Sinterable bonding paste and bonded structure

Abstract

The purpose of the present disclosure is to provide a sinterable bonding paste with which it is possible to obtain a bonded structure that, when used in sintering bonding, can be sintered at a low temperature, is not likely to cause defects such as cracks propagating in a sintered part or cracking of a semiconductor element such as Si or SiC or a substrate such as DBC, which is an object to be bonded, and has excellent thermal conductivity.　Provided is a sinterable bonding paste which contains a silver powder (A) and particles (B) of an element other than silver having silicon oxide on the surface, and which is characterized in that: a resin and a binder are contained or are not contained; and the total content of the resin and the binder is 3 parts by mass or less with respect to a total of 100 parts by mass of the silver powder (A) and the particles (B) of an element other than silver having silicon oxide on the surfaces.

Description

Sinterable bonding paste and bonded structure

[0001] This disclosure relates to a sinterable bonding paste and bonding structure used when joining semiconductor elements and heat dissipation substrates. This application claims priority to Japanese Patent Application No. 2024-157036, filed in Japan on September 10, 2024, and the contents of that application are incorporated herein by reference.

[0002] In semiconductor devices, electronic components such as semiconductor elements are mounted on metal substrates such as copper substrates, and these components are fixed in place with solder. In recent years, there has been a shift from conventional lead-containing solder to lead-free solder, taking into consideration the burden on human health and the environment. More recently, there has been consideration of using SiC chips, which have lower loss and superior characteristics compared to Si chips, which were widely used as semiconductor chips. However, in semiconductor devices with SiC chips mounted on substrates, the operating temperature can exceed 200°C. Therefore, it is necessary to use solder with a high melting point to fix the SiC chips to the substrate, but it is difficult to make solder with a high melting point lead-free.

[0003] In recent years, when die-bonding (die-attaching) semiconductor devices that operate at high temperatures, such as SiC chips, a sintering bonding method has been investigated in which a metal paste containing nano-sized or micro-sized particles of silver or copper is used as a bonding material. This bonding material is interposed between the objects to be bonded and heated for a predetermined time to sinter the silver or other metals in the bonding material, thereby joining the objects to be bonded together by a metal bonding layer (see, for example, Patent Document 1). This metal bonding technology is expected to have various applications in electronic devices such as power semiconductor devices and LED devices.

[0004] However, metals such as silver are too hard to be used as die attach materials, and the difference in thermal expansion coefficients between semiconductor elements such as Si and SiC and metal layers such as silver is very large. As a result, in thermal fatigue tests exceeding 200°C, cracks propagate in the sintered portion, or the semiconductor elements or insulating substrates such as DBC (Direct Bonded Copper) crack, making them unreliable. Furthermore, if the bonding material is a single metal, there is no way to improve bonding strength or heat resistance other than controlling the density of the sintering, and it is not possible to fundamentally change the mechanical properties of the bonded body.

[0005] To reduce the difference in thermal expansion coefficient between semiconductor elements such as Si and SiC and the metal layer, SiO2, which has a low coefficient of thermal expansion, is used. ２ The use of a paste mixed with such fillers is being considered (see, for example, Patent Document 2).

[0006] Japanese Patent Publication No. 2011-80147, Japanese Patent Publication No. 2018-170420

[0007] Here, SiO ２ Particles were generally thought not to sinter with metal parts at low temperatures, so SiO ２ All of the pastes containing this material also contained resin, and the structure was maintained by the resin. Therefore, there was a problem in that they had poor thermal conductivity, which is necessary for dissipating heat from semiconductor elements that operate at high temperatures.

[0008] Therefore, the object of this disclosure is to provide a sinterable bonding paste that, when used in sintering bonding, enables sintering at low temperatures, is less prone to crack propagation in the sintered portion, and is less likely to cause problems such as cracking of semiconductor elements such as Si and SiC or substrates such as DBC, and also provides a bonded structure with excellent thermal conductivity. Another object of this disclosure is to provide a bonded structure that is not prone to crack propagation in the sintered portion, is less likely to cause problems such as cracking of semiconductor elements such as Si and SiC or substrates such as DBC, and also provides a bonded structure with excellent thermal conductivity.

[0009] In order to solve the above problem, the inventors diligently studied and found that silver and SiO ２ They discovered that it can be directly sintered, and silver powder and SiO ２ We have found that using a sinterable bonding paste containing particles in sintering bonding reduces the likelihood of problems such as crack propagation in the sintered area or cracking of the bonded materials, such as semiconductor elements like Si and SiC or substrates like DBC, and also exhibits excellent thermal conductivity. This disclosure is based on these findings.

[0010] That is, the present disclosure provides a sinterable joining paste containing silver powder (A) and elemental particles (B) other than silver having silicon oxide on the surface, which may or may not contain a resin and a binder, and the total content of the resin and the binder is 3 parts by mass or less with respect to 100 parts by mass of the total amount of the silver powder (A) and the elemental particles (B) other than silver having silicon oxide on the surface.

[0011] In the sinterable joining paste, it is preferable that the element other than silver in the elemental particles (B) other than silver having silicon oxide on the surface does not form an intermetallic compound with silver.

[0012] The elemental particles other than silver in the elemental particles (B) other than silver having silicon oxide on the surface are preferably silicon particles or SiO ２ particles.

[0013] In the elemental particles (B) other than silver having silicon oxide on the surface, it is preferable that the ratio of silicon oxide occupying the surface of the particles (B) is 30 to 100%.

[0014] It is preferable that the silicon oxide is formed as a layer on the surface of the elemental particles (B) other than silver having silicon oxide on the surface, and the thickness of the layer is 3 nm or more and 300 nm or less.

[0015] and the ratio (the former / the latter; volume ratio) of the silver powder (A) to the elemental particles (B) other than silver having silicon oxide on the surface is preferably 5 / 95 to 95 / 5.

[0016] It is preferable that the elemental particles (B) other than silver having silicon oxide on the surface are further partially coated with silver.

[0017] It is preferable that the sinterable joining paste does not contain the resin and the binder.

[0018] The present disclosure also provides a joining structure in which a joined object is joined to a substrate through a silver joining layer including a sintered body of the sinterable joining paste.

[0019] In the joining structure, it is preferable that the joining surface of the joined object with the silver joining layer is silver-plated.

[0020] In the above bonding structure, the bonded object is preferably a SiC chip.

[0021] In the above bonding structure, the substrate is preferably a copper substrate.

[0022] When the sintering bonding paste of the present disclosure is used for sintering bonding, sintering can be performed at a low temperature, and problems such as cracks developing in the sintered part or substrates such as semiconductor elements such as Si and SiC or DBC as the bonded object cracking are unlikely to occur, and a bonding structure excellent in thermal conductivity can be obtained.

[0023] It is a cross-sectional view schematically showing an example of an embodiment of the bonding structure of the present disclosure.

[0024] [Sintering bonding paste] The sintering bonding paste in one embodiment of the present disclosure is a sintering bonding paste containing silver powder (A) and elemental particles (B) other than silver having silicon oxide on the surface, and may or may not contain a resin and a binder. The total content of the resin and the binder is 3 parts by mass or less with respect to 100 parts by mass of the total amount of the silver powder (A) and the elemental particles (B) other than silver having silicon oxide on the surface.

[0025] (Silver powder (A)) The average particle size (median diameter; D50) of the silver powder (A) is 0.1 μm to 20 μm in a preferred embodiment of the present disclosure, 0.2 μm to 9 μm in another preferred embodiment, and 0.3 μm to 8 μm in still another embodiment. The average particle size (median diameter) of the silver powder (A) can be measured by the laser diffraction / scattering method. Also, only one kind of the silver powder (A) may be used, or two or more kinds may be used.

[0026] Further, the specific surface area of the silver powder (A) is preferably 0.5 to 4.0 m[[ID=二十一]] ２ [[ID=二十二]] / g, more preferably 0.6 to 3.g [[ID=二十三]] ２ [[ID=二十四]] / g, still more preferably m 0.7 to 2.5 [[ID=二十五]] ２ [[ID=二十六]] / g, particularly preferably 0.8 to 2.0 m [[ID=二十七]] ２ [[ID=二十八]] / g. The specific surface area of the silver powder (A) can be measured by the BET method. [[ID=二十九]]

[0027] The shape of the silver powder (A) can be, for example, spherical, flake-shaped (flattened), or polyhedral. Silver powders of different shapes may be used in combination, or only silver powders of the same shape may be used. The shape of the silver powder (A) is preferably flake-shaped. When flake-shaped silver powder is used, the powder contains many grain boundaries formed during flake formation, which promotes crystal coarsening during heating and thus accelerates sintering.

[0028] When using the silver powder (A) in flake form, its average diameter is preferably 0.5 μm to 10 μm, more preferably 2 μm to 8 μm, and even more preferably 3 μm to 7 μm. Furthermore, when using the flake form, its average thickness is preferably 30 nm to 2 μm, more preferably 80 nm to 1 μm, and even more preferably 100 nm to 700 nm.

