Abstract:
A disc drive implementing a dual-stage actuation system having an improved scheme for electrically interconnecting a transducing head to a flexure includes a support structure supporting a slider in proximity to a surface of a rotatable disc. The support structure is coarsely positionable by a main actuator. A microactuator is also provided, including a stator attached to the support structure and a rotor operatively attached to the slider. The rotor is connected to the stator by at least one flexible beam. A first electrical interconnect is formed between the support structure and the stator of the microactuator. A conductive trace is formed on the flexible beam between the stator and the rotor of the microactuator. A second electrical interconnect is formed between the rotor of the microactuator and at least one bond pad on the slider electrically connected to the transducing head.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from Provisional Application No. 60/133,206 filed May 7, 1999 for “COMPLIMENT MICROACTUATOR TO HEAD INTEGRATED ELECTRICAL CONNECTION” by W. Bonin. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a disc drive microactuator system, and more particularly to an improved technique for electrically connecting a transducing head to a suspension flexure in the disc drive microactuator system. 
     The density of concentric data tracks on magnetic discs continues to increase (that is, the width of data tracks and radial spacing between data tracks are decreasing), requiring more precise radial positioning of the head. Conventionally, head positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor, to radially position a head on a flexure at the end of the actuator arm. The large-scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution head positioning mechanism, or microactuator, is necessary to accommodate the more densely spaced tracks. 
     One promising design for high resolution head positioning involves employing a high resolution microactuator in addition to the conventional lower resolution actuator motor, thereby effecting head positioning through dual-stage actuation. Various microactuator designs have been considered to accomplish high resolution head positioning. Most of the microactuator designs generate relatively small forces, so that the stiffness of the portions of the microactuator associated with the moving part, or rotor, must be very low (have a very small spring constant). Similarly, if the electrical connections from the head to the flexure are made by direct wire connections, the lateral spring constant of the flexure, microactuator springs and wire connections must together be sufficiently low to permit lateral head movement to occur with the relatively small microactuation force provided. Existing flexure technology cannot achieve the required flexibility, and even if such a flexure were achievable, there would be a force bias problem generated by mechanical offsets introduced by the inherently imperfect alignment between the flexure and the slider during bonding of the flexible electrical interconnects between the flexure and the head. This would result in a position shift, or mechanical bias of the microactuator from its center position. Since the total lateral stroke of the microactuator is typically on the order of 0.5 to 20 micro-meters (μm), and the force generated by the microactuator becomes non-linear near the limits of the stroke, any bias greater than a fraction of the microactuator stroke degrades the performance of the disc drive, yet is extremely difficult to avoid if the electrical interconnects are attached directly between the head and the flexure. 
     There is a need in the art for an improved head to flexure electrical interconnect in a disc drive microactuator to alleviate the above-described deficiencies in the current state of technology. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a disc drive implementing a dual-stage actuation system with an improved technique for electrically interconnecting the transducing head and the disc drive flexure. The disc drive includes a recording disc rotatable about an axis, a slider supporting the transducing head for transducing data with the disc and at least one bond pad electrically connected to the transducing head, and the dual-stage actuation assembly supporting the slider to position the transducing head adjacent a selected radial track of the disc. The dual-stage actuation system includes a support structure supporting the slider in proximity to a surface of the disc. The support structure is coarsely positionable by a main actuator. A microactuator is also included, with a stator attached to the support structure and a rotor operatively attached to the slider. The rotor is connected to the stator by at least one flexible beam. A first electrical interconnect is formed between the support structure and the stator of the microactuator. A conductive trace is formed on the flexible beam between the stator and the rotor of the microactuator. A second electrical interconnect is formed between the rotor of the microactuator and the at least one bond pad. By electrically connecting the support structure to the stator of the microactuator, where lateral stiffness is not a critical factor, the electrical interconnection scheme does not inhibit the lateral movement of the slider and transducing head by the microactuator. The electrical interconnect between the at least one bond pad and the rotor of the microactuator maybe formed by bonding a leg of a metal lead frame to the bond pad, bending and shaping the metal lead frame to contact a first conductive region on the rotor of the microactuator, and bonding the metal lead frame to the first conductive region on the rotor. The method of forming the electrical interconnect according to the present invention may be carried out at the slider level or on a bar of sliders cut from a wafer substrate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a dual-stage disc drive actuation system according to the present invention. 
     FIG. 2 is an exploded view of the portion of the disc drive system implementing the microactuator and carrying the slider according to the present invention. 
     FIG. 3 is a perspective view of the assembled portion of the disc drive system shown in FIG.  2 . 
     FIG. 4 is an exploded perspective view illustrating the relationship between the slider and the microactuator frame of the present invention. 
     FIG. 5 is a perspective view of the microactuator frame electrically and mechanically interconnected to the slider according to a first embodiment of the present invention. 
     FIG. 6 is a perspective view of the microactuator frame electrically and mechanically interconnected to the slider according to a second embodiment of the present invention. 
     FIG. 7 is a perspective view illustrating an etched lead frame for bonding to the slider according to the present invention. 
     FIG. 8 is a perspective view illustrating the etched lead frame of FIG. 7 bonded to the slider according to the present invention. 
     FIG. 9 is a perspective view illustrating the bent and trimmed leads of the lead frame bonded to the slider according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a perspective view of a disc drive  10  including a dual-stage disc drive actuation system for positioning a head-carrying slider over a track  34  of disc  30 . Disc drive  10  includes voice coil motor (VCM)  12  arranged to rotate actuator arm  16  on a spindle around axis  14 . Head suspension  18  is connected to actuator arm  16  at head mounting block  20 . A microactuator is attached to load beam  18  by flexure  22  and carries slider  24 , which in turn carries a transducing head for reading and/or writing data on concentric tracks of disc  30 . Disc  30  rotates around axis  32 , so that windage is encountered by slider  24  to keep it aloft a small distance above the surface of disc  30 . 
     VCM  12  is selectively operated to move actuator arm  16  around axis  14 , thereby moving the transducing head carried by slider  24  between tracks  34  of disc  30 . However, for disc drive systems with high track density, VCM  12  lacks sufficient resolution and frequency response to position the transducing head on slider  24  precisely over a selected track  34  of disc  30 . Therefore, a higher resolution actuation device is necessary. 
     FIG. 2 is an exploded view of the portion of the disc drive system implementing the microactuator and carrying the slider according to the present invention. Slider  24  is carried by microactuator frame  40 , which is mechanically bonded to flexure  22  to carry the structure as it follows the contours of the disc surface. Load beam  18  bears through flexure  22  with a specified pre-load force onto microactuator frame  40 , which is mechanically designed to transfer the pre-load force to slider  24  to maintain slider  24  proximate to the surface of the rotating disc during operation of the disc drive. Flex circuit  42  is provided to electrically interconnect the microactuator and the transducing head or heads carried by slider  24  to control circuitry and preamplifier circuitry located remotely from the head assembly. In one embodiment, microactuator frame  40  maybe formed of a material such as silicon, with features formed by etching or a similar high resolution feature formation technique. Load beam  18  and flexure  22  are typically formed of stainless steel or a similar type of material, while flex circuit  42  may be formed of an appropriate substrate material such as polyimide. 
     FIG. 3 is a perspective view of the assembled head and flexure portion of the disc drive system shown in FIG.  2 . Microactuator frame  40 , which carries slider  24 , includes conductive bond pads  50  providing access for electrical connection to the transducing head or heads carried by slider  24 , and also to the microactuator motor itself to control movement of the microactuator. Flex circuit  42  includes conductive wires  46  for interconnection to bond pads  50 , with the actual electrical connection being achieved by bent portions  48  of wires  46  to contact bond pads  50  on microactuator frame  40 . Because the connection between wires  46  and bond pads  50  are made at the stator portion of the microactuator, rather than at a moving portion of the microactuator such as slider  24  itself, the flexibility of bent portions  48  is not a critical design consideration, and connection may therefore be accomplished in a conventional manner. Bonding of wires  46  to bond pads  50  at bent portions  48  is achieved by ultrasonic lead bonding or a comparable attachment process known in the art. 
     FIG. 4 is an exploded perspective view, and FIG. 5 is a perspective view of the completed assembly, illustrating the relationship between slider  24  and microactuator frame  40  according to a first embodiment of the present invention. Microactuator frame  40  includes cavity  51  for receiving slider  24 . Slider  24  is preferably attached to microactuator frame  40  in cavity  51  by an adhesive such as epoxy, which fills in the small gap between slider  24  and the walls of cavity  51 . In the exemplary embodiment shown in FIGS. 4 and 5, slider  24  carries one or more transducing heads that are electrically contacted by bond pads  52   a ,  52   b ,  52   c  and  52   d  on the trailing edge surface of the slider. The transducing head or heads are typically embedded in slider  24  in a manner known in the art, to avoid exposure to the elements on the outer surfaces of slider  24 . Bent leads  54   a ,  54   b ,  54   c  and  54   d  are provided to contact bond pads  52   a ,  52   b ,  52   c  and  52   d , respectively, for electrical connection to respective bond pads  60   a ,  60   b ,  60   c  and  60   d  on microactuator frame  40 . In an exemplary embodiment, leads  54   a ,  54   b ,  54   c  and  54   d  are bonded to bond pads  52   a ,  52   b ,  52   c  and  52   d  and to bond pads  60   a ,  60   b ,  60   c  and  60   d  by ultrasonic direct lead bonding, or by another standard bonding process known in the art such as ball bonding, stitch bonding, conductive epoxy or reflow of plated solder. Thin conductive traces are provided on beams  56  and  58  of microactuator frame  40  to electrically interconnect bond pads  60   a ,  60   b ,  60   c  and  60   d  to respective bond pads  62   a ,  62   b ,  62   c  and  62   d  for further connection to interconnecting wires bent down from the overhanging flex circuit  42  (FIG.  3 ). In a preferred embodiment, an insulating layer of oxide, nitride, or a similar insulating material is provided on beams  56  and  58  to electrically insulate the conductive traces from the material forming beams  56  and  58  of microactuator frame  40 . 
