JPH04157713A - Laminated ceramic capacitor - Google Patents

Abstract

PURPOSE:To obtain a laminated ceramic capacitor whose cost is low and whose manufacturing process is simple by a method wherein an internal electrode is formed of a metal material whose melting point is equal to or lower than the baking temperature of a dielectric ceramic and a semiconductor layer is formed between an edge where the internal electrode has been exposed and an external electrode. CONSTITUTION:At this laminated capacitor, external electrodes 6, plated films 7 of nickel, copper or the like and plated films 8 of solder, tin or the like have been formed, via semiconductor layers 5, on both edges of a laminated dielectric ceramic 1 obtained by laminating a plurality of dielectric ceramics 2 via internal electrodes 3; it is formed as a chip type in a rectangular parallelepiped shape. Since the semiconductor layers are formed between the internal electrodes and the external electrodes in this constitution, the internal electrodes and the external electrodes are connected electrically, and the internal electrodes are shut off from the outside by the semiconductor layers and are in a completely hermetically sealed state. Thereby, even when the capacitor is baked at a temperature which is equal to or higher than the melting point of the internal electrodes, the internal electrodes which have been melted do not flow out to the outside, a cohesion is not caused and only the surface of an electrode material is oxidized.

Description

[Detailed description of the invention] 11 ohms ■ shells! The present invention relates to a multilayer ceramic capacitor in which external electrodes are disposed at both ends of a multilayer dielectric ceramic in which internal electrodes are embedded in layers.

A multilayer ceramic capacitor made by Nihon Mushi has internal electrodes embedded in layers between each dielectric ceramic to form a multilayer dielectric ceramic, and external electrodes are formed on the exposed surfaces of the internal electrodes at both ends of this multilayer dielectric ceramic. Those that did are common.

By the way, in this type of multilayer ceramic capacitor, if a metal or alloy having a melting point equal to or lower than the firing temperature of the dielectric ceramic is used as the material for the internal electrodes, the metal material that is the internal electrodes will melt during firing. The problem is that the capacitance cannot be taken out because the internal electrodes melt, aggregate, or leak out from the exposed surface of the internal electrodes, causing so-called internal electrode breakage, or because the internal electrodes become oxidized. It has points. For these reasons, metals that have a higher melting point than the sintering temperature of dielectric ceramics and are less likely to oxidize have been used as internal electrode materials for multilayer ceramic capacitors.

On the other hand, as shown in Japanese Unexamined Patent Publication No. 63-249319, fired ceramic thin plates are adhesively bonded with a conductor layer (formed with conductor paste or conductor adhesive) or a glass layer formed by a thick film method, or each layer is By forming a glass layer between the thin ceramic plates without creating any gaps between them, and by stacking and bonding the ceramic thin plates in multiple layers using materials that can be welded at relatively low temperatures, we can create a laminated structure with a low-melting point metal as the internal electrode. Ceramic capacitors have been proposed.

However, with conventional multilayer ceramic capacitors,
Since the dielectric ceramic layer is fired at a high temperature of 1200°C or higher, materials such as platinum and palladium, which have a high melting point and are difficult to oxidize at high temperatures, are used, but these materials are expensive, so multilayer ceramic This caused an increase in the cost of capacitors.

Furthermore, in order to lower the price of multilayer ceramic capacitors, attempts have been made to change the material of the internal electrodes from expensive platinum and palladium to inexpensive palladium-silver, silver, and base metals. However, in order to use inexpensive palladium-silver, silver, or base metals as internal electrodes, a dielectric ceramic that can be sintered at a temperature lower than the melting point of these metals is required, so the composition of the dielectric ceramic is As a matter of fact, it was limited.

On the other hand, in the multilayer ceramic capacitor having the structure disclosed in JP-A No. 63-249319, a dielectric ceramic composition can be selected from a wide range.
A metal with a low melting point can be used as the internal electrode. but,
The manufacturing process is complicated and the manufacturing cost is high, which is an obstacle to lowering the price of multilayer ceramic capacitors.

Therefore, the main object of the present invention is to solve the problem of having to use an internal electrode material with a melting point higher than the firing temperature of the dielectric ceramic, and to make it possible to select a dielectric ceramic composition over a wide range. The object of the present invention is to provide a multilayer ceramic capacitor that can be manufactured at low cost and with a simple manufacturing process.

In order to solve the above problems, the multilayer ceramic capacitor according to the present invention is a multilayer ceramic capacitor in which external electrodes are arranged on both end faces of a multilayer dielectric ceramic in which internal electrodes are buried in layers. In the capacitor, the internal electrode is made of a metal material having a melting point equal to or lower than the firing temperature of the dielectric ceramic, and a semiconductor layer is provided between the end surface where the internal electrode is exposed and the external electrode. It is characterized by the presence of

Due to the structure described above, a semiconductor layer is formed between the internal electrode and the external electrode, so both the internal and external electrodes are electrically connected, and the internal electrode is connected to the outside by the semiconductor layer. is closed and completely sealed. This results in
Even when fired at a temperature equal to or higher than the melting point of the internal electrode, the molten internal electrode does not flow out, no aggregation occurs, and oxidation of the electrode material is suppressed to only the surface. Therefore, electrode breakage inside the multilayer ceramic capacitor or failure of connection with the external electrode does not occur, and the capacitance drop or mW failure is eliminated.

