Patent Publication Number: US-2010128452-A1

Title: Stud, circuit board device using the stud, and method of mounting the circuit board device

Description:
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2008-300848, filed Nov. 26, 2008, the entire contents of which are incorporated herein. 
     TECHNICAL FIELD 
     The present invention relates to a stud, a circuit board device using the stud, and a method of mounting the circuit board device and, more particularly, to a stud structure for supporting a mounting component on a printed circuit board. 
     BACKGROUND ART 
     In general, in order to achieve miniaturization of a computer apparatus, there is required, e.g., an increase in the integration degree of devices. As one of approaches for increasing the integration degree, there is known a method in which a printed circuit board is formed in a mezzanine structure to be made three-dimensional. In this method, a stud which is a structure for fixing, on a printed circuit board, a mounting component, such as another printed circuit board or a device, is used. 
       FIG. 6  shows a circuit board device according to a related art which uses the abovementioned stud. The circuit board device shown in  FIG. 6  includes a plate  9 , a printed circuit board  12  having a pattern wiring (electric wiring)  11  provided on the plate  9 , and a plurality of stud portions each serving as a structure for mezzanine mounting a small printed circuit board (not shown) on the printed circuit board  12 . 
     Each of the stud portions  6  includes a plate stud  10  mounted on the plate  9  and a cylindrical stud  6  which is screw fixed on the plate stud  10  through a stud/screw portion  7 . A plurality of board holes  8  for stud each having a shape corresponding to the shape of the stud  6  are formed on the printed circuit board  5  so as to fix the stud  6  on the plate stud  10  though the stud/screw portion  7 . 
     In relation to the abovementioned technique, Patent Document 1 (JP-A-2007-12951) discloses, as a supporting member for supporting a plurality of printed circuit boards arranged at a predetermined interval, a stud having one end in which a screw hole for receiving a screw for fixing one printed circuit board and the other end having a convex-shaped step portion to be inserted into a board hole of the other printed circuit board. 
     In the case where the method in which a printed circuit board is formed in a mezzanine structure to be made three-dimensional is adopted as an approach for increasing the integration degree in order to achieve miniaturization of a computer apparatus, it has been necessary to form a hole in the printed circuit board for fixing of the stud to the plate. Thus, the printed circuit board has a hole therein. In the case where a pattern wiring is formed on such a printed circuit board, the length of the pattern wiring is increased for the wiring to bypass the hole, with the result that the pattern wiring density becomes high. This makes signals on the pattern wiring more likely to be affected by noise to deteriorate signal quality. When the number of layers of the printed circuit board is increased so as not to allow the pattern wiring density to increase, cost of the printed circuit board becomes higher. 
     That is, in the circuit board device shown in  FIG. 6 , in order to fix the stud  6  to the printed circuit board  5 , it has been necessary to form a board hole  8  in the printed circuit board  5  for fixing of the stud  6  to the plate  9 . Thus, the pattern wiring  11  which is an electric wiring in the printed circuit board  5  is formed in a bent shape so as to bypass the base plate  8 , as shown in  FIG. 7 . As a result, the length of the pattern wiring is accordingly increased to increase the wiring density as compared to a case where the pattern wiring  11  is linearly formed. This makes signals on the pattern wiring more likely to be affected by noise to deteriorate signal quality. Further, in order to reduce the wiring density, it is necessary to increase the number of layers of the printed circuit board  5 , resulting in an increase in cost of the printed circuit board. The same problems have been encountered in the cited Patent Document 1. 
     SUMMARY OF INVENTION 
     An exemplary object of the present invention is to provide a stud, a circuit board device using the stud, a method of mounting the circuit board device capable of solving the above problems so as to reduce the wiring density of the printed circuit board, reduce the number of layers of the printed circuit board, and allow the printed circuit board to be formed in a mezzanine structure. 
     According to a first aspect of the present invention, there is provided a stud which is a structure for supporting a mounting component on a printed circuit board, wherein the structure is surface-mounted on the printed circuit board. 
