JPH0211009B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for forming graphite for a solid electrolytic capacitor.

In general, solid electrolytic capacitor elements are made by press-molding metal powder that has a valve action, and then a metal wire that has a valve action is planted in advance as an anode lead, and then vacuum sintered and attached to the circumferential surface of the anode body. An oxide film layer is formed by anodic oxidation, and a semiconductor layer such as manganese dioxide is formed on the circumferential surface of this oxide film layer as a counter electrode. Further, in order to reduce contact resistance, a graphite layer is interposed, and a silver paste layer and a solder layer are successively provided to form a cathode conductor layer.

The element formed in this way has a solder layer directly on the paste layer underlying the cathode conductor layer.The heat of immersion in a molten solder bath causes decomposition of the organic binder contained in the underlying silver paste, causing the silver particles to melt into the solder. Diffuses into the bath. The so-called Ginkui small phenomenon occurs,
This method has disadvantages such as peeling of the solder layer and increased dielectric loss.

Conventionally, as a countermeasure to solve this problem, palladium was applied to the surface of the graphite layer by sequentially immersing it in an aqueous solution of stannous chloride and an aqueous solution of palladium chloride after forming the graphite layer, without intervening a silver paste layer that would cause the small silver bite phenomenon. After depositing and activating the surface, copper,
A method has been proposed in which a plating layer of nickel or the like is formed by electroless plating. However, the method of forming the plating layer described above has the following drawbacks.

That is, the pH of the aqueous solution of stannous chloride and the aqueous palladium chloride solution used to activate the graphite layer is 3.5 or less, and exhibits strong acidity.

When the device with the graphite layer formed is immersed in this acidic aqueous solution, the manganese dioxide of the semiconductor layer is exposed in the gaps between the graphite layers or in the peripheral areas of the anode leads where the graphite layer is not formed. Manganese dioxide was dissolved by the acidic aqueous solution, causing a significant increase in the tangent (tan δ) of dielectric loss. Furthermore, the plating layer formed by this conventional method has the disadvantage that it is easily peeled off because it is adhered to the graphite paste with palladium simply physically adsorbed therebetween. This drawback is the reason why a solid electrolytic capacitor with a plating layer formed by electroless plating has not yet been realized.

An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor that eliminates such conventional drawbacks.

According to the present invention, an oxide film layer,
In a method for manufacturing a solid electrolytic capacitor comprising a semiconductor layer, a graphite layer, a plating layer, and a solder layer, the graphite layer is replaced with palladium powder in a graphite paste made of resin, graphite powder, water, or an organic solvent. A method for manufacturing a solid electrolytic capacitor is obtained, which is characterized in that the mixed mixture is deposited and dried.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid tantalum electrolytic capacitor will be described below with reference to the drawings, comparing embodiments of the present invention with conventional products.

Figure 1A shows the first conventional non-sheathed solid electrolytic capacitor using silver paste, and Figure 1B
is based on the second conventional plating method,
FIG. 2 shows an embodiment of the present invention. As a first conventional sample using silver paste, tantalum powder was pressure-molded and a tantalum lead 1a was planted on an anode body 1 which was vacuum-sintered at high temperature, and then the anode body 1a was placed in a phosphoric acid aqueous solution at a formation voltage of 100V. was applied to perform anodic oxidation to form a tantalum oxide film (not shown) 2. Next, after being immersed in a manganese nitrate solution to adhere manganese nitrate, it was thermally decomposed in a constant temperature bath at a temperature of 250°C to 300°C to form a manganese dioxide layer (not shown) 3. This soaking and pyrolysis step is repeated several times. Next, the anode body on which the manganese dioxide layer 3 was formed was immersed in a graphite solution in which graphite powder was suspended in an aqueous solution of a water-soluble polymer material, and the anode body was heated to a temperature of 150°C to 200°C.
The graphite layer 4 was formed by drying in a constant temperature bath at .degree. Further, a silver paste was applied onto the graphite layer 4 and then dried to form a silver paste layer 6 to obtain an element. Next, this element is immersed in a solder bath to form a solder layer 7, and then a solderable plate lead 8, which will become an external terminal, is attached to the tantalum lead 1a at a location approximately 1 mm from the base of the tantalum lead 1a.
Welded it to produce a non-exposed chip tantalum capacitor.

Next, as a sample using the second prior art plating method, the same material as the first prior art product using silver paste is used, and the graphite layer 4 is formed through the same steps. Thereafter, it is immersed in a 2.5 g/aqueous solution of stannous chloride for 5 minutes. Subsequently, it is immersed in a 0.1 g/palladium chloride aqueous solution. After dipping, the elements were thoroughly washed with water and electroless plating was performed.

The plating solution is an electroless nickel plating solution (PH=6.7 at room temperature) that uses dimethylaminoborane as a reducing agent.
Plating was carried out at a temperature of 65° C. for several tens of minutes to form a plating layer 5 of electroless nickel with a thickness of about 6 microns.

After the plating is completed, the element is thoroughly washed with water, and then the temperature
The device was left in a constant temperature bath at 120° C. to evaporate moisture, and the device was immersed in a molten solder bath (not shown) to form a solder layer 7.

Next, a solderable plate-shaped lead 8 was welded to the tantalum lead 1b to produce a non-exposed chip tantalum capacitor.

