Gold paste

Abstract

The purpose of the present disclosure is to provide a gold paste capable of forming a conductor film having a smooth surface while suppressing foaming occurring during firing. The gold paste disclosed herein is characterized by containing at least gold particles, glass particles, and a dispersion medium, the glass particles containing at least one element selected from the group consisting of alkali metal elements and 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 ([mu] m)) of the gold particles in terms of BET is 0.11 or less. The gold paste according to the above-described configuration is capable of forming a conductor film having a smooth surface by suppressing foaming generated during firing.

Description

Technical Field

[0001] The present disclosure relates to gold pastes. Background Art

[0002] In recent years, ceramic electronic components such as thermistors, laminated ceramic capacitors, laminated inductors, and laminated piezoelectric elements (laminated varistors) have been used in a wide range of fields. For such ceramic electronic components, a technique is widely used in which a conductive material is formed on an insulating substrate into a conductor film and wiring is performed through the conductor film. The conductor film is formed, for example, by baking a paste containing conductive particles and glass particles. For example, a thermistor can have a structure comprising a thermistor body and a surface electrode as an example of a conductor film located on the surface of the thermistor body.

[0003] Conventionally, gold (Au) particles have been used as the conductive particles due to their chemical stability and excellent electrical conductivity. Patent Document 1, for example, discloses a low-temperature calcined gold paste formed by mixing 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, from the perspective of controlling the softening point of the glass particles and the fluidity of the melted glass component, uses a glass component containing alkali metal oxides or alkaline earth metal oxides. Patent Document 2, for example, is an example of such a technology.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Publication No. Heisei 10-340619

[0007] Patent Document 2: Japanese Patent No. 7082408 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] However, the present inventors' research has revealed that when a paste containing glass particles containing alkali metal oxides and alkaline earth metal oxides and gold particles is fired, the glass particles foam, causing irregularities on the surface of the resulting conductor film. The presence of irregularities on the surface of the conductor film is undesirable due to poor appearance.

[0010] The technology disclosed herein has been accomplished in view of the above circumstances, and an object thereof is to provide a gold paste capable of suppressing foaming generated during firing and forming a conductor film having a smooth surface.

[0011] Solutions for solving problems

[0012] To achieve the above objectives, the present inventors conducted research and focused on the relationship between the gold particles and the 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 this viewpoint, the present inventors conducted further in-depth research and found that the glass component reacts with the gold particles, causing foaming. Furthermore, the present inventors conducted further in-depth research and found that the total surface area S of the glass particles per gram of gold particles in the gold paste is proportional to the average particle size D of the gold particles based on BET conversion. BET The ratio (S t / D BET ) becomes an indicator, and the above S t / D BET By setting the content within a predetermined range, foaming generated during firing can be suppressed.

[0013] That is, the gold paste disclosed herein is characterized in that it comprises at least gold particles, glass particles, and a dispersion medium, wherein the glass particles comprise at least one selected from alkali metal elements or alkaline earth metal elements, and the total surface area S of the glass contained in the gold paste is t (m 2 ) relative to the average particle size D of the gold particles calculated based on BET BET (μm) ratio (S t / D BET ) is less than 0.11.

[0014] According to this configuration, by adding S t / D BET By setting the ratio to 0.11 or less, the contact between the glass particles and the gold particles in this gold paste is appropriately controlled. This suppresses the reaction of the glass particles and prevents bubbling. Therefore, the gold paste disclosed herein can suppress bubbling during firing, allowing the formation of a conductor film with a smooth surface.

[0015] 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 based on 100 parts by weight of the gold particles contained in the gold paste.

[0016] In a preferred embodiment of the gold paste disclosed herein, the content of the alkaline earth metal component or the alkali metal component in the entire glass particles is 15 wt % or more and 35 wt % or less in terms of oxide.

[0017] In a preferred embodiment of the gold paste disclosed herein, the glass particles have a softening point of 800° C. or higher and 900° C. or lower.

[0018] In a preferred embodiment of the gold paste disclosed herein, the average particle size D of the gold particles is BET (μm) is 0.35 μm or more and 1.5 μm or less.

[0019] In a preferred embodiment of the gold paste disclosed herein, the gold paste contains substantially no lead.

[0020] In a preferred embodiment of the gold paste disclosed herein, the glass particles comprise the following composition in terms of oxides:

[0021] SiO2: 35wt%~70wt%

[0022] B2O3: 2wt%~20wt%

[0023] Al2O3: 5wt%~20wt%

[0024] RO: 15wt%~35wt%

[0025] (Here, R includes at least one element selected from the group consisting of Mg, Ca, Zn, Ba, and Sr.)

[0026] In a preferred embodiment of the gold paste disclosed herein, the gold paste is used for forming a conductor film of a thermistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram schematically illustrating the structure of an NTC thermistor manufactured using the gold paste according to one embodiment.

[0028] Figure 2 is the S of the gold paste of the test example t / D BET A graph showing the relationship between the number of bubbles formed on a test piece of a conductor film including the gold paste.

[0029] Figure 3 This is an optical microscope image (50 times magnification) of the test piece (conductor film) of Example 5.

[0030] Figure 4 This is a surface SEM image (200 times magnification) of the test piece (conductor film) of Example 5.

[0031] Figure 5 This is an optical microscope image (50 times magnification) of the test piece (conductor film) of Example 9.

[0032] Figure 6 This is a surface SEM image (200 times magnification) of the test piece (conductor film) of Example 9.

