JP6631547B2 - Multilayer ceramic capacitors - Google Patents

Description

  The present invention relates to a multilayer ceramic capacitor, and more particularly, to a multilayer ceramic capacitor provided with external electrodes having a multilayer structure.

  In recent years, multilayer ceramic capacitors have come to be used even in harsh environments that are more susceptible to impacts than in the past, and are required to have mechanical strength that can cope with such environments. For example, multilayer ceramic capacitors used in mobile devices such as mobile phones and portable music players are required to withstand shocks such as dropping. Specifically, it is necessary that the multilayer ceramic capacitor does not fall off from the mounting substrate even if it receives an impact such as dropping, so that cracks do not occur. Further, multilayer ceramic capacitors used in in-vehicle devices such as ECUs are required to withstand shocks such as thermal cycles. Specifically, the multilayer ceramic capacitor needs to be free from cracks even when subjected to a flexural stress caused by linear expansion / contraction of the mounting substrate in a thermal cycle or a tensile stress applied to an external electrode.

  For the purpose of meeting the above demands, a multilayer ceramic capacitor including an external electrode including a thermosetting resin layer is known. Patent Document 1 discloses such a multilayer ceramic capacitor.

  The multilayer ceramic capacitor disclosed in Patent Literature 1 has a multi-layer structure including an electrode layer formed on both end surfaces of a capacitor body as a baked electrode and a conductive thermosetting resin layer formed on the surface of the electrode layer. It has electrodes. In the multilayer ceramic capacitor of Patent Literature 1, in the external electrode having a multilayer structure, the electrode layer has a function of securing moisture resistance reliability, and the thermosetting resin layer has a function of suppressing cracks in the capacitor body.

JP-A-11-162771

In the multilayer ceramic capacitor as disclosed in Patent Literature 1, since the thermosetting resin layer contains a resin, the content of the metal contained in the thermosetting resin layer is low. Therefore, the adhesion between the thermosetting resin layer and the electrode layer formed on the lower surface tends to be weak. As a result, the multilayer ceramic capacitor as disclosed in Patent Literature 1 has a problem in that moisture or the like enters between the thermosetting resin layer and the electrode layer, and the moisture resistance reliability and the electrical characteristics are deteriorated.
As a method for solving the above problem, there is a method of forming an alloy layer between the electrode layer and the thermosetting resin layer.However, if the amount of alloy between the electrode layer and the thermosetting resin layer is too large, There is a problem in that the crack suppressing function of the curable resin layer is reduced.

  Therefore, a main object of the present invention is to improve mechanical strength by using an external electrode, and to provide good moisture resistance reliability and electric resistance by firmly adhering a base electrode layer and a conductive resin layer included in the external electrode. An object of the present invention is to provide a multilayer ceramic capacitor having characteristics.

A multilayer ceramic capacitor according to the present invention is formed on a laminate formed by laminating a plurality of ceramic layers and a plurality of internal electrodes, and on a surface of the laminate so as to be electrically connected to the internal electrodes. A multilayer ceramic capacitor including a pair of external electrodes, wherein each of the pair of external electrodes is formed on a surface of the multilayer body, a base electrode layer containing Cu, and partially formed on a surface of the base electrode layer. , A bonding portion containing a Cu ₃ Sn alloy, a base electrode layer and a conductive resin layer formed on the surface of the bonding portion, and the total area of the bonding portion is 2.7% or more of the total area of the base electrode layer. It is a multilayer ceramic capacitor characterized by being 40.6% or less.
The thickness of the bonding portion is 0.1μm or more 1.2μm or less, a laminated ceramic capacitor.
Further, the bonding portion is a multilayer ceramic capacitor that is formed by a reaction between Cu contained in the base electrode layer and an alloy containing Sn and at least one of Ag and Cu contained in the conductive resin layer. is there.
Preferably, the width of the joint is from 1.3 μm to 13.3 μm.

