JPS6316897B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a high-voltage ceramic capacitor that is easy to manufacture, inexpensive, and has stable characteristics. Conventionally, electrode materials for ceramic electronic components that utilize the functional properties of dielectrics, piezoelectrics, semiconductors, etc., include Ag, Ag-Pd, Ag-Pt, and Ag-Ni, which contain glass frit on the surface of the ceramic body. The baked electrode method, which uses precious metals such as, has been put into practical use.
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 form baked silver electrodes on the surface of the porcelain body and then provide metal electrodes with nickel electrodes and copper electrodes by electrode plating, but this method Since the surface of the baked metal layer is rough and has many small pores, the plating solution penetrates into the small holes during the plating process, resulting in a disadvantage that the adhesive strength between the baked metal layer and the porcelain body deteriorates. Another method is the commonly known electroless plating method, which typically first undergoes a catalytic activation treatment through a chemical reaction between tin chloride and palladium chloride. It was hot. However, there are many problems when using it as a high voltage ceramic electrode. In other words, depending on the type of electrode material and related materials and the mounting method, tensile strength (reduced to 1/2 compared to silver baked electrodes) and electrical properties such as withstand voltage (characteristics deteriorate due to life test)
etc. were significantly deteriorated. For example, when forming the electrodes of a ceramic capacitor, the electroless nickel plating method tends to form them on the entire circumferential surface of the substrate due to the nature of the method. Metal ions penetrated between grains or inside the grain boundaries on the peripheral side, and when a high voltage was applied, destruction occurred along the grain boundaries. In this case, the creepage withstand voltage distance is determined by the thickness of the board, and dielectric breakdown is likely to occur due to concentration of electric field at the electrode peripheral edge, so the board thickness cannot be made too thin, and the peripheral side part is also designed It was necessary to grind deeper than the specified value. However, these methods also had poor reproducibility and many problems. In contrast to these methods, a partial plating method involves applying a resin plating resist to the required portions of the porcelain surface in advance, and then activating the porcelain surface before plating to form a metal layer with a desired pattern on the porcelain surface. Methods such as removing the resist and then applying electroless plating to form a metal layer on the porcelain surface, vacuum evaporation method, photo etching method, etc.
There are various methods. However, none of these methods yields satisfactory results as electrodes for high-voltage ceramic capacitors. In other words, the adhesion of plating is poor with conventional plating methods, and the thickness of capacitor products intended for high voltage applications is 0.8 mm.
It is as thick as ~10m/m, and has various shapes ranging from 4.5 to 16φm/m, making it difficult to mass-produce it. Furthermore, in order to increase the breakdown voltage as much as possible, there is a method of providing an edge of several m/m on the electrode part of the porcelain surface,
Many methods have been used, such as applying glass to the peripheral side, but there is no definitive method. The inventors' experiments have revealed that this is closely related to the dielectric material itself, as well as the electrode material, formation method, etc. The present invention eliminates many of the drawbacks mentioned above and
This paper proposes a method for manufacturing high voltage ceramic capacitors that have extremely stable lifetime characteristics. That is, in the present invention, the Ag component is 99.5 to 0.5 wt%, the Ni component is
A paste consisting of a base active electrode material consisting of a mixed powder or alloy powder in a ratio range of 0.5 to 99.5 wt% and an organic varnish is applied to a dielectric ceramic substrate polished to a surface grain size of 3 to 7 μm on its peripheral side. After that, heat treatment is performed at a temperature range of 300 to 800℃ to form a metal particle layer of 1.5 μm or less on the substrate, and then a layer of metal particles containing one or two of Pd and Pt ions is applied. The Ag and Ni in solution
is replaced with Pd or Pt, and then a metal conductive film of nickel, copper, etc. is formed using an electroless plating solution, and then the peripheral side of the substrate is polished to a surface roughness of 5 μm or less. The high-voltage ceramic capacitor obtained by the method of the present invention exhibits less Ag ion migration in high temperature and high humidity than those obtained by the conventional baked silver electrode method. The deterioration of characteristics due to heat is extremely small, and it is also stable against high voltages, and these effects can only be achieved by combining the electrode materials and construction methods of the present invention, as well as the design. Hereinafter, the present invention will be explained with reference to Examples. First, as a dielectric ceramic substrate,
Using SrTiO ₃ −CaTiO ₃ −Bi ₂ O ₃ based substrate, the thickness
4.0 m/m and a shape of 15 φm/m was surface polished to a surface roughness of 3 to 7 μm. Thereafter, the base active electrode material of the present invention was applied by printing using a mask that left the peripheral side portion, and a baking process was performed. In addition, the method for preparing the electrode paste for base activation of the Ag-Ni component is to use Ag powder with a particle size of 0.2 μm,
0.5 μm Ni powder is used as the electrode metal component, and the metal component is about 3 to 30 wt%, cellulose type,
The organic binder such as acrylic is approximately 3 to 15 wt%, and the solvent component is approximately 55 to 82 wt% such as turpentine oil or butylcarbyl acetate.This paste is approximately 30,000 to 60,000 cps for printing, and approximately 100 to 400 cps for spraying. The viscosity was adjusted to , and applied to the front and back of a ceramic substrate. Then, after drying at a temperature of 80 to 100℃ to evaporate the solvent,
Baking was performed at a temperature range of ~800°C to form a layer of metal fine particles of 1.5 μm or less. Here, it is necessary to perform baking between 300 and 800℃ in order to form a strong base metal particle layer on the ceramic substrate surface, and if the heat treatment temperature is lower than 300℃, organic substances will not be completely scattered. , the electroless plating of nickel or copper becomes incomplete, the adhesion strength between the element body and the electrode decreases, and in terms of electrical properties, it causes a decrease in breakdown voltage, and furthermore, the loss angle worsens, which is undesirable.
