JP2676620B2 - Multilayer ceramic capacitor and manufacturing method thereof - Google Patents

Description

The present invention relates to a laminated ceramic capacitor having an Ag or Ag-Pg conductor as an internal electrode and a method for manufacturing the same.

[Prior Art] With the miniaturization and high density of electronic components, a monolithic ceramic capacitor has come to the spotlight as a capacitor that is small and can obtain a large capacitance. Further, with the diversification of this monolithic ceramic capacitor, there has been an increasing demand for a reduction in manufacturing cost for the monolithic ceramic capacitor, and various techniques are being developed to meet this demand. For example, we have tried to develop a dielectric ceramic material that can be sintered at low temperature, thereby reducing the firing cost, and the paste material for printing that forms internal electrodes and external electrodes can be fired at a relatively low temperature, and the cost is low. A typical example is a measure such as being able to form a paste mainly composed of metal. As a result, it is attempted to reduce the manufacturing cost while maintaining the characteristics required for the ceramic capacitor, and as a result, the cost is reduced.

The monolithic ceramic capacitor is obtained by printing a conductive paste in a rectangular shape on an unfired ceramic sheet and then stacking the conductive paste so that the patterns of the conductive paste are alternately displaced.
Then, it is cut into chips so that the patterns of the conductive paste are alternately exposed on the opposite end faces. The laminated chip thus formed is introduced into a firing furnace and fired,
External electrodes are formed on opposite ends of the same chip by means of applying a conductive paste, baking, and further plating.
As a result, the monolithic ceramic capacitor is completed.

FIG. 1 shows the structure of the monolithic ceramic capacitor manufactured in this manner, 5 is a dielectric formed by sintering the ceramic sheet, 6 is electrodes facing each other with the dielectric sandwiched therebetween, and 3 Are these opposing electrodes 6,
6 are external electrodes formed so as to be electrically connected to the end surfaces of the laminated body, and the upper and lower surfaces and side surfaces that are continuous with the opposed end surfaces.

As the conductive paste for printing, which is a material for forming the internal electrodes 6, 6 of the monolithic ceramic capacitor, the one mainly using Pd as a conductor has been used so far, but it contains Ag. By using a conductive paste that uses a rare Ag-Pd alloy as a conductor, by using a dielectric ceramic material that can be fired at a relatively low temperature,
The cost was reduced.

[Problems to be Solved by the Invention] However, in reality, there are problems in the following points.

First, considering the cost of the conductive paste, since Pd has about 10 times the price in the market compared to Ag, if the ratio of Ag is small, no cost advantage can be obtained, and in reality Ag is 50 The cost advantage can be obtained only when the ratio is at least%. Even when considering the electric resistance of the conductor, if the amount of Ag is 50% by weight or more,
The larger the amount of Ag, the lower the electric resistance of the formed internal electrode. Specifically, unless the Ag content is 70% by weight or more, the electrical resistance of the internal electrodes becomes high, and the high frequency characteristics of the multilayer capacitor deteriorate, which is not practical.

On the other hand, Ag used as a conductor for a conductive paste or an Ag-Pd alloy in which the ratio of Ag exceeds 70% by weight has a low melting point or solidus temperature. The melting point of Ag is 960 ℃, A
The g-Pd alloy has a solidus temperature of 1070 ° C., for example, when the proportion of Ag in the alloy is 80% by weight.

When firing a chip of a multilayer capacitor, when the conductive paste for forming the internal electrodes is fired at a temperature lower than the melting point or solidus temperature of the conductor material, the conductor material diffuses inside the dielectric ceramic and The insulation of the body ceramic is lowered, and the reliability of the capacitor is lowered. Therefore, in order to solve this problem, conventionally, a temperature lower than the melting point or solidus temperature of the conductor material by about 100 ° C., specifically, an Ag-Pd alloy paste having an Ag ratio in the alloy of 80% by weight is used. Even in such a case, the laminate was fired at a temperature of around 970 ° C.

However, in order to fire the laminate at a low temperature, it is necessary to use a dielectric ceramic material that can be fired at a low temperature,
Therefore, it is necessary to take measures such as pulverizing the ceramic raw material powder or adding a large amount of a sintering aid to the raw material. However, the dielectric ceramic material using the fine powder raw material is expensive and has the drawback of increasing the cost of the multilayer capacitor. Also, if a large amount of sintering aid is added, the relative dielectric constant of the dielectric ceramic and the quality of the capacitor will increase. There is a drawback in that the coefficient (Q) is lowered.

Furthermore, even if the laminated body is fired at a low temperature of around 970 ° C as described above, it is still impossible to completely prevent the diffusion of the conductor into the dielectric ceramic and prevent the deterioration of the capacitor characteristics. There was a problem that I could not do it.

