An extrudable magnet composition includes composite particles including thermoplastic resin and magnetic material, and a surface additive selected from silicon dioxide particles and ferrite particles, wherein the surface additive is applied to a surface of the composite particles.

1. Field of Invention
The present invention relates to extrudable magnets. More particularly the present invention relates to an extrudable magnet compound with improved flow properties in the extrusion processing equipment. Improved flow properties are provided by adding an external surface additive to the extrudate compound. The present invention also related to methods and materials for producing permanent extruded magnets.
2. Description of Related Art
Permanent magnets of a wide variety of design and made by a wide variety of methods are known in the art, and have been employed in a wide range of applications. For example, permanent magnets are known for use with various types of electric motors, holding devices and transducers, including loudspeakers and microphones. For many of these applications, the permanent magnets have a circular cross section constituting a plurality of arc segments comprising a circular permanent magnet assembly. Other cross-sectional shapes, including square, pentagonal and the like may also be used. With magnet assemblies of this type, and particularly those having a circular cross section, the magnet is typically characterized by anisotropic crystal alignment.
Various designs of permanent magnets have been produced by a number of different methods, including compression molding, injection molding and extrusion molding.
Compression molding is generally a method wherein a magnet composition comprising a magnetic powder and a thermosetting resin is filled into a mold in a press at room temperature. The composition is then compressed and heated to cure the resin, thereby molding a magnet. In the case of the compression molding method, since the resin content of the magnet composition is lower than that for the other molding methods, the freedom of shape in molding a magnet is smaller although the magnetic properties of the resultant magnet are often better.
Injection molding is a method wherein a magnet composition comprising a magnet power and a resin component is heat-melted to prepare a melt having sufficient fluidity. The melt is then injected into a mold where the melt is molded into a desired shape. In the case of the injection molding, in order to impart sufficient fluidity to the magnet composition, the resin content of the magnet composition is higher than that for the compression molding method, which often results in lowered magnetic properties. The freedom in molding, however, is generally higher than that for the compression molding method.
Extrusion molding is a method wherein a magnet composition comprising a magnet powder and a resin component is heat-melted to prepare a melt having sufficient fluidity. The melt is then formed into a desired shape by extruding the melt through a die. The melt is then set by cooling, thereby providing a product having a desired shape. In the extrusion method, like the injection molding method, the resin content needs to be high enough to impart the magnet composition the desired and necessary fluidity. An advantage of the extrusion method is that a thin-walled and long magnet can be easily produced.
Among the above methods, injection molding and extrusion generally use a thermoplastic resin as the resin. These are disclosed in Japanese Patent Laid-Open Nos. 123702/1987, 152107/1987, 194503/1985 and 211908/1985. These methods, and others, are also disclosed in U.S. Pat. Nos. 5,888,416, 5,047,205 and 4,881,984, the entire disclosures of which are incorporated herein by reference.
Accordingly, for various permanent magnet applications, it is known to produce a fully dense rod or bar of a permanent magnet alloy, which is then divided and otherwise fabricated into the desired magnet configuration. Such a bar can be formed by any of the above-described processes, although the extrusion method is particularly well suited for forming such a bar, as the process can be operated on a continuous basis.
A problem generally encountered in using the extrusion method, however, is that the material being extruded must exhibit good flow properties both in the granular material state and during processing, i.e., in the dynamic state wherein mechanical and thermal forces are applied to melt, mix, and move the xe2x80x9cbinder resinxe2x80x9d and other additives through the processing equipment. For example, in the granular state, the material must be able to flow from the feed hopper into the extruder in a stable or uniform manner over time. If the flow is not stable and uniform, a problem can arise that material can cake on or adhere to the walls of the hopper. If the hopper is heated, as it often is, the caked material can solidify into solid chunks. These chunks can in turn further deteriorate or completely impede the flow of material into the extruder, and can result in unuseable extruded products. Similarly, and equally important, in the melted state the compound must flow properly in order to extrude into the proper shape.
To address the problem of flow properties, it is generally known to add various flow additives to the extrusion material. For example, it is known to add various calcium and/or zinc stearates to improve the flow properties of the material, in both the granular and the melted state. However, this approach is not always suitable in all applications due to potential unwanted side effects. For example, in the case of calcium stearates, a high temperature is required subsequent to extrusion to burn off any residual calcium from the product. However, these high burn-off temperatures can exceed the processing temperatures of the material, and thus either excess calcium must be tolerated, or the extruded material is degraded by the high temperatures. Similarly, in the case of zinc stearates, the zinc can be detrimental to the mechanical and magnetic properties of the material. Furthermore, zinc can be incompatible with some product materials, and can result in out gassing of chlorine gas. Additionally, incorporating the aforementioned flow additives into the bulk of the compound prior to granulation has little or no impact on the granular flow properties.
There is thus a need in the art for improved manufacturing methods and materials for producing high quality permanent magnets in a reliable process. In meeting this need, it is required that the process and materials be compatible with the processing equipment, without degrading the magnetic and other properties of the magnets being produced.
These and other objects are satisfied by the present invention, by adding an external additive to the extrudate material, to improve the flow properties of the material in the processing equipment, while at the same time not degrading performance characteristics. The additive thus improves the flow properties of the material, both in the granular and in the melted state. This is achieved in the present invention by using, as an external flow additive, materials such as, for example, extremely small particle size fumed silicon dioxide, commonly sold under the trade name AEROSIL, or a fine particle size ferrite.
More particularly, in embodiments, the present invention provides an extrudable magnet composition, comprising:
composite particles comprising thermoplastic resin and magnetic material, and
a surface additive selected from the group consisting of fumed silicon dioxide (or AEROSIL) particles and ferrite particles,
wherein said surface additive is applied to a surface of said composite particles.
The present invention also provides methods of making extrudable magnets using such a composition, and magnets made thereby and therefrom.
Broadly, the method of the present invention provides for the production of a fully dense, or substantially so, permanent magnet alloy article by producing a particle charge of a permanent magnet alloy composition from which the article is to be made. The charge is placed in a container and the container is evacuated, sealed and heated to elevated temperature. It is then extruded to compact the charge to full density, or substantially to full density, to produce the desired fully dense article. Alternatively, or more preferably, the extrusion operation may be operated continuously, where extrusion (or a permanent magnet alloy composition) material is fed continuously or batch-wise into the extruder.
The permanent magnet composition according to the present invention generally comprises a magnet powder and a thermoplastic resin. The composition may further comprise effective amounts of one or more additives, such as about 0.1 to about 2.0 wt % of a chelating agent, about 0.1 to about 2.0 wt % of an antioxidant, about 0.1 to about 2.0 wt % of a solid lubricant (such as calcium stearate), and 0.01 to about 6 wt % of an AEROSIL or ferrite particle external surface flow additive. As is known in the art, a wide variety of other additives, including but not limited to surfactants, lubricants, flow additives, and the like, may be incorporated into the permanent magnet composition, in their known amounts for their known purposes.
The permanent magnet composition may contain one or more chelating agents, used in known amounts for their known effects. Suitable chelating agents include, but are not limited to, those having a phenol structure such as isopropylmalonic acid, phthalic acid, diethyltriamine, phenanthroline, glutamic acid, glycine, phenothiazine, N-Salicyloyl-Nxe2x80x2-aldehydehydrazine, N-Salicyloyl-Nxe2x80x2-acetylhydrazine, N,N-bis greater than 3-(3,5-di-t-butyl-4-hydroxyphenyl)! Propionylhydrazine, N,N-Diphenyloxamide, and N,N-Hexamethylenebis(3,5-t-butyl-4-hydroxy-hydrocinnamide). When included, the chelating agent can be included in any desired amount, such as from about 0.1 to about 2.0 percent by weight, based on a weight of the total composition. Amounts outside this range can also be used, as desired.
The permanent magnet composition may also contain one or more antioxidants, used in known amounts for their known effects. Suitable antioxidants include, but are not limited to, hydrazine antioxidants, 4,4xe2x80x2-Butylidene-bis(3-methyl-6-t-butylphenol), 1,3,5-Trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, N,Nxe2x80x2-Hexamethylene-bis(3,5-t-butyl-4-hydroxy-hydrocinnamide), and phenyl-beta-naphthylamine. When included, the antioxidant can be included in any desired amount, such as from about 0.1 to about 2.0 percent by weight, based on a weight of the total composition. Amounts outside this range can also be used, as desired.
In embodiments, when both a chelating agent and an antioxidant are included, it is preferred, although not required, that the total content of both the chelating agent and an antioxidant be from about 0.1 to about 2.0 percent by weight, based on a weight of the total composition. Incorporation of the chelating agent and an antioxidant generally help to ensure heat stability of the bonded magnet composition during kneading and molding, thereby enabling the composition to be stably molded. Further, they enable the volume percent of the magnet powder in the magnet composition to be optimized, improving the performance of the molded magnet. Furthermore, the chelating agent/antioxidant combination tends to inactivate the active magnetic powder, such as rare-earth magnetic powders, and, hence, improve the corrosion resistance of the resultant magnet.
With respect to the magnet material itself, any suitable permanent magnet material may be used, as desired. By way of example only, and without being limited thereto, suitable magnet powder materials include, but are not limited to, barium ferrite powder (BaOxe2x80xa26Fe2O3), strontium ferrite powder (SrOxe2x80xa26Fe2O3 ), barium-strontium ferrite powder (BaxSr1xe2x88x92xOxe2x80xa26Fe2O3), SmCo5-based powder, Sm2Co17-based powder, Nd2Fe14B-based powder, Sm2Fe17N3-based powder, (NdDy)15Fe79B6, an Nd-Fe-B-based quenched magnetic powder (such as the product MQP-B manufactured by GM), ferrite particles, and the like. Any other suitable magnet material can also be used.
