Abstract:
An electronic device comprising a first magnetic powder; a second magnetic powder, wherein the mean particle diameter of the first magnetic powder is larger than the mean particle diameter of the second magnetic powder, the Vicker&#39;s Hardness of the first magnetic powder is greater than the Vicker&#39;s Hardness of the second magnetic powder by a first hardness difference, and the first magnetic powder mixes with the second magnetic powder; and a conducting wire buried in the mixture of the first magnetic powder and the second magnetic powder; wherein by means of the first hardness difference of the first magnetic powder and the second magnetic powder, the mixture of the first magnetic powder and the second magnetic powder and the conducting wire buried therein are combined to form an integral magnetic body at a temperature lower than the melting point of the conducting wire.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/294,164 filed on Jun. 3, 2014, which is a continuation of U.S. patent application Ser. No. 13/561,266 filed on Jul. 30, 2012, which is a continuation of U.S. patent application Ser. No. 12/703,495 filed on Feb. 10, 2010, which claims priority of Taiwan application Ser. No. 98116158 filed on May 15, 2009. The entirety of the above-mentioned patent applications are hereby incorporated by reference herein and made a part of specification. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a magnetic element and a method for manufacturing the same. More particularly, the present invention relates to an electronic device and a method for manufacturing the same. 
         [0004]    2. Description of Related Art 
         [0005]    An electronic device functions as stabilizing current in a circuit and filtering noises. The function of an electronic device is similar with that of a capacitor—they both adjust the stability of current by storing and discharging the electric power in the circuit. While a capacitor stores the electric power in a form of an electric field (electric charge), an electronic device does the same in a form of a magnetic field. There are energy losses in wires and magnetic core (usually called “core loss”) when it comes to the application of an electronic device. In related art, a wire of an electronic device is buried inside a magnetic body. The method of manufacturing this kind of electronic device is to firstly place the wire in a mold, to fill in the mold with iron powder which includes an adhesive and is in the similar size of the particle diameter to cover the wire, and to compress the iron powder into the magnetic body by means of a pressure molding. Then, the adhesive is heated up to be cured. The permeability of the electronic device with its magnetic body made of iron powder will slump in a high frequency above 10 KHz. Therefore, the conventional electronic device cannot be applied in the practice of high frequencies. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides an electronic device. A magnetic body thereof includes a plurality of kinds of magnetic powder with different hardness and different mean particle diameters to improve the permeability of the electronic device. 
         [0007]    The present invention provides a method of manufacturing an electronic device, and the method adopts a plurality of kinds of magnetic powder with different hardness and different mean particle diameters to manufacture a magnetic body so as to improve the permeability of the electronic device. The present invention relates to an electronic device including a magnetic body and a wire. The magnetic body includes a first magnetic powder and a second magnetic powder, wherein the Vicker&#39;s Hardness of the first magnetic powder is greater than the Vicker&#39;s Hardness of the second magnetic powder, the mean particle diameter of the first magnetic powder is larger than the mean particle diameter of the second magnetic powder, and the first magnetic powder mixes with the second magnetic powder. According to an embodiment of the present invention, the Vicker&#39;s Hardness of the first magnetic powder is greater than or equal to 150 and the Vicker&#39;s Hardness of the second magnetic powder is smaller than or equal to 100. According to an embodiment of the present invention, the Vicker&#39;s Hardness of the first magnetic powder is greater than or equal to 250 and the Vicker&#39;s Hardness of the second magnetic powder is smaller than or equal to 80. According to an embodiment of the present invention, the mean particle diameter of the first magnetic powder is substantially 10 μm to 40 μm. According to an embodiment of the present invention, the mean particle diameter of the second magnetic powder is smaller than or equal to 10 μm. According to an embodiment of the present invention, the mean particle diameter of the second magnetic powder is smaller than or equal to 4 μm. 
         [0008]    According to an embodiment of the present invention, the ratio of the mean particle diameter of the first magnetic powder to the mean particle diameter of the second magnetic powder is larger than 2. According to an embodiment of the present invention, the ratio of the mean particle diameter of the first magnetic powder to the mean particle diameter of the second magnetic powder is 2.5-10. According to an embodiment of the present invention, the material of the first magnetic powder includes metal alloy. According to an embodiment of the present invention, the material of the first magnetic powder includes Fe—Cr—Si alloy, Fe—Ni alloy, amorphous alloy, Fe—Si alloy, or Fe—Al—Si alloy. According to an embodiment of the present invention, the material of the second magnetic powder includes iron or ferroalloy. According to an embodiment of the present invention, the material of the first magnetic powder includes amorphous alloy, and the material of the second magnetic powder includes iron. 
         [0009]    According to an embodiment of the present invention, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.25-4. 
         [0010]    According to an embodiment of the present invention, when the material of the first magnetic powder includes amorphous alloy and the material of the second magnetic powder includes iron, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.67-1.5. According to an embodiment of the present invention, when the material of the first magnetic powder includes Fe—Cr—Si alloy and the material of the second magnetic powder includes iron, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 1.5-4. According to an embodiment of the present invention, a wire includes a buried part buried in the magnetic body or a winding part winding on the magnetic body. 
         [0011]    According to an embodiment of the present invention, the magnetic body is manufactured by a molding process, and the molding pressure of the molding process is 6 t/cm 2 -11 t/cm 2 . The present invention provides an electronic device, comprising: a magnetic body, comprising: a first magnetic powder; and a second magnetic powder, wherein the Vicker&#39;s Hardness of the first magnetic powder is greater than the Vicker&#39;s Hardness of the second magnetic powder, the mean particle diameter of the first magnetic powder is larger than the mean particle diameter of the second magnetic powder, and the first magnetic powder mixes with the second magnetic powder; an adhesive, joining the first magnetic powder and the second magnetic powder; and a wire. 
         [0012]    According to an embodiment of the present invention, the content of the adhesive is 2 wt %-3 wt % of the total weight of the magnetic body. 
         [0013]    According to an embodiment of the present invention, a material of the adhesive is thermoset resin. 
         [0014]    Based on the above, the magnetic body is made of magnetic powder of different mean particle diameters in the present invention. Therefore, during the molding process, magnetic powder of small mean particle diameter is filled in the space among magnetic powder of large mean particle diameter such that the density of compression is increased so as to improve the permeability of the electronic device. Moreover, the magnetic body is made of magnetic powder of different hardness in the present invention. Therefore, the strains of magnetic powder caused during the molding process are largely reduced and the core loss of the electronic device of the present invention is further decreased. In addition, the present invention does not require performing a high temperature heat treatment to the electronic device for releasing the strains of the magnetic powder so that the present invention can avoid a problem of oxidation of the wire for being unable to stand the high temperature. In order to make the aforementioned and other features and advantages of the present invention more comprehensible, several embodiments accompanied with figures are described in detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
           [0016]      FIG. 1  is a cross-sectional view illustrating an electronic device according to an embodiment of the present invention. 
           [0017]      FIGS. 2A-2D  are cross-sectional views of a manufacturing process of the electronic device in  FIG. 1 . 
           [0018]      FIG. 3  is a schematic view illustrating an electronic device according to another embodiment of the present invention. 
           [0019]      FIG. 4  is a cross-sectional view illustrating an electronic device according to yet another embodiment of the present invention. 
           [0020]      FIGS. 5A-5C  are cross-sectional views of a manufacturing process of the electronic device in  FIG. 4 . 
           [0021]      FIG. 6  is a schematic view illustrating an electronic device according to a further embodiment of the present invention. 
           [0022]      FIG. 7  illustrates variation condition of inductance values of an electronic device in two frequencies when the ratio of a first magnetic powder to a second magnetic powder in a magnetic body changes. 
           [0023]      FIG. 8  illustrates variation condition of inductance values of an electronic device in two frequencies when the ratio of a first magnetic powder to a second magnetic powder in a magnetic body changes. 
           [0024]      FIG. 9  is a graph showing the changes of inductance values of an electronic device while wires of different thread diameters are adopted. 
           [0025]      FIG. 10A  illustrates variation condition of density of a magnetic body and inductance values of an electronic device when the ratio of a first magnetic powder to a second magnetic powder in the magnetic body changes. 
           [0026]      FIG. 10B  illustrates variation condition of density of the magnetic body and permeability of an electronic device when the ratio of the first magnetic powder to the second magnetic powder in the magnetic body changes. 
           [0027]      FIG. 11A  illustrates variation condition of inductance values of an electronic device when the ratio of a first magnetic powder to a second magnetic powder in the magnetic body changes and also illustrates variation condition of inductance values of the electronic device in two applied frequencies. 
           [0028]      FIG. 11B  illustrates variation condition of inductance values of an electronic device when the ratio of a first magnetic powder to a second magnetic powder in the magnetic body changes and also illustrates variation condition of inductance values of the electronic device manufactured by two molding pressures. 
           [0029]      FIG. 12  illustrates variation condition of inductance values of an electronic device in two frequencies when the ratio of a first magnetic powder to a second magnetic powder in a magnetic body changes. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0030]      FIG. 1  is a cross-sectional view illustrating an electronic device according to an embodiment of the present invention. Referring to  FIG. 1 , an electronic device  100  of the embodiment includes a magnetic body  110  and a wire  120 . The magnetic body  100  includes a first magnetic powder  112  and a second magnetic powder  114 , and the first magnetic powder  112  is mixed with the second magnetic powder  114 , wherein the magnetic body  100  is manufactured by a molding process. The Vicker&#39;s Hardness of the first magnetic powder  112  is greater than the Vicker&#39;s Hardness of the second magnetic powder  114 . The Vicker&#39;s Hardness of the first magnetic powder  112  is, for example, larger than or equal to 150. Preferably, the Vicker&#39;s Hardness of the first magnetic powder  112  is larger than or equal to 250. The Vicker&#39;s Hardness of the second magnetic powder  114  is, for example, smaller than or equal to 100. Preferably, the Vicker&#39;s Hardness of the second magnetic powder  114  is smaller than or equal to 80. 
