Patent Publication Number: US-11031180-B2

Title: Multi-layer ceramic electronic component and method of producing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. § 119 of Japanese Application No. 2017-237062 filed Dec. 11, 2017, which is hereby incorporated in its entirety. 
     BACKGROUND 
     The present disclosure relates to a multi-layer ceramic electronic component including side margins provided in a subsequent step, and to a method of producing the multi-layer ceramic electronic component. 
     In recent years, along with miniaturization of electronic devices and achievement of high performance thereof, there have been increasingly strong demands for miniaturization and increase in capacitance with respect to multi-layer ceramic capacitors used in the electronic devices. In order to meet those demands, it is effective to enlarge internal electrodes of the multi-layer ceramic capacitor. In order to enlarge the internal electrodes, it is necessary to thin side margins for ensuring insulation properties of the periphery of the internal electrodes. 
     Meanwhile, in a general method of producing a multi-layer ceramic capacitor, it is difficult to form side margins having a uniform thickness because of precision in each step (e.g., patterning of internal electrodes, cutting of a multi-layer sheet, etc.). Therefore, in such a method of producing a multi-layer ceramic capacitor, as the side margins are made thinner, it is more difficult to ensure insulation properties of the periphery of the internal electrodes. 
     Japanese Patent Application Laid-open No. 2012-209539 discloses a technique of providing side margins in a subsequent step. In other words, in this technique, a multi-layer sheet is cut to produce a multi-layer unit whose internal electrodes are exposed from the side surfaces of the multi-layer unit, and side margins are provided to the side surfaces. This enables side margins having a uniform thickness to be formed and thus enables insulation properties of the periphery of the internal electrodes to be ensured also when the side margins are made thin. 
     SUMMARY 
     In the multi-layer ceramic capacitor including the side margins provided in a subsequent step, moisture is likely to infiltrate along a gap between the side surface of the multi-layer unit and the side margin. Further, as the side margin is made thinner, moisture is more likely to pass through the side margin in the thickness direction thereof and reach the side surface of the multi-layer unit. This makes it difficult to ensure insulation properties between the internal electrodes, which are exposed from the side surfaces of the multi-layer unit, in the multi-layer ceramic capacitor. 
     In view of the circumstances as described above, it is desirable to provide a multi-layer ceramic electronic component having optimal moisture resistance and a method of producing the multi-layer ceramic electronic component. 
     According to an embodiment of the present disclosure, there is provided a multi-layer ceramic electronic component including a multi-layer unit and a side margin. 
     The multi-layer unit includes ceramic layers laminated in a first direction, internal electrodes disposed between the ceramic layers, a main surface that faces in the first direction, and a side surface that faces in a second direction orthogonal to the first direction, the internal electrodes being exposed from the side surface. 
     The side margin includes a side-surface-covering portion that is disposed on the side surface, and an end portion that extends from the side-surface-covering portion to an upper side of the main surface, the end portion having a lower porosity than a porosity of the side-surface-covering portion, the end portion being rounded. 
     In this configuration, since the end portion of the side margin extends to the upper side of the main surface of the multi-layer unit, a path through which moisture infiltrates between the multi-layer unit and the side margin and reaches a region where the internal electrodes are disposed in the side surface of the multi-layer unit becomes long. This provides high moisture resistance to the multi-layer ceramic electronic component. 
     Further, since the end portion of the side margin has a low porosity, moisture is less likely to infiltrate into the end portion. Accordingly, the end portion of the side margin can inhibit moisture from passing therethrough even though the end portion is rounded and thus thinner than the side-surface-covering portion. This provides much higher moisture resistance to the multi-layer ceramic electronic component. 
     The end portion may have a porosity of 5% or less. 
     The side-surface-covering portion may have a thickness of 10 μm or more and may have a porosity of 10% or less. 
     In those configurations, the moisture resistance of the multi-layer ceramic electronic component can be further improved. 
