Electronic device and method of manufacturing electronic device

Abstract

The electronic device of the present application is characterized by having: a substrate; a bonding layer provided on the substrate and containing more than 0 mass% and 60 mass% or less of copper having a crystal grain size of 50 nm or less; an electronic component provided on the bonding layer; and a coating film covering a side surface of the bonding layer and containing at least one compound selected from copper (I) oxide and copper (II) oxide, the copper (I) oxide being Cu2O and the copper (II) oxide being CuO.

Description

Technical Field

[0001] This invention relates to an electronic device and a method for manufacturing the electronic device. Background Technology

[0002] Traditionally, in electronic devices such as LED lights, a method of bonding with silver paste (hereinafter referred to as silver paste) containing a large amount of organic resins such as epoxy resin and silicone resin has been used as a method to ensure the conduction of the light-emitting element and the package while bonding (for example, see Patent Document 1).

[0003] In addition, when it is desired to obtain a bonding layer with higher reliability for the same purpose, gold-tin paste with excellent thermal conductivity and bonding strength is sometimes used (for example, see Patent Document 2).

[0004] In contrast, silver sintering paste using sinterable silver particles has been proposed in recent years (for example, see Patent Document 3). Compared with gold-tin paste, silver sintering paste is cheaper and has superior thermal conductivity and bonding reliability, and is expected to become a substitute for gold-tin paste.

[0005] On the other hand, in the field of automotive LEDs, the sulfur resistance of LEDs has always been a necessary requirement. This is because LEDs are exposed to exhaust gases (SO2) and combustion gases (SO2, H2S), and standardized sulfur resistance test methods such as JIS C 60068-2-42 (1993), JIS C 60068-2-43 (1993), and JIS C 60068-2-60 (2018) have been used to evaluate the sulfur resistance of bonding materials such as silver paste.

[0006] For example, in the case of silver paste, although the above-mentioned vulcanization test revealed an increase in thermal resistance and a decrease in bonding reliability caused by the vulcanization of silver, depending on the content of the resin components, it is sometimes possible to obtain test results that can meet customer requirements.

[0007] However, recently the requirements for sulfur resistance have become even more stringent, with the introduction of extreme tests (hereinafter referred to as sulfur gas (S8) tests) for the use of sulfur powder in automotive LEDs. As a result, the sulfur resistance tests for silver paste have become very rigorous, with silver sintering pastes containing less resin exhibiting even more stringent requirements.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent document 1: Japanese Patent Application Publication No. 2007-67452.

[0011] Patent Document 2: Japanese Patent Application Publication No. 2014-54653.

[0012] Patent document 3: Japanese Patent Application Publication No. 2017-75334. Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] Because sulfur is highly corrosive to silver, electronic devices using silver paste as a bonding material cannot withstand the aforementioned sulfur gas (S8) test. Additionally, copper paste containing copper powder is generally considered as a bonding material because copper is less susceptible to sulfur corrosion than silver. However, even in electronic devices using copper paste as a bonding material, resistance to the aforementioned sulfur gas (S8) test is insufficient.

[0015] The present invention was made in view of the above circumstances, and its object is to provide an electronic device with excellent sulfur resistance and a method for manufacturing the electronic device.

[0016] Methods for solving problems

[0017] The inventors conducted in-depth research to solve the above-mentioned problems and found that the problems can be solved by forming a copper oxide-containing film, wherein the bonding layer contains a specific amount of copper with a crystal grain size of less than 50 nm, and the copper oxide-containing film is formed in such a way as to cover the side of the bonding layer.

[0018] This invention was made based on the following insights.

[0019] That is, the invention in this application relates to the following.

[0020] [1] An electronic device, characterized in that it comprises: a substrate; a bonding layer disposed on the substrate and comprising more than 0% by mass and less than 60% by mass of copper with a crystal grain size of 50 nm or less; an electronic component disposed on the bonding layer; and a coating covering the side of the bonding layer and comprising at least one compound selected from copper oxide (I) and copper oxide (II), wherein the copper oxide (I) is Cu2O and the copper oxide (II) is CuO.

[0021] [2] The electronic device as described in [1] above is characterized in that the bonding layer has a chamfer that protrudes laterally beyond the side end of the electronic component, and the film covers the chamfer.

