Multilayer ceramic capacitor and circuit board

Abstract

The invention provides a multilayer ceramic capacitor and a circuit board. The laminated ceramic capacitor comprises a cuboid-shaped main body, a ceramic capacitor includes a laminate in which ceramic layers and internal electrodes having a metal as a main component are alternately laminated, and a pair of covering portions disposed at both ends of the laminate in a lamination direction and covering a surface of the laminate. And an edge portion that covers at least a portion of an end portion of the ceramic layer and an end portion of the internal electrode in the laminate and connects the pair of cover portions to each other. And a plurality of terminal electrodes electrically connected to the internal electrodes and disposed on at least a mounting surface of the surfaces forming the surface of the main body at intervals, the mounting surface being a surface facing a circuit board to be mounted, the terminal electrodes being electrically connected to the internal electrodes with respect to at least a partial region of the cover portion or the edge portion. The following relational expression (1) is satisfied, where Po is the porosity of the surface layer portion, and Pi is the porosity of the inner portion located closer to the laminate than the surface layer portion: Pi < Po... (1).

Description

Technical Field

[0001] This invention relates to multilayer ceramic capacitors and circuit boards. Background Technology

[0002] In high-frequency communication systems, such as mobile phones, a wide variety of ceramic electronic components are used. These components require miniaturization and thinning, and miniaturization and thinning are also being researched in multilayer ceramic capacitors.

[0003] Patent Document 1 discloses a thin and durable multilayer ceramic capacitor in which through-hole electrodes electrically connect the internal electrode layers to each other and to the terminal electrodes, and the multilayer ceramic capacitor has a structure with voids formed inside. In the multilayer ceramic capacitor disclosed in Patent Document 1, terminal electrodes are formed on the upper surface of the element body (main body) which has a flat shape.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-72263 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] Patent Document 1 discloses a multilayer ceramic capacitor with terminal electrodes formed only on the upper surface of an opposing upper and lower surface. In this type of multilayer ceramic capacitor, the exposed area of ​​the main body on the lower surface, where no terminal electrodes are formed, becomes larger. Since the surface of the main body is mostly made of brittle materials such as ceramic, when handling the multilayer ceramic capacitor or after mounting it on a circuit board, impacts to the exposed surface of the main body can sometimes cause breakage or damage. These breakages and damages on the main body surface become pathways for deteriorating factors such as moisture, thus reducing the durability and reliability of the multilayer ceramic capacitor. Therefore, it is necessary to improve the surface toughness of the main body in the multilayer ceramic capacitor.

[0009] The present invention was made to address the above-mentioned requirements, and its object is to provide a multilayer ceramic capacitor with improved toughness of the main body surface, and a circuit board on which the multilayer ceramic capacitor is mounted.

[0010] Technical solutions for solving technical problems

[0011] In order to solve the above problems, the inventors conducted various studies and found that the above objectives could be achieved by making at least a portion of the main surface of the multilayer ceramic capacitor have a larger porosity than the inner side, thus completing the present invention.

[0012] A first aspect of the present invention for solving the above-mentioned technical problems is a multilayer ceramic capacitor, comprising: a cuboid body having a multilayer having ceramic layers and metal-based internal electrodes alternately stacked; a pair of covering portions disposed at both ends of the multilayer in the stacking direction and covering the surface of the multilayer; and an edge portion covering at least a portion of the ends of the ceramic layers and the ends of the internal electrodes in the multilayer, thereby connecting the pair of covering portions to each other; and a plurality of terminal electrodes electrically connected to the internal electrodes, which are spaced apart from each other and disposed on at least one of the surfaces forming the surface of the body, the mounting surfaces being the surfaces opposite to a circuit board to which they are mounted; and, regarding at least a portion of the covering portions or the edge portions, when the porosity of the surface portion is set to P... o The porosity of the inner portion located closer to the laminate than the surface layer is set as P. i When the following relation (1) is satisfied:

[0013] P i <P o ……(1).

[0014] Furthermore, a second aspect of the present invention for solving the above-mentioned technical problems is a circuit board equipped with the stacked ceramic capacitor of the first aspect described above.

[0015] Invention Effects

[0016] According to the present invention, it is possible to provide a multilayer ceramic capacitor with improved toughness of the main body surface and a circuit board on which the multilayer ceramic capacitor is mounted. Attached Figure Description

[0017] Figure 1 This is a schematic diagram (perspective view) showing the structure of the multilayer ceramic capacitor according to the first embodiment of the present invention.

[0018] Figure 2 yes Figure 1 AA section view (LT section view) in the image.

[0019] Figure 3 This diagram illustrates the method for determining the porosity in the surface layer, inner layer, and through-hole surface layer of a multilayer ceramic capacitor, which is used to describe the formation of the covering portion of the opposite surfaces.

[0020] Figure 4 This is a diagram illustrating the method for determining the porosity in the surface and inner layers of a multilayer ceramic capacitor, specifically the edge portion.

[0021] Figure 5This is a diagram illustrating a method for determining the percentage of void cells in a cross-section of a multilayer ceramic capacitor with a through-hole surface portion relative to the total number of cells.

[0022] Figure 6 This is a schematic diagram (LT cross-sectional view) showing the structure of the multilayer ceramic capacitor according to the second embodiment of the present invention.

[0023] Figure 7 This is a schematic diagram (perspective view) showing the structure of the stacked ceramic capacitor according to the third embodiment of the present invention.

