WO2024085091A1 - Conductive paste and method for manufacturing electronic component - Google Patents

Abstract

This conductive paste contains: a conductive powder mainly composed of copper; a glass frit; a binder resin; and an organic solvent. The conductive paste is characterized in that: the conductive powder mainly composed of copper has, in a laser diffraction particle size distribution measurement, a volume-based cumulative 50% particle size distribution D50_C of 0.3-4.5 μm , a ratio of the average major axis X to the average minor axis Y of 1.0-3.0, a ratio of the average major axis X to the average thickness Z of 1.1-9.0, and a ratio of the average major axis X to the average thickness Z of 1.1-9.0; and the glass frit has, in a laser diffraction particle size distribution measurement, a volume-based cumulative 50% particle size distribution D50_G of 0.3-2.0 μm. According to the present invention, a thin and dense terminal electrode having excellent continuity, even when fired at a low temperature, can be formed while maintaining high productivity. Moreover, an electronic component having a thin and dense terminal electrode having excellent continuity, even when fired at a low temperature, can be manufactured while maintaining high productivity.

Description

Conductive paste and method for manufacturing electronic components

The present invention relates to a conductive paste using conductive powder whose main component is copper. In particular, the present invention relates to a conductive paste for forming terminal electrodes of multilayer electronic components such as multilayer ceramic capacitors, multilayer inductors, and multilayer piezoelectric actuators. The present invention also relates to a method for manufacturing multilayer electronic components. In particular, the present invention relates to a method for manufacturing electronic components by forming terminal electrodes on a multilayer base body for multilayer electronic components.

Layered ceramic electronic components such as laminated ceramic capacitors, laminated inductors, and laminated piezoelectric actuators are generally manufactured as follows.

First, a conductive paste for the internal electrodes is printed in a specified pattern on a dielectric ceramic green sheet such as a barium titanate ceramic. Then, a number of these sheets are stacked and pressed together to obtain an unfired laminate in which ceramic green sheets and internal electrode paste layers are alternately stacked. The resulting laminate is cut into chips of a specified shape to obtain a laminate element. Note that the laminate element may be fired at a high temperature at this point, or it may not be fired at this point and may be fired simultaneously with a terminal electrode paste layer that is formed later using a conductive paste for the terminal electrodes. In either case, the laminate in the state before the terminal electrode paste layer is formed is referred to as a "laminated element."

Then, a conductive paste for the terminal electrodes, which is composed of conductive powder, binder resin, organic solvent, glass frit, etc., is printed on the exposed ends of the internal electrodes of the laminated body using a method such as dip printing to form a conductive paste layer, which is then dried as necessary and fired at a high temperature to form the terminal electrodes.

Furthermore, after this, a plating layer of nickel, tin, etc. may be formed on the terminal electrodes by electroplating, etc., as necessary.

Precious metals such as palladium, silver-palladium, and platinum have traditionally been used as internal electrode materials. However, there is a demand for resource conservation and cost reduction, and in sintered types in particular, there is a demand for preventing delamination and cracks caused by the oxidative expansion of palladium and silver-palladium when sintered, so in recent years the use of base metals such as nickel, cobalt, and copper has become mainstream. For this reason, copper, nickel, cobalt, or alloys of these metals, which easily form good electrical connections with base metal internal electrodes, are being used as terminal electrode materials instead of the conventional silver and silver-palladium.

When base metals are used for the internal electrodes and terminal electrodes in this way, the terminal electrodes are usually fired in a non-oxidizing atmosphere with as low an oxygen partial pressure as possible, for example an inert gas atmosphere with an oxygen content of several ppm to several tens of ppm, at a high peak temperature of around 800°C, so that these base metals are not oxidized during firing.

However, when firing in a low-oxygen atmosphere, particularly when using metal powder whose main component is copper, it is difficult to properly remove the binder, which burns, decomposes, and scatters organic components such as binder resin. If the binder is not sufficiently removed at the relatively low temperature stage in the early stages of firing, before the glass fluidizes and the copper powder sinters, carbon and organic residues will become trapped in the film after sintering begins, causing various problems such as blistering defects at the subsequent high-temperature stage.

Therefore, the main challenge for conductive pastes using metal powders containing base metals, especially copper, has traditionally been how to efficiently remove the binder in the early stages of firing and reduce residual carbon before the copper powder begins to sinter at high temperatures.

As a method for solving this problem, for example, Patent Document 1 discloses a conductor paste for terminal electrodes that uses an aliphatic amine as a surface treatment agent for copper-based conductive powder, thereby improving the dispersibility of the conductive powder and significantly improving the binder removal properties, thereby enabling the formation of dense terminal electrodes with excellent adhesion and conductivity.

Patent Document 2 also discloses a conductive paste that contains copper powder, glass frit, and an organic vehicle, the copper powder being a mixture of 0-70 vol% coarse copper powder with an average particle size of 1.0 μm-3.0 μm and 30-100 vol% fine copper powder with an average particle size of 0.1-0.8 μm. It also discloses an electronic component that includes a laminate having multiple ceramic layers and internal electrodes, and external electrodes formed on the outer surface of the laminate, electrically connected to the internal electrodes, and baked with the conductive paste, in which the carbon content in the external electrodes is 0.007 wt% or less when the sintering density of the external electrodes is 80%.

JP 2006-004734 A JP 2011-187225 A

In recent years, there has been a demand to lower the firing temperature when forming the aforementioned terminal electrodes in order to reduce the environmental impact, manufacturing costs, and thermal stress on the laminated body. In addition, there is a demand to miniaturize electronic components, which has led to a demand for thinner terminal electrodes. In other words, there is a demand for a conductive paste that is suitable for thin layers, can properly remove the binder, and can be used at a lower firing temperature.

The conductive pastes described in Patent Documents 1 and 2 are designed on the assumption that they will be fired at high temperatures, such as 800°C. Therefore, when fired at 800°C, sintering proceeds sufficiently after the binder is removed, resulting in a dense fired film. However, when the inventors of the present invention attempted firing at a low temperature, such as 720°C, using the above-mentioned paste, they were unable to allow sintering to proceed sufficiently after the binder was removed with firing times of several tens of minutes or hours.

The present invention therefore aims to provide a conductive paste that can form terminal electrodes that are thin, dense, and highly continuous, while maintaining high productivity, even when fired at low temperatures. The present invention also aims to provide a method for manufacturing electronic components that have terminal electrodes that are thin, dense, and highly continuous, while maintaining high productivity, even when fired at low temperatures.

As a result of intensive research to solve the above problems, the present inventors have found that by combining a fine conductive powder containing copper as a main component, and having a volume-based cumulative 50% particle diameter D50 _C of 0.3 μm or more and 4.5 μm or less, a ratio of the average major diameter X to the average minor diameter Y of 1.0 or more and 3.0 or less, and a ratio of the average major diameter X to the average thickness Z of 1.1 or more and 9.0 or less, with a fine glass frit having a volume-based cumulative 50% particle diameter D50 _G of 0.3 μm or more and 2.0 μm or less, as measured by laser diffraction particle size distribution measurement, it is possible to form a terminal electrode that is thin, dense, and excellent in continuity while maintaining high productivity, even when fired at a low temperature, and have completed the present invention.

That is, the present invention (1) is a conductive paste containing a conductive powder mainly composed of copper, a glass frit, a binder resin, and an organic solvent,
The copper-based conductive powder has a volume-based cumulative 50% particle diameter _D50C of 0.3 μm or more and 4.5 μm or less in a laser diffraction particle size distribution measurement, a ratio of an average major diameter X to an average minor diameter Y of 1.0 or more and 3.0 or less, and a ratio of an average major diameter X to an average thickness Z defined below of 1.1 or more and 9.0 or less,
The glass frit has a volume-based cumulative 50% particle diameter _D50G of 0.3 μm or more and 2.0 μm or less in a laser diffraction particle size distribution measurement.
The present invention provides a conductive paste characterized by the above-mentioned.
(Average thickness)
The conductive paste containing the copper-based conductive powder is cast onto a PET film with an applicator to form a coating film with a thickness of 250 μm, and the coating film is dried under conditions of air, 150° C., and 10 minutes to form a dry film. A cross section of the dry film is exposed by ion milling, and the cross section of the dry film is observed with a scanning electron microscope. 500 conductive particles are randomly selected and the minor axis is measured as the thickness to determine the average value of the thicknesses, and this average value is defined as the "average thickness."

