External electrode paste

Abstract

Provided is an external electrode paste for forming an external electrode of a multi-layer ceramic capacitor which reduces ESR and can improve the fixing strength between the external electrode and a laminate and the compactness of the external electrode itself.　The external electrode paste according to the present invention is used for forming an external electrode of a multi-layer ceramic capacitor and contains copper (Cu) powder, glass powder, a resin, and a solvent. The volume ratio of the glass powder to the total volume of the copper (Cu) powder and the glass powder is 3 to 20 vol%. The particle diameter of the copper (Cu) powder is 500 nm or less. The particle diameter of the glass powder is 300 nm or less. The particle diameter of the copper (Cu) powder is greater than or equal to the particle diameter of the glass powder.

Description

Paste for external electrodes 【0001】 This invention relates to a paste for external electrodes. 【0002】 As electronic devices operate at higher frequencies, multilayer ceramic capacitors used in these devices are required to handle high frequencies, such as several GHz or higher. In multilayer ceramic capacitors for high frequencies, copper (Cu) is used for both the internal and external electrodes to reduce ESR and improve the Q value. To densify the external electrodes and fix them to the laminate, the external electrode paste, which is a precursor to the external electrodes, contains insulating oxides such as glass or other insulating materials. However, if insulating oxides remain on the external electrodes after firing, it reduces the electrical conductivity of the external electrodes, leading to an increase in ESR and a decrease in the Q value. Therefore, if too much insulating oxide remains on the external electrodes, it can lead to a decrease in the characteristics of the multilayer ceramic capacitor. 【0003】 Patent Document 1 discloses a multilayer ceramic capacitor comprising a ceramic laminate in which a ceramic dielectric layer and an internal electrode layer mainly composed of a transition metal other than an iron group are alternately stacked, and a plurality of the stacked internal electrode layers are alternately exposed on different end faces, and at least one pair of external electrodes formed on the end faces of the ceramic laminate where the internal electrode layers are exposed. Furthermore, the external electrodes of this multilayer ceramic capacitor are provided in contact with the ceramic laminate and comprise a base conductor layer mainly composed of a transition metal other than an iron group or a noble metal, and a first plating layer covering the base conductor layer, and the secondary phase of the base conductor layer is the same ceramic as the main component of the ceramic dielectric layer, with calcium zirconate (CaZrO3) being the main component, in this multilayer ceramic capacitor. 【0004】 Patent Document 2 discloses a multilayer ceramic capacitor comprising a laminate formed by stacking a plurality of ceramic layers and a plurality of internal electrode layers arranged in the stacking direction, and an external electrode formed on the end face of the laminate. Furthermore, the disclosed multilayer ceramic capacitor is characterized in that the external electrode contains metal and glass, and the volume ratio of glass in the external electrode is 29% or less. 【0005】 Japanese Patent Application Laid-Open No. 2019-87627, Japanese Patent Application Laid-Open No. 2021-77828 【0006】 However, when reducing the amount of glass or co-materials, which are insulating oxides, aiming at reducing ESR and improving the Q value, the adhesion strength of the interface between the laminate and the external electrode decreases, and the density of the external electrode itself also decreases. On the other hand, if too much insulating oxide such as glass or co-materials is added to improve the adhesion strength and density, the ESR increases and the Q value decreases. 【0007】 Therefore, the main object of this invention is to provide an external electrode paste for forming an external electrode of a multilayer ceramic capacitor that can reduce ESR and improve the adhesion strength between the external electrode and the laminate and the density of the external electrode itself. 【0008】 The external electrode paste according to this invention is an external electrode paste used for forming an external electrode of a multilayer ceramic capacitor, and contains copper (Cu) powder, glass powder, resin, and a solvent. The volume ratio of the glass powder in the total volume of the copper (Cu) powder and the glass powder is 3 vol% or more and 20 vol% or less. The particle diameter of the copper (Cu) powder is 500 nm or less, the particle diameter of the glass powder is 300 nm or less, and the particle diameter of the copper (Cu) powder is equal to or larger than the particle diameter of the glass powder. 