[0024] Explanation of reference numerals in the attached figures

[0025] 100, 200, 300 multilayer ceramic capacitors

[0026] 10 main bodies

[0027] 11 mounting surfaces

[0028] 12 opposite sides

[0029] 13 Lead-out surfaces

[0030] 20-layer stack

[0031] 21 ceramic layers

[0032] 22 (22a, 22b) Internal electrodes

[0033] 23 (23a, 23b) Through-hole conductor

[0034] 31 Coverage Department

[0035] 32 Edge

[0036] 3o (covering or edge) surface layer

[0037] 3ov through-hole surface layer

[0038] 3i (inner side of the covering or edge)

[0039] 40 (40a, 40b) terminal electrodes

[0040] 41 Substrate Conductor

[0041] 42 Plated Conductor

[0042] 50 (50a, 50b) External conductor

[0043] B circuit board

[0044] p-gap. Detailed Implementation

[0045] The structure and effects of the present invention will be described below with reference to the accompanying drawings and in conjunction with the technical concept. However, the working mechanism includes speculation, and its accuracy does not limit the present invention.

[0046] Multilayer ceramic capacitors

[0047] <First Implementation Method>

[0048] One embodiment of the multilayer ceramic capacitor of the first aspect of the present invention is taken as the first embodiment. Figure 1 and Figure 2 The first embodiment of the multilayer ceramic capacitor 100 is a cuboid shape, comprising a pair of faces orthogonal to each of three axes: the L-axis (length direction), the W-axis (width direction), and the T-axis (height direction). The cuboid is not limited to the mathematically defined cuboid; it can be any shape that is recognized as a cuboid when observing the overall shape. Therefore, cases where the edges and corners are slightly rounded, the edges are slightly curved, or the resulting surfaces are surfaces with low curvature are also equivalent to the cuboid shape in this invention. The dimensions of the multilayer ceramic capacitor 100 in the length (L) direction, width (W) direction, and height (T) direction can each independently take any value.

[0049] Examples of dimensions for the multilayer ceramic capacitor 100 include an L-direction dimension of 200 μm or more and 2000 μm or less, a W-direction dimension of 100 μm or more and 2000 μm or less, a T-direction dimension of 30 μm or more and 220 μm or less, and a W / L ratio of 0.3 or more and 1.0 or less. Preferably, among the above dimensions, the L-direction dimension is 400 μm or more and 1200 μm or less, the W-direction dimension is 400 μm or more and 1200 μm or less, the T-direction dimension is 40 μm or more and 150 μm or less, and the W / L ratio is 0.4 or more and 1.0 or less. From the perspective of being less limited by the design of the mounted circuit board, a T-direction dimension of 100 μm or less is more preferable.

[0050] Figure 2 This illustrates an example of a multilayer ceramic capacitor 100 mounted on circuit board B. The multilayer ceramic capacitor 100 of the first embodiment is shown below. Figure 2The diagram schematically illustrates a cross-sectional view of a body 10, which includes: a laminate 20 in which ceramic layers 21 and metal-based internal electrodes 22 are alternately stacked in the T direction; a pair of covers 31 covering the surface of the laminate 20; and an edge portion 32 covering at least a portion of the ends of the ceramic layers 21 and the ends of the internal electrodes 22 in the laminate 20 and connecting the pair of covers 31 to each other. The internal electrodes 22 include an internal electrode 22a of one polarity electrically connected to each other, and an internal electrode 22b of a different polarity electrically connected to each other.

[0051] The method for electrically connecting the internal electrodes 22a to each other and the internal electrodes 22b to each other is not particularly limited. In this embodiment, the internal electrodes 22a and 22b are connected via through-hole conductors 23 (23a, 23b) along the stacking direction. The through-hole conductors 23 are disposed inside the body 10, penetrating the ceramic layer 21 in the stacking direction of the laminate 20. One end of the through-hole conductor 23 penetrates the cover portion 31 on the positive side of the T direction and reaches its surface, while the other end of the through-hole conductor 23 does not penetrate the cover portion 31 on the negative side of the T direction and is covered by the cover layer 1. Alternatively, as shown in the second embodiment described later, the internal electrodes can be led out to the end face of the body and connected by connecting conductors provided on the surface of the body. Figure 2 The stacked ceramic capacitor 100 shown includes two through-hole conductors 23, but the number of through-hole conductors in the stacked ceramic capacitor 100 of the first aspect of the present invention is not limited thereto.

[0052] On the surface of the main body 10, a covering portion 31 is disposed on a surface perpendicular to the T direction of the laminate 20, and an edge portion 32 is disposed on a surface perpendicular to the W direction of the laminate and a surface perpendicular to the L direction. Furthermore, as described in the second embodiment below, when the internal electrode is led out to the end face of the main body, no edge portion is disposed on the end face (lead-out face) where the internal electrode is led out.

[0053] The multilayer ceramic capacitor 100 of the first embodiment includes a plurality of terminal electrodes 40 (40a, 40b), which are arranged at least spaced apart from each other on at least one mounting surface 11 of each surface forming the body 10, and are electrically connected to internal electrodes 22 (22a, 22b). The mounting surface 11 is the surface opposite to the board surface of the circuit board B when the multilayer ceramic capacitor 100 is mounted on the circuit board B. The terminal electrodes 40 are connected to electrode pads on the board surface of the circuit board B, for example, by solder. The method of electrically connecting the terminal electrodes 40 (40a, 40b) to the internal electrodes 22 (22a, 22b) is not particularly limited. In this embodiment, the terminal electrodes 40a, 40b are connected to the internal electrodes 22a, 22b respectively via through-hole conductors 23a, 23b. One end of the through-hole conductors 23a, 23b extends through the cover layer 31 on the positive side in the T direction and contacts the terminal electrodes 40a, 40b respectively. Furthermore, as shown in the second embodiment described later, this connection can also be achieved via an external conductor instead of through-hole conductors 23a and 23b. Additionally, Figure 2 The stacked ceramic capacitor 100 shown includes two terminal electrodes 40, but the number of terminal electrodes in the stacked ceramic capacitor 100 of the first aspect of the present invention is not limited thereto.