[0029] As the silver powder (A) mentioned above, a commercially available product may be used, for example, the product "AgC-239" (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) can be used.

[0030] (Elemental particles other than silver having silicon oxide on the surface (B)) As for the element other than silver in elemental particles other than silver having silicon oxide on the surface (B), it is preferable to use an element that does not form an intermetallic compound with silver (Ag), and specifically silicon (Si) is preferred because its coefficient of linear expansion is small, less than 10 ppm / °C. Also, as for elemental particles other than silver having silicon oxide on the surface (B), Si particles, SiO ２ Examples include particles. In this disclosure, "elemental particles other than silver having silicon oxide on their surface (B)" may be simply referred to as "particles (B)". Furthermore, only one type of elemental particles other than silver having silicon oxide on their surface (B) may be used, or two or more types may be used.

[0031] The average particle size (median diameter; D50) of elemental particles other than silver (B) having silicon oxide on the surface is preferably 0.1 μm to 100 μm, with a lower limit of preferably 0.2 μm or more, more preferably 0.3 μm or more, and even more preferably 0.4 μm or more. The upper limit is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less.

[0032] The elemental particles (B) other than silver having silicon oxide on the above surface are specifically SiO ２ If it is a particle, generally available SiO ２ Particles are also acceptable. Furthermore, if the elemental particles other than silver are Si particles, the elemental particles other than silver (B) having silicon oxide on their surface can be obtained by oxidizing the surface of the Si particles. When oxidizing the surface of the Si particles, the method is not limited and includes methods such as heating in the presence of oxygen, forming with an oxidizing agent such as a hot nitric acid solution, and forming using oxygen radicals. Note that Si particles may have a native oxide film formed when exposed to air at room temperature, but such native oxide films are usually less than a few nanometers in size, and the coating state and amount of silicon oxide are often insufficient, making them unsuitable for this disclosure.

[0033] In the elemental particles (B) other than silver having silicon oxide on their surface, the proportion of silicon oxide on the surface of the elemental particles other than silver is preferably, for example, 30 to 100%. While there is no particular lower limit, it is preferably 35% or more, more preferably 50% or more, even more preferably 70% or more, particularly preferably 90% or more, and most preferably 95% or more. While there is no particular upper limit, it may be 99.9% or less, or 99.5% or less. Because the silicon oxide on the surface of particle (B) can be sintered with the silver powder (A), a higher proportion of silicon oxide on the surface of particle (B) results in a stronger bond, making it less likely for cracks to propagate in the sintered portion or for semiconductor elements such as Si or SiC, or substrates such as DBC, to crack. The proportion R (%) of the silicon oxide coating layer on the surface of particle (B) is determined by SEM observation, using particle images taken at 3000x magnification, and the area S of the elemental particles other than silver that is not covered. １ This can be calculated and determined by the following formula. Note that S is the surface area of ​​elemental particles other than silver. R (%) = {(S - S １ ) / S} × 100

[0034] In the elemental particles other than silver (B) having silicon oxide on the above surface, the elemental particles other than silver are SiO ２Otherwise, it is preferable that a layer of silicon oxide is formed on the surface of elemental particles other than silver. Furthermore, the thickness of the above layer is preferably 3 nm or more, more preferably 5 nm or more, even more preferably 10 nm or more, and particularly preferably 30 nm or more. There is no particular upper limit, but it may be 300 nm or less, 100 nm or less, or 50 nm or less. The above thickness can be controlled, for example, in the case of Si particles, by the oxidation time in the process of oxidizing the surface of the Si particles. The silicon oxide formed in the above layer does not need to be uniformly formed throughout the entire particle, and the internal particles may be partially exposed. In this case, the preferred proportion of silicon oxide on the surface is as described above. In this case, the thickness of the silicon oxide layer is calculated as the average value of the thickness of the silicon oxide layer in the parts where silicon oxide is formed, excluding the parts where silicon oxide is not formed. The thickness of the above silicon oxide layer depends on the thickness of the silicon oxide, but it can be measured by TEM or SEM.

[0035] The elemental particles (B) other than silver having silicon oxide on their surface may be further coated with silver. The shape of the coated silver is not particularly limited, but specifically, it may be a layered coating on a portion of the elemental particles (B) other than silver having silicon oxide on their surface, or it may be a coating on a portion of granular silver.