[0033] Description of Reference Numerals

[0034] 1 NTC thermistor

[0035] 10 Thermistor body

[0036] 20 Surface electrodes

[0037] 30 leads

[0038] 32 Connecting electrodes

[0039] 40 Sealing part DETAILED DESCRIPTION

[0040] The following describes preferred embodiments of the technology disclosed herein. It should be noted that matters required for the implementation of the technology disclosed herein, other than matters specifically mentioned in this specification, can be understood as design matters for those skilled in the art based on the prior art in this field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and technical common sense in this field. It should be noted that the expression "A to B" indicating a numerical range in this specification means "above A and below B".

[0041] [Gold paste]

[0042] The gold paste disclosed herein contains at least gold particles, glass particles, and a dispersion medium. Hereinafter, each component of the gold paste disclosed herein will be described.

[0043] 1. Gold particles

[0044] Gold (Au) particles are a material used to form highly conductive conductor films (electrodes) that serve as conductors in electronic components, etc. Gold particles are typically used in the form of gold powder, which is a collection of multiple gold particles. The composition of the gold powder is not particularly limited as long as it is a powder (collection of particles) with gold as the main component, and gold powder with the desired conductivity and other physical properties can be used. Here, the main component refers to the largest component among the components that make up the gold powder. Examples of gold powder include gold powder composed of gold, gold alloys, and mixtures or composites thereof. For example, core-shell particles can be used, in which the core is composed of a metal other than gold, a gold alloy, or the like, and the shell covering the core is composed of gold. In addition, core-shell particles can be used, in which the core is composed of gold, and the shell covering the core is composed of a metal other than gold, a gold alloy, or the like. Gold powder tends to have higher conductivity as its purity (content) increases, so it is preferable to use high-purity gold powder. The gold powder preferably has a purity of 95% or more, more preferably 97% or more, further preferably 98% or more, and particularly preferably 99% or more. In the technology disclosed herein, for example, even when gold powder having a purity of 99.99% or less (eg, 99.9% or less) is used, the foaming suppression effect can be obtained.

[0045] In addition, from the viewpoint of suppressing the aggregation of gold particles in the paste, the BET specific surface area of ​​the gold particles is preferably 2.00 m 2 / g or less, more preferably 1.50m 2 / g or less, more preferably 1.20m 2 / g or less, particularly preferably 1.00m 2 On the other hand, if the BET specific surface area of ​​the gold particles increases, the contact area between the gold particles increases, so there is a tendency for the conductivity of the conductor film after baking to improve. From this point of view, the BET specific surface area of ​​the gold particles is preferably 0.10 m 2 / g or more, more preferably 0.12m 2 / g or more, more preferably 0.15m 2 / g or more, particularly preferably 0.2m 2 / g or more. It should be noted that the "BET specific surface area" in this specification can be determined by measuring the amount of gas adsorption using a gas adsorption method (constant volume adsorption method) using nitrogen (N2) gas as the adsorbate, and calculating the BET specific surface area based on this amount of gas adsorption using a BET method (e.g., the BET single-point method). As an apparatus for measuring the BET specific surface area, for example, a Macsorb HM Model-1201 (MOUNTECH Co., Ltd.) can be used.

[0046] Average particle size D of gold particles based on BET conversion BET It is preferably 0.35 μm or more, more preferably 0.45 μm or more, and further preferably 0.55 μm or more. BET As the average particle size D of the gold particles increases, the foaming of the glass particles during the firing of the gold paste is appropriately suppressed, thereby improving the filling property of the gold particles. BET If the gold paste is too large, it is necessary to expose the gold paste to high temperature for a long time when sintering the gold paste. BET It is preferably 1.5 μm or less, more preferably 1.2 μm or less, further preferably 1 μm or less, and particularly preferably 0.9 μm or less.

[0047] It should be noted that the "average particle size based on BET conversion" in this specification 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".

[0048] Average particle size D based on BET conversion BET =6 / (BET specific surface area·ρ)(1)

[0049] Although not particularly limited, the median particle size of the gold particles can be 0.20 μm or more, 0.30 μm or more, or 0.40 μm or more. In addition, the median particle size of the conductive particles can be 3.0 μm or less, 2.0 μm or less, or 1.5 μm or less. It should be noted that the "median particle size" in this specification is the particle size (equivalent sphere diameter) equivalent to 50% of the cumulative value from the smaller particle size side in the volume-based particle size distribution based on the laser diffraction scattering method. As an apparatus used for measuring the median particle size, for example, a Microtrac MT-3000 (Microtrac BEL Corp.) can be used.

[0050] The shape of the gold particles is not particularly limited. For example, the shape of the gold particles can be spherical or non-spherical. Non-spherical particles can be, for example, plate-shaped, scaly, flake-shaped, or irregular in shape. From the perspective of easily increasing the packing density of the gold particles, spherical gold particles can preferably have an aspect ratio of 1.2 or less, preferably 1.15 or less, for example, 1.1 or less. In addition, from the perspective of easily increasing the contact area between multiple gold particles, non-spherical gold particles can have an aspect ratio of 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. From the perspective of synergizing the above-mentioned effects, spherical gold particles and non-spherical gold particles can be mixed. As a result, when the solvent is removed from the paste by drying, the multiple gold particles are in proper contact, which can improve the conductivity of the conductor film. It should be noted that the "aspect ratio" in this specification is the arithmetic mean of the values ​​(aspect ratios) obtained by the ratio (b / a) of the length of the long side (b) to the length of the short side (a) when a rectangle circumscribing the particles is drawn for 100 particles in an electron microscope photograph.

