Conductive paste, electrode, electronic component, and electronic device

Abstract

Provided is a conductive paste comprising conductive particles (A), binder resin (B), and glass frits (C), wherein the conductive particles (A) have metal particles and a surface treatment layer containing a palladium compound, the surface treatment layer being placed on at least a part of the surface of the metal particles. The softening point of the glass frits (C) is 800 °C or below. Even when containing glass frits with a low softening point, this conductive paste can suppress outflow of glass components from an electrode during firing, and exhibits excellent sulfidation resistance.

Description

Conductive paste, electrodes, electronic components and electronic equipment

[0001] The present invention relates to a conductive paste used, for example, to form electrodes of electronic components, and also to electrodes formed using the conductive paste and electronic components such as chip resistors having such electrodes.

[0002] A conductive paste containing silver powder (silver particles) is used to form the electrodes of a chip resistor, which is a type of electronic component. FIG. 1 shows an example of the cross-sectional structure of a chip resistor 100. The chip resistor 100 has a rectangular alumina substrate 102. On the upper surface of the alumina substrate 102, a resistor 104 and an extraction electrode 106 for extracting electricity from the resistor 104 are formed. On the lower surface of the alumina substrate 102, a lower electrode 108 for mounting the chip resistor 100 to the substrate is formed. Furthermore, a connection electrode 110 for connecting the extraction electrode 106 and the lower electrode 108 is formed on an end surface of the alumina substrate 102. The extraction electrode 106 and the lower electrode 108 are formed by applying a conductive paste to the upper and lower surfaces of the alumina substrate 102 by printing and then firing the paste. Generally, a nickel-plated film 112 and a tin-plated film 114 are formed on the extraction electrode 106 , the lower electrode 108 , and the connection electrode 110 .

[0003] As a conductive paste used to form electrodes, Patent Document 1 discloses a paste for upper electrodes of chip resistors, which is made by dispersing conductive powder, glass frit, and an inorganic binder in an organic vehicle.

[0004] Furthermore, Patent Document 2 discloses a conductive paste containing (A) surface-treated metal particles containing Ag and Sn, (C) glass frit, and (B) a binder resin, in which the weight ratio of Sn in the (A) conductive particles is less than 10 wt %.

[0005] The formation of electrodes using conductive paste is achieved by firing the paste as described above. However, in recent years, the diversification of components due to the high performance of electronic devices and electronic components, consideration of environmental impact, productivity, etc., have led to a demand for the development of conductive pastes that can be fired at low temperatures. ２ O ３ -B ２ O ３ One example is a technique in which a glass component having a low softening point, such as a glass component of the type described above, is contained in a paste (Patent Document 3).

[0006] Japanese Patent Application Laid-Open No. 7-335402 International Publication No. 2021 / 145269 Japanese Patent Application Laid-Open No. 2007-273178

[0007] Firing a conductive paste at low temperatures reduces the thermal load on the adherend and other electronic components, and also reduces energy costs, making it an advantageous method for manufacturing high-definition electronic components. However, the glass component with a low softening point used in Patent Document 3 has high glass fluidity, so it flows out onto the adherend, such as the electronic component substrate, during firing. When the glass component flows out, plating is applied to that area, resulting in a phenomenon known as plating spread, in which the plating is deposited outside the electrode. Furthermore, because the glass component flows out along with the conductive particles in the paste, short circuits and migration may occur at the outflow destination.

[0008] In addition to the leakage of glass components, conductive pastes can also contain other factors that can cause short circuits in electrodes. The combustion of fossil fuels in gasoline-powered automobiles and thermal power plants releases large amounts of sulfur oxides into the atmosphere. Furthermore, in sewage treatment plants and garbage disposal facilities, sulfur is reduced by anaerobic bacteria to produce hydrogen sulfide. Therefore, sulfur-containing components, such as sulfur oxides and hydrogen sulfide, exist in the atmosphere.

[0009] When sulfur-containing components in the atmosphere reach the surface of a metal such as silver, the sulfur components adhere to the surface and react with the metal, forming metal sulfides such as silver sulfide. For example, a similar reaction occurs in electrodes primarily made of silver, such as those found in chip resistors, whereby metals such as silver inside the electrodes can become metal sulfides such as silver sulfide. The formation of metal sulfides such as silver sulfide inside an electrode can cause disconnection in the electrode. Therefore, devices such as chip resistors that have electrodes made of metals such as silver can malfunction. This phenomenon is called disconnection due to sulfurization. Disconnection due to sulfurization can also occur in electrodes made of copper, indium, aluminum, and alloys containing at least one of these materials, in addition to silver.

[0010] To prevent disconnections due to sulfuration, electrodes made primarily of metals such as silver used in devices such as chip resistors need to be highly sulfur-resistant.

[0011] It has been proposed to use palladium alone or to add a predetermined amount (e.g., about 20 wt %) of palladium as conductive particles in a conductive paste to form an electrode with high sulfidation resistance. However, because palladium is expensive, the cost of the conductive paste increases when palladium alone or when palladium is added, which results in a problem of increased cost for the electrode.

[0012] In view of the above problems, the present invention aims to provide a conductive paste that can suppress the outflow of glass components from the electrode during firing, even when it contains glass frit with a low softening point, and that has excellent sulfidation resistance.

[0013] In order to solve the above problems, the present invention has the following configuration.

[0014] (Configuration 1) Configuration 1 is a conductive paste comprising: (A) conductive particles; (B) a binder resin; and (C) a glass frit, wherein the conductive particles of (A) have a surface treatment layer containing metal particles and a palladium compound disposed on at least a portion of the surface of the metal particles; and the softening point of the glass frit of (C) is 800°C or lower.

[0015] (Configuration 2) Configuration 2 is the conductive paste of configuration 1, wherein the content of the palladium compound contained in the surface treatment layer is 0.01 to 1.0 parts by weight per 100 parts by weight of the metal particles.

[0016] (Configuration 3) Configuration 3 is the conductive paste of configuration 1 or 2, in which the surface treatment layer further contains an organic substance.

[0017] (Configuration 4) Configuration 4 is the conductive paste of any one of Configurations 1 to 3, wherein the metal particles contain 50% or more by weight of silver.

[0018] (Configuration 5) Configuration 5 is the conductive paste of any one of Configurations 1 to 4, wherein the average particle size (D50) of the (A) conductive particles is 0.1 to 10 μm.

[0019] (Configuration 6) Configuration 6 is the conductive paste of configuration 5, in which the average particle size (D50) of the conductive particles (A) is 0.1 to 6 μm.

[0020] (Configuration 7) Configuration 7 is an electrode obtained by firing or heat treating the conductive paste of any one of configurations 1 to 6 above.

[0021] (Configuration 8) Configuration 8 is an electronic component or electronic device including the electrode of configuration 7.

[0022] According to the present invention, even when a glass frit having a low softening point is contained, it is possible to provide a conductive paste that can suppress the outflow of glass components from the electrode during firing and has excellent sulfuration resistance.

[0023] 1 is a schematic diagram showing an example of the cross-sectional structure of a chip resistor. FIG. 1 is a schematic diagram showing the shape of a test piece for sulfurization resistance tests in Examples and Comparative Examples. FIG. 2 is an optical microscope photograph showing the shape of a test print pattern of a test piece for migration resistance tests in Examples and Comparative Examples. FIG. 3 is an optical microscope photograph enlarging the center of the optical microscope photograph of the test print pattern of a test piece for migration resistance tests shown in FIG. 3. FIG. 4 is a scanning electron microscope (SEM) photograph (magnification: 5000x) of the surface of a fired body of a conductive paste after a test piece prepared under the same conditions as in Example 3 has been stored in a gas atmosphere containing sulfur for 150 hours to be sulfurized. FIG. 5 is a scanning electron microscope (SEM) photograph (magnification: 5000x) of the surface of a fired body of a conductive paste after a test piece prepared under the same conditions as in Comparative Example 1 has been stored in a gas atmosphere containing sulfur for 150 hours to be sulfurized. FIG. 6 is a diagram showing the change over time in insulation resistance values ​​of Example 1, Example 3, and Comparative Example 1 when a migration resistance test is performed. 1 shows backscattered electron images (magnification: 500 times) of the side surfaces of the thick electrode films of Examples 20 and 23 and Comparative Examples 6 and 9 after firing, taken with an SEM.

