Abstract:
A disk drive assembly includes a movable assembly having a mounting arm, a stationary electronics module, a flexible printed circuit board (PCB) electrically connecting the movable assembly to the stationary electronics module, and a flexible support sandwiched between the flexible PCB and the mounting arm. The flexible support is attached to the mounting arm and the flexible PCB, and extends past the mounting arm of the movable assembly. The flexible support is flexible enough to flex with the flexible PCB but has sufficient rigidity so that an exit point and an exit angle of the flexible PCB can vary during movement of the movable assembly. In addition, the flexible PCB is attached to the flexible support through an adhesive layer that damps vibrations in the flexible PCB.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention relate generally to magnetic disk drives and, more particularly, to a magnetic disk drive assembly having a flexible support for a flexible printed circuit board. 
         [0003]    2. Description of the Related Art 
         [0004]    Magnetic disk drives are commonly used in computer systems since such drives can inexpensively store large quantities of non-volatile data for quick access. Magnetic disk drives generally include one or more rotatable magnetic media disks having concentric data tracks defined for storing data, a magnetic read/write transducer for reading data from and/or writing data to the various data tracks, a slider mechanism for supporting the read/write transducer in close proximity to the data tracks, and a rotatable positioning actuator coupled to the transducer/slider combination for moving the read/write transducer across the media to the desired data track and maintaining the transducer over the data track center line during a read or write operation. An actuator flex cable, also referred to as a flexible printed circuit board (flex PCB), provides the electrical contact between the read/write transducer disposed on the slider mechanism and disk drive electronics external to the positioning actuator, and is typically comprised of a plurality of electrical conductors encapsulated within an insulating material. 
         [0005]    In operation, the flex PCB carries electrical signals to and from the positioning actuator via a flexible connection, thereby allowing the positioning actuator to move freely during operation of the disk drive. The radial motion of the actuator allows the read/write transducer to access data tracks on the disk surfaces located at any radial position on the disk, from the inside diameter to the outside diameter. A preferred method of fixing the flex PCB between the external electronics and the positioning actuator is to form the flex PCB in a loop to produce minimal constraint on the movement of the positioning actuator. 
         [0006]    Disk drive performance as measured by track misregistration (TMR) is degraded by vibration of components within the disk drive, particularly the flex PCB loop connecting the positioning actuator with the external electronics. For example, radial movement of the positioning actuator to position the read/write transducer to a selected track on the disk produces oscillations in the flex PCB at the relatively low frequencies known to significantly affect the position of the read/write transducer, i.e., frequencies less than approximately 1000 Hz. In addition, the acceleration and deceleration of the positioning actuator when moving the read/write transducer to a selected track further excites low-frequency resonances in the flex PCB, increasing stabilization time of the read/write transducer and eroding drive performance. 
         [0007]      FIG. 1  is a graph of read/write transducer position of a disk drive with respect to a selected track versus time. The oscillatory nature of the read/write transducer position relative to the intended location indicates that the positioning actuator is “ringing” with a low-frequency resonance after arriving at a desired track, in this example at approximately 320 Hz. For this disk, a 320 Hz resonance has been measured directly on the connecting loop of the flex PCB, which corresponds to the frequency of the resonance detected in the positioning actuator. Methods are known in the art for reducing and/or damping the vibration of the flex PCB. However, such solutions involve designs solutions that are complex, difficult to manufacture, and/or require costly materials. 
         [0008]    In light of the above, there is a need in the art for a means to minimize the effect of flexible PCB vibration that occurs during operation of a disk drive. 
       SUMMARY OF THE INVENTION 
       [0009]    A disk drive assembly according to one or more embodiments of the invention includes a movable assembly having a read/write head and a mounting arm, a stationary electronics module, a flexible printed circuit board (PCB) electrically connecting the movable assembly to the stationary electronics module, and a flexible support attached to the flexible PCB and the mounting arm. The flexible support extends past the mounting arm of the movable assembly and is flexible enough to flex with the flexible PCB but has sufficient rigidity so that an exit point and an exit angle of the flexible PCB can vary during movement of the movable assembly. 
         [0010]    A disk drive assembly according a first embodiment includes a movable assembly having a mounting arm, a stationary electronics module, a flexible PCB electrically connecting the movable assembly to the stationary electronics module, and a flexible support having a first portion sandwiched between the flexible PCB and the mounting arm and a second portion attached to the flexible PCB that extends past the end of the mounting arm, wherein during movement of the movable assembly, the second portion of the flexible support flexes and reduces the amount of flex of the flexible PCB attached thereto. 
         [0011]    A disk drive assembly according a second embodiment includes a movable assembly having a mounting arm, a stationary electronics module, a flexible PCB electrically connecting the movable assembly to the stationary electronics module, and a flexible support sandwiched between the flexible PCB and the mounting arm and attached to the flexible PCB through an adhesive layer that damps vibrations in the flexible PCB. 
         [0012]    A disk drive assembly according a third embodiment includes a movable assembly having a mounting arm, a stationary electronics module, a flexible PCB electrically connecting the movable assembly to the stationary electronics module, and a flexible support having a first portion that is sandwiched between the flexible PCB and the mounting arm and a second portion attached to the flexible PCB that extends past the end of the mounting arm, wherein the second portion of the flexible support has a shape that is non-uniform along the length of the flexible PCB, so that the stiffness characteristics of the flexible PCB and flexible support combination differs along the length thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0014]      FIG. 1  is a graph of read/write transducer position with respect to a selected track versus time. 
           [0015]      FIG. 2  is a plan view of a disk drive including a vibration-damping system according to an embodiment of the invention. 
           [0016]      FIG. 3  illustrates a partial plan view of an actuator assembly, a J-block, and a vibration-damping system according to an embodiment of the invention. 
           [0017]      FIG. 4A  illustrates a flexible PCB of a disk drive exiting a J-block in a manner known in the art. 
           [0018]      FIG. 4B  illustrates a flexible PCB of a disk drive having a rigid support for the flexible PCB in a manner known in the art. 
           [0019]      FIG. 4C  illustrates a flexible PCB of a disk drive having a flexible support for the flexible PCB according to an embodiment of the invention. 
           [0020]      FIG. 5  is a schematic cross-sectional view of a vibration-damping system, where the vibration-damping system has a rectangular cross section, according to an embodiment of the invention. 
           [0021]      FIGS. 6A ,  6 B are graphs showing the power spectrum of vibrations occurring at a read/write transducer as it flies over a selected track of a magnetic disk. 
           [0022]      FIG. 7A  illustrates a partial side-view of a flexible stiffener having a uniform geometry, according to an embodiment of the invention. 
           [0023]      FIGS. 7B ,  7 C illustrate partial side-views of flexible stiffeners having non-uniform geometries, according to embodiments of the invention. 
           [0024]      FIG. 8  illustrates a partial plan view of an actuator assembly, a J-block, and a vibration-damping system according to another embodiment of the invention. 
       
    
    
       [0025]    For clarity, identical reference numbers have been used, where applicable, to designate identical elements that are common between figures. It is contemplated that features of one embodiment may be incorporated in other embodiments without further recitation. 
       DETAILED DESCRIPTION 
       [0026]    Embodiments of the invention contemplate a vibration-damping system for a disk drive that reduces vibration of a flexible printed circuit board (PCB) of the disk drive. The vibration-damping system includes a flexible stiffener attached to a flexible PCB via a viscoelastic adhesive layer to form a layered structure disposed at an attachment point of the connecting loop of the flexible PCB. The respective thicknesses of the flexible PCB, the viscoelastic adhesive layer, and the flexible stiffener provide the layered structure with an overall stiffness that maintains the flexible PCB oriented near an optimal exit angle from the flexible PCB attachment point throughout the range of motion of the flexible PCB, thereby reducing mechanical coupling between the flexible PCB and the actuator assembly of the disk drive. In addition, the viscoelastic adhesive layer damps resonances present in the flexible PCB. The damping treatment can be easily applied to the flexible PCB without significantly affecting cost or complexity of manufacturing the disk drive. 
         [0027]      FIG. 2  is a plan view of a disk drive  100  including a vibration-damping system  200  according to embodiments of the invention. Vibration-damping system  200  is shown in greater detail in  FIG. 3 . For clarity, disk drive  100  is illustrated in  FIG. 2  without a top cover. Disk drive  100  includes a housing  102 , one or more magnetic disks  106 , a spindle  108 , an actuator assembly  110 , a flexible PCB  122 , and an electronics bracket  124 . On the surface of magnetic disks  106 , digital data can be stored as magnetic signals formed along concentric tracks. Both sides of magnetic disks  106  may have such data stored thereon, and those skilled in the art will recognize that any number of such magnetic disks  106  may be included in the disk drive  100 . Magnetic disks  106  are mounted to spindle  108 , which is mechanically coupled to a spindle motor (not shown) that rotates magnetic disks  106  within housing  102 . 
         [0028]    Actuator assembly  110 , also referred to as a head stack assembly, includes an actuator arm  112  integrally connected with an E-block, or comb  114 , and a suspension assembly  116 . Suspension assembly  116  includes a slider/transducer assembly  118  at its distal end configured for movement across the surface of magnetic disk  106 . While only one suspension assembly  116  is illustrated in  FIG. 2 , those skilled in the art will appreciate that disk drive  100  may include a suspension assembly  116  for each side of each magnetic disk  106 . Actuator assembly  110  is mounted on a pivot bearing for rotational movement about a pivot point  128  to position slider/transducer assembly  118  over a selected data track on magnetic disk  106 . The pivotal motion of actuator assembly  110  and suspension assembly  116  across the surface  149  of magnetic disk  106  is indicated by arrow  136 . The motion of actuator assembly  110  is limited by contact between stops  138 ,  140 , and rearward extensions or VCM coil support arms  142 ,  144 , respectively. The limits of the actuator assembly rotation define the inner diameter (ID) track  151  and the outer diameter (OD) track  153  on the disk surface  149  that may be accessed by the slider transducer assembly  118 . 
         [0029]    Flexible PCB  122  carries signals between an amplifier chip  120  and external signal processing electronics via a connector pin assembly (not shown) attached to disk housing  102 . Flexible PCB  122  leads from the amplifier chip  120  to electronics bracket  124  and forms a connecting loop  122 A that is fixed at each end, as shown. One end of connecting loop  122 A is fixed to actuator assembly  110  at a J-shaped fixture, or J-block,  148 , and the other end is attached to electronics bracket  124 . Electronics bracket  124  directs flexible PCB  122  to a connector port (not shown) for connection to disk drive electronics external to housing  102 . J-block  148  provides mechanical support for flexible PCB  122  and directs flexible PCB  122  to form connecting loop  122 A between actuator assembly  110  and electronics bracket  124 . In the embodiment illustrated in  FIG. 2 , J-block  148  is also the connection point for layered vibration-damping system  200 . Connecting loop  122 A provides mechanical isolation for actuator assembly  110 , allowing rotary motion of actuator assembly  110  during operation of disk drive  100  with minimal mechanical constraint. 
         [0030]    In operation, movement of the actuator assembly  110  to position slider/transducer assembly  118  over a selected track on magnetic disk  106  generates oscillations in flexible PCB  122  due to the inertial and elastic properties of the material making up flexible PCB  122 . Such oscillations may be torsional as well as lateral, as indicated by arrows  150  and  152 , respectively. Mechanical coupling between flexible PCB  122  and slider/transducer assembly  118  translates the resonances of flexible PCB  122  to slider/transducer assembly  118 , thereby producing unwanted movement of slider/transducer assembly  118  away from the intended position of slider/transducer assembly  118 . 
         [0031]    To minimize the coupling of resonances initiated at flexible PCB  122  to slider/transducer assembly  118 , a series of experiments may be performed to tune the relative positions and orientations of connecting loop  122 A, J-block  148 , and the attachment location for flexible PCB  122  on electronics bracket  124 . Such experiments involve adjusting the exit angle of connecting loop  122 A from both J-block  148  and electronics bracket  124  and/or modifying the position of electronics bracket  124 , then characterizing the resonances that occur on connecting loop  122 A when actuator assembly  110  is operated normally. Such experiments, which can be readily devised by one of skill in the art, produce an optimal configuration for the relative positions and orientations of connecting loop  122 A, J-block  148 , and the attachment location for flexible PCB  122  on electronics bracket  124 , so that minimal coupling of flex PCB-initiated resonance to slider/transducer assembly  118  takes place. 
