Method for evaluating silver powder, and method for manufacturing silver powder including the same

Abstract

To provide a technique capable of easily evaluating the degree to which silver ions diffuse from silver powder into a base material when the silver powder is used.SOLUTION: According to the technique disclosed herein, a method for evaluating silver powder is disclosed. The method for evaluating silver powder includes: heating silver powder on a glass substrate; observing the coloration state of the glass substrate after heating; and evaluating the degree of diffusion of silver ions in the glass substrate on the basis of the coloration state.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating silver powder and a method for producing silver powder including the evaluation method. [Background technology]

[0002] The conductive paste disclosed in JP 2019-36435 A contains a conductive powder, a binder resin, and an organic solvent. In this conductive paste, the organic solvent has a Fedors solubility parameter of 9.0 (cal / cm 3 ) 0.5 A first solvent having a Fedors solubility parameter of 10.0 (cal / cm 3 ) 0.5 The mixed solvent contains a second solvent having a Fedors solubility parameter of 9.0 (cal / cm 3 ) 0.5 More than 10.1(cal / cm 3 ) 0.5 The publication states that the first solvent is useful for suppressing the occurrence of sheet attack, but that when used alone it is likely to cause permeation of conductive powder. The publication also states that the second solvent is useful for suppressing the permeation of conductive powder, but that when used alone it is likely to cause sheet attack. According to the technology described in the publication, the advantages of the first solvent and the second solvent are optimally utilized, making it possible to favorably form an electrode in which both the occurrence of sheet attack and the permeation of conductive powder are suppressed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-36435 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, silver powder is sometimes used to form internal electrodes of electronic components. The process for manufacturing electronic components may include a step of subjecting the silver powder to heat treatment to sinter the silver powder. It has long been known that heat treatment tends to generate silver ions from the silver powder and diffuse them into the substrate. The diffusion of silver ions generated by heat treatment is undesirable because it may lead to, for example, short circuits between internal electrodes. However, there has not been a method for evaluating the degree of diffusion of silver ions from the silver powder to the substrate when silver powder is used, the possibility of short circuits in electronic components, etc., prior to the manufacture of the object to be manufactured using silver powder.

[0005] In view of these circumstances, the present inventors would like to easily evaluate the degree to which silver ions diffuse from silver powder to a substrate when silver powder is used. [Means for solving the problem]

[0006] The technology disclosed herein provides a method for evaluating silver powder. This evaluation method includes heating silver powder on a glass substrate, observing the colored state of the glass substrate after heating, and evaluating the degree of silver ion diffusion in the glass substrate based on the colored state. This configuration makes it possible to easily evaluate the degree of silver ion diffusion from the silver powder to a substrate (glass substrate) when silver powder is used.

[0007] In a preferred embodiment of the evaluation method disclosed herein, the heating includes heating the silver powder within a temperature range in which silver colloid can be produced. According to this configuration, the accuracy of the evaluation can be improved.

[0008] In a preferred embodiment of the evaluation method disclosed herein, the glass substrate contains at least SiO2. This configuration can improve the reproducibility of the evaluation.

[0009] In a preferred embodiment of the evaluation method disclosed herein, the glass substrate contains at least one of an alkali metal element and an alkaline earth metal element, which can improve the reproducibility of the evaluation.

[0010] In a preferred embodiment of the evaluation method disclosed herein, the evaluation is performed by calculating the circle-equivalent diameter D0 of the region where the silver powder is placed on the glass substrate before heating and the circle-equivalent diameter D1 of the colored region on the glass substrate after heating using the following mathematical formula (X): Diffusion rate (%) = {(D1-D0) / D0} x 100 (X) Silver powder having a diffusion rate of 20% or less obtained using this method is evaluated as a non-defective product. This configuration can reduce the risk of problems occurring when the silver powder is actually used.

