Abstract:
Flexure tails are provided for coupling heads of head gimbal assemblies to a flex cable in a disk drive. An exemplary flexure tail comprises a substrate including a non-straight edge defining a protruding portion and a recessed portion. The recessed portion includes a first number of bonding pads arranged in a primary row, and the protruding portion including a second number of bonding pads arranged in a secondary row. Flexure tails for up and down heads fit together to form a flexure tail assembly in which the respective secondary rows form a single row. Flexure tail assemblies are joined to the flex cable in disk drives of the invention.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to the field of disk drives and more particularly to connecting electrical components of heads to circuitry thereof. 
   BACKGROUND OF THE INVENTION 
   Magnetic and optical disk drives store and retrieve data for digital electronic apparatuses such as computers. A typical disk drive comprises a head, including a slider and a transducer, in very close proximity to a surface of a rotatable disk. The transducer, in turn, includes a write element and/or a read element. As the disk rotates beneath the head, a very thin air bearing is formed between the surface of the disk and an air bearing surface of the slider. The air bearing causes the head to “fly” above the surface of the disk. As the head flies over the disk, the write element and the read element can be alternately employed to write and read data bits along a data track on the disk. 
   In order to keep the head properly oriented and at the correct height above the disk while in flight, and to move the head from one track to another, disk drives employ a head gimbal assembly (HGA) and voice coil actuator assembly. The HGA typically comprises the head and a suspension assembly that further includes a load beam, a gimbal that attaches the head to the load beam, and a swage mount. 
   The voice coil actuator assembly comprises a fixed magnet assembly and a pivoting actuator arm. One side of the actuator arm secures the load beam while the other side includes a voice coil. The voice coil is configured to move laterally within the magnet assembly. Translating the head is achieved by varying an electric current applied to the voice coil. Varying the current causes the voice coil to move laterally within the magnet assembly which rotates the actuator arm around the pivot, thus translating the head. 
   Most high capacity disk drives employ a stack of several closely spaced disks, and for each disk there are two heads, one positioned above the disk and one positioned below. If the head is disposed “above” one of the disks (i.e. closer to the disk drive top cover than the disk) of the disk stack and faces “downward” (i.e. away from the top cover), then the head is termed a “down head,” otherwise the head is termed an “up head.” It will be understood that the designations of “up” and “down” and “upward” and “downward” in this context, can be chosen arbitrarily by the disk drive designer to create a convenient terminology convention, and should not be understood to necessarily accord with any external frame of reference such as gravity. 
     FIG. 1  illustrates an exemplary head stack assembly (HSA)  100  for use in conjunction with a disk stack (not shown) in a high capacity disk drive. The HSA  100  comprises a pivot bearing cartridge, an actuator body, a coil, a coil support, and a number of HGAs  110  attached to a plurality of actuator arms  120  of the actuator body. The HSA  100  also comprises a flex clip and a preamp. Each HGA  110  comprises a suspension assembly, including a load beam  130 , and a head  140 . 
   As shown in  FIG. 2 , electrical components such as the transducer on each head  140  are able to communicate with circuits of the disk drive, or with testing circuits of a component tester for testing purposes prior to assembly, through a set of electrical traces  200  on a support that is sometimes referred to as a flexure tail  210 . The flexure tail  210  extends along the length of the load beam  130  and the actuator arm  120  ( FIG. 1 ). A set of bonding pads  220  are disposed at an end  230  of the flexure tail  210  to allow the head  140  to be connected to the circuitry of the disk drive. When multiple HGAs  110  are assembled to form the HSA  100  ( FIG. 1 ), the bonding pads  220  of each flexure tail  210  are soldered to connectors at an end of a flex cable  150  ( FIG. 1 ) to complete the disk drive circuits. An out of plane bend  240  in the flexure tail  210  allows the bonding pads  220  to lie in a plane that is perpendicular to a plane defined by the load beam  130  for assembly to the end of the flex cable  150 . 
   It will be appreciated that the ends  230  of the flexure tails  210  from each of the heads  140  of the HSA  100  are bonded to the same flex cable  150 , and a height of the flex cable  150  is limited by at least a height of the interior of the drive enclosure. Effectively, therefore, a height, h, of the end  230  of the flexure tail  210  is essentially limited to about half of the disk-to-disk spacing of the disk stack so that two ends  230  can fit the space between two adjacent disks of the disk stack. Due to the narrowness of the disk-to-disk spacing in current disk drives, the height, h, of the end  230  must be small. Accordingly, the bonding pads  220  on the end  230  of the flexure tail  210  are arranged in a single row. 
