JPS634693B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a semiconductor ceramic capacitor that is easy to manufacture, inexpensive, and has stable characteristics. Traditionally, BaTiO ₃ -based porcelain or SrTiO ₃ -based porcelain has been used in ceramic capacitors. These ceramics have a large dielectric constant and high insulation properties. When such porcelain is used in a capacitor, electrodes are formed by baking silver oxide or metallic silver onto both sides of the porcelain body. However, even if these are baked as is, they do not adhere strongly to the porcelain body, and their electrical properties are not very good. Therefore, it is known that this can be improved to some extent by mixing glass with a slightly lower melting point with the Ag component or adding an inorganic substance to the Ag component as an electrode material. The semiconductor ceramic capacitor of the present invention uses a semiconductor ceramic element having a relatively low resistivity, unlike the above-mentioned capacitor in which the ceramic element is an insulator. To put it simply, a semiconductor ceramic capacitor is one in which a capacitive insulating layer is formed at grain boundaries on the normal outer or inner surface of a semiconductor ceramic. In such semiconductor ceramic capacitors, the former is called a surface layer type, and the latter is called a grain boundary layer type. There are many types of semiconductor ceramic capacitors known so far, but most of them fall into one of the two types mentioned above. A surface layer type semiconductor ceramic capacitor has a thin insulating layer formed on the surface of its ceramic element, and utilizes the capacitance created by the thin insulating layer. Structurally, most of the thickness of the ceramic element is occupied by the conductor, and the thin layer on the surface acts as a dielectric, making it possible to obtain a capacitor with a large capacity at low voltage. On the other hand, grain boundary layer type semiconductor ceramic capacitors are made by coating the surface of a semiconductor ceramic element with a metal that acts to insulate it, such as Bi or Cu oxide, and heat-treating it to form a grain boundary layer. It is made of insulation. Since such a grain boundary layer is made into a dielectric material, it has excellent withstand voltage and can obtain resistance values and capacitances suitable for high voltage applications. Whether the insulating layer is primarily formed on the surface of the semiconductor ceramic element or at the grain boundaries of the crystal is subtly influenced by the diffusion of oxygen into the element and the localization of impurities. Further, when semiconductor ceramic is used as a capacitor, its characteristics are greatly influenced by its subcomponents. The ceramic elements traditionally used in grain boundary dielectric layer type semiconductor ceramic capacitors include
There are products in which oxides such as Sr, Bi, Zr, Sn, or Nb are dissolved in BaTiO ₃ . Although the effective dielectric constant is apparently large at 20,000 to 70,000, the rate of change in capacitance with temperature is large.
The maximum rate of change is extremely large, around ±50% in the temperature range of ℃. And the dielectric loss (tanδ) is also
It is large at around 0.05%. In _addition , Dy, Ce,
CaTiO ₃ with added oxides such as Mn, Ta, W, Nb, Si or Bi, and even a part of SrTiO ₃
It uses semiconductor porcelain made of substituted porcelain. The baked electrode method has been put into practical use for current capacitors that use these semiconductor ceramics, mainly using noble metals such as Ag, Ad-Pd, Ag-Pt, and Ag-Ni, which contain low-melting glass substances. has been done. However, with the recent rise in the price of precious metals, various plating methods are being developed. However, these methods also have many drawbacks. For example, it is possible to provide metal electrodes by forming baked silver electrodes on the surface of the ceramic element and then electrolytically plating nickel electrodes and copper electrodes.