Preferably, in embodiments, the magnet material forms a major amount by weight of the total composition. Accordingly, in embodiments, the magnet material is included in an amount of from about 50 to about 99 percent by weight based on a total weight of the composition. Preferably, the magnet material is included in an amount of from about 75 to about 99 percent by weight, more preferably from about 85 to about 95 percent by weight, and even more preferably from about 87 to about 92 percent by weight, based on a total weight of the composition. However, amounts outside these ranges can be used, as desired.
In addition to the magnet material, the composition also includes one or more thermoplastic resins. Suitable thermoplastic resins include, but are not limited to, polyamide resin, such as polyamide-12 (nylon 12), polyamide-6 (nylon 6), polyamide-6,6 (nylon 6,6), and the like; polyvinyl chloride; plasticized polyvinyl chloride; polyphenylene sulfide; liquid crystalline polymers such as polyethemitrile; polyesters; rubber compositions such as natural rubber, polyurethane rubber, neoprene rubber, butadiene rubber, ASCIUM(trademark), VITON(trademark), HYPALON(trademark), styrene-butadiene rubber (SBR), carboxylated SBR, acrylonitrile-butadiene rubber (NBR), butyl rubber, fluorinated rubber, chlorobutyl rubber, bromobutyl rubber, ethylene-propylene-diene rubber (EPDM), chlorinated polyethylene, chloro-sulfonated polyethylene, chloroprene, epichiorohydrin (ECO), isobutylene isoprene, isoprene, polysulfide, polyvinyl chloride-NBR, vinyl acetate ethylene, and the like; modified rubbers such as hydrogenated SBR, hydrogenated NBR, and carboxylated NBR; polyaramids (such as KEVLAR(trademark), available from DuPont); polypropylene; polyvinyl alcohol; polypropylene oxide; silicone; mixtures thereof; and the like. Particular examples of some of the above materials include NIPOL(trademark) 1052 NBR (available from Zeon, Louisville, Ky.), HYDRIN(trademark) 2000 ECO (available from Zeon, Louisville, Ky.), HYPALON(trademark) 48 (available from DuPont, Wilmington Del.), and NORDEL(trademark) 2760P EPDM (available from DuPont, Wilmington Del.).
Preferably, in embodiments, the thermoplastic resin forms a minor amount by weight of the total composition. Accordingly, in embodiments, the thermoplastic resin is included in an amount of from about 1 to about 50 percent by weight based on a total weight of the composition. Preferably, the thermoplastic resin is included in an amount of from about 1 to about 25 percent by weight, more preferably from about 5 to about 15 percent by weight, and even more preferably from about 11 to about 13 percent by weight, based on a total weight of the composition. However, amounts outside these ranges can be used, as desired.
Generally, the various components used to form the extrudable composition are combined together and formed into small particles. This can be done either directly, where small particles are formed comprising all of the constituent materials. However, better results are generally obtained by first forming a large mass of material having all of the constituent materials except for the external flow additives, granulating the large mass of material to the desired smaller particle size of, for example, from about 0.5 to about 5 mm mean diameter range, and then adding the external flow additives, such as including the fine AEROSIL or ferrite additives of the present invention.
To improve the bulk flow and storage properties of the composition, one or more external solid flow additives may be incorporated unto the compound particles after granulation of the compound to the desired size range. According to the present invention, the flow additive includes at least fine silicon dioxide, such as fumed silicon dioxide, particles and/or fine ferrite particles. By xe2x80x9cfinexe2x80x9d herein is meant particles having an average particle diameter of less than about 5 microns, and preferably less than about 1 micron.
Examples of suitable silicon dioxide particles include, for example, but are not limited to, fumed silicon dioxide particles such as Aerosil R972(trademark) and Aerosil R104(trademark), both available from Degussa, Inc. If desired, although not required, the silicon dioxide particles can also be surface treated and/or functionalized, to provide different properties to the material. For example, if desired, the silicon dioxide particles can also be surface treated and/or functionalized to provide increased hydrophobicity to the aerosil.
Examples of suitable ferrite particles include, but are not limited to, BG-12(trademark), available from Kane Magnetics; HM 170(trademark), available from Hoosier Magnetics; and FM 201(trademark), available from Toda America, Inc. In addition, any of the above-described magnet powder materials used to form the bulk material may also be used. Thus, the other examples of suitable ferrite particles include, but are not limited to, barium ferrite powder (BaOxe2x80xa26Fe2O3), strontium ferrite powder (SrOxe2x80xa26Fe2O3 ), barium-strontium ferrite powder (BaxSr1xe2x88x92xOxe2x80xa26Fe2O3), SmCo5-based powder, Sm2Co17-based powder, Nd2Fe14B-based powder, Sm2Fe17N3-based powder, (NdDy)15Fe79B6, an Nd-Fe-B-based quenched magnetic powder (such as the product MQP-B manufactured by GM), ferrite particles, and the like.
In embodiments, it is preferred that the external flow additives be the same material as the compound, or one of the constituent components of the magnetic compound particles, such as fine ferrite particles. In these embodiments, the magnetic properties of the entire composition will remain essentially unchanged, since the additive is also magnetic, although the bulk granulated material flow properties are improved.
According to the present invention, the flow additive is included in any suitable amount that provides the desired increased flow properties, while not rendering the composition unsuitable for its intended purposes. Thus, for example, the flow additive can be included in an amount of from about 0.01 or about 0.05 to about 5 or 6 percent by weight, based on a total weight of the entire composition. Preferably, the flow additive is included in an amount of from about 0.1 to about 3 percent by weight, more preferably from about 0.25 to about 2.0 percent by weight and even more preferably from about 0.5 to about 1.5 percent by weight, based on a total weight of the entire composition.
When the flow additive is incorporated into the composition, it can be added either as a separate component, or, preferably, as a surface treatment of other particles in the composition. For example, where the magnet material, thermoplastic resin, magnetic component, e.g. barium ferrite, other additives and the like are formed into small (such as, for example, from about 0.1 to about 10 mm diameter) particles, the flow additive can be included as a surface treatment or surface additive of the small particles. In this manner, the flow additive serves its finction generally by acting as a spacer or stilt particle, preventing the small particles of the composition from directly contacting each other, whereby they could tend to agglomerate.
Preferably, in embodiments of the present invention, the above-described flow additives are the only external flow additives added to the composition.
A particular benefit of the flow additives of the present invention is that they prevent agglomeration of the composition. This agglomeration prevention is evident not only during feeding into the extruder, but also during storage of the material. For example, without the inclusion of flow additive, the composition particles tend to agglomerate and solidify rather quickly. Thus, for example, a bulk material must generally be granulated on a daily basis, and only in an amount estimated to be used that day. If too much is granulated, agglomeration tends to set in, thus, rendering the material unuseable. However, with addition of flow additives according to the present invention, the granulated material is much more stable and less likely to agglomerate. The granulated materials thus have a longer useful lifetime.

Extrudable magnet compound with improved flow properties


A method for cleaning ceramic workpieces such as SiC boats used in semiconductor fabrication is disclosed. The method comprises washing a virgin or used ceramic workpiece with a strong acid and then using a pelletized CO2 cleaning process on the acid-washed component. The inventive method has been found to produce a workpiece having a very low level of metallic and particulate contaminants on its surface.

The present invention relates to methods for cleaning ceramic articles. More particularly, the present invention relates to method for removing both particle impurities and chemical impurities from ceramic articles used in the manufacture of semiconductor devices.
The manufacture of semiconductor devices typically requires subjecting the surface of a silicon wafer to high temperature processes such as diffusion, oxidation and deposition. In deposition processes, dielectric materials such as polycrystalline silicon, silicon nitride and silicon dioxide are deposited on the surface of the wafer. In diffusion processes, materials are diffused into the body of the silicon wafer. In oxidation processes, the surface of the wafer is oxidized to form a thin silica layer. Each of these processes typically involves placing the wafers to be processed in a holder, often called a xe2x80x9cboatxe2x80x9d. The boat is typically formed of a ceramic material and is configured to hold the wafer in either a horizontal or a vertical orientation. Once loaded with wafers to be processed, the boat is placed in an electrically-heated furnace or process tube, and then the environment inside the tube is altered to provide various atmospheres having temperatures typically ranging from 250xc2x0 C. to over 1200xc2x0 C.
Another common semiconductor process is etching. After a photolithographic pattern is deposited on the surface of a silicon wafer, the wafer is loaded into an etcher. The etcher, whose components are typically made of a ceramic material, uses a plasma etching process to remove the materials deposited on the wafer surface which are not protected by a photolithographic pattern. The typical etching process removes oxides, metals and/or polymers from the wafer surface.
Although each of the processes described above successfully develops the surface of the silicon wafer into a useable product, they also eventually contaminate the surfaces of the supporting equipment as well. For example, a nitride deposition process will leave a coating of silicon nitride; upon not only the wafer, but also upon the surface of the boat which supported the wafer during the deposition process. When this coating becomes too thick, it tends to flake and contaminate nearby wafers with particles.
