Multilayer ceramic electronic component and a method for manufacturing the same

In a method of manufacturing a multilayer ceramic electronic component, polishing is performed so that intersection lines extending from external surfaces of a green element body and interfaces between a green chip to be formed into a laminate portion and ceramic side surface layers are each located within a curved-surface formation range of a chamfer portion. Accordingly, since a green ceramic material is extended so as to fill the interfaces like so-called “putty”, and the adhesive strength between the green chip to be formed into the laminate portion and each of the ceramic side surface layers is increased.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayer ceramic electronic component and a method for manufacturing the same. In particular, the present invention relates to a multilayer ceramic electronic component in which a green ceramic material is provided after a laminating step to form side gap regions in association with internal electrodes of an element body and to a method for manufacturing the multilayer ceramic electronic component.

2. Description of the Related Art

In recent years, small portable electronic apparatuses, such as a cellular phone, a notebook personal computer, a digital camera, and a digital audio apparatus, have been increasingly in demand. Miniaturization of these portable electronic apparatuses is progressing, and at the same time, improvement in performance thereof is also progressing. Since many multilayer ceramic electronic components are mounted in these portable electronic apparatuses, improvement in performance is also required for the multilayer ceramic electronic components, and for example, an increase in capacity is required for multilayer ceramic capacitors. In response to this requirement, in the multilayer ceramic capacitor, a decrease in thickness of a ceramic layer has been carried out, and as a result, the number of ceramic layers to be laminated tends to be increased.

In general, a multilayer ceramic electronic component is manufactured in such a way that after internal electrode patterns are printed on ceramic green sheets to be formed into ceramic layers after firing, the ceramic green sheets are laminated to each other so as to shift the internal electrode patterns in a predetermined direction to form a mother block, and this mother block is cut into green chips each having a predetermined dimension.

In this manufacturing method, in order to prevent the internal electrode patterns from being exposed to side surfaces of the green chip caused by misalignment generated in a laminating and/or a cutting step, a margin of each side gap region between the side surface of the green chip and the side of the internal electrode pattern must be ensured. However, when miniaturization of the multilayer ceramic electronic component is performed, the ratio of the area of the side gap region to the area of the internal electrode is increased, and as a result, the capacity of the multilayer ceramic capacitor is inevitably decreased in an amount corresponding to the above increase in ratio.

In order to solve the above problem, Japanese Unexamined Patent Application Publication No. 6-349669 has disclosed that after a laminate is prepared in which two side ends of internal electrodes are exposed to side surfaces of the laminate, since ceramic green sheets are adhered to these side surfaces thereof to form side gap regions, miniaturization of a multilayer capacitor and an increase in capacity thereof can be achieved.

However, according to the technique disclosed in Japanese Unexamined Patent Application Publication No. 6-349669, the adhesive strength between the ceramic green sheet forming the side gap region and the green chip is not sufficient, and as the time passes by, the side gap region may be peeled off from a ceramic base body in some cases.

In addition, a problem similar to that described above may occur not only in multilayer ceramic capacitors but also in multilayer ceramic electronic components other than the multilayer ceramic capacitors.

SUMMARY OF THE INVENTION

Accordingly, preferred embodiments of the present invention provide a multilayer ceramic electronic component and a method of manufacturing thereof solve the problems described above.

According to a preferred embodiment of the present invention, a method for manufacturing a multilayer ceramic electronic component includes the steps of: forming an element body which includes a pair of principal surfaces facing each other, a pair of side surfaces facing each other, and a pair of end surfaces facing each other, rounded chamfer portions arranged along ridgelines between the side surfaces and the end surfaces, and a plurality of ceramic layers extending in a principal surface direction and laminated in a direction perpendicular or substantially perpendicular thereto and a plurality of pairs of internal electrodes which are arranged along interfaces between the ceramic layers, which have exposure ends each exposed to one of the pair of end surfaces, and which are not exposed to the side surfaces; and forming external electrodes at least on the pair of end surfaces of the element body so as to be electrically connected to the exposure ends of the internal electrodes.

The above step of forming an element body preferably includes the steps of preparing a green chip which includes parallel or substantially parallel side surfaces located inside and parallel or substantially parallel to the side surfaces of the element body and which has a laminate structure formed of a plurality of green ceramic layers and a plurality of pairs of green internal electrodes so that the green internal electrodes are exposed to the parallel or substantially parallel side surfaces; forming ceramic side surface layers on the parallel or substantially parallel side surfaces of the green chip to form the side surfaces of the element body by supplying a green ceramic material on the parallel or substantially parallel side surfaces of the green chip so as to cover the green internal electrodes exposed to the parallel or substantially parallel side surfaces; polishing the green chip provided with the ceramic side surface layers to obtain a green element body having chamfer portions; and firing the green element body.