[0054] The multilayer ceramic capacitor 100 of the first embodiment includes voids p formed in a manner that satisfies the following relationship (1). Here, the porosity of the surface portion 3o in at least a portion of the covering portion 31 or the edge portion 32 is set as P. o The porosity of the inner portion 3i, located closer to the laminate 20 than the surface portion 3o, is set as P. i (Refer to Figure 3 and Figure 4 ).

[0055] P i <P o ……(1)

[0056] Furthermore, the multilayer ceramic capacitor 100 has a main body 10 in which the entire area of ​​the cover portion 31 on the opposite side of the mounting surface 12 satisfies the above-mentioned relation (1). The cover portion 31 and the edge portion 32 on the mounting surface 11 side do not satisfy the above-mentioned relation (1). However, the cover portion 31 and the edge portion 32 of the multilayer ceramic capacitor 100 of the first aspect of the present invention are not limited to this. The part that satisfies the above-mentioned relation (1) may be only the entire area of ​​the edge portion, or it may be the entire area of ​​all the cover portions 31 and the edge portion 32, or it may be only a part of a specific cover portion 31 or edge portion 32.

[0057] When the thickness of the terminal electrodes 40 (40a, 40b) is removed from the T-direction dimension of the above-mentioned multilayer ceramic capacitor 100, the maximum thickness of the main body 10 is, for example, 20 μm or more and 200 μm or less, preferably 30 μm or more and 180 μm or less.

[0058] In the multilayer ceramic capacitor 100 of the first embodiment, the internal electrodes 22 (22a, 22b) and the terminal electrodes 40 (40a, 40b) are connected via through-hole conductors 23 (23a, 23b). Therefore, external conductors are not required on the opposing surface 12 opposite to the mounting surface 11 in the body 10, or on each surface perpendicular to the mounting surface 11 and the opposing surface 12, respectively. Thus, the multilayer ceramic capacitor 100 of the first embodiment is advantageous in that it allows for a reduction in element size by an amount corresponding to the thickness of the external conductor.

[0059] The components constituting the multilayer ceramic capacitor 100 of the first embodiment will be described in detail below.

[0060] (Ceramic layer)

[0061] The ceramic layer 21 is formed of ceramic. The composition of the ceramic is not particularly limited as long as it is formed by firing simultaneously with the internal electrode 22 (described later) to create a dense ceramic layer 21; it can be appropriately selected based on the characteristics required by the multilayer ceramic capacitor 100. Examples of ceramic compositions include substances primarily composed of barium titanate (BaTiO3), substances primarily composed of strontium titanate (SrTiO3), and substances with a perovskite structure. 1-x-y Ca x Sr y Ti 1-z Zr z Substances with O3 as the main component, etc. Ceramics may contain the aforementioned main component and additive elements. Examples of additive elements include at least one selected from Mo, Nb, Ta, W, Mg, Mn, V, Cr, and rare earth elements (Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), as well as Co, Ni, Li, B, Na, K, and Si. Additive elements may be included in the form of elemental monomers or in the form of compounds such as oxides, nitrides, and carbides. Furthermore, additive elements may exist in a state of solid solution within the aforementioned main component, or they may form a heterogeneous phase with the elements constituting the aforementioned main component or other additive elements.

[0062] (Internal electrodes)

[0063] The internal electrodes 22 (22a, 22b) are primarily composed of metal. The type of metal is not particularly limited; nickel (Ni), copper (Cu), palladium (Pd), platinum (Pt), silver (Ag), and gold (Au), as well as their alloys, can be used. Among these, nickel (Ni) is preferred as the primary component element because of its high heat resistance, which allows for higher firing temperatures during simultaneous firing with the ceramic layer 21, resulting in a dense ceramic layer 21, and its relatively low cost. Here, "primary component element" in this specification refers to the element with the highest content, expressed as atomic percentage (atomic %).

[0064] In addition to metal, the internal electrodes 22 (22a, 22b) may also contain ceramic particles and glass components having the same composition as the ceramic that constitutes the ceramic layer 21.

[0065] (Covered area and edge area)

[0066] Both the cover portion 31 and the edge portion 32 function to protect the ceramic layer 21 and the internal electrode 22. The material of the cover portion 31 and the edge portion 32 is not limited as long as it has high electrical insulation and low permeability to deteriorating factors such as moisture. From the viewpoint of ensuring uniform shrinkage during firing and mitigating internal stress within the multilayer ceramic capacitor 100 during manufacturing, it is preferable that the main components of the cover portion 31 and the edge portion 32 are the same as the ceramic forming the ceramic layer 21.

[0067] As described above, when the porosity of the surface layer 3o is set to P o The porosity of the inner portion 3i, which is located closer to the laminate 20 than the surface portion 3o, is set as P. i At that time, at least a portion of the covered portion 31 or the edge portion 32 satisfies:

[0068] P i <P o ……(1).

[0069] As a result, the toughness of the surface of the main body 10 is improved, and the occurrence of breakage and defects when subjected to impact is suppressed. It is speculated that this is because the voids existing in the surface layer 3o act as a deformation when stress is applied, in other words, as a buffer, thereby mitigating the stress and suppressing local stress concentration.