[0051] To improve the conductivity of the fired gold paste, the gold particle content in the gold paste is preferably 60 wt% or greater, more preferably 65 wt% or greater, and even more preferably 70 wt% or greater. On the other hand, to ensure a certain glass particle content and improve the density of the conductor 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. Unless otherwise specified, "content" in this specification refers to the weight ratio based on 100 wt% of the total mass of the gold paste.

[0052] 2. Glass particles

[0053] The gold paste disclosed herein contains glass particles. The glass particles are typically used in the form of a glass powder, which is a collection of multiple glass particles. When the glass particles reach their softening point during firing, they melt and form a liquid glass component. This liquid glass component fills the gaps between the gold particles, densifying the conductor film.

[0054] (1) Composition of glass particles

[0055] This section describes the specific composition of the glass particles disclosed herein. The glass particles of this embodiment contain at least one selected from alkali metal elements or alkaline earth metal elements. The alkali metal element or alkaline earth metal element is typically contained in the glass particles in the form of an alkali metal oxide or an alkaline earth metal oxide.

[0056] Alkali metal oxides (R'2O) penetrate into the three-dimensional glass mesh and, by imparting fluidity to the glass and lowering its softening point, lower the softening point of the glass, thereby improving its fluidity. Examples of such alkali metal oxides include lithium oxide (Li2O), sodium oxide (Na2O), potassium oxide (K2O), and rubidium oxide (Rb2O). To impart fluidity to the glass, the content of the alkali metal component in the overall glass particles is preferably 15 wt% or greater, more preferably 18 wt% or greater, and even more preferably 20 wt% or greater, calculated as oxides. On the other hand, to suppress foaming of the glass particles during gold paste firing, the content of the alkali metal component in the overall glass particles is preferably 35 wt% or less, preferably 32 wt% or less, and even more preferably 30 wt% or less.

[0057] Alkaline earth metal oxide (RO) is a component that has the effect of imparting fluidity to glass and raising the softening point. In addition, alkaline earth metal oxide functions as a mesh-modifying oxide (network modifier). Thus, the physical stability and thermal stability of the glass can be improved. Examples of the alkaline earth metal oxide include magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO). From the perspective of imparting fluidity to the 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 further preferably 20 wt% or more, calculated as oxide. On the other hand, from the perspective of suppressing the foaming of the glass particles during the firing of the gold paste, the content of the alkaline earth metal component in the entire glass particles is preferably 35 wt% or less, preferably 32 wt% or less, and further preferably 30 wt% or less.

[0058] In some preferred examples, the content of alkali metal components 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, the sum of the contents of alkaline earth metal oxides and alkali metal oxides (RO + R'2O (where R contains at least one element selected from the group consisting of Mg, Ca, Ba, and Sr, and R' contains at least one element selected from Li, Na, K, Rb, Cs, and Fr) when the entire glass particles are set to 100 wt%) is preferably 15 wt% or more and 35 wt% or less. This allows the glass to be given fluidity and appropriately suppresses foaming of the glass particles during the firing of the gold paste. From the perspective of imparting fluidity to the glass, the content of alkaline earth metal components 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 the glass particles during firing of the gold paste, the content of the alkaline earth metal component or alkali metal component in the entire glass particles is preferably 35 wt % or less, preferably 32 wt % or less, and more preferably 30 wt % or less.

[0059] 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 preferably contain the following composition in terms of oxides:

[0060] SiO2: 35wt%~70wt%

[0061] B2O3: 2wt%~20wt%

[0062] Al2O3: 5wt%~20wt%

[0063] RO: 15wt%~35wt%

[0064] (Here, 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 during firing of the gold paste. The specific reason is not yet clear, but it is believed that the fluidity of the softened glass decreases as the glass particles soften during the temperature rise caused by firing.

[0065] Silicon oxide (SiO2) is one of the components that can independently constitute the glass skeleton (glass skeleton constituent). As the proportion of SiO2 in the glass skeleton constituent increases, the thermal stability of the glass particles improves and the softening point becomes higher. In other words, it is difficult for a silicate glass containing a large amount of SiO2 to fully melt during the paste baking to produce a glass component with excellent fluidity. From this point of view, the content ratio of SiO2 in the glass particles is preferably 70wt% or less relative to the entire glass, more preferably 65wt% or less, and further preferably 60wt% or less. In addition, SiO2 also has the function of improving the chemical resistance of the glass particles. Therefore, the content ratio of SiO2 relative to the entire glass is preferably 35wt% or more, more preferably 40wt% or more, and further preferably 45wt% or more.

[0066] Boron oxide (B2O3) is one of the components constituting the glass skeleton. As the proportion of B2O3 in the components constituting the glass skeleton increases, there is a tendency for the fluidity of the glass component after melting to improve. From this point of view, the content of B2O3 is preferably 2wt% or more relative to the entire glass, more preferably 5wt% or more, and further preferably 7wt% or more. As a result, the glass component after melting is more easily diffused, and an external electrode with better density can be formed. On the other hand, B2O3 has the effect of lowering the softening point of the glass particles. From this point of view, the content of B2O3 in the glass particles is preferably 20wt% or less relative to the entire glass, more preferably 17wt% or less, and further preferably 15wt% or less.

