JPH1154358A - Laminated ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the insulation resistance of a dielectric ceramic layer and, at the same time, to stably electrically connect internal electrodes composed mainly of Ni layers to external electrodes by preventing the corrosion of the internal electrode layers through a plating solution. SOLUTION: A laminated ceramic capacitor is provided with a laminated body 10, formed by alternately laminating dielectric ceramic layers 1 and internal electrode layers 2, composed mainly of Ni upon another and external electrodes 3 formed on the end faces of the laminated body. Each external electrode 3 is composed of a baser conductor film 31 connected to half of the internal electrode layers 2, a thermosetting conducive resin film 32 formed on the surface of the conductor film 31, and a surface plated layer 33 formed on the surface of the resin film 32. At the same time, the conductor film 31 is composed mainly of Cu and is set to a thickness of 5-30 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer ceramic capacitor, and more particularly, to a multilayer body in which dielectric ceramic layers and internal electrode layers mainly containing Ni are alternately stacked, and formed on an end face of the multilayer body. And an external electrode.

[0002]

2. Description of the Related Art In recent years, an Ag--Pd alloy has been used as an internal electrode layer of a multilayer ceramic capacitor. However, in order to cope with recent cost reduction, Ni or Cu is used for the internal electrode layer.
Such base metal materials are used. Since the base metals such as Ni and Cu are easily oxidized, the oxidation of the internal electrode layer should be prevented particularly in the step of forming the internal electrode layer and in the step after the formation, for example, in the step of forming the external electrode. is important.

For example, the firing step of the internal electrode layer, that is, the firing step of the laminated molded body in which the dielectric ceramic layers and the internal electrode layers are alternately stacked, and the subsequent step of forming the external electrodes are performed at a low oxygen concentration ( The firing was performed in an atmosphere of 10 ^-8 to 10 ^-12 atm).

As an external electrode of a laminated ceramic capacitor using a base metal material such as Ni or Cu as an internal electrode layer material, Japanese Patent Publication No. 8-4055 discloses an external electrode composed of a baked copper electrode. The baked electrode of copper in such a multilayer ceramic capacitor includes 55 to 80% by weight of copper powder and 5 to 2% of glass frit.
A copper paste composed of 0% by weight and 10 to 30% by weight of an organic vehicle was applied and baked at 800 ° C. for 30 minutes in a weak reducing atmosphere. Such a baked copper electrode usually has a thickness of 60 to 10 to prevent peeling or the like.
The thickness was about 0 μm.

[0005]

However, since the thickness of the baked electrode of copper is as thick as 60 to 100 μm, even if the binder is removed, carbon in the electrode cannot be completely scattered and remains. When the above-described firing treatment with a low oxygen concentration is performed in the process or the formation process of the external electrode, the dielectric ceramic layer is reduced, and the characteristics of the dielectric ceramic material are changed. It causes a fatal problem of the decline.

In order to recover the insulation resistance value of the multilayer ceramic capacitor whose insulation resistance value has been reduced, it is conceivable to supplement the oxygen by, for example, performing a heat treatment in a high oxygen concentration atmosphere. For example, when heat treatment is performed at a high oxygen partial pressure in the baking step of the external electrode, which is a heat treatment step after sintering the laminate, the internal electrode layer is oxidized through the external electrode, and the internal electrode layer and the external electrode cannot be electrically connected. However, there is a problem that the capacitance varies. As a result, the external electrodes had to be baked at a low oxygen partial pressure, and it was difficult to improve the insulation resistance of the dielectric ceramic layer.

In order to prevent such a decrease in the insulation resistance of the dielectric ceramic layer, it is conceivable to reduce the thickness of the baked copper electrode. However, the surface of the copper baked electrode is generally plated to improve the wettability with solder and to prevent solder erosion of the external electrode. Penetrate, Ni
There is a problem in that the internal electrode layer mainly composed of aluminum is corroded and the electrical connection with the external electrode becomes unstable, and the internal electrode layer is corroded and peeled to cause cracks and delamination.

