JP4428001B2 - Manufacturing method of ceramic capacitor - Google Patents

Description

The present invention relates to a method for manufacturing a ceramic capacitor , and more particularly, to a method for manufacturing a ceramic capacitor including an external electrode formed by applying and baking a conductive paste containing glass frit.

Examples of the electronic component include an electronic component including an external electrode formed by applying and baking a conductive paste, such as a chip-type multilayer ceramic capacitor shown in FIG.
As shown in FIG. 1, this multilayer ceramic capacitor is disposed inside a ceramic element 1 such that a plurality of internal electrodes 3a and 3b face each other with a ceramic layer 2 therebetween, and one end side thereof is alternately arranged. A structure in which a pair of external electrodes 4a and 4b are arranged on both end sides of the ceramic element 1 so as to be electrically connected to the internal electrodes 3a and 3b while being drawn out to the end faces 5a and 5b on different sides of the ceramic element 1. Have.

  Such a multilayer ceramic capacitor is generally formed by laminating ceramic green sheets on which internal electrode patterns are printed, laminating ceramic green sheets for outer layers on which the internal electrode patterns are not printed on both upper and lower surfaces, and then crimping them. Then, the obtained mother laminate is cut at a predetermined position and divided into individual ceramic bodies (ceramic elements), then the ceramic bodies are fired, and both ends of the obtained sintered body (ceramic elements) It is manufactured by applying a conductive paste made by kneading metal powder together with glass frit, organic vehicle or the like into a paste and baking it to form an external electrode.

  By the way, in the step of baking the conductive paste applied to the ceramic element, for example, as shown in FIG. 5, the temperature is raised from room temperature to about 900 ° C. (maximum firing temperature) in about 25 minutes and then at 900 ° C. for 10 minutes. A firing method is known in which the temperature is lowered for about 8 minutes (about 0.625 ° C./sec) until the temperature at which the electronic component is taken out after being held (see, for example, Patent Document 1).

However, in the firing method (firing conditions) as described above, the glass frit in the conductive paste may segregate on the surface of the external electrode when the conductive paste is baked, and the glass frit segregates on the surface of the external electrode. Then, the following problems may occur.
(1) Since the glass frit segregated on the surface of the external electrode repels the solder used in the mounting process (that is, the solder wettability is bad), it causes a connection failure such as poor connection.
(2) When plating is performed on the surface of the external electrode formed using the conductive paste, if a glass frit as an insulator is segregated on the surface, a uniform plating film may be formed on the surface of the external electrode. It becomes difficult and causes poor connection.
JP-A-5-243083

The present invention solves the above problems, prevents the glass frit from segregating on the surface of the external electrode, makes it possible to form an external electrode with excellent solder wettability, and provides a surface on the surface of the external electrode. When plating and forming a metal plating film on the surface, it is possible to form a uniform plating film on the surface of the external electrode so that a highly reliable ceramic capacitor can be manufactured efficiently. Is an issue.

In order to solve the above problems, a method for manufacturing a ceramic capacitor of the present invention (Claim 1)
A method for producing a ceramic capacitor having an external electrode formed by applying and baking a conductive paste containing glass frit,
In the heat treatment process for baking the conductive paste for forming the external electrode applied to the ceramic capacitor element,
The conductive paste is baked at a predetermined baking temperature exceeding the softening point of the glass frit in the conductive paste, and then cooled to at least the softening point of the glass frit at a cooling rate of 2 ° C./sec or more. It is said.

In addition, the method of manufacturing the ceramic capacitor of the present invention (Claim 2) is as follows.
A method for producing a ceramic capacitor having an external electrode formed by applying and baking a conductive paste containing glass frit,
In the heat treatment process for baking the conductive paste for forming the external electrode applied to the ceramic capacitor element,
After baking the conductive paste at a predetermined baking temperature exceeding the softening point of the glass frit in the conductive paste, at least 2 ° C / sec and exceeding 150 ° C / sec to the softening point of the glass frit It is characterized by cooling at a low cooling rate.

The method for manufacturing a ceramic capacitor of the present invention (Claim 1) exceeds the softening point of the glass frit in the conductive paste in the heat treatment step for baking the conductive paste for forming an external electrode applied to the ceramic capacitor element. After baking the conductive paste at a predetermined baking temperature, cooling is performed at a cooling rate of 2 ° C./sec or more until at least the softening point of the glass frit, so that segregation of the glass frit is suppressed, It is possible to form an external electrode with excellent solder wettability, and when the surface of the external electrode is plated to form a metal plating film on the surface, the surface of the external electrode it is possible to form a uniform plated film, so that high ceramic capacitor reliability can be produced efficiently That.

