Monolithic ceramic electronic component

A monolithic ceramic electronic component includes a ceramic body including a stack of ceramic layers. Inner electrodes are disposed within the ceramic body and include exposed portions at the end surfaces of the ceramic body. A pair of outer electrodes is arranged on the end surfaces of the ceramic body so as to extend from the end surfaces to the main surfaces and side surfaces of the ceramic body. Each of the outer electrodes includes a lower electrode layer provided on the ceramic body, an intermediate electrode layer located on the lower electrode layer and defined by a plated Ni layer, and an upper electrode layer located on the intermediate electrode layer and defined by a plated Pd layer. A thickness of the intermediate electrode layer on the main surfaces and the side surfaces of the ceramic body is larger than a thickness of the intermediate electrode layer on the end surfaces of the ceramic body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a monolithic ceramic electronic component, and particularly to, for example, a monolithic ceramic electronic component in which outer electrodes are provided on both end surfaces of a multilayer body.

2. Description of the Related Art

In recent years, a large number of electronic components such as ceramic electronic components have come to be mounted on circuit substrates installed in electronic equipment. For mounting such electronic components on circuit substrates, Pb-containing solder has been commonly used. However, in recent years, in order to reduce environmental loads, studies on Pb-free mounting of electronic components have been increasingly performed.

In a known example of a Pb-free method of mounting electronic components on circuit substrates, electronic components are mounted with Pb-free solder or a conductive adhesive containing a thermosetting resin such as an epoxy thermosetting resin and conductive fine particles such as metal filler. A monolithic ceramic electronic component that is suitable for such mounting includes a ceramic body having inner electrodes formed of Ni or Ni alloy, and has, on the end surfaces of the ceramic body, outer electrodes each constituted by a lower electrode mainly formed of Cu or Cu alloy and an overlying outermost electrode layer mainly formed of Ag or Ag alloy. In such an electronic component, by forming Ag-containing electrode layers as outermost electrode layers of outer electrodes, the outer electrodes have enhanced compatibility with conductive adhesive to thereby increase the mounting strength of the electronic component (refer to Japanese Unexamined Patent Application Publication No. 2002-158137, for example).

However, in the monolithic ceramic electronic component described in Japanese Unexamined Patent Application Publication No. 2002-158137, electrochemical migration of Ag may cause short circuit failures between outer electrodes. In particular, for example, in the cases where electronic components are used within or near ECUs (electric control units) of automobiles, the atmosphere around electronic components may have a high temperature of 150° C. or more. In such an atmosphere, short circuit failures easily occur in the monolithic ceramic electronic component described in Japanese Unexamined Patent Application Publication No. 2002-158137 due to electrochemical migration of Ag.

As illustrated inFIG. 6, a conductive adhesive3is applied to lands2of a circuit substrate1and a monolithic ceramic electronic component4is mounted on the conductive adhesive3. At this time, the monolithic ceramic electronic component4presses down on the conductive adhesive3. This may cause the conductive adhesive3to spread to the surface of a ceramic body5or to the space between the ceramic body5and the circuit substrate1; or a capillary phenomenon may cause the conductive adhesive3to move along the surface of the ceramic body5. As a result, the conductive adhesive3may form a connection between outer electrodes6, causing short circuit failures.

SUMMARY OF THE INVENTION

Accordingly, preferred embodiments of the present invention provide a monolithic ceramic electronic component in which electrochemical migration of Ag is prevented and also prevents short circuit failures that are caused during mounting by unintended movement of conductive adhesive or formation of a connection between outer electrodes through conductive adhesive.

A monolithic ceramic electronic component according to a preferred embodiment of the present invention includes a ceramic body that includes a stack of a plurality of ceramic layers and includes opposing main surfaces, opposing side surfaces, and opposing end surfaces; inner electrodes that are disposed within the ceramic body and include exposed portions at the end surfaces of the ceramic body; and a pair of outer electrodes that is arranged on the end surfaces of the ceramic body so as to be connected to the exposed portions of the inner electrodes and so as to extend from the end surfaces of the ceramic body to the main surfaces and the side surfaces of the ceramic body, wherein each of the outer electrodes includes a lower electrode layer provided on the ceramic body, an intermediate electrode layer located on the lower electrode layer and defined by a plated Ni layer, and an upper electrode layer located on the intermediate electrode layer and defined by a plated Pd or Pd—Ni alloy layer, and a thickness of the intermediate electrode layer on the main surfaces and the side surfaces of the ceramic body is larger than a thickness of the intermediate electrode layer on the end surfaces of the ceramic body.