【0009】In the external electrode paste according to the present invention, the volume ratio of glass powder to the total volume of copper (Cu) powder and glass powder is 3 vol% to 20 vol%, the particle size of copper (Cu) powder is 500 nm or less, and the particle size of glass powder is 300 nm or less. Since the particle size of copper (Cu) powder is equal to or larger than that of glass powder, the amount of glass is relatively small, which can reduce the ESR of the external electrode. This can improve the Q value of the multilayer ceramic capacitor. Furthermore, because the glass domains are relatively small, the glass can be dispersed in the external electrode, so even with a relatively small amount of glass, the bonding strength between the laminate and the external electrode can be improved. In addition, since the structure of the external electrode can be made denser, it is possible to prevent the intrusion of plating solution and water vapor from the outside of the multilayer ceramic capacitor into the inside of the laminate. 【0010】 According to this invention, it is possible to provide an external electrode paste for forming external electrodes of a multilayer ceramic capacitor that can reduce ESR, improve the bonding strength between the external electrode and the laminate, and improve the density of the external electrode itself. 【0011】 The above-mentioned objectives, other objectives, features, and advantages of this invention will become even clearer from the following description of embodiments for carrying out the invention, with reference to the drawings. 【0012】 This is an external perspective view showing an example of a multilayer ceramic capacitor as an electronic component according to an embodiment of this invention. This is a cross-sectional view taken along line II-II in Figure 1. This is an enlarged SEM image of part A in Figure 2. This is an explanatory diagram showing the state of the adhesion performance test in an experimental example. 【0013】 The external electrode paste according to this embodiment of the invention is used to form the base electrode layer of a multilayer ceramic capacitor 10. The base electrode layer paste includes, for example, metal powder, which is copper (Cu) as the main component, glass powder, a binder resin, and a solvent. 【0014】Copper (Cu) powder consists of particles made up of at least one of copper (Cu) and copper (Cu) alloys. The particle size of the copper (Cu) powder is preferably 500 nm or less. More preferably, the particle size of the copper (Cu) powder is between 50 nm and 400 nm. 【0015】 The glass powder is not particularly limited, but is preferably B-Si glass, Ba-B-Si glass, Sr-B-Si glass, Ca-B-Si glass, Ba-Ca-B-Si glass, or Ba-Sr-B-Si glass. The particle size of the glass powder is preferably 300 nm or less. More preferably, the particle size of the glass powder is 50 nm or more and 300 nm or less. The shape of the glass powder may be, for example, spherical or flattened. 【0016】 The ratio of the particle size of copper (Cu) powder to the particle size of glass powder is not particularly limited, but it is preferable that 1 ≤ (particle size of copper (Cu) powder / particle size of glass powder) ≤ 5. This allows for good arrangement of glass domains in the sintered film when an external electrode is formed. 【0017】 The particle size of copper (Cu) powder is measured as follows. Specifically, the particle size of copper (Cu) powder can be determined by photographing the surface of the copper (Cu) powder with a scanning electron microscope (SEM) and using image analysis software. For example, copper (Cu) powder used in an external electrode paste is photographed with an SEM, and circular particle analysis is performed using image analysis software (e.g., A-Image-kun: manufactured by Asahi Kasei Engineering Co., Ltd.). The average value D50 of 500 particle size points is calculated, and this value is taken as the particle size of the copper powder. 【0018】 Furthermore, the particle size of the glass powder is measured as follows: A glass slurry is prepared by dispersing glass powder in an ethanol solvent using an ultrasonic disperser. The resulting glass slurry is measured using a laser diffraction particle size distribution analyzer (for example, LA-960V2: manufactured by Horiba, Ltd.), and the D50 value is taken as the particle size of the glass. It is preferable to disperse the powder sufficiently so that the particle size distribution forms a single peak. 【0019】The volume ratio of glass powder to the total volume of copper (Cu) powder and glass powder is 3 vol% to 20 vol%. More preferably, the volume ratio of glass powder to the total volume of copper (Cu) powder and glass powder is 3 vol% to 15 vol%. 【0020】 As the binder resin, known resins such as acrylic resin, ethylcellulose resin, and butyral resin can be used. As the solvent, alcohol-based solvents such as terpineol are preferably used. 【0021】 In addition, the paste for the external electrode may contain various additives such as dispersants, plasticizers, anti-settling agents, and thixotropes. 