Gold paste

Abstract

To provide a gold paste that can suppress foaming during firing and form a conductive film with a smooth surface.SOLUTION: A gold paste disclosed herein contains at least gold particles, glass particles, and a dispersion medium, the glass particles contain at least one selected from alkali metal elements or alkaline earth metal elements, and the ratio (St / DBET) of the total surface area St (m2) of the glass contained in the gold paste to the average particle diameter DBET (μm) of the gold particles based on BET conversion is 0.11 or less. The gold paste according to the embodiment can suppress foaming during firing and form a conductor film with a smooth surface.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to gold paste. [Background technology]

[0002] In recent years, ceramic electronic components such as thermistors, multilayer ceramic capacitors, multilayer inductors, and multilayer piezoelectric elements (multilayer varistors) have been used in a wide range of fields. For these ceramic electronic components, a technique of forming a conductor film on an insulating substrate using a conductive material and then wiring using this conductor film has been widely adopted. Such a conductor film is formed, for example, by firing a paste containing conductive particles and glass particles. For example, a thermistor may include a thermistor element body and a surface electrode, which is an example of a conductor film, on the surface of the thermistor element body.

[0003] Conventionally, gold (Au) particles have been used as the conductive particles due to their chemical stability and excellent conductivity. As a related technology, for example, Patent Document 1 discloses a low-temperature fired gold paste obtained by kneading and dispersing gold particles with a particle size of 1.0 μm or less, glass frit with a softening point of 450°C or less, and an organic vehicle. Furthermore, the glass component contained in the glass particles contains an alkali metal oxide or alkaline earth metal oxide in order to control the softening point of the glass particles and the fluidity of the glass component after melting. Patent Document 2, for example, discloses such a technology. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-340619 [Patent Document 2] Patent No. 7082408 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the inventors have found that when a paste containing gold particles and glass particles containing alkali metal oxides or alkaline earth metal oxides is fired, foaming of the glass particles causes unevenness on the surface of the resulting conductive film, which is undesirable in terms of poor appearance.

[0006] The technology disclosed herein was created in light of the above circumstances, and aims to provide a gold paste that can suppress foaming during firing and form a conductor film with a smooth surface. [Means for solving the problem]

[0007] In order to achieve the above object, the inventors conducted research and focused on the relationship between gold particles and glass particles in the gold paste. Specifically, the glass particles in the gold paste melt during firing to form a liquid glass component. Based on the above viewpoint, the inventors conducted further intensive research and found that when the glass component comes into contact with the gold particles, the glass component reacts and foams. Furthermore, as a result of further intensive research, the inventors found that the average particle diameter D of the gold particles in the gold paste based on BET conversion is BET The ratio of the total surface area S of glass particles per 1 g of gold particles to the total surface area S of glass particles per 1 g of gold particles (S t / D BET ) is an indicator, and the above S t / D BET It has been found that by setting the temperature within a predetermined range, foaming that occurs during firing can be suppressed.

[0008] That is, the gold paste disclosed herein contains at least gold particles, glass particles, and a dispersion medium, the glass particles containing at least one selected from alkali metal elements and alkaline earth metal elements, and the gold particles have an average particle diameter D based on BET conversion. BET (μm) versus the total surface area S of the glass contained in the gold paste t (m 2 ) ratio (S t / D BET ) is 0.11 or less.

[0009] According to this configuration, the S of the gold paste t / D BET By setting the ρ at 0.11 or less, contact between the glass particles and the gold particles in the gold paste is suitably controlled. This suppresses reaction of the glass particles and prevents foaming. Therefore, the gold paste disclosed herein can suppress foaming during firing and form a conductor film with a smooth surface.

[0010] In a preferred embodiment of the gold paste disclosed herein, the content of the glass particles is 0.8 parts by weight or more and 3.2 parts by weight or less per 100 parts by weight of the gold particles contained in the gold paste.

[0011] In a preferred embodiment of the gold paste disclosed herein, the content of alkaline earth metal components or alkali metal components in the entire glass particles is 15 wt % or more and 35 wt % or less in terms of oxide.

[0012] In a preferred embodiment of the gold paste disclosed herein, the softening point of the glass particles is 800°C or higher and 900°C or lower.

[0013] In a preferred embodiment of the gold paste disclosed herein, the average particle diameter D BET (μm) is 0.35 μm or more and 1.5 μm or less.

[0014] In one preferred embodiment of the gold paste disclosed herein, the gold paste is substantially free of lead.

[0015] In a preferred embodiment of the gold paste disclosed herein, the glass particles have the following composition in terms of oxides: SiO2: 35wt%~70wt% B2O3: 2wt%~20wt% Al2O3: 5wt%~20wt% RO: 15wt%~35wt% (wherein R includes at least one element selected from the group consisting of Mg, Ca, Zn, Ba, and Sr).

[0016] In one preferred embodiment of the gold paste disclosed herein, the gold paste is used to form a conductive film for a thermistor. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram for explaining the configuration of an NTC thermistor manufactured using a gold paste according to one embodiment. [Figure 2] FIG. 2 is a graph showing the relationship between the St / DBET of a gold paste according to a test example and the number of bubbles formed in a test piece provided with a conductor film of the gold paste. [Figure 3] FIG. 3 is an optical microscope image (50x magnification) of the test piece (conductor film) according to Example 5. [Figure 4] FIG. 4 is an SEM image (200x magnification) of the surface of the test piece (conductor film) according to Example 5. [Figure 5] FIG. 5 is an optical microscope image (50x magnification) of the test piece (conductor film) according to Example 9. [Figure 6] FIG. 6 is an SEM image (200x magnification) of the surface of the test piece (conductor film) according to Example 9. DETAILED DESCRIPTION OF THE INVENTION

[0018] Preferred embodiments of the technology disclosed herein are described below. Matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field. In this specification, the expression "A to B" indicating a numerical range means "greater than or equal to A and less than or equal to B."

