Multilayer ceramic capacitor

In an embodiment, a multilayer ceramic capacitor 10 has a capacitor body 11 having a first face f1 and a second face f2 in a length direction, a third face f3 and a fourth face f4 in a width direction, a fifth face f5 and a sixth face f6 in a height direction, and a first tapering face f5a between face f1 and face f5 and a second tapering face f5b between face f2 and face 5f; a first external electrode 12 that has a first part 12a along face f1, a second part 12b along face f5, and continuously a third part 12c along face f5a; and a second external electrode 13 that has a first part 13a along face f2, a second part 13b along face f5, and continuously a third part 13c along face f5b.

BACKGROUND

Field of the Invention

The present invention relates to a multilayer ceramic capacitor constituted by a capacitor body and external electrodes of roughly L shape provided on the opposing ends thereof.

Description of the Related Art

A known mode of external electrodes provided on the opposing ends of a multilayer ceramic capacitor involves external electrodes of roughly L shape, each having a part along one length-direction face, and a part along one height-direction face, of the capacitor body (refer to Patent Literature 1 mentioned later). The following explains the concerns raised by this conventional multilayer ceramic capacitor with external electrodes of roughly L shape, by usingFIGS. 1A through 1C.

As shown inFIGS. 1A and 1B, the size of the multilayer ceramic capacitor100is specified by the length L, width W, and height H. This multilayer ceramic capacitor100has a capacitor body101of roughly rectangular solid shape, a first external electrode102of roughly L shape, and a second external electrode103of roughly L shape. The capacitor body101has a built-in capacitive part (not accompanied by symbol) constituted by multiple first internal electrode layers104and multiple second internal electrode layers105stacked alternately with dielectric layers106in between. The first external electrode102has a first part102aalong one length-direction face (left face inFIG. 1B) of the capacitor body101, as well as a second part102balong one height-direction face (bottom face inFIG. 1B) of the capacitor body101, where one length-direction end (left end inFIG. 1B) of each of the multiple first internal electrode layers104is connected to the first part102a. The second external electrode103has a first part103aalong the other length-direction face (right face inFIG. 1B) of the capacitor body101, as well as a second part103balong one height-direction face (bottom face inFIG. 1B) of the capacitor body101, where the other length-direction end (right end inFIG. 1B) of each of the multiple second internal electrode layers105is connected to the first part103a.

FIG. 1Cshows a condition where the multilayer ceramic capacitor100is mounted on a circuit board CB. To mount the multilayer ceramic capacitor100on the circuit board CB, cream solder is printed on the surface of each conductor pad CP corresponding to the multilayer ceramic capacitor100, after which the multilayer ceramic capacitor100is installed in such a way that the exterior face of the second part102bof the first external electrode102, and the exterior face of the second part103bof the second external electrode103, each contact the cream solder. Next, the circuit board CB on which the multilayer ceramic capacitor100is installed is introduced into a reflow furnace or other heating furnace, to bond the second part102bof the first external electrode102to one conductor pad CP via solder SOL, and also bond the second part103bof the second external electrode103to the other conductor pad CP via solder SOL.

An appropriate amount of cream solder to not cause bonding failure is provided on the surface of each conductor pad CP, and therefore, in the aforementioned bonding process, a part of the molten solder on the first external electrode102side wets the exterior face of the first part102ato form a fillet FI, while a part of the molten solder on the second external electrode103side wets the exterior face of the first part103ato form a fillet FI, as shown inFIG. 1C.

This means that, if the circuit board CB warps or extends/contracts in a mounted condition as shown inFIG. 1C, the forces shown by the thick arrows in the figure are likely to apply to the first part102aof the first external electrode102and the first part103aof the second external electrode103from the respective fillets FI, and these forces may cause the first part102aof the first external electrode102to separate from one length-direction face of the capacitor body101, while causing the first part103aof the second external electrode103to separate from the other length-direction face of the capacitor body101.

BACKGROUND ART LITERATURES

SUMMARY

An object of the present invention is to provide a multilayer ceramic capacitor that, while mounted on a circuit board, does not cause the first part of its first external electrode or the first part of its second external electrode to separate easily, even when the circuit board warps or extends/contracts.

Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.