         [0032]    As noted above, an optimal configuration of connecting loop  122 A from J-block  148  and electronics bracket  124  for minimal coupling of resonances to actuator assembly  110  may be determined experimentally. However, the exit angle of connecting loop  122 A varies as actuator assembly  110  moves through its normal range of motion between inner diameter track  151  and the outer diameter track  153 . Consequently, connecting loop  122 A can be positioned with an optimal exit angle from J-block  148  and electronics bracket  124  only through a limited portion of the stroke of actuator assembly  110 . Thus, mechanical coupling between flexible PCB  122  and slider/transducer assembly  118  can be minimized only through a limited portion of the stroke of actuator assembly  110 , meaning that a trade-off exists between having minimal coupling to actuator assembly  110  in the inner diameter (ID) and outer diameter (OD) positions. 
         [0033]    Embodiments of the invention contemplate a vibration damping system that allows both the exit location and angle of flexible PCB  122  to vary slightly as actuator assembly  110  moves through its normal range of motion. In this way, mechanical coupling between flexible PCB  122  and actuator assembly  110  can be reduced throughout the range of motion of actuator assembly  110 . 
         [0034]      FIG. 3  illustrates a partial plan view of actuator assembly  110 , J-block  148 , and vibration-damping system  200 , according to an embodiment of the invention. Vibration-damping system  200  includes a flexible stiffener  201  attached to flexible PCB  122  via a viscoelastic adhesive layer  202  to form a layered structure. Vibration-damping system  200  is illustrated as being disposed at the attachment point of connecting loop  122 A to J-block  148  of flexible PCB  122 . 
         [0035]    Flexible stiffener  201  is a support member attached to flexible PCB  122  that is relatively flexible in the plane of motion of actuator assembly  110 , and bends easily in this plane. In addition, flexible stiffener  201  is relatively rigid and resistant to bending out of this plane. Flexible stiffener  201  may be a polymer or other elastic material having a relatively low stiffness properties that are only slightly greater than the stiffness of flexible PCB  122 . Examples of materials suitable for use as flexible stiffener  201  include Kapton®, manufactured by Dupont, a polyimide film. Other generic versions of polyimide film may be applied with equal effect. Unlike rigid supports known in the art that are used to prevent flexible PCBs in disk drives from torsional and/or out-of-plane bending, flexible stiffener  201  is configured to significantly deflect as actuator assembly  110  pivots about pivot point  128  during operation and J-block  148  moves with respect to electronics bracket  124 . The length and stiffness of flexible stiffener  201  may be used as tuning parameters when configuring flexible PCB  122  for minimal coupling to actuator assembly  110 . 
         [0036]      FIG. 4A  illustrates a flexible PCB  422  of a disk drive exiting a J-block  148  in a manner known in the art. As actuator assembly  110  pivots and J-block  148  rotates with respect to PCB  422 , the effective exit point  430  of PCB  422  remains substantially stationary with respect to J-block  148 .  FIG. 4B  illustrates a flexible PCB  422  exiting a J-block  448  having a rigid PCB support  450  in a manner known in the art, wherein the term “rigid” is herein defined as undergoing no significant deflection when subjected to the loads present in a disk drive PCB during normal operation of the disk drive. Rigid PCB support  450  provides a means by which the effective exit point  431  of PCB  422  from J-block  448  may be positioned as desired to reduce mechanical coupling between PCB  422  and the actuator assembly containing J-block  448 . However, as the actuator assembly containing J-block  448  pivots and J-block  448  rotates with respect to PCB  422 , the effective exit point  431  of PCB  422  remains substantially stationary with respect to J-block  448 . 
         [0037]      FIG. 4C  illustrates a flexible PCB  122  of disk drive  100  exiting J-block  148  according to an embodiment of the invention. As actuator assembly  110  pivots and J-block  148  rotates with respect to PCB  122 , the effective exit point  130  of PCB  122  varies with respect to J-block  148  as a function of the length and flexibility of flexible stiffener  201  in vibration-damping system  200 . Thus, the stiffness of flexible stiffener  201  and the distance  206  that flexible stiffener  201  extends from J-block  148  may be used as tuning parameters to minimize vibration coupling throughout the range of motion of actuator assembly  110 . The appropriate length  205  of flexible stiffener  201  and distance  206  that flexible stiffener  201  extends from J-block  148  is selected such that the optimal exit angle for flexible PCB  122  can be achieved for the entire range of motion of actuator assembly  110 . 
         [0038]    Referring back to  FIG. 3 , viscoelastic adhesive layer  202  includes an adhesive material for bonding flexible stiffener  201  to flexible PCB  122 . The adhesive material is selected to have significant damping properties in the range of frequencies that are intended to be damped by vibration-damping system  200  at the temperatures present during operation of disk drive  100 . Examples of materials suitable for use in viscoelastic adhesive layer  202  include viscoelastic damping polymers, such as 3M™ Viscoelastic Damping Polymers Type 110 or 112. Other appropriate materials may be used that meet the outgassing and cleanliness requirements necessary for hard drives. The damping properties of viscoelastic adhesive layer  202  may be tailored so that resonances in the requisite frequency range are significantly reduced. Both the thickness and the inherent stiffness properties of the material used for viscoelastic adhesive layer  202  determine the frequency range that is damped by viscoelastic adhesive layer  202 . In addition, because most vibration-damping materials vary in performance as a function of temperature, viscoelastic adhesive layer  202  is also selected based on the anticipated operating temperature at which vibration damping is desired. Upon reading the disclosure presented herein, one of skill in the art can readily select an appropriate viscoelastic material for viscoelastic adhesive layer  202  to damp resonances in a specific frequency range originating in flexible PCB  122 . 
         [0039]    As illustrated in  FIG. 3 , vibration-damping system  200  is a layered structure that attaches flexible PCB  122  to surface  250  of J-block  148 . Because vibration-damping system  200  is designed to be slightly more rigid than flexible PCB  122  in the plane of motion of actuator assembly  110 , vibration-damping system  200  influences the effective exit point and exit angle of flexible PCB  122  as actuator assembly  110  rotates between the ID position and the OD position. Consequently, when vibration-damping system  200  is configured with appropriate stiffness properties, vibration-damping system  200  minimizes vibration coupling throughout the range of motion of actuator assembly  110 . By way of illustration,  FIG. 3  shows the position of flexible PCB  122  and vibration-damping system  200  when actuator assembly  110  is in the ID position and in the OD position. 
         [0040]    Vibration-damping system  200  also serves two other purposes. First, viscoelastic adhesive layer  202  damps resonances originating in flexible PCB  122 . Because such resonances have been shown to result in the most serious unwanted displacement of actuator assembly  110 , such damping substantially improves disk drive performance. Second, vibration-damping system  200  helps prevent flexible PCB  122  from bending out of the plane of motion of actuator assembly  110 . Vibration-damping system  200  holds actuator assembly  110  in said plane due to the rigidity of vibration-damping system  200  with respect to bending out of said plane. 
         [0041]    Flexible PCB  122  is slightly under tension when actuator assembly  110  is in either the ID or the OD position. In this way, viscoelastic adhesive layer  202  is under compression at all times and there is no tendency for flexible PCB  122  to separate from flexible stiffener  201 . 
         [0042]    In one embodiment, vibration-damping system  200  is rectangular in cross section, to better promote flexibility in the plane of motion of actuator assembly  110  and resistance to bending out of said plane.  FIG. 5  is a schematic cross-sectional view of vibration-damping system  200  taken at section A-A in  FIG. 3 , where vibration-damping system  200  has a rectangular cross section, according to an embodiment of the invention. As shown, in such an embodiment, vibration-damping system  200  is a layered structure that includes flexible stiffener  201 , viscoelastic adhesive layer  202 , and flexible PCB  122 . All three elements of the layered structure are rectangular in cross section. Further, each of said rectangular cross sections may have a very high aspect ratio. To with, thicknesses  122 T,  202 T, and  201 T of flexible PCB  122 , viscoelastic adhesive layer  202 , and flexible stiffener  201 , respectively, may be approximately an order of magnitude smaller than the width  200 W of vibration-damping system  200 . Consequently, vibration-damping system  200  may be a ribbon-like structure having high flexibility in one plane and significant rigidity or resistance to bending in any orthogonal plane. 
