JPH06176956A - Laminated porcelain capacitor - Google Patents

Abstract

PURPOSE:To ensure higher resistance against external mechanical stress and thermal shock by constructing an external electrode with a glass frit and Ag and an alloy containing Ag and permitting the glass frit to contain PbO, TiO2, SiO2, and B2O3 as main ingredients. CONSTITUTION:In a laminated porcelain capacitor, a capacitor elementary structure 3 is formed by laminating a plurality of dielectric layers 1 through an internal electrode 2. The internal electrodes 3 are alternately laminated on the side of the capacitor elementary structure 3, and a plated film 5 is formed on the surface of an external electrode 4. The external electrode 4 is constructed with a metal conductor comprising Ag or an Ag alloy and a glass frit. The glass flit contains PbO of 57% by weight or more and TiO2O of 5-10% by weight with a remaining portion thereof comprising SiO2 and B2O3. Hereby, there is ensured higher resistance against an external mechanical stress and thermal shock.

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, external electrodes have generally been Ag, Ag /
A so-called glass bond type is used in which a metal conductor such as a Pd alloy 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, when the zinc borosilicate type glass as proposed in Japanese Patent Publication No. 62-1662 is used as the glass frit, the effect of improving the reduction resistance and the acid resistance is improved. Although it plays, it is not sufficient for the role of the glass frit described above. For example, when it is applied to a laminated ceramic capacitor body whose dielectric layer is most commonly made of barium titanate, the porcelain body is The glass frit reacts with each other to deteriorate the mechanical strength of the porcelain body, and as a result, when the element is mounted on the circuit board, the element is cracked due to bending of the board or the like.

[0006]

Therefore, in order to solve the above problems, the present inventors have examined a glass composition that suppresses the reaction with the porcelain body and does not deteriorate the mechanical strength of the porcelain. As a result, it was found that an electrode having an extremely fine structure is formed by adding an appropriate amount of TiO ₂ to lead borosilicate glass as the glass in the external electrode.

That is, the laminated porcelain capacitor of the present invention is formed on the side surface of the capacitor element body so as to be electrically connected to the capacitor element body in which a plurality of dielectric layers are laminated via the internal electrode and the internal electrode. A pair of external electrodes, wherein the external electrodes are glass frit and Ag or Ag.
Glass frit is made of an alloy containing PbO,
TiO ₂ , SiO ₂ and B ₂ O ₃ are contained as main components, PbO is 57 wt% or more, and TiO ₂ is 0.5 to 1
It is characterized by being present in a proportion of 0% by weight.

The present invention will be described in detail below. The multilayer ceramic capacitor according to the present invention has a structure basically similar to the conventional structure, and as shown in FIG. 1, a plurality of dielectric layers 1 are stacked via internal electrodes 2 to form a capacitor body 3.
Is formed. 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 is
Alternatively, it is composed of a metal conductor made of an Ag alloy and a glass frit, and the glass frit has a PbO content of 57% by weight or more, especially 6
7.2 to 70.2% by weight, TiO ₂ 0.5 to 10% by weight, particularly 1.4 to 3.6% by weight, with the balance being S
It is composed of iO ₂ and B ₂ O ₃ .

In the present invention, Pb in the glass frit
The amount of O was limited to the above range because PbO was 57% by weight.
If it is less, the glass reacts strongly with the porcelain and deteriorates the mechanical strength of the porcelain. Further, the amount of TiO ₂ is limited to the above range, because when TiO ₂ is less than 0.5% by weight, glass exudes to the electrode surface without completely filling the cavity in the metal and the internal structure of the electrode becomes dense. This is because if the content is more than 10% by weight, the softening temperature of the glass becomes high and the working temperature needs to be raised, so that the glass penetrates into the porcelain to deteriorate the porcelain and deteriorate the mechanical strength. .

The amounts of B ₂ O ₃ and SiO ₂ in the glass frit according to the present invention may be appropriately determined according to the softening point, but B ₂ O ₃ is approximately 15 to 22% by weight and SiO 2 ₂ is contained in a proportion of 8 to 15% by weight, and ZnO, an oxide of an alkali metal or an alkaline earth metal, Al ₂ O ₃ , Cr ₂ for adjusting the softening point of other glass.
It may also contain O ₃ and CuO.

The content of each component in the glass frit is described as an oxide amount for the sake of convenience. However, when determining each amount in the glass, the metal amount detected in the glass frit is used. It can be determined as an amount converted to oxide.

The external electrode in the present invention preferably has a glass frit of 13.5 to 22% by volume and the balance of Ag or Ag alloy, and the glass frit amount is 13.5.
If it is less than volume%, the adhesive force between the external electrode and the porcelain is not sufficient, and the electrode film structure becomes sparse and the thermal shock resistance tends to decrease,
If it exceeds 22% by volume, a strong glass layer is formed on the surface of the external electrode, and it tends to be difficult to form a plating film even if pretreatment such as acid treatment is performed.

The above-mentioned glass frit is a mixture of lead borosilicate glass powder with a predetermined ratio and TiO ₂ powder added, but the metal oxide powder constituting the glass is mixed in the whole composition at a predetermined temperature. It may be melted.

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]

According to the present invention, Ti is added to lead borosilicate glass.
By adding a small amount of O ₂ , TiO ₂ improves wettability with a metal and enhances dispersibility of glass in the external electrode, so that a dense external electrode film can be formed.

As a result, high resistance to external mechanical stress or thermal shock can be imparted without lowering the adhesion strength of the electrode to the capacitor body.
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. Apply the internal electrode paste made of Pd as a metal conductor to this green sheet,
These were laminated and pressure-bonded and then fired in the atmosphere at 1300 ° C. to prepare a capacitor element body.

Next, a glass composition having a ratio shown in Table 1 was mixed with a metal conductor made of Ag in an amount of 18% by volume in the external electrode to prepare an external electrode paste. 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.

3 for each of the obtained laminated porcelain capacitors
The presence of cracks in the porcelain was examined by immersing it in molten solder at 05 ° C, and the number of capacitors in 300 cracks was shown in Table 1.

According to the EIAJ test method, 20 capacitors each were mounted on a 1.6 mm-thick glass epoxy substrate and subjected to a flexure test. The flexure amount at the limit of device destruction was measured and averaged. The values are shown in Table 1.

[0023]

[Table 1]

As is clear from Table 1, according to the sample No. 1 in which the glass frit does not contain TiO ₂ at all, the inside of the electrode does not become dense, and the liquid enters the electrode during the plating process, so that heat is generated. A defective product was generated in the impact test, and the sample No. 8 containing TiO ₂ and having an amount of more than 10% by weight had insufficient flexural strength. On the other hand, the product of the present invention is excellent in thermal shock resistance, no defective product is generated in the 300 thermal shock test, and the flexural strength is 3.5 mm.
The capacitor having the above excellent strength was obtained.

[0025]

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 through 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, the external electrode is made of glass frit and Ag or an alloy containing Ag, and the glass frit is at least Pb.
Containing O, TiO ₂ , SiO ₂ and B ₂ O ₃ , Pb
O is 57 wt% or more, TiO ₂ is 0.5 to 10 wt%.
The multilayer ceramic capacitors are characterized in that they are present in respective proportions.