# Patent

## Title
Methods for orienting superabrasive particles on a surface and associated tools

## Abstract

Methods of making a superabrasive tool precursor are disclosed, along with such precursors and associated tools. Particularly, methods are disclosed for orienting superabrasive particles in a viscous binding material in order to provide tools based thereupon and having desired performance characteristics.

## Background
PRIORITY DATA
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/992,966, filed on Dec. 6, 2007, which is incorporated herein by reference.


FIELD OF THE INVENTION
The present invention relates generally to superabrasive tools and methods for making such tools. Accordingly, the present invention involves the chemical and material science fields.
BACKGROUND
A wide variety of applications rely on tools based on superabrasive cutting elements. These applications range from sawing and drilling through hard materials such as stone, masonry, concrete, and metal, to conditioning the pads used in chemical mechanical polishing (CMP) of silicon wafers for semiconductors. Each application requires different types of superabrasive tools and places different demands upon those tools. In order to better match tool performance with the demands of each application, tool manufacturing processes would benefit from methods that allow more effective control over the characteristics of each tool.
SUMMARY
The present invention provides methods of making an abrasive tool precursor. In one aspect, such a method may include the steps of placing a layer of a binding material on a surface of a substrate, distributing abrasive particles on the layer of binding material, and then allowing the abrasive particles to pass at least partially through the binding material and toward the substrate while rotating until at least a number of the abrasive particles exhibit substantially the same orientation.
A more particular embodiment provides a method of making a superabrasive tool precursor, comprising the steps of placing a layer of a viscous medium on a surface of a substrate, distributing superabrasive particles on the layer of viscous medium, and then heating the viscous medium to decrease its viscosity. The superabrasive particles then move at least partially through the viscous medium toward the substrate, being free to rotate while so moving, so that a percentage of the superabrasive particles exhibit substantially the same orientation when they come to rest. The movement of the particles may be induced by gravity or by other imposed forces such as centripetal force. In some embodiments of the present invention, other mechanisms for reducing the viscosity of the medium can be used, such as solvents or other agents/mechanisms. In yet further embodiments of the present invention, the viscosity of the material may not be reduced prior to the application of force on the particles, but rather, the viscosity may be sufficient to prevent substantial movement of the particles through the medium without the use of force, while allowing movement upon the application of force, such as those forces discussed herein.
The present invention also provides a method of making a superabrasive tool, comprising the steps of placing a layer of a binding material on an upper surface of a substrate; distributing superabrasive particles on the layer of binding material; inducing the superabrasive particles to pass at least partially through the binding material and toward the substrate while rotating until at least a number of the superabrasive particles exhibit substantially the same orientation; attaching a tool body to the portion of the superabrasive particles facing away from the substrate; and removing the substrate and the layer of binding material so as to expose the portion of the superabrasive particles that faced the substrate.
Also provided is a superabrasive tool precursor, comprising a substrate, a layer of binding material on a surface of the substrate, and a plurality of superabrasive particles distributed in the binding material. The binding material exhibits a viscosity such that the superabrasive particles are free to move through the binding material toward the substrate and to rotate in the binding material in response to an external force applied to them.



BRIEF DESCRIPTION OF THE DRAWINGS
Additional features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention; and, wherein:
FIG. 1 is a side view of a superabrasive tool precursor in accordance with an embodiment of the present invention;
FIG. 2 shows the making of a superabrasive tool element from a side view in which superabrasive particles are embedded in a metal;
FIG. 3 shows the making of a superabrasive tool element from a side view in which superabrasive particles are embedded in a resin; and
FIG. 4 shows the production of tool elements from a side view as shown in FIG. 3 and attachment thereof to a tool body.



Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
Before the methods and articles of the present invention are disclosed and described, it is to be understood that this invention is not limited to the particular process steps and materials disclosed herein, but is extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
It must be noted that, as used in this specification and the appended claims, the singular forms “a,” and, “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a “superabrasive particle” includes reference to one or more of such superabrasive particles.
DEFINITIONS
In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set forth below.
As used herein, “superabrasive particle” and “superabrasive crystal” or similar phrases may be used interchangeably, and refer to any natural or synthetic super hard crystalline, or polycrystalline substance, or mixture of substances and include but are not limited to diamond, polycrystalline diamond (PCD), cubic boron nitride (cBN), and polycrystalline cubic boron nitride (PcBN).
As used herein, “superhard” and “superabrasive” may be used interchangeably, and refer to a crystalline, or polycrystalline material, or mixture of such materials having a Vickers hardness of about 4000 kg/mm2 or greater. Such materials may include without limitation, diamond, and cubic boron nitride (cBN), as well as other materials known to those skilled in the art.
As used herein, “binding material” refers generally to a material capable of maintaining the relative positioning of particles suspended, embedded, or otherwise distributed therein. Such materials may have this capability by virtue of properties such as viscosity, adhesive properties, electrostatic properties, or any combination thereof.
As used herein, “chemical bond” means a covalent bond, such as a carbide, nitride, or boride bond, rather than mechanical or weaker inter-atom attractive forces.
As used herein, “working end” refers to an end of a particle which is oriented towards and makes contact with a workpiece during tool use. Most often the working end of a particle will be distal from a substrate to which the particle is attached.
As used herein, “sharp portion” means any narrow portion to which a particle may come, including but not limited to corners, ridges, edges, obelisks, and other protrusions.
As used herein, “orientation” means the position or arrangement of a particle in relation to a defined surface, such as a substrate to which it is attached.
As used herein, “substrate” means a solid surface in a tool precursor which supports abrasive particles, and on which abrasive particles may be arranged and stabilized in an arrangement. Substrates useful in the present invention may be any shape, thickness, or material, that is capable of supporting abrasive particles in a manner that is sufficient for its intended purpose. In one aspect, a substrate may be configured so as to hold abrasive particles in such a way that the particles may be attached to a tool.
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.
Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “about 1 to about 5” should be interpreted to include not only the explicitly recited values of about 1 to about 5, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc. This same principle applies to ranges reciting only one numerical value. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.
A method of making a superabrasive tool precursor can comprise placing a layer of a binding material on a surface of a substrate, distributing superabrasive particles on said binding material, and then allowing or inducing the particles to pass at least partially through the material toward the surface. The distribution may be random, or in a particular desired arrangement across the surface, depending on the dressing performance desired. In one embodiment, the substrate may be temporary and serves merely as a platform for this arrangement so that the arrangement may be eventually transferred to the working surface of a tool. In an alternative embodiment, the substrate is permanent and may itself be in the final tool as either part of the intended working surface, or supporting the intended working surface. In a particular embodiment, an adhesive may be overlaid on the binding material before or after the particles are distributed thereupon in order to preserve the particles' arrangement for subsequent steps in the process.
Various types of superabrasive particles may be utilized in various aspects of the present invention. Such superabrasive materials may include without limitation, diamond, polycrystalline diamond (PCD), cubic boron nitride (cBN) and polycrystalline cubic born nitride (PcBN). In some aspects, the superabrasive particles may include diamond. In one aspect, the diamond superabrasive particles may exhibit a combination of cubic and octahedral faces. Further, the superabrasive particles can be of a predetermined shape. For example, the superabrasive particles can be a euhedral shape or either a octahedral or cubo-octahedral shape. Polycrystalline particles may exhibit additional shapes, including cubic, rhomboidal, pyramidal, and decahedral. In addition to superabrasives, the methods of the present invention may be used with other abrasive particles including, without limitation, particles that comprise glass, metal, ceramics, composite materials such as cermets, and minerals having a Vickers hardness of 200 kg/mm2 or higher.
Superabrasive particles attached a tool may exhibit any number of orientations relative to the surface to which they are attached. Particle performance on a workpiece is largely dictated by the working end of the particle. Depending upon the shape of the particle, this working end can be a sharp portion of the particle, or a more planar portion of the particle. This can be illustrated by considering superabrasive particles having a euhedral crystalline shape that includes a plurality of faces, edges, and apexes. Each of these features will perform differently when serving as the working end of the crystal. On such a shape, the apexes, and to a lesser degree the edges, represent the sharp portions of the crystal. These will tend to cut deeper, narrower grooves in the material of a workpiece and therefore work more aggressively, but are also less durable than the face of the crystal. In contrast, a crystal face will tend to cut shallower, broader grooves, but are thought to be more durable than sharp portions and therefore wear more slowly. It can be appreciated, then, that the ability to choose the orientation that superabrasive particles will exhibit in a tool allows one to determine the performance characteristics of the tool. This is particularly possible when a plurality of particles can be made to assume a particular orientation. Accordingly, the present invention provides methods directed to these results.
Once the superabrasive particles are distributed as needed, it is desirable that the they be made to assume a common orientation or a set of orientations. This requires that at least some of the particles change their original orientation by rotating. The present invention provides for such rotation by inducing the particles to enter the binding material, so that the binding material serves as a medium that supports the particles while affording them freedom to rotate. In this sense, it is highly preferable that the binding material have some measurable viscosity so as to provide some measure of buoyancy, though said buoyancy should still be negative. In a particular embodiment, the binding material is a viscous medium. Viscosity serves the purpose of providing support to the particles. However, just as importantly, the viscosity provides for increased drag and frictional forces to be exerted against the planes and angles of the particles as the particles move within the medium. These forces and the shape of the particles interact to produce particle rotation that can be utilized to establish desired particle orientation.