Further, in order to prevent the insulation resistance of the dielectric ceramic layer from lowering, the copper paste may be fired at a low temperature of 800 ° C. or less, but in this case, the copper baked electrode cannot be densified. After plating, the internal electrode layer corroded, causing the same problem as described above.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to improve the insulation resistance of a dielectric ceramic layer, to prevent corrosion of an internal electrode layer by a plating solution, and to reduce the Ni content. An object of the present invention is to provide a multilayer ceramic capacitor capable of achieving stable electrical connection between an internal electrode layer composed of a main component and an external electrode.

[0010]

SUMMARY OF THE INVENTION A multilayer ceramic capacitor according to the present invention is formed by alternately stacking a dielectric ceramic layer and an internal electrode layer containing Ni as a main component, and formed on an end face of the multilayer body. A multilayer ceramic capacitor comprising an external electrode, a base conductive film connecting the external electrode to the internal electrode layer, a thermosetting conductive resin film formed on the surface of the base conductive film; And a surface plating layer formed on the surface of the curable conductive resin film, wherein the underlying conductor film is mainly composed of Cu and has a thickness of 5 to 30 μm.

[0011]

According to the present invention, the thickness of the underlying conductor film containing Cu as a main component is set to 5 to 30 μm, which is smaller than that of the conventional one. The body ceramic layer is not reduced, so that the insulation resistance is not reduced.

Further, a thermosetting conductive resin film is formed on the surface of the underlying conductive film, and a surface plating layer is formed on the surface of the thermosetting conductive resin film.
Even when the thickness is as thin as 30 μm, the plating solution is blocked by the thermosetting conductive resin film and does not corrode the internal electrode layer. As a result, there is no unstable electrical connection with the external electrode, and no cracks or delamination due to corrosion of the internal electrode layer. Further, the surface plating layer can supplement the solder wettability of the thermosetting conductive resin film and prevent the external electrode from being eroded by solder.

In addition, the junction between the internal electrode layer mainly composed of Ni and the underlying conductor film mainly composed of Cu is N
By forming an alloy of i and Cu, the internal electrode layer and the underlying conductor film are integrated, and the internal electrode layer and the external electrode can be firmly connected.

Further, according to the present invention, the laminated molded body before firing, in which the internal electrode layers mainly containing Ni and the dielectric ceramic layers are alternately laminated, has a low oxygen content such that the internal electrode layers are not oxidized. Baked in pressure, and then heat-treated in a high oxygen concentration atmosphere to recover the insulation resistance,
A base conductor film containing Cu as a main component is formed on the end face of the laminated sintered body with a thickness of 5 to 30 μm, and fired at an oxygen partial pressure that does not oxidize the base conductor film.

After that, a thermosetting conductive resin film is formed by performing a thermosetting process at 150 ° C. or more in an air atmosphere or the like, and a thermosetting conductive resin film constituting an external electrode is formed at a low temperature in the air. As a result, the internal electrode layer and the underlying conductor film are not oxidized, so that the insulation resistance value and the reliability do not deteriorate.

As a result, even if the decrease in insulation resistance is improved, a low-cost monolithic ceramic capacitor using Ni for the internal electrode layer with high bonding reliability between the internal electrode layer and the external electrode is obtained. Can be.

Conventionally, Japanese Patent Application Laid-Open No. Hei 8-107039 discloses that the internal electrode layer is made of Ag-Pd and the external electrode is
An underlying conductor film made of Ag, Ag-Pd, Cu connected to the internal electrode layer, and Ni, C formed on the underlying conductor film
u plated film, a conductive resin film formed on the plated film, and Sn, Sn− formed on the upper surface of the conductive resin film.
A multilayer capacitor comprising a Pb plating film is disclosed.

However, since the internal electrode layer made of Ag-Pd was used, there was a problem that the cost was increased as described above.
Since i is the main component, the cost can be reduced.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a multilayer ceramic capacitor according to the present invention. In the drawing, reference numeral 1 denotes a dielectric ceramic layer, 2 denotes an internal electrode layer mainly composed of Ni, and 3 denotes an external electrode. ing. In this multilayer ceramic capacitor, a dielectric ceramic layer 1 and an internal electrode layer 2 mainly composed of Ni are alternately laminated to form a laminated body 10, and external electrodes 3 are formed on both end surfaces of the laminated body 10. It is configured.

