JP3293320B2 - Manufacturing method of ceramic electronic components - Google Patents

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 an external electrode is electrically connected to the internal electrode. And improvements to ensure good metallic bonding between them.

[0002]

2. Description of the Related Art A ceramic electronic component which is of interest to the present invention is, for example, a multilayer ceramic capacitor. FIG. 5 is a cross-sectional view showing a conventional multilayer ceramic capacitor 1. The multilayer ceramic capacitor 1 includes a component body 2 made of a ceramic laminate. Parts body 2
Are formed with internal electrodes 3 and 4, respectively. 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. External electrodes 7 and 8 are formed on end surfaces 5 and 6 of component body 2 so as to be electrically connected to the respective edges of internal electrodes 3 and 4.

In manufacturing the above-described multilayer ceramic capacitor 1, a component body 2 on which internal electrodes 3 and 4 are formed is first prepared, and then an end face 5 of the component body 2 is formed.
And 6, a conductive paste to be external electrodes 7 and 8 is applied, and this conductive paste is
The internal electrodes 3 and 4 are fired at 900 ° C.
External electrodes 7 and 8 having a metallic junction between them are formed.

In order to reduce the cost of the multilayer ceramic capacitor 1, there is a type 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, for example. As described above, when at least one of the metal included in the internal electrodes 3 and 4 or the metal included 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 connection between the internal electrodes 3 and 4 and the external electrodes 7 and 8 may be hindered. Therefore, conventionally, in order to prevent such oxidation, when firing the conductive paste for the external electrodes 7 and 8, the oxygen concentration in the firing atmosphere is set to be low, for example, 20 ppm or less.

[0005]

However, as described above, when firing is performed under a low oxygen concentration, combustion of organic substances such as a binder contained in the conductive paste for the external electrodes 7 and 8 is incomplete. In addition, the wettability between the glass such as copper contained in the conductive paste and the glass is deteriorated, and the sintering of the metal in the conductive paste does not proceed, so that the external electrodes 7 and 8 become porous. Tend to be.

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

[0007]

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

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

The metal contained in the conductive paste serving as 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 a combination.

[0010]

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

On the other hand, even if a 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 interdiffuse, and Correspondingly, these metals sinter while displacing the boron oxide film, resulting in good metallic bonding between the internal and external electrodes.

Further, as described above, the boron oxide melted at about 300 ° C. covers the surface of the metal, thereby preventing oxidation of the metal. The oxygen concentration in the atmosphere can be relatively high. Thus, by increasing the oxygen concentration, the wettability between the glass and the metal contained in the conductive paste is improved, 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 selected to be 50 ppm or more, more preferably 100 ppm or more, and further preferably 200 ppm or more.

[0013]

Thus, according to the present invention, boric acid provided on the outer surface of the component body, at least on the portion where the internal electrode is exposed, is exerted in firing the conductive paste for the external electrode. The resulting heat transforms into boron oxide in a molten state, which dissolves and removes the metal oxide, and covers the metal surface thinly to prevent oxidation of the metal. Since it allows mutual diffusion with the metal contained in the electrodes, it is possible to apply sintering with a relatively high oxygen concentration while securing a good metallic junction between the internal electrode and the external electrode. Can be obtained. As a result, a ceramic electronic component having excellent moisture resistance and the like can be obtained.

When the present invention is applied to a method for manufacturing a multilayer ceramic capacitor, it is possible to prevent a decrease in capacitance and an increase in equivalent series resistance of the obtained multilayer 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 electrode is completed, the outer surface of the component body is covered with the boron oxide film. This boron oxide film advantageously prevents cracks in the ceramic component body due to residual stress or thermal stress during soldering or use.

[0016]

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

First, as shown in FIG. 1, a component body 12 made of a ceramic laminate is prepared. Internal electrodes 13 and 14 containing a base metal are provided inside the component body 12.
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 face 15 of the component body 12, and each edge of the internal electrode 14 is exposed on the other end face 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 at least at the portion 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 apply boric acid 17, for example, a solution in which boric acid is dissolved in water, alcohol or ketone is prepared, the component main body 12 is immersed in the solution, and then the component main body 12 is pulled up and dried. It is. The solution for dissolving the above-mentioned boric acid may be any of unsaturated, saturated, or supersaturated solutions. Instead of such an application method, the outer surface of the component main body 12 is wetted with, for example, water to make the powder easily adhered, and then the component main body 12 is brought into contact with boric acid powder. Boric acid 17 on top
May be added. Thus, the component body 1
The boric acid 17 provided on the outer surface of No. 2 is in a powder state, for example, in a layer having a thickness of about 5 μm. The thickness of the boric acid 17 is practically preferably 10 μm or less, more preferably 5 μm or less.

Next, as shown in FIG. 3, a conductive paste 18 serving as an external electrode is applied on 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 covering the outer surface of the component body 12 as well shown in the enlarged portion in FIG.

Next, the above-mentioned conductive paste 18 is baked, and as a result, as shown in FIG.
And 20 are formed. Further, the boric acid 17 is heated and dehydrated, and a glassy boron oxide film 21 is formed on the component body 12.
Formed on the outer surface of the Thus, the multilayer ceramic capacitor 11 is obtained.