[0024] Hereinafter, embodiments of the present invention will be described in detail. Note that the following embodiments are forms for realizing the present invention, and are not intended to limit the scope of the present invention.

[0025] The conductive paste of this embodiment includes (A) conductive particles, (B) a binder resin, and (C) a glass frit having a softening point of 800°C or less. The conductive paste of this embodiment can be preferably used to form electrodes for electronic components such as chip resistors. The (A) conductive particles include metal particles and a surface treatment layer containing a palladium compound disposed on at least a portion of the surface of the metal particles.

[0026] First, the components contained in the conductive paste of this embodiment will be described.

[0027] <(A) Conductive Particles> The conductive paste of this embodiment contains (A) conductive particles. The (A) conductive particles contain metal particles and a surface treatment layer disposed on at least a portion of the surface of the metal particles. The surface treatment layer is a thin film containing a palladium compound. The surface treatment layer is formed by surface treating the metal particles with the palladium compound. It is believed that the presence of the surface treatment layer on the (A) conductive particles appropriately controls the sintering rate, thereby enabling the glass frit to be retained without flowing out during the firing process. Furthermore, the inclusion of specified surface-treated metal particles in the (A) conductive particles can suppress sulfurization of the metal contained in the conductive particles. Therefore, by using the conductive paste of this embodiment, an electrode with high sulfurization resistance can be formed.

[0028] The inventors of the present invention have discovered that the inclusion of specific surface-treated metal particles in the (A) conductive particles of the conductive paste of this embodiment also improves the migration resistance of the resulting electrode as an additional effect. Migration resistance refers to the ability to suppress migration. Migration is a phenomenon in which, when a voltage is applied to a pair of electrodes (positive and negative electrodes), if water and / or water vapor is present near the electrodes, the metal contained in the electrodes and wiring ionizes and migrates from the positive electrode to the negative electrode, generating metal dendrites and reducing the insulation between the wiring. Migration may also occur even in an atmosphere unaffected by moisture, such as at temperatures above 100°C or in a vacuum. In this case, even if the pair of electrodes are close to a short circuit, dendrites, which are always observed when migration occurs in the presence of moisture, are not generated between the wiring, and no polarity is observed (i.e., migration occurs regardless of the polarity of the positive and negative electrodes). Migration resistance refers to the ability to suppress this type of migration, which has been widely known in the past. Metal migration can cause a pair of electrodes to short-circuit. Improved migration resistance can prevent short-circuiting of the electrodes. However, the advantage of improved migration resistance is not necessarily an essential effect of the conductive paste of this embodiment, but is considered to be one of its advantages.

[0029] The (A) conductive particles may contain metals other than the surface-treated metal particles. However, in order to reliably obtain an electrode that has low electrical resistance, suppresses the outflow of glass frit during firing, and has high sulfidation resistance, the (A) conductive particles preferably contain 50 wt % or more of surface-treated metal particles, more preferably contain 80 wt % or more of surface-treated metal particles, even more preferably contain 90 wt % or more of surface-treated metal particles, and particularly preferably consist of only surface-treated metal particles. In this specification, the phrase "the (A) conductive particles consist only of surface-treated metal particles" means that no metal other than the surface-treated metal particles is intentionally blended into the (A) conductive particles, and does not exclude the inclusion of conductive particles other than the surface-treated metal particles that are inevitably mixed in.

[0030] The (A) conductive particles may contain metal particles of materials such as Zn, In, Al, and / or Si as metal particles other than the surface-treated metal particles, as long as the effects of this embodiment are not impaired. The metal particles contained in the surface-treated metal particles and the metal particles other than the surface-treated metal particles may be metal particles of an alloy. Furthermore, the metal particles contained in the surface-treated metal particles and the metal particles other than the surface-treated metal particles may contain metal particles of multiple different metals or alloys.

[0031] The surface-treated metal particles include metal particles and a surface treatment layer disposed on at least a portion of the surface of the metal particles. The surface treatment layer is a thin film formed on at least a portion of the surface of the metal particles. By surface-treating the metal particles with a palladium compound, the surface treatment layer can be formed on at least a portion of the surface of the metal particles. Therefore, the surface-treated metal particles can be metal particles that have been surface-treated with a palladium compound.

[0032] The material of the metal particles to be surface-treated with a palladium compound can be Ag, Cu, In, Al, or an alloy thereof. Because of their relatively high electrical conductivity, the material of the metal particles is preferably Ag and / or Cu, and more preferably Ag.

[0033] In the conductive paste of this embodiment, the metal particles preferably contain 50 wt % or more of silver (Ag), more preferably 80 wt % or more of silver (Ag), even more preferably 90 wt % or more of silver (Ag), and particularly preferably 95 wt % or more of silver (Ag). In the most preferred embodiment, the surface-treated metal particles contained in the conductive paste of this embodiment consist solely of silver (Ag) particles. This is because the electrical conductivity of silver is relatively high compared to other metals. Note that in this specification, the phrase "the surface-treated metal particles consist solely of silver (Ag) particles" means that no metal particles other than silver (Ag) particles are intentionally used as the metal particles, and does not exclude the inclusion of metal particles other than silver (Ag) particles that are unavoidably mixed in. Similarly, other similar descriptions do not exclude unavoidable contaminants.

[0034] The conductive paste of this embodiment preferably contains 50 parts by weight or more, more preferably 70 parts by weight or more, and even more preferably 80 parts by weight or more of the surface-treated metal particles per 100 parts by weight of the conductive paste. The conductive paste of this embodiment preferably contains 50 to 99 parts by weight, more preferably 70 to 97 parts by weight or more, and even more preferably 80 to 95 parts by weight of the surface-treated metal particles per 100 parts by weight of the conductive paste. By satisfying the above range, a relatively low-cost electrode can be formed while exhibiting high sulfidation resistance and fully demonstrating the effect of suppressing the outflow of glass frit.

[0035] The method for producing the metal particles is not particularly limited, and they can be produced by, for example, a reduction method, a pulverization method, an electrolysis method, an atomization method, a heat treatment method, or a combination thereof. Flake-shaped metal particles can be produced, for example, by crushing spherical or granular metal particles using a ball mill or the like.

[0036] The surface-treated metal particles include a surface treatment layer disposed on at least a portion of the surface of the metal particles. The surface treatment layer is a thin film formed on at least a portion of the surface of the metal particles by surface treating the metal particles with a surface treatment agent containing a palladium compound.

[0037] The palladium compound used as a raw material for surface treatment of metal particles can be at least one selected from palladium(II) chloride, palladium(II) oxide, organic palladium compounds, palladium fluoride, palladium on carbon, n-allyl palladium complexes, cyclopentadienylallyl palladium, dichlorobis(triphenylphosphine)palladium(II), palladium bromide, and palladium complexes such as fatty acid complexes of palladium, such as palladium oleate. Palladium chloride is preferably used as the palladium compound used as a raw material for surface treatment of metal particles.

[0038] The surface treatment layer can be formed by surface treatment using a palladium compound by a known method. Specifically, the surface treatment layer is formed by attaching a palladium soap solvent (surface treatment agent) containing palladium or palladium ions, an organic substance for dispersing them, and a solvent to the surface of metal particles, followed by drying to remove the solvent. This allows a surface treatment layer containing a palladium compound to be formed on the surface of the metal particles. There is also a technique for forming a core-shell structure by coating the surface of metal particles with other metal particles through reduction treatment. However, when attempting to form a surface treatment layer using this technique, the amount of palladium metal particles present in the shell increases in order to precipitate a shell (e.g., palladium metal particles) on the surface of a core particle (e.g., silver particle). In other words, a large amount of palladium is used. On the other hand, in the present invention, the surface treatment layer is formed in a state in which a palladium compound is attached to the surface of the metal particle, thereby achieving the effect of allowing only a small amount of palladium to be used. Palladium is an expensive metal due to its scarcity and uneven distribution, and even a small amount has excellent sulfidation resistance and can suppress the outflow of glass components, which is an extremely important effect from a cost perspective.

[0039] The organic substance for dispersing palladium or palladium ions is preferably at least one selected from fatty acids and triazole compounds. When a fatty acid is used as the solvent, the fatty acid may be at least one selected from butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, palmitoleic acid, margaric acid, stearic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, arachidic acid, eicosadienoic acid, eicosatrienoic acid, eicosatetraenoic acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, cerotic acid, montanic acid, and melissic acid. Among these fatty acids, it is preferable to use at least one selected from palmitic acid, stearic acid, and oleic acid. It is more preferable to use oleic acid as the organic substance (fatty acid) contained in the surface treatment agent. When a triazole compound is used as the organic substance for dispersing palladium or palladium ions, benzotriazole can be used as the triazole compound.

[0040] The solvent contained in the surface treatment agent for forming the surface treatment layer may be any solvent that disperses palladium or palladium ions and effectively adheres the palladium compound to the metal particles. Examples of the solvent include alcohols such as methanol, ethanol, and isopropyl alcohol (IPA), organic acids such as ethylene acetate, aromatic hydrocarbons such as toluene and xylene, N-alkylpyrrolidones such as N-methyl-2-pyrrolidone (NMP), amides such as N,N-dimethylformamide (DMF), ketones such as methyl ethyl ketone (MEK), cyclic carbonates such as terpineol (TEL) and diethylene glycol monobutyl ether (butyl carbitol, BC), bis[2-(2-butoxyethoxy)ethyl]adipate, 2,2,4-trimethylpentane-1,3-diol monoisobutyrate (Texanol), and water.

[0041] A surface treatment agent containing the above-mentioned palladium compound dispersed in a solvent is applied to the surface of metal particles, and the solvent is then removed by drying, thereby forming a surface treatment layer on the surface of the metal particles. In this way, surface-treated metal particles can be obtained.

[0042] The surface-treated layer of surface-treated metal particles can be produced as follows. First, metal particles are dispersed in water. A solvent containing the aforementioned palladium compound dispersed therein as a coating agent is added to the water containing the dispersed metal particles to obtain an aqueous slurry containing metal particles coated with a palladium-containing coating agent. The metal particles coated with the coating agent are then allowed to settle by decantation. The supernatant is then removed, and the resulting wet metal particles coated with the coating agent are added to a polar solvent with a boiling point of 150 to 300°C together with an acrylic dispersant. The surface-treated metal particles can then be produced by drying in a nitrogen atmosphere at a temperature between room temperature and 100°C, preferably at a temperature of 80°C or lower, for 12 hours or longer to remove moisture. Note that drying at an excessively high temperature is undesirable because it can sinter the surface-treated metal particles.

[0043] The surface-treated metal particles contained in the conductive paste of this embodiment preferably further contain an organic substance. For example, when the surface-treated layer is formed using the above-mentioned palladium compound, the surface-treated layer contains an organic substance. By having the surface-treated metal particles have a surface-treated layer containing an organic substance, the resulting electrode can have high sulfidation resistance even with a small amount of palladium compound. The organic substance may be a liquid organic fatty acid or a solid fatty acid. Examples of liquid fatty acids include saturated fatty acids such as butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, and pelargonic acid, and unsaturated fatty acids such as myristoleic acid, palmitoleic acid, ricinoleic acid, oleic acid, linoleic acid, and linolenic acid. These fatty acids may be used alone or in combination of two or more. Among these, oleic acid, linoleic acid, or a mixture thereof is preferably used. Examples of solid fatty acids include saturated fatty acids having 10 or more carbon atoms, such as capric acid, palmitic acid, and stearic acid, and unsaturated fatty acids, such as crotonic acid and sorbic acid.

[0044] The surface treatment layer of the surface-treated metal particles used in this embodiment is a thin film of a palladium compound. This embodiment is characterized in that the surface treatment layer of the surface-treated metal particles is not a thin film made of palladium metal or a palladium alloy. If the surface treatment layer is a thin film made of palladium metal or a palladium alloy, the amount of palladium mixed may be too high, which may have adverse effects such as an increase in the electrical resistance of the resulting electrode. Furthermore, the presence of a large amount of palladium metal or palladium alloy on the surface of the metal particles after firing may reduce the wettability of the solder to metal particles such as silver particles, increasing the possibility of impeding soldering. Furthermore, the use of a large amount of palladium increases costs.

[0045] The surface treatment layer is a thin film formed on at least a portion of the surface of the metal particle. The surface treatment layer is preferably a thin film covering 50% or more of the surface of the metal particle, more preferably a thin film covering 80% or more of the surface of the metal particle, preferably a thin film covering 90% or more of the surface of the metal particle, and particularly preferably a thin film covering 95% or more of the surface of the metal particle. The surface treatment layer is most preferably a thin film covering the entire surface of the metal particle.

[0046] The thickness of the surface treatment layer of the surface-treated metal particles does not necessarily need to be uniform, but a uniform thickness is preferable in order to more effectively suppress sulfurization of the metal particles. The thickness of the surface treatment layer can be controlled, for example, by adjusting the viscosity of a palladium soap solvent (surface treatment agent) in which a palladium compound is dispersed in a solvent, and the concentration of the palladium compound in the palladium soap solvent (surface treatment agent). Furthermore, by controlling the thickness of the surface treatment layer, the amount of palladium contained in the surface treatment layer can be controlled. The thickness of the surface treatment layer is preferably 1 to 100 nm or less, more preferably 1 to 70 nm or less, and particularly preferably 1 to 50 nm or less. The thickness of the surface treatment layer can be measured, for example, by X-ray photoelectron spectroscopy. By setting the thickness of the surface treatment layer within this range, an electrode with high sulfurization resistance can be formed while using a small amount of palladium compound.

[0047] The conductive paste of this embodiment contains, as the (A) conductive particles, surface-treated metal particles that have been surface-treated with a palladium compound, so that an electrode having high sulfurization resistance can be formed without using a large amount of expensive palladium. Therefore, by using the conductive paste of this embodiment, an electrode having high sulfurization resistance and relatively low cost can be formed. In particular, when silver particles are used as the metal particles, silver is easily sulfurized. By using the conductive paste of this embodiment, disconnection of an electrode primarily made of silver due to sulfurization can be effectively prevented at low cost.

[0048] For example, when silver particles are used as metal particles, the reason why sulfurization of the silver particles can be suppressed by using surface-treated metal particles (surface-treated silver particles) surface-treated with a palladium compound can be inferred as follows. That is, it is presumed that the sulfurization resistance is improved by sintering palladium as the surface treatment component and the metal particles to form a uniform alloy layer. For example, palladium in the palladium compound exists with the metal particles as a palladium metal alloy layer (a palladium-silver alloy layer when the metal particles are silver particles) by firing at 400 to 900°C. This palladium metal alloy layer is thought to impart high sulfurization resistance to the metal particles. Note that the palladium content in the surface treatment layer is not very high. Therefore, compared to the case where palladium particles are added separately, a smaller amount of palladium is required, and high sulfurization resistance can be obtained at a relatively low cost. The electrode obtained in this manner has high sulfurization resistance and excellent adhesion to the substrate. The same inference can be applied to metal particles other than silver particles. However, the present invention is not bound by this inference.

[0049] The (A) conductive particles of the conductive paste of this embodiment contain specific surface-treated metal particles, which additionally improves the migration resistance of the resulting electrode. The reason why the use of surface-treated metal particles (surface-treated silver particles) surface-treated with a palladium compound can improve migration resistance is that the use of surface-treated metal particles surface-treated with a palladium compound improves the density of the electrode while retaining the migration resistance effect of palladium. It is presumed that this improves migration resistance. However, the present invention is not bound by this reasoning.

[0050] In the conductive paste of this embodiment, the content of palladium contained in the surface-treated metal particles is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, and particularly preferably 0.08 parts by weight or more, per 100 parts by weight of the metal particles. Furthermore, the content of palladium is preferably 1.0 parts by weight or less, more preferably 0.8 parts by weight or less, even more preferably 0.6 parts by weight or less, particularly preferably 0.4 parts by weight or less, and most preferably 0.3 parts by weight or less, per 100 parts by weight of the metal particles. By having the palladium content of the surface-treated metal particles within the above range, the amount of palladium used can be reduced, and the change in electrode resistance due to electrode sulfurization can be minimized while maintaining low cost. The palladium content of the surface-treated metal particles can be measured by ICP atomic emission spectroscopy (inductively coupled plasma atomic emission spectroscopy).

[0051] The shape of the (A) conductive particles is not particularly limited, and for example, spherical, granular, flake-shaped and / or scale-shaped surface-treated metal particles can be used.

[0052] The average particle size of the (A) conductive particles is preferably 0.1 μm to 10 μm, more preferably 0.2 μm to 8 μm, even more preferably 0.3 μm to 7 μm, and particularly preferably 0.4 to 6 μm. The average particle size here refers to the volume-based median diameter (D50) obtained by a laser diffraction / scattering particle size distribution measurement method. If the average particle size (D50) of the (A) conductive particles is greater than 10 μm, sintering properties are poor and a dense film cannot be obtained. Furthermore, if the average particle size (D50) of the (A) conductive particles is less than 0.1 μm, dispersibility tends to be poor, and it may be difficult to obtain a uniform thin film when the conductive paste is printed.

[0053] <(B) Binder Resin> The conductive paste of this embodiment contains (B) a binder resin.

[0054] Because the conductive paste of this embodiment contains (C) glass frit, an electrode can be formed by applying the conductive paste of this embodiment to a predetermined substrate so as to form a predetermined electrode pattern and firing the paste at, for example, 400 to 900°C. In this case, the binder resin (B) is burned away during firing. Therefore, the function of the binder resin (B) is to bind the conductive particles (A) together when the conductive paste of this embodiment is applied to a predetermined substrate so as to form a predetermined electrode pattern.

[0055] Examples of the binder resin (B) that can be used include cellulose-based resins such as ethyl cellulose resin and nitrocellulose resin, and thermoplastic resins such as acrylic resin, alkyd resin, saturated polyester resin, butyral resin, polyvinyl alcohol, and hydroxypropyl cellulose. These resins can be used alone or in combination of two or more.

[0056] As the binder resin (B), it is preferable to use at least one selected from cellulose-based resins such as ethyl cellulose resin and nitrocellulose resin, and alkyd resins.

[0057] The conductive paste of this embodiment may contain an epoxy resin as a binder resin (B) to improve adhesion between the surface-treated metal particles. The type of epoxy resin is not particularly limited, and known epoxy resins can be used. Examples of epoxy resins include bisphenol A, bisphenol F, biphenyl, tetramethylbiphenyl, cresol novolac, phenol novolac, bisphenol A novolac, dicyclopentadiene phenol condensation, phenol aralkyl condensation, and glycidylamine epoxy resins, as well as brominated epoxy resins, alicyclic epoxy resins, and aliphatic epoxy resins. These epoxy resins can be used alone or in combination of two or more. Furthermore, thermosetting resins other than epoxy resins may be used to improve adhesion between the surface-treated metal particles. Furthermore, thermoplastic resins such as polyurethane resins and / or polycarbonate resins may also be used.

[0058] The content of the (B) binder resin is preferably 0.1 to 30 parts by weight, more preferably 0.5 to 15 parts by weight, even more preferably 1 to 10 parts by weight, and particularly preferably 1.5 to 8 parts by weight, relative to 100 parts by weight of the (A) conductive particles. When the content of the (B) binder resin in the conductive paste is within the above range, the coating properties of the conductive paste onto the substrate (base material) and / or the paste leveling properties are improved, and an excellent print shape can be obtained. On the other hand, when the content of the (B) binder resin exceeds the above range, the amount of the (B) binder resin contained in the applied conductive paste is too high. As a result, it may be impossible to form electrodes, etc., with high precision.

[0059] <(C) Glass Frit> The conductive paste of this embodiment further contains (C) glass frit. The conductive paste of this embodiment is applied to a predetermined substrate so as to form a predetermined electrode pattern, and then fired at, for example, 400 to 900°C, thereby forming an electrode. In this case, the above-mentioned (B) binder resin is burned away during firing. The (C) glass frit contained in the conductive paste bonds the (A) conductive particles together, thereby allowing the shape of the electrode to be maintained after firing.

[0060] The glass frit is not particularly limited as long as it has a softening point of 800°C or less, but preferably has a softening point of 250°C or more, more preferably a softening point of 250 to 800°C, even more preferably a softening point of 250 to 750°C, and particularly preferably a softening point of 300 to 700°C. By using glass frit with a softening point of 800°C or less, firing can be carried out at a relatively low temperature. However, glass frit with a softening point of 800°C or more can also be used in combination, as long as the effects of the present invention are not impaired. The softening point of the glass frit can be measured using a thermogravimetric analyzer (for example, TG-DTA2000SA, manufactured by BRUKER AXS).

[0061] Examples of the (C) glass frit include borosilicate-based and barium borosilicate-based glass frits. Examples of the glass frit include bismuth borosilicate-based, alkali metal borosilicate-based, alkaline earth metal borosilicate-based, zinc borosilicate-based, lead borosilicate-based, lead borate-based, lead silicate-based, bismuth borate-based, and zinc borate-based glass frits. Two or more of these glass frits can also be used in combination. From the viewpoint of environmental considerations, the glass frit is preferably lead-free.

[0062] The glass frit is made of ZnO, Bi ２ O ３ , BaO, Na ２ O, CaO and Al ２ O ３ The glass frit preferably contains at least one selected from the group consisting of ZnO and Bi. ２ O ３ It is more preferable that the composition contains at least one selected from the group consisting of:

[0063] The glass frit more preferably contains ZnO. When a glass frit containing ZnO (zinc-based glass frit) is used as the glass frit, an electrode with higher sulfidation resistance can be obtained.

[0064] The glass frit is Bi ２ O ３ It is more preferable that the glass frit contains Bi. ２ O ３ When a glass frit containing bismuth (bismuth-based glass frit) is used, the density of the electrode can be improved.

[0065] The average particle size of the glass frit is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm, and particularly preferably 0.5 to 5 μm. The average particle size here refers to the volume-based median diameter (D50) obtained by a laser diffraction / scattering particle size distribution measurement method.

[0066] The content of (C) glass frit is preferably 0.05 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, even more preferably 1 to 6 parts by weight, and particularly preferably 2 to 4 parts by weight, per 100 parts by weight of (A) conductive particles. If the content of glass frit is less than this range, the adhesion of the electrode obtained by firing the conductive paste to the substrate (base material) decreases. If the content of glass frit is greater than this range, the resistance of the electrode obtained by firing the conductive paste increases, and the surface of the fired body is covered with glass components, resulting in poor plating adhesion. Note that when the content of glass frit is relatively low, an electrode with low resistance can be obtained. Furthermore, when the content of glass frit is relatively high, an electrode with excellent chemical resistance can be obtained. Chemical resistance is a required characteristic because plating pretreatment is necessary when forming a plating film on the surface of an electrode. Plating pretreatment is performed to remove contaminants from the electrode surface, activate the electrode surface, and make it clean and suitable for plating. Contaminants to be removed can be broadly divided into organic and inorganic contaminants. The pretreatment process is not a single process that removes all contaminants. For example, organic substances are removed using an alkaline cleaning agent, while inorganic substances are removed using an acid cleaning agent. Therefore, the electrodes must have high chemical resistance.

[0067] When the conductive paste of this embodiment contains zinc oxide as the (C) glass frit, the Zn component in the glass frit precipitates as ZnO at the crystallization temperature. At this time, the crystallized glass component precipitates on the surface of the fired body, and the glass frit can contribute to the sulfurization resistance of the (A) conductive particles after firing, similar to palladium in the surface-treated metal particles.

[0068] <(D) Additive> The conductive paste of the present embodiment may contain a dispersant as the additive (D). By containing a dispersant in the conductive paste of the present embodiment, the dispersibility of the conductive particles (A) in the conductive paste can be improved, and the aggregation of the conductive particles (A) can be prevented.

[0069] As the dispersant, a known dispersant can be used. Examples of the dispersant include fatty acid amides, acid-type low-molecular dispersants, and bismuth oxide (Bi ２ O ３ ) can be used.

[0070] The conductive paste of the present embodiment may contain, as additives (D) other than the dispersant, organic additives, inorganic additives, etc. Examples of additives (D) that can be used include silica filler, rheology modifiers, and / or pigments.

[0071] By adding an organic additive to the conductive paste as a (D) additive, the printability of the conductive paste can be improved. By adding a dispersant to the conductive paste as a (D) additive, the dispersibility of the (A) conductive particles and the like can be improved. By adding an inorganic additive to the conductive paste as a (D) additive, the adhesion of the conductive paste after firing can be improved.

[0072] <(E) Solvent> The conductive paste of this embodiment may contain (E) a solvent. Examples of the solvent include alcohols such as methanol, ethanol, and isopropyl alcohol (IPA), organic acids such as ethylene acetate, aromatic hydrocarbons such as toluene and xylene, N-alkylpyrrolidones such as N-methyl-2-pyrrolidone (NMP), amides such as N,N-dimethylformamide (DMF), ketones such as methyl ethyl ketone (MEK), cyclic carbonates such as terpineol (TEL) and diethylene glycol monobutyl ether (butyl carbitol, BC), bis[2-(2-butoxyethoxy)ethyl]adipate, 2,2,4-trimethylpentane-1,3-diol monoisobutyrate (Texanol), and water.

[0073] The content of the solvent in the conductive paste of this embodiment is not particularly limited and is, for example, preferably 1 to 100 parts by weight, more preferably 5 to 60 parts by weight, and even more preferably 8 to 35 parts by weight, relative to 100 parts by weight of the (A) conductive particles.

[0074] The viscosity of the conductive paste of this embodiment is preferably 50 to 700 Pa·s (shear rate: 4.0 sec －１ ), more preferably 100 to 300 Pa·s (shear rate: 4.0 sec －１ ). The viscosity of the conductive paste of this embodiment can be adjusted by appropriately controlling the content of the solvent. By adjusting the viscosity of the conductive paste to this range, the coating and / or handling properties of the conductive paste onto a substrate (base material) become good, and it becomes possible to apply the conductive paste to the substrate with a uniform thickness. The viscosity of the conductive paste can be measured using an HB-type viscometer (manufactured by Brookfield) (SC4-14 spindle) at a temperature of 25°C and 10 rpm.

[0075] <(F) Curing Agent> The conductive paste of the present embodiment may further contain a (F) curing agent. When the conductive paste of the present embodiment contains an epoxy resin as the (B) binder resin, the inclusion of the (F) curing agent makes it possible to appropriately control the curing of the epoxy resin.

[0076] The (F) curing agent may be a known curing agent. The (F) curing agent preferably includes at least one selected from a phenolic curing agent, a cationic polymerization initiator, an imidazole curing agent, and a boron trifluoride compound. Examples of the boron trifluoride compound include boron trifluoride monoethylamine, boron trifluoride piperidine, and boron trifluoride diethyl ether. The (F) curing agent preferably includes boron trifluoride monoethylamine.

[0077] In the conductive paste of this embodiment, when the total weight of the (A) conductive particles and the (B) epoxy resin binder resin is taken as 100 parts by weight, the conductive paste preferably contains 0.1 to 5 parts by weight, more preferably 0.15 to 2 parts by weight, even more preferably 0.2 to 1 part by weight, and particularly preferably 0.3 to 0.6 parts by weight of the (F) curing agent. By setting the weight ratio of the (F) curing agent within a predetermined range, the epoxy resin, which is the (B) binder resin component, can be appropriately cured, and an electrode of the desired shape can be obtained.

[0078] The conductive paste of this embodiment can be produced by mixing the above components using, for example, a mortar and pestle mixer, a pot mill, a three-roll mill, a rotary mixer, and / or a twin-screw mixer.

[0079] <Electrode> This embodiment is an electrode obtained by firing or heat treating the conductive paste of this embodiment described above.

[0080] An electrode can be formed by applying the conductive paste of this embodiment to a predetermined substrate in a predetermined electrode pattern and firing the paste in an air atmosphere, for example, at 400 to 900°C. Therefore, since the conductive paste of this embodiment contains (C) glass frit, the formed electrode can contain (A') conductive particles containing surface-treated metal particles and (C') glass component made from (C) glass frit. After firing, the (A') conductive particles are in a sintered state. Note that when the conductive paste of this embodiment is fired at, for example, 400 to 900°C, the (B) binder resin and (E) solvent contained in the conductive paste are vaporized or burned during firing. Therefore, the electrode is substantially free of the (B) binder resin and (E) solvent.

[0081] The surface-treated metal particles contained in the conductive paste of this embodiment are surface-treated with a palladium compound, and therefore the electrode of this embodiment contains palladium. The electrode of this embodiment preferably contains 0.01 to 10 wt % palladium, more preferably 0.05 to 5 wt %, even more preferably 0.07 to 1 wt %, and particularly preferably 0.08 to 0.5 wt % palladium. When the conductive paste of this embodiment contains (C) glass frit, the electrode of this embodiment may contain palladium resulting from the (C) glass frit. By including a predetermined amount of palladium in the electrode of this embodiment, the electrode of this embodiment can have high sulfidation resistance. The palladium content in the electrode can be measured by elemental analysis using EDS (Energy Dispersive X-ray Spectroscopy).

[0082] The electrode of this embodiment may contain zinc (zinc oxide) resulting from the glass frit (C). When the electrode of this embodiment contains zinc in addition to palladium, high sulfidation resistance can be obtained.

[0083] The sheet resistance of the thin film that will become the electrode of this embodiment varies depending on the film thickness, but can be approximately 10 mΩ / □ (10 mΩ / square) or less, and therefore can be preferably used to form electrodes that are required to have low resistance.

[0084] Next, a method for forming an electrode on a substrate (base material) using the conductive paste of this embodiment will be described. First, the conductive paste is applied to the substrate. The conductive paste can be applied by any method, and can be applied using known methods such as dispensing, jet dispensing, stencil printing, screen printing, pin transfer, or stamping.

[0085] After applying the conductive paste to the substrate, it is dried as necessary, and the substrate is placed in a firing furnace or the like. The conductive paste applied to the substrate is then fired at 400 to 900°C, more preferably 500 to 880°C, and even more preferably 500 to 870°C. A specific example of the firing temperature is 850°C. As a result, the solvent components contained in the conductive paste evaporate at 300°C or below, and the resin components are burned off at 400 to 600°C, forming a fired body (electrode) of the conductive paste. Furthermore, the organic components contained in the surface-treated metal particles are eliminated by firing in an air atmosphere, and the palladium in the palladium compound exists on the surface of the metal particles as a palladium metal alloy layer (or a palladium-silver alloy layer in the case of silver particles). The palladium metal alloy layer on the surface of the metal particles is thought to impart high sulfuration resistance to the metal particles. Therefore, by including a thin surface treatment layer containing a palladium compound in the metal particles, high sulfuration resistance can be obtained. Furthermore, the palladium content in the surface treatment layer is not very high. Therefore, compared to the case where palladium particles are added separately, the amount of palladium used can be reduced, and high sulfidation resistance can be obtained at a relatively low cost. The electrode obtained in this way has high sulfidation resistance and excellent adhesion to the substrate.

[0086] Electrodes obtained using the conductive paste of this embodiment exhibit little outflow of glass components, even after firing using the above-described method, making them less susceptible to problems such as plating elongation and short circuits. In particular, in conventional conductive pastes, when only small-diameter (1 μm or less) metal particles are used as conductive particles, the high sinterability of the metal particles can cause the glass components of the low-softening-point glass frit to be pushed outward, which can be a factor in outflow. In contrast, in the conductive paste of this embodiment, the presence of a surface treatment layer on the metal particles is thought to slow the sintering rate, allowing the glass components to be retained in the electrode. Outflow of glass components can be observed using a device such as a scanning electron microscope (SEM).

[0087] Furthermore, an electrode obtained as described above using the conductive paste of this embodiment can have the additional advantage of improved migration resistance. However, this advantage is not necessarily an essential effect of the conductive paste of this embodiment, but is considered to be one of its advantages.

[0088] <Electronic Component or Electronic Device> This embodiment is an electronic component or electronic device having the above-described electrode. In this specification, the term "electronic component" refers to a component used in electronic devices, such as a chip resistor or a substrate circuit. In this specification, the term "electronic component" refers to a component that operates electronically, and specifically may be a component that operates at 48 V DC or less. In this specification, the term "electronic device" refers to a device that includes an electronic component having the electrode of this embodiment.

[0089] The conductive paste of this embodiment can be used for forming circuits of electronic components or electronic equipment, forming electrodes, and bonding devices such as electronic components (e.g., semiconductor chips) to substrates (base materials).

[0090] The conductive paste of this embodiment can be preferably used to form electrodes of chip resistors. FIG. 1 shows an example of the cross-sectional structure of a chip resistor 100 of this embodiment. The chip resistor 100 can have a rectangular alumina substrate 102, a resistor 104, and an output electrode 106 arranged on the surface of the alumina substrate 102. The output electrode 106 is an electrode for extracting electricity from the resistor 104. A bottom electrode 108 for mounting the chip resistor 100 to a substrate can be arranged on the bottom surface of the alumina substrate 102. Furthermore, a connection electrode 110 for connecting the output electrode 106 and the bottom electrode 108 can be arranged on an end surface of the alumina substrate 102. At least one of the output electrode 106, the bottom electrode 108, and the connection electrode 110 can be formed using the conductive paste of this embodiment. In particular, the output electrode 106 is preferably formed using the conductive paste of this embodiment. A nickel-plated film 112 and a tin-plated film 114 may be disposed on the upper surfaces (surfaces opposite to the alumina substrate 102) of the extraction electrode 106, the lower electrode 108, and the connection electrode 110.

[0091] The electrodes of this embodiment are not limited to electrodes of chip resistors. Electrodes formed using the conductive paste of this embodiment can be used as electrodes for various types of electronic components. Examples of electronic components include passive components (e.g., chip resistors, capacitors, resistors, inductors, etc.), circuit boards (e.g., substrates such as alumina substrates, aluminum nitride substrates, and glass substrates on which predetermined circuits (electrodes or wiring) are formed), solar cells, and electromagnetic wave shields. Electrodes and / or wiring for these electronic components can be formed using the conductive paste of this embodiment. Examples of electronic devices including electronic components having electrodes of this embodiment include semiconductor devices, photovoltaic power generation modules, and electronic devices including circuit boards.

[0092] The conductive paste of this embodiment can be used as a die attach material for attaching a semiconductor chip in a semiconductor device. When the semiconductor device is a power semiconductor device, it can be used as a brazing material for attaching a power semiconductor chip. The conductive paste of this embodiment can be used as an electrode for a solar cell. The conductive paste of this embodiment can be used as a conductive adhesive. Furthermore, the conductive paste of this embodiment is not limited to the formation of terminal electrodes of chip resistors, and can also be suitably used as a conductive paste for terminal electrodes of passive components such as MLCCs and chip inductors.

[0093] By using the conductive paste of this embodiment, it is possible to form electrodes that have high sulfur resistance and low resistance at relatively low cost. Therefore, by using the conductive paste of this embodiment, it is possible to obtain electronic components such as chip resistors with highly reliable electrodes at relatively low cost.

[0094] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0095] [Preparation of Conductive Paste] Conductive pastes were prepared by mixing the following components (A) to (E) in the proportions shown in Tables 1 and 2. The proportions of each component shown in Tables 1 and 2 are all shown in parts by weight. In Tables 1 and 2, the weight of the (A) conductive particles (total weight of metal particles and surface-treated metal particles) is taken as 100 parts by weight. The average particle size refers to the volume-based median diameter (D50) obtained by a laser diffraction / scattering particle size distribution measurement method.

[0096] (A) Conductive Particles Table 3 shows metal particles a1 to a4 and surface-treated metal particles A1 to A6 used as the (A) conductive particles (component (A)) in the examples and comparative examples. Metal particles a1 and a2 are silver particles, and metal particle a4 is a palladium particle. Metal particles a1 to a4 were not surface-treated. Surface-treated metal particles A1 to A6 were surface-treated by adhering a palladium soap solvent (surface treatment agent) containing a palladium compound dispersed in a solvent to the surface of silver particles, and then removing the solvent by a drying process. Therefore, surface-treated metal particles A1 to A6 have a surface treatment layer containing a palladium compound. The "Pd Content" column in Table 3 shows the weight percentage of palladium contained in the surface treatment layer relative to the weight of surface-treated metal particles A1 to A6 in units of wt %. The weight percentage of palladium in the surface-treated metal particles was measured by ICP atomic emission spectroscopy (inductively coupled plasma atomic emission spectroscopy).

[0097] The surface treatment of silver particles with a palladium compound was carried out as follows. That is, the surface treatment of silver particles with a palladium compound was carried out using a palladium soap solvent (surface treatment agent) containing a palladium compound, an organic substance for dispersing the palladium compound, and a solvent. The surface treatment was carried out by attaching the palladium soap solvent (surface treatment agent) to the surfaces of the silver particles and removing the solvent by a drying process. Palladium chloride was used as the palladium compound. Furthermore, oleic acid was used as the solvent contained in the surface treatment agent for the silver particles. In this manner, a surface treatment layer was formed on surface-treated metal particles A1 to A6.

[0098] (B) Binder Resin Table 4 shows the (B) binder resins (resins B1 and B2) used in the examples and comparative examples. Tables 1 and 2 show the blending amounts of resins B1 and B2 in the conductive pastes of the examples and comparative examples.

[0099] (C) Glass Frit Table 5 shows the (C) glass frits (C1 to C8) used in the examples and comparative examples. Tables 1, 2, and 9 show the blending amounts of glass frits C1 to C8 in the conductive pastes of the examples and comparative examples.

[0100] (D) Additives Table 6 shows the (D) additives (additives D1 to D3) used in the examples and comparative examples. Tables 1 and 2 show the blending amounts of additives D1 to D3 in the conductive pastes of the examples and comparative examples. Additive D1 is an organic additive. Adding additive D1 can improve the printability of the conductive paste. Additive D2 is a dispersant. Adding additive D2 can improve the dispersibility of (A) conductive particles and the like. Additive D3 is an inorganic additive. Adding additive D3 can improve the adhesion of the conductive paste after firing.

[0101] (E) Solvents Table 7 shows the (E) solvents (solvents E1 to E3) used in the examples and comparative examples. Tables 1 and 2 show the blending amounts of solvents E1 to E3 in the conductive pastes of the examples and comparative examples.

[0102] [Preparation of Test Piece 50 for Sulfidation Resistance Test] Fig. 2 shows a schematic diagram of a test piece 50 for a sulfidation resistance test. (C) Using a conductive paste containing glass frit, test pieces 50 for the sulfidation resistance test of Examples 1 to 16 and Comparative Examples 1 to 5 were prepared by the following procedure.

[0103] First, a conductive paste was applied by screen printing to a 20 mm x 20 mm x 1 mm (t) alumina substrate 52 (purity 96%) for sulfuration resistance testing, so as to form a zigzag-shaped printed pattern 54 for sulfuration resistance testing, as shown in FIG. 2 . The length between the two ends 54a, 54b of the printed pattern 54 for sulfuration resistance testing was 71 mm, and the width of the printed pattern 54 for sulfuration resistance testing was 1 mm. To form the printed pattern 54 for sulfuration resistance testing of the conductive paste, screen printing was performed using a stainless steel 325 mesh screen (emulsion thickness 5 μm). Next, the printed pattern 54 for sulfuration resistance testing of the conductive paste was dried at 150°C for 10 minutes using a batch-type hot air dryer. After drying, the printed pattern 54 for sulfuration resistance testing of the conductive paste was fired using a belt-type firing furnace. The firing temperature was maintained at 850°C for 10 minutes. The total time from when the specimens were placed in the firing furnace until when they were removed was 60 minutes. In this manner, the test specimens 50 of Examples 1 to 16 and Comparative Examples 1 to 5 were prepared.

[0104] [Sulfuration Resistance Test Method] First, the electrical resistance (initial electrical resistance) between the two ends 54a, 54b of the printed pattern 54 of the test pieces of the Examples and Comparative Examples was measured. Next, a petri dish (height 18 mm, diameter 86 mm) containing 10 g of sulfur powder placed flat was placed in the bottom of a glass desiccator (height 420 mm, diameter 300 mm), and the test pieces of the Examples and Comparative Examples were placed on the inner lid. This desiccator was stored in a thermostatic chamber kept at a constant temperature of 60°C for 150 hours to sulfurize the test pieces. Next, the electrical resistance after sulfurization was measured. The "Resistance Change Rate (Sulfuration Resistance Test)" column in Tables 1 and 2 shows the resistance change rate of the electrical resistance after sulfurization relative to the initial electrical resistance of the Examples and Comparative Examples in percentage units. The resistance change rate can be expressed by the following formula: Resistance Change Rate = (Electrical Resistance After Sulfurization - Initial Electrical Resistance) / Initial Electrical Resistance

[0105] [Preparation of Test Pieces for Adhesion Strength Test] Using the prepared conductive paste, test pieces containing (C) glass frit for Examples 1 to 16 and Comparative Examples 1 to 5 were prepared according to the following procedure. First, the conductive paste was applied by screen printing to an alumina substrate (purity 96%) measuring 20 mm x 20 mm x 1 mm (t). This resulted in 25 (5 x 5) square pad-shaped adhesive strength test patterns with sides of 1.5 mm formed on the alumina substrate. To form the conductive paste adhesive strength test patterns, screen printing was performed using a stainless steel 325-mesh screen (emulsion thickness 5 μm).

[0106] Next, the conductive paste was dried at 150°C for 10 minutes using a batch-type hot air dryer. After drying the conductive paste adhesive strength test pattern, the conductive paste adhesive strength test pattern was fired using a belt-type firing furnace. The firing temperature was maintained at 850°C for 10 minutes. The total time from placing the pattern in the firing furnace to removing it was 60 minutes. In this manner, test pieces for Examples 1 to 16 and Comparative Examples 1 to 5 were prepared.

[0107] Next, the adhesive strength test pattern was subjected to Ni / Au plating. Next, solder (M705 manufactured by Senju Metal Industry Co., Ltd., a Sn alloy containing 3.0 wt % Sn—Ag and 0.5 wt % Cu) was applied to the adhesive strength test pattern at 260°C for 3 seconds, and then a Sn-plated annealed copper wire (0.8 mm diameter) was soldered to the adhesive strength test pattern. The Sn-plated annealed copper wire was soldered by soldering one Sn-plated annealed copper wire to each of the five second rows of five adhesive strength test patterns on the alumina substrate, and one Sn-plated annealed copper wire to each of the five fourth rows of five adhesive strength test patterns. A total of 10 Sn-plated annealed copper wires were soldered, and the tensile adhesive strength of the lead wires was measured using a strength tester. Specifically, the alumina substrate was placed vertically at a 90° angle to the strength tester with the adhesive strength test pattern facing upward, and the lead wire was pulled upward perpendicular to the alumina substrate to measure the tensile adhesive strength. The force (N) at which the lead wire peeled off was taken as the tensile adhesive strength.

[0108] The tensile adhesive strength of 10 test pieces for each Example and Comparative Example was measured to obtain the results of the adhesive strength test. The "Adhesive Strength (N)" column in Tables 1 and 2 shows the average tensile adhesive strength of the 10 test pieces for each Example and Comparative Example measured as described above.

[0109] 3 shows an optical microscope photograph of test print patterns 64a and 64b of an example of a test piece 60 for a migration resistance test. Using the prepared conductive paste, test pieces 60 for the migration resistance test of Examples 1 and 3 and Comparative Example 1 were produced by the following procedure.

[0110] The test pieces 60 for the migration resistance tests of Examples 1 and 3 and Comparative Example 1 were prepared according to the following procedure. First, a conductive paste was applied by screen printing to an alumina substrate 62 (purity 96%) for migration resistance testing, measuring 110 mm × 20 mm × 0.8 mm (t), so that two comb-shaped print patterns 64a, 64b for the migration resistance test were alternately formed, as shown in FIG. 3 and FIG. 4, which is an enlarged photograph of FIG. 3. The print pattern 64a for the migration resistance test was connected to the first electrode 66a, and the print pattern 64b for the migration resistance test was connected to the second electrode 66b. The print width L of the print patterns 64a, 64b for the migration resistance test was 200 μm, and the space S between the print patterns 64a, 64b for the migration resistance test was 200 μm. To form the conductive paste migration resistance test print patterns 64a, 64b and electrodes 66a, 66b, a 400-mesh stainless steel screen (emulsion thickness 10 μm) was used for screen printing. Next, the conductive paste migration resistance test print patterns 64a, 64b and electrodes 66a, 66b were dried at 150°C for 10 minutes using a batch-type hot air dryer. After drying the conductive paste migration resistance test print patterns 64a, 64b and electrodes 66a, 66b, the migration resistance test print patterns 64a, 64b and electrodes 66a, 66b were fired using a belt-type firing furnace. The firing temperature was maintained at 850°C for 10 minutes. The total time from insertion into the firing furnace to removal was 60 minutes. After firing, the thickness of the migration test print patterns 64a, 64b and electrodes 66a, 66b was 10 to 20 μm. In this manner, test pieces 60 for the migration resistance test of Examples 1 to 16 and Comparative Examples 1 to 5 were prepared.

[0111] The migration resistance of the printed patterns 64a, 64b for the migration resistance test of the test pieces 60 of Examples 1 and 3 and Comparative Example 1 was measured by the following procedure. First, as shown in FIG. 3 , a voltage (40 V) was applied between the first electrode 66a and the second electrode 66b of the two printed patterns 64a, 64b for the migration resistance test. The insulation resistance between the first electrode 66a and the second electrode 66b was measured while the test pieces were stored in an environment at a temperature of 85°C and a humidity of 85%. The insulation resistance was calculated from the measured value of the current flowing between the first electrode 66a and the second electrode 66b and the applied voltage of 40 V. The test pieces 60 to which the applied voltage of 40 V was applied were kept in an environment at a temperature of 85°C and a humidity of 85% for up to 487 hours. Table 8 shows the results of the migration resistance test. Before the test, the insulation resistance of all samples was 10 ７ Within 10 hours, the insulation resistance value was 10 ６ Test piece 60, which had an insulation resistance of 10 Ω or less, was judged to be defective and recorded as "defective" in Table 8. ６ Test piece 60, which did not have an insulation resistance of 10 Ω or less, was judged to have a fairly good migration resistance and may be usable for some applications, and was recorded as "usable" in Table 8. ６ Test piece 60, which did not reach Ω or less, was judged to have excellent migration resistance and was recorded as "good" in Table 8.

[0112] 7 shows the change in insulation resistance over time when the migration resistance test was conducted for Example 1, Example 3, and Comparative Example 1. Test piece 60 of Example 3, which was judged to have excellent migration resistance (listed as "good" in Table 8), had an insulation resistance of 10 even after 480 hours had elapsed. ６ The test piece 60 of Example 1 (listed as "usable" in Table 8), which was judged to be usable in some applications due to its excellent migration resistance, did not reach an insulation resistance value of 10 Ω or less even after 80 hours. ６ The test piece 60 of Comparative Example 1, which was judged to have poor migration resistance (listed as "poor" in Table 8), did not reach an insulation resistance value of 10 Ω or less within 10 hours. ６ It went below Ω.

[0113] [Soldering Heat Resistance Test] Using the prepared conductive paste, test pieces for the soldering heat resistance test of Examples 1 to 16 and Comparative Examples 1 to 5 containing (C) glass frit were produced by the following procedure.

[0114] First, a conductive paste was applied by screen printing to an alumina substrate (purity 96%) measuring 20 mm x 20 mm x 1 mm (t). This resulted in 25 (5 x 5) square pad patterns for adhesive strength testing, each measuring 1.5 mm on a side, being formed on the alumina substrate. To form the conductive paste adhesive strength test patterns, screen printing was performed using a 325-mesh stainless steel screen (emulsion thickness 5 μm).

[0115] Next, the conductive paste was dried at 150°C for 10 minutes using a batch-type hot air dryer. After drying the conductive paste adhesive strength test pattern, the conductive paste adhesive strength test pattern was fired using a belt-type firing furnace. The firing temperature was maintained at 850°C for 10 minutes. The total time from placing the pattern in the firing furnace to removing it was 60 minutes. In this manner, test pieces for Examples 1 to 16 and Comparative Examples 1 to 5 were prepared.

[0116] Next, the test piece was immersed for 10 seconds in a solder bath (solder temperature: 260° C.) containing solder (M705 manufactured by Senju Metal Industry Co., Ltd., an Sn alloy containing 3.0 wt % Sn—Ag and 0.5 wt % Cu).

[0117] After immersion in the solder bath, the test piece was removed, and those test pieces with 95% or more of the electrodes remaining were judged to have passed the solder heat resistance test. In the "Solder Heat Resistance" column of Tables 1 and 2, those that passed the solder heat resistance test were recorded as "Good," and those that failed the solder heat resistance test were recorded as "Poor."

[0118] [Surface and cross-sectional observation by SEM, and cross-sectional observation by EDS analysis] Fig. 5 shows an SEM photograph taken by a scanning electron microscope (SEM) at a magnification of 5000 times of the surface of a test piece prepared under the same conditions as test piece 50 of the sulfidation resistance test of Example 3, in which the rate of change in resistance value was relatively small. Fig. 6 shows an SEM photograph taken by an SEM at a magnification of 5000 times of the surface of a test piece prepared under the same conditions as test piece 50 of the sulfidation resistance test of Comparative Example 1, in which the rate of change in resistance value was large. Note that, as in the case of the sulfidation resistance test, the test piece was stored in a sulfur atmosphere (60°C) for 150 hours and then observed with the SEM.

[0119] [Evaluation] As is clear from the results shown in Tables 1 and 2, the electrode patterns obtained by firing the conductive pastes of Examples 1 to 16 had a relatively low resistance change rate of 65.0% (Example 11) or less. In contrast, the electrode patterns obtained by firing the conductive pastes of Comparative Examples 1 to 5 had a resistance change rate of 140% (Comparative Example 5) or more. Therefore, it can be said that the electrode patterns obtained by firing the conductive pastes of Examples 1 to 16 have excellent sulfurization resistance.

[0120] As is clear from the results shown in Tables 1 and 2, the tensile adhesive strength of the adhesive strength test patterns obtained by firing the conductive pastes of Examples 1 to 16 was a maximum of 17.8 N (Examples 11 and 15), indicating high tensile adhesive strength. On the other hand, the tensile adhesive strength of the electrode patterns obtained by firing the conductive pastes of Comparative Examples 1 to 4 ranged from 14.2 N (Comparative Example 4) to 15.2 N (Comparative Examples 1 to 3), which was within a range where tensile adhesive strength was acceptable. Furthermore, the tensile adhesive strength of the electrode pattern obtained by firing the conductive paste of Comparative Example 5 was 7.1 N. It is believed that the conductive paste of Comparative Example 5 had poorer sinterability than the other Examples and Comparative Examples, resulting in a low tensile adhesive strength.

[0121] As is clear from the results shown in Tables 1 and 2, the results of the solder heat resistance test for the electrode patterns obtained by firing the conductive pastes of Examples 1 to 16 were all pass ("good"). On the other hand, the results of the solder heat resistance test for the electrode patterns obtained by firing the conductive pastes of Comparative Examples 1 to 4 were fail ("poor"). The result of the solder heat resistance test for the electrode pattern obtained by firing the conductive paste of Comparative Example 5 was pass ("good"). From the above, it can be said that the electrode patterns obtained by firing the conductive pastes of Examples 1 to 16 have excellent solder heat resistance.

[0122] From the results shown in Table 8, it is clear that the electrodes of Examples 1 and 3 of this embodiment have superior migration resistance compared to Comparative Example 1.

[0123] Comparing the SEM photographs of Example 3 shown in FIG. 5 and Comparative Example 1 shown in FIG. 6, it can be seen that, compared to Example 3, Comparative Example 1 has larger crystals of silver sulfide 20 formed by sulfurization. Similar trends were observed for the other Examples and Comparative Examples. Therefore, it can be said that the electrodes of the Examples of this embodiment have higher sulfurization resistance than the Comparative Examples. Furthermore, when the Pd content in the depth direction of the sample of Example 3 was measured by X-ray photoelectron spectroscopy (XPS), it was confirmed that there was a portion with a Pd content of approximately 30 atomic % at a depth of 80 nm. This suggests that, at least in the sample of Example 3, the formation of a silver-palladium alloy layer on the surface of the electrode improved the sulfurization resistance of the electrode.

[0124]

[0125]

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[0130]

[0131]

[0132] Examples 17-29, Comparative Examples 6-9: Evaluation of Glass Component Flow-Out Conductive pastes were prepared in the same manner as in Example 1, using the formulations shown in Table 9. Next, the conductive paste of each Example and Comparative Example was applied to an alumina substrate in a pattern 1 mm wide and 71 mm long, with a thickness of approximately 15 μm. The paste was then dried at 150°C for 10 minutes and then fired at 850°C for 60 minutes to form a conductive thick film with a post-fired thickness of 10 μm. Backscattered electron images of the electrode side portions of the resulting conductive thick films were taken using a scanning electron microscope (SEM) at 500x magnification, and the length of glass flow was measured. Because the silver component that flows with the glass during firing appears white in the backscattered electron image, the area where the glass flowed out is observed as a black and white mottled pattern ( Figure 8 ). The distance the silver component flowed the most from the side of the electrode was defined as the length of glass flow. A glass flow length of 40 μm or less was deemed to indicate minimal flow (evaluated as "good"). The formulations and measurement results of each example and comparative example are shown in Table 9 together with the measurement results of sulfidation resistance.

[0133]

[0134] [Evaluation] In the conductive paste of the comparative example, glass outflow was confirmed, and the results of the sulfurization resistance test also showed a significant increase in resistance value, leaving concerns about short circuits and disconnections. In contrast, the conductive pastes of Examples 17 to 29 exhibited high sulfurization resistance, and as in Comparative Example 7 and Example 19, when the same glass frit was used, the outflow of glass components during firing was significantly suppressed, indicating that electrodes with little concern about short circuits and the like can be obtained even when a glass frit with a low softening point is used.

[0135] 50 Test piece for sulfuration resistance test 52 Alumina substrate for sulfuration resistance test 54 Printed pattern for sulfuration resistance test 54a, 54b End of printed pattern for sulfuration resistance test 60 Test piece for migration resistance test 62 Alumina substrate for migration resistance test 64a, 64b Printed pattern for migration resistance test 66a First electrode 66b Second electrode 100 Chip resistor 102 Alumina substrate 104 Resistor 106 Lead electrode 108 Lower electrode 110 Connection electrode 112 Nickel plating film 114 Tin plating film

Claims

1. (A) Conductive particles and (B) Binder resin and (C) Glass frit and A conductive paste containing, The conductive particles in (A) comprise metal particles and a surface treatment layer containing a palladium compound, which is disposed on at least a portion of the surface of the metal particles. The softening point of the glass frit (C) is 800°C or lower. Conductive paste.

2. The conductive paste according to claim 1, wherein the content of the palladium compound in the surface treatment layer is 0.01 to 1.0 parts by weight per 100 parts by weight of the metal particles.

3. The conductive paste according to claim 1, wherein the surface treatment layer further comprises an organic substance which is at least one selected from fatty acids and triazole compounds.

4. The conductive paste according to claim 1, wherein the metal particles contain 50% by weight or more of silver.

5. The conductive paste according to claim 1, wherein the average particle size (D50) of the conductive particles (A) is 0.1 to 10 μm.

6. The conductive paste according to claim 5, wherein the average particle size (D50) of the conductive particles (A) is 0.1 to 6 μm.

7. An electrode obtained by firing or heat-treating the conductive paste according to any one of claims 1 to 6.

8. An electronic component or electronic device comprising the electrode described in claim 7.