Abstract:
An inexpensive shielded-type inductor is disclosed to include a first powder compact member, a coil embedded in the first powder compact member with the bottom side of the coil body thereof kept in flush with the bottom side of the first powder compact member and two metal terminals thereof extending from the two opposite ends of the coil body to the outside of the first powder compact member, and a second powder compact member bonded to the bottom side of the first powder compact member to determine the inductance value of the inductor subject to the thickness of the second powder compact member and to protect the inductor against external environmental factors.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to inductors and more particularly, to a shielded-type inductor, which is inexpensive to manufacture and free from interference of external environmental factors and, allows fine adjustment of the inductance value by means of controlling the thickness of the second powder compact member thereof. 
         [0003]    2. Description of the Related Art 
         [0004]    For electronic products providers, the common way to survive in the competitive market is to lower the product cost, reduce the product size, and improves the product quality. An inductor is a basic component in electronic products. Information, communication and consumers electronic products use a big amount of inductors. To fit the small-sized characteristic of electronic products, powder core type small size and low profile inductors for big current application are required. 
         [0005]      FIG. 1  illustrates the structure of a conventional inductor. According to this prior art design, the inductor  90  is comprised of a powder compact member  91 , an air coil  92 , and two terminals  93  and  94 . The coil  92  is embedded in the powder compact member  91 . The two terminals  93  and  94  are respectively connected to the two opposite ends of the coil  92  and extended out of the powder compact member  91 . During fabrication, the two terminals  93  and  94  are respectively connected to the two opposite ends of the coil  92 , and then the coil  92  with the two terminals  93  and  94  are put in a mold, and a certain amount of magnetic powder material for powder compact member  91  is fed into the mold, and then the mold is compressed to compact the magnetic powder material and the coil  92 , thereby forming the desired inductor  90 . 
         [0006]    After fabrication, the inductance value of the inductor is fixed, i.e., the inductance value of the inductor is not adjustable after fabrication. If the inductance value is not in conformity with the designed specification, the worker cannot adjust the inductance value of the inductor, and the inductor cannot be used. Therefore, the yield rate according to this inductor fabrication method is low. 
         [0007]    The quality of the inductor made according to the aforesaid fabrication method is mainly determined subject to the quality of the magnetic powder material. Therefore, excellent magnetic powder material must be used for making high-quality inductors. However, using excellent magnetic powder material relatively increases the inductor&#39;s manufacturing cost, in consequence, lowers the supplier&#39;s competitive powder. 
         [0008]    Further, after an inductor is made, a product specification and/or company&#39;s logo or trade name have to be printed on the surfaced of the inductor. Printing a product specification and/or company&#39;s logo or trade name on the surface of an inductor may cause deformation of the inductor. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a shielded-type inductor, which allows use of less expensive materials to lower the manufacturing cost without affecting the product quality. It is another object of the present invention to provide a shielded-type inductor, which is highly stable and reliable, and free from the interference of external environmental factors (temperature, moisture, etc.). 
         [0010]    To achieve these and other objects of the present invention, the shielded-type inductor is comprised of a first powder compact member, a coil, and a second powder compact member. The first powder compact member has a bottom side and a top side. The coil comprises a coil body embedded in the bottom side of the first powder compact member in and two metal terminals respectively connected to the two opposite ends of the coil body and extending out of the first powder compact member. The second powder compact member is bonded to the bottom side of the first powder compact member and blocking the coil body in the bottom side of the first powder compact member. 
         [0011]    Further, before bonding the second powder compact member to the first powder compact member, the second powder compact member can be printed or embossed with the product specification and/or company&#39;s logo or trade name. By means of controlling the thickness of the second powder compact member, the inductance value of the inductor is fine-adjusted. Further, the second powder compact member can be prepared from a relatively less expensive magnetic metal material to lower the cost without changing the designed electric characteristics. 
