CN1135085A - Ceramic capacitor - Google Patents

Abstract

A ceramic capacitor having large capacitance and low dielectric loss is disclosed. A ceramic capacitor includes a dielectric ceramic body and electrodes formed on the ceramic body from a conductive paste by firing. The conductive paste contains copper powder, glass frit, organic vehicle, and any one of borate solution, boric acid solution and boron organic salt solution.

Description

ceramic capacitor

This invention relates to ceramic capacitors, and more particularly to ceramic capacitors having copper electrodes produced by a firing process.

A ceramic capacitor having a dielectric ceramic body and a pair of electrodes located within the dielectric ceramic body. Usually, a silver paste made of fine silver powder as a conductive component and a low-melting glass frit is screen-printed on a dielectric ceramic body, and then the coated silver paste is fired to form an electrode. Baked silver electrodes are easy to manufacture and have excellent electrical characteristics such as high-frequency characteristics and high reliability.

The disadvantage of ordinary silver-fired electrodes is that due to the high price of silver. Thus, there is a limit to reducing the manufacturing cost. Another disadvantage is the susceptibility to solder corrosion, i.e. the tendency for silver to diffuse into the feedstock when the lead wire is soldered to the silver-fired electrode. As a result, the adhesion of the electrode is poor, the characteristics are deteriorated, and the capacitance of the capacitor is reduced.

In addition, common silver-fired electrodes are prone to silver migration. This results in reduced dielectric strength and reliability. Especially when the dielectric ceramic body is subjected to thermal shock during welding, silver diffuses into tiny cracks, which further accelerates silver migration.

In order to overcome the disadvantages caused by the use of silver-fired electrodes, copper-fired electrodes can be used in ceramic capacitors.

For example, burnt copper electrodes are disclosed in Japanese Patent Laid-Open Heisei 1-51003. Burnt copper electrodes consist of copper powder and glass frit. The glass frit contains at least one of lead borosilicate, bismuth borosilicate and zinc borosilicate as a main component, and the glass frit is 2-40vol% of the volume of the copper powder. Copper powder and glass frit are dispersed in an organic solvent to prepare a slurry, and the prepared slurry is added to a dielectric ceramic body by a screen printing method, and then fired in a neutral gas (such as nitrogen), Made of burnt copper electrodes.

In this method, firing is usually performed at a temperature higher than 800°C to form a dense fired electrode. This is because if the electrodes are not fully baked, the solder will penetrate into the electrodes, which will adversely affect the capacitance and the strength of the terminals. Moreover, as the base metal, copper should be fired in a neutral atmosphere to prevent its oxidation.

Therefore, when a copper-fired electrode is used in a ceramic capacitor, it is necessary to heat-treat the dielectric ceramic body constituting the ceramic capacitor at 800°C. However, firing at a high temperature in a neutral atmosphere causes reduction of the dielectric ceramic body, thereby making the capacitance of the resulting capacitor small.

In order to overcome the oxidation and solderability problems of copper electrodes, Japanese Patent Publication Heisei 1-36243 discloses an electronic component, a conductive film composition and a manufacturing method thereof. According to the disclosed invention, the conductive film composition contains copper powder with a weight of 5 to 40 wt% fine boron powder. The lower limit (5wt%) of the boron powder content is determined to ensure that the copper powder (base metal) is not oxidized.

Furthermore, Japanese Patent Laid-Open No. Heisei 1-220303 also discloses a non-oxidizing thick-film copper conductor. The conductor is made by firing copper paste containing boron-manganese compound at 900°C. The disadvantage of this paste is that if fired at low temperature, thick film conductors with good electrical conductivity will not be obtained. Another disadvantage is that the resulting copper electrodes require an inorganic phosphate coating.

Japanese Patent Publication Heisei 3-176903 discloses a copper powder-based conductive paste. The boron and B ₂ O ₃ contained in the slurry are respectively 3.5-3.9wt% and 2.0-30.0wt% of the total weight (100wt%) of copper powder plus boron powder. Determine the lower limit to produce antioxidant effects.

According to the prior art, it is not possible to have satisfactory electrical and mechanical properties of ceramic capacitors with fired copper electrodes.

An object of the present invention is to provide a high-performance ceramic capacitor having a large capacity and low dielectric loss. The capacitor basically avoids solder corrosion and silver migration, and has excellent high frequency characteristics, reliability. solderability and longevity.

Another object of the present invention is to provide a highly reliable ceramic capacitor having only a small drop in capacitance and dielectric loss after a load test under humid conditions.

The ceramic capacitor of the present invention includes a dielectric ceramic body and electrodes formed thereon. The electrode is made by firing the conductive paste composition comprising copper powder, glass frit, organic vehicle and a solution selected from boric acid ester solution, boric acid solution and organic salt solution of boric acid.

The manufacturing method of the ceramic capacitor of the present invention comprises the following steps: adding a conductive paste to the dielectric ceramic body, forming an electrode pattern on the dielectric ceramic body; firing the electrode pattern with the conductive paste at a temperature not higher than 600°C dielectric ceramic body.

Fig. 1 is a cross-sectional view of a ceramic capacitor of the present invention;

Fig. 2 is a graph of TG (thermogravimetric analysis) and DTA (differential thermal analysis) of tributyl borate.

It is believed that the boron compound contained in the copper paste becomes B ₂ O ₃ , which prevents the copper from being oxidized by the slightly oxidizing atmosphere at the time of firing. Also, boron compounds may not be required if the paste is used to form capacitor electrodes. When used in a large amount, it is of course possible to prevent oxidation but the resistance value of the electrode increases, thus resulting in a decrease in capacitance and an increase in dielectric loss.

From the problems involved in the related art, it is known that boron is used in a small amount sufficient to prevent oxidation of the electrode so that its electrical properties such as electrostatic capacity and dielectric loss are not deteriorated. In other words, the amount of boron compound contained in the copper paste does not depend on its weight, but rather on its (ie boron) to copper weight ratio. For better dispersal of small amounts of boron, liquid borides _are preferred over solid forms of _boron or borides such as _B2O3 and _MnB2 .

Thus, the first aspect of the present invention is a ceramic capacitor, comprising a dielectric ceramic body and an electrode made of firing a conductive paste thereon, said conductive paste consisting of copper powder, glass frit, an organic vehicle and a borate ester solution, Boric acid solution, any one of boron organic salt solution or a combination thereof.

A second aspect of the present invention resides in the ceramic capacitor as defined in the first aspect, wherein the borate solution is a high-boiling or low-boiling borate solution in an alcohol having a high boiling point. The high boiling point mentioned in the specification is 220°C or higher, and the low boiling point is 220°C or lower.

A third aspect of the present invention resides in the ceramic capacitor as defined in the first or second aspect, wherein the high boiling point borate is represented by the molecular formula ( _{CnH2n +1O} ) _3B , where n≥4.

The fourth aspect of the present invention is the ceramic capacitor as defined in the first aspect or the second aspect, wherein the borate with low boiling point is a lower alkyl (C _1-5 ) ester compound, such as methyl borate, trimethyl borate , triethyl borate or tripropyl borate.

A fifth aspect of the present invention resides in the ceramic capacitor as defined in the first aspect, wherein the organic salt of boron is triethylboron, dimethylamineborane, or sodium borohydride.

The sixth aspect of the present invention lies in the ceramic capacitor as defined in the first aspect, wherein the content of boron in borate solution, boric acid solution or organic salt solution of boron is 0.01 to 0.5wt% of the total weight of boron and copper, and the content of copper powder is It is 99.5 to 99.99 wt% of the total weight of boron and copper. In other words, 0.01 to 0.5 parts boron per 100 parts copper (pph).

A seventh aspect of the present invention is the ceramic capacitor as defined in the first aspect, wherein the contents of the solid component and the organic vehicle are respectively 70 to 90 wt % and 10 to 30 wt %, and the content of copper powder in the solid component is 80 to 98 wt %, The glass frit content is about 2-20 wt%.

An eighth aspect of the present invention resides in the ceramic capacitor as defined in the first aspect, wherein the glass frit has a softening point of 350 to 500°C.

A ninth aspect of the present invention resides in the ceramic capacitor as defined in the first aspect, wherein the dielectric ceramic body is a barium titanate-based ceramic body.

According to the present invention, the electroconductive paste should contain the above specified amount of glass frit. That is, the glass frit content is more than 2 wt%, so that the conductive paste can adhere well to the dielectric ceramic body after firing. Moreover, the glass frit content should be less than 20 wt%, so that the conductive paste has sufficient conductivity and dielectric loss, and should be able to provide sufficient capacitance. The copper powder is preferably copper powder whose particle size is in the range of 0.1 μm to 10 μm measured by SEM (scanning electron microscope). The presence of blister copper powder is undesirable because it cannot be fully sintered.

According to the present invention, the content of boron in the borate solution is 0.01wt% to 0.5wt%, and the content of copper powder is 99.5wt% to 99.99wt%. In order to prevent oxidation, the amount of boron must be greater than 0.01 wt%, while in order to make it solderable and conductive, its content should be less than 0.5 wt%.

According to the present invention, the conductive paste is composed of 90-70 wt% of solid components (copper powder plus glass frit) and 10-30% of inert organic vehicle. The organic vehicle is, for example, ethylcellulose dissolved in terpineol. It is also possible to dissolve methylcellulose, butylcellulose or acrylic resin in terpineol to make an organic vehicle.

Glass frits for the conductive paste include, for example, boron-lead-zinc glass. Its softening point should be higher than 350°C, so that the viscosity of the conductive paste is low, so that it can diffuse into and adhere to the ceramic body well during firing. The upper limit of the softening point of the glass frit is 500°C. Therefore, firing can be completed at low temperature, and the fired product has no negative effect on adhesion, lead-out strength and dielectric loss.

According to the present invention, the electroconductive paste may contain a borate ester solution. When heated at 200°C, the borate _precipitates and vitrifies boron into _B2O3 . The _B2O3 coats the copper powder to prevent the copper powder from being _oxidized in a slight oxygen atmosphere during firing. Copper powder coated with _B2O3 is easily wetted by glass frit which softens at 350°C to 450°C _. Therefore, low-temperature firing at 600°C can produce copper electrodes that are dense enough to prevent solder penetration.

The ceramic capacitor of the present invention has a copper electrode made of a conductive paste containing any one of a borate solution, a boric acid solution, and a boron organic salt solution as an antioxidant for copper. The boron compound forms a B ₂ O ₃ film on the copper powder to produce an anti-oxidation effect. The amount of boron compound used in the present invention is less than that in the prior art. The electrical and physical properties of the burnt copper electrodes are equivalent to those of the burnt silver electrodes, and the ceramic capacitor of the present invention has good high-frequency characteristics.

In addition, the conductive paste of the present invention can be fired at a low temperature of about 600° C. to produce copper conductors. This means that the frit and ceramic body are not reduced upon firing. In other words, the ceramic body will not reduce the capacitance due to reduction, so the ceramic capacitor made has large capacitance and low dielectric loss.

example

The invention is described in detail in conjunction with the following examples.

FIG. 1 is a cross-sectional view of a ceramic capacitor 10 of the present invention. The ceramic capacitor 10 includes a flat-plate-shaped dielectric ceramic body 1 and a pair of copper electrodes 2 inside the dielectric ceramic body 1 . Lead terminals 3 are electrically connected to a pair of copper electrodes 2 through solder 4, respectively. The dielectric ceramic body 1 and the electrodes 2 are coated with an outer layer resin 5 .

A method of manufacturing a ceramic capacitor will be described below. First, an electroconductive paste for firing to form a copper electrode was prepared by the following method.

80wt% copper powder with a particle diameter of 1 μm, 8wt% glass frit and 12wt% organic vehicle are mixed together, and the glass frit is at least one of boron oxide, lead oxide, and zinc oxide as the main component of _Pb OB ₂ O ₃ -Z _n O based glass (as disclosed in Japanese Patent Application No. 6-120253). The organic vehicle was 8% ethyl cellulose in terpineol. The resulting mixture is mixed with any one of a solution of a high boiling point borate ester, a solution of a low boiling point borate ester in a high boiling point alcohol, and a solution of boron in an organic solvent. The amount of the boron-containing material is 0.01-0.5 wt% of boron based on the atomic weight of boron, and the corresponding amount of copper powder is 99.5-99.99 wt%. All components were then thoroughly mixed using a three-roll mixer.

The paste obtained contained 90.9 wt% of copper powder and 9.1 wt% of glass frit. The total amount of copper powder and glass frit is 88wt%, and the amount of organic vehicle is 12wt%.

The slurry is applied to the dielectric ceramic body 1 by screen printing, and a pair of electrode patterns are formed on the two main surfaces of the dielectric ceramic body 1. The dielectric ceramic body 1 is made of barium titanate and has a thickness of 0.5 mm. , with a diameter of 14.0mm. The dielectric ceramic body 1 may also be a ceramic body disclosed in Japanese Patent Laid-Open No. 60-31793. It consists of B _a T _i O ₃ (85-90wt%) CaZrO ₃ (8.5-12.0wt%), MgTiO ₃ (less than 0.5wt%), CeO ₂ (less than 0.5wt%), Bi ₂ O ₃ (0.1- 1.0wt%) and SnO ₂ (0.1-1.0wt%).

Thereafter, the dielectric ceramic body was fired for 60 minutes, during which the firing temperature was raised to 600° C. and kept at this temperature for 10 minutes. Calcined in a nitrogen atmosphere. After firing, the fired copper electrode 2 is formed on the dielectric ceramic body. The two lead-out ends 3 are respectively welded to the copper-burning electrodes 2 with rosin flux. Finally, the dielectric ceramic body is immersed in the tank filled with the outer layer resin, so that the burnt copper electrode 2 and the dielectric ceramic body 1 are covered with a layer of outer layer resin 5, and the ceramic capacitor 10 is produced.

The capacitance, dielectric loss, terminal strength, solderability, and solder penetration of the obtained ceramic capacitors were measured. The results are listed in Table 1.

When the lead wire (wire diameter: 0.6mm) welded to the electrode is pulled at a speed of 120mm/min, the lead-out end is calculated by testing the force required to peel off the electrode (thickness: 0.5mm, diameter: 14.0mm) from around the ceramic body strength.

Solderability was evaluated visually after the fired ceramic body was immersed in a solder bath with rosin flux. "Good" weldability means that the welded area is greater than 90%, "medium" means that the welded area is 50-90%, and "poor" means that the welded area is less than 50%.

Those samples in Table 1 that are not consistent with the present invention are marked with *.

Table 1

sample number Borate wt% Glass frit (wt%) Capacitance(nF) Dielectric loss 1%) Terminal Strength Weldability   12*345678*9*10*11121314*15*16171819* Tributyl borate Tributyl borate Tributyl borate Tributyl borate Tributyl borate Tributyl borate Tributyl borate Tributyl borate Methyl borate Methyl borate Methyl borate Methyl borate Ester boric acid boric acid boric acid boric acid boric acid 0.0050.0100.0100.0500.2000.4000.5000.5000.5500.0050.0100.2000.5000.5500.0050.0100.2000.5000.550 6.01.56.06.06.06.010.022.06.06.06.06.010.06.06.06.06.010.06.0 6.510.214.215.516.015.013.59.28.86.214.116.013.19.36.014.215.712 88.7 6.81.61.61.00.61.22.07.58.06.81.50.82.28.27.01.50.72.47.9 0.10.32.32.53.82.51.31.30.10.02.42.61.20.20.02.22.91.00.1 Poor Poor Moderately Good Moderately Poor Poor Moderately Good Moderately Poor Poor Moderately Good Moderately Poor

Table 1 shows that those samples consistent with the present invention had good solderability and terminal strength, and low dielectric loss.

Note that sample 2 has large capacity and low dielectric loss, but poor terminal strength and weldability. It was also found that Samples 1, 8, 9, 10, 14, 15 and 19 had large dielectric loss and low terminal strength, and poor solderability.

The results of thermogravimetric analysis and differential thermal analysis showed that boron in tributyl borate was vitrified at about 200 °C. as shown in picture 2. This produces the effect that the copper powder is isolated from the atmosphere, thus protecting the copper from oxidation by oxygen introduced into the nitrogen atmosphere to decompose the binder.

As mentioned above, the present invention has the following advantages:

First, the ceramic capacitor of the present invention has electrodes made of an electrically conductive paste including an antioxidant for preventing copper oxidation, such as any one of boric acid ester, boric acid, and/or organic salt of boron. Although these boron compounds are used in a small amount, they form a thin vitrified film of B ₂ O ₃ on the copper electrode to protect the copper from oxidation. As a result, there is low dielectric loss and large capacitance.

Second, the conductive paste can be fired (or sintered) at a low temperature of 600°C and the ceramics and glass frit will not be reduced in the firing atmosphere. Thus, the resulting ceramic capacitor has high capacitance and low dielectric loss.

