JP2018098475A - Multilayer ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer ceramic capacitor that improves mechanical strength by an external electrode and achieves high moisture resistance reliability and excellent electrical characteristics due to firm adhesion between an underlying electrode layer and a conductive resin layer included in the external electrode.SOLUTION: A multilayer ceramic capacitor 10 include: a laminate 20 formed by laminating a plurality of ceramic layers 30 and a plurality of internal electrodes 40a, 40b; and a pair of external electrodes 140a, 140b formed on both end surfaces 26a, 26b of the laminate 20 so as to be electrically connected to the internal electrodes 40a, 40b, respectively. Each of the pair of external electrodes 140a, 140b includes: an underlying electrode layer 142 formed on a surface of the laminate 20 and including Cu; a bonding portion 144 formed partially on a surface of the underlying electrode layer 142 and including a CuSn alloy; and a conductive resin layer 146 formed on surfaces of the underlying electrode layer 142 and the bonding portion 144. The total area of the bonding portion 144 is equal to or more than 2.7% and equal to or less than 40.6% of the total area of the underlying electrode layer.SELECTED DRAWING: Figure 3

Description

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

  In recent years, multilayer ceramic capacitors have been used even in harsh environments that are more susceptible to impacts than conventional ones, and thus are required to have mechanical strength that can cope with them. For example, multilayer ceramic capacitors used for mobile devices such as mobile phones and portable music players are required to withstand impacts such as dropping. Specifically, it is necessary that the multilayer ceramic capacitor does not fall off from the mounting substrate even when subjected to an impact such as dropping, and does not cause a crack. In addition, multilayer ceramic capacitors used for in-vehicle devices such as ECUs are required to withstand impacts such as thermal cycles. Specifically, the multilayer ceramic capacitor needs to prevent cracks from being generated even when subjected to a bending stress generated by linear expansion / contraction of the mounting substrate or a tensile stress applied to the external electrode in a thermal cycle.

  For the purpose of meeting the above requirements, a multilayer ceramic capacitor having 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 Document 1 has an external multi-layer structure including an electrode layer as a baked electrode formed on both end faces of a capacitor body and a conductive thermosetting resin layer formed on the surface of the electrode layer. With electrodes. In the multilayer ceramic capacitor disclosed in Patent Document 1, in an external electrode having a multilayer structure, the electrode layer has a function of ensuring moisture resistance reliability, and the thermosetting resin layer has a function of suppressing cracks in the capacitor body.

Japanese Patent Application Laid-Open No. 11-162771

Since the multilayer ceramic capacitor like patent document 1 contains resin in a thermosetting resin layer, the content rate of the metal contained in a thermosetting resin layer becomes low. Therefore, the adhesive force between the thermosetting resin layer and the electrode layer formed on the lower surface thereof tends to be weak. As a result, the multilayer ceramic capacitor as disclosed in Patent Document 1 has a problem that moisture and the like enter between the thermosetting resin layer and the electrode layer, resulting in deterioration of moisture resistance reliability and electrical characteristics.
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, but if the amount of the alloy between the electrode layer and the thermosetting resin layer is too large, There was a problem that the crack suppression function by the curable resin layer was lowered.

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

A multilayer ceramic capacitor according to the present invention is formed on a surface of a multilayer body so as to be electrically connected to the multilayer body formed by laminating a plurality of ceramic layers and a plurality of internal electrodes. A multilayer ceramic capacitor having a pair of external electrodes, each of the pair of external electrodes being formed on the surface of the multilayer body, and partially formed on the surface of the base electrode layer containing Cu and the base electrode layer , Cu ₃ Sn alloy, a base electrode layer and a conductive resin layer formed on the surface of the joint, the total area of the joint 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.
Preferably, the thickness of the joint portion is a multilayer ceramic capacitor having a thickness of 0.1 μm or more and 1.2 μm or less.
Preferably, the width of the bonding portion is a multilayer ceramic capacitor having a width of 1.3 μm or more and 13.3 μm or less.
Preferably, the bonding portion is a multilayer ceramic capacitor including an alloy layer including at least one of Ag and Cu and Sn.