Therefore, an object of the present invention is to provide a monolithic ceramic capacitor and a method for manufacturing the same that can solve the above problems.

[Means for Solving the Problems] That is, the gist of the means according to the present invention for achieving the above-mentioned object is, firstly, that the internal electrodes formed of a conductor containing Ag or an Ag alloy are opposed to each other via a dielectric ceramic layer. In the monolithic ceramic capacitor, the dielectric ceramic and the internal electrode are fired at a temperature lower than the melting point of Ag or the solidus concentration of Ag alloy in a low oxygen concentration atmosphere of 50,000 ppm or less. It is a monolithic ceramic capacitor.

Secondly, by applying a conductive paste containing Ag or an Ag alloy on an unfired dielectric ceramic sheet and stacking these ceramic sheets and firing them, the internal electrodes formed by the conductors pass through the dielectric ceramic. In the method of manufacturing the laminated ceramic capacitors facing each other, firing the laminated body of ceramic sheets at a temperature lower than the melting point of Ag or the solidus temperature of Ag alloy in a low oxygen concentration atmosphere of 50,000 ppm or less. It is a method for producing a characteristic multilayer ceramic capacitor.

Thirdly, the ceramic paste and the conductive paste containing Ag or Ag alloy are alternately applied, and by firing the obtained laminated body, the internal electrodes formed by the conductors are laminated facing each other through the derivative ceramic. A method for producing a ceramic capacitor, wherein a laminated body of ceramic sheets is fired at a temperature lower than the melting point of Ag or the solidus temperature of Ag alloy in an atmosphere of low oxygen concentration of 50,000 ppm or less. It is a method of manufacturing a capacitor.

[Function] Conductive paste containing Ag or Ag alloy is used in an atmosphere in which the concentration of acid law is sufficiently lower than in the atmosphere, more specifically, the oxygen concentration.
When fired in an atmosphere of 50,000 ppm or less, the activity of Ag is lowered and the diffusion of Ag into the ceramic during firing is extremely suppressed. Therefore, even if a ceramic laminate having the conductive paste layer inside is fired at a temperature close to the melting point of Ag or the solidus temperature of Ag alloy,
Is hard to spread. Therefore, the insulation resistance of the ceramic does not decrease. Therefore, it becomes possible to fire the dielectric ceramic and the conductive paste at a higher temperature than the conventional one while using the conductive paste having a higher Ag content than the conventional one.

[Examples] Next, specific examples of the present invention will be described in detail.

Example 1 An organic material prepared by dissolving polyvinyl butyral in a mixed solvent of ceramic raw material powder consisting of 97% by weight of TiO _{2, 2} % by weight of CuO and 1% by weight of ZrO ₂ , and toluene and ethanol in a ratio of 1: 1. Binder, dibutyl phthalate (plasticizer),
Oleic acid (dispersant) was mixed with a ball mill to prepare a ceramic raw material slurry.

After degassing the slurry with a vacuum degassing machine, a long green sheet having a thickness of 40 μm was formed by the doctor blade method. This green sheet was cut into a predetermined size, for example, 150 mm × 120 mm. On the green sheet, a commercially available Ag-Pd paste having a weight ratio of Ag: Pd of 8: 2 (solidus temperature about 1070 ° C) was screen-printed. Multiple such sheets are stacked so that the patterns of the conductive paste are staggered alternately, and while keeping the temperature at 100 ° C, 400 kg / cm ²
It was thermocompression bonded under the pressure of. The thus-prepared unfired ceramic substrate was cut into chips so that one ends of the internal electrodes formed of the conductor paste were alternately exposed on both end faces of the laminate.

First, in the air, the temperature was raised from room temperature to 500 ° C at a temperature gradient of 1.5 ° C / min, then the temperature of 500 ° C was maintained for 2 hours, and then cooled to room temperature at a temperature gradient of -3 ° C / min. , Debinder processing was performed.

Next, nitrogen gas was introduced into the furnace, the gas in the furnace was replaced with this, and the temperature was raised from room temperature to 1050 ° C at a temperature gradient of 5 ° C / min, and then the temperature of 1050 ° C was maintained for 1 hour. After that, −
It was cooled to room temperature with a temperature gradient of 5 ° C / min. The oxygen concentration in the furnace at this time was measured by a zirconia oxygen analyzer.
It was 10 ppm.

To the end face of the laminated chip after firing, the upper and lower faces connected to this and the end portion of the side face, a conductive paste containing Ag as a main component is applied, and this is baked at a temperature of 600 ° C. in the atmosphere, and the external The electrode was formed. Furthermore, on this external electrode
Ni-plated and solder-plated.