By forming, as the outermost layers of outer electrodes, Pd electrodes or Pd—Ni alloy electrodes, which do not contain Ag, electrochemical migration is prevented even in the monolithic ceramic electronic component that is capable of being mounted with conductive adhesive. In addition, the thickness of the intermediate electrode layer on the main surfaces and the side surfaces of the ceramic body is preferably larger than the thickness of the intermediate electrode layer on the end surfaces of the ceramic body. Thus, outer electrodes include large-thickness portions that are to be brought into contact with adhesive on the mounting surface of the circuit substrate. As a result, a sufficiently large distance (standoff) is ensured between the lowermost point of outer electrodes in the mounting surface of the monolithic ceramic electronic component to the surface of the ceramic body. Accordingly, when such a monolithic ceramic electronic component is mounted on a circuit substrate with conductive adhesive, spreading (movement) of the conductive adhesive over the monolithic ceramic electronic component is significantly reduced or prevented. Thus, a monolithic ceramic electronic component in which short circuit failures are significantly reduced or prevented is provided. By forming, as the outermost layers of outer electrodes, Pd electrodes or Pd—Ni alloy electrodes, the monolithic ceramic electronic component is also applicable to solder mounting or wire-bonding mounting and is also applicable to, for example, mounting combined with conductive-adhesive mounting (for example, a combination of conductive-adhesive mounting and wire-bonding mounting).

In such a monolithic ceramic electronic component, a ratio of the thickness of the intermediate electrode layer on the main surfaces and the side surfaces of the ceramic body to the thickness of the intermediate electrode layer on the end surfaces of the ceramic body is preferably about 120% or more and about 300% or less, for example.

When the ratio of the thickness of the intermediate electrode layers on the main surfaces and the side surfaces of the ceramic body to the thickness of the intermediate electrode layers on the end surfaces of the ceramic body is less than about 120%, a sufficiently large distance cannot be ensured from the lowermost point of outer electrodes in the mounting surface of the monolithic ceramic electronic component to the surface of the ceramic body. Accordingly, there is a possibility that, for example, spreading of the conductive adhesive during mounting cannot be suppressed or prevented. When the ratio of the thickness of the intermediate electrode layers on the main surfaces and the side surfaces of the ceramic body to the thickness of the intermediate electrode layers on the end surfaces of the ceramic body is more than about 300%, during a temperature-cycling test, tensile stress of the plating layers may cause generation of cracks in the ceramic body.

A mounting structure of a monolithic ceramic electronic component according to a preferred embodiment of the present invention includes a monolithic ceramic electronic component including a ceramic body that includes a stack of a plurality of ceramic layers and opposing main surfaces, opposing side surfaces, and opposing end surfaces, inner electrodes that are disposed within the ceramic body and include exposed portions at the end surfaces of the ceramic body, and a pair of outer electrodes that is arranged on the end surfaces of the ceramic body so as to be connected to the exposed portions of the inner electrodes and so as to extend from the end surfaces of the ceramic body to the main surfaces and the side surfaces of the ceramic body, wherein each of the outer electrodes includes a lower electrode layer provided on the ceramic body, an intermediate electrode layer located on the lower electrode layer and defined by a plated Ni layer, and an upper electrode layer located on the intermediate electrode layer and defined by a plated Pd or Pd—Ni alloy layer, and a thickness of the intermediate electrode layer on the main surfaces and the side surfaces of the ceramic body is larger than a thickness of the intermediate electrode layer on the end surfaces of the ceramic body; a mounting substrate including a pair of lands electrically connected to the pair of outer electrodes; and a pair of conductive adhesives bonding the pair of outer electrodes and the pair of lands of the mounting substrate, wherein the pair of outer electrodes is mounted on the mounting substrate with the pair of conductive adhesives, and a distance (standoff) from a lowermost point of the outer electrodes on a mounting surface of the monolithic ceramic electronic component to a surface of the ceramic body preferably is about 10.1 μm or more and about 20.1 μm or less, for example.

The outer electrodes of the monolithic ceramic electronic component are connected to the lands of the mounting substrate via conductive adhesives to provide a mounting structure of the monolithic ceramic electronic component. Such conductive adhesive has a composition in which a thermosetting resin such as an epoxy resin is mixed with a metal filler such as Ag filler. The outer electrodes of the monolithic ceramic electronic component are located on the lands of the mounting substrate with flowable conductive adhesive therebetween and heating is performed to cure the conductive adhesive. Thus, the outer electrodes are bonded to the lands. Prior to the heating, the conductive adhesive has flowability. Accordingly, when the outer electrodes are pressed down on the lands via the conductive adhesive, the conductive adhesive spreads to the surface of a ceramic body or to the space between the ceramic body and the mounting substrate, or a capillary phenomenon causes the conductive adhesive to move along the surface of the ceramic body. However, such spreading (movement) of the conductive adhesive during mounting of the monolithic ceramic electronic component is suppressed in the following manner: the intermediate electrode layers are configured to have a larger thickness on the main surfaces and the side surfaces of the ceramic body than on the end surfaces of the ceramic body; and a sufficiently large distance (standoff) preferably in the range of about 10.1 μm or more and about 20.1 μm or less, for example, is ensured from the lowermost point of the outer electrodes on a mounting surface of the monolithic ceramic electronic component to the surface of the ceramic body. As a result, a mounting structure of a monolithic ceramic electronic component in which short circuit failures are significantly reduced or prevented is provided.

Various preferred embodiments of the present invention provide a monolithic ceramic electronic component in which, during mounting of the monolithic ceramic electronic component on a circuit substrate, unintended movement of conductive adhesive and the resultant short circuit failures are significantly reduced or prevented and electrochemical migration of Ag does not occur.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a perspective view of a monolithic ceramic capacitor serving as an example of a monolithic ceramic electronic component according to a preferred embodiment of the present invention.FIG. 2is a plan view of this monolithic ceramic capacitor. A monolithic ceramic capacitor10includes a ceramic body12that has a rectangular or substantially rectangular parallelepiped shape. The ceramic body12includes a pair of opposing main surfaces14aand14b(surfaces defined by length L and width W), a pair of opposing side surfaces16aand16b(surfaces defined by length L and thickness T), and a pair of opposing end surfaces18aand18b(surfaces defined by width W and thickness T). In this case, the ceramic body12preferably has rounded corners and rounded ridges. InFIG. 1, the ceramic body preferably has a rectangular or substantially rectangular parallelepiped shape. Alternatively, depending on the type of the monolithic ceramic electronic component, the ceramic body12may have a shape other than rectangular or substantially rectangular parallelepiped shapes.

The ceramic body12may be formed of a dielectric ceramic containing, as a main component, for example, BaTiO3, CaTiO3, SrTiO3, or CaZrO3. Such a main component may be mixed with an auxiliary component such as a Mn compound, an Fe compound, a Cr compound, a Co compound, or a Ni compound. Alternatively, the ceramic body12may be formed of, for example, a piezoelectric ceramic such as PZT ceramic, a semiconductor ceramic such as spinel ceramic, or a magnetic ceramic such as ferrite.

As illustrated inFIG. 3, the ceramic body12includes first inner electrodes20aand second inner electrodes20b, which have a rectangular or substantially rectangular shape and are alternately disposed at regular intervals in the thickness T direction of the ceramic body12. End portions of the first inner electrodes20aare exposed at one end surface18aof the ceramic body12. End portions of the second inner electrodes20bare exposed at the other end surface18bof the ceramic body12. The main surfaces of the first inner electrodes20aand the main surfaces of the second inner electrodes20bare disposed so as to be parallel or substantially parallel with the main surfaces14aand14bof the ceramic body12and so as to be parallel or substantially parallel with one another. Thus, the first inner electrodes20aoppose adjacent second inner electrodes20bwith ceramic layers therebetween in the thickness T direction of the ceramic body12.

The thicknesses of the first inner electrodes20aand the second inner electrodes20bare not particularly limited. The first inner electrodes20aand the second inner electrodes20beach may preferably have a thickness of, for example, about 0.2 μm to about 2 μm. Examples of a material for the first inner electrodes20aand the second inner electrodes20binclude metals such as Ni, Cu, Ag, Pd, and Au and alloys containing one or more of these metals, such as Ag—Pd alloy.

In the ceramic body12according to this preferred embodiment, the first inner electrodes20aand the second inner electrodes20bare disposed so as to be parallel or substantially parallel with each other with dielectric ceramic layers therebetween, so that the ceramic body12defines and serves as a ceramic body for a monolithic ceramic capacitor. Instead of the dielectric ceramic layers, in the case of using piezoelectric ceramic layers, the ceramic body12defines and serves as a piezoelectric component; in the case of using semiconductor ceramic layers, the ceramic body12defines and serves as a thermistor; and, in the case of using magnetic ceramic layers, the ceramic body12defines and serves as an inductor. Such a ceramic layer preferably has a thickness of about 0.5 μm to about 10 μm, for example.

A first outer electrode22ais provided on the first end surface18aof the ceramic body12. A second outer electrode22bis provided on the second end surface18bof the ceramic body12. The first outer electrode22ais arranged so as to extend from the first end surface18aof the ceramic body12to the main surfaces14aand14band the side surfaces16aand16b. The second outer electrode22bis arranged so as to extend from the second end surface18bof the ceramic body12to the main surfaces14aand14band the side surfaces16aand16b. As illustrated inFIG. 4, the first outer electrode22aand the second outer electrode22beach include a lower electrode layer24, an intermediate electrode layer26provided on the lower electrode layer24, and an upper electrode layer28provided on the intermediate electrode layer26. InFIG. 4, one of the outer electrodes, the outer electrode22ais illustrated; however, the other one of outer electrodes, the outer electrode22bhas the same configuration as inFIG. 4.

The lower electrode layers24are configured so as to be connected to the first inner electrodes20aand the second inner electrodes20bexposed at the end surfaces18aand18bof the ceramic body12. The lower electrode layers24contain a glass component and a metal component. Examples of a metal used for the lower electrode layers24include Cu, Ni, Ag, Pd, Ag—Pd alloy, and Au. During mounting, the bottom surface portions (for example, on the main surface14aor14bside of the ceramic body12) of the lower electrode layers24preferably have a thickness of about 1 μm to about 15 μm, for example.

The intermediate electrode layers26are formed as Ni plating films. As a result of the formation of Ni plating films, immersion in Pd plating bath for forming Pd plating films serving as the upper electrode layers28on the intermediate electrode layers26does not cause dissolution of the lower electrode layers24in the Pd plating bath. In addition, the Ni plating films cover the lower electrode layers24having surfaces that are difficult to plate, such as portions having irregularities and glass-component segregated portions, to thus provide smooth surfaces. Thus, adhesion of the upper electrode layers28is enhanced so that these Pd plating films have a small thickness. The intermediate electrode layers26provided on the end surfaces18aand18bof the ceramic body12preferably have a thickness of about 2 μm to about 10 μm, for example. The intermediate electrode layers26provided on the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12preferably have a thickness of about 5 μm to about 20 μm, for example.

The upper electrode layers28preferably are defined by and formed as Pd plating films or Pd—Ni alloy films. By forming Pd plating films or Pd—Ni alloy films as the outermost layers of the first outer electrode22aand the second outer electrode22b, reliability of establishing an electric connection with metal filler such as Ag filler used for conductive adhesive for mounting on a circuit substrate is ensured. Thus, the monolithic ceramic capacitor10preferably is mounted with conductive adhesive. When the upper electrode layers28are formed by plating with a base metal such as Sn, problems of galvanic corrosion and oxidation occur and the connection reliability is not ensured. In addition, Pd plating films and Pd—Ni alloy films do not contain Ag and hence electrochemical migration is significantly reduced and prevented. The upper electrode layers28preferably have a thickness of about 0.01 μm to about 0.5 μm, for example.

The intermediate electrode layers26have a larger thickness on the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12than on the end surfaces18aand18bof the ceramic body12. Thus, without unnecessarily increasing the length dimension of the monolithic ceramic capacitor10, the thickness of the outer electrodes22aand22bis increased in the circuit-substrate-mounting surface of the monolithic ceramic capacitor10.

As illustrated inFIG. 5, the monolithic ceramic capacitor10is mounted such that the main surfaces14aand14bor the side surfaces16aand16bof the ceramic body12oppose a circuit substrate30defining and serving as a mounting substrate. Specifically, the first outer electrode22aand the second outer electrode22bof the monolithic ceramic capacitor10are located on a first land32aand a second land32blocated on the circuit substrate30; and the outer electrodes22aand22bare fixed to the lands32aand32bwith a first conductive adhesive34aand a second conductive adhesive34b.

The conductive adhesives34aand34bhave a composition in which a thermosetting resin such as an epoxy resin is mixed with a metal filler such as Ag filler. During bonding of the outer electrodes22aand22bto the lands32aand32b, the outer electrodes22aand22bare provided on the lands32aand32bvia uncured and flowable conductive adhesives34aand34band heating is performed to cure the conductive adhesives34aand34b.

In the mounting structure of the monolithic ceramic capacitor10, the intermediate electrode layers26are configured to have a larger thickness on the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12than on the end surfaces18aand18bof the ceramic body12. As a result, a sufficiently large distance (standoff) is ensured from the lowermost point of outer electrodes22aand22bin the mounting surface of the monolithic ceramic capacitor10to the surface of the ceramic body12. This standoff is preferably about 10.1 μm or more and about 20.1 μm or less, for example. When a sufficiently large standoff is thus ensured, during mounting of the monolithic ceramic capacitor10on the circuit substrate30with the conductive adhesives34aand34b, spreading (movement) of the conductive adhesives34aand34bover the monolithic ceramic capacitor10is significantly reduced or prevented. Note that the term “standoff” used here denotes a distance from the lowermost point of outer electrodes22aand22bin the mounting surface of the monolithic ceramic capacitor10to the surface of the ceramic body12. In general, the term “standoff” denotes a distance from the lowermost point of outer electrodes in the mounting surface of a monolithic ceramic electronic component to the surface of the ceramic body.

In order to ensure a standoff satisfying the above-described range, the ratio of the thickness of the intermediate electrode layers26on the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12to the thickness of the intermediate electrode layers26on the end surfaces18aand18bof the ceramic body12is preferably about 120% or more and about 300% or less, for example. When the ratio of the thickness of the intermediate electrode layers26on the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12to the thickness of the intermediate electrode layers26on the end surfaces18aand18bof the ceramic body12is less than about 120%, a sufficiently large distance cannot be ensured from the lowermost point of outer electrodes22aand22bin the mounting surface of the monolithic ceramic capacitor10to the ceramic body12. Accordingly, during mounting of the monolithic ceramic capacitor10on conductive adhesive, it cannot be sufficiently suppressed that the conductive adhesive being pressed spreads to the ceramic body12or a capillary phenomenon causes the conductive adhesive to move to the ceramic body12. As a result, short circuit failures may be caused. When the ratio of the thickness of the intermediate electrode layers26on the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12to the thickness of the intermediate electrode layers26on the end surfaces18aand18bof the ceramic body12is more than about 300%, during a temperature-cycling test, tensile stress of the plating layers may cause generation of cracks in the ceramic body12.

The thicknesses of the intermediate electrode layers26are preferably defined as follows: a section of the ceramic body is obtained by polishing the ceramic body12in the length direction of the ceramic body12, to the central portion of the main surfaces14aand14bin the width direction of the ceramic body12; in one of the outer electrodes in this section, the thickness of the intermediate electrode layer26on the end surface is measured on the central portion of the end surface, and the thickness of the intermediate electrode layer26on the main surface of the mounting-surface side of the ceramic body12is measured on the central portion of the main surface in the mounting-surface side.

In order to vary the thickness of the intermediate electrode layers26such that the thickness for the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12is different from the thickness for the end surfaces18aand18bof the ceramic body12, for example, the following method is preferably used. In barrel plating, about ⅓ or more of the volume of the barrel is loaded with the ceramic bodies12and metal media such that the volume ratio of the ceramic bodies12to the total loading volume is about 40% or more, for example. When this barrel is rotated at a low rate of about 20 rpm or less, it is highly likely that the ceramic bodies12within the barrel are plated while arranged in their length direction. Thus, the plating amount on the main surfaces and the side surfaces of each ceramic body12becomes larger. As a result, the intermediate electrode layers26preferably have a larger thickness on the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12than on the end surfaces18aand18bof the ceramic body12.

The above-described ceramic bodies12to be subjected to barrel plating include lower electrode layers thereon.

During mounting of the monolithic ceramic capacitor10, the distance from the circuit-substrate-30-side surface of the ceramic body12to the lowermost surfaces of the outer electrodes22aand22bin contact with the lands32aand32bof the circuit substrate30is preferably about 10 μm to about 50 μm, for example. When the distance from the surface of the ceramic body12to the lowermost surfaces of the outer electrodes22aand22bis less than about 10 μm, the distance (total thickness of lower electrode layer, intermediate electrode layer, and upper electrode layer) from the ceramic body12to the lands32aand32bof the circuit substrate30is not sufficiently large. Accordingly, during mounting of the monolithic ceramic capacitor10on conductive adhesive, the possibility that the conductive adhesive being pressed spreads to the ceramic body12or a capillary phenomenon causes the conductive adhesive to move to the ceramic body12cannot be significantly reduced or prevented. As a result, short circuit failures may be caused. When the distance (total thickness of lower electrode layer, intermediate electrode layer, and upper electrode layer) from the surface of the ceramic body12to the lowermost surfaces of the outer electrodes22aand22bis more than about 50 μm, during a temperature-cycling test, tensile stress of the plating layers may cause generation of cracks in the ceramic body12.

The reason why the standoff is not adjusted by controlling the thickness of the lower electrode layers24is that it becomes necessary to perform, several times, dipping of the ceramic body12in the lower electrode material, drying, and baking, which result in high production costs. The reason why the standoff is not adjusted by controlling the thickness of the upper electrode layers28is that the cost incurred for the Pd material becomes high.

In order to produce the monolithic ceramic capacitor10, ceramic green sheets containing a ceramic material used to form the ceramic body12are prepared. Subsequently, on some of the ceramic green sheets, a conductive paste is applied to form conductive patterns corresponding to the first inner electrodes20aand the second inner electrodes20b. This conductive paste can be applied by a method selected from various printing methods, such as screen printing. The conductive paste may contain, in addition to conductive fine particles, a known binder or a known solvent.

A plurality of ceramic green sheets not having conductive patterns thereon, the ceramic green sheets having conductive patterns corresponding to the first and second inner electrodes20aand20b, and a plurality of ceramic green sheets not having conductive patterns thereon are stacked in this order and pressed in the stack direction. Thus, a mother multilayer body is produced.

The mother multilayer body is cut along imaginary cutting lines thereon to provide a plurality of green ceramic bodies. The mother multilayer body can be cut by dicing or press-cutting. Such a green ceramic body may be subjected to, for example, barrel tumbling to round the ridges and corners of the green ceramic body.

The green ceramic body is fired to provide the ceramic body12including the first inner electrodes20aand the second inner electrodes20b. The firing temperature may be, for example, about 900° C. to about 1300° C.

A metal paste is applied, for example, by dipping, to the end surfaces18aand18bof the fired ceramic body12so as to extend to the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12. The applied metal paste is baked to form the lower electrode layers24. The metal paste is preferably baked at about 700° C. to about 900° C., for example.

On the lower electrode layers24, the intermediate electrode layers26are formed. At this time, by setting the loading amount of the monolithic ceramic bodies12to a relatively large amount, the intermediate electrode layers26can be formed so as to have a larger thickness on the main surfaces and the side surfaces of the ceramic bodies12. Specifically, in barrel plating, about ⅓ or more of the volume of the barrel is loaded with the ceramic bodies12and metal media such that the volume ratio of the ceramic bodies12to the total volume of the ceramic bodies12and metal media is about 40% or more, for example. When this barrel is rotated at a low rate of about 20 rpm or less, for example, it is highly likely that the ceramic bodies12within the barrel are plated while arranged in their length direction. Thus, the plating amount on the main surfaces and the side surfaces of each ceramic body12becomes larger. As a result, the intermediate electrode layers26are preferably formed so as to have a larger thickness on the main surfaces14aand14band the side surfaces16aand16bof the ceramic body12than on the end surfaces18aand18bof the ceramic body12.

The above-described ceramic bodies12to be subjected to barrel plating include lower electrode layers thereon.

The upper electrode layers28are provided. Thus, the monolithic ceramic capacitor10is produced, on the intermediate electrode layers26.

In the monolithic ceramic capacitor10, the upper electrode layers28of the first outer electrode22aand the second outer electrode22bare preferably formed of Pd or Pd—Ni alloy. Accordingly, electrochemical migration of Ag does not occur. In addition, the outer electrodes22aand22bare arranged on the main surfaces, the side surfaces, and the end surfaces of the ceramic body12so as to have thicknesses that satisfy a ratio within a certain range. As a result, during mounting of the monolithic ceramic capacitor10on the circuit substrate30, spreading or movement of the conductive adhesive is reliably prevented. In addition, generation of cracks in the ceramic body12due to stress of the outer electrodes22aand22bis also significantly reduced or prevented. Accordingly, a monolithic ceramic electronic component is provided in which short circuit failures tend not to occur; and a mounting structure is provided in which a monolithic ceramic electronic component mounted on the circuit substrate30tends not to be damaged.

EXAMPLES

An example of a ceramic body for a monolithic ceramic capacitor was prepared. This ceramic body included ceramic layers formed of BaTiO3and inner electrodes formed of Ni and had chip dimensions (L×W×T) of approximately 1.0 mm×0.5 mm×0.5 mm. Lower electrode layers were formed of Cu and had a thickness of about 30 μm on the central portions of the end surfaces of the ceramic body and had a thickness of about 5 μm on the main surfaces and the side surfaces of the ceramic body. Intermediate electrode layers had a thickness of about 5 μm on the central portions of the end surfaces of the ceramic body. Upper electrode layers had a thickness of about 0.1 μm on the central portions of the end surfaces of the ceramic body and had a thickness of about 0.1 μm on the main surfaces and the side surfaces of the ceramic body. The intermediate electrode layers were formed as Ni plating layers by Ni plating in Watts bath with about 0.5-mm-diameter media for approximately 60 minutes. The other plating conditions are described in Table 1. The upper electrode layers were formed as Pd plating layers by Pd plating in electroplating Pd bath with about 0.5-mm-diameter media for approximately 20 minutes. In addition to the above-described plating conditions, control was performed in terms of a ceramic-body-loading ratio in the barrel during formation of the intermediate electrode layers by plating and the ratio of volume of ceramic bodies/total volume of ceramic bodies and metal media. In this way, the intermediate electrode layers were formed so as to satisfy the target ratio (%) of main-surface-and-side-surface thickness to end-surface thickness.

Monolithic ceramic capacitors were produced as Examples 1 to 5 such that, in the ceramic bodies, the ratio of main-surface-and-side-surface thickness to end-surface thickness of the intermediate electrode layers was varied as described in Table 1. Another monolithic ceramic capacitor was produced as Comparative example 1 such that the intermediate electrode layers had the same thickness on the main surfaces, the side surfaces, and the end surfaces of the ceramic body. Another monolithic ceramic capacitor was produced as Comparative example 2 such that the ratio of main-surface-and-side-surface thickness to end-surface thickness of the intermediate electrode layers of the ceramic body was beyond the upper limit defined in a preferred embodiment of the present invention. Another monolithic ceramic capacitor was produced as Comparative example 3: outer electrodes were formed that were each constituted by a Cu lower electrode layer and an overlying Ag—Pd alloy thick electrode film; and the outer electrodes had a thickness of about 50 μm on the central portions of the end surfaces of the ceramic body and had a thickness of about 5 μm on the main surfaces and the side surfaces of the ceramic body.