[0022] [3] The electronic device as described in [1] or [2] above is characterized in that, when the thickness of the coating is denoted as Anm and the proportion of copper oxide (I) present in the copper oxide contained in the coating is denoted as B mass%, it has the following relationship (1), wherein the copper oxide (I) is Cu2O.

[0023] A≥10, B≥20 (1)

[0024] [4] The electronic device described in [3] above is characterized in that, when the thickness of the film is denoted as Anm and the proportion of copper oxide (I) in the copper oxide contained in the film is denoted as B mass%, the following formula (2) is satisfied, wherein the copper oxide (I) is Cu2O.

[0025] B≥1.15×A -0.2 ×100 (2)

[0026] [5] The electronic device as described in any one of [1] to [4] above is characterized in that the electronic component is an optical semiconductor element.

[0027] [6] A vehicle lamp, wherein it is composed of any one of the electronic devices described in any one of [1] to [5] above.

[0028] [7] A street light, wherein it is composed of any one of the electronic devices described in any one of [1] to [5] above.

[0029] [8] A method for manufacturing an electronic device, comprising: a firing step in which a substrate on which electronic components are disposed on copper paste is fired at 125 to 250°C in a reducing environment for 30 minutes to 10 hours, and the substrate and the electronic components are bonded via a copper-containing bonding layer; and an oxidation step in which the substrate is heated at 150 to 250°C in an oxygen-containing environment for 3 minutes to 10 hours, and the sidewalls of the bonding layer are oxidized to form a film comprising at least one compound selected from copper oxide (I) and copper oxide (II), wherein the copper oxide (I) is Cu2O and the copper oxide (II) is CuO.

[0030] The effects of the invention

[0031] The present invention provides an electronic device with excellent sulfur resistance and a method for manufacturing the electronic device. Attached Figure Description

[0032] Figure 1 This is a cross-sectional view showing a schematic configuration of one embodiment of the electronic device of the present invention.

[0033] Figure 2 This is a cross-sectional view showing a schematic configuration of one embodiment of the electronic device of the present invention. Detailed Implementation

[0034] The present invention will now be described in detail with reference to one embodiment.

[0035] <Electronic Devices>

[0036] The electronic device of this embodiment includes: a substrate; a bonding layer disposed on the substrate and containing more than 0% by mass and less than 60% by mass of copper with a crystal grain size of 50 nm or less; an electronic component disposed on the bonding layer; and a coating covering the side of the bonding layer and containing at least one compound selected from copper oxide (I) and copper oxide (II), wherein copper oxide (I) is Cu2O and copper oxide (II) is CuO.

[0037] Figure 1 and Figure 2 This is a cross-sectional view showing a schematic configuration of an embodiment of the electronic device according to the present invention. For example... Figure 1 As shown, the electronic device 10 of the present invention has a bonding layer 2 disposed on a substrate 1, and an electronic component 3 disposed on the bonding layer 2. Furthermore, a film 4 is formed to cover the sides of the bonding layer 2. Additionally, as... Figure 2 As shown, the bonding layer 12 may have a chamfer that protrudes further to the side than the side end of the electronic component 13. In the case that the bonding layer 12 has a chamfer, the film 14 is formed in such a way that it covers the chamfer of the bonding layer 12.

[0038] (Bonding layer)

[0039] The bonding layer is a layer that bonds the substrate to the electronic component, and it contains more than 0% to 60% by mass of copper with a grain size of 50 nm or less. When the bonding layer contains 0% by mass of copper with a grain size of 50 nm or less, there is a risk of deterioration in sinterability. On the other hand, when the bonding layer contains more than 60% by mass of copper with a grain size of 50 nm or less, there is a risk of reduced sulfur resistance in the resulting electronic device. From this point of view, the bonding layer can contain 5% to 55% by mass of copper with a grain size of 50 nm or less.

[0040] The content of copper with a crystal grain size of less than 50 nm in the above-mentioned bonding layer can be adjusted by appropriately adjusting the firing temperature and firing time of the bonding layer.

[0041] It should be noted that the content of copper with a crystal grain size of less than 50 nm in the above-mentioned bonding layer can be determined by electron backscatter diffraction pattern (EBSD) and calculated from the obtained crystal grain size distribution. Specifically, it can be determined by the method described in the embodiments.