[0019] [Gold paste] The gold paste disclosed herein contains at least gold particles, glass particles, and a dispersion medium. Each component of the gold paste disclosed herein will be described below.

[0020] 1. Gold particles Gold (Au) particles are a material used to form highly electrically conductive conductive films (electrodes) that serve as conductors in electronic devices and the like. Gold particles are typically used in the form of gold powder, which is an aggregate of multiple gold particles. The composition of the gold powder is not particularly limited as long as it is a powder (aggregate of particles) primarily composed of gold, and gold powders with desired conductivity and other physical properties can be used. Here, "main component" refers to the largest component among the components constituting the gold powder. Examples of gold powder include those composed of gold, gold alloys, and mixtures or composites thereof. For example, core-shell particles having a core composed of a metal other than gold or a gold alloy, and a shell covering the core composed of gold, can also be used. Core-shell particles having a core composed of gold and a shell covering the core composed of a metal other than gold or a gold alloy, can also be used. Since higher purity (content) of gold powder tends to increase conductivity, it is preferable to use gold powder with a high purity. The purity of the gold powder is preferably 95% or higher, more preferably 97% or higher, even more preferably 98% or higher, and particularly preferably 99% or higher. In the technology disclosed herein, even when gold powder with a purity of 99.99% or less (for example, 99.9% or less) is used, the foaming suppression effect can be obtained.

[0021] In addition, from the viewpoint of suppressing aggregation of gold particles in the paste, the BET specific surface area of ​​the gold particles is set to 2.00 m 2 / g or less is preferable, and 1.50m 2 / g or less is more preferable, and 1.20m 2 / g or less is more preferable, and 1.00m 2 / g or less is particularly preferred. On the other hand, as the BET specific surface area of ​​the gold particles increases, the contact area between the gold particles increases, which tends to improve the conductivity of the conductor film after firing. From this perspective, the BET specific surface area of ​​the gold particles is 0.10 m 2 / g or more is preferable, and 0.12m2 / g or more is more preferable, and 0.15m 2 / g or more is more preferable, and 0.2m 2 / g or more is particularly preferred. In this specification, the "BET specific surface area" can be determined by calculation using the BET method (e.g., the BET single-point method) based on the gas adsorption amount measured by a gas adsorption method (constant volume adsorption method) using nitrogen (N) gas as the adsorbate. An apparatus for measuring the BET specific surface area may be, for example, a Macsorb HM Model-1201 (Mountec Co., Ltd.).

[0022] Average gold particle diameter D based on BET conversion BET The average particle diameter D of the gold particles is preferably 0.35 μm or more, more preferably 0.45 μm or more, and even more preferably 0.55 μm or more. BET As the average particle diameter D of the gold particles increases, foaming of the glass particles during firing of the gold paste is effectively suppressed, and the packing of the gold particles tends to improve. BET If the average particle diameter D of the gold particles is too large, the gold paste must be exposed to high temperatures for a long time during sintering. BET is preferably 1.5 μm or less, more preferably 1.2 μm or less, even more preferably 1 μm or less, and particularly preferably 0.9 μm or less. In this specification, the "average particle size based on BET conversion" can be calculated from the true specific gravity ρ of the particles and the BET specific surface area based on the following formula (1) using the above-mentioned "BET specific surface area." Average particle size D based on BET conversion BET =6 / (BET specific surface area·ρ)···(1)

[0023] Although not particularly limited, the median diameter of the gold particles may be 0.20 μm or more, 0.30 μm or more, or 0.40 μm or more. The median diameter of the conductive particles may be 3.0 μm or less, 2.0 μm or less, or 1.5 μm or less. In this specification, the term "median diameter" refers to the particle size (volume equivalent sphere diameter) that corresponds to 50% of the cumulative value from the smallest particle size in a volume-based particle size distribution based on a laser diffraction scattering method. For example, a Microtrac MT-3000 (Microtrac Bell Corporation) can be used as an apparatus for measuring the median diameter.

[0024] The shape of the gold particles is not particularly limited. For example, the gold particles may be spherical or non-spherical. Non-spherical shapes may include, for example, plate-like, scale-like, flake-like, and irregular shapes. From the viewpoint of easily increasing the packing density of the gold particles, spherical gold particles having an aspect ratio of, for example, 1.2 or less, preferably 1.15 or less, for example, 1.1 or less, can be preferably used. Furthermore, from the viewpoint of easily increasing the contact area between multiple gold particles, non-spherical gold particles having an aspect ratio of, for example, more than 1.2, preferably 1.3 or more, 1.5 or more, for example, 1.7 or more, and more preferably 2 or more can be used. To synergize the above effects, spherical and non-spherical gold particles may be mixed. This allows multiple gold particles to contact each other favorably when the solvent is removed from the paste by drying, thereby improving the electrical conductivity of the conductive film. The "aspect ratio" in this specification refers to the arithmetic mean value of the value (aspect ratio) obtained by the ratio (b / a) of the long side length (b) to the short side length (a) when a rectangle circumscribing 100 particles is drawn in an electron microscope photograph.

[0025] From the viewpoint of improving the electrical conductivity of the gold paste after firing, the gold particle content in the gold paste is preferably 60 wt% or more, more preferably 65 wt% or more, and even more preferably 70 wt% or more. On the other hand, from the viewpoint of ensuring a certain level of glass particle content and improving the density of the conductive film, the upper limit of the gold particle content is preferably 90 wt% or less, more preferably 85 wt% or less, and even more preferably 80 wt% or less. In this specification, unless otherwise specified, "content" refers to the weight percentage when the total mass of the gold paste is 100 wt%.

