Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Patent
1996-09-03
1998-09-22
Kincaid, Kristine L.
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
361529, 361534, 361537, 29 2503, H01G 900
Patent
active
058123660
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates generally to solid electrolytic capacitors such as tantalum capacitors. More specifically, the present invention relates to a solid electrolytic capacitor which is suitably designed for surface mounting. The present invention also relates to a process for making such a solid electrolytic capacitor.
BACKGROUND ART
Conventionally, a capacitor element for use in a solid electrolytic capacitor of this type was most typically manufactured in the following manner.
First, as shown in FIG. 57 of the accompanying drawings, metal powder such as tantalum powder is compacted into a porous chip 2 from which a metal anode wire 3 made of e.g. tantalum projects out and thereafter sintered.
Then, as shown in FIG. 58, the chip 2 is immersed in a chemical solution A such as aqueous solution of phosphoric acid, and a direct current is passed between the anode wire 3 and the solution A for performing anodic oxidation. As a result, a dielectric film 4 of tantalum pentoxide for example is formed on the surfaces of the metal particles of the chip 2.
Then, as shown in FIG. 59, the steps are repeated plural times which comprise immersing the chip 2 in an aqueous solution B of manganese nitrate until the manganese nitrate solution B permeates into the chip 2, and thereafter lifting out the chip for baking. As a result, a solid electrolyte layer 5 of a metal oxide such as manganese dioxide is formed on the surface of the dielectric film 4.
Finally, a cathode film made of a metal such as silver or nickel is formed after graphitizing the surface of the solid electrolyte layer 5 of the chip 2. This provides a capacitor element 1.
As described above, in making the capacitor element 1 for the prior art solid electrolytic capacitor, the anode wire 3 projecting from the chip 2 is indispensable and cannot be obviated. Therefore, it was conventional to employ the structure of FIG. 60 or 61 for making a surface-mounting type solid electrolytic capacitor by incorporating the capacitor element 1.
Specifically, according to the structure shown in FIG. 60, the capacitor element 1 is arranged between a cathode lead terminal 6a and an anode lead terminal 6b. The chip 2 of the capacitor element 1 is attached to the cathode lead terminal 6b, whereas the anode wire 3 is attached to the anode lead terminal 6a. The capacitor element 1 together with the inner ends of the respective lead terminals 6a, 6b is enclosed in a molded synthetic resin package 7. The solid electrolytic capacitor of such a structure is disclosed in Japanese Patent Application Laid-open No. 60-220922 for example.
According to the structure shown in FIG. 61, on the other hand, the capacitor element 1 is enclosed in a molded synthetic resin package 8 in a manner such that the tip portion of the anode wire 3 and the end face of the chip 2 opposite to the anode wire 3 are exposed. The exposed tip portion of the anode wire 3 is formed with an anode terminal portion 9a made of e.g. solder, whereas the exposed end face of the chip is formed with a cathode terminal portion 9b made of e.g. solder.
However, in either one of the above-described solid electrolytic capacitors, the capacitor element 1 need be enclosed in the resin package 7, 8 in such a manner as to contain both the chip 2 and the projecting anode wire 3. Therefore, the package 7, 8 must be larger in size than the chip 2 of the capacitor element 1 by as much as the anode wire 3 projects out from the chip 2, so that the ratio of the volume of the chip 2 relative to the overall volume of the capacitor decreases to result in a volume efficiency reduction. Further, the effective volume of the chip 2 also reduces by as much as the anode wire 3 is embedded in the chip 2. Due to these factors, the prior art solid electrolytic capacitor poses difficulty in increasing the capacitance per unit volume while also giving rise to a weight increase problem. These problems are particularly remarkable with respect the solid electrolytic capacitor having the structure of FIGS. 60 which incorporates the two
REFERENCES:
patent: 4164005 (1979-08-01), Cheseldine
patent: 5005107 (1991-04-01), Kobashi et al.
patent: 5349496 (1994-09-01), Taniguchi et al.
patent: 5428501 (1995-06-01), Bruder
patent: 5638253 (1997-06-01), Hasegawa
Dinkins Anthony
Kincaid Kristine L.
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