[0036] Non-silver elemental particles (B) having silicon oxide on a surface partially coated with silver can be manufactured by coating a portion of the surface of non-silver elemental particles (B) with silver. Examples of non-silver elemental particles include spherical, flake-shaped (flattened), and polyhedral shapes, and different shapes may be used in combination, or only particles of the same shape may be used. As for the shape of non-silver elemental particles, spherical and polyhedral shapes are preferred in that they maintain uniform dispersion of the particles during the paste application process when forming the joint.

[0037] The method for coating a portion of the surface of elemental particles other than silver (B) having silicon oxide on their surface with silver is not particularly limited, but for example, a preferred method is to mix silver powder and elemental particles other than silver having silicon oxide on their surface by subjecting them to the three-dimensional motion of a three-dimensional ball mill to form a silver coating layer on the surface of the elemental particles other than silver. With this method, a silver coating layer can be formed on elemental particles other than silver (B) having silicon oxide on their surface at room temperature without surface treatment or other procedures.

[0038] The silver powder used when subjecting the three-dimensional ball mill to the three-dimensional motion of elemental particles other than silver (B) having silicon oxide on the surface (hereinafter sometimes referred to as "silver powder (C)") can be the silver powder exemplified in the section on silver powder (A) above. The silver powder (C) may be the same as the silver powder used as silver powder (A), or a different one may be used. Furthermore, if some of the silver powder (C) contains powder smaller than the elemental particles other than silver, it can be coated more efficiently.

[0039] Methods for coating the surface of elemental particles other than silver (B) having silicon oxide on the surface with silver include, in addition to the method using the three-dimensional ball mill described above, wet methods such as silver electroplating and silver electroless plating, and methods in which silver and elemental particles other than silver (preferably elemental particles that do not form intermetallic compounds with silver) are alloyed by melting, and then mechanically crushed or sprayed from a molten state.

[0040] In elemental particles (B) other than silver having silicon oxide on a silver-coated surface, the proportion of the silver coating layer on the surface of particle (B) is preferably 1 to 70%, more preferably 30 to 70%, and even more preferably 50 to 70%. The proportion R2 (%) of the silver coating layer on the surface of particle (B) is the area S of the surface of (B) that is not coated with silver, as seen in particle images taken at 3000x magnification using SEM observation. １ It can be calculated and determined by the following formula. Let S be the surface area of ​​particle (B). R² (%) = {(S - S １ ) / S} × 100

[0041] In the above-described sinterable bonding paste, the ratio (mass ratio) of silver powder (A) to elemental particles other than silver having silicon oxide on their surface (B) is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 to 90 / 10, even more preferably 20 / 80 to 70 / 30, and particularly preferably 25 / 75 to 60 / 40.

[0042] In the above-mentioned sinterable bonding paste, the ratio of the total amount of silver powder (A) and elemental particles other than silver having silicon oxide on their surface (B) to the total amount of sinterable bonding paste is preferably 30 to 95% by mass, more preferably 50 to 90% by mass, and even more preferably 60 to 80% by mass.

[0043] The above-mentioned sinterable bonding paste may contain conductive particles other than silver powder (A) and elemental particles other than silver having silicon oxide on their surface (B) (hereinafter sometimes referred to as "other conductive particles"). The content of other conductive particles is preferably, for example, 25% by mass or less of the total amount of conductive particles contained in the above-mentioned sinterable bonding paste, more preferably 20% by mass or less, even more preferably 15% by mass or less, particularly preferably 10% by mass or less, and most preferably 5% by mass or less. Including other conductive particles within the above range is preferable in that it is possible to form a bonding structure with particularly excellent electrical properties.

[0044] (Solvent) The above-mentioned sinterable bonding paste usually contains a solvent. As the solvent, solvents commonly used in conductive pastes can be used. Examples of such solvents include dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monoisobutyl ether, dipropylene glycol monopentyl ether, dipropylene glycol monoisopentyl ether, and other dipropylene glycol mono-C １－６Alkyl ethers; dipropylene glycol dimethyl ether, dipropylene glycol methyl ethyl ether, dipropylene glycol methyl propyl ether, dipropylene glycol methyl butyl ether, dipropylene glycol methyl isobutyl ether, dipropylene glycol methyl pentyl ether, dipropylene glycol methyl isopentyl ether, dipropylene glycol diethyl ether, dipropylene glycol ethyl propyl ether, dipropylene glycol ethyl butyl ether, dipropylene glycol ethyl isobutyl ether, dipropylene glycol ethyl pentyl ether, dipropylene glycol ethyl isopentyl ether, dipropylene glycol dipropyl ether Dipropylene glycol dibutyl ether, dipropylene glycol propyl isobutyl ether, dipropylene glycol propyl pentyl ether, dipropylene glycol propyl isopentyl ether, dipropylene glycol dibutyl ether, dipropylene glycol diisobutyl ether, dipropylene glycol butyl isobutyl ether, dipropylene glycol butyl pentyl ether, dipropylene glycol butyl isopentyl ether, dipropylene glycol isobutyl pentyl ether, dipropylene glycol isobutyl isopentyl ether, dipropylene glycol dipentyl ether, dipropylene glycol pentyl isopentyl ether, etc. １－６ Alkyl ethers can be cited (including isomers).

