Patent Publication Number: US-2018040352-A1

Title: Disk device with housing accommodating rotatable disk

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/371,302, filed Aug. 5, 2016, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a disk device. 
     BACKGROUND 
     As a disk device, a magnetic disk drive includes a housing having a base and a top cover, and a rotatable magnetic disk and an actuator supporting thereon magnetic heads are arranged in the housing. As a method of improving the performance of the disk drive, a method of reducing the rotational resistance of the magnetic disk and the magnetic head by filling the housing with a low-density gas such as helium or the like, and closely sealing the housing is proposed. 
     In such a magnetic disk drive, the top cover is laser-welded onto the base of the housing thereby forming a hermetically-sealed housing and increasing the airtightness of the housing. This laser welding is carried out along the entire outer circumference of the top cover. Further, in order to transmit an electrical signal of the magnetic head provided inside the housing to a control circuit board provided outside the device, a connector penetrating the bottom wall of the housing is provided. In such a gas-filled magnetic disk drive described above, it is desirable that a hermetic connector be used as the aforementioned connector in order to maintain the airtightness of the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an external view of a hard disk drive (HDD) according to a first embodiment. 
         FIG. 2  is an exploded perspective view of the HDD according to the first embodiment. 
         FIG. 3  is a perspective view showing a base of a housing of the HDD. 
         FIG. 4  is a perspective view showing the back surface side of the base. 
         FIG. 5  is an exploded perspective view showing a connector installation part and a connector unit of the base. 
         FIG. 6  is a cross-sectional view of the connector installation part and the connector unit taken along line VI-VI of  FIG. 4 . 
         FIG. 7  is an exploded perspective view showing a connector installation part and a connector unit of a base of an HDD according to a second embodiment. 
         FIG. 8  is a perspective view showing the first principal surface side of a connector unit. 
         FIG. 9  is a cross-sectional view of the connector installation part and the connector unit of the base of the HDD according to the second embodiment. 
         FIG. 10  is a cross-sectional view showing a connector installation part and a connector unit of an HDD according to a first modification example. 
         FIG. 11  is a cross-sectional view of a connector installation part and a connector unit of a base of an HDD according to a third embodiment. 
         FIG. 12  is a perspective view showing a sealing board of the connector unit. 
         FIG. 13  is a perspective view showing a sealing board of an HDD according to a second modification example. 
         FIG. 14  is a perspective view showing a connector installation part of an HDD according to a third modification example. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment, a disk device comprises a rotatable disk recording medium; a head which processes data on the recording medium; a housing comprising a base accommodating the recording medium and the head and a cover joined to the base, the base comprising a through-hole and an installation surface formed around the through-hole; and a sealing board fixed to the installation surface of the base to block the through-hole, the sealing board comprising a first principal surface, a second principal surface on an opposite side to the first principal surface, and a conduction path electrically connecting the first principal surface and the second principal surface to each other. One of the first principal surface of the sealing board and the installation surface includes a projection formed therein, and the sealing board is fixed to the installation surface by an adhesive material including at least a brazing material, provided on an outer side of the projection, between the first principal surface and the installation surface, with the other of the first principal surface and the installation surface abutting against the projection. 
     Hereinafter, hard disk drives (HDDs) according to embodiments will be descried in detail as disk devices. 
     First Embodiment 
       FIG. 1  is a perspective view showing an external view of an HDD according to a first embodiment, and  FIG. 2  is an exploded perspective view showing an internal structure of the HDD. 
     As shown in  FIG. 1  and  FIG. 2 , the HDD includes a flat and substantially rectangular housing  10 . 
     This housing  10  comprises a rectangular box-shaped base  12  opened at a top surface thereof, inner cover  14  screwed onto the base  12  by a plurality of screws  13  to thereby close the upper-end opening of the base  12 , and outer cover (top cover)  16  placed on top of the inner cover  14 , and a peripheral part of which is welded onto the base  12 . The base  12  includes a rectangular bottom wall  12   a  opposed to the inner cover  14  with a gap held between them, and side wall  12   b  provided to stand along the periphery of the bottom wall  12   a , and is integrally formed of, for example, aluminum. The side wall  12   b  includes a pair of long-side walls opposed to each other and a pair of short-side walls opposed to each other. A substantially rectangular frame-shaped fixing rib  12   c  is provided on the upper end surface of the side wall  12   b  in a projecting manner. 