     According to an embodiment of the present disclosure, there is provided a method of producing a multi-layer ceramic electronic component, the method including: producing a multi-layer unit including ceramic layers laminated in a first direction, internal electrodes disposed between the ceramic layers, and a side surface that faces in a second direction orthogonal to the first direction, the internal electrodes being exposed from the side surface; disposing a ceramic sheet on a base member, the base member having a Young&#39;s modulus of 10 kPa or more and 20 MPa or less, the Young&#39;s modulus being measured by a method conforming to JIS K 6251; and punching the ceramic sheet on the base member by the side surface of the multi-layer unit. 
     The base member may be made of a silicone-based elastomer. 
     This configuration can produce a multi-layer ceramic electronic component having optimal moisture resistance as described above. 
     It is possible to provide a multi-layer ceramic electronic component having optimal moisture resistance and a method of producing the multi-layer ceramic electronic component. 
     These and other objects, features and advantages of the present disclosure will become more apparent in light of the following detailed description of embodiments thereof, as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a multi-layer ceramic capacitor according to an embodiment of the present disclosure; 
         FIG. 2  is a cross-sectional view of the multi-layer ceramic capacitor taken along the A-A′ line in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the multi-layer ceramic capacitor taken along the B-B′ line in  FIG. 1 ; 
         FIG. 4  is a partially enlarged cross-sectional view of a region V 1  of the multi-layer ceramic capacitor shown in  FIG. 3 ; 
         FIG. 5  is a flowchart showing a method of producing the multi-layer ceramic capacitor; 
         FIG. 6  is a perspective view of an unsintered multi-layer unit produced in Step S 01  of the production method described above; 
         FIG. 7  is a cross-sectional view schematically showing Step S 02  of the production method described above; 
         FIG. 8  is a cross-sectional view schematically showing Step S 02  of the production method described above; 
         FIG. 9  is a partially enlarged cross-sectional view of a region V 2  of  FIG. 8 ; and 
         FIG. 10  is a cross-sectional view schematically showing Step S 02  of the production method described above. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present disclosure will be described with reference to the figures. 
     In the figures, an X axis, a Y axis, and a Z axis orthogonal to one another are shown as appropriate. The X axis, the Y axis, and the Z axis are common in all figures. 
     1. Overall Configuration of Multi-Layer Ceramic Capacitor  10   
       FIGS. 1 to 3  each show a multi-layer ceramic capacitor  10  according to an embodiment of the present disclosure.  FIG. 1  is a perspective view of the multi-layer ceramic capacitor  10 .  FIG. 2  is a cross-sectional view of the multi-layer ceramic capacitor  10  taken along the A-A′ line in  FIG. 1 .  FIG. 3  is a cross-sectional view of the multi-layer ceramic capacitor  10  taken along the B-B′ line in  FIG. 1 . 
     The multi-layer ceramic capacitor  10  includes a ceramic body  11 , a first external electrode  14 , and a second external electrode  15 . Typically, the ceramic body  11  is formed as a hexahedron having two main surfaces facing in the Z-axis direction, two side surfaces facing in the Y-axis direction, and two end surfaces facing in the X-axis direction. 
     The first external electrode  14  and the second external electrode  15  cover the end surfaces of the ceramic body  11  and face each other in the X-axis direction while sandwiching the ceramic body  11  therebetween. The first external electrode  14  and the second external electrode  15  extend to the main surfaces and the side surfaces from the end surfaces of the ceramic body  11 . With this configuration, both of the first external electrode  14  and the second external electrode  15  have U-shaped cross sections parallel to the X-Z plane and the X-Y plane. 
     It should be noted that the shapes of the first external electrode  14  and the second external electrode  15  are not limited to those shown in  FIG. 1 . For example, the first external electrode  14  and the second external electrode  15  may extend to one of the main surfaces from the end surfaces of the ceramic body  11  and have L-shaped cross sections parallel to the X-Z plane. Further, the first external electrode  14  and the second external electrode  15  may not extend to any of the main surfaces and the side surfaces. 
     The first and second external electrodes  14  and  15  are each formed of a good conductor of electricity. Examples of the good conductor of electricity forming the first and second external electrodes  14  and  15  include a metal or alloy mainly containing copper (Cu), nickel (Ni), tin (Sn), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), or the like. 
     The ceramic body  11  is formed of dielectric ceramics and includes a multi-layer unit  16  and side margins  17 . The multi-layer unit  16  has two main surfaces M facing in the Z-axis direction and two side surfaces S facing in the Y-axis direction. The side margins  17  cover the two side surfaces S of the multi-layer unit  16 . 
     The multi-layer unit  16  has a configuration in which a plurality of flat plate-like ceramic layers extending along the X-Y plane are laminated in the Z-axis direction. The multi-layer unit  16  includes a capacitance forming unit  18  and covers  19 . The covers  19  cover the capacitance forming unit  18  vertically in the Z-axis direction and constitute the two main surfaces M of the multi-layer unit  16 . 
     The capacitance forming unit  18  includes a plurality of first internal electrodes  12  and a plurality of second internal electrodes  13  that are disposed between the plurality of ceramic layers. The first and second internal electrodes  12  and  13  each have a sheet-like shape extending along the X-Y plane. The first and second internal electrodes  12  and  13  are alternately disposed along the Z-axis direction. In other words, the first internal electrode  12  and the second internal electrode  13  face each other in the Z-axis direction while sandwiching the ceramic layer therebetween. 
     The first and second internal electrodes  12  and  13  are formed over the entire width of the capacitance forming unit  18  in the Y-axis direction and are exposed from both the side surfaces S of the multi-layer unit  16 . In the ceramic body  11 , the side margins  17  that cover both the side surfaces S of the multi-layer unit  16  ensure insulation properties between the first internal electrodes  12  and the second internal electrodes  13 , which are adjacent to each other, in both the side surfaces S of the multi-layer unit  16 . 
     The first internal electrodes  12  are drawn to one of the end portions of the ceramic body  11 . The second internal electrodes  13  are drawn to the other end portion of the ceramic body  11 . With this configuration, the first internal electrodes  12  are connected to only the first external electrode  14 , and the second internal electrodes  13  are connected to only the second external electrode  15 . 
     With such a configuration, when a voltage is applied between the first external electrode  14  and the second external electrode  15  in the multi-layer ceramic capacitor  10 , the voltage is applied to the plurality of ceramic layers between the first internal electrodes  12  and the second internal electrodes  13 . Thus, the multi-layer ceramic capacitor  10  stores charge corresponding to the voltage applied between the first external electrode  14  and the second external electrode  15 . 
     In the ceramic body  11 , in order to increase capacitances of the ceramic layers provided between the first internal electrodes  12  and the second internal electrodes  13 , dielectric ceramics having a high dielectric constant is used. For the dielectric ceramics having a high dielectric constant, for example, a material having a Perovskite structure containing barium (Ba) and titanium (Ti), which is typified by barium titanate (BaTiO 3 ), is used. 
     It should be noted that the ceramic layer may be formed of a strontium titanate (SrTiO 3 ) based material, a calcium titanate (CaTiO 3 ) based material, a magnesium titanate (MgTiO 3 ) based material, a calcium zirconate (CaZrO 3 ) based material, a calcium zirconate titanate (Ca(Zr,Ti)O 3 ) based material, a barium zirconate (BaZrO 3 ) based material, a titanium oxide (TiO 2 ) based material, or the like. 
     The first and second internal electrodes  12  and  13  are each formed of a good conductor of electricity. Examples of the good conductor of electricity forming the first and second internal electrodes  12  and  13  typically include nickel (Ni), and other than nickel (Ni), include a metal or alloy mainly containing copper (Cu), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), or the like. 
     It should be noted that the multi-layer ceramic capacitor  10  according to this embodiment only needs to include the multi-layer unit  16  and the side margins  17 , and other configurations of the multi-layer ceramic capacitor  10  can be changed as appropriate. For example, the number of first and second internal electrodes  12  and  13  can be determined as appropriate according to the size and performance expected for the multi-layer ceramic capacitor  10 . 
     2. Detailed Configuration of Side Margin  17   
     As shown in  FIG. 3 , each of the side margins  17  includes a side-surface-covering portion  17   a  disposed at the center thereof in the Z-axis direction and end portions  17   b  disposed at both end portions thereof in the Z-axis direction. The side-surface-covering portion  17   a  is formed as a flat portion, which is formed to have a flat plate-like shape and has a substantially uniform thickness in the Y-axis direction. The end portions  17   b  extend outward in the Z-axis direction from the side-surface-covering portion  17   a  and slightly climb on the main surfaces M from the side surface S of the multi-layer unit  16 . 
       FIG. 4  is a partially enlarged cross-sectional view of a region V 1  of the multi-layer ceramic capacitor  10 , which is surrounded by a chain line of  FIG. 3 . In other words,  FIG. 4  shows the vicinity of an end portion  17   b  of the side margin  17 , which is shown in the upper right of  FIG. 3 . It should be noted that the other three end portions  17   b  of the side margins  17  are also configured to be similar to the end portion  17   b  shown in  FIG. 4 . 
     The boundary between the side-surface-covering portion  17   a  and the end portion  17   b  of the side margin  17  in the Z-axis direction corresponds to the boundary between the capacitance forming unit  18  and the cover  19 . In other words, the end portion  17   b  is defined as an outward region in the Z-axis direction relative to the outermost layer of the first and second internal electrodes  12  and  13  in the Z-axis direction. The end portion  17   b  shown in  FIG. 4  is disposed on the upper side in the Z-axis direction of the first internal electrode  12 , which is uppermost in the Z-axis direction. 
     The end portion  17   b  of the side margin  17  includes a curved portion  17   b   1  and an extended portion  17   b   2 . The curved portion  17   b   1  extends in the Z-axis direction from the side-surface-covering portion  17   a  to a ridge R connecting the side surface S and the main surface M of the multi-layer unit  16 . The extended portion  17   b   2  is continuous from the curved portion  17   b   1  and extends inward in the Y-axis direction from the ridge R of the multi-layer unit  16  along the main surface M of the multi-layer unit  16 . 
     In such a manner, the ridge R of the multi-layer unit  16  is covered with the end portion  17   b  of the side margin  17  and thus protected. Accordingly, in the ceramic body  11 , external impact is not directly applied to the ridge R of the multi-layer unit  16 . Therefore, in the ceramic body  11 , damages such as a crack generated from the ridge R of the multi-layer unit  16  can be inhibited from occurring. 
     Further, the curved portion  17   b   1  of the side margin  17  is rounded. In other words, the outer surface of the curved portion  17   b   1  is curved so as to protrude outward. Therefore, an external force is less likely to be locally applied to the ridge of the ceramic body  11 , which is formed by the end portion  17   b  of the side margin  17 . Accordingly, high impact resistance is obtained in the multi-layer ceramic capacitor  10 . 
     Furthermore, in the side margin  17 , the amount of dispersion of pores P of the end portion  17   b  is smaller than that of the side-surface-covering portion  17   a . In other words, in the side margin  17 , a porosity of the end portion  17   b  is lower than a porosity of the side-surface-covering portion  17   a . Here, the porosity is defined as a proportion of the areas of the pores P in an image where the cross section of the side margin  17  appears. 
     The porosity of the side-surface-covering portion  17   a  can be calculated in a region within a predetermined range extending in the Z-axis direction from the boundary with the end portion  17   b . The predetermined range of the side-surface-covering portion  17   a  can be set to, for example, three times as large as the dimension of the side-surface-covering portion  17   a  in the Y-axis direction at the boundary with the end portion  17   b . The porosity of the end portion  17   b  can be calculated in the entire region of the end portion  17   b.    
     With this configuration, moisture is less likely to infiltrate into the inside of the end portion  17   b . Therefore, as a distance from the side-surface-covering portion  17   a  increases, the end portion  17   b  has a smaller thickness, but the end portion  17   b  can inhibit moisture from passing therethrough in the Y-axis direction. This can provide high moisture resistance to the multi-layer ceramic capacitor  10 . 
     In the side margin  17 , it is favorable that the end portion  17   b  has a porosity of 5% or less. Further, it is more favorable that the thickness of the side-surface-covering portion  17   a  in the Y-axis direction is 10 μm or more and the side-surface-covering portion  17   a  has a porosity of 10% or less. With those configurations, the moisture resistance of the multi-layer ceramic capacitor  10  is further improved. 
