Abstract:
A surface-mount inductor including: a coil formed by winding insulated wire and bringing out lead ends therefrom; and a plurality of premolded bodies for accommodating the coil inside, thereby thermopressing to form, wherein a pair of metal terminals is embedded laterally on the outer surface of the surface-mount inductor, and the lead ends of the coil are brought out from the bottom surface of the surface-mount inductor and laterally laid on the outer surface of the metal terminals, as well as a method for manufacturing the same.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2014-258141, filed on Dec. 20, 2014, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a surface-mount inductor and a method for manufacturing the same. 
         [0004]    2. Description of the Related Art 
         [0005]    As shown in JP2010-245473 (patent document 1), an inductor having a coil embedded in magnetic resin, which is a mixture of magnetic powder and resin, has been widely used. A molded coil which is embedded in magnetic resin is configured as a surface-mount inductor which is built by forming electrodes for mounting on a printed wiring board. The electrodes being made by painting an electric conductive paste which is made by dispersing metal particles such as Ag in thermosetting resin such as epoxy resin, or adhering metal terminals to the molded coil. 
       SUMMARY OF THE INVENTION 
     Problem to be solved by the Invention 
       [0006]    As the electric conductive paste is expensive, it is costly to apply it over a large area. Thus, metal plates are widely used instead as external terminals of large-size surface-mount inductors. Methods for manufacturing such surface-mount inductors are disclosed in JP2010-087240 (patent document 2) and JP2011-054713 (patent document 3), for example. 
         [0007]    The patent document 2 discloses a method for manufacturing a surface-mount inductor in which a molded coil is formed by embedding a coil in magnetic resin with exposed lead ends brought out therefrom, preliminarily folding metal terminals in a predetermined shape, attaching the metal terminals to the molded coil, and electrically connecting the lead ends and the metal terminals by soldering or welding. 
         [0008]    The patent document 3 discloses another method for manufacturing a surface-mount inductor in which lead ends and metal terminals are connected by soldering or welding, the lead ends and a part of a metal plate including the connecting portion thereof are embedded in magnetic resin to form a molded coil, the metal plate exposed from the molded coil being folded along the outermost turn of the molded coil to form metal terminals. 
         [0009]    The method for manufacturing the surface-mount inductor in the patent document 2 has some issues. One of them is the large size of the surface-mount inductor due to the metal terminals being mounted after the completion of the coil. The size of the inductor varies with the thickness of the metal terminals. Another issue is the terminals falling off due to the adherence of the adhesive being deteriorated when soldering the metal terminals onto the molded coil. 
         [0010]    Further, the method for manufacturing the surface-mount inductor in the patent document 3 has a problem in that the portion connecting the metal terminals and the lead ends is embedded in the molded coil so that it is not possible to visually confirm the connecting state. 
       Means for Solving the Problem 
       [0011]    A surface-mount inductor according to the present invention is characterized by a surface-mount inductor including: a coil formed by winding insulated wire and bringing out lead ends therefrom; and a premolded body formed by thermopressing into a form a mixture of magnetic powder and thermosetting resin to accommodate the coil whose lead ends are brought out therefrom; comprising 
         [0012]    a pair of metal terminals made of deformable plates, and arranged on the outer exposed surface of the premolded body; and 
         [0013]    a coil the lead ends of which are embedded at the outer exposed surface. 
         [0014]    A method for manufacturing a surface-mount inductor according to the present invention is characterized by the steps of: 
         [0015]    mixing magnetic powder and thermosetting resin so as to produce a combination-type premolded body of predetermined shape; and 
         [0016]    preparing a coil formed by winding an insulated wire, accommodating the coil in the combination-type premolded body with the lead ends of the coil brought out therefrom, arranging the metal terminals on the outer surface of the premolded body, arranging the lead ends on the outer surface of the metal terminals, and thermopressing the premolded body into form. 
       Effect of the Invention 
       [0017]    According to the surface-mount inductor of the present invention, a surface-mount inductor may be manufactured without using any adhesive, thus metal terminals do not fall off since the metal terminals are partially embedded in the resin. And, the portion connecting the metal terminals and the lead ends is exposed on the surface of the surface-mount inductor so that the connecting state may be visually confirmed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a broken perspective view showing the structure of a surface-mount inductor according to the present invention. 
           [0019]      FIG. 2  is a development view of the metal terminals in the structure of  FIG. 1 . 
           [0020]      FIG. 3A  through  FIG. 3F  show steps in the manufacturing process of the surface-mount inductor according to the present invention. 
