Patent Grant
7372127
(1) Field of the Invention
This invention relates to resistors and, more particularly, to resistors molded of conductive loaded resin-based materials comprising micron conductive powders, micron conductive fibers, or a combination thereof, homogenized within a base resin when molded. This manufacturing process yields a conductive part or material usable within the EMF or electronic spectrum(s).
(2) Description of the Prior Art
Resistors are a basic building block in electrical and electronic systems. Resistors are based on a fundamental property of a material, namely the resistivity or, inversely, the conductivity of the material. Resistivity, or, conversely conductivity, is based on the relative ability, or inability, of a material to conduct current under a voltage bias. Low resistivity materials permit easy current flow and are typically called conductors. Metals, such as copper and aluminum, are examples of excellent conductors. High resistivity materials permit little or no current flow and are typically called insulators. Metal oxides, ceramics, and air are examples of excellent insulators.
The resistance of an object or device is simply a measure of the ratio of voltage to current in that object or a device. Resistance is defined, electrically, by the equation:
Resistance=Voltage/Current,
and is expressed in Ohms. Resistance depends, mostly, on two factors: (1) the inherent resistivity of the material that makes up the object or device and (2) the physical shape of the device. Resistivity is a material property that is essentially constant, excluding variation due to temperature, for the material once the composition of the material is established. Resistivity (ρ) is expressed in Ohms-cm. The shape of the object is important because actual resistance varies inversely with the available cross sectional area through which current may flow. Resistance may be easily calculated for a simple object once the physical shape and size are known and once the resistivity is known. Resistance is given by:
Resistance=ρ×(Areacross-secton/Length),
where ρ is the material resistivity. Another useful metric for resistance calculation is sheet resistance. Sheet resistance is defined as the resistance of a square area of a material and is particularly useful in technologies, such as integrated circuit devices, where resistor structures have one fixed dimension, such as depth, and two variable dimensions, such as length and width. Sheet resistance is given in ohms/square and may be used to calculate a resistance value using the equation:
Resistance=Sheet Resistance×(Length/Width).
All objects, even metal conductors, have a measurable resistance value across the object. In a metal conductor, this value is usually considered to be an undesirable feature and is termed “parasitic resistance.” In other cases, the resistance value is not only desired but, further, it is essential to correct operation of the electrical or electronics circuit. In this case the object or device is typically called a resistor. A resistor comprises two terminals, or connection points to the rest of the circuit, that are separated by the resistor bulk region. Resistors are constructed using a variety of techniques and materials.
Resistors may be categorized in a number of ways. For example, resistors may be discrete devices or may be integrated devices. Discrete resistors are manufactured as individual devices and then placed into, or onto, a circuit. Typically, discrete resistors are further electrically and mechanically attached by soldering. Integrated resistors are formed as part of the fabrication process of the overall circuit. For example, in a semiconductor integrated circuit device, a resistor may be formed by as a patterned line in a polysilicon layer where this same polysilicon layer is also fabricated into a transistor gate in another location on the circuit. This type of resistor is completely integrated into the design and manufacture of the article.
Resistor devices are manufactured using any of several approaches in the art. Film resistors are formed by covering a ceramic substrate with a resistive film. Carbon films and metal films, such as nichrome, are frequently used to create high value, low current resistors. Metal oxide resistors are formed by oxidizing a chemical, such as tin-chloride, on a ceramic substrate. Carbon composition resistors comprise a bulk piece of carbon-based material into which terminals are embedded. Wire wound resistors comprise a long metal wire that is wound around a core and encased in an insulator.
Resin-based polymer materials are used in many arts for the manufacture of a wide array of articles. These polymer materials combine many outstanding characteristics, such as excellent strength to weight ratio, corrosion resistance, electrical isolation, and the like, with an ease of manufacture using a variety of well-established molding processes. Many resin-based polymer materials have been introduced into the market to provide useful combinations of characteristics. However, most resin-based polymer materials are electrical insulators. Attempts to increase the conductivity of resin-based materials have been made in the art. However, the manufacture of useful resistors from resin-based materials has not been successful, to date, in the art. An important object of the present invention is to provide a new type of resistor device from a resin-based material.
