JP2691181B2 - Dielectric porcelain composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has a temperature coefficient of capacity of ± 30 ppm / ° C in the temperature range of -55 to + 125 ° C, and an Ag-Pd alloy as an internal electrode. The present invention relates to a dielectric ceramic composition for a temperature compensating ceramic capacitor.

(Background Art) In general, a high dielectric constant / temperature compensation porcelain capacitor, especially a commercially available laminated porcelain capacitor, is formed by laminating a plurality of thin-layer dielectrics having internal electrodes formed thereon, and alternately arranging the internal electrodes alternately. Simultaneous integral firing is performed so that the electrodes are connected in parallel to the external connection electrodes. This type of multilayer capacitor requires a relatively high firing temperature (1240 ° C) in order to be sufficiently densified so as to have a high dielectric constant.

Therefore, the metal used for this electrode must be an expensive noble metal (platinum or palladium) whose melting point is higher than the firing temperature of the dielectric, and such metal material cost is the total cost of this type of capacitor. Is high.

Therefore, the firing temperature of the dielectric and the internal electrode is lowered to replace the expensive precious metal as the internal electrode with inexpensive Ag-Pd.
Attempts have been made to obtain inexpensive multilayer ceramic capacitors by increasing the content of alloys, especially Ag. However, it is generally known that when the firing temperature of the dielectric is lowered, the crystallinity is lowered and the relative permittivity thereof is lowered. When firing at a temperature lower than the above firing temperature, a ceramic capacitor having a high permittivity is sufficiently obtained. Electrical characteristics and temperature characteristics cannot be obtained.

[Description of Prior Art]

As a conventional technique, JP-A-57-170405 discloses Nd ₂ Ti.
O _7, BaTiO _3, to the main component of TiO _2, Bi ₂ O ₃ and Pb ₃ O of ₄ compositions by adding appropriate amounts of ZnO and SiO _2, sintering the firing temperature in the range of 1,050 to 1,100 ° C. It is described that a low melting point and inexpensive Ag-Pd alloy can be used as an internal electrode in manufacturing a multilayer capacitor that can obtain a body and need to burn the internal electrode at the same time as firing the porcelain. .

[Problems to be solved by the invention]

However, when the present inventors previously used a system containing Bi ₂ O ₃ in a dielectric and using an Ag-Pd alloy as an internal electrode, Ag-Pd and Bi ₂ O ₃ were produced by high temperature firing (1100 ° C. or higher). PdO solid solution that forms a solid solution with Bi is formed by reacting directly with, and the electrical resistance of the Ag-Pd internal electrode is rapidly increased and the dielectric properties of the dielectric, especially the Q value and insulation resistance, are rapidly reduced. I got the result. Therefore, it was concluded that when firing Bi ₂ O ₃ simultaneously in a contact state, it is necessary to fire at 1050 ° C or lower.

On the other hand, according to the above-mentioned conventional technique, the firing temperature is 1050-1100 ° C., and the reaction suppression between Ag-Pd and Bi ₂ O ₃ described above is not substantially solved, and in terms of characteristics. The temperature coefficient of capacitance is applied to a relatively wide range of +30 to -300ppm / ° C, and there are fatal drawbacks for practical use, such as low insulation resistance, low breakdown voltage, and large variations. Was there.

Therefore, the present applicant has filed Japanese Patent Application No. 58-231180 (Japanese Patent Laid-Open No.
124306), a specific ratio of BaTiO ₃ , Nd ₂ O ₃ and T
When _{iO 2, Bi 2 O 3,} Pb 3 O 4 and SiO _2, ZnO and B ₂ O ₃ is blended at a specific ratio as additives with respect to the main component of the composition system, 1000-1
Baking at a temperature of 050 ℃ is possible, which allows Ag-Pd
And the reaction between Bi ₂ O ₃ and Bi ₂ O ₃ are suppressed, stable temperature characteristics can be obtained in the temperature coefficient of capacitance range of ± 30 ppm / ° C, and the insulation resistance decreases and the breakdown voltage is low. We have proposed a dielectric porcelain composition that is extremely excellent in use as a temperature-compensating porcelain capacitor that uses Ag-Pd as an internal electrode, with less variation.

Thus, the present inventor has found a new problem in putting the dielectric ceramic composition having this excellent property into practical use. That is, when using such a dielectric ceramic composition for a capacitor, first, the raw material powder is processed into a thin sheet-shaped molded body, and in this molding step, B ₂ O ₃ in the composition is soluble in water. Therefore, it is necessary to use a dispersion medium other than water, that is, an organic solvent such as toluene as the dispersion medium of the slurry. This is because when B ₂ O ₃ dissolves in water, it becomes boric acid, which lowers the hydrogen ion concentration of the slurry and changes the viscosity of the slurry, so that it is not possible to obtain a sheet-shaped compact with a stable thickness. is there.

However, the use of an organic solvent such as toluene is explosive in itself and affects the human body.Therefore, it is necessary to take complete explosion-proof measures in the molding / drying process during practical mass production. It was a major cause of rising product costs.

[Object of the invention]

The present inventor has intensively studied the excellent characteristics dielectric ceramic composition which can solve the above problems while maintaining, by the use of 2CaO · 3B ₂ O ₃ instead of B ₂ O _3, the dispersion medium As a result, we have found that water can be used, and we propose this here.

[Means for solving the problem]

The present invention, BaTiO ₃ and 18.0 to 27.0 wt%, the Nd ₂ O ₃ 31.6
~ 36.3 wt%, TiO ₂ 27.6-35.5 wt%, Bi ₂ O ₃ 2.5-
8.1 wt% and Pb ₃ O ₄ with respect to the main component of the composition range containing 5.6 to 9.0 wt%, the 2CaO · 3B ₂ O ₃ 0.15~2.0 wt%, SiO ₂
1.0 to 3.0% by weight and 0.5 to 3.0% by weight of ZnO are added, whereby a dielectric porcelain composition having excellent properties that can be fired at 1000 to 1050 ° C. can be obtained.

One of the major features of the present invention is that 2CaO.3B ₂ O ₃ is selected as one component of the additive. That is, 2CaO ・ 3
Since B ₂ O ₃ is insoluble in water, water can be used as a dispersion medium for the slurry, and each raw material powder is uniformly dispersed together with the emulsion organic binder, the water-soluble dispersant, and the surfactant to stabilize the thickness. Homogeneous green sheets can be produced inexpensively and with good workability without requiring any special equipment.

On the other hand, at the time of firing, 2CaO.3B ₂ O ₃ can co-exist with ZnO in the same manner as when B ₂ O ₃ is present alone to sinter a dense porcelain at 1000 to 1050 ° C.

FIG. 1 shows ZnO and B ₂ O which are one component in the composition of the present invention.
Fig. ₃ shows the binary phase diagram with ₃ and the figure shows that in the coexistence with ZnO, when B ₂ O ₃ is about 30 mol%, the liquidus line is lowered to about 960 ° C, and ZnO and B ₂ O ₃ It has been shown that when used in an appropriate composition, it acts effectively as a sintering accelerator flux.

Therefore, ZnO and 2
When CaO ・ 3B ₂ O ₃ is added at the same time and baked, 2CaO ・ 3B ₂ O ₃ becomes 9
ZnO, which reacts at a low temperature of 00 ℃ or less, is more stable at low temperatures of B ₂ O ₃
Forms a compound with CaO, which is the main component of B at high temperatures.
It is considered to react with aTiO ₃ .

Therefore, even if 2CaO.3B ₂ O ₃ is used instead of B ₂ O ₃ , the liquid phase component in the sintering process acts in the same manner, and has the effect of sintering at 1000 to 1050 ° C. Although CaO has a property of reacting with BaTiO _3, it has no effect on the entire system because the amount of CaO is very small.

