Patent Publication Number: US-2013237131-A1

Title: System, Method and Apparatus for Polishing Workpieces

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Disclosure 
     The present invention relates in general to polishing workpieces and, in particular, to an improved system, method and apparatus for final tape polishing magnetic media disks for disk drives. 
     2. Description of the Related Art 
     Disks in hard disk drives are provided with a layer of lubricant to better protect disks and the heads used to read data from and write data to the disks. There continues to be interest in reducing the thickness of the lubricant layer in order to increase hard disk drive capacity. However, goals for lubricant thickness have been reduced to such a value (e.g., approximately 10 Å or less) that it has become increasingly difficult to maintain a high yield while manufacturing media through the final tape polish (FTP) process. 
     FTP has set an upper limit on lubricant thickness that has become somewhat of a road block in the implementation of new types of lubricants. It would be advantageous to develop a new FTP process that is completely independent of disk lubricant. Ideally, such an FTP process would be useful and not affect media yield regardless of whether FTP was performed before or after the lubricant was applied to the disk, the type of lubricant used, and the thickness of the lubricant (if present). Thus, there continues to be interest in developing improved FTP processes. 
     SUMMARY 
     Embodiments of a system, method and apparatus for polishing workpieces are disclosed. For example, a method of polishing a workpiece may comprising rotating the workpiece; applying a liquid that is substantially pure to the workpiece adjacent to a polishing tape; applying the polishing tape to the workpiece at a pad load to polish the workpiece, such that the liquid acts as a lubricant between the workpiece and the polishing tape; and then completing polishing of the workpiece. 
     Some embodiments of a method of polishing a workpiece may comprise rotating the workpiece having no lubricant; applying a liquid to the workpiece adjacent to a polishing tape; applying the polishing tape to the workpiece at a pad load to polish the workpiece, such that the liquid acts as a transient lubricant between the workpiece and the polishing tape; and then lubricating the workpiece. 
     Other embodiments of a method of final tape polishing (FTP) a media disk may comprise rotating the media disk; applying a liquid that is substantially pure to the media disk adjacent to an FTP tape; applying the FTP tape to the media disk at a pad load to polish the media disk, such that the liquid acts as a transient lubricant between the media disk and the FTP tape; and completing FTP. 
     In still other embodiments, a method of final tape polishing (FTP) a media disk comprises mounting a media disk having no lubricant to a spindle; rotating the media disk on the spindle; applying a liquid to the media disk adjacent to an FTP tape; applying the FTP tape to the media disk at a pad load to polish the media disk, such that the liquid acts as a transient lubricant between the media disk and the FTP tape; completing FTP and removing the media disk from the spindle; and then lubricating the media disk. 
     The foregoing and other objects and advantages of these embodiments will be apparent to those of ordinary skill in the art in view of the following detailed description, taken in conjunction with the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the embodiments are attained and can be understood in more detail, a more particular description may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments and therefore are not to be considered limiting in scope as there may be other equally effective embodiments. 
         FIG. 1  is a schematic diagram of an embodiment of an FTP system and apparatus; 
         FIG. 2  is a plot of the performance of various embodiments disclosed herein with regard to friction and injection speed; 
         FIG. 3  discloses plots of the roughness performance of various embodiments disclosed herein with regard to unpolished media; and 
         FIG. 4  is schematic plan view of an embodiment of a disk drive. 
     
    
    
     The use of the same reference symbols in different drawings indicates similar or identical items. 
     DETAILED DESCRIPTION 
     Embodiments of a system, method and apparatus for polishing workpieces are disclosed. For example, and as shown in  FIG. 1 , a system and apparatus  11  may be used for final tape polishing (FTP) a media disk  13 . The media disk  13  may be lubricated before or after FTP. The method may comprise mounting the media disk  13  to a spindle  15 , and rotating the media disk  13  on the spindle  15 . The disk may be sputtered with layers prior to this initial step. 
     In some embodiments, a liquid  17  is applied to the media disk  13  adjacent an FTP tape  19 . The liquid  17  may be substantially pure, such as a neat, undiluted volatile solvent that is applied via a pump-operated needle syringe  21 . For example, the liquid  17  may comprise a fluorinated hydrocarbon and is inert relative to the media disk, such that the liquid does not texture the media disk. The liquid may be circulated through a particle filtration system prior to application to the disk. The liquid  17  is applied to the media disk  13  without an abrasive. Moreover, the method may comprise using no abrasive other than the FTP tape  19 . 
     The method may further comprise applying the FTP tape  19  to the media disk  13  at a pad load (e.g., via pad  23 ) to polish the media disk  13 , such that the liquid  17  acts as a lubricant between the media disk  13  and FTP tape  19 . The method also may comprise completing FTP and removing the media disk  13  from the spindle  15 . As shown in  FIG. 1 , both sides of the media disk  13  may be simultaneously polished in this manner. 
     In some embodiments, the disk  13  is lubricated with a lubricant prior to FTP. The lubricant may have a thickness on the media disk of about 10 Å or less. The lubricant may be bonded to the media disk, such that the lubricant is substantially unremoved by the liquid  17 . Alternatively, the lubricant may be soluble in the liquid. In still other alternatives, the lubricant is not bonded to the media disk, and the lubricant is non-soluble in the liquid. 
     In still other embodiments, the method may further comprise adjusting a pad load (i.e., in an axial direction) on the media disk; adjusting an injection speed of the liquid onto the media disk; and/or adjusting a linear velocity (i.e., in a circumferential direction) and a transverse velocity (i.e., in a radial direction) of the FTP tape relative to the media disk. 
     The method also may comprise spin-coating the liquid  17  onto the media disk  13  before applying the FTP tape  19 , and spinning off the liquid prior to unloading the media disk. The liquid may substantially completely evaporates from the media disk prior to disk removal. The liquid may substantially completely evaporate from the media disk in less than about 10 seconds, or in less than about 1 second. 
     Prototypes were tested on a desktop FTP tool using the solvent Vertrel XF as the liquid in a pump-operated needle syringe. FTP friction was tested at both the disk inner and outer diameters versus relative injection speed at two pad loads (i.e., 100 g and 150 g). As shown in  FIG. 2 , the FTP friction was reduced with solvent injection in a controllable manner through both injection speed and pad load. 
     As shown in  FIG. 3 , the effectiveness of such FTP processes may be depicted with roughness parameters. The roughness was measured by atomic force microscopy (AFM) on non-lubricated smooth media as well as non-lubricated rough media. Measurements were taken at both the inner diameter (ID) and the middle diameter (MD) between the ID and the outer diameter (OD). Some disk IDs were not final tape polished but also were measured for comparison. Generally, a reduction in maximum peak height (Rp) is provided with media treated by the embodiments disclosed herein.  FIG. 3  also discloses media measurements of average roughness (Rq or RMS) and maximum valley depth (Rv). Performance varies based on the initial roughness of the media (i.e., prior to FTP), as well as the abrasiveness of the FTP tape. 
     The embodiments disclosed herein may be used to inject a volatile liquid onto a disk near the FTP pad. The injected liquid may be spin-coated on the disk region right before the FTP tape engages the disk. The liquid may subsequently spin off the disk and evaporate. Injection speed, pad load, linear and transverse velocity, etc., may be adjusted for optimal results. The liquid may comprise fluorinated hydrocarbons, such as Vertrel XF or HFE 7100, which are commonly used as solvents for lubricants. In addition, the liquid may be circulated through a particle filtration system such as those used on lubricant dipping baths. 
     In some embodiments, a method of final tape polishing (FTP) a media disk comprises (a) rotating the media disk; (b) applying a liquid that is substantially pure to the media disk adjacent to an FTP tape; (c) applying the FTP tape to the media disk at a pad load to polish the media disk, such that the liquid acts as a transient lubricant between the media disk and the FTP tape; and (d) completing FTP. The media disk may be lubricated after step (d). 
     The media disk may be sputtered with layers prior to step (a), or the media disk may be lubricated with a lubricant prior to step (a). The lubricant may have a thickness on the media disk of about 10 Å or less. The lubricant may be bonded to the media disk, such that the lubricant is substantially unremoved by the liquid. The lubricant may be soluble in the liquid. The lubricant may not be bonded to the media disk, and the lubricant may be non-soluble in the liquid. 
     The liquid may be applied to the media disk without an abrasive, such that no abrasive is used in the method other than the FTP tape. The liquid may comprise a neat, undiluted volatile solvent that is applied via a pump-operated needle syringe. The liquid may comprise a fluorinated hydrocarbon and is inert relative to the media disk, such that the liquid does not texture the media disk. 
     The method may further comprise at least one of adjusting the pad load on the media disk; adjusting an injection speed of the liquid onto the media disk; and adjusting a linear velocity and a transverse velocity of the FTP tape relative to the media disk. The method also may further comprise spin-coating the liquid onto the media disk before step (c), and spinning off the liquid prior to step (d). The liquid may be substantially completely evaporated from the media disk prior to step (d) in, for example, less than about 10 seconds, or less than about 1 second. The method also may comprise circulating the liquid through a particle filtration system prior to step (b). 
     In still other embodiments, a method of final tape polishing (FTP) a media disk comprises mounting a media disk having no lubricant to a spindle; rotating the media disk on the spindle; applying a liquid to the media disk adjacent to an FTP tape; applying the FTP tape to the media disk at a pad load to polish the media disk, such that the liquid acts as a transient lubricant between the media disk and the FTP tape; completing FTP and removing the media disk from the spindle; and then lubricating the media disk. 