[0026] 2. Glass particles The gold paste disclosed herein contains glass particles. The glass particles are typically used in the form of glass powder, which is an aggregate of multiple glass particles. When the softening point of the glass particles is reached during firing, the glass particles melt and become a liquid glass component. This liquid glass component fills the gaps between the gold particles and serves to densify the conductor film.

[0027] (1) Composition of glass particles This section describes the specific composition of the glass particles disclosed herein. The glass particles according to this embodiment contain at least one selected from alkali metal elements and alkaline earth metal elements. Such alkali metal elements or alkaline earth metal elements are typically contained in the glass particles as alkali metal oxides or alkaline earth metal oxides.

[0028] Alkali metal oxides (R'O) penetrate into the three-dimensional glass network, imparting fluidity to the glass and lowering its softening point. These components lower the softening point of the glass, thereby increasing its fluidity. Examples of alkali metal oxides include lithium oxide (LiO), sodium oxide (NaO), potassium oxide (KO), and rubidium oxide (RbO). To impart fluidity to the glass, the alkali metal content of the glass particles is preferably 15 wt% or more, more preferably 18 wt% or more, and even more preferably 20 wt% or more, calculated as oxide. To suppress foaming of the glass particles during firing of the gold paste, the alkali metal content of the glass particles is preferably 35 wt% or less, more preferably 32 wt% or less, and even more preferably 30 wt% or less.

[0029] Alkaline earth metal oxides (RO) are components that impart fluidity to glass and increase its softening point. They also function as network modifiers, improving the physical and thermal stability of glass. Examples of such alkaline earth metal oxides include magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO). To impart fluidity to glass, the content of the alkaline earth metal component in the entire glass particles is preferably 15 wt% or more, more preferably 18 wt% or more, and even more preferably 20 wt% or more, calculated as oxide. To suppress foaming of glass particles during firing of the gold paste, the content of the alkaline earth metal component in the entire glass particles is preferably 35 wt% or less, more preferably 32 wt% or less, and even more preferably 30 wt% or less.

[0030] In some preferred examples, the content of alkali metal or alkaline earth metal components in the entire glass particles is preferably 15 wt% or more and 35 wt% or less, calculated as oxides. In other words, when the entire glass particles are taken as 100 wt%, the sum of the contents of alkaline earth metal oxides and alkali metal oxides (RO+R'O (where R includes at least one element selected from the group consisting of Mg, Ca, Ba, and Sr, and R' includes at least one element selected from Li, Na, K, Rb, Cs, and Fr)) is preferably 15 wt% or more and 35 wt% or less. This makes it possible to impart fluidity to the glass while suitably suppressing foaming of the glass particles during firing of the gold paste. From the viewpoint of imparting fluidity to the glass, the content of alkaline earth metal or alkali metal components in the entire glass particles is preferably 15 wt% or more, more preferably 18 wt% or more, and even more preferably 20 wt% or more, calculated as oxides. On the other hand, from the viewpoint of suppressing foaming of glass particles during firing of the gold paste, the content of alkaline earth metal components or alkali metal components in the entire glass particles is preferably 35 wt% or less, more preferably 32 wt% or less, and even more preferably 30 wt% or less.

[0031] Although the glass composition is not particularly limited, the glass particles contained in the gold paste disclosed herein may contain the following components in addition to at least one selected from alkali metal elements or alkaline earth metal elements. In some preferred embodiments, the glass particles have the following composition in terms of oxides: SiO2: 35wt%~70wt% B2O3: 2wt%~20wt% Al2O3: 5wt%~20wt% RO: 15wt%~35wt% (where R includes at least one element selected from the group consisting of Mg, Ca, Sr, and Ba). Glass particles with a composition that satisfies the above range can suppress foaming of the glass particles when the gold paste is fired. While the exact reason is unclear, it is thought to be due to the low fluidity of the softened glass during the process in which the glass particles soften due to the temperature rise caused by firing.

[0032] Silicon oxide (SiO2) is one of the components (glass skeleton components) that can independently form a glass skeleton. As the proportion of SiO2 in the glass skeleton components increases, the thermal stability of the glass particles improves and the softening point becomes higher. In other words, silicate-based glasses containing a large amount of SiO2 are difficult to melt sufficiently during paste firing to produce glass components with excellent fluidity. From this perspective, the SiO2 content in the glass particles is preferably 70 wt% or less, more preferably 65 wt% or less, and even more preferably 60 wt% or less, relative to the total glass. SiO2 also has the function of increasing the chemical resistance of the glass particles. For this reason, the SiO2 content is preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 45 wt% or more, relative to the total glass.

[0033] Boron oxide (BO) is one of the components that constitute the glass skeleton. As the proportion of BO in the glass skeleton components increases, the fluidity of the glass components after melting tends to improve. From this perspective, the BO content is preferably 2 wt% or more, more preferably 5 wt% or more, and even more preferably 7 wt% or more, based on the total glass. This makes it easier to diffuse the glass components after melting, allowing for the formation of external electrodes with superior density. On the other hand, BO lowers the softening point of the glass particles. From this perspective, the BO content in the glass particles is preferably 20 wt% or less, more preferably 17 wt% or less, and even more preferably 15 wt% or less, based on the total glass.

[0034] Aluminum oxide (Al2O3) has the function of stabilizing the glass skeleton and controlling the fluidity of the glass components. From the viewpoint of adjusting the softening point and fluidity of the glass particles within a suitable range, the Al2O3 content is preferably 5 wt% or more, more preferably 7 wt% or more, and even more preferably 10 wt% or more, based on the total glass. On the other hand, the Al2O3 content is preferably 20 wt% or less, more preferably 17 wt% or less, and even more preferably 15 wt% or less, based on the total glass.

[0035] It should be noted that the above description is not intended to limit the composition of the glass particles disclosed herein to the above components. The glass particles disclosed herein may contain, for example, P2O5, Bi2O3, etc. as glass skeleton-forming components. Furthermore, they may contain, for example, ZnO, TiO2, MnO, FeO, Fe2O3, Fe3O4, SnO, SnO2, V2O5, ZrO2, Nb2O5, CuO, Cu2O, La2O3, CeO2, etc. as glass skeleton-modifying components. When the glass particles contain other components (i.e., components other than alkali metal oxides, alkaline earth metal oxides, SiO2, B2O3, and Al2O3), the content ratio thereof is, for example, 5 wt% or less, preferably 3 wt% or less, more preferably 2 wt% or less, and even more preferably 1 wt% or less.

[0036] From an environmental perspective, the glass particles of the gold paste disclosed herein preferably contain substantially no PbO. In this specification, "substantially no PbO" refers to the absence of intentional PbO addition. Therefore, trace amounts of components that may be interpreted as PbO due to raw materials or manufacturing processes are included in the concept of "substantially no PbO" in this specification. For example, a glass particle can be said to be "substantially free of PbO" if its lead (Pb) content in the entire glass particle is 1000 ppm or less (preferably 500 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less). The lead (Pb) content in the entire glass particle can be measured, for example, using inductively coupled plasma (ICP) emission spectroscopy. The lead content in the entire gold paste, described below, can also be measured using a similar method.

[0037] (2) Shape and properties of glass powder Next, the shape, properties, etc. of the glass powder will be described.

[0038] The gold paste disclosed herein has an average particle diameter D of gold particles based on BET conversion. BET (μm) versus the total surface area S of glass per 1 g of gold particles contained in the gold paste t (m 2 ) ratio (S t / D BET ) is 0.11 or less. When a paste containing glass particles containing alkaline earth metal elements and / or alkali metal elements (typically alkaline earth metal oxides and / or alkali metal oxides) and gold particles is fired, the molten glass component comes into contact with the gold particles, and the glass component reacts, causing foaming of the glass component. This causes unevenness due to foaming on the surface of the conductor film after firing the gold paste, resulting in poor appearance. Therefore, S t / D BET In a gold paste having a ρ of 0.11 or less, the contact between the glass particles and the gold particles is suitably controlled. This suppresses the reaction of the glass components and prevents foaming. Therefore, the gold paste disclosed herein can suppress foaming during firing and form a conductor film with a smooth surface.

[0039] In order to effectively suppress foaming during firing of the gold paste, the S of the gold paste is t / D BET is preferably 0.10 or less, more preferably 0.08 or less, and even more preferably 0.07 or less. t / D BET The lower limit of is not particularly limited, but may be, for example, 0.01 or more, preferably 0.02 or more, and more preferably 0.03 or more.

[0040] The BET specific surface area of ​​the glass particles is, for example, 10 m from the viewpoint of suppressing foaming. 2 / g or less, and 2 / g or less is preferable, and 5m 2 / g or less is more preferable, and 4m 2 / g or less is more preferable, and 3.6m 2On the other hand, from the viewpoint of obtaining adhesiveness to the substrate, the BET specific surface area of ​​the glass particles is preferably 1.0 m / g or less. 2 / g or more is preferable, and 2.0m 2 / g or more is more preferable, and 2.8m 2 / g or more is more preferable.

[0041] The total surface area of ​​glass per gram of gold particles contained in the gold paste, S t is 0.16m 2 Less than 0.12m is preferable 2 Less than 0.09m is preferable. 2 Less than 0.07m is more preferable. 2 The following is particularly preferred. The smaller the total surface area of ​​glass per 1 g of gold particles contained in the gold paste, the more likely it is that foaming during firing of the gold paste will be effectively suppressed. On the other hand, from the viewpoint of obtaining adhesion to the substrate, the total surface area S of glass per 1 g of gold particles contained in the gold paste is t is 0.01m 2 More than 0.02m is preferable. 2 More than 0.03m is preferable. 2 The above is even more preferable. In this specification, the "total surface area of ​​glass per 1 g of gold particles contained in the gold paste" can be calculated based on the following formula (2). The total surface area of ​​glass per gram of gold particles contained in the gold paste, S t (m 2 ) = BET specific surface area of ​​glass particles (m 2 / g) × glass particle content (parts by weight) when gold particles contained in gold paste are taken as 100 parts by weight ÷ 100 (2)

[0042] In some preferred embodiments, the glass particle content is preferably 0.8 parts by weight or more, more preferably 1.3 parts by weight or more, even more preferably 1.5 parts by weight or more, and particularly preferably 1.7 parts by weight or more, based on 100 parts by weight of gold particles contained in the gold paste. This allows for sufficient adhesion of the molten glass particles to the substrate. On the other hand, the higher the glass particle content, the higher the electrical resistance of the conductive film. Furthermore, the lower the glass particle content, the more effectively foaming during firing of the gold paste is suppressed. From this perspective, based on 100 parts by weight of gold particles contained in the gold paste, the glass particle content is preferably 3.2 parts by weight or less, more preferably 2.5 parts by weight or less, even more preferably 2.2 parts by weight or less, and particularly preferably 1.9 parts by weight or less.

[0043] The softening point of the glass particles is preferably 800°C or higher, more preferably 810°C or higher, and even more preferably 820°C or higher. This allows the molten glass particles to have sufficient adhesive properties to the substrate. On the other hand, if the softening point of the glass particles is too high, there is a risk that the molten glass will corrode the substrate during firing. From this perspective, the softening point of the glass particles is preferably 900°C or lower, more preferably 890°C or lower, and even more preferably 880°C or lower. Note that the "softening point" in this specification refers to the temperature at which glass begins to soften and deform under its own weight. Typically, the softening point is the temperature at which the "glass viscosity is about 10" measured in accordance with JIS R 3103-1 (2001). 7.6 The temperature at which the viscosity becomes dPa·s can be defined as the "temperature at which the viscosity becomes dPa·s."

[0044] Although not limiting the technology disclosed herein, the median diameter of the glass particles is preferably 10 μm or less, more preferably 7 μm or less, even more preferably 5 μm or less, and particularly preferably 3 μm or less. As the median diameter of the glass particles becomes smaller, the glass particles tend to melt more easily during paste firing, thereby tending to fully exhibit adhesive performance. On the other hand, if the median diameter of the glass particles becomes too small, the inorganic particles (gold powder, glass particles) tend to aggregate together in the paste, which tends to increase the paste viscosity. From this perspective, the median diameter of the glass powder is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 0.7 μm or more, and particularly preferably 1 μm or more.

[0045] The BET particle diameter of the glass particles is preferably 0.15 μm or more, more preferably 0.2 μm or more, even more preferably 0.3 μm or more, and particularly preferably 0.35 μm or more. Glass particles with a large BET particle diameter (small BET specific surface area) tend to appropriately suppress foaming. The upper limit of the BET particle diameter of the glass particles is not particularly limited. For example, the BET particle diameter of the glass particles may be 12 μm or less, 10 μm or less, 7 μm or less, or 5 μm or less.

[0046] The shape of the glass particles is not particularly limited. The glass powder may be spherical or non-spherical (for example, rugby ball-shaped, columnar, needle-shaped, etc.). From the viewpoint of suppressing an increase in the viscosity of the paste, the glass powder is preferably spherical or approximately spherical. For example, the average aspect ratio of the glass powder is typically 1 to 5, preferably 1 to 3, more preferably 1 to 2, and even more preferably 1 to 1.5.

[0047] 3.Dispersion medium The dispersion medium is a liquid medium that disperses the powder materials (gold particles, glass powder, etc.). The specific components of the dispersion medium are not particularly limited, and any conventionally known dispersion medium that can be used to prepare gold pastes can be used. Furthermore, since the dispersion medium is a component that is assumed to disappear upon drying and firing, it is preferable that the boiling point be approximately 150°C or higher and 300°C or lower (e.g., approximately 170°C or higher and 270°C or lower).

[0048] An example of the dispersion medium is an organic dispersion medium (non-aqueous dispersion medium). Examples of such organic dispersion mediums include alcohol-based solvents such as methanol, sclareol, citronellol, phytol, geranylinalool, texanol, benzyl alcohol, phenoxyethanol, 1-phenoxy-2-propanol, terpineol, dihydroterpineol, isoborneol, butylcarbitol, and diethylene glycol; ester-based solvents such as terpineol acetate, dihydroterpineol acetate, isobornyl acetate, carbitol acetate, and diethylene glycol monobutyl ether acetate; and mineral spirits. Among these, alcohol-based solvents (e.g., texanol) are preferably used as the dispersion medium.

[0049] The content of the dispersion medium is preferably adjusted appropriately, taking into consideration the workability when applying the gold paste. Because the workability when applying the paste can vary depending on the application method, the content of the dispersion medium is not limited to a specific value. For example, when screen printing is used as the application method, the content of the dispersion medium can be adjusted to within a range of 5 to 25 parts by weight (preferably 10 to 20 parts by weight, and more preferably 13 to 17 parts by weight) per 100 parts by weight of gold particles.

[0050] 4. Other additives The gold paste disclosed herein can contain any of the conventional additives known to be used in this type of gold paste, without particular limitation, as long as they do not significantly impair the effect of the technology disclosed herein (suppression of foaming). For example, the gold paste may contain binders, dispersants, sintering aids, thickeners, plasticizers, pH adjusters, stabilizers, leveling agents, antifoaming agents, antioxidants, preservatives, colorants (pigments, dyes, etc.), etc.

[0051] For example, a binder (binding agent) is an additive that contributes to improving the adhesion of the paste when applied to a substrate and the bonding between conductive particles. Similarly to the dispersion medium, the binder is preferably a material that disappears during firing. Therefore, the binder is preferably an organic binder (typically, an organic compound with a burnout temperature of 500°C or less). The specific components of the binder in the conductive paste disclosed herein are not particularly limited, and conventionally known binders can be used without particular limitations. Examples of such binders include organic polymer compounds such as rosin-based resins, cellulose-based resins, polyvinyl alcohol-based resins, polyvinyl acetal-based resins, acrylic resins, urethane-based resins, epoxy-based resins, phenol-based resins, polyester-based resins, and ethylene-based resins. Although it is difficult to generalize because it depends on the combination with the dispersion medium, among these organic compounds, cellulose-based resins, polyvinyl alcohol-based resins, polyvinyl acetal-based resins, and acrylic resins are preferred as binders. The binder may be any one of the above organic compounds, or a combination of two or more of them. The binder may also be a copolymer or block copolymer obtained by copolymerizing these organic compounds. The binder content is preferably adjusted appropriately to achieve suitable fixation. For example, the binder content is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, even more preferably 1.5 parts by weight or more, and particularly preferably 2 parts by weight or more, per 100 parts by weight of gold particles. On the other hand, from the viewpoint of preventing binder residue after firing, the binder content is preferably 10 parts by weight or less, more preferably 8 parts by weight or less, even more preferably 6 parts by weight or less, and particularly preferably 4 parts by weight or less.

[0052] The dispersant is an additive that suppresses aggregation of inorganic particles (e.g., conductive particles, glass powder) in the paste. Specifically, the dispersant stabilizes the solid-liquid interface between the inorganic particles and the dispersion medium, preventing aggregation of the inorganic particles. Therefore, the glass powder in the paste can be uniformly dispersed, and the adhesive properties of the glass powder can be more effectively exhibited. The type of dispersant is not particularly limited, and a conventionally known dispersant can be appropriately selected as needed. An example of such a dispersant is an anionic dispersant. Anionic dispersants have excellent adsorption power to inorganic particles, allowing them to disperse inorganic particles appropriately for a long period of time. Examples of such anionic dispersants include carboxylic acid dispersants. Specific examples of such carboxylic acid dispersants include stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linolenic acid. The conductive paste may contain two or more dispersants. The content of such dispersant is preferably adjusted within the range of 0.05 to 3 parts by weight (preferably 0.1 to 2 parts by weight, more preferably 0.15 to 1 part by weight, and even more preferably 0.2 to 0.5 parts by weight) per 100 parts by weight of gold particles.

[0053] Sintering aids are additives that aid in the sintering of the paste. Sintering aids are typically components primarily composed of transition metal oxide particles. Addition of a sintering aid can impart appropriate sinterability, contribute to improved electrical conductivity, and favorably demonstrate the adhesive properties of the gold paste. The transition metal oxide used as the sintering aid can be appropriately selected depending on, for example, the firing temperature of the gold paste. Examples of transition metal oxides used as sintering aids include CuO, Mn3O4, NiO, Fe2O3, ZnO, and CoO. CuO is particularly preferred as a sintering aid. The content of such sintering aids is preferably adjusted within the range of 0.1 to 4.0 parts by weight (preferably 0.2 to 3.0 parts by weight, more preferably 0.3 to 2.0 parts by weight, and even more preferably 0.4 to 1.0 parts by weight) per 100 parts by weight of gold particles.

[0054] From an environmental perspective, the gold paste disclosed herein preferably contains substantially no lead (Pb). In this specification, "substantially no lead" refers to the absence of intentional addition of lead (Pb) to the gold paste. Therefore, trace amounts of lead contained in the gold paste resulting from raw materials or the manufacturing process are encompassed within the concept of "substantially no lead" in this specification. For example, a gold paste can be said to be "substantially free of lead" when the lead content, calculated as Pb, is 1000 ppm or less (preferably 500 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less).

[0055] [Gold paste manufacturing method] Such a gold paste can be produced by weighing out the above-mentioned materials to a predetermined ratio (parts by weight) and mixing (kneading) them to a homogeneous mixture. The manner in which the above-mentioned materials are mixed is not particularly limited; for example, all components may be mixed at once, or they may be mixed in an appropriately set order. Any conventionally known stirring and mixing device can be used to knead the gold paste without any particular restrictions. Examples of devices that can be used to knead the gold paste in this disclosure include a three-roll mill, a roll mill, a magnetic stirrer, a planetary mixer, a disperser, and a bead mill.

[0056] [Uses of gold paste] The gold paste disclosed herein has been described above. The gold paste disclosed herein can be used, for example, to form a conductive film for ceramic electronic components. More specifically, the conductive film can be used, for example, as a wiring pattern or conductive circuit formed on a substrate, or as a surface electrode, extraction electrode, terminal electrode, or external electrode for elements or devices, such as piezoelectrics, dielectrics, semiconductors, or magnetic materials made of inorganic materials such as ceramics. In particular, the gold paste disclosed herein is suitable for use in forming the conductive film (electrodes) for thermistors, from the viewpoints of the stability of the conductive film after firing the gold paste and its adhesion to the substrate. Examples of thermistors include NTC (Negative Temperature Coefficient) thermistors and PTC (Positive Temperature Coefficient) thermistors.

[0057] As an example of the use of the gold paste disclosed herein, a method for manufacturing (forming) a conductor film using the gold paste will be described below. The conductor film manufacturing method described here includes a paste application step and a firing step. However, this manufacturing method is not limited to the following method.

[0058] 1.Paste application process In the paste application step, the gold paste disclosed herein is prepared and applied (typically printed) to a substrate. The substrate is not particularly limited as long as it has heat resistance sufficient to withstand the firing temperature in the firing step described below, and any conventionally known substrate can be used. The gold paste can be applied by any known method, including, for example, tip dipping, dispenser supply, screen printing, gravure printing, offset printing, inkjet printing, and other printing methods, and spray application.

[0059] 2. Firing process In the firing process, the substrate coated with the gold paste is fired at a predetermined temperature. This forms a conductive film on the substrate as a fired body of the gold paste. The use of the gold paste disclosed herein can suppress foaming of the gold paste during firing, thereby enabling the production of a conductive film with a smooth surface. The firing temperature (maximum firing temperature) in the firing process is not particularly limited, but is preferably higher than the softening point of the glass particles contained in the gold paste. Therefore, the firing temperature (maximum firing temperature) is preferably about 800°C to 950°C, and more preferably about 820°C to 900°C.

[0060] Next, an NTC thermistor will be described as an example of a ceramic electronic component manufactured using the gold paste disclosed herein. Fig. 1 is a schematic diagram illustrating the configuration of an NTC thermistor 1. As shown in Fig. 1, the NTC thermistor 1 includes a thermistor body 10, a surface electrode 20, lead wires 30, and a sealing portion 40. The surface electrode 20 is an example of a "conductive film."

[0061] Typically, one or more NTC thermistor materials selected from various NTC thermistor materials known in the art can be used for the thermistor element 10, depending on the intended use, etc. The NTC thermistor material can be selected from oxides or composite oxides of transition metal elements such as Ni, Co, Mn, and Fe.

[0062] Here, a pair of surface electrodes 20 are provided on the side surfaces of the thermistor element body 10. The surface electrodes 20 are formed by applying (printing) a conductive paste for the surface electrodes to the surface (and side surfaces) of the thermistor element body 10 and firing it. Here, when the gold paste of the present disclosure is used as the conductive paste for the surface electrodes, foaming of the gold paste is suppressed when the gold paste is fired. In other words, the gold paste of the present disclosure makes it possible to obtain a surface electrode 20 with a smooth surface.

[0063] The lead wires 30 are electrically connected to the surface electrode 20 via the connection electrode 32. As shown in Fig. 1, a pair of lead wires 30 are arranged so as to be approximately parallel to each other. The lead wires 30 are made of a conductive material such as Ni, Cu, Co, or Fe. The connection electrode 32 is made of a metal such as Au or Ag.

[0064] The sealing portion 40 is a portion that hermetically seals the thermistor body 10, the pair of surface electrodes 20, and portions of the pair of lead wires 30. The sealing portion 40 is typically formed of glass. Here, the sealing portion 40 has an elliptical spherical shape that extends along the extension direction of the lead wires 30. The glass used for the sealing portion 40 can be one or more types of glass selected from conventionally known glass materials used in NTC thermistors, depending on the application. Note that the method for forming the sealing portion 40 can use conventionally known techniques and is not a factor limiting the technology disclosed herein, so a detailed description will be omitted.

[0065] The use of the gold paste disclosed herein is not limited to the NTC thermistor described above. Other examples of ceramic electronic components for which the gold paste disclosed herein can be used include multi-layer ceramic capacitors (MLCCs), inductors, and piezoelectric elements (varistors). Even in these electronic components, foaming can occur on the surface of the conductor film during paste firing. In contrast, the gold paste disclosed herein makes it possible to provide a conductor film with reduced foaming. Therefore, by using the gold paste disclosed herein, it is possible to manufacture MLCCs, inductors, piezoelectric elements, and other components with conductor films (e.g., external electrodes) that have reduced foaming and a smooth surface.

[0066] As described above, specific aspects of the technology disclosed herein include those described in the following items.

[0067] [Item 1] At least gold particles, glass particles, and a dispersion medium are included, the glass particles contain at least one selected from alkali metal elements and alkaline earth metal elements, The average particle diameter of the above gold particles based on BET conversion, D BET (μm) versus the total surface area S of the glass per 1 g of the gold particles contained in the gold paste t (m 2 ) ratio (S t / D BET ) is less than or equal to 0.11, Gold paste.

[0068] [Item 2] the content of the glass particles is 0.8 parts by weight or more and 3.2 parts by weight or less when the content of the gold particles contained in the gold paste is 100 parts by weight; Gold paste as described in item 1.

[0069] [Item 3] The content of the alkali metal component or alkaline earth metal component in the entire glass particles is 15 wt% or more and 35 wt% or less in terms of oxide. The gold paste according to item 1 or 2.

[0070] [Item 4] The softening point of the glass particles is 800°C or higher and 900°C or lower. 4. The gold paste according to any one of items 1 to 3.

[0071] [Item 5] The average particle diameter of the above gold particles D BET (μm) is 0.35 μm or more and 1.5 μm or less, 5. The gold paste according to any one of items 1 to 4.

[0072] [Item 6] The gold paste is substantially free of lead. 6. The gold paste according to any one of items 1 to 5.

[0073] [Item 7] The glass particles have the following composition in oxide terms: SiO2: 35wt%~70wt% B2O3: 2wt%~20wt% Al2O3: 5wt%~20wt% RO: 15wt%~35wt% (wherein R comprises at least one element selected from the group consisting of Mg, Ca, Sr, and Ba), 7. The gold paste according to any one of items 1 to 6.

[0074] [Item 8] Used to form the conductor film of thermistors, 8. The gold paste according to any one of items 1 to 7.

[0075] [Test example] Next, test examples relating to the technology disclosed herein will be described. Note that the test examples shown below are not intended to limit the technology disclosed herein.

[0076] 1. Preparation of Gold Paste for Evaluation Here, we prepared a gold paste for evaluation in an evaluation test (foaming test). Specifically, we first prepared gold powder (median diameter: 0.5 μm, AU-2061, Noritake Co., Ltd.) as gold particles, glass particles (median diameter: 0.5 μm, softening point: 850°C), a binder (ethyl cellulose resin: EC), a dispersion medium (Texanol), and a sintering aid (CuO). The equipment and conditions used to measure the median diameters of the gold particles and glass particles are as follows: Measuring device: Microtrac MT-3000 (Microtrac Bell Co., Ltd.) Solvent: Ethanol Refractive index: 1.36 Dispersion time: 180 seconds Measurement time: 30 seconds

[0077] The glass particles prepared in this test example had the following glass components calculated as oxides relative to the total glass particles, and were substantially free of PbO. SiO2: 55wt% Al2O3: 14wt% B2O3: 9wt% CaO: 20wt% MgO: 2wt%

[0078] 31.4 g (100 parts by weight) of the gold particles prepared above were mixed with 2.9 parts by weight of EC, 0.64 parts by weight of CuO, and glass particles in the proportions shown in Table 1. The amount of Texanol was then adjusted to mix the paste for each example so that the total weight was 40 g. This mixture was kneaded using a three-roll mill. In this way, gold pastes for evaluation according to Examples 1 to 11 were prepared.