[0042] Furthermore, the bonding layer may contain 40% by mass and less than 100% by mass of copper with a crystal grain size exceeding 50 nm, or it may contain 45% to 95% by mass. By including copper with a crystal grain size exceeding 50 nm within the above-mentioned range in the bonding layer, electronic devices with excellent sulfur resistance can be obtained. It should be noted that the upper limit of the above-mentioned copper crystal grain size can be 1000 nm or 500 nm.

[0043] From the perspective of bonding reliability and thermal resistance, the thickness of the bonding layer can be 5–100 μm, 10–80 μm, or 30–50 μm.

[0044] (membrane)

[0045] The coating comprises at least one compound selected from copper oxide (I) (Cu₂O) and copper oxide (II) (CuO). By comprising at least one compound selected from Cu₂O and CuO, the coating is able to inhibit sulfur intrusion into the bonding layer, thereby inhibiting the formation of copper sulfide.

[0046] When the thickness of the film is denoted as A nm and the proportion of copper oxide (I) (Cu2O) in the copper oxide contained in the film is denoted as B mass%, from the viewpoint of improving sulfur resistance, the following relationship (1) can be obtained. Furthermore, by satisfying the following equation (2), an electronic device with excellent resistance to sulfur gas (S8) tests, which are more stringent than existing sulfur gas tests, can be obtained.

[0047] A≥10, B≥20 (1)

[0048] B≥1.15×A -0.2 ×100 (2)

[0049] When the film thickness (average) is 10 nm or more, sulfur intrusion into the bonding layer can be suppressed, thereby inhibiting the formation of copper sulfide. From this perspective, the film thickness can be 30 nm or more, or even 50 nm or more. On the other hand, from the perspective of thermal resistance, the upper limit of the film thickness can be 2000 nm, 1000 nm, or 500 nm.

[0050] The thickness of the aforementioned coating can be adjusted by appropriately regulating the oxidation temperature and oxidation time of the coating.

[0051] It should be noted that the thickness of the aforementioned coating can be measured using field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX), specifically, it can be measured using the methods described in the examples.

[0052] When the proportion of Cu2O in the copper oxide contained in the coating is 20% by mass or more, the sulfur resistance of the obtained electronic device can be improved. From this perspective, the proportion of Cu2O in the copper oxide contained in the coating can be 25% by mass or more, 60% by mass or more, 75% by mass or more, or even 100% by mass.

[0053] The proportion of Cu2O in the copper oxide contained in the above-mentioned coating can be adjusted by appropriately adjusting the oxidation temperature and oxidation time of the coating.

[0054] It should be noted that the proportion of copper oxide (I) (Cu2O) can be determined by X-ray diffraction (XRD) equipment, specifically by the method described in the examples.

[0055] The proportion of copper(II) (CuO) in the copper oxide contained in the coating can be 0–80% by mass, 0–75% by mass, 0–40% by mass, or 0–25% by mass.

[0056] The proportion of copper(II)(CuO) mentioned above can be determined by X-ray diffraction (XRD).

[0057] In addition, the total amount of copper oxide contained in the coating can be 40-100% by mass, 60-100% by mass, or 80-100% by mass.

[0058] (Substrate)

[0059] Examples of substrates include those made of copper, copper-plated copper, PPF (pre-plated lead frame), glass epoxy, ceramics, etc.

[0060] (Electronic components)

[0061] Examples of electronic components include semiconductor elements, heat-generating components, and heat dissipation components.

[0062] As semiconductor components, examples include light semiconductor components (light-emitting elements) such as LEDs, transistors, diodes, etc., which can also be light semiconductor components.

[0063] There are no particular restrictions on the types of optical semiconductor devices. For example, devices that use nitride semiconductors such as InN, AlN, GaN, InGaN, AlGaN, and InGaAlN formed on a substrate as the light-emitting layer can be cited.

[0064] The heat-generating component can be the aforementioned semiconductor element or a component having the semiconductor element, or it can be any other heat-generating component. Examples of heat-generating components other than semiconductor elements include optical pickups and power transistors. Additionally, examples of heat-dissipating components include heat sinks and heat sinks.

[0065] Because the electronic device of the present invention has excellent sulfur resistance, it is suitable for vehicle lamps, street lamps, etc.

