JP2971993B2 - Multilayer ceramic capacitors - Google Patents

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 structure of an internal electrode.

[0002]

2. Description of the Related Art Conventionally, multilayer ceramic capacitors (hereinafter referred to as "capacitors") have a wide range of excellent characteristics, such as small size, large capacity, semi-permanent life, and low resistance at high frequencies. It is widely used, especially as a power source for exchanges. In the manufacturing method, a ferroelectric ceramic powder is mixed and dispersed using an organic binder and a solvent to obtain a slurry, and then a green sheet having a constant thickness is formed by a doctor blade method or the like. Gold (Au), palladium (Pd), silver (A
g) A paste containing a metal powder in which a low-resistance metal powder such as copper (Cu), nickel (Ni) or the like is dispersed in an organic vehicle is screened so as to obtain an outlet for alternately connecting external electrodes in a certain shape. Printing is performed, the green sheet is punched out, and when forming the external electrodes later, the capacitors are laminated so as to take a parallel structure of the capacitors, thereby obtaining a raw chip of a multilayer ceramic capacitor. Thereafter, after removing the binder, firing is performed, and the external electrode connected to the internal electrode is baked to obtain a capacitor element. FIG. 5 shows a cross-sectional view of a conventional multilayer ceramic capacitor. The multilayer ceramic capacitor has a structure in which the ferroelectric ceramics 1 and the internal electrodes 2a are alternately laminated, and a difference occurs between a portion where the internal electrodes are printed and a portion where the internal electrodes are not printed by the thickness of the internal electrodes. Since the contraction rate of the low-resistance metal and the ferroelectric ceramic, which form the internal electrodes during firing, differ, cracks and delaminations occur, resulting in products with insufficient electrical shorts and reliability. I will. Therefore, attempts have been made to form a capacitor element using an internal electrode paste mixed with an inorganic filler such as a ceramic powder which is the same as a ferroelectric ceramic (hereinafter referred to as ceramics) powder constituting the capacitor. Has an equivalent series resistance (hereinafter referred to as ES) due to the presence of an inorganic filler in
R) increases, and when an AC voltage is applied, the ripple current increases, and the capacitor element itself generates heat, which causes a problem in use.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the occurrence of delamination caused by a difference in shrinkage between a ferroelectric ceramic and an internal electrode, and to provide a highly reliable laminate having a small equivalent series resistance. It is to provide a ceramic capacitor.

[0004]

SUMMARY OF THE INVENTION The present invention provides a multilayer ceramic capacitor which surrounds a periphery of an internal electrode.
A multilayer ceramic formed by printing and applying an internal electrode material mixed with a fine ceramic powder of the same composition as the ferroelectric ceramic material forming the capacitor element, and a metal paste of the same material as the conventional material consisting of silver palladium etc. It is characterized by being used as an internal electrode of a capacitor.

That is, the present invention relates to a multilayer ceramic capacitor in which ferroelectric ceramic layers and internal electrode layers made of a low-resistance metal are alternately stacked, and the internal electrode layers are connected to different external electrodes every other one. An inorganic filler containing 5% to 75% by weight of a ceramic powder forming a ferroelectric ceramic layer added to a low resistance metal forming the internal electrode so as to surround the inner electrode layer; A multilayer ceramic capacitor characterized in that the electrodes are formed to have a width of 200 microns or less than 20% of the width of the internal electrode from the end surface of the internal electrode so as to surround the periphery of the internal electrode except for the external electrode outlet.

[0006]

The internal electrodes of the multilayer ceramic capacitor according to the present invention have a U shape around the metal-only internal electrodes of the conventional multilayer ceramic capacitor, except for the outlet to the external electrodes.
An inner electrode containing an inorganic filler in which 5% to 75% by weight of a ferroelectric ceramic powder constituting a capacitor is added to the metal electrode material is connected to the metal electrode around the metal internal electrode in the shape of a letter. By forming the inner electrode with a forming width of at least 200 microns and a maximum width of one side and not more than 20% of the width of the internal electrode, the ESR value is almost the same as that of the conventional metal internal electrode. The laminated ceramic capacitor has a lamination generation rate of 1/3 or less. In the internal electrode of the multilayer ceramic capacitor of the present invention, the metal internal electrode portion has a low ESR value, is connected to the metal internal electrode, and has an inorganic filler containing an inorganic filler added with ceramic powder formed around the metal internal electrode. The electrode portion promotes partial sintering between ceramics of the ceramic portion to be laminated, and acts to reduce the rate of occurrence of delamination. If the amount of ceramics added to the inorganic filler-containing internal electrode is too small relative to the weight of the metal internal electrode, the rate of delamination will increase, and if the amount is large, the capacitance of the capacitor will vary. Therefore, the addition amount of the ceramic powder having the effect of the present invention is in the range of 5% to 75%, preferably 15% to 40% by weight based on the metal electrode material. Range. In addition, the width value of the internal electrode containing the inorganic filler formed around the metal internal electrode of the internal electrode of the present invention varies depending on the size of the capacitor. In this case, the value of one width may be 20% of the width of the internal electrode.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to reduce the difference in shrinkage during sintering between internal electrodes and ceramics, which has occurred in conventional multilayer ceramic capacitors, the present invention usually mixes dielectric ceramics constituting the multilayer ceramic capacitors as a filling material. The obtained metal paste is connected to an internal electrode made of a metal, and an internal electrode having a certain width and containing an inorganic filler is provided around the internal electrode.