In addition, according to preferred embodiments of the present invention, in order to solve the above technical problems, in the above polishing step, intersection lines each extending from the interface between the green chip and the ceramic side surface layer and an external surface of the green element body are formed so as to be located within respective curved-surface formation ranges of the chamfer portions.

In the manufacturing method according to a preferred embodiment of the present invention, in order to prepare the green chip, when a step forming a plurality of lines of internal electrode patterns each having a substantially belt shape on ceramic green sheets, a step of laminating the ceramic green sheets to form a mother block while the ceramic green sheets are shifted by predetermined intervals along a width direction perpendicular to a longitudinal direction in which the belt-shaped electrode patterns extend, and a step of cutting the mother block along imaginary cutting lines in the longitudinal direction and imaginary cutting lines in the width direction are performed, at least one green chip can be efficiently obtained.

In the above preferred embodiments, the belt-shaped internal electrode pattern includes one pair of sides linearly extending along the longitudinal direction, and the imaginary cutting line in the longitudinal direction may be located so as to equally divide the belt-shaped internal electrode pattern into two portions in the width direction.

In this case, when the belt-shaped internal electrode pattern includes hole portions in which no internal electrode pattern is formed, the hole portions are provided at the center or approximate center of the belt-shaped internal electrode pattern in the width direction with predetermined pitches along the longitudinal direction, and the imaginary cutting line in the longitudinal direction is located so as to equally divide the hole portion into two portions in the width direction, as for the shape of the internal electrode, the width of the exposure end of an extending portion can be decreased as compared with that of the other portions thereof when viewed in a width direction between the side surfaces.

In the preferred embodiments described above, the belt-shaped internal electrode pattern preferably includes one pair of zigzag sides extending along the longitudinal direction so as to be engaged with adjacent belt-shaped internal electrode patterns, a zigzag gap region extending in the longitudinal direction is formed between adjacent belt-shaped internal electrode patterns, and the imaginary cutting line in the longitudinal direction may be located so as to equally divide the gap region into two portions in the width direction.

According to another preferred embodiment of the present invention, a multilayer ceramic electronic component includes an element body which includes a pair of principal surfaces facing each other, a pair of side surfaces facing each other, and a pair of end surfaces facing each other, rounded chamfer portions arranged along ridgelines between the side surfaces and the end surfaces, and a plurality of ceramic layers extending in a principal surface direction and laminated in a direction perpendicular or substantially perpendicular thereto and a plurality of pairs of internal electrodes which are provided along interfaces between the ceramic layers, which include exposure ends each exposed to one of the pair of end surfaces, and which are not exposed to the side surfaces; and external electrodes provided at least on the pair of end surfaces of the element body so as to be electrically connected to the exposure ends of the internal electrodes.

The internal electrodes each include a facing portion including a pair of sides parallel or substantially parallel to the side surfaces and facing an adjacent internal electrode with at least one of the ceramic layers interposed therebetween and an extending portion extending from the facing portion to the end surface to define the exposure end at the end of the extending portion. The width of the exposure end of the extending portion is preferably smaller than that of the facing portion when viewed in a width direction between the side surfaces.

In addition, when a gap dimension from the side of the facing portion to the side surface of the element body is represented by Wg, the curvature radius of a curved surface of the chamfer portion is represented by Rd, and the distance from the side of the facing portion to the exposure end is represented by D, Wg<Rd and Rd<Wg+D are satisfied.

In the multilayer ceramic electronic component according to preferred embodiments of the present invention, 15 μm≦Wg and 55 μm≦Rd are preferably satisfied.

In the method for manufacturing a multilayer ceramic electronic component according to a preferred embodiment of the present invention, since polishing is performed so that the intersection line formed from the interface between the green chip and the ceramic side surface layer and the external surface of the green element body is located within the curved-surface formation range of the chamfer portion, the green ceramic material forming the green chip and/or the ceramic side surface layer is extended so as to fill the interface between the green chip and the ceramic side surface layer. Therefore, this green ceramic material functions as so-called “putty”, and as a result, the adhesive strength between the green chip and the ceramic side surface layer is increased, and peeling (gap peeling) between the green chip and the ceramic side surface layer is prevented.

In the multilayer ceramic electronic component according to a preferred embodiment of the present invention, Wg<Rd and Rd<Wg+D are preferably satisfied, that is, the exposure end of the extending portion does not extend to the curved-surface formation range of the chamfer portion. In the chamfer portion, since the thickness of an underlayer of the external electrode formed thereon is liable to be small, when the extending portion is exposed thereto, the moisture resistance is likely to be degraded. However, according to preferred embodiments of the present invention, the moisture resistance is prevented from being degraded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, for description of preferred embodiments of the present invention, as a multilayer ceramic electronic component, a multilayer ceramic capacitor will be described by way of example.

FIGS. 1 to 9are views illustrating a first preferred embodiment of the present invention.

