Abstract:
This invention is a method to salvage suspensions from defective head gimbal assembly units. At present the hard disk industry is undergoing rapid product cycles. The products are being upgraded faster and faster, and the ability for sliders to meet higher density requirement becomes more urgent. Therefore, the performance of a slider becomes more sensitive to signals. As the wafer manufacturing process produces a lower yield, a suspension salvage method is developed to recycle damaged head gimbal assembly in order to minimize material loss.

Description:
REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims priority from PCT Application Serial No. PCT/CN01/00536, filed Mar. 28, 2001, entitled “Wireless Suspension Salvage Method”, which is incorporated herein by reference in its entirity.  
         FIELD OF THE PATENT  
         [0002]    The present patent relates to wireless suspension salvage technology in the hard disk industry. In particular, it relates the methods of salvaging head gimbal assembly with damaged sliders.  
         BACKGROUND OF THE INVENTION  
         [0003]    This invention relates to a wireless suspension salvage methods used in a hard disk storage system or the like.  
           [0004]    With increasing use of multimedia, Internet and therefore computers, demands for larger and faster data storage devices continue to grow, making the magnetic recording industry a dynamic and fast-growing sector. Magnetic recording through hard disks remain the most commonly used among the currently available storage devices in the market: floppy disks, magneto-optical disks and magnetic tapes.  
           [0005]    As the size of the storage devices becomes smaller, the slider also needs to be produced with higher density. Lower assembly yields coming from the wafer manufacturers translate into economic burden to the manufacturers. In order to be more efficient and to save material loss, there is a need to develop a method to salvage suspensions, one of the main parts on a head gimbal assembly (“HGA”).  
           [0006]    A hard disk drive consists of a motor, spindle, platters, read/write heads, actuator, frame, air filter, and electronics. The heads are bonded to a metal suspension (or head arm) which is a small arm that holds the head in position above or beneath a disk. A head and a suspension combined forms a head gimbals assembly or HGA. The HGA&#39;s are stacked together into a head-stack assembly, which is propelled across the disk surface by the actuator. Since the size of a hard disk is only a few inches long, it could be imagined that the length of a head gimbals assembly is no more than a few centimeters.  
           [0007]    Structure of the HGA  
           [0008]    Traditionally, the suspension, or a suspension assembly, in a HGA consists of a slider, a suspension bonding pad, four gold balls, and UV epoxy. The slider is mounted on tongue of the suspension with UV epoxy, and 4 gold balls are welded on both of the slider and the suspension bonding pad by ultrasonic oscillation to ensure the electrical circuit connection between the slider and the suspension connection.  
           [0009]    Several problems are inherent in the traditional approach:  
           [0010]    1) Gold balls need to be bonded to the slider pad and the suspension pad to ensure electrical circuit connection at the head assembly level; consequently, it is difficult to separate slider and suspension without causing damages to the suspension.  
           [0011]    2) Slider and suspension are bonded together using UV epoxy, causing additional difficulties in removing slider without causing damages to the suspension.  
           [0012]    3) It is difficult to remove the residue epoxy on suspension tongue completely.  
           [0013]    Therefore, there is a need for a novel method to salvage the suspension from a HGA with defective slider.  
         SUMMARY  
         [0014]    This invention relates to methods for salvaging wireless suspensions from damaged head gimbal assembly. The slider in a head gimbal assembly is removed by horizontal twisting or vertical lifting of a pair of metal tweezers. The UV epoxy used for bonding is removed by high temperature provided by a heat gun and/or by immersion in a solvant. The gold balls from the head gimbal assembly may be separated from the damaged slider by a vertical separation, or be removed with a horizontal cut. The gold balls, if removed, can be removed either before or after the slider is removed from the head gimbal assembly.  
           [0015]    The advantages of these methods include the reduction of production costs and overall avoidance of waste materials. The other features and advantages to this invention will be apparent in light of the following drawings and detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1( a ) is a top view of a sample slider attached to a suspension with electrical circuit.  
         [0017]    [0017]FIG. 1( b ) is an enlarged, prospective view of a slider.  
         [0018]    [0018]FIG. 1( c ) is an enlarged cross-sectional view of the slider of FIG. 1( b ).  
         [0019]    [0019]FIG. 1( d ) is an enlarged view of the gold balls together with the bonding pads of FIG. 1( b ).  
         [0020]    [0020]FIG. 2 is the first flow chart with descriptive drawings describing a first suspension salvage method implemented according to the principles of the present invention.  
         [0021]    [0021]FIG. 3 is the second flow chart with descriptive drawings showing a second suspension salvage method implemented according to the principles of the present invention.  
         [0022]    [0022]FIG. 4 is the third flow chart with descriptive drawings showing a third suspension salvage method implemented according to the principles of the present invention.  
         [0023]    Like parts in different figures are identified by like numbers 
     
    
     DETAILED DESCRIPTION  
       [0024]    Traditionally, referring to FIGS.  1 ( a )- 1 ( d ), a HGA assembly consists of a slider  100  attached to a suspension  110 , suspension bonding pads  120 ,  122 ,  124 ,  126  (pads  122 - 126  not shown), four gold balls  150 ,  160 ,  170 , and  180 , and UV epoxy  140 . The slider  100  is mounted on the tongue portion of the suspension  110  using UV epoxy, and the gold balls  150 - 180  are welded to both slider  100  and suspension bonding pad  120  by ultrasonic oscillation to ensure the electrical circuit between slider  100  and suspension  110  remain intact.  