   Increasingly sophisticated disk drives are being designed that require HGAs having additional electrical components beyond just the read and write transducers (e.g. microactuators, heaters for dynamic fly height control, etc.), and each additional electrical component requires further bonding pads on the end of the flexure tail. However, other dimensional limitations of the connector at the end of the flex cable  150  prevent the ends  230  from becoming increasingly long, and soldering and other electrical connection requirements prevent bonding pads  220  from being made smaller and more closely spaced. Accordingly, accommodating additional electrical components poses a problem for joining flexure tails  210  to flex cables  150 . 
   SUMMARY 
   An exemplary head gimbal assembly comprises a flexure tail. The flexure tail comprises a substrate including a non-straight edge defining a protruding portion and a recessed portion. The recessed portion includes a first number of bonding pads arranged in a primary row, and the protruding portion including a second number of bonding pads, less than the first number of bonding pads, arranged in a secondary row. Flexure tails coupled to up and down heads are termed up head flexure tails and down head flexure tails, respectively. Up and down head flexure tails are complementary in that they generally fit together such that the respective secondary rows form a single row when the non-straight edges of the two flexure tails are mated together to form a flexure tail assembly. 
   A head stack assembly comprises a flexure tail assembly. The flexure tail assembly, according to an embodiment of the invention, comprises an up head flexure tail and a down head flexure tail. The up head flexure tail includes a first number of bonding pads arranged in an up head primary row and a second number of bonding pads, less than the first number of bonding pads, arranged in an up head secondary row. Similarly, the down head flexure tail includes a third number of bonding pads arranged in a down head primary row and a fourth number of bonding pads, less than the third number of bonding pads, arranged in a down head secondary row. The secondary rows of the two flexure tails are generally aligned with one another to form a single row, according to this exemplary embodiment. 
   A disk drive, according to an embodiment of the invention, comprises a head stack assembly and a flex cable having at one end a flex cable connector, including a preamp. The head stack assembly includes an up head, a down head, and a flexure tail assembly joined to the flex cable connector. An up head flexure tail of the flexure tail assembly is coupled to the up head, and a down head flexure tail of the flexure tail assembly is coupled to the down head. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  shows a perspective view of a head stack assembly according to the prior art. 
       FIG. 2  shows a perspective view of a head gimbal assembly with a flexure tail according to the prior art. 
       FIG. 3  shows a top view of a portion of a flexure tail according to an embodiment of the present invention. 
       FIG. 4  shows a top view of a portion of a flexure tail according to another embodiment of the present invention. 
       FIG. 5  shows a top view of a flexure tail assembly according to an embodiment of the present invention. 
       FIG. 6  shows a top view of a flexure tail assembly according to another embodiment of the present invention. 
       FIG. 7  shows a top view of two flexure tail assemblies attached to a flex cable connector according to an embodiment of the present invention. 
       FIGS. 8-10  show successive layers of flexure tail according to an embodiment of the present invention. 
       FIG. 11  shows the layers of  FIGS. 8-10  superimposed to form a flexure tail according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3  illustrates a portion of a flexure tail  300  for a HGA according to an exemplary embodiment of the invention. The flexure tail  300  comprises a substrate  305  including a primary row  310  of a first number of bonding pads  315  and a secondary row  320  of a second number of bonding pads  315 . The substrate  305  also includes a non-straight edge  325  that defines a protruding portion  330  and a recessed portion  335 . The recessed portion  335  includes the primary row  310  while the protruding portion  330  includes the secondary row  320 . The second number of bonding pads  315 , in some embodiments, is less than the first number of bonding pads  315 . 
   In the embodiment illustrated in  FIG. 3 , the primary row  310  includes four bonding pads  315  and the secondary row  320  includes two bonding pads  315 . In another exemplary embodiment, shown in  FIG. 4 , a flexure tail  400  having a total of eight bonding pads  315  comprises a primary row  410  including five bonding pads  315  and a secondary row  420  including three bonding pads  315 . An exemplary size for the bonding pads  315  in these embodiments is 400 μm×400 μm. In some embodiments, the primary row  310  and the secondary row  320  are substantially parallel. 
   As will be discussed with respect to  FIG. 5 , the flexure tail  300  can be mated with a complementary flexure tail to form a flexure tail assembly that can be attached to a flex cable. Because of the shape of the substrate  305  and the particular arrangement of bonding pads  315  thereon, the secondary row  320  of the flexure tail  300  generally aligns with a secondary row of the complementary flexure tail to form a single row of bonding pads  315 . This allows for two flexure tails, one for an up and one for a down head, to form a flexure tail assembly with only three rows of bonding pads. 