First, as shown inFIGS. 1 to 5, a multilayer ceramic capacitor1includes an element body2. The element body2includes one pair of principal surfaces3and4facing each other, one pair of side surfaces5and6facing each other, and one pair of end surfaces7and8facing each other and has an approximately rectangular parallelepiped shape, for example.

As shown inFIGS. 2 and 5, the element body2includes a laminate portion12of a laminate structure including a plurality of ceramic layers9extending in the direction of the principal surfaces3and4and laminated in the direction perpendicular or substantially perpendicular to the principal surfaces3and4and a plurality of pairs of first and second internal electrodes10and11arranged along the interfaces between the ceramic layers9. In addition, as shown inFIG. 5, the element body2includes one pair of ceramic side surface layers13and14provided on the respective side surfaces of the laminate portion12so as to define the pair of side surfaces5and6described above. The ceramic side surface layers13and14preferably have the same thickness.

Although the details of the shapes of the internal electrodes10and11will be described later, the first internal electrode10includes an exposure end15exposed to the first end surface7, and the second internal electrode11includes an exposure end16exposed to the second end surface8. However, since the ceramic side surface layers13and14described above define side gap regions, the internal electrodes10and11are not exposed to the side surfaces5and6of the element body2.

Furthermore, the multilayer ceramic capacitor1includes external electrodes17and18provided at least on the pair of end surfaces7and8of the element body2so as to be electrically connected to the respective exposure ends15and16of the internal electrodes10and11.

In the element body2, rounded chamfer portions19are arranged along the ridgelines between the side surfaces5and6and the end surfaces7and8as shown inFIGS. 3 and 4; rounded chamfer portions20are arranged along the ridgelines between the principal surfaces3and4and the side surfaces5and6as shown inFIGS. 1 and 5; and furthermore, as shown inFIG. 2, rounded chamfer portions21are arranged along the ridgeline between the principal surfaces3and4and the end surfaces7and8.

As clearly shown inFIG. 3, the first internal electrode10includes a facing portion24including a pair of sides22and23parallel or substantially parallel to the side surfaces5and6and facing the second internal electrode11with at least one ceramic layer9interposed therebetween and an extending portion25extending from the facing portion24to the first end surface7to provide the exposure end15at the end of the extending portion. The exposure end15of the first internal electrode10exposed to the first end surface7is shown inFIG. 5.

In the plan shape of the first internal electrode10, when viewed in the width direction between the side surfaces5and6, the width of the exposure end15of the extending portion25is preferably smaller than the width of the facing portion24. In particular, in this preferred embodiment, the extending portion25has a width direction dimension which is gradually decreased toward the end surface7.

As in the case described above, the second internal electrode11shown by the dotted line inFIG. 3also includes a facing portion28including a pair of sides26and27parallel or substantially parallel to the side surfaces5and6and facing the first internal electrode10with at least one ceramic layer9interposed therebetween and an extending portion29extending from the facing portion28to the second end surface8to provide the exposure end16at the end of the extending portion. The second internal electrode11has a plan shape symmetrical to that of the first internal electrode10described above.

As described above, since the facing portion24of the first internal electrode10and the facing portion28of the second internal electrode11face each other with at least one ceramic layer9interposed therebetween, electrical properties are obtained between these facing portions24and28. That is, in the case of this multilayer ceramic capacitor1, an electrostatic capacity is formed.

The facing portion24of the first internal electrode10is substantially flat in the direction between the sides22and23. That is, the facing portion24does not get thin in the vicinities of the sides22and23and does not warp in the laminate direction. The facing portion28of the second internal electrode11is also provided as described above.

The extending portions25and29of the first and the second internal electrodes10and11are extended to the end surfaces7and8, respectively. At this stage, as shown inFIG. 4, when a gap dimension from the side22of the facing portion24to the side surface5of the element body2is represented by Wg, the curvature radius of the curved surface of the chamfer portion19is represented by Rd, and the distance from the side22of the facing portion24to the end of the exposure end15is represented by D, Rd<Wg+D is satisfied. That is, the exposure ends15and16each do not extend to a curved-surface formation range of the chamfer portion19. The reason for this is that since the thickness of an underlayer of the external electrode17provided on the chamfer portion19is decreased, when the extending portion25is exposed to this area, the moisture resistance may be degraded in some cases.

As an electrical conductive material for the internal electrodes10and11, for example, Ni, Cu, Ag, Pd, a Ag—Pd alloy, or Au may be used.

The thickness of each of the internal electrodes10and11is preferably about 0.3 μm to about 2.0 μm, for example. In addition, the extending portions25and29each may have a thickness larger than that of each of the facing portions24and28. Accordingly, the step of the laminate portion12, which is liable to be generated in association with the extending portions25and29, can be minimized.

As a ceramic material forming the ceramic layer9and the ceramic side surface layers13and14, for example, a dielectric ceramic containing BaTiO3, CaTiO3, SrTiO3, CaZrO3, or the like as a primary component can be used. Accessory components, such as a Mn compound, a Mg compound, a Si compound, a Co compound, a Ni compound, and a rare earth element compound, may be added to the dielectric ceramic, if needed.

