Abstract:
An electronic apparatus comprises a first and a second printed circuit board. An elastic conductive member is interposed between the first and second printed circuit boards. The elastic conductive member is employed to establish an electric connection between the first and second printed circuit boards in place of, for example, a prior art connector comprising a plug and a receptacle component. The elastic conductive member may comprise a plurality of brass wires penetrating through an elastic insulation plate made of silicon. The wires are designed to establish signal channels between the first and second printed circuit boards. Since the brass wires can be made short, the space between the first and second printed circuit boards can be suppressed even when the elastic conductive member is interposed between the first and second printed circuit boards. Accordingly, an electric connection can be established between a pair of printed circuit boards in a smaller space.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to surface connection for establishing an electric connection between a pair of printed circuit boards. 
     2. Description of the Prior Art 
     A multilayered printed circuit board is well known, which comprises layers of wiring patterns embedded in a substrate. Such a printed circuit board usually allows only input/output contact pads to expose at the surface of the substrate. On the other hand, a wiring pattern cannot be embedded in a substrate of some printed circuit boards such as flexible printed circuit boards, since such printed circuit boards cannot contain a large number of layers. A wiring pattern should be exposed at the surface of the substrate. The wiring pattern is covered with a protection film on the surface of the substrate. 
     In general, a connector is employed when an electric connection is to be established between the flexible printed circuit board and other circuit boards. Such a connector comprises a plug component mounted on either of the boards and a receptacle component mounted on the other of the boards. When the plug component is received in the receptacle component, a contact pin on the plug component enters a contact socket on the receptacle component. Electric connection can be established between the contact pin and socket. Combinations of pins and sockets are allowed to provide a large number of signal channels in a single connector. 
     The contact pins and sockets are supported in housings of synthetic resin material, respectively. The housings serve to electrically insulate the adjacent contact pins and sockets from each other. However, such housings are supposed to hinder reduction in size of the plug and receptacle components. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the present invention to provide a connecting mechanism capable of establishing an electric connection between a pair of printed circuit boards in a smaller space. 
     According to the present invention, there is provided an electronic apparatus comprising: a first and a second printed circuit board; a conductive pattern formed on a surface of a substrate in at least one of the first and second printed circuit boards; a protection film formed on the substrate so as to cover over at least partly the conductive pattern; and an elastic conductive member interposed between the first and second printed circuit boards. 
     With this structure, the elastic conductive member is employed to establish an electric connection between the first and second printed circuit boards in place of, for example, a prior art connector comprising a plug and a receptacle component. The elastic conductive member may comprise a plurality of brass wires penetrating through an elastic insulation plate made of silicon. The wires are designed to establish signal channels between the first and second printed circuit boards. Since the brass wires can be made short, the space between the first and second printed circuit boards can be suppressed even when the elastic conductive member is interposed between the first and second printed circuit boards. Accordingly, an electric connection can be established between a pair of printed circuit boards in a smaller space. 
     In order to realize the aforementioned electronic apparatus, a printed circuit board may comprise: a substrate; a conductive pattern formed on a surface of the substrate; a protection film formed on the substrate so as to cover over at least partly the conductive pattern; and a conductive contact protruding from a surface of the conductive pattern so as to reach a level above a surface of the protection film. 
     For example, a conventional anisotropic conductive rubber plate may comprise a plurality of brass wires uniformly arranged over the entire area of an elastic insulation plate. When the anisotropic conductive rubber plate has been interposed between a pair of printed circuit boards, the brass wires are arranged not only at a location aligned with the contact pads for establishing signal channels in the conductive pattern but also at a location off the contact pads. If the protection film covers over the conductive pattern off the contact pads, the brass wires cannot reach the contact pads because the brass wires off the contact pads first contact the protection film so as to hinder the brass wires from approaching the contact pads. An electric connection cannot be established between the brass wires and the contact pads. 
     On the other hand, the electronic apparatus of the present invention may employ a conductive contact protruding from a surface of the conductive pattern so as to reach a level above a surface of the protection film. The conductive contact in this manner is adapted to allow the brass wires to first contact the conductive contact when the anisotropic conductive rubber plate is superposed on the printed circuit board. The protection film surely fails hinder establishment of signal channels leading from the conductive pattern to the brass wires. Such conductive contact may comprise a contact pad shaped in the conductive pattern, and a solder bump formed on a surface of the contact pad. Otherwise, the conductive contact may be integrated with the conductive pattern. 