[0070] P i and P o The value of P is not particularly limited as long as it satisfies the above relationship (1). Considering the aspect of significantly improving the toughness of the surface of the main body 10, o / P iThe value is preferably 1.5 or more, more preferably 2 or more, and even more preferably 2.5 or more. On the other hand, from the perspective of fully utilizing the original function of inhibiting the intrusion of deteriorating factors such as moisture into the laminate 20, such as the covering portion 31 and the edge portion 32, P... o / P i The value is preferably 100 or less, more preferably 50 or less, and even more preferably 10 or less. From the perspective of fully utilizing the original function of inhibiting the intrusion of deteriorating factors such as moisture into the laminate 20, such as the covering portion 31 and the edge portion 32, P i The individual value is preferably small, and can be 0%. From the perspective of effectively improving the toughness of the surface of the body 10, P o The individual value is preferably 1% or more, more preferably 2% or more, and even more preferably 3% or more. On the other hand, from the perspective of fully utilizing the original function of inhibiting the intrusion of deteriorating factors such as moisture into the laminate 20, such as the covering portion 31 and the edge portion 32, P o The individual value is preferably 10% or less, more preferably 9% or less, and even more preferably 8% or less. Based on the above, as P o Individual values, preferably 2% ≤ P o ≤10%, more preferably 3%≤P o ≤9%, more preferably 4%≤P o ≤8%.

[0071] 100-layer ceramic capacitor Figure 2 As shown, in the main body 10, the surface opposite to the mounting surface 11, i.e., the opposing surface 12, does not have any terminal electrodes 40 (40a, 40b) or any conductor electrically connected to them. When the covering portion 31 or edge portion 32 forming the opposing surface 12 satisfies the above-mentioned relationship (1), the suppression effect of increased toughness leading to fracture and defects becomes significant. It is speculated that this is because, since the exposed area of ​​the opposing surface 12 is large, the frequency of impact on the exposed portion is higher, and therefore the difference in the probability of fracture and defects caused by the porosity of the surface portion 3o becomes significant.

[0072] The multilayer ceramic capacitor 100 not only satisfies the above-mentioned relation (1) in at least a portion of the covering portion 31 covering the ends of the through-hole conductors 23 (23a, 23b), but also, when viewed from the stacking direction (T direction) of the multilayer 20, the porosity P of the area overlapping with the through-hole conductors 23 (23a, 23b) located in the covering portion 31, i.e., the through-hole surface portion 3ov, in the surface portion 3o of the covering portion 31. ov The following relation (2) must be satisfied:

[0073] P o <P ov ……(2).

[0074] Therefore, the deviation of the electrostatic capacitance of the multilayer ceramic capacitor 100 is suppressed, resulting in a multilayer ceramic capacitor with high reliability. It is speculated that this is because when stress in the T direction is applied to the through-hole conductors 23 (23a, 23b) or their interface with the multilayer 20, the void p existing in the surface layer 3ov of the through-hole acts as a displacement of the end of the through-hole conductors 23 (23a, 23b) to alleviate the stress. As a result, the generation of cracks at the interface between the through-hole conductors 23 (23a, 23b) and the multilayer 20, and the resulting poor connection between the through-hole conductors 23 (23a, 23b) and the internal electrodes 22 (22a, 22b) are suppressed.

[0075] Regarding P o and P ov From the perspective of significantly suppressing the deviation of electrostatic capacitance, a value of P is preferred. ov / P o The value of P is 2 or higher, more preferably 2.5 or higher, and particularly preferably 3 or higher. On the other hand, considering the full utilization of the original function of the covering portion 31 or edge portion 32 in inhibiting the intrusion of deteriorating factors such as moisture into the laminate 20, regarding P... o and P ov The value of P is preferred. o / P i The value of P is preferably 10 or less, more preferably 9 or less, and particularly preferably 8 or less. From the perspective of significantly suppressing electrostatic capacitance deviation, P... ov The individual value is preferably 2% or more, more preferably 3% or more, and even more preferably 4% or more. On the other hand, from the perspective of fully utilizing the original function of the covering portion 31 or edge portion 32 in inhibiting the intrusion of deteriorating factors such as moisture into the laminate 20, P ov The individual value is more preferably 10% or less, further preferably 9% or less, and particularly preferably 8% or less. Based on the above, as P ov Individual values, more preferably 4% ≤ P ov ≤10%, more preferably 5%≤P ov ≤9%, preferably 6%≤P ov ≤8%.

[0076] Here, the aforementioned P i P o and P ovThe values ​​are determined through the following steps. First, the terminal electrodes 40 formed on the mounting surface 11 of the multilayer ceramic capacitor 100 are removed, exposing the through-hole conductor 23 on the mounting surface 11. Methods for removing the terminal electrodes 40 include grinding and acid dissolution. Next, the multilayer ceramic capacitor 100 is cut with a surface near the center of gravity of the through-hole conductor 23 exposed on the mounting surface 11 and parallel to the stacking direction, to prepare an observation sample. Alternatively, the observation sample can be prepared by grinding a surface orthogonal to the mounting surface 11 until it is near the center of gravity of the through-hole conductor 23 exposed on the mounting surface 11. Next, the observation sample is embedded in resin with the cut or ground surface exposed, and the cut surface is mirror-polished. Then, the mirror-polished cut or ground surface is observed using an optical microscope or a scanning electron microscope (SEM) to obtain the desired results. Figure 3 The opposing surface 12, the internal electrode 22 closest to the opposing surface 12, and the through-hole conductor 23 disposed in the cover portion 31 forming the opposing surface 12 are all within the same field of view, and an image of the gap can be clearly seen in the cover portion 31. Next, in the acquired image, the following line segments are drawn respectively: (a) line segment h1 delineating the opposing surface 12; (b) line segment h2 parallel to line segment h1 and tangent to the end of the through-hole conductor 23; and (c) two line segments v1 and v2 orthogonal to line segment h2 and tangent to the through-hole conductor 23 in the cover portion 31. Furthermore, the region in the cover portion 31 located closer to the internal electrode 22 than line segment h2 is designated as the inner portion 3i, and the region located closer to the opposing surface 12 than line segment h2 is designated as the surface portion 3o. In addition, the region located between line segments v1 and v2 in the region of the surface portion 3o is designated as the through-hole surface portion 3ov. Next, for each region, which is the inner part 3i, the surface part 3o, and the through-hole surface part 3ov, the area of ​​the void p is calculated by using image analysis software. The obtained values ​​are divided by the total area of ​​each region and then multiplied by 100, and the resulting values ​​are set as P. i P o and P ov Furthermore, when drawing line segment h1, if the opposite surface 12 observed in the image forms a curve or polyline, the curve or polyline is linearly approximated as a line segment.

