Patent Publication Number: US-9837195-B2

Title: Mounting structure of flexible inductor and electronic device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mounting structure of a flexible inductor that connects two circuits and an electronic device that includes the mounting structure. 
     2. Description of the Related Art 
     In the related art, an electronic device that uses a high-frequency signal often employs a structure in which the electronic device includes members of a mounting circuit, such as a plurality of substrates, in a housing of the electronic device, and in which the members are connected by flexible cables. In addition, there is a case where a planar coil-shaped conductive pattern is provided as a portion of a flexible cable as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2011-18505. 
     For example, in a small-sized communication terminal device, metallic objects, such as a ground conductor, a battery pack, and a shield case, are densely mounted. When a cable that includes a coil-shaped conductive pattern is mounted in such a small-sized electronic device, metallic parts (metallic objects) are forced to be positioned in the vicinity of the coil-shaped conductive pattern. As a result, an eddy current is generated in the metallic parts, and accordingly, the Q value of an inductor is decreased. 
     The influence of the metallic parts, which are positioned in the vicinity of the coil-shaped conductive pattern, can be reduced to a minimum value by forming a closed magnetic circuit structure by covering the coil-shaped conductive pattern with a magnetic material, such as ferrite, like the flexible cable described in Japanese Unexamined Patent Application Publication No. 2011-18505. 
     However, in the case of such a structure that includes a magnetic material, management and manufacturing processes for adding the magnetic material become complex, and in addition, the size of a flexible cable, which would have been thin, becomes large. In addition, in the case where a ceramic-based ferrite is used as the magnetic material, the flexibility of the flexible cable is degraded. 
     SUMMARY OF THE INVENTION 
     Accordingly, preferred embodiments of the present invention provide a mounting structure of a flexible inductor in which the flexible inductor is less likely to be influenced by a metallic part even if the flexible inductor is positioned in the vicinity of the metallic part, and also provide an electronic device that includes such a mounting structure. 
     A mounting structure includes a housing and a flexible inductor including a sheet-shaped flexible base member including an inductor, the sheet-shaped flexible base member including a first input/output terminal, a second input/output terminal, and a sheet-shaped and coil-shaped conductive pattern that includes a first end connected to the first input/output terminal, and a second end connected to the second input/output terminal, and that is wound several times. The flexible inductor is positioned near a metallic part disposed in the housing, or a metallic portion of the housing. The flexible inductor is bent and mounted in the housing in such a manner that one side of the coil-shaped conductive pattern that is close to the metallic part or the metallic portion is on an inner side of a bent portion of the flexible inductor. 
     The flexible base member may preferably include a first main surface and a second main surface, and the first main surface may preferably be spaced further apart from the metallic part or the metallic portion than the second main surface, and the first main surface may preferably include the coil-shaped conductive pattern. 
     An electronic device includes a flexible inductor including a sheet-shaped flexible base member including a first input/output terminal, a second input/output terminal, and a sheet-shaped and coil-shaped conductive pattern that is wound a plurality of times, and a housing configured to accommodate the flexible inductor. The flexible inductor is positioned near a metallic part disposed in the housing, or a metallic portion of the housing. The flexible inductor is bent and mounted in the housing in such a manner that one side of the coil-shaped conductive pattern that is close to the metallic part or the metallic portion is on an inner side of a bent portion of the flexible inductor. 
     The metallic part or the metallic portion may preferably be a ground electrode of a wiring board disposed in the housing. 
     According to various preferred embodiments of the present invention, a magnetic field on the inner side of a flexible inductor, which is bent, is weak relative to a magnetic field on the outer side of the bent flexible inductor, and even if a metallic part is present on the inner side of the bent flexible inductor, the flexible inductor is less likely to be influenced by the metallic part. Therefore, a significant decrease in the Q value of the flexible inductor due to the metallic part, which is positioned in the vicinity of the flexible inductor, is significantly reduced or prevented. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a flexible inductor according to a first preferred embodiment of the present invention. 