         [0031]    The mean particle diameter D1 of the first magnetic powder  112  is greater than the mean particle diameter D2 of the second magnetic powder  114 . The mean particle diameter D2 of the second magnetic powder  114  is smaller than or equal to 10 μm. 
         [0032]    The mean particle diameter D1 of the first magnetic powder  112  can substantially be 10 μm-40 μm, and the mean particle diameter D2 of the second magnetic powder  114  can substantially be smaller than or equal to 4 μm. The ratio of the mean particle diameter D1 of the first magnetic powder  112  to the mean particle diameter D2 of the second magnetic powder  114  is, for example, greater than 2. Preferably, the ratio of the mean particle diameter D1 to the mean particle diameter D2 is 2.5-10. 
         [0033]    The material of the first magnetic powder  112  is, for example, metal alloy, and the metal alloy is such as Fe—Cr—Si alloy, Fe—Ni alloy, amorphous alloy, Fe—Si alloy, or Fe—Al—Si alloy. The material of the second magnetic powder  114  is, for example, iron or ferroalloy. Preferably, the material of the first magnetic powder  112  is, for example, amorphous alloy, and the material of the second magnetic powder  114  is such as iron. The magnetic body  110  further includes an adhesive (not shown), and the adhesive is mixed with the first magnetic powder  112  and the second magnetic powder  114 . The first magnetic powder  112  and the second magnetic powder  114  are mutually joined by the adhesive. The material of the adhesive can be thermoset resin, e.g. epoxy resin. The content of the adhesive is 2 wt %-3 wt % of the total weight of the magnetic body  110  and the contents of the first magnetic powder  112  and the second magnetic powder  114  is 98 wt %-97 wt % of the total weight of the magnetic body  110 . The weight proportion of the first magnetic powder  112  is 20 wt %-80 wt % and the weight proportion of the second magnetic powder  114  is 80 wt %-20 wt %. That is, the ratio of the weight of the first magnetic powder  112  to the weight of the second magnetic powder  114  can be 0.25-4. 
         [0034]    The wire  120  has a buried portion  122  buried in the magnetic body  110  and end portions E 1  and E 2  extending from two ends of the buried portion  122  and out of the magnetic body  110 , wherein the end portions E 1  and E 2  are adopted to an electric connection with other electric elements (not shown). More specifically, the magnetic body  110  is a rectangular body and end portions E 1  and E 2  can be extended to a side S 3  of the magnetic body  110  along two opposite side walls S 1  and S 2  of the magnetic body  110 . As a result, the electronic device  100  can be electrically connected to other electric elements by surface mounting. The wire  120  is such as a copper wire and the buried portion  122  is, for example, a wound coil. 
         [0035]    It should be noted that, in the present embodiment, the mean particle diameter and the hardness of the first magnetic powder  112  are both greater than the mean particle diameter and the hardness of the second magnetic powder  114 . Therefore, during a molding process, the second magnetic powder  114  is easily filled in spaces among the first magnetic powder  112 , and strains caused by the mutual compression of the second magnetic powder  114  and the first magnetic powder  112  can be reduced. Therefore, the density of compression is increased and the permeability of the electronic device formed can be improved. In addition, it can be avoid using greater molding pressure and high temperature heat treatment so as to improve the density of compression and the permeability. 
         [0036]    Moreover, the magnetic body  110  includes the first magnetic powder  112 , which has less core loss than iron powder does. Therefore, compared with electronic devices in the related art, of which iron powder is used as a magnetic body, the electronic device according to the present embodiment provides less core loss and the efficiency of the electronic device is increased. In addition, the cost of material of the magnetic body  110  including the first magnetic powder  112  and the second magnetic powder  114  is lower than that of a magnetic body manufactured with metal alloy. 
         [0037]      FIGS. 2A-2D  are cross-sectional views of a manufacturing process of the electronic device in  FIG. 1 . A detailed manufacturing process of the electronic device  100  in  FIG. 1  is described in  FIGS. 2A-2D . First, referring to  FIG. 2A , a wire  120  is provided. Next, referring to  FIG. 2B , a mixture M is provided, which includes a first magnetic powder  112 , a second magnetic powder  114  and an adhesive (not shown). Then, referring to  FIG. 2C , a buried portion  122  of the wire  120  is disposed inside a mold cavity (not shown), two end portions E 1  and E 2  of the wire  120  are extended outward the mold cavity, and the mixture M is filled in the mold cavity. After that, a molding process is performed on the mixture M to form a magnetic body  110  which covers the buried portion  122 . In the molding process, for example, a molding pressure is applied to the mixture M so as to compress the first magnetic powder  112 , the second magnetic powder  114  and the adhesive. According to the present embodiment, the molding process performed on the mixture M is a pressure molding process and the pressure applied to the mixture M is such as 6 t/cm 2 -10 t/cm 2 . In other embodiments, the molding process can also be a cast molding process, an injection molding process, or other suitable molding process. Next, the adhesive is solidified, for example, by a heating method, and the temperature of the heating is equal to or slightly higher than the solidified temperature of the adhesive, such as lower than 300° C. 
