Abstract:
A method of fabricating a coil-embedded inductor provides steps for obtaining uniform density of coil-embedded inductor. The cavity of a first die is filled with dust before being flipped, and then filled with dust a second time. The dust in the cavity is pressed only once for improving the density.

Description:
BACKGROUND 
   The present invention relates to a method of fabricating an inductor, and particularly to a method of fabricating a coil-embedded inductor. 
   Generally, an inductor comprises an iron core wound by a coil. Coil-embedded inductors are utilized to provide an inductor with reduced volume. 
   Refer to  FIGS. 1A to 1D  and  2 A to  2 D together.  FIGS. 1A ,  1 B,  1 C, and  1 D show a coil of a conventional coil-embedded inductor.  FIGS. 2A ,  2 B,  2 C, and  2 D show a conventional coil-embedded inductor. In fabrication of the coil-embedded inductor, a wrapped coil  1  with two terminals  10  is enclosed by a core housing  20 , exposing the terminals  10 , as shown in  FIG. 2A  and  FIG. 2B . 
   Ferrite powder and ferromagnetic metal powder are widely used to form the iron core by powder die-casting. With ferrite powder, powder sintering is further required to increase inductance and strength of the iron core. As a result, ferromagnetic metal powder is utilized more frequently due to enhanced magnetic flux density and DC-bias characteristics. 
   U.S. Publication No. 2001/0016977 discloses a method of fabricating a coil-embedded inductor, in which an iron core base  2  illustrated in  FIG. 2  of this art thereof is formed previously, and a coil is inserted therein later. Press forming completes fabrication of the coil-embedded inductor. Detailed process of the method is illustrated in  FIG. 5A  to  FIG. 5I  of the related art thereof. This method, however, requires iron core base  2  to be fabricated prior to press forming, such that a gap may occur between the iron core base  2  and the coil due to non-uniform density distribution. The area near the gap shows increased magnetic flux density, achieving magnetic saturation easily, affecting the electrical characteristics of the coil-embedded inductor. 
   U.S. Publication No. 2003/0141952 discloses another method of fabricating a coil-embedded inductor, described with reference to  FIG. 3  and  FIG. 11A  to  FIG. 11D  of this art thereof. The terminals of the coil are bent to a single plane. The coil is then placed in a die for formation of the coil-embedded inductor. Due to this reason, resistance of the coil-embedded inductor will increase from the bent terminals of the coil results in heat production at high electric current levels, affecting the electrical characteristics of the coil-embedded inductor. 
   As a result, there is a need for a coil-embedded inductor with a core housing having uniform density distribution. 
   SUMMARY 
   Accordingly, embodiments of the invention disclose a method of fabricating a coil-embedded inductor, comprising: providing a first die with a cavity, disposing a coil positioning die in the first die via a first end of the cavity, disposing a coil in the cavity of the first die, wherein the coil is positioned on the coil positioning die, performing a first dust filling process on the cavity of the first die, disposing a second die in the first die via a second end of the cavity of the first die, reversing the first die with the coil positioning die and the second die, removing the coil positioning die from the first die, performing a second dust filling process to the cavity of the first die, disposing a third die in the first die via the cavity of the first die, and pressing the second die and the third die. 
   Another method of fabricating a coil-embedded inductor comprises: providing a first die with a cavity, disposing a coil positioning die in the first die via a first end of the cavity of the first die, disposing a coil with a terminal in the cavity of the first die via a second end thereof, wherein the coil is positioned on the coil positioning die and the terminal is fixed in a terminal supporting base of the first die, connecting a supplementary die to the second end of the first die, wherein the supplementary die comprises a terminal fixing block corresponding to the terminal supporting base of the first die, with the terminal is fixed by the first die and the supplementary die and a cavity of the supplementary die has the same cross section as the cavity of the first die, performing a first dust filling process on the cavity of the first die, disposing a second die in the supplementary die via the cavity of the supplementary die, reversing the first die with the coil positioning die, the supplementary die, and the second die, removing the coil positioning die from the first die, performing a second dust filling process to the cavity of the first die, disposing a third die in the first die via the cavity of the first die, and pressing the second die and the third die. 
