Multilayer ceramic capacitor

Abstract

Provided is a multilayer ceramic capacitor 1 in which distortion in the vicinity of an interface of a terminal electrode 19 of a ceramic layer 28 is reduced. An external electrode 22 of the multilayer ceramic capacitor 1 includes a first metal grain 40. In a cross section parallel to a height direction T and a length direction L, two or more grain boundaries 46 of the first metal grain 40 are present at a junction 50 between an internal electrode 27 and the external electrode 22, and the grain size of the first metal grain 40 in which the grain boundary 46 is present in the junction 50 is 1.2 times or less of a thickness 67 in the height direction T of the internal electrode 27.

Description

Multilayer ceramic capacitors

[0001] The present invention relates to a multilayer ceramic capacitor.

[0002] Multilayer ceramic capacitors are required to have a high level of reliability. The reliability of multilayer ceramic capacitors may be reduced by stress acting on the multilayer ceramic capacitor. Patent Document 1 discloses a conductive paste that is used in ceramic electronic components to form a conductive structure that can withstand stress.

[0003] Japanese Patent Application Laid-Open No. 2000-215729

[0004] The ceramic layers of conventional multilayer ceramic capacitors have a large amount of distortion near the interface with the terminal electrodes. This distortion reduces the reliability of the multilayer ceramic capacitor. No technology has been proposed to reduce the distortion near the interface between the ceramic layers and the terminal electrodes.

[0005] An object of the present invention is to provide a multilayer ceramic capacitor in which distortion in the vicinity of the interface between the ceramic layer and the terminal electrode is reduced.

[0006] The present invention provides a multilayer ceramic capacitor comprising: a ceramic body including a plurality of stacked ceramic layers and a plurality of stacked internal electrodes, the ceramic body having six surfaces: a first main surface and a second main surface opposing each other in a height direction; a first side surface and a second side surface opposing each other in a width direction perpendicular to the height direction; and a first end surface and a second end surface opposing each other in a length direction perpendicular to the height direction and the width direction; and external electrodes provided on the ceramic body and connected to some of the internal electrodes, wherein the external electrodes include first metal grains, and in a cross section parallel to the height direction and the length direction, two or more grain boundaries of the first metal grains are present at a joint between the internal electrode and the external electrode, and the grain diameter of the first metal grains where a grain boundary is present at the joint is 1.2 times or less the thickness of the internal electrode in the height direction.

[0007] According to the present invention, it is possible to provide a multilayer ceramic capacitor in which distortion in the vicinity of the interface between the ceramic layer and the terminal electrode is reduced.

[0008] 1 is a perspective view of a multilayer ceramic capacitor according to an embodiment of the present invention; FIG. 2 is a cross-sectional view taken along line II of FIG. 1; FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1; FIG. 3 is an SEM photograph of a portion corresponding to the framed area 90 of FIG. 2; FIG. 4 is a diagram showing a state of bonding between an internal electrode and an external electrode; FIG. 5 is a diagram showing another state of bonding between an internal electrode and an external electrode; FIG. 6 is a grain map of first metal grains; FIG. 7 is a histogram of grain diameters of first metal grains; FIG. 8 is a grain map of conventional first metal grains; FIG. 9 is a histogram of grain diameters of conventional first metal grains; FIG. 10 is a stress map of an inner ceramic layer; FIG. 11 is a stress map of a conventional inner ceramic layer; FIG. 12 is an LT cross-sectional view showing an interface between an internal electrode and an external electrode before surface diffusion; FIG. 13 is a perspective view showing an overview of a ceramic body 2;

[0009] (Multilayer Ceramic Capacitor) An embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 is a perspective view of a multilayer ceramic capacitor 1 according to an embodiment of the present invention. FIG. 1 shows a so-called two-terminal multilayer ceramic capacitor. The multilayer ceramic capacitor 1 is not limited to a two-terminal multilayer ceramic capacitor. The multilayer ceramic capacitor 1 may be a multilayer ceramic capacitor with three or more terminals, such as three terminals.

[0010] The multilayer ceramic capacitor 1 includes a ceramic body 2 and terminal electrodes 19. The terminal electrodes 19 include a first terminal electrode 20 and a second terminal electrode 21.

[0011] The ceramic body 2 includes a plurality of laminated ceramic layers and a plurality of internal electrodes, and is shaped like a rectangular parallelepiped.

[0012] The direction in which the ceramic layers and internal electrodes are stacked is called the height direction T. The direction perpendicular to the height direction T is called the width direction W. The direction perpendicular to the height direction T and the width direction W is called the length direction L.

[0013] Of the two surfaces of the ceramic body 2 that face each other in the height direction T, one surface is called the first main surface 3. The remaining surface is called the second main surface 4. Of the two surfaces of the ceramic body 2 that face each other in the width direction W, one surface is called the first side surface 5. The remaining surface is called the second side surface 6. Of the two surfaces of the ceramic body 2 that face each other in the length direction L, one surface is called the first end surface 7. The remaining surface is called the second end surface 8.