This is exemplified in a particular embodiment of the present invention illustrated in FIG. 1, where superabrasive particles 10 are distributed onto a substantially horizontal substrate 20 covered with a binding material 30. Optionally adhesive 40 may be applied to the substrate and/or binding material to provide stability. The particles are then induced or allowed by gravity to descend into the material. This settling is governed by the principles and forces involved in sedimentation. As each particle settles into the medium, the particle's flat surfaces 12 encounter more drag than the edges 14 or apexes 16. As a consequence, each particle will rotate so as to achieve a lower drag, i.e. it will tend to assume a favored orientation that is dictated by the particle's shape and the forces involved. For many particle shapes, this favored orientation will be with an edge or apex leading the way down through the medium. Eventually each particle will come to rest on the underlying surface, with a substantial number of particles exhibiting a common edge-down or apex-down orientation. In a particular embodiment, the surface may include a plurality of pits 50, where each pit designates the eventual resting place of one or more superabrasive particles. In one aspect, each pit may have been shaped so as to more easily accommodate and stabilize a particle in the favored position.
In order to more effectively control particle placement and orientation, it may be desirable to control the onset of the entry of the particles into the binding material. One way to delay onset until desired is to utilize a binding material that is sufficiently dense that the particles initially float on top of the material once distributed. Therefore in one aspect of the present invention, entry may be initiated by changing the viscosity of the binding material, such as by heating. In a particular aspect, the binding material may be in a solid or semi-solid state when it is laid upon the tool precursor surface and then heated to assume a liquid state after superabrasive particles are applied. Once the density or viscosity of the binding material decreases sufficiently, the superabrasive particles descend into the binding material while rotating in response to forces exerted by the material. For example, where diamond (ρ=3.5 gm/cc) is used as the superabrasive, the density of the binding medium should be low enough to allow the diamond to descend—preferably the density is below about 2.0.
Other methods of initiating particle entry into the binding material may involve a more proactive selection of the nature and onset of the force inducing the particles to move toward the tool precursor surface. For example, forces that are similar in nature to gravity can be created by placing the tool precursor elements in a centrifuge. In such an embodiment, particles are induced to enter the medium by the resulting centripetal force acting on them when the centrifuge is activated. In another embodiment, a magnetic or electromagnetic force may be used to move particles made of materials responsive to this force. An added aspect of this approach is that it provides a greater degree of control over many aspects of the process, particularly the magnitude and duration of force to be applied to the particles. By selecting these characteristics, as well as the properties of the binding material and of the superabrasive particles themselves, it is possible to influence the number of particles that will eventually share a given orientation in the finished tool.
It can be appreciated that the magnitude of force will have an effect on the movement of the particles in the binding material. For example, applying greater centripetal force may cause the particles to move more rapidly through the layer of binding material, in turn reducing that amount of time each particle has to change its orientation. However, a more viscous binding material will slow the movement of particles, as well as exerting greater drag forces on them, both promoting more completed rotation and orientation of particles. Other factors that will influence the process are the shape of the particles and the thickness of the binding material layer. One skilled in the art will appreciate that all of these factors can be selected and manipulated to a degree so as to determine the characteristics of the final product. For example, in a particular embodiment the centripetal force is applied until all of the particles come to rest on the substrate. Alternatively, a shorter duration may be chosen in which the particles only pass partially through the binding material. In the present invention, a layer of binding material should be applied to the substrate at a sufficient depth so as to allow the particles to rotate at least somewhat before coming to rest on the substrate. In a particular embodiment, the depth allows the particles to rotate at least 180°.
The combination of force and materials chosen in a given application of the disclosed process to a tool precursor will result in a frequency distribution of orientations among the particles. The fraction of particles occupying an orientation will depend partly on the number and magnitude of forces favoring that orientation and on the opportunity afforded the particle to respond to those forces, with the latter depending on the duration of the forces and the distance traveled. For a given particle shape there may be a number of possible orientations each favored to different degrees by the forces involved. In that case, upon completion of the process the most favored orientations will be most heavily represented with the other possible orientations represented according to what degree each is favored. Accordingly, the factors involved in the process may be manipulated so as to result in nearly all of the superabrasive particles occupying a particular orientation. Alternatively, the process may be directed so that a given frequency distribution of orientations results among the particles. In one aspect the resulting percentage of particles sharing a particular orientation may be from about 50% to about 100%, while in a more particular aspect, the percentage may be from about 65% to about 85%. In either of these aspects, the orientation may be the most favored orientation, e.g. with an apex toward the substrate, or a less favored orientation, e.g. an edge toward the substrate. Furthermore, the remaining particles may share another orientation or may exhibit a frequency distribution of orientations. Because of the different cutting behavior each orientation provides, manipulating the frequency distribution of orientations on a tool allows for subtle manipulation of its overall cutting performance.
Once the placement and orientation of superabrasive particles is complete, the binding material can serve to hold them in place for further processing. For binding materials that are applied in a solid or semi-solid state, the material can simply be allowed to cool and regain its solidity after orientation is complete. Where liquid medium is to be used, it is preferable to use a medium that can be cured to form a solid so as to hold the superabrasive particles in place. Materials that may be used as binding materials in accordance with the present invention include but are not limited to plastics, adhesives, resins, rubbers, and slurries. In a particular embodiment, a plastic is used. In a still more specific embodiment, a thermal plastic is used that changes from substantially solid to liquid upon heating. As mentioned above, the characteristics of the binding material can affect the behavior of particles moving through them. For example, some binding materials may exert less drag on flat portions of particles, making particles less likely to rotate away from a face-down orientation. It may be possible, therefore, to choose a binding material so as to more directly influence the final orientation of particles. One can further use this approach to produce different orientations or distributions of orientations in different subsets of particles in the tool. For example, a given tool precursor of the present invention may include a substrate in which different binding materials are placed in different zones of the surface, so that the resulting tool will present on its working surface a plurality of zones each having differently oriented particles.
