MXPA97000369A - Devices for the protection of variable voltage, of a single layer and of multiple layers and methods to manufacture - Google Patents

Abstract

The present invention relates to a variable voltage protection device for electronic devices, which in one aspect comprises a thin layer of polymer, glass or ceramic (12), pure dielectrics placed in a ground plane (14) and a conductor electrical (10) for the protection of the overvoltage, in which the pure polymer, glass or ceramic layer does not include the presence of conductive or semiconducting particles. Also described is the combination of a thin layer (12) of pure dielectric polymer, glass or ceramic placed on a conventional voltage protection material (13) comprising a binder containing conductive, semiconducting or insulating particles. A multi-layer voltage protection component is described, comprising three layers of surge protection material (15, 16, 17) in which the two outer layers contain a smaller percentage of conductive, semiconducting and / or insulating particles and wherein the inner layer contains a higher percentage of particles, semiconductors and / or insulators. The multi-layer component can optionally be used in combination with the layer (12, 12 ') of pure dielectric polymer, glass or ceramic and optionally may have interposed metal layers (18, 18'). A method is disclosed for dispersing colloidal insulating particles and conductive, semiconducting and / or insulating particles using a volatile solvent for the dispersion of the colloidal insulating particles and the conductive, semiconducting or insulating particles before mixing the resulting particles with the agglutinate

Description

VARIABLE VOLTAGE PROTECTION DEVICES. OF A SINGLE LAYER AND OF MULTIPLE LAYERS AND METHODS TO MANUFACTURE THEM DESCRIPTION The present invention relates in general to devices for the protection of variable voltage used to protect electronic circuits against transient overvoltages, caused by lightning, electromagnetic pulses, electrostatic discharges, currents against overvoltage "" "- induced by the ground circuit or surges of inductor power. The present invention relates particularly to construction materials for variable voltage protection components and methods for manufacturing components and devices for variable voltage protection. 15 Transient voltage can induce very high currents and voltages that can penetrate devices __._ electrical and damaging them, either by causing hardware damage, such as semiconductor heating or electronic disturbances, such as loss of transmission or loss of stored data. Transient voltages produce large voltage spikes with high peak currents (ie overvoltage). The three basic overvoltage threats are electrostatic discharge, transient line surges and lightning. The electrostatic discharge typically occurs when the static charge dissipates from the body of a person in direct physical contact with an operating electronic system or an individual component, such as an integrated circuit chip. Transient line overextensions are surges in the AC power lines. Transient line surges can also occur due to the closing of a switch or ignition of an engine. Lightning strikes can hit stationary objects such as a building, or moving objects such as an airplane or cell phones. Such hits can suddenly overload the electronic components of a system. At maximum power, each of these threats is capable of destroying the sensitive structure of an integrated circuit chip. Various surge protection materials have been used previously. These materials are also known as non-linear strength materials and are referred to herein as variable voltage materials. In operation, the variable voltage material initially has high electrical resistance. When the circuit experiences a surge tip, the variable voltage material rapidly changes to a low electrical resistance state, to form a short circuit of the overvoltage to a ground. After the overvoltage has passed, the material immediately returns back to a state of high electrical resistance. The key operational parameters of the variable voltage material are the response type, the fixed voltage, the maximum or peak voltage and the maximum or peak power. The time it takes the variable voltage material to change from insulation to conductor is the response time. The voltage at which the variable voltage material limits the sudden increase in voltage is called the fixed voltage. In other words, after the material changes to conductor, the material ensures that the integrated circuit chip, for example, will not be subjected to a voltage greater than the fixed voltage. The voltage at which the variable voltage material will change (under sudden rise conditions) from insulator to conductor is the interrupting voltage. These materials typically consist of divided semiconductor or conductive particles finely dispersed in an organic resin or other insulating medium. For example, U.S. Patent No. 3,685,026 (akabayashi, et al.), the United States Patent No. 4,977,357 (Shrier) and the United States Patent No. 4,726,991 (Hyatt et al.) Describe such materials. Variable voltage materials and components containing variable voltage materials have been incorporated into surge protection devices in many forms. For example, U.S. Patent No. 5,142,263 and 5,189,387 (both issued to Childers et al.) describe a surface support device, which includes a pair of conductive sheets and variable voltage material positioned between the pair of conductive sheets. U.S. Patent No. 4,928,199 (Diaz et al.) Discloses an integrated circuit chip pack 5, which comprises a cable structure, an integrated circuit chip protected by an electrode cover, which is connected to ground on one side and a variable voltage interrupting device that includes the variable voltage material connected to the 0 electrode cover on the other side. U.S. Patent No. 5,246,388 (Collins et al.) Relates to a device having a first set of electrical contacts that are interconnected with signal contacts of an electrical connector, a second set of contacts that are connected to each other. a ground and a rigid plastic housing that holds the first and second set of contacts, such ^ _ way there is an accurate gap to be filled with the overvoltage material. The Patent of the United States No. 5,248,517 (Shrier et al.) Discloses painting 0 or printing the variable voltage material onto a substrate, such that the conformal coating with the variable voltage material of large areas and intricate surfaces can be achieved. By directly printing the variable voltage material onto a substrate, the variable voltage material functions as a discrete device or as part of the associated circuitry. The aforementioned prior US Patents are incorporated herein by reference. Although the prior