To achieve the aforementioned object, the multilayer ceramic capacitor proposed by the present invention is a multilayer ceramic capacitor comprising: (1) a capacitor body having a first face and a second face that are facing each other in the length direction, a third face and a fourth face that are facing each other in the width direction, and a fifth face and a sixth face that are facing each other in the height direction, as well as a built-in capacitive part constituted by multiple first internal electrode layers and multiple second internal electrode layers stacked alternately with dielectric layers in between; (2) a first external electrode having a first part along the first face, and a second part along the fifth face, of the capacitor body, where ends of the multiple first internal electrode layers are connected to the first part, respectively; and (3) a second external electrode having a first part along the second face, and a second part along the fifth face, of the capacitor body, where ends of the multiple second internal electrode layers are connected to the first part, respectively; wherein the capacitor body has, over the entire width direction and at a position adjacent to the first face, a first tapering face that decreases the height-direction dimension of the first face, and also has, over the entire width direction and at a position adjacent to the second face, a second tapering face that decreases the height-direction dimension of the second face; the first external electrode has, between the first part and the second part, a third part along the first tapering face of the capacitor body; the second external electrode has, between the first part and the second part, a third part along the second tapering face of the capacitor body; and the first external electrode and second external electrode are each shaped in such a way that, when the exterior face of the second part of the first external electrode and the exterior face of the second part of the second external electrode are each contacting a virtual plane, a first clearance that narrows from the outer side toward the inner side is formed between the exterior face of the third part of the first external electrode and the virtual plane, while a second clearance that narrows from the outer side toward the inner side is formed between the exterior face of the third part of the second external electrode and the virtual plane.

According to the present invention, a multilayer ceramic capacitor can be provided that, while mounted on a circuit board, does not cause the first part of its first external electrode or the first part of its second external electrode to separate easily, even when the circuit board warps or extends/contracts.

DESCRIPTION OF THE SYMBOLS

10- - - Multilayer ceramic capacitor,11- - - Capacitor body, f1- - - First face of the capacitor body, f2- - - Second face of the capacitor body, f3- - - Third face of the capacitor body, f4- - - Fourth face of the capacitor body, f5- - - Fifth face of the capacitor body, f5a- - - First tapering face on the fifth face, f5b- - - Second tapering face on the fifth face, f6- - - Sixth face of the capacitor body, f6a- - - First tapering face on the sixth face, fhb - - - Second tapering face on the sixth face,12- - - First external electrode,12a- - - First part of the first external electrode,12b- - - Second part of the first external electrode,12c- - - Third part of the first external electrode,13- - - Second external electrode,13a- - - First part of the second external electrode,13b- - - Second part of the second external electrode,13c- - - Third part of the second external electrode, VP - - - Virtual plane, CL1- - - First clearance, GP1a- - - Length-direction gap in the first clearance, GP1b- - - Width-direction gap in the first clearance, CL2- - - Second clearance, GP2a- - - Length-direction gap in the second clearance, GP2b- - - Width-direction gap in the second clearance.

DETAILED DESCRIPTION OF EMBODIMENTS

First, a multilayer ceramic capacitor10to which the present invention is applied is explained usingFIGS. 2 to 6.

It should be noted that, while the multilayer ceramic capacitor10depicted inFIGS. 2 to 6has its length L, width W and height H as described below meeting a relationship of “Length L>Width W=Height H,” the relationship of length L, width W and height H can be “Length L>Width W>Height H,” “Length L>Height H>Width W,” “Width W>Length L=Height H,” “Width W>Length L>Height H,” or “Width W>Height H>Length L.” Also, while the number of the first internal electrode layers14as described below is eight and that of the second internal electrode layers15as described below is also eight, and the number of the dielectric layers16as described below is 15, this is merely for the purpose of illustration and the number of first internal electrode layers14and that of second internal electrode layers15can be nine or more (the number of dielectric layers16is 17 or more), or seven or less (the number of dielectric layers16is 13 or less).

The size of the multilayer ceramic capacitor10is specified by its length L, width W, and height H. This multilayer ceramic capacitor10has a capacitor body11of roughly rectangular solid shape, a first external electrode12of roughly L shape, and a second external electrode13of roughly L shape.

The capacitor body11has a first face f1and a second face f2that are facing each other in the length direction, a third face f3and a fourth face f4that are facing each other in the width direction, and a fifth face f5and a sixth face f6that are facing each other in the height direction. Also, the capacitor body11has a built-in capacitive part (not accompanied by symbol) constituted by eight first internal electrode layers14and eight second internal electrode layers15that are stacked alternately with dielectric layers16in between, wherein both sides in the width direction, and both sides in the height direction, of the capacitive part, are covered with dielectric margin parts (not accompanied by symbol). It should be noted that the eight first internal electrode layers14each have a rectangular contour, while the eight second internal electrode layers15each have a rectangular contour, and the contour dimensions and thickness of each first internal electrode layer14are roughly the same as the contour dimensions and thickness of each second internal electrode layer15. Also, the 15 dielectric layers16each have roughly the same thickness.