In the multilayer ceramic capacitor according to the present invention, in the external electrode having the multilayer structure, the external electrode is partially formed on the surface of the base electrode layer, and is metal-bonded via a bonding portion containing a Cu ₃ Sn alloy, and the total area of the bonding portion is , And not less than 2.7% and not more than 40.6% of the total area of the base electrode layer. Thereby, since the base electrode layer included in the external electrode and the conductive resin layer are firmly adhered to each other, the moisture resistance reliability and the electrical characteristics are improved, and the occurrence of cracks in the multilayer ceramic capacitor can be suppressed. Furthermore, since the external electrode includes the conductive resin layer, mechanical strength such as substrate bending resistance and drop impact resistance is improved. As a result, a multilayer ceramic capacitor having improved mechanical strength by the external electrode, and having good moisture resistance reliability and electric characteristics by tightly adhering the base electrode layer and the conductive resin layer included in the external electrode is provided. Obtainable.
Furthermore, in the multilayer ceramic capacitor according to the present invention, the thickness of the joint is 0.1 μm or more and 1.2 μm or less. As a result, the electrical characteristics are improved while suppressing the occurrence of cracks in the multilayer ceramic capacitor.
Further, the width of the joint is 1.3 μm or more and 13.3 μm or less. Thereby, generation of cracks in the multilayer ceramic capacitor can be more reliably suppressed.
Further, in the multilayer ceramic capacitor according to the present invention, when the bonding portion includes an alloy layer containing at least one of Ag and Cu and Sn, a multilayer ceramic capacitor having good electrical characteristics can be obtained more reliably. Can be.

  According to the present invention, a laminate having good moisture resistance reliability and electrical characteristics is obtained by improving mechanical strength by an external electrode and by firmly adhering a base electrode layer and a conductive resin layer included in the external electrode. A ceramic capacitor may be provided.

  The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments for carrying out the invention with reference to the drawings.

1 is an external perspective view showing a multilayer ceramic capacitor according to one embodiment of the present invention. FIG. 2 is a cross-sectional view of the multilayer ceramic capacitor according to the embodiment of the present invention, taken along line II-II of FIG. 1. FIG. 3 is an enlarged view of a first external electrode and its vicinity in the cross-sectional view of FIG. 2 showing the multilayer ceramic capacitor according to one embodiment of the present invention. It is the figure which showed typically the SEM image which shows the junction part formed in an external electrode.

1. Hereinafter, a multilayer ceramic capacitor according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view showing a multilayer ceramic capacitor according to one embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1 showing the multilayer ceramic capacitor according to one embodiment of the present invention. FIG. 3 is an enlarged view of the first external electrode and its vicinity in the cross-sectional view of FIG. 2 showing the multilayer ceramic capacitor according to one embodiment of the present invention.

  The multilayer ceramic capacitor 10 according to this embodiment includes a multilayer body 20, a first external electrode 140a and a second external electrode 140b (a pair of external electrodes).

(Laminate 20)
The laminated body 20 is formed by laminating a plurality of ceramic layers 30, a plurality of first internal electrodes 40a and a plurality of second internal electrodes 40b.

  The laminated body 20 is formed in a rectangular parallelepiped shape, and opposes the first main surface 22a and the second main surface 22b, the opposing first side surface 24a and the second side surface 24b, and the opposing first end surface 26a and And a second end surface 26b. Here, the direction connecting the first end surface 26a and the second end surface 26b is the length (L) direction, which is orthogonal to the L direction, and the direction connecting the first side surface 24a and the second side surface 24b is the width. The direction orthogonal to the (W) direction, the L direction and the W direction, and connecting the first main surface 22a and the second main surface 22b is the height (T) direction.

  It is preferable that the laminate 20 be rounded at some or all of its corners and ridges. Moreover, the rectangular parallelepiped shape of the laminated body 20 is a shape including the first and second main surfaces 22a and 22b, the first and second side surfaces 24a and 24b, and the first and second end surfaces 26a and 26b. Is not particularly limited. For example, the laminated body 20 has steps or irregularities on a part or all of the first and second main surfaces 22a and 22b, the first and second side surfaces 24a and 24b, and the first and second end surfaces 26a and 26b. May be formed.

(Ceramic layer 30)
The ceramic layer 30 is sandwiched between the first internal electrode 40a and the second internal electrode 40b, and is stacked in the T direction. The thickness of the ceramic layer 30 is preferably about 0.5 μm or more and 10 μm or less.

As the ceramic material of the ceramic layer 30, for example, a dielectric ceramic composed of a main component such as BaTiO ₃ , CaTiO ₃ , SrTiO ₃ , CaZrO ₃ can be used. In addition, an auxiliary component such as a Mn compound, an Fe compound, a Cr compound, a Co compound, or a Ni compound may be added to these main components.

(First and second internal electrodes 40a, 40b)
The first internal electrode 40a extends in a plate shape at the interface of the ceramic layer 30 and is exposed on the first end surface 26a of the multilayer body 20. On the other hand, the second internal electrode 40b extends in a plate shape at the interface of the ceramic layer 30 so as to face the first internal electrode 40a via the ceramic layer 30, and is exposed to the second end surface 26b. Therefore, the first and second internal electrodes 40a and 40b include opposing portions opposing each other with the ceramic layer 30 interposed therebetween, and a drawing portion drawn to the first and second end surfaces 26a and 26b. When the first internal electrode 40a and the second internal electrode 40b face each other via the ceramic layer 30, a capacitance is generated. It is preferable that the thicknesses of the first and second internal electrodes 40a and 40b be approximately 0.2 μm or more and 2.0 μm or less.

  The first and second internal electrodes 40a and 40b are made of a suitable conductive material such as a metal such as Ni, Cu, Ag, Pd, or Au, an Ag-Pd alloy, or an alloy containing at least one of these metals. It is preferred to be constituted by

(First and second external electrodes 140a, 140b)
The first external electrode 140a extends from the first end surface 26a of the multilayer body 20 to a part of each of the first and second main surfaces 22a and 22b and a part of each of the first and second side surfaces 24a and 24b. And is electrically connected to the first internal electrode 40a at the first end face 26a. On the other hand, the second external electrode 140b extends from the second end surface 26b of the multilayer body 20 to a part of each of the first and second main surfaces 22a and 22b and each of the first and second side surfaces 24a and 24b. It is formed so as to reach a part and is electrically connected to the second internal electrode 40b at the second end face 26b.

  Each of the first and second external electrodes 140a and 140b has a multilayer structure including a base electrode layer 142, a bonding part 144, a conductive resin layer 146, and a plating layer 150. Note that the first and second external electrodes 140a and 140b may not include the plating layer 150.

(Base electrode layer 142)
The base electrode layer 142 extends from the first or second end surface 26a, 26b of the laminate 20 to a part of each of the first and second main surfaces 22a, 22b, and the first and second side surfaces 24a, 24b, respectively. Is preferably formed so as to reach a part. Note that the base electrode layer 142 may be formed only on the first or second end surface 26a, 26b of the laminate 20. The thickness of the thickest portion of the base electrode layer 142 is preferably, for example, not less than 10 μm and not more than 50 μm.

  The base electrode layer 142 is formed, for example, by applying and baking a conductive paste containing a conductive metal and glass. As the conductive metal, for example, Cu or a Cu alloy can be used. As the glass, for example, a glass containing B, Si, Ba, Mg, Al, Li, or the like can be used. The base electrode layer 142 may be formed by simultaneous firing with the first and second internal electrodes 40a and 40b, or may be formed by applying and baking a conductive paste.

(Joining part 144)
The bonding portion 144 is formed on the surface so as to partially cover the base electrode layer 142. Specifically, the bonding portion 144 is formed on the surface of the base electrode layer 142 formed on the first or second end surface 26a, 26b of the multilayer body 20, from which the first and second main surfaces 22a are formed. , 22b and the surface of the base electrode layer 142 formed on a part of each of the first and second side surfaces 24a, 24b. Note that the bonding portion 144 may be formed only on the surface of the base electrode layer 142 formed on the first or second end surface 26a, 26b of the multilayer body 20.

  The joint 144 may have a roughened surface. Specifically, it is preferable that the value of the surface roughness Ra of the bonding portion 144 be 0.2 μm or more and 5.1 μm or less. When the value of the surface roughness Ra of the bonding portion 144 is smaller than 0.2 μm, the interface separation between the bonding portion 144 and the conductive resin layer 146 tends to occur. If the value of the surface roughness Ra of the bonding portion 144 is larger than 5.1 μm, the contact area of the conductive resin layer 146 becomes too small, and similarly, the interface separation easily occurs.

The joint 144 includes a Cu ₃ Sn alloy. In addition, the joint 144 may include an alloy containing Sn and at least one of Ag and Cu. The atomic ratio Cu: Sn (atom%) of the bonding portion 144 is 70 or more and 80 or less: 20 or more and 30 or less atom%. The Cu ₃ Sn alloy or the alloy containing Sn and at least one of Ag and Cu in the joint portion 144 is formed by the heat treatment step when manufacturing the multilayer ceramic capacitor 10, in which the Cu contained in the base electrode layer 142 is electrically conductive with Cu. It is generated by a reaction between at least one of Ag and Cu contained in the resin layer 146 and an alloy containing Sn. That is, the base electrode layer 142 and the conductive resin layer 146 are metal-bonded via the bonding portion 144.

The total area of joint portion 144 is not less than 2.7% and not more than 40.6% of the total area of base electrode layer 142. Further, it is preferable that the thickness of the joining portion 144 be 0.1 μm or more and 1.2 μm or less. Further, it is preferable that the width of the joining portion 144 is not less than 1.3 μm and not more than 13.3 μm. If the thickness of the bonding portion 144 is less than 0.1 μm, the Cu ₃ Sn alloy is not sufficiently generated, so that the metal bonding is incomplete and the adhesion between the base electrode layer 142 and the conductive seed layer 146 is weakened. If there is no bonding portion 144, the base electrode layer 142 and the conductive resin layer 146 are not metal-bonded, so that the adhesion between the base electrode layer 142 and the conductive seed layer 146 is weakened. As a result, the electrical characteristics are not stable, and furthermore, sufficient humidity resistance reliability cannot be obtained. Further, even if the width of the bonding portion 144 is less than 1.3 μm and the total area of the bonding portion 144 is less than 2.7% of the total area of the base electrode layer 142, the metal bonding becomes incomplete and the base electrode layer The adhesive force between the conductive resin layer 146 and the conductive resin layer 146 is weakened. As a result, the electrical characteristics are not stable, and furthermore, sufficient humidity resistance reliability cannot be obtained.
On the other hand, if the thickness of the joint 144 exceeds 1.2 μm, the width of the joint 144 exceeds 13.3 μm, and the total area of the joint 144 exceeds 40.6% of the total area of the base electrode layer, the external force When stress is generated in the first and second external electrodes 140a and 140b, the stress cannot be relieved, and the crack suppressing function of the conductive resin layer 146 decreases.

The total area, thickness, and width of the joint portion 144 are polished in cross section to a half position (W / 2 position) in the width direction of the above-described multilayer ceramic capacitor, and are enlarged to a predetermined magnification as shown in FIG. Measured at exposed cross section. Each measuring method is as follows.
First, the total area of the joint 144 is determined at the center position (T / 2 position) of the exposed cross section, in the region where the joint is present, in the field of view of the SEM image of the exposed cross section enlarged to a predetermined magnification. The ratio of the presence of the joint to the length of the electrode layer 142 is measured as the total area of the joint 144.
In addition, the thickness of the joint 144 can be determined at the center position (T / 2 position) of the exposed cross section, in the region where the joint is present, in the field of view of the SEM image of the exposed cross section enlarged to a predetermined magnification in the field of view. The thickness along the direction perpendicular to the tangent to the interface with the layer 142 was measured as the thickness of the joint 144.
Further, the width of the joint 144 can be confirmed at the center position (T / 2 position) of the exposed section, in the region where the joint is present, within the field of view of the SEM image of the exposed section enlarged to a predetermined magnification. Was measured as the width of the joint 144.

(Conductive resin layer 146)
The conductive resin layer 146 is formed on the surface so as to cover the base electrode layer 142 and the joint 144. Specifically, the conductive resin layer 146 is formed on the surface of the joint 144 formed on the first or second end surface 26a, 26b of the laminate 20, and the first and second main surfaces are formed therefrom. It is preferable that the first and second side surfaces 24a and 24b are formed so as to reach a part of each of the first and second side surfaces 24a and 24b. The thickness of the conductive resin layer 146 is preferably, for example, not less than 10 μm and not more than 150 μm.

  The conductive resin layer 146 includes a conductive filler and a resin.

  The conductive filler may have a spherical or flat particle shape. When the shape of the conductive filler is spherical, flat, or the like, it is preferable to use a mixture of the spherical shape and the flat shape. The shape of the particles of the conductive filler is not particularly limited. Further, the average particle size of the conductive filler may be, for example, 0.3 μm or more and 10 μm or less, but is not particularly limited.

As the conductive filler, a metal having conductivity can be used. For example, Cu, Ag and Sn or an alloy containing these metals can be used. In particular, the reason why Cu, Ag and Sn or an alloy containing these metals is used is to form a Cu ₃ Sn alloy or a joint 144 containing an alloy of Ag, Cu and Sn.

  The conductive filler mainly plays a role in conducting the conductive resin layer 146. Specifically, a conductive path is formed inside the conductive resin layer 146 by contact between the conductive fillers.

  As the resin contained in the conductive resin layer 146, for example, a known thermosetting resin such as an epoxy resin, a phenol resin, a urethane resin, a silicone resin, and a polyimide resin can be used. In particular, as a resin included in the conductive resin layer 146, an epoxy resin is preferably used. Epoxy resin has excellent heat resistance, moisture resistance, adhesion, and the like, and is one of the most suitable resins. The conductive resin layer 146 preferably contains a curing agent together with the thermosetting resin. When an epoxy resin is used as the thermosetting resin, a known compound such as a phenol-based, amine-based, acid anhydride-based, or imidazole-based compound can be used as the curing agent.

  Since the conductive resin layer 146 contains a resin, the conductive resin layer 146 is more flexible than, for example, a conductive layer made of a baked product of a plating film or a conductive paste. Therefore, the conductive resin layer 146 functions as a layer for buffering a physical impact applied to the multilayer ceramic capacitor 10 and an impact caused by a thermal cycle. Thereby, it is possible to prevent the occurrence of cracks in the multilayer ceramic capacitor 10. That is, since the multilayer ceramic capacitor 10 includes the conductive resin layer 146, mechanical strength such as substrate bending resistance and drop impact resistance is improved.

(Plating layer 150)
The plating layer 150 is formed on the surface so as to cover the conductive resin layer 146. Specifically, the plating layer 150 is formed on the surface of the conductive resin layer 146 formed on the first or second end surface 26a, 26b of the laminate 20, and the first and second main surfaces are formed therefrom. It is preferable that the conductive resin layer 146 be formed so as to reach a part of each of the conductive resin layers 146 formed on a part of each of the first and second side surfaces 24a and 24b. Note that the plating layer 150 may be formed only on the surface of the conductive resin layer 146 formed on the first or second end surface 26a, 26b of the laminate 20.

  The plating layer 150 includes at least one selected from Cu, Ni, Sn, Ag, Pd, an Ag-Pd alloy, Au, and the like.

  The plating layer 150 has a two-layer structure including a first plating layer 152 and a second plating layer 154. The plating layer 150 may have a single-layer structure composed of only the first plating layer 152, or may have a multilayer structure of three or more layers. The thickness per one plating layer 150 is preferably 1 μm or more and 15 μm or less.

  The first plating layer 152 is formed on the surface so as to cover the conductive resin layer 146. The first plating layer 152 is preferably a Ni plating layer. Accordingly, when mounting the multilayer ceramic capacitor 10 on a mounting board, it is possible to prevent the base electrode layer 142 and the conductive resin layer 146 from being eroded by solder used for mounting. Further, the first plating layer 152 may have a multilayer structure.

  The second plating layer 154 is formed on the surface so as to cover the first plating layer 152. The second plating layer 154 is preferably a Sn plating layer. Thereby, when the multilayer ceramic capacitor 10 is mounted on the mounting board, the wettability of the solder used for mounting to the external electrodes 140a and 140b can be improved. Therefore, mounting of the multilayer ceramic capacitor 10 can be easily performed.

(effect)
In the multilayer ceramic capacitor 10 according to one embodiment of the present invention, in the external electrodes 140a and 140b having a multilayer structure, the base electrode layer 142 and the conductive resin layer 146 contain a Cu ₃ Sn alloy, and Ag and Cu are used. Metal bonding is performed via a bonding portion 144 that may include a Sn alloy, and the total area of the bonding portion is 2.7% or more and 40.6% or less of the total area of the base electrode layer. Thereby, since the base electrode layer 142 and the conductive resin layer 146 included in the external electrodes 140a and 140b are firmly adhered to each other, the moisture resistance reliability and the electrical characteristics are improved, and the occurrence of cracks in the multilayer ceramic capacitor is suppressed. can do. Further, since the external electrodes 140a and 140b include the conductive resin layer 146, mechanical strength such as substrate bending resistance and drop impact resistance is improved. As a result, in the multilayer ceramic capacitor 10, the mechanical strength is improved by the external electrodes 140 a and 140 b, and the base resin layer 142 and the conductive resin layer 146 included in the external electrodes 140 a and 140 b are firmly adhered to each other. Has good moisture resistance reliability and electrical properties.