Example Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, the multilayer ceramic capacitor according to the present invention has a multilayer dielectric ceramic 10 obtained by stacking a plurality of dielectric ceramics 2 with internal electrodes 3 interposed between the two end faces. An external electrode 6, a plating film 7 of Nikkeno copper, etc., and a plating film 8 of solder, tin, etc. are formed through the semiconductor layer 5, and the chip type is a rectangular parallelepiped.

Next, the manufacturing steps will be explained in order.

First, the laminated dielectric ceramic 1 is formed. This laminated dielectric ceramic 1 is manufactured as follows. In other words, as shown in Figure 2, it is a ceramic 2 (green sheet) made by slurrying material powder and rolling it out into a sheet.
Prepare the internal electrode 3 by applying conductive paste on its negative side.
Form a conductive paste layer. A required number of dielectric ceramics 2 having a conductive base layer which will become the internal electrodes 3 are laminated, and as shown in FIG. 3, the internal electrodes 3 are sandwiched and crimped with dielectric ceramics 4 that do not expose the internal electrodes 3 to form a laminate.

Next, semiconductor layers 5 are formed on both end faces of this laminate. This semiconductor layer 5 is made of, for example, a paste in which a binder is mixed with a semiconducting agent that converts the dielectric ceramic into a semiconductor, or a paste in which a binder is mixed in the ceramic powder contained in the dielectric ceramic and the above-mentioned semiconducting agent. It is formed by coating and firing at a predetermined temperature.

Subsequently, the laminated dielectric ceramic 1 fired as described above is
External electrodes 6 are formed on the end faces of. This external electrode 6 is
It is formed by applying and baking a conductive paste made of metal powder such as silver, and covers the surface of the semiconductor layer 5. Thereafter, plating with nickel, copper, etc. is applied to the external electrodes 6 to form a plating film 7. Finally, this plating film 7
A plating film 8 is formed by plating with solder, tin, etc., to obtain a chip-type multilayer ceramic capacitor.

Specifically, as the composition material of the dielectric ceramic, the main components are Ba"ribs: 84 mo1%, Ca5nOg
: 10 mo1%, Carrys: 6 mo1% lQQwt% (composition number ζ where MnO is added at a ratio of 1 t%)
A mixed powder added at a ratio of 25 wt% was used.

[Margin below] Using PVA (polyvinyl alcohol) as a binder, a surfactant, a dispersant, and water were added and kneaded to the raw material powder to obtain a slurry.

Subsequently, this slurry was formed into a sheet by a doctor blade method to form a green sheet with a thickness of 35 μm. Thereafter, a conductive paste of A1 was printed on one side of the green sheet by screen printing to form a conductive paste layer that would become the internal electrodes 3 shown in FIG. A plurality of green sheets having a conductive paste layer serving as the internal electrodes 3 can be stacked according to the required capacitance. At this time, one end 2a that is electrically connected to the internal electrode 3 and the other end 2b that is not connected are stacked alternately (see FIG. 3). By being thermocompressed in this state, the internal electrode 3
An unfired laminate was obtained in which the edges 2a and 2b were not exposed.

Next, semiconductor layers 5 electrically connected to internal electrodes 3 are formed on both end faces of this stacked body. This semiconductor layer 5 was prepared by adding a paste consisting of ethyl cellulose resin and butylcellosolp solvent to 10% Lazos as a semiconductor agent and kneading the mixture to obtain a semiconductor agent paste. and,
This paste was applied to both end surfaces of the laminate. Furthermore, after drying this laminate, it was fired in air at 850 to 900°C, which is higher than the melting point of the A1 internal electrode 3, 660°C, for 2 hours, thereby making the laminate into a ceramic and forming the semiconductor layer 5 at the same time. As a result, the semiconductor forming agent was diffused into both end faces of the laminate, and a laminate dielectric ceramic 1 having a structure in which the semiconductor layer 5 and the internal electrode 3 were electrically connected was obtained.

Subsequently, external electrodes 6 are formed on both end surfaces of the laminated dielectric ceramic 1. This external electrode 6 is made by applying silver paste to the Pii end face on which the semiconductor layer 5 is formed, and leaving it in the air for 80 minutes.
It was formed by baking at 0°C. Thereafter, a plating film 7 is formed on the external electrode 6. As this plating material, a nickel plating solution consisting of nickel sulfate or nickel chloride and boric acid was prepared, and nickel was plated on the external electrode 6 by barrel plating. Finally, a plating film 8 was formed on this plating film 7. For this plating, a solder plating solution made of an AS bath (alkanol sulfonic acid) was prepared, and the plating film 7 was soldered using a barrel plating method.