At processing temperatures exceeding 800°C, the metal particle layer is partially oxidized, making plating difficult. Moreover, the electrical characteristics are also deteriorated, which is not preferable. After heat treatment at a temperature within the above range to form a metal particle layer of 1.5 μm or less (not including 0), replace for 1 minute in a solution containing 0.05 wt% of one or both of Pd and Pt ions. Apply processing. Note that this replacement process is performed as follows. 2Ag＋Pd ⁺⁺ →Pd＋2Ag ⁺ Ni＋Pd ⁺⁺ →Pd＋Ni ⁺⁺ 2Ag＋Pt ⁺⁺ →Pt＋2Ag ⁺ Ni＋Pt ⁺⁺ →Pt＋Ni ⁺⁺ Then, for nickel electroless plating, nickel sulfate is mixed with sodium hypophosphite (or hydrazine, boron hydride). A nickel metal film was formed by immersing it in a plating solution containing a chemical compound, etc.). Further, electroless plating of copper was performed using copper sulfate as the copper plating, formalin as the reducing agent, Rothsiel's salt as the complexing agent, and sodium hydroxide as the alkaline agent. Here, in the present invention, on the metal particle layer with a thickness of 1.5 μm or less (not including 0) after baking the paste,
The function as an electrode is created for the first time by depositing metal ions such as Pd and Pt, and then electroless plating with Ni or Cu. Incidentally, baked silver, which has conventionally been used as an electrode material for capacitors, etc., needs to be formed with a thick film thickness of 3 to 20 μm after baking, and the film itself can be used as an electrode layer. The metal particle layer after baking is extremely thin, less than 1.5μm, and does not function as an electrode by itself, nor can it be soldered.After the subsequent ion precipitation of Pd, Pt, etc.,
Electroless nickel or copper plating can be used for the first time as an electrode function, and soldering is also possible. The present invention can fully exhibit its function as long as the metal particle layer after baking has an average thickness of 1.5 μm or less, and when used as an electrode for a high-voltage ceramic capacitor, If the thickness exceeds μm, the adhesive strength with the board after plating will drop significantly, and when electroless plating is applied, the plating will adhere to areas other than the designated areas, reducing the withstand voltage, especially in terms of humidity load life characteristics. Electrical characteristics deteriorate. Polishing the front and back surfaces of the dielectric ceramic substrate of the present invention to a roughness of 3 to 7 μm strengthens the adhesion with the electrodes, eliminates variations in withstand voltage, and improves corona voltage and stable characteristics. This is to obtain a value, and if it is less than 3 μm, the adhesiveness will decrease and the withstand voltage will also deteriorate. On the other hand, if the roughness exceeds 7 μm, the dielectric loss tangent deteriorates, and the electrical characteristics deteriorate significantly in terms of humidity characteristics. Furthermore, after forming the metal conductive film, it is necessary to polish the peripheral surface of the element body to a thickness of 5 μm or less to improve the corona voltage and to prevent the migration of the Ag-Ni component, which is the underlying active metal, to the ceramic grain boundaries in humidity. This is to prevent the phenomenon of yellowing and whisker generation of Ag-Ni particles to obtain stable characteristics.If the surface roughness exceeds 5μm, the characteristics will vary and deteriorate significantly over the humidity life. Undesirable. In addition, in the conventionally known general electroless plating method, in which tin chloride and palladium chloride are first subjected to a catalytic activation treatment through a chemical reaction, and then electroless plating is performed, the entire surface of the element body is Furthermore, when used as a high-voltage electrode due to the action of Sn ions, its life in humidity was significantly reduced. Here, a general idea is to polish the peripheral side after plating the entire surface, but this also causes a diffusion phenomenon to the grain boundaries, resulting in poor electrical properties and is not suitable for application to high-voltage capacitors. It was hot. In addition, conventionally known baked silver electrodes suffer from significant Ag ion migration during their lifetime in humidity, and in order to prevent this, methods have been used to coat the peripheral sides with glass, etc., but this is not perfect. By the method of the present invention, it has become possible to obtain a complete high voltage ceramic capacitor for the first time. Next, the characteristic values of the high voltage ceramic capacitor obtained by the method of the present invention are shown in the table below along with various conditions. Here, the high voltage ceramic capacitor is manufactured using the method specified above.
