JPH07302727A - Manufacture of ceramic electronic component - Google Patents

Abstract

PURPOSE:To form a dense outer electrode while ensuring excellent metallic junction between inner electrodes and an outer electrode, by applying boric acid to the part on the outer surface of a component main body on which part the inner electrodes are exposed. CONSTITUTION:A component main body 12 constituted of ceramic laminate is prepared. Inner electrodes 13 and 14 containing base metal are formed in the component main body 12. End edges of the inner electrodes 13 and 14 are exposed on the outer surface of the component main body 12. Boric acids applied to the part of the outer surface of the component main body on which part at least the inner electrodes 13 and 14 are exposed. Conductive paste 18 turning to an outer electrode is applied to the end surfaces 15 and 16 of the component main body 12. The conductive paste 18 is applied so as to cover the boric acid 17 covering the outer surface of the component main body 12. The conductive paste 18 is baked, and the outer electrode is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ceramic electronic component having a structure in which an internal electrode contains a base metal and the external electrode is electrically connected to the internal electrode. It relates to an improvement to ensure a good metallic bond between the two.

[0002]

2. Description of the Related Art A ceramic electronic component of interest to the present invention is, for example, a monolithic ceramic capacitor. FIG. 5 is a sectional view showing a conventional monolithic ceramic capacitor 1. The monolithic ceramic capacitor 1 includes a component body 2 made of a ceramic laminate. Parts body 2
Internal electrodes 3 and 4 are respectively formed inside the. The respective edges of the internal electrodes 3 and 4 are exposed on the outer surface of the component body 2, more specifically on the end faces 5 and 6. Then, external electrodes 7 and 8 are formed on the end surfaces 5 and 6 of the component body 2 so as to be electrically connected to the respective edges of the internal electrodes 3 and 4.

When manufacturing the monolithic ceramic capacitor 1 as described above, the component body 2 having the internal electrodes 3 and 4 is first prepared, and then the end surface 5 of the component body 2 is prepared.
A conductive paste to be the external electrodes 7 and 8 is provided on the electrodes 6 and 6, and the conductive paste is
By being fired at 900 ° C., the internal electrodes 3 and 4
External electrodes 7 and 8 are formed with a metallic connection between the external electrodes 7 and 8.

In order to reduce the cost of the monolithic ceramic capacitor 1, there is a monolithic ceramic capacitor 1 in which a base metal such as nickel is used for the internal electrodes 3 and 4 and copper is used for the external electrodes 7 and 8. Thus, when at least one of the metal contained in the internal electrodes 3 and 4 or the metal contained in the external electrodes 7 and 8 is easily oxidized, in the step of firing the conductive paste for the external electrodes 7 and 8, Such oxidation may occur, and as a result, the metallic contact between the inner electrodes 3 and 4 and the outer electrodes 7 and 8 may be hindered. Therefore, conventionally, in order to prevent such oxidation, when the conductive paste for the external electrodes 7 and 8 is fired, the oxygen concentration in the firing atmosphere has been set low, for example, 20 ppm or less.

[0005]

However, as described above, when firing is performed under a low oxygen concentration, the combustion of organic substances such as the binder contained in the conductive paste for the external electrodes 7 and 8 is incomplete. Or, the wettability between the metal such as copper contained in the conductive paste and the glass becomes poor, and the sintering of the metal in the conductive paste does not proceed, so that the external electrodes 7 and 8 become porous. There is a tendency to end up.

Therefore, it is an object of the present invention to form a fine external electrode in a ceramic electronic component provided with an internal electrode using a base metal while ensuring good metallic bonding between the internal electrode and the external electrode. Is to try to provide a way to.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a component body made of ceramic, and an internal electrode which is formed inside the component body and whose edges are exposed on the outer surface of the component body and which contains a base metal. And an external electrode formed on an outer surface of a component body so as to be electrically connected to an edge of the internal electrode, the method is directed to a method for manufacturing a ceramic electronic component, which In order to solve the problem, it is characterized by including the following steps.