In an etching process, the deliberate removal of various layers of material from the wafer-in-process can cause contaminant particles such as silica, nitrides, and alumina to be deposited on the surface of etcher components. Since contaminants adversely affect the processing of future wafers to be processed by these components, contaminant particles must be carefully cleaned from the surfaces of these components. Because of the decreasing line widths of silicon wafers, it has become increasingly important to remove more sub-micron particles from the surface of these components, more particularly sub-micron particles having a width of no more than 0.7 microns.
Several methods for cleaning used ceramic boats are known in the prior art. In one method, a used component which is coated with a deposited material such as silicon nitride, polysilicon or silica undergoes a two-step cleaning process whereby the component is first exposed to a stream of hard pellets, such as silicon carbide pellets, in a process akin to sand-blasting, and then to a stream of frozen carbon dioxide (CO2) pellets. The first step, termed preliminary cleaning, successfully strips deposited material from the component surface, leaving behind some debris particles on the order of one micron. In the second step, termed primary cleaning, the frozen CO2 pellets are believed to cause the micro-sized debris particles to freeze, thereby becoming brittle, and then break, thereby allowing them to be easily flushed from the surface.
Preliminary cleaning is ordinarily carried out either by impinging or xe2x80x9cblastingxe2x80x9d glass, aluminum oxide, silicon carbide, titanium oxide, walnut shell particles, or other hard beads against the part being cleaned. The beads are typically carried in a pressurized stream of air or other gas. The beads can be spherical, granular, or any other desired shape and dimension. One commonly used bead material is 98% black SiC grit. The pressure under which the beads are directed to the surface depends on the composition of the part being cleaned. When a ceramic part is to be cleaned, the beads typically are applied in a gas at a pressure in the range of about 20-35 psi. Once completed, the bead blasting, preliminary cleaning, step is followed by a CO2 cleaning process. CO2 cleaning processes have been described in the patent literature. See, for example, U.S. Pat. No. 4,707,951, entitled xe2x80x9cInstallation for the Projection of Particles of Dry Icexe2x80x9d.
In another method of cleaning a used boat which is coated with deposition layers, one manufacturer recommends subjecting the used boat to an acid treatment, preferably using a strong acid such as HF, followed by baking. This HF treatment removes the deposited layer of material.
The cleanliness of virgin semiconductor processing equipment has also been a concern in the art. However,-for a virgin part, the concern has typically been metallic, rather than particulate, contamination. In one conventional method of manufacturing SiC diffusion components, the virgin SiC diffusion components are subjected to a weak acid and then baked. This process serves to remove some metallic contaminants and fingerprints from the part being cleaned.
In another conventional method of insuring the cleanliness of virgin components, the component is subjected to a strong acid such as HF prior to installing it in a furnace. Similarly, hot HCl cleaning has been used in connection with semiconductor diffusion components. For example, in UK Patent Application No. GB 2,130,192, the investigators disclose a manufacturing step of subjecting a virgin SiC component to hot HCl treatments prior to use in a semiconductor furnace.
In some cases, HF treatment by itself has been considered sufficient for cleaning both virgin boats (to reduce metallic contamination) and used boats (to chemically strip coatings deposited during semiconductor processing). That notwithstanding, the use of HF alone fails to remove problematic debris particles that may still be present after such treatment.
In sum, conventional methods of providing a clean virgin semiconductor component involve acid cleaning to remove metallic contamination, while conventional methods of cleaning used components involve either i) a two-step process of mechanical stripping of deposited coats via bead blasting followed by CO2 cleaning to remove small debris particles, or ii) hot strong acid cleaning to remove a coat of deposited material.
The fabrication of semiconductor devices requires the use of process components having a high level of surface purity, whether those components are new or reconditioned. In certain workpieces, such as ceramic boats used to position and maintain semiconductor wafers during processing, the long depth and narrow spacing of the wafer-retaining slots define a boat geometry with a contoured surface having an aspect ratio that prevents bead blasting from sufficiently stripping coatings from the deeper portions of these slots. In particular, aspect ratios, (i.e., the ratio of slot depth to slot width), of greater than about 4:1 are typically beyond the ability of conventional cleaning methods. The present invention presents a method for overcoming this and other shortcomings by providing a process in which the inorganic surface of semiconductor fabrication components is cleaned by chemical stripping followed by CO2 cleaning. In one embodiment, the chemical stripping is carried out using a solvent containing a strong acid. In a more preferred embodiment, the chemical stripping is carried out using a solvent having at least 1 v/o of an acid selected from the group consisting of HF, acids having a pKa of less than about one, and mixtures thereof. As used herein, xe2x80x9cv/oxe2x80x9d represents a volume percent, and xe2x80x9cstrong acidxe2x80x9d represents a solution having at least 1 v/o of an acid having a pKa of less than about one.
The CO2 cleaning step employs particles of dry ice which are projected against the surface being cleaned. The combination of the chemical stripping and the CO2 cleaning step has been found to successfully remove both particulate and metallic contaminants from the surface of the workpiece.
Workpieces cleaned using the inventive process have been found to have a surface contaminant particle density of no more than about 0.4 particles, and preferably no more than about 0.2 particles, larger than about 0.3 xcexcm per square centimeter. Such workpieces have also been found to have a surface metallic contaminant concentration of no more than about 600 ppm, as measured by SIMS at a depth of about 10 nm. Of the surface metallic contamination, no more than about 400 ppm of metal contaminants other than alkaline and alkaline earth metals, and no more than about 225 ppm of iron, (as measured by SIMS at a depth of about 10 nm), remain following application of the inventive cleaning process to typical workpieces.
The present invention is based upon the recognition that problematic debris particles may still be present after HF treatment, and that CO2 cleaning steps, while removing particulate contaminants, are unable to remove non-particulate metallic contaminants. To date, the art has lacked any suggestion of the present invention which employs HF treatment to remove metallics followed by a CO2 cleaning step to remove any remaining debris particles. Combining a CO2 cleaning step with HF treatment is unique in that CO2 cleaning has traditionally been used only after a used workpiece underwent mechanical stripping which produced debris particles.
The present invention also relates to workpieces, such as ceramic boats used in semiconductor processing, that have been cleaned using the process of the present invention. The resulting workpieces are unique in that their level of metallic and particulate surface contamination is significantly below that which has previously been obtainable using processes known to those skilled in the art.
The present invention provides a process for providing ceramic workpieces, such a ceramic boats used in semiconductor fabrication with a lower level of metallic and particulate surface contamination than has previously been available. Specifically, whereas it is known in the art to use acid cleaning, and whereas it is also known in the art to use bead-blast cleaning in combination with CO2 cleaning, to date, there has been no suggestion in the art to combine an acid cleaning step with a CO2 cleaning step for cleaning either virgin or used, coated ceramic workpieces. The recognition that an acid cleaning step can be combined with a CO2 cleaning step yields a cleaning process that is well-suited for use with both virgin and used, coated workpieces.
As noted above, use of the inventive process has provided workpieces having a surface contaminant particle density of no more than about 0.4 particles larger than about 0.3 xcexcm per square centimeter, and a surface metallic contaminant concentration of no more than about 600 ppm, as measured by SIMS at a depth of about 10 nm.
Traditionally, upon receiving a virgin workpiece such as a ceramic boat from a manufacturer, the user would subject the workpiece to an acid cleaning process in order to remove any metallic contaminants that may have deposited on the workpiece during manufacture, packaging, shipping, etc. In some instances, used, coated workpieces would be cleaned by chemical stripping using a strong acid. As with the virgin workpieces, the acid cleaning provided a satisfactory means for removing metallic contaminants form the surface of the workpiece.
Although acid cleaning provides a surface having metallic contaminants lowered to satisfactory levels, the process fails to provide a surface having a sufficiently low level of particulate contamination. In fact, some evidence exists that the acid cleaning step actually contributes to particulate contamination. Without wishing to be tied to any particular theory, in cleaning a workpiece such as a used ceramic boat, workpieces cleaned using HF to chemically strip a coating still have a high level of particulate contamination because the stripping process leaves particulate contaminants on the ceramic surface.
Furthermore, particulate contamination does not result solely from the acid cleaning process and post-processing steps. Rather, in the case of virgin workpieces, it is believed that machining the component, such as an SiC boat, produces particles which deposit upon the surface of the component. Of course, particles also may deposit upon a virgin component because of exposure of such components to non-clean-room environments. It should be noted that, in the case of either virgin or used components, and pre-processing, processing or post-processing steps, many mechanisms for the formation of particles on the workpiece may exist, and the present invention is not intended to be limited to any particular particle formation or deposition mechanism.
As noted previously, CO2 cleaning procedures have traditionally been used in combination with a preliminary cleaning step such as bead-blasting. The combination of bead-blasting and CO2 cleaning has generally not been used on virgin workpieces, but rather, has been employed on used workpieces that have had CVD coatings deposited on their surfaces during semiconductor processing. While this method has been found to be satisfactory for the removal of particulate contaminants, it lacks the ability to remove metallic contamination that occurs on both virgin and used workpieces.
The present invention recognizes that until the workpiece, be it a virgin component or a chemically-stripped component, is subjected to a final CO2 cleaning step, problematic submicron particles which need to be eliminated from the surface of the components will remain. The need for removal of such particulate contaminants, as well as the manner in which such removal is achieved is neither appreciated nor performed in conventional processes.