The ceramic material forming the ceramic side surface layers13and14preferably includes at least the same primary component as that of the ceramic material forming the ceramic layer9. In this case, ceramic materials having the same composition are most preferably used for the ceramic layer9and the ceramic side surface layers13and14.

Incidentally, the present invention can also be applied to multilayer ceramic electronic components other than the multilayer ceramic capacitor. When the multilayer ceramic electronic component is, for example, a piezoelectric element, a piezoelectric ceramic, such as a PZT ceramic, is preferably used, and in the case of a thermistor, a semiconductor ceramic, such as a spinel ceramic, is preferably used.

Although the external electrodes17and18are preferably provided at least on the pair of end surfaces7and8, respectively, of the element body2as described above, in this preferred embodiment, the external electrodes are preferably arranged to extend from the end surfaces7and8to portions of the principal surfaces3and4and portions of the side surfaces5and6, respectively.

Although not shown in the figure, the external electrodes17and18each preferably include an underlayer and a plating layer provided thereon. As an electrical conductive material for the underlayer, for example, Cu, Ni, Ag, Pd, an Ag—Pd alloy, or Au may be used.

The underlayer may be formed by using a co-firing method in which an electrical conductive paste is applied on a green element body2and is then simultaneously fired therewith or a post-firing method in which an electrical conductive paste is applied on the fired element body2and is then baked. Alternatively, the underlayer may be formed by direct plating or may be formed by curing an electrical conductive resin containing a thermosetting resin.

In addition, when the conditions of the curvature radius of the curved surface of the chamfer portion19which will be described later are taken into consideration, in the specific case in which the underlayer is formed using an electrical conductive paste, a significant effect can be obtained by a preferred embodiment of the present invention.

The thickness of the underlayer is preferably about 10 μm to about 150 μm at the thickest position, for example.

As a metal forming the plating layer provided on the underlayer, for example, a metal selected from the group consisting of Cu, Ni, Sn, Pb, Au, Ag, Pd, Bi, and Zn or an alloy containing at least one of the aforementioned metals may be used. The plating layer may include a plurality of layers. When the plating layer includes a plurality of layers as described above, a two-layer structure of Ni plating and Sn plating provided thereon is preferable. In addition, the thickness of the plating layer is preferably about 1 μm to about 15 μm per layer, for example.

Between the underlayer and the plating layer, an electrical conductive resin layer for stress relaxation may also be provided.

As clearly shown inFIG. 4, the side22of the facing portion24of the internal electrode10is located on an interface30between the laminate portion12and the ceramic side surface layer13. As in the case described above, the side26of the facing portion28of the internal electrode11is located on the interface30between the laminate portion12and the ceramic side surface layer13. Therefore, the gap dimension Wg from each of the sides22and26of the facing portions24and28of the internal electrodes10and11, respectively, to the side surface of the element body2corresponds to the thickness of the ceramic side surface layer13.

In the relationship with the curvature radius Rd of the curved surface of the chamfer portion19, the gap dimension Wg is set so as to satisfy Wg<Rd. That is, since the curvature radius Rd is larger than the gap dimension Wg, an intersection line32extending from the interface30between the laminate portion12and the ceramic side surface layer13and the external surface of the element body2is located within the curved-surface formation range of the chamfer portion19.

Although not shown inFIG. 4, the same positional relationship as described above is also satisfied in each of the chamfer portions19located at an upper right, a lower left, and a lower right of the element body2shown inFIG. 3.

As described above, if Wg<Rd is satisfied, the ceramic side surface layers13and14can be sufficiently prevented from being peeled off from the laminate portion12.

In particular, the gap dimension Wg preferably satisfies 15 μm≦Wg. When Wg is about 15 μm or more, cracks generated in a gap portion can be more reliably prevented. In addition, in order to achieve miniaturization of the multilayer ceramic capacitor and an increase in capacity thereof, Wg≦35 μm is preferably satisfied.

The curvature radius Rd of the curved surface of the chamfer portion19preferably satisfies 55 μm≦Rd. When Rd is about 55 μm or more, cracks and/or chips can be more reliably prevented from being generated in the element body2. In addition, in order to more reliably prevent the thickness of the underlayer of each of the external electrodes17and18provided on the chamfer portions19from being locally decreased, Rd≦95 μm is preferably satisfied. As a result, the moisture resistance can be more reliably prevented from being degraded.

The distance D from the side22of the facing portion24to the end of the exposure end15preferably satisfies 90 μm≦D. Since moisture which may enter between the end of the external electrode17and the element body2is not likely to reach the exposure end15when D is about 90 μm or more, the moisture resistance can be more reliably prevented from being degraded.

