Solid electrolytic capacitor with a deoxidized anode

Abstract

A capacitor including a capacitor element is provided. The capacitor element includes a deoxidized and sintered anode body formed from a powder having a specific charge of more than about 35,000 μF*V / g. Further, a dielectric is coated over the anode body, and a solid electrolyte is coated over the dielectric. The capacitor also exhibits a normalized aging leakage current of about 0.1% or less.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 082,071, filed on September 23, 2020, the entire content of which is incorporated herein by reference. Background Art

[0003] Solid electrolytic capacitors (e.g., tantalum capacitors) are typically made by pressing metal powder (e.g., tantalum) around a metal lead, sintering the pressed component, anodizing the sintered anode, and then applying a solid electrolyte. Unfortunately, one problem that many solid electrolytic capacitors have is that when using powders with a high specific charge (“CV / g”), the sintered anodes tend to have a relatively low level of compressive strength. This can lead to the formation of microcracks in the anode body, which can create potential failure points in the capacitor under extreme conditions (e.g., at high temperatures and / or high humidity levels). The complexity of these problems lies in that high - specific - charge powders are typically formed from particles with very small sizes and large surface areas, which results in the formation of small pores between the particles that are difficult to impregnate with dielectric and solid electrolyte solutions. Difficulty in impregnating such small pores leads to the solid electrolyte formed not adhering well to the dielectric coating and being less likely to achieve good surface coverage, which results in poor electrical performance of the capacitor. Therefore, there is a current need for a solid electrolytic capacitor with improved performance. Summary of the Invention

[0004] According to one embodiment of the present invention, a capacitor including a capacitor element is disclosed. The capacitor element includes: a deoxidized and sintered anode body formed from a powder having a specific charge of greater than about 35,000 μF*V / g. In addition, a dielectric is disposed over the anode body, and a solid electrolyte is disposed over the dielectric. The capacitor also exhibits a normalized aged leakage current of less than about 0.1%, which is determined according to the following equation:

[0005] Normalized aged leakage current = 100×(aged DCL / CV)

[0006] Wherein,

[0007] aged DCL is the leakage current measured for about 60 seconds at a temperature of about 23°C and the rated voltage after the capacitor has undergone a life test at a temperature of 85°C and the rated voltage for 120 hours and then recovered at a temperature of about 23°C for 60 minutes;

[0008] C is the initial capacitance (farads) determined at a temperature of about 23°C and an operating frequency of 120 Hz; and

[0009] V is the rated voltage (volts).

[0010] According to another embodiment of the present invention, a method for forming a solid electrolytic capacitor is disclosed. The method includes forming an anode by a process including: pressing a powder having a specific charge of more than about 35,000 μF*V / g into a porous anode body, subjecting the porous anode body to a deoxidation process to form a deoxidized anode body, and sintering the deoxidized anode body. Further, anodizing the deoxidized and sintered anode body to form a dielectric overlying the anode body, and forming a solid electrolyte overlying the dielectric.

[0011] Other features and aspects of the present invention are set forth in greater detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the remainder of this specification, a complete and enabling disclosure of the present invention, including the best mode thereof, for one of ordinary skill in the art is set forth in more detail. This specification makes reference to the following drawings, in which:

[0013] Figure 1 is a cross-sectional view of one embodiment of the capacitor of the present invention. DETAILED DESCRIPTION

[0014] One of ordinary skill in the art will appreciate that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present invention, which broader aspects are embodied in the exemplary construction.

[0015] Generally, the present invention relates to a capacitor capable of exhibiting good electrical performance under a variety of different conditions. More specifically, the capacitor includes a capacitor element that includes a sintered porous anode body and a dielectric overlying the anode body. The anode body is formed from a powder containing a valve metal (i.e., a metal capable of being oxidized) or a valve metal-based compound (e.g., tantalum, niobium, aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitrides thereof, etc.). The powder has a relatively high specific charge, such as more than about 35,000 μF*V / g, in some embodiments more than about 50,000 μF*V / g, in some embodiments from about 70,000 to about 350,000 μF*V / g, in some embodiments from about 80,000 to about 325,000 μF*V / g, and in some embodiments from about 100,000 to about 300,000 μF*V / g. As is known in the art, the specific charge can be determined by multiplying the capacitance by the anodization voltage employed and then dividing the product by the weight of the anodized electrode body.

[0016] During the formation of the capacitor, the anode body is pressed and subsequently subjected to deoxidation to minimize the oxygen present within the anode body. The resulting anode body can thus have a relatively low oxygen content. For example, the anode body can have no more than about 5,500 ppm of oxygen, no more than about 5,000 ppm of oxygen in some embodiments, and about 500 ppm to about 4,500 ppm of oxygen in some embodiments. The oxygen content can be measured by a LECO oxygen analyzer, and the oxygen content includes oxygen in the native oxide on the tantalum surface and bulk oxygen in the tantalum particles. The bulk oxygen content is controlled by the period of the tantalum lattice, and the bulk oxygen content increases linearly with increasing oxygen content in the tantalum until the solubility limit is reached. This method is described in “Critical Oxygen Content In Porous Anodes Of Solid Tantalum Capacitors”, Pozdeev-Freeman et al., Journal of Materials Science: Materials In Electronics 9, (1998) 309-311311 (Pozdeev-Freeman et al.’s “Critical Oxygen Content in Porous Anodes of Solid Tantalum Capacitors”, Journal of Materials Science: Materials in Electronics 9, (1998) 309-311), where X-ray diffraction analysis (XRDA) is used to measure the period of the tantalum lattice. Oxygen in the sintered tantalum anode may be confined to a thin native surface oxide, with little oxygen in the bulk of the tantalum.

[0017] The inventors have found that, through the selective control of specific aspects of the deoxidation process, the resulting capacitors can have a unique and beneficial set of properties. For example, the sintered anode body can exhibit a high level of compressive strength, such as above about 1 kilogram-force (“kgf”), above about 5 kgf in some embodiments, and about 10 kgf to about 100 kgf in some embodiments. Among other things, the high level of compressive strength can help limit the formation of microcracks in the anode body, which results in better electrical performance of the capacitor under various extreme conditions (such as at high temperature and / or humidity levels). Minimizing the oxygen content using the specific deoxidation process described herein can also enhance the degree of penetration of the dielectric and solid electrolyte, thereby further improving the electrical performance.

[0018] For example, a capacitor can exhibit low leakage current (“DCL”) under various conditions. More specifically, the capacitor can exhibit a DCL of only about 20 microamps (“μA”) or less, about 10 μA or less in some embodiments, about 5 μA or less in some embodiments, about 1 μA or less in some embodiments, about 0.5 μA or less in some embodiments, and from about 0.01 μA to about 0.3 μA in some embodiments, at a temperature of about 23 °C after being subjected to an applied voltage (e.g., the rated voltage or a multiple of the rated voltage, such as 1.1 × the rated voltage) for a period of time from about 5 seconds to about 500 seconds, and in some embodiments from 20 seconds to about 400 seconds (e.g., 60 seconds or 300 seconds). Of course, the absolute value of the DCL can depend on certain aspects of the capacitor, including the specific charge of the powder, the size of the capacitor element, etc. In this regard, the normalized DCL can be determined as a percentage of the nominal charge by the following equation:

[0019] Normalized DCL = 100 × (DCL / CV)

[0020] where C is the initial capacitance (in farads) and V is the rated voltage (in volts).

[0021] For example, the capacitors of the present invention can exhibit a normalized DCL of about 0.5% or less, about 0.2% or less in some embodiments, about 0.1% or less in some embodiments, about 0.09% or less in some embodiments, about 0.08% or less in some embodiments, and from about 0.01% to about 0.07% in some embodiments, as determined at a temperature of about 23 °C after being subjected to an applied voltage (e.g., the rated voltage or a multiple of the rated voltage, such as 1.1 × the rated voltage) for a period of time from about 5 seconds to about 500 seconds, and in some embodiments from 20 seconds to about 400 seconds (e.g., 60 seconds or 300 seconds).

[0022] Notably, even at high temperatures, low DCL values can remain stable. For example, even after exposure to a life test for a period of time at temperatures above about 80 °C and in some embodiments from about 85 °C to about 150 °C (e.g., about 85 °C, 105 °C, 125 °C, or 150 °C), the capacitor can exhibit an "aged" DCL value within the above range, such a period of time being, for example, more than about 50 hours, in some embodiments from about 100 hours to about 3,000 hours, and in some embodiments from about 120 hours to about 2,500 hours (e.g., 120, 250, 500, 750, or 1,000 hours). In one embodiment, for example, the aged DCL of a capacitor after exposure to a life test at a high temperature (e.g., about 85 °C) for 120 hours and then recovery at room temperature (e.g., about 23 °C) for 60 minutes can be about 0.5 μA or less, in some embodiments about 0.3 μA or less, in some embodiments about 0.25 μA or less, and in some embodiments about 0.2 μA or less, and in some embodiments from about 0.01 μA to about 0.1 μA. Similarly, the ratio of the aged DCL of a capacitor after exposure to a high temperature (e.g., about 85 °C) for up to 120 hours and then recovery at room temperature (e.g., about 23 °C) for 60 minutes to the initial DLC of the capacitor can be about 5 or less, in some embodiments about 3 or less, in some embodiments about 2 or less, in some embodiments about 1.5 or less, and in some embodiments from about 0.6 to about 1.2. Further, the normalized aged DCL of the capacitor can be determined as a percentage of the nominal charge by the following equation:

[0023] Normalized aged DCL = 100 × (aged DCL / CV)

[0024] wherein the aged DCL is the leakage current after exposure to a life test at 85 °C for 120 hours and then recovery at room temperature (about 23 °C) for 60 minutes, C is the initial capacitance (farads), and V is the rated voltage (volts).

[0025] The normalized aging average DCL can be about 0.1% or less, about 0.075% or less in some embodiments, about 0.07% or less in some embodiments, about 0.065% or less in some embodiments, about 0.06% or less in some embodiments, and about 0.001% to about 0.006% in some embodiments. Similarly, the ratio of the normalized aging DCL of the capacitor after exposure to high temperature (e.g., about 85 °C) for 120 hours and subsequent recovery for 60 minutes to the initial normalized aging DCL of the capacitor (e.g., at about 23 °C) can also be about 5 or less, about 3 or less in some embodiments, about 2 or less in some embodiments, about 1.5 or less in some embodiments, and about 0.6 to about 1.2 in some embodiments.

[0026] Other electrical properties of the capacitor can also be good and remain stable under various conditions. For example, the capacitor can exhibit a relatively low equivalent series resistance ("ESR") measured at an operating frequency of 100 kHz and a temperature of 23°C, such as about 200 mohms, less than about 150 mohms in some embodiments, from about 0.01 mohms to about 125 mohms in some embodiments, and from about 0.1 mohms to about 100 mohms in some embodiments. Even after being exposed to a temperature of about 80°C or higher, from about 100°C to about 150°C in some embodiments, and from about 105°C to about 130°C (e.g., 105°C or 125°C) in some embodiments for a relatively long period of time, such as about 100 hours or more, and from about 150 hours to about 3,000 hours (e.g., 3,000 hours) in some embodiments, the capacitance can still exhibit such an ESR value. In one embodiment, for example, the ratio of the ESR of the capacitor after being exposed to a high temperature (e.g., 105°C) for 3,000 hours to the initial ESR value of the capacitor (e.g., at 23°C) is about 2.0 or less, about 1.5 or less in some embodiments, and from about 1.0 to about 1.3 in some embodiments. Further, the ratio of the capacitance ("charge-discharge capacitance") after being subjected to repeated cycles of surge voltage to the initial capacitance value before such testing can be from about 0.7 to 1, from about 0.8 to 1 in some embodiments, from 0.85 to 1 in some embodiments, from about 0.9 to 1 in some embodiments, and from 0.91 to 0.99 in some embodiments. The surge voltage can be applied for 4,000 to 16,000 cycles (e.g., 4,000, 8,000, 12,000, or 16,000 cycles). In addition, even after being exposed to a high temperature of about 80°C or higher, from about 100°C to about 150°C in some embodiments, and from about 105°C to about 130°C (e.g., 105°C or 125°C) in some embodiments for a relatively long period of time, such as about 100 hours or more, and from about 150 hours to about 3,000 hours (e.g., 3,000 hours) in some embodiments, the capacitance can remain stable. In one embodiment, for example, the ratio of the capacitance after being exposed to a high temperature (e.g., 105°C) for 3,000 hours to the initial capacitance value (e.g., at 23°C) is from about 0.7 to 1, from about 0.8 to 1 in some embodiments, from about 0.9 to 1 in some embodiments, and from 0.91 to 0.99 in some embodiments. The actual capacitance value (dry) can vary, but the actual capacitance value measured at a frequency of 120 Hz is typically about 1 millifarad per square centimeter ("mF / cm2 ”) above, about 2 mF / cm in some embodiments 2 above, about 5 mF / cm in some embodiments 2 to about 50 mF / cm 2 and about 8 mF / cm in some embodiments 2 to about 20 mF / cm 2 .

[0027] The capacitor can also exhibit a high percentage of wet capacitance, which enables it to have only small capacitance losses and / or fluctuations in the presence of atmospheric humidity. This performance characteristic is quantified by the “wet-to-dry capacitance percentage,” which is determined by the following equation:

[0028] Wet-to-dry capacitance = (dry capacitance / wet capacitance) × 100

[0029] The capacitor can exhibit a wet-to-dry capacitance percentage of about 50% or more, about 60% or more in some embodiments, about 70% or more in some embodiments, and about 80% to 100% in some embodiments.