Several prior art inventions relate to resistors and methods of manufacturing resistors. U.S. Patent Publication US 2003/0197589 A1 to Taguchi et al. teaches a variable resistor and its means of production. The resistor is formed on a substrate by means of screen printing and utilizes a thermosetting binder resin, a solvent for dissolving the binder resin, and carbon black as the conductive filler. U.S. Patent Publication US 2004/0012479 A1 to Yamada et al teaches a method of manufacturing a chip resistor with a superior surge property. U.S. Pat. No. 4,365,230 to Feldman teaches a lead screw type variable resistor wherein the lead screw is a conductive plastic and acts as a resistive element. U.S. Pat. No. 2,901,381 to Teal teaches a method of manufacture for film resistors. U.S. Pat. No. 6,359,545 B1 to Bressers teaches an adjustable resistor with a slider made of conductive rubber or a conductive plastic and formed with dual resistance strips. U.S. Pat. No. 4,036,786 to Tiedemann teaches a resistor comprising a fluorinated carbon composition as the essential conductive component. This invention also teaches 35% by weight of a conductive filler comprising partially fluorinated acetylene black and utilizes a polysulfone resin as the base resin.
A principal object of the present invention is to provide effective and very manufacturable resistors.
A further object of the present invention is to provide resistors comprising conductive loaded resin-based material.
A further object of the present invention is to provide both discrete and integrated resistors comprising conductive loaded resin-based material.
A further object of the present invention is to provide methods to form resistors of conductive loaded resin-based material.
A further object of the present invention is to provide methods to form both discrete and integrated resistors.
A yet further object of the present invention is to provide resistors molded of conductive loaded resin-based material and further incorporating a metal layer to provide improved connectivity.
A yet further object of the present invention is to provide methods to fabricate resistors from a conductive loaded resin-based material incorporating various forms of the material.
A yet further object of the present invention is to provide a method to fabricate resistors from a conductive loaded resin-based material where the material is in the form of a fabric.
In accordance with the objects of this invention, a resistor device is achieved. The devices comprise a resistive element of a conductive loaded, resin-based material comprising conductive materials in a base resin host. A first terminal is connected at a first end of the resistor element. A second terminal is connected at a second end of the resistor element.
Also in accordance with the objects of this invention, a resistor device is achieved. The resistor device comprises a resistive element of a conductive loaded, resin-based material further comprising conductive materials in a base resin host. The conductive materials comprise between 20% and 40% of the total weight of the conductive loaded resin-based material. A first terminal connected at a first end of the resistor element. A second terminal connected at a second end of the resistor element.
Also in accordance with the objects of this invention, a method to form a resistive element device is achieved. The method comprises providing a conductive loaded, resin-based material further comprising conductive materials in a resin-based host. The conductive loaded, resin-based material is molded into a resistive element device.
In the accompanying drawings forming a material part of this description, there is shown:
a and 5b illustrate a fourth preferred embodiment wherein conductive fabric-like materials are formed from the conductive loaded resin-based material.
a and 6b illustrate, in simplified schematic form, an injection molding apparatus and an extrusion molding apparatus that may be used to mold resistors of a conductive loaded resin-based material.
a through 7c illustrate a second preferred embodiment of the present invention showing, in cross sectional representation, a resistor device of conductive loaded resin-based material with metal plated terminals.
a through 8d illustrate a third preferred embodiment of the present invention showing, in cross sectional representation, a resistor device of conductive loaded resin-based material with embedded metal terminals.
a through 11c illustrate a sixth preferred embodiment of the present invention showing, in cross sectional representation, an circuit or wiring board with a resistor device of conductive loaded resin-based material molded thereon.
This invention relates to resistors molded of conductive loaded resin-based materials comprising micron conductive powders, micron conductive fibers, or a combination thereof, homogenized within a base resin when molded.
The conductive loaded resin-based materials of the invention are base resins loaded with conductive materials, which converts the base resin from an insulator into a conductor. The resins provide the structural integrity to the molded part. The micron conductive fibers, micron conductive powders, or a combination thereof, are homogenized within the resin during the molding process, providing the electrical continuity.