In this method, since the baked metal surface is rough and has many small holes, the plating solution penetrates into the small holes during the plating process, which deteriorates the adhesion strength between the baked metal layer and the ceramic element. As another method, an electroless plating method has been used, and in electroless nickel plating, it is common to first perform a catalyst activation treatment by chemically reacting tin chloride and palladium chloride. However, there are many problems when using it as an electrode for a ceramic capacitor. In other words, depending on the type of electrode material and related materials and the mounting method, the tensile strength (reduced to 1/2 compared to silver-baked electrodes) and electrical properties (property deterioration due to life test) can be significantly degraded. Ta. For example, when forming electrodes on a ceramic capacitor, the electroless nickel plating method tends to form electrodes on the entire circumferential surface of the substrate due to the nature of the method. However, in this case, the creepage withstand voltage distance is determined by the thickness of the substrate, and dielectric breakdown is likely to occur due to concentration of electric field at the peripheral edge of the electrode, making it impossible to reduce the thickness of the substrate very much. In contrast to these methods, the partial plating method involves applying a resin plating resist to the required portions of the porcelain surface in advance, activating the porcelain surface, and then , a method of removing the plating resist and then applying electroless plating to form a metal layer on the porcelain surface, and a vacuum evaporation method,
There are various methods such as photoetching, but none of them yields satisfactory results as electrodes for ceramic capacitors. That is, in the conventionally known plating method, the adhesion of the plating is poor and it is difficult to achieve mass production. Furthermore, if an electrode is formed on the entire surface in order to obtain as large a capacitance value as possible, the life characteristics will be extremely poor as mentioned above, and from the viewpoint of reliability, it is necessary to provide an edge on the electrode part on the porcelain surface in the design. It was necessary. The present invention relates to a method for manufacturing a semiconductor ceramic capacitor which eliminates many of the above-mentioned drawbacks and has extremely stable lifetime characteristics. That is, in the present invention, a paste containing a printable or sprayable Ag compound is applied to a semiconductor ceramic substrate so that the end surface remains, and then 350
Heat treated in the temperature range from ℃ to 850℃, and then applied to the substrate.
Forming a metallic silver particle layer of 0.01 μm or more and 1.5 μm or less,
After that, a substitution treatment is performed in a solution containing at least one of Pd and Pt ions,
This is a method for manufacturing a semiconductor ceramic capacitor, characterized in that a metal electrode of Ni or Cu is then formed by electroless plating, and the electrode obtained by the present invention is different from that obtained by the conventional baked silver electrode method. It has very good properties and can provide sufficient functionality. The method of the present invention will be described below with reference to Examples and Comparative Examples. Example 1 First, SrCO ₃ , CaCO ₃ , TiO ₂ , Nb ₂ O ₅
Mix according to the composition shown in the table, wet mix, dry,
After pre-calcining at a temperature of 1200°C, the powder is pulverized to an average size of 2.5 μm, an aqueous polyvinyl alcohol solution is added and mixed as a binder, and the sized powder is sized into 32 mesh passes, with a diameter of 15 mm and a thickness of 0.5 mm. molded into a disc shape with a pressure of about 1 ton/cm ² , and heat-treated the molded bodies at 1000°C in air.
1390℃ in a mixed gas flow of % _N2-10 % _H2
Baked for 4 hours at a temperature of approximately 12.5mm in diameter and approximately 12.5mm thick.
A 0.4 mm disk-shaped semiconductor porcelain was obtained. A paste-like diffusing agent was applied to these semiconductor ceramics, and heat treatment was performed at a temperature of 1150° C. for 2 hours to form a dielectric layer at the grain boundaries. The composition of the diffusing agent at this time was 67.6 mol% _Bi2O3 , 12 mol% _Cu2O , 2.4 mol% _MnO2 , 6.0 mol% _{B2O3 ,} 4.0 mol for all _samples . % La ₂ O ₃ and 8.0 mol % TiO ₂ . The coating amount is 1 semiconductor element
It was 1.9 mg per sheet (250 mg).