[0079] Before preparing the gold paste, the BET specific surface area (m 2 The BET specific surface area was measured using the following equipment and conditions. Measuring device: Macsorb HM Model-1201 (Mountec Co., Ltd.) Preheater temperature: 200℃ Preheat time: 15 minutes Sample size: 0.8g Degassing device: Pre-Heat Unit Model-PH5 (Mountec Co., Ltd.) Degassing temperature: 120℃ Degassing time: 5 minutes

[0080] Furthermore, the BET specific surface area of ​​the gold particles was used to calculate the average particle diameter of the gold particles (D BET ) (μm) (corresponding to the "BET equivalent particle diameter of gold particles" in Table 1) was calculated. In addition, the total surface area of ​​glass particles per 1 g of gold particles (S t )(m 2 Using the results obtained above, the ratio of the total surface area of ​​glass particles per 1 g of gold particles to the average particle size of gold particles calculated by BET conversion (S t / D BET The results are shown in Table 1.

[0081] 2. Evaluation of gold paste (foaming test) (1) Preparation of test specimens Here, test pieces for use in the foaming test were prepared. Specifically, an alumina substrate was first prepared. Each of the gold pastes prepared in Examples 1 to 11 above was applied to the prepared substrate by screen printing. A drying process was then carried out at 120°C for 10 minutes using a box-type hot air dryer. This resulted in a dried film with a dry thickness of approximately 10 μm. The resulting dried film was then subjected to a firing process. The firing temperature was set to 900°C, and the firing atmosphere was set to a nitrogen atmosphere. The total processing time, including the temperature rise time (the time from the start to the end of firing), was set to 1 hour, and the top temperature was maintained for 10 minutes. In this way, a test piece was obtained in which a conductive film with a thickness of about 7.5 μm was formed on an alumina substrate.

[0082] (2) Evaluation of the number of bubbles The number of bubbles was evaluated for the test pieces prepared above. Specifically, the conductor film of each sample obtained was observed using a scanning electron microscope (SEM) with a magnification of 500 times as one field of view, and the number of bubbles in the conductor film was counted. This observation was carried out for five fields of view for each sample, and the total number of bubbles in the five fields of view was taken as the number of bubbles for each sample. The results are shown in the "Number of bubbles" column in Table 1. Also, Figure 2 shows the number of bubbles in the S of gold paste. t / D BET 1 is a graph showing the relationship between the number of bubbles in the test piece obtained by firing the gold paste and the S t / D BET The white circles indicate cases where ≦0.11 is satisfied, and S t / D BET ≦0.11 (i.e., S t / D BET >0.11) Examples are plotted as black circles. The dashed lines in Figure 2 represent "S t / D BET =0.11" and "Number of bubbles = 100".

[0083] [Table 1]

[0084] FIG. 3 is an optical microscope image (50x magnification) of the test piece (conductor film) of Example 5. FIG. 4 is an SEM image (200x magnification) of the surface of the test piece (conductor film) of Example 5. FIG. 5 is an optical microscope image (50x magnification) of the test piece (conductor film) of Example 9. FIG. 6 is an SEM image (200x magnification) of the surface of the test piece (conductor film) of Example 9. The circled areas in FIG. 6 indicate bubbles that occurred during firing of the gold paste. As shown in Table 1 and FIG. 2, S t / D BET In the conductive films obtained using gold pastes with a S value of 0.11 or less (Examples 1 to 5, 7, and 10 to 11), the number of bubbles observed was less than 100 in all examples. t / D BET In the conductive film obtained using the gold paste of Example 9, where the S value was 0.16, bubbles were observed during firing of the gold paste. On the other hand, as shown in Figures 3 and 4, the conductive film obtained using the gold paste of Example 5 had less irregularities than the conductive film of Example 9 (Figures 5 and 6), and a smoother surface was obtained. From these results, it is clear that S t / D BET It was confirmed that a gold paste having a ρ of 0.11 or less suppresses foaming of glass particles during firing, and a conductor film with a smooth surface can be obtained.

[0085] The technology disclosed herein has been described in detail above, but these are merely examples, and various modifications can be made to the present disclosure without departing from the spirit thereof. [Explanation of symbols]

[0086] 1 NTC thermistor 10 Thermistor element 20 Surface electrode 30 lead wire 32 connecting electrode 40 Sealing part

Claims

1. A gold paste for forming a conductor film by firing, the gold paste containing at least gold particles, glass particles, and a dispersion medium, the glass particles contain at least one selected from an alkali metal element and an alkaline earth metal element, The average particle diameter D of the gold particles based on BET conversion ＢＥＴ The total surface area S of the glass per 1 g of the gold particles contained in the gold paste (μm) ｔ (m ２ ) ratio (S ｔ / D ＢＥＴ ) is 0.11 or less, Gold paste.

2. the content of the glass particles in the gold paste is 0.8 parts by weight or more and 3.2 parts by weight or less when the content of the gold particles in the gold paste is 100 parts by weight; The gold paste according to claim 1 .

3. When the entire glass particles are taken as 100 wt %, the sum of the contents of the alkali metal component and the alkaline earth metal component is 15 wt % or more and 35 wt % or less in terms of oxide. The gold paste according to claim 1 or 2.

4. The softening point of the glass particles is 800°C or higher and 900°C or lower. The gold paste according to claim 1 or 2.

5. The average particle diameter D of the gold particles ＢＥＴ (μm) is 0.35 μm or more and 1.5 μm or less, The gold paste according to claim 1 or 2.

6. The gold paste is substantially free of lead. The gold paste according to claim 1 or 2.

7. The glass particles have the following composition in terms of oxides: SiO ２ :35wt%~70wt% B ２ O ３ :2wt%~20wt% Al ２ O ３ :5wt%~20wt% RO: 15wt% to 35wt% (wherein R comprises at least one element selected from the group consisting of Mg, Ca, Sr, and Ba), The gold paste according to claim 1 or 2.

8. Used to form the conductor film of thermistors, The gold paste according to claim 1 or 2.

Images