[0014] The cross sections of the ceramic body 2 are referred to as follows: The cross section taken along line II in Fig. 1 is referred to as the LT cross section, and the cross section taken along line II-II in Fig. 1 is referred to as the WT cross section.

[0015] A portion where three faces of the ceramic body 2 intersect is called a corner of the ceramic body 2. A portion where two faces of the ceramic body 2 intersect is called a ridge of the ceramic body 2. The corners and ridges preferably have rounded shapes.

[0016] The sections of the ceramic body 2 will be described with reference to Figures 2 and 3. Figure 2 is a cross-sectional view taken along line II in Figure 1. Figure 3 is a cross-sectional view taken along line II-II in Figure 1. As shown in Figures 2 and 3, in the ceramic body 2, internal electrodes 27 and ceramic layers 28 are stacked in the height direction T.

[0017] 2, the division of the ceramic body 2 in the height direction T will be described. The ceramic body 2 is divided in the height direction T into a first main surface side outer layer portion 10, an inner layer portion 11, and a second main surface side outer layer portion 12.

[0018] The first main surface side outer layer portion 10 is a portion between the first main surface 3 and a plane including the internal electrode 27 closest to the first main surface 3. The internal layer portion 11 is a portion between the plane including the internal electrode 27 closest to the first main surface 3 and a plane including the internal electrode 27 closest to the second main surface 4. The second main surface side outer layer portion 12 is a portion between the second main surface 4 and a plane including the internal electrode 27 closest to the second main surface 4.

[0019] (Length Direction Division) The length direction L of the ceramic body 2 will be described with reference to Fig. 2. The ceramic body 2 is divided in the length direction L into a first end drawn portion 13, a lengthwise opposing portion 14, and a second end drawn portion 15.

[0020] The longitudinally facing portion 14 is a portion where the internal electrodes 27 drawn to different end faces face each other in the height direction T. The first end face side drawn portion 13 is a portion between the longitudinally facing portion 14 and the first end face 7. The second end face side drawn portion 15 is a portion between the longitudinally facing portion 14 and the second end face 8.

[0021] The longitudinal opposing portions 14 correspond to opposing electrode portions of the internal electrodes 27. The first end surface side lead portions 13 and the second end surface side lead portions 15 correspond to lead electrode portions of the internal electrodes 27.

[0022] (Division in the Width Direction) The division in the width direction W of the ceramic body 2 will be described with reference to Fig. 3. The ceramic body 2 is divided in the width direction W into a first side gap portion 16, a widthwise opposing portion 17, and a second side gap portion 18.

[0023] The widthwise facing portion 17 is a portion where internal electrodes 27 drawn out to different end faces face each other in the height direction T. The first side surface side gap portion 16 is a portion between the widthwise facing portion 17 and the first side surface 5. The second side surface side gap portion 18 is a portion between the widthwise facing portion 17 and the second side surface 6.

[0024] (Ceramic Layers) The ceramic layers 28 include an outer ceramic layer 30 and an inner ceramic layer 31. The outer ceramic layer 30 is the ceramic layer 28 included in the first main surface side outer layer portion 10 and the second main surface side outer layer portion 12. The inner ceramic layer 31 is the ceramic layer 28 included in the inner layer portion 11.

[0025] Examples of the main material of the ceramic layer 28 include barium titanate, calcium titanate, strontium titanate, and calcium zirconate. The ceramic layer 28 may contain a secondary material. Examples of the secondary material include manganese compounds, iron compounds, chromium compounds, cobalt compounds, and nickel compounds.

[0026] The total number of ceramic layers 28 stacked in the ceramic body 2 is preferably 15 to 2000.

[0027] The preferred thickness of each ceramic layer 28 is 0.3 μm or more and 10 μm or less.

[0028] (Internal Electrodes) The internal electrodes 27 will be described. The internal electrodes 27 include a plurality of first internal electrodes 32 and a plurality of second internal electrodes 33. The first internal electrodes 32 are internal electrodes 27 exposed at the first end face 7. The second internal electrodes 33 are internal electrodes 27 exposed at the second end face 8.

[0029] The first internal electrode 32 is divided into a first opposing electrode portion 34 and a first lead electrode portion 36. The first opposing electrode portion 34 is a portion that faces the second internal electrode 33. The first lead electrode portion 36 is a portion that is led out from the first opposing electrode portion 34 to the first end face 7.

[0030] The second internal electrode 33 is divided into a second opposing electrode portion 35 and a second lead electrode portion 37. The second opposing electrode portion 35 is a portion that faces the first internal electrode 32. The second lead electrode portion 37 is a portion that is led out from the second opposing electrode portion 35 to the second end face 8.

[0031] Examples of materials for the internal electrodes 27 are nickel, copper, silver, palladium, and gold. The material for the internal electrodes may also be an alloy containing at least one of the aforementioned metals, such as a silver-palladium alloy.

[0032] The preferred thickness of the internal electrode 27 is 0.3 μm or more and 2.0 μm or less. The preferred total number of the first internal electrodes 32 and the second internal electrodes 33 is 15 or more and 2000 or less.