The present invention (2) also provides a conductive paste according to (1), in which the copper-based conductive powder has an aliphatic amine on at least a portion of its surface.

The present invention (3) also provides the conductive paste described in (2) in which the aliphatic amine is 0.01 part by mass or more and 1.0 part by mass or less per 100 parts by mass of the conductive powder mainly composed of copper.

The present invention (4) provides the conductive paste according to any one of (1) to (3), wherein, when the volume-based cumulative 10% particle diameter of the glass frit is D10 _G and the volume-based cumulative 90% particle diameter of the glass frit is D90 _G in a laser diffraction particle size distribution measurement, (D90 _G -D10 _G )/D50 _G is 7.5 or less.

The present invention (5) provides the conductive paste according to any one of (1) to (4), in which, when the volume-based cumulative 10% particle diameter of the copper-based conductive powder is _D10C and the volume-based cumulative 90% particle diameter of the copper-based conductive powder is _D90C , ( _D90C - _D10C )/ _D50C is 7.5 or less, as measured by laser diffraction particle size distribution measurement.

The present invention (6) provides a conductive paste according to any one of (1) to (5), which satisfies at least one of the following: the ratio of the viscosity at a shear rate of 0.4 s ^{- 1} to the viscosity at a shear rate of 40 s-1, when measured at 25°C, is 2.0 or more and 20.0 or less; and when a strain amount of 1% is applied to the conductive paste at an angular frequency of 1 Hz, the phase difference δ between the strain and the stress generated by the strain is 45° or more and 80° or less.

The present invention (7) also provides a conductive paste according to any one of (1) to (6), which satisfies all of the following, as calculated by the following evaluation tests: the electrode area ratio of the terminal electrodes is 90% or more, the average maximum thickness of the terminal electrodes is 40 μm or less, and the average minimum thickness of the terminal electrodes is 1.0 μm or more.
<Terminal electrode area ratio evaluation test>
The evaluation test samples prepared by the evaluation test sample preparation method described below are observed using a scanning electron microscope in 10 visual fields for each sample, and the ratio of the electrode area to the observed visual fields is calculated as the electrode area ratio of the terminal electrode.
<Maximum terminal electrode thickness evaluation test>
An evaluation test sample prepared by the evaluation test sample preparation method described below is observed with a scanning electron microscope, and when a perpendicular line is drawn from the outer periphery of the terminal electrode to the end face of the laminated body in the evaluation test sample, the point where the length of the perpendicular line is longest is measured as the maximum thickness, and the maximum thicknesses of 20 electronic components whose maximum thicknesses were measured are averaged to calculate the average maximum thickness of the terminal electrode.
<Terminal electrode minimum thickness evaluation test>
An evaluation test sample prepared by the evaluation test sample preparation method described below is observed with a scanning electron microscope, and the thickness of the evaluation test sample at the point where the length of a perpendicular line drawn from the outer periphery of the terminal electrode to the end face of the laminated body is the shortest, and the thickness of the point where the distance between the corner of the laminated body and the outer periphery of the terminal electrode is the shortest are measured. The thickness of the thinnest of these points is measured as the minimum thickness, and the minimum thicknesses of 20 electronic components whose minimum thicknesses were measured are averaged to calculate the average minimum thickness of the terminal electrodes.
<How to prepare samples for evaluation tests>
A laminated element having a rectangular shape and a length of 0.6 mm, a width of 0.3 mm, and a height of 0.3 mm, in which a dielectric layer containing barium titanate and an internal electrode layer containing nickel are laminated in multiple layers, is prepared, and the conductive paste is applied to the end of the laminated element where the internal electrode is exposed by a dip printing method with a lowering speed of the laminated element of 300 μm/s and a lifting speed of 100 μm/s. The laminated element is then held in an air atmosphere at 150° C. for 10 minutes, and then heated in a nitrogen atmosphere at a heating rate of 50° C./min. After reaching 720° C., the temperature is held for 15 minutes to form terminal electrodes, thereby producing 20 electronic components equipped with terminal electrodes, and the 20 electronic components are each embedded in resin. Each electronic component is cut so as to pass through the center of both end face portions of each electronic component and in the stacking direction (perpendicular to the dielectric layers and internal electrode layers) to expose a cross section of each electronic component, thereby preparing an evaluation test sample.

The present invention (8) also provides a method for manufacturing an electronic component, comprising a laminate body preparation step of preparing a laminate body for a laminate-type electronic component, which is composed of a plurality of ceramic layers and a plurality of internal electrode layers, and a terminal electrode formation step of applying a conductive paste to the exposed ends of the internal electrodes of the laminate body, and then firing the applied conductive paste to form terminal electrodes, the conductive paste being the conductive paste described in any one of (1) to (7).

The present invention (9) also provides a method for manufacturing an electronic component as described in (7), in which the peak temperature of the firing is 720°C or less.

The present invention (10) provides the conductive paste according to any one of (1) to (7), wherein the conductive paste is a sintered conductive paste to be used after sintering, and when the peak temperature of the sintering is T ₁ °C, the glass frit is placed in a cylindrical container having an inner diameter of 5 mm, and a pressure of 3 MPa is applied in the axial direction for 10 seconds to produce a cylindrical green compact having a diameter of 5 mm and a height of 1 mm, the green compact is placed on a copper plate having a surface roughness Ra of 100 nm such that a flat surface of the green compact is in contact with the copper plate, and the green compact is heated in a nitrogen atmosphere at a heating rate of 10 °C/min to T ₁ °C to melt the glass constituting the green compact, whereby a contact angle of the glass with the copper plate is 80° or less.

The present invention (11) also provides the conductive paste according to any one of (1) to (7) and (10), which has a viscosity of 10.0 ^Pa ·s or more and 80.0 Pa·s or less at a shear rate of 4 s-1 when measured at 25°C.

The present invention (12) also provides a method for manufacturing an electronic component as set forth in (8) or (9), wherein the electrode area ratio of the terminal electrode calculated by the following calculation method is 90% or more.
<How to calculate the electrode area ratio of terminal electrodes>
The 20 electronic components are each embedded in resin, and each electronic component is cut through the center of both end face portions of the electronic component and in the stacking direction (perpendicular to the dielectric layers and internal electrode layers) to expose a cross section of each electronic component. The cross sections are observed using a scanning electron microscope in 10 fields of view for each electronic component, and the ratio of the electrode area to the observed fields of view is calculated as the electrode area ratio.

The present invention (13) also provides a method for producing an electronic component as set forth in any one of (8), (9), and (12), in which an average value of the maximum thickness of the terminal electrodes calculated by the following calculation method is 40 μm or less.
<How to calculate the average maximum thickness of terminal electrodes>
The 20 electronic components are each embedded in resin, and each electronic component is cut so as to pass through the center of both end face portions of each electronic component and in the stacking direction (perpendicular to the dielectric layers and internal electrode layers) to expose a cross-section of each electronic component. The cross-section is observed with a scanning electron microscope, and when a perpendicular line is drawn from the outer periphery of the terminal electrode to the end face portion of the laminated body on the cross-section, the point where the length of the perpendicular line is longest is measured as the maximum thickness. The maximum thicknesses of the 20 electronic components whose maximum thicknesses were measured are averaged to calculate an average maximum thickness of the terminal electrodes.

The present invention (14) also provides a method for producing an electronic component as set forth in any one of (8), (9), (12), and (13), in which an average value of the minimum thickness of the terminal electrodes calculated by the following calculation method is 1.0 μm or more.
<How to calculate the average minimum thickness of terminal electrodes>
The 20 electronic components are each embedded in resin, and each electronic component is cut so as to pass through the center of both end face portions of each electronic component and in the stacking direction (perpendicular to the dielectric layers and internal electrode layers) to expose a cross-section of each electronic component. The cross-section is observed with a scanning electron microscope, and the thickness of the point on the cross-section where the length of a perpendicular line drawn from the outer periphery of the terminal electrode to the end face portion of the laminated body is the smallest, and the thickness of the point where the distance between the corner portion of the laminated body and the outer periphery of the terminal electrode is the shortest are measured. The thickness of the thinnest of these parts is measured as the minimum thickness, and the minimum thicknesses of the 20 electronic components whose minimum thicknesses were measured are averaged to calculate an average minimum thickness of the terminal electrodes.

