METHODS FOR MACHINING INORGANIC, NON-METALLIC WORKPIECES

TECHNICAL FIELD

The present invention is generally directed to methods for machining workpieces, as well as fluids utilized during machining operations.

BACKGROUND ART

Machining operations, broadly including grinding, lapping and polishing operations, are widely used throughout various industries in order to obtain desired surface finishes and to shape components. Machining operations are widely utilized hi the context of non-metal, inorganic components, such as glass, glass-ceramic and ceramic components, which are deployed in a wide variety of end uses. For example, glass and glass-ceramic components are utilized widely as building materials in both commercial and residential applications. Also, glass materials are widely utilized in electronic packaging, optical applications, and solar applications, and as advanced materials in lighting and architectural applications, and increasingly as flat panel displays.

The various design requirements placed upon demanding applications for glass, glass-ceramics and ceramics have further heightened the need for precise machining operations that ideally characterized by high material removal rates arid controlled or minimized surface defects due to undesirable scratching, pitting, galling, or other surface defect mechanisms.

Particularly in the context of flat workpiece preparation, lapping and polishing operations are widely used, which incorporates use of a fixed abrasive, in which the abrasive grams are fixed in position. Here, a fixed abrasive is generally defined as one of two types of abrasive components, a bonded abrasive or a coated abrasive component. Coated abrasives generally have a flexible backing to which abrasive grains are bonded, while bonded abrasives are generally composed of abrasive grains that are bonded together such as by a matrix that forms an intergranular bonding phase. Such fixed abrasives should be contrasted against free abrasives or abrasive slurries, in which the abrasive grains are generally loose, often times in a fluidic suspension, such as an aqueous suspension. Fixed abrasives provide numerous advantages during machining operations including potentially improved planarity and improved process control. However, a need continues to exist in the art for improved machining operations utilizing fixed abrasive components, particularly in the context of glass, glass-ceramic and ceramic components.

DISCLOSURE OF INVENT] ON

According to a first aspect of the present invention, a method for machining a workpiece is provided in which a fluid is applied between a Eϊxed abrasive component and a workpiece, and the fixed abrasive component and the workpiece are moved relative to each other to remove material from

the workpiece. According to a particular feature, the workpiece is comprised mainly of a glass, glass- ceramic or ceramic composition, and the fluid includes an anti-clogging agent. The anti-clogging agent is comprised of a phosphorus-containing organic chemistry.

According to another embodiment, a method of machining a glass workpiece is provided in which a fluid is provided between a fixed abrasive component and the glass workpiece, and the fixed abrasive component and the glass workpiece are translated relative to each other to remove material from the workpiece. The anti-clogging agent may be comprised of an organic chemistry having a phosphonate functional group.

According to yet another aspect of the present invention, a method of machining a glass workpiece is provided, in which a non-abrasive lapping fluid is provided between a fixed abrasive component and a glass workpiece, and the fixed abrasive component and the glass workpiece are moved relative to each other. The lapping fluid generally comprises an anti-clogging agent and a lubricious component, the anti-clogging agent comprising an organic chemistry having a phosphonate functional group and the lubricious component being selected from a group consisting of non-ionic functional chemistries, anionic functional chemistries, cationic functional chemistries, and amphoteric functional chemistries.

DESCRIPTION OF THE E]V[BODIMENT(S)

According to an aspect of the present invention, a method for machining a workpiece is provided, which begins with application of a fluid between a fixed abrasive component and a workpiece. Generally, a fixed abrasive component is defined as noted above, that is, a component in which the abrasive grains are fixed in position, generally fixed in position relative to each other (bonded abrasive), or fixed in position relative to each other and to a backing member (coated abrasive). The actual configuration of the fixed abrasive may vary widely depending upon the application. For example, coated abrasives may utilize a paper, cloth, stitch bonded cloth, nonwoven and woven materials, fiber or film backing, and the coated abrasive may take on several different geometric forms, including belts, discs, sheets, interlined sleeves, rolls, flap discs, flap wheels, and other geometric configurations. On the other hand, bonded abrasives are typically in the foπn of solid, integrated structures, such as in the form of grinding wheels, cylindrical wheels, cup wheels, dish wheels, segments, cones, mounted wheels, and points, bricks, and sticks. The bond matrix of the bonded abrasive component may be in the form of a glassy phase, such as a vitrified bond, or alternatively, may in the form of a resin bond, or a combination thereof.

Furthermore, in the particular context of coated abrasives, the fixed abrasive may be in the form of an engineered abrasive, which generally has a pattern of raised surface features, such in the form of pyramids, mounds, ridges, or other surface features.

Turning to the workpiece, generally aspects of the present invention are limited to non-metallic, inorganic materials, such as glass, glass-ceramic or ceramic compositions. Of the foregoing, those

compositions having a notable glass phase, such as glass and glass-ceramic composites are machined according to certain embodiments of the present invention, and indeed, often times the workpiece may consist essentially of glass, that is, contains no other non-amorphous species that substantially affects its machinability. With respect to glass workpleces, the glass may be silica-based, having a silica microstructural backbone. Particular species of silica-based glass include borosilicate glass containing a notable content of B ₂ O ₃ , and optionally other oxides such as Na ₂ O/K ₂ O and Al ₂ O ₃ . Other species include soda-lime glass, containing notable contents OfNa ₂ O, CaO, MgO, and Al ₂ O ₃ .