When Wg, Rd, and D are measured from the multilayer ceramic capacitor1as a finished product, in a surface parallel or substantially parallel to the principal surfaces3and4which is obtained by cutting the element body2at approximately one-half height thereof, the curvature radiuses Rd at the four corner portions, the gap dimensions Wg in the two gap regions, and the distance D from the side of the facing portion of the internal electrode to the end of the exposure end may be measured. In addition, in the relationship between each corner portion and each gap region, it may be confirmed that Wg<Rd is satisfied, Rd<Wg+D is satisfied, each Rd satisfies 55 μm≦Rd, and each Wg satisfies 15 μm≦Wg.

Next, a method for manufacturing the multilayer ceramic capacitor1described above will be described with reference toFIGS. 6A to 9.

First, ceramic green sheets to be formed into the ceramic layers9, an electrical conductive paste for the internal electrodes10and11, ceramic green sheets for the ceramic side surface layers13and14, and an electrical conductive paste for the external electrodes17and18are prepared. Binders and solvents are contained in these ceramic green sheets and the electrical conductive pastes, and as these binders and solvents, known organic binders and organic solvents can be used, respectively.

Next, as shown inFIGS. 6A and 6B, the electrical conductive paste is printed on ceramic green sheets41, for example, by a screen printing method, to have predetermined patterns. Accordingly, the ceramic green sheets41on each of which internal electrode patterns42to be used as the internal electrodes10and11are formed are obtained.

According to this preferred embodiment, a plurality of lines of internal electrode patterns42each having a substantially belt shape is formed on each ceramic green sheet41. InFIGS. 6A and 6B, imaginary cutting lines43in a longitudinal direction (up and down direction inFIGS. 6A and 6B) in which the belt-shaped internal electrode patterns42extend and imaginary cutting lines44in a width direction (left and right direction inFIGS. 6A and 6B) perpendicular or substantially perpendicular thereto are shown. The belt-shaped internal electrode pattern42has a shape in which a plurality of sets each including the two internal electrodes10and11connected to each other at the respective extending portion25and29is arranged along the longitudinal direction.

The belt-shaped internal electrode pattern42includes one pair of sides45and46linearly extending along the longitudinal direction. In addition, in each belt-shaped internal electrode pattern42, rhombic hole portions47, in each of which no internal electrode pattern is formed, are arranged at the center in the width direction with predetermined pitches along the longitudinal direction. This structure is derived from the shapes of the extending portions25and29described above.

Next, a predetermined number of the ceramic green sheets41on which the internal electrode patterns42are formed as described above are laminated to each other in a predetermined order to form a laminate, and a predetermined number of ceramic green sheets for external layers on which no electrical conductive paste is printed are laminated on each of the top and the bottom of the above laminate, so that a mother block48, a portion of which is shown inFIG. 7, is formed.FIG. 7shows the state of the mother block48obtained by removing the ceramic green sheets for external layers provided on the ceramic green sheets41on which the internal electrode patterns42are formed.

In the laminating step described above, as shown inFIGS. 6A and 6B, the ceramic green sheets41are laminated to each other while being shifted by predetermined intervals, each of which is about half of the width direction dimension of the internal electrode pattern42, along the width direction of the belt-shaped internal electrode pattern42.

Next, the mother block48is pressed in the laminating direction by a method, such as hydrostatic pressure pressing, if needed.

Next, the mother block48is cut along the imaginary cutting lines43in the longitudinal direction and the imaginary cutting lines44in the width direction shown inFIGS. 6A and 6B, and a green chip49as shown inFIG. 8is obtained. As shown inFIG. 7, an area of the mother block48to be formed into the green chip49is surrounded by the dotted line.

As shown inFIGS. 6A,6B and7, one imaginary cutting line43in the longitudinal direction is located to equally divide the belt-shaped internal electrode pattern42into two portions in the width direction, that is, is located to equally divide the hole portion47into two portions in the width direction, and on the other hand, another imaginary cutting line in the longitudinal direction adjacent to the imaginary cutting line43is located so as to equally divide an area between the sides45and46of adjacent internal electrode patterns42into two portions in the width direction.

As shown inFIG. 8, the green chip49includes parallel or substantially parallel side surfaces50and51located inside and parallel to the side surfaces5and6of the element body2. These side surfaces50and51are formed from cut surfaces along the imaginary cutting lines44in the width direction described above. The green chip49corresponds to the laminate portion12at a green stage and has a laminate structure including a plurality of green ceramic layers9and a plurality of pairs of green internal electrodes10and11.

In general, as is the green chip49or the laminate portion12described above, in a laminate structure including ceramic layers and internal electrodes without side gap regions, the number of areas at which the ceramic layers are adhered to each other is decreased, and hence, delamination is liable to occur. In addition, the present inventors discovered that delamination is liable to occur particularly at a corner of the extending portion of the internal electrode (which is exposed to the corner portion of the green chip or the laminate portion after cutting) in the vicinity of each of the external layers (upper and lower ceramic layers on which the internal electrodes are not formed). The reason for this is estimated that a stress is liable to be concentrated when the mother block is cut to have a predetermined dimension, and a corner portion having a small adhesion area is liable to function as a starting point of delamination.