That is, first, a component body having internal electrodes is prepared. Next, it should be noted that boric acid is applied on the outer surface of the component body, at least in the portion where the internal electrodes are exposed. Then, on the outer surface of the component body to which the boric acid has been applied, a conductive paste to be an external electrode is applied and fired.

The metal contained in the conductive paste to be the external electrode may be any metal as long as it can achieve metallic bonding with the base metal contained in the internal electrode by alloying or the like. As a combination of the base metal contained in the internal electrode and the metal contained in the external electrode, for example, the former is nickel and the latter is copper, the former and the latter are both nickel, the former and the latter are both copper, the former is copper and the latter is silver. ,
There is such a combination.

[0010]

The boric acid (H ₃ BO used in the present invention
_3), when heated to about 300 ° C., to produce boron oxide (B ₂ O ₃₎ by dehydration reaction, the molten state. The molten boron oxide has a property of wetting along with the metal oxide and dissolves the metal oxide. Therefore, the metal surface from which the oxide is removed is thinly covered with the molten boron oxide. This boron oxide prevents further oxidation of the metal.

On the other hand, even if the thin film of boron oxide is interposed as described above, when the base metal contained in the internal electrode and a part of the metal particles contained in the external electrode come into contact with each other, they diffuse into each other, and Correspondingly, these metals sinter, displacing the boron oxide film, and a good metallic bond between the inner and outer electrodes is achieved.

Further, as described above, the boron oxide melted at about 300 ° C. covers the surface of the metal, thereby preventing the metal from being oxidized, so that the conductive paste for the external electrode is baked in the step of baking. The oxygen concentration in the atmosphere can be made relatively high. In this way, by increasing the oxygen concentration, the wettability between the glass and the metal contained in the conductive paste becomes good, and the sintering of the metal proceeds smoothly,
A dense external electrode can be obtained. The oxygen concentration in the above-mentioned firing atmosphere is preferably 50 ppm or more, more preferably 100 ppm or more, and further preferably 200 ppm or more.

[0013]

Therefore, according to the present invention, the boric acid applied to at least the portion where the internal electrodes are exposed on the outer surface of the component body affects the firing of the conductive paste for the external electrodes. Due to the heat generated, it becomes molten boron oxide, which dissolves and removes the metal oxide, and at the same time covers the metal surface thinly to prevent oxidation of the metal, while at the same time eliminating the base metal contained in the internal electrode and the external Since it allows mutual diffusion with the metal contained in the electrodes, firing with a relatively high oxygen concentration can be applied while ensuring a good metallic bond between the internal electrode and the external electrode. Can be obtained. As a result, it is possible to obtain a ceramic electronic component having excellent moisture resistance and the like.

When the present invention is applied to a method for manufacturing a monolithic ceramic capacitor, it is possible to prevent a decrease in electrostatic capacity and an increase in equivalent series resistance of the obtained monolithic ceramic capacitor.

In the present invention, boric acid is preferably applied to the entire outer surface of the component body. According to this, when the firing of the conductive paste for the external electrodes is completed, the outer surface of the component body is covered with the film of boron oxide. This film of boron oxide advantageously prevents cracks from being formed in the component body made of ceramic due to residual stress or thermal stress during soldering or during use.

[0016]

1 to 4 are sectional views showing typical steps included in a method of manufacturing a ceramic electronic component according to an embodiment of the present invention. This embodiment is particularly directed to a method of manufacturing a monolithic ceramic capacitor 11 as shown in FIG.

First, as shown in FIG. 1, a component body 12 made of a ceramic laminate is prepared. Inside the component body 12, internal electrodes 13 and 14 containing a base metal are provided.
Are formed. The respective edges of the internal electrodes 13 and 14 are exposed on the outer surface of the component body 12. More specifically, each edge of the internal electrode 13 is exposed on one end surface 15 of the component body 12, and each edge of the internal electrode 14 is exposed on the other end surface 16 of the component body 12.

