Abstract:
A suspension for a hard disk drive has a vibration sensor which is impervious to influence by external noise, to obtain more stable positioning precision of the head on the suspension. The suspension has a load beam, a vibration sensor sandwiched by a first electrode and a second electrode, and a conductive wiring pattern on the load beam for electrically connecting the first electrode and the second electrode to an external detection circuit. The first electrode is sandwiched by the second electrode via the vibration sensor and a shield layer via an insulating layer. The second electrode and the shield layer are at a same potential.

Description:
[0001]    The present invention relates to a suspension equipped with a vibration sensor. In particular, the present invention relates to a structure of a vibration sensor with which a suspension is equipped and a manufacturing method thereof. 
       BACKGROUND OF THE INVENTION 
       [0002]      FIG. 1  shows a perspective view of a conventional magnetic disk apparatus, and  FIG. 2  shows an enlarged perspective view of an actuator shown in  FIG. 1 . A magnetic recording medium  2  fixed to a spindle motor  1  rotates at high speed. With this rotation, air is drawn between a head slider  3  and the magnetic recording medium  2 . The head slider  3  is floated by pressurization of the air. 
         [0003]    As shown in  FIG. 2 , an actuator  4  has a suspension  6  at one end of a carriage  5  and a voice coil  7  at the other end. The actuator  4  is fixed rotatably to a housing  9  ( FIG. 1 ) by a pivot through a shaft bearing  8  and moves in an approximate radius direction of the magnetic recording medium  2 . Therefore, the head slider  3  mounted to the suspension  6  moves over the magnetic recording medium  2  in the approximate radius direction. Then, a head mounted to the head slider  3  is positioned on a predetermined track to write/read information. 
         [0004]    In recent years, with digitization and computerization, a large-capacity recording apparatus is needed. Moreover, a magnetic recording apparatus such as an HDD is rapidly developing with high density. With high density, the recording size is becoming increasingly smaller. Moreover, higher head positioning precision is demanded for the actuator. 
         [0005]    One factor inhibiting head positioning is disk flutter. This is a phenomenon in which a stream of air generated by rotation of a recording medium causes vibration of the recording medium. The suspension fixing the head slider floating over a recording medium also vibrates together with the recording medium, affecting head positioning precision adversely. 
         [0006]    Japanese Patent Application Laid-Open Publication No. 2003-217244 discloses a technology for decreasing disk flutter. A strain gauge for detecting displacement in an axial direction with respect to a recording medium is mounted on a suspension. Then, a correction control signal is generated from output of the strain gauge and sent to an actuator to correct a shift of the head position with respect to the track on the recording medium. 
         [0007]    It is also publicly known that a piezoelectric sensor can be used for detection of deformation and vibration of a member. For example, Japanese Patent No. 3208386 describes a method of inhibiting resonance by detecting actuator deformation by a piezoelectric sensor and a mounting method of the piezoelectric sensor. 
         [0008]    However, a vibration sensor used in a suspension is very highly sensitive. Thus, if external noise mainly originating from a power supply is produced, the vibration sensor senses external noise and thus will unable to correct a head position shift correctly. In view of higher densities in the future, measures taken against external noise are very important in order to obtain satisfactory head positioning precision. 
         [0009]    Therefore, an object of the present invention is to provide a suspension equipped with a vibration sensor having a structure impervious to external noise. Another object of the present invention is to provide a method of easily manufacturing a suspension equipped with a vibration sensor having a structure impervious to external noise. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with an aspect of an embodiment, a suspension has a load beam, a vibration sensor sandwiched by a first electrode and a second electrode, and a conductive wiring pattern on the load beam for electrically connecting the first electrode and the second electrode to an external detection circuit. The first electrode is sandwiched by the second electrode via the vibration sensor and a shield layer via an insulating layer, and the second electrode and the shield layer are at the same potential. 
         [0011]    In addition, in accordance with another aspect of an embodiment, a method of manufacturing the suspension includes the step of arranging the vibration sensor between the first electrode and second electrode via the insulating layer on the shield layer electrically connected to the conductive wiring pattern. A first vibration sensor terminal land part is electrically connected to the conductive wiring pattern and the first electrode, and a second vibration sensor terminal land part is electrically connected to the conductive wiring pattern and shield payer and the second electrode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will be explained with reference to the accompanying drawings. 
           [0013]      FIG. 1  is a perspective view of a conventional magnetic disk apparatus; 
           [0014]      FIG. 2  is a perspective view of an actuator in  FIG. 1 ; 
           [0015]      FIG. 3  is a perspective view of a suspension; 
           [0016]      FIG. 4  is an exploded view of the suspension; 
           [0017]      FIG. 5  is a plan view of a suspension equipped with a vibration sensor according to a first embodiment of the present invention; 
           [0018]      FIG. 6  is a sectional view along  6 - 6  in  FIG. 5 ; 
           [0019]      FIG. 7  is a sectional view along  7 - 7  in  FIG. 5 ; 
           [0020]      FIG. 8  is a plan view of a suspension equipped with a vibration sensor according to a second embodiment of the present invention; 
           [0021]      FIG. 9  is a sectional view along  9 - 9  in  FIG. 8 ; 
           [0022]      FIG. 10  is a perspective view of a suspension according to a third embodiment of the present invention before a vibration sensor is mounted; 
           [0023]      FIG. 11  is a perspective view of the suspension according to the third embodiment of the present invention after the vibration sensor is mounted; and 
           [0024]      FIG. 12  is a perspective view when viewed from an X direction in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Embodiments of the present invention will be described below with reference to attached drawings. 
         [0026]      FIG. 3  shows a perspective view of a suspension of the present invention. In the suspension  6 , a load beam  11  is fixed to a base plate  10  to be connected to a carriage. On the load beam  11 , flexures  12   a  and  12   b  and a wiring pattern  13  are arranged in order. The head slider  3  is arranged on a portion of the flexure  12   b . A vibration sensor  14  is arranged on a portion of the wiring pattern  13 . 
         [0027]      FIG. 4  shows an exploded view of the suspension of the present invention. A hollow part  22  is provided in the load beam  11  to constitute a elastic part. The flexures  12   a  and  12   b  are separated by the hollow part  22  of the load beam  11 . The wiring pattern  13  is formed of insulating layers  15   a  and  15   b , a conductive wiring pattern  16 , and an insulating cover layer  21 . A head terminal of the head slider  3  is electrically connected to head terminal land parts  17   a  and  17   b  formed at tip parts of the conductive wiring pattern  16  by soldering or the like. The conductive wiring pattern  16  also has a first vibration sensor terminal land part  18  and a second vibration sensor terminal land part  19  to be electrically connected to the vibration sensor formed thereon. Further, a shield layer  20  is formed as a portion for mounting the vibration sensor. The shield layer  20  and the second vibration sensor terminal land part  19  are connected. The head and vibration sensor are connected to outside circuits via the conductive wiring pattern  16 . Incidentally, no cover layer is attached to the head terminal land parts  17   a  and  17   b , the first vibration sensor terminal land part  18 , and the second vibration sensor terminal land part  19 , which serve as an electrical connection portion between the conductive wiring pattern  16  and vibration sensor terminal and between the head terminal and vibration sensor terminal. 
         [0028]    In the present embodiment, the wiring pattern  13  is provided in such a way that the hollow part  22  of the suspension  6  is crossed. The vibration sensor  14  is mounted in a portion where the hollow part  22  of the suspension  6  is crossed by the wiring pattern  13 . Therefore, the increase of the spring stiffness of the suspension  6  and the decrease of the vibration sensor can be suppressed. Incidentally, the vibration sensor is mounted using an adhesive or pressure sensitive adhesive tape. 
         [0029]    Further, a state in which the vibration sensor is mounted on the shield layer  20  will be described.  FIG. 5  is a plan view of a suspension equipped with a vibration sensor according to a first embodiment of the present invention.  FIG. 6  is a sectional view along  6 - 6  in  FIG. 5 .  FIG. 7  is a sectional view along  7 - 7  in  FIG. 5 . As shown in  FIGS. 6 and 7 , an upper electrode  23  and a lower electrode  24  are formed on the upper and lower surfaces of a piezoelectric material  25  in the vibration sensor  14 . The piezoelectric material is typically piezoelectric ceramic such as PZT (Pb(Zr—Ti)O3: lead-zirconate-titanate). A piezoelectric polymeric material is suitable because it is excellent in flexibility, processibility (easy to process), and impact resistance. And output sensitivity is advantageous when used with voltage amplifier circuit. The piezoelectric polymeric material includes, for example, PVDF (PolyVinyliDene Fluoride). When PVDF is used, electrodes are formed on the surface thereof by screen printing or the like. 
         [0030]    As shown in  FIG. 5 , a portion of the upper electrode  23  which is connected to the second vibration sensor terminal land part  19  of the wiring pattern and a portion of the lower electrode (not shown) which is connected to the first vibration sensor terminal land part  18  of the wiring pattern are not overlapping as viewed perpendicular to the upper and lower electrode. These portions are connected by conductive adhesives  27  and  28 . For example, first a vibration sensor is arranged on the shield layer  20  and, as shown in  FIG. 6 , the conductive adhesive  27  is arranged so that the second vibration sensor terminal land part  19  and the upper electrode  23  are connected to each other. Next, as shown in  FIG. 7 , the conductive adhesive  28  is arranged so that the first vibration sensor terminal land part  18  and the lower electrode  24  are connected. In this manner, a suspension according to the present invention is manufactured. 
         [0031]    With a structure described above, the upper electrode  23  of the piezoelectric material  25 , the second vibration sensor terminal land part  19 , and the shield layer  20  are at the same potential. An influence of external noise can be significantly reduced by grounding the pattern wire drawn out of the second vibration sensor terminal land part  19  and selecting an electrode mounted to the suspension, that is, the lower electrode  24  as an output electrode. This is because the output electrode has a shield structure surrounded by the grounding electric potential. 
         [0032]      FIG. 8  shows a plan view of a suspension equipped with a vibration sensor according to a second embodiment of the present invention. The vibration sensor is arranged with a configuration similar to that of the first embodiment. Next,  FIG. 9  shows a sectional view along  9 - 9  in  FIG. 8 . The sectional view is the same as that in the first embodiment except that a through hole  29  is formed in the vibration sensor  14 . The through hole  29  provides a through-hole in the vibration sensor  14  and the lower electrode  24  is drawn upward to wrap the through-hole. Therefore, in work efficiency of arranging adhesive between the first vibration sensor terminal land part  18  and the lower electrode  24 , efficiency can be improved while ensuring reliable electric connection even if the arranging direction of the conductive adhesive  28  is one direction from above. 
         [0033]      FIG. 10  shows a perspective view of a suspension according to a third embodiment of the present invention before a vibration sensor is mounted. In the third embodiment, the shield layer used in the first and second embodiments is not provided. On the other hand, a flexure connection land part  31  is arranged on the insulating layer. Also in the third embodiment, vibration sensor terminal land parts  30   a  and  30   b  are arranged on an insulating layer positioned differently from the first and second embodiments. Next,  FIG. 11  shows a perspective view of the suspension according to the third embodiment of the present invention after the vibration sensor is mounted. A two-part vibration sensor  32   a ,  32   b  is fixed to both ends of the hollow part  22  of the load beam  11  by a non-conductive adhesive  36  ( FIG. 12 ). 
         [0034]    Here,  FIG. 12  shows a perspective view when viewed from an X direction in  FIG. 11 . The lower electrode  24  of vibration sensors  32   b  (and  32   a ) and the vibration sensor terminal land parts  30   b  (and  30   a ) are electrically connected by conductive adhesives  33   b  (and  33   a ). Also, the upper electrode  23  of the vibration sensors  32   b  (and  32   a ) and the load beam  11  are electrically connected by conductive adhesives  34   b  (and  34   a ). Further, the flexure connection land part  31  and the flexure  12  are electrically connected by a conductive adhesive  35 . 
         [0035]    The upper electrode  23  of the vibration sensor  32 , the load beam  11 , and the flexure  12  are at the same potential. A pattern wire drawn out of the flexure connection land part  31  is grounded and the lower electrode  24  mounted on the suspension is selected as an output electrode. The output electrode has a shield structure surrounded by the grounding electric potential, leading to significant reduction of an influence of external noise. 
         [0036]    According to a suspension in the present embodiment, a suspension equipped with a vibration sensor impervious to an influence of external noise can be provided. Therefore, stable positioning precision of a head can be obtained. Also, according to a manufacturing method of a suspension in the present embodiment, such a suspension can be manufactured easily.