Moreover, the effect of adding 2CaO.3B ₂ O ₃ is not limited to lowering the sintering temperature, and when used as a capacitor as shown in Example 2, as in the case of adding B ₂ O ₃ alone. In addition, the Q value can be improved, the variation in the insulation resistance value can be reduced, and the breakdown voltage can be increased, which is a great effect.

The reason for setting each of the above-mentioned compositions to the above-mentioned composition range will be described. When BaTiO ₃ is less than 18.0% by weight, a sufficiently densified porcelain cannot be obtained unless the firing temperature is relatively high.
If it exceeds 27.0% by weight, similarly, if the firing temperature is not high, the densification is not sufficient and the insulation resistance (IR) becomes small in this case. If Nd ₂ O ₃ is less than 31.6% by weight, the densification will not be sufficient unless the firing temperature is high, the insulation resistance (IR) will be small, and the quality factor (Q) will tend to be small.
When it exceeds 36.3% by weight, the temperature coefficient of capacity (ppm / ℃) is (+)
Although there is a large shift to the side, this tendency is diminished when the BaTiO ₃ content is low, while the densification is not sufficient unless the firing temperature is raised. If TiO ₂ is less than 27.6% by weight, densification will not be sufficient unless the firing temperature is increased, and if it exceeds 35.5% by weight, the temperature coefficient of capacity (ppm / ° C) tends to increase to the (-) side. Bi
_{When 2} O ₃ is less than 2.5% by weight, the capacity temperature coefficient (ppm / ° C) shifts to the (-) side, and unless the firing temperature is raised, it will not be sufficiently densified, and the insulation resistance (IR) and quality factor will be high. (Q
Value becomes smaller, and when it exceeds 8.1% by weight, the temperature coefficient of capacity (ppm / ° C) shifts to the (-) side and the insulation resistance (IR) becomes smaller. When Pb ₃ O ₄ is less than 5.6% by weight, the temperature coefficient of capacity (ppm / ° C) shifts significantly to the (-) side and the densification is not sufficient unless the firing temperature is raised, and when it exceeds 9.0% by weight Temperature coefficient (ppm / ° C) shifts to the (+) side.

The addition without component serving 2CaO · 3B ₂ O ₃ is obtained above effect of the addition of less than 0.15 wt%, the firing temperature has to be higher not sufficiently densified, and increase the variation in insulation resistance (IR) and This causes an increase in breakdown voltage. On the other hand, if it exceeds 2.0 wt%, fusion with a setter such as alumina tends to occur during firing. Further, if the SiO ₂ content is less than 1.0% by weight or more than 3.0% by weight, the densification will not be sufficient unless the firing temperature is raised, and the insulation resistance (IR) and quality factor (Q value) will decrease. Finally ZnO
If less than 0.5% by weight, it will not be sufficiently densified unless the firing temperature is high, and the insulation resistance (IR) and quality factor (Q value) will be small, and if it exceeds 3.0% by weight, the quality factor (Q value) will be small. At the same time, the capacity temperature coefficient (ppm / ° C) increases toward the (+) side. As described above, BaTiO ₃ , Nd ₂ O ₃ , TiO ₂ , Bi ₂ O ₃ , Pb
_{When 3} O ₄ , ₂ CaO / 3 B ₂ O ₃ , SIO and ZnO are out of the range of the present invention, quality factor (Q value), insulation resistance (IR) and breakdown voltage are too low, or low temperature (1050 ° C or less) Sintering is not sufficient to meet the purpose of the present invention. 2CaO ・ 3B ₂ O ₃ is preferable
0.45-1.35 wt%, SiO ₂ 1.0-3.0 wt% and ZnO 1.0
It is advisable to add to the above main component in the range of up to 2.5% by weight.

 Hereinafter, embodiments of the present invention will be described.