Next, as shown in the enlarged portion of FIG. 2, boric acid 17 is applied to the outer surface of the component body 12 and at least the portions where the internal electrodes 13 and 14 are exposed. In this embodiment, boric acid 17 is applied to the entire outer surface of the component body 12. In order to provide boric acid 17, for example, a solution of boric acid in water, alcohol or ketone is prepared, the component body 12 is dipped therein, and then the component body 12 is pulled up and dried. Be done. The above boric acid-dissolving solution may be unsaturated, saturated, or supersaturated. Instead of such an application method, the outer surface of the component body 12 is wetted with, for example, water so that the powder easily adheres, and then the component body 12 is brought into contact with boric acid powder to obtain the outer surface of the component body 12. Boric acid 17 on top
May be given. In this way, the component body 1
The boric acid 17 applied to the outer surface of No. 2 is in a powder state and forms a layer having a thickness of about 5 μm, for example. The thickness of boric acid 17 is practically 10 μm or less, and more preferably 5 μm or less.

Next, as shown in FIG. 3, a conductive paste 18 serving as an external electrode is applied onto the end surfaces 15 and 16 of the component body 12. The conductive paste 18 is applied so as to further cover the boric acid 17 that covers the outer surface of the component body 12, as is often shown in the enlarged portion of FIG.

Next, the above-mentioned conductive paste 18 is fired, and as a result, as shown in FIG.
And 20 are formed. In addition, the boric acid 17 is heated and dehydrated, and the glassy boron oxide film 21 is removed from the component body 12
On the outer surface of the. In this way, the monolithic ceramic capacitor 11 is obtained.

Next, an example of an experiment carried out based on the above-mentioned embodiment will be described. In this experimental example, a multilayer ceramic capacitor in which nickel is used for the internal electrodes and copper is used for the external electrodes is manufactured.

First, a solution prepared by dissolving 1 g of boric acid in 100 cc of acetone was 3.2 mm × 1.6 mm × 0.8 m.
500 parts main bodies each having a size of m were put and the solution was stirred for 5 minutes. Then, the component body was taken out of the solution and dried at room temperature (25 ° C.) for 10 minutes. At this stage, when the outer surface of the component body was magnified 1000 times with a microscope and observed, white powder of boric acid was confirmed.

Next, a conductive paste containing copper to be external electrodes was applied to each component body. Then, this conductive paste was fired at a maximum temperature of 750 ° C. to obtain a target monolithic ceramic capacitor. In this firing step, an experiment was performed for each of the cases where the oxygen concentration in the firing atmosphere was 20 ppm and 200 ppm. Also, as a comparative example, the same experiment was performed in the case where boric acid was not added.

The capacitance and the degree of sintering of the external electrodes of the thus-obtained multilayer ceramic capacitor as each sample were evaluated. The results are shown in Table 1 below. In Table 1, the capacitance is an average value of 20 samples and its unit is nF. The degree of sintering was evaluated by observing the cross section of the external electrode with an SEM, and when a hole exceeding 10 μm was formed, it was determined to be “porous”.

[0025]

[Table 1]

As shown in Table 1 above, the oxygen concentration was adjusted to 200
When ppm is given, regardless of whether boric acid is added or not,
Although a dense external electrode can be obtained, when boric acid is not added, the capacitance is significantly reduced. This is because the internal electrodes were oxidized. On the other hand, when boric acid is applied, the capacitance almost as designed is obtained.

On the other hand, when the oxygen concentration was set to 20 ppm, the electrostatic capacitance remained high, but the external electrodes were in a porous state regardless of whether boric acid was applied or not. Each sample provided with such a porous external electrode has a temperature of 70 ° C. and a relative humidity of 90 to 95%.
In the humidity resistance load test in which the rated voltage is applied under the atmosphere, the results of all of them were bad.

The following experiment was conducted in order to investigate what principle boric acid exerts its effect as in the above-described experimental example. First, a copper plate was prepared, a boric acid powder was placed thereon, and the copper plate was heated. According to this heating, when the copper plate reached about 300 ° C., boric acid became boron oxide and melted. The molten boron oxide wets the copper plate along the copper oxide existing on the surface of the copper plate, and the copper oxide is dissolved in the molten boron oxide. Therefore, metallic copper was present below the molten boron oxide film. The same phenomenon was confirmed for the nickel plate. Therefore, in the above-described experimental example, when the conductive paste is fired, the molten boron oxide obtained from boric acid thinly covers both the surfaces of copper contained in the external electrode and nickel contained in the internal electrode. In this state, when nickel and copper partially contact with each other, mutual diffusion occurs, and copper is sintered even if the film of boron oxide is pushed away. In such a firing step, the boron oxide film prevents further oxidation of copper and nickel.
Even if the oxygen concentration is as high as 0 ppm, copper and nickel do not oxidize, and such a high oxygen concentration improves the wettability between the glass contained in the conductive paste and the copper, resulting in a dense external surface. The electrodes will be obtained.