According to the present invention, even when firing at low temperatures, thin, dense, and highly continuous terminal electrodes can be formed while maintaining high productivity. In addition, even when firing at low temperatures, electronic components equipped with thin, dense, and highly continuous terminal electrodes can be manufactured while maintaining high productivity.

FIG. 1 is a schematic diagram for explaining a method for measuring the fired film thickness of a terminal electrode formed from a conductive paste.

<Conductive paste>
The conductive paste of the present invention contains a conductive powder mainly composed of copper, a glass frit, a binder resin, and an organic solvent, and the conductive powder has a cumulative 50% particle diameter D50C based on volume in a laser diffraction particle size distribution measurement of 0.3 μm to 4.5 μm, a ratio of the average major diameter X to the average minor diameter Y is 1.0 to 3.0, and a ratio of the average major diameter X to the average thickness Z is 1.1 to 9.0, and the glass frit has a cumulative 50% particle diameter _D50G based on volume in a laser diffraction particle size distribution measurement of 0.3 μm to 2.0 μm. This makes it possible to form a terminal electrode that is thin, dense, and excellent in continuity while maintaining high productivity, even when sintered at a low temperature. In particular, when the copper-based conductive powder of the present invention has an aliphatic amine described below on at least a part of the surface, the effect of the present invention is more remarkable.

By using the conductive powder mainly composed of copper, the filling property of the conductive powder in the coating film of the conductive paste is improved, so that the sintering of the conductive powder can proceed easily even when the conductive paste is fired at a low temperature. In addition, by using a glass frit having a D50 _G within the above range, the fine glass frit is uniformly dispersed even inside the film before firing in which the conductive powder is densely packed, so that the conductive powder can be uniformly sintered throughout the film, and a debindering path can be properly secured throughout the film, so that a thin, dense, and highly continuous terminal electrode can be formed. In addition, by setting the upper limit of D50 _G as above, the discontinuous portion of the terminal electrode caused by the voids generated after the glass flows can be reduced.

In addition, by surface treating the conductive powder, the dispersibility of the conductive powder is improved, and the filling of the conductive powder in the coating film is further improved. However, the improved filling narrows the binder removal path, reducing the binder removal property, and the surface treatment agent itself must be debindered, which may result in poor sintering or other problems such as blister defects due to insufficient binder removal. In a preferred embodiment of the present invention, by using an aliphatic amine as the surface treatment agent described below, the conductive powder can be properly debindered even when packed densely. That is, by using the conductive powder of the present invention that has been surface-treated with an aliphatic amine, the conductive powder can be packed even more densely in the coating film before firing, while the glass frit of the present invention is used and the surface treatment agent for the conductive powder is an aliphatic amine, improving the binder removal property, so that sintering is more likely to proceed even when firing at a low temperature, and a dense fired film is more likely to be obtained.

The conductive paste of the present invention is preferably used by applying the conductive paste to a laminated body or the like to form a coating film, drying the coating film as necessary to form a dry film, and then firing the paste. There are no particular limitations on the peak firing temperature, and firing is possible at 600°C or higher, which is lower than conventional firing temperatures. From the viewpoints of reducing the environmental load, reducing manufacturing costs, and reducing thermal stress on the laminated body, a peak firing temperature of 600°C or higher and 720°C or lower is preferable, and a peak firing temperature of 600°C or higher and 700°C or lower is particularly preferable.

<Conductive powder>
The conductive powder in the present invention may be one that contains copper as a main component, but the ratio of copper in the conductive powder is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, even more preferably 95% by mass or more and 100% by mass or less, and particularly preferably 100% by mass (pure copper). When the ratio of copper in the conductive powder is within the above range, the conductive powders are easily sintered together, making it easier to obtain a dense sintered film. In addition, as long as the conductive powder in the present invention contains copper as a main component, it may be a mixed powder of copper powder and other element metal powder such as nickel powder or silver powder, or an alloy powder of copper and other element metal such as nickel or silver. Furthermore, it may be a composite powder in which copper powder is coated with glass or ceramic, or may have an oxide film on the surface. Furthermore, it may be surface-treated with an organometallic compound or a surfactant, or two or more of these conductive powders may be mixed and used. In this specification, the term "main component" refers to the component being more than 50 mass% relative to the whole, and in particular, in a conductive powder containing copper as the main component, it refers to the copper component being more than 50 mass% relative to the total conductive powder contained in the conductive paste of the present invention, including the above-mentioned mixed powder, alloy powder, etc.

The conductive powder mainly composed of copper in the present invention may have a volume-based cumulative 50% particle diameter D50 _C in a laser diffraction particle size distribution measurement of 0.3 μm or more and 4.5 μm or less, but is preferably 0.3 μm or more and 4.0 μm or less, more preferably 0.5 μm or more and 4.0 μm or less, more preferably 0.5 μm or more and 3.0 μm or less, more preferably 0.7 μm or more and 3.0 μm or less, even more preferably 1.0 μm or more and 3.0 μm or less, and particularly preferably 1.5 μm or more and 2.5 μm or less. By having the D50 _C of the conductive powder mainly composed of copper in the above range, the sintering of the conductive powder is facilitated even when sintered at a low temperature, and a dense sintered film is easily formed. In addition, a thin sintered film is easily formed.

The copper-based conductive powder of the present invention may have a ratio of the average major axis X to the average minor axis Y of 1.0 or more and 3.0 or less, and preferably 1.0 or more and 2.5 or less. When the ratio of the average major axis X to the average minor axis Y of the copper-based conductive powder is in the above range, sintering proceeds easily even when sintering at a low temperature, making it easier to form a dense sintered film. It also makes it easier to form a thin sintered film (terminal electrode) with excellent continuity.

The above-mentioned average major axis X and average minor axis Y can both be measured, for example, by scanning electron microscope observation. That is, they can be measured by randomly selecting a number of conductive particles (e.g., 500 particles) using a scanning electron microscope, measuring the major axis and minor axis, and calculating the average value of each. They can also be measured, for example, by a flow-type particle image analyzer. That is, they can be measured by using a flow-type particle image analyzer to measure the major axis and minor axis of a number of conductive particles (e.g., 500 particles) and calculating the average value of each. As a flow-type particle image analyzer, for example, the FPIA-3000S manufactured by Sysmex Corporation can be used.

The copper-based conductive powder of the present invention may have a ratio of the average major axis X to the average thickness Z defined below of 1.1 to 9.0, preferably 1.1 to 7.5, more preferably 1.2 to 7.5, more preferably 1.2 to 6.0, more preferably 1.5 to 5.0, more preferably 1.6 to 4.5, more preferably 1.6 to 4.0, even more preferably 1.7 to 3.0, and particularly preferably 1.8 to 2.5. By having the ratio of the average major axis X to the average thickness Z of the copper-based conductive powder in the above range, sintering is facilitated even when sintering at a low temperature, making it easier to form a dense sintered film. In addition, it is easier to form a thin sintered film (terminal electrode) with excellent continuity.
(Average thickness)
The conductive paste containing the copper-based conductive powder is cast on a PET film with an applicator to form a coating film with a thickness of 250 μm, the coating film is dried under atmospheric conditions at 150° C. for 10 minutes to form a dry film, the cross section of the dry film is exposed by ion milling, the cross section of the dry film is observed with a scanning electron microscope, 500 conductive particles are randomly selected, the minor axis is measured as the thickness, and the average value of the thickness is calculated. This average value is defined as the "average thickness" in this specification (the present invention).

The average thickness Z can be measured, for example, by observing the cross section of a dried film formed using the conductive paste of the present invention under a scanning electron microscope. More specifically, for example, the conductive paste of the present invention is cast on a PET film using an applicator to form a coating film having a thickness of 250 μm, and the coating film is dried under conditions of air atmosphere, 150 ° C., and 10 minutes to form a dried film, and the cross section of the dried film is exposed using an ion milling device (e.g., IM4000 manufactured by Hitachi High-Tech Corporation), and the cross section of the dried film is observed using a scanning electron microscope (e.g., SU-8020 manufactured by Hitachi High-Tech Corporation), and a plurality of conductive particles (e.g., 500 particles) are randomly selected from the observation, and the minor axis is measured as the thickness, and the average value of the thickness is obtained. As the conductive paste of the present invention, for example, 100 parts by mass of conductive powder mainly composed of copper, acrylic resin (7 parts by mass as resin) dissolved in terpineol, and 10 parts by mass of glass frit are mixed, then kneaded using a three-roll mill, then diluted with terpineol, and adjusted to have a viscosity of 30 Pa·s at 25°C and a shear rate of 4 s ^-1 . It should be noted that even if the conductive powder mainly composed of copper contains other powders such as glass frit, the average thickness of the conductive powder mainly composed of copper can be measured by distinguishing it from the other powders. As a method of distinction, for example, the conductive powder mainly composed of copper can be distinguished from other powders by observing the element distribution in the cross section of the dried film by EDX (Energy dispersive X-ray spectroscopy).