Each of the samples prepared above was mounted, with conductive adhesives34aand34b, on first and second Ag lands32aand32bformed on the upper surface of an alumina circuit substrate30. The conductive adhesives34aand34bcontained about 50 vol % of Ag powder in an epoxy resin. Uncured conductive adhesives34aand34bwere applied to the first and second lands32aand32b. After that, each sample was placed on the conductive adhesives34aand34band heating was performed at about 140° C. for approximately 30 minutes to cure the conductive adhesives34aand34b. Thus, the mounting structures of the samples were obtained.

The thicknesses of the intermediate electrode layers were measured as follows: a section of each sample was obtained by polishing the sample in the length L direction of the sample, to the central portion of the main surfaces in the width direction of the sample; for one of the outer electrodes in this section, an optical microscope was used to measure the thickness of the intermediate electrode layer on the central portion of the end surface and the thickness of the intermediate electrode layer in the central portion of the outer electrode on the mounting-surface side of the sample. From these measured thicknesses, the ratio was calculated.

The monolithic ceramic capacitors were evaluated in terms of occurrence of electrochemical migration, occurrence of short circuit failures, and generation of cracks caused by a thermal shock cycling test.

The evaluation in terms of occurrence of electrochemical migration was performed as follows. Each sample was subjected to a high temperature loading test at about 150° C. under application of about 32 V for approximately 2000 hours. After the test, the sample was observed as to whether the ceramic body defining and serving as the inter-electrode portion of the sample discolored or not; and the length of dendrites was measured. A sample in which the inter-electrode portion of the sample discolored and dendrites had a length of about 50 μm or more was evaluated as a sample in which electrochemical migration occurred.

The evaluation in terms of occurrence of short circuit failures was performed as follows. The resistance of each sample was measured with an IR meter (SS-867) at about 25V DC. A sample having a resistance of about 1 MΩ or less was evaluated as a sample in which short circuit failures occurred. The number ratio of samples in which short circuit failures occurred to all the samples evaluated is described as a ratio of occurrence of short circuit.

The evaluation in terms of generation of cracks caused by a thermal shock cycling test was performed as follows. The thermal shock cycling test was performed by 2000 cycles of holding a sample at about −55° C. for approximately 30 minutes in an air chamber and holding the sample at about 150° C. for approximately 30 minutes in an air chamber. After the thermal shock cycling test was performed, the sample was polished in a direction perpendicular to the substrate-mounting surface and in the length direction of the sample, to the central portion of the main surfaces in the width direction of the sample. The resultant polished surface was observed with a metallographic microscope at a magnification of 100 to 500 as to whether cracks extending from the edge of bent portions of outer electrodes to the ceramic region were generated or not.

The standoff distance was determined by measuring, with a laser displacement meter, the distance from a possible mounting surface of the ceramic body to the point of outer electrodes that is farthest from the possible mounting surface of the ceramic body in the thickness direction of the outer electrodes formed on the possible mounting surface of the ceramic body. Each value in Table 1 is the average of values of 20 samples.

As indicated in Table 1, according to preferred embodiments of the present invention, the outermost layers of outer electrodes are defined by Pd electrodes not containing Ag. As a result, while such a component is applicable to mounting with conductive adhesive, the occurrence of electrochemical migration is significantly reduced or prevented. In addition, the intermediate electrode layers are preferably configured to have a larger thickness on the main surfaces and the side surfaces of the ceramic body than on the end surfaces of the ceramic body, so that the outer electrodes have a large thickness in the substrate-mounting surface. As a result, a sufficiently large distance (standoff) is ensured from the lowermost point of outer electrodes in the mounting surface of the monolithic ceramic electronic component to the surface of the ceramic body. Accordingly, when such a monolithic ceramic electronic component is mounted on a circuit substrate with conductive adhesive, spreading (movement) of the conductive adhesive over the monolithic ceramic electronic component is significantly reduced or prevented. Thus, monolithic ceramic electronic components in which short circuit failures tend not to occur are provided.

The ceramic bodies in Table 1 had lower electrode layers thereon.