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Copper termination inks containing lead free and cadmium free glasses for capacitorsCopper termination inks containing lead free and cadmium free glasses for capacitors description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20050276002, Copper termination inks containing lead free and cadmium free glasses for capacitors. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to lead-free and cadmium-free copper termination inks containing reduction resistant lead-free and cadmium-free glasses for use in producing electronic capacitors. BACKGROUND OF THE INVENTION [0002] Capacitors are electrical components that have the capability of storing electrical energy. This energy is stored in an electrostatic field that is created by electrical charges accumulating on conducting plates placed across an electrical potential and separated by an insulating medium such as ceramics, for example barium titanate (BaTiO.sub.3), magnesium titanate (MgTiO.sub.3). These ceramic capacitors are used in various applications such as in temperature compensation, in semiconductors, and in applications requiring various dielectric constants, for example Low K class I ceramics and Higher K class II ceramics. [0003] A conventional structure for ceramic capacitors is a structure of multiple layers in which dielectric layers of ceramic are interleaved with conductive electrodes. Alternating conductive electrodes are electrically connected, resulting in a device having two effective electrodes with a capacitance many times the capacitance of the single dielectric layer, packed in a relatively very small volume. These multilayer ceramic capacitors (MLCCs) are the most reliable component for high energy density storage banks. This type of capacitor has been developed to meet demands for high-density ceramic capacitors. [0004] MLCCs consist of a plurality of interleaved and staggered layers of an electrically conductive film of metal known as electrodes, formed by the deposition (usually by screen printing or the like) of a thick film paste or ink, and electrically insulating layers of a dielectric ceramic oxide, formed by laying a cast dielectric tape or by casting a dielectric slurry over the dried electrode. Such capacitors are well known in the art. U.S. Pat. No. 2,389,420, for example, describes the structure, manufacture and properties of monolithic multilayer ceramic capacitors formed using cast dielectric green (unfired) tape. [0005] In a typical MLCC the end termination provides the vital electrical path between the inner electrodes and components exterior to the capacitor. A typical end termination is made by post firing an end termination ink on a pre fired MLCC structure. A typical end termination ink comprises metal particles and glass particles dispersed in an organic medium. Despite its relatively small proportion in an end termination ink, glass plays a major role in providing adhesion to the capacitor body, providing thermal expansion matching between the end termination and the capacitor body to avoid cracking at the interface, ensuring good metal densification, allowing a wider firing window, and preventing penetration of plating solution into the termination during subsequent processing. [0006] Multi-layered ceramic capacitors incorporate multiple printed layers of electrode plates and ceramic sheets. These capacitors are more compact and have better temperature characteristics than single-layered ceramic capacitors. Air fired conventional multi-layered ceramic capacitors are, however, rather expensive because their electrode plates use precious metals, such as silver, gold, platinum, palladium and alloys thereof. Therefore MLCCs with base metal electrodes have been developed. However these have to be fired in atmospheres containing very little O.sub.2, such as N.sub.2 atmosphere with less than 10 ppm oxygen. Development of novel reduction resistant end termination inks in general, reduction resistant Pb free and Cd free glasses for use in termination ink in particular, is the subject of this present invention. SUMMARY OF THE INVENTION [0007] The present invention provides a lead-free and cadmium-free copper containing termination ink for use in producing a multilayer capacitor. The ink includes a glass component. The glass component contains at least one glass frit. At least one of the glass frits is partially crystallizing to maintain a high viscosity to prevent a defect called glassing which will interfere with proper solder wetting and adhesion. In general, the present