Moreover, it appears that products resulting from the inventive process also possess superior levels of metallic purity as compared to re-worked products processed by cleaning methods which use CO2 cleaning to clean the used coated workpieces. As noted above, one conventional process mechanically strips the coating from a used component, such as a boat, via bead blasting, and then uses CO2 cleaning to complete the cleaning. Without wishing to be tied to any particular theory, in the case of a used boat, the conventional understanding is that surface metallic contamination is not a problem. Conversely, even if surface metallic contamination did give rise to problems, it was wrongly assumed that such problems could be sufficiently eliminated using techniques known in the prior art.
In contrast, some evidence suggests that a-bead blasting step actually acts to increase the concentration of metallic impurities at the surface of the workpiece. This undesirable effect may be the result of the use of impure blasting media.
The process of the present invention is superior to the conventional bead blasting/CO2 cleaning process in that it does not result in metallic contamination of the surface of the stripped workpiece. In fact, the present inventive process acts to reduce the concentration of metals at the surface.
Likewise, for a virgin workpiece, such as an unused SiC boat, the conventional understanding of surface metallic impurity has been that HF or hot HCl cleaning offered only marginal utility because it served only to incrementally reduce the concentration of metals at the surface of the component to a level slightly below that of the bulk material forming the workpiece (1-10 ppm for SiC), and that this relative purity advantage over the bulk disappeared over time as subsequent use under high temperature environments promoted the diffusion of bulk metals into the surface region of the component. Accordingly, the art did not require HF cleaning in all circumstances.
The surface of materials representing virgin SiC components has been analyzed by one conventional method (x-ray photoelectron spectroscopy, referred to herein as XPS) and by another method (secondary ion mass spectroscopy, referred to herein as SIMS). A conventional XPS analysis provides information at a depth of about 3 nm and has a sensitivity of about 0.1-1.0% depending upon the element of interest. In contrast, the SIMS analysis can provide information at a depth of about 10 nm and has a sensitivity of about 0.2-3.0 ppm. For this reason, the SIMS test provides a more accurate method for measuring the surface concentration of metals in semiconductor processing components. It has been found that in instances where XPS failed to detect any metals, (and thus failed to provide any indication of an elevated surface metals concentration), the SIMS test reported about 2000 ppm metals at a depth of 10 nm. In the field of high temperature semiconductor processing, these surface levels are clearly undesirable. Accordingly, as a result of the SIMS analysis, there is now a demonstrated need to clean the surface of a virgin ceramic component, preferably using a strong acid solution, in order to reduce the high surface level of metallic contaminants present at the surface of semiconductor processing components. It should be appreciated that, in one embodiment of the present invention, the surface is a CVD surface, which optionally may have been subjected to machining or other post-processing steps.
More particularly, it should be understood that the process of the present invention is intended to be applied to a wide variety of inorganic surfaces employed by semiconductor processing components. Such surfaces typically comprise ceramic materials such as those ceramics commonly used in semiconductor fabrication, however, the process may be applied to non-ceramic surfaces such as silicon and diamond as well. Thus, while the discussion has focussed primarily on semiconductor processing components such as ceramic boats, and particularly those formed of SiC, it should be understood that the invention is not intended to be limited in this manner. Rather, the invention is intended to apply to any of the semiconductor processing components that have inorganic surfaces associated with semiconductor wafer processing techniques. These surfaces include, but are not limited to silicon (Si), silicon carbide (SiC), silicon nitride (Si3N4), diamond, yttria (Y2O3), zirconia (ZrO2), aluminum nitride (AlN), aluminum oxide (Al2O3) and quartz.
The surfaces may be vapor-deposited, and as discussed above may be deposited using CVD techniques. Such surfaces include, but are not limited to polycrystalline or other CVD Si, CVD SiC, CVD SiO2, CVD Si3N4 and CVD diamond surfaces. Of course, it should be understood that despite the applicability of the present invention to surfaces having inorganic coatings thereon, the process may also be applied to uncoated, inorganic surfaces.
In considering SiC workpieces, several varieties are used in the art. In one embodiment, a workpiece formed simply of SiC is used. In another embodiment, the workpiece comprises a reduced porosity SiC formed by loading the pores of a SiC structure with Si. Because the silicon tends to escape from the pores, such workpieces are often provided with a CVD SiC layer. More specifically, these components typically are formed of a porous xcex1-SiC body having Si occupying the pores. To prevent the Si from escaping, a layer of very pure xcex2-SiC is deposited on the surface of the component using CVD methods. The xcex2-SiC is intended to seal the surface and inhibit loss of Si near the surface of the workpiece.
It should be understood that the xcex2-SiC material deposited on the workpiece to prevent Si from escaping is not intended to be removed by the process of the present invention. Rather, when referring herein to the removal of coatings from used workpieces, the subject coatings are those that have been deposited on the workpiece during its use in semiconductor processing. Thus, a virgin coated workpiece refers to a newly manufactured workpiece having a desired coating formed thereon, while a used, coated workpiece refers to a workpiece having an undesired coating deposited during semiconductor processing. Of course, upon use, the virgin coated workpiece acquires an additional, undesired coating, and it is the removal of the coating which forms one embodiment of the present invention.
While useful with vertical racks, it should be understood that the process of the present invention employing a strong acid clean followed by a CO2 clean provides unexpected benefits not only for vertical racks, but also for semiconductor processing equipment of any shape. Examples of semiconductor processing components used in single wafer processing to which the present invention may be applied include, but are not limited to, bell jars, electrostatic chucks, focus rings, shadow rings, chambers, susceptors, lift pins, domes, end effectors, liners, supports, injector ports, manometer ports, wafer insert passages, screen plates, heaters, and vacuum chucks. Examples of semiconductor processing components used in batch processing to which the present invention may be applied include, but are not limited to, paddles, process tubes, wafer boats, liners, pedestals, long boats, and dummy wafers. Examples of semiconductor processing components used in chemical mechanical polishing (CMP) to which the present invention may be applied include, but are not limited to, conditioning pads and wafer holders.
Lastly, it is believed that the process of the present invention provides for the first time a ready-to-install product, that is, a product that can be safely taken out of a protective shipping bag at the user""s facility and directly installed in a semiconductor furnace without any further cleaning by the user. This is achievable because such components already have the lowest possible amounts of surface metals and particles achievable by surface treatments.
More particularly, in one aspect of the present invention, immediately upon completing the CO2 cleaning step, the cleaned workpiece is installed either into a furnace used for processing semiconductor wafers, or into a bag used for the shipping and storage of cleaned semiconductor processing components. In the former process, the workpiece is transferred directly from CO2 cleaning into the furnace without any further cleaning steps. In the latter process, the workpiece is packaged, i.e., bagged, directly following CO2 cleaning without any further cleaning steps. In this latter case, upon removing the workpiece from its packaging, it is installed directly into a furnace used for processing semiconductor wafers without any further cleaning steps. Unlike processes known in the art in which it is necessary to provide additional cleaning steps between removal of the workpiece from its packaging and installation in the furnace, components cleaned using the method of the present invention may be installed into the furnace immediately upon removal from their packaging. This is advantageous in that it eliminates additional processing steps which can, among other things, actually lead to increased levels of contamination, particularly particulate contamination.
Although several prior art cleaning regimes, and their advantages and disadvantages, have been described previously herein, none of those known in the art offer the ability to provide a surface having the low contamination level of metallics and particles available from the inventive process described herein. Washing in a strong acid solution, such as a solution containing HF or other acid having a pKa of less than about one, provides a surface having unsatisfactory levels of particulate contaminants. Alternatively, washing in a weak acid solution or bead-blasting followed by a CO2 cleaning results in less desirable levels of metallic contaminants. It was not until the present invention, in which a strong acid cleaning is followed by CO2 cleaning, that one could achieve acceptable levels of both metallic and particulate contamination.
In another embodiment of the present invention, the acid cleaning and CO2 cleaning steps are coupled with a modified bead blasting step. Specifically, in this embodiment, the invention includes the steps of bead-blasting the surface of the workpiece using green SiC particles. Subsequently, the surface is contacted with a solvent having at least 1 v/o of an acid selected from the group consisting of HF, acids having a pKa of less than about one, and mixtures thereof. The surface is then treated using CO2 cleaning. The use of green SiC in the bead-blasting step is unique in that, to date, only black SiC has been used for bead-blasting purposes. In the present invention it has been found that bead-blasting using green SiC beads provides surfaces that are significantly lower in contaminants. This is believed to be the result of the composition of the black SiC beads versus the green SiC beads. Whereas the former comprise a grit containing about 98% SiC, (and an impurity level of about 2%), the latter contain impurities in the range of approximately 1000-2000 parts per million, (i.e., 0.1-0.2% impurities).
In still another embodiment of the present invention, the strong acid step can be eliminated entirely and replaced with a bead blasting step using green SiC beads described above. Thus, the process employs the steps of bead-blasting with green SiC followed by a CO2 cleaning.
In yet another embodiment, the use of an acid cleaning step can be eliminated when cleaning certain components. Specifically, as noted above, certain workpieces may be provided with coatings. Such coatings may be provided by any of a wide variety of processes including chemical vapor deposition, sputter deposition and spray coating. For example, a workpiece formed of xcex1-SiC may be provided with a CVD deposited xcex2-SiC coating to form a very pure surface. Likewise, thick CVD deposited SiC films of up to about 500 microns in thickness usually do not require additional machining steps, and thus avoid one significant source of metallic contamination. Alternatively, workpieces formed from other ceramic materials may be such that they do not require certain processing steps, such as sandblasting, that introduce metallic impurities onto the ceramic surface. These workpieces also have surfaces that are low in metallic contaminants. New workpieces having such coated or otherwise pure surfaces are relatively free of metallic contaminants. Of course, any of the surfaces described above will include some low level of unavoidable metallic impurities, however, such impurity levels are significantly lower than those introduced by machining steps such as sandblasting. As such, these workpieces can be cleaned using only the CO2 process and installed directly into a furnace or immediately packaged without any additional cleaning steps. Likewise, the packaged workpieces of this type can be removed from their packaging and directly installed into a furnace without any additional cleaning steps. Thus, although the prior art includes processes in which the CO2 process is used without an acid cleaning step, none of these processes are used in connection with virgin workpieces of the type described above. By eliminating the acid cleaning step for certain virgin workpieces, cleaning time and process complexity can be minimized.