As a result of measuring 20 insulation resistances of the monolithic ceramic capacitors manufactured by the above method at DC100V, the average value is 3.
It was 5 × 10 ¹² Ω. The above results are shown in column E1 of the table below.

(Examples 2 to 6) In Example 1 described above, the nitrogen gas and air in the furnace atmosphere during firing were 2500: 1, 500: 1, 100: 1, 20: 1, and 3.2: 1.
A monolithic ceramic capacitor was manufactured under the same conditions as in Example 1 except that the mixed gas mixed in the ratio was changed. At this time, the oxygen concentration in the furnace is E2 to E6 in the table below.
It was as shown in the column.

The average insulation resistance measured for each of the 20 multilayer ceramic capacitors manufactured in this way is E2-E6.
It was the value shown in the column.

(Example 7) In Example 1, the composition of the ceramic pigment powder was 95 wt% TiO ₂ , 4 wt% CuO and 1 wt% ZrO, and the conductive paste used was Ag pest. Example 1 except that the firing temperature was changed from 1050 ° C to 940 ° C
Multilayer ceramic capacitors were manufactured under the same conditions as above. The oxygen concentration in the furnace at this time was as shown in column E7 in the table below.

The average of the measured values of the insulation resistance measured for each of 20 manufactured multilayer ceramic capacitors was the value shown in the column of E7.

(Comparative Examples 1 and 2) In the above-mentioned Example 1, when the ratio of nitrogen gas to air in the furnace atmosphere during firing was 1: 1 and when the furnace atmosphere was entirely air, Multilayer ceramic capacitors were manufactured under the same conditions as in Example 1.

The average insulation resistance measured for each of the 20 multilayer ceramic capacitors manufactured in this way is P1, P2.
It was the value shown in the column.

Comparative Example 3 A laminated ceramic capacitor was manufactured under the same conditions as in Example 7 except that the atmosphere in the furnace during firing was replaced by nitrogen gas instead of nitrogen gas.

The average of the measured values of the insulation resistance measured for each of the 20 manufactured multilayer ceramic capacitors was the value shown in the column of P3.

FIG. 2 is a graph showing the relationship between the average value and the maximum value and the minimum value of the insulation resistance of the multilayer ceramic capacitor based on the results of the above Examples and Comparative Examples and the oxygen concentration in the firing atmosphere of the multilayer chip. .

[Effects of the Invention] As described above, according to the present invention, it is possible to fire a laminated ceramic capacitor using Ag or Ag alloy as a conductor at a higher temperature than before without lowering its insulating property. . This achieves the effect that a highly reliable multilayer ceramic capacitor can be provided at low cost while maintaining the characteristics required as a ceramic capacitor.

[Brief description of the drawings]

FIG. 1 is a partially sectional conceptual perspective view showing an example of a monolithic ceramic capacitor, and FIG. 2 is a relationship between the average value and the maximum and the minimum value of the insulation resistance of the monolithic ceramic capacitor with the oxygen concentration in the firing atmosphere of the monolithic chip. Is a graph represented by. 3 ... External electrode, 5 ... Dielectric, 6 ... Internal electrode

Claims (3)

(57) [Claims] 1. A monolithic ceramic capacitor in which internal electrodes formed of a conductor containing Ag or an Ag alloy are opposed to each other through a dielectric ceramic layer, wherein the dielectric ceramic and the internal electrodes have a low oxygen content of 50,000 ppm or less. A monolithic ceramic capacitor characterized by being fired at a temperature lower than the melting point of Ag or the solidus temperature of Ag alloy in a concentrated atmosphere. 2. Ag on a non-fired dielectric ceramic sheet
Alternatively, in a method for producing a laminated ceramic capacitor in which a conductive paste containing an Ag alloy is applied, and these ceramic sheets are laminated and fired, the internal electrodes formed by the conductors face each other through a dielectric ceramic, A method for producing a monolithic ceramic capacitor, comprising: firing a laminated body of ceramic sheets in a low oxygen concentration atmosphere of 50,000 ppm or less at a temperature lower than a melting point of Ag or a solidus temperature of Ag alloy. 3. A ceramic paste and a conductive paste containing Ag or an Ag alloy are applied alternately, and the resulting laminate is fired so that the internal electrodes formed by the conductors face each other with the dielectric ceramic interposed therebetween. In a method of manufacturing a monolithic ceramic capacitor, a ceramic sheet laminate and a low oxygen concentration atmosphere of 50,000 ppm or less,
A method for manufacturing a monolithic ceramic capacitor, which comprises firing at a temperature lower than the melting point of Ag or the solidus temperature of Ag alloy.