JP2000302544A - Dielectric ceramics and dielectric ceramic capacitors - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic capacitor having a high AC insulation withstand voltage and a high partial discharge voltage generated when AC is applied, which is suitable for a noise filter for a power converter. SOLUTION: The main component is Ba, Ti, Ca, Zn, N
BaTi composed of oxides of b and Mn and a composite oxide
O ₃ based ceramics as a raw material, 100 wt on the total weight
%, BaTiO ₃ : 87 to 90 wt%, BaZr
O ₃ : 4 to 6 wt%, CaTiO ₃ : 2 to ₃ wt%, Zn
_{TiO 3: 2~3wt%, Nb 2} O 5: 0.5~1.5w
t%, Mn ₃ O ₄ : 0 to 0.08 wt%, BaCO ₃ :
0.4-0.6wt%, kaolinite: 0-0.4wt
% Of these components in a weight ratio of
Fired to obtain dielectric ceramics. When molding this dielectric ceramic with resin, the lead wire is separated from the edge of the electrode by at least 0.3 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grounding dielectric suitable for use as a noise filter of a power converter for filtering switching noise generated by a switching operation of a semiconductor switch element constituting a power converter such as an inverter. The present invention relates to a body ceramic capacitor.

[0002]

2. Description of the Related Art As is well known, the switching operation of a semiconductor switch element constituting a power converter such as an inverter is performed by a pulse-width-converted (PWM) drive signal having a carrier frequency of several kHz to about several tens kHz. It is done based on. And, by this switching operation, more than ten kilohertz
Switching noise of a frequency component equal to or higher than z is generated from this power converter.

[0003] In recent years, various legal regulations have been imposed on the power converter in order to suppress the adverse effect of the frequency component of the switching noise of 100 kHz or more on external devices. To respond to this legal regulation,
A noise filter for the power converter is installed in this power converter.

As a conventional noise filter for a power converter of this type, a single reactor in which an electric wire is wound around a core made of ferrite, an amorphous alloy, a crystal alloy, or the like,
A single capacitor composed of a film or a ceramic chip, etc., is connected between phases and ground, and this filter is used to filter the switching noise generated by the switching operation of the semiconductor switch element. I have.

In particular, since a grounding capacitor requires a high AC withstand voltage, a film capacitor having a large capacity is connected to the series to reduce the voltage applied to each capacitor, or a capacitor having a small capacity is used. They were connected in parallel to form a circuit, and there was no optimal capacitor. In particular, the AC capacitor withstand voltage of AC 3000V × 1S (Br
eak Down Voltage; hereinafter referred to as BDV (AC)), and it was difficult to satisfy the above BDV (AC) characteristics with a dielectric sheet having a high dielectric constant and a small thickness.

Further, there is no capacitor having a high partial discharge voltage generated when an alternating current is applied to the capacitor.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a ceramic capacitor suitable for use as a noise filter for a power converter, which has solved the above-mentioned conventional problems and is smaller, thinner and lower in manufacturing cost. It is in.

[0008]

According to one aspect of the present invention, there is provided a dielectric ceramic for use in a capacitor constituting a noise filter for filtering switching noise, the main component of which is: Ba, Ti, C
BaTiO ₃ ceramics composed of oxides of a, Zn, Nb, and Mn and a composite oxide are used as raw materials, and the total weight is 100 wt%, and BaTiO ₃ : 87 to 90 wt.
%, BaZrO ₃ : 4-6 wt%, CaTiO ₃ : 2-3
_{wt%, ZnTiO 3: 2~3wt%} , Nb 2 O 5: 0.
_{5~1.5wt%, Mn 3 O 4:} 0~0.08wt%, B
aCO ₃ : 0.4-0.6 wt%, kaolinite: 0-
It is characterized in that these components are mixed and pulverized at a weight ratio of 0.4 wt%, then molded and fired.

An object of the present invention is to provide a power converter having a combination of a plurality of L and C provided for filtering a switching noise generated by a switching operation of a semiconductor switch element constituting a power converter. An object of the present invention is to provide a dielectric ceramic suitable for use in a high withstand voltage small capacitor for a ground capacitor used in a noise filter for a converter.

The relative dielectric constant of BaTiO ₃ ceramics is
6000-70 near Curie temperature (about 120 ° C)
It becomes 00. However, when this ceramic was used as it was for a capacitor, the BDV (AC) characteristic was very low because the ceramic also had piezoelectricity. The ceramic used for the noise filter for the power converter has a dielectric constant of about 3000 and a BDV (AC)
Must be able to withstand 3 kV or more as an effective value.
With respect to BDV (AC), it is sufficient to increase the plate thickness. On the other hand, when the plate thickness is increased, the capacity as a capacitor is reduced. Further, for miniaturization, it is preferable that the plate thickness is as thin as possible. That is, the electric field strength of BDV (AC) is required to be high.