[0033] (Ceramic element body) The size of the ceramic element body 2 is not particularly limited. The length of the ceramic element body 2 in the longitudinal direction L is preferably 0.2 mm or more and 10 mm or less. The length of the ceramic element body 2 in the width direction W is preferably 0.1 mm or more and 5 mm or less. The length of the ceramic element body 2 in the height direction T is preferably 0.1 mm or more and 5 mm or less.

[0034] (Terminal Electrodes) The terminal electrodes 19 will be described. As described above, the terminal electrodes 19 include the first terminal electrode 20 and the second terminal electrode 21. The first terminal electrode 20 is the terminal electrode 19 connected to the first internal electrode 32. The second terminal electrode 21 is the terminal electrode 19 connected to the second internal electrode 33.

[0035] The first terminal electrode 20 is arranged on the first end face 7, part of the first main face 3, part of the second main face 4, part of the first side face 5, and part of the second side face 6. The second terminal electrode 21 is arranged on the second end face 8, part of the first main face 3, part of the second main face 4, part of the first side face 5, and part of the second side face 6.

[0036] The terminal electrode 19 includes an external electrode 22, a nickel-plated film 24, and a tin-plated film 25. These are arranged in this order from the surface of the ceramic body 2: the external electrode 22, the nickel-plated film 24, and the tin-plated film 25.

[0037] (External Electrode) The external electrode 22 is disposed on the end face of the ceramic body 2. The external electrode 22 covers the end face. The external electrode 22 extends from the end face to part of the main surface and part of the side face.

[0038] The external electrodes 22 contain metal and glass. Examples of metals are copper, nickel, silver, palladium, silver-palladium alloy, and gold. The external electrodes 22 are formed by applying a conductive paste containing metal and glass to the ceramic body 2 and firing the paste. The metal is contained in the conductive paste as metal powder. The glass is contained in the conductive paste as glass powder. The preferred thickness of the external electrodes 22 is 3 μm or more and 25 μm or less.

[0039] (Nickel Plated Film, Tin Plated Film) The nickel plated film 24 is disposed so as to cover the external electrodes 22. The tin plated film 25 is disposed so as to cover the nickel plated film 24.

[0040] The nickel plating film 24 prevents the external electrodes 22 from being corroded by solder when mounting the multilayer ceramic capacitor 1. The tin plating film 25 improves the wettability of the solder when mounting the multilayer ceramic capacitor 1.

[0041] The size of the multilayer ceramic capacitor 1 is not particularly limited. The length in the length direction L of the multilayer ceramic capacitor 1 including the ceramic body 2 and the terminal electrodes is preferably 0.2 mm or more and 10 mm or less. The length in the height direction T of the multilayer ceramic capacitor 1 is preferably 0.1 mm or more and 5 mm or less. The length in the width direction W of the multilayer ceramic capacitor 1 is preferably 0.1 mm or more and 10 mm or less.

[0042] (External Electrode) The external electrode 22 will be described in detail. Fig. 4 is an SEM photograph of a portion corresponding to the framed area 90 in Fig. 2. Fig. 2 shows an LT cross section near the second end face 8. Three frames, framed area 92, framed area 93, and framed area 94, are shown in Fig. 2. Enlarged views of a portion of framed area 92 are shown in Fig. 5 and Fig. 6.

[0043] 5 and 6 are diagrams showing the state of joining between the second internal electrode 33 and the external electrode 22. The shape of the tip 54 of the second internal electrode 33 is different between Fig. 5 and Fig. 6.

[0044] The tip 54 of the second internal electrode 33 shown in Fig. 5 is substantially flush with the second end face 8. The tip 54 of the second internal electrode 33 shown in Fig. 6 protrudes from the second end face 8 in the length direction L toward the external electrode 22.

[0045] (Second Metal Grains) The joining of the second internal electrode 33 and the external electrode 22 will be described with reference to Fig. 5. The second internal electrode 33 includes a plurality of second metal grains 45. The second metal grains are particles of the metal that constitutes the internal electrode 27, such as nickel. The second metal grains 45 that form the tip 54 of the second internal electrode 33 contact the external electrode 22 at a joint 50.

[0046] (Joint Portion) The joint portion 50 will now be described. In the LT cross section of the multilayer ceramic capacitor 1, points 100 and 101 indicate the points at which the second end face 8 contacts the second internal electrode 33. The outline 39 of the second internal electrode 33 in the LT cross section, from point 100 through the tip 54 of the second internal electrode 33 to point 101, is defined as the joint portion 50.

[0047] At the joint 50, the internal electrode 27 faces the external electrode 22. The internal electrode 27 facing the external electrode 22 includes the internal electrode 27 being in contact with the external electrode 22 and the internal electrode 27 being in close proximity to the external electrode 22.

[0048] The external electrode 22 includes a metal and a glass. The internal electrode 27 facing the external electrode 22 includes the internal electrode 27 facing a metal portion of the external electrode 22 (such as the first metal grains 40) and the internal electrode 27 facing a glass portion of the external electrode 22 (such as the glass portion 47).

[0049] (First Metal Grains) The external electrode 22 includes a plurality of first metal grains 40 and a glass portion 47. The first metal grains 40 are particles of a metal, such as copper, that constitutes the external electrode 22. The glass portion 47 is a portion made of a glass component contained in the external electrode 22.

