JPH06151235A - Laminated type porcelain capacitor - Google Patents

Abstract

PURPOSE:To give a high resistance against the mechanical stress and thermal shock coming from outside without decreasing adhesive strength of the capacitor element of an electrode by a method wherein the glass frit of an external electrode is constituted by the glass having additional PbO and ZnO borosilicate glass characteristics. CONSTITUTION:There is no change in the structure of this laminated type porcelain capacitor when compared with the conventional structure, and a capacitor element 3 is formed by laminating a plurality of dielectric layers 1 through the intermediary of an inner electrodes 2. The inner electrodes 2 are led out alternately to the side face of the capacitor element 3, a pair of outer electrodes 4 are formed on the side face of the inner electrodes 2, and besides, a plated film 5 is formed on the surface of the outer electrodes 4. The outer electrodes 4 are composed of glass frit of 13.5 to 22.0vol.%, desirably 15 to 18vol.%, and the remaining part consisting of a metal conductor, the glass frit contains at least B2O3 and SiO2, and Pb of 53.1 to 60.2wt.% in terms of an oxide, and Zn of 10.2 to 15.3wt.% in terms of an oxide are contained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated porcelain capacitor. More specifically, it is possible to improve thermal shock resistance and mechanical strength by improving external electrodes, and to cope with large capacity and high lamination. It concerns a porcelain capacitor.

[0002]

2. Description of the Related Art FIG. 1 shows a typical structure of a laminated ceramic capacitor. According to FIG. 1, a plurality of dielectric layers 1 are laminated via an internal electrode 2, and a pair of external electrodes electrically connected to the internal electrode 2 is provided on a side surface of the capacitor body 3. 4 are formed. Further, the surface of the external electrode 4 is coated with a plating film 5 of Ni, Sn, or the like.

Conventionally, a so-called glass bond type external electrode has been generally used in which a metal conductor such as Ag or Pd is bonded to a capacitor body porcelain by a glass frit to provide mechanical strength. The glass frit component contained in the external electrode is (1) mechanically bonded to the porcelain body and the metal (mainly Ag) as the main component of the external electrode, and (2) filled in the pores of the sintered metal conductor. And has a dual role of densifying the structure of the external electrode film. In addition, recently, as the capacity of capacitors has increased, the number of layers has increased, and thermal shock resistance is being demanded. For this reason, liquid does not penetrate into the electrodes during wet processing such as plating, so a precise external electrode is required. There is also a need to be.

[0004] In order to satisfy such an object, various improvements have been proposed in the component composition of the external electrode. For example, in Japanese Examined Patent Publication No. 62-1662, a glass frit that constitutes an external electrode is composed of a glass composition in which an alkali metal oxide and an alkaline earth oxide are added to zinc borosilicate glass whose main component is zinc oxide. It is disclosed that the reduction resistance and the acid resistance are improved by doing so.

[0005]

However, according to the glass composition proposed in Japanese Patent Publication No. 62-1662, although the reduction resistance and the acid resistance are improved,
It is insufficient for the role of the glass frit described above. For example, when it is applied to the laminated porcelain capacitor element body whose dielectric layer is most commonly made of barium titanate, the porcelain element body and the glass frit are used. Reacts to deteriorate the mechanical strength of the porcelain body, and as a result, when the element is mounted on a circuit board, the element is cracked due to the bending of the board or the like.

Further, in the external electrode in which Ag is selected as the metal conductor and mixed with the glass frit, it is necessary to contain about 8% by weight or more of glass frit with respect to Ag in order to densify the electrode film. Becomes Since the specific gravity of this type of glass frit is about 3.0, the volume is about 28% or more with respect to Ag. When a large amount of glass frit is contained in the external electrode in this way, the region that reacts with the porcelain deepens from the interface, and the thermal expansion coefficient of the reaction layer differs greatly from that peculiar to the porcelain. There are problems that cracks are generated when firing and that the substrate is broken by a slight deflection after mounting on the substrate. On the contrary, when the amount of glass frit is reduced, the film structure is not sufficiently densified, and there is a problem that the plating solution penetrates into the electrode and deteriorates thermal shock resistance in the subsequent step of applying the plating film. .

