JPH0449246B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a multilayer capacitor in which a plurality of electrode films are embedded in a dielectric made of ceramic.

(b) Prior art and its disadvantages A dielectric material of a multilayer capacitor has a high dielectric constant in order to obtain large capacitance in a small size. However, conventionally, the dielectric covering the outer layer of the electrode film, which is formed overlappingly with a dielectric layer in between, is also separated from the inner layer dielectric for manufacturing convenience, even though it does not affect the capacitance. Since they were made of the same material, they also exhibited a high dielectric constant, which resulted in the drawback that the capacitance when mounted was different from when measured as a single component.

For example, as shown in FIG. 3, when a multilayer capacitor 1 is mounted on a printed circuit board 2 and a wiring pattern 3 is formed on the back side of the printed circuit board 2, the lowermost dielectric layer 4 is Due to the high dielectric constant, the stray capacitance generated between the lowermost electrode film 5 and the wiring pattern 3 buried thereon becomes a value that cannot be ignored, and the apparent capacitance of the multilayer capacitor 1 becomes larger than the set value. It is.
Furthermore, even when a plurality of such conventional multilayer capacitors 1 are mounted side by side so that the electrode films 5 are located in parallel as shown in FIG. 4, stray capacitance is generated between each multilayer capacitor. may occur and the apparent capacity may differ from the set value.

(c) Purpose of the Invention This invention has been made in view of the above circumstances, and by constructing the outer layer of dielectric material with a low dielectric constant, it is possible to reduce the amount of heat generated between the buried electrode film and the outside. An object of the present invention is to provide a multilayer capacitor that can reduce stray capacitance to an insignificant level.

(d) Structure and Effects of the Invention The multilayer capacitor of the present invention is a multilayer capacitor in which a plurality of electrode films are embedded in a dielectric, and the outer ceramic layer formed on both the front and back surfaces has a dielectric constant lower than that of the inner ceramic layer. It is characterized by what it did.

When the present invention is configured as described above, when the electrode films at both ends and the external wiring pattern etc. are close to each other and face each other when mounting a multilayer capacitor,
Since the dielectric constant of the outer layer dielectric located between the two is lower than that of the inner layer dielectric, a very large capacitance does not occur. Therefore, if the dielectric constant of the outer layer dielectric is made sufficiently low, the stray capacitance can be reduced to an extent that does not affect the set capacitance. Therefore, the present invention can provide a multilayer capacitor that is easy to use and whose capacitance does not vary depending on mounting conditions.

(e) Embodiment FIG. 1 is a longitudinal sectional view of a multilayer capacitor which is an embodiment of the present invention.

The multilayer capacitor 1 of this embodiment is composed of a three-layer dielectric 4, a two-stage electrode film 5 and an external electrode 6 buried therebetween. The dielectric 4 is made of ceramic, and the dielectric 4b placed in the center of the three layers is made of a material with a high dielectric constant. Also,
Outermost dielectric layer 4 formed on both front and back ends of the three layers
For a and 4c, a material having a sufficiently lower dielectric constant than the center dielectric 4b is used. The electrode film 5 is the dielectric material 4
The upper electrode film 5 has an end exposed only on one side surface, and the lower electrode film 5 has an end exposed only on the other opposing side surface. To form these dielectrics 4a, 4b, 4c and electrode films 5, 5, for example, as shown in FIG. 2, three ceramic green sheets 7 are prepared, and only the surfaces of two of them are coated with silver-palladium paste. 8
etc., are stacked on top of each other, and fired. Usually, an appropriate number of green sheets to which no electrode film is provided are further superimposed on the thus-superposed green sheets. Note that the green sheet 7 at this time uses a material having a low dielectric constant only for the outermost layer. The external electrodes 6, 6 are conductors formed to cover both side surfaces and the periphery of the thus formed laminate. Therefore, the external electrode 6 formed on one side is electrically connected to the upper electrode film 5, and the external electrode 6 formed on the other side is electrically connected to the lower electrode film 5.

The difference in the degree of capacitance change during mounting between the multilayer capacitor 1 of this embodiment configured as described above and the conventional multilayer capacitor 1 is shown. Here, the dielectric constant ε of the dielectric 4 in the conventional example and the middle layer dielectric 4b in this example is assumed to be 10,000, and the dielectric constant ε' of the outermost layer dielectrics 4a and 4c in this example is assumed to be 10.

When these multilayer capacitors 1 are mounted on a printed circuit board 2 as shown in FIG. 3, the ratio of the thickness d ₁ of the lowermost layer dielectric 4c to the thickness d ₂ of Bakelite of the printed circuit board 2 is 1: 1, this embodiment was able to suppress the influence of stray capacitance to about 1/2 compared to the conventional example.

In addition, each of these multilayer capacitors 1 is
When the two multilayer capacitors 1 _and 1 are mounted side by side on the printed circuit board ₂ as shown in FIG. The distance between d ₃ +
When d was ₄ , this example was able to suppress the influence of stray capacitance to about 1/3 compared to the conventional example.

As explained above, in this embodiment, since the dielectric constants of the outer layer dielectrics 4a and 4b are sufficiently low,
The influence of stray capacitance generated between the external wiring pattern 3 and the like can be sufficiently reduced. Therefore, there is no fear that the capacitance will exceed the allowable range due to the arrangement during mounting, and the multilayer capacitor 1 becomes easy to use.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional front view of a multilayer capacitor which is an embodiment of the invention, Fig. 2 is a perspective view showing the steps for forming the multilayer capacitor, and Figs. They are a front view and a plan view. 1... Multilayer capacitor, 4... Dielectric, 5... Electrode film.

Claims (1)

[Claims] 1. A multilayer capacitor in which a plurality of electrode films are embedded in a dielectric material, characterized in that an outer ceramic layer formed on both the front and back surfaces has a dielectric constant lower than that of an inner ceramic layer.