【table】

[Table] * Comparative sample Next, electrodes were applied to both sides of the semiconductor ceramic element by electroless plating. Specifically, a printing and spraying method was performed using a mask that left a 1 mm edge on both sides of the element. The method for preparing the active paste for electroless plating is usually AgNO ₃ ,
A silver compound such as Ag ₂ SO ₄ or AgCN is used, a solvent such as H ₂ O or butyl carbitol, terpine oil, or ethylene alcohol is used, and an organic binder such as ethyl cellulose, cellulose acetate, butyl rubber, or polyvinyl butyl alcohol is used. Uses resin. In this example, AgNO ₃ was used at 95
Parts by weight, 5 parts by weight of ethyl cellulose, to which butyl carbitol was added, and for printing,
The viscosity is about 30,000 to 60,000 cps, about 100 for spraying.
Adjusted to ~400cps, and applied 1~ to the front and back sides of the semiconductor ceramic substrate.
It was applied at a thickness of 10 μm. Then, after drying at a temperature of 80℃ to 100℃ to evaporate the solvent, use an electric furnace to
Baking was performed at a temperature range of 350°C to 850°C to precipitate metallic silver particles. Then Pd and Pt ions
Substitution treatment was performed for 1 minute in a solution containing 0.05% by weight, and after washing with water, Ni plating was immersed in a plating solution containing sodium hypophosphite (or hydrazine boron hydride compound, etc.) in nickel sulfate.
A nickel film was formed. Electroless plating of copper was performed using copper sulfate, formalin as a reducing agent, Rothsiel's salt as a complexing agent, and sodium hydroxide as an alkaline agent. As a method for preparing Pd and Pt aqueous solutions, PdCl ₂ ,
A solution was prepared by using H ₂ Pt ₆ ·6H ₂ O, using HCl or alcohol for dissolution, and diluting with H ₂ O.
After that, the element on which the metal silver particle layer of 1.5 μm or less has been deposited is immersed, a replacement treatment is performed, and then washed with water.
Perform metsuki. The active metal material for electroless plating of the present invention can exhibit its function as long as the metal silver particle layer is present with a thickness of 0.01 μm or more and 1.5 μm or less, and when used as an electrode for a capacitor. ,
For 1.5μm or more, conventional baked silver (silver thickness 5~
Compared to 20 μm), it does not have any features in terms of price, and especially in terms of humidity load life characteristics, Ag ion migration occurs, making it undesirable. In addition, in the present invention, the metal silver particle layer after paste baking is Pd, Pt, etc. on the particle layer of 1.5 μm or less
precipitating at least one of the metals, and further
By plating with Ni and Cu, it functions as an electrode. Incidentally, baked silver, which has been conventionally used as an electrode material for capacitors, has a thick film thickness of 3 to 20 μm after baking, and the film layer itself can be used as an electrode layer. The underlying metal silver particle layer is extremely thin, less than 1.5 μm, and does not function as an electrode by itself, nor can it be soldered. , Cu plating allows it to be used as an electrode, and also enables soldering. In addition, in the present invention, it is necessary to apply a paste containing an Ag compound and then perform baking within a temperature range of 350°C to 850°C to form a stable metallic silver particle layer on the substrate surface of semiconductor porcelain. If the temperature is lower than 350°C, the resin component remains, making it difficult to form a metal silver electrode, resulting in a decrease in the adhesive strength of the electrode. If the temperature exceeds 850°C, the silver metal particles will melt, resulting in uneven formation of Ni and Cu plating films and deterioration of electrical properties. For comparison, a paste consisting of Ag powder and low melting point glass powder was applied to the surface of semiconductor porcelain.
Baking was performed at 800°C for 130 minutes to form an Ag electrode.
Further, electrodes were formed by a conventionally known plating method, and then the circumference was polished. The electrical properties and physical properties of the semiconductor ceramic capacitor thus obtained were measured.
The results are summarized in Table 2. In the table below, the dielectric constant ε and dielectric loss tan δ were measured at a frequency of 1 KHz and a temperature of 20°C. In addition, the insulation resistance is determined by the DC voltage
50V was applied and the resistance value was measured after 1 minute. Note that the left side of the sample number corresponds to the sample number in Table 1. In addition, the sample numbers marked with a cross are comparative examples and are outside the scope of the claims.