         [0043]    In one embodiment, resonances produced by flexible PCB  122  having frequencies of approximately 1000 Hz and below are damped by the modification of flexible PCB  122  with vibration-damping system  200 . In such an embodiment, flexible PCB  122  has a thickness  122 T of 0.05 mm and is formed of outside polyimide layers encasing thin copper electrical traces, viscoelastic adhesive layer  202  has a thickness  202 T of 0.05 mm and is formed of 3M™ Viscoelastic Damping Polymers Type 112, and flexible stiffener  201  has a thickness  201 T of 0.05 mm and length  205  of 6 mm, and is formed of polyimide film. Flexible stiffener  201  extends from J-block  148  a distance  206  of 3.5 mm.  FIG. 6A  is graph  600 A showing the power spectrum of non-repeatable vibrations occurring at a read/write transducer as it flies over a selected track of a magnetic disk. At 1000 Hz and below, several resonances  601  are detected. The frequencies of resonances  601  have been demonstrated to correspond to the frequencies of resonances measured directly on flexible PCB  122 . Significantly, resonances  601  are in the low frequencies demonstrated to cause substantial and unwanted displacement of actuator assembly  110  during operation of disk drive  100 .  FIG. 6B  is graph  600 B showing the power spectrum of vibrations occurring under the same conditions as graph  600 A, except that flexible PCB  122  is modified with vibration-damping system  200  having the thicknesses  122 T,  202 T,  201 T, length  205 , and materials described above. As shown in  FIG. 6B , the addition of vibration-damping system  200  has removed resonances  601  from the power spectrum of vibrations occurring at a read/write transducer without noticeably exacerbating the resonances at any other frequencies. 
         [0044]    The flexibility of a flexible stiffener may be varied across its length by forming the flexible stiffener with a non-uniform geometry.  FIG. 7A  illustrates a partial side-view of a flexible stiffener  701  having a uniform geometry and attached to flexible PCB  122 , according to an embodiment of the invention. Flexible stiffener  701  is a uniform rectangle along the entire length  711  thereof, and therefore is a support member having a uniform stiffness along length  711 .  FIG. 7B  illustrates a partial side-view of a flexible stiffener  710  having a non-uniform geometry, according to an embodiment of the invention. In such an embodiment, flexible stiffener  701  is trapezoidal, triangular, or otherwise varies in height  702  or thickness (into page) across a portion of its length  703 . An advantage of this embodiment is that the stiffness of flexible stiffener  710  and, hence, any vibration-damping system that includes flexible stiffener  710 , may be fine-tuned to align a flexible PCB with an optimal exit angle.  FIG. 7C  illustrates a schematic side-view of a flexible stiffener  720  having a non-uniform geometry, according to an embodiment of the invention. Similar to flexible stiffener  710 , flexible stiffener  720  also varies in height  702  across a portion of its length  703 . However, flexible stiffener  720  has a region of minimal stiffness in a center portion  721  of flexible stiffener  720 , rather than at an end. Other configurations of flexible stiffeners having non-uniform geometries are also contemplated. 
         [0045]      FIG. 8  illustrates a partial plan view of an actuator assembly  110 , a J-block  148 , and a vibration-damping system  800  according to another embodiment of the invention. In this embodiment, vibration-damping system  800  includes a first flexible stiffener  801  attached to flexible PCB  122  via a first viscoelastic adhesive layer  802  and a second flexible stiffener  803  attached to the first flexible stiffener  801  via a second viscoelastic adhesive layer  804  to form a layered structure. As shown, the distance that flexible stiffener  803  extends from J-block  148  is shorter than the distance that flexible stiffener  801  extends from J-block  148  by about two-thirds. 
         [0046]    Examples of materials suitable for use as first and second flexible stiffeners  801 ,  803  include Kapton®, manufactured by Dupont, a polyimide film. Other generic versions of polyimide film may be applied with equal effect. The materials used in first and second viscoelastic adhesive layers  802 ,  804  include viscoelastic damping polymers, such as 3M™ Viscoelastic Damping Polymers or other appropriate materials that meet the outgassing and cleanliness requirements necessary for hard drives, with different characteristics. The first viscoelastic adhesive layer  802  employs a viscoelastic damping polymer that has been optimized for higher temperatures relative to the second viscoelastic adhesive layer  804 , and the second viscoelastic adhesive layer  804  employs a viscoelastic damping polymer that has been optimized for lower temperatures relative to the first viscoelastic adhesive layer  802 . With this configuration, the effective temperature range of vibration-damping system  800  can be increased. 
         [0047]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.