     These systems, methods and apparatus have several advantages over conventional solutions. Such an FTP process is completely independent of lubricant presence, type and thickness. It can be done before or after lubricant application (e.g., dipping), and is readily incorporated into existing FTP equipment with minimal modification. These embodiments do not require additional processes, tools, delay time, floor space or operations. This solution saves time and cost in FTP process optimization when lubricant type or thickness is altered. 
       FIG. 4  depicts a hard disk drive assembly  100  comprising a housing or enclosure  101  with one or more media disks  111  rotatably mounted thereto. The disk  111  comprises magnetic recording media rotated at high speeds by a spindle motor (not shown) during operation. Disk  111  may be configured, manufactured and fabricated as described elsewhere herein. 
     Magnetic data tracks  113 , which may be concentric, are formed on either or both of the disk surfaces to receive and store information. The tracks are formed by the creation of bit-patterned islands with one magnetic property which are surrounded by material with a different magnetic property. 
     A write head is used to direct the magnetic state of the magnetic bits to one of two directions to write data. The resting state of the magnetization of the bit can be pointed perpendicular to the plane of the disk. A read head is used to detect which direction the magnetization is pointed in. Typically the read and write heads are integrated on a single slider and the slider is attached to a suspension which is rotated to different radii on the disk to read and write information from various tracks. The read head is also uses to control servo positioning of the head. 
     Embodiments of a read/write slider  110  having read/write heads may be moved across the disk surface by an actuator assembly  106 , allowing the slider  110  to read and/or write magnetic data to a particular track  113 . The actuator assembly  106  may pivot on a pivot  114  or by a linear actuator. The actuator assembly  106  may form part of a closed loop feedback system, known as servo control, which dynamically positions the read/write slider  110  to compensate for thermal expansion of the magnetic recording media  111  as well as vibrations and other disturbances or irregularities. Also involved in the servo control system is a complex computational algorithm executed by a microprocessor, digital signal processor, or analog signal processor  116  that receives data address information from a computer, converts it to a location on the disk  111 , and moves the read/write slider  110  accordingly. 
     In some embodiments of hard disk drive systems, read/write sliders  110  periodically reference servo patterns recorded on the disk to ensure accurate slider positioning. Servo patterns may be used to ensure a read/write slider  110  follows a particular track  113  accurately, and to control and monitor transition of the slider  110  from one track to another. Upon referencing a servo pattern, the read/write slider  110  obtains head position information that enables the control circuitry  116  to subsequently realign the slider  110  to correct any detected error. 
     Servo patterns or servo sectors may be contained in engineered servo sections  112  that are embedded within a plurality of data tracks  113  to allow frequent sampling of the servo patterns for improved disk drive performance, in some embodiments. In a typical magnetic recording media  111 , embedded servo sections  112  may extend substantially radially from the center of the magnetic recording media  111 , like spokes from the center of a wheel. The servo features may be similarly sized to the data features or may be larger. The size of the features is determined by the mask pattern. Unlike spokes however, servo sections  112  form a subtle, arc-shaped path calibrated to substantially match the range of motion of the read/write slider  110 . Both sides of the disk can be patterned. 
     Alternate embodiments are suitable for still other applications and other types of workpieces. For example, other than FTP, some embodiments may be adapted for the final polish of raw disk substrates (e.g., glass, AlMg, etc.) that are typically free of any kind of lubricant. The disk substrates are typically inspected for cleanliness and roughness prior to a wash process, which itself precedes layers of material (e.g., magnetic layers) being added to them, such as by sputtering. Other embodiments include the polishing of sliders for hard disk drives. The sliders are typically integrally formed as a wafer that is lapped and polished and then cut to fabricate the individual sliders. The wafer of sliders may be characterized as having an air bearing surface (ABS) side that may be polished as a workpiece as described herein. 
     Additional embodiments may include polishing any type of highly technical workpiece, such as lenses, minors, single crystals, windows for transmitting infrared or ultraviolet light, etc. For example, a method of polishing a workpiece may comprising rotating the workpiece; applying a liquid that is substantially pure to the workpiece adjacent to a polishing tape; applying the polishing tape to the workpiece at a pad load to polish the workpiece, such that the liquid acts as a lubricant between the workpiece and the polishing tape; and then completing polishing of the workpiece. Other embodiments of a method of polishing a workpiece may comprise rotating the workpiece having no lubricant; applying a liquid to the workpiece adjacent to a polishing tape; applying the polishing tape to the workpiece at a pad load to polish the workpiece, such that the liquid acts as a transient lubricant between the workpiece and the polishing tape; and then lubricating the workpiece. 
     This written description uses examples to disclose the embodiments, including the best mode, and also to enable those of ordinary skill in the art to make and use the invention. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 
     Note that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed. 
     In the foregoing specification, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention. 
     As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive-or and not to an exclusive-or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
     Also, the use of “a” or “an” are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
     Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. 
     After reading the specification, skilled artisans will appreciate that certain features are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, references to values stated in ranges include each and every value within that range.