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(12) United States Patent (10) Patent No.: US 6,436,268 B1 Melody Et Al

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(12) United States Patent (10) Patent No.: US 6,436,268 B1 Melody Et Al USOO6436268B1 (12) United States Patent (10) Patent No.: US 6,436,268 B1 Melody et al. (45) Date of Patent: Aug. 20, 2002 (54) NON-AQUEOUSELECTROLYTES FOR 5,587,871. A 12/1996 Ue et al. ANODIZING 5,605,561 A 2/1997 Iwabuchi et al. 5,670,741. A * 9/1997 Stromcuist et al. ...... 149/109.6 (75) Inventors: Brian John Melody; John Tony 5,687,057. A 11/1997 Dapo Kinard, both of Greer; David 5,716,511 A 2/1998 Melody et al. Alexander Wheeler, Williamston; 6,051,044. A 4/2000 Fife Philip Michael Lessner, Simpsonville, FOREIGN PATENT DOCUMENTS all of SC (US) EP O569 121 11/1993 GB 537474 6/1941 (73) Assignee: Kemet Electronics Corporation, GB 2168383 6/1986 Greenville, SC (US) WO WO98/19811 5/1998 Notice: Subject to any disclaimer, the term of this OTHER PUBLICATIONS patent is extended or adjusted under 35 Jackson N.F. et al., Institute of Electrical Engineers Steve U.S.C. 154(b) by 77 days. nage, GB, “The use of niobium as an anode material in liquid filled electrolytic capacitors', Database accession No. (21) Appl. No.: 09/630,605 733083 XP002144913 Abstract & Electrocomponent Sci (22) Filed: Aug. 2, 2000 ence and Technology, Sep. 1974, UK vol. 1, No. 1, pp. 27 37. (51) Int. Cl................................................. C25D 11/02 Patent Abstracts of Japan, vol. 10, No. 373, Abs Grp No.: (52) U.S. Cl. ........................ 205/234; 205/322; 205/332 C391, Abstracting Applin. No. 60–8438, Dec. 1986. (58) Field of Search ................................. 205/234, 322, Melody et al., An Improved Series of Electrolytes For Use 205/332 In The Anodization of Tantalum Capacitor Anodes, Pre Sented at the Capacitor and Resistor Technology Symposium (56) References Cited (C.A.R.TX. 92), Mar. 17, 1992, pp. 1-11. U.S. PATENT DOCUMENTS * cited by examiner 3,180.809 A 4/1965 Gregori Primary Examiner Nam Nguyen 3,359,191 A 12/1967 Minami et al. ASSistant Examiner William T. Leader 3,496,424 A 2/1970 Behrend (74) Attorney, Agent, or Firm-Banner & Witcoff, Ltd. 3,563.863 A 2/1971 Vierow 3,796,644 A 3/1974 Bernard (57) ABSTRACT 3,943,041 A 3/1976 Jackson 4,196,060 A 4f1980 Patrie et al. Non-aqueous electrolytic Solutions Suitable for anodizing 4,383,897 A 5/1983 Gillich et al. Valve metal derivative anodes, methods of anodizing using 4,388,156 A 6/1983 Gillich et al. non-aqueous electrolytic Solutions, and capacitors prepared 4,476,517 A 10/1984 Fresia with non-aqueous electrolytic Solutions. The non-aqueous 4,479,166 A 10/1984 Finkelstein et al. electrolytic Solution comprises glycerine and at least one 4,781.802 A 11/1988 Fresia 4,823,236 A 4f1989 Fresia soluble salt formed by the neutralization of at least one 5,111,365 A 5/1992 Dapo non-halogen-containing organic or inorganic acid anion with 5,185,075 A * 2/1993 Rosenberg et al. ......... 205/234 at least one alkali metal, ammonium, or protonated amine 5,211,741 A 5/1993 Fife cation; wherein the acid anion is derived from an acid having 5,385,662 A 1/1995 Kurze et al. a pKa lower than phosphoric acid. 5,560,761. A 10/1996 Naito 5,580,367 A 12/1996 Fife 7 Claims, No Drawings US 6,436,268 B1 1 2 NON-AQUEOUSELECTROLYTES FOR It is widely recognized that the growth of the electronics ANODIZING industry is driven by greater device performance at lower cost, as time advances. Thus, while the capacitance per unit FIELD OF THE INVENTION Volume continues to increase, the price per unit of capaci The present invention is directed to non-aqueous electro tance for Solid tantalum capacitors continues to decrease lytic Solutions Suitable for anodizing valve metal derivative with time, as it must in order for these devices to conform anodes, to methods of anodizing using non-aqueous elec to the So-called learning curve of device manufacturing cost trolytic Solutions, and to capacitors prepared with non versus the logarithm of the cumulative number of devices aqueous electrolytic Solutions. Sold worldwide. This learning curve of the cost requirements for components must be Satisfied in order to maintain the BACKGROUND OF THE INVENTION growth rate of the electronics industry. For many years, So-called Solid tantalum capacitors have It is widely recognized that, in Spite of the device manu Set the market Standard for high capacitance per unit volume facturing cost learning curve, Surface area per unit weight of combined with high reliability. Since their introduction in tantalum cannot be increased indefinitely. It is also recog the 1950's, Solid tantalum capacitors have continued to 15 nized that the increasing demand for tantalum is forcing Shrink in size due to the introduction of tantalum powders tantalum producers to process lower quality ores in order to having higher Surface area per unit weight (i.e., Smaller meet demand for the metal. The extraction cost per pound of particle size). High Surface area