[0011] The technology disclosed herein provides a method for producing silver powder. The method includes preparing silver powder, evaluating the prepared silver powder using the evaluation method disclosed herein, and selecting good silver powder based on the results of the evaluation. This configuration allows for the production of silver powder with a lower risk of defects during actual use. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multilayer chip inductor 1. As shown in FIG. [Figure 2] FIG. 2 is an image of the pellet of Example 11 and the glass substrate after heat treatment. [Figure 3] FIG. 3 is an image of the pellet of Example 12 and the glass substrate after heat treatment. [Figure 4] FIG. 4 is an image of the pellet of Example 15 and the glass substrate after heat treatment. [Figure 5] FIG. 5 is an image of the pellet and the glass substrate after the first heat treatment. [Figure 6] Figure 6 is an image of the glass substrate with the pellet removed. [Figure 7]FIG. 7 is an image of the pellet and glass substrate after the second heat treatment. [Figure 8] FIG. 8 is an image of the pellet of Example 41 and the glass substrate after heat treatment. [Figure 9] FIG. 9 is an image of the pellet of Example 42 and the glass substrate after heat treatment. [Figure 10] FIG. 10 is an image of the pellet of Example 43 and the glass substrate after heat treatment. [Figure 11] FIG. 11 is an image of the pellet of Example 44 and the glass substrate after heat treatment. [Figure 12] FIG. 12 is an image of the pellet of Example 45 and the glass substrate after heat treatment. [Figure 13] FIG. 13 is an image of the pellet of Example 46 and the glass substrate after heat treatment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the technology disclosed herein are described below. Matters necessary for implementing the technology disclosed herein, other than those specifically mentioned in this specification, can be understood based on the technical content taught by this specification and the general technical common sense of a person skilled in the art. The technology disclosed herein can be implemented based on the content disclosed in this specification and the general technical common sense of a person skilled in the art. In this specification and claims, the terms A to B (A and B are arbitrary numerical values) refer to values ​​greater than A and less than B, and also encompass values ​​greater than A and less than B.

[0014] The present disclosure provides a method for evaluating silver powder, which includes heating silver powder on a glass substrate, observing the colored state of the glass substrate after heating, and evaluating the degree of silver ion diffusion in the glass substrate based on the colored state.

[0015] This evaluation method includes, for example, a placement step, a first heating step, a second heating step, and an evaluation step.

[0016] The disposing step is, for example, a step of disposing silver powder on a glass substrate. In this embodiment, in the disposing step, a compressed product of silver powder is disposed on the glass substrate. In this embodiment, the compressed product of silver powder contains silver powder, a resin binder, and, as needed, any additive components. In preparing the compressed product of silver powder, a silver paste containing silver powder may be first prepared. The silver paste may, for example, contain silver powder, a resin binder, an organic solvent, and, as needed, any additive components.

[0017] In this embodiment, the silver powder contained in the silver paste is the silver powder to be evaluated by the evaluation method disclosed herein. The silver powder is not particularly limited, and may be, for example, a silver powder used for this type of application. Considering the intended use of the evaluation method disclosed herein, silver powder containing impurities (e.g., boron, calcium, chromium, copper, iron, sodium, nickel, phosphorus, silicon, zinc, etc.) can be preferably used as the silver powder. Among these, silver powder produced using an atomization method can be preferably used. The silver content in the silver powder and the impurity content in the silver powder can be measured, for example, by using ICP atomic emission spectroscopy.

[0018] The average particle size of the silver powder is not particularly limited and is generally 0.5 μm to 20 μm. In this specification, the term "average particle size" refers to the 50% cumulative particle size in the particle size distribution (number basis) of equivalent circle diameters based on electron microscope observation.

[0019] When the entire silver paste is taken as 100% by mass, the content of silver powder is, for example, 80% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more. This can improve, for example, the accuracy of evaluation. When the entire silver paste is taken as 100% by mass, the content of silver powder is approximately 99% by mass or less, for example, 98% by mass or less, preferably 97% by mass or less, more preferably 96% by mass or less, and even more preferably 95% by mass or less. This can, for example, allow other components to be appropriately contained in the silver paste, thereby achieving preferable moldability for the silver paste.

[0020] The resin binder is, for example, a component that binds the particles constituting the silver powder together. The resin binder is preferably a component that burns out in the heat treatment step described below (when no particular distinction is made between the first and second heat treatment steps, this is also simply referred to as the "heat treatment step"). The resin binder is not particularly limited, but examples include celluloses such as methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, and polybutyl methacrylate; epoxy resins; phenolic resins; alkyd resins; polyvinyl alcohol; polyvinyl butyral; rosin, maleated rosin, and the like. As the resin binder, one of the above-mentioned types may be used alone, or two or more types may be used in combination. When the entire silver paste is taken as 100% by mass, the content of the resin binder is generally 0.1% by mass to 3% by mass, and preferably 0.3% by mass to 1% by mass.

[0021] The organic solvent is a component that dissolves or disperses, for example, silver powder, a resin binder, and other components. The type of organic solvent is not particularly limited and can be selected from among conventionally known organic solvents. For example, the organic solvent can be one of the organic solvents described below, or two or more of them can be used in appropriate combination. Examples include alcohol-based solvents having an -OH group, ether-based solvents having an ether bond (RO-R'), ester-based solvents having an ester bond (RC(=O)-O-R'), and hydrocarbon-based solvents composed of carbon atoms and hydrogen atoms.