Hence, as in this preferred embodiment, when the widths of the exposure ends15and16are made smaller than the widths of the facing portions24and28, respectively, so that the corners of the extending portions25and29of the internal electrodes10and11are withdrawn inside, the above adverse influence can be significantly reduced and minimized, and as a result, the delamination can be prevented from being generated.

Furthermore, since margin regions generated at the two sides of the extending portions25and29are adhered to each other in the lamination direction, the delamination can also be prevented from being generated.

Next, as shown inFIG. 9, green ceramic side surface layers13and14defining the side surfaces5and6, respectively, of the element body2are formed on the side surfaces50and51of the green chip49, thereby forming the green element body2before polishing.

Hence, a green ceramic material is supplied on the parallel side surfaces50and51of the green chip49. For the supply of this green ceramic material, the above ceramic green sheets are used, and these ceramic green sheets are adhered on the side surfaces50and51of the green chip49. Alternatively, a ceramic paste may be applied on the side surfaces50and51of the green chip49, for example, by a printing method, such as a screen printing method, an ink jet method, a coating method, such as a gravure coating method, or a spray method. In the method for adhering ceramic green sheets among these supply methods described above, since a separate object is adhered to the green chip49, the adhesive strength is liable to decrease as compared with that obtained by the other methods; hence, the advantageous effects of preferred embodiments of the present invention can be particularly achieved. Since the ceramic side surface layers13and14are formed, the green internal electrodes10and11exposed to the side surfaces50and51are covered therewith.

Next, a polishing step is performed on the green element body2. As the polishing method, for example, barrel polishing may be used. The chamfer portions19to21described above are formed by this polishing method.

In this polishing step, the intersection line32extending from each of the interfaces of the green chip49and the ceramic side surface layers13and14(corresponding to each of the interfaces30and31of the laminate portion12and the ceramic side surface layers13and14, seeFIGS. 3 to 5) and each external surface of the green element body2is made to be located within the curved-surface formation range of the chamfer portion19. In other words, the dimension of the gap region formed by each of the green ceramic side surface layers13and14(corresponding to the gap dimension Wg) is preferably set smaller than the curvature radius Rd of the curved surface of the chamfer portion19.

When the polishing step is performed so as to satisfy the above conditions, since the green ceramic material of the green chip49and/or the ceramic side surface layers13and14is extended so as to fill the interfaces between the green chip49and the ceramic side surface layers13and14, this green ceramic material functions as so-called “putty”, and as a result, the adhesive strength between the green chip49and each of the ceramic side surface layers13and14is increased.

In this polishing step, as described above, the exposure ends15and16of the green internal electrodes10and11exposed to the end surfaces7and8of the green element body are each formed so as not to extend to the curved-surface formation range of the chamfer portion19.

Next, the green element body2is fired. Although depending on the ceramic material of the ceramic green sheet41and the ceramic side surface layers13and14and the metal material of the internal electrodes10and11, a firing temperature is preferably set, for example, in a range of about 900° C. to about 1,300° C.

Next, the underlayers of the external electrodes17and18are formed by applying an electrical conductive paste on the two ends surfaces7and8of the fired element body2, followed by baking. A baking temperature is preferably approximately about 700° C. to about 900° C., for example.

In addition, if needed, plating is performed on the surfaces of the underlayers of the external electrodes17and18, and the multilayer ceramic capacitor1shown inFIG. 1is completed.

In the first preferred embodiment described above, the shapes of the extending portions25and29of the internal electrodes10and11can be variously changed by changing the shape of the hole portion47.

Next, non-limiting experimental examples carried out in order to confirm the effect in the range of preferred embodiments of the present invention or in a more preferable range will be described.

According to the first preferred embodiment described above, a multilayer ceramic capacitor used as a sample was formed. In this example, the dimensions of the multilayer ceramic capacitor used as the sample were 2.0 mm×1.25 mm×1.25 mm. In addition, a width dimension of 1.25 mm was a target value when Wg was set to 30 μm, and when the value of Wg is changed, the width dimension is changed in an amount corresponding thereto. In addition, the ceramic layer was formed from a ceramic primarily composed of BaTiO3to have a thickness of 0.8 μm. The internal electrode was formed using Ni as an electrical conductive component to have a thickness to 0.5 μm, and the number of lamination layers was set to 900. In addition, in a reducing atmosphere, firing was performed at a highest temperature of 1,200° C. The exterior electrodes were each formed by performing Ni plating and Sn plating on a Cu-baked film.

The multilayer ceramic capacitors as described above were variously formed by variously changing the gap dimension Wg from the side of the facing portion of the internal electrode to the side surface of the element body, the curvature radius Rd of the curved surface of the chamfer portion, and the distance D from the side of the facing portion to the end of the exposure end as shown in Table 1.