Third, the ceramic capacitor of the present invention can be produced by short-time low-temperature firing (or sintering) in a kiln made of cheap refractory materials. Thereby reducing costs. The electrical and physical properties (or high-frequency characteristics) of ceramic capacitors with copper electrodes are equivalent to those of ceramic capacitors with silver electrodes.

Fourth, the ceramic capacitor of the present invention can substantially avoid silver migration and solder corrosion, thereby maintaining high reliability and long life even when microscopic cracks occur in the dielectric ceramic body due to soldering heat shock.

Fifth, the ceramic capacitor of the present invention has sintered electrodes that are not easily peeled off.

Those skilled in the art will find that there are other specific forms of embodiments without departing from the spirit and main characteristics of the present invention. The disclosed embodiments are only for illustration and not for limitation of the invention. In addition to the content described in the description, the scope of the invention specified by the appended claims and all changes belong to the scope of protection of the present invention.

Claims (17)

1. A ceramic capacitor comprising: a dielectric ceramic body; and An electrode on a dielectric ceramic body, the electrode is composed of a fired conductive paste, the conductive paste contains copper powder, glass frit, organic vehicle, and a solution containing boric acid ester, boric acid, organic salt of boron or a combination thereof. 2. The ceramic capacitor according to claim 1, wherein the borate-containing solution is a borate solution with a high boiling point. 3. The ceramic capacitor according to claim 2, characterized in that the high-boiling point borate is represented by the formula ( _{CnH2n +1O} ) _3B , where n≥4. 4. The ceramic capacitor according to claim 1, wherein the borate-containing solution is a solution of a low-boiling borate in a high-boiling alcohol. 5. The ceramic capacitor according to claim 4, characterized in that the low-boiling borate is selected from the group consisting of methyl borate, trimethyl borate, triethyl borate and tripropyl borate. 6. The ceramic capacitor according to claim 1, wherein the solution of the boron-containing organic salt is selected from the group consisting of triethylboron, dimethylamineborane and sodium borohydride. 7. The ceramic capacitor according to claim 1, wherein the solution is used in an amount of 0.01 to 0.5% based on the mixed weight of boron and copper powder and based on the atomic weight of boron. 8. The ceramic capacitor according to claim 1, wherein the slurry contains about 70-90wt% copper powder and glass frit, wherein the copper powder is 80 to 98wt%, and the glass frit is 2-20wt%; the organic vehicle is 10- 30 wt%. 9. The ceramic capacitor according to claim 1, wherein the glass frit has a softening point of 350 to 500. 10. The ceramic capacitor of claim 1, wherein the dielectric ceramic body comprises barium titanate. 11. A method of manufacturing a ceramic capacitor, comprising the following process steps: Adding a conductive paste on the surface of the dielectric ceramic body to form an electrode pattern on the dielectric ceramic body, the conductive paste includes a solution of copper powder, glass frit, organic carrier and borate, boric acid, boron organic salt or a mixture thereof; and The dielectric ceramic body with the electrode pattern of the conductive paste is fired at a temperature not higher than 600°C. 12. The method of manufacturing a ceramic capacitor according to claim 11, wherein boric acid glass-coated copper powder derived from boron in solution at a temperature of about 200 DEG C. during the firing step. 13. The method of manufacturing a ceramic capacitor according to claim 11, wherein the solution is a solution of a high boiling point borate ester, or a solution of a low boiling point borate ester in a high boiling point alcohol. 14. by the method for the manufacture ceramic capacitor of claim 11, it is characterized in that, the amount of boric acid ester, boric acid or boron organic salt solution is by the mixed atomic weight of boron and copper powder and by boron atomic weight in the slurry and is 0.01 to 0.5 wt%. 15. The method of manufacturing a ceramic capacitor according to claim 11, wherein the glass frit has a softening point of 350 to 500°C. 16. by the method for the manufacture ceramic capacitor of claim 15, it is characterized in that, borate solution in the slurry, boric acid, or the weight of boron organic salt solution is by the mixed atomic weight of boron and copper powder and by boron atomic weight 0.01 to 0.5 wt%. 17. A method of manufacturing a ceramic capacitor according to claim 16, wherein the copper powder is coated with boric acid glass derived from boron in solution during firing at a temperature of about 200°C.