tantalum powders facilitate tantalum increases significantly with decreasing ore quality. the use of Smaller anodes having the Same capacitance when In an effort to reduce the cost of the valve metal compo anodized to equivalent anodic oxide thickness compared nent of Solid capacitors, other valve metals in addition to with older tantalum powders. tantalum have been tested for use in Solid capacitor manu The utility of tantalum capacitors has been extended by facture. The metal, niobium, is most closely related to the widespread introduction of Surface mount Solid tantalum tantalum in chemical and physical properties. For many capacitors in the 1980s. The heat-resistance properties years, attempts have been made to fabricate Successful Solid inherent to Solid tantalum capacitors due to the manganese 25 capacitors from niobium powder. Early niobium powders dioxide counter electrode material used in the fabrication contained a relatively large amount of impurities and gave renders tantalum capacitorS relatively immune to the rise to highly flawed oxide during anodization at the tem destructive effects of heating during reflow-Soldering com peratures normally used to anodize tantalum anodes (i.e., pared with aluminum electrolytic capacitors which contain a 80° C. to 90° C.) in dilute phosphoric acid. It was found that liquid, organic-Solvent-based electrolyte. Consequently, a the production of blister-like flaws in the anodic oxide on large fraction of the applications which formerly utilized niobium could be minimized through the use of anodizing miniature aluminum electrolytic capacitors have been con temperatures below about 25 C. Unfortunately, Solid nio verted to Solid tantalum capacitors of the Surface mount bium capacitors were found to give increasing leakage current and shorted devices upon testing under Voltage at configuration. 35 Further eXtending the utility of Solid tantalum capacitors elevated temperatures (e.g., 85 C.). has been the introduction of inherently conductive polymers Niobium powders prepared recently appear much as counter electrode materials in place of the manganese improved with respect to impurity content and may be dioxide traditionally present in these devices. The high anodized at traditional anodizing temperatures (i.e., 80 C. electrical conductivity of inherently conductive polymers 40 to 90° C.) with the production of relatively flaw-free oxide gives rise to a significant reduction in equivalent Series at low anodizing voltages (60 volts or less). Particularly resistance and loSS of capacitance at higher frequencies in good dielectric properties, as indicated by wet-cell testing of Solid tantalum capacitors containing them. Solid tantalum anodized niobium anodes, are obtained through the use of capacitors with conductive polymer cathodes have the addi the electrolytes and methods described in co-pending tional advantage of being resistant to ignition in the event of 45 applications, Ser. No. 09/143,373 and Ser. No. 09/489,471. a short circuit occurring within the capacitor. Unfortunately, even Solid capacitors manufactured from The recent introduction of Surface mount, Solid tantalum relatively pure niobium powder are Subject to increasing capacitors having multiple anode elements in parallel to leakage current and short circuit failures on life test at reduce the equivalent Series resistance of the devices to well elevated temperature. The failures have been traced to the under 10 milliohms further extends the use of Solid tantalum 50 migration of oxygen from the anodic oxide into the niobium capacitors to applications where previously only ceramic or Substrate. This failure mechanism is also known in tantalum metallized film capacitors could be used. The tantalum capacitors, but the effect is much more pronounced with capacitors are generally much Smaller than the ceramic or niobium. metallized film capacitors which they replace. Fortunately, a Solution to the problem of oxygen migra The improvements in tantalum capacitors, described 55 tion from the anodic film to the valve metal Substrate has above, combined with the explosive growth in the computer been found and has been demonstrated for tantalum and and mobile telephone industries have resulted in the growth niobium. On Mar. 9, 2000, at the 20th Capacitor And in Worldwide demand for tantalum capacitors from a few Resistor Technology Symposium, Dr. Terrance Tripp pre million pieces per year in the 1950s to well over a billion sented a paper, entitled: “Tantalum Nitride: A New Substrate pieces per month today. In spite of the improvements in 60 for Solid Capacitors” (Authors: T. Tripp, R. Creasi, B. Cox; Surface area per unit weight made by the Suppliers of reprinted in the Symposium proceedings, on pages tantalum capacitor powder over the years, the demand for 256-262). This paper describes the anodic oxide-to-valve tantalum for capacitor purposes has grown Steadily since the metal Substrate thermally-driven oxygen migration problem 1950's.
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