One length-direction end (left end inFIG. 6) of each first internal electrode layer14constitutes a lead part14a, where the end of each lead part14ais led out to the first face f1of the capacitor body11, and each end is connected to the first part12aas described below of the first external electrode12. Also, one length-direction end (right end inFIG. 6) of each second internal electrode layer15constitutes a lead part15a, where the end of each lead part15ais led out to the second face f2of the capacitor body11, and each end is connected to the first part13a, as described below, of the second external electrode13.

The first face f1, second face f2, third face f3, and fourth face f4of the capacitor body11are each a roughly or substantially flat surface. The fifth face f5is a convex curved face with a bulged center in the width direction, except for the parts corresponding to the first tapering face f5aand second tapering face f5bas described below, while the sixth face f6is a convex curved face with a bulged center in the width direction, except for the parts corresponding to the first tapering face f6aand second tapering face f6bas described below.

Additionally, the fifth face f5of the capacitor body11has, over the entire width direction and at a position adjacent to the first face f1, a first tapering face f5athat decreases the height-direction dimension of the first face f1, and also has, over the entire width direction and at a position adjacent to the second face f2, a second tapering face f5bthat decreases the height-direction dimension of the second face f2. The sixth face f6of the capacitor body11has, over the entire width direction and at a position adjacent to the first face f1, a first tapering face f6athat decreases the height-direction dimension of the first face f1, and also has, over the entire width direction and at a position adjacent to the second face f2, a second tapering face f6bthat decreases the height-direction dimension of the second face f2.

To be specific, the first tapering face f5aon the fifth face f5is a convex curved face having a bulged center in the width direction and inclined toward the first face f1, and the second tapering face f5bis also a convex curved face having a bulged center in the width direction and inclined toward the second face f2. The first tapering face f6aon the sixth face f6is a convex curved face having a bulged center in the width direction and inclined toward the first face f1, and the second tapering face f6bis also a convex curved face having a bulged center in the width direction and inclined toward the second face f2. Referring toFIGS. 5A and 5B, the first tapering face f5aand second tapering face f5bon the fifth face f5and the first tapering face f6aand second tapering face f6bon the sixth face f6are convex curved faces, respectively, that satisfy the condition of “h1>h2>h3” where h1 represents the maximum height-direction dimension between the fifth face f5and sixth face f6, h2 represents the maximum height-direction dimension of the first face f1and that of the second face f2, respectively, and h3 represents the minimum height-direction dimension of the first face f1and that of the second face f2, respectively.

It is clear fromFIG. 6that, because the first tapering face f5aand second tapering face f5bon the fifth face f5are each a convex curved face, and the first tapering face f6aand second tapering face f6bon the sixth face f6are each a convex curved face, one length-direction end (left end inFIG. 6) of each of the several first internal electrode layers14close to these faces and one length-direction end (right end inFIG. 6) of each of the several second internal electrode layers15close to these faces are curved inward, respectively. It is also clear fromFIGS. 5A and 5Bthat, because the fifth face f5is a convex curved face except for the parts corresponding to the first tapering face f5aand second tapering face f5b, and the sixth face f6is a convex curved face except for the parts corresponding to the first tapering face f6aand second tapering face f6b, both width-direction ends (left and right ends inFIG. 5A) of each of the several first internal electrode layers14close to these faces and both width-direction ends (left and right ends inFIG. 5B) of each of the several second internal electrode layers15close to these faces are also curved inward, respectively.

It should be noted that, while the first tapering face f5a, second tapering face f5b, first tapering face f6a, and second tapering face f6bshown inFIGS. 2 to 6are roughly the same, respectively, in terms of their length-direction dimension and configuration of convex curved face, each can have a slightly different length-direction dimension or a slightly different configuration of convex curved face. Also, the first tapering face f5a, second tapering face f5b, first tapering face f6a, and second tapering face f6bneed not all be a convex curved face having a single radius of curvature; instead, they can each be a curved face whose radius of curvature varies but which assumes the shape of a convex curved face overall, or a combination of multiple curved faces of different shapes that together assume the shape of a convex curved face, or a face with some roughly flat areas that assumes the shape of a convex curved face overall, for example.

The first external electrode12has a first part12aalong the first face f1of the capacitor body11, a second part12balong the fifth face f5(excluding the first tapering face f5a) of the capacitor body11, and a third part12calong the first tapering face f5aon the fifth face f5of the capacitor body11. On the other hand, the second external electrode13has a first part13aalong the second face f2of the capacitor body11, a second part13balong the fifth face f5(excluding the second tapering face f5b) of the capacitor body11, and a third part13calong the second tapering face f5bon the fifth face f5of the capacitor body11. It should be noted that the first external electrode12and second external electrode13have roughly the same thickness, except at their outer peripheries, respectively. Although not illustrated, the first external electrode12and second external electrode13each have a two-layer structure constituted by a base film contacting the exterior face of the capacitor body11and a surface film contacting the exterior face of the base film, or a multi-layer structure constituted by a base film, a surface film, and at least one intermediate film in between.

As shown inFIGS. 3 and 5A, the first part12aof the first external electrode12has a part (not accompanied by symbol) that extends slightly onto the first tapering face f6aon the sixth face f6of the capacitor body11, while the first part13aof the second external electrode13has a part (not accompanied by symbol) that extends slightly onto the second tapering face fhb on the sixth face f6of the capacitor body11. Also, the third part12cof the first external electrode12along the first tapering face f5aon the fifth face f5of the capacitor body11has a shape matching the first tapering face f5a, while the third part13cof the second external electrode13along the second tapering face f5bon the fifth face f5of the capacitor body11has a shape matching the second tapering face f5b. To be specific, the third part12cof the first external electrode12and the third part13cof the second external electrode13are each shaped in such a way that, when the exterior face of the second part12bof the first external electrode12and the exterior face of the second part13bof the second external electrode13are each contacting a virtual plane VP, a first clearance CL1that narrows from the outer side toward the inner side is formed between the exterior face of the third part12cof the first external electrode12and the virtual plane VP, while a second clearance CL2that narrows from the outer side toward the inner side is formed between the exterior face of the third part13cof the second external electrode13and the virtual plane VP.

As described earlier, the first tapering face f5aon the fifth face f5of the capacitor body11is a convex curved face having a bulged center in the width direction and inclined toward the first face f1, and therefore the first clearance CL1includes a length-direction gap GP1aformed between the exterior face of the third part12cof the first external electrode12and the virtual plane VP, as well as two width-direction gaps GP1bcontinuing from the length-direction gap GP1a. Also, the second tapering face f5bon the fifth face f5of the capacitor body11is a convex curved face having a bulged center in the width direction and inclined toward the second face f2, and therefore the second clearance CL2includes a length-direction gap GP2aformed between the exterior face of the third part13cof the second external electrode13and the virtual plane VP, as well as two width-direction gaps GP2bcontinuing from the length-direction gap GP2a. In addition, the fifth face f5is a convex curved face having a bulged center in the width direction, except for the parts corresponding to the first tapering face f5aand second tapering face f5b, and therefore the two width-direction gaps GP1bconstituting the first clearance CL1also extend to the outer edges, in the width direction, of the second part12bof the first external electrode12, while the two width-direction gaps GP2bconstituting the second clearance CL2also extend to the outer edges, in the width direction, of the second part13bof the second external electrode13.

As additional features of the materials, etc., preferably a dielectric ceramic whose primary component is barium titanate, strontium titanate, calcium titanate, magnesium titanate, calcium zirconate, calcium titanate zirconate, barium zirconate, titanium oxide, etc., or more preferably a dielectric ceramic of ε>1000 or Class 2 (high dielectric constant type), can be used for the capacitor body11, except for each first internal electrode layer14and each second internal electrode layer15.

Also, preferably a good conductor whose primary component is nickel, copper, palladium, platinum, silver, gold, alloy thereof, etc., can be used for each first internal electrode layer14and each second internal electrode layer15.

In addition, the base film of the first external electrode12and that of the second external electrode13are each constituted by a baked film or plating film, for example, and preferably a good conductor whose primary component is nickel, copper, palladium, platinum, silver, gold, alloy thereof, etc., can be used for such base film. The surface film is constituted by a plating film, for example, and preferably a good conductor whose primary component is copper, tin, palladium, gold, zinc, alloy thereof, etc., can be used for such surface film. The intermediate film is constituted by a plating film, for example, and preferably a good conductor whose primary component is platinum, palladium, gold, copper, nickel, alloy thereof, etc., can be used for such intermediate film.

Next, two manufacturing examples appropriate for the manufacture of the multilayer ceramic capacitor10are explained by citing the symbols inFIGS. 2 to 6as deemed appropriate.

First Manufacturing Example

For the manufacture, a ceramic slurry containing dielectric ceramic powder, and an electrode paste containing good conductor powder, are prepared. Next, the ceramic slurry is coated on the surface of carrier films and then dried, to prepare first green sheets. Also, the electrode paste is printed on the surface of first green sheets and then dried, to prepare second green sheets on which internal electrode patterns are formed and which will become first internal electrode layers14and second internal electrode layers15.

Next, a specified number of unit sheets cut out from the first green sheets are stacked and thermally bonded one by one, to prepare an area corresponding to one margin part in the height direction. Also, a specified number of unit sheets (including internal electrode patterns) cut out from the second green sheets are stacked and thermally bonded one by one, to prepare an area corresponding to the capacitive part. Furthermore, a specified number of unit sheets cut out from the first green sheets are stacked and thermally bonded one by one, to prepare an area corresponding to the other margin part in the height direction. Finally, the entire stack is thermally bonded for one last time to prepare an unsintered laminate sheet. In this preparation process of unsintered laminate sheet, the thickness or shape of the elastic sheet used for bonding, made of synthetic rubber, etc., is changed so that the surface curves corresponding to the fifth face f5(including the first tapering face f5aand second tapering face f5b) and sixth face f6(including the first tapering face f6aand second tapering face fhb) of the capacitor body11as shown inFIGS. 2 to 6are formed on the top face and bottom face of the unsintered laminate sheet.

Next, the unsintered laminate sheet is cut to a grid to prepare unsintered chips, each corresponding to the capacitor body11. Next, the multiple unsintered chips are sintered (including binder removal and sintering) all at once in an ambience and at a temperature profile appropriate for the dielectric ceramic powder contained in the ceramic slurry and for the good conductor powder contained in the electrode paste, to prepare sintered chips. Next, the multiple sintered chips are barreled all at once to round the corners and ridgelines, to prepare capacitor bodies11.

Next, the first face f1and second face f2of each capacitor body11are dipped in an electrode paste (same as the aforementioned electrode paste or a different electrode paste containing a different type of good conductor powder), respectively, and then dried, followed by baking, to form a base film for the external electrodes. It should be noted that this base film can also be formed by sputtering, vacuum deposition, or other dry plating method that forms a good conductor film on the first face f1and second face f2of the capacitor body11, respectively.

Next, an electrode paste (same as the aforementioned electrode paste or a different electrode paste containing a different type of good conductor powder) is printed on both length-direction ends of the fifth face f5of the capacitor body11, respectively, and then dried, followed by baking, to form another base film for the external electrodes in a manner continuing from the aforementioned base film. It should be noted that this base film can also be formed by sputtering, vacuum deposition, or other dry plating method that forms a good conductor film on both length-direction ends of the fifth face f5of the capacitor body11, respectively.

Next, a surface film covering the two continuous base films, or an intermediate film and a surface film, is/are formed by electroplating, electroless plating, or other wet plating method, or by sputtering, vacuum deposition, or other dry plating method, to prepare a first external electrode12and a second external electrode13, respectively.

Second Manufacturing Example

For the manufacture, a ceramic slurry containing dielectric ceramic powder, and an electrode paste containing good conductor powder, are prepared. Next, the ceramic slurry is coated on the surface of carrier films and then dried, to prepare first green sheets. Also, the electrode paste is printed on the surface of first green sheets and then dried, to prepare second green sheets on which internal electrode patterns are formed and which will become first internal electrode layers14and second internal electrode layers15. Furthermore, the electrode paste is printed on the surface of first green sheets and then dried, to prepare third green sheets on which base patterns are formed. These base patterns are aggregates of roughly rectangular patterns corresponding to the base film at the second part12bof the first external electrode12and those corresponding to the base film at the second part13bof the second external electrode13.

Next, a specified number of unit sheets cut out from the first green sheets are stacked and thermally bonded one by one, to prepare an area corresponding to one margin part in the height direction. Also, a specified number of unit sheets (including internal electrode patterns) cut out from the second green sheets are stacked and thermally bonded one by one, to prepare an area corresponding to the capacitive part. Furthermore, a specified number of unit sheets cut out from the first green sheets are stacked and thermally bonded one by one, and then unit sheets (including base patterns) cut out from the third green sheets are stacked and thermally bonded one by one, to prepare an area corresponding to the other margin part in the height direction. Finally, the entire stack is thermally bonded for one last time to prepare an unsintered laminate sheet. In this preparation process of unsintered laminate sheet, the thickness or shape of the elastic sheet used for bonding, made of synthetic rubber, etc., is changed so that the surface curves corresponding to the fifth face f5(including the first tapering face f5aand second tapering face f5b) and sixth face f6(including the first tapering face f6aand second tapering face fhb) of the capacitor body11as shown inFIGS. 2 to 6are formed on the top face and bottom face of the unsintered laminate sheet.

Next, the unsintered laminate sheet is cut to a grid to prepare unsintered chips, each corresponding to the capacitor body11. These unsintered chips each have a base pattern present on both length-direction ends of the face corresponding to the fifth face f5of the capacitor11. Next, the multiple unsintered chips are sintered (including binder removal and sintering) all at once in an ambience and at a temperature profile appropriate for the dielectric ceramic powder contained in the ceramic slurry and for the good conductor powder contained in the electrode paste, to prepare sintered chips. Next, the multiple sintered chips are barreled all at once to round the corners and ridgelines, to prepare capacitor bodies11. These capacitor bodies11each have a base or underlying film for the second part12bof the first external electrode12on one of the length-direction ends of the fifth face f5, as well as a base or underlying film for the second part13bof the second external electrode13on the other end.

Next, the first face f1and second face f2of each capacitor body11are dipped in an electrode paste (same as the aforementioned electrode paste or a different electrode paste containing a different type of good conductor powder), respectively, and then dried, followed by baking, to form another base film for the external electrodes in a manner continuing from the aforementioned base film. It should be noted that this base film can also be formed by sputtering, vacuum deposition, or other dry plating method that forms a good conductor film on the first face f1and second face f2of the capacitor body11, respectively.

Next, a surface film covering the two continuous base films, or an intermediate film and a surface film, is/are formed by electroplating, electroless plating, or other wet plating method, or by sputtering, vacuum deposition, or other dry plating method, to prepare a first external electrode12and a second external electrode13, respectively.

Next, the effects achieved by the multilayer ceramic capacitor10are explained by usingFIGS. 7, and 8A through 8C.

InFIG. 7, CB represents a circuit board, CP represents each of two rectangular contoured conductor pads provided on the circuit board CB, and SOLa represents cream solder. The length-direction dimension of each conductor pad CP is slightly longer than the length-direction dimension L1(refer toFIG. 4) of the first external electrode12and of the second external electrode13when the multilayer ceramic capacitor10is viewed from the fifth face f5side of the capacitor body11, while the width-direction dimension of each conductor pad CP is roughly the same as the width W (refer toFIG. 4) of the multilayer ceramic capacitor10.

To mount the multilayer ceramic capacitor10on the circuit board CB, cream solder SOLa is printed on the surface of each conductor pad CP, after which the multilayer ceramic capacitor10is installed in such a way that the exterior face of primarily the second part12bof the first external electrode12, and the exterior face of primarily the second part13bof the second external electrode13, each contact the cream solder SOLa, as shown inFIG. 7. Next, the circuit board CB on which the multilayer ceramic capacitor10is installed is introduced into a reflow furnace or other heating furnace to bond the second part12band third part12cof the first external electrode12to one conductor pad CP via solder SOL, and also bond the second part13band third part13cof the second external electrode13to the other conductor pad CP via solder SOL, as shown inFIG. 8A through 8C.

In the bonding process, the molten solder on the first external electrode12side behaves in a manner being suctioned into the first clearance CL1that narrows from the outer side toward the inner side, while the molten solder on the second external electrode13side behaves in a manner being suctioned into the second clearance CL2that narrows from the outer side toward the inner side. This suppresses formation of fillets as a result of solder oozing out to the outer side of the first external electrode12and that of the second external electrode13. In other words, application of the forces indicated by the thick arrows in FIG.1C to the first part12aof the first external electrode12and to the first part13aof the second external electrode13can be avoided, even when the circuit board CB warps or extends/contracts while the multilayer ceramic capacitor10is mounted on it, and consequently a phenomenon where the first part12aof the first external electrode12separates from the first face f1of the capacitor body11does not occur easily, and a phenomenon where the first part13aof the second external electrode13separates from the second face f2of the capacitor body11does not occur easily, either.

In addition, fillet formation can be suppressed and the required bonding can be implemented even when the contour dimension of each conductor pad CP of the circuit board CB is reduced to a minimum, such as when the length-direction dimension of each conductor pad CP is made roughly the same as the length-direction dimension L1(refer toFIG. 4), which reduces the mounting area needed to mount the multilayer ceramic capacitor10on the circuit board CB and thereby contributes to high-density mounting.

