Conductive paste, electrode, electronic component, and electronic device

Abstract

Provided is a conductive paste comprising conductive particles (A) and a binder resin (B), 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. This conductive paste contains the conductive particles (A) in an amount of 80 parts by weight or more with respect to 100 parts by weight of the conductive paste. The conductive paste exhibits high sulfidation resistance, and can achieve excellent printing characteristics even with an increased content of conductive particles.

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] With the recent trend toward higher performance in electronic devices and electronic components, there is a demand for even lower resistance in electrodes, wiring, and the like. One method for reducing resistivity is to highly fill conductive particles. For example, Patent Document 3 discloses a conductive paste containing a high proportion of silver powder (85 parts by weight or more). Meanwhile, conductor patterns for electrodes, wiring, and the like tend to become more precise and complex as the performance of electronic devices and electronic components improves. Therefore, conductive pastes are required to have adhesive properties for adhesion to substrates and excellent printing properties that enable the formation of fine patterns, such as leveling properties for forming a smooth coating film upon application and smoothness of the coating film for further plating processes on the applied surface. Patent Document 3 discloses that printability and adhesion are affected when the amount of silver powder exceeds 95 parts by weight per 100 parts by weight of the total of silver powder and binder resin.

[0006] Japanese Patent Application Laid-Open No. 7-335402 International Publication No. 2021 / 145269 Japanese Patent Application Laid-Open No. 2005-294254

[0007] Low resistance, high printability, and high adhesiveness of conductive pastes are all required characteristics as electronic devices advance, but there is a trade-off between these two characteristics, and there is a demand for conductive pastes that excel in all performance areas. Furthermore, there are other characteristics required for high-definition electronic devices besides low resistance, high printability, and high adhesiveness.

[0008] 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 compounds, 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] Since the sulfuration reaction occurs more frequently as the metal particle loading increases, it is necessary to be able to prevent disconnections due to sulfuration even when the resistance of the conductive paste is reduced. 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 resistant to sulfuration.

[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] Therefore, an object of the present invention is to provide a conductive paste that has high sulfuration resistance and can achieve excellent printing characteristics even when the content of conductive particles is increased.

[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; and (B) a binder resin, 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 conductive particles of (A) are contained in an amount of 80 parts by weight or more per 100 parts by weight of the conductive paste.

[0015] (Configuration 2) Configuration 2 is the conductive paste of configuration 1, having a viscosity in the range of 50 to 700 Pa·s as measured with an HB type viscometer at 25° C. and 10 rpm.

[0016] (Configuration 3) Configuration 3 is the conductive paste of Configuration 1 or 2, in which the thixotropic index (TI), which is the ratio of the viscosity at a rotation speed of 1 rpm to the viscosity at a rotation speed of 10 rpm, measured with an HB-type viscometer at 25°C, is 2.5 or less.

[0017] (Configuration 4) Configuration 4 is the conductive paste of any one of Configurations 1 to 3, in which the average particle size (D50) of the (A) conductive particles is 0.1 to 10 μm.

[0018] (Configuration 5) Configuration 5 is the conductive paste of any one of Configurations 1 to 4, wherein the metal particles contain 50% or more by weight of silver.

[0019] (Configuration 6) Configuration 6 is the conductive paste of any one of Configurations 1 to 5, 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 conductive particles.

[0020] (Configuration 7) Configuration 7 is the conductive paste of configuration 6, wherein the content of the palladium compound contained in the surface treatment layer is 0.2 to 0.4 parts by weight per 100 parts by weight of the conductive particles.

[0021] (Configuration 8) Configuration 8 is the conductive paste of any one of Configurations 1 to 7, wherein the surface treatment layer further contains an organic substance.

[0022] (Configuration 9) Configuration 9 is an electrode obtained by firing or heat treating the conductive paste of any one of configurations 1 to 8.

[0023] (Configuration 10) Configuration 10 is the electrode of configuration 9, in which the electrode surface has an arithmetic mean roughness (Ra) of 0.5 μm or less as measured in accordance with JIS B 0601 (1994).

[0024] (Configuration 11) Configuration 11 is an electronic component or electronic device including the electrode of configuration 9 or 10.

[0025] According to the present invention, it is possible to provide a conductive paste that has high sulfuration resistance and can achieve excellent printing characteristics even when the content of conductive particles is increased.

[0026] 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. FIG. 7 is a stereomicroscope photograph of a thin film using the conductive paste of Example 22. 10 is a stereomicroscope photograph of a thin film using the conductive paste of Comparative Example 6.

[0027] 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.

[0028] The conductive paste of this embodiment includes (A) conductive particles and (B) a binder resin. 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, and are included in an amount of 80 parts by weight or more per 100 parts by weight of the conductive paste.

[0029] First, the components contained in the conductive paste of this embodiment will be described.

[0030] <(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 metal particles with the palladium compound. When the (A) conductive particles contain surface-treated metal particles having a predetermined surface treatment layer, sulfurization of the metal contained in the conductive particles can be suppressed. Therefore, by using the conductive paste of this embodiment, an electrode with high sulfurization resistance can be formed.

[0031] The inventors of the present invention have discovered that the inclusion of a predetermined surface treatment layer 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, metals contained in the electrodes and wiring ionize and migrate from the positive electrode to the negative electrode, generating metal dendrites and reducing 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. By improving migration resistance, electrode short-circuiting can be suppressed. Furthermore, it has been discovered that the migration resistance of the resulting electrodes is improved not only in the case of a conductive paste of the present embodiment that is fired at a relatively high temperature (e.g., 500 to 900°C), but also in the case of a thermosetting conductive paste that is thermally cured by heat treatment at a relatively low temperature (e.g., 100 to 200°C). However, the advantage of improved migration resistance is not necessarily an essential effect of the conductive paste of the present embodiment, but is considered to be one of its advantages.

[0032] The (A) conductive particles may contain metals other than the surface-treated metal particles. However, in order to reliably obtain an electrode having low electrical resistance and high sulfidation resistance, the (A) conductive particles preferably contain 50 wt % or more of surface-treated metal particles, more preferably 80 wt % or more of surface-treated metal particles, even more preferably 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 of only surface-treated metal particles" means that the (A) conductive particles do not intentionally contain metals other than the surface-treated metal particles, and does not exclude the inevitable inclusion of conductive particles other than the surface-treated metal particles.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The conductive paste of this embodiment preferably contains 50 parts by weight or more of surface-treated metal particles per 100 parts by weight of the conductive paste, more preferably 70 parts by weight or more, and even more preferably 80 parts by weight or more. The conductive paste of this embodiment preferably contains 50 to 99 parts by weight of surface-treated metal particles per 100 parts by weight of the conductive paste, more preferably 70 to 97 parts by weight or more, and even more preferably 80 to 95 parts by weight. By being in the above range, it is possible to form an electrode that has high sulfuration resistance and is relatively low cost.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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 the palladium compound is attached to the surface of the metal particle, thereby achieving the effect of requiring only a small amount of palladium. Palladium is an expensive metal due to its scarcity and uneven distribution, and the excellent sulfidation resistance and printing properties it provides, even in small amounts, is an extremely important effect from a cost perspective.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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, a highly sulfur-resistant electrode can be formed even with a small amount of palladium compound.

[0050] 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.

[0051] 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 the formation of a uniform alloy layer by sintering palladium as a surface treatment component and the metal particles. In the case of a conductive paste that is fired at a relatively high temperature (e.g., 500 to 900°C), the palladium in the palladium compound exists as a palladium metal alloy layer with the metal particles (a palladium-silver alloy layer when the metal particles are silver particles) upon firing. It is believed that this palladium metal alloy layer imparts high sulfurization resistance to the metal particles. Furthermore, in the case of a thermosetting conductive paste that is thermally cured by heat treatment at a relatively low temperature (e.g., 100 to 200°C), it is believed that sulfurization resistance is achieved by the formation of a thin film of the palladium compound on the surface of the metal particles, such as silver particles. It should be noted that 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 manner has high sulfidation 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 limited to this inference.

[0052] 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.

[0053] 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, particularly preferably 0.08 parts by weight or more, and most preferably 0.2 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, resulting in low cost and minimizing changes in the resistance value of the electrode due to sulfurization of the electrode. Furthermore, when formed into a paste, the fluidity of the conductive particles is improved, thereby further improving leveling during printing. The palladium content of the surface-treated metal particles can be measured by ICP atomic emission spectroscopy (inductively coupled plasma atomic emission spectroscopy).