         [0038]    It should be noted that, the heating temperature adopted in the present embodiment is merely adequate for solidifying the adhesive. Last, referring to  FIG. 2D , two end portions E 1  and E 2  are bended so that two end portions E 1  and E 2  are extended to a side S 3  of the magnetic body  110  respectively along two opposite side walls S 1  and S 2  of the magnetic body  110 . 
         [0039]      FIG. 3  is a schematic view illustrating an electronic device according to another embodiment of the present invention. Referring to  FIG. 3 , the material of a magnetic body  210  is the same with that of the magnetic body  110  in  FIG. 1  and needs not to be described again. The differences between an electronic device  200  of the present embodiment and the electronic device  100  of  FIG. 1  lie in that a buried portion  222  can include a plurality of bent structures  222   a  and these bent structures  222   a  are substantially disposed on the same plane. 
         [0040]      FIG. 4  is a cross-sectional view illustrating an electronic device according to yet another embodiment of the present invention. Referring to  FIG. 4 , the material of a magnetic body  310  is the same with that of the magnetic body  110  in  FIG. 1  and needs not to be described again. The differences between an electronic device  300  of the present embodiment and the electronic device  100  of  FIG. 1  lie in that a magnetic body  310  of the present embodiment is a drum-like structure and a wire  320  is disposed outside the magnetic body  310 . The magnetic body  310  of the present embodiment includes a center column  312 , a first board-shaped body  314  and a second board-shaped body  316 , wherein two ends  312   a  and  312   b  of the center column  312  connect the first board-shaped body  314  and the second board-shaped body  316  respectively, and the wire  320  winds around the center column  312 . More specifically, a winding space C is formed among the first board-shaped body  314 , the second board-shaped body  316  and the center column  312 . The wire  320  includes two end portions E 1  and E 2  and a winding portion  322  connected between the two end portions E 1  and E 2 . The winding portion  322  is disposed inside the winding space C and winds around the center column  312  while the two end portions E 1  and E 2  extend from inside the winding space C to outside the winding space C and electrically connect other electric elements (not shown). Besides, the winding space C can be filled in with a magnetic material  330  or a resin material (not shown) so that the winding space C is filled in and the winding portion  322  of the wire  320  is covered. 
         [0041]      FIGS. 5A-5C  are cross-sectional views of a manufacturing process of the electronic device in  FIG. 4 . A detailed manufacturing process of the electronic device  300  in  FIG. 4  is described in  FIGS. 5A-5C . First, referring to  FIG. 5A , a mixture M is provided. The material of the mixture M here is the same with that of the mixture M in  FIG. 2B . Next, referring to  FIG. 5B , a molding process is performed on the mixture M to form the magnetic body  310 . In the present embodiment, the molding process includes a pressure molding process, a cast molding process, or an injection molding process. During the pressure molding process, the pressure applied to the mixture M is such as 6 t/cm 2 -11 t/cm 2 . Then, the adhesive (not shown) is solidified by a heating method, and the temperature of the heating is equal to or slightly higher than the solidified temperature of the adhesive, such as lower than 300° C. It should be noted that, the heating temperature adopted in the present embodiment is merely adequate for solidifying the adhesive. Last, referring to  FIG. 5C , the winding portion  322  of the wire  320  is wound on the magnetic body  310 . 
         [0042]      FIG. 6  is a schematic view of an electronic device according to another embodiment of the present invention. Referring to  FIG. 6 , the material of a magnetic body  410  is the same with that of the magnetic body  110  in  FIG. 1  and needs not to be described again. In the present embodiment, the magnetic body  410  includes a first surface  412 , a second surface  414  opposite to the first surface  412 , and a through hole  416  going through the first surface  412  and the second surface  414 . A wire  420  is such as a conductive piece and includes two end portions E 1  and E 2  and a winding portion  422  connected between the two end portions E 1  and E 2 . The winding portion  422  goes through the through hole  416  and the two end portions E 1  and E 2  extend to a third side  418  of the magnetic body  410  along the first surface  412  and the second surface  414  of the magnetic body  410 . The third surface  418  connects the first surface  412  and the second surface  414 . The magnetic body  410  can selectively include a slice G going through the third surface  418  and leading to the through hole  416 . 
         [0043]    The results of electric tests on electronic devices  100  and  300  including different ratios of a first magnetic powder and a second magnetic powder are provided below. 
       Experiment 1 
       [0044]    The structure of an electronic device in Experiment 1 is the same with the structure of the electronic device  100  in  FIG. 1 . The thread diameter A of the wire  120  is 0.32 mm, the diameter B of the coil is 2.4 mm, the number of turns of the coil is 11.5, and the molding pressure for the magnetic body  110  is 11 t/cm 2 . The major ingredient, mean particle diameter, and hardness of a first magnetic powder and a second magnetic powder in Experiment 1 are all listed in Table 1. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Mean particle 
                   