           [0021]      FIG. 4A  is a cross sectional view of the surface-mount inductor before the forming process according to the present invention. 
           [0022]      FIG. 4B  is a cross sectional view of the surface-mount inductor after the forming process according to the present invention. 
           [0023]      FIG. 5  is an enlarged cross sectional view of the surface-mount inductor according to the present invention. 
           [0024]      FIG. 6  is a photograph showing a cross sectional view of the surface-mount inductor according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    The surface-mount inductor according to the present invention is described below, referring to  FIGS. 1-6 . 
         [0026]      FIG. 1  is an exploded perspective view from bottom up describing the structure of the surface-mount inductor of the present invention, and  FIG. 2  is a development view of the metal terminals in the structure of  FIG. 1 . 
         [0027]    The surface-mount inductor  10  includes: premolded bodies  20 ,  30  formed by pressure forming magnetic resin, which is a mixture of magnetic powder and thermosetting resin such as epoxy resin; coil  40  formed by winding an insulated wire; and a pair of metal terminals  50   a ,  50   b  formed by punching a thin metal plate and by folding in a predetermined shape which are connected with both of the lead ends  41   a ,  41   b , respectively. 
         [0028]    The premolded body  20  has a rectangular parallelepipedic profile, a cylindrical pot-like space inside, and a protruded portion  21  provided at the center of the bottom surface inside the space. The premolded body  20  has an E-shaped longitudinal section, and the outer wall thereof is partially cut out at the corners to make open portions  22   a ,  22   b.    
         [0029]    The premolded body  30  fitted with the premolded body  20  is substantially rectangular in plan view and the corners  31   a ,  31   b  are chamfered. 
         [0030]    The coil  40  is wound to be cylindrical in shape, and the lead ends are brought out from the outermost turn in radial directions outwardly and folded about 90° in the direction of the center axis of the coil  40 . 
         [0031]    As shown in  FIG. 2 , the metal terminals  50   a  and  50   b  consisting of a metal plate having an L-shaped cross section, includes: a bottom surface  51 ; and a side surface  52  formed by folding at 90° along the broken line close to the center. The side surface  52  has tongue-like embedding portions  53  formed by folding at 90° in the same direction as that of the bottom surface  51  at the position indicated by the other broken line closer to the end, and a cutout  54   a  at the lower part in  FIG. 2 . The metal terminals  50   a  and  50   b  are symmetrical, with the metal terminal  50   b  having a cutout  54   b  similarly to the metal terminal  50   a.    
         [0032]    The method for manufacturing the surface-mount inductor according to the present invention is described referring sequentially to  FIGS. 3A through 3F . 
         [0033]      FIG. 3A : The coil  40  is accommodated in the premolded body  20  in a manner that the lead ends  41   a ,  41   b  are placed at the open portions  22   a ,  22   b.    
         [0034]      FIG. 3B : The metal terminals  50   a ,  50   b  are arranged at both sides of the premolded body  30  in a manner that the corner portion  31   a  is in line with the cutout  54   a  and the corner portion  31   b  is in line with the cutout  54   b , respectively. 
         [0035]      FIG. 3C : The premolded body  30  is overlapped with the premolded body  20  in a manner that the lead ends  41   a ,  41   b  are brought out from the cutouts  54   a ,  54   b  of the metal terminals  50   a ,  50   b.    
         [0036]      FIGS. 3D, 3E : The lead ends  41   a ,  41   b  brought out from the premolded body  30  are folded at the base portions  42 ,  42  which are exposed from the premolded body  30 , and arranged along the upper surface of the metal terminals  50   a ,  50   b . The surface-mount inductor in  FIG. 3E  is referred to as “pre-formed surface-mount inductor  10 A” hereinbelow. 
         [0037]      FIG. 3F : The pre-formed surface-mount inductor  10 A is thermopressed (“forming” hereinbelow) in the mold to form “formed surface-mount inductor  10 B (before connecting to terminals)”. 
         [0038]    Processing the formed surface-mount inductor  10 B by dip soldering, the insulation layer of the lead ends  41   a ,  41   b  are removed and at the same time the lead ends  41   a ,  41   b  and the metal terminals  50   a ,  50   b  are electrically connected to form the surface-mount inductor  10  as a formed article. Here, dip soldering may be replaced by thermocompression bonding. 
         [0039]      FIG. 4A  is a longitudinal sectional view of the pre-formed surface-mount inductor  10 A (along section A-A in  FIG. 3E ), and  FIG. 4B  is a longitudinal sectional view of the formed surface-mount inductor  10 B (along section A-A in  FIG. 3F ). 
         [0040]    As shown in  FIG. 4A , the pre-formed surface-mount inductor  10 A has the lead ends  41   a ,  41   b  mounted on the metal terminals  50   a ,  50   b , and there are vacant spaces  60  between the coil  40  and the premolded bodies  20 ,  30  and vacant spaces of the open portions  22   a ,  22   b  ( FIG. 1 ,  FIG. 3A-3E ) inside the premolded bodies  20 ,  30 . 
         [0041]    As shown in  FIG. 4B , the surface-mount inductor  10 B is so configured that the premolded bodies  20 ,  30  are pressed as to inversely deform so as to fill the vacant spaces, and in turn the embedding portions  53  ( FIG. 2 ) are buried in the mold coil  11 . The metal terminals  50   a ,  50   b  are embedded into the mold coil  11  to a depth corresponding to their thickness, and the lead ends  41   a ,  41   b  are embedded into the metal terminals  50   a ,  50   b  to a depth equal to their diameter. The thermosetting resin is then completely hardened by heating which result in the surface-mount inductor  10  having a flat surface. 
         [0042]      FIG. 5  is an enlarged-sectional view showing the longitudinal section (section B-B in  FIG. 3F ) around the base portion  42  of the coil  40 . 
         [0043]    As shown in  FIG. 5 , “springback” (effect) in the coil  40  is moderated because the outer periphery (“C” in  FIG. 5 ) of the lead ends  41   a  is filled with resin around the base portion  42 . 
         [0044]    Since the metal terminals  50   a ,  50   b  are preferably thin so that the lead ends  41   a ,  41   b  are easily embedded therein, the material of the metal terminals  50   a ,  50   b  is preferably soft so as to easily deform when the lead ends  41   a ,  41   b  embed therein, tough pitch copper being preferable to phosphor bronze thus the use of relatively soft normalized hardness of less than 1/2H, for example, thin metal terminals  50   a ,  50   b  is ideal. 
         [0045]      FIG. 6  is a photograph showing the cross sectional view of the surface-mount inductor manufactured by the method described above. The surface-mount inductor is configured to have a 6 mm width×6 mm length×3 mm height, with the diameter of the wire being 0.23 mm, the thickness of the metal terminals made of phosphor bronze being 0.08 mm, and the forming pressure being 10 kg/cm 2 . 
         [0046]    As shown in  FIG. 6 , the lead ends sink into the metal terminals, and the metal terminals are embedded into the surface-mount inductor in their thickness direction. 
         [0047]    The surface-mount inductor described above enables preventing the falling off of the metal terminals because the metal terminals are partially embedded in the mold coil, and the state of the connection may be visually recognized. 
         [0048]    Further, the metal terminals do not increase the size of the surface-mount inductor because the lead ends sink in the metal terminals and in turn the metal terminals sink in the mold coil. 
         [0049]    Furthermore, since the base portions of the lead ends are also embedded in resin, the position shift caused by the spring back before electrically connecting the lead ends to the metal terminals, and the loss of connection between the lead ends and the metal terminals when melting solder to solder on the mounting board, is minimized. 
         [0050]    In the process of forming the premolded body, resin from the magnetic resin permeates the premolded body and covers a part of the bottom surface thus obstructing the mounting of the surface-mount inductor. In such a case, the premolded body should be processed by means of barrel polishing and the like to remove the permeating resin. 
         [0051]    In addition, the portion embedding the metal terminals may be selected to have, for example, a wide-top shape or a hollow structure in order to provide a surface-mount inductor with metal terminals which do not easily fall off therefrom. 
       EXPLANATION OF CODES 
       [0052]      10  surface-mount inductor 
         [0053]      10 A pre-formed surface-mount inductor 
         [0054]      10 B formed surface-mount inductor 
         [0055]      11  mold coil 
         [0056]      20 ,  30  premolded body 
         [0057]      21  protruded portion 
         [0058]      22   a ,  22   b  open portion 
         [0059]      31   a ,  31   b  chamfered portion 
         [0060]      40  coil 
         [0061]      41   a ,  41   b  lead end 
         [0062]      42  base portion 
         [0063]      50   a ,  50   b  metal terminal 
         [0064]      51  bottom surface 
         [0065]      52  side surface 
         [0066]      53  embedded portion 
         [0067]      54  cutout