The conductive loaded resin-based materials can be molded, extruded or the like to provide almost any desired shape or size. The molded conductive loaded resin-based materials can also be cut, stamped, or vacuumed formed from an injection molded or extruded sheet or bar stock, over-molded, laminated, milled or the like to provide the desired shape and size. The thermal or electrical conductivity characteristics of resistors fabricated using conductive loaded resin-based materials depend on the composition of the conductive loaded resin-based materials, of which the loading or doping parameters can be adjusted, to aid in achieving the desired structural, electrical or other physical characteristics of the material. The selected materials used to fabricate the resistor devices are homogenized together using molding techniques and or methods such as injection molding, over-molding, thermo-set, protrusion, extrusion or the like. Characteristics related to 2D, 3D, 4D, and 5D designs, molding and electrical characteristics, include the physical and electrical advantages that can be achieved during the molding process of the actual parts and the polymer physics associated within the conductive networks within the molded part(s) or formed material(s).
The use of conductive loaded resin-based materials in the fabrication of resistors significantly lowers the cost of materials and the design and manufacturing processes used to hold ease of close tolerances, by forming these materials into desired shapes and sizes. The resistors can be manufactured into infinite shapes and sizes using conventional forming methods such as injection molding, over-molding, or extrusion or the like. The conductive loaded resin-based materials, when molded, typically but not exclusively produce a desirable usable range of sheet resistance from between about 5 and 25 ohms per square, but other resistivities can be achieved by varying the doping parameters and/or resin selection(s).
The conductive loaded resin-based materials comprise micron conductive powders, micron conductive fibers, or any combination thereof, which are homogenized together within the base resin, during the molding process, yielding an easy to produce low cost, electrically conductive, close tolerance manufactured part or circuit. The micron conductive powders can be of carbons, graphites, amines or the like, and/or of metal powders such as nickel, copper, silver, or plated or the like. The use of carbons or other forms of powders such as graphite(s) etc. can create additional low level electron exchange and, when used in combination with micron conductive fibers, creates a micron filler element within the micron conductive network of fiber(s) producing further electrical conductivity as well as acting as a lubricant for the molding equipment. The micron conductive fibers can be nickel plated carbon fiber, stainless steel fiber, copper fiber, silver fiber, or the like, or combinations thereof. The structural material is a material such as any polymer resin. Structural material can be, here given as examples and not as an exhaustive list, polymer resins produced by GE PLASTICS, Pittsfield, Mass., a range of other plastics produced by GE PLASTICS, Pittsfield, Mass., a range of other plastics produced by other manufacturers, silicones produced by GE SILICONES, Waterford, N.Y., or other flexible resin-based rubber compounds produced by other manufacturers.
The resin-based structural material loaded with micron conductive powders, micron conductive fibers, or in combination thereof can be molded, using conventional molding methods such as injection molding or over-molding, or extrusion to create desired shapes and sizes. The molded conductive loaded resin-based materials can also be stamped, cut or milled as desired to form create the desired shape form factor(s) of the heat sinks. The doping composition and directionality associated with the micron conductors within the loaded base resins can affect the electrical and structural characteristics of the resistors and can be precisely controlled by mold designs, gating and or protrusion design(s) and or during the molding process itself. In addition, the resin base can be selected to obtain the desired thermal characteristics such as very high melting point or specific thermal conductivity.
A resin-based sandwich laminate could also be fabricated with random or continuous webbed micron stainless steel fibers or other conductive fibers, forming a cloth like material. The webbed conductive fiber can be laminated or the like to materials such as Teflon, Polyesters, or any resin-based flexible or solid material(s), which when discretely designed in fiber content(s), orientation(s) and shape(s), will produce a very highly conductive flexible cloth-like material. Such a cloth-like material could also be used in forming resistors that could be embedded in a person's clothing as well as other resin materials such as rubber(s) or plastic(s). When using conductive fibers as a webbed conductor as part of a laminate or cloth-like material, the fibers may have diameters of between about 3 and 12 microns, typically between about 8 and 12 microns or in the range of about 10 microns, with length(s) that can be seamless or overlapping.
