Abstract:
According to an aspect of the present invention, there is provided a printed wiring board including: a substrate including a pair of edges and a fixing hole adjacent to the pair of edges and configured to receive a bolt; a land provided in a vicinity of the fixing hole and extending in a direction from the fixing hole toward a center of the substrate and along the pair of edges; and an insulating height adjuster provided between the fixing hole and the pair of edges and configured to have substantially the same height as the land.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-232392, filed on Sep. 10, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     An aspect of the present invention relates to a printed wiring board having a land and an electronic apparatus having the printed wiring board. 
     2. Description of the Related Art 
     For example, a printed wiring board in which a land for grounding is provided around a fixing hole for bolting the printed wiring board is disclosed. This printed wiring board comprises a substrate, a fixing hole provided to penetrate through the substrate, a land provided in doughnut shaped around the fixing hole in a surface of the substrate, and a solder cream printed on the surface of the land. 
     In printed wiring boards of this type, usually, the surfaces of the lands are subjected to solder plating to prevent corrosion of the lands and attain reliable grounding. A printed wiring board having a cost advantage over ones in which the lands are subjected to solder plating is provided by supplying solder also to the land surfaces when cream solder is supplied to mounting patterns of other components (see JP-A-2000-244080, for instance). 
     In recent years, with the increase in miniaturization and functionality of digital equipment, the high-density mounting on a printed wiring board and the securing of a wide mounting area have come to be required increasingly. However, the above donut-shaped lands raise a problem that the mounting area on the printed wiring board is reduced by areas corresponding to the spaces for formation of the lands. For another thing, to secure a wide mounting area on a printed wiring board, it is effective to locate the fixing holes as close to the outer periphery of the board as possible. However, in the printed wiring boards, the fixing holes cannot be located sufficiently close to the outer periphery because margins for formation of the donut-shaped lands need to be secured around the respective fixing holes. 
     Each of these margins needs to be set taking into consideration not only the space for formation of the land but also a variation that may occur when a land pattern is formed by etching. This is because if a land is formed in contact with the periphery the land is exposed in an end face of the printed wiring board, as a result of which the printed wiring board may be short-circuited with another component. This also requires sufficient margins around the respective fixing holes. 
     On the other hand, one method for reducing the above margins is to narrow the widths of the donut-shaped lands. However, if the land widths are narrowed, a land pattern may be disconnected due to a variation in forming the pattern. Furthermore, since the lands are reduced in strength, the land patterns are prone to peel off when bolting is performed through the fixing holes. Further, since the land is a part for grounding on the casing, a contact area between the land and the bolt is narrowed if the width of the land is made smaller, possibly resulting in the lower reliability of the grounding. 
     For the above reasons, the printed wiring boards cannot sufficiently satisfy the recent requirements of high-density mounting and securing of a wider mounting area. 
     SUMMARY 
     According to an aspect of the invention, there is provided a printed wiring board including: a substrate including a pair of edges and a fixing hole adjacent to the pair of edges and configured to receive a bolt; a land provided in a vicinity of the fixing hole and extending in a direction from the fixing hole toward a center of the substrate and along the pair of edges; and an insulating height adjuster provided between the fixing hole and the pair of edges and configured to have substantially the same height as the land. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A general architecture that implements the various feature of the present invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the present invention and not to limit the scope of the present invention. 
         FIG. 1  is an exemplary perspective view of a portable computer according to a first embodiment; 
         FIG. 2  is an exemplary sectional view along the horizontal direction of a main body unit of the portable computer as shown in  FIG. 1 ; 
         FIG. 3  is an exemplary enlarged plan view showing a part of a printed wiring board contained inside a casing of the main body unit as shown in  FIG. 2 ; 
         FIG. 4  is an exemplary sectional view along the longitudinal direction of the printed wiring board as shown in  FIG. 3 ; 
         FIG. 5  is an exemplary enlarged plan view showing a part of a printed wiring board of a portable computer according to a second embodiment; 
         FIG. 6  is an exemplary enlarged plan view showing a part of a printed wiring board of a portable computer according to a third embodiment; 
         FIG. 7  is an exemplary enlarged plan view showing a part of a printed wiring board of a portable computer according to a fourth embodiment; 
         FIG. 8  is an exemplary perspective view showing a printed wiring board contained inside the casing of a hard disk device according to a fifth embodiment; and 
         FIG. 9  is an exemplary sectional view along the longitudinal direction of the printed wiring board as shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 to 4 , a first embodiment of an electronic apparatus will be described below. A portable computer as one example of the electronic apparatus is a so-called notebook personal computer, as shown in  FIG. 1 . In  FIGS. 1 and 2 , a description will be made with a notation that the forward direction and the backward direction are denoted by arrows F and R, respectively. 
     The portable computer  11  is equipped with a main body unit  12 , a display unit  13 , and hinge mechanisms  14  which connect the main body unit  12  and the display unit  13 , as shown in  FIG. 1 . Supporting the display unit  13 , the hinge mechanisms  14  make it possible to rotate the display unit  13  with respect to the main body unit  12 . The display unit  13  has a display  15  and a cover  16  surrounding the display  15 . The display  15  is a liquid crystal display, for example. 
     The main body unit  12  has a casing  21  made of synthetic resin, a keyboard  22 , and a touch pad  23  and a button  24  that are a pointing device. The main body unit  12  further has, inside the casing  21 , a printed circuit board  25  and bolts  26  for fixing the printed circuit board  25  on the casing  21 , as shown in  FIGS. 2 and 4 . The printed circuit board  25  has a printed wiring board  31  and a plurality of circuit components  32  mounted on the printed wiring board  31 . The plural circuit components  32  include a CPU and a north bridge, for example. In  FIG. 2 , the bolts  26  are not illustrated. The inside surfaces of the casing  21  are uniformly covered with a conductive ground layer  46 . The ground layer  46  prevents outward leakage of electromagnetic waves from the portable computer  11 . 
     For example, the printed wiring board  31  is a copper-clad lamination plate in which a plurality of copper wiring layers are laminated, for example. The printed wiring board  31  has a substrate  33 , a land  34  and a height adjuster  37  provided on the substrate  33 , a solder resist layer  38  covering the surface of the substrate  33 , and a through hole plating  52  for electrically connecting the land  34  with a ground portion  41 . The substrate  33  is formed by alternately laminating insulating layers made of a glass-cloth-incorporated resin and wiring layers sandwiched between the insulating layers. The substrate  33  has a first edge  35 A and a second edge  35 B that are a pair of edges defining a part of the outer periphery of the substrate  33 , and a fixing hole  36  provided at a position adjacent to the first edge  35 A and the second edge  35 B. The fixing hole  36  is disposed closer to the first edge  35 A and the second edge  35 B. 
     The ground portion  41  is grounded to the ground layer  46  via the through hole plating  52 , the land  34  and the bolt  26 , as shown in  FIGS. 3 and 4 . 
     The substrate  33  further has through holes  42  for bolting the printed wiring board  31  on the casing  21 , in addition to the fixing hole  36 , as shown in  FIGS. 2 to 4 . A second land  43  of the conventional shape, namely, a doughnut shape is formed around the through hole  42 . When the printed circuit wiring  31  is fixed to the casing  21 , the bolts  26  are inserted through the fixing hole  36  and the through-holes  42 . 
     The bolt  26  has a head portion  26 A covering the land  34  or the second land  43  and contacted by the land  34  or the second land  43 , and a shank portion  26 B passed through the fixing hole  36  or the through hole  42 . An external thread is formed on the outer periphery of the shank portion  26 B. 
     The land  34  is provided at a position around the fixing hole  36  and in a vicinity of the fixing hole  36 . The land  34  extends from the fixing hole  36  in the range between the direction D 1  from the fixing hole  36  to a central portion  45  of the substrate  33  and the direction D 2  along the direction where one pair of edges  35 A and  35 B extend. That is, the land  34  is shaped like a sector around the fixing hole  36 , and located to extend toward the central portion  45  of the substrate  33 . An angle of the sector shape of the land  34  in this embodiment is about 90 degrees, for example. The land  34  is formed in the shape of the sector by etching a copper foil on the surface layer of the substrate  33 , for example. 
     The height adjuster  37  is formed of a solder resist, for example, and has the insulating property. The height adjuster  37  is formed to be continuous to the solder resist layer  38  covered on the surface of the substrate  33 . The height adjuster  37  is provided between the fixing hole  36  and a pair of edges  35 A and  35 B. More specifically, the height adjuster  37  is disposed like a band along the edges  35 . The height adjuster  37  has the same height as the upper surface of the land  34 . The height adjuster  37  and the solder resist layer  38  are formed by printing (screen printing) a solder resist on the surface of the substrate  33 , after forming the land  34  by etching. A gap  39  is provided between the solder resist layer  38  and the height adjuster  37  and the land  34 . Though the solder resist layer  38  and the height adjuster  37  may be misregistered and printed on the substrate  33 , this gap  39  prevents the solder resist layer  38  and the height adjuster  37  misregistered from being formed over the land  34 . 
     Though in this embodiment, a plurality of through holes  42  are provided, and one fixing hole  36  is provided, it should be noted that a plurality of fixing holes  36  may be provided instead of the through holes  42 . Also, the height adjuster  37  is formed of solder resist in this embodiment, but not limited thereto. It should be noted that the height adjuster  37  may be anything having the insulating property, and may be formed of silk printed on the surface of the substrate  33 , for example. Also, though no plating is applied on the inside surface of the fixing hole  36  in this embodiment, the fixing hole may be formed as a through hole by coating the plating on the inside surface of the fixing hole  36 . 
     According to the first embodiment, the portable computer  11  comprises the casing  21  having the conductive ground layer  46  on the inside surface, the printed wiring board  31  contained inside the casing  21 , and the bolt  26  for fixing the printed wiring board  31  on the casing  21  and grounding the printed wiring board  31  to the ground layer  46 , wherein the printed wiring board  31  has the substrate  33  having a pair of edges  35 A and  35 B defining a part of the outer periphery and the fixing hole  36  provided at a position adjacent to the pair of edges  35 A and  35 B and passing the bolt  26  through it, the land  34  provided in the vicinity of the fixing hole  36  and extended from the fixing hole  36  in the range between the direction D 1  from the fixing hole  36  to the central portion  45  of the substrate  33  and the direction D 2  along the direction where the pair of edges  35 A and  35 B extend, and the insulating height adjuster  37  provided at a position between the fixing hole  36  and the pair of edges  35 A and  35 B and having the same height as the land  34 . 
     With this configuration, the land  34  is formed in the direction D 1  toward the central part  45  of the substrate  33 , and the land  34  is not formed between the fixing hole  36  and the edges  35 . Thereby, space for disposing the land  34  at the position between the fixing hole  36  and the edges  35  is unnecessary, whereby the fixing hole  36  can be disposed as close to the edges  35  as possible. Therefore, it is possible to secure a wide mounting area on the printed wiring board  31 . Also, since the height adjuster  37  having the same height as the land  34  is provided, the bolt  26  is not inclined and installed in fixing the printed wiring board  31  by fastening the bolt  26  into the fixing hole  36 . Therefore, the bolt  26  is not suspended over the land  34 , whereby the printed wiring board  31  can be securely grounded. 
     In this embodiment, the land  34  is shaped like the sector extended toward the central portion  45  around the fixing hole  36 . With this configuration, the land  34  having enough strength can be realized in a simple shape. Particularly, because the shape of the land  34  is the sector, the head portion  26 A of the bolt  26  easily contacts the land  34 , making it possible to securely ground the printed wiring board  31  to the ground layer  46  of the casing  21 . 
     Referring to  FIG. 5 , a second embodiment of the portable computer will be described below. The portable computer  11  that is one example of the electronic apparatus according to the second embodiment is different from the first embodiment in that the fixing hole  36  is provided in the vicinity of an edge  35 , and the shape of a land  54  is different, but the other portions are common. Therefore, the different portions from the first embodiment will be mainly described below, in which the common portions are designated by the common numerals, and the explanation thereof is omitted. 
     A printed wiring board  51  for the portable computer  11  of the second embodiment has the substrate  33 , the land  54  and the height adjuster  37  provided on the substrate  33 , the solder resist layer  38  covering the surface of the substrate  33 , and a through hole plating  52  for electrically connecting the land  54  and the ground portion  41 . 
     The substrate  33  has the edge  35  defining a part of the outer periphery of the substrate  33 , and the fixing hole  36  provided at a position adjacent to this edge  35 . The fixing hole  36  is disposed closer to the edge  35 . 
     The land  54  is provided around the fixing hole  36  and in the vicinity of the fixing hole  36 . The land  54  extends from the fixing hole  36  in the range between the direction D 1  from the fixing hole  36  to a central portion  45  of the substrate  33  and the direction D 2  along the direction where the edge  35  extends. The land  54  is shaped like a sector around the fixing hole  36 , and located to extend toward the central portion  45  of the substrate  33 . An angle of the sector shape of the land  54  in this embodiment is about 180 degrees, for example. 
     The height adjuster  37  is formed of solder resist, for example, and has an insulating property. The height adjuster  37  is formed to be continuous to the solder resist layer  38  covered on the surface of the substrate  33 . The height adjuster  37  is provided at a position between the fixing hole  36  and the edge  35 , and located like a band along the edge  35 . The height adjuster  37  has the same height as the upper surface of the land  54 . The height adjuster  37  and the solder resist layer  38  are formed by printing (screen printing) a solder resist on the surface of the substrate  33 , after forming the land  54  by etching. A gap  39  is provided between the solder resist layer  38  and the height adjuster  37  and the land  54 . The height adjuster  37  may be formed of silk, like the first embodiment. 
     With the second embodiment, even though the fixing hole  36  is provided in the vicinity of the edge  35 , the land  34  is formed in the direction D 1  toward the central portion  45  of the substrate  33 , and the land  34  is not formed between the fixing hole  36  and the edge  35 . Hence, the fixing hole  36  can be disposed as close to the edge  35  as possible, whereby it is possible to secure a wide mounting area on the printed wiring board  31 . Also, since the height adjuster  37  having the same height as the land  34  is provided, the bolt  26  is not inclined and installed in fixing the printed wiring board  51  by fastening the bolt  26  into the fixing hole  36 . Therefore, the printed wiring board  51  can be securely grounded. 
     Referring to  FIG. 6 , a third embodiment of the portable computer will be described below. The portable computer  11  that is one example of the electronic apparatus of the third embodiment is different from the first embodiment in the configuration of a height adjuster  72  in a printed wiring board  71 , and the installed positions of the fixing hole  36  and the land  34 , but the other portions are common. Therefore, the different portions from the first embodiment will be mainly described below, in which the common portions are designated by the common numerals, and the explanation thereof is omitted. 
     The printed wiring board  71  for the portable computer  11  of the third embodiment has the substrate  33 , the land  34  and the height adjuster  72  provided on the substrate  33 , the solder resist layer  38  covering the surface of the substrate  33 , and the through hole plating  52  for electrically connecting the land  54  and the ground portion  41 . 
     The substrate  33  has the first edge  35 A and the second edge  35 B that are a pair of edges defining a part of the outer periphery of the substrate  33 , and the fixing hole  36  provided at a position adjacent to the first edge  35 A and the second edge  35 B. The fixing hole  36  is disposed as close to one edge  35  as possible. 
     The land  34  is provided at a position around the fixing hole  36  and in the vicinity of the fixing hole  36 . The land  34  extends from the fixing hole  36  in the range between the direction D 1  from the fixing hole to a central portion  45  of the substrate  33  and the direction D 2  along the direction where the edges  35  extend. The land  34  is shaped like a sector, and located to extend toward the central portion  45  of the substrate  33 . An angle of the sector shape of the land  34  in this embodiment is about 90 degrees, for example. 
     The height adjuster  72  is formed of solder resist, for example, and has an insulating property. The height adjuster  72  is formed independently of the solder resist layer  38  covered on the surface of the substrate  33 . The height adjuster  72  is provided between the fixing hole  36  and one edge  35 , but located outside the region between the edge  35  and a part  34 A of the land  34  opposed to the edge  35 . The height adjuster  72  is located at a position where a pair of edges  35 A and  35 B intersect, namely, at a corner portion of the printed wiring board  71 . 
     The height adjuster  72  has the same height as the upper surface of the land  34 . The height adjuster  72  and the solder resist layer  38  are formed by printing (screen printing) a solder resist on the surface of the substrate  33 , after forming the land  34  by etching. A gap  39  is provided between the solder resist layer  38  and the land  34 . Even if the height adjuster  72  is formed separately from the solder resist layer  38  as in this embodiment, the manufacturing process is not complicated. 
     With the third embodiment, the height adjuster  72  is disposed at outside the region between the edge  35  and the part  34 A of the land  34  opposed to the edge  35 , where one pair of edges  35 A and  35 B intersect. With this configuration, the height adjuster  72  is disposed not at the position between the edge  35  and the part  34 A of the land  34  opposed to the edge  35 , but at the so-called corner portion of the printed wiring board  71 . Therefore, the space for requiring the installation of the height adjuster  72  is smaller than in the first embodiment, whereby the fixing hole  36  and the land  34  can be disposed closer to the corner portion of the printed wiring board  71  to locate a part of the land  34  in the empty space. Thereby, it is possible to secure a wider mounting space on the printed wiring board  71  than in the first embodiment. 
     Referring to  FIG. 7 , a fourth embodiment of the portable computer will be described below. The portable computer  11  that is one example of the electronic apparatus of the fourth embodiment is different from the second embodiment in the configuration of the height adjuster  72  for a printed wiring board  81  and the installed positions of the fixing hole  36  and the land  54 , but the other portions are common. Therefore, the different portions from the second embodiment will be mainly described below, in which the common portions are designated by the common numerals, and the explanation thereof is omitted. 
     The printed wiring board  81  for the portable computer  11  of the forth embodiment has the substrate  33 , the land  54  and the height adjuster  72  provided on the substrate  33 , the solder resist layer  38  covering the surface of the substrate  33 , and the through hole plating  52  for electrically connecting the land  54  and the ground portion  41 . 
