CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Patent Application No. 61/506,253, filed Jul. 11, 2011, the disclosure of which is incorporated herein by reference.
The present disclosure broadly relates to lapping carriers and processes for abrading a workpiece using them.
A need often arises to grind or polish flat workpieces such as disk-shaped articles (e.g., silicon wafers, sapphire disks, optical elements, or glass or aluminum substrates for magnetic recording devices like), such that the two major surfaces are both parallel and free from significant scratches. Such grinding or polishing operations, differing in the rate of material removal and final surface finish, may be referred to collectively as lapping.
A typical lapping machine used for finishing the disks may include two superposed platens respectively disposed over and under one or more of the disks, so that opposing surfaces of the disks can be ground or polished simultaneously. Moreover, the lapping machine may include lapping carriers that position and retain the disks during the grinding or polishing operation. Such lapping carriers may be adapted to rotate relative to the platens. For example, the lapping machine may also include an outer ring gear, disposed around an outer periphery of the platens, and an inner gear, that projects through a hole formed in a center of the platens. The lapping carriers can have a toothed outer periphery, which engages with the teeth or pins of the outer ring gear and the teeth or pins of the inner gear. Rotation of the inner gear and outer gear in opposite directions, for example, thus causes the lapping carrier to rotate globally around the inner gear, and about an axis of the lapping carrier. Typically, the surfaces of the platens are relatively flat and planar, and are suitable for most polishing operations using a lapping technique.
In certain lapping machines, fixed abrasive articles disposed over the working surfaces of the platens have been used to reduce maintenance costs and the accompanying unproductive time associated with periodic dressing of the platens to the necessary degree of flatness and coplanarity. In use, a workpiece is disposed within an aperture of the lapping carrier, the platens are brought together to exert a predetermined pressure upon the workpiece, and the lapping carrier and workpiece are rotated, thus planarizing, polishing, and/or thinning the surface(s) of the workpiece.
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During the lapping processes, flexing of the lapping carrier may cause it to contact the fixed abrasive article(s). If the lapping carrier is made of a durable material such as, for example, steel, such contact between the lapping carrier and the fixed abrasive article typically results in premature wear of the fixed abrasive article. Despite the above-mentioned publications, there remains a need for technical improvement in reducing premature wear of the fixed abrasive articles.
In one aspect, the present disclosure provides, a lapping carrier comprising:
a base having first and second opposed major surfaces and at least one aperture extending from the first major surface to the second major surface; and
a first wear layer disposed on the first major surface of the base, the wear layer comprising:
a first outer polymer layer secured to the base, wherein the first outer polymer layer has a first exposed major surface, and wherein the first outer polymer layer comprises at least one of polyether ether ketone or ultrahigh molecular weight polyethylene; and
a first adhesive layer disposed between the first outer polymer layer and the base.
In some embodiments, the lapping carrier further comprises:
a second wear layer disposed on the second major surface of the base, the wear layer comprising:
a second outer polymer layer secured to the base, wherein the second outer polymer layer has a second exposed major surface, and wherein the second outer polymer layer comprises at least one of polyether ether ketone or ultrahigh molecular weight polyethylene; and
a second adhesive layer disposed between the first outer polymer layer and the base.
Advantageously, lapping carriers according to the present disclosure may exhibit wear characteristics during lapping-type abrading processes that are comparable or superior to those of commercial lapping carriers.
Lapping carriers according to the present disclosure are useful for lapping a workpiece. Accordingly, in another aspect, the present disclosure provides a method of lapping comprising:
placing a workpiece in the at least one aperture of a lapping carrier according to the present disclosure;
placing the lapping carrier into a lapping machine having at least one lapping surface; and
providing relative motion between the workpiece and the at least one lapping surface thereby abrading the workpiece.
The features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
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FIG. 1 is a schematic side view of an exemplary lapping carrier according to the present disclosure.
FIG. 2 is a plan view of an exemplary lapping carrier according to the present disclosure.
FIGS. 3A-3C are exemplary partial sections of workpiece carriers according to the present disclosure.
It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the disclosure. The figures may not be drawn to scale. Like reference numbers may have been used throughout the figures to denote like parts.
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Referring to FIG. 1, exemplary lapping carrier 110 comprises base 112 having first and second opposed major surfaces 115, 116. Wear layers 114 are disposed on respective first and second major surfaces 115, 116. Wear layers 114 comprise outer polymer layers 150 secured to base 112 by adhesive layers 130. Outer polymer layers 150 comprise at least one of polyether ether ketone or ultrahigh molecular weight polyethylene. Optional base adhesion promoting layers 120, are disposed between adhesive layers 130 and the first and second major surfaces 115, 116 of base 112. Optional polymer adhesion promoting layers 140 are disposed between adhesive layers 130 and outer polymer layers 150. The optional components in the wear layers may be present in one wear layer and not in the other.
The base may comprise any dimensionally stable material such as, for example, metal, glass, polymer, or ceramic. Exemplary metals include titanium and steels (e.g., mild steel and stainless steel). Exemplary polymers include thermoset polymers, thermoplastic polymers and combinations thereof. The polymer may contain one or more fillers or additives, chosen for a specific purpose. Inorganic fillers may be employed to lower the cost of the carrier. Additionally, reinforcing fillers such as particles or fibers may be added to the polymer (e.g., a fiberglass/epoxy composite). Typical reinforcing fillers are inorganic in nature and may comprise surface modification to improve the reinforcing effect, although these are not requirements. Nanoparticles, e.g., nanosilica, may also be of utility. The polymer may also contain layers or regions of reinforcing matting, typically woven materials, e.g., polymeric fiber matting, fiber glass matting or a metal screen.
The base may have any thickness, typically depending on the intended workpiece, but advantageously is suitable for use at minimal thicknesses.
In some embodiments, the base has one or more apertures for introduction of a workpiece, and the base has one or more apertures for delivery of a slurry. In other embodiments such as, for example, those using a fixed abrasive pad, the base has one or more apertures for introduction of a workpiece, but may optionally have no aperture(s) for introduction of polishing slurry. It is believed that eliminating such apertures increases rigidity of the lapping carrier and decreases wear of the lapping carrier and fixed abrasive surfaces that it may contact. Increasing thickness of the base typically increases rigidity, and balancing between the thickness of the base relative to the thickness of the wear layer is generally desired for optimal wear properties. For example, if intended for use with for 300 mm diameter Si wafers, a stainless steel base may have a thickness in a range of from about 400 microns to about 800 microns. Likewise if intended for use with for 450 mm diameter Si wafers, a stainless steel base may have a thickness in a range of from about 500 to about 950 microns.
In order to facilitate bonding of the adhesive layer to the base, a base adhesion promoting layer may optionally be included in the wear layer between the adhesive layer and the base. The polymer adhesion promoting layer may comprise any material(s) or treatments that enhance bonding between the base and the adhesive layer. Examples include plasma treatments of the major surface(s) of the base, inorganic coatings, organic coatings, silane coupling agents, polymeric primers, surface texturing or abrasion and combinations thereof.
For example, the base adhesion promoting layer may be formed by chemical modification of one or more of the base\'s surfaces or by providing a coating on one or more of the base\'s surfaces. Chemical modification of the base\'s surface may be accomplished by conventional techniques, e.g., plasma, e-beam or ion beam processing. An exemplary process is plasma processing in the presence of one or more gases. Useful gases include, for example, tetramethylsilane, oxygen, nitrogen, hydrogen, butane, and argon. Plasma surface treatment results in the formation of various functional groups on the surface of the base. Desirable functional groups include atom pairs that comprise oxygen bonded to carbon, oxygen bonded to silicon, nitrogen bonded to carbon and hydrogen bonded to nitrogen. Plasma processing can also be used to clean the surface of the base prior to applying the base adhesion promoting layer. Argon gas is useful for this purpose.
Modification of the surface may also be accomplished by treatment with a cleaning or etching solution such as, for example, an alkali metal metasilicate treatment, and ALKONOX detergent wash (from Alconox, Inc., White Plains, N.Y.), or a phosphate wash.
The base adhesion promoting layer may comprise an inorganic coating and/or organic coating. Useful inorganic coatings include metals and metal oxides.
Physical vapor deposition techniques such as sputtering, ion plating, and cathodic arc type techniques are useful in precisely controlling the thickness and uniformity of the coatings for metals, alloys, nitrides, oxides, and carbides. These vacuum deposition techniques allow for a solvent-free, dry and clean process.
Useful organic coatings (e.g., polymeric primers) can vary widely in chemical composition and form. Generally, an organic base adhesion promoting layer has chemical characteristics, e.g., one or more functional groups that enhance the adhesion between the base and the wear layer. The organic coatings, in final form, are typically polymeric, although low molecular weight compounds may also be useful in enhancing adhesion.
Polymeric primers may initially comprise monomers and/or oligomers that are polymerized and/or crosslinked after coating onto the appropriate surface. When applied to the base, polymeric primers may be substantially one hundred percent in solids content or it may contain solvent that is substantially removed after coating. Polymeric primers may also be a polymer solution in which the solvent is substantially removed after coating. The polymeric primers may be polymerized and/or crosslinked after coating via standard techniques, including thermal curing and radiation curing.
Examples of polymeric primers include alkyd polymers, epoxy ester polymers, epoxy novolac polymers, vinyl polymers, chlorinated rubber polymers, polyamide-cured epoxy polymers, polyurethane polymers (aromatic or aliphatic), amine-cured epoxy polymers, phenolic polymer, organic zinc-rich coating, inorganic zinc-rich coating, phosphate conversion coatings, chromate conversion coatings, chromate-free conversion coatings, polyurea polymers, alkali silicate polymers, acrylic polymers, and combinations thereof. Acrylic polymeric primers such as that available as 3M TAPE PRIMER 94 from 3M Company, St. Paul, Minn., may be particularly useful. Adhesion Promoter 111 adhesion promoter available from 3M Company may also be useful.
Silane coupling agents, e.g., aminosilanes, epoxysilanes, vinylsilanes, isocyanatosilanes, and ureidosilanes may also be useful as, or as a component in, the base adhesion promoting layer. An example of a useful epoxysilane coupling agent include 3-(glycidoxypropyl) trimethoxysilane (available from Gelest, Inc., Morrisville, Pa.).
The adhesive layer may comprise any material capable of adhering the wear layer to the base. Examples of suitable materials include hot melt adhesives, pressure-sensitive adhesives, glues, and structural adhesives. Desirably, the adhesive layer is comprises a pressure-sensitive adhesive in order to facilitate fabrication of the lapping carrier. Acrylic pressure-sensitive adhesives are typically useful in this regard. Examples include 3M 300 LSE 2 mil pressure-sensitive adhesive transfer tape, 3M 501F1 mil pressure-sensitive adhesive transfer tape, 3M 9457 1 mil pressure-sensitive adhesive transfer tape, 3M 9458 1 mil pressure-sensitive adhesive transfer tape, 3M 9009 2 mil pressure-sensitive adhesive transfer tape, 3M 9471 2 mil pressure-sensitive adhesive transfer tape, 3M 9461P 1 mil pressure-sensitive adhesive, all available from 3M Company. The adhesive layer may have any thickness, but is desirably thin. For example the adhesive layer may have a thickness in a range of from about 10 to about 75 microns, from about 15 to about 30 microns, or even from about 20 to about 30 microns.
The outer polymer layer comprises at least one of polyether ether ketone (PEEK) or ultrahigh molecular weight polyethylene (UHMW PE).
Ultrahigh molecular weight polyethylene (UHMW PE), which is also known as high-modulus polyethylene (HMPE) or high-performance polyethylene (HPPE), is a polyethylene characterized by extremely long polymer chains, with molecular weight numbering in the millions (e.g. above one million grams per mole), usually between 2 and 6 million grams per mole. It is resistant to corrosive chemicals, with the exception of oxidizing acids. UHMW PE may be readily obtained from commercial sources as film, pellets, or granules. Examples include 3M SQUEAK REDUCTION TAPE 9325—5 mil and 3M UHMW-PE 5425—4.5 mil (both from 3M Company), and UHMW-PE Ultra High Molecular Weight Polyethylene from McMaster Carr, Chicago, Ill.
PEEK is a generally colorless organic polymer thermoplastic used in engineering applications. PEEK has the structural formula
wherein n is a number greater than or equal to 5. PEEK polymers are obtained by step-growth polymerization by the dialkylation of bisphenolate salts. Typical is the reaction of 4,4′-difluorobenzophenone with the disodium salt of hydroquinone, which is generated in situ by deprotonation with sodium carbonate. The reaction is conducted around 300° C. in polar aprotic solvents such as, e.g., diphenylsulfone. PEEK is highly resistant to thermal degradation as well as attack by both organic and aqueous environments. It is attacked by halogens and strong Brønsted and Lewis acids as well as some halogenated compounds and aromatic hydrocarbons at high temperatures.
While the outer polymer layer typically consists or consists essentially of UHMW-PE and/or PEEK, it may further comprise additional components such as, e.g., lubricants, antioxidants, fillers, plasticizers, melt processing aids, and anti-static agents. Additionally, the outer polymer layer can be optionally textured through molding, scoring, embossing, etc.
Typically, the outer polymer layer is provided a film prior to incorporation into the wear layer. The film may be obtained, for example, from a commercial source or extruded into a film from pellets or granules. One commercial source of PEEK is available as VICTREX PEEK from Victrex Plc, Lancashire, England. One commercial source of UHMW PE is under the trade designation GUR UHMW PE from Ticona Polymers, Dallas, Tex. Examples of commercially available PEEK films include PEEK POLYETHER ETHER KETONE FILM—2 mil and PEEK Polyether Ether Ketone film—3 mil (both from McMaster Carr), and PEEK POLYETHER ETHER KETONE FILM—3 mil from C.S. Hyde, Lake Villa, Ill. The outer polymer layer may have any thickness, depending, e.g., on the workpiece chosen. In some embodiments, the outer polymer layer has a thickness in a range of from 25 microns to 155 microns.
Advantageously, outer polymer layers according to the present disclosure exhibit relatively lower coefficients of friction as compared to a commercially successful lapping carrier, and also have good durability.
The lapping carrier may have any thickness, typically depending on the intended workpiece and the thickness of the included components, but advantageously is suitable for use at minimal thicknesses. For example, in some embodiments, the lapping carrier may have a maximum thickness in a range of from about 600 to about 975 microns
In order to facilitate bonding of the adhesive layer to the outer polymer layer, a polymer adhesion promoting layer may optionally be included in the wear layer between the outer polymer layer and the adhesive layer. The polymer adhesion promoting layer may comprise any material(s) or treatments that enhance bonding between the outer polymer layer and the adhesive layer. Examples include plasma treatments (e.g., corona discharge or plasma etch) of the bonding surface of the outer polymer layer, a polymeric primer, and combinations thereof. Examples of such are given hereinabove with regard to the base adhesion promoting layer. Alternatively, or in addition, the outer polymer layer may be texturized.
Prior to conducting chemical modification or applying an adhesion promoting layer to the base surface or wear layer surface, it is often desirable to clean the surface. Conventional cleaning techniques may be employed, such as, washing the surface with a soap solution followed by rinsing with water or washing the surface with an appropriate solvent (e.g., methyl ethyl ketone, isopropanol, or acetone) followed by drying. Depending on the composition of the carrier or wear layer, cleaning with an acid or base solution may also be useful. Sonication may also be used in conjunction with the above cleaning techniques. Additionally, plasma cleaning/surface contamination removal with argon as the gas is a preferred cleaning technique, particularly when the base being coated is a metal, e.g., stainless steel. Methods of implementing the adhesion promoting layers will vary according to the option selected, and will be known to those of ordinary skill in the art.
The outer polymer layer may be secured to the base by a lamination or adhesive bonding process. For example, a hot melt adhesive or glue may be used to secure the outer polymer layer to the base. Alternatively, lamination (e.g., of an adhesive coated outer polymer layer to the base) may be used.
After applying the wear layer to the base, further drying, annealing, and/or curing of the wear layer may be desirable in order for the polymeric layer to reach its optimal utility.
Different lapping applications may require different levels of adhesion between the base and the outer polymer layer. For example, a lapping process employing corrosive polishing solutions, high temperatures or having high degrees of shear transferred to the carrier may require higher adhesion between the base and wear layers compared to a process employing less severe conditions. The selection of the various adhesion promoting layers subsequently may depend on the lapping process conditions and or workpieces being abraded.
Referring now to FIG. 2, exemplary lapping carrier 110 has an aperture 22 within lapping carrier 110 and teeth 24 around its perimeter. Typically, the aperture corresponds to the dimensions of the workpiece with which it is intended to be used, but in some instances, the circumference of the aperture in the lapping carrier is fabricated to be larger and may be of a different shape than the required circumference and shape to hold the workpiece. An insert (not shown), having a second aperture of the desired circumference and shape to facilitate holding of the workpiece, may then be mounted within the lapping carrier aperture. Any known insert can be used, e.g., those described in U.S. Pat. No. 6,419,555 (Goers). The insert typically comprises a different material from that of the lapping carrier. The lapping carrier may include one or more apertures for holding one or more workpieces. The lapping carrier teeth engage corresponding teeth or pins (not shown) disposed around an outer periphery of the platens of a lapping machine, and an inner gear, sometimes referred to as a sun gear, that projects through a hole formed in a center of the platens. The lapping carriers can then have a toothed outer periphery, which engages with the teeth or pins of the outer ring gear and the teeth or pins of the inner gear. Rotation of the inner gear and outer gear in opposite directions, for example, thus causes the lapping carrier to rotate globally around the inner gear, and about an axis of the lapping carrier. Lapping carriers also can be designed to rotate about a platen using a sun gear and a ring gear, which may move in the same direction but at different speeds.