The copper-based conductive powder of the present invention is not particularly limited in shape, so long as it has a _D50C of 0.3 μm or more and 4.5 μm or less, a ratio of the average major axis X to the average minor axis Y of 1.0 or more and 3.0 or less, and a ratio of the average major axis X to the average thickness Z of 1.1 or more and 9.0 or less, and may have, for example, a flat, cylindrical, elliptical cylindrical, truncated conical, elliptical truncated conical, rectangular parallelepiped, or other shape. The conductive powder of the present invention does not exclude powders of other shapes, such as spherical, and it is sufficient that the " _D50C ", "ratio of the average major axis X to the average minor axis Y", and "ratio of the average major axis X to the average thickness Z" of the conductive powder as a whole satisfy the above-mentioned numerical ranges. In this case, the content of the conductive powder satisfying the numerical range relative to the total conductive powder is not particularly limited, but is preferably more than 50 mass%, more preferably 55 mass% or more, more preferably 60 mass% or more, more preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and particularly preferably 95 mass% or more.

In the present invention, the copper-based conductive powder has a volume-based cumulative 10% particle diameter D10 _C and a cumulative 90% particle diameter D90 _C , and the (D90 _C -D10 _C )/D50 _C is preferably 7.5 or less, more preferably 6.5 or less, more preferably 5.0 or less, more preferably 4.0 or less, even more preferably 3.0 or less, and particularly preferably 2.0 or less. The lower limit of (D90 C -D10 _C )/D50 _C is not particularly limited, but can be, for example, 0.2 or more. When the (D90 _C -D10 _C )/D50 _C of _the copper-based conductive powder is in the above range, that is, the particle size distribution of the conductive powder is narrow, the sintering of the conductive powder can proceed uniformly throughout the entire film. In other words, since the local sintering in the film can be suppressed, a binder removal path can be properly secured throughout the film, resulting in the formation of a thin, dense, and highly continuous terminal electrode. Also, the terminal electrode can be prevented from becoming thicker due to the use of extremely large conductive powder.

The specific surface area of the conductive powder is preferably 0.2 m ² /g or more and 3.0 m ² /g or less, and particularly preferably 0.3 m ² /g or more and 2.0 m ² /g or less. When the specific surface area of the conductive powder containing copper as a main component is in the above range, sintering proceeds easily even when sintering is performed at a low temperature, and a dense sintered film is easily formed. In addition, a thin sintered film is easily formed.

The method for producing the conductive powder in the present invention is not particularly limited, and can be produced, for example, by producing spherical conductive powder by spray pyrolysis, physical vapor phase method, chemical vapor phase method, liquid phase reduction method, atomization method, etc., then surface treating the conductive powder with a surface treatment agent such as an aliphatic amine described below as necessary, and then pulverizing using a bead mill, ball mill, stamp mill, etc. Furthermore, the particle size distribution can be adjusted by classification before or after the pulverization process as necessary.

<Glass frit>
The volume-based cumulative 50% particle diameter _D50G of the glass frit in the present invention, as measured by laser diffraction particle size distribution measurement, may be 0.3 μm or more and 2.0 μm or less, and preferably 0.5 μm or more and 1.5 μm or less. When the _D50G of the glass frit is in the above range, a dense fired film is easily formed, and a fired film (terminal electrode) having excellent continuity is easily formed.

In the present invention, when the cumulative 10% particle diameter of the glass frit on a volume basis in a laser diffraction particle size distribution measurement is D10 _G and the cumulative 90% particle diameter is D90 _G , (D90 _G -D10 _G )/D50 _G is preferably 7.5 or less, more preferably 6.5 or less, more preferably 5.0 or less, even more preferably 3.5 or less, and particularly preferably 2.5 or less. The lower limit of (D90 _G -D10 _G )/D50 _G is not particularly limited, but can be, for example, 0.2 or more. When (D90 _G -D10 _G )/D50 _G of the glass frit is in the above range, that is, when the particle size distribution of the glass frit is narrow, the glass frit having a uniform size is uniformly distributed even inside the film before firing in which the conductive powder is densely packed, and the conductive powder is easily sintered uniformly throughout the film. This also makes it possible to suppress the local sintering in the film, thereby ensuring an appropriate binder removal path throughout the film, and as a result, a thin, dense, and highly continuous terminal electrode can be formed. The small amount of extremely small glass frit that exists in agglomeration and is prone to softening and flowing makes it easier to suppress the local sintering and the local binder removal failure caused by the sintering. The small amount of extremely large glass frit also makes it possible to suppress exposure of the laminated body due to voids that occur in places where the glass frit flows during the firing process, thereby improving the continuity of the terminal electrode.

When the conductive paste of the present invention is a sintered conductive paste to be used, and the peak temperature of the sintering is T ₁ ° C., the glass frit is placed in a cylindrical container with an inner diameter of 5 mm, and a pressure of 3 MPa is applied in the axial direction for 10 seconds to create a cylindrical green compact with a diameter of 5 mm and a height of 1 mm. The green compact is placed on a copper plate with a surface roughness Ra of 100 nm so that the flat surface of the green compact is in contact with the copper plate, and the green compact is heated in a nitrogen atmosphere at a heating rate of 10 ° C./min to T ₁ ° C. to melt the glass constituting the green compact. The contact angle of the glass with respect to the copper plate is preferably 80 ° or less, more preferably 75 ° or less, more preferably 70 ° or less, more preferably 65 ° or less, even more preferably 60 ° or less, and particularly preferably 55 ° or less. The lower limit of the contact angle of the glass with respect to the copper plate is not particularly limited, but can be, for example, 10 ° or more. When the contact angle of the glass with the copper plate is within the above range, the glass has good wettability with the conductive powder whose main component is copper, and while the flow of the glass is suppressed up to the desired temperature in order to properly remove the binder, the glass can quickly wet and spread in the vicinity of the conductive powder once the desired temperature is reached, making it easier to form a terminal electrode that is thin, dense, and highly continuous.

The composition of the glass frit in the present invention is not particularly limited, and for example, glasses such as BaO-ZnO-based, BaO-ZnO-B ₂ O ₃ -based, RO-ZnO-B ₂ O ₃ -MnO ₂ -based, RO-ZnO-based, RO-ZnO-MnO ₂ -based, RO-ZnO-SiO ₂ -based, ZnO-B ₂ O ₃ -based, SiO ₂ -B ₂ O ₃ -R' ₂ O-based, and SiO ₂ -RO-R' ₂ O-based (wherein R is an alkaline earth metal element, and R' is an alkali metal element) can be used.

The glass transition point of the glass frit in the present invention is preferably 400°C or higher and 550°C or lower. When the glass transition point of the glass frit is in the above range, the glass is more likely to wet and spread throughout the film even when fired at a low temperature, making it easier to form a dense fired film.

The softening point of the glass frit in the present invention is preferably 500°C or higher and 650°C or lower. When the softening point of the glass frit is in the above range, the glass is more likely to wet and spread throughout the film even when fired at a low temperature, making it easier to form a dense fired film.

The specific surface area of the glass frit is preferably 2.0 m ² /g or more and 7.0 m ² /g or less, particularly preferably 3.0 m ² /g or more and 6.0 m ² /g or less. When the specific surface area of the glass frit is in the above range, the glass frit is easily dispersed uniformly in the film, and therefore, a dense fired film is easily formed.

The amount of glass frit per 100 parts by mass of conductive powder is preferably 1 part by mass to 20 parts by mass, more preferably 4 parts by mass to 18 parts by mass, even more preferably 6 parts by mass to 16 parts by mass, and particularly preferably 8 parts by mass to 14 parts by mass. By having the amount of glass frit in the above range, it becomes easier to form a dense fired film.