[0045] Furthermore, as the solvent, for example, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monoisopropyl ether, tripropylene glycol monobutyl ether, tripropylene glycol monoisobutyl ether, tripropylene glycol monopentyl ether, tripropylene glycol monoisopentyl ether, etc. １－６Alkyl ethers; tripropylene glycol dimethyl ether, tripropylene glycol methyl ethyl ether, tripropylene glycol methyl propyl ether, tripropylene glycol methyl butyl ether, tripropylene glycol methyl isobutyl ether, tripropylene glycol methyl pentyl ether, tripropylene glycol methyl isopentyl ether, tripropylene glycol diethyl ether, tripropylene glycol ethyl propyl ether, tripropylene glycol ethyl butyl ether, tripropylene glycol ethyl isobutyl ether, tripropylene glycol ethyl pentyl ether, tripropylene glycol ethyl isopentyl ether, tripropylene glycol dipropyl ether Tripropylene glycol dibutyl ether, tripropylene glycol propyl isobutyl ether, tripropylene glycol propyl pentyl ether, tripropylene glycol propyl isopentyl ether, tripropylene glycol dibutyl ether, tripropylene glycol diisobutyl ether, tripropylene glycol butyl isobutyl ether, tripropylene glycol butyl pentyl ether, tripropylene glycol butyl isopentyl ether, tripropylene glycol isobutyl pentyl ether, tripropylene glycol isobutyl isopentyl ether, tripropylene glycol dipentyl ether, tripropylene glycol pentyl isopentyl ether, etc. １－６ Alkyl ethers can be cited (including isomers).

[0046] Furthermore, as the solvent, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, and other ethylene glycol mono-C １－６Alkyl ethers; ethylene glycol diC such as ethylene glycol methyl-n-propyl ether, ethylene glycol methyl-n-butyl ether, and ethylene glycol methyl isoamyl ether. １－６ Alkyl ethers; such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, etc. １－６ Alkyl ethers; such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol methyl-n-butyl ether, etc. １－６ Alkyl ethers; triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, etc. １－６ Alkyl ethers; triethylene glycol diC such as triethylene glycol methyl-n-butyl ether １－１０ Examples include alkyl ethers (including isomers).

[0047] Furthermore, as the solvent, for example, C is a solvent such as ethylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, or propylene glycol monomethyl ether acetate. ２－３ Alkylene glycol C １－６ Alkyl ether C １－１０ Alkyl esters; such as diethylene glycol-n-butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether acetate, etc. ２－３ Alkylene glycol C １－６ Alkyl ether C １－１０ Alkyl esters; such as triethylene glycol-n-butyl ether acetate, triethylene glycol ethyl ether acetate, triethylene glycol butyl ether acetate, tripropylene glycol methyl ether acetate, etc. ２－３Alkylene glycol C １－６ Alkyl ether C １－１０ Alkyl esters; such as propylene glycol diacetate C ２－３ Alkylene glycol di C １－１０ Examples include alkyl esters (including isomers).

[0048] In addition to the solvents mentioned above, other solvents such as ethyl lactate, tetrahydrofurfuryl acetate, tetrahydrofurfuryl alcohol, and ethylene glycol can also be used.

[0049] The above solvents can be used individually or in combination of two or more.

[0050] In the above-described sinterable bonding paste, the solvent content is preferably 1 to 50 parts by mass, more preferably 2 to 40 parts by mass, and even more preferably 3 to 35 parts by mass, based on 100 parts by mass of the total amount of silver powder (A) and elemental particles other than silver having silicon oxide on their surface (B).