(Example 1) BaTiO ₃ having a purity of 99.8% or more synthesized in advance from equimolar amounts of BaCO ₃ and TiO ₂ at 1200 ° C., Nd ₂ O ₃ having a purity of 98% or more, and titanium dioxide (anatase having a purity of 99.5% or more). ) And a purity of 95
% Bi ₂ O ₃ and Pb ₃ O ₄ having a purity of 95% or more were weighed so as to have the composition of each material described in the main component composition column of Table 1 so that the total weight was 500 g. Furthermore, 95% purity
The above 2CaO ・ 3B ₂ O ₃ , SiO ₂ and ZnO were weighed and added to the main components so that the composition of each sample described in the sub-components column of Table 1 was obtained, and the bulk was placed in a porcelain pot with an internal volume of 1.6. Volume 0.8 (1.
(5 kg) with alumina balls (17 mmφ), then add emulsion acrylic resin together with dispersant and surfactant, and ion-exchanged water as dispersion medium.
A raw material slip obtained by rotating at 72 ppm for 24 hours was molded into a green sheet having a thickness of 25 μm by the doctor blade method. Twenty-five of these green sheets were stacked and hot pressed to form a green molded plate, which was cut into green square plates of about 10 mm square and 0.50 mm thick. 1000-1100 green square plates
Silver electrodes were provided on the entire upper and lower surfaces of a square plate of about 8 mm square and a thickness of 0.4 mm obtained by firing at a temperature of ° C for 2 hours to obtain a single-layer rectangular plate type capacitor, which was an evaluation sample. After measuring the capacitance and quality factor (Q value) of each sample thus obtained at a frequency of 1 MHz and an input power level of 1 Vrms, and after measuring the insulation resistance (IR) by applying a DC voltage of 50 V for 1 minute. The temperature coefficient of capacitance at −55 ° C. and + 125 ° C. at a frequency of 1 MHz was measured. In addition, the vertical (L) and horizontal (W) dimensions of the sample are ± 5
The thickness (t) is measured with an accuracy of ± 1 μm with an accuracy of μm, The relative permittivity was calculated from

The measurement results or calculation results of the electrical characteristics thus obtained are shown in Table 1 together with the chemical composition and firing temperature of each sample.

Sample Nos. 1, 2, 3, 7, 9, 11, 12, 15, of Table 1
16, 17, 21, 22, 25, 26 and 29 are all those in which any of the compositions does not meet the composition range of the present invention,
A firing temperature of 1100 ° C or higher is required, which is not suitable for the purpose of the present invention. Further, the sample numbers 11, 12, 21, 25, 26 and 29 have a quality factor (Q value) of less than 1000, which is too small to meet the purpose of the present invention. In addition, sample numbers 7, 11, 15, 16, 17, 21, 22, 25
26 and 26 have too small an insulation resistance (IR) to meet the purpose of the present invention.

In addition, sample numbers 7, 9, 11, 12, 15, 16, 21, 25 and
In No. 29, the capacity temperature coefficient (ppm / ° C) deviates from the range of ± 30 ppm / ° C, which does not meet the object of the present invention. In this example, a single plate type capacitor having a silver electrode attached to a single plate firing porcelain is used as an evaluation sample. However, when these are actually fired as a laminated type, the firing temperature is further lowered by about 20 ° C. Therefore, it has been confirmed that the capacitance temperature coefficient (ppm / ° C) shifts to about 15 ppm / ° C (+) side particularly when the (-) side is large.

On the other hand, each of the samples other than the above is sufficiently sintered at a temperature of 1050 ° C or less, exhibits an insulation resistance (IR) of 10 ⁶ MΩ or more, and has a relative dielectric constant (εr) of 50 or more (substantially the minimum In the case of Sample No. 10, which is as high as εr = 67), the quality factor (Q value) is 1000 or more, which shows excellent electrical characteristics, and the capacitance temperature coefficient (ppm / ° C) is ± 30 ppm / ° C. It can be understood that it has a constant temperature characteristic within the range of.

(Example 2) Sample No. 14 within the scope of the present invention in Table 1,
A paste made by adding an organic binder and its melting material to an alloy of 70% by weight of Ag and 30% by weight of Pd on a dielectric green sheet of Sample No. 17 outside the scope of the present invention without adding 2CaO / 3B ₂ O _3. Each was printed. Each of the 58 green sheets provided with the metal print film was laminated, and the upper and lower 8 green sheets having no print film were added and hot pressed.

