Abstract:
This application discloses a hard disk drive, a head stack assembly, and a printed circuit board configured to include impedance patches on the flex ground plane, the flex power plane, the printed circuit ground plane and/or the printed circuit power plane over or under a connector site in the disk base that conveys access read and write differential signals for the sliders&#39; access of rotating disk surfaces. These impedance patches minimize impedance discontinuities in the read and/or write differential signals through the connector site, which may improve the ability of the hard disk drive to transmit these signals at higher frequencies.

Description:
TECHNICAL FIELD 
     This invention relates to hard disk drives with connectors between a main flex circuit on their head stack assembly and a printed circuit board on the opposite side of the disk base from the head stack assembly. 
     BACKGROUND OF THE INVENTION 
     For many years, it has been common to place a printed circuit board on the opposite side of the disk base from the disks and voice coil motor in a hard disk drive. The electrical interface between the sliders and the printed circuit board frequently includes a main flex circuit that uses a preamplifier integrated circuit that buffers the write differential signal from the printed circuit board and the read differential signal going to the printed circuit board. The main flex circuit is electrically coupled through a flex ribbon to a flex circuit interface that goes through a connector site to electrically couple to the printed circuit board. 
     As the hard disk drives grow in memory capacity, there is a need particularly for the differential signal paths to be able to operate at higher frequencies. This invention addresses this need. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention include a hard disk drive comprising a head stack assembly containing at least one slider to access a rotating disk surface and a main flex circuit communicatively coupled to the slider to communicate the access to a flex circuit interface positioned in a through connector site in the disk base, with the flex circuit interface including a flex ground plane and/or a flex power plane with at least one flex impedance patch over the connector site. The hard disk drive further comprises a printed circuit board mounted on the disk base and communicatively coupled to the flex circuit interface, with the printed circuit board comprising a printed circuit ground plane and/or power plane with at least one printed circuit impedance patch under the connector site. 
     Such embodiments may have smaller impedance discontinuities in the read differential and/or write differential signal paths through the connector site of the hard disk drive thereby supporting higher transmission frequencies for such signals. This may improve the ability of the hard disk drive to operate at higher data capacities. 
     Embodiments of the invention also include the head stack assembly electrically coupled to the flex circuit interface and the printed circuit board configured to communicatively couple with the flex circuit interface under the through connector site. Any of the ground planes and/or power planes may further include more than one flex impedance patch, which may or may not be the same shape and/or size. The impedance patches may form a two dimensional grid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a top view of an example of an embodiment of the invention as a hard disk drive including a disk base to which a spindle motor is mounted to rotate at least one disk to create a rotating disk surface. A head stack assembly is pivotably mounted to the disk base to position at least one slider to access data stored on the rotating disk surface. The head stack assembly also includes a main flex circuit communicatively coupled to the slider and through a flex ribbon to a flex circuit interface that communicates the disk access with a printed circuit board mounted on the other side of the disk base. 
         FIG. 2  shows the bottom view of the disk base and its through connector site with the flex interface mounted to provide the printed circuit interface in the through connector site. 
         FIG. 3  shows the bottom view of the flex circuit interface with the flex ribbon communicatively coupled to the printed circuit interface across the body of the connector. 
         FIG. 4A  shows the top view of the printed circuit board with the printed circuit contact region highlighted, which is where the printed circuit board connects to the printed circuit interface. 
         FIG. 4B  shows the bottom view of the printed circuit board, which does not contact the printed circuit interface. 
         FIG. 5  shows a simplified layer diagram of the flex ribbon, the flex circuit interface and the printed circuit contact region. 
         FIGS. 6A and 6B  show perspective views of the top and the bottom of the prior art flex circuit interface electrically coupled with the printed circuit board showing ground planes as essentially uniform sheets of conductive material. The power planes are also essentially uniform sheets of conductive material. 
         FIG. 7  shows a graph of the simulated impedance discontinuities found in read and/or write differential signals near the prior art flex circuit interface and its electrical coupling to the prior art printed circuit board. 
         FIG. 8  shows a perspective view of the printed circuit interface its body, the flex circuit couplings and the contacts in greater detail. 
         FIGS. 9A and 9B  show perspective views of the top and bottom of the flex circuit interface coupled to the printed circuit with their ground planes including impedance patches. 
         FIG. 10  shows a graph of the improvement in the simulated impedance discontinuities of the read and/or write differential signals near the flex circuit interface and its electrical coupling to the printed circuit board. 
         FIG. 11  shows an example of the flex circuit interface with the flex ground plane including a flex impedance patch that is elliptical. 
       And  FIG. 12  shows an example of the printed circuit board with the printed circuit power plane including a two dimensional grid  84  of printed circuit impedance patches that are rectangular with rounded corners. 