     The connection scheme shown in FIGS. 4 and 5 permits movement of the microactuator rotor with respect to the microactuator stator that is not inhibited by the inherent flexibility constraints of interconnecting leads to the transducing head or heads. Microactuator frame  40  essentially comprises outer frame  64  serving as the microactuator stator, and inner frame  66  serving as the microactuator rotor. Inner frame  66  is connected to outer frame  64  by beams  56  and  58 , which are deformable in response to lateral force applied by microactuator motor  68  to alter the position of inner frame  66  (and thus slider  24 ) with respect to fixed outer frame  64 . Thus, electrical interconnections made by bent wires from overhanging flex circuit  42  (FIG. 3) to bond pads  62   a ,  62   b ,  62   c  and  62   d  located on outer frame  64  of microactuator frame  40  do not add to the lateral stiffness of inner frame  66 . As a result, the microactuator is able to perform efficiently while still allowing relatively simple electrical connection to microactuator motor  68  and bond pads  52   a ,  52   b ,  52   c  and  52   d  electrically connected to the transducing head or heads. 
     FIG. 6 is a perspective view of microactuator frame  40  electrically and mechanically interconnected to slider  24  according to a second embodiment of the present invention. The essential parts of the embodiment shown in FIG. 6 are identical to those shown in FIGS. 4 and 5, except for the arrangement of bond pads  62   a ,  62   b ,  62   c  and  62   d  on outer frame  64  of microactuator frame  40 . The locations of bond pads  62   a ,  62   b ,  62   c  and  62   d  shown in FIG. 6 are compatible with the particular arrangement of bent portions  46  of conductive wires  46  shown in flex circuit  42  of FIG.  3 . In addition, it should be understood that the embodiment shown in FIG. 6 illustrates a simplistic form of the microactuator frame, with single beams  56  and  58  connecting outer frame  64  to inner frame  66  and carrying the conductive traces electrically connecting bond pads  60   a ,  60   b ,  60   c  and  60   d  to respective bond pads  62   a ,  62   b ,  62   c  and  62   d . In other embodiments of the invention, a plurality of beams on each side of the slider may instead be employed, with the conductive traces potentially being carried by different beams to ensure electrical insulation between traces. The electrical interconnecting scheme of the present invention contemplates such variations in the microactuator frame structure. 
     FIG. 7 is a perspective view illustrating etched lead frame  70  for bonding to slider  24  according to the present invention. Lead frame  70  is composed of a conductive material such as gold plated copper in one embodiment, and is formed to include conductive teeth defining leads  54   a ,  54   b ,  54   c  and  54   d . Lead frame  70  is bonded to slider  24  as shown in FIG. 8, with leads  54   a ,  54   b ,  54   c  and  54   d  being connected to respective bond pads  52   a ,  52   b ,  52   c  and  52   d  electrically connected to the transducing head or heads carried by slider  24 . One preferred method of bonding lead frame  70  involves bonding a series of lead frames to an entire row of sliders cut from a wafer substrate, referred to in the art as “bar-level” processing. One advantage of bar-level processing is that the lead frames provide electrostatic discharge (ESD) protection to the sliders during slider machining processes. Lead frame  70  is then bent and trimmed as shown in FIG. 9 for connection to appropriate bond pads on microactuator frame  40  (FIGS.  4 - 6 ). Maximum ESD protection is achieved when lead frame  70  is trimmed after it has been bent and bonded to bond pads  60   a ,  60   b ,  60   c  and  60   d  (FIGS. 4-6) on the microactuator frame. This technique requires additional process safeguards to ensure that the microactuator frame is not mechanically damaged while trimming lead frame  70  after bonding has occurred. 
     The present invention provides an improved scheme for electrically interconnecting leads from an overhanging flex circuit to a microactuator motor and one or more transducing heads carried by the disc drive slider. The interconnection scheme attaches the flex circuit leads to the stator of the microactuator, where lateral stiffness is not a critical factor, thereby allowing the microactuator rotor to move with sufficient displacement for a given amount of force generated by the microactuator motor. Electrical connection between the transducing head or heads carried by the slider (carried by the microactuator rotor) and the microactuator stator is achieved by forming leads to rigidly connect the head or heads to the microactuator rotor, and depositing thin conductive leads on the flexible beams connecting the microactuator stator to the microactuator rotor. These thin conductive leads do not materially affect the lateral stiffness of the beams themselves, and therefore do not impede the performance of the microactuator. In a preferred embodiment, the thin conductive leads on the microactuator beams may be formed simultaneously with the microactuator frame itself, for expedient processing. As a result of the present invention, microactuator motors having limited force outputs maybe used to generate sufficient microactuator strokes with low mechanical bias to ensure accurate movement for high resolution positioning of one or more transducing heads carried by the disc drive slider. 
     In the exemplary embodiments shown and described above, microactuator motor  68  is implemented as an electrostatic, interdigitated comb microactuator. It will be understood by those skilled in the art that other microactuator motor types may also be used in order to realize the dual-stage disc drive actuation system of the present invention, utilizing the improved electrical interconnection scheme described herein. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.