[0054] 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.

[0055] 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.

[0056] The content of the (A) conductive particles is 80 parts by weight or more, preferably 83 parts by weight or more, and more preferably 85 parts by weight or more, based on 100 parts by weight of the conductive paste. There is no particular upper limit to the content of the conductive particles, but from the viewpoint of providing the conductive paste with sufficient printing properties, it is preferably 99.9 parts by weight or less, more preferably 99.5 parts by weight or less, even more preferably 99 parts by weight or less, and particularly preferably 95 parts by weight or less, based on 100 parts by weight of the conductive paste.

[0057] <(B) Binder Resin> The conductive paste of this embodiment contains (B) a binder resin.

[0058] The (B) binder resin binds the (A) conductive particles together in the conductive paste. The conductive paste of this embodiment may or may not contain the (C) glass frit described below. The function of the (B) binder resin contained in the conductive paste of this embodiment differs depending on whether the (C) glass frit is contained or not.

[0059] When the conductive paste of this embodiment contains (C) glass frit, the conductive paste of this embodiment can be applied to a predetermined substrate to form a predetermined electrode pattern, and then fired at a relatively high temperature (e.g., 500 to 900°C) to form an electrode. In this case, the binder resin (B) is burned away during firing. Therefore, the function of the binder resin (B) in this case is to bind the conductive particles (A) together when the conductive paste of this embodiment is applied to a predetermined substrate to form a predetermined electrode pattern.

[0060] When the conductive paste of this embodiment does not contain (C) glass frit, the conductive paste of this embodiment can be applied to a predetermined substrate to form a predetermined electrode pattern, and then heat-treated at a relatively low temperature (e.g., 100 to 200°C) to form an electrode. In this case, the (B) binder resin is not burned away during the heat treatment. In this case, the function of the (B) binder resin is to bind the (A) conductive particles together when the conductive paste of this embodiment is applied to a predetermined substrate to form a predetermined electrode pattern, and also to bind the (A) conductive particles together after the heat treatment, thereby maintaining the shape of the electrode after the heat treatment.

[0061] 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.

[0062] 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.

[0063] When the conductive paste of this embodiment does not contain (C) glass frit, 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 type, bisphenol F type, biphenyl type, tetramethylbiphenyl type, cresol novolac type, phenol novolac type, bisphenol A novolac type, dicyclopentadiene phenol condensation type, phenol aralkyl condensation type, and glycidyl amine type 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.

[0064] The content of the (B) binder resin is preferably 25 parts by weight or less, more preferably 18 parts by weight or less, even more preferably 11 parts by weight or less, and particularly preferably 9 parts by weight or less, relative to 100 parts by weight of the (A) conductive particles. The lower limit of the content of the (B) binder resin is preferably 0.1 parts by weight, more preferably 0.5 parts by weight, even more preferably 1 part by weight, and particularly preferably 1.5 parts by weight. When the content of the (B) binder resin in the conductive paste is within the above range, the coating properties of the conductive paste on the substrate (base material) and / or the paste leveling properties are improved, resulting in an excellent print shape. On the other hand, when the content of the (B) binder resin exceeds the above upper limit, the amount of the (B) binder resin contained in the applied conductive paste is too high. This may make it difficult to form electrodes, etc., with high precision.

[0065] <(C) Glass Frit> The conductive paste of the present embodiment may further contain (C) glass frit.

[0066] When the conductive paste of this embodiment contains (C) glass frit, the conductive paste of this embodiment can be applied to a predetermined substrate so as to form a predetermined electrode pattern, and then fired at a relatively high temperature (e.g., 500 to 900°C) to form 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 electrode to maintain its shape after firing.

[0067] The glass frit is not particularly limited, but preferably has a softening point of 300° C. or higher, more preferably 400 to 900° C., and even more preferably 500 to 800° C. The softening point of the glass frit can be measured using a thermogravimetric analyzer (for example, TG-DTA2000SA, manufactured by BRUKER AXS).

[0068] 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 mixed and used. It is preferable that the glass frit be lead-free from the viewpoint of environmental considerations.

[0069] 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:

[0070] When the conductive paste of the present embodiment contains the glass frit (C), 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.