<Surface treatment agent>
The copper-based conductive powder of the present invention preferably has an aliphatic amine on at least a part of its surface. The copper-based conductive powder has an aliphatic amine on at least a part of its surface, which prevents oxidation of the copper-based conductive powder and improves the dispersibility of the conductive powder in the paste, thereby improving the filling of the conductive powder in the coating film of the conductive paste of the present invention, thereby forming a fired film with excellent density even when fired at a low temperature. In addition, the conductive powder can be well dispersed in the paste, which makes it easier to form a thin terminal electrode with excellent continuity.

In the present invention, the aliphatic amine is preferably 0.01 to 1.0 parts by mass, more preferably 0.02 to 1.0 parts by mass, more preferably 0.03 to 1.0 parts by mass, more preferably 0.04 to 1.0 parts by mass, more preferably 0.05 to 1.0 parts by mass, and particularly preferably 0.1 to 0.5 parts by mass. When the amount of aliphatic amine is within the above range, the dispersibility of the conductive powder in the paste is improved, and the binder removal property is improved during firing, making it easier to form a thin, dense, and highly continuous terminal electrode.

As the aliphatic amine in the present invention, various amines can be used, such as primary amines such as octylamine, laurylamine, myristylamine, stearylamine, oleylamine, beef tallow amine, beef tallow propylenediamine, etc., secondary amines such as distearylamine, etc., and tertiary amines such as triethylamine, dimethyloctylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dimethylbehenylamine, dimethyllaurylamine, trioctylamine, etc. Two or more of these amines may be used in combination, and a mixture of several aliphatic amines that are usually commercially available as "aliphatic amines" can also be used. In particular, from the standpoint of ease of coating treatment on copper powder and adsorption to metal, alkylamines with a main chain of about 8 to 20 carbon atoms, or aliphatic amines containing such alkylamines as the main component, are preferred.

<Binder Resin>
The binder resin in the present invention is not particularly limited, but preferably contains an acrylic resin. The ratio of the acrylic resin to the entire binder resin is preferably more than 50% by mass, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. When an acrylic resin is used, it has excellent thermal decomposition properties in a nitrogen atmosphere, so that the binder resin can be removed well without oxidizing copper.

The amount of binder resin per 100 parts by mass of conductive powder is not particularly limited, but is preferably 3 parts by mass to 11 parts by mass, more preferably 4 parts by mass to 10 parts by mass, even more preferably 5 parts by mass to 9 parts by mass, and particularly preferably 6 parts by mass to 8 parts by mass. By using an amount of binder resin within the above range, it becomes easier to form a terminal electrode that is thin, dense, and has excellent continuity.

The weight-average molecular weight of the acrylic resin is not particularly limited, but for example, one between 20,000 and 1,000,000 can be used. Two or more types of acrylic resins with different weight-average molecular weights, structures, etc. may be used in combination.

<Organic Solvent>
The organic solvent in the present invention is not particularly limited, and examples thereof include terpineol, dihydroterpineol, dihydroterpineol acetate, secondary butyl alcohol, butyl carbitol, butyl carbitol acetate, and benzyl alcohol.

<Additives>
In addition to the above components, the conductive paste of the present invention may contain additives such as antifoaming agents, plasticizers, dispersants, and rheology modifiers, as necessary, so long as the effects of the present invention are not impaired. Examples of plasticizers include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, butyl benzyl phthalate, dioctyl adipate, diisononyl adipate, dibutyl sebacate, diethyl sebacate, dioctyl sebacate, tricresyl phosphate, chlorinated paraffin, and cyclohexane 1,2 dicarboxylate diisononyl ester. Examples of rheology modifiers include silica powder.

<Conductive paste properties>
The viscosity of the conductive paste of the present invention at a shear rate of 4 s ⁻¹ measured at 25° C. is not particularly limited, but is preferably 10.0 Pa·s or more and 80.0 Pa·s or less, and particularly preferably 20.0 Pa·s or more and 60.0 Pa·s or less. When the viscosity of the conductive paste is in the above range, it becomes easy to form a terminal electrode that is thin, dense, and excellent in continuity.

The ratio of the viscosity at a shear rate of 0.4 s ^-1 to the viscosity at a shear rate of 40 s ^-1 when measured at 25°C of the conductive paste of the present invention is not particularly limited, but is preferably 2.0 to 20.0, particularly preferably 3.0 to 8.0. When the viscosity ratio of the conductive paste is within the above range, it becomes easy to form a terminal electrode that is thin, dense, and excellent in continuity.

When a strain of 1% is applied to the conductive paste of the present invention at an angular frequency of 1 Hz, the value of the phase difference δ between the strain and the stress generated by the strain is not particularly limited, but is preferably 45° or more and 80° or less, and particularly preferably 45° or more and 78° or less. By having the phase difference δ value of the conductive paste within the above range, it becomes easier to form a terminal electrode that is thin, dense, and has excellent continuity.

The conductive paste of the present invention can be used to calculate the electrode area ratio of the terminal electrodes, the average maximum thickness of the terminal electrodes, and the average minimum thickness of the terminal electrodes, as described below, using evaluation test samples prepared, for example, by the following method. The evaluation test sample is prepared, for example, by preparing a rectangular parallelepiped laminated body having a length of 0.6 mm, a width of 0.3 mm, and a height of 0.3 mm, in which a dielectric layer containing barium titanate and an internal electrode layer containing nickel are laminated in multiple layers, applying the conductive paste to the end of the laminated body where the internal electrode is exposed by dip printing with a lowering speed of the laminated body of 300 μm/s and a lifting speed of 100 μm/s, then holding it in an air atmosphere at 150° C. for 10 minutes, then heating it in a nitrogen atmosphere at a heating rate of 50° C./min, and holding it for 15 minutes after reaching 700° C. or 720° C. to form terminal electrodes, thereby producing 20 electronic components with terminal electrodes, embedding each of the 20 electronic components in resin, and cutting each electronic component so as to pass through the center of both end face portions of each electronic component and in the lamination direction (perpendicular to the dielectric layer and the internal electrode layer) to expose the cross section of each electronic component.

<Electronic component manufacturing method>
The conductive paste of the present invention is suitable as a conductive paste for forming electrodes on an electrode-formed body (hereinafter also referred to as an electrode-formed body for electronic components) on which electrodes are formed in the manufacture of electronic components, and is particularly suitable as a conductive paste for forming terminal electrodes on a laminated base body for multilayer electronic components.

A suitable method for manufacturing electronic components using the conductive paste of the present invention includes a preparation step of preparing an electronic component electrode-forming body, and an electrode formation step of applying a conductive paste to the outer surface of the electronic component electrode-forming body and then firing the applied conductive paste to form an electrode, and the method forms an electrode on the electronic component electrode-forming body using the conductive paste of the present invention. By using the conductive paste of the present invention in the above-mentioned method for manufacturing electronic components, even when firing is performed at a low temperature in the electrode formation step, thin, dense, and highly continuous electrodes can be formed while maintaining high productivity. In other words, according to the above-mentioned method for manufacturing electronic components, even when firing is performed at a low temperature in the electrode formation step, electronic components having thin, dense, and highly continuous electrodes can be manufactured while maintaining high productivity.

The preparation step is a step of preparing an electrode-forming body for electronic components. An electrode-forming body for electronic components refers to an object on which an electrode is formed in the manufacturing process of electronic components. Examples of electrode-forming bodies for electronic components include laminates for multilayer electronic components consisting of multiple ceramic layers and multiple internal electrode layers, and cathode-forming bodies for solid electrolytic capacitors consisting of an anode and a dielectric layer formed on the surface of the anode.

The electrode formation process is a process in which a conductive paste is applied to the outer surface of an electronic component electrode formation body, and the applied conductive paste is fired to form an electrode. Examples of methods for applying the conductive paste include dip printing, screen printing, and roll coating. Of these, the dip printing method is preferred.

In the electrode formation process, the position and method of forming the electrodes, the thickness of the electrodes, the number of electrodes, the type of metal that constitutes the electrodes, the shape of the conductive powder used to form the electrodes, etc. are appropriately selected depending on the electronic components to be manufactured.

In the electrode formation process, after electrodes are formed on the electronic component electrode formation body, appropriate processes can be included depending on the type of electronic component. For example, in the case of a multilayer electronic component, in the electrode formation process, electrodes are formed in predetermined positions on the electronic component laminate base body, and then a plating layer is formed on the surface of the electrode.