The multilayer ceramic capacitor shown in FIG. 1 formed in this manner is as follows.

External dimensions Width = 3.2mm long:
1.6mm Thickness: 1.2mt.

Ceramic unit thickness: 20μm Total number of effective dielectrics: 19 Opposing electrode area per layer: 1.3mm2 In order to understand the electrical characteristics of the multilayer ceramic capacitor of this example, a conventional product was used as a comparative example and tested under the same conditions. I did it.

First, using an automatic bridge measuring instrument, 1k)l was added to each sample.
□ The capacitance (C) and dielectric loss (tan δ) were measured by applying a voltage of IVrms. Next, the temperature characteristics of the dielectric constant were measured in the temperature range of -25 to +85 °C with +20 °C as the standard. The results of the above tests are shown in Table 2.

In the example shown in Example B, conventional multilayer ceramic capacitors rarely have good characteristics, whereas the multilayer ceramic capacitor according to the present invention has a temperature that is equal to or higher than the melting point of the internal electrode. Even after firing, sufficient electrical properties were obtained.

That is, when fired at 850 to 900°C, which is higher than the melting point of the A1 internal electrode, 660°C, the comparative example has a capacitance (
C) was not obtained at all. This indicates that the internal electrode 3 buried between the laminated dielectric ceramics is not electrically connected properly to the external electrode 6, or that the electrode is broken. In other words, this confirms that the internal electrode 3 was melted during firing because it was fired at a temperature higher than 660°C, which is the melting point of the A1 internal electrode, and it either flowed out from the end of the multilayer ceramic capacitor or was agglomerated. .

Therefore, for confirmation, the unit of the comparative example was hardened with resin, further polished, and the cross section was observed using an optical microscope. As a result, void layers due to elution of the internal electrodes were observed at the ends of all internal electrodes 3.

On the other hand, in the example of the present invention, the capacitance (C) was at a firing temperature of 850~
It was 10 nF or more at 900°C, and the dielectric loss (tan&> was also 0.9 to 1.0%. When the cross section was observed in the same manner as in the comparative example, no bead-shaped aggregation of the internal electrodes 3 was observed.
Moreover, no void layer was observed. This indicates that the internal electrodes are not eluted to the outside. Even if the internal electrodes melt when fired at a temperature higher than the melting point of the internal electrodes, the semiconductor layer 5 blocks the leaching to the outside. It was confirmed that the internal electrode 3 interposed between the dielectric ceramics 2 was maintained in the same state as before firing.

Note that the multilayer ceramic capacitor according to the present invention is not limited to the above-mentioned embodiments, and can be variously modified within the scope of the gist.

In particular, the semiconductor agent for forming the semiconductor layer 5 can have various compositions, and the same applies to dielectric ceramic materials and the like. In addition, various methods such as sputtering, vapor phase deposition, spraying, and dipping can be used to attach the semiconducting agent to both end surfaces of the laminate, and these methods can also be used when forming the external electrodes 6. It is possible.

Effects of the Invention As detailed above, according to the present invention, since a semiconductor layer is formed between both end faces of the laminated dielectric ceramic and the external electrode, melting does not occur when firing at a temperature higher than the melting point of the internal electrode. The internal electrodes are isolated from the outside by the semiconductor layer and are prevented from leaking to the outside. Therefore, disconnection of the electrode inside the multilayer ceramic capacitor or poor electrical connection with the external electrode is eliminated. In other words, it is not necessary to use a material with a melting point higher than the firing temperature for the internal electrodes, and therefore it is possible to use an inexpensive material with a low melting point and obtain a low-cost multilayer ceramic capacitor through normal manufacturing processes. It has become possible.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention; FIG. 1 is a central vertical cross-sectional view of a multilayer ceramic capacitor, FIG. 2 is a plan view of a dielectric ceramic before lamination, and FIG. 3 is a dielectric ceramic laminate similar to that shown in FIG. 2. FIG. DESCRIPTION OF SYMBOLS 1... Laminated dielectric ceramic, 2... Dielectric ceramic, 3... Internal electrode, 5... Semiconductor layer, 6...
External electrode, 7... plating film, 8... plating film. Patent applicant Takeshi Morishita, patent attorney representing Murata Manufacturing Co., Ltd. - Figure 1 Figure 2

Claims (1)

[Claims] 1. In a multilayer ceramic capacitor in which external electrodes are arranged on both end faces of a multilayer dielectric ceramic in which internal electrodes are embedded in layers, the internal electrodes are made of a metal material having a melting point equal to or lower than the firing temperature of the dielectric ceramic. A multilayer ceramic capacitor comprising: a semiconductor layer provided between the end face where the internal electrode is exposed and the external electrode.