【0022】 As described above, by using the external electrode paste according to the present invention, the amount of glass powder is relatively small, which allows for a reduction in the ESR of the multilayer ceramic capacitor while maintaining the adhesion strength between the laminate and the external electrode. This improves the Q value of the multilayer ceramic capacitor 10. Furthermore, by using the external electrode paste according to the present invention, the glass domains in the base electrode layer 32 are miniaturized and well dispersed, which improves the adhesion strength between the laminate 12 and the external electrode 30, and also improves the density of the external electrode itself, even with a relatively small amount of glass. Moreover, by using the external electrode paste according to the present invention, the structure of the base electrode layer 32 can be made denser, which prevents the intrusion of plating solution and water vapor from the outside of the multilayer ceramic capacitor 10 into the inside of the laminate 12. Furthermore, by using the external electrode paste according to the present invention, the amount of glass in the base electrode layer 32 is relatively small, which reduces the amount of glass that floats to the surface of the base electrode layer 32. Therefore, the plating adhesion to the base electrode layer 32 can be improved. Furthermore, by using the external electrode paste according to the present invention, the amount of copper (Cu) in the base electrode layer 32 becomes relatively higher, which improves the bonding with the internal electrode layer 16 and thus reduces ESR. 【0023】Next, an example of a multilayer ceramic capacitor equipped with external electrodes formed by an external electrical paste according to an embodiment of the present invention will be described. 【0024】 Figure 1 is an external perspective view showing an example of a multilayer ceramic capacitor as an electronic component according to an embodiment of the present invention. Figure 2 is a cross-sectional view taken along line II-II in Figure 1. Figure 3 is an enlarged SEM image of part A in Figure 2. 【0025】 As shown in Figure 1, the multilayer ceramic capacitor 10 includes a rectangular parallelepiped-shaped laminate 12 and external electrodes 30 arranged at both ends of the laminate 12. 【0026】 The laminate 12 has a first main surface 12a and a second main surface 12b facing the stacking direction x, a first side surface 12c and a second side surface 12d facing the width direction y perpendicular to the stacking direction x, and a first end surface 12e and a second end surface 12f facing the length direction z perpendicular to the stacking direction x and the width direction y. 【0027】 The laminate 12 includes a plurality of ceramic layers 14. The plurality of ceramic layers 14 are stacked in the stacking direction x. As the dielectric material for forming the ceramic layers 14, for example, a dielectric ceramic containing components such as calcium zirconate (CaZrO3) can be used. 【0028】 The thickness of the ceramic layer 14 after firing is preferably 0.4 μm or more and 50.0 μm or less. This makes it possible to increase the number of layers while keeping the multilayer ceramic capacitor 10 miniaturized, thereby contributing to higher capacitance. 【0029】 The dimensions of the laminate 12 are not particularly limited, but for example, the dimension in the length direction z is 0.2 mm or more and 1.8 mm or less, the dimension in the stacking direction x is 0.1 mm or more and 1.0 mm or less, and the dimension in the width direction y is 0.1 mm or more and 1.0 mm or less. Each dimension of the laminate 12 can be measured with a micrometer. 【0030】The laminate 12 has a plurality of internal electrode layers 16, which include a plurality of first internal electrode layers 16a drawn out from the first end face 12e and a plurality of second internal electrode layers 16b drawn out from the second end face 12f. The plurality of first internal electrode layers 16a and the plurality of second internal electrode layers 16b are embedded so as to be alternately arranged at equal intervals along the stacking direction x of the laminate 12, with the ceramic layer 14 in between. 【0031】 The thickness of the first internal electrode layer 16a and the second internal electrode layer 16b is preferably 1.0 μm or more and 4.0 μm or less. 【0032】 The first internal electrode layer 16a and the second internal electrode layer 16b can be made primarily of copper (Cu). 【0033】 External electrodes 30 are arranged on the first end face 12e and the second end face 12f of the laminate 12, as shown in Figures 1 and 2. 【0034】 The external electrode 30 has a first external electrode 30a and a second external electrode 30b. 【0035】 The first external electrode 30a is positioned on at least the surface of the first end face 12e and is connected to the first internal electrode layer 16a. In this embodiment, the first external electrode 30a extends from the first end face 12e and is also positioned on a portion of the first main surface 12a and a portion of the second main surface 12b, as well as a portion of the first side surface 12c and a portion of the second side surface 12d. 【0036】 The second external electrode 30b is positioned on at least the surface of the second end face 12f and is connected to the second internal electrode layer 16b. In this embodiment, the second external electrode 30b extends from the second end face 12f and is also positioned on a portion of the first main surface 12a and a portion of the second main surface 12b, as well as a portion of the first side surface 12c and a portion of the second side surface 12d. 【0037】Within the laminate 12, capacitance is formed when the first opposing electrode portion 26a of the first internal electrode layer 16a and the second opposing electrode portion 26b of the second internal electrode layer 16b face each other via the ceramic layer 14. As a result, capacitance can be obtained between the first external electrode 30a to which the first internal electrode layer 16a is connected and the second external electrode 30b to which the second internal electrode layer 16b is connected, and the characteristics of a capacitor are exhibited. 【0038】 The thickness of the first external electrode 30a and the second external electrode 30b at both end faces in the center of the stacking direction is preferably 10 μm or more and 50 μm or less. 【0039】 The external electrode 30 is preferably composed of a base electrode layer 32 and a plating layer 34. In this embodiment, the external electrode 30 includes a base electrode layer 32 and a plating layer 34 disposed on the base electrode layer 32. The plating layer 34 includes a first plating layer 34a and a second plating layer 34b. The first external electrode 30a has a first base electrode layer 32a, a first lower plating layer 34a1 disposed on the first base electrode layer 32a, and a first upper plating layer 34a2 disposed on the first lower plating layer 34a1. The second external electrode 30b has a second base electrode layer 32b, a second lower plating layer 34b1 disposed on the second base electrode layer 32b, and a second upper plating layer 34b2 disposed on the second lower plating layer 34b1. 【0040】 The first base electrode layer 32a is connected to the first internal electrode layer 16a and is positioned on the surface of the first end face 12e. In this case, the first base electrode layer 32a is electrically connected to the first lead-out electrode portion 28a of the first internal electrode layer 16a. In this embodiment, the first base electrode layer 32a extends from the first end face 12e and is also positioned on a part of the first main surface 12a and a part of the second main surface 12b, as well as a part of the first side surface 12c and a part of the second side surface 12d. 【0041】The second base electrode layer 32b is connected to the second internal electrode layer 16b and is disposed on the surface of the second end face 12f. In this case, the second base electrode layer 32b is electrically connected to the second lead-out electrode portion 28b of the second internal electrode layer 16b. In the present embodiment, the second base electrode layer 32b extends from the second end face 12f and is also disposed on a part of the first main face 12a, a part of the second main face 12b, a part of the first side face 12c, and a part of the second side face 12d. 【0042】 The base electrode layer 32 may be a plurality of layers. The base electrode layer 32 is formed by applying a conductive paste (paste for external electrodes) containing a conductive metal or the like to the laminate 12 and baking it, and may be baked simultaneously with the ceramic layer 14 and the internal electrode layer 16, or may be baked after baking the ceramic layer 14 and the internal electrode layer 16. In addition, by including glass in the base electrode layer 32, the adhesion between the laminate 12 and the base electrode layer 32 can be improved. 【0043】 The thicknesses of the first and second baked layers at the central portion in the stacking direction x of the first and second base electrode layers 32a and 32b located on the first end face 12e and the second end face 12f are preferably, for example, about 3 μm or more and 35 μm or less. When the base electrode layer 32 is provided on the first main face 12a, the second main face 12b, the first side face 12c, and the second side face 12d, the thicknesses of the first and second baked layers at the central portion in the length direction z of the first and second base electrode layers 32a and 32b located on the first main face 12a, the second main face 12b, the first side face 12c, and the second side face 12d are preferably, for example, about 1 μm or more and 20 μm or less. 【0044】 The base electrode layer 32 contains a conductive metal and glass. 【0045】 The conductive metal contained in the base electrode layer 32 contains, for example, copper (Cu). The conductive metal in the present embodiment is mainly copper (Cu). 【0046】The glass contained in the base electrode layer 32 is preferably B-Si-based glass, Ba-B-Si-based glass, Sr-B-Si-based glass, Ca-B-Si-based glass, Ba-Ca-B-Si-based glass, or Ba-Sr-B-Si-based glass, etc. 