The multilayer ceramic capacitor according to the present invention is formed on the surface of the base electrode layer in an external electrode having a multilayer structure, and is metal-bonded via a joint including a Cu ₃ Sn alloy. The total area of the joint is And 2.7% to 40.6% of the total area of the base electrode layer. As a result, since the base electrode layer and the conductive resin layer included in the external electrode are in close contact with each other, the moisture resistance reliability and electrical characteristics are improved, and the occurrence of cracks in the multilayer ceramic capacitor can be suppressed. Furthermore, when the external electrode includes the conductive resin layer, mechanical strength such as substrate bending resistance and drop impact resistance is improved. As a result, it is possible to improve the mechanical strength by the external electrode, and to provide a multilayer ceramic capacitor having good moisture resistance reliability and electrical characteristics by firmly bonding the base electrode layer and the conductive resin layer contained in the external electrode. Can be obtained.
Furthermore, in the multilayer ceramic capacitor according to the present invention, the thickness of the joint is from 0.1 μm to 1.2 μm. As a result, the occurrence of cracks in the multilayer ceramic capacitor is further suppressed, and the electrical characteristics are also improved.
Moreover, the width | variety of a junction part is 1.3 micrometers or more and 13.3 micrometers or less. Thereby, generation | occurrence | production of the crack with respect to a multilayer ceramic capacitor can be suppressed more reliably.
Furthermore, the multilayer ceramic capacitor according to the present invention can provide a multilayer ceramic capacitor having better electrical characteristics more reliably when the joint portion includes an alloy layer containing at least one of Ag and Cu and Sn. Can do.

  According to this invention, the external electrode is used to improve mechanical strength, and the base electrode layer and the conductive resin layer included in the external electrode are firmly adhered to each other, thereby providing a good moisture resistance reliability and electrical characteristics. A ceramic capacitor may be provided.

  The above-described object, 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 an embodiment of the present invention. It is II-II sectional drawing of FIG. 1 which shows the laminated ceramic capacitor which concerns on one embodiment of this invention. FIG. 3 is an enlarged view of the first external electrode and the vicinity thereof 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. Multilayer Ceramic Capacitor 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 an embodiment of the present invention. 2 is a cross-sectional view taken along the line II-II of FIG. 1 showing a multilayer ceramic capacitor according to an embodiment of the present invention. FIG. 3 is an enlarged view of the first external electrode and the vicinity thereof 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 and a first external electrode 140a and a second external electrode 140b (a pair of external electrodes).

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

  The laminated body 20 is formed in a rectangular parallelepiped shape, and is opposed to the first main surface 22a and the second main surface 22b, the first side surface 24a and the second side surface 24b opposed to each other, and the first end surface 26a and A second end face 26b is included. Here, the direction connecting the first end surface 26a and the second end surface 26b is the length (L) direction, orthogonal to the L direction, and the direction connecting the first side surface 24a and the second side surface 24b is the width. A 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.

  The laminate 20 is preferably rounded at a part or all of its corners and ridges. The rectangular parallelepiped shape of the stacked 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. There is no particular limitation. For example, the laminated body 20 has a step or unevenness on 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 laminated in the T direction. The thickness of the ceramic layer 30 is preferably about 0.5 μm to 10 μm.

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

(First and second internal electrodes 40a and 40b)
The first internal electrode 40 a extends in a flat plate shape at the interface of the ceramic layer 30 and is exposed to the first end face 26 a of the multilayer body 20. On the other hand, the second internal electrode 40b extends in a flat plate shape at the interface of the ceramic layer 30 so as to face the first internal electrode 40a through the ceramic layer 30, and is exposed to the second end face 26b. Therefore, the first and second internal electrodes 40a, 40b include a facing portion that faces each other with the ceramic layer 30 interposed therebetween, and a lead portion that is drawn to the first and second end faces 26a, 26b. The first internal electrode 40a and the second internal electrode 40b are opposed to each other with the ceramic layer 30 interposed therebetween, thereby generating a capacitance. The thickness of the first and second internal electrodes 40a, 40b is preferably about 0.2 μm or more and 2.0 μm or less.

  The first and second internal electrodes 40a and 40b are made of an appropriate 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 preferable that it is comprised.

(First and second external electrodes 140a and 140b)
The first external electrode 140a extends from the first end face 26a of the multilayer body 20 to a part of each of the first and second main faces 22a and 22b and a part of each of the first and second side faces 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 stacked 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.

  The first and second external electrodes 140 a and 140 b have a multilayer structure including a base electrode layer 142, a joint portion 144, a conductive resin layer 146, and a plating layer 150. 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 is formed from the first or second end face 26a, 26b of the stacked body 20, a part of each of the first and second main faces 22a, 22b, and each of the first and second side faces 24a, 24b. It is preferable to be formed so as to reach a part of. The base electrode layer 142 may be formed only on the first or second end face 26a, 26b of the stacked body 20. The thickness of the thickest portion of the base electrode layer 142 is preferably, for example, 10 μm or more and 50 μm or less.

  The base electrode layer 142 is formed, for example, by applying and baking a conductive paste containing a conductive metal and glass. For example, Cu or Cu alloy can be used as the conductive metal. As the glass, for example, 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.

(Junction 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 face 26a, 26b of the stacked body 20, and from there, the first and second main surfaces 22a are formed. , 22b and the surface of the base electrode layer 142 formed on each of the first and second side surfaces 24a, 24b. The joint portion 144 may be formed only on the surface of the base electrode layer 142 formed on the first or second end face 26a, 26b of the stacked body 20.

  The surface of the bonding portion 144 may be roughened. Specifically, the value of the surface roughness Ra of the joint portion 144 is preferably 0.2 μm or more and 5.1 μm or less. When the value of the surface roughness Ra of the joint portion 144 is smaller than 0.2 μm, interface peeling between the joint portion 144 and the conductive resin layer 146 is likely to occur. Further, when the value of the surface roughness Ra of the joint portion 144 is larger than 5.1 μm, the adhesion area of the conductive resin layer 146 becomes too small, and similarly, interface peeling easily occurs.

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

The total area of the bonding portion 144 is 2.7% or more and 40.6% or less of the total area of the base electrode layer 142. Moreover, it is preferable that the thickness of the junction part 144 is 0.1 micrometer or more and 1.2 micrometers or less. Furthermore, it is preferable that the width | variety of the junction part 144 is 1.3 micrometers or more and 13.3 micrometers or less. When 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 tree layer 146 is weakened. Note that if the bonding portion 144 is not present at all, the base electrode layer 142 and the conductive resin layer 146 are not metal-bonded, and thus the adhesion between the base electrode layer 142 and the conductive tree layer 146 is weakened. As a result, the electrical characteristics are not stabilized, and sufficient moisture resistance reliability cannot be obtained. Further, even when 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 adhesion between 142 and the conductive resin layer 146 is weakened. As a result, the electrical characteristics are not stabilized, and sufficient moisture resistance reliability cannot be obtained.
On the other hand, when the thickness of the bonding portion 144 exceeds 1.2 μm, the width of the bonding portion 144 exceeds 13.3 μm, and the total area of the bonding portion 144 exceeds 40.6% of the total area of the base electrode layer, When stress is generated in the first and second external electrodes 140a and 140b, the stress cannot be relaxed, and the crack suppressing function by the conductive resin layer 146 is lowered.

Note that the total area, thickness, and width of the joint 144 are subjected to cross-sectional polishing to the 1/2 position (W / 2 position) in the width direction of the multilayer ceramic capacitor described above, and are expanded to a predetermined magnification as shown in FIG. Measure in the exposed cross section. Each measuring method is as follows.
First, the total area of the joint 144 can be confirmed within the field of view of the SEM image of the exposed cross section enlarged at a predetermined magnification in the region where the joint exists at the central position (T / 2 position) of the exposed cross section. The ratio of the bonding portion to the length of the electrode layer 142 is measured as the total area of the bonding portion 144.
The thickness of the joint 144 can be confirmed in the field of the SEM image of the exposed cross section enlarged at a predetermined magnification in the region where the joint exists at the central position (T / 2 position) of the exposed cross section. 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 within the field of view of the SEM image of the exposed cross section enlarged to a predetermined magnification in the region where the joint exists at the center position (T / 2 position) of the exposed cross section. 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 portion 144. Specifically, the conductive resin layer 146 is formed on the surface of the joint portion 144 formed on the first or second end face 26a, 26b of the laminate 20, and from there, the first and second main surfaces are formed. It is preferable to be formed so as to reach the surface of the joint portion 144 formed in a part of each of 22a and 22b and a part of each of the first and second side surfaces 24a and 24b. The thickness of the conductive resin layer 146 is preferably 10 μm or more and 150 μm or less, for example.

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

  The conductive filler may have a spherical shape, a flat shape, or the like. In addition, when the shape of the particle | grain is a spherical shape, a flat shape, etc., it is preferable that a conductive filler mixes and uses a spherical shape and a flat shape. In addition, the shape of the particle | grains of an electroconductive filler is not specifically limited. 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 joint portion 144 containing a Cu ₃ Sn alloy or an alloy of Ag, Cu, and Sn.

  The conductive filler mainly bears the conductivity of 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 included 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, or a polyimide resin can be used. In particular, as a resin contained in the conductive resin layer 146, an epoxy resin is preferably used. The epoxy resin is excellent in heat resistance, moisture resistance, adhesion, and the like, and is one of the most suitable resins. The conductive resin layer 146 preferably includes a curing agent together with the thermosetting resin. As the curing agent, when an epoxy resin is used as the thermosetting resin, a known compound such as phenol, amine, acid anhydride, or imidazole can be used.

  When the conductive resin layer 146 contains a resin, it is more flexible than, for example, a conductive layer made of a fired product of a plating film or a conductive paste. Therefore, the conductive resin layer 146 functions as a layer that buffers physical impacts applied to the multilayer ceramic capacitor 10 and impacts caused by thermal cycles. Thereby, it is possible to prevent the multilayer ceramic capacitor 10 from being cracked. That is, the multilayer ceramic capacitor 10 includes the conductive resin layer 146, thereby improving the mechanical strength such as the substrate bending resistance and the drop impact resistance.

(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 from there, the first and second main surfaces are formed. It is preferable that the conductive resin layer 146 is formed so as to reach a part of each of 22a and 22b and a part of each of the first and second side surfaces 24a and 24b. The plating layer 150 may be formed only on the surface of the conductive resin layer 146 formed on the first or second end face 26a, 26b of the stacked body 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. Note that the plating layer 150 may have a single-layer structure including only the first plating layer 152 or a multilayer structure of three or more layers. The thickness per 150 plating layers 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. Thereby, when the multilayer ceramic capacitor 10 is mounted on the mounting substrate, it is possible to prevent the base electrode layer 142 and the conductive resin layer 146 from being eroded by the solder used for mounting. 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 substrate, the wettability of the solder used for mounting to the external electrodes 140a and 140b can be improved. Therefore, the multilayer ceramic capacitor 10 can be easily mounted.

(effect)
In the multilayer ceramic capacitor 10 according to one embodiment of the present invention, in the multi-layered external electrodes 140a and 140b, the base electrode layer 142 and the conductive resin layer 146 include a Cu ₃ Sn alloy, and Ag and Cu Metal bonding is performed through a bonding portion 144 that may include an 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. As a result, 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, so that the moisture resistance reliability and the electrical characteristics are improved, and the occurrence of cracks in the multilayer ceramic capacitor is also suppressed. can do. Furthermore, 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, the multilayer ceramic capacitor 10 is improved in mechanical strength by the external electrodes 140a and 140b, and 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. Good moisture resistance reliability and electrical properties.

  Furthermore, in the multilayer ceramic capacitor 10 according to one embodiment of the present invention, if the thickness of the joint portion 144 is 0.1 μm or more and 1.2 μm or less, the electrical characteristics are suppressed while suppressing the occurrence of cracks in the multilayer ceramic capacitor. Will also be good. Moreover, if 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 multilayer ceramic capacitor 10 according to one embodiment of the present invention, when the joint portion 144 includes an alloy layer including at least one of Ag and Cu and Sn, the electrical characteristics are more reliably improved. The multilayer ceramic capacitor 10 having the above can be obtained.

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

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

  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. Moreover, a ceramic green sheet in which the internal electrode forming conductive pattern is not formed is also obtained. In addition, the ceramic paste and the conductive paste for forming the internal electrode may include, for example, a known binder or solvent.

  Then, a predetermined number of ceramic green sheets without the internal electrode forming conductive pattern are laminated, and a ceramic green sheet with the internal electrode forming conductive pattern is laminated on the surface, and the internal electrode is formed on the surface. A predetermined number of ceramic green sheets on which no conductive pattern is formed are stacked. In this way, a mother laminate is manufactured.

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

  Furthermore, a plurality of raw laminates are formed by cutting the mother laminate into a predetermined shape. At this time, the raw laminate may be subjected to barrel polishing or the like to form roundness in the ridge line portion or the corner portion.

  Finally, by firing the raw laminate, the first and second internal electrodes are arranged inside, the end of the first internal electrode is drawn out to the first end surface, and the second internal electrode A laminated body in which the end portion is drawn out to the second end surface is formed. Note that the firing temperature of the raw laminate can be appropriately set according to the ceramic material or the conductive material. The firing temperature of the raw laminate can be, for example, about 900 ° C. or higher and 1300 ° C. or lower.

(Formation of external electrode for laminate)
First, a conductive paste is applied and baked on both end faces 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 higher and 900 ° C. or lower.

  Next, a conductive resin paste containing a conductive filler containing at least 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. to 300 ° C. to thermally cure the resin. . The maximum temperature for the heat treatment is preferably 240 ° C. or higher and 260 ° C. or lower. In this case, the Sn content in the conductive resin paste is preferably 10 wt% or more and 40 wt% or less. In this way, the conductive resin layer is formed so as to cover the base electrode layer. At this time, a junction is partially formed on the surface of the base electrode layer. The thickness and width of the joint can be adjusted by changing the maximum heat treatment temperature 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 it.

Note that the atmosphere during the heat treatment is preferably an N ₂ atmosphere. Moreover, it is preferable to suppress oxygen concentration to 100 ppm or less. Thereby, scattering of 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.

  Further, if necessary, an 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 Example Hereinafter, an experimental example performed by the inventors to confirm the effect of the present invention will be described. In the experimental example, samples No. 1 to No. 20 were prepared according to the method for manufacturing a multilayer ceramic capacitor described above, and mechanical strength and electrical characteristics were evaluated.

The specifications of the multilayer ceramic capacitor which is the sample of sample number 1 to sample number 20 are as follows.
Size (design value) L x W x T: 1.6 mm x 0.8 mm x 0.8 mm
Ceramic material: BaTi ₂ O ₃
Capacitance: 22μF
Rated voltage: 6.3V
External electrode structure: a multi-layer structure consisting of a base electrode layer, a conductive resin layer, and a plating layer. A junction is partially formed on the surface of the base electrode layer. Base electrode layer: conductive metal (Cu) and glass Baking electrode containing Joint part: Alloy of Cu and Sn Conductive resin layer: Conductive filler containing Ag and Sn, and resin containing resol type phenol resin system Structure of plating layer: Ni plating layer (first plating layer) And a two-layer structure consisting of a Sn plating layer (second plating layer) Heat treatment conditions: time 18 min, in N ₂ atmosphere

  Each sample of sample number 1 to sample number 20 has a content of Sn contained in the conductive resin paste used for forming the conductive resin layer and a curing temperature for thermosetting the conductive resin paste. It is a sample in which the maximum temperature is changed.

In Sample No. 1 to Sample No. 5, the maximum curing temperature was 240 ° C., and the Sn content was changed between 0 wt% and 40 wt%.
In Sample Nos. 6 to 10, the maximum curing temperature was 260 ° C., and the Sn content was changed between 0 wt% and 40 wt%.
In Sample No. 11 to Sample No. 15, the maximum temperature of the curing temperature was 280 ° C., and the Sn content was changed between 0 wt% and 40 wt%.
In Sample No. 16 to Sample No. 20, the maximum curing temperature was 300 ° C., and the Sn content was changed between 0 wt% and 40 wt%.

(Evaluation method)
The mechanical strength and electrical characteristics of each sample No. 1 to No. 20 were evaluated.

  The test for mechanical strength was performed as follows. Reflow mounting was performed on the JEITA land substrate using lead-free solder (Sn-3.0Ag-0.5Cu). The substrate was bent by 1 mm per second, and held for 5 seconds when it was bent by 5 mm. Thereafter, the chip was removed from the substrate, embedded in a resin, and cross-sectional polished to a half position (W / 2 position) in 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 cracks generated was counted. The number of samples for evaluating the mechanical strength was 12.

  The test relating to the electrical characteristics was performed as follows. Each sample was subjected to an electrical characteristic test by scanning with an impedance analyzer (Agilent Technology 4294A) at a voltage of 1 Vrms and a frequency of 1 kHz to 10 MHz, and an ESR at 1 MHz was measured. Note that 16044A manufactured by Agilent Technologies was used as the test fixture. Samples that averaged 15 mΩ or less were judged good. The number of evaluation samples in the electrical property test was 10.

(Analysis method)
An analysis method for determining whether or not the external electrode of the multilayer ceramic capacitor, which is each sample of Sample No. 1 to Sample No. 20, includes a junction, is as follows. A multilayer ceramic capacitor was selected at random, embedded in resin, and cross-section polished 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, in the exposed cross section, the presence or absence of a joint portion of the external electrode at the center of the end face of the multilayer ceramic capacitor was observed using a FE-SEM at a predetermined magnification.

The total area, thickness, and width of the bonded portion were measured on the exposed cross section polished to the half position (W / 2 position) in the width direction of the multilayer ceramic capacitor described above. The measuring method is as follows.
First, the total area of the junction can be confirmed within the field of view of the SEM image of the exposed section magnified at a predetermined magnification in the region where the junction exists at the center position (T / 2 position) of the exposed section. The proportion of joints present relative to the length of the layer was measured as the total area of the joints and calculated as the average of three samples.
In addition, the thickness of the joint portion can be confirmed in the field of the SEM image of the exposed cross section enlarged at a predetermined magnification in the region where the joint portion exists at the center position (T / 2 position) of the exposed cross section. The thickness along the direction perpendicular to the tangent to the interface was measured as the thickness of the joint and was calculated as the average of three samples.
Further, the width of the joint portion can be confirmed within the field of view of the SEM image of the exposed cross section enlarged at a predetermined magnification in the region where the joint portion exists at the center position (T / 2 position) of the exposed cross section. The maximum length was measured as the width of the joint and calculated as the average of 3 samples.

(Evaluation results)
Table 1 shows the evaluation results of the mechanical strength characteristics of the samples No. 1 to No. 20.

As shown in Table 1, in Sample Nos. 1 to 10, the Sn content is 0 wt% or more and 40 wt% or less, and the maximum curing temperature is 240 ° C. or more and 260 ° C. or less. Sample was not present.
In Sample No. 11 to Sample No. 14, since the Sn content was 0 wt% or more and 30 wt% or less and the maximum curing temperature was 280 ° C., there was no sample with cracks.
Further, in Sample No. 16 to Sample No. 19, since the Sn content was 0 wt% or more and 30 wt% or less and the maximum curing temperature was 300 ° C., there was no sample in which cracks occurred.

On the other hand, in Sample No. 15, the maximum curing temperature is 280 ° C. and the Sn content is 40 wt%, so the total area of the joint is 58.8% and the thickness of the joint is 1. Since it was 8 μm and the width of the joint portion was 27.7 μm, one out of 12 cracks occurred, so the crack generation rate was 8.3%.
In sample No. 20, the maximum curing temperature is 300 ° C. and the Sn content is 40 wt%, so the total area of the joint is 81.9% and the thickness of the joint is 2. Since it was 6 μm and the width of the joint portion was 41.6 μm, 9 out of 12 cracks occurred, so the crack generation rate was 75%.

  Next, when the ESR of each sample was confirmed, sample No. 1, sample No. 6, sample No. 11 and sample No. 16 did not contain Sn because the conductive resin paste did not contain Sn. High ESR was obtained.

  On the other hand, samples No. 2 to No. 5, No. 7 to No. 10, No. 12 to No. 15, and No. 17 to No. 20 contain Sn in the conductive resin paste. Good multilayer ceramic capacitors having ESR values lower than those of Sample No. 1, Sample No. 6, Sample No. 11 and Sample No. 16 having no part were obtained.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is carried out within the range of the summary.

DESCRIPTION OF SYMBOLS 10 Multilayer 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 Two internal electrodes 140a First external electrode 140b Second external electrode 142 Base electrode layer 144 Joining portion 146 Conductive resin layer 150 Plating layer 152 First plating layer 154 Second plating layer

Claims (4)

A laminated body formed by laminating a plurality of ceramic layers and a plurality of internal electrodes, and a pair of external electrodes formed on the surface of the laminated body so as to be electrically connected to the internal electrodes Multilayer ceramic capacitor,
Each of the pair of external electrodes is
A base electrode layer partially formed on the surface of the laminate and containing Cu;
A junction formed on the surface of the base electrode layer and containing a Cu ₃ Sn alloy;
Including the base electrode layer and a conductive resin layer formed on the surface of the joint,
The multilayer ceramic capacitor according to claim 1, wherein a total area of the junction is 2.7% or more and 40.6% or less of a total area of the base electrode layer.   The multilayer ceramic capacitor according to claim 1, wherein a thickness of the joint portion is 0.1 μm or more and 1.2 μm or less.   3. The multilayer ceramic capacitor according to claim 1, wherein a width of the joint portion is 1.3 μm or more and 13.3 μm or less.   4. The multilayer ceramic capacitor according to claim 1, wherein the joining portion includes an alloy containing at least one of Ag and Cu and Sn.