The actual geometric configuration of the workpiece may vary, such as in the form of convex or concave contours, including tubing, optical fibers, and other configurations. Often, at least one major surface of the workpiece is planar, and that surface may be subjected to machining operations as described herein. Workpieces may be in the form of microlithography components, such as soda-line glass or I-line glass, fused silica, and calcium fluoride, wafer blank substrates, laser windows, and other forms. The workpiece may also be in the form of flat glass, such as utilized in commercial and residential construction industries, and may broadly include glass-ceramic compositions. Yet other common workpieces include glass components for optical devices, ranging from interference filters to parallel plane workpieces and instrument glasses, for example.

The composition of the grains of the fixed abrasive may vary among suitable materials, including aluminum oxide, zirconia, cerium oxide, silicon oxide, silicon carbide, boron carbide, garnet, cubic boron nitride, diamond and any other common abrasive being used. Embodiments of the present invention use particularly aggressive abrasives, and demonstrate high levels of efficacy in such contexts, such is as with diamond abrasives, carbide abrasives such as boron carbide (including cubic boron carbide), and silicon carbide, as well as garnet.

Further, the median particle size of the fixed abrasive grains may be fine, such as within a range of about 0.01 microns to about 1.5 microns, typically within a slightly narrower range, such as within a range of about 0.1 to 1.0 microns such as 0.10 to 0.50 microns. Specification of the median particle size to be under 1 micron generally denotes a polishing process in which a fine surface finish is provided by carrying out a machining operation at low material removal rates. However, according to other embodiments, the median particle size of the fixed abrasive may be higher, above 1 micron, such as on the order of 2 to 50 microns, or 2 to 10 microns. In this case, typically the machining operation is characterized as a lapping operation.

According to various embodiments, methods for machining a workpiece continue with the application of a fluid between the fixed abrasive component and the workpiece, followed by a translation of the fixed abrasive component and the workpiece relative to each other to remove material from the workpiece. In this respect, the fixed abrasive may be held stationary and the workpiece translated, the workpiece may be held stationary and the fixed abrasive component translated, or alternatively, both the fixed abrasive component and the workpiece may be translated. Translation may be carried out along different paths such as linear translation, as in the case of translating a closed loop coated abrasive belt on a stationary workpiece, may be rotational, as in the case of a rotating grinding

disk or wheel, or a may be a combination of relational and orbital, as in the case of a rotating fixed abrasive component, with the workpiece or fixed abrasive component orbiting about a central axis.

According to a particular feature, the fluid contains an anti-clogging agent, the anti-clogging agent generally comprising a phosphorus containing organic chemistry. The phosphorus-containing organic chemistry may have a functional group selected from the group consisting of phosphonates, phosphates, phosphoramides, phosphonamides, thiophosphates, thiophosphonates and phosphites. According to a particular embodiment, the functional group is a phosphonate. For example, phosphonates may be selected from the group consisting of gylcine-N,N-di (GDMP), aminotri (ATMP), N-2 hydroxyethyl-N,N-di (HEMPA), ethylenediaminetetra (EDTMPA), hexamethylenediaminetetra, diethylenetriaminepenta, phosphonoformate salts, hydroxyphosphono acetic acid (HPA), 2-phosphonobutane-l,2,4-tricarboxylic acid (PBTC), l-hydroxyethylidine-1,1'- diphosphonic acid (HEDP) and salts thereof. According to particular working embodiments described herein, the anti-clogging agent includes at least HEDP.

According to another feature, the fluid may also include a lubricious component, the component being selected from the group consisting of 1) nonionic functional chemistries including alcohols, thiols, esters, amides, amines, amine oxides or imides and derivatives thereof, 2) anionic functional chemistries including phosphates, phosphonates, sulfates, sulfonates or carboxylates and derivatives thereof, 3) cationic functional chemistries such as quaternary amines or amine salts and derivatives thereof, and 4) amphoteric functional chemistries including proprionates, betaines, glycinates or sultaines and derivatives thereof.

Typically, the lubricious component is selected from non-ionic and anionic functional chemistries, and in the context of non-ionic functional chemistries, may be selected from the group consisting of alcohols, thiols, esters, imides, amides, imides, and derivatives thereof.