   A detailed description is given in the following embodiments with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
       FIG. 1A  is a perspective view of the coil of the conventional coil-embedded inductor; 
       FIG. 1B  is a plan view of the coil in  FIG. 1A ; 
       FIG. 1C  is a side view of the coil in  FIG. 1A ; 
       FIG. 1D  is a front view of the coil in  FIG. 1A ; 
       FIG. 2A  is a perspective view of another conventional coil-embedded inductor; 
       FIG. 2B  is a plan view of the coil-embedded inductor in  FIG. 2A ; 
       FIG. 2C  is a side view of the coil-embedded inductor in  FIG. 2A ; 
       FIG. 2D  is a front view of the coil-embedded inductor in  FIG. 2A ; 
       FIG. 3A  is a cross-section of an embodiment of the first die before the coil is disposed therein according to the present invention; 
       FIG. 3B  is a top view of an embodiment of the first die before the coil is disposed therein; 
       FIG. 3C  is a top view of an embodiment of the first die after the coil is disposed therein; 
       FIG. 3D  is a cross-section of an embodiment of the supplemental die along the A-A′ direction in  FIG. 3C  before disposal in the first die; 
       FIG. 3E  is a cross-section of an embodiment of the supplemental die along the B-B′ direction in  FIG. 3C  before disposal in the first die; 
       FIG. 3F  is a cross-section of an embodiment of the supplemental die along the A-A′ direction in  FIG. 3C  after disposal in the first die; 
       FIG. 3G  is a cross-section of an embodiment of the supplemental die along the B-B′ direction in  FIG. 3C  after disposal in the first die; 
       FIG. 3H  is a cross-section of the first die during the first dust filling process; 
       FIG. 3I  is a cross-section of the first die when the second die is disposed in the cavity after the first dust filling process; 
       FIG. 3J  is a cross-section of the first die when the first die is flipped and the coil positioning die is removed from the first die; 
       FIG. 3K  is a cross-section of the first die during the second dust filling process; 
       FIG. 3L  is a cross-section of the first die when the third die is disposed in the cavity of the first die and a force is applied to the second die and the third die; 
       FIG. 3M  is a cross-section of another embodiment of the supplemental die along the B-B′ direction in  FIG. 3C  before disposal in the first die; and 
       FIG. 3N  is a cross-section of yet another embodiment of the supplemental die along the B-B′ direction in  FIG. 3C  after disposal in the first die. 
   

   DETAILED DESCRIPTION 
   Disclosed is a coil-embedded inductor in which the terminals of the coil are not limited to a single plane. 
   An embodiment of the fabrication process of the coil-embedded inductor according to the method is hereinafter described in detail with reference to  FIG. 3A  to  FIG. 3L  in sequence. 
   As shown in  FIG. 3A , a first die  30  with a cavity  300  in the center thereof is provided. A coil positioning die  31  is disposed in the first die  30  via a first end (i.e. the bottom end in  FIG. 3A ) of the cavity  300  and is movable therein. When the coil positioning die  31  moves to a fixed position as shown in  FIG. 3A , the coil positioning die  31  is temporarily fixed to receive the coil  1 . A first positioning block  310  and a second positioning block  311  are disposed at the top surface of the coil positioning die  31 . The first positioning block  310  is conical or cylindrical, and the second positioning block  311  is rectangular with a curved recess. The first die  30  has a first terminal supporting base  301  and a second terminal supporting base  302  on a side near the cavity  300 . The first terminal supporting base  301  and the second terminal supporting base  302  are different in height. 
     FIG. 3B  is a top view of the first die in  FIG. 3A . The curved recess of the second positioning block  311  corresponds to a side of the coil  1 . Shape and position of the first terminal supporting base  301  and the second terminal supporting base  302  in the first die  30  are illustrated in  FIG. 3B . 