     Further, in the side margin  17 , the end portion  17   b  seamlessly extends from the side surface S to the main surface M of the multi-layer unit  16 . In other words, a path through which moisture infiltrates between the multi-layer unit  16  and the side margin  17  and reaches the capacitance forming unit  18  is extended by the length of the extended portion  17   b   2  and is bent at the ridge R of the multi-layer unit  16 . 
     This makes it difficult for moisture to reach the capacitance forming unit  18  in the multi-layer ceramic capacitor  10 . In the side margin  17 , in order to effectively obtain the action of extending such a moisture infiltration path, it is favorable that the extended amount of the extended portion  17   b   2  inward in the Y-axis direction relative to the side surface S of the multi-layer unit  16  is set to 5 μm or more. 
     In such a manner, in the multi-layer ceramic capacitor  10 , the action of the end portion  17   b  of the side margin  17  makes it possible to suppress infiltration of moisture into a region where the capacitance forming unit  18  is disposed in the side surface S of the multi-layer unit  16 . Therefore, high moisture resistance can be obtained in the multi-layer ceramic capacitor  10 . 
     3. Method of Producing Multi-Layer Ceramic Capacitor  10   
       FIG. 5  is a flowchart showing a method of producing the multi-layer ceramic capacitor  10 .  FIGS. 6 to 10  are views each schematically showing a production process of the multi-layer ceramic capacitor  10 . Hereinafter, the method of producing the multi-layer ceramic capacitor  10  will be described according to  FIG. 5  with reference to  FIGS. 6 to 10  as appropriate. 
     3.1 Step S 01 : Production of Multi-Layer Unit 
     In Step S 01 , an unsintered multi-layer unit  16  shown in  FIG. 6  is produced. The multi-layer unit  16  includes a plurality of laminated unsintered dielectric green sheets on which the first and second internal electrodes  12  and  13  are patterned as appropriate. With this configuration, an unsintered capacitance forming unit  18  and unsintered covers  19  are formed in the multi-layer unit  16 . 
     3.2 Step S 02 : Formation of Side Margins 
     In Step S 02 , unsintered side margins  17  are provided to the side surfaces S of the multi-layer unit  16  produced in Step S 01 , to produce an unsintered ceramic body  11 . Hereinafter, description will be given on an example of a method of providing the unsintered side margins  17  to the side surfaces S of the multi-layer unit  16  in Step S 02 . 
     First, as shown in  FIG. 7 , a ceramic sheet  17   s  is disposed on a flat plate-like base member E, and one side surface S of the multi-layer unit  16 , the other side surface S of which is held with a tape T, is caused to face the ceramic sheet  17   s . The base member E is made of, for example, a soft material having a small Young&#39;s modulus, such as a silicone-based elastomer. 
     The ceramic sheet  17   s  is formed as a large-sized dielectric green sheet for forming the unsintered side margin  17 . The ceramic sheet  17   s  can be formed into a flat sheet having a uniform thickness by using, for example, a roll coater or a doctor blade. 
     Next, as shown in  FIG. 8 , the ceramic sheet  17   s  is pressed by the side surface S of the multi-layer unit  16 . The multi-layer unit  16  locally sinks deep into the base member E having a low Young&#39;s modulus together with the ceramic sheet  17   s . With this configuration, the portion of the ceramic sheet  17   s , which is sunk together with the multi-layer unit  16 , is cut off as a side margin  17 . 
       FIG. 9  is a partially enlarged cross-sectional view of a region V 2 , which is surrounded by a chain line of  FIG. 8 . The side-surface-covering portion  17   a  of the side margin  17  receives a pressing force substantially uniform in the Y-axis direction while being sandwiched between the side surface S of the multi-layer unit  16  and the base member E. Accordingly, in the side-surface-covering portion  17   a , the flat shape of the ceramic sheet  17   s  is maintained. 
     Meanwhile, the corner of the end portion  17   b  of the side margins  17  is removed and rounded by a pressing force applied from the base member E around the end portion  17   b . This leads to the formation of the curved portion  17   b   1 . Further, the end portion  17   b  is extended along the main surface M of the multi-layer unit  16  when being cut off from the ceramic sheet  17   s . This leads to the formation of the extended portion  17   b   2 . 