The fluid preferably utilizes water as the carrier solvent, but other appropriate solvents, such as glycols, alcohols and carbonates can be used. The primary consideration in solvent use is the ability of the solvent to solubilize the anti-clogging agent and lubricious components. The solvent also assists the anti-clogging agent through solvation and transport of debris from the fixed abrasive component. A particular concentration of the anti-clogging agent is between 0.001%w/w and 10%w/w, such as

0.1%w/w and 1.0%w/w (w/w = weight of anti-clogging agent / weight of fluid). Similarly, the lubricious component is typically used at concentrations between 0.01%w/w and 49%w/w. The solvent concentration is considered to be the balance of the concentration up to 100%w/w. In some embodiments the solvent and lubricious component are considered the same, as in the use of ethylene glycol for the balance of the concentration up to 100%w/w. Usable pH values, the negative log of the hydrogen ion concentration, lie within a range of 1.0 to 14.0, and for certain fluids a particular pH range is between 7.0 and 13.0. In instances where the pH of the fluid exceeds that of the anti-clogging agent dissolved in water, a base is used to attain the desired pH. For purposes of this invention, a base is considered a Lewis base, or any chemical substance capable of donating electron density. Examples

of suitable bases include sodium hydroxide, ammonia or ethanolamine, but many others are acceptable. The preferred base is potassium hydroxide.

Examples Composition A 0.175% 1-hydroxyethylidine-l ,l'-diphosphonic acid (HEDP) 0.125% potassium hydroxide (KOH) 99.700% water pH = 7.0

Composition B

0.175% 1 -hydroxy ethylidine-l,l'-diphosphonic acid (HEDP) 0.185% potassium hydroxide (KOH) 0.100% Ucon 50-HB-660 99.540% water pH = 11.0

Composition C

0.175% 1-hydroxyethylidine-l, r-diphosphonic acid (HEDP) 0.185% potassium hydroxide (KOH) 0.200% Tomah AO-405 99.440% water pH = 11.0

Composition D 0.175% 1 -hydroxyethylidine- 1 , 1 '-diphosphonic acid (HEDP)

0.125% potassium hydroxide (KOH)

0.220% Acusol 445

99.480% water pH = 7.0

The test apparatus was a production size doublesided lapping machine (Speedfam 16B) equipped with fixed abrasive pads. Comparative lapping tests were carried out with only water and a coolant as the carrier fluid, while examples corresponding to embodiments of the present invention as described above incorporate a phosphorus-containing organic chemistry, particularly HEDP in connection with the Examples noted above. The machining was of various types of optical glass and the purpose was to remove stock quickly prior to a polishing step.

In the comparative lapping tests, after one or two production cycles, the abrasive pad would load with debris from grinding and two things would happen: 1) flatness would deteriorate 2) Material removal would drop dramatically because the abrasive was exposed much less. In contrast, the HEDP additive improved and maintained material removal performance for up to a week of grinding. In addition, it was found that the HEDP addition was effective with just water, where the lubricant was left out.

According to embodiments herein, applicants have discovered that utilization of a machining fluid incorporating an anti-c logging agent in the context of particular fixed abrasive machining applications of workpieces as described above, has notable impact on machining performance. It is generally known within the machining industry to utilize fixed abrasives in the context of machining operations, optionally with fluid additives to aid in material removal and swarf removal, for example. In addition, it is generally understood that in certain machining operations, it is desirable to utilize chemical species that have a chemical interaction with the workpiece undergoing machining, to aid in material removal and optionally aid in planarization of the workpiece, as in the case of CMP operations utilizing a loose abrasive. In contrast, according to embodiments of the present invention, it has been discovered that in fixed abrasive machining operations, utilization of the particular anti-clogging agents as described above has a notable impact on preventing clogging of the fixed abrasive.

In the particular context of machining borosilicate glass, fixed diamond pads have been utilized in grinding operations, such as 3M Trizact pads. However, during machining, oftentimes such pads would fully load or clog with material removed from the workpiece (substrate), sometimes within only two to three cycles. Such clogging has notable negative impacts, such as negatively impacting flatness of the workpiece. To address clogging and loading issues, pads may be dressed with a ceramic component, such as an alumina dressing pad, to remove clogged material. However, such dressing pads generally wear quickly and are costly to purchase in light of the fact that they are essentially consumables in the context of dressing applications. Applicants have noted substantial clogging of such pads even when used in combination with state of the art lubricious fluids, such as those described above, including, for example, Saberlube 9016.

Incorporation of an anti-clogging agent in the context of machining operations of borosilicate glass has been found to greatly improve the duration of machining between dressing operations. Indeed, it was found that machining could be operated for an entire week without dressing, which represents a 90% improvement over the state of the art with the same number of cycles per day.

While functional chemistries such as phosphonate functional chemistries have been utilized in the context of machining operations with free abrasive slurries to aid in material removal, aspects of the present invention take advantage of an anti-clogging phenomenon in the context of fixed abrasive machining. Such combination with fixed abrasive machining notably improves processability of inorganic, non-metallic workpieces such as glasses, glass-ceramics and ceramics,

While embodiments of the invention have been illustrated and described as phosphonate based anti-clogging agents and compositions incorporating same, the invention is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the scope of the present invention. For example, additional or equivalent substituents can be provided and additional or equivalent production steps can be employed. As such, further modifications and equivalents of the invention herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the scope of the invention as defined by the folio whig claims: