 due to the foaming. However, in Comparative Example 2, unlike in Comparative Example 1, the copper plate and copper chip were pressed together during the firing of the heated material in the joining process, thus a metal member joint was obtained.

[0261] Figure 9 shows TEM imaging data of the boundary between the copper chip and metallic silver (conductive junction) and the surrounding region. In Figure 9, the area on the left of the image is a copper chip, and the area on the right of the image is metallic silver. In Figure 9, the areas that are not colored, including those indicated by arrows, are minute voids (which may be referred to as "microvoids" in this specification and in the drawings). As is clear from Figure 9, between the copper chip and the metallic silver, two distinct regions, namely region 9-1 and region 9-2, were observed, extending across the top and bottom of the image.

[0262] Figure 10 shows the imaging data from the same region as Figure 9 when silver element is detected by EDS (EDX). In Figure 10, as in Figure 9, two distinct regions, namely region 10-1 and region 10-2, were observed between the copper chip and the metallic silver, extending across the top and bottom of the image. The shape of region 10-1 was similar to that of region 9-1, and the shape of region 10-2 was similar to that of region 9-2. The acquired imaging data showed fluorescence generation in the metallic silver region and region 10-1, indicating the detection of silver in these regions. On the other hand, this imaging data did not show significant fluorescence generation in other regions, including region 10-2, and silver was not significantly detected in these regions.

[0263] Figure 11 shows the imaging data from the same region as in Figure 9, when copper element detection was performed using EDS (EDX). In Figure 11, as in Figure 9, two distinct regions, namely region 11-1 and region 11-2, were observed between the copper chip and the metallic silver, extending across the top and bottom of the image. The shape of region 11-1 was similar to that of region 9-1, and the shape of region 11-2 was similar to that of region 9-2. The acquired imaging data showed fluorescence generation in the copper chip region and region 11-2, indicating the detection of copper in these regions. On the other hand, this imaging data did not show significant fluorescence generation in other regions, including region 11-1, and copper was not significantly detected in these regions.

[0264] Figure 12 shows the imaging data from the same region as in Figure 9, when oxygen element is detected using EDS (EDX). Unlike in Figure 9, in Figure 12, a distinct region, region 12-1, was observed between the copper chip and the metallic silver, extending across the top and bottom of the image. The shape of region 12-1 was similar to that of region 9-2. The acquired imaging data showed fluorescence generation in region 12-1, and oxygen was detected in this region. On the other hand, while the imaging data suggested weak fluorescence generation in other regions, the fluorescence intensity was negligible compared to the fluorescence intensity in region 12-1, and the amount of oxygen detected was minute.

[0265] From these results, it was determined that regions 9-1, 10-1, and 11-1 represent the same region, and that this region is a layer whose main constituent element is silver. Furthermore, regions 9-2, 10-2, 11-2, and 12-1 represent the same region, and it was found that this region is a layer whose main constituent elements are copper and oxygen. In other words, it was found that the metal component assembly obtained above has, between the copper chip and the metallic silver, a layer with silver as the main constituent element, and a layer with copper and oxygen as the main constituent elements, in that order, from the copper chip side toward the metallic silver side. Thus, the metal component assembly has a laminated structure in which the copper chip, the layer with silver as the main constituent element, the layer with copper and oxygen as the main constituent elements, and the metallic silver are arranged in this order, with silver and copper elements arranged alternately.

[0266] The above results were obtained by analyzing the boundary between the copper chip and metallic silver (conductive joint) and the surrounding area. However, similar results were obtained by analyzing the opposite side of the metal component joint, i.e., the boundary between the copper plate and metallic silver (conductive joint) and the surrounding area. In other words, it was found that the metal component assembly has, between the copper plate and the metallic silver, a layer with silver as the main constituent element, and a layer with copper and oxygen as the main constituent elements, in that order, from the copper plate side toward the metallic silver side. Thus, the metal component assembly has a laminated structure in which the copper plate, the layer with silver as the main constituent element, the layer with copper and oxygen as the main constituent elements, and the metallic silver are arranged in this order, with silver and copper elements arranged alternately.

[0267] In the layers on both the copper chip side and the copper plate side, where copper and oxygen are the main constituent elements, oxygen could exist as a product of reaction with copper, such as copper oxide, or it could exist independently without reacting with copper.

[0268] The fact that the metal component joint has the laminated structure described above is consistent with the fact that the die-shear strength of the metal component joint is sufficiently large. [Industrial applicability]

[0269] This invention can be used in the manufacture of various devices equipped with metal component assemblies, including circuit boards. [Explanation of Symbols]

[0270] 1,2...Metal member joint, 11...First metal member, 11a...First surface of the first metal member, 12...Second metal member, 12a...First surface of the second metal member, 13,23...Metallic silver (conductive joint), 130...Silver ink composition, 130'...Heated silver ink composition

Claims

1. A metal member joint, The aforementioned metal member joint is constructed by joining a first metal member and a second metal member via metallic silver. Either one or both of the first and second members are made of copper. If the first member is made of copper, the metal member assembly comprises, between the first member and the metallic silver, a layer in which silver is the main constituent element, and a layer in which copper and oxygen are the main constituent elements, in this order, from the first member side toward the metallic silver side. If the second member is made of copper, the metal member assembly comprises, between the second member and the metallic silver, a layer in which silver is the main constituent element, and a layer in which copper and oxygen are the main constituent elements, in this order, from the second member side toward the metallic silver side. The die shear strength of the aforementioned metal member joint is 17.5 to 35 MPa. Either one or both of the first member and the second member are formed from a non-metallic member or joined to form a composite with the non-metallic member. A metal member assembly in which the non-metallic member is a semiconductor wafer, a semiconductor chip, an organic insulating substrate, an inorganic insulating substrate, or an organic-inorganic composite insulating substrate.

2. The metal member joint according to claim 1, wherein both the first member and the second member are made of copper.

3. The semiconductor wafer or semiconductor chip is a wafer or chip whose constituent material is silicon, silicon carbide, or gallium nitride. The aforementioned organic insulating substrate is a polytetrafluoroethylene substrate, a polyimide substrate, a liquid crystal polymer substrate, or a cycloolefin polymer substrate. The inorganic insulating substrate is a ceramic substrate, The metal member joint according to claim 1 or 2, wherein the organic-inorganic composite insulating substrate is a glass epoxy resin substrate.

Images