That is, after the conductive paste is baked at a predetermined baking temperature exceeding the softening point of the glass frit in the conductive paste, cooling is performed at a cooling rate of 2 ° C./sec or more until at least the softening point of the glass frit. Thus, the sintered body of the conductive paste in a state where the glass frit is in a molten state and well dispersed before the glass frit is extruded from the sintered body obtained by sintering the conductive paste and segregates on the surface of the external electrode. When it is possible to cure the whole, it is possible to form an external electrode with excellent solder wettability, and when plating the surface of the external electrode and forming a metal plating film on the surface Because the glass frit, which is an insulator, is not segregated on the surface of the external electrode, it is possible to form a uniform plating film on the surface of the external electrode. It is possible to efficiently produce a high ceramic capacitor.

  In the present invention, the rate of temperature rise until reaching a predetermined baking temperature exceeding the softening point of the glass frit, the holding time at the predetermined baking temperature, etc. do not significantly affect the segregation of the glass frit, It has been confirmed that the cooling rate from the baking temperature to the softening point of the glass frit is a factor that greatly affects the segregation of the glass frit.

The method for manufacturing a ceramic capacitor according to the present invention (Claim 2) is characterized in that at least a softening point of the glass frit is obtained after the conductive paste is baked at a predetermined baking temperature exceeding the softening point of the glass frit in the conductive paste. Since the cooling is performed at a cooling rate of 2 ° C./sec or more and not exceeding 150 ° C./sec, the conductive paste is sintered without damaging the ceramic capacitor due to thermal shock. It becomes possible to cure the entire sintered body of the conductive paste while the glass frit is well dispersed before the glass frit is extruded from the bonded body and segregated on the surface of the external electrode. It is possible to reliably suppress and prevent the segregation of the glass frit.

  Hereinafter, examples of the present invention will be shown and features thereof will be described in more detail.

In the first embodiment, as shown in FIG. 1, a plurality of internal electrodes 3a and 3b are disposed inside a ceramic capacitor element (ceramic electronic component element) 1 so as to face each other with a ceramic layer 2 interposed therebetween. In addition, a pair of external electrodes 4a, 4b are alternately drawn out to end faces 5a, 5b on different sides of the ceramic element 1 and are electrically connected to the internal electrodes 3a, 3b at both ends of the ceramic element 1. In the case of manufacturing a multilayer ceramic capacitor having a structure in which an external electrode is formed, an example in which an external electrode is formed by applying and baking a conductive paste containing glass frit will be described.

[Production of ceramic capacitor element (chip element)]
(1) First, a ceramic powder is prepared by mixing a dielectric powder containing BaTiO ₃ as a main component, an organic binder, a dispersant and a solvent, and forming the ceramic slurry to form a plurality of ceramic green sheets. .
(2) Then, an internal electrode pattern is formed by printing an internal electrode forming conductive paste prepared by kneading Pd powder and an organic vehicle on the surface of the ceramic green sheet.
(3) Then, a predetermined number of ceramic green sheets on which internal electrode patterns are formed are laminated, and ceramic green sheets on which no internal electrode patterns are formed are laminated on the upper and lower sides of the ceramic green sheets. Form.
(4) Next, this mother laminated body is cut and divided into individual elements, and then fired under predetermined conditions to obtain a ceramic capacitor element (chip element). The size of the chip element after firing is 3.2 mm in length, 2.5 mm in width, and 2.5 mm in height.

[Formation of external electrodes on ceramic capacitor elements (chip elements)]
Then, a conductive paste for forming an external electrode was applied to both ends of the fired ceramic capacitor element and baked to form an external electrode.
The composition, firing conditions, and cooling conditions of the conductive paste used for forming the external electrodes are as follows.

<Composition of conductive paste for external electrode formation>
(a) Conductive component Ag / Pd powder (Ag: Pd = 90/10 (weight ratio): 80% by weight)
(b) Glass frit Borosilicate zinc glass: 3.0% by weight
Softening point: about 600 ° C
(c) Organic vehicle (resin + solvent)
Resin: 9.5 + Solvent: 7.5 = 17.0 wt%

<Baking conditions>
Maximum firing temperature: 930 ° C
Keeping time at maximum firing temperature: 10 min
Firing atmosphere: Air

<Cooling conditions>
In Example 1, baking is performed with a temperature profile as shown in FIG. 2, and after holding at a maximum baking temperature (baking temperature) of 930 ° C. for 10 minutes, the highest baking temperature (baking temperature) of 930 ° C. is changed to a conductive paste. As shown in Table 1, the cooling rate of the “cooling section” up to the softening point (about 600 ° C.) of the glass frit included is 200 ° C./sec, 150 ° C./sec, 100 ° C./sec, 10 ° C./sec, It was changed to 2.0 ° C./sec, 0.67 ° C./sec, 0.5 ° C./sec, and 0.33 ° C./sec.

