Patent Publication Number: US-2009231077-A1

Title: Inductor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a passive electrical component, and more particularly to an inductor. 
     2. Description of the Prior Art 
     A conventional method for making an inductor is shown in Japanese patent No. H04-286305. A first powder member and a second powder member are made of the same magnetic powder by a pressure molding process. A hollow coil is positioned between the first powder member and the second powder member and then an integrated inductor is formed by the pressure molding process. However, since the inductor is made of only one kind of the magnetic powder, the inductor properties, such as the inductance, the saturation current, and the direct current resistance, can be adjusted only by one set of parameters (i.e., those of the magnetic powder). As such, the inductor properties are not easily adjusted. Moreover, because the mold for making the powder member has to be produced according to the size of the coil, it causes a higher mold cost. 
     Another conventional method for making an inductor is shown in U.S. Pat. No. 6,204,744. A powder magnetic material is made of a first iron powder and a second iron powder which are mixed uniformly. A coil and the powder magnetic material are placed within a mold cavity of a pressure molding machine, and then the inductor is formed by a high forming pressure. Because the inductor is not fully supported within the pressure molding machine, the insulating coating of the coil may come away by the high forming pressure. As a result, the inductor may have the problem that the coil is shorted.  FIG. 1  compares an inductor made of iron powder and stainless steel powder (Fe—Cr—Si Alloy) which are mixed uniformly according to the conventional method for making an inductor shown in U.S. Pat. No. 6,204,744, with an inductor made of iron powder, and an inductor made of stainless steel powder (Fe—Cr—Si Alloy). The properties of the inductor made of the iron powder and the stainless steel powder are almost the same as the properties of the inductor made of the stainless steel powder. Therefore, by the conventional method for making an inductor shown in U.S. Pat. No. 6,204,744, it is not easy to adjust the inductor&#39;s properties, such as the inductance, the saturation current, and the direct current resistance, by the method of mixing two kinds of magnetic powder material uniformly. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention is an inductor. By using a first magnetic body and a second magnetic body which have different magnetic properties and are disposed in different layers, it is capable of increasing the number of parameters for adjusting the inductor properties so as to enable the inductor properties to be adjusted more easily. 
     The present invention can provide an inductor so as to increase the inductance of the inductor and decrease the cost of making the inductor. 
     The present invention can provide an inductor, where, for the same inductance, the inductor has a lower direct current resistance and a lower cost of making the inductor. 
     The present invention can provide an inductor, where, during the pressure molding process, the coil is supported to a greater extent than in the method of U.S. Pat. No. 6,204,744, so as to improve the problem that the coil may be shorted. 
     In one embodiment, the present invention provides an inductor including a coil and a magnetic body. The magnetic body includes a first magnetic body and a second magnetic body. The coil is disposed within the magnetic body. The first magnetic body has a first magnetic property. The second magnetic body has a second magnetic property. The first magnetic property is different from the second magnetic property. 
     Other objectives, features, and advantages of the present invention will be further understood from the further technology features disclosed by the embodiments of the present invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the relationship between the current and the inductance for three different conventional inductors; 
         FIG. 2A  shows a sectional view of an inductor in accordance with a preferred embodiment of the present invention; 
         FIG. 2B  shows the relationship between the current and the inductance change rate for one possible implementation of the inductor shown in  FIG. 2A  and two different conventional inductors; 
         FIGS. 3A ,  3 C, and  3 D show sectional views of inductors in accordance with other preferred embodiments of the present invention; 