         FIG. 2A  is a plan view of the flexible inductor, and  FIG. 2B  is a sectional view taken along line A-A of  FIG. 2A . 
         FIG. 3  is a sectional view of the flexible inductor at a mounting position. 
         FIG. 4  is a plan view of an electronic device that includes flexible inductors disposed in a housing of the electronic device. 
         FIGS. 5A and 5B  are conceptual diagrams illustrating the intensity of a magnetic field generated by a conductive pattern of the flexible inductor, the conductive pattern having a rectangular spiral shape. 
         FIG. 6A  is a plan view of a flexible inductor according to a second preferred embodiment of the present invention, and  FIG. 6B  is a sectional view taken along line A-A of  FIG. 6A . 
         FIG. 7  is a sectional view of the flexible inductor at a mounting position. 
         FIG. 8  is a conceptual diagram illustrating the intensity of a magnetic field generated by a conductive pattern of the flexible inductor. 
         FIG. 9  is an exploded perspective view of a flexible inductor according to a third preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Preferred Embodiment 
       FIG. 1  is an exploded perspective view of a flexible inductor  101  according to a first preferred embodiment of the present invention.  FIG. 2A  is a plan view of the flexible inductor  101 , and  FIG. 2B  is a sectional view taken along line A-A of  FIG. 2A . 
     The flexible inductor  101  includes a flexible base member  10  that preferably is a multilayer body, which includes flexible resin base members  11  and  12 , and various conductive patterns that are provided on the resin base members  11  and  12 . 
     The resin base member  11  preferably has a rectangular (elongated) planar shape, and a first input/output terminal  41  and a second input/output terminal  42  are respectively provided on a first end portion and a second end portion of a top surface of the resin base member  11 . In addition, wiring patterns  21  and  22  are provided on the top surface, and a conductive pattern having a rectangular spiral shape is provided on a substantially central portion of the top surface. A wiring pattern  23  is provided on a bottom surface of the resin base member  12 . 
     The wiring pattern  21  connects an outer periphery end of the conductive pattern  31  and the first input/output terminal  41 . A first end of the wiring pattern  22  is connected to the second input/output terminal  42 . The wiring pattern  23  connects an inner periphery end of the conductive pattern  31  and a second end of the wiring pattern  22  via interlayer connection conductors (via hole conductors)  121  and  122 , which are provided in the resin base members  11  and  12 . 
     Each of the resin base members  11  and  12  preferably is formed by, for example, molding a resin, such as a liquid crystal polymer (LCP) or a thermoplastic polyimide, into the form of a sheet and corresponds to the “flexible base member”. The conductive pattern  31  preferably having a rectangular spiral shape is formed by, for example, patterning a metal thin film, such as a Cu foil or an Al foil, into a spiral shape and corresponds to the “coil-shaped conductive pattern”. The conductive pattern  31  preferably having a rectangular spiral shape also has flexibility. 
     A resist layer  61  is formed in a region of the top surface of the resin base member  11  excluding regions in which the first input/output terminal  41  and the second input/output terminal  42  are located. A resist layer  62  is formed over the entire bottom surface of the resin base member  12 . Note that the resist layer  62  need not be provided. In addition, the resist layer  62  is also flexible, and accordingly, the entire flexible inductor  101  has flexibility. 
     The flexible base member  10 , which is illustrated in  FIGS. 2A and 2B , is formed preferably by stacking the resin base members  11  and  12 , which are illustrated in  FIG. 1 , one on top of the other. The conductive pattern  31  having a spiral shape is a so-called several-turn planar coil pattern that is wound several times, and a coil axis of the conductive pattern  31  is oriented in a perpendicular or substantially perpendicular direction with respect to a surface of the flexible base member  10 . 
     The conductive pattern  31 , the first and second input/output terminals  41  and  42 , the wiring patterns  21  to  23  each include a metal foil such as, a Cu foil or an Al foil, and are each harder than the resin base members  11  and  12 , and thus, in  FIG. 2B , the region in which the first input/output terminal is located is a relatively rigid region RR due to the presence of the first input/output terminal  41 , which has a large area. Similarly, the region in which the second input/output terminal  42  is located is another relatively rigid region RR due to the presence of the second input/output terminal  42 , which has a large area. The region other than the rigid regions RR is a flexible region FR. 
       FIG. 3  is a sectional view of the flexible inductor  101  at a mounting position.  FIG. 4  is a plan view of an electronic device that includes flexible inductors  101 A and  101 B disposed in a housing of the electronic device. 
     As illustrated in  FIG. 3 , printed wiring boards  71  and are different circuit boards like, for example, an antenna substrate and an RF circuit board. Connection electrodes  51  and  52  are respectively provided on the printed wiring boards  71  and  72 , and the first and second input/output terminals  41  and  42  of the flexible inductor  101  are respectively soldered to the connection electrodes  51  and  52 . Note that the method of connecting the flexible inductor  101  to a substrate may be connector connection using a surface mount connector. 
     A ground electrode  81  is provided in the printed wiring board  71 . The connection electrode  51  on the printed wiring board  71  and the connection electrode  52  on the printed wiring board  72  are positioned at different levels, and the flexible inductor  101  is mounted in a state where the conductive pattern  31 , which is a coil-shaped conductive pattern, is bent. In other words, the coil axis of the conductive pattern  31  is bent in such a manner that one side of the coil axis closer to the ground electrode  81  of the printed wiring board  71  than the other side is the inner side of the flexible inductor  101 , which is bent. 
     In the example illustrated in  FIG. 4 , the printed wiring boards  71  and  72 , a printed wiring board  73 , a battery pack  83 , and the like are accommodated in a housing  91  of a communication terminal device, such as a smartphone or a tablet terminal, or the like. The printed wiring board  73  is provided with an antenna  88 . The printed wiring boards  71  and  72  are connected to each other by a flexible inductor  101 A, and the printed wiring boards  71  and  73  are connected to each other by a flexible inductor  101 B. The structure of each of the flexible inductors  101 A and  101 B is the same as that of the flexible inductor  101  illustrated in  FIG. 1  and  FIGS. 2A and 2B . 
       FIGS. 5A and 5B  are conceptual diagrams illustrating the intensity of a magnetic field generated by the conductive pattern  31  of the flexible inductor  101 , the conductive pattern  31  preferably having a rectangular spiral shape.  FIG. 5A  is a sectional view of the flexible inductor  101  with magnetic equipotential lines representing the intensity of the magnetic field generated by the conductive pattern  31 , and  FIG. 5B  is a diagram illustrating four sides  31   a ,  31   b ,  31   c , and  31   d  of the conductive pattern  31 . 
     The sides  31   a  and  31   b  of the conductive pattern  31  are curved as a result of the flexible inductor  101  being bent. Consequently, a magnetic field generated by a current that flows through the sides  31   a  and  31   b  of the conductive pattern  31  will be expanded to the inner side of the bent flexible inductor  101  to only a small extent and will be expanded to the outer side of the bent flexible inductor  101  to a relatively large extent. This will become notable as the number of times the conductive pattern  31  is wound (the number of turns of the conductive pattern  31 ) increases, and thus, it is preferable that the number of times the conductive pattern  31  is wound be two or more, or more preferably, three or more. Therefore, the magnetic field generated by the conductive pattern  31  will not be strongly coupled with a metallic part, such as a ground electrode, and an eddy current that will be generated in the metallic part is small. Accordingly, a decrease in the Q value of the flexible inductor  101  is significantly reduced or prevented. 
     Second Preferred Embodiment 
       FIG. 6A  is a plan view of a flexible inductor  102  according to a second preferred embodiment of the present invention, and  FIG. 6B  is a sectional view taken along line A-A of  FIG. 6A . 
     The flexible inductor  102  includes various conductive patterns provided on a flexible base member  13 , which is a flexible resin base member. 
     A first input/output terminal  41 , a second input/output terminal  42 , and a wiring pattern  22  are provided on a top surface of the flexible base member  13 . A wiring pattern  21 , and a conductive pattern  31 , which preferably has a rectangular spiral shape, are provided on a bottom surface of the flexible base member  13 . In addition, an interlayer connection conductor, such as a plated through hole or a via hole conductor, that connects the wiring pattern  21  and the first input/output terminal  41  and an interlayer connection conductor, such as a plated through hole or a via hole conductor, that connects the wiring pattern  22  and the conductive pattern  31  are provided in the flexible base member  13 . 
     As described above, a single-layer flexible resin base member that does not have a multilayer structure may be used as the flexible base member  13 . 
       FIG. 7  is a sectional view of the flexible inductor  102  at a mounting position.  FIG. 8  is a conceptual diagram illustrating the intensity of a magnetic field generated by the conductive pattern  31  of the flexible inductor  102 . 
     A ground electrode  81  is provided in the printed wiring boards  71  and  72 . Connection electrodes  51  and  52  are respectively provided on the printed wiring boards  71  and  72 , and the first and second input/output terminals  41  and  42  of the flexible inductor  102  are respectively soldered to the connection electrodes  51  and  52 . 
     Similar to the flexible inductor  101  of the first preferred embodiment, as a result of the flexible inductor  102  being bent, a magnetic field generated by the conductive pattern  31  will not be strongly coupled with a metallic part, such as a ground electrode. Therefore, an eddy current that will be generated in the metallic part is small, and a decrease in the Q value of the flexible inductor  102  is significantly reduced or prevented. 
     In particular, since the conductive pattern  31  is provided on one of main surfaces of the flexible base member  13  that is positioned farther from the metallic part, the conductive pattern  31  is at a position that is spaced apart from the metallic part, and a decrease in the Q value of the flexible inductor  102  is more effectively significantly reduced or prevented. 
     Third Preferred Embodiment 
       FIG. 9  is an exploded perspective view of a flexible inductor  103  according to a third preferred embodiment of the present invention. Unlike the flexible inductor  101  of the first preferred embodiment illustrated in  FIG. 1 , conductive patterns  31  and  32  each preferably having a rectangular spiral shape are respectively formed on resin base members  11  and  12 . An inner periphery end of the conductive pattern  31  and an inner periphery end of the conductive pattern  32  are connected to each other by a via hole conductor  122 . An outer periphery end of the conductive pattern  32  and an end of wiring pattern  21  are connected to each other by a via hole conductor  121 . In other words, the conductive patterns  31  and  32 , each of which has a coil shape, define a multilayer coil pattern. The rest of the configuration of the flexible inductor  103  is the same as that of the flexible inductor  101  described in the first preferred embodiment. 
     In the flexible inductor  103  of the third preferred embodiment, the opening diameter of a coil, which is the conductive pattern  31 , is larger than the opening diameter of a coil, which is the conductive pattern  32 . The conductive pattern  31 , which is the coil having a large opening diameter, is located closer to a metallic part than the conductive pattern  32 , and is to be located on the inner side of the flexible inductor  103  when the flexible inductor  103  is bent. With this configuration, an advantageous effect in which a magnetic field generated by the coil expands in a direction toward the outer side of the bent flexible inductor  103  to a larger extent than in a direction toward the inner side of the bent flexible inductor  103  is obtained. 
     Note that, although the case where the flexible inductor  101  is preferably positioned in the vicinity of a metallic part, which is disposed in a housing, has been described in some of the above preferred embodiments, the present invention can also be applied to the case where the metallic part is a portion of a metallic housing. In addition, the conductive pattern  31 , which is the coil-shaped conductive pattern, may be a single-function inductance element as in the preferred embodiments, and alternatively, for example, the flexible inductor  101  may further include a capacitance element and define a resonance circuit together with the coil-shaped conductive pattern. Alternatively, the flexible inductor  101  may be used as a coil antenna of an HF communication system. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.