JPH07105306B2 - Method for manufacturing monolithic ceramic capacitor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip component surface-mounted on a circuit board, which is effective for reducing the size and weight of an electronic device, and more particularly to a method for manufacturing a monolithic ceramic capacitor which is most often used. It is a thing.

2. Description of the Related Art A monolithic ceramic capacitor has a structure in which electrodes and a dielectric ceramic material are layered and is integrated and solidified by a ceramic manufacturing technique. Furthermore, since the electrodes are built-in, it has few magnetic induction components and exhibits excellent performance in high-frequency applications. In addition, since the chip type does not have lead wires, it can be directly mounted when mounting components, and it meets the demand for smaller and lighter electronic devices, and further development is expected in the future.

On the other hand, according to the classification of capacitor materials, alumina,
Electrolysis, tantalum electrolysis, paper, organic film, etc. are listed, and they have a competitive relationship with all of them due to the capacity range of multilayer ceramic capacitors. Therefore, items to be required of the monolithic ceramic capacitor in the future include large capacity, small size, high reliability, low price, and the like, and there is a particularly great demand for the low price. When looking at the price of the monolithic ceramic capacitor from its components, it is said that the internal electrode material cost accounts for 70% or more. If the number of layers is increased to obtain a large capacity, the ratio of the internal electrode material cost to the price becomes higher. Therefore, it is no exaggeration to say that the cost of the monolithic ceramic capacitor depends on the internal electrode material. Although Pt, Pd, Au, and Ag are commonly used as the metal for the internal electrode, a metal having a melting point higher than the dielectric sintering temperature must be selected because of the necessity of co-firing with the dielectric. The melting points of Pt, Pd, Au, and Ag are 1773 ° C, 1555 ° C, and 1063, respectively.
Since the temperature is 96 ° C and 960.5 ° C, Au is not used because of its high price, and Ag has a low melting point, so it is not used alone. It is usually used as an alloy of Pt-Pd-Au and Pt-Pd, and the internal electrode cost accounts for a high proportion in the multilayer capacitor for the reasons described above. Various studies have been made in various fields with the aim of reducing these costs. Above all, among these precious metals, attention is focused on Ag, which is relatively inexpensive, and how to use Ag in a large amount, that is, to develop a dielectric material that is sintered at a lower temperature. This technology is called low-temperature sintering material technology and is being studied in various fields. (For example, JP-A-49-19399).

On the other hand, the fact that the binary alloy of Pd and Ag is a solid solution makes it possible to respond to the decrease in the firing temperature of the ceramic dielectric.
A method of increasing the amount of Ag used was adopted. With this method, the amount of Pd used can be reduced.
It was useful for suppressing the generation of cracks and delamination due to redox of. However
Although Ag has low cost and high conductivity, it is less reliable because it easily migrates. Therefore, in order to suppress migration, it is the current situation that Pd is unwillingly included.

Therefore, a method using a base metal material has been attracting attention in recent years. Typical base metals are Ni and Cu, which are mainly used at low cost and have good migration property, and their use is expected to be expanded more and more in the future. Next, a method of manufacturing a multilayer capacitor using a base metal material as an electrode will be briefly described. Cu or
A base metal such as Ni will be oxidized unless it is fired in an inert atmosphere such as nitrogen and will not function as an electrode. On the other hand, some oxygen is required to decompose and remove the organic binder inside the capacitor material and the organic binder contained in the base metal paste. Therefore, firing of a multilayer capacitor using a base metal material must be carried out while maintaining an atmosphere in which both carbon oxidation, which is thermodynamically shown, and reduction of the base metal are compatible in the entire temperature range during firing. As another method, a base metal oxide such as nickel oxide or copper oxide is used as a starting material for the electrode material, and the organic components contained in the dielectric sheet and the base metal oxide are completely removed by heat treatment in air. After that, there is also a method of reducing the base metal oxide to a base metal by a reduction treatment, and finally firing and sintering in an inert atmosphere such as nitrogen. (For example, JP-A-61-144813 and JP-A-61-160002) This method makes it very easy to control the atmosphere during firing.