         [0012]    Further, the first powder compact member and the second powder compact member are respectively prepared from a thermosetting resin mixture containing metal grains. The metal grains are coated with a layer of phosphoric acid (H 3 PO 4 ) that protects the inductor against moisture attack. Further, the electrically insulative thermosetting resin used for the first powder compact member and the second powder compact member has strong toughness when hardened, thereby well protecting the inductor against the interference of external environmental factors (such as temperature, humidity, etc). Therefore, a shielded-type inductor made according to the present invention is high stable and reliable. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a sectional view showing the internal structure of an inductor according to the prior art. 
           [0014]      FIG. 2  is a sectional view of the present invention, showing the second powder compact member bonded to the coil body-embedded bottom side of the first powder compact member. 
           [0015]      FIG. 3  is an exploded view in section of the present invention, showing the second powder compact member separated from the coil body-embedded bottom side of the first powder member. 
           [0016]      FIG. 4  is a schematic plain view showing a circular coil for shielded-type inductor according to the present invention. 
           [0017]      FIG. 5  is a schematic plain view showing a rectangular coil for shielded-type inductor according to the present invention. 
           [0018]      FIG. 6  is a sectional view of a first mold for the fabrication of a shielded-type inductor according to the present invention. 
           [0019]      FIG. 7  is a sectional view of a second mold for the fabrication of a shielded-type inductor according to the present invention. 
           [0020]      FIG. 8  is a shielded-type inductor fabrication flow according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Referring to  FIGS. 2 and 3 , a shielded-type inductor  10  in accordance with the present invention is shown comprised of a coil  1 , a first powder compact member  2 , and a second powder compact member  3 . 
         [0022]    Referring to  FIGS. 2 and 3  again, the coil  1  comprises a coil body  11 , and two terminals  12  and  13  respectively connected to the two opposite ends of the coil body  11 . The coil body  11  has a bottom side  111  and a top side  112 . The coil body  11  is made out of a wire conductor (such as enameled wire) by means of a standard winding process on a center shaft. The coil body  11  can be formed by means of circular winding technique or rectangular winding technique. When circular winding technique is employed, the coil body  11  thus obtained shows the configuration of a circular multi-layer air coil (see  FIG. 4 ). When rectangular winding technique is employed, the coil body  11  thus obtained shows the configuration of a rectangular multi-layer air coil (see  FIG. 5 ). When compared to circular winding technique, the coil body  11  obtained from rectangular winding technique has an extra coil core cross-section about 27.39%. Therefore, the coil body  11  obtained from rectangular winding technique has a relatively higher inductance value and saturated current. The two terminals  12  and  13  are respectively connected to the two opposite ends of the coil body  11 . Preferably, the two terminals  12  and  13  are formed of a wire conductor (for example, copper wire) and coated with two layers of electrically conductive metal coatings (for example, one layer of nickel coating and one layer of tin coating). The two terminals  12  and  13  may be respectively fastened to the two opposite ends of the coil body  11  by means of crimping or welding technique. 
         [0023]    Referring to  FIGS. 2 and 3  again, the first powder compact member  2  surrounds the coil body  11 , i.e., the coil body  11  is embedded in the first powder compact member  2 . The first powder compact member  2  is comprised of magnetic metal grains, a protective material, and an electrically insulative thermosetting resin (see  FIG. 2 ). The magnetic metal grains are coated with a layer of the protective material. The protective material-coated magnetic metal grains are mixed with the electrically insulative thermosetting resin. The magnetic metal grains can be prepared from one single metal material, or multiple different metal materials. The protective material is phosphoric acid (H 3 PO 4 ). Further, the first powder compact member  2  has a bottom side  21 , and a top side  22 . The coil body  11  is embedded in the first powder compact member  2  such that the bottom side  111  of the coil body  11  is kept in flush with the bottom side  21  of the first powder compact member  2 , and the top side  22  of the first powder compact member  2  is spaced above the top side  112  of the coil body  11  at a distance D 1 . 