     In such a manner, in Step S 02 , plastic working is additionally performed on the curved portion  17   b   1  and the extended portion  17   b   2 . In the curved portion  17   b   1  and the extended portion  17   b   2 , voids gradually disappear in the course of plastic deformation, which progresses the densification. Accordingly, the curved portion  17   b   1  and the extended portion  17   b   2  that form the end portions  17   b  have a higher degree of compactness than that of the side-surface-covering portion  17   a.    
     The Young&#39;s modulus of the base member E is favorably 10 kPa or more and 20 MPa or less, and more favorably, 10 kPa or more and 1 MPa or less. With this configuration, a shear force applied to the ceramic sheet  17   s  along the ridge R of the multi-layer unit  16  is suppressed, and the curved portion  17   b   1  and the extended portion  17   b   2  can be optimally formed. 
     When the multi-layer unit  16  is moved upward in the Y-axis direction so as to separate from the base member E as shown in  FIG. 10 , only the part of the side margin  17 , which is attached to the side surface S of the multi-layer unit  16 , separates from the base member E. With this configuration, the side margin  17  is formed on one side surface S of the multi-layer unit  16 . 
     Subsequently, the orientation of the side surface S of the multi-layer unit  16  in the Y-axis direction is inverted by transferring the multi-layer unit  16  to a tape different from the tape T shown in  FIG. 10 . In the manner similar to the above, the side margin  17  is formed also on the side surface S on the other side of the multi-layer unit  16 , on which the side margin  17  is not formed. This provides an unsintered ceramic body  11 . 
     It should be noted that a method of forming the side margins  17  is not limited to the above method as long as the end portion  17   b  including the curved portion  17   b   1  and the extended portion  17   b   2  can be formed. For example, the side margins  17 , which are formed on the side surfaces S of the multi-layer unit  16  by an optional publicly known technique, may be subjected to ex-post plastic working to form the curved portion  17   b   1  and the extended portion  17   b   2 . 
     3.3 Step S 03 : Sintering 
     In Step S 03 , the unsintered ceramic body  11  obtained in Step S 02  is sintered to produce the ceramic body  11  of the multi-layer ceramic capacitor  10  shown in  FIGS. 1 to 3 . In the side margins  17  of the ceramic body  11 , the porosity of the end portions  17   b  having a higher degree of compactness is lower than the porosity of the side-surface-covering portion  17   a.    
     A sintering temperature in Step S 03  can be determined on the basis of a sintering temperature for the ceramic body  11 . For example, when a barium titanate (BaTiO 3 ) based material is used, the sintering temperature can be set to approximately 1,000 to 1,300° C. Further, sintering can be performed in a reduction atmosphere or a low-oxygen partial pressure atmosphere, for example. 
     3.4 Step S 04 : Formation of External Electrodes 
     In Step S 04 , the first external electrode  14  and the second external electrode  15  are formed on both the end portions of the ceramic body  11  in the X-axis direction obtained in Step S 03 , to produce the multi-layer ceramic capacitor  10  shown in  FIGS. 1 to 3 . A method of forming the first external electrode  14  and the second external electrode  15  in Step S 04  is optionally selectable from publicly known methods. 
     By the above steps, the multi-layer ceramic capacitor  10  is completed. In this production method, the side margins  17  are provided to the side surfaces S, from which the first and second internal electrodes  12  and  13  are exposed, of the multi-layer unit  16  in a subsequent step. Thus, the positions of the end portions of the first and second internal electrodes  12  and  13  in the Y-axis direction in the ceramic body  11  are aligned with one another along the Z-axis direction with variations of 0.5 μm or less. 
     4. Other Embodiments 
     While the embodiment of the present disclosure has been described, the present disclosure is not limited to the embodiment described above, and it should be appreciated that the present disclosure may be variously modified. 
     For example, in the embodiment described above, the multi-layer ceramic capacitor  10  has been described as an example of a multi-layer ceramic electronic component, but the present disclosure can be applied to general multi-layer ceramic electronic components. Examples of such multi-layer ceramic electronic components include a chip varistor, a chip thermistor, and a multi-layer inductor.