[0071] When the conductive paste of the present embodiment contains (C) glass frit, 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.

[0072] 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.

[0073] When the conductive paste of this embodiment contains (C) glass frit, 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 create a clean state suitable for plating. Contaminants that need to be removed can be broadly divided into organic and inorganic. The pretreatment process is not a single process that removes all contaminants. For example, organic substances are removed in a process that uses an alkaline cleaning agent, while inorganic substances are removed in a process that uses an acid cleaning agent. For this reason, the electrodes must have high chemical resistance.

[0074] When the conductive paste of this embodiment contains (C) glass frit, the glass frit softens as the temperature rises, and the sintering (firing) of the (A) conductive particles progresses. When the glass frit content is high, the glass component may be extruded onto the surface of the fired body. In this case, the surface of the fired body may be covered with the glass component. When the (C) glass frit contains zinc oxide, the Zn component in the glass frit precipitates as ZnO at the crystallization temperature, which can contribute to the sulfidation resistance of the (A) conductive particles after firing, similar to palladium in the surface-treated metal particles.

[0075] <(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.

[0076] 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.

[0077] 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.

[0078] By adding an organic additive to the conductive paste as a (D) additive, the printing characteristics 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.

[0079] <(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.

[0080] 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.

[0081] The viscosity of the conductive paste of this embodiment varies depending on the conditions for viscosity measurement. However, it was measured using an HB type viscometer (manufactured by Brookfield) (SC4-14 spindle) at a temperature of 25° C., a rotation speed of 1 rpm (shear rate of 0.4 sec －１ ) the viscosity is preferably 100 to 1000 Pa s, more preferably 200 to 800 Pa s. 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 applicability and / or handleability of the conductive paste to a substrate (base material) is improved, and the conductive paste can be applied to the substrate with a uniform thickness.

[0082] The viscosity of the conductive paste of this embodiment can be expressed as a value under conditions different from the above conditions. The viscosity was measured using an HB type viscometer (manufactured by Brookfield) (SC4-14 spindle) at a temperature of 25°C, a rotation speed of 10 rpm (shear rate of 4.0 sec －１ ) the viscosity is preferably 50 to 700 Pa·s, more preferably 100 to 300 Pa·s. 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 applicability and / or handleability of the conductive paste to a substrate (base material) is improved, and the conductive paste can be applied to the substrate with a uniform thickness.

[0083] The conductive paste of this embodiment preferably has a thixotropic index (TI), which is the ratio of the viscosity at a rotation speed of 1 rpm to the viscosity at a rotation speed of 10 rpm, measured using an HB-type viscometer at 25°C, of ​​2.5 or less, and more preferably 2.4 or less. The thixotropic index is the ratio of the viscosities measured under measurement conditions where the viscometer rotation speed is in a ratio of 1:10, and is a value that serves as an indicator of fluidity. A TI of 2.5 or less is preferable because it facilitates obtaining good leveling properties due to moderate fluidity. There is no particular lower limit for TI, but from the viewpoint of preventing printing spread and maintaining dimensional stability, it is preferably 1.3 or more.

[0084] <(F) Curing Agent> The conductive paste of the present embodiment preferably further contains 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.

[0085] 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.

[0086] In the conductive paste of this embodiment, when the total weight of the (A) conductive particles and the (C) 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 properly cured, and an electrode of the desired shape can be obtained.

[0087] 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.

[0088] <Electrode> This embodiment is an electrode obtained by firing or heat treating the conductive paste of this embodiment described above.

[0089] When 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 in a predetermined electrode pattern and firing the paste at a relatively high temperature (e.g., 500 to 900°C) in an air atmosphere. Therefore, when the conductive paste of this embodiment contains (C) glass frit, the 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 a relatively high temperature (e.g., 500 to 900°C), the (B) binder resin and (E) solvent contained in the conductive paste vaporize or burn during firing. Therefore, the electrode is substantially free of the (B) binder resin and (E) solvent.

[0090] When the conductive paste of this embodiment does not contain (C) glass frit, the conductive paste of this embodiment can be applied to a predetermined substrate in a predetermined electrode pattern and then heat-treated at a relatively low temperature (e.g., 100 to 200°C) to form an electrode. Therefore, when the conductive paste of this embodiment does not contain (C) glass frit, the electrode of this embodiment can contain (A') conductive particles containing surface-treated metal particles and (B') binder component made from (B) binder resin. The (A') conductive particles are bonded together via the (B') binder component.