【0047】 Next, the first plating layer 34a and the second plating layer 34b, which are the plating layers 34 disposed on the base electrode layer 32, will be described with reference to FIG. 2. 【0048】 The first plating layer 34a is disposed so as to cover the first base electrode layer 32a on the first end face 12e side. Further, the first plating layer 34a may be disposed so as to cover the first base electrode layer 32a on the first main surface 12a, the second main surface 12b, the first side surface 12c, and the second side surface 12d sides. However, the first plating layer 34a may be disposed only on the first base electrode layer 32a on the first end face 12e side. 【0049】 The second plating layer 34b is disposed so as to cover the second base electrode layer 32b on the second end face 12f side. Further, the second plating layer 34b may be disposed so as to cover the second base electrode layer 32b on the first main surface 12a, the second main surface 12b, the first side surface 12c, and the second side surface 12d sides. However, the second plating layer 34b may be disposed only on the second base electrode layer 32b on the second end face 12f side. 【0050】 The first plating layer 34a and the second plating layer 34b include at least one selected from, for example, copper (Cu), nickel (Ni), tin (Sn), silver (Ag), palladium (Pd), Ag-Pd alloy, gold (Au), etc. 【0051】The plating layer 34 may be formed from multiple layers. For example, the first plating layer 34a has a two-layer structure consisting of a first lower plating layer 34a1 and a first upper plating layer 34a2 covering the first lower plating layer 34a1, and the second plating layer 34b has a two-layer structure consisting of a second lower plating layer 34b1 and a second upper plating layer 34b2 covering the second lower plating layer 34b1. Preferably, the first lower plating layer 34a1 and the second lower plating layer 34b1 are Ni plating layers, and the first upper plating layer 34a2 and the second upper plating layer 34b2 are Sn plating layers. 【0052】 The first and second lower plating layers 34a1 and 34b1, made of Ni plating, are used to prevent the underlying electrode layer 32 from being corroded by the solder when mounting the multilayer ceramic capacitor 10. The first and second upper plating layers 34a2 and 34b2, made of Sn plating, are used to improve the wettability of the solder when mounting the multilayer ceramic capacitor 10, thereby facilitating easier mounting. 【0053】 The first and second lower plating layers 34a1 and 34b1, which are Ni plating layers, are preferably 1 μm or more and 15 μm or less in thickness. The first and second upper plating layers 34a2 and 34b2, which are Sn plating layers, are preferably 1 μm or more and 15 μm or less in thickness. 【0054】 The dimensions of the multilayer ceramic capacitor 10, including the laminate 12, the first external electrode 30a, and the second external electrode 30b, are defined as L in the length direction z, T in the stacking direction x, and W in the width direction y. The dimensions of the multilayer ceramic capacitor 10, including the laminate 12, the first external electrode 30a, and the second external electrode 30b, are defined as L, T in the stacking direction x, and W in the width direction y. The dimensions of the multilayer ceramic capacitor 10 are such that the L dimension in the length direction z is 0.2 mm or more and 2.0 mm or less, the W dimension in the width direction y is 0.1 mm or more and 1.2 mm or less, and the T dimension in the stacking direction x is 0.1 mm or more and 1.2 mm or less. The dimensions of the multilayer ceramic capacitor 10 can also be measured using a microscope. 【0055】Next, a method for manufacturing a multilayer ceramic capacitor according to an embodiment of this invention will be described. 【0056】 First, a dielectric sheet for the ceramic layer and a conductive paste for the internal electrode layer are prepared. The dielectric sheet and the conductive paste for the internal electrode layer contain a binder and a solvent. The binder and solvent may be known. 【0057】 A slurry is prepared by adding a binder and solvent to ceramic powder. This slurry is formed into a sheet using the doctor blade method, and then cut to obtain ceramic green sheets of a predetermined size. 【0058】 Prepare a conductive paste for the internal electrode layer. The conductive paste consists of a metallic material such as copper (Cu), a co-material, a dispersant, and a binder. 【0059】 Then, a conductive paste for the internal electrode layer is printed onto the dielectric sheet in a predetermined pattern, for example, by screen printing or gravure printing. This prepares a dielectric sheet with the pattern for the first internal electrode layer formed on it, and a dielectric sheet with the pattern for the second internal electrode layer formed on it. 