Patent Description:
Electrolytic capacitors (e.g., tantalum capacitors) are increasingly being used in the design of circuits due to their volumetric efficiency, reliability, and process compatibility. For example, one type of capacitor that has been developed is a solid electrolytic capacitor element that includes a tantalum anode, dielectric layer, and conductive polymer solid electrolyte. In order to surface mount the capacitor element, the anode is connected to an anode termination and the solid electrolyte is connected to a cathode termination. Further, to help protect the capacitor from the exterior environment and provide it with good mechanical stability, the capacitor element is also encapsulated with a resinous casing material (e.g., epoxy resin) so that a portion of the anode and cathode terminations remain exposed for mounting to a surface. Unfortunately, it has been discovered that high temperatures that are often used during manufacture of the capacitor (e.g., reflow) can cause micro-cracks to form in the anode and/or cathode terminations. When exposed to high humidity levels, these micro-cracks can absorb moisture, which can result in oxidation of the conductive polymer solid electrolyte and lead to a rapid deterioration of the electrical properties.

As such, a need exists for an improved solid electrolytic capacitor for use at high humidity levels. For example, <CIT> discloses a solid electrolytic capacitor comprising a capacitor element that includes a sintered porous anode body, a dielectric that overlies the anode body, a solid electrolyte that overlies the dielectric, and a moisture barrier layer that overlies the solid electrolyte, wherein the solid electrolyte includes a conductive polymer and an organometallic coupling agent that contains an organic chain with at leat one reactive group bonded to a metal atom, and further wherein the moisture barrier layer includes a hydrophobic elastomer. <CIT> discloses a capacitor comprising an anode, a cathode comprising a conductive polymer layer and a work function modifier layer adjacent the conductive polymer layer and a dielectric layer between the anode and the cathode. <CIT> discloses a solid electrolytic capacitor equipped with the armoring resin which coats/covers the capacitive element.

The present invention provides a capacitor assembly defined in claim <NUM>. Preferred embodiments are reflected in the dependent claims.

In accordance with one embodiment of the present invention, a capacitor assembly is disclosed that comprises a solid electrolytic capacitor element that contains a sintered porous anode body, a dielectric that overlies the anode body, and a solid electrolyte that overlies the dielectric. An anode termination is in electrical connection with the anode body and a cathode termination is in electrical connection with the solid electrolyte. A first coating is disposed on at least a portion of the anode termination that contains an organometallic compound and a second coating is disposed on at least a portion of the cathode termination that contains an organometallic compound. Further, a casing material encapsulates the capacitor element and leaves exposed a mounting surface of the anode termination and the cathode termination.

Other features and aspects of the present invention are set forth in greater detail below.

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, which makes reference to the appended figure in which:
<FIG> is a schematic illustration of one embodiment of a capacitor that may be formed in accordance with the present invention.

Repeat use of references characters in the present specification and drawing is intended to represent same or analogous features or elements of the invention.

It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary construction.

Generally speaking, the present invention is directed to a capacitor assembly that contains a capacitor element that contains a sintered porous anode body, a dielectric overlying the anode body, and a solid electrolyte overlying the dielectric. The anode body is in electrical contact with an anode termination and the solid electrolyte is in electrical contact with a cathode termination. Further, the capacitor element is encapsulated with a casing material so that at least one surface of the anode termination and the cathode termination remains exposed for mounting to an electronic component (e.g., printed circuit board). Notably, a first coating is disposed on at least a portion of the anode termination and a second coating is disposed on at least a portion of the cathode termination. The first and second coatings contain an organometallic compound, which can improve the adhesion of the casing material to the terminations and thus help to reduce the number of micro-cracks that would otherwise form after exposure to high temperatures (e.g., during reflow), such as at a peak reflow temperature of from about <NUM> to about <NUM>, and in some embodiments, from <NUM> to about <NUM> (e.g., <NUM>).

Due to its unique structure, the resulting capacitor assembly is not highly sensitive to moisture and can thus exhibit excellent electrical properties even when exposed to high humidity levels, such as when placed into contact with an atmosphere having a relative humidity of about <NUM>% or more, in some embodiments about <NUM>% or more, in some embodiments about <NUM>% or more, and in some embodiments, about <NUM>% or more (e.g., about <NUM>% to about <NUM>%). Relative humidity may, for instance, be determined in accordance with ASTM E337-<NUM>, Method A (<NUM>). The humid atmosphere may be part of the internal atmosphere of the capacitor assembly itself, or it may be an external atmosphere to which the capacitor assembly is exposed during storage and/or use. The capacitor may, for instance, exhibit a relatively low equivalence series resistance ("ESR") when exposed to the high humidity atmosphere (e.g., <NUM>% relative humidity), such as about <NUM> mohms, in some embodiments less than about <NUM> mohms, in some embodiments from about <NUM> to about <NUM> mohms, and in some embodiments, from about <NUM> to about <NUM> mohms, measured at an operating frequency of <NUM>. The capacitor assembly may exhibit a DCL of only about <NUM> microamps ("µA") or less, in some embodiments about <NUM>µA or less, in some embodiments about <NUM>µA or less, and in some embodiments, from about <NUM> to about <NUM>µA. The capacitor assembly may also exhibit a high percentage of its wet capacitance, which enables it to have only a small capacitance loss and/or fluctuation in the presence of atmosphere humidity. This performance characteristic is quantified by the "wet-to-dry capacitance percentage", which is determined by the equation:.

The capacitor assembly may exhibit a wet-to-dry capacitance percentage of about <NUM>% or more, in some embodiments about <NUM>% or more, in some embodiments about <NUM>% or more, and in some embodiments, from about <NUM>% to <NUM>%. The dry capacitance may be about <NUM> nanoFarads per square centimeter ("nF/cm<NUM>") or more, in some embodiments about <NUM> nF/cm<NUM> or more, in some embodiments from about <NUM> to about <NUM>,<NUM> nF/cm<NUM>, and in some embodiments, from about <NUM> to about <NUM>,<NUM> nF/cm<NUM>, measured at a frequency of <NUM>.

Notably, the ESR, DCL, and capacitance values may even be maintained for a substantial amount of time at the high humidity levels. For example, the values may be maintained for about <NUM> hours or more, in some embodiments from about <NUM> hours to about <NUM> hours, and in some embodiments, from about <NUM> hours to about <NUM> hours (e.g., <NUM> hours, <NUM> hours, or <NUM> hours) when tested at a temperature of from about <NUM> to about <NUM>, and in some embodiments, from <NUM> to about <NUM> (e.g., <NUM>).

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

The capacitor element includes an anode that contains a dielectric formed on a sintered porous body. The porous anode body may be formed from a powder that contains a valve metal (i.e., metal that is capable of oxidation) or valve metal-based compound, such as tantalum, niobium, aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitrides thereof, and so forth. The powder is typically formed from a reduction process in which a tantalum salt (e.g., potassium fluotantalate (K<NUM>TaF<NUM>), sodium fluotantalate (Na<NUM>TaF<NUM>), tantalum pentachloride (TaCl<NUM>), etc.) is reacted with a reducing agent. The reducing agent may be provided in the form of a liquid, gas (e.g., hydrogen), or solid, such as a metal (e.g., sodium), metal alloy, or metal salt. In one embodiment, for instance, a tantalum salt (e.g., TaCl<NUM>) may be heated at a temperature of from about <NUM> to about <NUM>,<NUM>, in some embodiments from about <NUM> ,<NUM> to about <NUM> ,<NUM>, and in some embodiments, from about <NUM>,<NUM> to about <NUM> ,<NUM>, to form a vapor that can be reduced in the presence of a gaseous reducing agent (e.g., hydrogen). Additional details of such a reduction reaction may be described in <CIT>. After the reduction, the product may be cooled, crushed, and washed to form a powder.