[0066] <Methods for Manufacturing Electronic Devices>

[0067] The method for manufacturing an electronic device according to the present invention comprises: a firing step in which a substrate on which electronic components are disposed on copper paste is fired at 125 to 250°C in a reducing environment for 30 minutes to 10 hours, and the substrate and the electronic components are bonded via a copper-containing bonding layer; and an oxidation step in which the substrate is heated at 150 to 250°C in an oxygen-containing environment for 3 minutes to 10 hours, and the side surface of the bonding layer is oxidized to form a film comprising at least one compound selected from copper oxide (I) and copper oxide (II), wherein the copper oxide (I) is Cu2O and the copper oxide (II) is CuO.

[0068] (Firing process)

[0069] In this process, firstly, copper paste is applied to the substrate, and then electronic components are placed on the copper paste.

[0070] The substrate and electronic components described in the above <Electronic Devices> can be used.

[0071] As a copper paste, there are no particular limitations as long as it contains copper particles. It can contain copper particles, large-diameter copper particles with a particle size larger than the copper particles, and organic solvents.

[0072] [Copper particles]

[0073] From the perspective of the density of the bonding layer, the average particle size of copper particles can be 1–1000 nm, 20–800 nm, or 30–500 nm.

[0074] It should be noted that the average particle size of the copper particles mentioned above was calculated as the average of 10 copper particles (n=10) randomly selected from images observed using a scanning electron microscope (e.g., Nippon Electron Ltd., trade name: JSM-7600F; SEM). It should also be noted that the average is an arithmetic mean, and this calculation can use more than 10 copper particles.

[0075] Methods for manufacturing copper particles

[0076] For example, copper particles can be obtained by reducing a copper compound with a reducing compound in the presence of a carboxylic acid amine salt. Alternatively, the copper compound, the carboxylic acid amine salt, and the reducing compound can be mixed in an organic solvent.

[0077] The heating temperature in the above mixture is the temperature at which the copper compound is thermally decomposed and reduced to generate copper particles. For example, it can be 70-150°C or 80-120°C.

[0078] There are no particular limitations on copper compounds as long as they contain copper atoms; examples include copper carboxylate, copper oxide, copper hydroxide, and copper nitride. From the perspective of reaction homogeneity, copper compounds can be copper carboxylate. These can be used alone or in combination of two or more.

[0079] Examples of copper carboxylate include anhydrous or hydrated forms such as copper formate (I), copper acetate (I), copper propionate (I), copper butyrate (I), copper valerate (I), copper hexanoate (I), copper octanoate (I), copper decanoate (I), copper formate (II), copper acetate (II), copper propionate (II), copper butyrate (II), copper valerate (II), copper hexanoate (II), copper octanoate (II), copper decanoate (II), and copper citrate (II). From the viewpoint of productivity and ease of acquisition, copper carboxylate can be copper acetate (II) monohydrate. Furthermore, these can be used alone or in combination of two or more.

[0080] Carboxylic acid amine salts can be produced from carboxylic acid compounds and amine compounds. Commercially available carboxylic acid amine salts can be used, or pre-synthesized carboxylic acid amine salts can be used. Alternatively, during the copper particle manufacturing process, carboxylic acid compounds and amine compounds can be separately added to a reaction vessel for in-situ generation.

[0081] Carboxylic acid amine salts are produced by mixing carboxylic acid and amine compounds in equal amounts with functional groups in an organic solvent under relatively mild temperature conditions, such as room temperature (25°C) to 100°C. The carboxylic acid amine salt can be removed from the reaction solution containing it using methods such as distillation and recrystallization.

[0082] There are no particular limitations on carboxylic acid compounds that constitute carboxylic acid amine salts, as long as they have a carboxyl group. Examples include monocarboxylic acids, dicarboxylic acids, aromatic carboxylic acids, and hydroxy acids. These can be used alone or in combination of two or more.

[0083] As amine compounds constituting carboxylic acid amine salts, there are no particular limitations as long as they contain an amino group; examples include alkyl monoamines, alkyl diamines, and alkanolamines. These can be used alone or in combination of two or more.

[0084] There are no particular limitations on reducing compounds as long as they have the reducing power to reduce copper compounds and ionize metallic copper.