  Furthermore, in the multilayer ceramic capacitor 10 according to one embodiment of the present invention, when the thickness of the joining portion 144 is 0.1 μm or more and 1.2 μm or less, the generation of cracks in the multilayer ceramic capacitor is suppressed, and Is also good. Further, when the width of the joint portion 144 is 1.3 μm or more and 13.3 μm or less, the occurrence of cracks in the multilayer ceramic capacitor can be more reliably suppressed.

  Furthermore, in the monolithic ceramic capacitor 10 according to one embodiment of the present invention, when the joint portion 144 includes an alloy layer containing at least one of Ag and Cu and Sn, good electrical characteristics are more reliably achieved. The laminated ceramic capacitor 10 can be obtained.

2. Manufacturing method of multilayer ceramic capacitor Next, a manufacturing method of the multilayer ceramic capacitor will be described.

(Preparation of laminate)
First, a ceramic green sheet is formed by applying a ceramic paste containing a ceramic powder in a sheet shape by, for example, a screen printing method and then drying.

  Next, a conductive paste for forming an internal electrode is applied to the surface of the ceramic green sheet in a predetermined pattern by, for example, a screen printing method, to obtain a ceramic green sheet on which the conductive pattern for forming an internal electrode is formed. Further, a ceramic green sheet having no conductive pattern for forming an internal electrode is also obtained. In addition, the ceramic paste and the conductive paste for forming the internal electrode may include, for example, a known binder and a solvent.

  Then, a predetermined number of ceramic green sheets on which the internal electrode forming conductive patterns are not formed are stacked, and a ceramic green sheet on which the internal electrode forming conductive patterns are formed is stacked on the surface thereof, and the internal electrode forming conductive patterns are formed on the surface. A predetermined number of ceramic green sheets having no conductive pattern formed thereon are laminated. Thus, a mother laminate is manufactured.

  In addition, you may press a mother laminated body in a lamination direction as needed. As a method of pressing the mother laminate, for example, an isostatic press or the like can be considered.

  Further, a plurality of raw laminates are formed by cutting the mother laminate to a predetermined shape and size. At this time, the raw laminate may be subjected to barrel polishing or the like so as to form ridges or corners with roundness.

  Finally, by firing the green laminate, the first and second internal electrodes are arranged inside, the end of the first internal electrode is drawn out to the first end face, and the second internal electrode is The end forms a laminate that is drawn out to the second end face. The firing temperature of the green laminate can be set as appropriate depending on the ceramic material or conductive material. The firing temperature of the green laminate can be, for example, about 900 ° C. or more and 1300 ° C. or less.

(Formation of external electrode on laminate)
First, a conductive paste is applied and baked on both end surfaces of the laminate obtained as described above to form a base electrode layer of an external electrode. The baking temperature at this time is preferably 700 ° C. or more and 900 ° C. or less.

  Next, a conductive resin paste containing at least a conductive filler containing Sn and a resin is applied so as to cover the base electrode layer, and heat treatment is performed at a maximum temperature of 200 ° C. or more and 300 ° C. or less to thermally cure the resin. . Note that the maximum temperature of the heat treatment is preferably from 240 ° C to 260 ° C. In this case, the content of Sn in the conductive resin paste is preferably 10 wt% or more and 40 wt% or less. Thus, the conductive resin layer is formed so as to cover the base electrode layer. At this time, a joint is formed partially on the surface of the base electrode layer. The thickness and width of the joint can be adjusted by changing the maximum temperature of the heat treatment and the heat treatment time. In this embodiment, the thickness and width of the joint are adjusted by changing the maximum temperature of the heat treatment. Specifically, the thickness and width of the joint can be reduced by lowering the maximum temperature of the heat treatment, and can be increased by raising the temperature.

Note that the atmosphere during the heat treatment is preferably an N ₂ atmosphere. Further, it is preferable to suppress the oxygen concentration to 100 ppm or less. Thereby, scattering of the resin can be prevented, and oxidation of various metal components can be prevented.

  Then, if necessary, a Ni plating layer (first plating layer) is formed on the surface of the conductive resin layer. Electroplating can be used as a method for forming the Ni plating layer.

  If necessary, a Sn plating layer (second plating layer) is formed on the surface of the Ni plating layer (first plating layer).

  As described above, the multilayer ceramic capacitor according to the present invention is manufactured.

3. Experimental Examples Hereinafter, experimental examples performed by the inventors to confirm the effects of the present invention will be described. In the experimental examples, samples Nos. 1 to 20 were prepared according to the above-described method for manufacturing a multilayer ceramic capacitor, and the mechanical strength and the electrical characteristics were evaluated.

The specifications of the multilayer ceramic capacitors which are the sample Nos. 1 to 20 are as follows.
Size (design value) L × W × T: 1.6 mm × 0.8 mm × 0.8 mm
Ceramic material: BaTi ₂ O ₃
Capacitance: 22μF
Rated voltage: 6.3V
External electrode structure: A multilayer structure composed of a base electrode layer, a conductive resin layer, and a plating layer, and a junction is partially formed on the surface of the base electrode layer. Base electrode layer: A conductive metal (Cu) and glass Bonding part: Alloy of Cu and Sn Conductive resin layer: Conductive filler containing Ag and Sn, and resin containing resol-type phenolic resin Plating layer structure: Ni plating layer (first plating layer) And Sn plating layer (second plating layer) Two-layer structure Heat treatment conditions: 18 minutes in N ₂ atmosphere

  Each of Sample Nos. 1 to 20 has a Sn content contained in the conductive resin paste used for forming the conductive resin layer and a curing temperature for thermally curing the conductive resin paste. This is a sample in which the maximum temperature was changed.

In Sample Nos. 1 to 5, the maximum curing temperature was 240 ° C., and the Sn content was varied between 0 wt% and 40 wt%.
In Sample Nos. 6 to 10, the maximum curing temperature was set to 260 ° C., and the Sn content was changed from 0 wt% to 40 wt%.
In Sample Nos. 11 to 15, the maximum curing temperature was 280 ° C., and the Sn content was varied between 0 wt% and 40 wt%.
In Sample Nos. 16 to 20, the maximum curing temperature was set at 300 ° C., and the Sn content was varied between 0 wt% and 40 wt%.

(Evaluation method)
The mechanical strength and electrical characteristics of each of Sample Nos. 1 to 20 were evaluated.

  The test regarding mechanical strength was performed as follows. Reflow mounting was performed on a JEITA land substrate using lead-free solder (Sn-3.0Ag-0.5Cu). The substrate was bent by 1 mm per second, and was held for 5 seconds when the substrate was bent by 5 mm. Thereafter, the chip was removed from the substrate, embedded in a resin, and polished in cross section to a half position (W / 2 position) of the width direction dimension of the multilayer ceramic capacitor along the length direction of the multilayer ceramic capacitor. The presence or absence of cracks at the edge of the base electrode layer in the exposed cross section was observed, and the number of occurrences of cracks was counted. The number of evaluation samples for mechanical strength was set to 12.

  The test regarding the electrical characteristics was performed as follows. Each sample was scanned with an impedance analyzer (4294A manufactured by Agilent Technologies) at a voltage of 1 Vrms and a frequency of 1 kHz to 10 MHz, and an ESR at 1 MHz was measured. The test fixture used was 16044A manufactured by Agilent Technologies. Samples having an average of 15 mΩ or less were judged to be good. The number of evaluation samples for the electrical property test was 10.

(Analysis method)
A method of analyzing whether or not the external electrode of the multilayer ceramic capacitor as each of the sample numbers 1 to 20 includes a joint is as follows. A multilayer ceramic capacitor was randomly selected, embedded in a resin, and polished in cross section to a half position (W / 2 position) in the width direction of the multilayer ceramic capacitor along the length direction of the multilayer ceramic capacitor. Thereafter, on the exposed cross section, the presence or absence of a joint was observed at a predetermined magnification of the external electrode at the center of the end face of the multilayer ceramic capacitor using FE-SEM.