art discloses various materials and devices, there is a long felt and felt need to provide cost effective, improved variable voltage materials and devices with more consistent operating properties to avoid variations in the fixed voltage under various conditions in the which materials and devices will be used. This invention comprises in one aspect, a device for the protection of variable voltage, which comprises a single layer of polymer, glass or ceramic, pure dielectrics, placed between a ground plane and an electrical conductor of an electronic device. Surprisingly it has been found that overvoltage protection can be effectively provided by such a polymer as a glass or ceramic layer, provided that the polymer, glass or ceramic layer is sufficiently thin to provide the desired interruption and fixed voltage characteristics. for a given protective device for a given electronic device. It has been found that for certain polymers, the thickness should first be about 0.0406 mm (1.6 mils) and for other polymers the thickness should be less than about 0.0203 mm (0.8 mils), preferably less than about 0.0127 mm (0.5 thousandths of an inch) and more preferably less than about 0.005 mm (0.2 thousandths of an inch). For certain glasses and ceramics, the thickness should be less than about 0.127 mm (5 mils), preferably less than about 0.0965 mm (3.8 mils), and ** "more preferred less than about 0.0406 mm (1.6 thousandths of an inch), with thicknesses less than 0.0203 mm (0.8 thousandths of an inch) preferred in many applications. In another aspect of the present invention, superior operation can be provided by a variable voltage protection component, which comprises the combination of (a) a layer of variable voltage protective material, comprising a binder containing conductive particles and / or semiconductor particles; and (b) a polymer, glass or pure dielectric ceramic layer in contact with a surface of the layer of variable voltage material; wherein the pure polymer, glass or dielectric ceramic layer is present in a thickness of less than about 0.0406 mm (1.6 mils). The presence of the thin layer of pure dielectric polymer, glass or ceramic on the The binder surface / particle type of the variable voltage protective material provides a component that has advantageous voltage setting properties, as well as other advantageous properties. In another aspect, this invention provides a component for variable voltage protection, in layers comprising a first layer of variable voltage protection material comprising a binder having at least about 20% by volume of conductive particles dispersed therein. or semiconductors; a second layer of variable voltage protection material in contact with the first layer comprising a binder having dispersed therein at least 40% by volume of conductive or semiconducting particles; and a third layer of variable voltage protection material in contact with the second layer comprising a binder having at least 20% by volume of conductive or semiconducting particles dispersed therein. It has been found that the construction of the multiple layer provides an opportunity to vary the conductive particle charge and / or the semiconductor particle charge in each layer, such that the outer layers contain loads of smaller particles than the inner layer, for achieve a wide range of fixed voltage and other desired properties. In a further aspect of this invention, the outer layer in contact with the electrical conductor of the electronic device, must have a lower particle charge than the inner layer with a larger particle load, but in that case the other outer layer in contact with the ground plane may be larger or smaller in the particle load. In a further aspect of this invention, that multi-layer variable voltage protection component may further be provided with a thin layer of dielectric polymer, glass or ceramic, pure as mentioned above on an outer surface or both outer surfaces, to provide additional properties and characteristics of the component. In this aspect of the invention, the layer on the side of the electrical conductor may have a charge of particles greater or less than the inner layer with the condition that the pure polymer, glass or dielectric ceramic layer is placed between the outer layer and the electrical conductor. In another aspect of this invention, this multi-layer component can be provided with a conductive layer, for example a metal, interposed between the first layer and the second layer and / or between the second layer and the third layer of voltage protection material. variable. In yet another aspect of this invention, these multi-layer components themselves can be stacked, with or without the outer layers of pure dielectric polymer, glass or ceramic layers and with or without a polymer intervention layer, glass or ceramic di electric, pure between the components to achieve the desired performance characteristics. In another aspect, this invention provides a method for manufacturing a material for variable voltage protection comprising forming a mixture comprising (a) conductive, semiconducting and / or insulating particles and (b) colloidal insulating particles in (c) a solvent light organic; mix the mixture to disperse the colloidal insulating particles in the conductive / semiconducting / insulating particles; evaporating at least a portion, preferably all the solvent; and mixing the resulting mixture of conductive / semiconducting / insulating particles and colloidal insulating particles with binder to form a variable voltage protection material. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of an illustration of a variable voltage protection device incorporating a pure polymer, glass or dielectric ceramic layer. Figure 2 is a cross-sectional view of an illustration of a variable voltage protection composite having a layer of variable voltage material comprising a binder and conductive particles, semiconducting particles and / or insulating particles in combination with a layer of polymer, glass or dielectric ceramic, pure. Figure 3 is a cross-sectional view of an illustration of a voltage protection component variable, multi-layer according to this invention and incorporating an optional outer layer of polymer, glass or pure dielectric ceramic. Figure 4 is a cross-sectional view of -. an illustration of a voltage protection component Variable, multi-layered according to this invention, incorporating optional interposed metal layers between the layers of variable voltage protective material. With reference to the first aspect of this invention, which comprises a voltage protection device Variable, it comprises as the variable voltage protection material a thin layer of polymer, glass or pure dielectric ceramic, it has been found that such a device is