     The inner cover  14  is formed of stainless steel into a rectangular plate. The inner cover  14  is screwed onto the top surface of the side wall  12   b  at a peripheral part thereof by means of screws  13  to thereby be fixed to the inside of the fixed rib  12   c . The outer cover  16  is formed of, for example, aluminum into a rectangular plate-like shape. The outer cover  16  is formed in a planar size slightly greater than the inner cover  14 . The outer cover  16  is welded onto the fixed rib  12   c  of the base  12  at the entire peripheral part thereof and is hermetically fixed. In each of the inner cover  14  and the outer cover  16 , vents  46  and  48  through which the inside of the housing  10  communicates with the outside are formed, respectively. The air inside the housing  10  is exhausted through the vents  46  and  48  and, furthermore a low-density gas (inert gas), for example, helium having a density lower than that of air is infused through these vents  46  and  48 . For example, a sealant (an adhesive material including at least a brazing material)  52  is stuck on the outer surface of the outer cover  16  so as to close the vent  48 . 
     As shown in  FIG. 2 , a plurality of magnetic disks  18  serving as recording mediums, and a spindle motor  20  serving as a drive section configured to support and rotate the magnetic disks  18  are provided in the housing  10 . The spindle motor  20  is arranged on the bottom wall  12   a . Each of the magnetic disks  18  is formed into a size of, for example, 88.9 mm (3.5 inches) in diameter, and includes a magnetic recording layer in the top surface and/or in the undersurface thereof. Each of the magnetic disks  18  is fitted on a hub (not shown) of the spindle motor  20  coaxially with each other, and is clamped by a clamp spring to thereby be fixed to the hub. Each of the magnetic disks  18  is supported in a state where the disk  18  is positioned parallel to the bottom wall  12   a  of the base  12 . Each of the magnetic disks  18  is rotated by the spindle motor  20  at a predetermined rotational speed. 
     It should be noted that as shown in  FIG. 2 , although, for example, five magnetic disks  18  are accommodated in the housing  10  in this embodiment, the number of the magnetic disks  18  is not limited to this. Further, a single magnetic disk  18  may be accommodated in the housing  10 . 
     In the housing  10 , a plurality of magnetic heads  32  configured to carry out recording/reproduction of information on/from the magnetic disks  18 , and a head stack assembly (actuator)  22  configured to support these magnetic heads  32  to freely move the magnetic heads  32  with respect to the magnetic disks  18  are provided. Further, in the housing  10 , a voice coil motor (hereinafter referred to as a VCM)  24  configured to rotate and position the head stack assembly  22 , ramp loading mechanism  25  configured to retain the magnetic head  32  at an unloading position separate from the magnetic disk  18  when the magnetic head  32  has moved to the outermost circumference of the magnetic disk  18 , and board unit  21  on which electronic components such as a conversion connector (third connector)  52 , and the like are mounted are provided. The board unit  21  is constituted of a flexible printed circuit (FPC), and this FPC is electrically connected to the magnetic heads  32  and the voice coil of the VCM  24  through a relay FPC on the head stack assembly  22 . 
     The head stack assembly  22  includes a rotatable bearing unit  28 , a plurality of arms  30  extending from the bearing unit  28 , and suspensions  34  extending from the arms  30 , and the magnetic head  32  is supported on a distal end part of each suspension  34 . 
     A control circuit board  54  to be described later is screwed onto an outer surface of the bottom wall  12   a  of the base  12 . The control circuit board  54  controls the operation of the spindle motor  20 , and controls the operations of the VCM  24  and the magnetic heads  32  through the board unit  21 . 
       FIG. 3  is a perspective view showing the base  12  of the housing  10 , in a state where the constituent elements are removed therefrom,  FIG. 4  is a perspective view showing the back surface side of the housing and the control circuit board,  FIG. 5  is an exploded perspective view showing a connector installation part and a connector unit of the base, and  FIG. 6  is a cross-sectional view of the connector installation part and the connector unit taken along line VI-VI of  FIG. 4 . 
     As shown in  FIG. 3  and  FIG. 4 , in the bottom wall  12   a  of the base  12 , for example, a rectangular through-hole (open hole)  58  is formed at an end part of the base  12  near one short side. The through-hole  58  is opened to the inner surface and the outer surface (rear surface) of the bottom wall  12   a . Further, a first connector  62   a  of the connector unit  60  is attached to or inserted in the through-hole  58 . 
     As shown in  FIG. 5  and  FIG. 6 , in the rear surface (outer surface) of the bottom wall  12   a , a substantially rectangular installation recess  70  is formed in the area including the through-hole  58 . The bottom face of the recess  70  constitutes an installation surface  72  positioned around the through-hole  58 . An annular, for example, a rectangular frame-shaped rib (projection)  74  surrounding the periphery of the through-hole  58  is provided on the installation surface  72  in a projecting manner. The inner circumferential surface of the rib  74  is flush with the inner circumferential surface of the through-hole  58 . The rib  74  has a constant projection height (for example, 0.5 mm) and a constant width (for example, 1 mm) throughout the entire circumference thereof and, furthermore, the end face (contact surface)  74   a  of the rib  74  is formed flat. 