[0050] In the multilayer ceramic capacitor 1 of this embodiment, in the LT cross section, two or more grain boundaries 46 of the first metal grains 40 exist at the joint 50 between the internal electrode 27 and the external electrode 22 .

[0051] The grain diameter of the first metal grains 40 in which the grain boundaries 46 exist in the joint 50 is 1.2 times or less the thickness 67 in the height direction T of the internal electrode.

[0052] 5 , the first metal grains 40 include metal grains whose grain boundaries 46 contact the joint 50 and metal grains whose grain boundaries 46 do not contact the joint 50. The metal grains whose grain boundaries 46 contact the joint 50 are called joint metal grains 41. The metal grains whose grain boundaries 46 do not contact the joint 50 are called non-joined metal grains 42.

[0053] 5, two joining metal grains 41 contact the second internal electrode 33 at the joint 50. There are two joining metal grains 41 for one second internal electrode 33.

[0054] 2 indicates the thickness 67 in the height direction T of the internal electrode 27. The double arrow 69 indicates the grain diameter 69 of the joining metal grain 41. The grain diameter 69 of the joining metal grain 41 is 1.2 times or less the thickness 67.

[0055] In the multilayer ceramic capacitor 1 of this embodiment, the thickness 67 is 0.3 μm or more and 2.0 μm or less in the LT cross section. The grain diameter of the bonding metal grains 41 is 0.1 μm or more and 0.8 μm or less.

[0056] In the multilayer ceramic capacitor 1 of this embodiment, the glass portion 47 contacts at least one of the internal electrodes 27 and the ceramic layers 28 .

[0057] (Another form of joint) Another state of joint between the second internal electrode 33 and the external electrode 22 will be described with reference to Fig. 6. Regarding Fig. 6, differences from Fig. 5 will be mainly described. As described above, the tip 54 of the second internal electrode 33 shown in Fig. 6 protrudes from the second end face 8 in the length direction L toward the external electrode 22.

[0058] 6 , there are three joining metal grains 41 for one second internal electrode 33. When the tip 54 of the second internal electrode 33 protrudes from the second end face 8 toward the external electrode 22, the length of the joining portion 50 becomes longer than when the tip 54 does not protrude. Therefore, the grain boundaries 46 of the first metal grains 40 are more likely to exist in the joining portion 50.

[0059] (Grain diameter) The grain diameter of the first metal grains 40 will be described. The coefficient of variation of the grain diameter of the joining metal grains 41 of the first metal grains 40 is 20% or less. The coefficient of variation of the grain diameter of the joining metal grains 41 of this embodiment is smaller than the coefficient of variation of the grain diameter of the conventional joining metal grains 41.

[0060] Fig. 7A is a grain map of the first metal grains 40 of this embodiment. Fig. 7B is a histogram of grain diameters of the first metal grains 40 of this embodiment. Fig. 8A is a grain map of the conventional first metal grains 40. Fig. 8B is a histogram of grain diameters of the conventional first metal grains 40. The X-axis of Figs. 7B and 8B represents grain diameter (µm). The Y-axis of Figs. 7B and 8B represents area fraction.

[0061] 7A and 8A show the results of EBSD (electron backscatter diffraction) analysis of the first metal grains 40. A sample for EBSD analysis is prepared as follows: The fired multilayer ceramic capacitor 1 is embedded in resin. The sample is then polished until a predetermined surface is exposed, and the surface is trimmed to obtain a sample.

[0062] As can be seen from a comparison between FIG. 7A and FIG. 8A, the grain size of the first metal grains 40 of this embodiment tends to be smaller than the grain size of the conventional first metal grains 40 .

[0063] The histogram of Figure 7B shows the grain size of the first metal grains 40 obtained from the EBSD analysis shown in Figure 7A. The histogram of Figure 8B shows the grain size of the first metal grains 40 obtained from the EBSD analysis shown in Figure 8A.

[0064] As can be seen from a comparison between FIG. 7B and FIG. 8B, the particle size distribution of the first metal grains 40 of this embodiment is narrower than the particle size distribution of the conventional first metal grains 40.

[0065] The first metal grains 40 of this embodiment differ from the conventional first metal grains 40 in that they do not contain grains with a grain size exceeding 1.0 μm.

[0066] In the multilayer ceramic capacitor 1 of this embodiment, the particle size distribution of the first metal grains 40 is narrow, and the first metal grains 40 do not contain large grains with a particle size exceeding 1.0 μm, for example. This makes it easy to have two or more grain boundaries 46 of the first metal grains 40 present in the joint 50 in the LT cross section.

[0067] If the size of the first metal grains 40 of the terminal electrode 19 is not uniform, the bonding state between the terminal electrode 19 and the internal electrode 27 is likely to vary. As a result, the distortion contained in the ceramic layer 28 increases.