         [0025]    [0025]FIG. 1( b ) shows the slider portion of the HGA with enlarged details. As shown in the figure, slider  100  is mounted on tongue of suspension  110  with UV epoxy. FIG. 1( c ) shows the cross sectional view cut along axis  115  of FIG. 1( b ) of the bound slider  100 , gold balls  150 - 180 , suspension  110 , and pads (only bonding pad  120  is shown). A layer  140  of UV epoxy is used to bond the slider  100  to suspension  110 . As FIG. 1( d ) shows, there are four gold balls  150 ,  160 ,  170 , and  180 . Each gold ball has its own bonding pad. The number of gold balls is for illustrative purpose only and are not intended to be restrictive.  
         [0026]    [0026]FIG. 2 illustrates a flow chart for the first suspension salvage method. This method is fit for wireless HGA without conformal coating on gold ball area. At step  1  HGA with damaged slider  200  is put on a gold ball fixture  210 , or support, for cutting and is additionally fixed in position with clamp  215  to ensure the HGA will not deform while the gold ball  250  and others are being cut along the direction of slider bonding pad. The cut separates the electrical circuit connection of slider  200  and suspension  212 . At step  2 , the HGA is loaded on the remove slider fixture  213 . A hot air gun  225 , such as Hakko 851 of Hakko Corporation headquartered in Osaka, Japan, is used to heat slider area for about 5 seconds to 10 seconds at 200 to 240 degrees Celsius, which process will cause partial removal of UV epoxy. A pair of metal tweezers  220  is used to clamp slider  200  and slightly twist horizontally to remove slider  200 . At step  3 , the HGA with residue gold ball and UV epoxy is loaded on an immerse fixture  235  to immerse, for about 45 minutes, the tongue area of the HGA in a solvent  230  to dissolve UV epoxy. In one embodiment, the solvent is acetone. In other embodiments, the solvent is a mix solvent the formula of which is disclosed in more detail in the international application filed by the same applicant under application number PCT/CN00/00295 on Sep. 30, 2000. At step  4 , the HGA is cleaned in de-ionized water mixed with approximately 0.5% to 1% of cleaner to remove the residue solvent on suspension  212 . A typical cleaner is Crest 14 produced by Crest Ultrasonics of Trenton, N.J. At step  5 , the salvaged suspension with original gold balls  250  and others is reprocessed. A slider  260  is mounted on the salvage suspension  212  as normal head assembly procedure. At step  6 , after slider potting, the HGA is loaded on a general Gold Ball Bonding fixture  280  using the Gold Ball bond tip without gold wire to bond the four original gold balls  250  and others onto the both the slider  260  and the suspension pad for electrical circuit connection. At step  7 , the reprocessed HGA will be handed off to general processing as a normal assembly product. This method retains the gold balls and only removes the damaged slider.  
         [0027]    [0027]FIG. 3 is the second method implementing the principles of salvaging suspension. This flow applies to wireless HGA without conformal coating on gold ball area. At step  8 , HGA with a damaged slider  300  is loaded onto cut gold ball fixture  210  and fixed with a clamp  215  to prevent HGA deformation while the gold balls  350  are being cut horizontally along the direction of suspension bonding pad to separate the electrical circuit connection between slider  300  and suspension  312 . At step  9 , the HGA is loaded onto a remove slider fixture  213 , using a hot air gun  225  to heat slider area for a moment, to weaken the bonding strength of UV epoxy. A pair of metal tweezers  220  is used to clamp slider  300  and twists slightly in a horizontal direction to remove slider  300 . At step  10 , the HGA with the residue UV epoxy is put on immerse fixture  235  to immerse the tongue area of the HGA to into solvent  230  to dissolve UV epoxy. At step  11 , the HGA is cleaned to remove the residue solvent on suspension. The appearance and performance of a salvaged suspension is almost identical to those of a regular suspension, except a residue gold layer  360  left behind by the gold ball  350  remains on the bonding pad of a salvaged suspension.  
         [0028]    [0028]FIG. 4 is the third implementation of the suspension salvage principle. This method applies to wireless HGA with conformal coating on gold ball area. At step  12 , a HGA with damaged slider  400  is loaded, and hot air gun  225  is applied to heat the slider area for a moment,  20  weakening the bonding strength of UV epoxy. A pressure bar  410  is then used to press on the gold ball  450  (there may be more than one gold ball) with conformal coating, followed by motion of a pair of metal tweezers  220  to clamp slider  400  and to lift slider  400  up slowly. Pressure bar  410 , in one implementation, is a thin metal plate of about 100 um in thickness, 700 um in width, and 10 cm in length. At step  13 , after slider removal, the potting epoxy, gold ball  450  and conformal coating remain on suspension  412 . At step  14 , the HGA with the residue gold ball, UV epoxy is put on immerse fixture  235  to immerse the tongue area of the HGA into solvent  230  to dissolve UV epoxy. The HGA is cleaned to remove the residue solvent on suspension. At step  15 , the suspension  412  which is being salvaged is loaded onto a cut ball fixture  460  and fixed with clamp  215  to ensure the HGA is not deformed while gold ball  450  is being cut by blade  310  along the direction of the suspension bonding. At step  16 , the HGA has completed all salvage steps. The appearance and performance of salvaged suspension  412  is almost identical to that of a normal suspension, except for a residue gold layer  470  remaining on the bonding pad of the salvaged suspension  412 .  
         [0029]    In practicing the principles of this invention, appropriate fixtures may be used during the cutting process and removing process to ensure precise positioning and to avoid deformation. After cleaning the HGA, in one implementation, can be baked in a box oven commonly known in the art for approximately 30 minutes at 80 to 120 degrees Celsius.  
         [0030]    The above embodiments of the invention are for illustrative purposes only. Many widely different embodiments of the present invention may be adopted without departing from the spirit and scope of the invention. Those skilled in the art will recognize that the method and structures of the present invention has many applications, and that the present invention is not limited to the specific embodiments described in the specification and should cover conventionally known variations and modifications to the system components described herein.