[0067] Alumina (Al2O3) stabilizes the glass framework and controls the fluidity of the glass components. To maintain the softening point and fluidity of the glass particles within appropriate ranges, the Al2O3 content relative to the total glass is preferably 5% by weight or greater, more preferably 7% by weight or greater, and even more preferably 10% by weight or greater. On the other hand, the Al2O3 content relative to the total glass is preferably 20% by weight or less, more preferably 17% by weight or less, and even more preferably 15% by weight or less.

[0068] It should be noted that the above description is not intended to limit the composition of the glass particles disclosed herein to the aforementioned components. The glass particles disclosed herein may contain, for example, P2O5, Bi2O3, etc. as glass skeleton-forming components. Furthermore, glass skeleton-modifying components may include, for example, ZnO, TiO2, MnO, FeO, Fe2O3, Fe3O4, SnO, SnO2, V2O5, ZrO2, Nb2O5, CuO, Cu2O, La2O3, CeO2, etc. When other components (i.e., components other than alkali metal oxides, alkaline earth metal oxides, SiO2, B2O3, and Al2O3) are included, 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.

[0069] It should be noted that, from an environmental perspective, the glass particles of the gold paste disclosed herein preferably contain substantially no PbO. It should be noted that "substantially no PbO" in this specification means that PbO is not intentionally added. Therefore, it can be interpreted that the concept of "substantially no PbO" in this specification includes the case where the PbO component originates from the raw materials, the manufacturing process, etc. and contains trace amounts. For example, when the content of lead (Pb) element in the entire glass particles is 1000 ppm or less (preferably 500 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less), it can be said that "substantially no PbO is contained". It should be noted that the content of lead (Pb) element in the entire glass particles can be measured, for example, using inductively coupled plasma (ICP: Inductivity coupled plasma) emission spectroscopy. In addition, the content of lead element in the entire gold paste described later can also be measured using the same method.

[0070] (2) Shape and properties of glass powder

[0071] Next, the shape, properties, etc. of the glass powder will be described.

[0072] The gold paste disclosed herein is characterized in that the total surface area S of the glass per 1 g of gold particles contained in the gold paste is t (m 2 ) relative to the average particle size D of gold particles based on BET conversion BET (μm) 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, thereby causing foaming of the glass component. As a result, the surface of the conductor film after the gold paste is fired will have unevenness caused by the foaming, resulting in poor appearance. Therefore, S t / D BET A gold paste with a viscosity of 0.11 or less appropriately controls the contact between the glass particles and the gold particles. This suppresses the reaction of the glass component and prevents bubbling. Therefore, the gold paste disclosed herein can suppress bubbling during firing and form a conductor film with a smooth surface.

[0073] It should be noted that, from the viewpoint of appropriately suppressing foaming during the firing of the gold paste, the S content of the gold paste is t / D BET It is preferably 0.10 or less, more preferably 0.08 or less, and further preferably 0.07 or less. t / D BET The lower limit of is not particularly limited, and may be, for example, 0.01 or more, preferably 0.02 or more, and more preferably 0.03 or more.

[0074] From the viewpoint of suppressing foaming, the BET specific surface area of ​​the glass particles is, for example, 10 m 2 / g or less, preferably 7m 2 / g or less, more preferably 5m 2 / g or less, more preferably 4m 2 / g or less, particularly preferably 3.6m 2 On the other hand, from the viewpoint of obtaining good adhesion to the substrate, the BET specific surface area of ​​the glass particles is preferably 1.0 m 2 / g or more, more preferably 2.0m 2 / g or more, more preferably 2.8m 2 / g or above.

[0075] The total surface area S of the glass per 1g of gold particles contained in the gold paste t Preferably 0.16m 2 Below, more preferably 0.12m 2 Below, more preferably 0.09m 2 Below, particularly preferably 0.07m 2There is a tendency that the smaller the total surface area of ​​glass per 1g of gold particles contained in the gold paste, the more appropriately the foaming during the firing of the gold paste is suppressed. On the other hand, from the viewpoint of obtaining good adhesion to the substrate, the total surface area S of glass per 1g of gold particles contained in the gold paste is preferably t Preferably 0.01m 2 More than 0.02m 2 More than 0.03m 2 In addition, the "total surface area of ​​the glass per 1g of gold particles contained in the gold paste" in this specification can be calculated based on the following formula (2).

[0076] The total surface area S of the glass per 1g of gold particles contained in the gold paste t (m 2 ) = BET specific surface area of ​​glass particles (m 2 / g)×the content of the glass particles (parts by weight) when the gold particles contained in the gold paste are set to 100 parts by weight÷100(2)

[0077] In some preferred embodiments, the content of glass particles is preferably 0.8 parts by weight or more, more preferably 1.3 parts by weight or more, further 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 the 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 content of glass particles, the higher the resistance of the conductor film. Furthermore, the lower the content of glass particles, the more effectively foaming is suppressed during firing of the gold paste. From this perspective, the content of glass particles is preferably 3.2 parts by weight or less, more preferably 2.5 parts by weight or less, further preferably 2.2 parts by weight or less, and particularly preferably 1.9 parts by weight or less, based on 100 parts by weight of the gold particles contained in the gold paste.

[0078] The softening point of the glass particles is preferably 800°C or higher, more preferably 810°C or higher, and further preferably 820°C or higher. In this way, sufficient adhesion of the molten glass particles to the substrate can be obtained. On the other hand, if the softening point of the glass particles is too high, the molten glass may corrode the substrate during firing. From this viewpoint, the softening point of the glass particles is preferably 900°C or lower, more preferably 890°C or lower, and further preferably 880°C or lower. It should be noted that the "softening point" in this specification is the temperature at which the glass begins to soften and deform due to its own weight. Typically, the softening point can be set as the "glass viscosity reaches about 10" measured in accordance with JISR3103-1 (2001). 7.6 dPa·s temperature".