Lead wires were attached to it using Pb-Sn solder, and a phenol-based coating resin was used to create a high-voltage ceramic capacitor. Each value in the table is the average value of 10 pieces, and the humidity load life at 85°C and 85% RH is the value of the time at which the first piece breaks down (hereinafter abbreviated as puncture).

【table】

[Table] (Note) * Outside the scope of the claims of the present invention As is clear from the table above, the high voltage ceramic capacitor made using the electrode material, mounting method, and processing method of the present invention ranks No. 1 in terms of various characteristics.
1, 10, 11, 16, 22, 23, 28, and 32 are comparative examples outside the scope of the claims of the present invention. And No. 1 to 10 are Ag−
The ratio of Ni components is changed, the heat treatment temperature of the paste is constant at 400℃, the average thickness of the Ag-Ni metal particle layer after heat treatment is constant at 0.5 μm, and the surface roughness of the ceramic element surface and peripheral side is average. These are samples with a thickness of 5 μm and 2 μm, and with only the No. 1 Ag component, the breakdown voltage and lifetime moisture load resistance characteristics were extremely poor. Further, as in No. 10, when using only the Ni component, the adhesion of Ni plating was poor and the various properties were also poor. On the other hand, Nos. 2 to 9 exhibited extremely good characteristics, and Nos. 6 and 7 in particular were excellent in terms of breakdown voltage and high corona voltage. Next, No.11-16
is an example of changing the heat treatment temperature of the paste,
As can be seen from the table, the optimum temperature is around 400 to 550°C, and both the low temperature of No. 11 and the high temperature of No. 16 had poor characteristics. moreover,
Nos. 17 to 22 have different thicknesses of the Ag-Ni component metal particle layer after heat treatment, and the optimal thickness is 0.3 to 22.
It is around 0.8 μm, and if it is thick like No. 22, the characteristics will deteriorate and it is not preferable. Although not shown in the table, when the thickness exceeds 1.5 μm like No. 22, the adhesive strength after electroless plating decreases significantly. Further, in the examples shown in the above table, Nos. 1 to 32 were nickel plated as electroless plating, and the nickel plating thickness of these was about 1.5 μm. Generally speaking, there seems to be a relationship between the thickness of the nickel plating and the adhesive strength, but with the electrode forming method of the present invention, almost no difference is observed, and a thickness of the plating of around 1 to 3 μm is sufficient. Ta. In addition, Nos. 23 to 28 are examples of polished surfaces of dielectric ceramic bodies, and Nos. 24 to 27 within the scope of the present invention have good characteristics, especially when the surface roughness is 4 to 6 μm. It was observed that the voltage was significantly improved. Although not shown in this example, when polished to about 0.1 to 0.5 μm, the breakdown voltage decreased to 10 kV/mm or less, and other properties were also poor. No.29～32
is an example in which the peripheral side of the element was polished after electrode formation; in this case, the smaller the roughness, the better, and No. 29 with a roughness of 0.5 μm was excellent. No.32 is
It was as rough as 6 μm, and its electrical properties tended to deteriorate. Furthermore, Nos. 33 to 35 are examples of Cu plating,
Although the characteristics are slightly lower than Ni-metsuki,
There were no practical problems at all, and it was excellent. As described above, the high voltage ceramic capacitor produced by the method of the present invention has extremely stable characteristics and is a manufacturing method of great industrial value suitable for industrial mass production.

Claims (1)

[Claims] 1 Ag component 99.5-0.5wt%, Ni component 0.5-99.5wt
A paste consisting of a base active electrode material consisting of a mixed powder or alloy powder within a ratio of 1.5% and an organic varnish is applied to a dielectric ceramic substrate polished to a surface roughness of 3 to 7 μm so that its peripheral side remains. After that, heat treatment is performed at a temperature range of 300 to 800℃ to form a metal particle layer of 1.5 μm or less on the substrate, and then coated in a solution containing one or both of Pd and Pt ions. Then, the Ag and Ni were replaced with the Pd or Pt, and then a nickel or copper metal conductive film was formed using an electroless plating solution, and then the peripheral side of the substrate was polished to a surface roughness of 5 μm or less. A manufacturing method for high-voltage ceramic capacitors.