[0022] Examples of alcohol-based solvents and ether-based solvents include terpineol, texanol, dihydroterpineol, benzyl alcohol, 3-methoxy-3-methyl-1-butanol, diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol-n-butyl ether, dipropylene glycol methyl-n-propyl ether, dipropylene glycol methyl ether acetate, and dipropylene glycol methyl-n-butyl ether.

[0023] Examples of ester-based solvents include 3-methoxy-3-methyl-1-butanol acetate, 3-methoxybutyl acetate, 1,3-butylene glycol diacetate, 1,4-butanediol diacetate, 1,6-hexanediol diacetate, propylene glycol monomethyl ether acetate, isobornyl acetate, carbitol acetate, ethyl diglycol acetate, butyl cellosolve acetate, propylene glycol diacetate, diethylene glycol monobutyl ether acetate, terpineol acetate, dihydroterpineol acetate, etc. Examples of hydrocarbon-based solvents include aliphatic hydrocarbon solvents such as petroleum hydrocarbons, naphtha, dipentene, turpentine oil, and mineral spirits; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; paraffin-based solvents such as normal paraffins and isoparaffins; and naphthenic solvents such as monocyclic naphthenes and bicyclic naphthenes. When the entire silver paste is taken as 100% by mass, the content of the organic solvent is generally 0.5% by mass to 10% by mass, and preferably 2% by mass to 7% by mass.

[0024] For example, the silver paste may contain optional additive components in addition to the above-described components, as needed, to improve moldability or to prevent the silver powder from deteriorating during the evaluation method. Examples of additive components include dispersants, surfactants, viscosity modifiers, antifoaming agents, plasticizers, and antioxidants. When the entire silver paste is taken as 100% by mass, the content of the additive components is generally 5% by mass or less, for example, 3% by mass or less, preferably 2% by mass or less, and more preferably 1% by mass or less.

[0025] The silver paste is prepared, for example, by mixing the above-described components. As a mixer for mixing, any conventional mixer used for this type of application can be used without any particular limitation.

[0026] For example, in order to increase the amount of silver powder placed on the glass substrate and improve the accuracy of the evaluation, the silver paste may be formed into a pellet. This allows a compressed silver powder to be obtained. When forming the silver paste into a pellet, powder obtained by drying the silver paste may be used. There are no particular limitations on the forming method, but for example, a commercially available uniaxial forming machine may be used. Here, the powder obtained by drying the silver paste is filled into a mold of the forming machine and pressurized at a predetermined pressure (approximately 50 MPa to 100 MPa, preferably 70 MPa to 90 MPa) to form into a pellet having a predetermined diameter (approximately 5 mm to 10 mm).

[0027] In this embodiment, in the disposing step, the compressed silver powder obtained as described above is disposed on a glass substrate. The glass substrate is not particularly limited, and various conventionally known glass substrates can be used. The glass substrate is preferably made of glass containing at least silica (SiO2), and more preferably made of soda-lime glass.

[0028] The glass substrate is preferably made of glass containing at least one of an alkali metal element and an alkaline earth metal element, and more preferably made of soda-lime glass. Examples of alkali metal elements include lithium, sodium, potassium, and rubidium. The alkali metal elements can be contained in the glass substrate as alkali metal oxides (lithium oxide, sodium oxide, potassium oxide, rubidium oxide, etc.). Examples of alkaline earth metal elements include magnesium, calcium, strontium, and barium. The alkaline earth metal elements can be contained in the glass substrate as alkaline earth metal oxides (magnesium oxide, calcium oxide, strontium oxide, barium oxide, etc.).

[0029] The first heating step is, for example, a step of heating the silver powder and the glass substrate at a first temperature. In this embodiment, the first temperature is a temperature at which the silver powder is expected to be used. The first temperature is not particularly limited, as it can be appropriately changed depending on the application of the silver powder. For example, if an electronic component including a fired film of silver powder as an internal electrode is expected to be used at 600°C, the first temperature is 600°C. Alternatively, if this electronic component is expected to be used at 700°C, the first temperature is 700°C. When the silver powder is used to form an electronic component, the first temperature is, for example, 500°C or higher and approximately 950°C or lower, for example, 900°C or lower, or may be 850°C or lower, or may be 800°C or lower. The treatment time of the first heat treatment is preferably approximately 15 minutes to 2 hours. The first heat treatment is preferably performed in an oxygen-containing atmosphere, such as the air atmosphere.