Problems to be Solved by the Invention However, there is a problem in the method using the above base metal oxide. It is the unwanted diffusion of electrode material into the dielectric material. This diffusion adversely affects the initial characteristics of the monolithic ceramic capacitor and the characteristics after the life test. Although the base metal oxide, which is the starting material of the electrode material in the reduction process, is almost completely reduced to metal, there is a base metal oxide diffused in the dielectric during the binder removal process,
These oxides cannot be reduced sufficiently. Therefore, in the next firing step, the above-mentioned diffused oxide is further diffused into the dielectric. As a result, the characteristics of the monolithic ceramic capacitor are degraded. In addition, since a mixed gas of nitrogen and hydrogen is used in the reduction step, the base metal oxide simple substance is usually reduced at a temperature higher than that in hydrogen. Thereby,
The degree of reduction is low in reproducibility, and the base metal oxide may remain in the electrode part (insufficient reduction) or even the dielectric component may be reduced (excess reduction).

Means for Solving the Problems In order to solve the above problems, in the method for manufacturing a multilayer ceramic capacitor of the present invention, Cu can be used as a metal material as an internal electrode, and a lead compound is used as a dielectric material. It is configured so that it is possible. That is, a step of producing a green sheet containing at least an organic binder and a plasticizer in a ceramic dielectric material containing a lead compound as a main component, and cupric oxide (Cu) on the green sheet.
O) is used to print an electrode pattern with a paste composition as a main component, and a desired number of electrode pattern-formed green sheets different from the green sheet are laminated to form a multilayer, or the green sheet is formed on the green sheet. After printing the electrode pattern with the cupric oxide paste, a fresh green sheet is newly laminated, and the step of repeating the method of printing the electrode pattern with the cupric oxide paste to form a multilayer, and the multilayer body. Heat treatment in air at a temperature sufficient to decompose and scatter the organic binder inside the multilayer body, and then in a hydrogen atmosphere.
Performing a reduction heat treatment at a temperature between 175 ° C and 250 ° C,
Further, a step of sintering the reduced multilayer body in a powder of carbon or graphite or in a container made of carbon or graphite in a nitrogen atmosphere and further forming an external terminal electrode It is obtained by the step of

Action The present invention, by using cupric oxide as a starting material of the electrode material, and by making the manufacturing process conditions as follows,
(EN) A method of manufacturing a monolithic ceramic capacitor, which has Cu as an internal electrode and a lead compound as a dielectric material, has excellent characteristics and has little deterioration in characteristics even after a life test. First, the reducing process is performed in a hydrogen atmosphere. The cupric oxygen powder is sufficiently reduced at a temperature of about 150 ° C. or higher in a hydrogen atmosphere. On the other hand, when a lead compound, which is a dielectric material, is also subjected to reduction treatment in a hydrogen atmosphere, metallic lead is produced when it is heat-treated at a temperature of 250 ° C. or higher. As mentioned above,
The temperature range in which cupric oxide is reduced and the dielectric material is not reduced is about 100 ° C. when heat-treated in a hydrogen atmosphere.
Therefore, the condition that only cupric oxide is sufficiently reduced and the dielectric is not reduced (does not change) can be easily set. Next, regarding the firing process, when firing in a nitrogen atmosphere, the reduced monolithic ceramic capacitor is embedded in carbon or graphite powder or placed in a container made of carbon or graphite. That is. As a result, the atmosphere around the multilayer capacitor is slightly reduced during firing, and the cupric oxide (CuO) and cuprous oxide (Cu ₂ O) remaining in the electrodes are reduced and metal C
Further, it has the effect of suppressing the diffusion of cupric oxide diffused in the dielectric during the binder removal step.
Also, even if copper oxide and carbon or graphite react with each other, CO or CO ₂ is generated and is removed as a gas, so a reaction that deteriorates the characteristics with the electrode or dielectric material. No products are made.

Example An example of a method for manufacturing a monolithic ceramic capacitor according to the present invention will be described below with reference to the drawings.

First, the dielectric material according to the present invention is Pb (Mg _1/3 Nb _2/3 ) O ₃
Made by TAM Ceramics Co., Ltd., dielectric material (Y5U15
3U) was used. The average particle size is 1.5 μm and the temperature characteristics are Y5U.
It is considerable. Firing is 950 ° C.-3 hrs. This dielectric material was used as an inorganic component, butyral resin as an organic binder, th-n-butyl phthalate as a plasticizer, and toluene as a solvent were mixed in the composition shown in Table 1 to form a slurry.