[0030] It is also believed that the loss factor of the capacitor can be maintained at a relatively low level. The dissipation factor generally refers to the losses that occur in a capacitor and is typically expressed as a percentage of the ideal capacitor performance. For example, the dissipation factor of a capacitor measured at a frequency of 120 Hz is generally about 250% or less, about 200% or less in some embodiments, and about 1% to about 180% in some embodiments. The capacitor can also be used in high-voltage applications, such as applications with a rated voltage of about 35 volts or more, about 50 volts or more in some embodiments, and about 60 volts to about 200 volts in some embodiments. For example, the capacitor can exhibit a relatively high “breakdown voltage” (the voltage at which the capacitor fails), such as about 60 volts or more, about 70 volts or more in some embodiments, about 80 volts or more in some embodiments, and about 100 volts to about 300 volts in some embodiments. Similarly, the capacitor can also withstand the relatively high surge currents common in high-voltage applications. For example, the peak surge current can be about 100 amperes or more, about 200 amperes or more in some embodiments, and about 300 amperes to about 800 amperes in some embodiments.

[0031] Various embodiments of the capacitor will now be described in more detail.

[0032] I. Capacitor element

[0033] A. Anode body

[0034] As described above, the anode body is formed from a powder containing a valve metal or a valve metal-based compound. For example, in one embodiment, the powder is formed from tantalum. If desired, a reduction process can be employed in which a tantalum salt (e.g., potassium heptafluorotantalate (K2TaF7), sodium heptafluorotantalate (Na2TaF7), tantalum pentachloride (TaCl5), etc.) is reacted with a reducing agent. The reducing agent can be provided in the form of a liquid, a gas (e.g., hydrogen), or a solid (such as a metal (e.g., sodium), a metal alloy, or a metal salt). For example, in one embodiment, a tantalum salt (e.g., TaCl5) can be heated at a temperature of about 900 °C to about 2,000 °C, in some embodiments about 1,000 °C to about 1,800 °C, and in some embodiments about 1,100 °C to about 1,600 °C to form a vapor that can be reduced in the presence of a gaseous reducing agent (e.g., hydrogen). Other details of such a reduction reaction can be described in Maeshima et al. WO2014 / 199480. After reduction, the product can be cooled, crushed, and washed to form a powder.

[0035] The powder can be a free-flowing, subdivided powder containing primary particles. Optionally, after subjecting the particles to 70 seconds of ultrasonic vibration, the median size (D50) of the primary particles of the powder is typically about 5 to about 250 nanometers, in some embodiments about 10 to about 200 nanometers, and in some embodiments about 20 to about 150 nanometers, as measured, for example, using a laser particle size distribution analyzer (e.g., LS 230) manufactured by BECKMAN COULTER Corporation. The primary particles typically have a three-dimensional granular shape (e.g., nodular or angular). Such particles typically have a relatively low "aspect ratio", which is the average diameter or width of the particle divided by the average thickness ("D / T"). For example, the aspect ratio of the particles can be about 4 or less, in some embodiments about 3 or less, and in some embodiments about 1 to about 2. In addition to the primary particles, the powder can also contain other types of particles, such as secondary particles formed by aggregating (or agglomerating) the primary particles. The median size (D50) of such secondary particles can be about 1 to about 500 micrometers, and in some embodiments about 10 to about 250 micrometers.

[0036] Agglomeration of the particles can occur by heating the particles and / or by using a binder. For example, agglomeration can occur at a temperature of from about 0 °C to about 40 °C, in some embodiments from about 5 °C to about 35 °C, and in some embodiments from about 15 °C to about 30 °C. Suitable binders can likewise include, for example, poly(vinyl butyral); poly(vinyl acetate); poly(vinyl alcohol); poly(vinyl pyrrolidone); cellulose polymers such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and methyl hydroxyethyl cellulose; atactic polypropylene, polyethylene; polyethylene glycol (e.g., Carbowax from Dow Chemical Co.); polystyrene, poly(butadiene / styrene); polyamides, polyimides, and polyacrylamides, high molecular weight polyethers; copolymers of ethylene oxide and propylene oxide; fluoropolymers such as polytetrafluoroethylene, polyvinylidene fluoride, and fluorinated olefin copolymers; acrylic polymers such as sodium polyacrylate, poly(lower alkyl acrylates), poly(lower alkyl methacrylates), and copolymers of lower alkyl acrylates and methacrylates; and fatty acids and waxes such as stearic acid and other soapy fatty acids, vegetable waxes, microcrystalline wax (purified paraffin wax), etc. If desired, the powder can also be doped with a sintering flame retardant in the presence of a dopant such as an aqueous acid (e.g., phosphoric acid). The amount of dopant added depends in part on the surface area of the powder, but is typically present in an amount not exceeding about 200 parts per million (ppm). The dopant can be added before, during, and / or after agglomeration. The powder can also be subjected to one or more deoxidation treatments. For example, the powder can be exposed to a getter material (e.g., magnesium) as described, for example, in U.S. Patent No. 4,960,471. The temperature at which deoxidation of the powder occurs can vary, but is typically in the range of about 700 °C to about 1,600 °C, in some embodiments from about 750 °C to about 1,200 °C, and in some embodiments from about 800 °C to about 1,000 °C. The total time of the deoxidation treatment can be in the range of about 20 minutes to about 3 hours.

[0037] The resulting powder has certain properties that enhance its ability to form a capacitor anode. For example, the specific surface area of the powder is typically from about 0.5 to about 10.0 m 2 / g, in some embodiments from about 0.7 to about 5.0 m 2 / g, and in some embodiments from about 2.0 to about 4.0 m 2 / g. Likewise, the bulk density of the powder can be from about 0.1 to about 0.8 grams per cubic centimeter (g / cm 3 ) and in some embodiments from about 0.2 to about 0.6 g / cm3 and, in some embodiments, from about 0.4 to about 0.6 vg / cm 3 .

[0038] Once the powder is formed, the resulting powder is typically pressed or compacted using any conventional powder pressing equipment to form pellets. For example, a die press can be employed, which is a single station compaction press containing a die and one or more punches. Alternatively, an anvil type compaction die using only a die and a single lower punch can be used. There are several basic types of single station compaction presses available for use, such as cam presses, toggle / link presses, and eccentric / crank presses with different performances (such as single action, double action, floating die, movable platen, opposed ram, screw, impact, hot pressing, coining, or sizing). The powder is typically compacted to a density of about 0.5 to about 20 g / cm 3 and, in some embodiments, from about 1 to about 15 g / cm 3 and, in some embodiments, from about 2 to about 10 g / cm 3 . The powder can be pressed around the anode lead, which can be in the form of a wire, sheet, etc. Alternatively, the lead can be simply connected to the surface of the anode body after lead formation. The lead can extend in the longitudinal direction of the anode body and can be formed of any conductive material (such as tantalum, niobium, aluminum, hafnium, titanium, etc., and their conductive oxides and / or nitrides). The connection of the lead can also be achieved using other known techniques, such as by welding the lead to the anode body or embedding the lead in the anode body during the formation process (e.g., before pressing and / or sintering). After compaction, any binder can be removed by heating the pellet under vacuum at a certain temperature (e.g., about 150 °C to about 500 °C) for several minutes. Alternatively, the binder can also be removed by contacting the pellet with an aqueous solution, such as Bishop et al. as described in U.S. Patent No. 6,197,252.

[0039] After removing the binder, the anode body can be subjected to a deoxidation process. For example, in one embodiment, the deoxidation process includes exposing the anode body to a getter material (e.g., magnesium, titanium, etc.), which can remove oxygen from the anode body through chemical reactions, adsorption, etc. More specifically, the anode body is first inserted into an encapsulation body (e.g., a tantalum box) that also contains the getter material. The atmosphere within the encapsulation body is typically an inert atmosphere (e.g., argon). To initiate deoxidation, the atmosphere within the encapsulation body is heated to a temperature sufficient to melt and / or vaporize the getter material and deoxidize the anode body. The temperature can vary depending on the specific charge of the anode powder, but is typically in the range of about 700 °C to about 1200 °C, in some embodiments about 750 °C to about 1,100 °C, and in some embodiments about 800 °C to about 1,000 °C. The total time for deoxidation can be in the range of about 20 minutes to about 3 hours. This can occur in one or more steps. After completion of deoxidation, the getter material typically evaporates and forms a precipitate on the walls of the encapsulation body. To ensure removal of the getter material, the anode body can also be subjected to one or more acid leaching steps, such as acid leaching steps with solutions of nitric acid, hydrofluoric acid, hydrogen peroxide, sulfuric acid, water, etc. or combinations thereof.

[0040] After deoxidation, the anode body can be sintered to form a porous integral mass. The anode body is typically sintered at a temperature of from about 700 °C to about 1,600 °C, in some embodiments from about 800 °C to about 1,500 °C, and in some embodiments from about 900 °C to about 1,200 °C for a time of from about 5 minutes to about 100 minutes, and in some embodiments from about 8 minutes to about 15 minutes. This can occur in one or more steps. If desired, sintering can occur in an atmosphere that limits the transfer of oxygen atoms to the anode. For example, sintering can occur in a reducing atmosphere (such as vacuum, inert gas, hydrogen, etc.). The pressure of the reducing atmosphere can be from about 10 Torr to about 2,000 Torr, in some embodiments from about 100 Torr to about 1,000 Torr, and in some embodiments from about 100 Torr to about 930 Torr. A mixture of hydrogen and other gases (e.g., argon or nitrogen) can also be employed. As described above, sintering of the anode body typically occurs after deoxidation. However, it should be understood that the anode body can also undergo one or more pre-sintering steps prior to oxidation to help provide the desired level of green strength for the deoxidation process. Such pre-sintering steps can be carried out under the same or different conditions as the sintering process that occurs after deoxidation. For example, pre-sintering can occur in one or more steps at a temperature of from about 700 °C to about 1,600 °C, in some embodiments from about 800 °C to about 1,500 °C, in some embodiments from about 900 °C to about 1,200 °C for a time of from about 5 minutes to about 100 minutes, and in some embodiments from about 8 minutes to about 15 minutes. Pre-sintering can also occur in a reducing atmosphere (such as in vacuum, inert gas, hydrogen, etc.).

[0041] B. Dielectric

[0042] The anode body is coated with a dielectric. The dielectric is formed by anodizing (anodizing) the sintered anode body such that a dielectric layer is formed above and / or within the anode body. For example, a tantalum (Ta) anode can be anodized to tantalum pentoxide (Ta2O5). Typically, anodization is performed by first applying a solution to the anode (such as by immersing the anode in an electrolyte). A solvent is typically employed, such as water (e.g., deionized water). To enhance ionic conductivity, a compound capable of dissociating in the solvent to form ions can be employed. Examples of such compounds include, for example, acids, such as those described below with reference to the electrolyte section. For example, an acid (e.g., phosphoric acid) can account for from about 0.01 wt% to about 5 wt% of the anodizing solution, in some embodiments from about 0.05 wt% to about 0.8 wt%, and in some embodiments from about 0.1 wt% to about 0.5 wt%. If desired, blends of acids can also be employed.

[0043] An electric current is passed through an anodizing solution to form a dielectric layer. The value of the forming voltage controls the thickness of the dielectric layer. For example, the power supply is initially set to a constant current mode until the desired voltage is reached. Then, the power supply can be switched to a constant potential mode to ensure that the desired dielectric thickness is formed over the entire surface of the anode. Of course, other methods can also be employed, such as pulsed constant potential method or step constant potential method. The forming voltage employed during anodizing is typically above about 20 volts, above about 30 volts in some embodiments, above about 35 volts in some embodiments, and from about 35 to about 70 volts in some embodiments, and the temperature is in the range of above about 10 °C, from about 20 °C to about 200 °C in some embodiments, and from about 30 °C to about 100 °C in some embodiments. The resulting dielectric layer can be formed on the surface of the anode and within the pores of the anode.

[0044] By selectively controlling the specific manner of forming the anode body, the inventors have found that the resulting capacitor can exhibit a high level of dielectric strength, which can improve capacitance stability. "Dielectric strength" generally refers to the ratio of the "breakdown voltage" of the capacitor (the voltage at which the capacitor fails, in volts, "V") to the thickness of the dielectric (in nanometers, "nm"). Capacitors generally exhibit a dielectric strength of above about 0.4 V / nm, above about 0.45 V / nm in some embodiments, above about 0.5 V / nm in some embodiments, from about 0.55 to about 1 V / nm in some embodiments, and from about 0.6 to about 0.9 V / nm in some embodiments. For example, a capacitor can exhibit a relatively high breakdown voltage, such as above about 30 volts, above about 35 volts in some embodiments, above about 50 volts in some embodiments, above about 65 volts in some embodiments, above about 85 volts in some embodiments, above about 90 volts in some embodiments, above about 95 volts in some embodiments, and from about 100 volts to about 300 volts in some embodiments, such as determined by increasing the applied voltage in 3-volt increments until the leakage current reaches 1 mA. Although the thickness of the dielectric can generally vary depending on the specific location of the anode body, for determining the dielectric strength, the "dielectric thickness" is generally considered to be the maximum thickness of the dielectric, and the thickness of the dielectric is generally in the range of about 50 to about 500 nm, in the range of about 80 to about 350 nm in some embodiments, and in the range of about 100 to about 300 nm in some embodiments. The dielectric thickness can be measured using a Zeiss Sigma FESEM at a magnification of 20,000x to 50,000x, where the sample is prepared by cutting the finished component in a plane perpendicular to the longest dimension of the finished component, and the thickness is measured at a location perpendicular to the cut through the dielectric layer.

[0045] C. Solid electrolyte

[0046] A solid electrolyte is disposed over the dielectric. The total thickness of the solid electrolyte is typically from about 1 to about 50 μm, and in some embodiments from about 5 to about 20 μm. The solid electrolyte can include one or more layers of a conductive inorganic oxide (e.g., manganese dioxide), a conductive polymer (e.g., a polyheterocycle such as polypyrrole, polythiophene, polyaniline, etc.), polyacetylene, poly(phenylene), polyphenolate, etc. In one embodiment, for example, the solid electrolyte can include manganese dioxide. As is known in the art, manganese dioxide can be formed by the pyrolytic decomposition of manganese nitrate (Mn(NO3)2), such as Sturmer et al. described in U.S. Patent No. 4,594,452. For example, the heating can occur in a furnace at a temperature of about 150°C to about 300°C, in some embodiments from about 180°C to about 290°C, and in some embodiments from about 190°C to about 260°C. The heating can be carried out in a wet or dry atmosphere. The conversion time depends on the furnace temperature, heat transfer rate, and atmosphere, but is typically about 3 to about 5 minutes. After pyrolysis, the leakage current may sometimes increase due to damage to the dielectric film during the deposition of manganese dioxide. To help further reduce this leakage, the capacitor can be reformed in an anodizing bath known in the art. For example, the capacitor can be immersed in an electrolyte such as that described above and then subjected to a DC current.

[0047] D. Moisture barrier layer

[0048] If desired, a moisture barrier layer can be disposed over the solid electrolyte. The moisture barrier layer can be formed from a variety of different materials, such as a hydrophobic elastomer, e.g., silicone, fluoropolymer, etc. Silicone polymers are particularly suitable for the moisture barrier layer of the present invention. These elastomers are typically derived from polysiloxanes, such as those having the following general formula:

[0049]

[0050] wherein,

[0051] x is an integer greater than 1; and

[0052] R1, R2, R3, R4, R5, R6, R7, and R8 are independently monovalent groups typically containing from 1 to about 20 carbon atoms, such as alkyl groups (e.g., methyl, ethyl, propyl, pentyl, octyl, undecyl, octadecyl, etc.); alkoxy groups (e.g., methoxy, ethoxy, propoxy, etc.); carboxymethyl groups (e.g., acetyl); cycloalkyl groups (e.g., cyclohexyl); alkenyl groups (e.g., vinyl, allyl, butenyl, hexenyl, etc.); aryl groups (e.g., phenyl, tolyl, xylyl, benzyl, 2-phenylethyl, etc.); and halogenated hydrocarbon groups (e.g., 3,3,3-trifluoropropyl, 3-chloropropyl, dichlorophenyl, etc.). Examples of such polysiloxanes can include, for example, polydimethylsiloxane ("PDMS"), polymethylhydrosiloxane, dimethyldiphenylpolysiloxane, dimethyl / methylphenylpolysiloxane, polymethylphenylsiloxane, methylphenyl / dimethylsiloxane, vinyl dimethyl-terminated polydimethylsiloxane, vinyl methyl / dimethylpolysiloxane, vinyl dimethyl-terminated vinyl methyl / dimethylpolysiloxane, divinyl methyl-terminated polydimethylsiloxane, vinyl phenyl methyl-terminated polydimethylsiloxane, dimethyl hydrogen-terminated polydimethylsiloxane, methyl hydrogen / dimethylpolysiloxane, methyl hydrogen-terminated methyl octyl polysiloxane, methyl hydrogen / phenyl methylpolysiloxane, fluorine-modified polysiloxane, etc. To form an elastomer, the polyorganosiloxane can be crosslinked using any known technique, such as catalytic curing (e.g., platinum catalyst), room temperature vulcanization, moisture curing, etc. The crosslinking agent can be an alkoxysilane such as Si-OR, where R is H, alkyl (e.g., methyl), hydrocarbon group, carboxyl group (e.g., acetyl), etc.

[0053] In addition to hydrophobicity, it is generally desirable for the material used to form the moisture barrier layer to have a relatively low modulus and a certain degree of flexibility, which can help absorb some of the thermal stress caused by the expansion of the housing, and also be able to withstand compressive forces. The flexibility of the material is characterized by a correspondingly low elastic modulus ("Young's modulus"), for example, a modulus of less than about 5000 kilopascals ("kPa") measured at a temperature of about 25 °C, about 1 to about 2000 kPa in some embodiments, and about 2 to about 500 kPa in some embodiments. The material also generally has a certain degree of strength such that it can maintain its shape even when subjected to compressive forces. For example, the tensile strength of the material measured at a temperature of about 25 °C can be about 1 to about 5000 kPa, about 10 to about 2000 kPa in some embodiments, and about 50 to about 1000 kPa in some embodiments. Under the conditions mentioned above, the hydrophobic elastomer can even further enhance the ability of the capacitor to function under extreme conditions.

[0054] To help obtain the desired flexibility and strength properties, non-conductive fillers can be employed in the moisture barrier layer. When such additives are used, they typically comprise from about 0.5 wt.% to about 30 wt.% of the moisture barrier layer, from about 1 wt.% to about 25 wt.% in some embodiments, and from about 2 wt.% to about 20 wt.% in some embodiments. The silicone elastomer comprises from about 70 wt% to about 99.5 wt% of the moisture barrier layer, from about 75 wt% to about 99 wt% in some embodiments, and from about 80 wt% to about 98 wt% in some embodiments. A specific example of such a filler includes, for example, silica. Although most forms of silica have a relatively hydrophilic surface due to the presence of silanol groups (Si-OH), the silica can optionally be surface-treated such that its surface contains (CH3) n -Si-groups (where n is an integer from 1 to 3), which further enhances the hydrophobicity of the moisture barrier layer. For example, the surface treatment agent can be an organosilicon compound monomer having a hydrolyzable group, or a partial hydrolyzate thereof. Examples of such compounds can include organosilazanes, silane coupling agents, etc., such as those described above.

[0055] The moisture barrier layer can be applied to any surface of the capacitor to provide the desired performance. For example, the moisture barrier layer can be located on the top surface, bottom surface, and / or side surface of the capacitor. The moisture barrier layer can equally be located on the front surface and / or back surface of the capacitor. The moisture barrier layer can cover the entire area of the surface region to which it is applied or only cover a portion of the surface region to which it is applied. In one embodiment, for example, the moisture barrier layer covers more than about 30% of the capacitor surface to which it is applied, more than about 40% in some embodiments, and more than about 50% in some embodiments.

[0056] Reference Figure 1 , for example, shows an embodiment of a capacitor 30 that includes a capacitor element 33 having a generally rectangular shape and including a front surface 36, a back surface 38, a top surface 37, a bottom surface 39, a first side surface 32, and a second side surface (not shown). In the illustrated embodiment, the anode lead 16 is embedded within the anode body 40 and extends longitudinally from the front surface 36 of the capacitor element 33. Alternatively, the anode lead 16 can simply be connected (e.g., welded) to the front surface 36 of the capacitor element 33. The capacitor element 33 includes a dielectric (not shown) overlying the anode body 40, a solid electrolyte 44 overlying the dielectric, and a cathode coating 46 overlying the solid electrolyte 44. As shown, except for the front surface 36, the solid electrolyte 44 and the cathode coating 46 are typically present at each surface of the capacitor 30. Of course, it should be understood that such layers can be applied to any surface of the capacitor and need not be applied in the manner shown.

[0057] The capacitor element 33 also includes an optional moisture barrier layer 63, which includes a hydrophobic material. In certain embodiments, the moisture barrier layer 63 covers the solid electrolyte 44 at the rear surface 38, the top surface 37, and the side surfaces (not shown). The moisture barrier layer 63 is also present at the front surface 36, although it may not necessarily cover the solid electrolyte at this surface, as described above. Of course, it should be understood that, as Figure 1 shown, the moisture barrier layer 63 does not need to be located on the surface of the capacitor element 33. In another embodiment, for example, the moisture barrier layer may be located only at the side surfaces of the capacitor element 33. Regardless of where the moisture barrier layer is located, the moisture barrier layer can cover any desired portion of the surface. For example, the moisture barrier layer can substantially cover all the surfaces on which they are located, such as covering more than about 90%, and in some embodiments more than about 95%. However, again, this is optional, and the layer does not have to cover most of the surface.

[0058] E. Other optional components

[0059] If desired, the capacitor element may also include other layers known in the art. For example, an adhesive layer may optionally be formed between the dielectric and the solid electrolyte. The adhesive layer is typically formed from a relatively insulating resin material (natural or synthetic). The specific resistivity of such a material can be greater than about 10 Ω·cm, in some embodiments greater than about 100 Ω·cm, in some embodiments greater than about 1,000 Ω·cm, in some embodiments greater than about 1×10 5 Ω·cm, and in some embodiments greater than about 1×10 10 Ω·cm. Some resin materials that can be used in the present invention include, but are not limited to, polyurethane, polystyrene, esters of unsaturated or saturated fatty acids (e.g., glycerol esters), etc. For example, suitable esters of fatty acids include, but are not limited to, esters of lauric acid, myristic acid, palmitic acid, stearic acid, eleostearic acid, oleic acid, linoleic acid, linolenic acid, aleuritic acid, shellac acid, etc. It has been found that these esters of fatty acids are particularly useful when used in relatively complex combinations to form a "drying oil", which allows the resulting film to rapidly polymerize into a stable layer. Such drying oils can include monoglycerides, diglycerides, and / or triglycerides, which have a glycerol backbone with one, two, and three esterified fatty acyl residues, respectively. For example, some suitable drying oils that can be used include, but are not limited to, olive oil, linseed oil, castor oil, tung oil, soybean oil, and shellac. These and other adhesive layer materials are described in more detail in Fife et al. U.S. Patent No. 6,674,635.

[0060] If desired, the component can also be separately applied with a carbon layer (e.g., graphite) and a silver layer. For example, the silver coating can act as a weldable conductor, contact layer, and / or charge collector of the capacitor, and the carbon coating can limit the contact of the silver coating with the solid electrolyte. These coatings can cover some or all of the solid electrolyte.

[0061] II. Terminations

[0062] Once formed, the capacitor element can be provided with terminations, especially when used in surface mount applications. For example, the capacitor can include an anode termination and a cathode termination, with the anode lead of the capacitor element electrically connected to the anode termination and the cathode of the capacitor element electrically connected to the cathode termination. Any conductive material can be used to form the terminations, such as conductive metals (e.g., copper, nickel, silver, nickel, zinc, tin, palladium, lead, copper, aluminum, molybdenum, titanium, iron, zirconium, magnesium, and their alloys). Particularly suitable conductive metals include, for example, copper, copper alloys (e.g., copper-zirconium, copper-magnesium, copper-zinc, or copper-iron), nickel, and nickel alloys (e.g., nickel-iron). The thickness of the terminations is typically selected to minimize the thickness of the capacitor. For example, the thickness of the terminations can be in the range of about 0.05 mm to about 1 mm, in some embodiments in the range of about 0.05 mm to about 0.5 mm, and in the range of about 0.07 mm to about 0.2 mm. An exemplary conductive material is a copper-iron alloy metal sheet available from Wieland (Germany). If desired, the surfaces of the terminations can be electroplated with nickel, silver, gold, tin, etc. as known in the art to ensure that the finished component can be mounted on a circuit board. In a particular embodiment, the two surfaces of the terminations are electroplated with bright nickel and bright silver respectively, and the mounting surface is also electroplated with a solder layer.

[0063] These terminations can be connected to the capacitor element using any technique known in the art. For example, in one embodiment, a lead frame defining the cathode termination and the anode termination can be provided. To attach the electrolytic capacitor element to the lead frame, a conductive adhesive can first be applied to the surface of the cathode termination. The conductive adhesive can include, for example, conductive metal particles contained in a resin composition. The metal particles can be silver, copper, gold, platinum, nickel, zinc, bismuth, etc. The resin composition can include a thermosetting resin (e.g., epoxy resin), a curing agent (e.g., acid anhydride), and a compound (e.g., silane compound). A suitable conductive adhesive can be in Osako et al.is described in U.S. Patent Application Publication No. 2006 / 0038304. Any of a variety of techniques can be used to apply the conductive adhesive to the cathode terminal. For example, printing techniques can be employed because of the practical and cost-saving benefits. The anode lead can also be electrically connected to the anode terminal using any technique known in the art (e.g., mechanical welding, laser welding, conductive adhesives, etc.). Once the anode lead is electrically connected to the anode terminal, the conductive adhesive can then be cured to ensure that the electrolytic capacitor element adheres sufficiently to the cathode terminal.