[0068] (Distortion of Ceramic Layer) The distortion of the ceramic layer 28 will now be described. As the size of the first metal grains 40 becomes more uniform, the bonding state between the terminal electrode 19 and the internal electrode 27 becomes more stable. As a result, the distortion in the ceramic layer 28 decreases. In particular, as the number of grain boundaries of the first metal grains 40 in contact with the second internal electrode 33 increases, interdiffusion between the second internal electrode 33 and the first metal grains 40 is promoted. This interdiffusion is also known as the Kirkendall effect. The interdiffusion between the second internal electrode 33 and the first metal grains 40 is, for example, the interdiffusion between nickel and copper. By promoting interdiffusion, the bonding state between the terminal electrode 19 and the internal electrode 27 becomes more stable. As a result, the distortion of the ceramic layer 28 decreases.

[0069] (Distorted Portion) The distorted portion 52 of the ceramic layer 28 will be described. The ceramic layer 28 has a distorted portion 52. The distorted portion 52 is a portion of the ceramic layer 28 where internal stress is concentrated. The distorted portion 52 is identified from an image of the ceramic layer 28 taken by EBSD (electron backscatter diffraction). A method for identifying the distorted portion 52 will be described later. The distorted portion 52 will be described below using the inner ceramic layer 31 as an example.

[0070] Fig. 9 is a stress map of the inner ceramic layer 31. Fig. 10 is a stress map of the conventional inner ceramic layer 31. As can be seen from a comparison between Fig. 9 and Fig. 10, the strained portions 52 present in the inner ceramic layer 31 of this embodiment are smaller than the strained portions 52 present in the conventional inner ceramic layer 31.

[0071] In the multilayer ceramic capacitor 1 of this embodiment, the area of ​​the distorted portion 52 in a cross section parallel to the height direction T and the length direction L is 5% or less of the area of ​​the ceramic layer 28 .

[0072] In the cross section of the inner ceramic layer 31 shown in FIG. 9, the area of ​​the distorted portion 52 is 5% or less of the total area of ​​the inner ceramic layer 31 .

[0073] The ceramic layer 28 includes ceramic grains (not shown), such as particles of barium titanate.

[0074] (Diameter of Distorted Portion) In the multilayer ceramic capacitor 1 of this embodiment, the longest diameter of the distorted portion 52 per ceramic grain is 0.5 μm or less in a cross section parallel to the height direction T and the length direction L. "The longest diameter of the distorted portion per ceramic grain is 0.5 μm or less" means "The longest diameter of the distorted portion contained within one ceramic grain is 0.5 μm or less."

[0075] (Dispersion of Strained Portions) In the multilayer ceramic capacitor 1 of this embodiment, the dispersion of the distribution of the strained portions 52 in a cross section parallel to the height direction T and the length direction L is 1.00 or less.

[0076] (Observation Method) A method for observing grain boundaries and the like will be described. A sample used for observation is prepared as follows. The multilayer ceramic capacitor 1 is embedded in resin and polished. The polishing process exposes the LT cross section at a position half the length of the multilayer ceramic capacitor 1 in the width direction W. The LT cross section is observed in a field of view that can accommodate 10 or more internal electrodes 27.

[0077] The following description will be made with reference to Fig. 4. The ranges of framed areas 92, 93, and 94 in Fig. 4 are the field of view. The length of framed area 93 in the height direction T is indicated by an arrow 60. Length 60 is, for example, not less than 20 µm and not more than 200 µm.

[0078] The number of frames to be observed is three. The three frames are located at the center in the height direction T and at both ends in the height direction T. The center position in the height direction T of frame 92 is defined as position 96. The center position in the height direction T of frame 93 is defined as position 97. The center position in the height direction T of frame 94 is defined as position 98.

[0079] The distance in the height direction T between the first main surface 3 and position 96 is defined as length 62. The distance in the height direction T between position 96 and position 97 is defined as length 63. The distance in the height direction T between position 97 and position 98 is defined as length 64. The distance in the height direction T between position 98 and the second main surface 4 is defined as length 65. Lengths 62, 63, 64, and 65 are equal.

[0080] By observing the ranges of the framed enclosures 92, 93, and 94 as the field of view, three locations, namely, the center in the height direction T and both ends in the height direction T, can be observed.

[0081] (Grain Size) Images of the three framed areas 92, 93, and 94 are taken using the electron backscattered diffraction (EBSD) method. The size of the first metal grains 40 contained in the external electrode 22 is calculated. The size is calculated using software processing in the EBSD method. By using energy dispersive X-ray spectroscopy (EDX) in combination with the EBSD method, the difference in composition between the external electrode 22 and the internal electrode 27 can be grasped. The difference in composition allows the external electrode 22 to be separated from the internal electrode 27 by region. After the region separation, the grain size of the first metal grains 40 is calculated.

[0082] (Thickness of Internal Electrode) The thickness 67 of the internal electrode 27 in the height direction T can be measured by grasping the scale from an SEM (Scanning Electron Microscope) image of the LT cross section.

[0083] The thickness 67 is measured as follows. In the above-mentioned LT cross section, the internal electrode 27 is divided into five equal-length sections in the longitudinal direction L. The thickness of the internal electrode 27 in the height direction T is measured at the center position of each section in the longitudinal direction L. The average of the five measured values ​​is taken as the thickness 67 of the internal electrode 27 in the height direction T.