         FIG. 3B  shows the relationship between the current and the efficiency for the inductor shown in  FIG. 3A  and a conventional inductor; 
         FIG. 4  shows a flow diagram of one possible method for making an inductor of the present invention; 
         FIG. 5A  shows a sectional view of the first magnetic body for the method of  FIG. 4 ; 
         FIG. 5B  shows a top view of the first magnetic body for the method of  FIG. 4 ; 
         FIG. 5C  shows the coil fixed on the first magnetic body for the method of  FIG. 4 ; 
         FIG. 5D  shows the second magnetic body fixed on the coil for the method of  FIG. 4 ; 
         FIG. 5E  shows the first magnetic body and the second magnetic body formed as an integrated magnetic body for the method of  FIG. 4 ; 
         FIG. 5F  shows the formed electrode portion for the method of  FIG. 4 ; 
         FIG. 6A  and  FIG. 6B  show sectional views of an inductor in accordance with another preferred embodiment of the present invention; and 
         FIG. 7  shows a top view of the inductor of  FIG. 5F  indicating that the electrode portion is connected to the coil by a soldering process. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The detailed description of the present invention will be discussed in the following embodiments, which are not intended to limit the scope of the present invention, but can be adapted for other applications. While drawings are illustrated in details, it is appreciated that the quantity of the disclosed components may be greater or less than that disclosed, except expressly restricting the amount of the components. 
     Referring to  FIG. 2A , an inductor  200  in accordance with a preferred embodiment of the present invention includes a coil  210 , an integrated magnetic body  220 , and at least one electrode portion  230 . The coil  210  is a hollow coil formed from a metal wire having insulation coating. The metal wire can be a copper wire, although other suitable conducting materials are also possible. The integrated magnetic body  220  includes a first magnetic body  221  and a second magnetic body  222 . The coil  210  is disposed within the integrated magnetic body  220 . The first magnetic body  221  and the second magnetic body  222  are disposed in different layers. There is an interface  223  between the first magnetic body  221  and the second magnetic body  222 . The first magnetic body  221  includes a resin material and a first magnetic powder material; the second magnetic body  222  includes a resin material and a second magnetic powder material. The resin material can be a thermosetting resin, such as epoxy resin, although other suitable materials are also possible. The electrode portion  230  is connected to the coil  210  and extends to the outside of the integrated magnetic body  220 , wherein the electrode portion  230  is attached to the second magnetic body  222 . 
     The first magnetic body  221  has a first set of magnetic properties, which includes permeability and saturation current. The permeability is defined as the ratio of the magnetic flux (B) to the magnetic field (H) in the magnetic curve when the magnetic field (H) approaches to zero. The unit of the permeability is in the c.g.s. system. The saturation current is defined as the current when the inductance is decreased to 80% of the inductance when the current is near 0 mA. The second magnetic body  222  has a second set of magnetic properties, which includes permeability and saturation current. At least one of the magnetic properties of the second magnetic body is different from the corresponding magnetic property of the first magnetic body. 
     Referring to  FIG. 2B , the first magnetic body  221  of the inductor  200  of  FIG. 2A  comprises iron powder and resin material, the second magnetic body  222  of the inductor  200  comprises stainless steel powder (Fe—Cr—Si Alloy) and resin material. The inductor properties of the inductor  200  are compared with (1) the inductor properties of an inductor made of only the iron powder and (2) the inductor properties of an inductor made of only the stainless steel powder (Fe—Cr—Si Alloy). As shown in  FIG. 2B , the inductor properties of the inductor  200  are between the inductor properties of the inductor made of only the iron powder and the inductor properties of the inductor made of only the stainless steel powder (Fe—Cr—Si Alloy). Therefore, it is possible to design an inductor having desired inductor properties by adjusting the material properties and/or the volume ratio of the first magnetic body  221  to the second magnetic body  222 . Compared to conventional inductors, the number of parameters for adjusting the inductor properties is increased so as to enable the inductor properties to be adjusted more easily. 