Also, the first clearance CL1on the first external electrode12side includes a length-direction gap GP1aand two width-direction gaps GP1bcontinuing from the length-direction gap GP1a, while the second clearance CL2on the second external electrode13side includes a length-direction gap GP2aand two width-direction gaps GP2bcontinuing from the length-direction gap GP2a. As a result, the molten solder on the first external electrode12side flows smoothly in a manner filling the length-direction gap GP1aand the two width-direction gaps GP1bcontinuing from the length-direction gap GP1a, while the molten solder on the second external electrode13side flows smoothly in a manner filling the length-direction gap GP2aand the two width-direction gaps GP2bcontinuing from the length-direction gap GP2a. In other words, fillet formation in the bonding process can effectively be suppressed, and this contributes to suppressing the occurrence of the aforementioned separation phenomena.

Furthermore, the fifth face f5is a convex curved face having a bulged center in the width direction, except for the parts corresponding to the first tapering face f5aand second tapering face f5b, which means that the two width-direction gaps GP1bconstituting the first clearance CL1also extend to the outer edges, in the width direction, of the second part12bof the first external electrode12, while the two width-direction gaps GP2bconstituting the second clearance CL2also extend to the outer edges, in the width direction, of the second part13bof the second external electrode13. This makes it possible to increase the amount of solder accommodated in the first clearance CL1on the first external electrode12side and in the second clearance CL2on the second external electrode13side, and accordingly fillet formation in the bonding process can be effectively suppressed even when the amount of cream solder SOLa provided on the surface of each conductor pad CP exceeds the tolerance on the plus side (the over tolerance). In addition, the area over which the solder SOL contacts the first external electrode12, and the area over which it contacts the second external electrode13, can be increased, which also contributes to increasing the bonding force.

Next, the verification results of the aforementioned effects, especially the verification results pertaining to the suppression of occurrence of separation phenomena, are explained.

For verification,100evaluation multilayer ceramic capacitors each corresponding to the multilayer ceramic capacitor10shown inFIGS. 2 to 6, and 100comparison multilayer ceramic capacitors each corresponding to the multilayer ceramic capacitor100shown inFIGS. 1A through 1C, were manufactured according to <First Manufacturing Example> above, and 200 test circuit boards were also prepared. The specifications of the evaluation multilayer ceramic capacitor, specifications of the comparison multilayer ceramic capacitor, and specifications of the test circuit board, are described below. It should be noted that all specification values are design reference values and do not include manufacturing tolerances.

<Specification of Evaluation Multilayer Ceramic Capacitor (Citing the Symbols inFIGS. 2 to 6)>The multilayer ceramic capacitor10has a length L of 400 μm, width W of 200 μm, and height H of 200 μm.The capacitor body11has a length of 370 μm, width of 200 μm, and height of 185 μm.The primary component of the capacitor body11, except for each first internal electrode layer14and each second internal electrode layer15, is barium titanate.The primary component of each first internal electrode layer14and each second internal electrode layer15is nickel, each layer has a thickness of 0.5 μm, and there are 145 first internal electrode layers and 145 second internal electrode layers.The thickness of each dielectric layer16present between a first internal electrode layer14and a second internal electrode layer15, is 0.5 μm.The thickness of the width-direction margin, and that of the height-direction margin, of the capacitor body11, are 15 μm, respectively.The radius of curvature of the fifth face f5of the capacitor body11, except for the parts corresponding to the first tapering face5aand second tapering face5b, is 750 μm.The radius of curvature of the sixth face f6of the capacitor body11, except for the parts corresponding to the first tapering face6aand second tapering face6b, is 750 μm.The first tapering face5aand second tapering face5bof the fifth face f5of the capacitor body11each have a height-direction dimension (h1−h2 shown inFIG. 5A) of 10 μm and a length-direction dimension of 20 μm.The first tapering face6aand second tapering face6bof the sixth face f6of the capacitor body11each have a height-direction dimension (h1−h2 shown inFIG. 5A) of 10 μm and a length-direction dimension of 20 μm.The length-direction dimension L1of the first external electrode12, and the length-direction dimension L1of the second external electrode13, as shown inFIG. 4, are 100 μm, respectively.The thickness of the first external electrode12, and that of the second external electrode13, are 15 μm, respectively.The first external electrode12and second external electrode13each have a three-layer structure, constituted by a base film whose primary component is copper and thickness is 10 μm, an intermediate film whose primary component is nickel and thickness is 2 μm, and a surface film whose primary component is tin and thickness is 3 μm.