A particularly suitable method for manufacturing electronic components using the conductive paste of the present invention includes a laminate body preparation step for preparing a laminate body for a laminate-type electronic component consisting of a plurality of ceramic layers and a plurality of internal electrode layers, and a terminal electrode formation step for applying a conductive paste to the exposed ends of the internal electrodes of the laminate body and then firing the applied conductive paste to form terminal electrodes, in which the conductive paste of the present invention is used to form terminal electrodes on the laminate body. By using the conductive paste of the present invention in the above-mentioned method for manufacturing electronic components, even when firing is performed at a low temperature in the terminal electrode formation step, thin, dense, and highly continuous terminal electrodes can be formed while maintaining high productivity. In other words, according to the above-mentioned method for manufacturing electronic components, even when firing is performed at a low temperature in the terminal electrode formation step, electronic components having thin, dense, and highly continuous terminal electrodes can be manufactured while maintaining high productivity.

　Laminated bodies for multilayer electronic components consist of multiple ceramic layers and multiple internal electrode layers. In laminated bodies for multilayer electronic components, the ceramic layers and internal electrode layers are stacked alternately. Examples of laminated bodies for multilayer electronic components include laminated bodies for multilayer ceramic capacitors, laminated bodies for multilayer ceramic inductors, and laminated bodies for piezoelectric actuators.

Materials for forming the ceramic layers that make up the laminated body for laminate-type electronic components include barium titanate, strontium titanate, calcium titanate, barium zirconate, strontium zirconate, calcium zirconate, and strontium calcium zirconate.

The materials forming the internal electrode layers that make up the laminated element for laminate-type electronic components include nickel, palladium, silver, copper, and gold, or alloys containing one or more of these (e.g., an alloy of silver and palladium).

In the terminal electrode formation process, the conductive paste of the present invention is applied to the exposed ends of the internal electrodes of the laminate body for multilayer electronic components, and the applied conductive paste is fired to form terminal electrodes. There are no particular limitations on the method for applying the conductive paste, and examples of the method include dip printing, screen printing, and roll coating. Of these, dip printing is preferred. After the conductive paste is applied to the laminate body, it may be dried and then fired.

In this specification, both ends of the laminated body where the internal electrodes are exposed are referred to as "ends", the faces of the ends where the internal electrodes are particularly exposed are referred to as "end faces", and the outer edge parts of the ends are referred to as "corner parts". Normally, when applying conductive paste to the ends in the terminal electrode formation process, the conductive paste is applied so as to cover the end faces and corner parts.

The size of the laminated element in which the conductive paste of the present invention is used is not particularly limited, and it can be used, for example, in laminated elements for 2012 size laminated ceramic capacitors, laminated elements for 1608 size laminated ceramic capacitors, laminated elements for 1005 size laminated ceramic capacitors, laminated elements for 0603 size laminated ceramic capacitors, laminated elements for 0402 size laminated ceramic capacitors, and laminated elements for 0201 size laminated ceramic capacitors. Thinning of the terminal electrodes is particularly required for small laminated ceramic capacitors, and the conductive paste of the present invention can be suitably used in laminated elements for 1005 size laminated ceramic capacitors, laminated elements for 0603 size laminated ceramic capacitors, laminated elements for 0402 size laminated ceramic capacitors, and laminated elements for 0201 size laminated ceramic capacitors.

The electrode area ratio of the terminal electrodes of the laminated electronic components obtained by the present invention is not particularly limited, but is preferably 90% or more, and more preferably 99% or more. This makes it easier to prevent the plating solution from penetrating into the laminated body when plating the terminal electrodes. The electrode area ratio can be calculated, for example, by the following method. That is, a plurality of electronic components (e.g., 20 components) are embedded in resin, and each electronic component is cut through the center of both end faces of each electronic component and in the lamination direction (perpendicular to the dielectric layer and internal electrode layer) to expose the cross section of each electronic component, and the cross section is observed with a scanning electron microscope (e.g., 10 fields of view for each electronic component), and the ratio of the electrode area in the observed field of view can be calculated as the electrode area ratio.

The maximum thickness of the terminal electrodes measured by the method described below is preferably 40 μm or less, more preferably 30 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, and particularly preferably 10 μm or less. The average maximum thickness of the terminal electrodes calculated by the method described below is preferably 40 μm or less, more preferably 30 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, and particularly preferably 10 μm or less. This allows the size of the multilayer electronic component to be reduced. Furthermore, in a multilayer electronic component of a given size, the thinner the terminal electrodes are, the larger the size of the multilayer base body can be, i.e., the electrode area and number of layers can be increased, thereby improving the performance of the multilayer electronic component. The method for measuring the maximum thickness is not particularly limited, but for example, the electronic component is embedded in resin, and the electronic component is cut through the center of both end face portions of the electronic component in the lamination direction (perpendicular to the dielectric layers and internal electrode layers) to expose the cross section of the electronic component, and the cross section is observed with a scanning electron microscope. When a perpendicular line is drawn from the outer periphery of the terminal electrode to the end face portion of the laminated body on the cross section, the point where the length of the perpendicular line is the maximum can be measured as the maximum thickness. The method for calculating the average maximum thickness is not particularly limited, but for example, the maximum thickness of each terminal electrode of a plurality of electronic components (e.g., 20 electronic components) is measured by the above-mentioned method, and the average of the maximum thicknesses can be calculated.

The minimum thickness of the terminal electrodes measured by the method described below is preferably 1.0 μm or more, more preferably 2.5 μm or more, and particularly preferably 5.0 μm or more. The average value of the minimum thickness of the terminal electrodes calculated by the method described below is preferably 1.0 μm or more, more preferably 2.5 μm or more, and particularly preferably 5.0 μm or more. This makes it easier to prevent the plating solution from penetrating into the laminated body when plating the terminal electrodes. The method for measuring the minimum thickness is not particularly limited, but for example, the electronic component is embedded in resin, and the electronic component is cut so as to pass through the center of both end face portions of the electronic component and in the lamination direction (perpendicular to the dielectric layer and the internal electrode layer) to expose the cross section of the electronic component, and the cross section is observed with a scanning electron microscope. In the cross section, the thickness of the part where the length of the perpendicular line is the shortest when a perpendicular line is drawn from the outer periphery of the terminal electrode to the end face portion of the laminated body, and the thickness of the part where the distance between the corner portion of the laminated body and the outer periphery of the terminal electrode is the shortest are measured, and the thickness of the thinnest part among these is measured as the minimum thickness. In addition, the method for calculating the average value of the minimum thickness is not particularly limited, but for example, the minimum thickness of each of the terminal electrodes of a plurality of electronic components (e.g., 20 electronic components) is measured by the above-mentioned method, and the average of the minimum thicknesses is calculated to calculate the average minimum thickness of the terminal electrodes.

The present invention will be explained below based on specific experimental examples, but the present invention is not limited to these.

