Valve metal ribbon type fibers for solid electrolytic capacitors

Abstract

A method for making superconducting material useful for forming electrolytic devices comprising the steps of establishing multiple valve metal rods in a primary billet of a ductile material; working the primary billet to a series of reduction steps to form said valve metal rods into a plurality of elongated elements surrounded at least in part by the ductile material; cutting the elongated elements from step (b) and bundling the cut elements to form a secondary billet; working the secondary billet through a series of reduction steps followed by rolling to final thickness; removing the ductile material, whereby to leave valve metal elongated fibers; and sintering the elongated fibers from step (e) under vacuum.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority from U.S. Provisional Application Ser. No. 60 / 783,329, filed Mar. 17, 2006.BACKGROUND OF THE INVENTION [0002] Solid electrolytic capacitors are made of valve metals, which are metals such as tantalum, aluminum, niobium, vanadium and the like. For high reliability devices, tantalum is the preferred metal, and efforts to improve the performance of capacitors made of tantalum are highly desired. Miniaturization is one of the main technology drivers in the electronics industry. For capacitors, miniaturization is achieved by increasing volumetric efficiency, which is the normalized capacitance per volume or CV / cm3 or normalized capacitance per gram or CV / g. The capacitance (C) of a dielectric is given by: C=ε0·ε·A / d where ε0 is the permeability in vacuum, ε is the dielectric constant of the anodic oxide layer, and A and d are the surface area and thickness of the oxide respectively. Since ε0, is a physical c...

AI Technical Summary

Benefits of technology

[0008] The present invention provides an improvement over prior art methods for making electrolytic capacitors. More particularly, the present invention provides an improved method for making capacitor anodes by producing filamentary valve metal fibers by a co-reduction of valve metal filaments within a copper matrix by a combination of drawing and rolling. The copper matrix is then removed leaving valve metal fibers in the form of continuous flat, ribbon-like fibers that have a relatively high aspect ratio of width to thickness, typically of at least about 10 to 1, and as a result relatively high surface area. By producing the fibers in a bundled continuous strip form, they can be made into thin anodes without pressing, thus maintaining the high surface area through subsequent anode sintering and formation.

Problems solved by technology

For a given voltage rating, a thinner anodic oxide layer will provide less resistance to dielectric breakdown leading to lower reliability.

However, as reported in Y. Pozdeev-Freeman, “How Far Can We Go With High CV Capacitors”, T.I.C. Bulletin, No. 122, June 2005, pp 4-8, these high CV powders suffer from extremely rapid fall-off in CV / g with increasing formation voltages.

Additionally flat fibers with high surface area are easier to produce than high surface area round fibers because it is very difficult to produce uniformly round fine filaments by conventional wire drawing techniques.

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