     In order to realize the aforementioned electronic apparatus, an elastic conductive member may comprise: an elastic insulation plate defining through holes; and a conductive pin selectively received in the through hole. This type of elastic conductive member allows the conductive pin to be selectively arranged only at location aligned with the conductive pattern exposed at the breaks of the protection film. Such conductive pin is allowed to first contact the conductive pattern without inducing collision against the protection film when the elastic conductive member is superposed on the surface of the printed circuit board. The elastic conductive member serves to reliably establish a signal channel leading from the conductive pattern to the conductive pin. 
     The elastic conductive member may employ an insulation plate defining an operative through hole only for receiving the conductive pin. Otherwise, an insulation plate may define, in addition to the operative through hole, an additional or inoperative through hole of a diameter identical to that of the operative through hole. Employment of such an inoperative through hole is designed to allow the conductive pin to be relocated from the operative through hole to the inoperative through hole. Accordingly, the elastic conductive member is allowed to easily change the pattern of electric connection between a pair of printed circuit boards. The through holes uniformly arranged in a larger area enable any combination of the operative through holes, so that the elastic conductive member is allowed to deal with the contact pads in various arrangement without redesigning the insulation plate and the conductive pin. In producing the insulation plate, it is not necessary to distinct the operative and inoperative through holes from each other, since the operative and inoperative through holes have the same dimension. 
     The present invention may be applied to any types of printed circuit boards assembled within an electronic apparatus such as a computer hardware, a PDA (personal digital assistant), and the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a partially exploded perspective view illustrating a small-sized computer unit; 
     FIG. 2 is an enlarged perspective view illustrating a flexible painted circuit board combined with a support member; 
     FIG. 3 is an exploded view illustrating the flexible printed circuit board; 
     FIG. 4 is a perspective view schematically illustrating a card slot mounted on the flexible printed circuit board; 
     FIG. 5 is an enlarged sectional view schematically illustrating a connecting mechanism according to the present invention; 
     FIG. 6 is a perspective view schematically illustrating the assembly process of the connecting mechanism; 
     FIG. 7 is a perspective view schematically illustrating an anisotropic conductive rubber plate according to another specific embodiment; and 
     FIG. 8 is an enlarged sectional view schematically illustrating a connecting mechanism according to another specific embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 schematically illustrates a small-sized computer unit. The small-sized computer unit  10  comprises a box-shaped enclosure  11  and a back panel  12  as a first printed circuit board. The back panel  12  functions as a bottom plate of the enclosure  11 . The front opening of the enclosure  11  is closed with a front panel  14 . A handle  13  may be attached to the front panel  14 . 
     Connectors, not shown, are mounted on the surface of the back panel  12  so as to receive circuit boards upright to the surface of the back panel  12 . The circuit boards may include a CPU (central processing unit) board on which a CPU of the computer unit  10  is mounted, a memory board on which memory units are mounted, and the like. The circuit boards received in the connectors are housed within the enclosure  11 . Any electronic parts, in addition to the connectors, may be mounted on the opposite surfaces of the back panel  12 . 
     The end of a flexible printed circuit board  16 , as a second printed circuit board, is connected to the back panel  12  through a connecting mechanism according to the present invention. Receptacle components  17  of so-called MS connectors are connected to the other end of the flexible printed circuit board  16 , for example. When the front panel  14  is coupled to the enclosure  11 , the receptacle components  17  of the MS connectors protrude forward of the front panel  14  out of openings  18 , respectively, formed in the front panel  14 . The protruding receptacle components  17  are designed to receive plug components, not shown, of the MS connectors. 
     As shown in FIG. 2, the flexible printed circuit board  16  comprises a flexible substrate  21  on which the receptacle components  17  of the MS connectors are mounted. The flexible substrate  21  may be made from a synthetic resin material. At least six rigid backing plate members  22  are adhered to the flexible substrate  21 , for example. Each of the backing plate members  22  may be superposed on either of the opposite surfaces of the flexible substrate  21 . The backing plate members  22  are designed to back and support corresponding sections of the flexible substrate  21 . The respective backing plate members  22  are adapted to prevent deformation of the corresponding sections. Parallel six folds  23  serve to define the sections on the flexible substrate  21 . The substrate  21  backed by the backing plate members  22  is combined with a metallic support member  24  after being bent at the folds  23 . For example, screws  25  may be employed to fix the flexible substrate  21  to the support member  24 . The flexible printed circuit board  16  fixed to the support member  24  is finally assembled into the enclosure  11 . 
     FIG. 3 schematically illustrates the exploded view of the substrate  21 . A conductive pattern  27  is printed on the surface of the flexible substrate  21  at an end of the flexible substrate  21 . The conductive pattern  27  is designed to realize the connecting mechanism according to the present invention, namely, a surface connection. The conductive pattern  27  is electrically connected to the receptacle components  17  at the other end of the flexible substrate  21  through a printed wiring pattern, not shown, extending between the opposite longitudinal ends of the flexible substrate  21 . When electric connection is established between the conductive pattern  27  and the back panel  12  through the surface connection, the receptacle components  17  are allowed to exchange electric signals with the back panel  12  through the conductive pattern  27  and the printed wiring pattern. 
     Referring also to FIG. 4, a card slot or connector  31  may be attached to the flexible substrate  21  for receiving a memory card  30  such as a flash memory card. The card slot  31  may be mounted on the surface of the flexible substrate  21 . Electric connection is likewise established between the card slot  31  and the back panel  12  through the conductive pattern  27  and the printed wiring pattern. In this manner, any electronic parts may be, in addition to the aforementioned MS connectors and card slot, mounted on the flexible substrate  21 . On the contrary, no electronic parts may be mounted on the flexible substrate while allowing only printed wiring pattern to spread over the surface of the flexible substrate  21 . 
     As shown in FIG. 5, protection film pattern  32  is formed, at least partly, on the surface of the conductive pattern  27 . The protection film pattern  32  is adapted to cover over not only the conductive pattern  27  but also the surface of the flexible substrate  21 . For example, a cured photoresist film may result in the protection film pattern  32 . In addition, the protection film pattern  32  also covers over the printed wiring pattern connecting the conductive pattern  27  to the receptacle components  17 . The conductive pattern  27  and the printed wiring pattern covered with the protection film pattern  32  is reliably prevented from corrosion and oxidation. 
     As shown in FIG. 5, the conductive pattern  27  comprises contact pads  33  formed on the surface of the flexible substrate  21 . The aforementioned protection film pattern  32  is not designed to cover over the contact pads  33 . The contact pads  33  is adapted to keep exposed on the surface of the flexible substrate  21 . Solder bumps  34  are formed on the respective contact pads  33  so as to provide a conductive contact of the present invention. The solder bumps  34  are designed to protrude from the surface of the conductive pattern  27 , namely, the contact pads  33  so as to reach a level above the surface of the protection film pattern  32 . 
     For example, assume that an anisotropic conductive rubber plate  36  and the aforementioned flexible printed circuit board  16  are sequentially superposed on the surface of the back panel  12 , as shown in FIG. 6. A plurality of conductive contact pads  35  are arranged on the surface of the back panel  12 . When the superposed anisotropic conductive rubber plate  36  and flexible printed circuit board  16  are fixed by screws  37  on the back panel  12 , the assembly of a connecting mechanism is completed according to the present invention. 
     The anisotropic conductive rubber plate  36  as an elastic conductive member comprises, for example, an elastic insulation plate  38  made of silicon, and a plurality of brass wires  39  embedded in the elastic insulation plate  38 , as shown in FIG.  5 . The respective brass wires  39  are designed to penetrate through the elastic insulation plate  38 . The opposite ends of the brass wire  39  are adapted to protrude from the opposite surfaces of the elastic insulation plate  38 . When the opposite ends of the brass wire  39  contact the conductive contact pad  35  on the surface of the back panel  12  and the solder bump  34  on the corresponding contact pad  33  on the flexible printed circuit board  16 , electric connection is established between the contact pads  33 ,  35 . Since the length of the respective brass wires  39  can relatively be reduced, the space can be reduced between the back panel  12  and the flexible printed circuit board  16 . Accordingly, electric connection can be established between the back panel  12  and the flexible printed circuit board  16  in a smaller space. 