[0030] The second heating step is, for example, a step of heating the glass substrate to a second temperature in the first heating step when the first temperature does not reach a temperature at which silver colloid can be produced. By performing the second heating step, for example, silver ions diffused from the silver powder to the glass substrate become silver colloid, thereby coloring the glass substrate. Here, the second temperature is a temperature at which silver colloid can be produced. Here, the temperature at which silver colloid can be produced is generally 680°C or higher. Therefore, the second temperature is preferably set to, for example, 680°C or higher, more preferably 700°C or higher. Although not particularly limited, the second temperature is preferably approximately 900°C or lower, or may be 850°C or lower, or may be 800°C or lower. The second heating step is, for example, a process of maintaining the silver powder and the glass substrate at the second temperature for a predetermined period of time. The maintenance period in the second heating step is preferably approximately 15 minutes to 2 hours. In carrying out the second heating step, the second heating treatment may be applied to both the glass substrate and the silver powder (here, the compressed product), or the second heating treatment may be applied only to the glass substrate from which the silver powder has been removed after the first heating step.

[0031] The second heating treatment may be carried out in an oxygen-containing atmosphere, such as the air atmosphere. If the first heating treatment is carried out at a temperature at which silver colloid can be produced, the second heating step may not be carried out. Therefore, if the first heating treatment is carried out at a temperature at which silver colloid can be produced, the second heating step may not be carried out separately after the first heating step.

[0032] The evaluation step is, for example, a step of observing the colored state on the glass substrate subjected to the second heating process and evaluating the degree of diffusion of silver ions in the glass substrate based on the colored state. While not particularly limited, the degree of diffusion of silver ions in the glass substrate can be evaluated based on, for example, the circle-equivalent diameter D0 of the area where the silver powder is placed on the glass substrate before the first heating process and the circle-equivalent diameter D1 of the colored area on the glass substrate after the second heating process (after the first heating process if the first heating process is performed at a temperature capable of producing silver colloid). In this embodiment, the circle-equivalent diameter D0 is the diameter of the silver paste pellet. The circle-equivalent diameter D1 is a measured value obtained, for example, by acquiring an image of the colored area of ​​the glass substrate and analyzing it with image analysis software or the like. The circle-equivalent diameter D0 and the circle-equivalent diameter D1 can be calculated using the following formula (X): Diffusion rate (%) = {(D1-D0) / D0} x 100 (X) The spreading factor can be calculated using

[0033] The greater the diffusion rate calculated using the above formula (X), the greater the degree of diffusion of silver ions in the glass substrate. Conversely, the smaller the diffusion rate, the less the degree of diffusion of silver ions in the glass substrate, indicating a good product, for example, a low risk of short circuits occurring in electronic components. The diffusion rate is, for example, 30% or less, may be 25% or less, or 20% or less, preferably 15% or less, more preferably 10% or less, even more preferably 7.5% or less, and particularly preferably 6% or less, and the smaller the better. In the evaluation process, for example, silver powders that are determined to have a diffusion rate of 30% or less may be evaluated as good products and selected. Silver powders that are not evaluated as good products may, for example, be discarded.

[0034] One embodiment of the evaluation method disclosed herein has been described above. In the above embodiment, a silver paste containing silver powder to be evaluated was prepared, and a pellet-shaped compressed product of the silver powder was obtained from the silver paste and subjected to subsequent processing. However, the technology disclosed herein is not limited to this embodiment. For example, it is not necessary to prepare a silver paste. The silver powder to be evaluated may be compressed into a pellet-shaped compressed product and subjected to subsequent processing.

[0035] As described above, the evaluation method disclosed herein involves heating silver powder on a glass substrate, observing the colored state of the glass substrate after heating, and evaluating the degree of diffusion of silver ions in the glass substrate based on the colored state.

[0036] In the evaluation method, silver powder is heated on a glass substrate, which facilitates diffusion of silver ions from the silver powder to the glass substrate and causes the diffused silver ions to form colloids. This causes the silver ion diffusion site on the glass substrate (the site where the diffused silver ions have become colloidal due to heating) to become colored. The evaluation method includes evaluating the degree of silver ion diffusion in the glass substrate based on the colored state of the glass substrate. Thus, the evaluation method allows the degree of silver ion diffusion in the glass substrate to be evaluated by observing the colored state of the glass substrate. Therefore, when silver powder is used, the degree of diffusion of silver ions from the silver powder to the substrate (here, the glass substrate) can be easily evaluated. Furthermore, by using this evaluation method, the degree of silver ion diffusion from the silver powder in actual use can be easily evaluated.

[0037] In the evaluation method, the heating step may include heating the silver powder within a temperature range in which silver colloid can be produced. This allows the silver ions diffused in the glass substrate to be efficiently converted into colloids, thereby more accurately coloring the areas where the silver ions have diffused, thereby improving the accuracy of the evaluation.