[0077] Additionally, regarding the cover portion 31 on the edge portion 32 or the mounting surface 11 side, the porosity P is determined. i and P oIn the case of a value, the following steps are performed to determine it. Furthermore, the steps described below describe the determination of the porosity of the edge portion 32, but the same steps are also used for the cover portion 31 on the mounting surface 11 side. First, the stacked ceramic capacitor 100 is cut as an observation sample in a plane perpendicular to the edge portion 32 of interest, parallel to the opposing surfaces, and where the distance from each surface is more than 1 / 3d and less than 2 / 3d relative to the interval d between the surfaces. Next, the observation sample is embedded in resin with the cut surface exposed, and the cut surface is mirror-polished. Then, the mirror-polished cut surface is observed using an optical microscope or a scanning electron microscope (SEM) to obtain a result such as... Figure 4 An image showing the surface of the edge portion 32 and the internal electrode 22 closest to that surface entering the same field of view, and where the gap can be clearly identified in the edge portion 32. Next, in the acquired image, the following line segments are drawn: (d) line segment l1 delineating the surface of the edge portion 32; (e) line segment l2 parallel to line segment l1 and tangent to the end of the internal electrode 22; and (f) line segment l3 parallel to line segments l1 and l2 and located at equal distances from each of these line segments. Furthermore, the region in the edge portion 32 located closer to line segment l2 than line segment l3 is designated as the inner portion 3i, and the region located closer to line segment l1 than line segment l3 is designated as the surface portion 3o. Next, for each region as the inner portion 3i and the surface portion 3o, the area of ​​the gap p is calculated using image analysis software, and the value obtained is divided by the total area of ​​each region and then multiplied by 100, and the resulting value is designated as P. i and P o .

[0078] When the surface portion 3ov of the through-hole satisfies the above-described relationship (2), when dividing the cross-section parallel to the T direction using square cells with one side of 1 μm, it is more preferable that the percentage of cells containing voids p relative to the total number of cells is 10% or more. This means that voids p are widely distributed in the surface portion 3ov of the through-hole, thereby making the aforementioned effect of suppressing electrostatic capacitance deviation more significant. The percentage is further preferably 20% or more, and particularly preferably 30% or more.

[0079] Here, the percentage of cells with voids in the cross-section of the through-hole surface portion 3ov relative to the total number of cells is determined by the following steps. First, with the aforementioned P... i P o and P ovSimilarly, the steps for determining the value are as follows: acquire a microscope image of the cut or ground surface of the specimen for observation, and plot line segments h1, h2, v1, and v2 in the image. Next, measure the distance between line segments h1 and h2, divide this distance by the length corresponding to 1 μm in the microscope image, and set the remainder as H. r Additionally, the distance between line segments v1 and v2 is measured, and this distance is divided by the length corresponding to 1 μm in the microscope image. The remainder is then set as V. r Next, in the microscope image, as... Figure 5 As shown, draw lines parallel to line segment h1 and at a distance H from that line segment. r The line segment h3 is parallel to line segment h2 and is H''''''''''''''''''''''''''''''''''''''''''" 'H' ... r The line segment h4 is 2 / 2, parallel to the line segment v1, and its distance from the line segment is V. r The line segment v3 is 2 / 2, and the line segment v2 is parallel to it and extends at a distance V from that line segment. r / 2 line segment v4. Next, between line segment h3 and line segment h4, line segments parallel to line segment h3 are drawn at intervals corresponding to 1 μm in the microscopic image. Additionally, between line segment v3 and line segment v4, line segments parallel to line segment v3 are drawn at intervals corresponding to 1 μm in the microscopic image. Next, for the rectangular region enclosed by line segments h3, h4, v3, and v4, the total number of cells drawn within it and the number of cells containing gaps p are counted. At this point, if a gap exists across multiple cells, it is determined that a gap exists in that cell. Then, the number of cells with gaps is divided by the total number of cells and multiplied by 100 to calculate the percentage of cells with gaps relative to the total number of cells.

[0080] (Through-hole conductor)

[0081] The through-hole conductors 23 (23a, 23b) and the internal electrodes 22 (22a, 22b) are both primarily composed of metal. Examples of usable metals include those used for the internal electrodes 22 (22a, 22b). The composition of the through-hole conductors may differ from that of the internal electrodes 22 (22a, 22b), but it is preferable that they are the same. By making the through-hole conductors (23a, 23b) and the internal electrodes 22 (22a, 22b) have the same composition, deformation caused by shrinkage during firing is consistent during the manufacture of the multilayer ceramic capacitor 100, and deformation is suppressed. Furthermore, the resistivity of the conductive paths in the multilayer ceramic capacitor 100 becomes more uniform, which helps to suppress localized heating during use.