               
               
                   
                 Major  
                 diameter 
                 Hardness 
               
               
                   
                 ingredient 
                 ( D50 ) 
                 ( Hv ) 
               
               
                   
               
             
             
               
                 First magnetic powder 
                 Fe—Cr—Si 
                 10 μm 
                 250 
               
               
                 Second magnetic 
                 iron 
                  4 μm 
                 30-80 
               
               
                 powder 
               
               
                   
               
             
          
         
       
     
         [0045]    Based on Table 1, the ratio of D1 to D2 is 2.5.  FIG. 7  illustrates variation condition of inductance values of the electronic device in two frequencies (25 KHz and 100 KHz) when the ratio of the first magnetic powder to the second magnetic powder in the magnetic body changes. Referring to  FIG. 7 , the inductance values of an electronic device with the proportion of 20 wt %-80 wt % of the first magnetic powder are all greater than the inductance values of an electronic device with the proportion of 100 wt % of the first magnetic powder or the second magnetic powder. In preferred conditions, the proportion of the first magnetic powder is 60 wt % and the proportion of the second magnetic powder is 40 wt %. That is, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 1.5. Or, the proportion of the first magnetic powder is 60 wt %-80 wt % and the proportion of the second magnetic powder is 40 wt %-20 wt %, i.e. the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 1.5-4. 
       Experiment 2 
       [0046]    The structure of an electronic device in Experiment 2 is the same with the structure of the electronic device  100  in  FIG. 1 . The thread diameter A of the wire  120  is 0.32 mm, the diameter B of the coil is 2.4 mm, the number of turns of the coil is 11.5, and the molding pressure for the magnetic body  110  is 11 t/cm 2 . The major ingredient, mean particle diameter, and hardness of a first magnetic powder and a second magnetic powder in Experiment 2 are all listed in Table 2. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Mean particle 
                 Hardness 
               
               
                   
                   
                 diameter 
                   
               
               
                   
                 Major ingredient 
                 ( D50 ) 
                 ( Hv ) 
               
               
                   
               
             
             
               
                 First magnetic powder 
                 Amorphous alloy 
                 40 μm 
                 900~1,000 
               
               
                 Second magnetic 
                 iron 
                  4 μm 
                 30~80   
               
               
                 powder 
                   
                   
                   
               
               
                 Second magnetic 
                 Fe—Cr—Si 
                 10 μm 
                 250 
               
               
                 powder 
               
               
                   
               
             
          
         
       
     