In the present embodiment, a powder having a lead (Pb) -based composite perovskite structure and a particle diameter of 1 μm or less is used as a ferroelectric ceramic serving as a base material of a capacitor, and silver (Ag) is used as an internal electrode. ) And palladium (Pd) are 7
A paste using an alloy powder at a ratio of 0:30 is used to print and apply around the internal electrodes. As the internal electrode paste containing the inorganic filler, a paste obtained by adding and kneading 30% by weight of the dielectric ceramic powder as the base material of the capacitor with respect to the AgPd alloy powder was used. As shown in FIG. 2, a green sheet 4 made of a dielectric ceramic was formed to a thickness of 20 μm by a doctor blade method, and the width of the green sheet 4 was substantially equal to the width of the end face of the ceramic except for a portion connected to an external electrode. First, print the metal paste of the internal electrode 2 to a thickness of 5 μm on the inner side of 0.9 mm, temporarily dry it with a drier, and replace it with another screen using a pin guide provided on the screen. A part of the internal electrode paste 3 containing an inorganic filler, which is formed by adding and kneading 30% of the ceramic powder to the weight of the metal internal electrode and kneading it around the internal electrode applied to Then, a 5 micron thick print was formed in a U-shape except for the electrode mounting portion. A 5 mm x 5 mm chip is used, ferroelectric ceramics are placed on both the upper and lower surfaces, and the ferroelectric ceramics and the internal electrode plate are alternately placed on the surface.
Layer stacking was performed to obtain a multilayer ceramic capacitor according to an embodiment of the present invention in which an internal electrode 3 containing an inorganic filler was provided around the internal electrode 2 shown in FIG.

[0009] 1000 laminated ceramic capacitors according to the present embodiment were prepared, and first, the values of the delamination occurrence rate and the equivalent series resistance (ESR) change rate were measured. FIG. 3 shows the results of the internal electrode formation conditions and the delamination occurrence rate.
FIG. 4 shows the equivalent series resistance (ESR) change rate. When the internal electrode is a silver-palladium electrode, the delamination occurrence rate shown in FIG. 3 is based on a silver-palladium internal electrode containing 100% inorganic filler and 30% by weight of dielectric ceramic powder added to silver palladium. In the case of the internal electrode of the present invention, the internal electrode containing an inorganic filler containing 30% by weight of a silver palladium ceramic material is replaced with the internal electrode of only silver palladium except for the external electrode mounting opening around the silver palladium internal electrode according to the present invention. The following shows the characteristics under the three conditions in the case of the internal electrode having a structure attached in a belt shape around the periphery. Depending on the structure of the internal electrode, the rate of delamination is 4.4% for a conventional silver-palladium-only internal electrode, 0.8% for a 100% inorganic-filled internal electrode, and the internal electrode according to the embodiment of the present invention. In the case of the internal electrode of the present invention, the rate of occurrence of delamination is 1/3 that of the silver-palladium internal electrode, which is 1.3% in the case of the internal electrode containing an inorganic filler. It is 75 times.

The rate of occurrence of delamination is measured by applying an ultrasonic deep wound and using a delamination detection device in which the delamination portion is displayed as an image, by the occurrence of peeling, cracks, etc. displayed on the image. did.

FIG. 4 is a characteristic diagram showing the relationship between the value of the equivalent series resistance (ESR) and the structure of the internal electrode.
The SR change rate was set to 0%, and the average value of ESR measured using a multilayer ceramic capacitor having a different internal electrode structure was determined as the change rate based on the value of the silver palladium internal electrode. When comparing the rate of change of the average value of ESR,
The internal electrode in which 30% by weight of a ceramic powder is added to silver palladium has an ESR increase of 14% as compared with the case of an internal electrode of 100% silver palladium, and the embodiment of the present invention shows an increase of 2%. No change was observed compared to the value of the silver-palladium internal electrode.

The equivalent series resistance was measured at a frequency of 10 KHz using an impedance meter. The value of ESR in the case of a silver palladium internal electrode is approximately 40 mΩ under the conditions of this embodiment. According to the results shown in FIGS. 3 and 4, by employing the structure of the internal electrode of the multilayer ceramic capacitor according to the present invention, the rate of occurrence of delamination is reduced to 1/3 of that in the case of the internal electrode made only of silver palladium. The value of ESR is almost the same as that of the internal electrode made of only silver / palladium, and is 1/7 of the ESR change rate compared to the case of the internal electrode containing 100% inorganic filler. According to the present invention, a multilayer ceramic capacitor having a low delamination rate and an ESR value equal to that of a conventional silver-palladium internal electrode can be obtained.

In the embodiment of the present invention, the proportion of the ceramic added to the internal electrode containing the inorganic filler formed around the silver-palladium-only internal electrode in the embodiment is a weight ratio with respect to the value of the silver-palladium-only internal electrode. A value of 5% to 75% is suitable, preferably in the range of 15% to 40%. If the amount of ceramic added is 5% or less, the rate of occurrence of delamination increases, and if it is 75% or more, the number of cut electrodes increases, and the variation in capacitance of the multilayer ceramic capacitor increases.

On the other hand, the width of the inorganic filler-containing internal electrode provided around the silver-palladium internal electrode varies depending on the area on which the internal electrode of the multilayer ceramic capacitor is printed.
When the area of the internal electrode is larger than 0 μm, the maximum width is preferably 20% or less of the internal electrode width on one side of the internal electrode.

The internal electrode material of the embodiment of the present invention has been described using an example in which silver-palladium alloy powder containing 70% by weight of silver and 30% by weight of palladium is used. Naturally, the structure of the internal electrode of the multilayer ceramic capacitor of the present invention can be applied using nickel, copper, or gold powder.

Although the embodiment of the present invention has been described with reference to an example of a multilayer ceramic capacitor, the present invention is also applied to a piezoelectric actuator having a structure similar to the internal electrode structure of the present invention, whereby a conventional metal-only internal electrode is formed. Naturally, the rate of delamination can be reduced as compared with the piezoelectric actuator.

[0015]

The multilayer ceramic capacitor according to the present invention is characterized in that the internal electrode is formed with an inorganic filler containing a ferroelectric ceramic powder added and filled around the metal internal electrode. Can be obtained, which is almost the same value as in the case of using the same, and has a delamination occurrence rate of 1/3 the value in the case of the metal internal electrode.

[Brief description of the drawings]

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

FIGS. 2A and 2B show a manufacturing process of a multilayer ceramic capacitor according to the present invention, wherein FIG. 2A is a plan view of a green sheet made of ferroelectric ceramics, and FIG. Plan view with paste printed,
FIG. 2C is a plan view in which an internal electrode containing an inorganic filler added with a ferroelectric ceramic powder is printed around a metal internal electrode on a green sheet.

FIG. 3 is a characteristic diagram showing the relationship between the structure of each internal electrode and the rate of occurrence of delamination.

FIG. 4 is a characteristic diagram showing a relationship between each internal electrode structure and an equivalent series resistance change rate.

FIG. 5 is a view showing a conventional multilayer ceramic capacitor;
5A is a front sectional view, and FIG. 5B is a transverse sectional view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ferroelectric ceramics 2, 2a Internal electrode 3 Internal electrode containing inorganic filler 4 Green sheet 5 External electrode

Claims (1)

(57) [Claims] 1. A multilayer ceramic capacitor in which a ferroelectric ceramic layer and internal electrode layers made of a low-resistance metal are alternately laminated, and the internal electrode layers are connected to different external electrodes every other one. An internal electrode containing an inorganic filler, in which 5% to 75% by weight of a ceramic powder constituting a ferroelectric ceramic layer is added to and kneaded with a low-resistance metal constituting an electrode, and the periphery of the internal electrode except for an external electrode outlet. Characterized in that it is connected to the end face of the internal electrode and formed to have a width of 200 μm or less than 20% of the internal electrode width so as to surround the multilayer ceramic capacitor.