[0082] The diameter of the through-hole conductors (23a, 23b) is not particularly limited. From the perspective of ensuring the capacitance of the multilayer ceramic capacitor 100 and reducing resistance to suppress heat generation during circuit driving, it is preferably 5μm or more and 100μm or less, and more preferably 10μm or more and 50μm or less.

[0083] (Terminal electrode)

[0084] The material of the terminal electrodes 40 (40a, 40b) is not limited as long as it is conductive. Examples of materials include metals such as nickel (Ni), copper (Cu), tin (Sn), palladium (Pd), platinum (Pt), silver (Ag), and gold (Au), alloys with any of these as the main component elements, and conductive resins.

[0085] The terminal electrodes 40 (40a, 40b) may also have a base conductor 41 in contact with the body 10 and a plated conductor 42 formed on the surface of the base conductor 41. The terminal electrodes 40 (40a, 40b) with this structure can improve the bonding force to the body 10 by utilizing the base conductor 41, and can improve the solder wettability by utilizing the plated conductor 42 when the multilayer ceramic capacitor 100 is mounted on the circuit board B.

[0086] Ni can be used as the material for the substrate conductor 41. The thickness of the substrate conductor 41 can be 0.1 μm or more and 10 μm or less, preferably 0.5 μm or more and 5 μm or less.

[0087] The plated conductor 42 can be formed from a single layer or from multiple layers. When the plated conductor 42 is formed from multiple layers, the number of layers is preferably two or more and four or less. Examples of materials and structures for the plated conductor 42 include those formed sequentially with Cu, Ni, and Sn. The thickness of the plated conductor 42 can be 1 μm or more and 20 μm or less, preferably 3 μm or more and 10 μm or less.

[0088] The area of ​​the terminal electrodes 40 (40a, 40b), that is, the area of ​​the terminal electrodes 40 (40a, 40b) as observed when viewing the multilayer ceramic capacitor 100 from a direction perpendicular to the mounting surface 11, is not particularly limited, as long as it is large enough to facilitate mounting to the circuit board B and small enough to prevent short circuits between electrodes of different polarities. Preferably, the ratio of the total area of ​​the terminal electrodes 40 to the area of ​​the mounting surface 11 is 0.2 or more and 0.9 or less, more preferably 0.3 or more and 0.8 or less.

[0089] <Second Implementation Method>

[0090] In another embodiment (second embodiment) of the multilayer ceramic capacitor of the first aspect of the present invention, the internal electrodes are electrically connected to each other through external conductors. Figure 6The image shows an example of a multilayer ceramic capacitor 200 according to the second embodiment. In the multilayer ceramic capacitor 200, the internal electrodes 22 (22a, 22b) leading to the lead surface 13 of the main body 10 are electrically connected to each other via external conductors 50 (50a, 50b), and the external conductors 50 (50a, 50b) are electrically connected to the terminal electrodes 40 (40a, 40b) disposed on the mounting surface 11. Furthermore, in the multilayer ceramic capacitor 200, the external conductors 50 (50a, 50b) are formed on a pair of opposing end faces, but the multilayer ceramic capacitor of the third embodiment may also have a structure in which the external conductors are formed on only one end face, or it may have a structure in which the external conductors are formed on the lead surface 13 without wrapping around the opposing surface 12.

[0091] Regarding the multilayer ceramic capacitor 200, the porosity P of the edge portion 32 or the cover portion 31 is determined. i and P o In the case of a certain value, the step of determining the porosity of the edge portion 32 described above, or the step of replacing the edge portion 32 with the covering portion 31 in that step, is adopted.

[0092] <Third Implementation Method>

[0093] In another embodiment (third embodiment) of the multilayer ceramic capacitor of the first aspect of the present invention, the number of terminal electrodes disposed on the mounting surface is four or more. Figure 7 The image shows an example of a multilayer ceramic capacitor 300 according to the third embodiment. Furthermore, in the multilayer ceramic capacitor 300, the number of terminal electrodes 40 disposed on the mounting surface 11 is four, but the number of terminal electrodes disposed on the mounting surface 11 is not limited to this. The multilayer ceramic capacitor 300 can suppress the amount of current flowing through the through-hole conductors 23 (23a, 23b) electrically connected to each terminal electrode 40 (40a, 40b), thus having the advantage of reducing resistive heating. Furthermore, when the polarities of the closest terminal electrodes 40 (40a, 40b) within the mounting surface 11 are different, the direction of the current flowing in the through-hole conductors 23 (23a, 23b) electrically connected to each terminal electrode 40 (40a, 40b) is opposite among the closest through-hole conductors 23 (23a, 23b), thus also having the advantage of being able to mutually cancel the magnetic field generated by the current and reduce the equivalent series inductance (ESL). When the spacing (L-direction dimension) of one set of two sets of surfaces of the multilayer ceramic capacitor 400 that are parallel to and opposite to each other in the stacking direction of the multilayer body is set to Lμm, and the spacing (W-direction dimension) of the other set is set to Wμm (where L≥W), the above-mentioned ESL reduction effect becomes significant when the ratio of W to L, i.e. W / L, is 0.8 or more and 1 or less, i.e. when the mounting surface 11 has a nearly square shape.

[0094] [Manufacturing method of multilayer ceramic capacitors]

[0095] The multilayer ceramic capacitors 100, 200, and 300 of the first aspect of the present invention can be manufactured by the steps described below.

[0096] ((A) Preparation of ceramic powder)

[0097] First, prepare the ceramic powder. Commercially available ceramic powder can be used appropriately. When making your own ceramic powder, simply mix various raw material powders containing its constituent elements in a prescribed ratio and then perform a pre-firing process. When mixing the various raw material powders in the prescribed ratio, you can also add the aforementioned additives, sintering aids, and other additives. These additives can also be added to the pre-fired powder.

