JPS6258125B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to an electrode in a ceramic capacitor, an electrical resistance film made of a resistive film baked on a ceramic substrate, and a method for manufacturing the same. (Prior Art) Conventionally, in order to form electrodes on insulators, semiconductor ceramics, etc., low melting point glass powder, so-called frit, was dispersed in silver paint to form a paste, which was then applied by printing and baking. However, if there are many frits, the adhesive strength between the electrode and the substrate is strong, but the solder does not adhere to the electrode easily, and if there are few frits, although the solder adheres easily, the solder may alloy the silver. As a result, the electrodes easily peeled off from the porcelain, resulting in weaker strength. As a measure against the above, the applicant has
No. 21528 and Japanese Patent Publication No. 50-4058 proposed a method of coating the surface of the frit adhesive type silver electrode with nickel or copper by electrodeposition. Since the electrodes of ceramic capacitors are only partially formed on the surface of the dielectric material, it is difficult to connect or secure a current path, and it has been considered difficult to apply the electrodeposition method to small-sized ceramic capacitors in particular. However, in the method described in the above patent publication, a large number of ceramic elements are housed in a rotating barrel and rotated, thereby making contact between electrodes evenly and uniformly every moment to ensure a current path. Success was achieved by easily coating each of the device's silver electrodes with electrodeposited nickel or copper, making mass production possible. Metals such as nickel coated in this way adhere strongly to silver electrodes and easily adhere to solder, making it possible to solder without using flux.
The mechanical strength of the resulting soldered part was increased. On the other hand, in the case of a multilayer chip capacitor, several to several dozen or more positive electrodes and negative electrodes are stacked alternately with dielectric ceramic layers interposed (internal electrodes).
However, in this case, it is necessary to bake the internal electrode together with the porcelain substrate at a temperature of 1000°C or higher (for example, 1300°C), so silver, which evaporates at about 960°C, cannot be used; platinum, palladium, palladium- silver alloy,
It is necessary to use a heat-resistant metal such as palladium-gold alloy, palladium-platinum-silver alloy, palladium-gold-silver alloy. Therefore, for the external electrodes that connect the positive and negative internal electrodes exposed on both end faces of the multilayer chip capacitor to the external circuit, metals that have a high affinity with the above metals, such as the same or similar metals, are used in consideration of electrical connectivity. First, it is necessary to form a base with metal. For example palladium or palladium-
Silver alloy, silver, etc. are used. (Problems with the prior art) However, the silver electrode mentioned above and the palladium electrode mentioned in the previous section do not have the necessary heat resistance against the soldering temperature even if nickel is attached by the method disclosed in the patent publication. No strength was obtained, and the limit was approximately 270°C for 10 seconds (assuming an electrode thickness of approximately 20μ). Of course, increasing the thickness of the electrode increases the solder heat resistance, but this directly causes an increase in costs.
In this way, a common drawback in all cases was that the soldering heat resistance was weak. Recently, especially when soldering the printed circuit boards of various electronic devices, the soldering process is not just once, but twice.
The use of recirculating circuits is becoming more common, and under these circumstances, it has become necessary to improve the heat resistance of capacitor electrodes. (Summary of the Invention) As a result of various studies on this subject, the present inventor first electrodeposited copper instead of directly electrodepositing nickel on a palladium or other metal base provided on a porcelain substrate.
Next, by electrodepositing nickel and further electrodepositing tin or a tin alloy, a porcelain capacitor having excellent adhesive strength and heat resistance strength could be provided. Copper has an ionization tendency that is just right for the ionization tendency of the base metal and the electrodeposited metal, so it improves the adhesive strength. This will be shown later in Examples. Furthermore, when tin is electrodeposited after nickel, the solder adhesion is significantly improved. If only the nickel layer is used, it will be easily oxidized by air, requiring the use of strongly acidic flux, which will not only deteriorate the characteristics of the capacitor, but also reduce the reliability of the equipment, such as oxidation of the printed circuit board on which it is attached. let Note that the ceramic capacitor is one example, and the present invention can also be embodied in a ceramic element using the above-mentioned heat-resistant alloy or metal as the base metal, such as an electrode of a ceramic substrate to which a thin film resistor is attached. Furthermore, the present invention also provides an improved method of the electrodeposition method described above, in which a large number of non-metallic beads such as small metal balls or glass balls are placed in the electrolytic plating barrel in order to improve the efficiency of electrodeposition onto the underlying metal of the porcelain substrate. Small balls with metal coating are housed and used as an auxiliary material. It is a further object of the present invention to provide an improved method of increasing operating efficiency by blowing inert gas bubbles into an electrolytically plated barrel. (Example) The present invention will be described below with reference to the drawings. FIG. 1 is an enlarged and exaggerated sectional view of a multilayer chip capacitor manufactured according to the present invention, and shows a dielectric material such as barium titanate or a ceramic material.
It consists of positive and negative internal electrodes 2 (several to over 100 pieces) connected by external electrodes on both end faces, and external electrodes 7 connected to each set of these internal electrodes.
Each electrode 7 has a base metal layer 3, a copper layer 4,
It is composed of a nickel layer 5 and a tin or tin alloy layer 6. The base metal layer 3 may be made of any of the above-mentioned metals, but palladium and its alloys are particularly preferred. The base metal is printed as a fritted paste on one and both end faces of the multilayer chip capacitor of FIG. 1 according to conventional methods. Copper layer 4, nickel layer 5 and tin or tin alloy layer 6
are sequentially electrodeposited onto the base metal according to the method of the above-mentioned patent publication or according to the improved method of the present invention. Now, to show one example of a typical electrode, the thickness of the base metal layer 3 is about 15-40μ, the copper layer 4 of the electrolytically plated metal is 4-6μ, the nickel layer 5 is 1-4μ and tin or tin. The alloy layer 6 has a thickness of 4-6μ. FIG. 2 shows a rotating barrel type electrolytic plating bath used to form the electrodeposited layers 4, 5, and 6 described above. However, the tank case and electrolyte are excluded for clarity. Actually, as shown in Figure 3, the electrolytic tank 2
2. It shall have necessary means such as an electrode 23. The rotating barrel 14 is cage-shaped with holes 17 for good electrolyte flow. rotating barrel 1
Ring-shaped electrodes 15 and 16 protrude from the axial direction of the rotating barrel, and a gear 18 and a shaft 19 for applying rotational force are formed around the rotating barrel, and the rotating barrel is further connected to a power source by a brush 20. Porcelain capacitor body 21 inserted into this rotating barrel
is electrodeposited on the base metal layer 3 by being rotated by the drive gear 25 in an electrolytic solution, or on a previous electrodeposited layer of a different type. FIG. 2 also shows an example in which small metal balls or glass balls 27 coated with metal, for example by electroless plating, are inserted. FIG. 3 further shows an electrolytic plating bath with additional means for introducing bubbles of inert gas. In the example shown in the figure, air bubbles 30 are introduced into the barrel from the hole 17 of the barrel 14 by discharging inert gas from the inert gas supply tank 31 such as nitrogen into the electrolytic cell 22 through the pipe 28 and the hole 29 using a pump. Blow up. As a result, the capacitor body 21 is separated from the wall of the barrel and becomes fluidized, and new contacts between the electrodes 7 are successively created, thereby increasing the electrodeposition efficiency. Furthermore, the electrolytic solution is also fluidized, further increasing the electrodeposition efficiency. Unlike air blowing, there is no risk of oxidation of the surface of the electrode 7, and when different types of electrodeposited layers are successively formed (electrodeposition operations at each stage are performed in the same type but in different tanks) good electrodeposition can be achieved. Next, an example of an electrode formed by sequentially forming copper, nickel, and tin or a tin alloy on a base metal according to the present invention will be given, and its heat resistance strength and tensile strength will be shown.

[Table] In this case, the base metal and glass frit are made into a paste mixture according to the conventional method, and the diameter is 1.6 mm.
Length 3mm, length of wraparound to the side of base metal 0.3
~0.9m was used by printing and baking on a porcelain body for a multilayer chip capacitor. The heat resistance strength is determined by adding flux (rosin) to the finished multilayer chip capacitor.
Soak H63A solder (JIS K5902) and then apply H63A solder (JIS K5902).
75 of the total external electrode area when immersed in Z3238)
The point where less than % of the electrode was eaten by the solder was defined as the limit point of the heat resistance temperature. Further, the tensile strength was determined by soldering leads of 1 mm diameter to the electrodes at both ends of the multilayer chip capacitor and peeling them off using a Schopper tester. What can be seen from the table is that when the amount of frit is as low as 3%, the tensile strength is low, so a certain amount or more is required. However, even when the frit is 7%, the tensile strength is low when nickel is directly electrodeposited on the base metal. Furthermore, if tin or tin alloy is present on the outermost surface, solder will easily adhere to it.
It was found that it contributes to the strength of solder (although it is not shown in the table). Furthermore, the heat resistance strength is 350℃
The duration was more than 10 seconds, which was satisfactory. The quality of the tensile strength was judged based on the fact that a tensile strength of 1.5 or more was stably obtained. Therefore,
Examples 1 and 4 in the above table are excluded from the present invention. As described above, it can be seen that according to the present invention, a multilayer chip capacitor having sufficiently high tensile strength and heat resistance strength can be obtained. It can also be seen that efficient electrode formation can be achieved by the method of the present invention. It is clear that the electrodes and electrodeposition methods described above can be directly applied to the manufacture of resistors based on porcelain materials. FIG. 4 shows an example. The same reference numerals have been used for parts common to FIG. 1.
2' is a film type resistor. As is clear from the figure, the explanation regarding FIG. 1 is self-explanatory, so the explanation will be omitted here.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a multilayer chip capacitor according to the present invention, FIG. 2 is a partially cutaway sectional view of an apparatus for implementing the method of the present invention, and FIG. 3 is a partially cutaway sectional view of another apparatus for implementing the method. and FIG. 4 are schematic cross-sectional views of the resistor of the present invention. The main members in the figure are as follows. 1: dielectric or ceramic, 2: internal electrode, 3: base metal layer,
4: Copper layer, 5: Nickel layer, 6: Tin or tin alloy layer, 8: Electrode, 14: Rotating barrel, 15, 16:
Ring-shaped electrode, 17: hole, 18: gear, 19:
shaft, 20: brush, 21: ceramic capacitor body, 22: electrolytic layer, 23: electrode, 28: pipe, 29: hole, 30: bubble.

Claims (1)

[Scope of Claims] 1 A metal selected from palladium, platinum, gold, silver, or an alloy thereof is baked onto a porcelain substrate, and a base metal with a frit of more than 3% based on the metal is baked with copper, nickel, and tin. Or an electrode structure made by electrodepositing tin alloys in this order. 2. Metal coating in which a metal or non-metal ball is coated with a metal or non-metal ball by using a porcelain body as a base metal by baking a metal selected from palladium, platinum, gold, silver, or an alloy thereof and frit on a porcelain base. Manufacture of an electrode structure characterized by sequentially immersing small balls together with a rotating barrel type electrolytic plating tank for electrodeposition of copper, nickel, tin or tin alloys, and sequentially electrodepositing metal layers on the base metal. Method. 3. A method for manufacturing an electrode structure according to item 2, characterized in that inert gas bubbles are blown into a rotating barrel.