[0007]

Therefore, as a result of repeated studies on the above problems, the inventors of the present invention have found that after forming the external electrode by firing, the site where the glass composition is present inside the electrode is detailed. As a result, it was found that the dispersion state of the glass in the electrode has a certain tendency depending on the composition of the glass frit. That includes B ₂ O _3, SiO _2, ZnO many, if PbO is no or less includes strong tendency glass is unevenly distributed on the electrode surface and the B ₂ O _3, SiO ₂ conversely PbO It has been found that when the amount of ZnO is large and ZnO is absent or small, the glass tends to be unevenly distributed at the interface between the electrode and the ceramic capacitor body. On the other hand, it contains B ₂ O ₃ and SiO ₂ , and ZnO
It has been found that when ZnO and PbO are contained in a certain range, the glass is dispersed uniformly in the electrode.
That is, an electrode having a dense film structure can be formed by strongly bonding the metal conductor and the porcelain, and at least B ₂ O ₃ and SiO ₂ are contained as a frit that does not deteriorate the mechanical strength of the porcelain, and Pb and Zn are specified. It was found that an external electrode having excellent characteristics can be obtained by selecting the glass contained at a ratio of, and the present invention has been completed.

That is, the laminated ceramic capacitor of the present invention is
A capacitor element body in which a plurality of dielectric layers are laminated via internal electrodes, and a pair of external electrodes formed on a side surface of the capacitor element body so as to be electrically connected to the internal electrodes, The external electrode is composed of 13.5 to 22% by volume of a glass frit and the balance is a metal conductor made of Ag or an alloy containing Ag, and the glass frit contains at least B ₂ O ₃ and SiO ₂ , and further Pb. Is 53.1 to 60.2% by weight in terms of oxide, and Zn is 10.2 to 15.3% by weight in terms of oxide.

The present invention will be described in detail below. The multilayer ceramic capacitor according to the present invention has the same structure as the conventional one, and as shown in FIG. 1, a plurality of dielectric layers 1 are stacked via internal electrodes 2 to form a capacitor body 3. The internal electrodes 2 are alternately led out to the side surfaces of the capacitor body 3, a pair of external electrodes 4 are formed on the side surfaces, and a plating film 5 is formed on the surfaces of the external electrodes 4.

According to the invention, this external electrode 4 comprises a glass frit of 13.5-22.0% by volume, in particular 15-18.
% By volume, the balance being composed of a metal conductor, the glass frit containing at least B ₂ O ₃ and SiO ₂ , and 53.1 to 60.2% by weight of Pb in terms of oxide.
Particularly, 57.0 to 59.0% by weight, Zn is 1 in terms of oxide.
The content is 0.2 to 15.3% by weight, particularly 11.0 to 12.0% by weight.

In the present invention, the amount of glass frit in the external electrode is limited to the above range because the amount is 13.
If it is less than 5% by volume, the adhesive force between the external electrode and the porcelain is not sufficient, and the electrode film structure becomes sparse to reduce the thermal shock resistance. Further, if the amount of glass frit exceeds 22% by volume, a strong glass layer is formed on the surface of the external electrode, and it becomes difficult to form a plated film even if pretreatment such as acid treatment is performed.

Also, the amount of Pb and Z in the glass frit
The amount of n is limited to the above range because the flexural strength of the capacitor decreases when Pb is less than 53.1% by weight or Zn is more than 15.3% by weight, and Pb is more than 60.2% by weight. This is because if the amount is large or Zn is less than 10.2% by weight, pores remain inside the electrode film and the film cannot be sufficiently densified.

[0013] Incidentally, B ₂ O ₃ and SiO ₂ content of glass frit in the present invention may be determined the amount appropriately in accordance with the softening point but, approximately B ₂ O ₃ is 15 to 22 wt%, SiO ₂ is contained in a proportion of 8 to 15% by weight, and other than that, alkali metal, alkaline earth metal, TiO ₂ , A
In some cases, it may contain 1 ₂ O ₃ or the like.

The glass frit as described above is preferably a mixture of lead borosilicate glass and zinc borosilicate glass so that the overall composition is in the above-mentioned ratio. It is also possible that the material powder is prepared in the whole composition and melted at a predetermined temperature.

Further, Ag or an alloy of Ag and Pd is used as the metal conductor forming the external electrode, and Ag / Pd alloy or Pd is used as the internal electrode.

Further, the dielectric layer is made of a well-known dielectric, for example, BaTiO ₃ system, Pb (Mg _1/3 N).
b _2/3 ) O ₃ system, Pb (Zn _1/3 Nb _2/3 ) O ₃ system, P
It is possible to select a dielectric material according to desired characteristics from a b (FeNdNb) O ₃ system or the like.

[0017]

[Function] Contains B ₂ O ₃ and SiO ₂ , contains a large amount of ZnO, and P
Zinc borosilicate glass, which has no or a small amount of bO,
As a component of the glass frit of the external electrode, the metal conductor and the capacitor porcelain body can be strongly coupled, but the thermal expansion coefficient of the reaction layer formed by the glass reacting strongly with the porcelain body is peculiar to that of porcelain. And the mechanical strength of the porcelain is deteriorated, and the glass tends to be unevenly distributed on the electrode surface. On the contrary, B ₂ O ₃ , SiO ₂
Lead borosilicate glass containing a large amount of PbO and a low amount or a small amount of ZnO causes the electrode to be strongly bonded to the porcelain body,
Moreover, the reaction with the porcelain is slight, the thermal expansion coefficient of the reaction part is not much different from that peculiar to porcelain, and the mechanical strength of the porcelain body is not deteriorated, but at the interface between the electrode and the porcelain body Strong tendency to be unevenly distributed.