[0038] The glass substrate should preferably contain at least SiO2. For example, silver ions are easily held by silica. This improves the reproducibility of the evaluation.

[0039] The glass substrate preferably contains at least one of an alkali metal element and an alkaline earth metal element. The alkali metal component containing an alkali metal element and the alkaline earth metal component containing an alkaline earth metal element can, for example, impart fluidity to the glass substrate and lower its softening point. This allows the degree of silver ion diffusion in the glass substrate to be stably measured. This improves the reproducibility of the evaluation.

[0040] In the evaluation, the circle-equivalent diameter D0 of the area where the silver powder was placed on the glass substrate before heating and the circle-equivalent diameter D1 of the colored area on the glass substrate after heating were calculated using the following formula (X): Diffusion rate (%) = {(D1-D0) / D0} x 100 (X) Silver powder with a diffusion rate of 10% or less obtained using the method should be evaluated as a good product. By evaluating silver powder with a diffusion rate of 20% as a good product, the risk of problems occurring during actual use of the silver powder can be reduced.

[0041] The evaluation method may include a disposing step, a first heating step, a second heating step, and an evaluation step. The disposing step may be a step of disposing silver powder on a glass substrate. The first heating step may be a step of heating the silver powder and the glass substrate at a first temperature. The first temperature may be a temperature at which the silver powder is expected to be used. The second heating step may be a step of raising the temperature of the glass substrate to a second temperature and performing a second heating treatment if the first temperature in the first heating treatment does not reach a temperature at which silver colloid can be produced. The second temperature may be a temperature at which silver colloid can be produced. The evaluation step may be a step of observing the colored state on the glass substrate that has been subjected to the second heating treatment and evaluating the degree of diffusion of silver ions in the glass substrate based on the colored state.

[0042] In the first heating step, the silver powder and the glass substrate are heated at a first temperature, thereby enabling evaluation of the degree of diffusion of silver ions from the silver powder to the glass substrate at the temperature at which the silver powder is expected to be used. In the second heating step, if the first temperature has not reached a temperature at which silver colloid can be produced, the glass substrate is heated to a second temperature and subjected to a second heating treatment, thereby further increasing the sensitivity of detecting the site of diffusion of silver ions and ultimately improving the accuracy of the evaluation. In the evaluation step, the degree of diffusion of silver ions in the glass substrate is evaluated based on the color state of the glass substrate subjected to the second heating treatment. This allows for a simple evaluation of the degree of diffusion of silver ions from the silver powder to the substrate when silver powder is used.

[0043] The technology disclosed herein provides a method for producing silver powder. The method for producing silver powder may include preparing silver powder, evaluating the prepared silver powder using the evaluation method disclosed herein, and selecting good silver powder based on the results of the evaluation. This production method includes using the evaluation method disclosed herein to evaluate the degree of diffusion of silver ions from the prepared silver powder and selecting good products based on the results of this evaluation. By including this, for example, it is possible to produce silver powder with a lower risk of defects occurring in actual use.

[0044] In preparing the silver powder, the silver powder may be prepared by, for example, a wet method using a solvent or a dry method not using a solvent. Considering ease of production, such as reducing production costs, the silver powder is preferably prepared by a dry method. Examples of dry methods include an atomization method. The method for producing silver powder includes obtaining silver powder by an atomization method, evaluating the degree of diffusion of silver ions from the silver powder using the evaluation method disclosed herein, and selecting non-defective products. By doing so, silver powder can be produced more cheaply and with a lower risk of defects occurring in actual use.

[0045] Silver powder evaluated as a non-defective product by the evaluation method disclosed herein, or silver powder obtained by the silver powder manufacturing method disclosed herein, can be preferably used, for example, in the manufacture of electronic components. Such silver powder is preferably used, for example, to form electrodes of electronic components such as inductance components and capacitor components. This silver powder is a silver powder that has been determined to have a low degree of silver ion diffusion. Therefore, by using such silver powder, electronic components with a reduced risk of defects can be provided.

[0046] The following describes a multilayer chip inductor, an example of an electronic component. Figure 1 is a schematic cross-sectional view of a multilayer chip inductor 1. Note that the dimensional relationships (length, width, thickness, etc.) in Figure 1 do not necessarily reflect the actual dimensional relationships. The symbols X and Z in the drawing represent the left-right and up-down directions, respectively. However, these are directions merely used for convenience of explanation.

[0047] 1 is not particularly limited to a specific size, but may be, for example, a 1608 shape (1.6 mm × 0.8 mm), a 2520 shape (2.5 mm × 2.0 mm), etc. The multilayer chip inductor 1 includes a main body 10 and external electrodes 20.