The total area, thickness, and width of the joint were measured on an exposed cross section polished to a half position (W / 2 position) in the width direction of the above-described multilayer ceramic capacitor. The measuring method is as follows.
First, the total area of the joint is determined at the center position (T / 2 position) of the exposed cross section, in the region where the joint is present, in the field of view of the SEM image of the exposed cross section enlarged to a predetermined magnification in the field of view. The proportion of the joint present relative to the length of the layer was measured as the total area of the joint and calculated as the average of three samples.
In addition, the thickness of the bonding portion can be confirmed at the center position (T / 2 position) of the exposed cross section, in the region where the bonding portion exists, in the field of view of the SEM image of the exposed cross section enlarged to a predetermined magnification in the field of view. The thickness along the direction perpendicular to the tangent to the interface with was measured as the thickness of the joint, and calculated as the average value of three samples.
Furthermore, the width of the joint can be confirmed at the center position (T / 2 position) of the exposed cross section in the field of the SEM image of the exposed cross section enlarged to a predetermined magnification in the region where the joint exists. The maximum length was measured as the width of the joint and calculated as the average of three samples.

(Evaluation results)
Table 1 shows the evaluation results of the mechanical strength characteristics of each sample for Sample Nos. 1 to 20.

As shown in Table 1, in Sample Nos. 1 to 10, the Sn content was 0 wt% or more and 40 wt% or less, and the highest curing temperature was 240 ° C or more and 260 ° C or less. No sample was present.
In Sample Nos. 11 to 14, the content of Sn was 0 wt% or more and 30 wt% or less, and the maximum curing temperature was 280 ° C., so that no cracked sample was present.
Furthermore, in Sample Nos. 16 to 19, the content of Sn was 0 wt% or more and 30 wt% or less, and the maximum curing temperature was 300 ° C., so that no cracked sample was present.

On the other hand, in sample No. 15, since the maximum curing temperature is 280 ° C. and the Sn content is 40 wt%, the total area of the joint is 58.8% and the thickness of the joint is 1. Since the width was 8 μm and the width of the joint was 27.7 μm, one of 12 cracks was generated, and the crack generation rate was 8.3%.
In sample 20, the maximum curing temperature is 300 ° C. and the Sn content is 40 wt%, so that the total area of the joint is 81.9% and the thickness of the joint is 2.10%. 6 μm, and the width of the joint was 41.6 μm, so that cracks occurred in 9 out of 12 cracks, and the crack occurrence rate was 75%.

  Next, when the ESR of each sample was confirmed, the sample No. 1, the sample No. 6, the sample No. 11 and the sample No. 16 did not contain Sn in the conductive resin paste, and thus no joint was present. A very high ESR was obtained.

  On the other hand, in the samples of Sample Nos. 2 to 5, Sample Nos. 7 to 10, Sample Nos. 12 to 15, and Sample Nos. 17 to 20, the conductive resin paste contains Sn. A good multilayer ceramic capacitor having a lower ESR than the ESRs of Sample No. 1, Sample No. 6, Sample No. 11 and Sample No. 16 having no part was obtained.

  It should be noted that the present invention is not limited to the above-described embodiment, but may be variously modified within the scope of the invention.

DESCRIPTION OF SYMBOLS 10 Laminated ceramic capacitor 20 Laminated body 22a 1st main surface 22b 2nd main surface 24a 1st side surface 24b 2nd side surface 26a 1st end surface 26b 2nd end surface 30 ceramic layer 40a 1st internal electrode 40b 1st 2 internal electrode 140a 1st external electrode 140b 2nd external electrode 142 base electrode layer 144 joint 146 conductive resin layer 150 plating layer 152 first plating layer 154 second plating layer

Claims (2)

A laminate formed by laminating a plurality of ceramic layers and a plurality of internal electrodes; and a pair of external electrodes formed on a surface of the laminate so as to be electrically connected to the internal electrodes. A multilayer ceramic capacitor,
Each of the pair of external electrodes,
A base electrode layer partially formed on the surface of the laminate and containing Cu;
A bonding portion formed on the surface of the base electrode layer and including a Cu ₃ Sn alloy;
Including a conductive resin layer formed on the surface of the base electrode layer and the bonding portion,
The total area of the junction, Ri 40.6% der less 2.7% or more of the total area of the underlying electrode layer,
The thickness of the joining portion is 0.1 μm or more and 1.2 μm or less,
The bonding portion is formed by reacting Cu contained in the base electrode layer and an alloy containing Sn and at least one of Ag and Cu contained in the conductive resin layer and Sn. A multilayer ceramic capacitor. 2. The multilayer ceramic capacitor according to claim 1, wherein a width of the joint is 1.3 μm or more and 13.3 μm or less. 3.