The external electrode 3 is connected from the end face side of the laminate 10 to C
It is composed of a base conductor film 31 mainly composed of u, a thermosetting conductive resin film 32, and a surface plating layer 33.

The dielectric ceramic layer 1 is a dielectric porcelain containing barium titanate or barium titanate containing indium oxide, magnesium oxide, magnesium carbonate, etc., and has a thickness of 10 to 30 μm per layer after firing. desirable.

The internal electrode layer 2 is composed of Ni as a main component and is a substantially rectangular conductor film. The first, third, fifth,... 2 has one end thereof extending to one end face of the laminate 10 and a second layer from the top,
One end of each of the fourth, sixth,... Internal electrode layers 2 extends to the other end surface of the laminate 10.

The internal electrode layer 2 mainly composed of Ni is N
Although the concept includes the case of only i, it may include an oxide of Ni, and further includes, for example, Cr, C
In the present invention, even when a metal or a compound such as o or Cu is intentionally included or as an impurity, these are collectively referred to as an internal electrode layer 2 mainly containing Ni in the present invention.

Base conductive film 3 constituting a part of external electrode 3
1 is formed by applying a conductive paste containing Cu as a main component and baking the laminated body 10 on both end surfaces of the laminated body 10 after firing.

The underlying conductive film 31 containing Cu as a main component is
Although the concept includes the one made only of Cu, it may contain an oxide of Cu.
Metals and compounds such as Co, Ni and Zn are collectively referred to as C, including those intentionally and as impurities.
It is referred to as a base conductor film 31 containing u as a main component. An alloy of Ni and Cu is formed at the junction between the underlying conductor film 31 mainly containing Cu and the internal electrode layer 2 mainly containing Ni.

The thickness of the base conductor film 31 is 5-30.
μm. When the thickness of the base conductor film 31 is less than 5 μm, the bonding with the internal electrode layer becomes unstable, so that the capacity variation increases. When the thickness is more than 30 μm, carbon in the electrode is reduced even if the binder is removed. It remains without being completely scattered, and the firing process of the internal electrode layer 2 and the external electrode 3
This is because, in the forming step, when the above-described firing treatment with a low oxygen concentration is performed, the dielectric ceramic layer 1 is reduced, the insulation resistance value as a capacitor is reduced, and the occurrence of poor reliability increases. The thickness of the underlying conductor film 31 is preferably 20 to 30 μm from the viewpoint of capacity and reliability.

The thermosetting conductive resin film 32 is made of, for example, a thermosetting resin such as an epoxy-based material containing an Ag-based (Ag alone or Ag alloy) conductive material. 31 and is formed by heat treatment at 150 to 300 ° C. in the air atmosphere.

Further, the surface plating layer 33 has a laminated structure composed of, for example, a Ni plating layer, a Sn plating layer, a solder plating layer, and the like formed sequentially on the surface of the thermosetting conductive resin film 32. It compensates for the solder wettability of the conductive resin film 32 and prevents the external electrodes 3 from being eroded by solder.

As described above, in the multilayer ceramic capacitor of the present invention, since the material mainly containing Ni is used for the internal electrode layer 2, the cost of the entire multilayer ceramic capacitor can be reduced. Moreover, the external electrode 3
And a base conductor film 31 connected to the internal electrode layer 2
When the base conductor film 31 is baked, the internal electrode layer 2 and the base conductor film 3
The joint with the first electrode 1 forms an alloy of Ni and Cu, the internal electrode layer 2 and the external electrode 3 are integrated, and the connection between the internal electrode layer 2 and the underlying conductor film 31 can be strengthened. .

Further, according to the present invention, the thickness of the underlying conductor film 31 containing Cu as a main component is set to 5 to 30 μm, which is thinner than the conventional one, so that the organic solvent can be completely scattered in the binder removal treatment. The dielectric ceramic layer 1 is not reduced during firing, and thus the insulation resistance is not reduced.