[0048] The multilayer chip inductor 1 includes a main body 10 and external electrodes 20 provided on both side surfaces of the main body 10 in the left-right direction X. In the main body 10, for example, a plurality of magnetic layers 12 are stacked in the up-down direction Z and integrated with each other. Examples of materials that can be used to form the magnetic layers 12 include metal materials such as ferrite magnetic materials such as Ni-Cu-Zn ferrite, Fe-Cr-Si alloys, Fe-Al-Si alloys, and Fe-Si-M soft magnetic alloys (wherein M is at least one of chromium, aluminum, and titanium).

[0049] Coil conductors are provided between the magnetic layers 12 as internal electrode layers 14. In this embodiment, the coil conductors are silver powder evaluated as non-defective by the evaluation method disclosed herein, or sintered films of silver powder obtained by the silver powder manufacturing method disclosed herein. Two coil conductors adjacent to each other in the vertical direction Z, sandwiching the magnetic layer 12 therebetween, are electrically connected through via holes provided in the magnetic layer 12. As a result, the internal electrode layers 14 are configured in a three-dimensional coil shape (spiral shape). Both ends of the coil conductor are connected to external electrodes 20, respectively.

[0050] The multilayer chip inductor 1 can be manufactured, for example, by the following procedure. First, a magnetic paste containing the metal material constituting the magnetic layer 12, a binder, and an organic solvent is prepared, and then this is applied to a carrier sheet to form a green sheet. Next, the green sheet is rolled and dried. The green sheet is then cut to the desired size to obtain multiple magnetic layer-forming sheets. Next, via holes are formed in predetermined positions on the magnetic layer-forming sheets using a punch or the like. Next, a silver paste containing silver powder evaluated as non-defective by the evaluation method disclosed herein or silver powder obtained by the silver powder manufacturing method disclosed herein is printed in a predetermined coil pattern on predetermined positions on multiple magnetic layer-forming sheets and dried. Next, these are stacked and pressed together to form a laminate of unfired green sheets. This is fired to integrally fire the green sheets, forming the main body 10 including the magnetic layer 12 and the internal electrode layer 14. Then, an appropriate external electrode-forming paste is applied to both ends of the main body 10 and fired to form the external electrodes 20. In this manner, the multilayer chip inductor 1 can be manufactured.

[0051] Test examples relating to the technology disclosed herein will be described below, but it is not intended that the technology disclosed herein be limited to the following test examples.

[0052] Seven types of silver powder, designated Silver Powder A to Silver Powder G, were prepared for use in this test example. All seven types of silver powder were commercially available. The impurities contained in each of the seven types of silver powder were measured. The impurities measured here were boron, calcium, chromium, copper, iron, sodium, nickel, phosphorus, silicon, and zinc. The impurity content (ppm) in each silver powder is shown in the corresponding column in Table 1. The impurity content shown in Table 1 is the measured value obtained using an ICP optical emission spectrometer (PS3520VDDII manufactured by Hitachi High-Tech Corporation). The average particle size of each silver powder shown in Table 1 is the nominal value provided by the manufacturer.

[0053] [Table 1]

[0054] <Test 1> --Example 11-- Silver powder A was prepared as the silver powder. Ethyl cellulose was prepared as the resin binder. Diethylene glycol monobutyl ether acetate was prepared as the organic solvent. The silver powder, resin binder, and organic solvent were mixed using a mixer to produce a silver paste. Here, when the total of the silver powder, resin binder, and organic solvent was 100% by mass, the silver powder content was 95% by mass, the resin binder content was 0.5% by mass, and the organic solvent content was 4.5% by mass. Next, the silver paste was dried and pulverized to obtain paste powder. Next, using a uniaxial molding machine (hydraulic press PHK5-S manufactured by Towa Seiki Co., Ltd.), the paste powder was filled into a mold and pressed along the axial direction at a pressure of 78 MPa to obtain cylindrical pellets of paste powder with a diameter of 8 mm. Next, the pellets were placed on a glass substrate (soda-lime glass, "S7213" manufactured by Matsunami Glass Industry Co., Ltd.) and heat-treated in a belt furnace in an air atmosphere at 700°C for 0.5 hours.

[0055] The formation of colored areas was observed on the substrate after the heat treatment. Here, the diameter (circle equivalent diameter) of the colored area was measured using image analysis software, and the diameter was calculated using the following formula (A): Spread from the pellet (mm) = diameter of the colored area - diameter of the pellet (A) Furthermore, the following formula (B): Diffusion rate (%) = (spread from pellet / diameter of pellet) x 100 (B) The diffusion rate (%) of silver ions from the pellet to the glass substrate was calculated based on the above. The results are shown in the corresponding columns in Table 2. For reference, an image of the pellet and glass substrate of Example 11 after the above heat treatment is shown in Figure 2.