     The substrate  33  has one edge  35  defining a part of the outer periphery of the substrate  33 , and the fixing hole  36  provided at a position adjacent to one edge  35 . The fixing hole  36  is disposed as close to one edge  35  as possible. 
     The land  54  is provided at a position around the fixing hole  36  and in the vicinity of the fixing hole  36 . The land  54  extends from the fixing hole  36  in the range between the direction D 1  from the fixing hole  36  to a central portion  45  of the substrate  33  and the direction D 2  along the direction where the edge  35  extends. The land  54  is shaped like a sector, and located to extend toward the central portion  45  of the substrate  33 . The angle of the sector shape of the land  54  in this embodiment is about 180 degrees, for example. 
     The height adjuster  72  is formed of solder resist, for example, and has an insulating property. The height adjuster  72  is formed independently of the solder resist layer  38  covered on the surface of the substrate  33 . The height adjuster  72  is provided between the fixing hole  36  and one edge  35 , but located outside the region between the edge  35  and a part  54 A of the land  54  opposed to the edge  35 . That is, the height adjuster  72  is provided only in the vicinity of some of one edge  35  diametrically opposed to the fixing hole  36 . 
     The height adjuster  72  has the same height as the upper surface of the land  54 . The height adjuster  72  and the solder resist layer  38  are formed by printing (screen printing) a solder resist on the surface of the substrate  33 , after forming the land  54  by etching. A gap  39  is provided between the solder resist layer  38  and the height adjuster  72  and the land  54 . Even if the height adjuster  72  is formed separately from the solder resist layer  38  as in this embodiment, the manufacturing process is not complicated. 
     With the fourth embodiment, the height adjuster  72  is disposed outside the region between the edge  35  and the part  54 A of the land  54  opposed to the edge  35 . With this configuration, the space for requiring the installation of the height adjuster  72  is smaller than in the first embodiment, whereby the fixing hole  36  and the land  34  can be disposed closer to the edge  35  of the printed wiring board  81  to locate a part of the land  54  in the empty space. Thereby, it is possible to secure a wider mounting space on the printed wiring board  81  than in the second embodiment. 
     Referring to  FIGS. 8 and 9 , a fifth embodiment of the electronic apparatus will be described below. In the fifth embodiment, the invention is applied to a hard disk device  91  as one example of the electronic apparatus. The hard disk device  91  as one example of the electronic apparatus is different in the configuration of each part from the first to fourth embodiments, but substantially common in the configuration of the printed wiring board  31  to the first embodiment. Therefore, the different portions from the second embodiment will be mainly described below, in which the common parts are designated by the common numerals, and the explanation thereof is omitted. 
     The hard disk device  91  has a casing  21 , a printed circuit board  25  contained inside the casing  21 , a storage portion  92  for storing a plurality of disks, and a spindle motor  93  for rotating and driving the plurality of disks. The hard disk device  91  further has a bolt  26  for fixing the printed circuit board  25  on the casing  21 . The printed wiring board  25  has the printed wiring board  31  and a plurality of circuit components disposed on the printed wiring board  31 , though the illustration of the circuit components is omitted in  FIG. 9 . 
     The printed wiring board  31  is different from the second embodiment in that it has an opening portion  94  for disposing the spindle motor  93 , but the other configuration is the same as the first embodiment. The substrate  33  of the printed wiring board  31  has one fixing hole  36  provided with the land  34  shaped like a sector around the periphery, and two through holes  42  provided with the second land  43  shaped like a doughnut around the periphery. The land  34  is the same as the land  34  of the first embodiment. The height adjuster  37  is formed of the solder resist, but may be formed of silk as in the first embodiment. 
     According to the fifth embodiment, even if the hard disk device  91  as one example of the electronic apparatus is used, the fixing hole  36  can be disposed as close to the edge  35  as possible. Therefore, it is possible to secure a wide mounting space on the printed wiring board  31 . Also, since the height adjuster  37  has the same height as the land  34 , the bolt  26  is not inclined and installed in fixing the printed wiring board  31  by fastening the bolt into the fixing hole. Therefore, the bolt  26  is not suspended over the land  34 , whereby the printed wiring board  31  can be securely grounded. 
     Though the printed wiring board that is the same as the printed wiring board  31  of the first embodiment is employed in the fifth embodiment, it should be noted that the printed wiring board of the second to fourth embodiments may be alternatively employed. 
     The electronic apparatus of the invention is not limited to the portable computer  11  or the hard disk device  91 , but may be any other electronic apparatus such as a cell phone, for example. Other various modifications can be made of the above-described electronic apparatus without departing from the spirit and scope of the invention.