Patent Publication Number: US-2011075300-A1

Title: Reducing the Propagation of Vibrations to an HDD Head

Description:
FIELD OF THE INVENTION 
     Embodiments of the invention generally relate to reducing the propagation of vibrations to a hard-disk drive (HDD) head. 
     BACKGROUND OF THE INVENTION 
     A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator. 
     A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of a magnetic-recording disk must be tightly controlled. To provide a uniform distance between a read/write head and the surface of a magnetic-recording disk, an actuator relies on air pressure inside the hard drive enclosure to support the read/write heads at the proper distance away from the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A read/write head therefore is said to “fly” over the surface of the magnetic-recording disk. That is, the air pulled along by a spinning magnetic-recording disk forces the head away from the surface of the magnetic-recording disk. When the magnetic-recording disk stops spinning, a read/write head must either “land” or be pulled away. 
     A write-head of a HDD records data onto the surface of a magnetic-recording disk in a series of concentric tracks. When a write-head writes data to a desired track of a magnetic-recording disk, it is important for the write-head to be located close to the desired track; failure to do so may result in a squeeze event, which may compromise data integrity and throughput, and in extreme cases, may result in hard errors and data loss. A squeeze event occurs when a write-head writes data too close to or overlapping with an adjacent track such that there is not enough of the adjacent track left for the adjacent track to be read properly by a read-head. 
     References markers may be recorded in each track of a magnetic-recording disk. These reference markers are referred to as servo information. To help properly position a read/write head, a HDD employs a servo mechanical control loop to maintain the read/write head in the correct position using the servo information stored on the magnetic-recording disk. When a read/write head reads the servo information (servo information being read may be referred to as a position-error signal, or PES), a relative position of the read/write head may be determined by a servo processor to enable the position of the read/write head, relative to the desired track, to be adjusted if necessary. 
     It is desirable, for a variety of reasons, to maintain a constant or approximately constant distance between the read/write head and the surface of the magnetic-recording disk to ensure proper operation of the read/write head. If the distance between a read/write head and the surface of a magnetic-recording disk fluctuates, then the strength of the magnetic dipole field between the read/write head and the surface of the magnetic-recording disk will also fluctuate, which may cause problems in reading data from or writing data to the magnetic-recording disk. Also, if the read/write head touches the surface of the magnetic-recording medium, then read/write head may scrape across the surface of a platter, which could grind away the thin magnetic film on the surface magnetic-recording medium and therefore cause data loss and potentially render the HDD inoperable. 
     SUMMARY OF THE INVENTION 
     It is observed that vibrations experienced by a lead suspension of a hard-disk drive (HDD) may be propagated to a head. The lead suspension may start to vibrate for different reasons, such as the HDD experiencing a mechanical shock, the circulating air flow within the HDD, and resonance vibrations. 
     Approaches are discussed herein for reducing the propagation of vibrations to a head of a persistent storage medium, such as a HDD. An HDD may compromise a lead suspension that includes a magnetic read/write head. The magnetic read/write head may be connected to the lead suspension by a plurality of leads. A portion of each of the plurality of leads, such as the solder ball joints, may be covered by a dampening material that is designed to absorb vibrations occurring in the lead suspension to prevent transmission of the vibrations to the magnetic read/write head. Alternately, the dampening material may be applied to other locations which can transmit vibrations to the magnetic read/write head, such as the limiter engagements. In this way, the dampening material reduces or eliminates the propagation of vibrations from the lead suspension to the read/write head. 