It is noted that in each of the embodiments employing green SiC described above, the CO2 cleaning step may employ techniques and apparatus that are known in the art. One example of a satisfactory CO2 method and delivery system is that described in U.S. patent application Ser. No. 08/890,116, entitled xe2x80x9cCarbon Dioxide Cleaning Processxe2x80x9d, the teachings of which are incorporated herein by reference.
Further improvements include the use of high purity CO2 in the CO2 cleaning step and the application of the present process, to the extent possible, in a clean-room environment. Needless to say, any reduction in impurities in the environment surrounding the workpiece during or after cleaning will result, ultimately, in a cleaner workpiece.

Semiconductor processing component having low surface contaminant concentration

Saint-Gobain Ceramics and Plastics, Inc.


A disk brake comprising: a disk, which comprises a plurality of coaxially disposed arcuate shaped recesses and a plurality of radially disposed channels; arcuate shaped pads matingly mounted therein the arcuate shaped recesses; a caliper comprising caliper pads, the caliper pads mounted adjacent and thereabout the disk mounted arcuate shaped pads. The disk brake has improved braking efficiency, does not become overheated or warp, is light weight, durable, long lasting, and may be manufactured or retrofit with replacement parts quickly, easily, and efficiently.

1. Field of the Invention
The present invention relates generally to disk brakes and more particularly to disk brakes having carbon—carbon friction material, and the like.
2. Background Art
Disk brakes and the like have been known. Brake rotors are typically attached to the automobile or vehicle's axles. As the automobile or vehicle travels, the brake rotors rotate with the wheels of the automobile or vehicle. Brake caliper assemblies, having brake pistons and brake pads, are rigidly mounted to the automobile or vehicle's frame. Upon application of the brake pedal, hydraulic fluid drives the brake pistons outward from cylinders in the caliper assemblies, forcing the brake pads to engage the rotors of the disk brakes, causing the frictional braking force that stops the automobile or vehicle from traveling.
Such disk brakes, particularly in automobiles and other similar vehicles, typically required the application of asbestos based friction materials against steel or cast iron rotors to stop the automobile or vehicle. Such braking is often applied in intermittent and irregular intervals, which results in substantial amounts of kinetic energy being transferred to both the pads and the steel or cast iron rotors in the form of friction heat, with the pads and rotors reaching temperatures in excess of 670K. With braking in intermittent and irregular intervals at such high heat levels, the pads often crack and deteriorate, as a result of repeated application of heat and differences in heat expansion coefficients of the pads and associated back plates, and the rotors often warp, because of the variation of heat applied to different portions of the rotors, the outer portions of the rotors often being subjected to a substantially higher temperature than the inner portions of the rotors.
Since the discovery of the toxic effects of asbestos, brake pad construction has shifted toward the use of semi-metallic or non-asbestos organic composite pads. However, disk brakes having the semi-metallic or non-asbestos organic composite pads, typically have problems, such as noise, shudder, vibration, short lifetimes of the pads and rotors, and aesthetic problems, such as brake pad dust on the wheels. Rotors have also tended to warp, owing to greater heat generation, as a result of the use of such brake pads. In addition, such pads wear out quickly, requiring the use of hydraulic brake pistons, which have a long travel to compensate for rapid wear of the brake pads, which necessitates the use of a larger caliper assemblies and larger pistons, which adds weight to the disk brakes.
With the introduction of aluminum alloy rotors, in order to lighten the automobile or vehicle, and improve fuel efficiency, additional problems have been introduced. Aluminum alloy rotors tend to scuff and score more easily, thus, making it less feasible to replace cast iron or steel rotors with aluminum rotors. The coefficient of friction of the pads was reduced, in order to be compatible with the aluminum alloy rotors, which resulted in decreased braking efficiency. Abrasive, materials, such as alumina, were then introduced to the friction material, which resulted in an increase of the coefficient of friction and an increase in braking ability; however loading of the back plate increased, and the back plate tended to become overheated.
There is thus a need for a disk brake that has improved braking efficiency, does not become overheated or warp, is light weight, durable, long lasting, and may be manufactured or retrofit with replacement parts quickly, easily, and efficiently.
Different disk brakes have heretofore been known. However, none of the disk brakes adequately satisfies these aforementioned needs.
Brakes, friction disks, clutches, and flywheels have been disclosed.
U.S. Pat. No. 5,558,186 (Hyde, et al.) discloses a friction disk assembly, which comprises an annular structural carrier including a plurality of recessed regions and torque drive notches spaced around its circumferential direction, and a friction lining mounted on the carrier, the friction lining having a flat wear (rubbing) face and an obverse face including raised areas corresponding to and matingly engaging the recessed regions of the carrier to prevent rotation of the lining relative to the carrier. The carrier may be formed of steel or other suitable structural material. The lining may be formed of virgin or recycled carbon, ceramic or other suitable friction material. The lining may be retained to the carrier by rivets, and may be provided with a structural casing configured to engage the recessed regions of the carrier. The assembly may be refurbished by simple replacement of the worn lining. The carrier and the lining may be formed as unitary annular members or as segments of annular members.
U.S. Pat. No. 3,708,042 (Krause) discloses a friction disk for a disk brake having a plurality of interleaved brake rotor and stator disks, which are forced together to provide a friction effect. The rotor is provided with a plurality of segments, each of which includes a carbon block having friction material pads fixedly secured to opposite faces thereof. The segments are attached to a ring or strap, which holds the segments in fixed spaced-apart relationship to define an annular rotor disk.
U.S. Pat. No. 5,709,288 (Riebe) discloses a friction assembly, comprising an annular structural carrier, including a plurality of recessed and/or raised regions and torque drive notches spaced around its circumferential direction, and a segmented friction lining mounted on the carrier. Each segment of the friction lining comprises a clamshell-shaped friction cup including a pair of cup members containing a puck of friction material, each pair of cup members being joined by a deformable strap and together defining a U-shaped configuration. The obverse side of each cup member includes projections and/or depressed areas that are complementary in size, shape and location to the recessed and/or raised regions of the associated carrier operatively engaged therewith, to prevent movement of the lining relative to the carrier during a braking event. The carrier may be formed of steel or other suitable structural material. The lining may be formed of suitable friction material, e.g. sintered metal. The lining may be retained to the carrier by rivets that pass through lugs extending from the cup members. The friction pucks are provided with a structural casing configured to engage the recessed and/or raised regions of the carrier. The assembly may be refurbished by simple replacement of the worn lining together with its associated structural casing.
U.S. Pat. Nos. 3,712,427 and 3,800,392 (Cooke, et al.) disclose a brake disk assembly in the form of a carbon or graphite disk, which is provided on both sides with thin wear plates of carbon or graphite material. The plates are either in segmented or full circle form, and are secured to the core by rivets and bushings, which also secure keyway drives of the disks.
U.S. Pat. No. 4,613,021 (Lacombe, et al.) discloses a disc brake disk comprising a core designed to withstand mechanical stresses, the core including a hub, a plurality of spokes surrounding the hub and hooks at the end of the spokes, each of the spokes having two opposite flat faces and two opposite edges, removable friction pads fitted on both sides of the core, each of the friction pads including a plurality of annular sectors, each sector having an axially outside friction surface and an axially inside mounting surface with lands and recesses, each sector having a radially outer edge with an oblique surface and a radially inner edge with an oblique surface, the hooks cooperating with the oblique surfaces of the outer edges of the sectors to form stops against both axial and radial movement of the sectors, the lands of the sectors on each side of the core bearing axially against one another back to back, each sector covering two angular spaces between spokes by overlapping one middle spoke and halves of two side spokes, the lands and recesses comprising a radial center slot having a bottom and edge walls and two radial half-width slots in the ends of the sector, the edge walls cooperating with the edges of the middle spoke for radial guidance and annular locking of the sector, a clearance being left between the bottom and the flat surface of the middle spoke, the half-width slots leaving room with clearance for the side spokes, the sectors on one side of the core being offset circumferentially relative to the sectors on the opposite side of the core by a half-sectors breadth and spring rings attached to the hub pushing elastically against corresponding oblique surfaces of the inner edges of the sectors so as removably to mount the sectors on the core.
U.S. Pat. No. 5,769,185 (Main, et al.) discloses carbon brake disc assemblies and methods for making the same, which allow for increased carbon utilization. In one embodiment of the invention, worn or spent discs from a carbon brake disc assembly are used to fabricate new brake discs. The separate discs, individually unsuited for further use in a brake assembly, are secured together with like wear material and subjected to chemical vapor infiltration to configure a disc suitable for use as a new disc. In other embodiments, previously used discs or new carbon material is employed to configure wear pads or wear discs, which are affixed to opposite sides of a carrier plate, and then subsequently used in a brake disc assembly. In all of the embodiments, carbon screws or threaded rods are employed to hold the components of the disc together. Such carbon screws or threaded rods are fabricated from otherwise worn or spent carbon discs or from new carbon.