   As shown in  FIG. 3 , electrical traces  340  connect each of the bonding pads  315  to a corresponding electrical component such as a transducer (not shown). In some embodiments, the traces  340  continue from each bonding pad  315  to a detachable test pad set (not shown). In  FIG. 3 , the transducer is disposed to one side of the illustrated portion of the flexure tail  300  while the detachable test pad set is disposed to a side opposite the one side. The detachable test pad set is used to test the electrical components on the transducer before individual HGAs are assembled into a HSA. During the assembly process, the detachable test pad set is removed. 
     FIG. 5  illustrates a flexure tail assembly  500  according to an exemplary embodiment of the invention. The flexure tail assembly  500  comprises an up head flexure tail  510  and a down head flexure tail  520 . The up and down head flexure tails  510  and  520  are complementary to one another in that one is for an up head and one is for a down head. Each of the up and down head flexure tails  510  and  520  include primary and secondary rows of bonding pads. When the up and down head flexure tails  510  and  520  are mated together, as shown in  FIG. 5 , the secondary rows of the two flexure tails  510  and  520  are generally aligned with one another to form a single row  530 . 
   It will be appreciated from  FIG. 5  that the up and down head flexure tails  510  and  520  need not be mirror images to be complementary to one another and may vary from one another in a number of ways so long as the two head flexure tails  510  and  520  generally fit together so that the two secondary rows form a single row  530 . For example, as shown in  FIG. 6 , an up head flexure tail  610  and a down head flexure tail  620  of a flexure tail assembly  600  each include 10 bonding pads but up head primary row  630  includes seven bonding pads while down head primary row  640  includes six bonding pads. 
   In other embodiments the total number of bonding pads on the two flexure tails is different, for example, where only one of the up and down heads includes a grounding circuit. Also, the centers of the bonding pads on a row are not required to be collinear as shown in  FIGS. 3-6 . In other words, the centers of the bonding pads on a row can lie both above and below the statistical average line that defines the row. Moreover, the non-straight edges of the two flexure tails are not required to be contiguous, although shown as contiguous in the illustrated embodiments. There is likewise no requirement that the respective recessed and protruding portions be the same for complementary flexure tails, though in some embodiments a width, w, of the protruding portions  650  and  660  are substantially equal. 
   Further still, flexure tails according to some embodiments of the invention can include more than one primary or secondary row. Thus, for example, two complementary flexure tails can each have one primary row and two secondary rows so that a flexure tail assembly has four rows of which two rows are shared. As another example, two complementary flexure tails can each have two primary rows and one secondary row so that a flexure tail assembly has five rows of which one row is shared. 
     FIG. 7  illustrates two flexure tail assemblies  700 ,  710  mounted on a flex cable connector  720  at one end of a flex cable  150  ( FIG. 1 ) according to an exemplary embodiment of the invention. The flex cable connector  720  of the flex cable also comprises various attachment points and components including a preamp  730 . It can be seen from  FIG. 7  that the space available for the flexure tail assemblies  700 ,  710  is limited by the layout of the flex cable connector  720  of the flex cable  150 . 
     FIGS. 8-10  illustrate exemplary layers of an embodiment of a flexure tail  1100  shown in  FIG. 11 .  FIG. 8  shows a semi-rigid support layer  800 . The support layer  800  can be made from a thin piece of stainless steel, for example. A dielectric layer  900  is shown in  FIG. 9 . The dielectric layer is formed, in some embodiments, from polyimide.  FIG. 10  shows a trace layer  1000 , made of copper in one embodiment. 
   In the flexure tail  1100  of  FIG. 11  the dielectric layer  900  is disposed between, and electrically insulates, the trace layer  1000  and the support layer  800 . In some embodiments, copper, polyimide, and stainless steel are laminated together and then masked and etched in multiple steps to create the flexure tail  1100 . It will be noted that aligned apertures in both of the support and dielectric layers  800  and  900  allow bonding pads of the flexure tail  1100  to be accessed from either side. Additionally, the traces on one side  1110  of the flexure tail  1100  continue to the transducer of the head, while the traces on the other side  1120  of the flexure tail  1100  continue to a detachable test pad set. 
   In the foregoing specification, the invention is described with reference to specific embodiments thereof, but those skilled in the art will recognize that the invention is not limited thereto. Various features and aspects of the above-described invention may be used individually or jointly. Further, the invention can be utilized in any number of environments and applications beyond those described herein without departing from the broader spirit and scope of the specification. The specification and drawings are, accordingly, to be regarded as illustrative rather than restrictive. It will be recognized that the terms “comprising,” “including,” and “having,” as used herein, are specifically intended to be read as open-ended terms of art.