     Embodiments discussed in the Summary of the Invention section are not meant to suggest, describe, or teach all the embodiments discussed herein. Thus, embodiments of the invention may contain additional or different features than those discussed in this section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a plan view of an HDD according to an embodiment of the invention; 
         FIG. 2  is a plan view of a head-arm-assembly (HAA) according to an embodiment of the invention; 
         FIG. 3A  is a chart that depicts the modulation of a head due to resonance vibrations; 
         FIG. 3B  is a chart that depicts a frequency plot (FFT) of the distortion depicted in  FIG. 3A ; 
         FIG. 4  is a flow chart depicting the high level functional steps of reducing the propagation of vibrations to a head-disk drive (HDD) head according to an embodiment of the invention; 
         FIG. 5A  is a first illustration of a plurality of solder ball joints that each have been applied with dampening material according to an embodiment of the invention; 
         FIG. 5B  is a first illustration of a plurality of solder ball joints that each have been applied with dampening material according to an embodiment of the invention; 
         FIG. 6A  is a graph depicting the distortion of head  110   a  caused by resonance vibrations when lead suspension  110   c  vibrates at 4 kHz according to the known state of the art; 
         FIG. 6B  is a graph depicting the elimination of the distortion of a head after the dampening material has been applied to each solder ball joint connecting the lead suspension to the thin-film connectors at the trailing edge of the head according to an embodiment of the invention; and 
         FIG. 7  is an illustration of a limiter engagement to which a dampening material has been applied according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Approaches for reducing the propagation of vibrations to a hard-disk drive (HDD) head are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described herein. It will be apparent, however, that the embodiments of the invention described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein. 
     PHYSICAL DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION 
     Embodiments of the invention may be implemented using a variety of different storage mediums. For example, embodiments of the invention may be implemented using a magnetic-recording storage medium, such as a hard-disk drive (HDD). With reference to  FIG. 1 , in accordance with an embodiment of the invention, a plan view of a HDD  100  is shown.  FIG. 1  illustrates the functional arrangement of components of the HDD including a slider  110   b  including a magnetic-recording head  110   a . The HDD  100  includes at least one HGA  110  including the head  110   a , a lead suspension  110   c  attached to the head  110   a , and a load beam  110   d  attached to the slider  110   b , which includes the head  110   a  at a distal end of the slider  110   b ; the slider  110   b  is attached at the distal end of the load beam  110   d  to a gimbal portion of the load beam  110   d . The HDD  100  also includes at least one magnetic-recording disk  120  rotatably mounted on a spindle  124  and a drive motor (not shown) attached to the spindle  124  for rotating the disk  120 . The head  110   a  includes a write element, a so-called writer, and a read element, a so-called reader, for respectively writing and reading information stored on the disk  120  of the HDD  100 . The disk  120  or a plurality (not shown) of disks may be affixed to the spindle  124  with a disk clamp  128 . The HDD  100  further includes an arm  132  attached to the HGA  110 , a carriage  134 , a voice-coil motor (VCM) that includes an armature  136  including a voice coil  140  attached to the carriage  134 ; and a stator  144  including a voice-coil magnet (not shown); the armature  136  of the VCM is attached to the carriage  134  and is configured to move the arm  132  and the HGA  110  to access portions of the disk  120  being mounted on a pivot-shaft  148  with an interposed pivot-bearing assembly  152 . 
     With further reference to  FIG. 1 , in accordance with an embodiment of the invention, electrical signals, for example, current to the voice coil  140  of the VCM, write signal to and read signal from the read/write head (typically PMR)  110   a , are provided by a flexible cable  156 . Interconnection between the flexible cable  156  and the head  110   a  may be provided by an arm-electronics (AE) module  160 , which may have an on-board pre-amplifier for the read signal, as well as other read-channel and write-channel electronic components. The flexible cable  156  is coupled to an electrical-connector block  164 , which provides electrical communication through electrical feedthroughs (not shown) provided by an HDD housing  168 . The HDD housing  168 , also referred to as a casting, depending upon whether the HDD housing is cast, in conjunction with an HDD cover (not shown) provides a sealed, protective enclosure for the information storage components of the HDD  100 . 