The ceramics for a capacitor of the present invention comprises:
Based on BaTiO ₃ , oxides and composite oxides of Ca, Zr, Nb, and Mn are added while maintaining a high dielectric constant, and are fired densely with as small a particle size as possible to improve AC withstand voltage characteristics. (BDV (AC) is ≧ 6 kV / m
m, permittivity ≧ 3000) to improve the temperature characteristics of permittivity. Further, by lowering the firing temperature, the cost of manufacturing is also reduced.

In addition, taking into account the insulation properties and flame retardancy between the terminal exteriors of the capacitor itself and the pot life of the molding resin, an epoxy powder mold containing a filler is low as the outer mold of the capacitor. Practical at cost. However, when using this mold,
It was difficult to fill the details of the capacitor with the powdered resin. In particular, the resin did not enter under the Ag electrode edge where the partial discharge easily occurs and the lead wire extending horizontally from the electrode surface, and the partial discharge voltage was low.

On the other hand, in the present invention, the partial discharge extinction voltage is ≧ 1 kV or more by increasing the distance between the lead wire drawn from the ceramic capacitor and the electrode edge. A capacitor having this configuration limited is claim 2 of the present invention. That is, the dielectric ceramic capacitor according to claim 2 of the present invention is a capacitor constituting a noise filter that filters switching noise,
Electrodes are formed on both sides of the dielectric ceramic according to claim 1, lead wires are connected to these electrodes, and the dielectric ceramic is formed by molding the dielectric ceramic with a resin. At least 0. 0 from the edge of the dielectric ceramic electrode.
It is characterized by being fixed at a distance of 3 mm or more.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 of the reference drawings shows a circuit diagram of an entire noise filter for a power converter comprising a ceramic capacitor 5 according to the present invention. The capacitor 5 of the present invention has a ground E
Is a capacitor for grounding. Reference numeral 6 in the figure denotes a reactor. 2 and 3 are a top view and a cross-sectional view of the ceramic capacitor of the present invention, showing a method of extracting the lead wire 3. FIG. 2 and 3
In the figure, 1 is a dielectric ceramic, 2 is an Ag electrode, 3 is a lead wire, and 4 is a mold resin.

Example 1 Complex oxides BaTiO ₃ , BaZrO ₃ , CaTiO ₃ , ZnTiO _{3 with a} purity of 99% or more
And kaolinite (Kagome clay (KH)) mainly composed of oxides Nb ₂ O ₅ , Mn ₃ O ₄ , BaCO _3, and SiO ₂ and Al ₂ O ₃ as sintering aids. It was prepared as a raw material for ceramics.

These are blended and mixed at a blending ratio shown in Table 1,
The mixture was pulverized and mixed for 48 hours by wet pulverization using a ball mill, and pulverized to 1 μm or less. Then, a binder such as polyvinyl butyral was added, and a granulated powder having high fluidity was produced by a spray drier.

A certain amount of this granulated powder was taken, placed in a mold, and press-molded at a molding pressure of 1 to ² ton / cm ² . In the present embodiment, it was placed in a φ40 mm mold and press-molded to a thickness of 1 mm. Then, firing was performed at a temperature in the range of 1150 ° C. to 1350 ° C., to produce a dielectric ceramic having a diameter of about 32 mm and a thickness of 0.8 mm.

As shown in FIGS. 2 and 3, Ag electrodes 2 having a diameter of 30 mm are screen-printed on both surfaces of the obtained dielectric ceramic 1 so as to have a thickness of 5 to 15 μm.
Bake at 0 ° C. Next, the pre-soldered lead wire 3,
3 was soldered to each of the Ag electrodes 2 on both sides.

Thereafter, the entire dielectric ceramic was coated with an epoxy resin to form a mold 4.

The dielectric constant, temperature characteristics, and BDV (AC) of the thus obtained dielectric ceramic capacitor were evaluated. Further, the dielectric ceramic 1 was cut, its cross section was polished, and the cross section was observed with an SEM to measure the particle size. Table 2 shows the results of these measurements.

The added BaZrO ₃ is a shifter for lowering the Curie temperature at the time of heating and manufacturing ceramics to a lower temperature side.

The relative dielectric constant of BaTiO ₃ ceramics is
6000-70 near Curie temperature (about 120 ° C)
It becomes 00. When this ceramic is used as it is for a capacitor, the BDV (AC) characteristic is very low due to poor temperature characteristics and high piezoelectricity.

In the present invention, the purpose of the BDV (AC) characteristic is 6 kV / mm or more. At this value, it is actually a ceramic with a thickness of 0.5 mm,
Since it can withstand 3 kVAC and is thin, a large capacitance can be secured with a small electrode shape.
Further, the dielectric constant is 3000 or more, and the temperature characteristic is aimed at the XB standard.

Therefore, in the present invention, BaZrO ₃ is added as a shifter for moving the Curie temperature to a lower temperature side,
CaTi as a depressor to flatten the temperature characteristics
O ₃ is added. Further, for the main purpose of lowering the sintering temperature, Frogme clay containing ZnTiO ₃ and kaolinite as main components is added.