     A positioning pin  76  is provided at each of two corners opposed to each other in a diagonal direction of the installation surface  72  in a standing manner. The projection height of the positioning pin  76  is made substantially identical to the depth of the installation recess  70 . It should be noted that the rib  74  and the two positioning pins  76  are formed integral with the bottom wall  12   a  of the base  12 . 
     In this embodiment, a stepped portion  78  one step higher than the installation surface  72  is formed at each of the two corners opposed to each other in the diagonal direction of the installation surface  72 , and the positioning pins  76  are provided at the stepped portions  78  in a standing manner. The height (step height) of the stepped portion  78  is made lower than the height of the rib  74 . A plated layer, for example, a nickel-plated layer  80  is formed on the installation surface  72  except the end face  74   a  of the rib  74 . 
     As shown in  FIG. 5  and  FIG. 6 , the connector unit  60  includes a sealing board  64 , and a first connector  62   a  and a second connector  62   b  mounted on this sealing board. The sealing board  64  is formed into a substantially rectangular shape corresponding to the installation recess  70  of the base  12 , and is formed in a planar size slightly smaller than the installation recess  70 . The sealing board  64  is constituted of, for example, a multi-layered circuit board formed by laminating a number of printed circuit boards. The sealing board  64  has a flat first principal surface  64   a  and a flat second principal surface  64   b  on the opposite side of the first principal surface  64   a.    
     The first connector  62   a  is mounted on a substantially central part of the first principal surface  64   a . The second connector  62   b  is mounted on a substantially central part of the second principal surface  64   b , and is opposed to the first connector  62   a . The first connector  62   a  and the second connector  62   b  are electrically connected to each other through conductive paths each of which is formed of a conductive layer or a through-hole formed in the sealing board  64 . 
     A positioning hole  66  is formed at each of two corners opposed to each other in a diagonal direction of the sealing board  64 . These positioning holes  66  are provided at positions corresponding to the positioning pins  76  of the base  12 , and each of the positioning holes  66  is formed so that the positioning pin  76  can be inserted therein. 
     As shown in  FIG. 4  through  FIG. 6 , the connector unit  60  is installed in the installation recess  70  formed in the bottom wall  12   a  of the base  12 . That is, the sealing board  64  is installed in the installation recess  70  in a state where the first principal surface  64   a  and the first connector  62   a  are directed to the bottom wall  12   a  side. Each of the pair of positioning pins  76  is inserted in the corresponding positioning hole  66  of the sealing board  64 . Thereby, the sealing board  64  is positioned in terms of the position in the plane direction with respect to the bottom wall  12   a . The first principal surface  64   a  of the sealing board  64  is in contact with the end face  74   a  of the rib  74 . Thereby, the sealing board  64  is positioned by the rib  74  in terms of the position in the thickness direction thereof. The first connector  62   a  is inserted in the through-hole  58  of the bottom wall  12   a . The first connector  62   a  is exposed to the inside of the base  12  through the through-hole  58 , and is accessible from the inside of the base  12 . 
     At a part around the outside of the rib  74 , a sealant (brazing material)  82  is provided between the installation surface  72  of the installation recess  70  and the first principal surface  64   a  of the sealing board  64 . The sealing board  64  is fixed to the installation surface  72  by means of the sealant  82 . In this embodiment, as the sealant  82 , for example, solder is used. In the fixing and sealing process, as shown in  FIG. 5 , for example, a solder sheet  82   a  formed into an annular shape is arranged on the installation surface  72  around the outside of the rib  74 . The sealing board  64  is implemented in the installation recess  70 , the first principal surface  64   a  is made in contact with the end face  74   a  of the rib  74 , and the first principal surface  64   a  is arranged on the solder sheet  82   a . In this state, the solder sheet  82   a  is heated from the inner surface side or from the outer surface side of the base  12 , thereby melting the solder sheet  82   a . The molten solder wettedly spreads along the first principal surface  64   a  of the sealing board  64  and the installation surface  72  to thereby stick to the first principal surface  64   a  and the installation surface  72 . At this time, the molten solder is prevented from flowing into the through-hole  58  by the rib  74 . Furthermore, the nickel-plated layer  80  is formed on the installation surface  72  except the end face  74   a  of the rib  74 , and hence the wettability of the molten solder on the installation surface  72  is improved. At the same time, the molten solder is prevented from flowing into the gap between the end face  74   a  of the rib  74  and the first principal surface  64   a  of the sealing board  64 . Further, in this embodiment, the molten solder is restrained from excessively flowing to the outside by the stepped portion  78  provided on the proximal end side of each positioning pin  76 . Thereby, most of the solder remains at the part between the rib  74  and the stepped portions  78 , and sufficiently fills the space between the installation surface  72  and the first principal surface  64   a  therewith. 
