JPH047573B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a ceramic laminate that is sintered by atmosphere firing, and in which the atmosphere during firing or other heat treatment extends to the inside of the ceramic laminate. It is related to the structure for

Summary of the Invention The present invention provides a ceramic laminate in which a dummy layer that becomes porous during firing of the ceramic is formed in a state extending from the inside of the ceramic laminate to the outer surface thereof, thereby making it possible to improve the dummy layer during firing or other heat treatment. The idea is to allow the atmosphere to reach the interior through this porous dummy layer.

BACKGROUND ART An example of a ceramic laminate manufactured by atmosphere firing is a laminated capacitor which uses a metal such as nickel as an internal electrode and is fired in a reducing or neutral atmosphere containing hydrogen gas or the like.

In the manufacturing process of such a laminated capacitor, the atmosphere during firing as described above must first reach the inside of the laminated body. In addition, after firing, the multilayer capacitor is coated with external electrodes.
The ceramic is oxidized by heat treatment in air or in an atmosphere with a moderate oxygen concentration, and the electrical performance of the ceramic is improved, for example, the insulation resistance at high temperatures is improved. Even in this case, the effect of the oxidation treatment must reach the inside of the multilayer capacitor.

Problems to be Solved by the Invention By the way, for the purpose of increasing the capacity of a multilayer capacitor, there is a method of increasing the number of stacked internal electrodes in order to increase the overlapping area of the internal electrodes. If this method is adopted, the number of laminated layers of the multilayer capacitor will increase, and the multilayer capacitor will become thicker. Therefore, in the above-mentioned atmosphere firing and oxidation treatment, there is a problem in that the respective atmospheric gases have difficulty reaching the inside of the multilayer capacitor. If such a situation occurs, uniform sintering of the ceramic will be inhibited during the atmosphere firing stage, leaving a porous part near the center of the multilayer capacitor, and in extreme cases, the internal electrodes will be damaged. It may even melt and run out. In addition, during the oxidation treatment stage, if the atmospheric gas does not reach the inside of the multilayer capacitor during heat treatment, the oxidation treatment effect will not be sufficiently effective, resulting in a decrease in insulation resistance and poor life characteristics. This leads to a decline in quality.

As a method of obtaining a large-capacity multilayer capacitor, a method has been proposed in which a medium-capacity multilayer capacitor chip is made into blocks, cased, and sealed with resin, but the manufacturing process is complicated.

Therefore, the present invention aims to provide a ceramic laminate in which the atmosphere is distributed as uniformly as possible to the inside during heat treatment such as firing or oxidation treatment.

Means for solving the problem The above problem can be solved by taking a technical measure of forming a dummy layer that becomes porous during the firing stage of the ceramic and extending from the inside of the ceramic laminate to the outer surface. resolved.

Function First, in the firing stage of ceramics, the dummy layer is porous at least at the time when sintering of the ceramic is achieved, so the atmosphere during firing can easily penetrate into the inside of the laminate through this dummy layer. reach. Further, after firing, the dummy layer remains porous, so that the atmosphere for oxidation treatment, etc. reaches the inside of the laminate through this layer.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 to 4. Here, multilayer capacitor 1
It is shown.

This multilayer capacitor 1 is indicated by dotted lines in FIGS.
As shown in the figure and FIG. 4, two dummy layers 2 are provided. The other configurations are similar to conventional multilayer capacitors. The structure will be clarified by explaining the manufacturing process of the multilayer capacitor 1 below.

First, as for the method of forming the dummy layer 2, the method disclosed in, for example, US Pat. No. 3,679,950 is used. That is, as shown in FIG. 3, a paste made by mixing the dielectric ceramic powder constituting the multilayer capacitor 1 with carbon powder or resin that burns and disappears is printed on a ceramic green sheet 3 (however, as shown in FIG. 3). (Figure 3 shows the state after sintering.)
dry. The internal electrodes 4 are also formed by screen printing or the like, for example, by applying nickel paste onto a ceramic green sheet and drying it.

When these printed ceramic green sheets are stacked, after a predetermined number of internal electrode printed sheets are stacked, the dummy layer printed sheet 3 is sandwiched between them, and then a predetermined number of internal electrode printed sheets are stacked. These steps are repeated to obtain a laminated block in which dummy layer printed sheets 3 are sandwiched at predetermined intervals. A laminate chip 5 is obtained by press-bonding this laminate block and then cutting it. However, the laminate chip 5 shown in the drawing is shown as a stage after firing.

The above-mentioned laminate chip 5 before firing is heated slowly to a temperature range in which carbon, resin, etc. contained in the dummy layer 2 burns, and the carbon, resin, etc. are thereby dissipated. As shown in the figure and FIG. 2, the dummy layer 2 becomes porous.

This porous dummy layer 2 remains porous at least during the intermediate stage of the ceramic sintering process of the laminate chip 5, at the final stage, and even after the sintering is completed. Therefore, in the ceramic sintering stage, reducing or neutral atmospheric gas such as hydrogen gas reaches the center of the laminate chip 5 through the porous dummy layer 2, and the ceramic is heated. Promotes sintering.

Further, when the laminate chip 5 is subjected to oxidation treatment after firing, oxygen gas acts through the porous dummy layer 2 to the center of the laminate chip 5. Therefore, a uniform oxidation treatment effect can be expected.