         [0024]    Referring to  FIGS. 2 and 3  again, the second powder compact member  3  is fastened to the bottom side  21  of the first powder compact member  3 . Similarly, the second powder compact member  3  is comprised of magnetic metal grains, a protective material, and an electrically insulative thermosetting resin. The magnetic metal grains are coated, with a layer of the protective material. The protective material-coated magnetic metal grains are mixed with the electrically insulative thermosetting resin. The magnetic metal grains can be prepared from one single metal or metal alloy material, or multiple different metal materials or their compound. The protective layer is phosphoric acid (H 3 PO 4 ). Further, it is allowable to change the initial magnetic permeability (Ui value) subject to the composition of the magnetic metal grains, thereby fine-adjusting the inductance value of the finished product. If the composition of the magnetic metal grains remains unchanged, changing the thickness D 1  of the second powder compact member  3  (see  FIG. 2 ) can fine-adjust the inductance value of the finished product. 
         [0025]    The fabrication of the shielded-type inductor  10  is outlined hereinafter with reference to  FIGS. 2 through 8 . As stated, the shielded-type inductor  10  is comprised of a coil  1 , a first powder compact member  2 , and a second powder compact member  3 . Further, the shielded-type inductor  10  is made by means of the application of a first mold  4  and a second mold  5 . As shown in  FIGS. 6 and 7 , the first mold  4  is comprised of a female die  41 , a bottom die  41 , a locating block  43 , and a top die  44 . The female die  41  has a die cavity  411 , and two receiving cavities  412  and  413  at two opposite sides relative to the die cavity  411 . The die cavity  411  is adapted to mold the first powder compact member  2 . The two receiving cavities  412  and  413  are adapted to receive the two terminals  12  and  13 . The bottom die  42  has two bearing portions  421  and  422  respectively fitted into the two receiving cavities  412  and  413  at the bottom side. The locating block  43  is movably mounted in the die cavity  411  at the top. The locating block  43  has two positioning portions  431  and  432  respectively inserted into the two receiving cavities  412  and  413  at the top and spaced above the two bearing portions  421  and  422  of the bottom die  42  a respective gap for accommodating the two terminals  12  and  13 . The top die  44  is linearly movable (vertically movable) in the die cavity  411  of the bottom die  41 . The second mold  5  is comprised of a female die  51 , a bottom die  52 , and a top die  53 . The female die  51  has a die cavity  511  for molding the second powder compact member  3 . The bottom die  52  is movably mounted in the bottom side of the die cavity  511 . The top die  53  is linearly movable (vertically movable) in the die cavity  511 . 
         [0026]    The fabrication procedure includes the steps of: 
         [0027]    (a) first mixing, where magnetic metal grains are mixed with a protective solution to have the metal grains be coated with a layer of protective material; 
         [0028]    (b) second mixing, wherein an electrically insulative thermosetting resin is mixed with the protective material-coated magnetic metal grains to form a magnetic metal grain and resin mixture; 
         [0029]    (c) winding, wherein a wire conductor material is wound round a shaft to form a coil body; 
         [0030]    (d) terminal connection, where two metal terminals are respectively connected to the two opposite ends of the coil body thus obtain, forming a coil; 
         [0031]    (e) first material feeding, where a first mold is prepared, the coil thus obtained from step (d) is put in the first mold, and then a certain amount of the magnetic metal grain and resin mixture thus obtained from step (b) is fed into the first mold; 
         [0032]    (f) first compression molding, wherein the first mold is compressed to compact the coil and the applied magnetic metal grain and resin mixture in the first mold, forming the desired first powder compact member; 
         [0033]    (g) secondary material feeding, where a second mold is prepared, and then a certain amount of the magnetic metal grain and resin mixture thus obtained from step (b) is fed into the second mold; 
         [0034]    (h) secondary compression molding, wherein the second mold is compressed to compact the applied magnetic metal grain and resin mixture in the second mold, forming the desired second powder compact member; 
         [0035]    (i) bonding, where the second powder compact member thus obtained from step (f) is bonded to the bottom side of the first powder compact member and the bottom side of the coil body thus obtained from step (h), thereby forming the desired shielded-type inductor  10 . 
         [0036]    Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention.