Patent Application
20110244770
Lapping is a well-known process of abrasion metal-removal or machining for smoothing or polishing surfaces to a high degree of refinement or accuracy using loose abrasive lapping compound embedded in soft plate referred to as lapping plates. The lapping compound is often in a liquid suspension or semi-liquid form, and is called lapping slurry.
Polishing quality produced on a lapping plate is a strong function of the abrasive height distribution and abrasive density. The tighter the height distribution one can achieve the smoother the finish of the final polishing surfaces. Protruding abrasives from the mean height distribution of the diamonds produce scratches in the polishing surface. An ideal state of a uniform height distribution produces atomically smooth surfaces.
A typical example of magnetic slider bars with trailing edges composed of metallic layers and ceramic layers present very severe challenges during lapping. Composite structures of hard and soft layers present differential lapping rates when lapped using conventional abrasive substrates. The variable polishing rates of the metallic and ceramic materials lead to severe recessions, sensor damage, and other problems.
U.S. Pat. Nos. 7,198,533 and 6,123,612 disclose an abrasive article including a plurality of abrasive particles securely affixed to a substrate with a corrosion resistant matrix material. The matrix material includes a sintered corrosion resistant powder and a brazing alloy. The brazing alloy includes an element which reacts with and forms a chemical bond with the abrasive particles, thereby securely holding the abrasive particles in place. A method of forming the abrasive article includes arranging the abrasive particles in the matrix material, and applying sufficient heat and pressure to the mixture of abrasive particles and matrix material to cause the corrosion resistant powder to sinter, the brazing alloy flows around, react with, and forms chemical bonds with the abrasive particles, and allows the brazing alloy to flow through the interstices of the sintered corrosion resistant powder and forms an inter-metallic compound therewith.
The nanospheres can be fabricated hollow. Full nanosphere nano particles have a wide variety industrial and biomedical uses. The manufacturing of uniform and regular nanosphere is becoming a common in an industrial setting. U.S. Pat. No. 6,720,007 B2 addresses the formation of polymeric micro-nano spheres.
The abrasive particles may include diamonds, Aluminum oxides, Titanium oxides, ceria, and the like.
The present invention improves the embedded abrasive height distribution in lapping plates. The height distribution of diamonds improves the surface finish and reduces the number of scratches. When lapping under ideal conditions of a very uniform abrasive height distribution a super smooth surface is attained with no scratches and surface damage.
The invention proposes the addition of flexible polymeric nanospheres as an additive to existing lubricant based abrasive slurries. The sphere diameter distribution and sphere density produce a cushion balancing the applied dressing wheel preload. Manufactured nanospheres are not uniform in diameter or shape distribution (Walt et al., U.S. Pat. No. 6,700,007 B2), a Gaussian distribution can be used to characterize the incoming height distribution. The nanospheres can be coated with non-polar materials to avoid agglomeration as described in Walt et al., U.S. Pat. No. 6,700,007 B2 and Walsh et al., U.S. Pat. No. 6,207,195 B1. The nanospheres can be full sphere or hollow spheres as shown in Walt et al., U.S. Pat. No. 6,700,007 B2 and Walsh et al., U.S. Pat. No. 6,207,195 B1.
The embodiments described herein relate to methods for plate dressing using slurry charged with abrasives and micro-nano sphere additives to produce substantially uniform abrasive height. In particular, soft polymeric nanospherical additives produce a constant spacing between the dressing wheel and the polishing substrate under a given load. Protruding hard abrasives are forced to embed by the dressing wheel in the softer substrate until the resistance of the uniform diameter nan micro-nano sphere balances the applied wheel load. The soft polymeric micro-nano sphere deform under the dressing wheel load to provide a uniform spacing between the lapping plate and the dressing wheel. The slurry contains both abrasives and micro-nano sphere additives. Since the abrasive have a substantially higher hardness, they will embed into the soft lapping substrate while the soft polymeric micro-nano sphere additives deform under the applied load without embedded into the plate and regain their original shape once the load is removed. The micro-nano sphere can be thought of a large number of springs resisting the applied load from the dressing wheel. Upon deforming under the applied load the nanospheres reach an equilibrium state assuring a spacing equal to the mean original height of the nanospheres minus the mean deformation of the nanospheres.
In accordance with one aspect of the present invention, a lapping slurry which includes soft polymer nanospheres dispersed in a carrier fluid charged with abrasive particles.
In accordance with a second aspect of the present invention, a lapping slurry includes abrasive particles and soft polymeric nanospheres dispersed in a carrier fluid. Carrier fluids are often formed from oil, water, glycerine, triethanolamine according to U.S. 2007/0135317 A1.
In one example embodiment, the nanosheres are removed, such as by removal of the lubricant and nanoshperes from the substrate 16 after removing the applied load of the dressing wheel 10 (shown in
Soft coatings 23 include self assembled polymers providing a substantially conformal layer throughout the lapping plate. A very thin film of gold is applied to the polishing plate to enhance the adhesion and growth of the self assembled polymer. The self assembled layer can be grown to various precise thickness 28 which is very desirable. Self assembled polymers have good tribological properties of resistance wear and erosion during the abrasive particles embedding process. The abrasive particles easily penetrate the self assembled coating. The self assembled layer can be thought of as an infinite number of springs resisting the dressing wheel applied load to provide a substantially uniform diamond protrusion height.
During the application of the load 29 to embed the abrasive particles, the load will remain constant while the charging wheel 20 experience a displacement equaling the amount of abrasive particles 14, 24 penetration in the soft lapping plate 16, 26. Once the charging wheel contacts the micro-nano spheres or the coating, the reaction due to the deformation of the micro-nano spheres 13 or the coating resists 23 the charging wheel 10, 20 displacement to reach equilibrium between the applied load and the micro-nano spheres or the coating deformations. The contact stiffness attained is directly proportional to the mean height of the protruding abrasive particles. The amount of deformation of the micro-nano spheres or the coating equals the height of protruded abrasive particles.
Multiple layers of soft coatings can be used in combination. For example, a non light sensitive coating can be deposited first, followed by a light sensitive polymer. Desired patterns can be formed and developed onto the light sensitive material. An abrasive slurry is then dispersed.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these inventions belong. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present inventions, the preferred methods and materials are now described. All patents and publications mentioned herein, including those cited in the Background of the application, are hereby incorporated by reference to disclose and described the methods and/or materials in connection with which the publications are cited.
The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present inventions are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.
Other embodiments of the invention are possible. Although the description above contains much specificity, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the example embodiments of this invention. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above.
Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.
This application claims the benefits of the filing date of U.S. Provisional Patent Application Ser. No. 61/320,787, which is entitled “Lapping slurry formulations containing nanospheres additives” filed Apr. 5, 2010, which is hereby incorporated herein in their entirety by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61320787 | Apr 2010 | US |