         [0047]      FIG. 8  illustrates variation condition of inductance values of the electronic device in two frequencies when the ratio of the first magnetic powder to the second magnetic powder in the magnetic body changes. Referring to  FIG. 8 , the inductance values of the electronic device with the proportion of 20 wt %-80 wt % of the first magnetic powder are all greater than the inductance values of the electronic device with the proportion of 100 wt % of the first magnetic powder or the second magnetic powder when the material of the second magnetic powder is iron and the ratio of D1 to D2 is 10. In preferred conditions, the proportion of the first magnetic powder is 40 wt % and the proportion of the second magnetic powder is 60 wt %. That is, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.67. Or, the proportion of the first magnetic powder is 40 wt %-60 wt % and the proportion of the second magnetic powder is 60 wt %-40 wt %, i.e. the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.67-1.5. 
         [0048]    The inductance values of the electronic device with the proportion of 20 wt %-80 wt % of the first magnetic powder are greater than the inductance values of the electronic device with the proportion of 100 wt % of the first magnetic powder and the inductance values of the electronic device with the proportion of 20 wt %-40 wt % of the first magnetic powder are slightly higher than the inductance values of the electronic device with the proportion of 100 wt % of the second magnetic powder when the material of the second magnetic powder is Fe—Cr—Si alloy and the ratio of D1 to D2 is 4. Therefore, in preferred conditions, the proportion of the first magnetic powder is 20 wt %-40 wt % and the proportion of the second magnetic powder is 80 wt %-60 wt %. That is, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.25-0.67. 
         [0049]    Based on the above, it can be known that the smaller the mean particle diameter of the second magnetic powder is, the better effects of the inductance value of the electronic device will be by means of the second magnetic powder of different mean particle diameters and the same first magnetic powder. 
         [0050]    The following experiment is conducted with a magnetic body including 40 μm of amorphous alloy of the proportion of 40 wt % and 4 μm of iron powder of the proportion of 60 wt %. The variation condition of core loss is listed in Table 3. The variation condition of efficiency is listed in Table 4.  FIG. 9  is a graph showing the changes of inductance values of the electronic device while wires of different thread diameters are adopted. The frequency of the experiment in Table 3 is 300 KHz, and the intensity of the magnetic induction is 30 mT. The applied current in Table 4 is 2 amperes. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Molding pressure 
                 Core loss 
               
               
                 Material of magnetic body 
                 (t/cm 2 ) 
                 (mW) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Iron 100 wt % 
                 6 
                 614.73 
               
               
                 Amorphous alloy 100 wt % 
                 6 
                 1010.4 
               
               
                 Amorphous alloy 100 wt %, performed 
                 6 
                 445.2 
               
               
                 with high temperature heat treatment 
                   
                   
               
               
                 after molding process 
                   
                   
               
               
                 Amorphous alloy 40 wt % +  
                 6 
                 424.5 
               
               
                 Iron 60 wt % 
                 11 
                 414 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                 Molding pressure 
                 Molding pressure 
               
               
                   
                   
                 11(t/cm 2 ) 
                 8.5(t/cm 2 ) 
               
               
                   
                   
               
             
             
               
                   
                 Efficiency in frequency  
                 76.59 
                 77.28 
               
               
                   
                 of 25 KHz (%) 
                   
                   
               
               
                   
                 Efficiency in frequency  
                 90.18 
                 90.09 
               
               
                   
                 of 300 KHz (%) 
                   
                   
               
               
                   
                   
               
             
          
         
       
     
         [0051]    Based on Table 3, 40 μm of amorphous alloy is adopted as the first magnetic powder and 4 μm of iron powder is adopted as the second magnetic powder in the present embodiment. The proportion of the first magnetic powder is 40 wt % and the proportion of the second magnetic powder is 60 wt %. Compared with the core loss resulted when the proportion of iron powder is 100 wt %, the proportion of amorphous alloy is 100 wt %, and the proportion of amorphous alloy (performed with high temperature heat treatment after molding process) is 100 wt %, the core loss resulted in the present embodiment is less. And the greater the molding pressure is, the less the core loss is. As a result, it can be shown that, according to the present embodiment, by adopting first magnetic powder and second magnetic powder of different mean particle diameter and hardness, less core loss can be obtained without the performance of high temperature heat treatment. Therefore, a step of high temperature heat treatment is omitted and a process is simplified. In addition, the material cost of the magnetic body  110  including the first magnetic powder  112  and the second magnetic powder  114  is lower than that of the magnetic body including the proportion of 100 wt % of the first magnetic powder. 
         [0052]    Based on Table 4, in the frequency of 25 KHz, the efficiency of the electronic device of the present embodiment can reach above 76%, and in the frequency of 300 KHz, the efficiency of the electronic device of the present embodiment can reach above 90%. It is clear that the efficiency performance of the electronic device of the present embodiment is excellent. It should be noted that, the efficiency of the electronic device of the molding pressure of 8.5 t/cm 2  is greater than that of 11 t/cm 2 . 
         [0053]    Based on  FIG. 9 , under the prerequisite of the same coil diameter B and the same number of turns, the smaller the thread diameter of the wire is, the higher the inductance value of the electronic device is. Therefore, the inductance value of the electronic device can be adjusted by the changes of the thread diameter of the wire. 
       Experiment 3 
       [0054]    The structure of an electronic device in Experiment 3 is the same with the structure of the electronic device  100  in  FIG. 1 . The thread diameter A of the wire  120  is 0.32 mm, the diameter B of the coil is 2.4 mm, the number of turns of the coil is 13.5, and the molding pressure for the magnetic body  110  is 11 t/cm 2 . The major ingredient, mean particle diameter, and hardness of a first magnetic powder and a second magnetic powder in Experiment 3 are all listed in Table 5. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                 Mean particle 
                   