[0056] -Example 12 to Example 15- The silver powder used was the silver powder shown in the corresponding column of Table 2. Other than that, the pellets of this example were produced using the same materials and procedures as in Example 11, and the diffusivity was calculated. For reference, an image of the pellets of Example 12 and the glass substrate after the heat treatment is shown in FIG. 3. For reference, an image of the pellets of Example 15 and the glass substrate after the heat treatment is shown in FIG. 4.

[0057] (Short evaluation) Multilayer inductors were fabricated using the silver powders of Examples 11 to 15, and the occurrence of short circuits in the multilayer inductors was evaluated. The occurrence of short circuits was determined by measuring the L value (inductance) of 100 multilayer inductors, and if even one of the 100 did not show the L value, it was evaluated as having a short circuit. The results are shown in the corresponding columns in Table 2.

[0058] [Table 2]

[0059] As shown in the results of Test 1, the degree of diffusion of silver ions from the silver powder into the glass substrate could be evaluated using an evaluation method that included heating silver powder on a glass substrate, observing the coloration of the glass substrate after heating, and evaluating the degree of diffusion of silver ions from the silver powder based on the coloration. As shown in Table 2 and Figures 2 to 4, the evaluation method disclosed herein confirmed differences in the degree of silver ion diffusion in the silver powders used in Test 1. Regarding Examples 11 to 15, in which short circuit evaluations were performed, short circuits occurred in the multilayer inductors fabricated using the silver powders of Examples 11 and 15, which had relatively large spread and diffusivity. In contrast, short circuits did not occur in the multilayer inductors fabricated using the silver powders of Examples 12 to 14, which had relatively small spread and diffusivity. These results demonstrate that the evaluation method disclosed herein can be preferably used to predict whether short circuits will occur when silver powder is used in electronic components.

[0060] <Test 2> The pellet produced in Example 12 of Test 1 was placed on a glass substrate. Thereafter, the pellet and the glass substrate were subjected to a heat treatment (first heat treatment) in an air atmosphere at 600°C for 0.5 hours in a belt furnace. The pellet was then removed from the glass substrate. Then, the glass substrate from which the pellet had been removed was subjected to a heat treatment (second heat treatment) in an air atmosphere at 700°C for 0.5 hours in a belt furnace. An image of the pellet and the glass substrate after the first heat treatment is shown in FIG. 5. An image of the glass substrate from which the pellet had been removed is shown in FIG. 6. An image of the pellet and the glass substrate after the second heat treatment is shown in FIG. 7.

[0061] The results shown in Figures 5 and 6 indicate that coloring of the glass substrate may not be observed depending on the temperature of the first heat treatment. In such cases, as shown in Figure 7, colored areas are generated on the glass substrate by performing a second heat treatment at a higher temperature on the glass substrate alone. The coloring of the glass substrate is due to silver colloid. If the temperature of the first heat treatment does not reach the temperature at which silver colloid is generated, coloring may not be observed on the glass substrate. In this case, colored areas can be generated by heating the glass substrate to a temperature range at which silver colloid is generated (performing the second heat treatment).

[0062] <Test 3> -Example 31 to Example 37- The silver powder used was the silver powder shown in the corresponding column in Table 3. In this example, a paste was not prepared, and the silver powder was pelletized using the same uniaxial molding machine and procedure as in Example 11. Furthermore, the diffusivity was calculated using the same procedure as in Example 11. The results are shown in the corresponding column in Table 3.

[0063] [Table 3]

[0064] As shown in Table 3, the seven types of silver powder used in Test 3 were found to have different spreading and diffusivity. The results of Test 3 demonstrated that, if silver powder is used, the evaluation method disclosed herein can be carried out to obtain appropriate evaluation results without necessarily preparing a paste containing silver powder. Referring to Tables 1 and 3, Examples 31, 35, and 36, in which silver powder A, silver powder E, and silver powder F containing phosphorus as an impurity were used, respectively, had greater spreading and diffusivity than the other examples (examples in which phosphorus was not detected as an impurity). This demonstrates that the use of silver powder containing phosphorus as an impurity increases the degree of diffusion of silver ions from the silver powder to the glass substrate.