【0060】 Then, a conductive paste for the internal electrode layer is printed on the ceramic green sheet in a predetermined pattern, for example, by screen printing or gravure printing, to form the internal electrode pattern. A predetermined number of ceramic green sheets without the internal electrode pattern are stacked, and ceramic green sheets with the internal electrode pattern are sequentially stacked on top of them, and a predetermined number of ceramic green sheets without the internal electrode pattern are stacked on top of those to produce a laminated sheet. 【0061】 Next, the laminated sheets are pressed in the lamination direction using means such as a hydrostatic press to produce a laminated block. The laminated block is cut to a predetermined size to cut out laminated chips. At this time, the corners and edges of the laminated chips may be rounded by barrel polishing or other methods. The laminated chips are fired to produce a laminated body. 【0062】When using a copper (Cu)-based paste as the conductive paste for the internal electrode layer, the firing temperature is preferably 850°C or higher and 1050°C or lower. 【0063】 Next, external electrodes are formed on the end face of the laminate from which the internal electrode layer has been extracted. To ensure more reliable extraction of the internal electrode layer from the laminate, barrel polishing may be applied to the end face of the laminate. 【0064】 (Step to form external electrodes) Next, the first external electrode 30a and the second external electrode 30b are formed on the first end face 12e and the second end face 12f of the laminate 12. 【0065】 The paste for the external electrode layer according to the present invention is applied to the first end face 12e and the second end face 12f of the laminate 12 and baked, forming the first base electrode layer 32a of the first external electrode 30a and the second base electrode layer 32b of the second external electrode 30b. The baking temperature is preferably 700°C or higher and 950°C or lower. For example, a dipping method can be used to apply the paste for the external electrode layer. 【0066】 Next, if necessary, plating is applied to the surface of the base electrode layer to form a plating layer. In this embodiment, two plating layers are formed on the surface of the base electrode layer. Specifically, a Ni plating layer and a Sn plating layer are formed on the base electrode layer. Electrolytic plating is preferred as the plating process. The Ni plating layer and the Sn plating layer are formed sequentially, for example, by barrel plating. 【0067】 As described above, the multilayer ceramic capacitor 10 according to this embodiment is manufactured. 【0068】(a) Samples of the experimental examples prepared Next, we will specifically describe experimental examples of multilayer ceramic capacitors manufactured using the external electrode paste according to the present invention. For the experiment, samples of external electrode paste were prepared for each of Examples 1 to 4 and Comparative Examples 1 to 3, in which the particle size of copper (Cu) powder and the particle size of glass powder were varied. Samples of external electrode paste were also prepared in which the volume ratio of glass powder to the total volume of copper (Cu) powder and glass powder was varied. For each of Examples 1 to 4, the particle size of copper (Cu) powder contained in the external electrode paste was 280 nm. For each of Examples 1 to 4, the particle sizes of glass powder contained in the external electrode paste were 100 nm, 130 nm, 130 nm, and 130 nm. For each of Examples 1 to 4, the volume ratio of glass powder to the total volume of copper (Cu) powder and glass powder was 3.8%, 7.0%, 10.0%, and 13.0%, respectively. For Comparative Examples 1 to 3, copper (Cu) powder particles with particle sizes of 280 nm, 120 nm, and 3000 nm were prepared for the external electrode pastes. For Comparative Examples 1 to 3, glass powder particles with particle sizes of 100 nm, 650 nm, and 1000 nm were prepared for the external electrode pastes. For Comparative Examples 1 to 3, the volume ratio of glass powder to the total volume of copper (Cu) powder and glass powder was prepared to be 2.0%, 23.0%, and 14.4%, respectively. 【0069】 (b) Method for measuring the particle size of copper (Cu) powder The particle size of copper (Cu) powder was measured as follows. Specifically, the particle size of copper (Cu) powder was determined by photographing the surface of the copper (Cu) powder with a scanning electron microscope (SEM) and using image analysis software. Specifically, for example, copper (Cu) powder used in the paste for external electrodes was photographed with an SEM, and circular particle analysis was performed using image analysis software (for example, A-Image-kun: manufactured by Asahi Kasei Engineering Co., Ltd.) to find the average value D50 of 500 particle size points, and this value was taken as the particle size of the copper powder. 【0070】(c) Method for measuring the particle size of glass powder particles The particle size of the glass powder was measured as follows: A glass slurry prepared by dispersing glass powder in an ultrasonic disperser in an ethanol solvent was measured using a laser diffraction particle size distribution analyzer (e.g., LA-960V2: manufactured by Horiba, Ltd.), and the D50 value was taken as the particle size of the glass powder. The measurement was performed after sufficient dispersion so that the particle size distribution was evenly distributed. 