In the above firing step, so there is no need to use a sock powder such as alumina powder, using alumina Napishtim subjected zirconia coating and fired putting ceramic capacitor element in an alumina Napishtim, maximum firing temperature (baking In the “cooling section” from the temperature) to the softening point of the glass frit (about 600 ° C.), the cooling rate as shown in Table 1 was realized by controlling the replacement amount of the atmospheric gas (atmosphere).

Then, the ceramic capacitor element on which the external electrode was formed by baking the conductive paste was placed in a barrel together with the polishing medium, and polishing (barrel finishing) was performed by rotating the barrel.

[Characteristic evaluation]
And about the sample (multilayer ceramic capacitor) produced in this way, while performing the measurement test of "solderability", "the number of crack generation" was investigated.
In addition, the measurement test of “solderability” was performed on a sample of 20 lots using a flux consisting of 25% rosin and alcohol (residue) under the conditions of a soldering temperature of 230 ° C. ± 5 ° C. and an immersion time of 2 seconds. The sample was immersed in the solder, and the case where the solder coverage by appearance observation was 90% or more was evaluated as acceptable.
Further, the “number of cracks” is a value obtained by observing the presence or absence of cracks with a microscope after cross-section polishing for 20 samples per lot.
The results are shown in Table 1.

  As shown in Table 1, when the cooling rate of the “cooling section” is 2 ° C. to 150 ° C./sec, solderability is good, and cracks due to thermal shock are not observed, and desirable results are obtained. It was confirmed that it was obtained. On the other hand, when the cooling rate in the “cooling section” exceeded 150 ° C./sec, cracks due to thermal shock occurred, and at 200 ° C./sec, cracks were observed in two of the 20 samples.

Further, it was found that when the cooling rate was less than 2 ° C./sec, precipitation of the glass frit on the surface of the external electrode became remarkable, resulting in poor solderability.
From the above results, it was confirmed that the cooling rate in the “cooling section” is desirably 2 ° C./sec or more in order to ensure solderability.
Furthermore, it was confirmed that the cooling rate in the “cooling section” is preferably 2 ° C. to 150 ° C./sec in order to reduce the occurrence of cracks while ensuring solderability.

[Production of ceramic capacitor element (chip element)]
An external electrode is formed by applying and baking a conductive paste for forming an external electrode on both ends of a fired ceramic capacitor element (chip element) manufactured under the same conditions as in Example 1 above. did.
The composition, firing conditions, and cooling conditions of the conductive paste used for forming the external electrodes are as follows.

<Composition of conductive paste for external electrode formation>
(a) Conductive component Ag powder: 70% by weight
(b) Glass frit Zinc borosilicate glass: 7.0% by weight
Softening point: about 700 ° C
(c) Organic vehicle (resin + solvent)
Resin: 7.5 + Solvent: 5.5 = 13.0 wt%

<Baking conditions>
Maximum firing temperature: 840 ° C
Keeping time at maximum firing temperature: 10 min
Firing atmosphere: Air

<Cooling conditions>
In Example 2, baking is performed with a temperature profile as shown in FIG. 4, and the maximum baking temperature (baking temperature) is held at 840 ° C. for 10 minutes. As shown in Table 2, the cooling rate of the “cooling section” up to the softening point (about 700 ° C.) of the glass frit is 200 ° C./sec, 150 ° C./sec, 100 ° C./sec, 10 ° C./sec, 2. It was changed to 0 ° C./sec, 0.67 ° C./sec, 0.5 ° C./sec, and 0.33 ° C./sec.
The cooling rate was adjusted by controlling the replacement amount of the atmospheric gas (atmosphere) as in the case of Example 1.

Thereafter, Ni plating and Sn plating are performed on the ceramic capacitor element in which the external electrode is formed by baking the conductive paste, and as shown in FIG. 3, the Ni plating film 6 is formed on the external electrodes 4a and 4b. Further, an Sn plating film 7 was formed on the Ni plating film 6. In FIG. 3, the parts denoted by the same reference numerals as those in FIG. 1 indicate the same or corresponding parts.

[Characteristic evaluation]
For the sample plated as described above, a “solder heat resistance” measurement test is performed, the “number of cracks generated” is examined, and the “Ni plating film formed on the external electrodes 4a and 4b” is further examined. "Thickness" was examined.
“Solder heat resistance” measurement test is performed on 20 samples per lot, using a flux consisting of 25% rosin and alcohol (residue) under the conditions of a soldering temperature of 270 ° C. ± 5 ° C. and an immersion time of 5 seconds. Was immersed in the solder, and the case where the solder coverage in appearance was 100% was evaluated as a pass.
The “number of cracks generated” was determined by observing the presence or absence of cracks with a microscope after cross-section polishing for 20 samples per lot.
Further, the “thickness of the plating film” was performed by examining the thickness of the Ni plating film with a microscope after the cross section of the external electrode was polished.
The results are shown in Table 2.

As shown in Table 2, when the cooling rate of the “cooling section” is 2 ° C. to 150 ° C./sec, the solder heat resistance is good, and cracks due to thermal shock are not observed, and a desirable result is obtained. It was confirmed that it was obtained. On the other hand, when the cooling rate in the “cooling section” exceeded 150 ° C./sec, cracks due to thermal shock occurred, and at 200 ° C./sec, occurrence of cracks was observed in 4 of 20 samples.
Further, it was found that when the cooling rate was less than 2 ° C./sec, precipitation of the glass frit on the surface of the external electrode became remarkable, resulting in poor solder heat resistance.
From the above results, it was confirmed that the cooling rate of the “cooling section” is preferably 2 ° C./sec or more in order to ensure solder heat resistance, and further cracks occurred while ensuring solder heat resistance. In order to reduce this, it was confirmed that the cooling rate in the “cooling section” is desirably 2 ° C. to 150 ° C./sec.

  In addition, the present invention is not limited to the above-described Examples 1 and 2 in other points, and relates to the type of glass frit contained in the conductive paste, the shape of the external electrode, etc. Various applications and modifications can be added.

According to the method for manufacturing a ceramic capacitor of the present invention (Claim 1), it is possible to suppress and prevent segregation of the glass frit, and to form an external electrode excellent in solder wettability. When plating the surface of the metal and forming a metal plating film on the surface, it becomes possible to form a uniform plating film on the surface of the external electrode, and a highly reliable ceramic capacitor is efficiently manufactured. Will be able to.
In addition, when the conductive paste is baked and then cooled to the softening point of the glass frit at a cooling rate of 2 ° C./sec or more and not exceeding 150 ° C./sec, A highly reliable ceramic capacitor can be efficiently manufactured without damaging the ceramic capacitor .

It is sectional drawing which shows the structure of the multilayer ceramic capacitor concerning one Example (Example 1) of this invention. It is a figure explaining the baking and cooling process at the time of manufacturing the multilayer ceramic capacitor concerning one Example (Example 1) of this invention. It is sectional drawing which shows the structure of the multilayer ceramic capacitor concerning the other Example (Example 2) of this invention. It is a figure explaining the baking and cooling process at the time of manufacturing the multilayer ceramic capacitor concerning other examples (Example 2) of this invention. It is a figure which shows the baking conditions of the electrically conductive paste in the conventional copper terminal electrode formation method of a ceramic electronic component.

1 Ceramic capacitor element (ceramic electronic component element)
2 Ceramic layer 3a, 3b Internal electrode 4a, 4b External electrode 5a, 5b End face of ceramic element 6 Ni plating film 7 Sn plating film

Claims (2)

A method for producing a ceramic capacitor having an external electrode formed by applying and baking a conductive paste containing glass frit,
In the heat treatment process for baking the conductive paste for forming the external electrode applied to the ceramic capacitor element,
The conductive paste is baked at a predetermined baking temperature exceeding the softening point of the glass frit in the conductive paste, and then cooled to at least the softening point of the glass frit at a cooling rate of 2 ° C./sec or more. A method for manufacturing a ceramic capacitor . A method for producing a ceramic capacitor having an external electrode formed by applying and baking a conductive paste containing glass frit,
In the heat treatment process for baking the conductive paste for forming the external electrode applied to the ceramic capacitor element,
After baking the conductive paste at a predetermined baking temperature exceeding the softening point of the glass frit in the conductive paste, at least 2 ° C / sec and exceeding 150 ° C / sec to the softening point of the glass frit A method for producing a ceramic capacitor , characterized in that cooling is performed at a cooling rate that does not occur.

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