In addition, by using the multilayer ceramic capacitors of the respective samples, as shown in Table 1, “gap peeling”, “moisture resistant defect”, “external layer peeling”, “gap crack”, and “chip and crack” were evaluated.

The presence of peeling at the gap portion was evaluated by observing the sample using a stereoscopic microscope at a magnification of 50 times, and as the “gap peeling”, the ratio of samples in which peeling occurred to 300 samples was obtained. As the stereoscopic microscope, SMZ645 manufactured by Nikon Corp. was used. The stereoscopic microscope was also used for other evaluations.

After a voltage of 4 V was applied to the sample for 1,000 hours under the environment of a temperature of 85° C. and a relative humidity of 85%, a sample having an insulating resistance of less than 0.13 MΩ was regarded as a defective, and the ratio of the defective samples to 100 samples was obtained as the “moisture resistance defect”. For the insulation resistance measurement, 4-Channel High Resistance Meter 4349B manufactured by Agilent was used.

The presence of peeling of the ceramic layer in the vicinity of the external layer was evaluated by observing the sample using a stereoscopic microscope at a magnification of 50 times, and the ratio of samples in which peeling occurred to 300 samples was obtained as the “external layer peeling”.

The “gap crack” is a defect that indicates breakage of the ceramic green sheet forming the ceramic side surface layers13and14and is generated in the surface in the form of a linear scratch or the like. This “gap crack” was evaluated by observing 300 samples using a stereoscopic microscope at a magnification of 50 times whether a crack was present at the gap portion or not.

The presence of chip and crack in the sample particularly at the corner portions thereof was observed using a stereoscopic microscope at a magnification of 50 times, and the ratio of samples in which chip and crack were generated to 300 samples was obtained as the “chip and crack”.

According to Samples 3 to 5, 12 to 14, 16 to 18, 20 to 22, and 24 to 26, the conditions, Wg<Rd, Rd<Wg+D, 15 μm≦Wg, and 55 μm≦Rd, were satisfied, and the defects, that is, the “gap peeling”, the “moisture resistance defect”, the “external layer peeling”, the “gap crack”, and the “chip and crack”, were not generated.

On the other hand, according to Samples 1 and 2, Rd≧Wg+D held, the “moisture resistance defect” was generated, and in particular, according to Sample 1, the “external layer peeling” was also generated.

According to Samples 6 to 10, Rd was less than 55 μm. Therefore, the “chip and crack” could not be completely prevented. Among Samples 6 to 10, although the “gap peeling” and the “moisture resistance defect” could be prevented in Samples 6 to 8 in which Wg<Rd was satisfied, according to Samples 9 and 10 in which Wg≧Rd held, the “gap peeling” and the “moisture resistance defect” could not be completely prevented.

According to Samples 11, 15, 19, 23, and 27 besides Sample 6 described above, since Wg was less than 15 μm, the “gap crack” could not be completely prevented.

Besides Samples 23 and 27 described above, according to Samples 28 and 29, since Rd≧Wg+D held, the “moisture resistance defect” could not be completely prevented.

Next, a second preferred embodiment of the present invention will be described with reference toFIGS. 10 to 12. Incidentally,FIG. 10corresponds toFIG. 3,FIGS. 11A and 11Bcorrespond toFIGS. 6A and 6B, andFIG. 12corresponds toFIG. 7. InFIGS. 10 to 12, elements corresponding to each other shown in the corresponding figures are designated by the same reference numerals, and a duplicate description will be omitted.

According to the second preferred embodiment, as shown inFIG. 10, the extending portions25and29of the internal electrodes10and11have widths smaller than those of the facing portions24and28and each extend by a predetermined width. In addition, the regions of the facing portions24and28extending to the extending portions25and29have widths which are gradually decreased so as to be equal to the widths of the extending portions25and29.

In order to obtain the internal electrodes10and11described above, ceramic green sheets61on each of which internal electrode patterns62as shown inFIGS. 11A and 11Bare formed are prepared. InFIGS. 11A and 11B, imaginary cutting lines63extending in the up and down direction and imaginary cutting lines64extending in the left and right direction perpendicular or substantially perpendicular thereto are shown. The internal electrode pattern62has a substantially network shape, and areas each to be formed into the facing portion24of the internal electrode10and areas each to be formed into the facing portion28of the internal electrode11are alternately connected to each other in the up and down direction.

In the network-shape internal electrode pattern62, longitudinal octagonal hole portions65, in each of which no internal electrode pattern is formed, are arranged in a staggered manner in the up and down direction. Between adjacent hole portions65arranged in the up and down direction, areas to be formed into the extending portions25and29are located.

In laminating the ceramic green sheets61described above, as shown inFIGS. 11A and 11B, the ceramic green sheets61are laminated to each other while being shifted along the left and right direction so as to shift the internal electrode patterns62with predetermined intervals, each of which is the space between the hole portions65in the left and right direction.