[0084] To quantify the size of the first metal grains 40 of the external electrode 22, it is desirable to photograph the vicinity of the joint 50 with the internal electrode 27. However, similar structural analysis results can be obtained within a range from the interface between the ceramic layer 28 and the external electrode 22 in the thickness direction of the external electrode 22, i.e., within one-third of the length in the length direction L.

[0085] (Stress Evaluation) Stress evaluation will be described. Whether or not the ceramic layer 28 has a structure with little distortion is confirmed as follows. As described above, the multilayer ceramic capacitor 1 is embedded in resin and polished. Frames 92, 93, and 94 are photographed using the EBSD method. Images corresponding to each frame are analyzed to identify the distorted portion 52 and determine its area. The criterion for determining whether a portion is distorted is an area in the orientation difference map (kernel average misorientation map) where the difference in average orientation (°) between adjacent measurement points within the same crystal grain (within a 5° difference in orientation angle) is displayed in pseudocolor.

[0086] (Degree of Dispersion) The degree of dispersion for the distribution of the distorted portions 52 is calculated as follows: The distorted portions 52 are binarized using image analysis software. The dispersion is calculated by dividing the variation (σ) of the distance between the centers of gravity of the distorted portions 52 by the average value of the distance between the centers of gravity of the distorted portions 52.

[0087] (Determination Criteria) The determination criteria will be explained below. For example, "two or more grain boundaries 46 of the first metal grains 40 are present at the joint 50 between the internal electrode 27 and the external electrode 22" means that, as a result of observing three locations, namely the center and both ends in the height direction T, "two or more grain boundaries 46 of the first metal grains 40 are present at the joint 50 between the internal electrode 27 and the external electrode 22" for at least one internal electrode 27 included therein at least at one location.

[0088] The same applies to the other evaluation items. For example, if at least one of the internal electrodes 27 included in at least one of the frames 92, 93, and 94 satisfies a desired condition, the multilayer ceramic capacitor 1 is deemed to satisfy that condition. The grain diameter is the average grain size measured by D50.

[0089] The above has described the joining between the internal electrode 27 and the external electrode 22 using the second internal electrode 33 and the second end face 8 as examples. The same applies to the joining between the first internal electrode 32 and the external electrode 22 at the first end face 7.

[0090] (Other Measurement Methods) The following describes the methods for measuring the length, thickness, etc. of each part. The multilayer ceramic capacitor 1 is polished to the center position in the width direction W. The LT cross section exposed by polishing is observed with an optical microscope or the like, and the length, thickness, etc. are measured.

[0091] (Preferred Manufacturing Method 1) A preferred manufacturing method for obtaining the multilayer ceramic capacitor 1 of this embodiment will be described. The entire manufacturing method for the multilayer ceramic capacitor 1 will be described later. Here, characteristic features for obtaining the multilayer ceramic capacitor 1 of this embodiment will be described.

[0092] In order to improve the bonding strength between the internal electrode 27 and the external electrode 22, it is desirable that the contact area between the internal electrode 27 and the external electrode 22 is large before the metal contained in the internal electrode 27 and the metal contained in the external electrode 22 diffuse into each other's surfaces. This will be explained using the second internal electrode 33 as an example. The following explanation also applies to the first internal electrode 32.

[0093] Fig. 11 is an LT cross-sectional view showing the interface between the second internal electrode 33 and the external electrode 22 before surface diffusion. Even if the second internal electrode 33 before firing is not exposed on the surface of the inner ceramic layer 31, as shown in Fig. 11, the bonding between the second internal electrode 33 and the external electrode 22 can be stabilized by the following means, thereby providing a structure with less distortion in the ceramic layer 28.

[0094] When the thickness 67 of the second internal electrode 33 in the height direction T is 0.3 μm or more and 2.0 μm or less, the particle size of the metal powder used in the external electrode 22 is set to 0.2 μm or more and 1.0 μm or less. This makes it possible to stabilize the bonding between the second internal electrode 33 and the external electrode 22.

[0095] (Coarse Particles) When the proportion of coarse particles in the metal powder used for the external electrode 22 increases, the probability of contact between the metal powder and the second internal electrode 33 decreases. Therefore, it is preferable to remove coarse particles from the metal powder used for the external electrode 22. An example of a method for removing coarse particles is wet classification.

[0096] The crystallite diameter per particle of the metal powder used for the external electrodes 22 is preferably 0.01 μm or more and 0.30 μm or less. The shape of the metal powder preferably has a circularity of 0.6 or more.

[0097] (Preferred Manufacturing Method 2) Another method for improving the bonding between the internal electrode 27 and the external electrode 22 will now be described. Fig. 12 is a perspective view showing an outline of the ceramic body 2. As shown in Fig. 12, before forming the external electrode 22, the ceramic layer 28 on the WT surface of the ceramic body 2 where the internal electrode 27 is exposed is removed. This exposes the recessed internal electrode 27. By removing the ceramic layer 28, the second internal electrode 33 that is not exposed on the surface of the inner ceramic layer 31 is exposed. An example of a method for removing the ceramic layer 28 is sandblasting.