     As shown in  FIG. 6 , the sealing board  64  is fixed to the installation surface  72  of the base  12  by the sealant  82 , and covers the through-hole  58  of the base  12 . At the same time, the space between the first principal surface  64   a  of the sealing board  64  and the installation surface  72  is hermetically sealed with the sealant  82 . Thereby, the connector unit  60  hermetically seals the through-hole  58  on the rear surface side of the base  12 . The first connector  62   a  of the connector unit  60  is inserted in the through-hole  58 , and is exposed to the inside of the base  12  through the through-hole  58 . That is, the first connector  62   a  is provided so that another connector can be connected to the first connector  62   a  from inside the base  12 . A third connector  52  of the board unit  21  provided inside the base  12  is connected to the first connector  62   a  of the connector unit  60 . 
     The second connector  62   b  of the connector unit  60  is exposed to the outer surface (rear surface) side of the base  12 . As shown in  FIG. 4  and  FIG. 6 , the control circuit board  54  is arranged to be opposed to the rear surface of the bottom wall  12   a  of the base  12 , and is screwed onto the bottom wall  12   a  by means of a plurality of screws. The control circuit board  54  is provided to cover the connector unit  60 . A fourth connector  56  is mounted on the control circuit board  54 . This fourth connector  56  is connected to the second connector  62   b  of the connector unit  60 . As described above, the magnetic heads  32  and the voice coil of the VCM provided inside the base  12  are electrically connected to the control circuit board  54  provided outside the base  12  through the relay FPC, board unit  21 , third connector  52 , connector unit  60 , and fourth connector  56  in a state where the airtightness inside the housing  10  is maintained by the connector unit  60 . 
     According to the HDD associated with the first embodiment configured as described above, in the fixation structure of the connector unit  60 , the annular rib (projection)  74  is provided on the installation surface  72  around the through-hole  58 , and the sealing board  64  is arranged in a state where the first principal surface  64   a  of the sealing board  64  is made in contact with the end face  74   a  of the rib  74 , whereby it is possible to position the sealing board  64  in terms of the height position, i.e., the position in the thickness direction of the sealing board  64  with respect to the installation surface  72 . Thereby, it is possible to maintain the gap between the first principal surface  64   a  of the sealing board  64  and the installation surface  72  constant, and manage the thickness of the sealant  82  to be filled into this gap constant. Further, it is possible by the rib  74  to prevent the sealant  82  from flowing into the through-hole  58 , and retain the sealant  82  in the desired space. Furthermore, according to this embodiment, the stepped portions  78  are provided on the installation surface  72  on the outside of the rib  74 . By virtue of these stepped portions  78 , it is possible to suppress the flow of the sealant  82 , and retain the sealant  82  in the desired space. Therefore, according to this embodiment, it becomes possible to reduce unnecessary spread and wetting of the sealant, and securely seal the desired space with a minimum amount of the sealant. 
     Further, according to this embodiment, by inserting the positioning pins provided on the installation surface  72  of the base  12  in a standing manner in the positioning holes  66  of the sealing board  64 , the sealing board  64  is positioned in terms of the position in the plane direction with respect to the base  12 . Accordingly, the in-plane positional accuracy of the first connector  62   a  and the second connector  62   b  is improved. Further, the influence of misalignment between the first connector  62   a  and the second connector  62   b  is made less significant irrespectively of the size of the first and second connectors  62   a  and  62   b . Thereby, the third connector  52  inside the housing  10  and the fourth connector  56  outside the housing  10  can easily and stably be connected to the first connector  62   a  and the second connector  62   b , respectively. 
     From the above description, according to the first embodiment, it is possible to obtain a disk device which is improved in the airtightness of the housing, and can easily be connected to the connector or the control circuit board outside the housing. 
     Next, an HDD according to another embodiment will be described. It should be noted that in another embodiment to be described in the following, parts identical to the aforementioned first embodiment are denoted by reference symbols identical to the first embodiment, their detailed descriptions are simplified or omitted, and parts different from the first embodiment are mainly described in detail. 
     Second Embodiment 
       FIG. 7  is an exploded perspective view showing a connector installation part and a connector unit of a base of an HDD according to a second embodiment.  FIG. 8  is a perspective view showing the first principal surface side of a connector unit.  FIG. 9  is a cross-sectional view of the connector installation part and the connector unit. 
     As shown in  FIG. 7  and  FIG. 8 , according to the second embodiment, an installation surface  72  of an installation recess  70  is formed flat, and an annular rib  74  serving as a projection is provided on a first principal surface  64   a  of a sealing board  64 . A positioning pin  76  is provided at each of two corners opposed to each other in a diagonal direction of the installation surface  72  in a standing manner. The projection height of the positioning pin  76  is made substantially identical to the depth of the installation recess  70 . The two positioning pins  76  are formed integral with a bottom wall  12   a  of the base  12 . 
     The connector unit  60  includes the sealing board  64 , and a first connector  62   a  and second connector  62   b  mounted on this sealing board. The sealing board  64  is formed into a substantially rectangular shape corresponding to the installation recess  70  of the base  12 , and is formed in a planar size slightly smaller than the installation recess  70 . The sealing board  64  is formed of, for example, glass or ceramic. The sealing board  64  has a flat first principal surface  64   a  and a flat second principal surface  64   b  on the opposite side of the first principal surface  64   a . The first connector  62   a  is mounted on a substantially central part of the first principal surface  64   a . The second connector  62   b  is mounted on a substantially central part of the second principal surface  64   b , and is opposed to the first connector  62   a . The first connector  62   a  and the second connector  62   b  are electrically connected to each other through a plurality of conductive pins (conductive paths)  65  embedded in the sealing board  64 . 
     An annular, for example, a rectangular frame-shaped rib (projection)  74  surrounding the periphery of the first connector  62   a  is provided on the first principal surface  64   a  of the sealing board  64  in a projecting manner. The rib  74  has a constant projection height (for example, 0.1 mm) and a constant width (for example, 0.5 mm) throughout the entire circumference thereof and, furthermore, the end face (contact surface)  74   a  of the rib  74  is formed flat. The rib  74  is formed of glass or ceramic and is formed integral with the sealing board  64 . A positioning hole  66  is formed at each of two corners opposed to each other in a diagonal direction of the sealing board  64 . These positioning holes  66  are provided at positions corresponding to the positioning pins  76  of the base  12 , and each of the positioning holes  66  is formed so that the positioning pin  76  can be inserted therein. 
     As shown in  FIG. 9 , the connector unit  60  is implemented in the installation recess  70  formed in the bottom wall  12   a  of the base  12 . The sealing board  64  is arranged in the installation recess  70  in a state where the first principal surface  64   a  and the first connector  62   a  are directed to the bottom wall  12   a  side. Each of the pair of positioning pins  76  is inserted in the corresponding positioning hole  66  of the sealing board  64 . Thereby, the sealing board  64  is positioned in terms of the position in the plane direction with respect to the bottom wall  12   a . Further, the sealing board  64  is installed in the installation recess  70  in a state where the end face  74   a  of the rib  74  is in contact with the installation surface  72  of the installation recess  70 . Thereby, the sealing board  64  is positioned by the rib  74  in terms of the position in the thickness direction thereof, and the first principal surface  64   a  is opposed to the installation surface  72  with a gap corresponding to the height of the rib  74  held between them. The first connector  62   a  is inserted in the through-hole  58  of the bottom wall  12   a . Thereby, the first connector  62  is exposed to the inside of the base  12 , and is accessible from the inside of the base  12 . 
     The space between the installation surface  72  of the installation recess  70  and the first principal surface  64   a  of the sealing board  64  is filled with a sealant  82  around the outside of the rib  74 . According to this embodiment, as the sealant  82 , a resin adhesive or gluing agent may be used. The sealant  82  is filled into the space between the first principal surface  64   a  of the sealing board  64  and the installation surface  72  in a state where the rib  74  of the sealing board  64  is pressed against the installation surface  72 , i.e., in a state where the rib  74  of the sealing board  64  is made in contact with the installation surface  72 . The sealing board  64  is fixed to the installation surface  72  by means of the sealant  82 . At the same time, the space between the first principal surface  64   a  and the installation surface  72 , and the part around the through-hole  58  are sealed with the sealant  82 . 
     As described above, the sealing board  64  of the connector unit  60  is fixed to the installation surface  72  of the base  12  by means of the sealant  82 , and covers the through-hole  58  of the base  12 . At the same time, the space between the first principal surface  64   a  of the sealing board  64  and the installation surface  72  is hermetically sealed with the sealant  82 . Thereby, the connector unit  60  hermetically seals the through-hole  58  on the back surface side of the base  12 . The first connector  62   a  of the connector unit  60  is inserted in the through-hole  58 , and is exposed to the inside of the base  12  through this through-hole  58 . A third connector  52  of a board unit  21  provided inside the base  12  is connected to the first connector  62   a  of the connector unit  60 . The second connector of the connector unit  60  is exposed to the outer surface (back surface) side of the base  12 . A fourth connector  56  mounted on a control circuit board  54  is connected to the second connector  62   b  of the connector unit  60 . 
     According to the HDD associated with the second embodiment configured as described above, in the fixation structure of the connector unit  60 , the annular rib (projection)  74  is provided on the first principal surface  64   a  of the sealing board  64  around the first connector  62   a , and the sealing board  64  is arranged in a state where the end face  74   a  of the rib  74  is made in contact with the installation surface  72  of the base  12 , whereby it is possible to position the sealing board  64  in terms of the height position, i.e., the position in the thickness direction of the sealing board  64  with respect to the installation surface  72 . Thereby, it is possible to maintain the gap between the first principal surface  64   a  of the sealing board  64  and the installation surface  72  constant, and manage the thickness of the sealant  82  to be filled into this gap constant. Further, it is possible by the rib  74  to prevent the sealant  82  from flowing into the inside of the through-hole  58 , and retain the sealant  82  in the desired space. Furthermore, according to this embodiment, the stepped portions  78  are provided on the installation surface  72  on the outside of the rib  74 . By virtue of these stepped portions  78 , it is possible to suppress the flow of the sealant  82 , and retain the sealant  82  in the desired space. Therefore, according to this embodiment, it becomes possible to reduce unnecessary spread and wetting of the sealant, and securely seal the desired space with a minimum amount of the sealant. 
     Further, according to this embodiment, by inserting the positioning pins provided on the installation surface  72  of the base  12  in a standing manner in the positioning holes  66  of the sealing board  64 , the sealing board  64  is positioned in terms of the position in the plane direction with respect to the base  12 . Accordingly, the in-plane positional accuracy of the first connector  62   a  and the second connector  62   b  is improved. Further, the influence of misalignment between the first connector  62   a  and the second connector  62   b  is made less significant irrespectively of the size of the first and second connectors  62   a  and  62   b . Thereby, it becomes possible to easily and stably connect the third connector  52  inside the housing  10  and the fourth connector  56  outside the housing to the first connector  62   a  and the second connector  62   b , respectively. 
     From the above description, according to the second embodiment too, it is possible to obtain a disk device which is improved in the airtightness of the housing, and can easily be connected to the connector or the control circuit board outside the housing. 
     It should be noted that in the second embodiment, the material of the sealing board  64  of the connector unit  60  is not limited to glass or ceramic, and a multi-layered circuit board similar to the first embodiment may be used. In this case, the rib (projection)  74  of the sealing board  64  can be formed of, for example, a resist layer formed on the surface of the circuit board. As the sealant  82 , brazing material may be used. 
     Further, the configuration of the rib  74  of the sealing board  64  is not limited to the configuration in which the rib  74  is provided at a position in line with the inner circumferential surface of the through-hole  58  of the base  12 , and the rib  74  may be provided at a position separate from the through-hole  58 . 
       FIG. 10  is a cross-sectional view showing a connector installation part and a connector unit of an HDD according to a first modification example. As shown in this view, according to the first modification example, an annular rib  74  of a sealing board  64  is provided at a position outwardly separate from an inner circumferential surface of a through-hole  58  of a base  12 . Outside and inside the rib  74 , a sealant  82  is filled into the space between a first principal surface  64   a  of the sealing board  64  and an installation surface  72 . When an adhesive or a gluing agent having no electrical conductivity is used as the sealant  82 , even if the sealant flows into the through-hole  58  of the base, no problem of electrical continuity is caused. Accordingly, at the part between the rib  74  and the through-hole  58 , the sealant  82  can be filled into the space between the first principal surface  64   a  of the sealing board  64  and the installation surface  72 . 
     Third Embodiment 
       FIG. 11  is a cross-sectional view of a connector installation part and a connector unit of a base of an HDD according to a third embodiment, and  FIG. 12  is a perspective view showing a sealing board of the connector unit. 
     As shown in  FIG. 11  and  FIG. 12 , according to the third embodiment, the connector unit  60  includes only the sealing board  64 , and first and second connectors are omitted. The sealing board  64  hermetically seals a through-hole  58  of the base  12 , and functions also as a conductive member configured to electrically connect a conversion connector (third connector)  52  inside the base  12  and a fourth connector  56  on a printed circuit board  54  provided outside the housing to each other. Thereby, the so-called one piece connection structure configured to directly connect the conversion connector (third connector)  52  and the fourth connector  56  to each other can be obtained. 
     The structure of the instrumentation part in a bottom wall  12   a  of the base  12  is identical to the aforementioned first embodiment. That is, in the rear surface (outer surface) of the bottom wall  12   a , a substantially rectangular installation recess  70  is formed in the area including a through-hole  58 . The bottom face of the installation recess  70  constitutes an installation surface  72  positioned around the through-hole  58 . An annular, for example, a rectangular frame-shaped rib (projection)  74  surrounding the periphery of the through-hole  58  is provided on the installation surface  72  in a projecting manner. The inner circumferential surface of the rib  74  is arranged flush with the inner circumferential surface of the through-hole  58 . A positioning pin  76  is provided at each of two corners opposed to each other in a diagonal direction of the installation surface  72  in a standing manner. The projection height of the positioning pin  76  is made substantially identical to the depth of the installation recess  70 . It should be noted that the rib  74  and the two positioning pins  76  are formed integral with the bottom wall  12   a  of the base  12 . A plated layer, for example, a nickel-plated layer  80  is formed on the installation surface  72  except the end face  74   a  of the rib  74 . 