[0051] The above-mentioned sinterable bonding paste may contain additives containing organic components, such as adhesives, thickeners, binders, resins, etc. However, this disclosure is limited to Ag and SiO ２ This invention is based on the discovery that the material can be directly sintered, and it is preferable that it does not contain any components that remain after sintering, such as binders or resins. The content of these organic components is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less, and particularly preferably 1 part by mass or less, based on 100 parts by mass of the total amount of silver powder (A) and elemental particles other than silver having silicon oxide on their surface (B). If organic components are included for purposes such as improving sinterability, it is preferable to include 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more.

[0052] In particular, the above-mentioned sinterable bonding paste preferably does not contain resin and binder, and the total content of resin and binder is 3 parts by mass or less, preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, and most preferably none, based on 100 parts by mass of the total amount of silver powder (A) and non-silver elemental particles (B) having silicon oxide on their surface. By having the resin and binder content within the above range, excellent thermal conductivity can be achieved.

[0053] [Bonding Structure] In one embodiment of the bonding structure of the present disclosure, the objects to be bonded are bonded to a substrate via a silver bonding layer containing a sintered body of the sinterable bonding paste described above. Figure 1 is a schematic cross-sectional view showing an example of an embodiment of this bonding structure. 1 is the bonding structure, 10 is the substrate, 20 is the silver bonding layer, and 30 is the objects to be bonded.

[0054] Examples of substrates 10 include metal substrates such as copper substrates, ceramic substrates, SiC substrates, gallium nitride substrates, glass epoxy substrates, BT resin substrates, glass substrates, and resin substrates. Since the sinterable bonding paste, which is one embodiment of this disclosure, can be sintered at low temperatures, heat-sensitive substrates can also be used. Copper substrates are particularly preferred as substrate 10. Furthermore, it is preferable that the bonding surface of the substrate 10 with the silver bonding layer 20 is silver-plated.

[0055] Examples of the object to be bonded 30 include electronic components and heat dissipation substrates. Examples of electronic components include power semiconductor elements and LED elements (chips, dies). The bonding surface of the object to be bonded 30 with the silver bonding layer 20 is preferably silver plated. The material of the object to be bonded 30 may be any of Si (silicon) or SiC (silicon carbide), but SiC (silicon carbide) is particularly preferred as it provides excellent results.

[0056] The above-described bonded structure can be manufactured by applying the above-described sinterable bonding paste to a substrate 1 by a printing method (specifically, a dispenser printing method, a mask printing method, a screen printing method, an inkjet printing method, etc.), placing the objects to be bonded 3 on the coated layer, and then sintering them.

[0057] The sintering temperature is, for example, 150°C or higher and less than 300°C, and in one preferred embodiment, 160 to 280°C, in another preferred embodiment, 200 to 270°C, and in yet another preferred embodiment, 230 to 260°C. The sintering time is, for example, 0.1 to 2 hours, and in one preferred embodiment, 0.5 to 1.5 hours.

[0058] The above sintering may be carried out in an air atmosphere, or in an inert gas atmosphere such as a nitrogen atmosphere or an argon atmosphere.

[0059] The thickness to which the above-mentioned sinterable bonding paste is applied onto the substrate 1 is such that the thickness of the bonded structure formed by the above method is, for example, 15 to 400 μm, in one preferred embodiment, 20 to 250 μm, and in another preferred embodiment, 40 to 180 μm.

[0060] According to this disclosure, since a sintered joint containing silicon oxide is formed by sintering, the mechanical properties of the joint itself (strength and thermal expansion coefficient) can be changed. Therefore, it is possible to fundamentally improve properties such as the thermal fatigue resistance of the joint. Furthermore, since no resin or binder is included during sintering, it is possible to achieve excellent thermal conductivity.

[0061] The configurations and combinations thereof in each embodiment of this specification are examples, and additions, omissions, substitutions, and other modifications are permitted as appropriate, without departing from the spirit of this disclosure. This disclosure is not limited by the embodiments, but is limited only by the scope of the claims.

[0062] An embodiment of this disclosure will be described in more detail below based on examples.

[0063] The average particle size (median diameter) of the following particles was measured using laser diffraction and scattering methods.