[0065] <Test 4> -Example 41 to Example 43- To the silver paste, 0 parts by mass (Example 41), 0.05 parts by mass (Example 42), or 0.1 parts by mass (Example 43) of a barium compound (here, barium 2-methoxyethoxide) was added per 100 parts by mass of silver powder. Pellets of this example were prepared using the same materials and procedures as in Example 11, and the pellets and glass substrate after heat treatment were observed. Images of the pellets and glass substrate of Example 41 after the heat treatment are shown in Figure 8. Images of the pellets and glass substrate of Example 42 after the heat treatment are shown in Figure 9. Images of the pellets and glass substrate of Example 43 after the heat treatment are shown in Figure 10.

[0066] -Example 44~Example 46- To the silver paste, 0 parts by mass (Example 44), 0.05 parts by mass (Example 45), or 0.1 parts by mass (Example 46) of a barium compound (here, barium 2-methoxyethoxide) was added per 100 parts by mass of silver powder. Matsunami Glass Industry Co., Ltd.'s "S1225" (soda-lime glass) glass substrate was used. Other than that, pellets of this example were prepared using the same materials and procedures as in Example 11, and the pellets and glass substrate after heat treatment were observed. Images of the pellets and glass substrate of Example 44 after the heat treatment are shown in Figure 11. Images of the pellets and glass substrate of Example 45 after the heat treatment are shown in Figure 12. Images of the pellets and glass substrate of Example 46 after the heat treatment are shown in Figure 13.

[0067] As shown in Figures 8 to 10, in Examples 42 and 43, in which a barium compound was added to the silver paste, the colored area around the pellet was smaller than in Example 41, in which no barium compound was added to the silver paste. As shown in Figures 11 to 13, in Examples 45 and 46, in which a barium compound was added to the silver paste, the colored area around the pellet was smaller than in Example 44, in which no barium compound was added to the silver paste. Comparing Figures 8 to 10 with Figures 11 to 13, similar trends were observed in Examples 41 to 43 and Examples 44 to 46.

[0068] The technology disclosed herein may include the following items. Section 1: A method for evaluating silver powder, comprising: heating the silver powder on a glass substrate; observing the colored state of the glass substrate after heating; and evaluating the degree of diffusion of silver ions in the glass substrate based on the colored state; An evaluation method that includes: Section 2: Item 1. The evaluation method according to Item 1, wherein the heating comprises heating the silver powder in a temperature range capable of producing silver colloid. Section 3: Item 3. The evaluation method according to item 1 or 2, wherein the glass substrate contains at least SiO2. Section 4: 4. The evaluation method according to any one of items 1 to 3, wherein the glass substrate contains at least one of an alkali metal element and an alkaline earth metal element. Section 5: In the evaluation, the circle-equivalent diameter D0 of the region where the silver powder was placed on the glass substrate before the heating and the circle-equivalent diameter D1 of the colored region on the glass substrate after the heating were calculated using the following formula (X): Diffusion rate (%) = {(D1-D0) / D0} x 100 (X) Item 5. The evaluation method according to any one of items 1 to 4, wherein a silver powder having a diffusion rate of 20% or less obtained using the method is evaluated as a non-defective product. Item 6: A method for producing silver powder, comprising: Prepare silver powder; Evaluating the prepared silver powder using the evaluation method described in any one of items 1 to 5; sorting the silver powder as a non-defective product based on the evaluation results; The manufacturing method includes the steps of: [Explanation of symbols]

[0069] 1 Multilayer chip inductor 10 Main Unit 12 Magnetic layer 14 Internal electrode layer 20 External electrodes

Claims

1. A method for evaluating silver powder, comprising: heating the silver powder on a glass substrate; Observing the colored state of the glass substrate after heating; and evaluating the degree of diffusion of silver ions in the glass substrate based on the colored state; An evaluation method that includes:

2. The evaluation method according to claim 1, wherein the heating comprises heating the silver powder within a temperature range capable of producing silver colloid.

3. The glass substrate is made of at least SiO ２ The evaluation method according to claim 1 , comprising:

4. The evaluation method according to claim 1 , wherein the glass substrate contains at least one of an alkali metal element and an alkaline earth metal element.

5. In the evaluation, the circle-equivalent diameter D0 of the region where the silver powder was placed on the glass substrate before the heating and the circle-equivalent diameter D1 of the colored region on the glass substrate after the heating were calculated using the following formula (X): Diffusion rate (%) = {(D1 - D0) / D0} × 100 (X) The evaluation method according to claim 1, wherein a silver powder having a diffusivity of 20% or less obtained using the method is evaluated as a non-defective product.

6. A method for producing silver powder, comprising: Prepare silver powder; Evaluating the prepared silver powder using the evaluation method according to any one of claims 1 to 5; Selecting non-defective silver powder based on the evaluation results; The manufacturing method includes the steps of:

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