In order to improve the insulation resistance, Nb ₂ O ₅ and Mn ₃ O ₄ are added mainly for the purpose of preventing reduction.
These additives and excess BaCO ₃ contribute to low temperature firing and improvement of grain boundary insulation. The characteristics of the dielectric ceramics 1 shown in Table 2 are the result of a delicate compounding ratio of the whole starting raw materials, and various compounding ratios other than Table 1 were examined.
The weight blending ratio of the mark 満 足 satisfied the characteristics for use in the filter capacitor.

[0026]

[Table 1]

[0027]

[Table 2]

(Embodiment 2) In Embodiment 2, when the Ag electrode 2 is printed on the dielectric ceramic 1 of Embodiment 1 and the lead wire 3 is attached, as shown in FIG. 2 and FIG. 0.3 from the end of Ag electrode 2 on both sides
It is characterized in that the lead wire 3 is separated by a distance X of not less than mm.

Generally, in consideration of the insulation and flame retardancy between the terminal exteriors of the grounding capacitor 5 itself and the pot life of the molding resin 4, an epoxy powder mold containing a filler is practical at low cost. is there. However, in the case of using this molding material, it has been conventionally difficult to fill the powder resin into details. In the conventional capacitor mold mulch, the resin does not enter into the end portion (edge portion) of the Ag electrode 2 where partial discharge is likely to occur and the lead wire 3 extending horizontally from the electrode surface. Since voids were formed and the creepage distance of the lead wire to the dielectric ceramics was reduced, the partial discharge initiation and extinction voltage were low.

Therefore, in the present invention, as shown in FIG.
By molding the lead wire 3 away from the edge of the electrode 2, the partial discharge voltage can be reduced.

In the second embodiment, Nippon Pernox P
Using CE282GREY 4A as a mold resin, molding was carried out by dipping the powder into a powder flowing tank several times as follows.

Molding step: first preheating (140 ° C. × 1.
5min) → dipping into resin → second preheating (140 ° C)
× 1.5 min) → dipping into resin → third preheating (1
40 ℃ × 1.5min) → Dipping into resin → After cure (140 ℃ × 1.5min) → Cure (1
50 ° C. × 1 hr).

At the time of making the mold, a test was performed by changing the distance X between the lead wire 3 and the edge of the electrode 2. As a result, if a distance of 0.3 mm or more is taken, no gap is formed at the edge of the Ag electrode 2 immediately below the lead wire 3 and molding becomes possible, and the partial discharge extinction voltage can be set to ≧ 1 kVAC. It turned out that.

[0034]

According to the present invention, it is possible to obtain a high BDV (AC) characteristic even with a thin dielectric ceramic, which leads to a thin and compact ceramic capacitor.
Further, by using a thin dielectric ceramic, it is possible to obtain a large capacitance as a capacitor.

In addition, by fixing the lead wire away from the edge of the electrode, there is no gap in the mold at the edge of the electrode, and a partial discharge voltage of 1 kVAC or more can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an example of a power conversion noise filter realized by the present invention.

FIG. 2 is a top view of the dielectric ceramic capacitor according to the present invention.

FIG. 3 is a sectional view of a dielectric ceramic capacitor according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Dielectric ceramics 2 Ag electrode 3 Lead wire 4 Mold resin 5 Grounding capacitor (ceramic capacitor) 6 Reactor E Ground

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4G031 AA04 AA06 AA11 AA12 AA14 AA19 AA26 AA40 BA09 5E001 AB01 AC09 AE00 AE02 AE03 AE04 AF00 AF03 AG01 AH01 AH05 AH09 AJ01 AJ02 AJ03

Claims (2)

[Claims] 1. A dielectric ceramic used for a capacitor constituting a noise filter for filtering switching noise, the main component of which is selected from oxides and composite oxides of Ba, Ti, Ca, Zn, Nb and Mn. BaTiO ₃ ceramics as a raw material, and the total weight is 100 wt%,
_{BaTiO 3: 87~90wt%, BaZrO 3} : 4~6
_{wt%, CaTiO 3: 2~3wt%} , ZnTiO 3: 2
３3 wt%, Nb ₂ O ₅ : 0.5-1.5 wt%, Mn _{3
O 4: 0~0.08wt%, BaCO 3} : 0.4~0.6
A dielectric ceramic characterized in that these components are mixed and pulverized at a weight ratio of 0 wt% to kaolinite: 0 to 0.4 wt%, and then molded and fired. 2. A capacitor constituting a noise filter for filtering switching noise, wherein electrodes are formed on both sides of the dielectric ceramic according to claim 1, lead wires are connected to these electrodes, and said dielectric ceramic is A dielectric ceramic capacitor molded with a resin, wherein the lead wire is fixed at least 0.3 mm or more away from an edge of an electrode of the dielectric ceramic. .