This slurry was formed into a green sheet on the organic film by the doctor blade method. The thickness of the green sheet after drying was about 45 μm. At this time, a system was used in which film formation, drying, and punching in arbitrary dimensions were continuously performed. Next, the conductor paste is cupric oxide (average particle size 2 μm
m) as a main component, in order to improve the adhesive strength as an additive, 10% by weight of the same powder as the dielectric material is added as an inorganic component, and polybutyl methacrylate (PBMA) as an organic binder is used. A vehicle dissolved in terpineol was added, and the mixture was kneaded by a three-stage roll so as to have an appropriate viscosity. This conductor paste was screen-printed on the processed green sheet to form an electrode pattern. A desired number of electrode-formed green sheets produced in the same manner were laminated so as to be configured as a counter electrode, and laminated by a hot press at a pressure of 80 ° C.-100 kg / cm ² . Then, cut into a predetermined size. As a result, a green sheet laminated body as shown in FIG. 1 is formed. Next, the binder of the green sheet laminate is removed. The organic binder in the green sheet material and the organic binder in the conductor paste used in this example are butyral and PBMA, respectively. Therefore, in order to decompose and remove by heat treatment in air, the temperature must be about 400 ° C or higher. Therefore, in this example, binder removal was performed at a temperature of 450 ° C. for 2 hours. The temperature rising speed was 50 ° C./hr. The binder removal temperature may be equal to or higher than the temperature at which the binder decomposes. However, if heat treatment is performed at a higher temperature than necessary, unnecessary diffusion of CuO, which is an inorganic component of the conductor paste, into the dielectric material occurs. For example, if the binder is removed at 800 ° C for 2 hours,
CuO of the electrode layer is completely diffused into the dielectric layer, and the electrode layer is lost.

Further, the de-byering temperature is determined based on the result of thermal analysis of the organic binder in advance,
After the binder removal step, it is desirable to analyze the residual carbon amount to confirm that the binder has been removed sufficiently. As a result of carbon analysis of the multilayer ceramic capacitor sample debindered under the debindering conditions used in this example, it was confirmed that the binder was sufficiently removed. The temperature profile of this binder removal step is shown in FIG. Next, in the reduction step, the debindered laminate was inserted into a tubular furnace using a 120 mmφ alumina furnace core tube, and the inside of the furnace was replaced with nitrogen gas and then replaced with hydrogen. Flow rate of hydrogen gas after replacement with hydrogen is 0.5 / min
After that, the inside of the furnace was heated to 200 ° C. at a heating rate of 50 ° C./hr, and reduction treatment was performed for 2 hours. Although this reduction process was performed at 200 ° C, it is possible to create a condition that CuO is completely reduced to metallic Cu and the dielectric material does not change in the reduction temperature range of 175 ° C to 250 ° C. An example of the temperature profile of this reduction process is shown in FIG. Next, the firing step was performed using the same tubular furnace as the reduction step. A sample was prepared by filling the reduced laminate in carbon powder. The outline of the sample is shown in FIG. Numeral 10 is a 96% Al ₂ O ₃ sintered substrate, and numeral 20 is bed powder, and BN (boron nitride) was used in this embodiment. 30 is a reduced laminate and 40 is carbon powder. The 96% Al ₂ O ₃ sintered substrate used as the base and the BN of the spread powder
Does not react with the derivative material. Therefore, the substance is not limited to the above substances as long as it does not react with the dielectric and is stable in the temperature and atmosphere of the firing process. The sample thus prepared was placed in a tubular furnace and sintered at 950 ° C. in a nitrogen atmosphere. The internal residual oxygen amount was 1 to ₂ ppm as measured by an O ₂ concentration meter. The temperature profile is shown in FIG.

An electrode for taking out external terminals, a so-called external electrode (application of metallic copper paste, drying and baking in a nitrogen atmosphere at 600 ° C.) is provided on the laminated ceramic ceramic capacitor manufactured as described above, and evaluation as a capacitor is performed. I did.

For comparison, the reduction process was carried out at a temperature of 300 ° C. in a mixed atmosphere of nitrogen and hydrogen (flow rate was 0.8 / min for nitrogen gas and 0.2 / min for hydrogen gas). Was the same, but was fired without filling the laminate in carbon powder. Both the monolithic ceramic capacitor manufactured according to the manufacturing method of the present invention and the monolithic ceramic capacitor manufactured for comparison were processed under exactly the same conditions until the binder removal step. Also, for the capacitors for comparison, the external electrodes were formed by baking metallic copper paste in nitrogen at 600 ° C. The initial characteristics (capacitance, tan δ, insulation resistance) of the monolithic ceramic capacitor manufactured as described above,
The characteristics after the life test were evaluated. Life test is 60 ℃, 95% R
This is the characteristic after holding for 500 hours under the condition of H, 50VDC bias. Table 2 shows the average values of the evaluation results. Ten samples were prepared under each condition.

As is clear from Table 2, those manufactured by the method for manufacturing a monolithic ceramic capacitor of the present invention exhibit extremely excellent characteristics and are practically sufficient characteristics. In particular, it can be said that the multilayer ceramic capacitor has extremely high reliability after the life test, with almost no change from the initial characteristics. When the results of the examples of the present invention are compared with those of the comparative examples, the initial characteristics and the characteristics after the life test are excellent by the manufacturing method of the present invention. From these results, it is very effective to obtain excellent characteristics and reliability by using a hydrogen atmosphere during the reduction process, reducing at a low temperature, and embedding the sample in carbon powder during the firing process. It is clear that Also, when looking at the sample after firing, the sample according to the present invention has the same light yellow color as the dielectric material powder, whereas the sample of the comparative example clearly shows that the dielectric component is persimmon color. It can be seen that the diffusion of copper oxide is unnecessarily excessive.

Although the amount of carbon powder was not mentioned in the present example, the same experiment was conducted by changing the amount of carbon powder. No effect was observed on the initial characteristics and the characteristics after the life test. In addition, instead of burying in carbon powder, the sample was put in a carbon container and fired in the same manner, and the characteristics were examined. A monolithic ceramic capacitor having

EFFECTS OF THE INVENTION As described above, according to the manufacturing method of the present invention, not only a lead compound having extremely excellent dielectric properties and high reliability can be used as a dielectric material, but also each step of binder removal, reduction, and firing can be performed. By manufacturing under the above-mentioned constitutional conditions, a monolithic ceramic capacitor having excellent initial characteristics and extremely high reliability can be obtained. That is, since a dielectric material using a lead compound is generally excellent in dielectric properties and can be fired at a low temperature, it is a dielectric material extremely suitable for mass production. Further, the multilayer ceramic capacitor having Cu as an internal electrode obtained by the manufacturing method of the present invention can sufficiently exhibit the advantages of low conductor resistance, good migration property, and low cost, which are extremely effective. Invention.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a laminated ceramic capacitor using a green sheet manufactured by the manufacturing method of the present invention,
FIG. 2 is a graph showing an example of a temperature profile in the binder removal step of the manufacturing method of the present invention, and FIG. 3 is a graph showing an example of a temperature profile of the reducing step in the manufacturing method of the present invention.
FIG. 4 is an explanatory view showing an example of the state of the sample at the time of firing in the manufacturing method of the present invention, and FIG. 5 is a graph showing an example of the temperature profile in the firing step of the manufacturing method of the present invention. 1 ... Lead compound dielectric material, 2 ... internal electrode, 10 ... 96
% Al ₂ O ₃ , sintered substrate, 20 …… lay powder, 30 …… reduced laminate, 40 …… carbon powder.

Claims (1)

[Claims] 1. A step of producing a green sheet containing at least an organic binder and a plasticizer in a ceramic dielectric material containing a lead compound as a main component, and a paste composition containing cupric oxide as a main component on the green sheet. The electrode pattern is printed with, and a desired number of electrode pattern-formed green sheets other than the green sheet are laminated to form a multilayer, or an electrode pattern is printed on the green sheet with the cupric oxide paste. After,
A step of forming a multilayer by newly laminating a fresh sheet and further repeating the method of printing an electrode pattern with the cupric oxide paste thereon, and decomposing the organic binder inside the multilayer body in the air, Heat treatment at a temperature sufficient to disperse, and then in a hydrogen atmosphere at 175 ℃ -250 ℃
A step of performing a reduction heat treatment at a temperature between ℃, and further, the reduced multilayered body is embedded in carbon or graphite powder, or in a nitrogen atmosphere in a container made of carbon or graphite A step of sintering,
A method of manufacturing a monolithic ceramic capacitor, further comprising the step of forming an external terminal electrode.