surprisingly effective in a desired range of its fixed voltage with the proviso that the layer of polymer, glass or pure dielectric ceramic is sufficiently thin. For some polymers, a layer of less than approximately 0.0203 mm (0.8 mils) will provide effective protection against overvoltage under various conditions, while for other polymers a layer of less than Approximately 0.0406 mm (1.6 mils) provides the desired performance characteristics. It is preferable in many variable voltage protection applications that the polymer layer be less than about 0.0127 mm (0.5 mil) and more preferably less than about 0.0051 mm (0.2 mil). Similarly, when the layer is a glass or ceramic, it is preferred that the layer be less than about 0.0203 mm (0.8 mils), but for some glasses in certain applications, a thickness of up to about 0.0965 mm (3.8) is appropriate. thousandths of an inch). As will be appreciated with one skilled in the art the actual thickness of the glass polymer layer or pure dielectric ceramic, used in a particular variable voltage protection function, variety depending on the type of polymer glass or ceramic used, its dielectric properties , the operating conditions of the device in which the variable voltage protection element is employed and the required operating properties of the protection device. Figure 1 illustrates the device of this invention where the layer 12 is placed between the electrical conductors 10 and the ground plane 14. When used in the disclosure and description of the present invention the term "dielectric polymer, glass or ceramic, pure "refers to a polymeric glass or ceramic material which can act as a dielectric or insulating material under normal voltage and current conditions of intended use and which is unfilled, ie, does not contain conductive or semiconducting particles such as those typically used in binders or associated in any other way with variable voltage protection materials of the prior art. However, "pure dielectric polymer, glass or ceramic" is intended to include polymeric, glass or ceramic materials which meet the above criteria, but which may contain or have been added to them insulating or inerting particles or materials, which are inactive or do not interfere with the variable voltage / dielectric protection properties of the polymer, glass or ceramic layer as used in the present invention. In the polymer, glass or ceramic layer useful in the present invention, it can be formed or cured in situ or it can be provided in a pre-formed or pre-cured sheet and film and placed in position for use in accordance with this invention. Additionally, the polymer layer can be a block of pre-cured polymer from which the sheets or layers of polymer can be cut or separated in the desired thickness. In addition, the polymer, glass or ceramic layer can be provided in the form of a polymer fiber sphere, glass or ceramic or particles which are compressed or in any other form to provide the polymer, glass or ceramic layer in the desired thickness and properties for use in this invention. Such a sphere, which may contain an adhesive or binder for the fibers, may be heated or heat treated, while compressing to provide a sheet of glass or ceramic polymer fibers of desired thickness for use in this invention. The polymers, glasses and ceramics useful in this aspect of the invention can be selected from polymers known in the art which are useful as binders in materials for variable voltage protection, conventional to the extent that such polymers are known to have high strength. to the tracking and high resistance for the formation of arc. In addition, other polymers, glasses and ceramics previously not suitable for or used as such binders, are also useful in the present invention, if they exhibit sufficient dielectric properties, sufficient tracking strength and sufficient resistance to arcing under the selected operating conditions. for a device according to this invention. In general, the types of dielectric polymers useful in the present invention include silicone rubber and elastomer, natural rubber, organopolysiloxane, polyethylene, polypropylene, polystyrene, poly (methyl methacrylate), polyacrylonitrile, polyacetal, polycarbonate, polyamide, polyester, resin phenol formaldehyde, epoxy resin, alkyd resin, polyurethane, polyimide, phenoxy resin, polysulphur resin, polyphenylene oxide resin, polyvinyl chloride, fluoropolymer and chlorofluoropolymer. These and other useful polymers can be used by themselves or can include various substituent groups and can be mixtures, combinations or copolymers thereof, in the that the final polymer is selected according to the criteria described in the above. A particularly preferred polymer is a conventional and commercially available General Electric "615" silicone and it is also particularly preferred to cure this polymer during about 15 minutes at about 200 ° C to obtain better properties suitable for use in this invention. In such a preparation, the curable liquid polymer is coated on the desired ground plane to the desired thickness, then cured as indicated. The polymer layer The curing then is placed in contact with the conductor or electrical conductors of an electronic device to form the variable voltage protection device of this invention. It has been found that the polymer provides good performance in a thickness of about 0.0051 mm (0.2 thousandths of an inch). Another form of polymer useful in this invention are woven or non-woven polymer fibers compressed in a sphere of desired thickness. For example, a polymer fiber material useful in the present invention is a layer of non-woven aramid fibers (aromatic polyamide), commercially available as the "KEVLAR" or "NOMEX" non-woven fiber sphere of E.l. DuPont de Nemours & Company The non-woven aramid fiber sphere of approximately 0.0406 mm (1.6 mils) has been found to provide good performance when compressed to a thickness of 0.0203 mm (0.8 mil). The dielectric glass materials useful in this invention are also glass materials which have been used as binders in variable voltage materials such as sodium silicate. As with the polymer type material, the glass material can either be coated on or form a place on the desired substrate, such as the ground plane, or it can be preformed into a sheet and assembled between the ground plane and the electrical conductor to form the device of this invention. Dielectric glass such as sodium silicate is generally useful in this invention in thicknesses similar to those described above for polymer materials but is also useful in some cases, in thicker layers, for example up to about 0.127 mm (5 mils), but usually less than about 0.0965 mm (3.8 mils) and preferably less than about 0.0406 mm (1.6 mils). In addition, the glass fibers can be used to form the dielectric