【table】

【table】

【table】

[Table] * Comparison sample As is clear from Table 2, the plated sample is superior to the sample with Ag baked electrodes in terms of dielectric constant and lead wire tensile strength. However, when the thickness of the metal silver particle layer becomes thinner than 0.01 μm, the dielectric properties and the tensile strength of the lead wire decrease, and the overall properties become equal to or worse than those of the Ag baked electrode. If the thickness of the metal silver particle layer exceeds 1.5 μm, the tensile strength of the lead wire tends to decrease and it becomes easy to peel off. Furthermore, if the baking temperature of the Ag compound-containing paste is less than 350°C, the dielectric properties and the tensile strength of the lead wire will decrease, and if it exceeds 850°C, the dielectric properties and the tensile strength of the lead wire will similarly decrease. Although not described in the examples, the tensile strength of the lead wire is improved by thermal aging within a temperature range of 130 to 200° C. after applying the plating electrode according to the present invention. Furthermore, when the semiconductor ceramic body is within the composition range of the present invention, it has good dielectric properties and insulation resistance. That is, even if the SrO component exceeds 50.23 mol% or the TiO ₂ component is less than 49.72 mol%, the sintered grain size of the semiconductor porcelain becomes small and an apparent dielectric constant of 5000 cannot be ensured. Further, even if the SrO component is less than 49.47 mol% and the TiO ₂ component exceeds 50.23 mol%, the sintered grain size of the semiconductor porcelain becomes small and an apparent dielectric constant of 5000 cannot be ensured, which is not desirable. In addition, in SrTiO ₃ , which is the main component of semiconductor porcelain, replacing the SrO component with CaO component has the effect of reducing the rate of capacitance temperature change as the CaO component increases, but on the other hand, grain growth tends to be suppressed. in the
When the CaO content exceeds 22.60 mol% (approximately corresponding to the composition of Sr _0.55 Ca _0.45 TiO ₃ ), the sintered grain size of the semiconductor porcelain decreases, making it impossible to secure the minimum apparent dielectric constant of 5000 required in practice. Therefore, it is undesirable.
It is composed of SrO component and TiO ₂ components
Excess SrO added beyond a certain limit to SrTiO ₃ solid or (Sr ₁ - _x Ca _x ) TiO ₃ solid consisting of SrO component, CaO component and TiO ₂ component
When components, CaO components, and TiO ₂ components are mixed,
SrTiO ₃ particles or (Sr ₁ ― _x Ca _x ) during sintering
This is because grain growth of TiO ₃ particles is suppressed. Also, Nb ₂ O ₅ is composed of SrO component and TiO ₂ component
A necessary component to convert SrTiO ₃ solid solution or (Sr ₁ - _x Ca _x ) TiO ₃ solid solution consisting of SrO component, CaO component and TiO ₂ component into a semiconductor based on the principle of valence control, and its Nb ₂ O If the amount of _{the five} components is less than 0.05 mol% (approximately 0.10 mol% with respect to SrTiO ₃ or _{Sr 1 - x} Ca ₁ ― _x Ca _x TiO ₃ ), SrTiO ₃ porcelain or Sr ₁ ― _x Ca _x TiO ₃
This is undesirable because grain growth of the porcelain is suppressed and an apparent permittivity of 5000 cannot be ensured. Example 2 Using the element of sample number 8 of Example 1, Example 1
After processing in the same manner and applying a plating electrode, Pb
-The solder components of the Sr-based solder material were changed, lead wires were attached using the dipping method, and the electrical and physical properties were measured. The measurement results are shown in Table 3. Note that the sample numbers marked with a cross are comparative examples and are outside the scope of the claims of the present invention.

[Table] *marked is a sample for comparison As described above, the present invention produces semiconductor porcelain capacitors of high quality and excellent characteristics by forming electrodes made of Ni or Cu on SrTiO ₃ -based semiconductor porcelain using the plating method. It can be made. In the above embodiments, the case where the electroless plating method was used as the method for forming the electrode was explained, but it goes without saying that the same effect can be obtained even if the electrode is provided by the electrolytic plating method.

Claims (1)

[Claims] 1. Strontium oxide (SrO) component is 50.23~
49.47 mol%, titanium oxide (TiO ₂ ) component is 49.72 ~
50.23 mol%, niobium oxide (Nb ₂ O ₅ ) component is 0.05~
A composition consisting of 0.30 mol% is fired in a neutral or reducing atmosphere, and printed or sprayed onto a grain boundary dielectric layer type semiconductor ceramic substrate, which is made by converting the crystal grain boundary layer of the obtained semiconductor ceramic element into an insulator. A paste made of a possible Ag compound or a mixture or alloy powder of one or more of Ag metal and Ni, Cu, Zn, and Al metals is applied to the required location, and then heated at 350℃~
Heat treated within a temperature range of 850℃, and then placed on the substrate.
A metal particle layer with a thickness of 0.01 μm or more and 15 μm or less is formed, and then at least one of Pb and Pt is applied to the surface of the metal particle layer in a solution containing at least one of Pd and Pt ions. A method for manufacturing a semiconductor ceramic capacitor, which comprises performing an active substitution treatment to precipitate fine metal particles, and then forming a Ni or Cu metal electrode by electroless plating. 2 The composition of the semiconductor porcelain is such that the total amount of strontium oxide (SrO) component and calcium oxide (CaO) component is 50.23 to 49.47 mol%, calcium oxide (CaO) component is 22.00 mol% or less, and titanium oxide (TiO ₂ ) component 49.72 _to 50.23 mol%, and the niobium oxide ( _Nb2O5 ) component is 0.05 to 0.30 mol%. 3. The method of manufacturing a semiconductor ceramic capacitor according to claim 1 or 2, characterized in that terminal attachment is carried out using a solder material containing at least 37 to 75% of Pb component.