invention comprises a termination ink having a metal component and a glass component. The metal component comprises copper. The glass component comprises up to about 65 mole % ZnO, up to about 51 mole % SrO, about 0.1 to about 61 mole % B.sub.2O.sub.3, up to about 17 mole % Al.sub.2O.sub.3, about 0.1 to about 63 mole % SiO.sub.2, up to about 40 mole % BaO+CaO, up to about 20 mole % MgO, and the molar ratio of B.sub.2O.sub.3 to SiO.sub.2 is from about 0.7 to about 5. The copper termination ink for dipping will have a viscosity of about 15,000 to about 35,000 centipoise, when measured using Brookfield HAT type SC4 14/5R viscometer and spindle assembly. [0008] New conductive materials, including termination inks, are continually being sought in the MLCC industry which provide improved adhesion to substrates, improved chemical resistance to plating solutions, a wider processing window, and better metal sintering. The termination inks of the present invention provide such desired characteristics. The invention further provides a novel capacitor made using the inventive termination ink and a method of fusing such end termination inks. [0009] The copper termination inks of the present invention upon firing exhibit superior adhesion to BaTiO.sub.3 and display good compatibility with base metal electrodes. The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed. BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIG. 1 is an elevational cross-sectional view of a multilayer ceramic chip capacitor according to the invention. DETAILED DESCRIPTION OF THE INVENTION [0011] The present invention provides a termination ink comprising a metal component, a glass component and a binder component. The invention further provides a capacitor made using the termination ink disclosed herein. [0012] In the description and accompanying claims, all compositional percentages relating to the glass component are in mole %, and ratios are molar ratios. A statement that a composition contains, for example, "about 15 to about 35 mole % BaO+CaO" means that with respect only to the BaO and CaO in the composition, the combined total of BaO and CaO is about 15 to about 35 mole % of the total composition on a molar basis. For example, 10 mole % CaO and 25 mole % BaO. All compositional percentages relating to the composition of the termination ink are in weight percent (wt %). [0013] The glass component of the present invention is lead-free and cadmium-free. As used throughout the instant specification and the appended claims, the phrases "lead-free" and "cadmium-free" mean that no lead, PbO, or lead-containing glasses, cadmium, CdO, or cadmium containing glasses have been intentionally added to the composition. While trace elements could be present from contaminants of raw materials, with respect to the overall inorganic portion of the ink, the content of Pb will be less than 200 ppm and similarly, the Cd content will be less than 200 ppm. The glass frit or frits of the present invention may include ZnO, SrO, SiO.sub.2, B.sub.2O.sub.3 Bi.sub.2O.sub.3, Al.sub.2O.sub.3, BaO, CaO, MgO, CuO, SnO.sub.2, CeO.sub.2, MnO.sub.2, CO.sub.3O.sub.4 as well as alkali oxides such as Li.sub.2O, Na.sub.2O, K.sub.2O, Rb.sub.2O, Cs.sub.2O and Fr.sub.2O. It is possible and sometimes desirable to practice the invention wherein the glass component excludes alkali oxides. [0014] It will be appreciated that the glass component according to the invention can comprise one glass frit, or it can comprise a mixture of several glass frits, including non-crystallizing glass frits, or a mixture of glass frits and inorganic oxides such as SiO.sub.2, ZnO, B.sub.2O.sub.3, CO.sub.3O.sub.4, and others, so as to provide the desired glass composition. The glass frit or frits of the glass component may be prepared utilizing conventional glass melting techniques. A conventional ceramic refractory, fused silica, or platinum crucible may be used to prepare the glass frit. Typically, a mixture of selected raw materials designed to give the desired glass composition are smelted at temperatures of from about 1000.degree. C. to about 1550.degree. C. for about 60 minutes. The molten glass formed in the crucible is then converted to glass flakes or cullets using water-cooled steel rollers or quenching in a tank of water. Pouring onto cold steel rolls results in thin flakes suitable for milling. These flakes or cullets are then milled to a suitable particle size distribution (e.g., average particle size of about 1 to about 6 microns). It will be appreciated that a coarser particle size of 40-50 microns