               
               
                   
                   
                 diameter 
                 Hardness 
               
               
                   
                 Major ingredient 
                 ( D50 ) 
                 ( Hv ) 
               
               
                   
               
             
             
               
                 First magnetic powder 
                 Amorphous alloy 
                 20 μm 
                 900~1,000 
               
               
                 Second magnetic 
                 iron 
                  4 μm 
                 30~80   
               
               
                 powder 
               
               
                   
               
             
          
         
       
     
         [0055]    Based on Table 5, the ratio of D1 to D2 is 5.  FIG. 10A  illustrates variation condition of density of a magnetic body and inductance values of an electronic device when the ratio of a first magnetic powder to a second magnetic powder in the magnetic body changes.  FIG. 10B  illustrates variation condition of density of the magnetic body and permeability of an electronic device when the ratio of the first magnetic powder to the second magnetic powder in the magnetic body changes. 
         [0056]    Referring to  FIGS. 10A and 10B , the inductance values, the density of the magnetic body, and the permeability of the electronic device with the proportion of 20 wt %-60 wt % of the first magnetic powder are all greater than the inductance values, the density of the magnetic body, and the permeability of the electronic device with the proportion of 100 wt % of the first magnetic powder or the second magnetic powder. Preferably, the proportion of the first magnetic powder is 40 wt % and the proportion of the second magnetic powder is 60 wt %. That is, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.67. Or, the proportion of the first magnetic powder is 40 wt %-60 wt % and the proportion of the second magnetic powder is 60 wt %-40 wt %, i.e. the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.67-1.5. 
         [0057]    Table 6 lists the efficiency performance of the electronic device of the present embodiment under the same current (2 amperes), same molding pressure (11 t/cm 2 ), and two frequencies. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                   
                 Amorphous alloy  
                 Amorphous alloy  
               
               
                   
                   
                 20% + iron 
                 40% + iron 
               
               
                   
                   
                 powder 80% 
                 powder 60% 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Efficiency in frequency  
                 75.44 
                 75.57 
               
               
                   
                 of 25 KHz (%) 
                   
                   
               
               
                   
                 Efficiency in frequency  
                 90.9 
                 90.61 
               
               
                   
                 of 300 KHz (%) 
                   
                   
               
               
                   
                   
               
             
          
         
       
     
         [0058]    Based on Table 6, the efficiency of the electronic device of a proportion of 20 wt %-40 wt % of amorphous alloy and a proportion of 80 wt %-60 wt % of iron powder can reach above 75% in the frequency of 25 KHz and above 90% in the frequency of 300 KHz. It is clear that the efficiency performance of the electronic device of the present embodiment is excellent. 
       Experiment 4 
       [0059]    The structure of an electronic device in Experiment 4 is the same with the structure of the electronic device  300  in  FIG. 4 . The thread diameter A of the wire  320  is 0.32 mm, the diameter B of the coil is 2.4 mm, the number of turns of the coil is 11.5, and the molding pressure for the magnetic body  310  is 8 or 11 t/cm 2 . The major ingredient, mean particle diameter, and hardness of a first magnetic powder and a second magnetic powder in Experiment 4 are all listed in Table 7. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 7 
               
               
                   
               
               
                   
                 Major 
                 Mean particle 
                 Hardness 
               
               
                   
                 ingredient 
                 diameter 
                 Hv 
               
               
                   
               
             
             
               
                 First magnetic powder 
                 Fe—Cr—Si 
                 10 μm 
                 250 
               
               
                 Second magnetic 
                 iron 
                  4 μm 
                 30~80 
               
               
                 powder 
               
               
                   
               
             
          
         
       
     
         [0060]    Based on Table 7, the ratio of D1 to D2 is 2.5.  FIG. 11A  illustrates variation condition of inductance values of an electronic device when the ratio of a first magnetic powder to a second magnetic powder in the magnetic body changes and also illustrates variation condition of inductance values of the electronic device in two applied frequencies.  FIG. 11B  illustrates variation condition of permeability of the electronic device when the ratio of the first magnetic powder to the second magnetic powder in the magnetic body changes and also illustrates variation condition of permeability of the electronic device manufactured by two molding pressures. 
         [0061]    Based on  FIG. 11A , the inductance values of the electronic device with the proportion of 20 wt %-80 wt % of the first magnetic powder are all greater than the inductance values of an electronic device with the proportion of 100 wt % of the first magnetic powder or the second magnetic powder. Preferably, the proportion of the first magnetic powder is 60 wt % and the proportion of the second magnetic powder is 40 wt %. That is, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 1.5. Or, the proportion of the first magnetic powder is 60 wt %-80 wt % and the proportion of the second magnetic powder is 40 wt %-20 wt %, i.e. the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 1.5-4. In addition, based on  FIG. 11B , when the molding pressure is higher, the permeability of the electronic device is greater. Therefore, the permeability of the electronic device can be adjusted by the changes of the molding pressure. 
       Experiment 5 
       [0062]    The structure of an electronic device in Experiment 5 is the same with the structure of the electronic device  300  in  FIG. 4 . The thread diameter A of the wire  320  is 0.32 mm, the diameter B of the coil is 2.4 mm, the number of turns of the coil is 11.5, and the molding pressure for the magnetic body  310  is 11 t/cm 2 . The major ingredient, mean particle diameter, and hardness of a first magnetic powder and a second magnetic powder in Experiment 5 are all listed in Table 8. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 8 
               