[0098] ((B) Production of raw film)

[0099] Next, the ceramic powder is mixed with a binder and a dispersion medium to prepare a slurry, which is then shaped into sheets to obtain a green sheet.

[0100] As a binder, an binder is used that can maintain the shape of the green sheet and is not volatilized due to residual carbon or other substances after binder removal treatment before firing. Examples of binders that can be used include polyvinyl alcohol, polyvinyl butyral, cellulose, carbamate, and vinyl acetate binders. There is no particular limitation on the amount of binder used, but since it is a substance to be removed in subsequent processes, it is preferable to minimize its use while still achieving the desired formability / shape retention, thus reducing raw material costs.

[0101] The dispersion medium used is one that does not cause agglomeration of the pre-burned powder and binder, and can be easily removed by evaporation or the like after the green sheet is formed (described later). Examples of dispersion media that can be used include water and alcohol solvents.

[0102] Dispersants, plasticizers, and thickeners can be added to the slurry to adjust its properties.

[0103] The method of mixing the above-mentioned powder with the binder and dispersion medium is not particularly limited as long as it can prevent the introduction of impurities and uniformly mix the components. As an example, ball milling can be used for mixing.

[0104] As a method for forming the prepared slurry into sheets to obtain green sheets, conventional methods such as the doctor blade method and the die coating method can be used.

[0105] (C) Formation of internal electrode patterns)

[0106] Next, an internal electrode pattern containing metal is formed on the green sheet. The internal electrode pattern can be formed by printing or coating an internal electrode paste in a prescribed pattern, or by vapor deposition or sputtering to form a metal film in a prescribed pattern. The internal electrode pattern is formed with sufficient margin to ensure electrical insulation from the via conductor pattern that does not contact it in the subsequently formed via conductor pattern.

[0107] When using an internal electrode paste to form an internal electrode pattern, the internal electrode paste is obtained by mixing metal particles and a carrier using a three-roll mill. In addition to the components mentioned above, the internal electrode paste may also contain glass powder or ceramic powder.

[0108] There are no restrictions on the types and amounts of adhesives and solvents contained in the carrier used, as long as the viscosity of the paste used for the internal electrodes, ease of processing, and compatibility with the green sheet are considered and appropriate selections are made.

[0109] The printing of internal electrodes onto the green sheet using paste can be carried out, for example, using a screen mask with a predetermined internal electrode pattern. During printing, the space that would become the edge portion when forming the multilayer ceramic capacitor can also be separated. In this case, to ensure that the edge portion to be formed satisfies the above-described relationship (1), the green sheet can be made of a green sheet with a lower proportion of ceramic powder at the position corresponding to the surface portion of the edge portion than at the position corresponding to the inner side portion of the edge portion.

[0110] (D) Fabrication of green laminates)

[0111] Next, a predetermined number of green sheets with internal electrode patterns are stacked together and pressed together to obtain a green laminate. The stacking and pressing can be performed using conventional methods, such as heating the stacked green sheets while pressing them in the stacking direction, or hot pressing with an adhesive.

[0112] In order to manufacture a multilayer ceramic capacitor in which at least a portion of the cover portion 31 satisfies the above-mentioned relation (1), a green sheet with a region having a lower proportion of ceramic powder than a green sheet with an internal electrode pattern may be added at the end in the stacking direction during stacking and pressing.

[0113] (E) Formation of through-hole conductor pattern)

[0114] In manufacturing the multilayer ceramic capacitor 100 of the first embodiment, holes are then formed in the green laminate, and conductive paste is filled into these holes to form a through-hole conductor pattern. Hole formation can be achieved using conventional methods such as drilling or laser processing. Laser processing is preferred for creating a smooth surface. The filling of the holes with conductive paste can be achieved using conventional methods such as injection with a syringe or printing with a metal mask. Printing with a metal mask is preferred for excellent filling performance of small-diameter holes. The conductive paste can be composed of the same components as the internal electrode paste described above; the proportions of each component are determined considering the hole filling performance.

[0115] (F) Formation of terminal electrode pattern)

[0116] Next, a terminal electrode pattern is formed on at least one side (mounting surface 11) of the green laminate perpendicular to the lamination direction. Alternatively, a green sheet can be pressed into the cover portion 31 on the side where the terminal electrode pattern is not formed, covering the through-hole conductor pattern, when the laminated ceramic capacitor is completed. By having the pressed green sheet have a region with a lower proportion of ceramic powder compared to the green sheet with the internal electrode pattern, a laminated ceramic capacitor in which at least a portion of the cover portion satisfies the above-described relation (1) can be obtained. Furthermore, by selectively reducing the proportion of ceramic powder in the pressed green sheet at the location where the through-hole conductor pattern is formed, a laminated ceramic capacitor in which the cover portion also satisfies the above-described relation (2) can be obtained. The terminal electrode pattern can be formed by printing or applying a terminal electrode paste, or by forming a metal film using vapor deposition or sputtering. Alternatively, the terminal electrode pattern can be formed using a mask with a predetermined pattern, or by first forming a paste film or metal film on the entire mounting surface of the green laminate, and then removing the portion other than the terminal electrode pattern. When removing the portion other than the terminal electrode pattern, a face mill or tumbler grinding method can be used. In removing the portion other than the terminal electrode pattern, a portion of the surface of the green laminate is also removed, thereby forming a recess at the position corresponding to the intersection with the mounting surface side. When using a terminal electrode paste to form the terminal electrode pattern, the same paste as the internal electrode paste described above can be used, and the mixing amount of each component can be determined in a way that allows for a uniform pattern to be obtained at a specified thickness.