U.S. Pat. No. 4,825,981 (Otto, et al.) discloses an axially split brake disk, which includes two brake bands, that form a brake ring, and which are interconnected by ribs. The brake disk further includes two brake ring halves, that are separated by concentric and radially extending seams of division, in each of which one of the brake ring halves is provided with a projection that extends in a concentric direction, while the other brake ring half is provided with a corresponding U-shaped recess, that accommodates the projection. The width of the projection is less than the width of the brake ring, as measured in a radial direction. The projection of the one brake ring half, as well as that portion of the other brake ring half in which the recess is provided, are provided with corresponding radially extending bores for receiving a holding mechanism, such as a sleeve-like or rod-like member, that is provided with pin-like elements, for preventing the holding mechanism from shifting in a radial direction relative to the brake ring halves.
U.S. Pat. No. 4,018,311 (Tickle) discloses a rotor and braking ring disc assembly, for use in a railway disc brake, comprising a plurality of arcuate elements or segments of a braking ring, which are attached to the rotor so that each element or segment can thermally expand and contract relative to the rotor, and pairs of circumferentially spaced locating abutments for preventing radial inward and outward movement of the element or segment relative to the rotor at predetermined locations, which are selected, so that when the element undergoes thermal expansion or contraction with respect to the rotor, there is no movement of the element into or out of engagement with the abutments. The abutments may take the form of radial projections on the element or segment or rotor, which projections are urged into engagement with a groove in the rotor or disc element, respectively by further abutments, such as in the form of camming wedges or springs. Alternatively, the abutments may be lateral projections on the rotor, which are a sliding fit in elongated grooves in the element or segment.
U.S. Pat. No. 4,132,294 (Poli) discloses a brake disc with replaceable linings, for brake-discs, comprising a hub provided with a circumferential radial flange structure extending therefrom, and having front and rear annular faces; at least two sector shaped lining parts, which together form an annular assembly, each part being of monolithic construction, and including confronting front and rear sector-shaped linings, all of the linings together forming front and rear annular linings, the outer surfaces of which are acted on by braking jaws, during use of the assembly, each of the parts being removably fitted over the flange structure in concentric relationship with the hub, so that the front and rear faces of the flange structure lie between the opposed surfaces of the confronting front and rear sector-shaped linings, the linings having radially extending inner ribs projecting therefrom, so as to form cooling passages, open at both their radial inner and outer ends, at least some of the ribs having edges, which serve as guides for the lining parts, during fitting of the latter over the flange in a radial direction, the rib edges engaging the flange structure in the completed brake disc assembly; and for each sector-shaped lining part, a single removable connecting element extending parallel to the axis of the hub and connecting the respective lining part with the flange structure, each of the connecting elements being located approximately at the center of the respective lining part.
U.S. Pat. No. 4,903,801 (Kobelt) discloses an internally air cooled brake disc assembly, manufactured by casting in small pieces, for eliminating problems associated with casting large discs with integral air cooling passages. The assembly has a main disc member and a plurality of disc segments secured to the main disc member. The disc segments are separate entities, and can expand and contract independently of each other, thus, reducing distortion from thermal effects. Assembled outer surfaces of each disc segment are generally flat, and provide an annular surface to be swept by brake pads. The inner surface of each disc segment has a plurality of ridges and at least one groove, for spacing the ridges apart. The ridges contact the main disc member, so that at least one passage is formed between the disc segment and the disc member, to receive a flow of cooling air. When the disc segments are secured on each side of the main disc member, the disc assembly has a plurality of cooling passages on each side of the main disc member. An optional external fan means can be provided adjacent inner ends of each disc segment, to provide a forced flow of air over the outer surfaces of the disc.
U.S. Pat. No. 6,334,515 (Martin) discloses a brake disk for disk brakes of vehicles, which is made of a material of the carbon group, the brake disk being formed as a ventilated brake disk, made up of two individual friction rings, which are undetachably connected with one another. The two friction rings are connected with one another by way of pins, which have a thickened center part and end parts, which are set off thereto. The end parts are fitted into respective bores in the friction rings.
U.S. Pat. No. 5,005,676 (Gassiat) discloses an improved rotor for a disk brake, having a multi-piece construction. The rotor has a central web extending around a driving drum portion, such that the web defines several generally radially extending cooling passages. The central web is mounted on the driving drum portion, so as to be capable of sliding laterally, but may not rotate relative to the driving drum. Friction elements, completely separate from the central web, are located on either side of the central web, and are mounted on the driving drum, so as to be also capable of lateral movement. The friction elements are also prevented from rotating relative to the driving drum portion of the rotor.
U.S. Pat. No. 4,745,996 (Wirth) discloses a brake ring for brake disks, especially disk brakes for rail vehicles, consisting of two annular bodies arranged adjacently at a distance from each other, having stud bolts bridging the distance and rigidly connected with the annular bodies. The stud bolts are so arranged, for the purpose of the most even distribution possible, that the axes of the stud bolts extend through the intersecting points of three systems of straight lines, extending in one radial plane. The straight lines of the first system are parallel, and are at an equal distance from each other; the second system of straight lines is formed by a rotation of 60 degrees from the first system of straight lines; and the third system of straight lines is formed by a rotation of 120 degrees from the first system of straight lines. Preferably, the ratio of the distance of the stud bolt axes and the diameter of the stud bolts is approximately 1.7. The brake ring has only minor aeration losses, but high heat transmission by cooling air. When the brake ring heats up, the stresses within the annular bodies and the stud bolts are evenly distributed, and the risk of fracture is reduced.
U.S. Pat. No. 4,263,992 (Moore, et al.) discloses a fabricated disc brake rotor assembly, in which a brake disc rotor is formed from two disc shaped members, with each disc having a flat surface and integrally formed fins extending from an opposing surface thereof. The ends of the fins are welded together to form the rotor. The fins of one member are welded to a convoluted outer rim section of a hat, which is secured to a wheel bearing assembly.
U.S. Pat. No. 5,332,067 (Prud'homme) discloses a disk brake pad device, which includes a carbon—carbon lining pad. A pad is attached to a caliper, and at least one pad positioning surface of the caliper has at least one pad actuating piston emerging therefrom. A first plate element of heat-insulating material, called a screen element, is located against the positioning surface, and at least one second element of heat-insulating material, called a spacer element, of adequate thickness, having reduced frontal contacts is located against the first element. A carbon—carbon lining pad of high-temperature friction material is located against the second element. The first element and/or the second element acts to retain the lining pad and to fix the first element and/or the second element to the caliper.
U.S. Pat. No. 4,051,930 (Masclet) discloses a disc brake with graphite friction linings. The disc brake comprises a rotor and a stator, wherein the rotor and/or the stator includes a mounting member provided with a friction lining formed at least in part by a plurality of graphite plates, each plate having two flat side faces and a peripheral surface, which is perpendicular to the two flat side faces, each plate being received in a recess in a side face of the mounting member, each recess having a flat bottom surface, and being of a depth less than the thickness of the plate, the side wall of the recess being parallel to the peripheral surface of the plate and spaced from the peripheral surface of the plate by a distance greater than that necessary to permit thermal expansion and contraction between the mounting member and the plate. The graphite plates of one of the rotor and the stator are formed of polycrystalline graphite, and the other of the rotor and the stator is formed and/or has graphite plates formed of structural graphite.
U.S. Pat. No. 4,982,818 (Pigford) discloses a cyclic brake disc overhaul technique and structure. The cyclic carbon brake disc overhaul technique comprises the steps of splitting a worn carbon disc into two equal disc halves, machining the disc halves to a predetermined axial thickness, and then bonding the disc halves of predetermined thickness to a core member. The disc halves may include drive regions at respective ends thereof, or the halves may have the drive regions removed therefrom. The core member may have axially extending drive portions, such that the disc halves of reduced radial length define wear grooves with the drive portions.
U.S. Pat. No. 6,308,808 (Krenkel, et al.) discloses a brake disk for a vehicle disk brake, in which a material from the carbon group is used for an internally ventilated disk brake. Individual components, such as friction rings and ribs, are manufactured individually or partially together, and can be fastened to one another, using an unreleasable connection, such as high temperature welding or gluing.
U.S. Pat. No. 5,099,960 (Alev) discloses a composite brake disk and method of extending the braking service life thereof. The composite brake disk provides an integral brake disk, comprising two brake disks, each of the brake disks having a disk thickness of one-half the design required disk thickness, and the two disks being clamped together in planar face-to-face orientation, by fasteners to form the integral brake disk. The integral brake disk has an inboard-facing brake wear surface, provided by a wear surface of a first of the combined brake disks, and an outboard-facing brake wear surface, provided by the second of the combined brake disks. The integral brake disk is put into braking service for a first period after which refurbishment is required. The integral brake disk is refurbished by declamping the two disks and grinding the worn wear surfaces to planar specification. The two disks are recombined at the ground planar surfaces, and reclamped to form a new integral brake disk. The refurbished integral brake disk has an inboard-facing brake wear surface, provided by the second of the two disks, and an outboard-facing brake wear surface, provided by the first of the recombined disks, and may be used for an additional period of braking service.