An enlarged mother block66obtained by the above lamination is partially shown inFIG. 12. The mother block66is cut along the imaginary cutting lines63and64shown inFIGS. 11A and 11B, and the green chip49as shown inFIG. 8is obtained. As shown inFIG. 12, the area of the mother block66to be formed into the green chip49is surrounded by the dotted line.

As shown inFIGS. 11A,11B and12, the imaginary cutting lines63extending in the up and down direction are located so as to equally divide the respective hole portions65into two portions in the left and right direction, and adjacent two imaginary cutting lines64in the left and right direction are located so as to intersect two positions of each hole portion65.

In the second preferred embodiment described above, the shapes of the extending portions25and29of the internal electrodes10and11and the shapes of the ends of the facing portions24and28extending therefrom can be variously changed by changing the shape of the hole portion65. For example, if the shape of the hole portion65is changed into a rectangle, the shapes of the internal electrodes10and11as shown in the following third preferred embodiment can be obtained.

Next, the third preferred embodiment of the present invention will be described with reference toFIG. 13. Incidentally,FIG. 13corresponds toFIG. 3. InFIG. 13, elements corresponding to the elements shown inFIG. 3are designated by the same reference numerals, and a duplicate description will be omitted.

According to the third preferred embodiment, as in the case of the second preferred embodiment, the extending portions25and29of the internal electrodes10and11have the widths smaller than those of the facing portions24and28and each extend with a predetermined width. However, the structure is not used in which the regions of the facing portions24and28extending to the extending portions25and29have the widths which are gradually decreased.

Next, a fourth preferred embodiment of the present invention will be described with reference toFIGS. 14 to 16. In addition,FIG. 14corresponds toFIG. 3,FIGS. 15A and 15Bcorrespond toFIGS. 6A and 6B, andFIG. 16corresponds toFIG. 7. InFIGS. 14 to 16, elements corresponding to each other shown in the corresponding figures are designated by the same reference numerals, and a duplicate description will be omitted.

According to the fourth preferred embodiment, as shown inFIG. 14, the exposure ends15and16of the internal electrodes10and11have widths smaller than those of the facing portions24and28, and the extending portions25and29have width direction dimensions which are gradually decreased toward the end surfaces7and8. Those described above are substantially the same as the case of the first preferred embodiment.

One of the unique features of the fourth preferred embodiment is that dummy electrodes69and70are exposed to the end surfaces8and7, respectively.

In order to obtain the internal electrodes10and11and the dummy electrodes69and70described above, ceramic green sheets71on each of which a plurality of lines of internal electrode patterns72each having a substantially belt shape as shown inFIGS. 15A and 15Bis formed are prepared. InFIGS. 15A and 15B, imaginary cutting lines73in a longitudinal direction (up and down direction inFIGS. 15A and 15B) in which the belt-shaped internal electrode patterns72extend and imaginary cutting lines74in a width direction (left and right direction inFIGS. 15A and 15B) perpendicular or substantially perpendicular thereto are shown. The belt-shaped internal electrode pattern72has the shape in which the facing portions24and28of the internal electrodes10and11are alternately connected to each other in the longitudinal direction.

The belt-shaped internal electrode pattern72includes a pair of zigzag sides75and76extending along the longitudinal direction so as to be engaged with adjacent internal electrode patterns72, and between adjacent belt-shaped internal electrode patterns72, a zigzag gap region77extending along the longitudinal direction is formed.

The imaginary cutting line73in the longitudinal direction described above is located so as to equally divide the gap region77into two portions in the width direction. At this stage, an area to be formed into the extending portion25or29of the internal electrode10or11is formed at one imaginary cutting line73side, and an area to be formed into the dummy electrode69or70is formed at the other imaginary cutting line73side.

In laminating the ceramic green sheets71described above, as shown inFIGS. 15A and 15B, the ceramic green sheets71are laminated to each other while being shifted by predetermined intervals, each of which is a half of the zigzag cycle of the sides75and76of the internal electrode pattern72, in the longitudinal direction.

A mother block78obtained by the above lamination is partly shown inFIG. 16. The mother block78is cut along the imaginary cutting lines73and74shown inFIGS. 15A and 15B, and the green chip49as shown inFIG. 8is obtained. As shown inFIGS. 15A and 15B, an area of the mother block78to be formed into the green chip49is surrounded by the dotted line.

When the internal electrode patterns72shown inFIGS. 15A,15B and16are used, the dummy electrodes69and70are formed at the sides opposite to the extending portions25and29, respectively, and each of the widths of the exposure ends15and16of these extending portions25and29and each of the widths of the exposure ends of the dummy electrodes69and70are approximately equal to each other.

When the dummy electrodes69and70are formed as in this preferred embodiment, the step liable to be generated at the laminate portion12or the green chip49in association with the extending portions25and29can be reduced, and the adhesive strengths of the external electrodes17and18to the element body2can also be increased.