     Referring to  FIG. 3A , an inductor  300  in accordance with another preferred embodiment of the present invention includes a coil  310 , an integrated magnetic body  320 , and at least one electrode portion  330 . The coil  310  is a hollow coil formed from a metal wire having insulation coating. The integrated magnetic body  320  includes a first magnetic body  321  and a second magnetic body  322 . The volume of the first magnetic body  321  is bigger than the volume of the second magnetic body  322 . The first magnetic body  321  comprises a first magnetic powder material and a first resin material. The first magnetic body  321  has a first permeability (u 1 ) and a first saturation current (I 1 ). The second magnetic body  322  comprises a second magnetic powder material and a second resin material. The second magnetic body  322  has a second permeability (u 2 ) and a second saturation current (I 2 ). The first permeability (u 1 ) is lower than the second permeability (u 2 ). The first saturation current (I 1 ) is higher than the second saturation current (I 2 ). The ratio of the second permeability (u 2 ) to the first permeability (u 1 ) is higher than 1.25. The ratio of the second saturation current (I 2 ) to the first saturation current (I 1 ) is higher than 0.5. In general, the larger the mean particle diameter (D 50 ) of a magnetic powder material, the higher the permeability. Therefore, in this embodiment, the mean particle diameter of the first magnetic powder material is smaller than the mean particle diameter of the second magnetic powder material. 
     The coil  310  is disposed within the integrated magnetic body  320 . A part of the first magnetic body  321  and a part of the second magnetic body  322  are disposed within a hollow portion of the coil  310 , as shown in  FIG. 3A . The volume of the first magnetic body  321  disposed within the hollow portion is bigger than the volume of the second magnetic body  322  disposed within the hollow portion. However, it is also possible to dispose a part of only the first magnetic body  421  within the hollow portion of the coil  410 , as shown in the embodiment of  FIG. 3C . 
     Referring again to  FIG. 3A , the electrode portion  330  is connected to the coil  310  and extends to the outside of the integrated magnetic body  320 . In this embodiment, the electrode portion  330  is attached to the second magnetic body  322 , while, in the embodiment of  FIG. 3D , the electrode portion  480  of inductor  450  is attached to the first magnetic body  471 , rather than to the second magnetic body  472 . If the permeability of the magnetic material used in the second magnetic bodies ( 321 ,  471 ) is greater than the permeability of the magnetic material used in the first magnetic bodies ( 322 ,  472 ), then the electrode portion  330  of  FIG. 3A  will have a higher inductance than the electrode portion  480  of  FIG. 3D . As a result, the inductor  300  of  FIG. 3A  will have a higher permeability than the inductor  450  of  FIG. 3D , so as to make the inductor  300  have better inductor properties than the inductor  450  of  FIG. 3D . 
     Referring again to  FIG. 3A , because the second permeability (u 2 ) of the second magnetic body  322  is higher than the first permeability (u 1 ) of the first magnetic body  321 , the inductance of the inductor  300  is increased as compared to a conventional inductor made from a single magnetic powder material having the first permeability (u 1 ). The volume of the first magnetic body  321  is bigger than the volume of the second magnetic body  322 . The first permeability (u 1 ) is lower than the second permeability (u 2 ). The first saturation current (I 1 ) is higher than the second saturation current (I 2 ). Therefore, the inductor  300  can be designed such that its properties are the same as the properties of the conventional inductor of U.S. Pat. No. 6,204,744. 
     The inductor  300  and a conventional inductor made of only a single powder were tested for the same number of turns of the coil, the same saturation current, and the same direct current resistance. The detailed conditions are shown in Table 1; the test results are shown in Table 2. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Turns of 
                 Resin 
                   
               
               
                 Condition 
                 the coil 
                 material 
                 Magnetic powder material 
               
               
                   
               
             
            
               
                 Conventional 
                 7.5 
                 Epoxy resin 
                 Iron powder: Fe &gt; 98.5% 
               
               
                 inductor 
                   
                   
                 (mean particle diameter is about 
               
               
                   
                   
                   
                 4 um) 
               
               
                 Inductor 300 
                 7.5 
                 Epoxy resin 
                 First magnetic body: 
               
               
                   
                   
                   
                 Iron powder 
               
               
                   
                   
                   
                 (Fe &gt; 98.5%; mean particle 
               
               
                   
                   
                   
                 diameter is about 4 um) 
               
               
                   
                   
                   
                 Second magnetic body: 
               
               
                   
                   
                   
                 Stainless steel powder 
               
               
                   
                   
                   
                 (Fe—9.5Cr—3Si; mean particle 
               
               
                   
                   
                   
                 diameter is about 20 um) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Condition 
                 Inductance 
                 Cost of magnetic powder material 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Conventional 
                  1.6 uH 
                 1 
               
               
                   
                 inductor 
               
               
                   
                 Inductor 300 
                 1.794 uH 
                 0.98 
               
               
                   
                   
               
            
           
         
       
     
     Referring to Table 1, according to one embodiment of the present invention, the first magnetic powder material is iron powder (Fe&gt;98.5%; mean particle diameter is about 4 um). The second magnetic powder material is stainless steel powder (Fe-9.5Cr-3Si; mean particle diameter is about 20 um). The first resin material and the second resin material are epoxy resin which has a cure temperature of about 120□. The first magnetic body  321  and the second magnetic body  322  are made respectively. Moreover, the volume ratio of the first magnetic body  321  to the second magnetic body  322  is about 1.4-1.6. The first permeability (u 1 ) of the first magnetic body  321  is about 22. The second permeability (u 2 ) of the second magnetic body  322  is about 28. The ratio of the second permeability (u 2 ) to the first permeability (u 1 ) is about 1.25 or higher. The conventional inductor is made of the iron powder (Fe&gt;98.5%) and the epoxy resin. As shown in Table 2, the inductance of the inductor  300  is increased compared to the inductance of the conventional inductor. Because the cost of the stainless steel powder is lower than the cost of the iron powder, the cost of the magnetic powder material for the inductor  300  is reduced. 
     The inductors of  FIGS. 3A and 3C  and a conventional inductor made of only a single powder were tested for the same dimension (6.5 mm×6.9 mm×3 mm), the same inductance (1.5 uH), and different volume ratios of the first magnetic body to the second magnetic body. The detailed conditions are shown in Table 3 and Table 5. The test results for the conditions shown in Table 3 are shown in Table 4 and  FIG. 3B . The test results for the conditions shown in Table 5 are shown in Table 6. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Volume ratio of the first magnetic body to the second 
               
               
                 magnetic body of about 1.4-1.6 
               
            
           
           
               
               
               
               
            
               
                   
                 Turns of 
                 Resin 
                   
               
               
                 Condition 
                 the coil 
                 material 
                 Magnetic powder material 
               
               
                   
               
               
                 Conventional 
                 7.5 
                 Epoxy resin 
                 Iron powder: Fe &gt; 98.5% 
               
               
                 inductor 
                   
                   
                 (mean particle diameter 
               
               
                   
                   
                   
                 is about 4 um) 
               
               
                 Inductor 300 
                 6.5 
                 Epoxy resin 
                 First magnetic body: 
               
               
                   
                   
                   
                 Iron powder 
               
               
                   
                   
                   
                 (Fe &gt; 98.5%; mean particle 
               
               
                   
                   
                   
                 diameter is about 4 um) 
               
               
                   
                   
                   
                 Second magnetic body: 
               
               
                   
                   
                   
                 Stainless steel powder 
               
               
                   
                   
                   
                 (Fe—9.5Cr—3Si; mean 
               
               
                   
                   
                   
                 particle diameter is about 
               
               
                   
                   
                   
                 20 um) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Test results for the test condition shown in Table 3 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 Direct 
                   
               
               
                   
                   
                   
                 current 
                 Change rate of the 
               
               
                   
                   
                 Turns of 
                 resistance 
                 inductance for fixed 
               
               
                   
                 Condition 
                 the coil 
                 (DCR) 
                 saturation current 
               
               
                   
                   
               
               
                   
                 Conventional 
                 7.5 
                 13.76 mΩ 
                 −15%~−21% 
               
               
                   
                 inductor 
               
               
                   
                 Inductor 300 
                 6.5 
                 12.71 mΩ 
                 −16%~−24% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Volume ratio of the first magnetic body to the second 
               
               
                 magnetic body of about 2.5-3 
               
            
           
           
               
               
               
               
            
               
                   
                 Turns of 
                 Resin 
                   
               
               
                 Condition 
                 the coil 
                 material 
                 Magnetic powder material 
               
               
                   
               
               
                 Conventional 
                 7.5 
                 Epoxy resin 
                 Iron powder: Fe &gt; 98.5% 
               
               
                 inductor 
                   
                   
                 (mean particle diameter is about 
               
               
                   
                   
                   
                 4 um) 
               
               
                 Inductor 400 
                 6.5 
                 Epoxy resin 
                 First magnetic body: 
               
               
                   
                   
                   
                 Iron powder 
               
               
                   
                   
                   
                 (Fe &gt; 98.5%; mean particle 
               
               
                   
                   
                   
                 diameter is about 4 um) 
               
               
                   
                   
                   
                 Second magnetic body: 
               
               
                   
                   
                   
                 Stainless steel powder 
               
               
                   
                   
                   
                 (Fe—9.5Cr—3Si; mean particle 
               
               
                   
                   
                   
                 diameter is about 20 um) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Test results for the test condition shown in Table 5 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 Direct 
                   
               
               
                   
                   
                   
                 current 
                 Change rate of the 
               
               
                   
                   
                 Turns of 
                 resistance 
                 inductance for fixed 
               
               
                   
                 Condition 
                 the coil 
                 (DCR) 
                 saturation current 
               
               
                   
                   
               
               
                   
                 Conventional 
                 7.5 
                 13.76 mΩ 
                 −15%~−21% 
               
               
                   
                 inductor 
               
               
                   
                 Inductor 400 
                 6.5 
                  13.4 mΩ 
                 −15.7~−22.6% 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 4, Table 6, and  FIG. 3B , the efficiency of the inductors of the present invention is almost the same as the efficiency of the conventional inductor. Because the inductors of  FIGS. 3A and 3C  have the second magnetic body, which has a higher permeability, for the same inductance and efficiency, the number of turns of the coil is fewer than in the conventional inductor. Moreover, since the direct current resistance is lower, the heat generated by the inductors of  FIGS. 3A and 3C  is also lower during use. Both the cost of the coil and the cost of the magnetic powder are reduced. When the volume ratio of the first magnetic body to the second magnetic body is about 1.4-1.6, as shown in  FIG. 3A , a part of the first magnetic body  321  and a part of the second magnetic body  322  are both disposed within a hollow portion of the coil  310 . The volume of the first magnetic body  321  disposed within the hollow portion is bigger than the volume of the second magnetic body  322  disposed within the hollow portion. When the volume ratio of the first magnetic body to the second magnetic body is about 2.5-3, as shown in  FIG. 3C , only a part of the first magnetic body  421  is disposed within a hollow portion of the coil  410  so as to make the inductor  400  have better saturation properties (e.g., a higher saturation current) than the inductor  300  of  FIG. 3A . 
     As shown in  FIG. 4 , the method for making the inductor of  FIG. 5F  includes providing a first magnetic body  621 , which has a first permeability (step  501 ); fixing a coil  610  to the first magnetic body  621  (step  502 ); providing a second magnetic body  622  which has a second permeability (step  503 ); fixing the second magnetic body to the coil  610  (step  504 ); forming the first magnetic body  621  and the second magnetic body  622  as an integrated magnetic body  620  by a pressure molding process (step  505 ); performing a baking process so as to solidify the integrated magnetic body  620  (step  506 ); and performing an electrode portion forming process (step  507 ). 
     In the step  501 , the first magnetic body  621  comprises a magnetic powder material and a resin material, and the first magnetic body  621  is formed by a pressure molding process, as shown in  FIG. 5A  and  FIG. 5B . The first magnetic body  621  has a section which is substantially in E-shape. The first magnetic body  621  also has an opening  628 , whose shape is substantially square, as shown in  FIG. 5B . The opening  628  is formed by side walls  625  of the first magnetic body. The opening  628  is larger than the outside diameter of the coil  610 . Therefore, it is possible to selectively dispose coils having different sizes within the opening  628 . The mold for making the first magnetic body  621  does not have to be produced according to the size of the coil respectively. The first magnetic body  621  has a core  626 , which is able to be inserted into the coil  610 . Therefore, the coil  610  is supported during the pressure molding process. As a result, the insulation coating of the coil  610  will typically not come away by the high forming pressure of the pressure molding process. Therefore, the problem that the coil  610  may be shorted has been improved. In this embodiment, the height H 1  of the side wall  625  is higher than the height H 2  of the core  626 . The material of the side wall  625  is able to fill up the clearance between the coil  610  and the opening  628 , thereby improving the conventional problem that the mold for making the powder member has to be produced according to the size of the coil. As a result, the mold cost can be effectively reduced. In this embodiment, the difference between the height H 1  of the side wall  625  and the height H 2  of the core  626  is less than 0.5 mm. 
     In the step  502 , as shown in  FIG. 5C , a coil  610  is provided. The coil  610  is a hollow coil formed from a metal wire having insulation coating. The two ends of the coil  610  are pressed to form the electrode portions  630 . The electrode portions  630  can also be formed by connecting the coil  610  to a lead frame. As shown in  FIG. 7 , the electrode portion  630  and the coil  610  can be connected by a laser soldering process to form at least one round solder joint  650  between the electrode portion  630  and the coil  610 , so as to improve the problem of the solder joint  650  having a sharp shape that may damage the insulation coating of the coil  610  during the pressure molding process. The electrode portion  630  has a turn portion  631  so as to position the electrode portion  630  to a mold  600 , shown in  FIG. 7 . During the process of fixing the coil  610 , a glue member  640   a  is disposed within the opening  628  of the first magnetic body  621  by a dispensing process, and then the core  626  is inserted into the hollow portion of the coil  610 , such that the coil  610  is fixed to the first magnetic body  621  by the glue member  640   a . After the coil  610  is fixed, the glue member  640   a  can be solidified by a baking process. In this embodiment, the material of the glue member  640   a  is the same resin of the first magnetic body  621  and the second magnetic body  622 , although other suitable adhesive materials are also possible. 
     In the step  503 , the second magnetic body  622  comprises a magnetic powder material and a resin material, and the second magnetic body  622  is formed by a pressure molding process. The second permeability of the second magnetic body  622  is different from the first permeability of the first magnetic body  621 . The second magnetic body  622  has a section which is substantially in I-shape. 
     In the step  504 , as shown in  FIG. 5D , during the process of fixing the second magnetic body  622  to the coil  610 , a glue member  640   b  is disposed on the second magnetic body  622  by a dispensing process. In this embodiment, the material of the glue member  640   b  is the same resin of the first magnetic body  621  and the second magnetic body  622 , although other suitable adhesive materials are possible. And then the second magnetic body  622  is fixed to the coil  610  by the glue member  640   b . The first magnetic body  621 , the coil  610 , and the second magnetic body  622  form a sandwich structure. There is a clearance d between the first magnetic body  621  and the second magnetic body  622 . After the second magnetic body  622  is fixed, the glue member  640   b  can be solidified by a baking process. 
     In the step  505 , as shown in  FIG. 5E  and  FIG. 7 , the sandwich structure formed in step  504  is placed within the mold  600 . The first magnetic body  621  and the second magnetic body  622  are formed as a single integrated magnetic body  620  by a forming pressure provided by the mold  600 . The coil  610  is disposed within the integrated magnetic body  620 , and the electrode portion  630  is exposed from the integrated magnetic body  620 . The forming pressure is higher than the forming pressure which forms the first magnetic body  621  and the second magnetic body  622 . In this embodiment, when the sandwich structure formed in step  504  is placed within the mold  600 , the turn portion  631  of the electrode portion  630  is fixed within the mold  600  so as to position the sandwich structure to the mold  600 . During the forming process, the electrode portion  630  will not be moved, thereby helping to prevent damage to the insulating coating of the coil  610 . 
     In the step  506 , after the first magnetic body  621  and the second magnetic body  622  are formed as an integrated magnetic body  620 , the integrated magnetic body  620  can be solidified by a baking process. The temperature of the baking process is higher than the cure temperature of the resin. In this embodiment, the temperature of the baking process is about 150-180□. In the step  507 , as shown in  FIG. 5F , the electrode portion  630  exposed from the integrated magnetic body  620  is formed by a bending process so as to attach the electrode portion  630  to the second magnetic body  622 , thereby finishing the method of making the inductor of  FIG. 5F . 
     Moreover, when the volume ratio of the first magnetic body and the second magnetic body is higher, such as 2.5-3, it is possible to increase the volume of the first magnetic body and decrease the volume of the second magnetic body. It is also possible use the method shown in  FIG. 6A  to make an inductor of the present invention. In this embodiment, an additional layer  727  having the same first permeability as the first magnetic body  721  is provided. The additional layer  727  comprises a magnetic powder material and a resin material, and the additional layer  727  is formed by a pressure molding process. Before the second magnetic body  722  is fixed to the coil, the additional layer  727  is fixed to the coil or fixed to the second magnetic body  722 . And then the steps  504 - 507  are performed so as to finish the method of making the inductor of  FIG. 6B . Because the E-shaped structure of the first magnetic body is more complicated than the I-shaped structure of the second magnetic body, changing the first magnetic body will typically increase the mold cost. By using the method mentioned above with respect to  FIGS. 6A-B , it is possible to change the volume ratio of the first magnetic body and the second magnetic body without changing the structure of the first magnetic body. Therefore, the making cost can be reduced. 
     Although the present invention has been described in the context of magnetic bodies formed from mixtures of a magnetic powder and a resin, each magnetic body may have additional materials, such as a filler and/or a lubricant. 
     Although the present invention has been described in the context of inductors having two magnetic bodies with different magnetic properties, the present invention can also be implemented in the context of inductors having more than two magnetic bodies with different magnetic properties. 
     Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.