A superabrasive tool precursor of the present invention will comprise a substrate overlaid by a layer of binding material with a plurality of superabrasive particles suspended therein. The binding material allows for the particles to rotate in response to sedimentation forces and external forces and thereby assume certain orientations. As stated above, one purpose of this precursor is to facilitate the transfer of the arrangement of superabrasive particle to a tool, while preserving the spatial arrangement and orientations of the particles attained on the precursor. Accordingly, a method of making a superabrasive tool can comprise the use of a tool precursor according to the present invention. There are a number of methods known in the art of attaching superabrasive particles to working surfaces of tools. One common approach involves depositing a metal layer onto an arrangement of superabrasive particles, securing the particles therein, where said layer may then be attached to or incorporated into the working surface of a tool. Another method is to apply a resin to the intended working surface, situate a plurality of superabrasive particles in the resin, then cure the resin to provide a means of securing the particles in place. The precursor tool of the present invention may be employed in conjunction with these and similar methods to make a tool with superabrasive particles that share a common orientation or set of orientations.
In a preferred embodiment, each oriented superabrasive crystal in a completed tool precursor is situated in solid binding material and oriented so that what will be its working end is facing the precursor substrate. The opposite end of each particle faces away from the substrate. Preferably, once particle orientation is complete the layer of binding material is rendered thin enough so that a substantial portion of this end of each particle is exposed. Still more preferably, the binding material covers about 20% to about 35% of the particle's height. This can be done by removing excess binding material either before or after curing if needed. For some binding materials, the process of curing may render the layer thinner due to the loss of water or volatiles.
Once the binding material is cured, the tool precursor can serve as a template for situating the superabrasive particles in the working surface of a tool or a tool element. In one embodiment as illustrated in FIG. 2, the particles 10 are embedded in a metal 60 that can be bonded to a tool or otherwise incorporated into its working surface. In a specific embodiment this metal is nickel. In a more specific embodiment, nickel is plated onto the top surface of the binding layer and particles. However, in order to seat the superabrasive particles more securely, it may be desirable to interpose a metal binding layer 70 that more readily forms a chemical bond with the particles. For example, carbide formers can form such bonds with diamond or cubic boron nitride superabrasive particles. Therefore, in another specific embodiment, a layer of carbide-forming metal is deposited onto the particles and binding layer. Examples of carbide-forming metals that may be used are chromium, titanium, molybdenum, tungsten, cobalt, and tantalum. In a preferred embodiment, the carbide-forming metal is chromium. The carbide-forming metal may be deposited by methods known in the art, such as chemical vapor deposition. Nickel may then be plated onto the carbide-forming metal layer and the exposed particles. The binding layer may then be removed to expose the cutting surfaces of the particles.
In an alternate embodiment shown in FIG. 3, the exposed ends of the superabrasive particles 10 are cast in a resin 80. Use of resins for retaining superabrasive particles for tool applications is set forth in detail in U.S. Pat. No. 7,258,708, which is incorporated herein by reference. The resin can be any resin which is curable to a degree of hardness that will retain the particles under working conditions. Some suitable resins include, but are not limited to, epoxy resins, polyimide resins, polycarbonate resins, formaldehyde resins, polyester resins, and polyurethane resins. The tool precursor may be placed in a mold 90 that will impart a shape to the piece that facilitates incorporation into the eventual tool. The resin material is then applied to the top surface of the binding material 30 and particles. Vacuum casting may be employed to minimize voids in the resin. Once the resin is cured, the binding agent can be peeled off to expose the working ends of the particles. Depending on the binding material and resin material used, it may be necessary to use a parting agent so that they may be separated after curing. In a preferred embodiment, before casting the top surface of the binding material and particles is sprayed with a parting agent.
Once the superabrasive particles are embedded into a material and the binding material is removed, the resulting tool or tool element exhibits a plurality of particles that share a substantially common orientation or set of orientations. In a particular aspect, where the particles were oriented allowed to rest against the substrate in the tool precursor, the particles in the resulting tool all protrude from the tool surface by substantially the same amount. For precursors utilizing a flat substrate, this method provides a tool with a substantially level cutting surface. However, it will be appreciated that substrates having other profiles may be used, so that the present method can provide a cutting surface with more complex contours, but where each superabrasive particle protrudes by the same amount. For example, a tool may be desired that has a cutting surface with a convex profile, where the center of the working surface extends farther toward the workpiece than does the periphery. This is particularly useful in compensating for the deformation that may occur in more flexible workpieces. CMP pads, for example, may flex under the pressure exerted by a superabrasive pad conditioner. A curved working surface allows more of the abrasive particles to maintain contact with the workpiece. To create such a tool, a precursor would be used that has a substrate with the opposite profile (i.e. concave). In accordance with the present invention, this precursor can be used to create a tool having a desired profile, while maintaining the particle height across the surface. Possible profiles included curved, wavy profiles, as well as profiles having polygonal bases, e.g. rhomboidal and pyramidal.
The tool element formed by the above process may be made the working surface of a tool by being attached to the tool. The tool element may be made initially in a shape that corresponds to the desired working surface. Alternatively, the particles may be embedded in a larger sheet of material that may then be divided so as to form multiple tool elements. For example, the method of embedding oriented particles in resin may be used in the mass production of tool elements as shown in FIG. 4, where a large number of particles 10 are oriented in a sheet of binding material 30 and then embedded in resin 80. The resin is then cured and cut into individual tool elements 100. These elements may each be attached to separate tools or, as shown here, a plurality of elements may be attached to a single tool 110. This allows the making of a composite superabrasive tool with a plurality of superabrasive elements which may have either similar or different particle arrangements and orientation distributions.
While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