   Coil  1  is disposed in the cavity  300  of the first die  30 . An outer diameter D of the bottom portion of the first positioning block  310 , as shown in  FIG. 3A , approximately equals an inner diameter d of the coil  1 , as shown in  FIG. 1A . Thus, the first positioning block  310  passes through the coil  1 . The two terminals  10  of the coil  1  are positioned on opposite sides of the second positioning block  311  and supported by the terminal supporting portion  312  of the second positioning block  311 . Thus, coil  1  is positioned and fixed temporarily on the upper end of the coil positioning die  31 . The height difference between the first terminal supporting base  301  and the second terminal supporting base  302  may equal that between the two terminals  10  of coil  1 . In this case, the two terminals  10  of coil  1  are positioned respectively on the first terminal supporting base  301  and the second terminal supporting base  302 .  FIG. 3C  is a top view of the first die  30 , in which the coil  1  in the cavity  300  of the first die  30  is clearly illustrated. 
   When coil  1  is disposed in the cavity  300  of the first die  30 , as shown in  FIG. 3D  and  FIG. 3E , a supplementary die  32  is disposed on the first die  30 . The supplemental die  32  has two terminal fixing blocks  321 ,  322  respectively corresponding to the first terminal supporting base  301  and the second terminal supporting base  302 . The shapes of the terminal fixing blocks  321 ,  322  may correspond to those of the first terminal supporting base  301  and the second terminal supporting base  302 . The cavity of the supplemental die  32  is similar in shape to the cavity  300  of the first die  30 . 
   Referring to  FIGS. 3E ,  3 F and  3 G, when the supplemental die  32  is disposed on the first die  30 , the terminals  10  are respectively clamped between the terminal fixing blocks  321 ,  322  and the terminal supporting bases  301 ,  302 . Thus, the coil  1  is positioned and fixed in a predetermined position. 
   In another embodiment as shown in  FIG. 3M  and  FIG. 3N , a recess is disposed on terminal fixing block  321  to contain the terminal  10 , and the shapes of terminal fixing blocks  321 ,  322  also may correspond to those of the first terminal supporting base  301  and the second terminal supporting base  302 . Therefore, the coil  1  is clamped by the supplementary die  32  and the first die  30 , and positioned and fixed in the predetermined position. 
   In some embodiments, the supplemental die  32  may be omitted. In this case, only the first die is provided, and two terminal supporting holes (not shown) in the cavity of the first die fix the terminals. 
   A first dust filling process is performed as shown in  FIG. 3H  to fill dust  4  in the cavity  300 . The material of the dust is selected from ferromagnetic metal powder and Ferrite powder. 
   Further, as shown in  FIG. 3I , a second die  33  is disposed in the supplementary die  32  via the cavity of the supplementary die  32 . Simultaneously, the second die  33  and the coil positioning die  31  are moved downward and through the cavity of the first die  30 , preferably at the same speed, to force the dust  4  downward. With the movement, the second die  33  is disposed in the cavity  300 . 
   It should be noted that when the second die  33  and the coil positioning die  31  move at the same speed, dust  4  is not compressed in the moving process. In some embodiments, when the second die  33  moves into the supplemental die  32 , the coil positioning die  31  is not necessary simultaneous moving with the second die  33 , or remain in place, dust  4  will be pre-shaped by this process. In this case, compression ratio of the pre-shaping process should be less than that of the pressing process, preferably less than 0.7 to obtain a core housing  20  with uniform density. 
   Further, as shown in  FIG. 3J , the first die  30 , comprising the supplemental die  32 , the coil positioning die  31  and the second die  33  therein, is reversed, and the coil positioning die  31  is removed from the first die  30 . Then, a second dust filling process fills dust  4  into the cavity  300  of the first die  30  as shown in  FIG. 3K . The material of the dust is also selected from ferromagnetic metal powder and Ferrite powder. 
   Further, as shown in  FIG. 3L , a third die  34  is disposed in the first die  30  via the cavity  300 , with force applied to and pressing the second die  33  and the third die  34 . The coil-embedded inductor is thus complete. The coil-embedded inductor can be removed from the first die  30  along with the supplemental die  32 . 
   The core housing  20  of the coil-embedded inductor is obtained by pressing only in the final step, such that uniform density can be provided. Further, by adjusting the position of the terminal supporting bases of the first die and the terminal fixing blocks of the supplemental die, coils with terminals of different heights or on different sides can be utilized. 
   While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.