glass layer according to this invention. For example, a glass fiber sphere may be formed to the desired thickness, for example about 0.0254 mm (1 mil) or less, to provide the desired performance characteristics for a particular application in which this invention will be used. As with the polymer fiber sphere, a sheet of nonwoven or woven glass fibers can be compressed, with or without a binder adhesive present, to the desired thickness under heat treatment to provide a resultant sheet of desired thickness for use in this. invention. The dielectric ceramics useful in this invention are glass ceramics, devitrified glass, crystallized glasses, crystalline ceramics, crystalline ceramic and diamond composite materials. Although the diamond is not technically a ceramic, it is included herein with the definition of "dielectric ceramic" because it possesses the dielectric properties of conventional ceramics, which are useful in this invention. Thus, the preferred ceramic materials for use in this invention are aluminum oxides and aluminum nitride, crystalline ceramic composite materials include those which include AIN, Al203, Si3 4 and TiN. As mentioned in the above for the glasses, ceramics can be used in this invention up to about 0.127 mm (5 mils), usually less than about 0.0965 mm (3.8 mils) and preferably less than 0.0406 mm (1.6 mils). As used in the present "glasses" is intended to include glasses of amorphous type and "ceramics" is intended to include glass-like glasses and ceramics and diamond crystals. In addition to the above assembly methods, fabrication and use, it will be annealed by one of skill in the art that the glass and ceramic layer can be applied for use in this invention by various known methods, such as solvent storage, coating sol-gel, cathodic position electrode, evaporation, chemical vapor deposition, plasma spraying, anodization and the like. As will be appreciated by one skilled in the art, various polymers, glasses and dielectric ceramics can be selected and used in this invention, following the teachings contained herein, with respect to the thickness that must be maintained for the polymer, glass or ceramic dielectrics, pure to exhibit the desired fixed voltage and other desired properties. Examples of polymers which may be employed in this invention include those described in U.S. Patent Nos. 4,298.4 | 6, 4,483,973, 4,499,234, 5 4,514,529, 4,523,001, 4,554,338, 4,563,498, 4,580,794, the descriptions of which are incorporated herein for reference. As indicated, other resins may be selected for use in accordance with this invention. In another aspect of this invention, it has been found that the pure polymer, glass or dielectric ceramic layer can be used in combination with a variable voltage material to modify and increase certain performance characteristics of the variable voltage material. As mentioned as part of this invention, the The variable voltage material may be a conventional variable voltage material, which comprises a binder which contains conductive particles and / or semiconductor particles and / or insulating particles mixed with or treated with colloidal insulating particles as described. in the present. As used in this invention, the variable voltage material may also include other new, modified and improved variable voltage materials or variable voltage components such as described in this specification and as described in U.S. Application Serial No. 08 / 275,947 filed July 14, 1994. Pure polymer, glass or dielectric ceramic layer which is used in combination with such variable voltage materials or components is placed in contact with one or both surfaces of the variable voltage component or material and can be the same dielectric, pure polymer, glass or ceramic mentioned and described in the above in this application. Figure 2 illustrates the device of this invention, where layer 12 of pure polymer, glass or dielectric ceramic is placed between the electrical conductors 10 and the variable voltage material 13. The ground plane 14 is provided in contact with the layer 13. In this aspect of the invention, the pure polymer, glass or dielectric ceramic layer can be applied to the surface of a desired variable voltage material or component as described above, for example in a liquid form and cured in its place or can be provided in a pre-cured or pre-formed sheet and laminated to the surface of the variable voltage component material. It will be recognized by one skilled in the art, that various conventional variable voltage materials and components, may be combined with the polymer, glass or pure dielectric ceramic layer as described herein, to form the combination of this invention, a Variable voltage material with a pure dielectric polymer, glass or ceramic outer layer to provide the desired performance characteristics. In particular, this aspect of the invention is preferred to provide in combination a multi-layered product as described in the following and a dielectric polymer, glass or ceramic layer, pure on one or both outer surfaces of such variable layer voltage component. multiple In another aspect, this invention comprises a multi-layer variable voltage protection component, which comprises at least three layers of variable voltage material, which comprises a binder containing conductive, semiconducting and / or insulating particles and optionally It may contain colloidal insulating particles. The multi-layer variable voltage protection component according to this invention comprises two outer layers containing a lower charge or concentration of conductive, semiconducting and / or insulating particles, while the inner layer of the component contains a higher charge or concentration of conductive, semiconducting and / or insulating particles. As described above, this component for multi-layer variable voltage protection may optionally further consist of either or both surfaces of the component, of a dielectric, polymer, glass or ceramic layer, pure to further increase or change the characteristics of the component. operation as desired. Figure 3 illustrates this invention where the individual layers of variable voltage protection material 15, 16 and 17 form the multi-layered product placed between the electrical conductors 10 and the ground plane 14. Optionally, a pure, dielectric polymer, glass or ceramic layer 12 can be placed in the outer layer 15 and in contact with the conductors 10 and / or the dielectric, pure polymer, glass or ceramic layer 12 'can be placed on the outside of the layer 17 and in contact with the ground plane 14. The individual layers of the multi-layer product of this invention can be formulated as conventionally described in the patents mentioned in the above background section or more preferably they can be formulated and manufactured by the method described herein, in the following. In general, it is preferred that two outer layers of the present multi-layered product contain at least about 20 percent by volume conductive, semiconductive and / or insulating particles, while the inner layer contains at least about 40 percent by volume of conductive, semiconducting and / or insulating particles in a binder. It is more preferred that the two outer layers contain at least 30 percent by volume of such particles and the inner layer contain at least about 50 percent and more preferably at least about 60 percent by volume of such particles in the binder. It is not necessary for the two outer layers of the product to contain the same charge or concentration of such particles, for example, an outer layer may contain 30 percent by volume of such particles, while the other outer layer contains 40 percent and the inner layer contains 60 percent by volume of such particles in the binder. Following the teachings of this invention, it will be apparent to one skilled in the art that the concentrations or charges of conductive, semiconducting and / or insulating particles in the various layers can be varied to obtain the desired performance characteristics. However, it will further be recognized that the teachings of this invention indicate that the outer layers of the component contain fillers of particles smaller than the inner layer or layers. It will further be recognized that the inner or inner layer of this component can itself be formed of multiple layers of variable voltage materials, which are larger in the charge or concentration of particles than the outer surface layers. When the first outer layer is in direct contact with the electrical conduit of the electronic device, the outer layer has a charge of conductive / semiconductor / insulating particles smaller than the inner layer, as described above, but the other outer layer is optional and may have more or less particle load than the inner layer. When the first outer layer comprises a layer of pure dielectric polymer, glass or ceramic, which is in contact with the electrical conductor, then the first outer layer may have more or less charge of particles than the inner layer and the other outer layer It is optional and may have more or less particle load than the inner layer. The thickness of each layer and the total thickness of the multiple layer component can be determined by one skilled in the art, following the present description to achieve the desired performance characteristics of the component. For example, a preferred embodiment comprises a first layer of 0.0254 mm (1.0 mil) that contains 30 percent by volume of conductive particles, with an inner layer of 0.0203 mm (0.8 mils) containing 60 percent by volume of conductive particles and a 0.0178 mm (0.7 mil) third layer containing 30 percent by volume of conductive particles. Similarly, another preferred embodiment comprises a first layer of 0.0254 mm (1.0 mil) of 30 percent by volume of conductive particles, an inner layer of 0.0508 mm (2 mils) of 60 percent by volume of conductive particles and a third layer of 0.0203 mm (0.8 thousandths of an inch) of 30 percent by 5 volume conductive particles. Multiple layer configurations such as these provide good performance characteristics. further, it will be recognized by someone with skill in the technique, that each layer which is -. it provides in the form of a polymeric binder or other dielectric binder containing the conductive, semiconducting, insulating and / or colloidal insulative particles contained therein, it can be applied in liquid form and then dried or cured. The multi-layer product of this invention can be formed by applying two or more of the layers and then curing or drying all the layers simultaneously or alternatively, the multi-layer product of this invention can be formed by applying the first layer, for example, to a flat metal ground member, and cure or dry that layer before applying subsequent layers 0. In this form, each layer can be applied and cured or dried to the desired thickness before the subsequent layer is applied. In this way, it will be recognized by one skilled in the art, that the multi-layer, variable voltage protection component according to this invention can be formed in various ways using various "" materials. However, a preferred embodiment is provided employing the method described herein in the following, to prepare the variable voltage shielding material forming the above multiple layer product of this invention in the particle loads and the thicknesses of the layer as described in the above. It will also be recognized by someone with skill in the art, each individual layer can be selected - as desired, in such a way that each of the layers of the The multi-layer product may be of a different type of binder materials and / or conductive, semiconducting, insulating or colloidal particles provided that the basic criteria are followed in that the outer layers of the multilayer product contain the lower concentration or charge of such particles, while the inner layer contains a higher charge of such particles. For example, each layer can be selected from the various conventional variable voltage materials available in the prior art, which comprise a binder containing various conductive and / or semiconducting and / or insulating particles. Alternatively, it will be recognized that each layer can be individually selected to employ the new and improved variable voltage protection component materials as describes in the present or in the United States Application Serial No. 08 / 275,947 filed on July 14, 1994. In this regard, the new variable voltage materials containing, for example, reinforcing spheres as described in the co-pending request may be selected to be used as individual individual layers in the multi-layered product of this invention. The multi-layer product of this invention can be constructed in such a way that each layer comprises a Binder, such as a dielectric polymer or dielectric glass binder, which contains conductive particles such as aluminum particles and optionally contains semiconducting particles, such as silicon carbide and in addition, optionally contains insulating particles such as aluminum oxide and / or colloidal insulating particles such as fuming silica. Each one of those diverse * __ components are well known in the art, as well as methods for forming the variable voltage materials with the binders and curing or drying the binders to form the desired final material. In this regard, the descriptions of the patents * mentioned in the above are incorporated herein since they provide basic materials and components, which can be used to produce the multi-layer product of according to the present invention.

For use in this invention, "conductive particles" include metal particles, such as copper, aluminum, molybdenum, and the like, and other conductive materials such as carbon black, carbonyl nickel, tantalum carbide, and the like. The "semiconductor particles" include silicon carbide, beryllium carbide, calcium oxide and the like. The "insulating particles" include aluminum oxide, glass spheres, calcium carbonate, barium sulfate and the like. "Colloidal particles" include the colloidal form of fuming silica, kaolin, kaolinite, aluminum trihydrate, feldspar, and the like. Reference is made to U.S. Patent No. 4,726,991 for other examples of particles and specific materials in each category which are useful in this invention following the procedure and teachings set forth herein. Figure 4 illustrates the invention where individual layers of variable voltage protection material 15, 16 and 17 are separated by optional metal layers 18 and 18 ', which together comprise the multi-layer variable voltage protection device placed between the electrical conductors 10 and the ground plane 14. In another aspect, this invention comprises an improved method for manufacturing a variable voltage protective material containing a binder and conductive particles and / or semiconductor particles in combination with insulating particles and colloidal insulating particles , all dispersed in the binder. As mentioned in the foregoing, each of these binder components, conductive particles, semiconductor particles, insulating particles and colloidal insulating particles are known in the art and are described in detail in several of the patents mentioned in the foregoing. The present aspect of this invention involves new methods of combining these conventional materials to produce new variable voltage protection materials having improved properties. The methods of the present invention comprise a step of dispersing the conductive and / or insulating particles and the desired amount of insulating particles. colloids in an organic solvent, whereby the conductive / insulating particles and the colloidal insulating particles «- are completely dispersed in the solvent mixture. The particles can be added to the solvent in any desired order, but it is generally preferred to disperse First the conductive and / or insulating particles in the solvent, then add the colloidal insulating particles. The mixture is then dried by removal of the solvent by evaporation. The dry particle mixture is usually in the form of a cake, which is then ground to a powder in a shredder. The resulting powder is then added to a dielectric polymer binder in a milling process to uniformly disperse the particles throughout the dielectric polymer. For example, the conductive particle may be aluminum, the insulating particle, aluminum oxide, the colloidal insulating particle, fuming silica and the methyl ethyl ketone solvent. In some formulations it is preferred to also include glass fibers as additional insulating particles. In a preferred aspect, the method further comprises forming a first solvent mixture of only the conductive particles and the colloidal insulating particles and forming a second solvent mixture of insulating particles and isolated colloidal particles. Both mixtures are dried separately; the two resulting dry mixtures are ground separately, then added simultaneously to a mill to be mixed in a polymer binder to form a desired variable voltage protection material. In a preferred method, the binder-particle mixture is mixed with an excess of a strong polar solvent, such as MEK, to expand the binder. Then this mixture is mixed in a high speed mixer to form a viscous material similar to a pigmented paint. This final mixture can be applied as desired, to form variable voltage protection components or layers by depositing the material as desired in layers of desired thickness and allowing the solvent to evaporate and allowing the binder to cure further, leaving the layer desired of variable voltage protection material. In a preferred formulation, Dow Corning STI fluorosilicone rubber (DC-LS2840) is used in combination with Dow Corning STI polydimethylsiloxane (HA2) in a volume ratio of about 4: 1. This mixture is milled until it becomes uniform and essentially transparent. At that point, a prepared mixture of aluminum oxide and fumed silica particles is added to the mill. The preparation of the mixture of aluminum oxide particles and fumed silica particles is as follows. A preferred aluminum oxide particle is an "A14" particle of 5 microns of Alcoa. This particle is dispersed in methyl alcohol and the particle-solvent mixture passes through a sieve of 10 microns. To the dispersion of the resulting solvent of aluminum oxide particles is added 1% by weight (based on the initial weight of the aluminum oxide) of a fumed silica particle which is "Cabosil TS530" predispersed in methyl alcohol and mixed until it is uniformly dispersed through the solvent mixture. Then the solvent is removed through evaporation to form a cake. The particle cake of dry aluminum oxide-Cabosil is then ground to a powder. A second solvent mixture of an aluminum particle designated "H10" from Alcoa, which is a particle of 10 microns, also dispersed in methyl alcohol is then mixed with 17% by weight of a fumed silica, which is "Cabosil M5. " As in the previous, the H10 aluminum particles are dispersed in the methyl alcohol and sieved through a 20 micron sieve, then the Cabosil M5 dispersed in methyl alcohol is added to the H10 aluminum particles sieved in the solvent. After mixing, the solvent evaporates to form a cake. The dried aluminum-Cabosil particle cake is then ground to a powder. The ratio of aluminum particles to aluminum oxide particles is about 2: 1 and about 45 parts per volume of particles are mixed with about 55 parts by volume of binder. Both of the aluminum and aluminum oxide powders are added to the mill and ground in the polymer mixture. After grinding for a sufficient time, such as 30 minutes to 1 hour, to obtain uniform mixing, the mixture is removed from the mill and mixed with methyl ethyl ketone in a ratio by weight of about one part of solvent per part of the total mixture of the windmill. That mixture is allowed to stand for a period of a few hours, such as overnight in the MEK, then mixed with a small amount such as, for example, about 4% by weight of a peroxide, which is 1,1- di-t-butylperoxy-3,5-trimethylcyclohexane and 17% by weight of a crosslinking agent, which is triallylisocyanurate, wherein the weight percent is based on the weight of the binder. This final mixture is then mixed at low speed to ensure complete mixing, then mixed at high speed until the mixture reaches the consistency of a pigmented paint. This final variable voltage protection combustion can then be coated or deposited on a ground plane or on electrical conductors or other substrates in desired patterns, the solvents are allowed to dry and the binder is further cured or crosslinked. If desired, a temperature of about 200 ° C for about 20 minutes can be used to aid in the drying and curing or cross-linking of the binder. The material for variable voltage protection, therefore, is provided in the desired thickness and configuration to serve as the variable voltage protection component or layer. This composition can be used to form the multilayer product of the invention described above or in combination with the dielectric polymer, glass or ceramic layer, pure of the invention described above. As used in the aspect, the above method of this invention, the organic solvent can be any solvent in which the desired particles will be dispersed and mixed with other particles. In general, the solvent may be a hydrocarbon of C 1 to C 1, which is substituted or unsubstituted and includes straight and branched chain hydrocarbons, alcohols, aldehydes, ketones, aromatics and the like. Examples of such solvents useful in this invention include methyl alcohol, ethyl alcohol, n- or iso-propyl alcohol, formaldehyde, methyl ethyl ketone, toluene, benzene, butane, pentane, chlorine / fluoro ethylenes (Du Pont's "Freon" solvents), and others. It will be recognized by one skilled in the art that a solvent that can easily evaporate under available conditions is advantageous. As used in the foregoing, in the invention the conductive particles, semiconductor particles and insulating particles are conventional as set forth in the above patents incorporated for reference. The principles, preferred embodiments and modes of operation of the present invention have been described in the above specification. However, the invention which is intended to be protected should not be considered as limited to the particular embodiments described. In addition, the modalities described herein are going to be considered as illustrative rather than restrictive. Variations and changes can be made by others and the equivalents employed without departing from the spirit of the present invention and it is expressly intended that all such variations, changes and equivalents, which fall within the spirit and scope of the present invention as defined in the claims are encompassed by it.

Claims (20)

1. CLAIMS 1. A variable voltage protection device characterized in that it comprises: a plane to ground; a pure dielectric polymer, glass or ceramic layer in contact with a surface of the ground plane; and at least one electrical conductor of an electronic device in contact with the dielectric, pure polymer, glass or ceramic layer; characterized in that the layer is placed between and in contact with the ground plane and the electrical conductor and consisting essentially of a layer of pure dielectric polymer having a thickness of less than about 0.0406 mm (1.6 mils) or consisting essentially of of a pure dielectric glass or ceramic layer having a thickness of less than about 0.127 mm (5 mils). The device according to claim 1, characterized in that the polymer layer is less than about 0.0203 mm (0.8 mils) and the glass or ceramic layer is less than about 0.0965 mm (3.8 mils). The device according to claim 1, characterized in that the polymer layer is less than about 0.0127 mm (0.5 mil) and the glass or ceramic layer is less than about 0.0203 mm (0.8 mil). The device according to claim 1, characterized in that the polymer layer is less than about 0.0051 mm (0.2 mil) and the glass or ceramic layer is less than about 0.0127 mm (0.5 mil). 5. A variable voltage protection component for positioning between the ground plane and an electronic circuit, comprising: a layer of variable voltage material comprising a binder containing conductive particles or semiconductor particles; and a dielectric, pure polymer, glass or ceramic layer in contact with a surface of the variable voltage material layer; characterized in that the pure dielectric polymer layer having a thickness of less than about 0.0406 mm (1.6 mils) or the pure dielectric glass or ceramic layer having a thickness of less than about 0.0127 mm (5 mils) ). 6. A variable voltage protection component for positioning between a ground plane and an electronic circuit, characterized in that it comprises: a first layer of variable voltage protection material, comprising a binder that has dispersed therein at least about 20% by volume of conductive or semiconducting particles; a second layer of variable voltage protection material in contact with the first layer, comprising a binder having at least 40% by volume of conductive or semiconducting particles dispersed therein; and a third layer of variable voltage protection material in contact with the second layer, comprising a binder having at least 20% by volume of conductive or semiconducting particles dispersed therein. The component according to claim 6, characterized in that the volume percent in the three layers comprises at least about 30%, at least about 40% and at least about 30%, respectively. The component according to claim 6, characterized in that the volume percent in the three layers comprises at least about 30%, at least about 60% and at least about 30%, respectively. 9. A variable voltage protection component for positioning between a ground plane and an electronic circuit, characterized in that it comprises: a first layer of variable voltage protection material, which is in direct contact with an electrical conductor in the electronic circuit and comprising a binder that has dispersed therein at least about 20% by volume of conductive or semiconducting particles.; 10 a second layer of variable voltage protection material, in contact with the first layer, comprising a binder having dispersed therein, at least 40% by volume of conductive or semiconducting particles. 10. A variable voltage protection component according to claim 9, further characterized • '. because it comprises a third layer of variable voltage protection material in contact with the second layer comprising a binder, having dispersed therein, conductive or semiconductive particles at a volume% which is different from that of the second layer. 11. A variable voltage protection component for placement between a ground plane and an electronic circuit, characterized in that it comprises: a pure dielectric polymer, glass or ceramic layer which is in direct contact with an electrical conductor in the circuit electronic; a first layer of variable voltage protective material, in contact with the pure dielectric polymer, glass or ceramic layer comprising a binder having at least about 20% by volume of conductive or semiconducting particles dispersed therein; a second layer of variable voltage protection material, in contact with the first layer, of variable voltage protection material comprising a binder having dispersed therein, conductive or semiconductive particles at a volume% which is different from that of the first layer. 12. The variable voltage protection component according to claim 11, further characterized in that it comprises a third layer of variable voltage protection material in contact with the second layer comprising a binder having conductive or semiconducting particles dispersed therein. a% by volume, which is different from the second layer. A method for manufacturing a variable voltage protective material, characterized in that it comprises: forming a mixture comprising conductive particles and colloidal insulating particles in a light organic solvent; mixing the mixture to disperse the colloidal insulating particles in the conductive particles; evaporating at least a portion of the solvent; and mixing the resulting mixture of conductive particles and colloidal insulating particles with a binder, to form a variable voltage protective material. The method according to claim 13, characterized in that it comprises: screening the conductive particles and the solvent before evaporating the solvent. The component according to claim 13, characterized in that it comprises: evaporating sufficient solvent to form a cake of the conductive particles and the colloidal insulating particles; and grinding the cake to form the resulting mixture of particles to mix with the binder. The method according to claim 13, characterized in that it comprises: forming a separate mixture comprising insulating particles and colloidal insulating particles in a light organic solvent; mix the mixture to disperse the colloidal insulating particles in the insulating particles; evaporating at least a portion of the solvent; and mixing the resulting mixture of conductive particles and colloidal insulating particles and the resulting mixture of insulating particles and colloidal insulating particles, with a binder to form a variable voltage protective material. 17. A variable voltage protective material characterized in that it is formed by: the formation of a mixture comprising conductive particles and colloidal insulating particles in a light organic solvent; mixing the mixture to disperse the colloidal insulating particles in the conductive particles; evaporating at least a portion of the solvent; and mixing the resulting mixture of conductive particles and colloidal insulating particles with a binder, to form a variable voltage protective material. 18. A variable voltage protective material characterized in that it is formed by: the fornation of a mixture of comprising conductive particles and colloidal insulating particles in a light organic solvent; mixing the mixture to disperse the colloidal insulating particles in the conductive particles; sift the mixture of particles and solvent; evaporate enough solvent to form a cake; grinding the cake to form a mixture of conductive particles and colloidal insulating particles; and mixing the resulting mixture of conductive particles and colloidal insulating particles with a binder, to form a variable voltage protective material. 19. A variable voltage protective material, characterized in that it is formed by: the formation of a first mixture comprising conductive particles and colloidal insulating particles in a light organic solvent; mixing the first mixture to disperse the colloidal insulating particles in the conductive particles; evaporating at least a portion of the solvent from the first mixture; forming a second mixture comprising insulating particles and colloidal insulating particles in a light organic solvent; mix the second mixture to disperse the colloidal insulating particles in the insulating particles; evaporating at least a portion of the solvent from the second mixture; and mixing the first resulting mixture of conductive particles and colloidal insulating particles and the second resulting mixture of insulating particles and colloidal insulating particles with a binder, to form a variable voltage protective material. 20. A variable voltage protection composition, characterized in that it comprises a mixture of a binder, a mixture of conductive particles and fumed silica and a mixture of insulating particles and fumed silica. SUMMARY A variable voltage protection device for electronic devices is described, which in one aspect comprises a thin layer of polymer, glass or ceramics (12), pure dielectrics placed between a ground plane (14) and an electrical conductor (10). ) for overvoltage protection, in which the pure polymer, glass or ceramic layer does not include the presence of conductive or semiconducting particles. Also described is the combination of a thin layer (12) of pure dielectric polymer, glass or ceramic placed on a conventional variable voltage protection material (13) comprising a binder containing conductive, semiconducting or insulating particles. A multi-layer variable voltage protection component is described, comprising three layers of surge protection material (15, 16, 17) wherein the two outer layers contain a smaller percentage of conductive, semiconductor and / or conductive particles. insulators and in which the inner layer contains a higher percentage of particles, semiconductors and / or insulators. The multi-layer component can optionally be used in combination with the layer (12, 12 ') of pure dielectric polymer, glass or ceramic and optionally may have interposed metal layers (18, 18'). A method is disclosed for dispersing colloidal insulating particles and conductive, semiconducting and / or insulating particles using a volatile solvent for the dispersion of the colloidal insulating particles and conductive, semiconducting or insulating particles before mixing the resulting particles with the binder.