Next, an experimental example performed based on the above-described embodiment will be described. In this experimental example, a multilayer ceramic capacitor using nickel for the internal electrodes and copper for the external electrodes is manufactured.

First, a solution prepared by dissolving 1 g of boric acid in 100 cc of acetone was added to a solution of 3.2 mm × 1.6 mm × 0.8 m.
500 parts of a component body having a size of m were put in the container, and the solution was stirred for 5 minutes. Next, 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 as an external electrode was applied to each component body. Thereafter, the conductive paste was fired at a maximum temperature of 750 ° C. to obtain a target multilayer ceramic capacitor. In this firing step, experiments were performed for the case where the oxygen concentration in the firing atmosphere was set to 20 ppm and the case where the oxygen concentration was set to 200 ppm. In addition, as a comparative example, the same experiment was performed for a case where boric acid was not added.

The capacitance of the multilayer ceramic capacitor as each sample thus obtained and the degree of sintering of the external electrodes were evaluated. The results are shown in Table 1 below. In Table 1, the capacitance is an average value of 20 samples, and the unit is nF. The sintering degree was evaluated by observing the cross section of the external electrode with an SEM. 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 200
ppm, regardless of the presence or absence of boric acid
Although a dense external electrode is obtained, when no boric acid is applied, the capacitance is significantly reduced. This is because the internal electrodes were oxidized. On the other hand, when boric acid was applied, a capacitance almost as designed was obtained.

On the other hand, when the oxygen concentration was set to 20 ppm, the capacitance was maintained at a high value, but the external electrode was in a porous state regardless of the presence or absence of boric acid. Each sample having such a porous external electrode was subjected to a temperature of 70 ° C. and a relative humidity of 90 to 95%.
In the humidity resistance load test in which the rated voltage was applied under the atmosphere described above, all of the samples showed poor results.

The following experiment was conducted in order to investigate on what principle boric acid exerts its effect as in the above-mentioned experimental example. First, a copper plate was prepared, 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 turned into boron oxide and melted. The molten boron oxide wetted the copper plate along the copper oxide present on the surface of the copper plate, and the copper oxide was dissolved in the molten boron oxide. Accordingly, metallic copper was present below the molten boron oxide film. A similar 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 surfaces of copper included in the external electrode and nickel included in the internal electrode. In this state, if nickel and copper partially come into contact with each other, mutual diffusion occurs, and copper is sintered if the boron oxide film is displaced. In such a firing step, the film of boron oxide prevents further oxidation of copper and nickel.
Even if the oxygen concentration is as high as 0 ppm, copper and nickel are not oxidized, and the high oxygen concentration improves the wettability between the glass and copper contained in the conductive paste, and allows the dense external An electrode will be obtained.

Next, in order to confirm the effect of the boron oxide film 21 shown in FIG. 4 for preventing cracks, each of the samples obtained in the above-described experimental example was immersed in molten solder from room temperature and heated to a temperature of 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 those having a boron oxide film, cracks occurred in three of the 100 samples. On the other hand, cracks occurred in 20 samples out of 100 samples in which no boron oxide film was formed.

Although the present invention has been described with reference to a multilayer ceramic capacitor, the present invention is not limited to a multilayer ceramic capacitor, but may be applied to other multilayer ceramic electronic components such as a multilayer inductor, a multilayer varistor, and a multilayer circuit board. On the other hand, the present invention can be applied to any ceramic electronic component having an internal electrode formed inside the component body, even to a ceramic electronic component having no laminated structure.

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 embodiment. And any combination of nickel, copper and copper, and copper and silver.

[Brief description of the drawings]

FIG. 1 is a component main body 1 provided with internal electrodes 13 and 14 which is prepared in a first step included in a method for manufacturing a multilayer ceramic capacitor according to one embodiment of the present invention.
FIG.

FIG. 2 shows a second step performed after the first step shown in FIG.
FIG. 5 is a partially enlarged cross-sectional view showing the component body 12 in which boric acid 17 is provided on the outer surface in the step of FIG.

FIG. 3 shows a third step performed after the second step shown in FIG. 2;
In the step, the component body 12 provided with boric acid 17
FIG. 4 is a partially enlarged cross-sectional view showing a state in which a conductive paste 18 is provided on the outer surface of FIG.

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

FIG. 5 is a cross-sectional view showing a conventional multilayer ceramic capacitor 11.

[Explanation of symbols]

 Reference Signs List 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)

(57) [Claims] 1. A component main body made of ceramic, an internal electrode formed inside the component main body, an edge of which is exposed on an outer surface of the component main body and contains a base metal; A method for manufacturing a ceramic electronic component, comprising: an external electrode formed on an outer surface of the component main body so as to be electrically connected to an edge, wherein the component main body having the internal electrode is prepared. Then, on the outer surface of the component main body, boric acid is applied to at least a portion where the internal electrode is exposed, and the external electrode is formed on the outer surface of the component main body to which the boric acid is applied. A method for producing a ceramic electronic component, comprising: applying a conductive paste; and firing the conductive paste. 2. A combination of a base metal included in the internal electrode and a metal included 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 manufacturing 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 more. 4. The method for producing 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.