[0079] There is no limitation on the technology disclosed herein, and the median particle size of the glass particles is preferably 10 μm or less, more preferably 7 μm or less, further preferably 5 μm or less, and particularly preferably 3 μm or less. As the median particle size of the glass particles becomes smaller, the glass particles are easily melted when the paste is fired, and therefore there is a tendency to fully exhibit the adhesive properties. On the other hand, if the median particle size of the glass particles is too small, the inorganic particles (gold powder, glass particles) in the paste aggregate with each other, and the viscosity of the paste tends to increase. From this viewpoint, the median particle size of the glass powder is preferably 0.1 μm or more, more preferably 0.5 μm or more, further preferably 0.7 μm or more, and particularly preferably 1 μm or more.

[0080] The BET particle size of the glass particles is preferably 0.15 μm or more, more preferably 0.2 μm or more, further preferably 0.3 μm or more, and particularly preferably 0.35 μm or more. Glass particles having a large BET particle size (small BET specific surface area) tend to appropriately suppress foaming. It should be noted that the upper limit of the BET particle size of the glass particles is not particularly limited. For example, the BET particle size of the glass particles may be 12 μm or less, 10 μm or less, 7 μm or less, or 5 μm or less.

[0081] The shape of the glass particles is not particularly limited. The glass powder may be spherical or non-spherical (e.g., rugby ball-shaped, columnar, needle-shaped, etc.). It should be noted that from the perspective of suppressing the 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.

[0082] 3. Dispersion medium

[0083] The dispersion medium is a liquid medium that disperses the aforementioned powdered materials (gold particles, glass powder, etc.). The specific composition of this dispersion medium is not particularly limited; any conventionally known dispersion medium used for preparing gold pastes can be used. Furthermore, since the dispersion medium is a component that disappears upon drying and calcining, it preferably has a boiling point of approximately 150°C to 300°C (e.g., 170°C to 270°C).

[0084] It should be noted that, as an example of a dispersion medium, an organic dispersion medium (non-aqueous dispersion medium) can be cited. As an example of such an organic dispersion medium, alcohol solvents such as methanol, sclareol, citronellol, phytol, geranyl linalool, TEXANOL, benzyl alcohol, phenoxyethanol, 1-phenoxy-2-propanol, terpineol, dihydroterpineol, isoborneol, butyl carbitol, and diethylene glycol can be cited; ester solvents such as terpineol acetate, dihydroterpineol acetate, isobornyl acetate, carbitol acetate, and diethylene glycol monobutyl ether acetate; and mineral spirits. Among them, an alcohol solvent (such as TEXANOL) can be preferably used as a dispersion medium.

[0085] It should be noted that the content of the dispersion medium is preferably adjusted appropriately to take into account the workability when applying the gold paste. It should be noted that the workability when applying the paste may vary depending on the coating method, so the content of the dispersion medium is not limited to a specific value. As an example, when screen printing is used as the coating method, the content of the dispersion medium can be adjusted to a range of 5 to 25 parts by weight (preferably 10 to 20 parts by weight, more preferably 13 to 17 parts by weight) per 100 parts by weight of the gold particles.

[0086] 4. Other additives

[0087] It should be noted that the gold paste disclosed herein may contain any conventionally known additives that are useful in such gold pastes without particular limitation, as long as they do not significantly impair the effects of the disclosed technology (suppression of foaming). For example, the gold paste may contain a binder, a dispersant, a sintering aid, a thickener, a plasticizer, a pH adjuster, a stabilizer, a leveling agent, a defoaming agent, an antioxidant, a preservative, a colorant (pigment, dye, etc.), and the like.

[0088] For example, a binder (adhesive) is an additive that helps improve the fixation of the paste when applied to the substrate and the adhesion between the conductive particles. In addition, the binder, like the dispersion medium, is preferably a material that disappears during baking. Therefore, the binder is preferably an organic binder (typically an organic compound with a burnout temperature of 500°C or less). It should be noted that 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 restrictions. Examples of such binders include organic polymer compounds such as rosin resins, cellulose resins, polyvinyl alcohol resins, polyvinyl acetal resins, acrylic resins, polyurethane resins, epoxy resins, phenolic resins, polyester resins, and vinyl resins. Since it also depends on the combination with the above-mentioned dispersion medium, it cannot be generalized. Among these organic compounds, cellulose resins, polyvinyl alcohol resins, polyvinyl acetal resins, acrylic resins, etc. are suitable as binders. The binder can use any one of the above-mentioned organic compounds, or a combination of two or more. In addition, the binder can also be a copolymer, block copolymer, etc. formed by copolymerizing these organic compounds. It should be noted that the content of the binder is preferably appropriately adjusted in a manner that can exert appropriate fixation. For example, the content of the binder is preferably 0.5 weight parts or more relative to 100 weight parts of gold particles, more preferably 1 weight part or more, further preferably 1.5 weight parts or more, and particularly preferably 2 weight parts or more. On the other hand, from the viewpoint of preventing the binder from remaining after baking, the content of the binder is preferably 10 weight parts or less, more preferably 8 weight parts or less, further preferably 6 weight parts or less, and particularly preferably 4 weight parts or less.

[0089] In addition, the dispersant is an additive that suppresses the aggregation of inorganic particles (conductive particles, glass powder, etc.) in the paste. Specifically, the dispersant has the function of stabilizing the solid-liquid interface between the inorganic particles and the dispersion medium and preventing the aggregation of the inorganic particles. Therefore, the glass powder in the paste can be evenly dispersed, and the adhesive properties of the glass powder can be more appropriately exhibited. It should be noted that the type of dispersant is not particularly limited, and a conventionally known dispersant can be appropriately selected as needed. As an example of such a dispersant, an anionic dispersant can be cited. Anionic dispersants have excellent adsorption capacity for inorganic particles and can therefore appropriately disperse inorganic particles for a long time. As such anionic dispersants, carboxylic acid dispersants can be cited. Specific examples of such carboxylic acid dispersants include stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, linolenic acid, etc. It should be noted that, in addition, the conductive paste may also contain two or more dispersants. The content of the dispersant is preferably adjusted within a 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) relative to 100 parts by weight of the gold particles.

[0090] A sintering aid is an additive that assists the sintering of the paste. The sintering aid is typically a component containing particles of a transition metal oxide as the main component. By adding a sintering aid, appropriate sintering properties can be imparted, which helps improve conductivity and, in addition, can appropriately demonstrate the adhesive properties of the gold paste. The transition metal oxide used for the sintering aid can be appropriately changed, for example, according to the calcination temperature of the gold paste. Examples of transition metal oxides used for the sintering aid include CuO, Mn3O4, NiO, Fe2O3, ZnO, and CoO. As a sintering aid, CuO is preferably used. The content of the sintering aid is preferably adjusted within a 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) relative to 100 parts by weight of the gold particles.

[0091] From an environmental perspective, the gold paste disclosed herein preferably contains substantially no lead (Pb). It should be noted that "substantially free of lead" in this specification means that no lead (Pb) has been intentionally added to the gold paste. Therefore, trace amounts of lead, derived from raw materials, manufacturing processes, and the like, are included in the concept of "substantially free of lead" in this specification. For example, a gold paste can be considered "substantially free of lead" if the lead content in the entire paste is 1000 ppm or less (preferably 500 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less) calculated as Pb.

[0092] [Method for producing gold paste]

[0093] Such a gold paste can be produced by weighing the above-mentioned materials in a manner of obtaining a prescribed blend (parts by weight) and mixing (kneading) them in a manner of obtaining a homogeneous mixture. It should be noted that the manner of mixing the above-mentioned materials is not particularly limited. For example, all the components can be mixed at once, or they can be mixed in an appropriately set order. It should be noted that the kneading of the above-mentioned gold paste can be carried out using a stirring and mixing device that is known in the art without particular limitation. As an example of an apparatus used for kneading the gold paste in the present disclosure, a three-roll mill, an open mill, a magnetic stirrer, a rotation-revolution mixer, a planetary mixer, a disperser, a bead mill, etc. can be cited.

[0094] [Uses of gold paste]

[0095] The gold paste disclosed herein has been described above. The gold paste disclosed herein can be used, for example, for forming a conductor film of a ceramic electronic component. In detail, as the above-mentioned conductor film, for example, it can be used as a wiring pattern formed on a substrate, a conductive circuit, a piezoelectric body composed of inorganic substances such as ceramics, a dielectric, a semiconductor, a magnetic body, etc., a surface electrode of a component, a lead-out electrode, a terminal electrode, and an external electrode. Among them, from the viewpoint of the stability of the conductor film after the gold paste is baked and the adhesion to the substrate, the gold paste disclosed herein is suitable for the formation of a conductor film (electrode) of a thermistor. As the above-mentioned thermistor, for example, a negative temperature coefficient (NTC, Negative Temperature Coefficient) thermistor, a positive temperature coefficient (PTC, Positive Temperature Coefficient) thermistor, etc. can be listed.

[0096] As an example of the use of the gold paste disclosed herein, a method for producing (forming) a conductive film using the gold paste is described below. The conductive film production method described here includes a paste coating step and a baking step. However, the production method is not limited to the following method.

[0097] 1. Paste coating process

[0098] In the paste coating 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 that can withstand the baking temperature in the baking step described below, and conventionally known substrates can be used. The gold paste can be applied by conventional methods, such as chip dipping, dispenser feeding, printing methods such as screen printing, gravure printing, offset printing, and inkjet printing, and spraying methods.

[0099] 2. Calcination process

[0100] In the firing process, the substrate coated with the gold paste is fired at a predetermined temperature. Thus, a conductive film is formed on the substrate as a fired body of the gold paste. It should be noted that by using the gold paste disclosed herein, the foaming of the gold paste during firing can be suppressed. Thus, a conductor film with a smooth surface can be obtained. It should be noted that the firing temperature (maximum firing temperature) in the firing process is not particularly limited, and is preferably a temperature 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.

[0101] Next, an NTC thermistor will be described as an example of a ceramic electronic component manufactured using the gold paste disclosed herein. Figure 1 Schematic diagram for schematically illustrating the structure of the NTC thermistor 1. Figure 1 As shown, the NTC thermistor 1 includes a thermistor element 10, a surface electrode 20, a lead 30, and a sealing portion 40. The surface electrode 20 is an example of a "conductive film."

[0102] Typically, the thermistor base body 10 can be made of one or more NTC thermistor materials from various conventionally known NTC thermistor materials, depending on the intended use. NTC thermistor materials can be selected from oxides or composite oxides of transition metal elements such as Ni, Co, Mn, and Fe.

[0103] Here, a pair of surface electrodes 20 are provided on the side surfaces of the thermistor body 10. The surface electrodes 20 are formed by applying (printing) a conductive paste for the surface electrodes onto the surface (and side surfaces) of the thermistor body 10 and then firing it. When the gold paste disclosed herein is used as the conductive paste for the surface electrodes, foaming of the gold paste is suppressed during firing. In other words, the gold paste disclosed herein can provide surface electrodes 20 with smooth surfaces.

[0104] The lead wire 30 is electrically connected to the surface electrode 20 via the connection electrode 32. Figure 1 As shown, here, a pair of lead wires 30 are arranged substantially in parallel. For example, conductive materials such as Ni, Cu, Co, and Fe are used as the lead wires 30. For example, metals such as Au and Ag are used as the connection electrodes 32.

[0105] The sealing portion 40 is a portion that hermetically seals the thermistor base 10, the pair of surface electrodes 20, and a portion of the pair of leads 30. The sealing portion 40 is typically formed of glass. Here, the sealing portion 40 has an elliptical spherical shape extending along the direction in which the leads 30 extend. Depending on the intended use, the glass used in the sealing portion 40 can be one or more glass materials used in conventionally known NTC thermistors. It should be noted that the method for forming the sealing portion 40 can utilize conventionally known techniques and is not a limiting factor of the techniques disclosed herein, so a detailed description will be omitted.

[0106] It should be noted that the use of the gold paste disclosed herein is not limited to the above-mentioned NTC thermistor. Other examples of ceramic electronic components that can use the gold paste disclosed herein include multi-layer ceramic capacitors (MLCC), inductors, piezoelectric elements (varistors), etc. In these electronic components, foaming may also occur on the surface of the conductor film when the paste is baked. In this regard, when the gold paste disclosed herein is used, a conductor film with suppressed foaming can be provided. Therefore, by using the gold paste disclosed herein, MLCCs, inductors, piezoelectric elements, etc. with conductor films (such as external electrodes, etc.) with suppressed foaming and smooth surfaces can be manufactured.

[0107] As described above, specific aspects of the technology disclosed herein include aspects described in the following items.

[0108] [Project 1]

[0109] A gold paste comprising at least gold particles, glass particles and a dispersion medium,

[0110] The glass particles contain at least one selected from alkali metal elements or alkaline earth metal elements,

[0111] The total surface area S of the glass per 1g of the gold particles contained in the gold paste is t (m 2 ) relative to the average particle size D of the gold particles calculated based on BET BET (μm) ratio (S t / D BET ) is less than 0.11.

[0112] [Project 2]

[0113] The gold paste according to item 1, wherein the content of the glass particles is 0.8 parts by weight or more and 3.2 parts by weight or less based on 100 parts by weight of the gold particles contained in the gold paste.

[0114] [Item 3]

[0115] The gold paste according to item 1 or 2, wherein the content of the alkali metal component or the alkaline earth metal component in the entire glass particles is 15 wt % or more and 35 wt % or less in terms of oxide.

[0116] [Item 4]

[0117] The gold paste according to any one of items 1 to 3, wherein the glass particles have a softening point of 800° C. or higher and 900° C. or lower.

[0118] [Item 5]

[0119] The gold paste according to any one of items 1 to 4, wherein the average particle size D of the gold particles is BET (μm) is 0.35 μm or more and 1.5 μm or less.

[0120] [Item 6]

[0121] The gold paste according to any one of items 1 to 5, wherein the gold paste does not substantially contain lead.

[0122] [Item 7]

[0123] The gold paste according to any one of items 1 to 6, wherein the glass particles comprise the following composition in terms of oxide:

[0124] SiO2: 35wt%~70wt%

[0125] B2O3: 2wt%~20wt%

[0126] Al2O3: 5wt%~20wt%

[0127] RO: 15wt%~35wt%

[0128] (Here, R includes at least one element selected from the group consisting of Mg, Ca, Sr, and Ba).

[0129] [Item 8]

[0130] The gold paste according to any one of items 1 to 7, which is used for forming a conductor film of a thermistor.

[0131] [Test Example]

[0132] Next, test examples related to the technology disclosed herein will be described. It should be noted that the test examples shown below are not intended to limit the technology disclosed herein.

[0133] 1. Preparation of Gold Paste for Evaluation

[0134] Here, a gold paste for evaluation was prepared for an evaluation test (foaming test). Specifically, gold powder (median particle size: 0.5 μm, AU-2061, Noritake Company Limited), glass particles (median particle size: 0.5 μm, softening point: 850°C), a binder (ethyl cellulose resin: EC), a dispersion medium (TEXANOL), and a sintering aid (CuO) were prepared. The apparatus and conditions used for measuring the median particle size of the gold and glass particles are as follows.

[0135] Measuring device: Microtrac MT-3000 (MicrotracBEL Corp.)

[0136] Solvent: ethanol

[0137] Refractive index: 1.36

[0138] Dispersion time: 180 seconds

[0139] Measurement time: 30 seconds

[0140] The glass particles prepared in this test example had the following glass components in terms of oxides relative to the entire glass particles and contained substantially no PbO.

[0141] SiO2: 55wt%

[0142] Al2O3: 14wt%

[0143] B2O3: 9wt%

[0144] CaO: 20wt%

[0145] MgO: 2wt%

[0146] 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 so that the total weight of the paste for each example was 40 g. The mixture was kneaded using a three-roll mill. Thus, the gold pastes for evaluation of Examples 1 to 11 were prepared.

[0147] It should be noted that before preparing the gold paste, the BET specific surface area (m 2 The apparatus and conditions used for the measurement of the BET specific surface area are as follows.

[0148] Measuring device: Macsorb HM Model-1201 (MOUNTECH Co., Ltd.)

[0149] Preheater temperature: 200℃

[0150] Warm-up time: 15 minutes

[0151] Sample amount: 0.8g

[0152] Degassing device: Pre-Heat Unit Model-PH5 (MOUNTECH Co., Ltd.)

[0153] Degassing temperature: 120℃

[0154] Degassing time: 5 minutes

[0155] Furthermore, the average particle size (D) of the gold particles based on BET conversion was calculated by the above method using the BET specific surface area of ​​the gold particles. BET )(μm)(corresponding to the "BET-converted particle size of gold particles" in Table 1). In addition, using the BET specific surface area of ​​the above-mentioned glass particles, the total surface area (S) of the glass particles per 1g of gold particles of each example was calculated. t )(m 2 Using the above results, the ratio of the total surface area of ​​the glass particles per 1g of gold particles to the average particle size of the gold particles based on BET conversion (S t / D BET ). The respective results are shown in Table 1.

[0156] 2. Evaluation of gold paste (foaming test)

[0157] (1) Preparation of test pieces

[0158] Here, a test piece for a foaming test is prepared. Specifically, first, an alumina substrate is prepared. The gold pastes of Examples 1 to 11 prepared above are respectively coated on the prepared substrate by screen printing. Then, a box-type hot air dryer is used to perform a drying process at 120°C for 10 minutes. Thus, a dry film having a dry film thickness of about 10 μm is obtained. The formed dry film is subjected to a calcination process. It should be noted that the calcination temperature is set to 900°C, and the calcination atmosphere is set to a nitrogen atmosphere. In addition, the total processing time (the time from the start of calcination to the end of calcination) including the heating time is set to 1 hour, and the holding time at the highest temperature is set to 10 minutes.

[0159] In this manner, a test piece was obtained in which a conductor film having a thickness of approximately 7.5 μm was formed on an alumina substrate.

[0160] (2) Evaluation of the number of foaming

[0161] The number of foams in the test pieces prepared above was evaluated. Specifically, a scanning electron microscope (SEM) was used to observe the conductor film of each sample obtained with a 500-fold field of view as one field of view, and the number of foams in the conductor film was counted. This observation was performed in 5 fields of view for each sample, and the total number in the 5 fields of view was taken as the number of foams in each sample. The results are shown in the "Number of Foams" column of Table 1. In addition, Figure 2 S stands for gold paste t / D BET The relationship between the number of foaming of the test piece obtained by baking the gold paste is shown in FIG. t / D BET Examples of ≤0.11 are drawn with white circles and do not meet S t / D BET ≤0.11 (i.e., S t / D BET >0.11) are drawn with black circles. Figure 2 The dotted lines represent "S t / D BET =0.11", "Number of bubbles = 100".

[0162] [Table 1]

[0163]

[0164] Figure 3 This is an optical microscope image (50 times magnification) of the test piece (conductor film) of Example 5. Figure 4 This is a surface SEM image (200 times magnification) of the test piece (conductor film) of Example 5. Figure 5 This is an optical microscope image (50 times magnification) of the test piece (conductor film) of Example 9. Figure 6 This is a surface SEM image (200 times) of the test piece (conductor film) of Example 9. Figure 6 The circled area represents the foaming generated during the firing of the gold paste. Figure 2 As shown, when using S t / D BET In the conductor films obtained with the gold pastes having a viscosity of 0.11 or less (Examples 1 to 5, 7, and 10 to 11), the number of bubbles observed was less than 100 in any of the examples. Figure 6 As shown, when using S t / D BET In the conductor film obtained by the gold paste of Example 9, which has a viscosity of 0.16, foaming was observed during the firing of the gold paste. Figure 3 and Figure 4 As shown, the conductor film obtained by the gold paste of Example 5 and the conductor film of Example 9 ( Figure 5 and Figure 6 ) is less concave and convex, and a smooth surface is obtained. From the above results, it can be confirmed that according to S t / D BET A gold paste having a viscosity of 0.11 or less can suppress the foaming of glass particles during firing, thereby obtaining a conductor film with a smooth surface.

[0165] As mentioned above, although the technology disclosed here was demonstrated in detail, these are only examples, and this disclosure can add various changes within the range which does not deviate from the summary.

Claims

1. A gold paste comprising 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, The total surface area S of the glass per 1 g of the gold particles contained in the gold paste is t The average particle size D of the gold particles calculated based on BET BET Ratio S t / D BET is below 0.11, S t The unit is m 2 , D BET The unit is μm.

2. The gold paste according to claim 1, wherein When the gold particles contained in the gold paste are 100 parts by weight, the content of the glass particles is 0.8 parts by weight or more and 3.2 parts by weight or less.

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

4. The gold paste according to claim 1 or 2, wherein The glass particles have a softening point of 800° C. or higher and 900° C. or lower.

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

6. The gold paste according to claim 1 or 2, wherein The gold paste contains substantially no lead.

7. The gold paste according to claim 1 or 2, wherein The glass particles comprise the following composition in terms of oxide conversion: SiO2: 35wt%~70wt% B2O3: 2wt%~20wt% Al2O3: 5wt%~20wt% RO: 15wt%~35wt% Here, R includes at least one element selected from the group consisting of Mg, Ca, Sr, and Ba. The gold paste according to claim 1 or 2, which is used for forming a conductor film of a thermistor.

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