can be used in dip coating and spraying applications. It will be further appreciated that the production the glass frit is not per se critical and any of the various techniques well known to those skilled in the art can be employed. [0015] In general the termination inks are applied and fired on a prefired MLCC pieces (i.e., used on a post fired basis). Typical firing temperatures of the inventive inks and glasses are from about 750.degree. C. to about 900.degree. C., preferably from about 780.degree. C. to about 850.degree. C., and more preferably from about 800.degree. C. to about 830.degree. C. [0016] The metal component comprises copper metal. Copper metal typically is provided in the form of at least one powder or flake. Copper powders may have particle sizes ranging from about 0.1 micron to about 40 microns. In particular, more than one size range of copper particles may be used. For example, a first, finer, copper powder may have a size distribution of d10=0.1-0.3 microns, d50=0.6-1.1 microns and d90=1.5-3.5 microns. A second, coarser, copper powder may have a size distribution range of d10=2-5 microns; d50=3-8 microns; and d90=15-25 microns. Commercially available copper powders suitable herein include Cu 10K-1 and Cu8ED from the Ferro Corporation of Cleveland, Ohio, and Cu 1050Y and Cu MA-CF-E from the Mitsui Mining and Smelting Co, Ltd, of Tokyo, Japan. It will be appreciated that sinter aids such as cobalt may be included with the metal component. [0017] The organic binder is usually an organic resin mixed with a suitable vehicle. The vehicle generally includes one or more solvents. The vehicle preferably comprises a solvent and a resin. Optionally, the vehicle may also comprise a thixotrope and a wetting agent in order to facilitate the application of the ink to the capacitor. Any essentially inert binder can be used in the practice of the present invention, including various organic liquids, with or without thickening and/or stabilizing agents and/or other common additives. Exemplary of the organic liquids which can be used are the aliphatic alcohols, esters of such alcohols, for example, the acetates and propionates. Terpenes also may be used, such as pine oil, alpha terpineol, and beta terpineol. Suitable terpenes include those available from Hercules Corporation under the Terpineol.RTM. trademark, including for example Terpineol.RTM. Prime 318. Also suitable are solutions of acrylic resins such as the polymethacrylates of lower alcohols, or solutions of ethyl cellulose in solvents such as pine oil, the monobutyl either of ethylene glycol monoacetate, and carbinol kerosene, dibutyl phthalate, hexylene glycol, 2,4,4-trimethyl-1,3-pentanediol monoisobutylrate, N-methyl-2-pyrrolidone, ethyl hydroxyethyl cellulose, wood rosin, mixtures of ethyl cellulose and phenolic resins, and the monobutyl ether of ethylene glycol monoacetate or mixtures thereof. Additionally, solvents sold under the Dowanol.RTM. or Carbitol.RTM. trademarks, commercially available from the Dow Chemical Company, Midland Mich., may be used. Such Dowanol.RTM. solvents suitable in the practice of the present invention include propylene glycol, methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, and the like. Suitable solvents sold under the Carbitol.RTM. trademark include butyl carbitol (diethylene glycol monobutyl ether), butyl carbitol acetate (diethylene glycol monobutyl ether acetate) and the like. Various combinations of these and other solvents may be formulated to obtain the desired viscosity and volatility requirements for each application. [0018] Examples of potential suitable thixotropic agents include organic based thixotropes such as, for example, ethyl cellulose, hydrogenated castor oil, silicates and derivatives thereof. [0019] Examples of potential suitable wetting agents (i.e., surfactants) include fatty acid esters, for example, N-tallow-1,3-diaminopropane di-oleate, N-tallow trimethylene diamine diacetate, N-coco trimethylene diamine, beta diamines, N-oleyl trimethylene diamine, N-tallow trimethylene diamine, and/or N-tallow trimethylene diamine di-oleate. Continue reading about Copper termination inks containing lead free and cadmium free glasses for capacitors... Full patent description for Copper termination inks containing lead free and cadmium free glasses for capacitors Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Copper termination inks containing lead free and cadmium free glasses for capacitors patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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