     As shown in  FIG. 11  and  FIG. 12 , the connector unit  60  includes a sealing board  64 . The sealing board  64  is formed into a substantially rectangular shape corresponding to the installation recess  70  of the base  12 , and is formed in a planar size slightly smaller than the installation recess  70 . The sealing board  64  is constituted of, for example, a multi-layered circuit board formed by laminating a number of printed circuit boards. The sealing board  64  has a flat first principal surface  64   a  and a flat second principal surface  64   b  on the opposite side of the first principal surface  64   a.    
     A plurality of conductive pads  86   a  are provided at a substantially central part of the first principal surface  64   a . These conductive pads  86   a  are provided to be arranged in two rows along the longitudinal direction of the first principal surface  64   a . On the first principal surface  64   a , an annular or a track-shaped plated layer, for example, a gold-plated layer  88  is formed around the conductive pads  86   a.    
     A plurality of conductive pads  86   b  are provided at a substantially central part of the second principal surface  64   b  of the sealing board  64 . These conductive pads  86   b  are provided to be arranged in two rows along the longitudinal direction of the second principal surface  64   b . Each of the conductive pads  86   b  and a corresponding conductive pad  86   a  on the first principal surface  64   a  side are electrically connected to each other through a conductive path constituted of a conductive layer, through-hole or the like formed in the sealing board  64 . 
     A positioning hole  66  is formed at each of two corners opposed to each other in a diagonal direction of the sealing board  64 . These positioning holes  66  are provided at positions corresponding to the positioning pins  76  of the base  12 , and each of the positioning holes  66  is formed so that the positioning pin  76  can be inserted therein. 
     As shown in  FIG. 11 , the sealing board  64  is installed in the installation recess  70  formed in the bottom wall  12   a  of the base  12 , and seals the through-hole  58 . That is, the sealing board  64  is implemented in the installation recess  70  in a state where the first principal surface  64   a  is directed to the bottom wall  12   a  side. Each of the pair of positioning pins  76  is inserted in the corresponding positioning hole  66  of the sealing board  64 . Thereby, the sealing board  64  is positioned in terms of the position in the plane direction with respect to the bottom wall  12   a . Further, the first principal surface  64   a  of the sealing board  64  is in contact with the end face  74   a  of the rib  74 . Thereby, the sealing board  64  is positioned by the rib  74  in terms of the position in the thickness direction thereof. 
     Around the outside of the rib  74 , a sealant  82  is filled into the space between the installation surface  72  of the installation recess  70  and the first principal surface  64   a  of the sealing board  64 . The sealing board  64  is fixed to the installation surface  72  by the sealant  82 . In this embodiment, as the sealant  82 , for example, solder is used. In the fixing and sealing process, for example, a solder sheet formed into an annular shape is arranged on the installation surface  72  around the outside of the rib  74 . The sealing board  64  is arranged in the installation recess  70 , the first principal surface  64   a  is made in contact with the end face  74   a  of the rib  74 , and the first principal surface  64   a  is arranged on top of the solder sheet. In this state, the solder sheet is heated from the inner surface side or from the outer surface side of the base  12 , thereby melting the solder sheet. The molten solder spreads along the first principal surface  64   a  of the sealing board  64  and the installation surface  72  in a wetting manner to thereby stick to the first principal surface  64   a  and the installation surface  72 . At this time, the solder is prevented from flowing into the inside of the through-hole  58  by the rib  74 . Moreover, the nickel-plated layer  80  is formed on the installation surface  72  except the end face  74   a  of the rib  74 , furthermore, the gold-plated layer  88  is formed on the first principal surface  64   a  of the sealing board  64 , and hence the wettability of the molten solder on the installation surface  72  and on the first principal surface  64   a  is improved. At the same time, the molten solder is prevented from flowing into the gap between the end face  74   a  of the rib  74  and the first principal surface  64   a  of the sealing board  64 . Further, in this embodiment, the molten solder is restrained from excessively flowing to the outside by the stepped portion  78  provided on the proximal end side of each positioning pin  76 . Thereby, most of the solder remains at the part between the rib  74  and the stepped portions  78 , and sufficiently fills the space between the installation surface  72  and the first principal surface  64   a  therewith. The sealing board  64  is fixed to the installation surface  72  of the base  12  by the sealant  82 , and covers the through-hole  58  of the base  12 . At the same time, the space between the first principal surface  64   a  of the sealing board  64  and the installation surface  72  is hermetically sealed with the sealant  82 . Thereby, the sealing board  64  of the connector unit  60  hermetically seals the through-hole  58  on the back surface side of the base  12 . The conductive pads  86   a  of the sealing board  64  are exposed to the inside of the base  12  through the through-hole  58 . The third connector  52  of a board unit  21  provided inside the base  12  is connected to the conductive pads  86   a.    