<Preparation of conductive powder>
First, a plurality of types of spherical copper powder and spherical silver powder having different particle sizes were prepared, and the particle size distribution and particle size were adjusted by classification. Next, zirconia beads having a diameter of 0.1 mm, spherical copper powder, secondary butyl alcohol, and a predetermined surface treatment agent (aliphatic amine) were mixed, and a bead mill was used to perform a pulverization process by appropriately adjusting the flow rate and the number of passes, and then a classification process was performed as necessary to adjust the particle size distribution and particle size, thereby obtaining copper powders 1 to 22 and silver powder 1 shown in Table 1. Note that the above-mentioned pulverization process was not performed for copper powder 1, copper powder 3, and silver powder 1. Copper powder 3 and silver powder 1 were obtained by performing a surface treatment using a predetermined surface treatment agent (aliphatic amine). For the obtained copper powders 1 to 22 and silver powder 1, the major axis and minor axis of 500 copper particles (silver particles in the case of silver powder 1, copper particles and silver particles in the case of mixed powder C) were measured by scanning electron microscope observation, and the average major axis and average minor axis were calculated. In addition, the conductive pastes prepared in Experimental Examples 1 to 16 and 20 to 25 described later were cast on a PET film with an applicator to form a coating film with a thickness of 250 μm, and the coating film was dried under conditions of air atmosphere, 150 ° C., and 10 minutes to form a dry film, and the cross section of the dry film was exposed with an ion milling device (Hitachi High-Tech Corporation, model number: IM4000), and the cross section of the dry film was observed with a scanning electron microscope (Hitachi High-Tech Corporation, model number: SU-8020), and 500 copper particles were randomly selected from the observation to measure the minor axis, and the minor axis was used as the thickness to calculate the average thickness. From the average major axis, average minor axis, and average thickness calculated as above, the ratio of the average major axis to the average thickness and the ratio of the average major axis to the average minor axis were calculated. In addition, the volume-based cumulative 10% particle diameter D10, cumulative 50% particle diameter D50, and cumulative 90% particle diameter D90 were measured using a laser diffraction particle size distribution analyzer (LA-960, manufactured by HORIBA, Inc.). Using these measured values, (D90-D10)/D50 was calculated. In addition, copper powder 3 and copper powder 5 were mixed in a mass ratio of 20:80 (used in Experimental Example 18 described later), mixed powder A was mixed in a mass ratio of 45:55 (used in Experimental Example 19 described later), mixed powder B was mixed in a mass ratio of 90:10 (used in Experimental Example 17 described later), and mixed powder C was mixed in a mass ratio of 90:10 (used in Experimental Example 17 described later). The mixed powders (i.e., the conductive powder as a whole) were measured and calculated by the above-mentioned method for the "ratio of average major axis to average thickness", "ratio of average major axis to average minor axis", "D50" and "(D90-D10)/D50". The average thickness of mixed powders A to C was measured and calculated by the same method as described above, except that the conductive pastes prepared in Experimental Examples 17 to 19 were used. The average thickness of silver powder 1 was measured and calculated by the same method as described above, except that a conductive paste was prepared in the same manner as in Experimental Example 1 except that silver powder 1 was used instead of copper powder 1, and the conductive paste was used. The results are shown in Table 1.

<Preparation of glass frit>
BaO-ZnO glass (BaO: 30 mol%, ZnO: 27 mol%, B ₂ O ₃ : 25 mol%, SiO ₂ : 7 mol%, CaO: 7 mol%, Al ₂ O ₃ : 4 mol%) was produced, and the particle size and particle size distribution were adjusted by pulverization and classification to prepare glass frits 1 to 8 shown in Table 2. The volume-based cumulative 10% particle diameter D10 _G , cumulative 50% particle diameter D50 _G , and cumulative 90% particle diameter D90 _G of the prepared glass frits were measured using a laser diffraction particle size distribution measuring device (LA-960, manufactured by HORIBA). Using these measured values, (D90 _G -D10 _G )/D50 _G was calculated. In addition, the glass transition point and softening point were measured using the above-mentioned glass frits. The glass frit was placed in a cylindrical container with an inner diameter of 5 mm and pressure of 3 MPa was applied in the axial direction for 10 seconds to prepare a cylindrical green compact with a diameter of 5 mm and a height of 1 mm, which was placed on a copper plate with a surface roughness Ra of 100 nm so that the flat surface of the green compact was in contact with the copper plate, and the green compact was heated in a nitrogen atmosphere at a temperature increase rate of 10°C/min to 700°C to melt the glass constituting the green compact, and the contact angle of the glass with the copper plate was measured. Note that the contact angle of glass frit 4 was also measured when the temperature was increased to 680°C and 720°C, and the contact angle was 50°, similar to the contact angle at 700°C.

<Preparation of conductive paste>
Conductive pastes were prepared by mixing conductive powder, binder resin, and glass frit in the mixing ratios shown in Tables 3 to 6. The amount of surface treatment agent shown in the tables indicates the amount attached to the powder surface by surface treatment when preparing the conductive powder described above.
・Copper powder 1 to 22, silver powder 1
The ratio of the average major axis X to the average thickness Z, the ratio of the average major axis X to the average minor axis Y, D50, and (D90-D10)/D50 are as shown in Table 1.
・Acrylic resin 1
Mitsubishi Chemical Corporation, Model: Dianale MB-2677, Weight average molecular weight: 700,000, Acrylic resin 2
Mitsubishi Chemical Corporation, Model: Dianale BR-105, Weight average molecular weight: 50,000, Glass frit 1-8
Table 2 shows D50 _G , (D90 _G −D10 _G )/D50 _G , the contact angle with respect to a copper plate, the softening point, and the glass transition point.

(Experimental Examples 1 to 35, 41, and 42)
The conductive powder shown in Table 1, the glass frit shown in Table 2, and the acrylic resin 1 dissolved in terpineol were mixed in the blending ratios shown in Tables 3 to 6, then kneaded using a three-roll mill (manufactured by Inoue Seisakusho), then diluted with terpineol, and the viscosity at 25°C and a shear rate of 4 s ^-1 was adjusted to the values shown in Tables 3 to 6 to prepare a conductive paste. The prepared conductive paste was used to carry out the evaluations described below. The results are shown in Tables 3 to 6. The experimental examples marked with "*" are experimental examples outside the scope of the present invention.

(Experimental Examples 36 to 40)
The conductive powder shown in Table 1, the glass frit shown in Table 2, and the acrylic resin 1 or acrylic resin 2 dissolved in terpineol were mixed in the blending ratios shown in Tables 3 to 6, then kneaded using a three-roll mill (manufactured by Inoue Seisakusho), and then diluted with terpineol and, if necessary, dipropylene glycol-n-propyl ether, and the viscosity and viscosity ratio at 25°C and a shear rate of 4 s ^-1 were adjusted to the values shown in Table 6 to prepare a conductive paste. The prepared conductive paste was used to perform the evaluations described below. The results are shown in Table 6.

(Experimental Example 43)
In this experimental example, the conductive paste prepared in experimental example 5 was used. The terminal electrodes were evaluated in the same manner as in experimental example 5, except that a laminated element having a length of 0.4 mm, a width of 0.2 mm, and a height of 0.2 mm and a substantially rectangular parallelepiped shape, in which a dielectric layer containing barium titanate and an internal electrode layer containing nickel were laminated in multiple layers, was used as the laminated element.

<Evaluation of the physical properties of conductive paste>
(viscosity)
The viscosity of the conductive paste was measured using a rotational viscometer (manufactured by Brookfield, model number: HADV-II+Pro) at 25° C. and a shear rate of 4 s ⁻¹ .

(Viscosity Ratio)
The viscosity of the conductive paste was measured at a shear rate of 0.4 s ^-1 and a shear rate of 40 s ^-1 at 25° C. using a rotational viscometer (Brookfield, model number: HADV-II+Pro). The ratio of the viscosity at a shear rate of 0.4 s- ¹ to the viscosity at a shear rate of 40 s ^- 1 was calculated as the viscosity ratio.

(Phase difference)
Using a rheometer (manufactured by TA Instrument, model number: AR2000), measurements were performed using parallel plates with a diameter of 40 mm under conditions of 25° C., an angular frequency of 1 Hz, and a strain of 1%, to obtain the phase difference value of the conductive paste.

<Terminal electrode evaluation test>
(Production of Electronic Components with Terminal Electrodes)
A laminated element having a length of 0.6 mm, a width of 0.3 mm, and a height of 0.3 mm, and having a dielectric layer containing barium titanate and an internal electrode layer containing nickel, was prepared. A conductive paste was applied to the end of the laminated element where the internal electrode was exposed by dip printing with a lowering speed of 300 μm/s and a lifting speed of 100 μm/s, and then the laminated element was held for 10 minutes in an air atmosphere at 150° C. After that, the temperature was raised at a heating rate of 50° C./min in a nitrogen atmosphere, and after reaching the temperatures shown in Tables 3 to 6, the temperature was held for 15 minutes to form terminal electrodes, and electronic components equipped with terminal electrodes were produced.

(Preparation of evaluation test samples)
Twenty of the above electronic components were prepared for each experimental example. Each electronic component was embedded in resin, and cut through the center of each end face of each electronic component in the lamination direction (perpendicular to the dielectric layers and the internal electrode layers) to expose the cross section of each electronic component to prepare an evaluation test sample, and the following evaluation was performed.

(Terminal electrode density (electrode area ratio))
The above-mentioned evaluation test samples were observed with a scanning electron microscope, with 10 visual fields per sample, for a total of 200 visual fields, and the ratio of the electrode area to the visual fields was calculated as the electrode area ratio. The electrode area ratio value was evaluated based on the following evaluation criteria and given a score of 1 to 3. A score of 2 or more was considered to be a pass.
<Evaluation criteria>
3: Electrode area ratio is 99% or more 2: Electrode area ratio is 90% or more and less than 99% 1: Electrode area ratio is less than 90%

(Fired film thickness of terminal electrode)
The above-mentioned evaluation test samples were observed with a scanning electron microscope, and the thicknesses of the thickest part (maximum thickness) and the thinnest part (minimum thickness) of the terminal electrodes (fired films) were measured, and the average values of the maximum thickness and the minimum thickness were calculated for each experimental example. The average values of the maximum thickness and the minimum thickness were evaluated based on the following evaluation criteria and given a score of 1 to 3. A score of 2 or more was considered to be a pass.
<Evaluation criteria>
3: The average maximum thickness is ≦20 μm and the average minimum thickness is ≧2.5 μm
2: The average maximum thickness is ≦40 μm and the average minimum thickness is ≧1.0 μm
(However, this does not include cases falling under the above rating 3.)
1: Average maximum thickness > 40 μm, or average minimum thickness < 1.0 μm

The method for measuring the fired film thickness will be described with reference to FIG.
FIG. 1 is a schematic diagram showing an evaluation test sample 10 obtained by forming terminal electrodes 4 on a laminated body 1 using a conductive paste.
In the cross section of the evaluation test sample 10 observed with the above-mentioned scanning electron microscope, the length of a perpendicular line drawn from the outer periphery 5 of the terminal electrode 4 to the end face 3 of the laminated element 1 is defined as D. The thickness at the point where the value of D is maximum is measured, and this thickness value is defined as the maximum thickness _Dmax . In addition, the thickness Da at the point where the value of D is minimum and the thickness Db at the point where the distance between the corner portion 2 of the laminated element 1 and the outer periphery 5 of the terminal electrode 4 is shortest are measured, and the smaller of Da and Db is defined as the minimum thickness _Dmin . Note that, in the cross section of the evaluation test sample 10 observed with the above-mentioned scanning electron microscope, if there is a portion where the laminated element 1 is exposed due to a hole being formed in the terminal electrode 4, the minimum thickness is defined as "0 μm".

As is clear from the above experimental examples, by using the conductive paste of the present invention, it is possible to form thin, dense, and highly continuous terminal electrodes while maintaining high productivity, even when firing at low temperatures such as 720°C or less.

1 laminated element 2 corner portion 3 end surface portion 4 terminal electrode 5 outer periphery portion 10 evaluation test sample D length of perpendicular line drawn from outer periphery portion to end surface portion Da thickness at point where D value is smallest Db thickness at point where distance between corner portion and outer periphery portion is shortest _Dmax thickness at point where D value is largest _Dmin smaller value of Da and Db

Claims (9)

1. A conductive paste containing a conductive powder mainly composed of copper, a glass frit, a binder resin, and an organic solvent,
   The copper-based conductive powder has a volume-based cumulative 50% particle diameter _D50C of 0.3 μm or more and 4.5 μm or less in a laser diffraction particle size distribution measurement, a ratio of an average major diameter X to an average minor diameter Y of 1.0 or more and 3.0 or less, and a ratio of an average major diameter X to an average thickness Z defined below of 1.1 or more and 9.0 or less,
   The glass frit has a volume-based cumulative 50% particle diameter _D50G of 0.3 μm or more and 2.0 μm or less in a laser diffraction particle size distribution measurement.
   A conductive paste comprising:
   (Average thickness)
   The conductive paste containing the copper-based conductive powder is cast onto a PET film using an applicator to form a coating film with a thickness of 250 μm, and the coating film is dried under conditions of air, 150° C., and 10 minutes to form a dry film. A cross section of the dry film is exposed by ion milling, and the cross section of the dry film is observed with a scanning electron microscope. 500 conductive particles are randomly selected and the minor axis is measured as the thickness to determine the average value of the thicknesses, and this average value is defined as the "average thickness."
2. The conductive paste according to claim 1, characterized in that the copper-based conductive powder has an aliphatic amine on at least a portion of its surface.
3. The conductive paste according to claim 2, characterized in that the aliphatic amine is present in an amount of 0.01 part by mass or more and 1.0 part by mass or less per 100 parts by mass of the copper-based conductive powder.
4. The conductive paste according to any one of claims 1 to 3, characterized in that, when the cumulative 10% particle diameter of the glass frit on a volume basis in a laser diffraction particle size distribution measurement is defined as D10 _G and the cumulative 90% particle diameter is defined as D90 _G , (D90 _G -D10 _G )/D50 _G is 7.5 or less.
5. The conductive paste according to any one of claims 1 to 4, characterized in that, when the volume-based cumulative 10% particle diameter of the copper-based conductive powder is _D10C and the cumulative 90% particle diameter is _D90C in a laser diffraction particle size distribution measurement, ( _D90C - _D10C ) / _D50C is 7.5 or less.
6. The conductive paste according to any one of claims 1 to 5, characterized in that the ratio of the viscosity at a shear rate of 0.4 s ^{- 1} to the viscosity at a shear rate of 40 s-1 when measured at 25 ° C. is 2.0 or more and 20.0 or less, and when a strain amount of 1% is applied to the conductive paste at an angular frequency of 1 Hz, the phase difference δ between the strain and the stress generated by the strain is 45 ° or more and 80 ° or less.
7. The conductive paste according to any one of claims 1 to 6, characterized in that the electrode area ratio of the terminal electrodes is 90% or more, the average maximum thickness of the terminal electrodes is 40 μm or less, and the average minimum thickness of the terminal electrodes is 1.0 μm or more, as calculated by each of the following evaluation tests.
   <Terminal electrode area ratio evaluation test>
   The evaluation test samples prepared by the evaluation test sample preparation method described below are observed using a scanning electron microscope in 10 visual fields for each sample, and the ratio of the electrode area to the observed visual fields is calculated as the electrode area ratio of the terminal electrode.
   <Maximum terminal electrode thickness evaluation test>
   An evaluation test sample prepared by the evaluation test sample preparation method described below is observed with a scanning electron microscope, and when a perpendicular line is drawn from the outer periphery of the terminal electrode to the end face of the laminated body in the evaluation test sample, the point where the length of the perpendicular line is longest is measured as the maximum thickness, and the maximum thicknesses of 20 electronic components whose maximum thicknesses were measured are averaged to calculate the average maximum thickness of the terminal electrode.
   <Terminal electrode minimum thickness evaluation test>
   An evaluation test sample prepared by the evaluation test sample preparation method described below is observed with a scanning electron microscope, and the thickness of the evaluation test sample at the point where the length of a perpendicular line drawn from the outer periphery of the terminal electrode to the end face of the laminated body is the shortest, and the thickness of the point where the distance between the corner of the laminated body and the outer periphery of the terminal electrode is the shortest are measured. The thickness of the thinnest of these points is measured as the minimum thickness, and the minimum thicknesses of 20 electronic components whose minimum thicknesses were measured are averaged to calculate the average minimum thickness of the terminal electrodes.
   <How to prepare samples for evaluation tests>
   A laminated element having a rectangular shape and a length of 0.6 mm, a width of 0.3 mm, and a height of 0.3 mm, in which a dielectric layer containing barium titanate and an internal electrode layer containing nickel are laminated in multiple layers, is prepared, and the conductive paste is applied to the end of the laminated element where the internal electrode is exposed by a dip printing method with a lowering speed of the laminated element of 300 μm/s and a lifting speed of 100 μm/s. The laminated element is then held in an air atmosphere at 150° C. for 10 minutes, and then heated in a nitrogen atmosphere at a heating rate of 50° C./min. After reaching 720° C., the temperature is held for 15 minutes to form terminal electrodes, thereby producing 20 electronic components equipped with terminal electrodes, and the 20 electronic components are each embedded in resin. Each electronic component is cut so as to pass through the center of both end face portions of each electronic component and in the stacking direction (perpendicular to the dielectric layers and internal electrode layers) to expose a cross section of each electronic component, thereby preparing an evaluation test sample.
8. a laminated body preparation step of preparing a laminated body for a multilayer electronic component, the laminated body including a plurality of ceramic layers and a plurality of internal electrode layers;
   a terminal electrode forming step of applying a conductive paste to the exposed ends of the internal electrodes of the laminated body and then firing the applied conductive paste to form terminal electrodes;
   having
   A method for producing an electronic component, comprising the conductive paste according to any one of claims 1 to 7.
9. The method for manufacturing electronic components described in claim 8, characterized in that the peak temperature of the firing is 720°C or less.

Images