## Claims

1. A method of making a superabrasive tool precursor, comprising:
(a) placing a layer of a viscous medium on a surface of a substrate, said viscous medium having a density and a viscosity;
(b) distributing superabrasive particles on the layer of viscous medium; and
(c) heating the viscous medium to decrease its viscosity, so that the superabrasive particles move at least partially through the viscous medium toward the substrate, during which the superabrasive particles are free to rotate,

wherein the viscosity is selected to affect the percentage of superabrasive particles exhibiting the same orientation; and
a percentage of from 65% to about 85% of the superabrasive particles exhibit substantially the same orientation when they come to rest.

2. The method of claim 1, wherein the superabrasive particles are diamond particles.

3. The method of claim 1, wherein the viscous medium has a lower density than that of the superabrasive particles.

4. The method of claim 1, wherein the movement of the superabrasive particles is due at least in part to a force selected from the group consisting of: gravitational, centripetal, magnetic, electromagnetic, and combinations thereof.

5. The method of claim 4, wherein the force is gravitational.

6. The method of claim 4, wherein the force is centripetal.

7. The method of claim 6, wherein a magnitude of centripetal force is selected to affect the percentage of superabrasive particles exhibiting the same orientation.

8. The method of claim 1, wherein the superabrasive particles come to rest in physical contact with the substrate.

9. The method of claim 1, wherein the percentage of the superabrasive particles are oriented with an apex toward the substrate.

10. The method of claim 1, wherein the percentage of the superabrasive particles are oriented with an edge toward the substrate.

11. The method of claim 1, wherein the viscous medium contains a wetting agent.

12. The method of claim 1, wherein the layer of viscous medium has a depth sufficient to allow the superabrasive particles to rotate at least 180° before contacting the substrate.