     With further reference to  FIG. 1 , in accordance with an embodiment of the invention, other electronic components (not shown), including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil  140  of the VCM and the head  110   a  of the HGA  110 . The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle  124  which is in turn transmitted to the disk  120  that is affixed to the spindle  124  by the disk clamp  128 ; as a result, the disk  120  spins in a direction  172 . The spinning disk  120  creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider  110   b  rides so that the slider  110   b  flies above the surface of the disk  120  without making contact with a thin magnetic-recording medium of the disk  120  in which information is recorded. The electrical signal provided to the voice coil  140  of the VCM enables the head  110   a  of the HGA  110  to access a track  176  on which information is recorded. Thus, the armature  136  of the VCM swings through an arc  180  which enables the HGA  110  attached to the armature  136  by the arm  132  to access various tracks on the disk  120 . Information is stored on the disk  120  in a plurality of concentric tracks (not shown) arranged in sectors on the disk  120 , for example, sector  184 . Correspondingly, each track is composed of a plurality of sectored track portions, for example, sectored track portion  188 . Each sectored track portion  188  is composed of recorded data and a header containing a servo-burst-signal pattern, for example, an ABCD-servo-burst-signal pattern, information that identifies the track  176 , and error correction code information. In accessing the track  176 , the read element of the head  110   a  of the HGA  110  reads the servo-burst-signal pattern which provides a position-error-signal (PES) to the servo electronics, which controls the electrical signal provided to the voice coil  140  of the VCM, enabling the head  110   a  to follow the track  176 . Upon finding the track  176  and identifying a particular sectored track portion  188 , the head  110   a  either reads data from the track  176  or writes data to the track  176  depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system. 
     Embodiments of the invention also encompass HDD  100  that includes the HGA  110 , the disk  120  rotatably mounted on the spindle  124 , the arm  132  attached to the HGA  110  including the slider  110   b  including the head  110   a.    
     With reference now to  FIG. 2 , in accordance with an embodiment of the invention, a plan view of a head-arm-assembly (HAA) including the HGA  110  is shown.  FIG. 2  illustrates the functional arrangement of the HAA with respect to the HGA  110 . The HAA includes the arm  132  and HGA  110  including the slider  110   b  including the head  110   a . The HAA is attached at the arm  132  to the carriage  134 . In the case of an HDD having multiple disks, or platters as disks are sometimes referred to in the art, the carriage  134  is called an “E-block,” or comb, because the carriage is arranged to carry a ganged array of arms that gives it the appearance of a comb. As shown in  FIG. 2 , the armature  136  of the VCM is attached to the carriage  134  and the voice coil  140  is attached to the armature  136 . The AE  160  may be attached to the carriage  134  as shown. The carriage  134  is mounted on the pivot-shaft  148  with the interposed pivot-bearing assembly  152 . 
     Note that embodiments of the invention are not limited to storage devices that use a rigid magnetic disk or a magnetic recording medium, as embodiments of the invention may be implemented using a flexible disk substrate or to a recording medium that includes a ferroelectric or phase change, for example. 
     Having described the physical description of an illustrative embodiment of the invention, discussion will now be presented describing how vibrations may originate as well as propagate to a read/write head. 
     How Vibrations May be Propagated to a Read/Write Head and the Problems Resulting Therefrom 
     If lead suspension  100   c  is undergoing vibrations, then these vibrations may be transmitted to head  110   a , as head  110   a  is physically connected to lead suspension  110   c . Vibrations may occur in lead suspension  110   c  for a variety of reasons. For example, lead suspension  110   c  may experience resonance vibrations. Resonance refers to the tendency of a system to oscillate at a larger amplitude at some frequencies than other frequencies. To illustrate,  FIG. 3A  is a chart  300  that depicts the modulation of head  110   a  due to resonance vibrations. The read/write head depicted in chart  300  is undergoing a high frequency distortion. As shown by chart  300 , the read/write head is moving +/−2 nanometers, which can negatively affect the operation of HDD  100 . 
       FIG. 3B  is a chart  350  that depicts a frequency plot (FFT) of the distortion depicted in chart  300 . As shown by chart  350 , the critical range of vibration is 33-39 kHz. When lead suspension  110   c  is vibrating between 33-39 kHz, then lead suspension  110   c  will undergo a larger distortion than when lead suspension  110   c  is vibrating at frequencies other than 33-39 kHz. Without the assistance of embodiments of the invention, the distortion that head  110   a  would undergo as a result of the distortion experienced by lead suspension  110   c  when lead suspension  110   c  is vibrating at frequencies between 33-39 kHz may result in an unacceptable amount of error conditions, as head  110   a  may not be able to read or write properly and/or may physically touch the surface of the disk. 
     Additionally, if HDD  100  is bumped, lead suspension  110   c  may oscillate or vibration due to the mechanical shock. The circulating air flow within the enclosure of HDD  100 , caused by the rotation of the platters, may also induce vibrations in lead suspension  110   c.    
     Vibrations may propagate from lead suspension  110   c  to head  110   a  at any point of physical contact between lead suspension  110   c  and head  110   a . In an embodiment, a main transmission area for the propagation of vibrations from lead suspension  110   c  to head  110   a  is at the solder lead connection of the lead suspension  110   c  to the thin-film connectors at the trailing edge of head  110   a . Another potential transmission area for the propagation of vibrations from lead suspension  110   c  to head  110   a  is the limiter engagements. A limiter, shown in  FIG. 7 , is a mechanical stop to prevent the gimbal assembly from separating away from the suspension assembly. 
     It is undesirable for vibrations to propagate from lead suspension  110   c  to head  110   a . If head  110   a  is vibrating, then errors in operations (some of which may be catastrophic and unrecoverable) may occur. If head  110   a  is experiencing vibrations, then the strength of the magnetic dipole field between head  110   a  and the surface of the magnetic-recording disk will fluctuate, which may cause problems with reading data from or writing data to the magnetic-recording disk. Also, if head  110   a  touches the surface of the magnetic-recording medium, then head  110   a  may scrape across the surface of the magnetic-recording disk, which could grind away the thin magnetic film on the surface magnetic-recording disk, causing scratches, dings and burnish marks and therefore cause data loss and potentially render the HDD inoperable. 
     Additionally, if head  110   a  is vibrating, it may be difficult for head  110   a  to read data from or write data to the appropriate track on the magnetic-recording disk. Head  110   a  may be particularly susceptible to vibrations during high stress conditions, such as loading head  110   a  on a ramp, unloading head  110   a  off a ramp, and track seeking. If head  110   a  picks up a resonance vibration that causes head  110   a  to vibrate before an air-bearing is established for head  110   a , then head  110   a  can crash into the magnetic-recording disk, and consequently, destroy the magnetic-recording disk and any information that the magnetic-recording disk has previously recorded. 
     Head  110   a  may also vibrate during normal operation of HDD  100 , such as when head  110   a  is seeking a single track or moving from track to track. When head  110   a  is seeking a single track in normal operation, lateral vibrations may prevent head  110   a  from being positioned correctly over the desired track, thereby preventing head  110   a  from being able to read from the desired track or write to the desired track causing track to track misalignment and position error. Also, vibrations during the normal operation of HDD  100  when head  110   a  is moving from track to track may cause fly height instability. 
     Consequently, embodiments of the invention provide an advantage over prior approaches by providing mechanisms for reducing or eliminating the propagation of vibrations, such as but not limited to resonance vibrations, from a lead suspension to a head. 
     Reducing Vibrations that are Propagated to a HDD Head 
       FIG. 4  is a flow chart depicting the high level functional steps of reducing the propagation of vibrations to a head-disk drive (HDD) head according to an embodiment of the invention. Advantageously, by employing embodiments of the invention, the number and magnitude of the vibrations which are propagated from lead suspension  110   c  to head  110   a  may be reduced. Thus, by using an embodiment of the invention, the read/write head depicted in chart  350  of  FIG. 3B  may operate with lead suspension  110   c  experiencing vibrations in the range of vibration is 33-39 kHz, as embodiments of the invention may dampen, reduce, or eliminate the propagation of vibrations from lead suspension  110   c  to head  110   a  to enable head  110   a  to function properly. 
     In step  410 , an appropriate dampening material is selected. The dampening material selected in step  410  will be applied to an appropriate location to reduce or eliminate the propagation of vibrations from lead suspension  110   c  to head  110   a . The dampening material selected in step  410  may be any material that can absorb vibrations occurring in the lead suspension  110   c  to prevent their transmission to head  110   a . Non-limiting, illustrative examples of a dampening material which may be employed in step  410  include a viscoelastic polymer, a viscous liquid, an epoxy, and glue. 
     In an embodiment, the particular dampening material selected in step  410  may be selected based on an outgassing property possessed by the dampening material. The outgassing property of a material refers to the type and amount of contaminants that are released or produced by the material. When building a new hard-disk drive (HDD), it is desirable to select a combination of materials which have low outgassing properties to minimize or avoid any contaminants introduced into the interior of HDD  100 . 
     After a particular dampening material is selected for use, in step  420 , the dampening material is applied to an appropriate location to prevent the propagation of vibrations to head  110   a . In step  420 , in an embodiment, the appropriate location (referred to as a transmission area) to which the dampening material is applied in step  420  is a location which is capable of propagating vibrations, such as resonance vibrations, from a source structure to head  110   a  by virtue of head  110   a  being physically connected to the source structure at the transmission area. 
     For example, lead suspension  110   c  may be a source of vibrations that are propagated to head  110   a . Embodiments of the invention may be employed to prevent the propagation of vibrations from a variety of different types of lead suspensions. To illustrate, in an embodiment, lead suspension  110   c  may be an electrical lead suspension, or more particularly, an integrated lead suspension (ILS), a circuit integrated suspension (CIS), or a flex-on suspension. A flex-on suspension (FOS) is a general term of art that refers to a technology for embedding wires into a polymer on a stiff and flexible substrate for the purpose of getting electronic connections to the magnetic head from the arm-electronics (AE) module  160 . 
     In an embodiment, the location on which the dampening material applied is the solder ball joint of each lead of the lead suspension. The leads may be built into the thin-film element of head  110   a  and may be coupled to electrical components of head  110   a , such as components responsible for reading data, writing data, and a heater element. Note that embodiments of the invention may have different numbers of leads. For example, while 8 leads are common now, 6 leads have been used previously and 10 leads may be used in the future. Thus, in an embodiment, dampening material may be applied to the solder ball joint of any number of leads in steps  420 . 
       FIG. 5A  and  FIG. 5B  are illustrations  500  and  550  of a plurality of solder ball joints that each have been applied with a dampening material according to an embodiment of the invention. As shown by  FIGS. 5A and 5B , in an embodiment, the dampening material may be applied to each solder ball joint connecting the lead suspension to the thin-film connectors at the trailing edge of the head. In such an embodiment, the dampening material would be applied to each solder ball joint. 
     To illustrate how the effect of applying the dampening material to the solder ball joints, consider  FIGS. 6A and 6B .  FIG. 6A  is a graph depicting the distortion of head  110   a  caused by resonance vibrations when lead suspension  110   c  vibrates at 4 kHz according to the known state of the art. As shown in  FIG. 6A , the head undergoes an undesirable amount of vibrations at 4 kHz.  FIG. 6B  is a graph depicting the elimination of the distortion of head  110   a  after the dampening material has been applied to each solder ball joint connecting the lead suspension to the thin-film connectors at the trailing edge of head  110   a.    
     The dampening material may be applied to any location which physically connects lead suspension  110   c  with head  110   a . To illustrate,  FIG. 7  is an illustration of a limiter engagement to which a dampening material has been applied according to an embodiment of the invention. In certain embodiments of the invention, dampening material may be applied to multiple locations, such as applying dampening material to both the limiter engagement and each solder ball joint connecting the lead suspension to the thin-film connectors at the trailing edge of the head. 
     Advantageously, embodiments of the invention are able to eliminate or reduce the propagation of vibrations to head  110   a . Desirably, the mass or the head and the flying characteristics of the head have not been modified, as would be the case if the dampening material would be applied to the slider. Also, by applying the dampening material to the location that physically connects lead suspension  110   a  and head  110   c , it is more certain that vibrations will not propagate to head  110   a  than if the dampening material were applied to the slider. 
     In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.