Next, in order to confirm the crack prevention effect of the boron oxide film 21 shown in FIG. 4, each sample obtained by the above-mentioned experimental example is immersed in molten solder from room temperature, and the temperature is about 325 ° C. A thermal shock due to the difference was applied. Then, the cross section of the component body was polished and the number of cracked samples was determined. As for the sample having the boron oxide film, cracks occurred in 3 of 100 samples. On the other hand, with respect to the samples in which the boron oxide film was not formed, cracks occurred in 20 of 100 samples.

Although the present invention has been described with reference to a monolithic ceramic capacitor, the present invention is not limited to a monolithic ceramic capacitor, but may be applied to other monolithic ceramic electronic components such as a monolithic inductor, a monolithic varistor and a multi-layer circuit board. The present invention can also be applied to any ceramic electronic component that has internal electrodes formed inside the component body, even if it is a ceramic electronic component that does not have a laminated structure.

Further, in such a ceramic electronic component, the combination of the base metal contained in the internal electrode and the metal contained in the external electrode is not limited to the combination of nickel and copper as in the above-described embodiments, but nickel is not limited. And nickel, copper and copper, and each combination of copper and silver.

[Brief description of drawings]

FIG. 1 is a component body 1 having internal electrodes 13 and 14 prepared in a first step included in a method for manufacturing a monolithic ceramic capacitor according to an embodiment of the present invention.
It is sectional drawing which shows 2.

FIG. 2 is a second process performed after the first process shown in FIG.
It is a partially expanded sectional view which shows the component main body 12 in which the boric acid 17 was provided on the outer surface in the process of.

FIG. 3 is a third process performed after the second process shown in FIG.
In the process of, the component body 12 to which boric acid 17 is added
FIG. 6 is a partially enlarged cross-sectional view showing a state in which a conductive paste 18 is applied on the outer surface of the.

4 is a cross-sectional view showing a monolithic ceramic capacitor 11 in which external electrodes 19 and 20 are formed by firing the conductive paste 18 applied in the third step shown in FIG.

FIG. 5 is a sectional view showing a conventional monolithic ceramic capacitor 11.

[Explanation of symbols]

 11 Multilayer Ceramic Capacitor 12 Component Body 13,14 Internal Electrode 15,16 End Face 17 Boric Acid 18 Conductive Paste 19,20 External Electrode 21 Boron Oxide Film

Claims (4)

[Claims] 1. A component body made of ceramic, an internal electrode formed inside the component body, the edge of which is exposed on the outer surface of the component body and containing a base metal; A method of manufacturing a ceramic electronic component, comprising: an external electrode formed on an outer surface of the component body so as to be electrically connected to an edge thereof, wherein the component body having the internal electrode is prepared. Then, on the outer surface of the component body, at least a portion where the internal electrode is exposed is provided with boric acid, and the boric acid is provided on the outer surface of the component body to be the external electrode. A method of manufacturing a ceramic electronic component, comprising: each step of applying a conductive paste and firing the conductive paste. 2. The combination of the base metal contained in the internal electrode and the metal contained in the external electrode is selected from nickel and copper, nickel and nickel, copper and copper, and copper and silver, respectively. A method for manufacturing a ceramic electronic component according to claim 1. 3. The method for producing a ceramic electronic component according to claim 1, wherein, in the step of firing the conductive paste, the oxygen concentration in the firing atmosphere is selected to be 50 ppm or higher. 4. The method for manufacturing a ceramic electronic component according to claim 1, wherein, in the step of applying boric acid, the boric acid is applied to the entire outer surface of the component body.