U.S. Pat. No. 5,803,210 (Kohno, et al.) discloses a disk pad type brake comprises a rotor disk provided with a carbon—carbon composite material (a) as a friction member, and at least one pad provided with a carbon—carbon composite material (b) as a friction member, wherein the difference in thermal conductivity between the materials (a) and (b) is 30 to 450 W/m.multidot.K in the radial direction; and a multi-disk type brake comprises at least one rotor disk provided with a carbon—carbon composite material (c) as a friction member, and at least one stator disk provided with a carbon—carbon composite material (d) as a friction member, wherein the difference in thermal conductivity between the materials (c) and (d) is 30 to 450 W/m.multidot.K in the radial direction.
U.S. Pat. No. 6,450,303 (Keck, et al.) discloses a brake disc for motor vehicles, with a bowl-shaped brake-disc chamber having a wall region and a bottom region, and with a disc-shaped friction ring surrounding the brake-disc chamber coaxially with respect to a common mid-axis, the friction ring having, on its inner circumference, clearances, into which projections formed on the wall region of the brake-disc chamber engage for the play-free transmission of a torque acting on the friction ring to the brake-disc chamber.
U.S. Pat. No. 6,077,607 (Zornik) discloses a brake/clutch disc, such as for a vehicle. In known SiC/C—C composites, the SiC layer is implemented as a diffusion layer, so that Si occurs even comparatively far within a C—C basic body having an SiC boundary layer. The brake/clutch disk is directed to friction discs, consisting of an SiC/C—C composite, and having essentially the mechanical properties of C—C discs, but a longer service life and a broader field of use than said C—C discs. This is achieved by a graphitized, machined basic body, provided with an SiC coating, consisting of a subsequently applied melt. In addition, a manufacturing method for such discs is provided.
U.S. Pat. No. 5,634,535 (Fennell, et al.) discloses a composite brake disc, such as a carbon composite brake disc having reinforcement provided by layers of carbon fiber material, in which the drive region is provided with additional reinforcement in addition to that of the friction region, by laying or otherwise providing additional fiber reinforcement material substantially uniformly in the drive region.
U.S. Pat. No. 5,143,184 (Snyder, et al.) discloses a carbon composite brake disc, with positive vibration damping, in which a carbon composite aircraft brake disc is manufactured to include an insert member, which effects positive vibration damping of the disc during operation of the brake.
U.S. Pat. No. 6,376,431 (Matsumoto, et al.) discloses reduced wear carbon brake material, which is carbon/carbon composite, comprising crystalline silicon carbide, which is essentially uniformly distributed on both internal and external surfaces of the composite in a low concentration, as well as a process for producing the composite and the use of the composite in brake materials for industrial roll goods, automotives, trucks, trains and aircrafts. It has been discovered that small amounts of crystalline silicon carbide uniformly distributed throughout the carbon/carbon composite results in reduced wear with either no change or a slight increase in the friction coefficient.
U.S. Pat. No. 5,868,888 (Don, et al.) discloses a method for near net-shape fabrication of friction disk ring structures, in which trapeziform paneled strips of friction paper or cloth are folded to make uniform 2-ply disks.
U.S. Pat. No. 5,454,990 (Chareire, et al.) discloses a process for the production of a part, particularly a carbon—carbon brake disk and to the part obtained In a process for manufacturing a carbon—carbon component, in particular a brake disk, a porous substrate in the shape of a brake disk is formed exclusively from carbon fibers. Holes, having axes parallel to the axis of rotation of the disk, are made in the substrate and are arranged on concentric circles centered on the axis of rotation. Areas free of holes are provided around keyways in the disk. The substrate is then impregnated by chemical vapor phase deposition. The holes in the substrate reduce the path of the gas in the substrate.
U.S. Pat. No. 3,069,209 (Bauer) discloses a method of bonding a bimetallic casting, the bond exhibiting improved heat transfer characteristics, and allows reduction in weight of certain components, such as brake drums.
U.S. Pat. No. 5,957,251 (Jones, et al.) discloses brake or clutch components having a ceramic-metal composite friction material, in which a braking component, such as a brake pad, brake rotor, brake drum or clutch disk is comprised of a metal substrate, having a friction material laminated on at least a portion of at least one face of the metal substrate, the friction material being a ceramic-metal composite comprised of a metal phase and a ceramic phase dispersed within each other, wherein the ceramic phase is present in an amount of at least about 20% by volume of the ceramic-metal composite. In particular, the braking component is a metal substrate, such as aluminum, having laminated thereto a ceramic-metal composite of a dense boron carbide-aluminum composite having high specific heat and tow density.
U.S. Pat. No. 5,857,550 (Atmur, et al.) discloses a polymer derived fiber reinforced ceramic matrix composite clutch, in which a structural fiber reinforced ceramic matrix composite (FRCMC) material is adapted for clutch use. The entirety of the frictional components of a clutch mechanism or only particular components thereof can be made of the FRCMC material. One embodiment has integrally molded fiber reinforced ceramic matrix composite clutch friction pads, forming the friction surfaces of metal clutch parts. Clutch components exhibiting a higher temperature and wear-resistance.
U.S. Pat. No. 5,655,637 (Hays) discloses an automotive clutch with improved heat shield, having a pressure ring, preferably formed of aluminum, with a heat shield, that includes a thin outer metallic ring, preferably of steel, which is laminated to a layer of an adhesive resin, that contains metallic elements, which are in substantially direct heat exchange between the outer steel ring and the aluminum pressure ring. For this purpose, copper screen of suitable mesh, from 10 to about 20 U.S. Standard, is embedded in the adhesive resin layer, reinforcing the adhesive layer, and providing a controlled degree of direct heat transmission from the steel ring to the aluminum ring. In preferred embodiments, the attachment of the steel ring to the pressure ring is enhanced by a plurality of countersunk, flush head fasteners, which are spaced about the periphery of the ring in a regular geometric array. Optionally, a plurality of slots are provided in the steel ring to compensate for the differences in thermal expansion of the steel ring and the aluminum pressure ring.
U.S. Pat. No. 4,830,164 (Hays) discloses a heat puck for clutches and flywheels, which has a trapezoidal shape with a steel base plate and a thick layer of a high heat capacity material such as copper. The heat puck is attached to either or both the pressure plate and flywheel of an otherwise conventional automotive clutch assembly. Preferably a circular array of heat pucks are mounted on a respective plate or flywheel. The puck is mounted with a large diameter shoulder member that extends through an aperture in the puck, and is received in an aligned receptacle in the surface of the plate or flywheel. A screw or rivet fastener extends through the shoulder member, puck and plate or flywheel to retain the assembly. The shoulder member provides the necessary torque resistance to the assembly, protection the fastener from stress failure.
U.S. Pat. Nos. RE37,548 and 5,184,704 (Hays) disclose a conversion for a clutch of a motor vehicle, which uses a conventional Belleville spring to bias a pressure plate and clamp a clutch disc between the pressure plate and the flywheel of the vehicle. Frictional linings of the conventional clutch are substituted by frictional linings, which are preferably located at optimum geometric spacing, and which have from 30–70 percent less surface area for frictional engagement than that conventionally furnished with the clutch. The conversion is particularly applicable to upgraded performance cars.
U.S. Pat. No. 5,355,986 (Biswas) discloses a clutch and disc brake friction assembly, for use on medium and heavy duty vehicles, which includes a metallic shoe having an exposed backing surface provided with a plurality of relatively spaced protuberances projecting therefrom. A sheet metal attachment lamina overlies the backing surface, and is provided with a plurality of holes through which the protuberances extend. Subsequent to the distal ends of the protuberance having passed through the holes, the holes are enlarged thereby affixing the attachment lamina to the backing surface. The attachment lamina has a plurality of openings relatively arranged to form a grid-like configuration. The openings are separated from one another by narrow elongated segments, each having a V cross-sectional configuration, with the sides thereof diverging from a shoe backing surface. A high temperature adhesive lamina overlies the backing surface and the divergent sides of the narrow elongated segments of the attachment lamina. A friction lamina overlies the adhesive lamina and the attachment lamina, whereby the divergent sides of the elongated segments and the adhesive lamina become embedded in the friction lamina.
U.S. Pat. No. 5,158,165 (Flotow) discloses a backing plate for connection to a clutch disc, which includes a pair of spaced friction material portions (or pads). A central channel extends between the two portions to allow air to flow over and cool a central area of the friction material. Clearances are defined at radially inner and outer areas of the channel and receive rivets to secure the backing plate to a clutch disc. The rivets are positioned radially between the radially inner and radially outer edge of the friction material, such that the backing plate is firmly secured to the clutch disc to prevent bowing. The improved backing plate ensures that the backing plate remains firmly secured to the clutch disc, and that the friction material is adequately cooled such that it efficiently transmits rotational forces from a drive source to a driven shaft.
U.S. Pat. No. 6,247,382 (Umeki, et al.) discloses a composite material flywheel device, which has a ring made from a composite material of carbon fiber reinforced plastics and a spoke member inserted in the ring. The spoke member is made from the fiber reinforced plastics having a lower modulus of elasticity than that of the ring. A tapered bush is press-fitted into a center portion of the spoke member. Both of the tapered bush and the spoke member are tightly fixed on a shaft by a first spring supported by a holder, and by a second spring urging the holder, so as to prevent vibrations, due to looseness thereof.
U.S. Pat. No. 5,123,514 (Gatins, Jr.) discloses a clutch or brake system for a heavy duty vehicle, having an assembly which includes a shoe having an exposed surface on which is attached a carrier member. A friction liner is molded onto the carrier member, which is provided with a plurality of apertures, each having a peripheral flange embedded into a concealed surface of the liner. The attachment of the carrier member to the shoe exposed surface permits relative adjustment therebetween, when the assembly is in a braking or clutching mode, so as to compensate for any differential in coefficients of thermal expansion between the shoe and the carrier member on which the liner is molded.