[0098] The exposed amount of the internal electrode 27 can be determined by measuring the area ratio of nickel with a fluorescent X-ray device. The area ratio of nickel is preferably 30% or more and 60% or less.

[0099] (Firing conditions) To form the external electrode 22, it is necessary to apply, dry, and fire a conductive paste for the external electrode 22. The conductive paste is composed of metal powder, glass, and a binder. It is believed that the portions other than the metal powder, i.e., the glass and binder, inhibit the bonding between the internal electrode 27 and the external electrode 22.

[0100] It is desirable that no binder remains at the time of joining the internal electrode 27 and the external electrode 22. Therefore, it is preferable to use a binder material that has good thermal decomposition properties and to fire the conductive paste under firing conditions that provide good degreasing properties.

[0101] The preferred firing conditions are a temperature range in which the binder thermally decomposes, a reducing atmosphere for copper and nickel, and an oxidizing atmosphere for carbon. Preferred firing conditions include an oxygen partial pressure of 1.0E-10 P / atm to 1.0E-18 P / atm, a temperature of 600°C to 850°C, and maintaining the temperature for 5 minutes or longer.

[0102] (Firing Delay) To promote degreasing, firing is desirably performed at a temperature below the temperature at which the internal electrodes 27 and external electrodes 22 undergo surface diffusion. Alternatively, the timing of bonding the internal electrodes 27 and external electrodes 22 may be delayed. One method for delaying the bonding timing is to attach one or more elements selected from the group consisting of silicon, titanium, aluminum, zirconium, tin, etc., to the surface of metal powder such as copper powder. The use of a conductive paste containing these elements enables sintering delay.

[0103] The glass is preferably finely divided and added in a small amount so as not to impair the bonding between the internal electrode 27 and the external electrode 22. The particle size of the glass particles is preferably 80% or less of the thickness 67 of the internal electrode 27. The amount of glass particles added is preferably 5 vol% or more and 40 vol% or less of the copper powder content.

[0104] (Manufacturing Method of Multilayer Ceramic Capacitor) A manufacturing method of the multilayer ceramic capacitor 1 will be described. A conductive paste for the dielectric sheets and the internal electrodes is prepared. The conductive paste for the dielectric sheets and the internal electrodes contains a binder and a solvent. The binder and the solvent may be a known organic binder and organic solvent, for example.

[0105] The conductive paste for the internal electrodes is printed on the dielectric sheet in a predetermined pattern. This printing process forms the internal electrode pattern. Examples of printing methods include screen printing and gravure printing.

[0106] A predetermined number of dielectric sheets for the outer layer portions are stacked. No internal electrode patterns are printed on the dielectric sheets for the outer layer portions. Dielectric sheets with internal electrode patterns printed on them are stacked in order on top of the stacked dielectric sheets. A predetermined number of dielectric sheets for the outer layer portions are stacked on top of these. A laminated sheet is produced by stacking these layers.

[0107] The laminated sheet is pressed in the height direction to produce a laminated block, for example, by isostatic pressing.

[0108] The laminated block is cut to a predetermined size. This cutting process cuts out laminated chips. When cutting, the corners and ridges of the laminated chips may be rounded. An example of a method for rounding is barrel polishing.

[0109] The laminated chip is fired to produce a ceramic body. The firing temperature is preferably 900° C. or higher and 1110° C. or lower. The firing temperature varies depending on the materials of the dielectric and the internal electrodes.

[0110] Terminal electrodes are formed. A conductive paste that will become the external electrodes 22 is applied to the two end surfaces of the ceramic body 2. The conductive paste contains metal and glass. An example of a method for applying the conductive paste is dipping. After application, firing is performed to form the external electrodes 22. A preferred firing temperature is 500°C or higher and 900°C or lower. A preferred firing time is 30 minutes or higher and 2 hours or lower.

[0111] Nickel plating films 24 are formed on the surfaces of the external electrodes 22. Tin plating films 25 are formed on the surfaces of the nickel plating films 24. The nickel plating films 24 and the tin plating films 25 are formed by barrel plating or the like. In this way, the multilayer ceramic capacitor 1 is manufactured.

[0112] The multilayer ceramic capacitor 1 of this embodiment achieves a structure in which there is little distortion in the ceramic layer 28 at the interface with the terminal electrode 19. This makes it possible to suppress a decrease in reliability due to large distortion in the ceramic layer 28 at the interface with the terminal electrode 19.

[0113] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and various changes and modifications are possible.

[0114] <1> A multilayer ceramic capacitor comprising: a ceramic body including a plurality of stacked ceramic layers and a plurality of stacked internal electrodes, the ceramic body having six surfaces: a first main surface and a second main surface opposing each other in a height direction; a first side surface and a second side surface opposing each other in a width direction perpendicular to the height direction; and a first end surface and a second end surface opposing each other in a length direction perpendicular to the height direction and the width direction; and external electrodes provided on the ceramic body and connected to some of the internal electrodes, wherein the external electrodes include first metal grains, and in a cross section parallel to the height direction and the length direction, two or more grain boundaries of the first metal grains are present at a joint between the internal electrode and the external electrode, and the grain diameter of the first metal grains where a grain boundary is present at the joint is 1.2 times or less the thickness of the internal electrode in the height direction.