[0064] Referring again to Figure 1 , for example, the electrolytic capacitor 30 is shown as including an anode terminal 62 and a cathode terminal 72 that are electrically connected to the capacitor element 33. Although it can be in electrical contact with any surface of the capacitor element 33, the cathode terminal 72 in the illustrated embodiment is in electrical contact with the lower surface 39 via a conductive adhesive 90. More specifically, the cathode terminal 72 includes a first member 73 that is in electrical contact with and generally parallel to the lower surface 39 of the capacitor element 33. The anode terminal 62 likewise includes a first member 63 that is positioned substantially perpendicular to a second member 64. The first member 63 is in electrical contact with and generally parallel to the lower surface 39 of the capacitor element 33. The second member 64 includes a region 51 that carries the anode lead 16. Although not shown in Figure 1 , the region 51 can have a "U-shape" to further enhance surface contact and mechanical stability of the lead 16.

[0065] The terminals can be connected to the capacitor element using any technique known in the art. For example, in one embodiment, a lead frame defining the cathode terminal 72 and the anode terminal 62 can be provided. To attach the electrolytic capacitor element 33 to the lead frame, the conductive adhesive 90 can first be applied to the surface of the cathode terminal 72. The conductive adhesive 90 can include, for example, conductive metal particles contained in a resin composition. The metal particles can be silver, copper, gold, platinum, nickel, zinc, bismuth, etc. The resin composition can include a thermosetting resin (e.g., an epoxy resin), a curing agent (e.g., an acid anhydride), and a coupling agent (e.g., a silane coupling agent). Suitable conductive adhesives can be described in Osako et al. U.S. Patent Publication No. 2006 / 0038304. Any of a variety of techniques can be used to apply the conductive adhesive to the cathode terminal 72. For example, printing techniques can be employed because of the practical and cost-saving benefits.

[0066] Generally, various methods can be employed to attach the terminals to the capacitor. In one embodiment, for example, the second member 64 of the anode terminal 62 is first bent upward to Figure 1The position shown. Thereafter, the capacitor element 33 is positioned on the cathode terminal 72 such that the lower surface 39 of the capacitor element contacts the adhesive 90, and the anode lead 16 is received through the area 51. If desired, an insulating material (not shown) such as a plastic pad or plastic tape can be positioned between the lower surface 39 of the capacitor element 33 and the first component 63 of the anode terminal 62 to electrically insulate the anode terminal and the cathode terminal.

[0067] Then, the anode lead 16 is electrically connected to the area 51 using any technique known in the art such as mechanical welding, laser welding, conductive adhesives, etc. For example, the anode lead 16 can be welded to the anode terminal 62 using a laser. Lasers typically include a resonator that includes a laser medium capable of releasing photons by stimulated emission and an energy source capable of exciting the laser medium element. A suitable type of laser is one in which the laser medium consists of aluminum and yttrium garnet (YAG) doped with neodymium (Nd). The excited particle is the neodymium ion Nd 3+ . The energy source can provide continuous energy to the laser medium to emit a continuous laser beam or be capable of releasing energy to emit a pulsed laser beam. Once the anode lead 16 is electrically connected to the anode terminal 62, the conductive adhesive can then be cured. For example, heat and pressure can be applied using a hot pressing method to ensure that the electrolytic capacitor element 33 adheres sufficiently to the cathode terminal 72 through the adhesive.

[0068] III. Case

[0069] The capacitor element is typically encapsulated within a housing such that at least a portion of the anode terminal and the cathode terminal are exposed for mounting to a circuit board. For example, as Figure 1 shown, the capacitor element 33 is encapsulated within the housing 92 such that a portion of the anode terminal 62 and a portion of the cathode terminal 72 are exposed. The housing is typically formed from a thermosetting resin. Examples of such resins include, for example, epoxy resins, polyimide resins, melamine resins, urea formaldehyde resins, polyurethane resins, phenolic resins, polyester resins, etc. Epoxy resins are also particularly suitable. Other additives can also be employed such as photoinitiators, viscosity modifiers, suspension aids, pigments, stress reducing agents, non-conductive fillers, stabilizers, etc. For example, the non-conductive filler can include inorganic oxide particles such as silica, alumina, zirconia, magnesia, iron oxide, copper oxide, zeolites, silicates, clays (e.g., montmorillonite clay), etc., as well as their composites (e.g., alumina-coated silica particles) and mixtures.

[0070] The present invention can be better understood by reference to the following examples.

[0071] Test Procedures

[0072] Breakdown Voltage

[0073] The breakdown voltage is measured using a Keithley 2400 SourceMeter at a temperature of 23 °C ± 2 °C. The individual capacitors are charged with a constant current determined by the following equation:

[0074] Current (A) = Nominal capacitance (F) × dU / dt,

[0075] where dU / dt represents the voltage slope, which is typically set to 10 V / s. The voltage is measured during charging, and when the applied voltage drops by more than 10%, the maximum voltage value reached is recorded as the breakdown voltage.

[0076] Equivalent series resistance (ESR)

[0077] The equivalent series resistance can be measured using an HP4284A LCR meter with Kelvin leads at a 0 V DC bias and a 10 mVAC signal. The operating frequency is 100 kHz, and the temperature is 23 °C ± 2 °C.

[0078] Dissipation factor

[0079] The dissipation factor can be measured using an HP4284A LCR meter with Kelvin leads at a 0 V DC bias and a 10 mVAC signal. The operating frequency can be 120 Hz, and the temperature can be 23 °C ± 2 °C.

[0080] Capacitance

[0081] The capacitance is measured using a Keithley 3330 Precision LCZ Tester with Kelvin leads, a 2.2 V DC bias, and a 0.5 V peak-to-peak sinusoidal signal. The operating frequency is 120 Hz, and the temperature can be 23 °C ± 2 °C.

[0082] Leakage current

[0083] The leakage current can be measured using a leakage tester (YHP4140B) at a temperature of 23 °C ± 2 °C, with a 1 kOhm resistor limiting the charging current and measuring the leakage current at the rated voltage after at least 60 seconds (e.g., 60 seconds or 300 seconds).

[0084] Life test

[0085] The life test can be carried out for a period of 500 hours at a temperature of 85 °C and a multiple of 1.0 × the rated voltage. The number of test groups is typically 12 samples. During and after the life test, the aged samples can be allowed to recover at room temperature for approximately 60 minutes. Then, the "recovered" DCL can be measured at the rated voltage and a temperature of 23 °C ± 2 °C for approximately 60 seconds. The period of the intermediate "recovered" DCL measurement is typically 120 hours.

[0086] Example 1

[0087] An anode sample was formed using 100,000 μFV / g tantalum powder. Each anode sample was compacted to a density of 6.0 g / cm 3 and sintered at 1275 °C. After sintering, a deoxidation process was carried out at 860 °C, the leads were welded, and a secondary sintering process was carried out at 1275 °C. The resulting pellets had dimensions of 1.19 × 1.68 × 0.95 mm. The pellets were anodized to 36.8 V in a water / nitric acid electrolyte with a conductivity of 7.3 mS at a temperature of 85 °C to form a dielectric layer. Then, the anode was immersed in an aqueous manganese(II) nitrate solution (1190 kg / m 3 ) for 180 seconds and then decomposed at 250 °C. This step was repeated nine times. Thereafter, the anode was immersed in an aqueous manganese(II) nitrate solution (1300 kg / m 3 ) and then decomposed at 250 °C to obtain a MnO2 cathode. Finally, the anode was subsequently immersed in a graphite dispersion and a silver dispersion and dried. The finished capacitor elements were completed by conventional assembly techniques. Multiple components (500) of 22F / 16V capacitors were fabricated in this way.