The conductive loaded resin-based material of the present invention can be made resistant to corrosion and/or metal electrolysis by selecting micron conductive fiber and/or micron conductive powder and base resin that are resistant to corrosion and/or metal electrolysis. For example, if a corrosion/electrolysis resistant base resin is combined with stainless steel fiber and carbon fiber/powder, then a corrosion and/or metal electrolysis resistant conductive loaded resin-based material is achieved. Another additional and important feature of the present invention is that the conductive loaded resin-based material of the present invention may be made flame retardant. Selection of a flame-retardant (FR) base resin material allows the resulting product to exhibit flame retardant capability. This is especially important in resistor applications as described herein.
The homogeneous mixing of micron conductive fiber and/or micron conductive powder and base resin described in the present invention may also be described as doping. That is, the homogeneous mixing converts the typically non-conductive base resin material into a conductive material. This process is analogous to the doping process whereby a semiconductor material, such as silicon, can be converted into a conductive material through the introduction of donor/acceptor ions as is well known in the art of semiconductor devices. Therefore, the present invention uses the term doping to mean converting a typically non-conductive base resin material into a conductive material through the homogeneous mixing of micron conductive fiber and/or micron conductive powder into a base resin.
As an additional and important feature of the present invention, the molded conductor loaded resin-based material exhibits excellent thermal dissipation characteristics. Therefore, resistors manufactured from the molded conductor loaded resin-based material can provide added thermal dissipation capabilities to the application. For example, heat can be dissipated from electrical devices physically and/or electrically connected to resistors of the present invention.
As a significant advantage of the present invention, resistors constructed of the conductive loaded resin-based material can be easily interfaced to an electrical circuit or grounded. In one embodiment, a wire can be attached to a conductive loaded resin-based resistor via a screw that is fastened to the resistors. For example, a simple sheet-metal type, self tapping screw can, when fastened to the material, achieves excellent electrical connectivity via the conductive matrix of the conductive loaded resin-based material. To facilitate this approach a boss may be molded into the conductive loaded resin-based material to accommodate such a screw. Alternatively, if a solderable screw material, such as copper, is used, then a wire can be soldered to the screw is embedded into the conductive loaded resin-based material. In another embodiment, the conductive loaded resin-based material is partly or completely plated with a metal layer. The metal layer forms excellent electrical conductivity with the conductive matrix. A connection of this metal layer to another circuit or to ground is then made. For example, if the metal layer is solderable, then a soldered connection may be made between the resistors and a grounding wire.
Referring now to
The resulting bulk resistivity of the molded conductive loaded resin-based material that constitutes the resistor body 14 is substantially less than the bulk resistivity exhibited by molding the same base resin sans the conductive loading. Further, it is found that this bulk resistivity of the molded conductive loaded resin-based material 14 is established by the percentage, by weight, of conductive loaded material in the total conductive loaded resin-based molding material, prior to molding. That is, a well-controlled bulk resistivity value in the molded resistor body 14 is easily manufactured by carefully formulating the percent weight of conductive loading in the conductive loaded resin-based molding material. Further yet, by selecting the conductive loading percent, by weight, in the ranges as taught in the present invention, well-controlled and sufficiently large resistivity values are generated such that excellent resistor devices 14 of, for example, between about 1 Ω and about 10 MΩ, can be easily molded.
As described earlier, the actual value, in ohms, of the resistor device 14 depends on the resistivity (ρ) and on the cross sectional area-to-length ratio of the device structure. In this exemplary structure, the direction of current flow is between the first terminal end A and the second terminal end B. Therefore, the critical cross sectional area is defined as the product of the height H and the width W. The resistor length is defined by L. Therefore, the value of the resistor is calculated as:
R=ρ×((H×W)/L).
Referring now to
Referring again to
Next, a plating resist layer 108 is applied to the resistive element 104 as is shown in
Referring now to
Referring now to
Referring now to
Referring now to
Referring now to
The preferred embodiments of
As an important feature of the fifth preferred embodiment, a conductive loaded resin-based resistor device 178 is conformally over-molded onto the case 174. The conductive loaded resin-based material is specifically formulated with conductive loading, by weight, to achieve a resistivity in a particularly useful range for the planned resistor. The resistor device 178 is over-molded onto the case 174 using an injection molding technique. If the case 174 comprises the same base resin as is used in the resistor element 178, then excellent polymeric bonding should occur. Further, if the case 174 further comprises conductive loaded resin-based material with a relatively low resistivity, then the case 174 effective acts as a conductor that is now mechanically and electrically bonded to the resistor device 178.