[0115] <2> The multilayer ceramic capacitor according to <1>, wherein the thickness of the internal electrode in the height direction is 0.3 μm or more and 2.0 μm or less, and the grain diameter of the first metal grain having a grain boundary at the joint is 0.1 μm or more and 0.8 μm or less.

[0116] <3> The multilayer ceramic capacitor according to <1> or <2>, wherein the coefficient of variation of the grain diameter of the first metal grains having grain boundaries at the joint is 20% or less.

[0117] <4> The multilayer ceramic capacitor according to any one of <1> to <3>, wherein the external electrodes include glass portions, and the glass portions are in contact with at least one of the internal electrodes and the ceramic layers.

[0118] <5> The multilayer ceramic capacitor according to any one of <1> to <4>, wherein the ceramic layers have distorted portions, and the area of ​​the distorted portions is 5% or less of the area of ​​the ceramic layers in a cross section parallel to the height direction and the length direction.

[0119] <6> The multilayer ceramic capacitor according to any one of <1> to <5>, wherein the ceramic layer has a distorted portion, the ceramic layer includes ceramic grains, and in a cross section parallel to the height direction and the length direction, the longest diameter of the distorted portion is 0.5 μm or less per ceramic grain.

[0120] <7> The multilayer ceramic capacitor according to any one of <1> to <6>, wherein the ceramic layers have strained portions, and a degree of dispersion of the strained portions in a cross section parallel to the height direction and the length direction is 1.00 or less.

[0121] REFERENCE SIGNS LIST 1 Multilayer ceramic capacitor 2 Ceramic body 3 First main surface 4 Second main surface 5 First side surface 6 Second side surface 7 First end surface 8 Second end surface 10 First main surface outer layer portion 11 Inner layer portion 12 Second main surface outer layer portion 13 First end surface side lead portion 14 Longitudinal opposing portion 15 Second end surface side lead portion 16 First side surface side gap portion 17 Widthwise opposing portion 18 Second side surface side gap portion 19 Terminal electrode 20 First terminal electrode 21 Second terminal electrode 22 External electrode 24 Nickel plating film 25 Tin plating film 27 Internal electrode 28 Ceramic layer 30 External ceramic layer 31 Internal ceramic layer 32 First internal electrode 33 Second internal electrode 34 First opposing electrode portion 36 First lead electrode portion 35 Second opposing electrode portion 37 Second extraction electrode portion 39 Outer periphery 40 First metal grain 41 Joined metal grain 42 Non-joined metal grain 45 Second metal grain 47 Glass portion 46 Grain boundary 50 Joint portion 52 Distorted portion 54 Tip of internal electrode

Claims

1. a ceramic body including a plurality of stacked ceramic layers and a plurality of stacked internal electrodes, and having six surfaces: a first main surface and a second main surface opposing each other in a height direction, a first side surface and a second side surface opposing each other in a width direction perpendicular to the height direction, and a first end surface and a second end surface opposing each other in a length direction perpendicular to the height direction and the width direction; an external electrode provided on the ceramic body and connected to some of the internal electrodes, the external electrode includes first metal grains; In a cross section parallel to the height direction and the length direction, two or more grain boundaries of the first metal grain are present at a joint between the internal electrode and the external electrode, a grain diameter of the first metal grains having grain boundaries at the joint portion is 1.2 times or less the thickness of the internal electrode in the height direction; Multilayer ceramic capacitor.

2. The thickness of the internal electrode in the height direction is 0.3 μm or more and 2.0 μm or less, the grain diameter of the first metal grains having grain boundaries at the joint is 0.1 μm or more and 0.8 μm or less; The multilayer ceramic capacitor according to claim 1 .

3. a coefficient of variation of the grain diameter of the first metal grains having a grain boundary at the joint is 20% or less; The multilayer ceramic capacitor according to claim 1 .

4. The coefficient of variation of the grain diameter of the first metal grain having a grain boundary at the joint is 20% or less. The multilayer ceramic capacitor according to claim 2 .

5. The external electrode includes a glass portion, the glass portion is in contact with at least one of the internal electrode and the ceramic layer; The multilayer ceramic capacitor according to claim 1 .

6. The ceramic layer has a strained portion, In a cross section parallel to the height direction and the length direction, the area of ​​the distorted portion is 5% or less of the area of ​​the ceramic layer. The multilayer ceramic capacitor according to claim 1 .

7. The ceramic layer has a strained portion, the ceramic layer includes ceramic grains; In a cross section parallel to the height direction and the length direction, the longest diameter of the distorted portion is 0.5 μm or less per ceramic grain. The multilayer ceramic capacitor according to claim 1 .

8. The ceramic layer has a strained portion, In a cross section parallel to the height direction and the length direction, the dispersity of the distribution of the strained portions is 1.00 or less. The multilayer ceramic capacitor according to claim 1 .