According to the present invention, these PbO-based, Zn
By constructing the glass frit of the external electrode with a glass having the characteristics of two O-based borosilicate glasses, the mechanical strength and thermal stress from the outside can be reduced without lowering the adhesion strength of the electrode to the capacitor body. High resistance to impact can be imparted. In addition, the flexural strength of the capacitor is improved, and since the film itself is dense, the plating solution does not penetrate into the film during the plating process, improving the yield during manufacturing and improving the thermal shock resistance. It withstands thermal stress when mounted on the board and can improve product reliability.

[0019]

EXAMPLES BaTiO ₃ 97.7% by weight, Nb ₂ O
₅ 1.47% by weight, Sm ₂ O ₃ 0.49% by weight, ZnO
An organic binder and a plasticizer were added to a mixed powder of 0.34% by weight to prepare a slurry, and a green sheet was prepared by a doctor blade method.

Pd is used as a metal conductor on this green sheet.
The internal electrode paste consisting of was applied, laminated and pressure-bonded, and then fired in the atmosphere at 1300 ° C. to prepare a capacitor element body.

Next, PbO62 was added to the metal conductor made of Ag.
˜75 wt%, B ₂ O ₃ 12 to 25 wt%, SiO ₂ 2
~ 20 wt% lead borosilicate glass and ZnO5
5 to 65% by weight, B ₂ O ₃ 25 to 40% by weight, SiO ₂
A zinc borosilicate glass having a composition of 5 to 20% by weight and Li ₂ O of 1.0 to 2.5% by weight is mixed and added so that the overall composition of the glass is as shown in Table 1 to prepare an external electrode paste. did. Then, each paste was applied to the end surface of the capacitor body, and then heat-treated in the atmosphere at 610 to 750 ° C. to burn the external electrodes to the capacitor body to obtain a laminated porcelain capacitor.

The obtained laminated porcelain capacitor was EIAJ
According to the test method, 20 capacitors are mounted on each glass epoxy substrate with a thickness of 1.6 mm, a flexure test is performed, and the flexure amount at the time when the element breaks is measured. The average value is shown in Table 1. It was

Each capacitor was immersed in molten solder at 305 ° C. and inspected for the presence of cracks in the porcelain, and the number of cracked capacitors out of 300 is shown in Table 1.

[0024]

[Table 1]

As is clear from Table 1, Sample Nos. 1 and 2 containing no lead in the glass frit have a low strength against bending, and the lead content of the system containing lead exceeds 60.2% by weight. Samples Nos. 6 and 7 have high flexural strength but low thermal shock resistance. Further, Sample No. 8 having a glass frit amount of less than 13.5% by volume has low thermal shock resistance, and Sample No. 11 having a glass frit amount of more than 22% by volume has sufficient strength against bending and thermal shock. There were no cracks in the capacitor porcelain body, but the plating film peeled off in 2 pieces /
There were 200 pieces. It is considered that this is because the glass layer was firmly formed on the surface of the external electrode, and a strong plating film could not be formed, which is not suitable. On the contrary,
In the capacitor of the present invention, no crack was found in the thermal shock test, there was no abnormality in appearance such as peeling of the plating film, and the flexural limit at the breaking limit was 4.0 mm or more, indicating excellent flexural strength. .

[0026]

As described in detail above, according to the present invention, it is possible to impart high resistance to external mechanical stress and thermal shock, enhance the flexural strength of the capacitor, and increase the flexural strength of the capacitor. Since it can withstand the thermal stress applied during mounting, the reliability of the product can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view for explaining the structure of a laminated ceramic capacitor.

[Explanation of symbols]

 1 Dielectric layer 2 Internal electrode 3 Capacitor element body 4 External electrode 5 Plating film

Claims (1)

[Claims] 1. A capacitor element body having a plurality of dielectric layers laminated via internal electrodes, and a pair of external electrodes formed on the side surfaces of the capacitor element body so as to be electrically connected to the internal electrodes. In the laminated ceramic capacitor described above, the external electrode is made of 13.5 to 22% by volume of glass frit and the balance is a metal conductor made of Ag or an alloy containing Ag, and the glass frit is at least B ₂ O ₃ and Si.
Containing O _2, further Pb in terms of oxide from 53.1 to 6
0.2 wt%, Zn converted to oxide 10.2 to 15.3
A laminated porcelain capacitor characterized by being contained in a weight percentage.