     
    
    
     DETAILED DESCRIPTION 
     This invention relates to hard disk drives with connectors between a main flex circuit on their head stack assembly and a printed circuit board on the opposite side of the disk base from the head stack assembly. Embodiments of the invention include a hard disk drive comprising a head stack assembly containing at least one slider to access a rotating disk surface and a main flex circuit communicatively coupled to the slider to communicate the access to a flex circuit interface positioned in a through connector site in the disk base, with the flex circuit interface including a flex ground plane and/or a flex power plane with at least one flex impedance patch over the connector site. The hard disk drive further comprises a printed circuit board mounted on the disk base and communicatively coupled to the flex circuit interface, with the printed circuit board comprising a printed circuit ground plane and/or power plane with at least one printed circuit impedance patch under the connector site. 
     To summarize the Figures, embodiments of the invention include a hard disk drive  10  that may comprise a disk base  2  with a through connector site  40  as shown in  FIG. 2 , and a spindle motor  14  mounted on the disk base to rotate at least one disk  8  to create at least one rotating disk surface  6  as shown in  FIG. 1 . The hard disk drive also comprises a head stack assembly  12  pivotably mounted to the disk base that contains at least one slider  16  to access the rotating disk surface and a main flex circuit  22  communicatively coupled to the slider to communicate the access to a flex circuit interface  20  positioned through the connector site, with the flex circuit interface including a flex ground plane  50  with at least one flex impedance patch  80  over the connector site as shown in  FIGS. 9A and 11 , and/or a flex power plane with at least one of the flex impedance patches. The hard disk drive may further comprise a printed circuit board  38  mounted on the disk base and communicatively coupled to the flex circuit interface, with the printed circuit board comprising a printed circuit ground plane  66  with at least one printed circuit impedance patch  82  under the connector site as shown in  FIG. 9B  and/or the printed circuit power plane  68  may include one of the printed circuit impedance patches as shown in  FIG. 12 . 
     Referring to the drawings more particularly,  FIG. 1  shows an example of an embodiment of the invention as a hard disk drive  10  including a disk base  2  to which a spindle motor  14  is mounted with at least one disk  8  rotatably coupled to the spindle motor to create a rotating disk surface  6 . A voice coil motor  36  may include a head stack assembly  12  pivotably mounted by an actuator pivot  30  to the disk base, responsive to its voice coil  32  interacting with a fixed magnetic assembly  34  mounted on the disk base and including at least one slider  16  to access data stored on the rotating disk surface. The hard disk drive includes a printed circuit board  38  also mounted on the disk base opposite the spindle motor and the voice coil motor. The slider is communicatively coupled to the main flex circuit  22  that uses a flex ribbon  18  to communicate the access of the slider to the flex circuit interface that is communicatively coupled to the printed circuit board  38 . A disk cover  4  is mounted on the disk base to encapsulate all of the shown components except the printed circuit board. 
     The hard disk drive  10  preferably accesses the data arranged in tracks on the rotating disk surface  6  by controlling the spindle motor  14  to rotate the disks  8  at a preferred rate. The data may be organized as tracks that may be configured as concentric circles or as a tightly packed spiral. The voice coil motor  36  operates by stimulating the voice coil  32  with a time varying electrical signal to magnetically interact with the fixed magnet assembly  34  causing the head stack assembly  12  to pivot about the actuator pivot  30  moving to position the slider  16  near the track on the rotating disk surface. In many embodiments, a micro-actuator assembly possibly coupled to the slider may be further stimulated to further control the position of the slider. A vertical micro-actuator either in the micro-actuator assembly, or in the slider, may be stimulated to alter the flying height of the slider over the rotating disk surface. 
       FIG. 2  shows the bottom side of the disk base  2  of  FIG. 1  with the flex circuit interface  20  showing its printed circuit interface  42  inserted into the through connector site  40  included in the disk base. 
       FIG. 3  shows a bottom view of some details of the flex circuit interface  20  including the printed circuit interface  42  on the body  58 , communicatively coupled to the flex ribbon  18 . 
       FIGS. 4A and 4B  show two sides of the printed circuit board  38  with a printed circuit contact region  46 .  FIG. 4A  shows the top side which makes contact with the printed circuit interface  42  and  FIG. 4B  shows the bottom side facing away from the disk base  2  and the printed circuit interface. 
       FIG. 5  shows a simplified layer diagram of the flex ribbon  18  coupled to the flex circuit interface  20  that is communicatively coupled to the printed circuit board  38  in the printed circuit contact region  46 . The flex ribbon may include a flex ribbon signal layer  70  and two flex dielectric layers  52 . The flex ribbon may include a flex ground trace  53  and a flex power trace  55  as part of the flex signal layer  54 . The flex circuit interface may include the following layers separated by flex dielectric layers: a flex ground layer  50  over a flex signal layer  54  that is electrically coupled to the flex circuit couplings  56  of the printed circuit interface. Preferably, the flex ground trace  53  may be electrically coupled to the flex ground plane. Also, the flex power trace  55  may be electrically coupled to the flex power plane  57 , which has not been shown. One or more of the flex dielectric layers of the flex ribbon may be coupled to one of the flex dielectric layers of the flex circuit interface as shown. The printed circuit interface  42  may include the flex circuit couplings on top supported by a body  58  and electrically coupled with contacts  60  on the bottom, that electrically couple to a signal layer  62  in the printed circuit contact region as shown in  FIG. 4A . The printed circuit contact region may further include the signal layer over a dielectric layer  64  that is over a printed circuit power plane  68  separated by another dielectric layer from a printed circuit ground plane  66  frequently with a second signal layer. In certain embodiments, there may be a rigid substrate that may be formed as one of the dielectric layers. 
     Frequently the flex dielectric layers  52  and/or the printed circuit dielectric layers  64  may be formed of a polyimide compound. The flex signal layers  54  and/or the printed circuit signal layers  62  may be made of a conductive metal such as copper. The flex ground plane  50  and/or the printed circuit ground plan  66  may also be made of a conductive metal such as copper. These layers may be successively deposited and etched to form the circuits shown in these Figures. In the electrical coupling of the contacts  60  and the signal layer  62  it may be preferred that a layer of nickel followed by a layer of gold may be deposited to create the electrical coupling between the flex circuit coupling and the printed circuit board  38  signals. 
       FIG. 6A  shows a prior art flex ground plane  50  over the printed circuit interface as essentially a uniform sheet of conductive material such as copper. Also  FIG. 6B  shows the printed circuit ground plane  66  under the printed circuit interface as another essentially uniform sheet of conductive material. The printed circuit power plane  68  may be an essentially uniform sheet of conductive material. 
       FIG. 7  shows the problem encountered by the inventor regarding such configurations in this graph of a simulated time domain reflectometer, that the differential signals for the read and write differential signals experience impedance discontinuities passing through the flex circuit interface  20  to the printed circuit board  38  as shown. 
     These fluctuations may be the result of the signal path between a preamplifier residing in the main flex circuit  22  and a channel interface circuit of the printed circuit board  38  forming a parasitic capacitance between the flex ground plane  50 , the flex signal layer  54 , the flex circuit couplings  56 , the contacts  60 , the signal layer  62  and the printed circuit ground layer  66 . This parasitic capacitance in turn may incorporate a parasitic inductance produced by the trace conductors and these components. This example shows one inductive peak and two capacitive dips. The parasitic capacitance and parasitic inductance may cause a resonance near the data transmission frequency, which if it occurs may degrade reading data at higher frequencies. 
       FIG. 8  shows a perspective view of an example of the printed circuit interface  42  including the flex circuit coupling  56  electrically coupling across the body  58  to the contacts  60 . 
       FIG. 9A  shows an example of the flex circuit interface  20  including at least one, and in this example, two flex impedance patches  80  in the flex ground plane  50  over the printed circuit interface. 
       FIG. 9B  shows an example of the printed circuit ground plane  66  including at least one, and in this example, two printed circuit impedance patches  82  under the flex circuit interface. 
     The impedance patches  80  and  82  may be formed by punching and/or etching holes in the ground planes  50  and  66  near the contacts for the read and/or write differential signals. These impedance patches act to reduce the surface area of the ground planes near the contacts for these signals, which tends to reduce the parasitic capacitance and possibly also reduce the parasitic inductance as well. 
     Such embodiments of the hard disk drive  10  may have smaller impedance discontinuities in the read differential and/or write differential signal paths through the connector site  40  of the hard disk drive thereby supporting higher transmission frequencies for such signals. This may improve the ability of the hard disk drive to operate at higher data capacities. This aspect of the invention is shown through the comparison of the graph of  FIG. 7  to the graph of  FIG. 10 . 
       FIG. 10  shows the simulated time domain reflectometer for the configuration using the impedance patches  80  and  82  of  FIGS. 9A and 9B , showing a significant reduction in impedance discontinuities over the prior art simulation shown in  FIG. 7 . 
       FIGS. 11 and 12  show some examples of alternative embodiments of the invention.  FIG. 11  shows a perspective view of the top of the flex circuit interface  20  with the flex ground plane  50  including a flex impedance patch  80  in an elliptical shape. And  FIG. 12  as shows a perspective view of the bottom of the flex circuit interface  20  with the printed circuit power plane  68  including a two dimensional grid of the printed circuit impedance patches  82  as rectangles with rounded corners. 
     Other embodiments of the invention may include the flex power plane instead of the flex ground plane  50  including flex impedance patches  80  that may or may not align one on top of the other and/or may or may not have the same shape. Similarly, the printed circuit ground plane  66  and the printed circuit power plane  68  may both include printed circuit impedance patches  82  that may or may not align one on to of the other and/or may or may not have the same shape. 
     The preceding embodiments provide examples of the invention, and are not meant to constrain the scope of the following claims.