【0071】 (d) Sample Evaluation Method (ESR Measurement Test) Ten samples each of the multilayer ceramic capacitors manufactured in the Examples and Comparative Examples were prepared, and the ESR values ​​were measured using an LCR meter (E4991B: manufactured by Agilent). The ESR value of each sample was the average of the 10 values. The measurement conditions were 1 GHz and 1 Vrms. If the ESR at 1 GHz was lower than 85 mΩ, it was judged as a good product ("○"), and if it was 85 mΩ or higher, it was judged as a defective product ("×"). The multilayer ceramic capacitors manufactured in the Examples and Comparative Examples each had an L dimension of 0.4 mm, a T dimension of 0.2 mm, and a W dimension of 0.2 mm, and were prepared with a capacitance equivalent to 18 pF. 【0072】(Adhesion Performance Test) The adhesion performance test evaluates the adhesion performance of the external electrodes to the laminate. More specifically, conductive paste for the base electrode layer (external electrode paste) shown in Table 1 was applied to both ends of the laminate by the dipping method, and the laminate was fired in a temperature range of 700°C to 900°C to form the base electrode layer. Then, Sn plating was formed on the surface of the base electrode layer to produce each sample of multilayer ceramic capacitor. Next, as shown in Figure 4, the laminate 12 of the sample multilayer ceramic capacitor 10 was placed upright on the substrate 40, and the multilayer ceramic capacitor 10 was fixed to the substrate 40 by applying solder 42 to the lower external electrode 30a. In this state, the upper external electrode 30b was pressed laterally as indicated by arrow F. The failure modes caused by this lateral pressure were classified into four categories: (1) delamination at the interface between the substrate 40 and the solder 42, (2) delamination at the interface between the solder 42 and the plating layer 34 on the external electrode 30, (3) delamination at the interface between the base electrode layer 32 and the laminate 12, and (4) cracking of the laminate 12. For each sample of 10, if even one sample exhibited failure mode (3), it was judged to be defective and marked with "×" as a defective product. 【0073】 (Humidity Resistance Reliability Test) Eighteen samples were prepared for each of Examples 1-4 and Comparative Examples 1-3, and humidity resistance reliability tests were conducted. More specifically, first, each sample was mounted on a circuit board using solder. Next, the insulation resistance value IR of each sample was measured. Then, the circuit boards were placed in a high-temperature, high-humidity chamber, and under conditions of 85°C and 85% RH relative humidity, a DC current of 25V was applied between the first and second external electrodes of each sample and maintained for 2000 hours (humidity resistance reliability test time). After the humidity resistance reliability test time, the insulation resistance value IR of each sample was measured (insulation resistance value after humidity resistance reliability test time). For the 18 samples, if even one sample's IR after the humidity resistance reliability test time was more than one order of magnitude lower than its IR before the humidity resistance reliability test time, it was classified as a defective product ("×"). If all 18 samples did not decrease by more than one order of magnitude, they were classified as good products ("〇"). 【0074】(Overall Evaluation) If the ESR measurement test, adhesion performance test, and humidity resistance reliability test all yield a "○", the product is considered good and receives an overall evaluation of "○". If any of the ESR measurement test, adhesion performance test, and humidity resistance reliability test yield a "×", the product is considered defective and receives an overall evaluation of "×". 【0075】 Table 1 shows the results for each sample. 【0076】 【0077】 (e) Results: Examples 1 to 4 received an overall evaluation of "○". Specifically, in Examples 1 to 4, the volume ratio of glass powder to the total volume of copper (Cu) powder and glass powder was within the range of 3 vol% to 20 vol%. In addition, the particle size of the copper (Cu) powder was within the range of 500 nm or less, and the particle size of the glass powder was within the range of 300 nm. Furthermore, the condition that the particle size of the copper (Cu) powder is greater than or equal to the particle size of the glass powder was met. 