Referring now to
Referring now to
The conductive loaded resin-based material typically comprises a micron powder(s) of conductor particles and/or in combination of micron fiber(s) homogenized within a base resin host.
Referring now to
Similarly, a conductive, but cloth-like, material can be formed using woven or webbed micron stainless steel fibers, or other micron conductive fibers. These woven or webbed conductive cloths could also be sandwich laminated to one or more layers of materials such as Polyester(s), Teflon(s), Kevlar(s) or any other desired resin-based material(s). This conductive fabric may then be cut into desired shapes and sizes.
Resistors formed from conductive loaded resin-based materials can be formed or molded in a number of different ways including injection molding, extrusion or chemically induced molding or forming.
b shows a simplified schematic diagram of an extruder 70 for forming resistors using extrusion. Conductive loaded resin-based material(s) is placed in the hopper 80 of the extrusion unit 74. A piston, screw, press or other means 78 is then used to force the thermally molten or a chemically induced curing conductive loaded resin-based material through an extrusion opening 82 which shapes the thermally molten curing or chemically induced cured conductive loaded resin-based material to the desired shape. The conductive loaded resin-based material is then fully cured by chemical reaction or thermal reaction to a hardened or pliable state and is ready for use. Thermoplastic or thermosetting resin-based materials and associated processes may be used in molding the conductive loaded resin-based articles of the present invention.
The advantages of the present invention may now be summarized. Effective and very manufacturable resistor devices are achieved. The resistors comprise conductive loaded resin-based material. Both discrete and integrated resistors are realized. Methods to form resistors of conductive loaded resin-based material are achieved. These methods are suitable for forming both discrete and integrated resistors. Resistors molded of conductive loaded resin-based material and further incorporating a metal layer to provide improved connectivity are achieved. Methods to fabricate resistors from a conductive loaded resin-based material incorporating various forms of the material are realized. Finally, a method is achieved to fabricate resistors from a conductive loaded resin-based material where the material is in the form of a fabric.
As shown in the preferred embodiments, the novel methods and devices of the present invention provide an effective and manufacturable alternative to the prior art.
While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.
This patent application claims priority to the U.S. Provisional Patent Application 60/484,454, filed on Jul. 2, 2003, which is herein incorporated by reference in its entirety. This patent application is a Continuation-in-Part of INT01-002CIP, filed as U.S. patent application Ser. No. 10/309,429, filed on Dec. 4, 2002 now U.S. Pat. No. 6,870,516, also incorporated by reference in its entirety, which is a Continuation-in-Part application of, filed as U.S. patent application Ser. No. 10/075,778, filed on Feb. 14, 2002 now U.S. Pat. No. 6,741,221, which claimed priority to U.S. Provisional Patent Applications Ser. No. 60/317,808, filed on Sep. 7, 2001, Ser. No. 60/269,414, filed on Feb. 16, 2001, and Ser. No. 60/268,822, filed on Feb. 15, 2001.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2901381 | Teal | Aug 1959 | A |
| 3801364 | Kojima et al. | Apr 1974 | A |
| 4036786 | Tiedemann | Jul 1977 | A |
| 4365230 | Feldman | Dec 1982 | A |
| 5893765 | Farnworth | Apr 1999 | A |
| 5973034 | Mori et al. | Oct 1999 | A |
| 6194990 | Lee et al. | Feb 2001 | B1 |
| 6359545 | Bressers | Mar 2002 | B1 |
| 6741221 | Aisenbrey | May 2004 | B2 |
| 6870516 | Aisenbrey | Mar 2005 | B2 |
| 20030197589 | Taguchi et al. | Oct 2003 | A1 |
| 20040012479 | Yamada et al. | Jan 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| 377449 | Jul 2001 | GB |
| Number | Date | Country | |
|---|---|---|---|
| 20050001287 A1 | Jan 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60484454 | Jul 2003 | US | |
| 60317808 | Sep 2001 | US | |
| 60269414 | Feb 2001 | US | |
| 60268822 | Feb 2001 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10309429 | Dec 2002 | US |
| Child | 10883913 | US | |
| Parent | 10075778 | Feb 2002 | US |
| Child | 10309429 | US |
