Abstract:
The manufacturing processes of lubrication and final tape polish (FTP) for magnetic media are combined into a single operation. A modified disk loading conveyor performs both lubricant dipping and FTP by immersing a cassette of disks in a lube bath. A single disk is lubed as it is unloaded. Upon unload, the lubed disk is put on an FTP spindle for polishing. After FTP, the disk is put in an empty cassette adjacent the lube bath. An automatic lift transports fill or empty cassettes into or out of the lube bath, respectively.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates in general to processing media and, in particular, to an improved system, method and apparatus for combining into a single operation the processes of lubrication and final tape polish for magnetic media in hard disk drives. 
         [0003]    2. Description of the Related Art 
         [0004]    The glide test is one of the operations performed at the end of manufacturing magnetic media for hard disk drives. To maintain or increase media glide yield, the amount of friction encountered during the processing step known as final tape polish (FTP) must be maintained or reduced. The friction is determined by the amount of free (i.e., non-bonded) lubricant present on the media during FTP. Generally, lubricant bonding to media increases with time until an equilibrium bonding is reached. The time required to reach equilibrium bonding varies with lubricant type and other variables, and may comprise anywhere from a few minutes to a few days. During manufacturing, the time delays for transitioning the media from the lubrication process to the FTP proess are kept as short as practically possible. For example, the time delay between these processes may take two to four hours. 
         [0005]    To reduce disturbance of the lubricant on the media and to avoid lubricant pickup in disk drives, media manufacturers continue to move toward higher bonding lubricants (e.g., Zdol to Z-Tetraol to ZTMD). However, high bonding lubricants also bond relatively quickly (e.g., within a few minutes). Since separate and independent lubrication and FTP processes are currently required, it is practically impossible to shorten the delay time between these operations from a few hours to only minutes. 
         [0006]    Another issue to address in order to increase production volume and/or to implement discrete track media and bit patterned media technologies, is the need for more clean room floor space for these operations. Although one way to solve this problem is to increase the size of the clean room facilities, this is a very expensive proposition. Moreover, some manufacturing sites have almost no room for expansion. Thus, an improved solution for addressing the lubricant and FTP requirements for media that addresses all of these issues would be desirable. 
       SUMMARY OF THE INVENTION 
       [0007]    Embodiments of a system, method, and apparatus for combining into a single operation the processes of lubrication and final tape polish (FTP) for magnetic media are disclosed. The invention uses a single tool to combine lubricant dipping with final tape polish using a modified disk loading conveyor. In one embodiment, a cassette of disks moved into and immersed in a lube bath, and a single disk is lubed as it is unloaded. Upon unload, the lubed disk is transported by a robot arm to the FTP spindle. After FTP, the disk is put in an empty cassette on the conveyor downstream from the lube bath. An automatic lift transports full or empty cassettes into or out of the lube bath with respect to the conveyor. 
         [0008]    The invention has the advantages of shortening the lube-to-FTP delay between those processes, which means more free lubricant, lower burnish friction, and a higher yield during the glide test for disk drive applications. The invention also reduces the floor space required for conventional implementations of lubrication and FTP equipment, giving room for expansion in a clean room facility without having to build larger clean rooms. In addition, the invention provides these advantages while maintaining the same throughput, lubricant uniformity, and media quality as conventional techniques. 
         [0009]    The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
           [0011]      FIGS. 1-8  are schematic diagrams of embodiments of processes in accordance with the invention; and 
           [0012]      FIGS. 9-14  are plots of performance for media constructed in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring to  FIGS. 1-14 , embodiments of a system, method and apparatus for combining into a single operation the processes of lubrication and final tape polish (FTP) for magnetic media in hard disk drives applications are disclosed. For example, in one embodiment, the invention comprises a method of processing workpieces or media with a single tool. As shown in  FIG. 1 , a conveyor  11  is segmented into three portions  11   a,    11   b  and  11   c  relative to a lubricant bath  13  containing a lubricant solution  15 . For example, a concentration of lubricant in the lubricant bath may be provided in a range of 0.04 to 0.08 g/100 mL of solvent. 
         [0014]    A plurality of media  21   a  (e.g., magnetic media disks) are loaded into a first cassette  23   a.  The cassettes  23  contact and support only the circumferential edges of the media  21 . The cassettes  23  have no covers and have openings in their bottoms that provide physical access to the media  21 . In operation, the cassette  23   a  is conveyed on the conveyor  11   a  toward and adjacent to the upstream end  25  of the lubricant bath  13 . 
         [0015]    As shown in  FIG. 2 , the cassette  23  of media  21  is lifted from the conveyor  11   a  (e.g., with an automated lift  27 ) and immersed in the lubricant bath  13  on the upstream end  25  (see, e.g., immersed media  21   b ). The automated lift  27  moves the cassette  23   a  of media  21  from the conveyor  11   a  to the lubricant bath  13 . The automated lift  27  also may be used to remove the empty cassette  23   a  (shown in  FIG. 6 ) from the downstream end  35  of the lubricant bath  13  after all of the media  21  is lifted from the cassette in the lubricant bath. 
         [0016]    In  FIG. 3 , the immersed cassette  23   a  of media  21   b  is moved along the bath conveyor  11   b.  For example, this step may comprise incrementally advancing the cassette  23   a  by a distance approximately equivalent to an axial distance d between the media  21  in the cassette  23   a.  The media  21  is lifted (see, e.g., lifted media  21   c ) from below by an arm  31  that extends through the cassette  23   a,  to coat a lubricant layer on the lifted media (see, e.g., lubricated media  21   d ). In one embodiment, only one media  21  is lifted at a time to coat the lubricant thereon, and only a circumferential edge  29  of the media  21  is contacted. This step may occur in a central portion  33  of the lubricant bath  13  between the upstream end  25  and a downstream end  35 . 
         [0017]    In some embodiments, this step comprises lifting the media  21  from the cassette  23  at a speed of approximately 5 mm/s, after “soaking” the media  21  (i.e., before it is lifted out of the lubricant bath  13 ) for a time of approximately two minutes. In some embodiments, any delay between the steps of lifting the media and FTP may occur in an interval of time of approximately one to two minutes. Thus, the soaking phase is the in-bath time between the immersing and lifting. 
         [0018]    Referring now to  FIGS. 4-8 , the lubricated media  21   d  is next final tape polished (FTP). An interval of time of about one second to a few seconds may transpire between the lifting step and FTP. The FTP step may comprise transporting the lubricated media  21  with a robot arm  37  to a FTP spindle  39 . The FTP media  21   e  is then placed into a second cassette  23   b  (e.g., with robot arm  37 ) adjacent to and on the downstream end  35  of the lubricant bath  13  on the conveyor  11   c.  The preceding steps may be repeated until the second cassette  23   b  is filled with FTP media  21   e.  Subsequently, the filled second cassette  23   b  of FTP media  21  is conveyed away from the lubricant bath  13  and the entire process may be repeated. 
         [0019]    In some embodiments, the shorter in-bath soaking time may affect lube thickness. For example, experiments with Z-Tetraol 2290 (see, e.g.,  FIG. 9 ) demonstrate that soaking the media does not affect lube thickness  171  beyond about two minutes. Longer soaking time does not affect final lube thickness as shown in  FIG. 9 . Otherwise, lube thickness would be different for each disk due to different soaking time. In order not to affect throughput, immersion can start as soon as the prior cassette is out of the way. To facilitate this, the upstream portion of the bath is sufficiently wide to accommodate multiple cassettes that are spaced apart from each other. With a throughput of about 120 disks per hour, immersion may start with at least four disks left in the prior cassette. Thus, soaking the media in the bath for two minutes or longer is workable for a throughput of 120 to 150 disks per hour.  FIG. 10  shows that lubricant thickness can be varied and controlled using in-bath concentrations  181 ,  183  and/or pulling-up speed. 
         [0020]    The plots  191 ,  201 , and  211  in  FIGS. 11-13 , respectively, illustrate that FTP friction is reduced by almost 50% by shortening the lube-to-FTP delay to no more than one minute for, e.g., fractions of ZTMD lubricant. Plot  221  of  FIG. 14  shows that the effect is consistent with the fast-bonding kinetics for the same lubricant. 
         [0021]    The invention has numerous advantages over prior art techniques, which include shortening the delay time between the lubrication and FTP processes. As a result, there is more free lubricant, lower burnish friction, and a higher glide yield. The invention also reduces the floor space required for current lubrication equipment, giving room for expansion without having to build larger clean rooms. In addition, the invention offers these advantages without loss of throughput, lubricant uniformity, or media quality compared to conventional techniques. In some embodiments, the improvements described herein still require set-ups for solvent-vapor collection over the bath and vibration isolation beneath the bath. 
         [0022]    While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.