[0091] 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).

[0092] When the conductive paste of the present embodiment contains the glass frit (C), the electrode of the present embodiment can contain zinc (zinc oxide) resulting from the glass frit (C). By containing zinc in addition to palladium, the electrode of the present embodiment can obtain high sulfidation resistance.

[0093] 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.

[0094] 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.

[0095] When the conductive paste of this embodiment contains (C) glass frit, the conductive paste is applied to a substrate, dried as necessary, and then placed in a firing furnace or the like. The conductive paste applied to the substrate is then fired at 500 to 900°C, more preferably 600 to 880°C, and even more preferably 700 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 if the metal particles are silver particles). The palladium metal alloy layer on the surface of the metal particles is believed 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 is small, 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.

[0096] When the conductive paste of this embodiment does not contain (C) glass frit, the conductive paste is applied to a substrate, and then the substrate is placed in a heat treatment furnace or the like. The conductive paste applied to the substrate is then heat-treated at 100 to 200°C, more preferably 150 to 200°C. The heat treatment time is preferably 20 to 90 minutes, more preferably 30 to 60 minutes. A specific example of the heat treatment conditions is 60 minutes at 150°C. This dries the solvent components contained in the conductive paste and thermally hardens the conductive paste, thereby forming a hardened conductive paste (electrode). The electrode obtained in this manner has high sulfurization resistance and excellent adhesion to the substrate.

[0097] When the conductive paste of this embodiment does not contain the glass frit (C), a particularly preferred example of the content of palladium contained in the electrode of this embodiment is 0.2 to 0.5 wt %.

[0098] The conductive paste of this embodiment has excellent printing properties as a coating film, and when formed into an electrode by the above-mentioned method, it has high coating film smoothness. High smoothness reduces the surface area of ​​the coating film and reduces the area affected by sulfur in the atmosphere, which is advantageous in terms of sulfuration resistance. Furthermore, a smooth coating film improves the accuracy of plating when further plating the electrode with nickel or the like. Therefore, the smoothness of the coating film contributes to the formation of fine electrodes. In this specification, the smoothness of the coating film is evaluated by the surface roughness Ra. Surface roughness Ra refers to the centerline average roughness (arithmetic mean roughness) and means the value measured using a surface roughness / shape measuring instrument in accordance with JIS B 0601 (1994). The arithmetic mean roughness (Ra) of the electrode surface is preferably 0.5 μm or less, more preferably 0.46 μm or less, and particularly preferably 0.43 μm or less.

[0099] Furthermore, an electrode obtained as described above using the conductive paste of this embodiment can have the additional advantage of improved migration resistance. This additional advantage can be obtained both in the case where the conductive paste contains (C) glass frit and in the case where the conductive paste does not contain (C) glass frit. 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.

[0100] <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.

[0101] 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).

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0107] [Preparation of Conductive Paste] Conductive pastes were prepared by mixing the following components (A) to (F) in the proportions shown in Tables 1 to 3. The proportions of each component shown in Tables 1 to 3 are all shown in parts by weight. In Tables 1 to 3, 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.

[0108] (A) Conductive Particles Table 4 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 4 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).

[0109] 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.

[0110] (B) Binder Resin Table 5 shows the (B) binder resins (resins B1 to B5) used in the examples and comparative examples. Tables 1 to 3 show the blending amounts of resins B1 to B5 in the conductive pastes of the examples and comparative examples.

[0111] (C) Glass Frit Table 6 shows the (C) glass frits (C1 to C5) used in the examples and comparative examples. Tables 1 to 3 show the blending amounts of glass frits C1 to C5 in the conductive pastes of the examples and comparative examples.

[0112] (D) Additives Table 7 shows the (D) additives (additives D1 to D3) used in the examples and comparative examples. Tables 1 to 3 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 printing characteristics 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.

[0113] (E) Solvents Table 8 shows the (E) solvents (solvents E1 to E3) used in the examples and comparative examples. Tables 1 to 3 show the blending amounts of solvents E1 to E3 in the conductive pastes of the examples and comparative examples.