     As described above, the top ends of the solder bumps  34  on the contact pads  33  are designed to reach the level above the protection film pattern  32  in the area of the conductive layer  27 . Accordingly, the connecting mechanism in the above manner allows the brass wires  39  to first contact the corresponding solder bumps  34  on the contact pads  33  when the anisotropic conductive rubber plate  36  is superposed on the flexible printed circuit board  16 . The brass wires  39  are reliably prevented from collision against the protection film pattern  32 . Signal channels are surely established to lead from the contact pads  33  to the brass wires  39 . Without the solder bumps  34 , the brass wires  39  first collide against the protection film pattern  32  at locations off the contact pads  33 ,  35 , since the brass wires  39  are uniformly arranged in the elastic insulation plate  38  over a broader area. No solder bumps  34  may result in the brass wires  39  spaced apart from the contact pads  33  even when the anisotropic conductive rubber plate  36  is superposed on the conductive pattern  27 , so that no electric connection is established between the contact pads  33 ,  35 . 
     The aforementioned connecting mechanism may employ an anisotropic conductive rubber plate  44  of the type as shown in FIG. 7 in place of the aforementioned anisotropic conductive rubber plate  36 . The anisotropic conductive rubber plate  44  as an elastic conductive member comprises an elastic insulation plate  42  having a plurality of through holes  41 , and one or more detachable conductive pins  43  selectively received in the through holes  41 . The opposite longitudinal ends of the through hole  41  are designed to open at the opposite surfaces of the elastic insulation plate  42 . The through holes  41  may be arranged regularly and uniformly all over the entire elastic insulation plate  42 . 
     The anisotropic conductive rubber plate  44  in this manner allows designation or selection of the operative through holes  45  receiving the detachable conductive pins  43 , as shown in FIG. 8, for example. Such operative through holes  45  should be aligned with the conductive pattern  27 , namely, the contact pads  33  exposed at the breaks of the protection film pattern  32  when the anisotropic conductive rubber plate  44  is superposed on the flexible printed circuit board  16 . No detachable conductive pins  43  are inserted in the through holes, namely, the inoperative or additional through holes  46  opposed to the surface of the protection film pattern  32 . Such selection of the operative through holes  45  serves to reliably prevent the detachable conductive pins  43  from colliding against the protection film pattern  32  when the anisotropic conductive rubber plate  44  is superposed on the surface of the flexible printed circuit board  16 . The detachable conductive pins  43  in the operative through holes  45  are reliably allowed to first contact the contact pads  33  in the conductive pattern  27 . Electric connection can reliably be established between the contact pads  33  and the detachable conductive pins  43 . Note that it is harmless to locate the inoperative through holes  46  at the aforementioned positions opposed to the protection film pattern  32 , at positions aligned with the contact pads  33 ,  35  which are not expected to be connected, at positions opposed to the conductive pattern  27 , and the like. 
     Since the detachable conductive pins  43  are selectively inserted into the through holes  41  uniformly arranged in the elastic insulation plate  42 , the contact pads  33 ,  35  may be arranged at any locations corresponding to the through holes  41 . Any combination of the through holes  41  can be accepted. The anisotropic conductive rubber plate  44  can be employed to connect the contact pads  33 ,  35  in various arrangement to each other without redesigning the elastic insulation plate  42  and the detachable conductive pin  43 . In addition, since the detachable conductive pins  43  can easily be relocated from the operative through hole  45  to the inoperative through hole  46 , the anisotropic conductive rubber plate  44  is allowed to easily change the pattern of electric connection between the first and second printed circuit boards, namely, the back panel  12  and the flexible printed circuit board  16 . On the contrary, all of through holes  41  may be designed to receive the detachable conductive pins  43  from the beginning. 
     In general, the flexible printed circuit board  16  is not allowed to comprise a large number of insulation layers alternated with conductive layers, as compared with a rigid printed circuit board such as the back panel  12 . An increased number of layers are supposed to cause not only the insulation layer or film to peel off the conductive layer but also circuit or wiring patterns within the conductive layer to break down at a higher probability when the flexible printed circuit board  16  is bent or folded. Less layers tend to result in employment of a printed circuit or wiring pattern extending on the exposed surface of the substrate  21 . The connecting mechanism according to the present invention is in particular very useful to a printed circuit board comprising less or limited layers.