     According to a second aspect of the present invention, there is provided a circuit board device including: the stud; and a printed circuit board on which the stud has been surface-mounted. 
     According to a third aspect of the present invention, there is provided a method of mounting a circuit board device including: surface-mounting a stud on a printed circuit board; and mounting a mounting component on the printed circuit board through the stud. 
     According to the present invention, the stud is surface-mounted on the printed circuit board, so that it is possible to eliminate the need to form a hole for the stud in the printed circuit board. This allows the wiring density of the printed circuit board to be reduced to thereby reduce noise due to higher wiring density. Further, the reduction in the wiring density allows the wiring formed in another layer of the printed circuit board to be formed in the same layer, thereby reducing the number of layers of the printed circuit board. Thus, the printed circuit board can be formed in a mezzanine structure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS  
       {FIG.  1 } A cross-sectional view showing a stud according to an exemplary embodiment of the present invention and a circuit board device using the stud. 
       {FIG.  2 } A plan view of a printed circuit board as viewed along A-A line of  FIG. 1 , which explains a pattern wiring image of the printed circuit board in which a board hole for stud has not been formed. 
       {FIG.  3 } A cross-sectional view showing a stud according to a first example of the present invention and a circuit board device using the stud. 
       {FIG.  4 } A cross-sectional view showing a stud according to a second example of the present invention and a circuit board device using the stud. 
       {FIG.  5 } A cross-sectional view showing a stud according to a third example of the present invention and a circuit board device using the stud. 
       {FIG.  6 } A cross-sectional view showing a circuit board device using a stud according to a related art. 
       {FIG.  7 } A plan view of a printed circuit board as viewed along B-B line of  FIG. 6 , which explains a pattern wiring image of the printed circuit board in which a board hole for stud has been formed. 
     
    
    
     DESCRIPTION OF EMBODIMENTS  
     An exemplary embodiment of a stud, a circuit board device using the stud, and a method of mounting the circuit board device will be described in detail below with reference to the accompanying drawings. 
     In a circuit board device using a stud according to the present exemplary embodiment, a stud which is a structure (columnar structure) used in screw fitting, on a printed circuit board, a mounting component, such as a small printed circuit board or a device having a smaller dimension than the printed circuit board, is formed of a component that can be surface-mounted. Hereinafter, such a stud which is a structure formed of a component that can be surface-mounted on a printed circuit board is referred to as “surface mount type stud”. In the present exemplary embodiment, the surface mount type stud is used to reduce the number of holes formed in the printed circuit board, improve wirability in the printed circuit board, and reduce the number of layers of the printed circuit board. 
       FIG. 1  shows a configuration of the main part of a stud according to the present exemplary embodiment and a circuit board device using the stud. The circuit board device shown in  FIG. 1  includes a printed circuit board  1  having a pattern wiring (electric wiring)  3  and a plurality of surface mount type studs (corresponding to studs of the present invention)  2  which are structures for mezzanine mounting, on the printed circuit board  1 , a mounting component (not shown) such as another printed circuit board or a device. 
     The surface mount type stud  2  has a columnar-shaped main body. One end of the main body in the axial direction is secured to a pad  4  provided on the printed circuit board  1  by soldering as in the case of other surface mount type electronic components (not shown), whereby the surface mount type stud  2  is surface-mounted on the printed circuit board  1  with the main body thereof raised. The other end of the surface mount type stud  2  in a raised state is configured to be able to be fixed to a component mezzanine mounted on the printed circuit board  1  by a fixing means (not shown) such as a locking screw. 
     In the present exemplary embodiment, a use of the surface mount type stud  2  eliminates the need to form a board hole for stud in the printed circuit board  1 , thereby allowing the pattern wiring  3  to be drawn to the inner layer of the printed circuit board  1  without forming the board hole for stud. 
     That is, there is no need for the pattern wiring  3  of the printed circuit board  1  to be formed in a bent manner in order to bypass the board hole for stud, so that the pattern wiring  3  can be linearly formed on the printed circuit board  1  as shown in  FIG. 2 . This allows the length of the pattern wiring to be reduced to thereby reduce the wiring density of the printed circuit board  1 . The reduction in the wiring density allows the wiring formed in another layer of the printed circuit board  1  to be formed in the same layer, thereby reducing the number of layers of the printed circuit board  1 . 