[0114] (F) Curing Agent In the conductive pastes of the Examples and Comparative Examples, boron trifluoride monoethylamine (STELLA CHEMIFA Corporation, model number: BF3MEA) was used as (F) curing agent F1. Tables 1 to 3 show the blending amounts of curing agent F1 in the conductive pastes of the Examples and Comparative Examples.

[0115] [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.

[0116] 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.

[0117] (C) For Examples 17 to 19 using conductive pastes that did not contain glass frit, similarly to Examples 1 to 16 and Comparative Examples 1 to 5, the conductive pastes of Examples 17 to 19 were used. A 20 mm x 20 mm x 1 mm (t) alumina substrate 52 (purity 96%) for sulfuration resistance testing was screen-printed to form a zigzag sulfuration resistance test pattern 54 (see FIG. 2) having a width of 1 mm and a length of 71 mm. Next, the conductive paste was heat-treated for 10 minutes at 150°C using a batch-type hot air dryer, thereby hardening the sulfuration resistance test pattern 54. In this manner, the test pieces 50 of Examples 17 to 19 were prepared.

[0118] [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 to 3 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

[0119] [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).

[0120] 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.

[0121] 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.

[0122] As with the test specimens of Examples 1 to 16 and Comparative Examples 1 to 5, the conductive paste prepared for Examples 17 to 19 was applied by screen printing to a 20 mm x 20 mm x 1 mm (t) alumina substrate (purity 96%). This resulted in 25 adhesive strength test patterns (5 x 5) consisting of square pads with sides of 1.5 mm on the alumina substrate. Next, the conductive paste adhesive strength test patterns were cured by heat-treating the conductive paste at 150°C for 10 minutes using a hot air dryer. In this manner, the test specimens of Examples 17 to 19 were prepared. Next, as with Examples 1 to 16 and Comparative Examples 1 to 5, Ni / Au plating was performed on the adhesive strength test patterns of Examples 17 to 19. Next, as with the test specimens of Examples 1 to 16 and Comparative Examples 1 to 5, Sn-plated annealed copper wires (lead wires) were soldered to the adhesive strength test patterns, and the tensile adhesive strength of the lead wires was measured using a strength tester.

[0123] The results of the adhesive strength test were obtained by measuring the tensile adhesive strength of 10 test pieces for each Example and Comparative Example. The "Adhesive Strength (N)" column in Tables 1 to 3 shows the average tensile adhesive strength of the 10 test pieces for each Example and Comparative Example measured as described above.

[0124] 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, 3, and 17 to 19 and Comparative Example 1 were produced by the following procedure.

[0125] 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.

[0126] The test specimens 60 for the migration resistance tests of Examples 17 to 19 were prepared according to the following procedure. First, similar to the test specimens 60 of Examples 1 and 3 and Comparative Example 1, a conductive paste was applied by screen printing to a 110 mm × 20 mm × 0.8 mm (purity) alumina substrate 62 for the migration resistance test, so that two comb-shaped print patterns 64a, 64b for the migration resistance test were alternated, as shown in Figures 3 and 4 . Next, the conductive paste was heat-treated at 200°C for 30 minutes using a hot air dryer, thereby hardening the conductive paste adhesive strength test pattern. In this manner, the test specimens for the migration resistance tests of Examples 17 to 19 were prepared.

[0127] The migration resistance of the printed patterns 64a, 64b for the migration resistance test of the test pieces 60 of Examples 1, 3, and 17-19 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 after storage in an environment at a temperature of 85°C and 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 humidity of 85% for up to 487 hours. Table 9 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 9. 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 9. 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 9.

[0128] 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 9), 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 9), 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 9), did not reach an insulation resistance value of 10 Ω or less within 10 hours. ６ It went below Ω.

[0129] [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.

[0130] 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).

[0131] 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.

[0132] Test pieces for the soldering heat resistance test of Examples 17 to 19 were prepared using a conductive paste that did not contain glass frit (C) in the same manner as the test pieces for the soldering heat resistance test of Examples 1 to 16 and Comparative Examples 1 to 5. However, in the case of the test pieces of Examples 17 to 19, instead of drying and firing the conductive paste adhesive strength test pattern, the conductive paste adhesive strength test pattern was cured by heat treating the conductive paste for 10 minutes at 150°C using a hot air dryer.

[0133] 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).

[0134] 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 Table 9, 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."

[0135] [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.

[0136] [Evaluation] As is clear from the results shown in Tables 1 to 3, the electrode patterns obtained by firing the conductive pastes of Examples 1 to 19 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 19 have excellent sulfurization resistance.

[0137] As is clear from the results shown in Tables 1 to 3, the tensile adhesive strengths of the adhesive strength test patterns obtained by firing the conductive pastes of Examples 1 to 19 ranged from 13.2 N (Example 17) to 17.8 N (Examples 11 and 15), and high tensile adhesive strengths were obtained. On the other hand, the tensile adhesive strengths 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 were within the acceptable range for tensile adhesive strength. 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.

[0138] As is clear from the results shown in Tables 1 to 3, the results of the solder heat resistance test for the electrode patterns obtained by firing the conductive pastes of Examples 1 to 19 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"). In addition, 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 19 have excellent solder heat resistance.

[0139] From the results shown in Table 9, it is clear that the electrodes of Examples 1, 3 and 17 to 19 of this embodiment have superior migration resistance compared to Comparative Example 1.

[0140] 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.

[0141]

[0142]

[0143]

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150] Examples 20-32, Comparative Examples 6-7: Evaluation of Coating Smoothness Conductive pastes were prepared in the same manner as in Example 1, using the formulations shown in Table 10. The viscosity of the resulting conductive pastes was measured at 25°C and 1 or 10 rpm using an HB-type viscometer (manufactured by Brookfield) (SC4-14 spindle), and the TI value was determined. Next, the conductive paste of each Example and Comparative Example was applied to a glass slide in a pattern 10 mm wide and 50 mm long, with a thickness of approximately 0.05 mm, and baked at 500°C for 20 minutes to form a conductive thin film with a post-baking film thickness of 0.2 μm. The surface roughness (Ra) of the resulting conductive thin film was measured using a surface roughness / shape measuring instrument (manufactured by Tokyo Seimitsu Co., Ltd., SURFCOM 1500SD2-12) in accordance with JIS B 0601 (1994). A surface roughness Ra of less than 0.4 μm was evaluated as particularly excellent (◯), a surface roughness of 0.4 to 0.5 μm was evaluated as acceptable for practical use (△), and a surface roughness of more than 0.5 μm was evaluated as rough (×). The formulations and measurement results of each example and comparative example are shown in Table 10, along with the measurement results of sulfurization resistance. The sulfurization resistance test was carried out in the same manner as in Examples 1 to 19 and Comparative Examples 1 to 5.

[0151]

[0152] [Evaluation] As is clear from the results shown in Table 10, the conductive paste of this embodiment not only had excellent sulfur resistance, but also had high fluidity due to its small TI value, improved leveling, and excellent printing characteristics. At the same time, the Ra value was small, allowing the formation of a smooth coating film. Stereomicroscope images of the conductive thin films of Example 22 and Comparative Example 6 are shown in Figures 8 and 9. A flat surface was observed in Example 22, but mesh marks were confirmed in Comparative Example 6. These results demonstrate that the conductive paste of this embodiment is particularly excellent as a paste for forming high-resolution electrode patterns.

[0153] 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 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. A conductive paste comprising the conductive particles of (A) in an amount of 80 parts by weight or more per 100 parts by weight of the conductive paste.

2. The conductive paste according to claim 1, wherein the viscosity measured with an HB-type viscometer at 25°C and 10 rpm is in the range of 50 to 700 Pa·s.

3. The conductive paste according to claim 1, wherein the thixotropic index value (TI), which is the ratio of the viscosity at 1 rpm to the viscosity at 10 rpm, measured with an HB-type viscometer at 25°C, is 2.5 or less.

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

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

6. 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 conductive particles.

7. The conductive paste according to claim 6, wherein the content of the palladium compound in the surface treatment layer is 0.2 to 0.4 parts by weight per 100 parts by weight of the conductive particles.

8. 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.

9. An electrode obtained by firing or heat-treating a conductive paste according to any one of claims 1 to 8.

10. The electrode according to claim 9, wherein the arithmetic mean roughness (Ra) of the electrode surface, measured in accordance with JIS B 0601 (1994), is 0.5 μm or less.

11. An electronic component or electronic device comprising the electrode described in claim 9.