【0078】 On the other hand, Comparative Examples 1 to 3 received an overall evaluation of "×". Specifically, in Comparative Example 1, the volume ratio of glass powder to the total volume of copper (Cu) powder and glass powder was less than 3 vol%, resulting in reduced adhesion between the laminate and the external electrode, and also low density of the external electrode, leading to poor results in the humidity load test. In Comparative Example 2, the particle size of the glass powder was larger than 300 nm, and the volume ratio of glass powder to the total volume of copper (Cu) powder and glass powder was greater than 20%, resulting in a high ESR of the sample and a poor result. In Comparative Example 3, the particle size of the copper (Cu) powder was larger than 500 nm, and the particle size of the glass powder was larger than 300 nm, resulting in reduced adhesion between the laminate and the external electrode, and also low density of the external electrode, leading to poor results in the humidity load test. 【0079】As described above, embodiments of the present invention are disclosed in the above description, but the present invention is not limited thereto. That is, without departing from the scope of the technical idea and objectives of the present invention, various modifications can be made to the embodiments described above in terms of mechanism, shape, material, quantity, position or arrangement, etc., and these are included in the present invention. 【0080】 <1> An external electrode paste used to form external electrodes of a multilayer ceramic capacitor, comprising copper (Cu) powder, glass powder, resin, and solvent, wherein the volume ratio of the glass powder to the total volume of the copper (Cu) powder and the glass powder is 3 vol% or more and 20 vol% or less, the particle size of the copper (Cu) powder is 500 nm or less, the particle size of the glass powder is 300 nm or less, and the particle size of the copper (Cu) powder is equal to or larger than the particle size of the glass powder. 【0081】 <2> The external electrode paste according to <1>, wherein the volume ratio of the glass powder to the total volume of the copper (Cu) powder and the glass powder is 3 vol% or more and 15 vol% or less. 【0082】 <3> The external electrode paste according to <1> or <2>, wherein the particle size of the copper (Cu) powder is 50 nm or more and 400 nm or less. 【0083】 <4> The external electrode paste according to any one of <1> to <3>, wherein the particle size of the glass powder is 50 nm or larger. 【0084】 <5> The external electrode paste according to any one of <1> to <4>, wherein the particle size of the copper (Cu) powder is larger than the particle size of the glass powder. 【0085】 <6> A method for manufacturing a multilayer ceramic capacitor, comprising the steps of: preparing a laminate having a plurality of ceramic layers stacked in the stacking direction and a plurality of internal electrode layers; applying an external electrode paste according to any one of <1> to <5> to the surface of the laminate; and firing the laminate to which the external electrode paste has been applied. 【0086】 10: Multilayer ceramic capacitor 12: Laminate 12a: First main surface 12b: Second main surface 12c: First side surface 12d: Second side surface 12e: First end surface 12f: Second end surface 14: Ceramic layer 16: Internal electrode layer 16a: First internal electrode layer 16b: Second internal electrode layer 30: External electrode 30a: First external electrode 30b: Second external electrode 32: Underlay electrode layer 32a: First underlay electrode layer 32b: Second underlay electrode layer 34: Plating layer 34a: First plating layer 34b: Second plating layer 34a1, 34b1: First and second underlay plating layers 34a2, 34b2 : First and second upper plating layers x: Lamination direction y: Width direction z: Length direction

Claims

1. An external electrode paste used to form external electrodes of a multilayer ceramic capacitor, comprising copper (Cu) powder, glass powder, resin, and solvent, wherein the volume ratio of the glass powder to the total volume of the copper (Cu) powder and the glass powder is 3 vol% or more and 20 vol% or less, the particle size of the copper (Cu) powder is 500 nm or less, the particle size of the glass powder is 300 nm or less, and the particle size of the copper (Cu) powder is equal to or larger than the particle size of the glass powder.

2. The external electrode paste according to claim 1, wherein the volume ratio of the glass powder to the total volume of the copper (Cu) powder and the glass powder is 3 vol% or more and 15 vol% or less.

3. The external electrode paste according to claim 1 or claim 2, wherein the particle size of the copper (Cu) powder is 50 nm or more and 400 nm or less.

4. The external electrode paste according to any one of claims 1 to 3, wherein the particle size of the glass powder is 50 nm or larger.

5. The external electrode paste according to any one of claims 1 to 4, wherein the particle size of the copper (Cu) powder is larger than the particle size of the glass powder.

6. A method for manufacturing a multilayer ceramic capacitor, comprising the steps of: preparing a laminate having a plurality of ceramic layers stacked in the stacking direction and a plurality of internal electrode layers; applying an external electrode paste according to any one of claims 1 to 5 to the surface of the laminate; and firing the laminate to which the external electrode paste has been applied.

Images