As shown in FIGS. 1, 3, and 4, the laminate chip 5 has an external electrode 6 after firing.
will be granted. The external electrode 6 may be provided before or after the above-mentioned oxidation treatment. When the external electrodes 6 are provided before the oxidation treatment, the dummy layer 2 is preferably opened on the outer surface of the multilayer chip 5 on which the external electrodes 6 are not formed. This is because the external electrode 6 closes the porous dummy layer 2, inhibiting the oxidation treatment effect. Furthermore, when a paste containing a solvent, such as silver paste, is applied as the external electrode 6, the solvent may be sucked into the porous dummy layer 2 and trapped within the dummy layer 2. In this case, when the applied paste is baked, the solvent is rapidly heated and expanded, so that the laminate chip 5 may peel off at the dummy layer 2 portion. For this reason as well, it is desirable that the dummy layer 2 be opened on the surface where the external electrode 6 is not formed.

Note that if the above-mentioned inconvenience does not become a problem, the dummy layer may have an opening on the surface where the external electrode is formed. Even in this case, the function of causing the atmospheric gas to reach the center of the laminate chip at least during the sintering process of the laminate chip can be sufficiently achieved.

For example, the multilayer capacitor 1 shown in FIG.
Although the dummy layer 2 is left open to the outside, even if it is used as is, there is no problem in terms of the basic performance of the capacitor. However, when considering the problems described below, it is preferable that the porous dummy layer 2 is finally filled with an organic material or the like.

For example, when applying an exterior resin coating to the multilayer capacitor 1, when the air trapped in the dummy layer 2 is expanded by heating and released to the outside,
Bubbles may be formed in the exterior resin. The generation of such bubbles must be avoided considering the purpose of the exterior resin coating.

Furthermore, if no exterior resin coating is applied, the porous dummy layer 2 will adsorb moisture in the air, and in extreme cases, there is a risk that electrical bridging will occur between the opposing external electrodes 6. This problem can be solved simply by shortening the length of the opening in the dummy layer 2 and maintaining the distance from the external electrode 6 as much as possible, but if the length of the opening is extremely shortened, the original purpose This is undesirable because it obstructs the inflow and outflow of atmospheric gases.

Therefore, as already mentioned, dummy layer 2
It is desirable that they be eventually filled with some kind of material. For example, it is conceivable to impregnate and seal the dummy layer 2 with plastic at the stage where all the heat treatments using atmospheric gases, such as oxidation treatments, have been completed. As this sealant, for example, one whose main component is a solvent-free, thermosetting methacrylic monomer is advantageously used. This sealant is impregnated into the dummy layer 2 under vacuum, for example, and then placed in hot water at 90°C and maintained in this state for 10 minutes, thereby being cured while filling the dummy layer 2. At this time, at the same time, excess sealant adhering to the surface of the laminate chip 5 is washed away with hot water.

Next, some other embodiments of this invention will be described.

First, the dummy layer 2 is not formed by interposing only one layer each in the middle of the stacked chip 5 as shown in FIG. 1, but by forming a plurality of dummy layers 2 together as shown in FIG. It may also be interposed within the laminate chip 5.

Further, as shown in FIG. 6, ceramic green sheets 7 and 8 each having a dummy layer 2 formed thereon are
may be stacked on each other so that the dummy layers 2 face each other to increase the thickness of the dummy layer 2 itself.

According to the embodiments shown in FIGS. 5 and 6, the area occupied by the dummy layer 2 within the stacked chip increases, making it easier for atmospheric gas to reach the inside.

In addition, the present invention not only allows ceramic firing in a reducing or neutral atmosphere and oxidation treatment of sintered ceramic to be advantageously performed, but also can be used for gas atmosphere firing and gas atmosphere heat treatment of other large ceramic laminates. It can also be used. Also,
The invention is not limited to laminated ceramic capacitors, but can also be applied to, for example, laminated piezoelectric actuators fired in an oxygen atmosphere.

In addition, as a method for forming a porous dummy layer, in addition to using a mixed paste of ceramic powder and carbon powder, for example, a porous dummy layer can be formed using nickel or palladium powder with a large particle size. Good too.

Effects of the Invention According to the present invention, since the porous dummy layer is formed extending from the inside of the ceramic laminate to the outer surface, a large-sized ceramic laminate can be integrally fired. It will be easier to commercialize capacitive multilayer capacitors, high voltage multilayer capacitors, and multilayer piezoelectric actuators.

Further, since good sintering is achieved even in the center of the ceramic laminate, a dense ceramic can be obtained. Furthermore, since the effect of heat treatment such as oxidation treatment is applied to the entire ceramic laminate, insulation resistance and life characteristics are significantly improved.

In addition, during the firing stage of the ceramic laminate, sintering of the inside and outside proceed almost simultaneously, so that no deviation in shrinkage occurs and physical defects such as delamination do not occur.

In addition, since good heat treatment becomes easier, firing time, oxidation treatment time, etc. can be shortened. As a result, it is possible to save energy, save resources, reduce capital investment, improve production efficiency, and expect a reduction in the cost of obtaining ceramic laminates.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional front view of a multilayer capacitor 1 according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line - in FIG. 1. Figure 3 shows the first
FIG. FIG. 4 is a perspective view of the multilayer capacitor 1 of FIG. 1. FIG. 5 is a cross-sectional front view of a laminate chip 5 as another embodiment of the present invention. FIG. 6 is a diagram for explaining still another embodiment of the present invention, and shows the state in which the dummy layers 2 are stacked. In the figure, 1 is a multilayer capacitor, 2 is a dummy layer, 5 is a multilayer chip, and 6 is an external electrode.

Claims (1)

[Scope of Claims] 1. A ceramic laminate in which a dummy layer, which has become porous during the firing stage of the ceramic, extends from the inside to the outer surface of the ceramic laminate in order to allow the atmosphere during heat treatment to reach the inside. laminate. 2. The ceramic laminate according to claim 1, wherein an external electrode is partially formed on the outer surface of the ceramic laminate, and the dummy layer is open on a surface where the external electrode is not formed.