               
                   
               
               
                   
                   
                 Mean particle 
                   
               
               
                   
                   
                 diameter 
                 Hardness 
               
               
                   
                 Major ingredient 
                 ( D50 ) 
                 ( Hv ) 
               
               
                   
               
             
             
               
                 First magnetic powder 
                 Amorphous alloy 
                 40 μm 
                 900~1,000 
               
               
                 Second magnetic 
                 iron 
                  4 μm 
                 30~80   
               
               
                 powder 
                   
                   
                   
               
               
                 Second magnetic 
                 Fe—Cr—Si 
                 10 μm 
                 250 
               
               
                 powder 
               
               
                   
               
             
          
         
       
     
         [0063]    Referring to  FIG. 12 , the inductance values of the electronic device with the proportion of 20 wt %-80 wt % of the first magnetic powder are all greater than the inductance values of the electronic device with the proportion of 100 wt % of the first magnetic powder or the second magnetic powder when the material of the second magnetic powder is iron and the ratio of D1 to D2 is 10. Preferably, the proportion of the first magnetic powder is 40 wt % and the proportion of the second magnetic powder is 60 wt %. That is, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.67. Or, the proportion of the first magnetic powder is 40 wt %-60 wt % and the proportion of the second magnetic powder is 60 wt %-40 wt %, i.e. the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.67-1.5. 
         [0064]    The inductance values of the electronic device with the proportion of 20 wt %-80 wt % of the first magnetic powder are greater than the inductance values of the electronic device with the proportion of 100 wt % of the first magnetic powder and the inductance values of the electronic device with the proportion of 20 wt %-40 wt % of the first magnetic powder are slightly higher than the inductance values of the electronic device with the proportion of 100 wt % of the second magnetic powder when the material of the second magnetic powder is Fe—Cr—Si alloy and the ratio of D1 to D2 is 4. Therefore, in preferred conditions, the proportion of the first magnetic powder is 20 wt %-40 wt % and the proportion of the second magnetic powder is 80 wt %-60 wt %. That is, the ratio of the weight of the first magnetic powder to the weight of the second magnetic powder is 0.25-0.67. 
         [0065]    Based on the above, it can be known that the smaller the mean particle diameter of the second magnetic powder is, the better effects of the inductance value of the electronic device will be by means of the second magnetic powder of different mean particle diameters and the same first magnetic powder. 
         [0066]    In summary, the present invention at least has the following advantages: 
         [0067]    1. The magnetic body is made of magnetic powder of different mean particle diameter in the present invention. Therefore, during the molding process, magnetic powder of small mean particle diameter is filled in the space among magnetic powder of large mean particle diameter such that the density of compression is increased so as to improve the permeability of the electronic device. 
         [0068]    2. The magnetic body is made of magnetic powder of different hardness in the present invention and magnetic powder of small mean particle diameter is filled in the space among magnetic powder of large mean particle diameter. Therefore, the molding pressure required in the molding process and the strains of magnetic powder caused during the molding process are largely reduced such that the core loss of the electronic device of the present invention is further decreased. In addition, the present invention can avoid performing a high temperature heat treatment to the electronic device for releasing the strains of the magnetic powder and can avoid the problem of oxidation of the wire for being unable to stand the high temperature. 
         [0069]    3. The first magnetic powder and the second magnetic powder are adopted to manufacturing the magnetic body in the present invention. Therefore, compared with prior art, in which iron powder is adopted to manufacture a magnetic body, the permeability and corresponding inductance value of the electronic device of the present invention is higher when in high frequency (25 KHz or 100 KHz). 
         [0070]    4. The first magnetic powder of metal alloy powder and the second magnetic powder are adopted in the present invention, and the material cost thereof is lower than that of a magnetic body completely manufactured with metal alloy powder. 
         [0071]    Although the present invention has been described with reference to the above embodiments, it will be apparent to one of the ordinary skill in the art that modifications to the described embodiment may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims not by the above detailed descriptions.