Further, each piece was cut into individual pieces each having a size of 5.2 mm by 4 mm, and each green chip of the laminated porcelain capacitor was prepared and fired at each temperature shown in Table 1 for 2 hours. Ag-Pd alloy electrodes were applied to both ends of both fired chips to produce a laminated ceramic capacitor.

Capacitance (nF) of multilayer ceramic capacitor thus obtained
And the quality factor (Q value) are measured at a frequency of 1MHz and an input voltage of 1Vrms, and a DC voltage of 50V is applied for 1 minute to insulate resistance (IR)
Was measured, and a DC voltage was applied, and the voltage (breakdown voltage) when the voltage was gradually raised to break down was measured. The respective measurement results are shown in Table 2. However, the number of measurement samples is 20 each
The capacitance (nF) and the quality factor (Q value) are average values, and the breakdown voltage is the average value x (V) and the variation index σ / x.
(%), Insulation resistance (IR) 10 ⁶ MΩ, 10 ⁵ and 1
The numbers on the order of 0 ⁴ MΩ are shown.

As shown in Table 2, sample number 1 that does not contain 2CaO / 3B ₂ O ₃
7 multilayer ceramic capacitors have an average breakdown voltage of 321x
(V) with a variation index of 22.4σ / x (%) and an insulation resistance (IR) of 1 in 20 ⁴ of 10 ⁴ MΩ.
Insulation resistance is insufficient because 7 out of 20 exist in 10 ⁵ MΩ order. On the other hand, sample number 1 containing 2CaO / 3B ₂ O ₃
4 multilayer ceramic capacitors have an average breakdown voltage of 760x
(V), which is more than twice that of the former, and the variation index is small at 9.6σ / x (%), and the insulation resistance (IR) is 20.
It is sufficient that 20 of them are 10 ⁶ MΩ or more.

〔The invention's effect〕

As described above in detail, the dielectric ceramic composition of the present invention is
Baking at low temperature range of 0 to 1050 ℃ is possible.
Even when used for a laminated porcelain capacitor with Ag-Pd as the internal electrode, the reaction between the internal electrode and Bi ₂ O ₃ is reduced,
It is possible to stabilize the dielectric properties. In addition, the temperature coefficient of capacity is ± 30ppm / in the temperature range of -55 ℃ to 125 ℃.
It has a characteristic that it can be set in the range of 0 ° C., the insulation resistance and the breakdown voltage are prevented from lowering and variations, and that it is sufficiently practical for a temperature-compensated multilayer capacitor. Furthermore, since an Ag-Pd alloy having a relatively low melting point and a high Ag content can be used as the internal electrodes, an inexpensive multilayer capacitor can be obtained.

The excellent effect described above is to maintain the effect of the prior application of the applicant using B ₂ O ₃ as an additive component, but the present invention replaces B ₂ O ₃ with 2CaO / 3B ₂ By using O ₃ , it becomes possible to use water as a binder during firing, which allows a filter press to be used in the dehydration / drying process, dramatically improving mass productivity and significantly reducing production costs. The remarkable advantage of being achieved is added.

[Brief description of the drawings]

FIG. 1 is a binary phase diagram of ZnO and B ₂ O ₃ .

Claims (1)

(57) [Claims] 1. BaTiO ₃ is contained in an amount of 18.0 to 27.0% by weight and Nd ₂ O ₃ is added in an amount of 31.6.
~ 36.3 wt%, TiO ₂ 27.6-35.5 wt%, Bi ₂ O ₃ 2.5-
8.1 wt% and Pb ₃ O ₄ with respect to the main component of the composition range containing 5.6 to 9.0 wt%, the 2CaO · 3B ₂ O ₃ 0.15~2.0 wt%, a SiO ₂ 1.0 to 3.0 wt%
And 0.5 to 3.0% by weight of ZnO, which is a dielectric ceramic composition.