[0064] The raw materials used are as follows: [Silver flake powder (silver flake powder)] - Product name "AgC-239": Average diameter 5.0 μm, average thickness 260 nm, specific surface area 1.2 m² ２ / g, manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd. [Silicon (Si) particles] ・Particle size D50 = 0.5 μm, manufactured by Sakai Chemical Industry Co., Ltd. [SiO ２ [Particles] Particle size D50 = 0.4 μm, manufactured by Sakai Chemical Industry Co., Ltd. [Solvent] Product name "DPNP": Dipropylene glycol n-propyl ether: Boiling point 212℃, manufactured by Daicel Corporation

[0065] [Evaluation] The cross-sections of the sintered pastes of the examples and comparative examples described later were observed at a magnification of 20,000x using an FE-SEM, and particles of 100 nm or larger that could be visually confirmed (silicon particles, SiO₂) were identified. ２ The number of particles and the number of particles bonding to the bonded material, such as silver flakes or Ag plating on a Cu substrate, were measured, and the proportion of sintered particles among particles 100 nm or larger was calculated as the particle sintering rate using the following formula (1): Particle sintering rate = (Total number of particles 100 nm or larger that are bonded to the bonded material in the image taken at 20,000x magnification using FE-SEM after sintering) / (Total number of particles 100 nm or larger in the image taken at 20,000x magnification using FE-SEM after sintering) (1)

[0066] Example 1: 70 parts by volume of silver flake powder (product name "AgC-239") and SiO ２ 30 parts by volume of particles were mixed. This mixed powder was called "Ag-30 volume% SiO ２ It may be referred to as "powder". The above "Ag-30 volume% SiO ２ Mix 100 parts by mass of powder with 21 parts by mass of solvent (product name "DPNP") and Ag-30 volume% SiO ２ "SiO" containing powder ２ -Ag paste was obtained. This paste had a viscosity suitable for use as a bonding paste. ２ -Ag paste was printed onto a silver-plated copper substrate (30 mm x 30 mm x 1 mm thick) using a metal mask to form a coating film approximately 100 μm thick. ２ - A test sample having a layer structure of Ag paste / copper substrate was heated on a hot plate in an air atmosphere at a temperature of 250°C for 60 minutes, and SiO was released. ２ - The silver paste was sintered. The particle sintering rate was 39%.

[0067] Comparative Example 1 70 parts by volume of silver flake powder (product name "AgC-239") and 30 parts by volume of Si particles were mixed. This mixed powder is sometimes referred to as "Ag-30% by volume Si powder". 100 parts by mass of the above "Ag-30% by volume Si powder" was mixed with 21 parts by mass of solvent (product name "DPNP") to obtain a "Si-Ag paste" containing Ag-30% by volume Si powder. This paste had a viscosity suitable for use as a bonding paste. The "Si-Ag paste" was printed onto a silver-plated copper substrate (30 mm x 30 mm x 1 mm thick) using a metal mask to form a coating film with a thickness of approximately 100 μm. The test sample having the obtained Si-Ag paste / copper substrate layer structure was heated on a hot plate in an air atmosphere at a temperature of 250°C for 60 minutes to sinter the Si-Ag paste. The particle sintering rate was 17%.

[0068] In the paste of Example 1, SiO ２ The Ag is sintered at a low temperature of 250°C, and while low-temperature sintering is possible, SiO ２ Because it contains powder, it is less prone to cracking and other defects when bonded to the object to be joined, and furthermore, because it does not contain resin or binder, it has excellent thermal conductivity. On the other hand, the paste of Comparative Example 1 did not contain elemental particles other than silver (B) having silicon oxide on its surface, and therefore the silver flake powder and Si powder could not be bonded.