<Specifications of Comparison Multilayer Ceramic Capacitor (Citing the Symbols inFIGS. 2 to 6)>Same as the evaluation multilayer ceramic capacitor except that the fifth face f5of the capacitor body11is roughly flat and has no first tapering face f5aor second tapering face f5b, and that the sixth face f6is roughly flat and has no first tapering face f6aor second tapering face f6b.

<Specifications of Test Circuit Board (Referring toFIG. 7)>The thickness of the circuit board CB is 150 μm.The primary component of the circuit board CB is epoxy resin.Each conductor pad CP has a length of 120 μm, width of 200 μm, and thickness of 15 μm.The interval between the conductor pads CP is 300 μm.The primary component of each conductor pad CP is copper.The cream solder SOLa is tin-antimony solder.The amount of cream solder SOLa is 30 μm in equivalent thickness.

The first external electrodes and second external electrodes of the evaluation multilayer ceramic capacitors were installed on the cream solder printed on the respective conductor pads of the test circuit boards, and the resulting boards were introduced into a reflow furnace, to prepare a total of 100 mounted evaluation boards each having an evaluation multilayer ceramic capacitor mounted on it. Also, the first external electrodes and second external electrodes of the comparison multilayer ceramic capacitors were installed on the cream solder printed on the respective conductor pads of the test circuit boards, and the resulting boards were introduced into a reflow furnace, to prepare a total of 100 mounted comparison boards each having a comparison multilayer ceramic capacitor mounted on it.

The effects were verified by testing the 100 mounted evaluation boards and 100 mounted comparison boards 30 times each, where each test consisted of warping the board in the direction indicated by the two-dot chain line inFIG. 8Aand then restoring its original shape, and then observing each multilayer ceramic capacitor to see whether or not the first part of the first external electrode and the first part of the second external electrode had separated after the tests. It should be noted that the aforementioned test was conducted by using support tools to support the locations (refer to the positions of the ∇ marks inFIG. 8A) on the outer sides of the respective conductor pads on one side of each mounted board, and in this condition, using a pressure tool to push up 50 μm the location corresponding to the length-direction center position of the multilayer ceramic capacitor (refer to the position shown by the thick broken-line arrow inFIG. 8A) on the other side of the mounted board, followed by recovering the original condition before the push-up.

As a result of the observation, separation of the first part of the first external electrode, or the first part of the second external electrode, of the evaluation capacitor, was not found on any of the 100 mounted evaluation boards; whereas, separation of the first part of the first external electrode, or the first part of the second external electrode, of the evaluation capacitor, was found on five of the 100 mounted comparison boards. This confirms that the multilayer ceramic capacitor10is effective in suppressing the occurrence of the separation phenomena described earlier.

Next, examples of variation of the multilayer ceramic capacitor10are explained.

First Example of Variation

InFIGS. 2 to 6, the sixth face f6of the capacitor body11has the first tapering face f6aand second tapering face f6b, and is a convex curved face with a bulged center in the width direction except for the parts corresponding to the first tapering face f6aand second tapering face f6b; however the aforementioned effects depend on the mode of the fifth face f5, which means that the first tapering face f6aand second tapering face f6bcan be eliminated from the sixth face f6of the capacitor body11, to make the entire sixth face f6a convex curved face with a bulged center in the width direction, or to make the entire sixth face f6a roughly flat surface.

Second Example of Variation

InFIGS. 2 to 6, the width-direction dimension of the first external electrode12corresponds to the width-direction dimension (width W) of the capacitor body11, while the width-direction dimension of the second external electrode13corresponds to the width-direction dimension (width W) of the capacitor body11; however, effects similar to those explained above can still be achieved even when the width-direction dimensions of the first external electrode12and second external electrode13are slightly smaller than the width W, respectively.

In the present disclosure where conditions and/or structures are not specified, a skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, in the present disclosure including the examples described above, any ranges applied in some embodiments may include or exclude the lower and/or upper endpoints, and any values of variables indicated may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, “a” may refer to a species or a genus including multiple species, and “the invention” or “the present invention” may refer to at least one of the embodiments or aspects explicitly, necessarily, or inherently disclosed herein. The terms “constituted by” and “having” refer independently to “typically or broadly comprising”, “comprising”, “consisting essentially of”, or “consisting of” in some embodiments. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

The present application claims priority to Japanese Patent Application No. 2016-035705, filed Feb. 26, 2016, the disclosure of which is incorporated herein by reference in its entirety including any and all particular combinations of the features disclosed therein.