[0117] (G) Preparation of small pieces before firing)

[0118] Next, the green laminate is divided into individual ceramic capacitor pieces to obtain pre-firing pieces. This single-piece division can be performed using conventional methods such as a cutting saw or a laser cutting machine. Alternatively, after the green laminate is single-pieced to form the surface with exposed internal electrode precursors, the surface can be covered with an edge-forming material to obtain a pre-firing piece. In this case, by using an edge-forming material with a lower proportion of ceramic powder compared to the green piece with the internal electrode pattern, it is possible to obtain a ceramic capacitor whose edge portion satisfies the above-described relationship (1).

[0119] (H) Removal of adhesive)

[0120] Next, the resulting pre-firing pieces are heated to evaporate and remove the binder. The heating conditions can be appropriately set by taking into account the evaporation temperature and content of the binder. As an example, it can be carried out in a nitrogen (N2) atmosphere at a temperature of 200°C to 500°C for 5 to 20 hours.

[0121] (I) Firing of small pieces before firing)

[0122] Next, the pre-firing pieces, with the binder removed, are heated to a predetermined temperature for firing. When setting the firing conditions, the sinterability of the ceramic powder, as well as the heat resistance and oxidation resistance of the metals contained in the internal electrode pattern, through-hole conductor pattern, and terminal electrode pattern, are preferably considered. Examples of firing conditions include holding the firing at 1100°C to 1400°C for 10 minutes to 2 hours in a reducing atmosphere containing a mixture of nitrogen (N2), hydrogen (H2), and water vapor (H2O). After firing, a re-oxidation treatment can be performed at 600°C to 1000°C in a nitrogen (N2) atmosphere or a low-oxygen atmosphere.

[0123] ((J) Formation of external conductors and terminal electrodes)

[0124] In manufacturing the multilayer ceramic capacitor 200 of the second embodiment, step (E) is omitted, and step (I) is then performed to form the external conductor; alternatively, steps (E) and (F) are omitted, and step (I) is then performed to form the external conductor and terminal electrodes. Examples of methods for forming the external conductor and terminal electrodes include methods such as sintering after attaching a conductive paste by printing or impregnation, and forming a metal film by physical vapor deposition (PVD) methods such as vapor deposition.

[0125] The sintered body obtained in this way can be used as a multilayer ceramic capacitor 100, 200, or 300 as is, or it can be used as a multilayer ceramic capacitor after a conductive layer is formed on the surface of the terminal electrode pattern by plating.

[0126] [Circuit Board]

[0127] The circuit board B of the second aspect of the present invention is equipped with the multilayer ceramic capacitors 100, 200, and 300 of the first aspect. The circuit board B exhibits excellent durability and reliability due to the improved surface toughness of the main body 10 of the multilayer ceramic capacitors 100, 200, and 300.

[0128] According to the present invention, a multilayer ceramic capacitor with improved toughness of its body surface and a circuit board mounted thereon can be provided. Therefore, the present invention is useful in providing a circuit board with excellent durability and reliability.

Claims

1. A multilayer ceramic capacitor, characterized in that, include: The main body is rectangular and has a stack of ceramic layers and internal electrodes with metal as the main component, which are alternately stacked. A pair of covering portions disposed at both ends of the stacking direction of the laminate and covering the surface of the laminate; and an edge portion covering at least a portion of the end of the ceramic layer and the end of the internal electrode in the laminate and connecting the pair of covering portions to each other; and A plurality of terminal electrodes electrically connected to the internal electrodes are spaced apart from each other and arranged on at least one mounting surface of each surface forming the body. The mounting surface is the surface opposite to the circuit board that is being mounted. Regarding at least a portion of the covered portion or the edge portion, the porosity of the surface portion is set to P. o The porosity of the inner portion located closer to the laminate than the surface layer is set as P. i When the following relation (1) is satisfied: P i <P o ……(1)。 2. The multilayer ceramic capacitor according to claim 1, characterized in that: The terminal electrode or any conductor electrically connected to it is not disposed on the opposite surface of the main body; the opposite surface is the surface opposite to the mounting surface. The covering portion or the edge portion forming the opposite surface as a whole satisfies the relation (1).

3. The multilayer ceramic capacitor according to claim 1, characterized in that: The main body also has multiple through-hole conductors. The through-hole conductor is disposed through the ceramic layer in the stacking direction of the laminate, is electrically connected to the internal electrode, and one end reaches the surface of one of the pair of covers and is electrically connected to the terminal electrode, while the other end is covered by the other of the pair of covers.

4. The multilayer ceramic capacitor according to claim 3, characterized in that: At least a portion of the covering portion covering the end of the through-hole conductor satisfies the relationship (1), and, In the surface layer of the cover portion, when viewed from the stacking direction of the laminate, the porosity P of the surface layer located at the through-hole is... ov The following relation (2) must be satisfied: P o <P ov ……(2), The through-hole surface layer is the area in the cover that overlaps with the through-hole conductor.

5. The multilayer ceramic capacitor according to claim 4, characterized in that: Regarding the through-hole surface portion, when dividing a cross section parallel to the stacking direction of the laminate using square cells with one side of 1 μm, the percentage of cells with gaps relative to the total number of cells is 10% or more.

6. The multilayer ceramic capacitor according to claim 1, characterized in that: The number of terminal electrodes is 4 or more.

7. The multilayer ceramic capacitor according to claim 6, characterized in that: The polarity of each terminal electrode is different from the polarity of the other terminal electrodes that are closest to it within the mounting surface.

8. A circuit board, characterized in that: The device is equipped with a multilayer ceramic capacitor as described in any one of claims 1 to 7.

Images