[0069] Variations of this disclosure are described below. [Note 1] A sinterable bonding paste comprising silver powder (A) and elemental particles other than silver having silicon oxide on its surface (B), wherein it may or may not contain a resin and a binder, and the total content of the resin and the binder is 3 parts by mass or less per 100 parts by mass of the total amount of silver powder (A) and elemental particles other than silver having silicon oxide on its surface (B). [Note 2] The sinterable bonding paste according to Note 1, wherein the average particle size (median diameter; D50) of the silver powder (A) is 0.1 μm to 20 μm. [Note 3] The specific surface area of ​​the silver powder (A) is 0.5 to 4.0 m². ２A sinterable bonding paste according to Appendix 1 or 2, wherein the amount is / g. [Appendix 4] A sinterable bonding paste according to any one of Appendix 1 to 3, wherein the shape of the silver powder (A) is flake-shaped. [Appendix 5] A sinterable bonding paste according to Appendix 4, wherein the average diameter of the silver powder (A) is 0.5 μm to 10 μm. [Appendix 6] A sinterable bonding paste according to Appendix 4 or 5, wherein the thickness of the silver powder (A) is 30 nm to 2 μm. [Appendix 7] A sinterable bonding paste according to any one of Appendix 1 to 6, wherein the average particle size (median diameter; D50) of the elemental particles (B) other than silver having silicon oxide on its surface is 0.1 μm to 100 μm. [Appendix 8] A sinterable bonding paste according to any one of Appendix 1 to 7, wherein the element other than silver in the elemental particles (B) other than silver having silicon oxide on its surface is an element that does not form an intermetallic compound with silver. [Note 9] In the elemental particles other than silver (B) having silicon oxide on the surface, the elemental particles other than silver are silicon particles or SiO ２A sinterable bonding paste according to any one of Appendix 1 to 8, wherein the particles are granular. [Appendix 10] A sinterable bonding paste according to any one of Appendix 1 to 9, wherein the proportion of silicon oxide on the surface of the (B) particle is 30 to 100% of the elemental particles (B) other than silver having silicon oxide on their surface. [Appendix 11] A sinterable bonding paste according to any one of Appendix 1 to 10, wherein the silicon oxide is formed as a layer on the surface of the elemental particles (B) other than silver having silicon oxide on their surface, and the thickness of the layer is 3 nm or more and 300 nm or less. [Appendix 12] A sinterable bonding paste according to any one of Appendix 1 to 11, wherein the ratio (former / latter; mass ratio) of the silver powder (A) to the elemental particles (B) other than silver having silicon oxide on their surface is 5 / 95 to 95 / 5. [Appendix 13] A sinterable bonding paste according to any one of Appendix 1 to 12, wherein the elemental particles (B) other than silver having silicon oxide on their surface are further coated with silver. [Note 14] A sinterable bonding paste according to any one of Notes 1 to 13, further comprising a solvent. [Note 15] The sinterable bonding paste according to Note 14, wherein the solvent content is 1 to 50 parts by mass per 100 parts by mass of the total amount of the silver powder (A) and the elemental particles other than silver having silicon oxide on their surface (B). [Note 16] A sinterable bonding paste according to any one of Notes 1 to 15, which does not include the resin and the binder. [Note 17] A bonding structure in which the object to be bonded is bonded to a substrate via a silver bonding layer containing a sintered body of the sinterable bonding paste according to any one of Notes 1 to 16. [Note 18] The bonding structure according to Note 17, wherein the bonding surface of the object to be bonded with the silver bonding layer is silver plated. [Note 19] The bonding structure according to Note 17 or 18, wherein the object to be bonded is a SiC chip. [Note 20] The bonding structure according to any one of Notes 17 to 19, wherein the substrate is a copper substrate.

[0070] 1: Bonded structure 10: Substrate 20: Silver bonding layer 30: Object to be bonded

Claims

1. A sinterable bonding paste comprising silver powder (A) and elemental particles other than silver having silicon oxide on its surface (B), wherein the paste may or may not contain a resin and a binder, and the total content of the resin and the binder is 3 parts by mass or less per 100 parts by mass of the total amount of silver powder (A) and elemental particles other than silver having silicon oxide on its surface (B).

2. The sinterable bonding paste according to claim 1, wherein the element other than silver in the elemental particles (B) other than silver having silicon oxide on its surface is an element that does not form an intermetallic compound with silver.

3. In the elemental particles other than silver (B) having silicon oxide on the surface, the elemental particles other than silver are silicon particles or SiO ２ A sinterable bonding paste according to claim 1 or 2, which is a particle.

4. The sinterable bonding paste according to claim 1 or 2, wherein in elemental particles (B) other than silver having silicon oxide on their surface, the proportion of silicon oxide on the surface of the (B) particles is 30 to 100%.

5. The sinterable bonding paste according to claim 1 or 2, wherein the silicon oxide is formed as a layer on the surface of elemental particles (B) other than silver having silicon oxide on their surface, and the thickness of the layer is 3 nm or more and 300 nm or less.

6. The sinterable bonding paste according to claim 1 or 2, wherein the ratio (mass ratio) of the silver powder (A) to the elemental particles other than silver having silicon oxide on their surface (B) is 5 / 95 to 95 / 5.

7. The sinterable bonding paste according to claim 1 or 2, wherein the elemental particles (B) other than silver having silicon oxide on their surface are further particles that are partially coated with silver.

8. The sinterable bonding paste according to claim 1 or 2, which does not include the resin and the binder.

9. A bonded structure in which the objects to be bonded are bonded to a substrate via a silver bonding layer containing a sintered body of the sinterable bonding paste described in claim 1 or 2.

10. The joining structure according to claim 9, wherein the joining surface with the silver joining layer of the objects to be joined is silver-plated.

11. The bonding structure according to claim 9, wherein the object to be bonded is a SiC chip.

12. The bonding structure according to claim 9, wherein the substrate is a copper substrate.

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