U.S. Pat. No. 5,092,443 (Nomura) discloses a clutch disc assembly in which facings comprising cerametallic pads secured to back plates are secured to opposite faces of a plate at an outer peripheral part of a clutch disc, characterized by that a heat insulating material is held between the plate and a back plate on the opposite faces, the insulating material having a thickness gradually increasing from a radial inside to a radial outside of the clutch disc. The clutch disc assembly is directed toward preventing failure in engagement and disengagement of the clutch, by preventing a strain caused by heat produced on the part of the plate on which the facings are provided.
U.S. Pat. Nos. 5,033,599 and 4,951,793 (Hays) discloses a clutch with dissimilar frictional facings and centrifugal assist, in which frictional engagement faces of a clutch are provided with an organic composite facing and a sintered metal facing. The benefits of both types of facings are obtained without many of the disadvantages that formerly plagued the use of these facings. The organic composite facing provides the low temperature service for the clutch, with a suitably high coefficient of friction, which is relatively constant from ambient to several hundred degrees F. The sintered metal facing provides high temperature service for the clutch. Thus, when the organic composite facings reach their maximum service temperature of around 500 degrees F., the sintered metal facings provide their optimum coefficient of friction, resulting in a subassembly in which the overall or average coefficient of friction remains substantially constant from ambient temperatures to the maximum service temperature of the sintered meta coatings, in excess of 900 degrees F. The result, when incorporated in an automotive clutch, is a clutch having a smooth, non-vibrational action, which does not exhibit premature wear and failure.
U.S. Pat. Nos. RE36,363 and 4,846,326 (Tilton, et al.) discloses a carbon to carbon friction clutch, in which carbon input disks are coupled to a flywheel by radial slots in their peripheries. Carbon input disks are coupled to a drive shaft by means of inner, radial slots and a metallic hub which contains slot-matching fingers. The input and output disks, as well as the hub, are axially free standing when the clutch is disengaged. The design distributes load more uniformly over the carbon plates than previous devices and allows greater service life of the clutch.
U.S. Pat. No. 5,769,973 (Smith, Jr.) discloses a high performance automotive clutch with modified pressure plate for sustained increased spring force. A Belleville spring pressure plate of increased height, for use in a high performance clutch assembly, exerts a greater force than the original height plate, is usable without modification of the original clutch, and is longer lasting in service, after being thermally conditioned to a martensitic state, to lose the memory of its original, lower height, and being stress tempered before being set in a new, increased height shape.
U.S. Pat. No. 5,415,262 (Bernal, et al.) discloses a carbon to carbon friction mechanism, which includes a lightweight pressure plate directly mounted to an adjacent carbon plate, so that the pressure plate is kept concentrically aligned during operation of the mechanism. The directly mounted pressure plate and adjacent carbon plate may be used as components of a carbon to carbon friction clutch. Sufficient clearances are provided between the pressure plate and its adjacent carbon plate, to allow for thermal expansion of the materials used for the pressure and carbon plates.
U.S. Pat. No. 6,155,397 (Killian) discloses a clutch driven disc assembly, which includes a hub and an annular spring plate fixed to the hub. A friction disc assembly is mounted concentric with an axis of rotation of the hub and is rotatably relative to the spring plate. A plurality of drive springs are operably disposed between the spring plate and the friction disc assembly. The friction disc assembly further includes a reinforcing plate and a substantially annular disc fixed to the reinforcing plate. A friction material button is fixed to the substantially annular disc. The friction material button has a metallic friction material cookie with at least three apertures. A backer plate is fixed to the friction material. The backer plate covers the apertures in the friction material cookie. At least three spot welds are within three corresponding apertures in the cookie. At least one of the welds is offset from a line joining two others of the welds. The welds join the substantially annular disc and the backer plate, in turn fixing the friction material button to the substantially annular disc.
U.S. Pat. No. 4,860,872 (Flotow) discloses a friction disc assembly, which includes a plurality of one piece or unitary friction elements, each containing a pair of opposed planar friction surfaces. Each element is adapted for being supported within an opening of a clutch driven disc, wherein a pair of backing plates virtually supports each disc, by trapping same within pairs of aligned openings. In a preferred form, the backing plates comprise an interference fit with the axially aligned boundaries of associated friction surfaces, and rivets, which hold the backing plates rigidly to the driven disc, are spaced from and hence out of contact with the friction elements. In a preferred form, each friction element includes a radially extending tongue, which has a thickness equal to the thickness of the driven disc.
U.S. Pat. No. 4,977,991 (Mahoney) discloses a multiple disc clutch, which comprises interleaved first and second sets of friction discs mounted for rotation of one disc set relative to the other disc set about an axis, the disc sets being shiftable axially of each other; a flywheel plate for mounting in driving engagement to a source of torque; and a plurality of separately formed dowels, for securing to the flywheel plate at its circumference, at circumferentially spaced locations, the dowels projecting axially therefrom through corresponding circumferentially spaced apertures adjacent the radially outward edge of the second disc set, for driving engagement with the second disc set, the number and spacing of the dowels being chosen with respect to the circumference of the second disc set, to promote air cooling of the multiple disc clutch, by circulation of air around the dowels and between discs of the disc sets.
U.S. Pat. No. 6,070,707 (Hofmann, et al.) discloses a friction clutch, in which an axial play is provided between an inner disk and a hub of a clutch disk. The axial play can be influenced by a device during assembly of the friction clutch in an engine and transmission of a motor vehicle drive train, such that the hub is displaced, within the axial play, into the position in the axial play, which lies closest to a flywheel of the friction clutch.
U.S. Pat. No. 5,857,546 (Hofmann, et al.) discloses a multiple-disk friction clutch, especially for motor vehicles, with a hub which has an internal toothing and can be placed on a gear shaft, so as to be rotationally fixed relative thereto. At least two clutch disks are connected with the hub, so as to be rotationally fixed relative thereto and project radially beyond the hub. A stop, which guides the hub axially relative to the clutch disks, is provided between the clutch disks. The hub is formed of two parts, and includes a hub body having an outer toothing and a hub ring, which has the same outer toothing, and sits on a radial shoulder of the hub body. The outer toothing of the hub ring is offset by one tooth relative to the toothing of the hub body, to form the stop for the clutch disks. The hub body and the hub ring are connected with one another, so as to be rotationally fixed relative to one another.
U.S. Pat. No. 6,035,987 (Fukuda) discloses a multi-plate clutch of a boss driving type, with structure to make it easy to replace a boss, and to limit the number of parts. The clutch includes a flywheel, a boss, a clutch cover assembly, and input-output friction members, such as clutch disks, an intermediate plate, and a pressure plate. The boss is detachably coupled to the flywheel, and includes an annular portion and a plurality of columnar portions, which are formed integrally with the annular portion. The columnar portions extend in an axial direction from the annular portion. Each of the columnar portions is disposed circumferentially next to one another in a circular pattern, with a radial pass-through space formed therebetween. The clutch cover assembly includes a clutch cover, which is detachably coupled to the boss, a pressure plate, and a diaphragm spring assembly. The clutch disks and the intermediate plate are disposed between the friction face and the pressure plate.
U.S. Pat. No. D395,325 (Fukuda) also discloses a friction clutch, especially for automotive racing applications.
U.S. Pat. No. 5,638,932 (Mizukami) discloses a dry multi-disk clutch. A clutch cover assembly is used with clutch friction disks of a dry multi-disk clutch, and is provided with a diaphragm spring, a clutch cover and a support structure. The outer periphery portion of the diaphragm spring loads the clutch friction disks. The support structure includes a first annular disk-like annular ring member possessing a first ring main body, which contacts a portion of the diaphragm spring from the clutch cover side, and a seating portion, which extends from the first ring main body, and seats against the clutch cover, a second annular disk-like annular ring member possessing a second ring main body, which contacts the diaphragm spring on the side opposite the first annular disk-like annular ring member, and bolts for fixing the first and second annular disk-like annular ring members to the clutch cover. One purpose of the invention is to suppress clutch cover wear, caused by annular disk-like wire rings. A hub flange having a boss and a flange extending from the boss to the outer periphery, where a drum-shaped element is formed, which extends axially to opposite sides of the outer periphery of the flange. Plural annular drive plates and plural annular driven plates are disposed between a flywheel and the clutch cover. In the flange, passage openings are formed, which provide air flow. In the two axially projecting portions of the second drum-shaped element, there are formed air passage holes, the openings and holes preventing the temperature in the friction disks in the dry multi-disk clutch from rising excessively.
U.S. Pat. No. D402,299 (Mizukami) also discloses a dry multi-disk clutch, especially for automotive racing applications.
U.S. Pat. No. 5,301,779 (Nash) discloses a friction clutch, which includes a hub and driven plate assembly, in which three carbon driven plates are mounted on a hub, the hub having radially outwardly extending splines thereon, and the driven plates having radially inwardly extending teeth, for engagement with the splines, such that the hub can slide axially relative to the driven plates, when the driven plates are held axially by driving plates. Roll pins are each held in holes through two adjacent splines, such that the roll pins are between the driven plates, and limit axial movement of the hub relative to the driven plates.
For the foregoing reasons, there is a need for a disk brake that has improved braking efficiency, does not become overheated or warp, is light weight, durable, long lasting, and may be manufactured or retrofit with replacement parts quickly, easily, and efficiently.