The specific charge of the powder typically varies from about <NUM>,<NUM> to about <NUM>,<NUM> microFarads*Volts per gram ("µF*V/g") depending on the desired application For instance, in certain embodiments, a high charge powder may be employed that has a specific charge of from about <NUM>,<NUM> to about <NUM>,<NUM>µF*V/g, in some embodiments from about <NUM>,<NUM> to about <NUM>,<NUM>µF*V/g, and in some embodiments, from about <NUM>,<NUM> to about <NUM>,<NUM>µF*V/g. In other embodiments, a low charge powder may be employed that has a specific charge of from about <NUM>,<NUM> to about <NUM>,<NUM>µF*V/g, in some embodiments from about <NUM>,<NUM> to about <NUM>,<NUM>µF*V/g, and in some embodiments, from about <NUM>,<NUM> to about <NUM>,<NUM>µF*V/g. As is known in the art, the specific charge may be determined by multiplying capacitance by the anodizing voltage employed, and then dividing this product by the weight of the anodized electrode body.

The powder may be a free-flowing, finely divided powder that contains primary particles. The primary particles of the powder generally have a median size (D50) of from about <NUM> to about <NUM> nanometers, in some embodiments from about <NUM> to about <NUM> nanometers, and in some embodiments, from about <NUM> to about <NUM> nanometers, such as determined using a laser particle size distribution analyzer made by BECKMAN COULTER Corporation (e.g., LS-<NUM>), optionally after subjecting the particles to an ultrasonic wave vibration of <NUM> seconds. 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 particles divided by the average thickness ("D/T"). For example, the aspect ratio of the particles may be about <NUM> or less, in some embodiments about <NUM> or less, and in some embodiments, from about <NUM> to about <NUM>. In addition to primary particles, the powder may also contain other types of particles, such as secondary particles formed by aggregating (or agglomerating) the primary particles. Such secondary particles may have a median size (D50) of from about <NUM> to about <NUM> micrometers, and in some embodiments, from about <NUM> to about <NUM> micrometers.

Agglomeration of the particles may occur by heating the particles and/or through the use of a binder. For example, agglomeration may occur at a temperature of from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>. Suitable binders may likewise include, for instance, poly(vinyl butyral); poly(vinyl acetate); poly(vinyl alcohol); poly(vinyl pyrollidone); cellulosic polymers, such as carboxymethylcellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and methylhydroxyethyl 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 fluoro-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 and other soapy fatty acids, vegetable wax, microwaxes (purified paraffins), etc..

The resulting powder may be compacted to form a pellet using any conventional powder press device. For example, a press mold may be employed that is a single station compaction press containing a die and one or multiple punches. Alternatively, anvil-type compaction press molds may be used that use only a die and single lower punch. Single station compaction press molds are available in several basic types, such as cam, toggle/knuckle and eccentric/crank presses with varying capabilities, such as single action, double action, floating die, movable platen, opposed ram, screw, impact, hot pressing, coining or sizing. The powder may be compacted around an anode lead, which may be in the form of a wire, sheet, etc. The lead may extend in a longitudinal direction from the anode body and may be formed from any electrically conductive material, such as tantalum, niobium, aluminum, hafnium, titanium, etc., as well as electrically conductive oxides and/or nitrides of thereof. Connection of the lead may also be accomplished using other known techniques, such as by welding the lead to the body or embedding it within the anode body during formation (e.g., prior to compaction and/or sintering).

Any binder may be removed after pressing by heating the pellet under vacuum at a certain temperature (e.g., from about <NUM> to about <NUM>) for several minutes. Alternatively, the binder may also be removed by contacting the pellet with an aqueous solution, such as described in <CIT>. Thereafter, the pellet is sintered to form a porous, integral mass. The pellet is typically sintered at a temperature of from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>, for a time of from about <NUM> minutes to about <NUM> minutes, and in some embodiments, from about <NUM> minutes to about <NUM> minutes. This may occur in one or more steps. If desired, sintering may occur in an atmosphere that limits the transfer of oxygen atoms to the anode. For example, sintering may occur in a reducing atmosphere, such as in a vacuum, inert gas, hydrogen, etc. The reducing atmosphere may be at a pressure of from about <NUM> Torr to about <NUM> Torr, in some embodiments from about <NUM> Torr to about <NUM> Torr, and in some embodiments, from about <NUM> Torr to about <NUM> Torr. Mixtures of hydrogen and other gases (e.g., argon or nitrogen) may also be employed.

The anode is also coated with a dielectric. The dielectric may be formed by anodically oxidizing ("anodizing") the sintered anode so that a dielectric layer is formed over and/or within the anode. For example, a tantalum (Ta) anode may be anodized to tantalum pentoxide (Ta<NUM>O<NUM>). Typically, anodization is performed by initially applying a solution to the anode, such as by dipping anode into the electrolyte. A solvent is generally employed, such as water (e.g., deionized water). To enhance ionic conductivity, a compound may be employed that is capable of dissociating in the solvent to form ions. Examples of such compounds include, for instance, acids, such as described below with respect to the electrolyte. For example, an acid (e.g., phosphoric acid) may constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the anodizing solution. If desired, blends of acids may also be employed.

A current is passed through the anodizing solution to form the dielectric layer. The value of the formation voltage manages the thickness of the dielectric layer. For example, the power supply may be initially set up at a galvanostatic mode until the required voltage is reached. Thereafter, the power supply may be switched to a potentiostatic mode to ensure that the desired dielectric thickness is formed over the entire surface of the anode. Of course, other known methods may also be employed, such as pulse or step potentiostatic methods. The voltage at which anodic oxidation occurs typically ranges from about <NUM> to about <NUM> V, and in some embodiments, from about <NUM> to about <NUM> V, and in some embodiments, from about <NUM> to about <NUM> V. During oxidation, the anodizing solution can be kept at an elevated temperature, such as about <NUM> or more, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>. Anodic oxidation can also be done at ambient temperature or lower. The resulting dielectric layer may be formed on a surface of the anode and within its pores.

Although not required, in certain embodiments, the dielectric layer may possess a differential thickness throughout the anode in that it possesses a first portion that overlies an external surface of the anode and a second portion that overlies an interior surface of the anode. In such embodiments, the first portion is selectively formed so that its thickness is greater than that of the second portion. It should be understood, however, that the thickness of the dielectric layer need not be uniform within a particular region. Certain portions of the dielectric layer adjacent to the external surface may, for example, actually be thinner than certain portions of the layer at the interior surface, and vice versa. Nevertheless, the dielectric layer may be formed such that at least a portion of the layer at the external surface has a greater thickness than at least a portion at the interior surface. Although the exact difference in these thicknesses may vary depending on the particular application, the ratio of the thickness of the first portion to the thickness of the second portion is typically from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>.

To form a dielectric layer having a differential thickness, a multi-stage process is generally employed. In each stage of the process, the sintered anode is anodically oxidized ("anodized") to form a dielectric layer (e.g., tantalum pentoxide). During the first stage of anodization, a relatively small forming voltage is typically employed to ensure that the desired dielectric thickness is achieved for the inner region, such as forming voltages ranging from about <NUM> to about <NUM> volts, in some embodiments from about <NUM> to about <NUM> volts, and in some embodiments, from about <NUM> to about <NUM> volts. Thereafter, the sintered body may then be anodically oxidized in a second stage of the process to increase the thickness of the dielectric to the desired level. This is generally accomplished by anodizing in an electrolyte at a higher voltage than employed during the first stage, such as at forming voltages ranging from about <NUM> to about <NUM> volts, in some embodiments from about <NUM> to about <NUM> volts, and in some embodiments, from about <NUM> to about <NUM> volts. During the first and/or second stages, the electrolyte may be kept at a temperature within the range of from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>.

The electrolytes employed during the first and second stages of the anodization process may be the same or different. Typically, however, it is desired to employ different solutions to help better facilitate the attainment of a higher thickness at the outer portions of the dielectric layer. For example, it may be desired that the electrolyte employed in the second stage has a lower ionic conductivity than the electrolyte employed in the first stage to prevent a significant amount of oxide film from forming on the internal surface of anode. In this regard, the electrolyte employed during the first stage may contain an acidic compound, such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc. Such an electrolyte may have an electrical conductivity of from about <NUM> to about <NUM>/cm, in some embodiments from about <NUM> to about <NUM>/cm, and in some embodiments, from about <NUM> to about <NUM>/cm, determined at a temperature of <NUM>. The electrolyte employed during the second stage typically contains a salt of a weak acid so that the hydronium ion concentration increases in the pores as a result of charge passage therein. Ion transport or diffusion is such that the weak acid anion moves into the pores as necessary to balance the electrical charges. As a result, the concentration of the principal conducting species (hydronium ion) is reduced in the establishment of equilibrium between the hydronium ion, acid anion, and undissociated acid, thus forms a poorer-conducting species. The reduction in the concentration of the conducting species results in a relatively high voltage drop in the electrolyte, which hinders further anodization in the interior while a thicker oxide layer, is being built up on the outside to a higher formation voltage in the region of continued high conductivity. Suitable weak acid salts may include, for instance, ammonium or alkali metal salts (e.g., sodium, potassium, etc.) of boric acid, boronic acid, acetic acid, oxalic acid, lactic acid, adipic acid, etc. Particularly suitable salts include sodium tetraborate and ammonium pentaborate. Such electrolytes typically have an electrical conductivity of from about <NUM> to about <NUM>/cm, in some embodiments from about <NUM> to about <NUM>/cm, and in some embodiments, from about <NUM> to about <NUM>/cm, determined at a temperature of <NUM>.

If desired, each stage of anodization may be repeated for one or more cycles to achieve the desired dielectric thickness. Furthermore, the anode may also be rinsed or washed with another solvent (e.g., water) after the first and/or second stages to remove the electrolyte.

As indicated above, a solid electrolyte overlies the dielectric and generally functions as the cathode for the capacitor assembly. The solid electrolyte may include materials as is known in the art, such as conductive polymers (e.g., polypyrroles, polythiophenes, polyanilines, etc.), manganese dioxide, and so forth. Typically, however, the solid electrolyte contains one or more layers containing extrinsically and/or intrinsically conductive polymer particles. One benefit of employing such particles is that they can minimize the presence of ionic species (e.g., Fe<NUM>+ or Fe<NUM>+) produced during conventional in situ polymerization processes, which can cause dielectric breakdown under high electric field due to ionic migration. Thus, by applying the conductive polymer as pre-polymerized particles rather through in situ polymerization, the resulting capacitor may exhibit a relatively high "breakdown voltage. " If desired, the solid electrolyte may be formed from one or multiple layers. When multiple layers are employed, it is possible that one or more of the layers includes a conductive polymer formed by in situ polymerization. However, when it is desired to achieve very high breakdown voltages, the present inventors have discovered that the solid electrolyte is formed primarily from the conductive particles described above, and that it is generally free of conductive polymers formed via in situ polymerization. Regardless of the number of layers employed, the resulting solid electrolyte typically has a total a thickness of from about <NUM> micrometer (µm) to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>.

Thiophene polymers are particularly suitable for use in the solid electrolyte. For instance, an "extrinsically" conductive thiophene polymer is employed in the solid electrolyte of the present invention that has repeating units of the following formula (III):
<CHM>
wherein,.

The polymers of formula (III) are generally considered to be "extrinsically" conductive to the extent that they typically require the presence of a separate counterion that is not covalently bound to the polymer. The counterion may be a monomeric or polymeric anion that counteracts the charge of the conductive polymer. Polymeric anions can, for example, be anions of polymeric carboxylic acids (e.g., polyacrylic acids, polymethacrylic acid, polymaleic acids, etc.); polymeric sulfonic acids (e.g., polystyrene sulfonic acids ("PSS"), polyvinyl sulfonic acids, etc.); and so forth. The acids may also be copolymers, such as copolymers of vinyl carboxylic and vinyl sulfonic acids with other polymerizable monomers, such as acrylic acid esters and styrene. Likewise, suitable monomeric anions include, for example, anions of C<NUM> to C<NUM> alkane sulfonic acids (e.g., dodecane sulfonic acid); aliphatic perfluorosulfonic acids (e.g., trifluoromethane sulfonic acid, perfluorobutane sulfonic acid or perfluorooctane sulfonic acid); aliphatic C<NUM> to C<NUM> carboxylic acids (e.g., <NUM>-ethyl-hexylcarboxylic acid); aliphatic perfluorocarboxylic acids (e.g., trifluoroacetic acid or perfluorooctanoic acid); aromatic sulfonic acids optionally substituted by C<NUM> to C<NUM> alkyl groups (e.g., benzene sulfonic acid, o-toluene sulfonic acid, p-toluene sulfonic acid or dodecylbenzene sulfonic acid); cycloalkane sulfonic acids (e.g., camphor sulfonic acid or tetrafluoroborates, hexafluorophosphates, perchlorates, hexafluoroantimonates, hexafluoroarsenates or hexachloroantimonates); and so forth. Particularly suitable counteranions are polymeric anions, such as a polymeric carboxylic or sulfonic acid (e.g., polystyrene sulfonic acid ("PSS")). The molecular weight of such polymeric anions typically ranges from about <NUM>,<NUM> to about <NUM>,<NUM>,<NUM>, and in some embodiments, from about <NUM>,<NUM> to about <NUM>,<NUM>.

Intrinsically conductive polymers may also be employed that have a positive charge located on the main chain that is at least partially compensated by anions covalently bound to the polymer. For example, one example of a suitable intrinsically conductive thiophene polymer may have repeating units of the following formula (IV):
<CHM>
wherein,.

In one particular embodiment, Z in formula (IV) is a sulfonate ion such that the intrinsically conductive polymer contains repeating units of the following formula (V):
<CHM>
wherein, R and X are defined above. In formula (IV) or (V), a is preferably <NUM> and b is preferably <NUM> or <NUM>. Likewise, X is preferably sodium or potassium.

If desired, the polymer may be a copolymer that contains other types of repeating units. In such embodiments, the repeating units of formula (IV) typically constitute about <NUM> mol. % or more, in some embodiments from about <NUM> mol. % to about <NUM> mol. %, and in some embodiments, from about <NUM> mol. % to about <NUM> mol. % of the total amount of repeating units in the copolymer. Of course, the polymer may also be a homopolymer to the extent that it contains <NUM> mol. % of the repeating units of formula (IV). Specific examples of such homopolymers include poly(<NUM>-(<NUM>,<NUM>-dihydrothieno-[<NUM>,<NUM>-b][<NUM>,<NUM>]dioxin-<NUM>-ylmethoxy)-<NUM>-butane-sulphonic acid, salt) and poly(<NUM>-(<NUM>,<NUM>-dihydrothieno-[<NUM>,<NUM>-b][l,<NUM>]dioxin-<NUM>-ylmethoxy)-l-propanesulphonic acid, salt).

Regardless of the particular nature of the polymer, the resulting conductive polymer particles typically have an average size (e.g., diameter) of from about <NUM> to about <NUM> nanometers, in some embodiments from about <NUM> to about <NUM> nanometers, and in some embodiments, from about <NUM> to about <NUM> nanometers. The diameter of the particles may be determined using known techniques, such as by ultracentrifuge, laser diffraction, etc. The shape of the particles may likewise vary. In one particular embodiment, for instance, the particles are spherical in shape. However, it should be understood that other shapes are also contemplated by the present invention, such as plates, rods, discs, bars, tubes, irregular shapes, etc..

Although not necessarily required, the conductive polymer particles may be applied in the form of a dispersion. The concentration of the conductive polymer in the dispersion may vary depending on the desired viscosity of the dispersion and the particular manner in which the dispersion is to be applied to the capacitor element. Typically, however, the polymer constitutes from about <NUM> to about <NUM> wt. %, in some embodiments from about <NUM> to about <NUM> wt. %, and in some embodiments, from about <NUM> to about <NUM> wt. % of the dispersion. The dispersion may also contain one or more components to enhance the overall properties of the resulting solid electrolyte. For example, the dispersion may contain a binder to further enhance the adhesive nature of the polymeric layer and also increase the stability of the particles within the dispersion. The binder may be organic in nature, such as polyvinyl alcohols, polyvinyl pyrrolidones, polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates, polyacrylic acid esters, polyacrylic acid amides, polymethacrylic acid esters, polymethacrylic acid amides, polyacrylonitriles, styrene/acrylic acid ester, vinyl acetate/acrylic acid ester and ethylene/vinyl acetate copolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers, polyesters, polycarbonates, polyurethanes, polyamides, polyimides, polysulfones, melamine formaldehyde resins, epoxide resins, silicone resins or celluloses. Crosslinking agents may also be employed to enhance the adhesion capacity of the binders. Such crosslinking agents may include, for instance, melamine compounds, masked isocyanates or crosslinkable polymers, such as polyurethanes, polyacrylates or polyolefins, and subsequent crosslinking. Dispersion agents may also be employed to facilitate the ability to apply the layer to the anode. Suitable dispersion agents include solvents, such as aliphatic alcohols (e.g., methanol, ethanol, i-propanol and butanol), aliphatic ketones (e.g., acetone and methyl ethyl ketones), aliphatic carboxylic acid esters (e.g., ethyl acetate and butyl acetate), aromatic hydrocarbons (e.g., toluene and xylene), aliphatic hydrocarbons (e.g., hexane, heptane and cyclohexane), chlorinated hydrocarbons (e.g., dichloromethane and dichloroethane), aliphatic nitriles (e.g., acetonitrile), aliphatic sulfoxides and sulfones (e.g., dimethyl sulfoxide and sulfolane), aliphatic carboxylic acid amides (e.g., methylacetamide, dimethylacetamide and dimethylformamide), aliphatic and araliphatic ethers (e.g., diethylether and anisole), water, and mixtures of any of the foregoing solvents. A particularly suitable dispersion agent is water.

In addition to those mentioned above, still other ingredients may also be used in the dispersion. For example, conventional fillers may be used that have a size of from about <NUM> nanometers to about <NUM> micrometers, in some embodiments from about <NUM> nanometers to about <NUM> micrometers, and in some embodiments, from about <NUM> nanometers to about <NUM> micrometers. Examples of such fillers include calcium carbonate, silicates, silica, calcium or barium sulfate, aluminum hydroxide, glass fibers or bulbs, wood flour, cellulose powder carbon black, electrically conductive polymers, etc. The fillers may be introduced into the dispersion in powder form, but may also be present in another form, such as fibers.

Surface-active substances may also be employed in the dispersion, such as ionic or non-ionic surfactants. Furthermore, adhesives may be employed, such as organofunctional silanes or their hydrolysates, for example <NUM>-glycidoxypropyltrialkoxysilane, <NUM>-aminopropyl-triethoxysilane, <NUM>-mercaptopropyltrimethoxysilane, <NUM>-metacryloxypropyltrimethoxysilane, vinyltrimethoxysilane or octyltriethoxysilane. The dispersion may also contain additives that increase conductivity, such as ether group-containing compounds (e.g., tetrahydrofuran), lactone group-containing compounds (e.g., γ-butyrolactone or γ-valerolactone), amide or lactam group-containing compounds (e.g., caprolactam, N-methylcaprolactam, N,N-dimethylacetamide, N-methylacetamide, N,N-dimethylformamide (DMF), N-methylformamide, N-methylformanilide, N-methylpyrrolidone (NMP), N-octylpyrrolidone, or pyrrolidone), sulfones and sulfoxides (e.g., sulfolane (tetramethylenesulfone) or dimethylsulfoxide (DMSO)), sugar or sugar derivatives (e.g., saccharose, glucose, fructose, or lactose), sugar alcohols (e.g., sorbitol or mannitol), furan derivatives (e.g., <NUM>-furancarboxylic acid or <NUM>-furancarboxylic acid), an alcohols (e.g., ethylene glycol, glycerol, di- or triethylene glycol).

The dispersion may be applied using a variety of known techniques, such as by spin coating, impregnation, pouring, dropwise application, injection, spraying, doctor blading, brushing, printing (e.g., ink-jet, screen, or pad printing), or dipping. The viscosity of the dispersion is typically from about <NUM> to about <NUM>,<NUM> mPas (measured at a shear rate of <NUM>-<NUM>), in some embodiments from about <NUM> to about <NUM>,<NUM> mPas, in some embodiments from about <NUM> to about <NUM>,<NUM> mPas, and in some embodiments, from about <NUM> to about <NUM> mPas.

The solid electrolyte is generally formed from one or more "inner" conductive polymer layers. The term "inner" in this context refers to one or more layers that overly the dielectric, whether directly or via another layer (e.g., pre-coat layer). One or multiple inner layers may be employed. For example, the solid electrolyte typically contains from <NUM> to <NUM>, in some embodiments from <NUM> to <NUM>, and in some embodiments, from about <NUM> to <NUM> inner layers (e.g., <NUM> layers). The inner layer(s) may, for example, contain intrinsically and/or extrinsically conductive polymer particles such as described above. For instance, such particles may constitute about <NUM> wt. % or more, in some embodiments about <NUM> wt. % or more, and in some embodiments, about <NUM> wt. % or more (e.g., <NUM> wt. %) of the inner layer(s). In alternative embodiments, the inner layer(s) may contain an in-situ polymerized conductive polymer. In such embodiments, the in-situ polymerized polymers may constitute about <NUM> wt. % or more, in some embodiments about <NUM> wt. % or more, and in some embodiments, about <NUM> wt. % or more (e.g., <NUM> wt. %) of the inner layer(s).

The solid electrolyte may also contain one or more optional "outer" conductive polymer layers that overly the inner layer(s) and are formed from a different material. For example, the outer layer(s) may contain extrinsically conductive polymer particles. In one particular embodiment, the outer layer(s) are formed primarily from such extrinsically conductive polymer particles in that they constitute about <NUM> wt. % or more, in some embodiments about <NUM> wt. % or more, and in some embodiments, about <NUM> wt. % or more (e.g., <NUM> wt. %) of a respective outer layer. One or multiple outer layers may be employed. For example, the solid electrolyte may contain from <NUM> to <NUM>, in some embodiments from <NUM> to <NUM>, and in some embodiments, from about <NUM> to <NUM> outer layers, each of which may optionally be formed from a dispersion of the extrinsically conductive polymer particles.

An external polymer coating may also overly the solid electrolyte. The external polymer coating generally contains one or more layers formed from pre-polymerized conductive polymer particles such as described above (e.g., dispersion of extrinsically conductive polymer particles). The external coating may be able to further penetrate into the edge region of the capacitor body to increase the adhesion to the dielectric and result in a more mechanically robust part, which may reduce equivalent series resistance and leakage current. Because it is generally intended to improve the degree of edge coverage rather to impregnate the interior of the anode body, the particles used in the external coating typically have a larger size than those employed in the solid electrolyte. For example, the ratio of the average size of the particles employed in the external polymer coating to the average size of the particles employed in any dispersion of the solid electrolyte is typically from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>. For example, the particles employed in the dispersion of the external coating may have an average size of from about <NUM> to about <NUM> nanometers, in some embodiments from about <NUM> to about <NUM> nanometers, and in some embodiments, from about <NUM> to about <NUM> nanometers.

If desired, a crosslinking agent may also be employed in the external polymer coating to enhance the degree of adhesion to the solid electrolyte. Typically, the crosslinking agent is applied prior to application of the dispersion used in the external coating. Suitable crosslinking agents are described, for instance, in <CIT> and include, for instance, amines (e.g., diamines, triamines, oligomer amines, polyamines, etc.); polyvalent metal cations, such as salts or compounds of Mg, Al, Ca, Fe, Cr, Mn, Ba, Ti, Co, Ni, Cu, Ru, Ce or Zn, phosphonium compounds, sulfonium compounds, etc. Particularly suitable examples include, for instance, <NUM>,<NUM>-diaminocyclohexane, <NUM>,<NUM>-bis(amino-methyl)cyclohexane, ethylenediamine, <NUM>,<NUM>-hexanediamine, <NUM>,<NUM>-heptanediamine, <NUM>,<NUM>-octanediamine, <NUM>,<NUM>-nonanediamine, <NUM>,<NUM>-decanediamine, <NUM>,<NUM>-dodecanediamine, N,N-dimethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-<NUM>,<NUM>-butanediamine, etc., as well as mixtures thereof.

The crosslinking agent is typically applied from a solution or dispersion whose pH is from <NUM> to <NUM>, in some embodiments from <NUM> to <NUM>, in some embodiments, from <NUM> to <NUM>, as determined at <NUM>. Acidic compounds may be employed to help achieve the desired pH level. Examples of solvents or dispersants for the crosslinking agent include water or organic solvents, such as alcohols, ketones, carboxylic esters, etc. The crosslinking agent may be applied to the capacitor body by any known process, such as spin-coating, impregnation, casting, dropwise application, spray application, vapor deposition, sputtering, sublimation, knife-coating, painting or printing, for example inkjet, screen or pad printing. Once applied, the crosslinking agent may be dried prior to application of the polymer dispersion. This process may then be repeated until the desired thickness is achieved. For example, the total thickness of the entire external polymer coating, including the crosslinking agent and dispersion layers, may range from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>.

If desired, the capacitor element may also employ a cathode coating that overlies the solid electrolyte and other optional layers (e.g., external polymer coating). The cathode coating may contain a metal particle layer includes a plurality of conductive metal particles dispersed within a resinous polymer matrix. The particles typically constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the layer, while the resinous polymer matrix typically constitutes from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the layer.

The conductive metal particles may be formed from a variety of different metals, such as copper, nickel, silver, nickel, zinc, tin, lead, copper, aluminum, molybdenum, titanium, iron, zirconium, magnesium, etc., as well as alloys thereof. Silver is a particularly suitable conductive metal for use in the layer. The metal particles often have a relatively small size, such as an average size of from about <NUM> to about <NUM> micrometers, in some embodiments from about <NUM> to about <NUM> micrometers, and in some embodiments, from about <NUM> to about <NUM> micrometers. Typically, only one metal particle layer is employed, although it should be understood that multiple layers may be employed if so desired. The total thickness of such layer(s) is typically within the range of from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>.

The resinous polymer matrix typically includes a polymer, which may be thermoplastic or thermosetting in nature. Typically, however, the polymer is selected so that it can act as a barrier to electromigration of silver ions, and also so that it contains a relatively small amount of polar groups to minimize the degree of water adsorption in the cathode coating. In this regard, the present inventors have found that vinyl acetal polymers are particularly suitable for this purpose, such as polyvinyl butyral, polyvinyl formal, etc. Polyvinyl butyral, for instance, may be formed by reacting polyvinyl alcohol with an aldehyde (e.g., butyraldehyde). Because this reaction is not typically complete, polyvinyl butyral will generally have a residual hydroxyl content. By minimizing this content, however, the polymer can possess a lesser degree of strong polar groups, which would otherwise result in a high degree of moisture adsorption and result in silver ion migration. For instance, the residual hydroxyl content in polyvinyl acetal may be about <NUM> mol. % or less, in some embodiments about <NUM> mol. % or less, and in some embodiments, from about <NUM> mol. % to about <NUM> mol. One commercially available example of such a polymer is available from Sekisui Chemical Co. under the designation "BH-S" (polyvinyl butyral).

To form the cathode coating, a conductive paste is typically applied to the capacitor that overlies the solid electrolyte. One or more organic solvents are generally employed in the paste. A variety of different organic solvents may generally be employed, such as glycols (e.g., propylene glycol, butylene glycol, triethylene glycol, hexylene glycol, polyethylene glycols, ethoxydiglycol, and dipropyleneglycol); glycol ethers (e.g., methyl glycol ether, ethyl glycol ether, and isopropyl glycol ether); ethers (e.g., diethyl ether and tetrahydrofuran); alcohols (e.g., benzyl alcohol, methanol, ethanol, n-propanol, iso-propanol, and butanol); triglycerides; ketones (e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethyl acetate, butyl acetate, diethylene glycol ether acetate, and methoxypropyl acetate); amides (e.g., dimethylformamide, dimethylacetamide, dimethylcaprylic/capric fatty acid amide and N-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile, butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethyl sulfoxide (DMSO) and sulfolane); etc., as well as mixtures thereof. The organic solvent(s) typically constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. of the paste. Typically, the metal particles constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the paste, and the resinous polymer matrix constitutes from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the paste.

The paste may have a relatively low viscosity, allowing it to be readily handled and applied to a capacitor element. The viscosity may, for instance, range from about <NUM> to about <NUM>,<NUM> centipoise, in some embodiments from about <NUM> to about <NUM>,<NUM> centipoise, and in some embodiments, from about <NUM> to about <NUM>,<NUM> centipoise, such as measured with a Brookfield DV-<NUM> viscometer (cone and plate) operating at a speed of <NUM> rpm and a temperature of <NUM>. If desired, thickeners or other viscosity modifiers may be employed in the paste to increase or decrease viscosity. Further, the thickness of the applied paste may also be relatively thin and still achieve the desired properties. For example, the thickness of the paste may be from about <NUM> to about <NUM> micrometers, in some embodiments from about <NUM> to about <NUM> micrometers, and in some embodiments, from about <NUM> to about <NUM> micrometers. Once applied, the metal paste may be optionally dried to remove certain components, such as the organic solvents. For instance, drying may occur at a temperature of from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>.

If desired, the capacitor may also contain other layers as is known in the art. In certain embodiments, for instance, a carbon layer (e.g., graphite) may be positioned between the solid electrolyte and the silver layer that can help further limit contact of the silver layer with the solid electrolyte. In addition, a pre-coat layer may be employed in certain embodiments that overlies the dielectric and includes an organometallic compound, such as described in more detail below.

Once the capacitor element is formed, the capacitor assembly may be provided with terminations. For example, the capacitor assembly may contain an anode termination to which an anode lead of the capacitor element is electrically connected and a cathode termination to which the cathode of the capacitor element is electrically connected. Any conductive material may be employed to form the terminations, such as a conductive metal (e.g., copper, nickel, silver, nickel, zinc, tin, palladium, lead, copper, aluminum, molybdenum, titanium, iron, zirconium, magnesium, and alloys thereof). Particularly suitable conductive metals include, for instance, 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 generally selected to minimize the thickness of the capacitor. For instance, the thickness of the terminations may range from about <NUM> to about <NUM> millimeter, in some embodiments from about <NUM> to about <NUM> millimeters, and from about <NUM> to about <NUM> millimeters. One exemplary conductive material is a copper-iron alloy metal plate available from Wieland (Germany). If desired, the surface of the terminations may be electroplated with nickel, silver, gold, tin, etc. as is known in the art to ensure that the final part is mountable to the circuit board. In one particular embodiment, both surfaces of the terminations are plated with nickel and silver flashes, respectively, while the mounting surface is also plated with a tin solder layer.

Regardless of the particular materials used to form the terminations, at least a portion of the anode termination contains a first coating and at least a portion of the cathode termination contains a second coating. The first and coating may be formed from the same or different materials. Regardless, both the first and second coatings contain an organometallic compound, which have the following general formula:
<CHM>
wherein,.

In certain embodiments, R<NUM>, R<NUM>, and R<NUM> may a hydroxyalkyl (e.g., OCH<NUM>). In other embodiments, however, R<NUM> may be an alkyl (e.g., CH<NUM>) and R<NUM> and R<NUM> may a hydroxyalkyl (e.g., OCH<NUM>).

Further, in certain embodiments, M may be silicon so that the organometallic compound is an organosilane compound, such as an alkoxysilane. Suitable alkoxysilanes may include, for instance, <NUM>-aminopropyltrimethoxysilane, <NUM>-aminopropyltriethoxysilane, <NUM>-aminopropylmethyldimethoxysilane, <NUM>-aminopropylmethyldiethoxysilane, <NUM>-(<NUM>-aminoethyl)aminopropyltrimethoxysilane, <NUM>-mercaptopropyltrimethoxysilane, <NUM>-mercaptopropyltriethoxysilane, <NUM>-mercaptopropylmethyldimethoxysilane, <NUM>-mercaptopropylmethyldiethoxysilane, glycidoxymethyltrimethoxysilane, glycidoxymethyltriethoxysilane, glycidoxymethyltripropoxysilane, glycidoxymethyltributoxysilane, β-glycidoxyethyltrimethoxysilane, β-glycidoxyethyltriethoxysilane, β-glycidoxyethyl-tripropoxysilane, β-glycidoxyethyltributoxysilane, β-glycidoxyethyltrimethoxysilane, α-glycidoxyethyltriethoxysilane, α-glycidoxyethyltripropoxysilane, α-glycidoxyethyltributoxysilane, γ-glycidoxypropyl-trimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyl-tripropoxysilane, γ-glycidoxypropyltributoxysilane, β-glycidoxypropyltrimethoxysilane, β-glycidoxypropyl-triethoxysilane, β-glycidoxypropyltripropoxysilane, α-glycidoxypropyltributoxysilane, α-glycidoxypropyltrimethoxysilane, α-glycidoxypropyltriethoxysilane, α-glycidoxypropyl-tripropoxysilane, α-glycidoxypropyltributoxysilane, γ-glycidoxybutyltrimethoxysilane, δ-glycidoxybutyltriethoxysilane, δ-glycidoxybutyltripropoxysilane, δ-glycidoxybutyl-tributoxysilane, δ-glycidoxybutyltrimethoxysilane, γ-glycidoxybutyltriethoxysilane, γ-glycidoxybutyltripropoxysilane, γ-propoxybutyltributoxysilane, δ-glycidoxybutyltrimethoxysilane, δ-glycidoxybutyltriethoxysilane, δ-glycidoxybutyltripropoxysilane, α-glycidoxybutyltrimethoxysilane, α-glycidoxybutyltriethoxysilane, α-glycidoxybutyltripropoxysilane, α-glycidoxybutyltributoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)-methyltrimethoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)methyl-triethoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)methyltripropoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)-methyltributoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)ethyl-trimethoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)ethyl-triethoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)ethyltripropoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)ethyltributoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)propyltrimethoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)propyltriethoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)propyltripropoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)propyltributoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)butyltrimethoxysilane, (<NUM>,<NUM>-epoxycyclohexy) butyltriethoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)butyltripropoxysilane, (<NUM>,<NUM>-epoxycyclohexyl)butyltributoxysilane, and so forth.

The particular manner in which the first and second coatings are applied to their respective terminations may vary as desired. In one particular embodiment, an organometallic compound is dissolved in an organic solvent to form a solution, which can then be coated onto a termination. Suitable coating techniques may include, for instance, screen-printing, dipping, electrophoretic coating, spraying, etc. The organic solvent may vary, but is typically an alcohol, such as methanol, ethanol, etc. Organometallic compounds may constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the solution. Solvents may likewise constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the solution. The particular location of a coating on a given termination may also vary as desired. Typically, it is desired that at least one surface of a termination (e.g., anode termination and/or cathode termination) that is in contact with the casing material contains a coating. For example, the upper surface, lower surface, and/or edges of a termination may contain a coating. The coating may cover the entire surface(s) of a termination, or it may be applied in a pattern. In particular embodiments of the present invention, each surface of the anode termination contains the first coating and each surface of the cathode termination contains the second coating. Once applied, the coatings may then be cured to ensure the desired degree of adhesion to the terminations. Curing may occur before, after, and/or during the process in which the casing material is applied. Typically, the curing process is performed at a relatively high temperature, such as a temperature of from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>.

Referring to <FIG>, one embodiment of a capacitor assembly <NUM> is shown as including an anode termination <NUM> and a cathode termination <NUM> in electrical connection with a capacitor element <NUM>. Although it may be in electrical contact with any of the surfaces of the capacitor element <NUM>, the cathode termination <NUM> in the illustrated embodiment is in electrical contact with the lower surface <NUM> via a conductive adhesive. More specifically, the cathode termination <NUM> contains a first component <NUM> that is in electrical contact and generally parallel with the lower surface <NUM> of the capacitor element <NUM>. The cathode termination <NUM> may also contain a second component <NUM> that is substantially perpendicular to the first component <NUM> and in electrical contract with a rear surface <NUM> of the capacitor element <NUM>. The anode termination <NUM> likewise contains a first component <NUM> positioned substantially perpendicular to a second component <NUM>. The first component <NUM> is in electrical contact and generally parallel with the lower surface <NUM> of the capacitor element <NUM>. The second component <NUM> contains a region <NUM> that carries an anode lead <NUM>. As discussed above, at least a portion of the anode termination <NUM> (e.g., first component <NUM> and/or second component <NUM>) contains the first coating (not shown) and at least a portion of the cathode termination <NUM> (e.g., first component <NUM> and/or second component <NUM>) may contain the second coating (not shown).

A variety of methods may generally be employed to attach the terminations. In one embodiment, for example, the second component <NUM> of the anode termination <NUM> is initially bent upward to the position shown in <FIG>. Thereafter, the capacitor element <NUM> is positioned on the cathode termination <NUM> so that its lower surface <NUM> contacts the adhesive and the anode lead <NUM> is received by the region <NUM>. If desired, an insulating material (not shown), such as a plastic pad or tape, may be positioned between the lower surface <NUM> of the capacitor element <NUM> and the first component <NUM> of the anode termination <NUM> to electrically isolate the anode and cathode terminations. The anode lead <NUM> is then electrically connected to the region <NUM> using any technique known in the art, such as mechanical welding, laser welding, conductive adhesives, etc. For example, the anode lead <NUM> may be welded to the anode termination <NUM> using a laser. Lasers generally contain resonators that include a laser medium capable of releasing photons by stimulated emission and an energy source that excites the elements of the laser medium. One type of suitable laser is one in which the laser medium consist of an aluminum and yttrium garnet (YAG), doped with neodymium (Nd). The excited particles are neodymium ions Nd<NUM>+. The energy source may provide continuous energy to the laser medium to emit a continuous laser beam or energy discharges to emit a pulsed laser beam. Upon electrically connecting the anode lead <NUM> to the anode termination <NUM>, the conductive adhesive may then be cured. For example, a heat press may be used to apply heat and pressure to ensure that the electrolytic capacitor element <NUM> is adequately adhered to the cathode termination <NUM> by the adhesive.

The capacitor element is generally encapsulated with a casing material so that at least a portion of the anode and cathode terminations are exposed for mounting onto a circuit board. As shown in <FIG>, for instance, the capacitor element <NUM> may be encapsulated within a casing material <NUM> so that a portion of the anode termination <NUM> and a portion of the cathode termination <NUM> are exposed.

In certain embodiments, the casing material may contain an epoxy composition that contains one or more inorganic oxide fillers and a resinous material that includes one more epoxy resins optionally crosslinked with a co-reactant (hardener). To help improve the overall moisture resistance of the casing material, the content of the inorganic oxide fillers is maintained at a high level, such as about <NUM> wt. % or more, in some embodiments about <NUM> wt. % or more, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the composition. The nature of the inorganic oxide fillers may vary, such as silica, alumina, zirconia, magnesium oxides, iron oxides (e.g., iron hydroxide oxide yellow), titanium oxides (e.g., titanium dioxide), zinc oxides (e.g., boron zinc hydroxide oxide), copper oxides, zeolites, silicates, clays (e.g., smectite clay), etc., as well as composites (e.g., alumina-coated silica particles) and mixtures thereof. Regardless of the particular fillers employed, however, a substantial portion, if not all, of the inorganic oxide fillers is typically in the form of vitreous silica, which is believed to further improve the moisture resistance of the casing material due to its high purity and relatively simple chemical form. Vitreous silica may, for instance, constitute about <NUM> wt. % or more, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the total weight of fillers employed in the composition, as well as from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the entire composition. Of course, other forms of silica may also be employed in combination with the vitreous silica, such as quartz, fumed silica, cristabolite, etc..

The resinous material typically constitutes from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the composition. Generally speaking, any of a variety of different types of epoxy resins may be employed in the present invention. Examples of suitable epoxy resins include, for instance, bisphenol A type epoxy resins, bisphenol F type epoxy resins, phenol novolac type epoxy resins, orthocresol novolac type epoxy resins, brominated epoxy resins and biphenyl type epoxy resins, cyclic aliphatic epoxy resins, glycidyl ester type epoxy resins, glycidylamine type epoxy resins, cresol novolac type epoxy resins, naphthalene type epoxy resins, phenol aralkyl type epoxy resins, cyclopentadiene type epoxy resins, heterocyclic epoxy resins, etc. To help provide the desired degree of moisture resistance, however, it is particularly desirable to employ epoxy phenol novolac ("EPN") resins, which are glycidyl ethers of phenolic novolac resins. These resins can be prepared, for example, by reaction of phenols with an excess of formaldehyde in the presence of an acidic catalyst to produce the phenolic novolac resin. Novolac epoxy resins are then prepared by reacting the phenolic novolac resin with epichlorihydrin in the presence of sodium hydroxide. Specific examples of the novolac-type epoxy resins include a phenol-novolac epoxy resin, cresol-novolac epoxy resin, naphthol-novolac epoxy resin, naphtholphenol co-condensation novolac epoxy resin, naphthol-cresol co-condensation novolac epoxy resin, brominated phenol-novolac epoxy resin, etc. Regardless of the type of resin selected, the resulting phenolic novolac epoxy resins typically have more than two oxirane groups and can be used to produce cured coating compositions with a high crosslinking density, which can be particularly suitable for enhancing moisture resistance. One such phenolic novolac epoxy resin is poly[(phenyl glycidyl ether)-co-formaldehyde]. Other suitable resins are commercially available under the trade designation ARALDITE (e.g., GY289, EPN <NUM>, EP <NUM>, EPN <NUM>, and EPN <NUM>) from Huntsman.

As indicated, the epoxy resin may optionally be crosslinked with a co-reactant (hardener) to further improve the mechanical properties of the composition and also enhance its overall moisture resistance as noted above. Examples of such co-reactants may include, for instance, polyamides, amidoamines (e.g., aromatic amidoamines such as aminobenzamides, aminobenzanilides, and aminobenzenesulfonamides), aromatic diamines (e.g., diaminodiphenylmethane, diaminodiphenylsulfone, etc.), aminobenzoates (e.g., trimethylene glycol di-p-aminobenzoate and neopentyl glycol di-p-aminobenzoate), aliphatic amines (e.g., triethylenetetramine, isophoronediamine), cycloaliphatic amines (e.g., isophorone diamine), imidazole derivatives, guanidines (e.g., tetramethylguanidine), carboxylic acid anhydrides (e.g., methylhexahydrophthalic anhydride), carboxylic acid hydrazides (e.g., adipic acid hydrazide), phenolic-novolac resins (e.g., phenol novolac, cresol novolac, etc.), carboxylic acid amides, etc., as well as combinations thereof. Phenolic-novolac resins may be particularly suitable for use in the present invention.

Apart from the components noted above, it should be understood that still other additives may also be employed in the epoxy composition used to form the casing, such as photoinitiators, viscosity modifiers, suspension aiding agents, pigments, stress reducing agents, coupling agents (e.g., silane coupling agents), stabilizers, etc. When employed, such additives typically constitute from about <NUM> to about <NUM> wt. % of the total composition.

The particular manner in which the casing material is applied to the capacitor body may vary as desired. In one particular embodiment, the capacitor element is placed in a mold and the casing material is applied to the capacitor element so that it occupies the spaces defined by the mold and leaves exposed at least a portion of the anode and cathode terminations. The casing material may be initially provided in the form of a single or multiple compositions. For instance, a first composition may contain the epoxy resin and the second composition may contain the co-reactant. Regardless, once it is applied, the casing material may be heated or allowed to stand at ambient temperatures so that the epoxy resin is allowed to crosslink with the co-reactant, which thereby causes the epoxy composition to cure and harden into the desired shape of the case. For instance, the composition may be heated to a temperature of from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>.

Although by no means required, a moisture barrier layer may also be employed that coats all or a portion of the casing material. The moisture barrier layer is generally formed from a hydrophobic elastomer, such as silicones, fluoropolymers, etc. Silicone elastomers are particularly suitable for use in the moisture barrier layer of the present invention. Such elastomers are typically derived from polyorganosiloxanes, such as those having the following general formula:
<CHM>
wherein,.

In addition to being hydrophobic, it is generally desired that the material used to form the moisture barrier layer has a relatively low modulus and a certain degree of flexibility, which can help absorb some of the thermal stresses caused by expansion of the casing and also allow it to be subjected to compressive forces. The flexibility of the material may be characterized by a corresponding low modulus of elasticity ("Young's modulus"), such as about <NUM>,<NUM> kilopascals ("kPa") or less, in some embodiments from about <NUM> to about <NUM>,<NUM> kPa, and in some embodiments, from about <NUM> to about <NUM> kPa, measured at a temperature of about <NUM>. The material also typically possesses a certain degree of strength that allows it to retain its shape even when subjected to compressive forces. For example, the material may possess a tensile strength of from about <NUM> to about <NUM>,<NUM> kPa, in some embodiments from about <NUM> to about <NUM>,<NUM> kPa, and in some embodiments, from about <NUM> to about <NUM>,<NUM> kPa, measured at a temperature of about <NUM>. With the conditions noted above, the hydrophobic elastomer can even further enhance the ability of the capacitor to function under extreme conditions.

To help achieve the desired flexibility and strength properties, a nonconductive filler may be employed in the moisture barrier layer. When employed, such additives typically constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the moisture barrier layer. The silicone elastomer may constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the moisture barrier layer. One particular example of such a filler includes, for instance, silica. While most forms of silica contain a relatively hydrophilic surface due to the presence of silanol groups (Si-OH), the silica may optionally be surface treated so that its surface contains (CH<NUM>)n-Si- groups, wherein n is an integer of <NUM> to <NUM>, which further enhances the hydrophobicity of the moisture barrier layer. The surface treatment agent may, for example, be an organosilicon compound monomer having a hydrolyzable group or a partial hydrolyzate thereof. Examples of such compounds may include organosilazanes, silane coupling agents such as described above, etc..

Due to its unique construction, the resulting capacitor assembly can exhibit a variety of beneficial properties. For example, the dissipation factor of the capacitor assembly may be maintained at relatively low levels. The dissipation factor generally refers to losses that occur in the capacitor and is usually expressed as a percentage of the ideal capacitor performance. For example, the dissipation factor of the capacitor of the present invention is typically from about <NUM>% to about <NUM>%, in some embodiments from about <NUM>% to about <NUM>%, and in some embodiments, from about <NUM>% to about <NUM>%, as determined at a frequency of <NUM>. The capacitor assembly may also be able to be employed in high voltage applications, such as at rated voltages of about <NUM> volts or more, in some embodiments about <NUM> volts or more, and in some embodiments, from about <NUM> volts to about <NUM> volts. The capacitor assembly may, for example, exhibit a relatively high "breakdown voltage" (voltage at which the capacitor fails), such as about <NUM> volts or more, in some embodiments about <NUM> volts or more, in some embodiments about <NUM> volts or more, and in some embodiments, from about <NUM> to about <NUM> volts. Likewise, the capacitor assembly may also be able to withstand relatively high surge currents, which is also common in high voltage applications. The peak surge current may be, for example, about <NUM> Amps or more, in some embodiments about <NUM> Amps or more, and in some embodiments, and in some embodiments, from about <NUM> Amps to about <NUM> Amps.

The present invention may be better understood by reference to the following examples.

Equivalence series resistance may be measured using a Keithley <NUM> Precision LCZ meter with Kelvin Leads <NUM> volt DC bias and a <NUM> volt peak to peak sinusoidal signal. The operating frequency may <NUM> and the temperature may be <NUM> ± <NUM>.

The dissipation factor may be measured using a Keithley <NUM> Precision LCZ meter with Kelvin Leads with <NUM> volt DC bias and a <NUM> volt peak to peak sinusoidal signal. The operating frequency may be <NUM> and the temperature may be <NUM> ± <NUM>.

The capacitance may be measured using a Keithley <NUM> Precision LCZ meter with Kelvin Leads with <NUM> volt DC bias and a <NUM> volt peak to peak sinusoidal signal. The operating frequency may be <NUM> and the temperature may be <NUM> ± <NUM>.

Leakage current may be measured using a leakage test meter at a temperature of <NUM> ± <NUM> and at the rated voltage (e.g., <NUM> volts) after a minimum of <NUM> seconds (e.g., <NUM> seconds, <NUM> seconds).

Moisture sensitivity level testing (J-STD-020E) may be conducted (<NUM> parts) after exposure to a temperature of <NUM> and <NUM>% relative humidity for a period of <NUM> hours, <NUM> hours. Electrical parameters and external cracks via using optical microscope can be recorded after the reflow at recovered samples and then compared.

<NUM>,<NUM>µFV/g tantalum powder was used to form anode samples. Each anode sample was embedded with a tantalum wire, sintered at <NUM>, and pressed to a density of <NUM>/cm<NUM>. The resulting pellets had a size of <NUM> x <NUM> x <NUM>. The pellets were anodized to <NUM> volts in water/phosphoric acid electrolyte with a conductivity of <NUM> at a temperature of <NUM> to form the dielectric layer. The pellets were anodized again to <NUM> volts in a water/boric acid/disodium tetraborate with a conductivity of <NUM> at a temperature of <NUM> for <NUM> seconds to form a thicker oxide layer built up on the outside.

The conductive polymer coating was formed by dipping the anodes into a dispersed poly(<NUM>,<NUM>-ethylenedioxythiophene) having a solids content <NUM>% and viscosity <NUM> mPa. s (Clevios™ K, Heraeus) directly without the pre-coat layer. Upon coating, the parts were dried at <NUM> for <NUM> minutes. This process was repeated <NUM> times. Thereafter, the parts were dipped into a dispersed poly(<NUM>,<NUM>-ethylenedioxythiophene) having a solids content <NUM>% and viscosity <NUM> mPa. s (Clevios™ K, Heraeus). Upon coating, the parts were dried at <NUM> for <NUM> minutes. This process was repeated <NUM> times. Thereafter, the parts were dipped into a dispersed poly(<NUM>,<NUM>-ethylenedioxythiophene) having a solids content of <NUM>% and viscosity <NUM> mPa. s (Clevios™ K, Heraeus). Upon coating, the parts were dried at <NUM> for <NUM> minutes. This process was repeated <NUM> times. The parts were then dipped into a graphite dispersion and dried. Finally, the parts were dipped into a silver dispersion and dried. Multiple parts (<NUM>) of 47µF/35V capacitors were made in this manner and encapsulated in a silica resin.

Capacitors were formed in the manner described in Example <NUM>, except that three (<NUM>) layers of an organometallic solution were applied to the anode and cathode portions of the leadframe before encapsulation with the silica resin. More particularly, the solution contained (<NUM>-glycidyloxypropyl)trimethoxysilane in ethanol (<NUM>%). Multiple parts (<NUM>) of 47µF/35V capacitors were formed. The median results of electrical parameters within moisture sensitivity level testing are set forth below in Table <NUM>. The external cracks within moisture sensitivity level testing from the top and the bottom side of capacitors are set forth below in Table <NUM>.

Claim 1:
A capacitor assembly (<NUM>) comprising:
a solid electrolytic capacitor element that contains a sintered porous anode body, a dielectric that overlies the anode body, and a solid electrolyte that overlies the dielectric,
wherein the solid electrolyte includes a plurality of conductive polymer particles containing an extrinsically conductive polymer having repeating units of the following formula (III):
<CHM>
wherein,
R<NUM> is a linear or branched, C<NUM> to C<NUM> alkyl radical, C<NUM> to C<NUM> cycloalkyl radical, C<NUM> to C<NUM> aryl radical, C<NUM> to C<NUM> aralkyl radical, or a combination thereof; and
q is an integer from <NUM> to <NUM>;
an anode termination (<NUM>) that is in electrical connection with the anode body, wherein a first coating is disposed on at least a portion of the anode termination (<NUM>), the first coating containing an organometallic compound;
a cathode termination (<NUM>) that is in electrical connection with the solid electrolyte wherein a second coating is disposed on at least a portion of the cathode termination (<NUM>), the second coating containing an organometallic compound; and
a casing material that encapsulates the capacitor element (<NUM>) and leaves exposed a mounting surface of the anode termination (<NUM>) and the cathode termination (<NUM>);
wherein the organometallic compound of the first coating, the organometallic compound of the second coating, or both has the following general formula:
<CHM>
wherein,
M is a metallic atom;
R<NUM>, R<NUM>, and R<NUM> are independently an alkyl or a hydroxyalkyl, wherein at least one of R<NUM>, R<NUM>, and R<NUM> is a hydroxyalkyl;
n is an integer from <NUM> to <NUM>;
X is an organic or inorganic functional group.