Abrading – Abrading process – With tool treating or forming
Reexamination Certificate
1999-08-16
2001-03-27
Scherbel, David A. (Department: 3723)
Abrading
Abrading process
With tool treating or forming
C451S072000, C451S403000, C451S262000, C451S264000, C451S255000, C451S259000
Reexamination Certificate
active
06206765
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for grinding rigid, thin-film substrates used in electronic equipment. More particularly, the present invention relates to a dresser for precision dressing of the grinding stones of the apparatus.
BACKGROUND
Rigid, thin-film disks are the primary storage medium for digital data used in computer disk drives. A rigid, thin-film disk recording medium includes a rigid substrate that is coated with a storage material, such as a magnetic or optical material. The storage capacity of these recording media can range from a few hundred kilobytes to several gigabytes. As technology advances, so does the need for rigid, thin-film disk recording media with increased storage capacity. One way of increasing the storage capacity of a rigid, thin-film disk is to maximize the surface area of the disk by extending recordable tracks to the outer edge of the disk. Tracks near the outer edge of a disk have a larger circumference and are, therefore, capable of storing more data than those located closer to the center of the disk.
In the manufacture of rigid, thin-film disk recording media, prior to their coating with a storage material, a conventional grinding apparatus grinds the surfaces of the rigid substrates to a desired finish. One such conventional grinding apparatus is a planetary grinder having two rotating platens: an upper platen; and a lower platen. Each platen includes a grinding wheel made up of several grinding stones for grinding a surface of the rigid substrates. A sun gear and a ring gear are mounted in close proximity to the lower platen. The grinder further includes a plurality of substrate carriers disposed between the grinding wheels of the platens. The substrate carriers, each of which is capable of carrying several substrates, are coupled to the sun and ring gears of the grinder. In operation, the substrate carriers are loaded with rigid substrates, and the upper platen is lowered onto the substrate carriers, such that the grinding stones of the upper and lower platens contact the respective upper and lower surfaces of the substrates. As the sun gear and/or ring gear rotates, the substrate carriers simultaneously revolve around the sun gear and rotate about their own axis between the two grinding wheels, thereby grinding the surfaces of the substrates.
Over time, the grinding stones become worn and require dressing to restore them to their original quality. Grinding stones are typically dressed using a conventional ring dresser. The ring dresser is an annular disk, similar in size to a substrate carrier, with teeth along its outer circumference and diamond pellets on both planar surfaces. During the dressing process, at least three substrate carriers are replaced with the ring dressers, and the upper platen is lowered until both grinding wheels are in contact with the ring dressers. As the sun gear is rotated, the ring dressers revolve around the sun gear and rotate about their axes to dress the grinding stones.
One problem with conventional ring dressers is that they fail to dress the grinding stones properly, resulting in rigid substrates with a high outer diameter (OD) radial curvature.
FIG. 1
illustrates the profile of a lower platen grinding stone immediately after being dressed with a conventional ring dresser. Portions of the grinding stone along the edges proximate the sun and ring gears receive less exposure to the ring dressers than areas in between. Because the ring dressers have the same dimensions as the substrate carriers, only the outer portion of the ring dressers dress the innermost and outermost portions of the grinding stone, and less material is removed from these areas of the grinding stone. As a result, the inner and outer edges of the grinding stone are highly aggressive and will remove more material from the rigid substrates than other portions of the grinding stone. These grinding stones will produce rigid substrates with a high OD radial curvature, because only the outermost edge of the substrates contacts the inner and outer edges of the grinding stones as the substrate carriers rotate and revolve around the sun gear. A high OD curvature, also referred to as “radial curvature,” “roll off” or “dub off,” significantly limits the storage capacity of a rigid, thin-film disk recording medium, because it reduces the number of recordable tracks along the outer edge of the disk.
Two known methods of addressing the OD curvature problem associated with ring dressers include the use of low grinding pressures and the use of toleranced carriers. The first method, operating at low grinding pressures, is an inefficient use of the grinder. Low grinding pressures extend run times, thereby decreasing the machine's throughput. In addition, low grinding pressures can result in premature grinding stone loading and increased costs.
The second method employs toleranced carriers. Toleranced carriers are substrate carriers that have a thickness very close to the desired thickness of the rigid substrate. The grinding apparatus grinds the substrates down to the toleranced carriers. Toleranced carriers, however are difficult to manufacture. In addition, because the grinding stones apply pressure loads to the toleranced carriers rather than to the rigid substrates, toleranced carriers extend run times and decrease throughput. Moreover, toleranced carriers are subject to wear and must be routinely replaced.
Thus, there is a need for a dresser which provides for preferential shaping of the grinding stones. In particular, the dresser should eliminate regions of high aggressiveness at the inner and outer edges of the grinding stones.
SUMMARY
In accordance with an embodiment of the present invention, a dresser for a grinder includes a frame and at least one abrasive block. The grinder has at least one platen that is rotatable about a vertical axis and at least one grinding stone mounted to the platen. The frame of the dresser is disposed proximate the platen. The abrasive block is coupled to the frame and contacts the grinding stone. The abrasive block extends across the grinding stone of the grinder to dress the grinding stone. Because the frame does not rotate with the platen, the abrasive block remains stationary when the platen rotates. The abrasive block of the dresser dresses the grinding stone, when the stone rotates while in contact with the surface of the abrasive block.
In accordance with another embodiment of the invention, a grinding apparatus includes at least one platen, a dresser frame and at least one abrasive block. The platen is rotatable about a vertical axis and includes at least one grinding stone. The dresser frame is removably mounted proximate the platen, and the abrasive block is coupled to the frame for contacting the grinding stone, as described above. The dresser frame does not rotate with respect to the rotatable platen and grinding stone.
In accordance with still another embodiment of the invention, a method of dressing grinding stones on a grinder includes mounting a dresser proximate at least one rotatable platen of the grinder. The dresser has at least one dressing surface for contacting at least one grinding stone mounted on the platen. The dressing surface of the dresser extends across the grinding stone. The method further includes rotating the platen while the dresser remains stationary so as to dress the grinding stone.
The present invention is advantageous because it eliminates the OD curvature problem. Since the abrasive blocks of the dresser extend across the entire length of the grinding stones, the dresser ensures that the amount of material removed along the inner and outer edges of the grinding stones is at least the same as, if not more than, the amount removed at other portions of the grinding stones. The present invention allows for preferential shaping of the grinding stones.
REFERENCES:
patent: 4208842 (1980-06-01), Katzke et al.
patent: 4635401 (1987-01-01), Nakaji
patent: 5010692 (1991-04-01), Ishida et al.
patent: 5538460 (1996-07-01), Onodera
patent: 5
Like Jolanda L.
Sanchez Michael E.
Sanders William A.
Komag Incorporated
McDonald Shantese
Scherbel David A.
Skjerven Morrill & MacPherson LLP
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