[0085] Hydrazine derivatives are commonly cited as reducing compounds. Examples of hydrazine derivatives include hydrazine monohydrate, methylhydrazine, ethylhydrazine, n-propylhydrazine, isopropylhydrazine, n-butylhydrazine, isobutylhydrazine, sec-butylhydrazine, tert-butylhydrazine, n-pentylhydrazine, isopentylhydrazine, neopentylhydrazine, tert-pentylhydrazine, n-hexylhydrazine, isohexylhydrazine, n-heptylhydrazine, n-octylhydrazine, n-nonylhydrazine, n-decylhydrazine, n-undecylhydrazine, n-dodecylhydrazine, cyclohexylhydrazine, phenylhydrazine, 4-methylphenylhydrazine, benzylhydrazine, 2-phenylethylhydrazine, 2-hydrazinoethanol, and acetylhydrazine. These can be used alone or in combination of two or more.

[0086] The organic solvent used in the manufacture of copper particles can be used without particular limitation, as long as it can be used as a reaction solvent that does not hinder the properties of complexes or the like formed from the mixture obtained by mixing the above-mentioned raw materials. Alcohols that demonstrate compatibility with the above-mentioned reducing compounds can be used as organic solvents.

[0087] Examples of the aforementioned alcohols include 1-propanol, 2-propanol, butanol, pentanol, hexanol, heptanol, octanol, ethylene glycol, 1,3-propanediol, 1,2-propanediol, butyl carbitol, butyl carbitol acetate, ethyl carbitol, ethyl carbitol acetate, diethylene glycol diethyl ether, and butyl cellosolve. These can be used alone or in combination of two or more.

[0088] The amounts of copper compound, carboxylic acid amine salt, and reducing compound used, relative to 1 mol of copper compound, can be 0.1–10 mol of carboxylic acid amine salt and 0.5–5 mol of reducing compound, or 1–5 mol of carboxylic acid amine salt and 0.5–3 mol of reducing compound.

[0089] The amount of organic solvent needed is sufficient to allow the above components to react completely; for example, about 50 to 2000 mL can be used.

[0090] [Large-diameter copper particles]

[0091] The average particle size of large-diameter copper particles can be greater than 1 μm and less than 30 μm, or it can be 1 to 20 μm. In addition, there are no particular limitations on the shape, and spherical, plate-shaped, plate-shaped, scale-shaped, dendritic, rod-shaped, and wire-shaped particles can be used.

[0092] It should be noted that the average particle size of the aforementioned large-diameter copper particles can be determined using a laser diffraction scattering particle size distribution measuring device, etc.

[0093] The aforementioned large-diameter copper particles can be treated with lubricants and rust inhibitors. Such treatment is typically carried out using carboxylic acid compounds. Examples of carboxylic acid compounds include, for example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, octanoic acid, caprylic acid, nonanoic acid, decanoic acid, palmitic acid, oleic acid, stearic acid, isostearic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, diethylene glycol, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, glycolic acid, lactic acid, tartaric acid, malic acid, glyceric acid, hydroxybutyric acid, tartaric acid, citric acid, isocitric acid, etc.

[0094] [Organic solvents]

[0095] Organic solvents that function as reducing agents can use known solvents.

[0096] The aforementioned organic solvents can be alcohols, such as aliphatic polyols. Examples of aliphatic polyols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, glycerol, polyethylene glycol, and other diols. These organic solvents can be used alone or in combination of two or more.

[0097] When combined with an organic solvent, the amount of organic solvent can be 7 to 20 parts by mass when the copper particles are 100 parts by mass. When the amount of organic solvent is 7 parts by mass or more, the viscosity will not become too high, which can improve workability. When it is 20 parts by mass or less, it can suppress viscosity reduction and suppress copper sedimentation in the paste, which can improve reliability.

[0098] In addition to the above-mentioned components, the copper paste may also contain, as needed, thermosetting resins, curing accelerators, rubber, silicone and other low-stress agents, coupling agents, defoamers, surfactants, pigments, dyes and other colorants, various polymerization inhibitors, antioxidants, etc., which are commonly used in such compositions, without hindering the effectiveness of the present invention. Each of these components may be used individually or in combination of two or more.

[0099] The copper paste can be prepared by thoroughly mixing the copper particles and, as needed, large-diameter copper particles and organic solvents, and then further kneading them using a disperser, kneader, three-roll mill, etc., followed by degassing.

[0100] Next, the substrate on which the electronic components are disposed on copper paste is fired at 125 to 250°C in a reducing environment for 30 minutes to 10 hours, and the substrate and the electronic components are bonded together via a copper-containing bonding layer.

[0101] When the firing temperature is below 125°C, there is a risk of poor bonding; when it exceeds 250°C, there is a risk of damaging the LED components. From this perspective, the firing temperature can be 150–230°C or 180–210°C.

[0102] Furthermore, when the firing time is less than 30 minutes, there is a risk that the content of copper with a crystal grain size of less than 50 nm in the bonding layer becomes excessive, which may reduce the sulfur resistance of the obtained electronic device. When the firing time exceeds 10 hours, there is a risk of damaging the LED components. From this point of view, the firing time can be 1 to 4 hours or 1 to 3 hours.

[0103] Examples of reducing environments include, for example, a hydrogen environment, or a mixture of nitrogen and hydrogen in the form of inert gases such as argon and nitrogen and / or syngas, as well as a formic acid environment.

[0104] (Oxidation process)

[0105] In this process, the substrate is heated at 150–250°C in an oxygen-containing environment for 3 minutes to 10 hours to oxidize the side surface of the bonding layer, forming a film containing at least one compound selected from copper oxide (I)(Cu2O) and copper oxide (II)(CuO).

[0106] When the heating temperature (oxidation temperature) is below 150°C, there is a risk of insufficient film formation; when it exceeds 250°C, there is a risk of an increase in the proportion of copper(II) oxide in the film. From this perspective, the heating temperature can be 180–230°C or 190–210°C.

[0107] Furthermore, when the heating time (oxidation time) is less than 3 minutes, there is a risk of insufficient film formation; when it exceeds 10 hours, there is a risk of an increase in the proportion of copper(II) oxide in the film. From this perspective, the heating time can be 0.25 to 4 hours, or 0.5 to 3 hours.

[0108] As an oxygen-containing environment, the atmospheric environment can be cited as an example.

[0109] Example

[0110] The invention will now be described in detail by way of examples, but the invention is not limited to these examples at all.

[0111] (Preparation Example 1) Preparation of carboxylic acid ammonium salts

[0112] 40 mmol of nonanoic acid (manufactured by Tokyo Chemical Industry Co., Ltd., trade name: nonanoic acid) as a carboxylic acid compound and 40 mmol of hexylamine (manufactured by Tokyo Chemical Industry Co., Ltd., trade name: hexylamine) as an amine compound were placed in a 50 mL sample vial and heated to 60°C while stirring / mixing in an aluminum block stirrer. Then, the mixture was stirred / mixed at 60°C for 15 minutes and cooled to room temperature (25°C) to obtain hexylamine nonanoate (yield 10.3 g, 99.2%).

[0113] (Synthesis Example 1) Synthesis of Copper Particles

[0114] 20 mmol of copper(II) acetate monohydrate (manufactured by Tokyo Chemical Industry Co., Ltd., trade name: copper(II) acetate monohydrate), 40 mmol of hexylnonanoate obtained in Preparation Example 1 as a carboxylic acid amine salt, and 3 mL of butyl cellosolve (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic solvent were placed in a 50 mL sample vial and mixed at 90°C for 5 minutes in an aluminum block-type heated stirrer to prepare a copper precursor solution. After cooling the copper precursor solution to room temperature (25°C), a solution containing 20 mmol of hydrazine monohydrate (manufactured by Fujifilm and Kagaku Pure Chemical Co., Ltd., trade name: hydrazine monohydrate), a reducing compound, dissolved in 3 mL of 1-propanol was added to the copper precursor solution in the sample vial and stirred for 5 minutes.

[0115] The mixture was heated and stirred again at 90°C using an aluminum block-type heating stirrer for 2 hours. After 5 minutes, 2 mL of ethanol (manufactured by Kanto Chemical Co., Ltd., premium grade) was added, and the mixture was centrifuged (4000 rpm (1 minute)) to obtain a solid. The centrifuged solid was dried under reduced pressure to obtain copper powder with a copper luster (average particle size 50 nm, yield 0.31 g, 97.8%).

[0116] It should be noted that the average particle size of the copper particles mentioned above was calculated as the average of 10 copper particles (n=10) randomly selected from the observation images of a scanning electron microscope (JEOL Ltd., trade name: JSM-7600F; SEM).

[0117] (Example 1)

[0118] Mix the components listed in Table 1 in terms of type and amount, and knead them with a roller to obtain a bonding paste (copper paste).

