High volumetric efficiency anodes for electrolytic capacitors
a technology of electrolytic capacitors and anodes, applied in the field of methods, can solve the problems of reducing the surface area of anodes, limiting the application of high cv powder to high working voltage capacitors, and placing an ongoing burden on component manufacturers, and achieves the effect of increasing density
Inactive Publication Date: 2009-11-12
KEMET ELECTRONICS CORP
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- Abstract
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- Application Information
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Benefits of technology
The present invention provides an improved capacitor that can make better use of high CV tantalum and niobium powders. The method of forming the capacitor allows for the use of these powders without the limitations of previous methods. The capacitor has a unique structure with a higher density inner region around the anode lead, which results in improved performance. The process for forming the anode involves pressing a powder into a pellet, heating it in the presence of Mg to form magnesium oxide, and then removing the magnesium oxide. This method ensures the formation of a high-quality anode. Overall, the present invention provides a better capacitor that can be easily manufactured using standard practices.
Problems solved by technology
This desire has placed an ongoing burden on component manufacturers to achieve ever more functionality with minimal size.
Unfortunately, with increased formation voltage these powders exhibit a phenomenon referred to as CV roll down which limits the application of high CV powder in high working voltage capacitors.
These oxide films clog the pores between the particles in sintered anodes thereby resulting in reduced anode surface area.
It is difficult to increase the formation voltage of high CV powders due to the precipitation of a crystalline oxide phase in the amorphous matrix of the anodic oxide film.
Crystalline inclusions in the amorphous oxide are believed to inhibit the formation of a thick dielectric film on the anode surface which provokes high and unstable d.c. leakage.
The disadvantage of the technology is the complexity and inefficiency of the equipment required.
During consequent sintering in vacuum, or in inert gas, Mg shunts can cause shortage of the power and control circuits.
This method therefore requires an extensive, and frequent, cleaning procedure to remove residual Mg which typically must be performed after each run of the furnace.
These problems prohibit large scale production.
The art is still lacking a method of providing a capacitor which achieves the potential offered by high CV powders.
Either the adhesion between the lead wire and pressed powder is insufficient or the manufacturing process is inoperative on a large scale.
Method used
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[0033]Rectangular anodes of 3.1 mm×4.5 mm×1.6 mm were pressed using Ta powder with 50,000 uFV / g weight efficiency. A 0.2 mm diameter Ta wire was embedded into the anodes during the pressing. For the inventive sample an area with 1.2 mm diameter and 10 gm / cm3 density was created around the wire by first compaction in the first die followed by loading into the second die where the rest of the anode was compacted with 6 g / cm3 density. For Control 1 anodes of the same size were pressed with a single density of 6 gm / cm3. The dual density and single density anodes were placed in tube with Mg chunks and deoxidized at about 1000° C. during 3 hours in a tube furnace at ambient pressure. The anodes were exposed to air, leached from Mg oxide in diluted water solution of H2SO4 and H2O2 and formed in 0.1% vol. phosphoric acid to 75 V. Control 2 anodes were prepared in accordance with U.S. Pat. No. 6,447,570 including heating in a vacuum oven. Control 3 anodes were pressed as Control 2 and sinter...
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Abstract
Description
FIELD OF THE INVENTION[0001]This invention relates to methods for formation of refractory valve metal-based anodes with improved volumetric efficiency specifically for application in electrolytic capacitors and capacitors formed thereby.BACKGROUND AND PRIOR ART[0002]There is an ongoing effort in the electronics industry to achieve increasing functionality in a decreased case size. This desire has placed an ongoing burden on component manufacturers to achieve ever more functionality with minimal size. Towards this goal the instant application is primarily focused on improved capacitors, and particularly electrolytic capacitors.[0003]In general, a capacitor comprises an anode and cathode separated by a dielectric. The anode is typically manufactured by pressing and sintering the powder. An anode lead extends from the anode. The dielectric is formed on the anode and the cathode is formed on the dielectric. Anode and cathode terminations are added to facilitate attachment of the capacit...
Claims
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IPC IPC(8): H01G9/04B22F3/12B22F7/04
CPCB22F7/08B22F2999/00H01G9/052H01G9/15Y10T29/417B22F3/10B22F2201/40B22F2207/17
InventorFREEMAN, YURILESSNER, PHILIP M.POLTORAK, JEFFREYHUSSEY, STEVEN C.
OwnerKEMET ELECTRONICS CORP