Next, as an example of the present invention, as shown in Fig. 2, an element with a grain size of 10
After being immersed in graphite paste mixed with palladium powder below micron, the temperature is 150℃~180℃.
It was dried in a constant temperature bath at .degree. C. to form a graphite layer 14.

The above-mentioned graphite paste was a mixture of 3% palladium powder, 15% graphite powder, 40% epoxy resin, and 42% inorganic additive by weight, and diluted with an organic solvent. Thereafter, the element was immersed in a 5% ammonia aqueous solution for 1 minute to activate the surface by absorbing hydrogen on the palladium surface, and then thoroughly washed with water and subjected to electroless plating. The electroless plating liquid type and plating conditions were the same as those of the conventional plating method, and plating was performed for several minutes to form an electroless nickel plating layer 15 of about 6 microns.

120℃ after thoroughly rinsing the element after plating
The element was left in a constant temperature bath to evaporate moisture, and the element was immersed in a molten solder bath to form a solder layer 17.

Next, a solderable plate-like lead 18 was welded to the tantalum lead 1a in the same manner as in the conventional example, to produce a non-sheathed chip tantalum capacitor.

Select any one of the above-mentioned two conventional examples and the non-exposed chip tantalum capacitor according to the embodiment of the present invention.
A solder heat resistance test was conducted by sampling 150 pieces at a time.

Figure 3 A, B and Figure 4 show each capacitor at 230°C, 250°C, and 270°C for 10 seconds.
The tan δ measured at a frequency of 120 Hz after being immersed in a bath of molten solder is shown.

The tan δ of the second conventional capacitor, which was nickel-plated by immersing it in an aqueous solution of tinnous chloride and palladium chloride, was so large that it was impossible to measure it (FIG. 3B). On the other hand, in the capacitor of the first conventional example using silver paste, tan δ has already increased after being immersed at 230°C for 10 seconds (Fig. 3A), whereas in the capacitor of the embodiment of the present invention As shown in the figure, no significant increase in tan δ was observed even after immersion at 270°C for 10 seconds. In addition, in the first conventional capacitor, after being immersed for 10 seconds at a temperature of 230°C, the solder layer peeled off from the ridgeline of the element, and the temperature
After dipping at 250°C for 10 seconds, in addition to peeling of the solder layer, a silver eating phenomenon occurred, and the solder layer became so thin that the unevenness of the manganese dioxide layer was visible.

Furthermore, after dipping for 10 seconds at a temperature of 270°C, most of the silver layer was eaten away, and almost no solder layer was attached to the surface of the element.

On the other hand, the capacitor according to the embodiment of the present invention has a temperature of 270°C.
Even after dipping at ℃ for 10 seconds, no peeling of the solder layer or silver eating phenomenon was observed.

As described above, an element in which electroless plating is performed on a graphite layer to which palladium powder of the present invention is added can (i) be removed without being immersed in a strongly acidic aqueous solution such as aqueous solution of stannous chloride or palladium chloride; Since palladium particles can be attached to the graphite paste, adverse effects such as dissolution of manganese dioxide caused by strong acids and damage to the dielectric film caused by residual chlorine can be removed, and stable electrical characteristics can be obtained.

(ii) Compared to the conventional method of physically adsorbing palladium onto graphite paste by immersing it in an aqueous palladium chloride solution, palladium can be fixed with the organic binder in the paste, which increases the adhesive strength between the electroless plating film and graphite paste. become much stronger.

(iii) Since the solder layer is formed without intervening a silver paste layer, there are no problems such as peeling of the solder layer, silver eating, deterioration of tan δ when immersed in a solder bath, and element damage due to silver migration in a humid atmosphere. Breakage, etc. can be eliminated, and a solid electrolytic capacitor with excellent heat resistance and moisture resistance can be obtained.

It goes without saying that the anode body is not limited to tantalum, and metals such as niobium and aluminum may also be used.

[Brief explanation of drawings]

FIGS. 1A and 1B are cross-sectional views of conventional non-external chip tantalum capacitors. FIG. 2 is a sectional view of a non-exposed chip tantalum capacitor according to an example of the present invention. FIGS. 3A and 3B are diagrams showing the solder heat resistance characteristics of tan δ of a conventional non-sheathed chip tantalum capacitor. FIG. 4 is a diagram showing the solder heat resistance characteristics of the non-exposed chip tantalum capacitor according to the present invention. 1...Anode body, 1a...Tantalum lead, 2...
...Anodized film (not shown), 3...Manganese dioxide layer (not shown), 4...Graphite layer, 1
4... (palladium-containing) graphite layer, 5,
15...Plated layer, 6...Silver paste layer, 7,1
7...Solder layer, 8, 18...Plate lead.

Claims (1)

[Claims] 1. Manufacturing of a solid electrolytic capacitor comprising the steps of sequentially forming an oxide film layer, a semiconductor layer, a graphite layer, a plating layer, and a solder layer on an anode body made of a valve metal having an anode lead to be led out. In the method, the graphite layer is formed by depositing a mixture of palladium powder on a graphite paste made of resin, graphite powder, water or an organic solvent, and drying the mixture. Production method. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the palladium powder has a particle size of 10 microns or less. 3 The palladium content is 0.5% to 5 by weight ratio
% of the solid electrolytic capacitor according to claim 1.