Further, in the subsequent heat treatment step of forming the thermosetting conductive resin film 32 of the external electrode 3,
The heat treatment is performed at 0 ° C. or more, for example, at about 150 to 300 ° C., but the external electrode 3 can be formed in the air atmosphere, and any stable bonding between the internal electrode layer 2 and the underlying conductor film 31 can be achieved. Unaffected.

Further, a thermosetting conductive resin film 32 is formed on the surface of the underlying conductive film 31 and a surface plating layer 33 is formed on the surface of the thermosetting conductive resin film 32. Even when the thickness is as thin as 5 to 30 μm,
The plating solution is blocked by the thermosetting conductive resin film 32,
The internal electrode layer 2 does not corrode through the underlying conductor film 31. As a result, there is no unstable electrical connection with the external electrode 3 and no cracks or delamination due to corrosion of the internal electrode layer 2.

The surface plating layer 33 can supplement the solder wettability of the thermosetting conductive resin film 32 and prevent the external electrode 3 from being eroded by solder.

In the multilayer ceramic capacitor of the present invention,
The bonding between the internal electrode layer and the underlying conductor film of the external electrode is very stable, and even when an oxidation treatment is performed to eliminate the oxygen deficiency generated during the ceramic firing step, the oxidation of the bonding portion between the two does not proceed, Moreover, since the conductive resin film constituting the external electrode can be formed in a low-temperature atmosphere, there is no change in thermal history, and no deterioration of insulation resistance and deterioration of reliability occur.
It becomes an inexpensive multilayer ceramic capacitor.

Next, an example of a method for manufacturing the multilayer ceramic capacitor of the present invention will be briefly described. First, a ceramic slurry is prepared by adding and stirring a binder comprising an organic binder and a medium to a dielectric ceramic composition. After that, a dielectric ceramic green sheet is formed by a doctor blade method using the obtained ceramic slurry.

On the obtained dielectric ceramic green sheet, a conductor film to be the internal electrode layer 2 is screen-printed in a predetermined shape using an internal electrode layer paste mainly containing Ni. Thereafter, the same ceramic paste as the above-mentioned dielectric ceramic is applied to form a dielectric layer serving as the dielectric ceramic layer 1, and a conductor film serving as the internal electrode layer 2 and a dielectric layer are alternately applied. In this way, each is repeated 100 times. The laminate thus obtained was cut into a predetermined size to produce a green chip (a laminate before firing).

The laminated molded body is subjected to a binder removal treatment and firing, and then to a reoxidation treatment in an air atmosphere. This makes it possible to recover from a decrease in the insulation resistance value of the dielectric ceramic layer 1.

Next, a paste containing Cu as a main component is applied to the end surface of the fired laminated body 10 and fired to form a base conductor film 3.
1, a conductive Ag paste made of an epoxy resin containing Ag is applied on the underlying conductive film 31 and cured to form a thermosetting conductive resin film, and then the thermosetting conductive resin is formed. By applying a surface plating layer on the surface of the film,
The multilayer ceramic capacitor of the present invention is obtained.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, barium titanate (BaTiO ₃ )
1 part by weight of yttrium oxide (Y ₂ O ₃ ) is added to 100 parts by weight of barium titanate, and magnesium oxide (M
gO), 0.2 parts by weight of manganese carbonate (MnCO ₃ )
An organic binder is added to a dielectric ceramic composition containing 0.1 part by weight and 0.5 part by weight of a glass component (Li: Si molar ratio of 1: 1) composed of Li ₂ O and SiO _2. After a ceramic slurry was prepared by adding and stirring a binder composed of a medium, the obtained ceramic slurry was defoamed, and a 7 μm thick dielectric ceramic green sheet was formed by a doctor blade method.

Screen printing was performed on the obtained dielectric ceramic green sheet using an internal electrode layer paste composed of Ni powder, ethyl cellulose, and terpineol. Thereafter, a ceramic paste having the same composition as the above-described dielectric ceramic green sheet was prepared and applied to form a dielectric layer molded body, and further, the application of the internal electrode layer paste and the application of the ceramic paste were alternately repeated 100 times. . The laminated molded body thus obtained was cut into a predetermined size (2125 type) to produce a green chip (the laminated molded body before firing).

