JPS646530B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming electrodes of a ceramic capacitor that is easy to manufacture, inexpensive, and has stable characteristics. Conventionally, the baked silver electrode method has been common for forming electrodes of ceramic capacitors, but as the prices of precious metal materials have soared in recent years, various plating methods are being developed. As a known method, there is an electroless plating method using a sensitive activation treatment in a tinnous chloride bath and a palladium chloride bath, but with this method, metal is likely to be formed on the entire circumferential surface of the element body, and it is difficult to form a counter capacitance electrode. In order to do this, it is necessary to remove the film on the side surface of the element body. In this case, the creepage withstand voltage distance is determined by the thickness of the element, and at the same time, the thickness of the element cannot be made too thin, and at the same time, the electric field is concentrated due to creepage contamination such as metal adhering or remaining on the edge of the element due to peripheral polishing. dielectric breakdown was likely to occur. Furthermore, with this method, depending on the type of electrode material and related materials and the mounting method, there is a significant reduction in tensile strength and electrical properties (particularly property deterioration due to life tests). It was necessary in the design to provide this. In the local plating method, after activating the entire surface of the element body, a resist is attached to the electrode formation area, and the outer periphery is further etched to remove the activation of that part. Next, there are various methods such as removing the resist and then forming a metal layer by plating, vacuum evaporation method, photo etching method, etc., but none of them yields satisfactory results for electrodes of ceramic capacitors. That is, the conventionally known methods do not have sufficient properties as electrodes, and there are various shapes of capacitors, making it difficult to mass-produce them. The present invention allows electrodes to be easily formed at required locations on a ceramic capacitor by a new method different from the conventional method as described above, and is particularly characterized by the metal material of the plating base and the method for forming the electrode. That is, the present invention applies a paste in which a platinum group compound such as palladium or platinum or metal powder is dispersed in an organic varnish to the electrode formation portion of a porcelain material, and heat-treats it to deposit active metals as a plating base on the surface of the ceramic material. This is a method for forming electrodes of a ceramic capacitor, which is characterized in that metal electrodes are formed by electroless nickel or copper plating, followed by electrolytic tin or solder plating. The present invention provides superior properties such as adhesive strength and electrical properties compared to conventional plating methods, and also provides comparable properties compared to baked silver electrode methods. Examples of the present invention and reasons for limitations will be described below. First, depending on the type of material, the surface of the porcelain element was roughened by mechanical processing or chemical treatment with acid to increase the adhesive strength between the element and the metal. To create a paste, a platinum group compound or metal powder is uniformly added to an organic varnish made by dissolving a resin such as ethyl cellulose, cellulose acetate, butyl rubber, polyvinyl butyral, or phenolic resin in an organic solvent such as carbitol, terpineol, cellosolve, or alcohol. dispersed into. The metal content of the paste is limited to the claimed range, but the reason is that if it is less than 0.03% by weight, sufficient activity cannot be obtained, and if it exceeds 5% by weight, the adhesion between the base body and the metal after plating treatment will be impaired. It becomes weak and there is no advantage in terms of cost. Table 1 shows examples of the deposition state of electroless nickel plating when the metal (palladium chloride) content of the paste was changed, and the tensile strength after electrolytic tin plating and lead wires were soldered.

【table】

[Table] Regarding the paste, in order to improve printing accuracy, it is also possible to add organic or inorganic substances as filler components that are insoluble and completely scatter within the heat treatment temperature. Next, the heat treatment temperature of the paste is limited to the claimed range, but the reason is that at temperatures lower than 420°C, the resin or filler components in the paste will not be completely dispersed and the plating will not be sufficiently precipitated. At higher temperatures, the precipitated particles become semi-molten and the activity decreases. Table 2 shows examples of the precipitation state of electroless nickel plating when the heat treatment temperature was changed and the tensile strength after electrolytic tin plating and lead wires were soldered.

[Table] Table 3 is a comparative example of tensile strength obtained by a known plating method and a silver baking method.

[Table] A nickel plating bath is a solution containing nickel sulfate, organic acid sodium salt as a complexing agent, and sodium hypophosphite (or hydrazine, borazane compound, etc.) as a reducing agent, and a copper plating bath is a solution containing copper sulfate and Rothsiel. Electroless plating was performed in a rotating barrel plating tank using a solution containing salt, caustic soda, and formalin. Furthermore, electrolytic plating with tin or solder was performed to form electrodes for a ceramic capacitor. The reason for plating twice is that although the first electroless plating of nickel or copper sufficiently functions as an electrode, the purpose is to prevent defects that are easily oxidized by air and to improve solder adhesion. It performs electrolytic plating of tin or solder. Table 4 shows the number of unattached solders over time when 100 samples were left in the air.

【table】

[Table] Table 5 shows examples and comparative examples of the present invention in electrical characteristics and life tests. For Nos. 1 to 4, the base paste for plating and the heat treatment conditions were kept constant. No. 5 is a sample in which the entire surface of the element body was plated and the peripheral area was ground after activation in a tinnous chloride bath and a palladium chloride bath. The strength was also low. No. 6 is a comparative example of a baked silver electrode that has been commonly used in the past, and the electrode forming method according to the present invention obtained excellent values in the life test.

[Table] As described above, the present invention is cheaper and has better characteristics than conventional baked silver electrodes, has high industrial value, and is suitable for mass production. The present invention provides a method for forming electrodes of ceramic capacitors, and its practical value is great.

Claims (1)

[Scope of Claims] 1 A platinum group compound or metal powder is dispersed in an organic varnish, and a paste containing 0.03 to 5.0% by weight as a metal component is applied to a porcelain body by a printing method, a spraying method, etc., and heated at 420 to 920°C. Electrode formation for a porcelain capacitor, characterized in that metal electrodes are formed by performing heat treatment in a temperature range of , attaching a base metal, electroless plating with nickel or copper, and electrolytically plating tin or solder thereon. Method. 2. The method for forming electrodes of a ceramic capacitor according to claim 1, characterized in that the surface of the ceramic body is roughened by a mechanical or chemical method.