[0119] Next, copper paste (manufactured by Sogyo Science & Technology Co., Ltd., trade name: REGAL aluminum substrate) was coated onto a substrate with a thickness of 30 μm after firing. Electronic components (manufactured by Nichia Chemical Co., Ltd., trade name: NVSW119CT) were then disposed on the copper paste. The substrate with the electronic components disposed on the copper paste was then fired at 200°C in a synthesis gas atmosphere for 1 hour, and the substrate and the electronic components were bonded together via a copper-containing bonding layer. Next, the side surfaces of the bonding layer were oxidized by heating the substrate at 250°C in an atmospheric atmosphere for 5 minutes to form a copper oxide film, thereby obtaining the electronic device of Example 1.

[0120] It should be noted that, using an electronic device observed by a scanning electron microscope (JEOL Ltd., trade name: JSM-7600F; SEM), it was confirmed that the bonding layer has a chamfer that protrudes further to the side than the side end of the electronic component, and the film is formed to cover this chamfer.

[0121] (Examples 2-7, Comparative Examples 1 and 2)

[0122] The components of the types and proportions listed in Table 1 were mixed and kneaded using a roller to obtain the bonding paste for each embodiment and comparative example. Using the obtained bonding paste, except for changing the firing temperature, firing time, heating temperature, and heating time as listed in Table 1, the electronic devices for each embodiment and comparative example were obtained by the method described in Example 1.

[0123] The details of each component listed in Table 1 used in the preparation of the bonding paste are as follows.

[0124] Copper particles: Copper particles (average particle size 50 nm) obtained in Synthesis Example 1.

[0125] Silver particles: Spherical silver particles (manufactured by Sannosei K.K. Co., Ltd., trade name: MDot, average particle size 50nm).

[0126] Copper powder: Cu-HWQ (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., trade name, average particle size 1.5μm).

[0127] Silver powder: AgC-212D (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., trade name, average particle size 5μm).

[0128] Organic solvent: diethylene glycol, manufactured by Tokyo Chemical Industry Co., Ltd.

[0129] The electronic devices obtained in the various embodiments and comparative examples were evaluated according to the following methods. The results are shown in Table 1.

[0130] <Evaluation Methods for Electronic Devices>

[0131] (1) The proportion of copper with a crystal grain size of less than 50 nm contained in the bonding layer

[0132] After embedding electronic devices with epoxy resin, the cross-section of the bonding layer is exposed through grinding / polishing / ion beam cross-section polishing (CP). The cross-section of the bonding layer is then analyzed using electron backscatter diffraction with a field emission scanning microscope (Hitachi High Technology Co., Ltd., trade name: SU5000), and a histogram of crystal grain sizes is output. The proportion of crystal grains smaller than 50 nm is calculated from the obtained histogram.

[0133] (2) Thickness of the film

[0134] After embedding electronic devices with epoxy resin, the cross-section of the bonding layer is exposed by grinding / polishing / ion beam profile grinding. Line analysis is performed on the vicinity of the coating using energy dispersive X-ray analysis with a field emission scanning microscope (manufactured by Hitachi High Technology Co., Ltd., trade name: SU5000). The distance at which oxygen atoms are detected is recorded as the coating thickness.

[0135] (3) The proportion of copper oxide (I) relative to the copper oxide contained in the film

[0136] The chamfered portion of the electronic device was analyzed using an X-ray diffraction apparatus (manufactured by Rigaku Corporation, Japan; trade name: SmartLab SE). The quantitative values ​​of copper oxide (I) and copper oxide (II) were calculated using the Ritwald method.

[0137] (4) Sulfurization resistance test A

[0138] According to the four mixed gas test in JIS C 60068-2-60:2018, the electronic device was subjected to a mixed gas (H2S: 10ppb, NO2: 200ppb, Cl2: 10ppb, SO2: 100ppb) at 40°C and 90%RH for 336 hours. The forward voltage (Vf) was measured and the rate of change (rate of rise) relative to the initial value was calculated. The device was then evaluated according to the following criteria.

[0139] A: The rate of increase of Vf is less than 10%.

[0140] B: The rate of increase of Vf is above 10% and less than 20%.

[0141] C: The rate of increase of Vf is over 20%.

[0142] (5) Sulfurization resistance test B

[0143] The electronic device was placed in a glass container containing 1g of sulfur powder. The glass container was then immersed in an oil bath at 100°C. After maintaining this temperature for 900 hours, the forward voltage (Vf) was measured and the rate of change (rate of rise) relative to the initial value was calculated. The device was then evaluated according to the following criteria.

[0144] A: The rate of increase of Vf is less than 10%.

[0145] B: The rate of increase of Vf is above 10% and less than 20%.

[0146] C: The rate of increase of Vf is over 20%.

[0147] [Table 1]

[0148]

[0149] It can be seen that the electronic devices of Examples 1 to 7, which contain copper with a crystal grain size of 50 nm or less in the bonding layer at a proportion of 60% by mass or less and have a copper oxide film covering the sides of the bonding layer, exhibit excellent sulfur resistance with a Vf increase rate of less than 10% in sulfur resistance test A and a Vf increase rate of less than 20% in sulfur resistance test B. On the other hand, the electronic device of Comparative Example 1, which contains copper with a crystal grain size of 50 nm or less in the bonding layer at a proportion of 70% by mass, exhibits poor sulfur resistance with a Vf increase rate of more than 20% in sulfur resistance test A, although the Vf increase rate in sulfur resistance test B is more than 20%. Furthermore, the electronic device of Comparative Example 2, which uses silver paste as the bonding paste, exhibits a Vf increase rate of more than 20% in both sulfur resistance tests A and B, and therefore exhibits poor sulfur resistance compared to the examples.

[0150] Explanation of reference numerals in the attached figures

[0151] 10, 20: Electronic devices; 1, 11: Substrate; 2, 12: Bonding layer; 3, 13: Electronic components; 4, 14: Coating.

Claims

1. An electronic device, characterized in that, It has the following characteristics: substrate; A bonding layer is disposed on the substrate and comprises 5 to 55% by mass of copper with a crystal grain size of less than 50 nm and 45 to 95% by mass of copper with a crystal grain size of more than 50 nm. An electronic component disposed on the bonding layer; as well as A coating covering the sides of the bonding layer and comprising at least one compound selected from copper oxide (I) and copper oxide (II), wherein copper oxide (I) is Cu₂O and copper oxide (II) is CuO. The thickness of the coating is 10 nm or more.

2. The electronic device as claimed in claim 1, characterized in that, The bonding layer has a chamfer that protrudes laterally beyond the side end of the electronic component, and the coating covers the chamfer.

3. The electronic device as claimed in claim 1 or 2, characterized in that, When the thickness of the film is denoted as A nm and the proportion of copper oxide (I) in the copper oxide contained in the film is denoted as B mass%, the following relationship (1) holds, where the copper oxide (I) is Cu2O. A≥10, B≥20 (1).

4. The electronic device as claimed in claim 3, characterized in that, When the thickness of the film is denoted as A nm and the proportion of copper oxide (I) in the copper oxide contained in the film is denoted as B mass%, the following equation (2) is satisfied, and the copper oxide (I) is Cu2O. B≥1.15×A -0.2 ×100 (2)。 5. The electronic device as claimed in any one of claims 1 to 2 and 4, characterized in that, The electronic component is an optical semiconductor element.

6. The electronic device as claimed in claim 3, characterized in that, The electronic component is an optical semiconductor element.

7. A vehicle-mounted light, wherein, It is composed of the electronic device according to any one of claims 1 to 6.

8. A street light, wherein, It is composed of the electronic device according to any one of claims 1 to 6.

9. A method for manufacturing an electronic device, wherein, It has the following characteristics: The firing process involves firing a substrate with electronic components mounted on copper paste at 125–250°C in a reducing environment for 30 minutes to 10 hours, bonding the substrate and the electronic components via a copper-containing bonding layer; and The oxidation process involves heating the substrate at 150–250°C in an oxygen-containing environment for 3 minutes to 10 hours to oxidize the sidewalls of the bonding layer, forming a film containing at least one compound selected from copper oxide (I) and copper oxide (II), wherein copper oxide (I) is Cu₂O and copper oxide (II) is CuO. The bonding layer comprises 5-55% by mass of copper with a crystal grain size of less than 50 nm and 45-95% by mass of copper with a crystal grain size of more than 50 nm. The thickness of the coating is 10 nm or more.

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