     The conductive pads  86   b  on the second principal surface  64   b  side of the sealing board  64  are exposed to the outer surface (rear surface) side of the base  12 . 
     The control circuit board  54  is arranged to be opposed to the back surface of the bottom wall  12   a  of the base  12 . A fourth connector  56  is mounted on the control circuit board  54 . This fourth connector  56  is connected to the conductive pads  86   b  of the sealing board  64 . Thereby, the fourth connector  56  is electrically connected to the third connector inside the base  12  through the conductive pads  86   a  and  86   b , and the conductive paths of the sealing board  64 . 
     As described above, the magnetic heads and the voice coil of the VCM provided inside the base  12  are electrically connected to the control circuit board  54  provided on the outside of the base  12  through the relay FPC, board unit  21 , third connector  52 , sealing board  64 , and fourth connector  56  in a state where the airtightness inside the housing  10  is maintained by the sealing board  64  of the connector unit  60 . 
     According to the HDD associated with the third embodiment configured as described above, in the fixation structure of the sealing board  64 , the annular rib (projection)  74  is provided on the installation surface  72  around the through-hole  58 , and the sealing board  64  is arranged in a state where the first principal surface  64   a  of the sealing board  64  is made in contact with the end face  74   a  of the rib  74 , whereby it is possible to position the sealing board  64  in terms of the height position, i.e., the position in the thickness direction of the sealing board  64  with respect to the installation surface  72 . Thereby, it is possible to maintain the gap between the first principal surface  64   a  of the sealing board  64  and the installation surface  72  constant, and manage the thickness of the sealant  82  to be filled into this gap constant. Further, it is possible by the rib  74  to prevent the sealant  82  from flowing into the inside of the through-hole  58 , and retain the sealant  82  in the desired space. Furthermore, according to this embodiment, the stepped portions  78  are provided on the installation surface  72  on the outside of the rib  74 . By virtue of these stepped portions  78 , it is possible to suppress the flow of the sealant  82 , and retain the sealant  82  in the desired space. Therefore, according to this embodiment, it becomes possible to reduce unnecessary spread and wetting of the sealant, and securely seal the desired space with a minimum amount of the sealant. Further, according to this embodiment, by omitting the connectors provided on the sealing board  64 , it becomes possible to reduce the number of components, and simplify the configuration. 
     From the above description, according to the third embodiment, it is possible to obtain a disk device which is improved in the airtightness of the housing, and can easily be connected to the connector or the control circuit board outside the housing. 
     In the third embodiment described above, although the configuration is contrived in such a manner that the projection in the installation part is provided on the installation surface of the base  12 , the configuration is not limited to this, and the projection may be provided on the sealing board  64  side. According to a second modification example shown in  FIG. 13 , a sealing board  64  includes a plurality of conductive pads  86   a  provided on a first principal surface  64   a , and a substantially rectangular projection  90  provided around these conductive pads  86   a . The projection  90  is formed of, for example, a resist layer provided on the first principal surface  64   a . The projection  90  has a constant height (for example, 0.1 mm) over the entire top surface thereof and, furthermore, the top surface (contact surface) of the projection  90  is formed flat. 
     Further, the sealing board  64  is not limited to a multi-layered circuit board, and may be formed of other materials, for example, glass or ceramic. When glass or ceramic is used as the material, the conductive paths of the sealing board  64  may be constituted of a plurality of conductive pins embedded in the sealing board  64 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 
     For example, in the first, second, and third embodiments, the projection is not limited to a continuous annular rib, and projection divisions formed by dividing a projection into a plurality of divisions may be used. The shape of the projection is not limited to the rectangular shape, and is variously selectable. The shape of the sealing board of the connector unit, and the formation material for the sealing board are not limited to those in the aforementioned embodiments, and can be variously varied. The number of the positioning pins or the positioning holes is not limited to two, three or more positioning pins or positioning holes may be provided as the need arises. As in a third modification example shown in  FIG. 14 , a notch  92  may be provided in a part of the rib  74  serving as a projection. When a sealant, for example, solder is to be filled into the space between the installation surface  72  and the sealing board, by exhausting air from the inside of the rib  74  through the notch  92 , it is possible to prevent air bubbles from occurring in the sealant. 
     Utilization of the connector unit  60  is not limited to the connection between the board unit inside the housing and the control circuit board outside the housing, and may be applied to a connection between other components. The materials, shapes, sizes, and the like of the elements constituting the disk drive may be changed as the need arises. In the disk drive, the number of magnetic disks, and the number of magnetic heads can be increased or decreased as the need arises, and the size of the magnetic disk is variously selectable.