     Thus, according to the present exemplary embodiment, it is possible to reduce the number of holes formed in the printed circuit board  1  to thereby significantly improve the wirability in the printed circuit board  1  of high density wiring. 
     Although the surface mount type stud  2  is surface-mounted on the printed circuit board  1  by soldering in the present exemplary embodiment, the present invention is not limited to this, but any connecting or fixing means can be used as long as it can surface mount the surface mount type stud  2  on the printed circuit board  1 . For example, the surface mount type stud  2  can be press-fit connected to the printed circuit board  1 . 
     Examples of the present invention will be described below. 
     FIRST EXAMPLE  
     A first example of the present invention will be described with reference to  FIG. 3 . 
     A circuit board device according to the present example shown in  FIG. 3  includes a plate  13 , a printed circuit board  12  having a pattern wiring (not shown) which is disposed on the plate  13 , and a plurality of surface mount type studs  14  which are columnar-shaped structures for mezzanine mounting, on the printed circuit board  12 , a small printed circuit board (another printed circuit board)  15  which is a mounting component having a smaller dimension than the printed circuit board  12  by fixing thereto by means of a screw (locking screw)  16 . 
     The surface mount type stud  14  of the present example has a columnar-shaped main body. One end of the main body in the axial direction is secured to a component pad  17  provided on the printed circuit board  12  by soldering as in the case of other surface mount type electronic components (not shown), whereby the surface mount type stud  14  is surface-mounted on the printed circuit board  12  with the main body thereof raised. In the case where the small printed circuit board  15  is mounted above the printed circuit board  12 , a screw hole of the small printed circuit board  15  is made to align with the axial direction other end side leading end of the main body of the surface mount type stud  14  mounted on the printed circuit board  12 , and a screw  16  is inserted into the screw hole for fixing between the small printed circuit board  15  and the leading end of the surface mount type stud  14 . 
     According to the present example, the surface mount type stud  14  is mounted on the printed circuit board  12 , so that a hole for fixing the stud need not be formed in the printed circuit board  12 . As a result, it is possible to reduce the wiring density of the printed circuit board  12  and reduce noise. Further, by forming wirings in a plurality of layers in a single layer, the number of layers of the printed circuit board  12  can be reduced. 
     SECOND EXAMPLE  
     A second example of the present invention will be described below with reference to  FIG. 4 . 
     Although the basic structure of a circuit board device according to the present example is the same as that of the circuit board device according to the first example, a further twist has been added to the structure of the surface mount type stud. The configuration is shown in  FIG. 4 . 
     A circuit board device shown in  FIG. 4  includes a plate  13 , a printed circuit board  12  having a pattern wiring (not shown) which is disposed on the plate  13 , and a plurality of surface mount type studs  14   a  which are columnar-shaped structures for mezzanine mounting, on the printed circuit board  12 , a small printed circuit board  15  which is a mounting component having a smaller dimension than the printed circuit board  12  by fixing thereto by means of a screw  16 . 
     The surface mount type stud  14   a  according to the present example is a separate type stud constituted by a plurality of structural parts that can adjust the relative positional relationship between the printed circuit board  12  and the small printed circuit board  15 . The plurality of structural parts include a stud upper portion (corresponding to a first structural part of the present invention)  18  disposed on the small printed circuit board  15  side, a stud lower portion (corresponding to a second structural part of the present invention)  19  disposed on the printed circuit board  12  side, and a stud/screw portion  20  that can adjust the position of the stud upper portion  18  with respect to the stud lower portion  19 . 
     The stud upper portion  18  has a columnar-shaped main body. A screw hole is formed in one end of the main body. A screw  16  is inserted into the screw hole in the axial direction with the center of the screw hole aligned with the center of a screw hole of the small printed circuit board  15 , whereby the stud upper portion  18  is fixed to the small printed circuit board  15 . The other end of the main body of the stud upper portion  18  is inserted into a mounting hole  192  formed in the main body of the stud lower portion  19 . The position of the stud upper portion  18  with respect to the stud lower portion  19  can be adjusted by the stud/screw portion  20  disposed at the insertion portion into the stud lower portion  19 . 
     The stud lower portion  19  has a columnar-shaped main body having a larger diameter than that of the stud upper portion  18 . On one side of the main body of the stud lower portion  19 , a concave portion (opening portion)  191  is formed, and on the other side thereof, a mounting hole  192  having a diameter large enough to allow the other end of the main body of the stud upper portion  18  to be inserted therethrough is formed so as to penetrate the main body to reach the concave portion  191 . The stud lower portion  19  has both side edge portions (opening edges)  193  of the concave portion  191 , which are secured by soldering to the component pads  17  provided on the printed circuit board  12  through lead portions  171 . 
     The stud/screw portion  20  is attached to the insertion portion into the mounting hole  192  formed in the stud lower portion  19  at the other end side of the main body of the stud upper portion  18 . A screw adjustment of the stud/screw portion  20  allows the axial direction position of the stud upper portion  18  with respect to the stud lower portion  19  to be adjusted. 
     The stud lower portion  19  is soldered to the printed circuit board  12  and, when the small printed circuit board  15  is mounted, the stud upper portion  18  and stud/screw portion  20  are screw fixed to the stud lower portion  19 . After that, the stud upper portion  18  and the small printed circuit board  15  are fixed to each other by the screw  16 . 
     In the first example shown in  FIG. 3 , the surface mount type stud  14  is directly mounted on the printed circuit board  12 , so that a large gradient or large mounting error in the horizontal direction occurs at the soldering portion between the surface mount type stud  14  and the component pad  17 . Thus, the portion at which the small printed circuit board  15  and the surface mount type stud  14  are fixed by the screw  16  is little influenced by the mounting error of the surface mount type stud  14  when the distance between the printed circuit board  12  and the small printed circuit board  15  is small; on the other hand, when the distance between the printed circuit board  12  and the small printed circuit board  15  is large, the fixing portion between the small printed circuit board  15  and the surface mount type stud  14  is influenced by the mounting error of the surface mount type stud  14 , so that a tension may be applied to the surface mount type stud  14 . 
     In the present example, as shown in  FIG. 4 , the surface mount type stud  14   a  is divided into two parts: the stud upper portion  18  and stud lower portion  19  to provide an allowance to the surface mount type stud  14   a,  thereby allowing the tension applied to the surface mount type stud  14   a  to be absorbed. Further, the lead portion  171  commonly used as a component for an IC (Integrated Circuit) is provided to the surface mount type stud  14   a  so as to reduce the gradient or horizontal direction mounting error of the surface mount type stud  14   a.    
     The shape of the stud lower portion  19  and shape of the component pad  17  at its surface mount portion in the present example are not especially limited but any shape may be used. Further, in the case where the surface mount type stud  14   a  according to the present example is employed, another component such as a device may be mounted above the printed circuit board  12  in place of the small printed circuit board  15 . 
     THIRD EXAMPLE 
     A third example of the present invention will be described with reference to  FIG. 5 . 
     In a circuit board device according to the third example, a further twist has been added to the structure of the surface mount type stud according to the second example. The configuration is shown in  FIG. 5 . 
     A circuit board device shown in  FIG. 5  includes a plate  13 , a printed circuit board  12  having a pattern wiring (not shown) which is disposed on the plate  13 , and a plurality of surface mount type studs  14   b  which are columnar-shaped structures for mezzanine mounting, on the printed circuit board  12 , a small printed circuit board  15  which is a mounting component having a smaller dimension than the printed circuit board  12  by fixing thereto by means of a screw  16 . 
     As in the case of the second example, the surface mount type stud  14   b  according to the present example is a separate type stud constituted by a plurality of structural parts that can adjust the relative positional relationship between the printed circuit board  12  and the small printed circuit board  15 . The plurality of structural parts include a stud upper portion (corresponding to a first structural part of the present invention)  18  disposed on the small printed circuit board  15  side, a press-fit type stud lower portion (corresponding to a second structural part of the present invention)  21  disposed on the printed circuit board  12  side, and a stud/screw portion  20  that can adjust the position of the stud upper portion  18  with respect to the press-fit type stud lower portion  21 . 
     The stud upper portion  18  has the same configuration as that in the second example. That is, the stud upper portion  18  has a columnar-shaped main body. A screw hole is formed in one end of the main body. A screw  16  is inserted into the screw hole in the axial direction with the center of the screw hole aligned with the center of a screw hole of the small printed circuit board  15 , whereby the stud upper portion  18  is fixed to the small printed circuit board  15 . The other end of the main body of the stud upper portion  18  is inserted into a mounting hole  212  formed in the press-fit type stud lower portion  21 . The position of the stud upper portion  18  with respect to the press-fit type stud lower portion  21  can be adjusted by the stud/screw portion  20  disposed at the insertion portion into the press-fit type stud lower portion  21 . 
     Unlike the case of the stud lower portion  19  of the surface mount type stud  14   a  according to the second example, the press-fit type stud lower portion  21  is not soldered to the printed circuit board  12  but is press-fitted to the printed circuit board  12  for fixing at several points. That is, the press-fit type stud lower portion  21  has a columnar-shaped main body having a larger diameter than that of the stud upper portion  18 . On one side of the main body of the press-fit type stud lower portion  21 , a concave portion (opening portion)  211  is formed, and on the other side thereof, a mounting hole  212  having a diameter large enough to allow the other end of the main body of the stud upper portion  18  to be inserted therethrough is formed so as to penetrate the main body to reach the concave portion  211 . Leading end portions  214  extending from both side edge portions (opening edges)  213  of the concave portion  211  are each formed to terminate in a tapered shape point. These leading end portions  214  are inserted into holes  12   a  formed in the printed circuit board  12  by press-fitting, whereby the press-fit type stud lower portion  21  is fitted to the printed circuit board  12 . 
     The stud/screw portion  20  has the same configuration as that in the second example. That is, the stud/screw portion  20  is attached to the insertion portion into the mounting hole  212  formed in the press-fit type stud lower portion  21  at the other end side of the main body of the stud upper portion  18 . A screw adjustment of the stud/screw portion  20  allows the axial direction position of the stud upper portion  18  with respect to the press-fit type stud lower portion  21  to be adjusted. 
     Even though the hole  12   a  for press-fitting needs to be formed in the printed circuit board  12  in the present example, the wiring density of the pattern wiring can significantly be reduced as compared to the above related art. 
     Further, the mounting error can be reduced in the case where the press-fit type stud lower portion  21  is employed as compared to the case where the surface mount type stud  14  according to the first example or the stud lower portion  19  according to the second example is employed. Thus, the use of the press-fit type stud lower portion  21  is effective in the case where the distance between the small printed circuit board  15  and the printed circuit board  12  is large. The surface mount type stud  14   b  and the small printed circuit board  15  in the present example are fixed to each other by means of the screw  16  as in the case of the first and second examples. 
     The shape and press-fit configuration of the press-fit type stud lower portion  21  in the present example are not especially limited but any shape or press-fit configuration may be used. Further, in the case where the surface mount type stud  14   b  according to the present example is employed, another component such as a device may be mounted above the printed circuit board  12  in place of the small printed circuit board  15 . 
     Although the present invention has been described in detail with reference to the above exemplary embodiment and examples, it should be understood that the present invention is not limited to the above exemplary embodiment and examples. Various changes that those skilled in the art can understand can be made to the configuration or details of the present invention without departing from the sprit and scope of the invention. 
     The present invention may suitably be applied to a stud for fixing a small printed circuit board or device on a printed circuit board, a circuit board device using the stud, and a method of mounting the circuit board device. 
     While the invention has been particularly shown and described with reference to exemplary embodiment and examples thereof, the invention is not limited to these embodiment and examples. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the sprit and scope of the present invention as defined by the claims.