[0088] Example 2

[0089] The capacitors were formed in the manner described in Example 1, except that the primary sintering process was omitted and the deoxidation process temperature was 960 °C. Multiple components (500) of 22F / 16V capacitors were fabricated in this way.

[0090] Example 3

[0091] The capacitors were formed in the manner described in Example 2, except that 150,000 μFV / g tantalum powder was used. The pellet anodes were anodized to 40 V. Multiple components (500) of 22F / 16V capacitors were fabricated in this way.

[0092] Example 4

[0093] The capacitors were formed in the manner described in Example 2, except that 200,000 μFV / g tantalum powder was used and the anodes were sintered at 1225 °C. The pellet anodes were anodized to 40 V. Multiple components (500) of 22F / 16V capacitors were fabricated in this way.

[0094] The average leakage current performance of the finished capacitors and the average leakage current performance after the life test were measured. The results are described below.

[0095] Table 1 DCL of the finished capacitors

[0096] Average DCL (μA) Normalized DCL (%) Example 1 0.332 0.094 Example 2 0.280 0.080 Example 3 0.224 0.064 Example 4 0.255 0.072

[0097] Table 2 DCL after the life test

[0098]

[0099] Without departing from the spirit and scope of the present invention, those of ordinary skill in the art may practice these and other modifications and variations of the present invention. Additionally, it should be understood that aspects of various embodiments may be substituted, in whole or in part, for each other. Furthermore, those of ordinary skill in the art will understand that the foregoing description is merely exemplary and is not intended to limit the present invention, which will be further described in the claims.

Claims

1. A solid electrolytic capacitor, the solid electrolytic capacitor comprising a capacitor element, the capacitor element comprising: A deoxidized and sintered anode body, the anode body being formed of tantalum powder having a specific charge of about 100,000 to about 350,000 μF*V / g; a dielectric, the dielectric including tantalum pentoxide and being formed at a formation voltage of more than about 35 volts, the dielectric being coated over the anode body; and a solid electrolyte, the solid electrolyte being coated over the dielectric, wherein the capacitor exhibits a dielectric strength of more than about 0.4 V / nm and an aged DCL of less than about 0.5 μA and a normalized aged leakage current of less than about 0.075%, the normalized aged leakage current being determined according to the following equation: Normalized aged leakage current = 100×(aged DCL / CV) wherein, the aged DCL is the leakage current measured for about 60 seconds at a temperature of about 23°C and a rated voltage after the capacitor has been subjected to a life test for 120 hours at a temperature of 85°C and the rated voltage and then recovered for 60 minutes at a temperature of about 23°C; C is the initial capacitance (farad) determined at a temperature of about 23°C and an operating frequency of 120 Hz; and V is the rated voltage (volt).

2. The solid electrolytic capacitor according to claim 1, wherein, The aged DCL is less than about 0.25 μA.

3. The solid electrolytic capacitor according to claim 1, wherein, The solid electrolyte includes manganese dioxide.

4. The solid electrolytic capacitor according to claim 1, wherein, The solid electrolytic capacitor further includes: a positive terminal, the positive terminal being electrically connected to the anode body; a negative terminal, the negative terminal being electrically connected to the solid electrolyte; and a housing, the housing encapsulating the capacitor element and exposing at least a portion of the positive terminal and the negative terminal.

5. The solid electrolytic capacitor according to claim 4, wherein, The housing is formed of a resinous material encapsulating the capacitor element.

6. The solid electrolytic capacitor according to claim 1, wherein, The tantalum powder has a specific charge ranging from about 100,000 μF*V / g to about 300,000 μF*V / g.

7. The solid electrolytic capacitor according to claim 1, wherein, A moisture barrier layer is coated over the solid electrolytic capacitor.

8. The solid electrolytic capacitor according to claim 1, wherein, There is no pre-sintering step before deoxidation.

9. The solid electrolytic capacitor according to claim 1, wherein, The deoxidized and sintered anode body exhibits a compressive strength of more than about 1 kilogram-force ("kgf").

10. A method for forming a solid electrolytic capacitor, the method comprising: forming an anode by a process including: pressing powder including tantalum having a specific charge of more than about 100,000 to 35,000 μF*V / g into a porous anode body, subjecting the porous anode body to a deoxidation process to form a deoxidized anode body, and sintering the deoxidized anode body; anodizing the deoxidized and sintered anode body at a formation voltage of more than about 35 volts to form a dielectric, the dielectric including tantalum pentoxide and being coated over the anode body; and forming a solid electrolyte coated over the dielectric; wherein the capacitor exhibits a dielectric strength of more than about 0.4 V / nm and an aged DCL of less than about 0.5 μA and a normalized aged leakage current of less than about 0.075%, the normalized aged leakage current being determined according to the following equation: Normalized aged leakage current = 100×(aged DCL / CV) wherein, The aged DCL is the leakage current measured for about 60 seconds at the temperature of about 23°C and the rated voltage after the capacitor as described has undergone a life test at a temperature of 85°C and the rated voltage for 120 hours and then recovered at a temperature of about 23°C for 60 minutes; C is the initial capacitance (farads) determined at a temperature of about 23°C and an operating frequency of 120 Hz; and V is the rated voltage (volts).

11. The method according to claim 10, wherein, The anode lead is connected to the porous anode body.

12. The method according to claim 10, wherein, The deoxidation process includes inserting the porous anode body into an encapsulation body containing a getter material.

13. The method according to claim 12, further comprising heating the atmosphere of the encapsulation body to a temperature of about 700°C to about 1200°C.

14. The method according to claim 10, wherein, Sintering is carried out at a temperature of about 700°C to about 1,600°C.

15. The method according to claim 10, further comprising pre-sintering the porous anode body before the deoxidation process.

16. The method according to claim 10, wherein, The aged DCL is about 0.25 μA or less.

17. The method according to claim 10, wherein, The powder has a specific charge ranging from about 100,000 μF*V / g to about 300,000 μF*V / g.

18. The method according to claim 10, wherein, The solid electrolyte includes manganese dioxide.

19. The method according to claim 10, wherein, The method further includes forming a moisture barrier layer over the solid electrolytic capacitor.

20. The method according to claim 10, wherein The method further includes not having a pre-sintering step before deoxidation.

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