The laminated molded body is subjected to a binder removal treatment at 400 ° C. in the air, and then 1250 ° C. (PO ₂ 10
^-11 atm) for 2 hours, followed by 80 in air
A reoxidation treatment was performed at 0 ° C.

Next, a paste composed of a Cu powder and an acrylic resin was applied to the end face of the fired laminate 10 by a roll transfer method, and fired at 900 ° C. at an oxygen concentration of 2 ppm. Forming a base conductor film 31 of
A conductive Ag paste made of an epoxy resin containing Ag was applied on the underlying conductive film 31 and cured at 200 ° C. for 30 minutes to form a thermosetting conductive resin film having a thickness of 60 μm.

Thereafter, the surface of the thermosetting conductive resin film 32 was subjected to Ni plating with a thickness of 2 μm and Sn plating with a thickness of 2 μm to produce a multilayer ceramic capacitor of the present invention. The obtained capacitor had 100 laminated dielectric ceramic layers, and the thickness per layer was 5 μm.

The obtained multilayer ceramic capacitor has an L
Using a CR meter 4284A, the capacitance and the dielectric loss DF were measured at a frequency of 1 KHz and an input signal of 1 Vrms.
Further, the insulation resistance IR was measured one minute after applying a voltage of 16 V. Furthermore, 300 high-temperature load tests in which 40 V was applied at 150 ° C. were performed, the number of failures within 40 hours was measured, and the reliability failure rate was calculated. Also, 250
The sample was immersed in a solder bath at ℃ and the state of crack generation was observed. Table 1 shows the results.

[0045]

[Table 1]

According to Table 1, in the sample of the present invention, when the thickness of the underlying conductor film made of Cu is 5 to 30 μm, the insulation resistance is not deteriorated by carbon during firing, and the insulation resistance is 22 GΩ. As described above, it can be seen that the reliability failure rate and cracks do not occur. It can be seen that when the thickness of the underlying conductor film made of Cu is greater than 30 μm, the insulation resistance is deteriorated, and the reliability failure rate and the crack generation rate are also increased.

The present inventor produced a multilayer ceramic capacitor in the same manner as described above, except that a surface plating layer was formed on the surface of the underlying conductor film without forming a conductive resin film. 720 nF, dielectric loss 3.4
%, Insulation resistance IR was 18 GΩ, reliability failure rate was 15%, and crack generation rate was 100%.

[0048]

As described above, since the thickness of the underlying conductor film containing Cu as the main component is 5 to 30 μm, which is smaller than that of the conventional one, the organic solvent can be completely scattered in the binder removal treatment, The dielectric ceramic layer is not reduced, and the insulation resistance is not reduced.

Further, a thermosetting conductive resin film is formed on the surface of the underlying conductive film, and a surface plating layer is formed on the surface of the thermosetting conductive resin film.
Even when the thickness is as thin as 30 μm, the plating solution is blocked by the thermosetting conductive resin film, and does not corrode the internal electrode layer via the underlying conductor film.

Further, the thermosetting conductive resin film can be formed by performing a thermosetting treatment at 150 ° C. or more in an air atmosphere or the like, but the thermosetting conductive resin film constituting the external electrode is formed at a low temperature in the air. Since it can be formed, the internal electrode layer and the underlying conductor film are not oxidized, so that the insulation resistance value and the reliability do not deteriorate.

[Brief description of the drawings]

FIG. 1 is a sectional view of a multilayer ceramic capacitor according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... dielectric ceramic layer 2 ... internal electrode layer 3 ... external electrode 10 ... laminated body 31 ... base conductor film 32 ... thermosetting conductive resin film 33 ... Surface plating layers

Claims (1)

[Claims] 1. A laminated ceramic capacitor comprising: a laminated body in which dielectric ceramic layers and internal electrode layers mainly containing Ni are alternately laminated; and external electrodes formed on end faces of the laminated body. A base conductor film for connecting the external electrode to the internal electrode layer, a thermosetting conductive resin film formed on the surface of the base conductor film, and a thermosetting conductive resin film formed on the surface of the thermosetting conductive resin film. A multilayer ceramic capacitor comprising a surface plating layer, wherein the underlying conductor film contains Cu as a main component and has a thickness of 5 to 30 μm.