Abstract:
A power inductor and its fabrication method are disclosed. The power inductor comprises a lower substrate, a coil provided on the lower substrate, and an intermediate layer which encloses the coil, wherein the lower substrate can be a soft magnetic entrainer or a non-magnetic entrainer. The coil is made of a conductive wire coated with insulated layer, and the intermediate layer is a material consisting of magnetic properties. The steps of fabrication consists of: forming a base conductive pole on the upper surface of the lower substrate, putting the coil connected to said base conductive pole, and enveloping said coil with magnetic material.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a power inductor and method for fabricating the same, and more particularly to a power inductor which has much more reliability when it is connected to outer electrode, and has enhanced function of heat radiation, as well as the method for fabricating the power inductor. 
         [0003]    2. Description of Prior Art 
         [0004]    Referring to  FIG. 1A through 1D , which are the drawings showing a conventional power inductor disclosed in an invention of U.S. Pat. No. 6,204,744B1. In the drawings, a coil  10  which is attached to a circuit board  12 , has an enclosure  14 . From the enclosure  14  there extend a first conductor  16  and a second conductor  18  each respectively welded to welding pads  20  and  22 . The coil  10  is a helical winding body  24  with multiple turns  30  of an erected rectangular cross sectional flat wire. The coil  10  includes an inner side end  26  and an outer side end  28 , and a lead frame  32  is attached to the winding body  24  with its two terminals  34  and  38  each respectively welded to the inner side end  26  and the outer side end  28  of the winding body  24 . Afterwards the winding body  24  with both welded conductors  16 ,  18  is set in a mold, and then the mold filled with preferably, a colloidal magnetic powder. After the magnetic powder is dried and hardened, the lead frame  32  is severed and taken away. The finished product of the inductor of the invention is obtained. 
         [0005]    However, the inductor fabricated according to U.S. Pat. No. 6,204,744B1 has the following flaws, namely:
   1. In fabricating the power inductor, the coil is welded to a conductive wire, and then placed into a casting mold, after that, inside the casting mold is filled with magnetic powder and adhesive gel and then pressed by pressure machine. If the pressure is not enough, the coil and magnetic powder won&#39;t adhesively compact together. If the pressure is over used, then the interface between two different materials shall be broken, a problem of reliability to power inductor after long timed application then is occurred.   2. The coil used in conventional power inductor is enveloped with magnetic material and adhesive gel, thus when it is applied in the circumstance of high current, the temperature of it shall quickly go up, even burn out the power inductor.   3. In a traditional power inductor, the way of connection of the inductor to the outer conductor terminals belongs to a point-to-point contact. In this manner, when the power inductor is used under the circumference in which the temperature is violently changed or loaded for a long time, the coil body and the outer electrical terminals may be easily disconnected causing an accidental open circuit, or moreover, a burn down of the load side electronic product.   4. One by one fabrication process as that conducted at present leads to a great loss of manpower and time with a result of low production efficiency. In the fabrication, the two ends of the coil are at first welded to the corresponding two supporting legs of the lead frame, and the connecting conductors are cut after completing the fabrication to separate the lead frame. This also causes the loss of material and increase of the fabrication cost.   
 
         [0010]    For these defects noticeable on the prior art, an improvement is seriously required. The inventor has dedicated great efforts for years to studying and improving these defects and finally come out with the present invention. 
       SUMMARY OF THE INVENTION 
       [0011]    Accordingly, it is an object of the present invention to provide a power inductor and method for fabricating the same in which the lower substrate is selected from a high heat conductive material having a thickness of 1 μm˜500 μm with heat conduction coefficient greater than 0.5 w/mk, such that the fabricated power inductor has the function of high heat conduction and radiation. 
         [0012]    To achieve the above object, the present invention provides a power inductor in which a conductive electrode is formed on a lower substrate, next, forming conductive coils among the electrodes, and then enclosing the conductive coil with a colloidal magnetic material, and then forming end electrode to obtain a surface mounting power inductor. 
         [0013]    According to the power inductor and method for fabricating the same of present invention, the mass production can be performed at one time efficiently, so as to curtail the production cost, and the finished product can fulfill the aims of light, thin, short and compact to meet the requirements of the present day electronic devices. 
         [0014]    In the present invention, the coil leads of a inductor unit do not have to be welded to the supporting legs of the lead frame to form the terminals of the inductor unit. In this way, the process of preparing the lead frame and welding the coil leads can be omitted so that the cost of fabrication can be greatly reduced. 
         [0015]    In the present invention, omission of preparing a lead frame results in saving the cost of the lead frame, and the cost of performing process of cutting off the lead frame. 
         [0016]    The power inductor fabricated as such not only has the advantageous features qualified for the modern electronic device as described above, but also has a significant feature that its coil is closely combined with the outer electric terminals within the main body of the inductor without the fear of accidental separation of coil from its lead wires resulting in breakdown of the whole electronic installation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The following drawings, which are included to provide further understanding of the invention and incorporated in and constitute part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention; wherein 
           [0018]      FIG. 1A˜FIG .  1 D show an embodiment of U.S. Pat. No. 6,204,744B1; 
           [0019]      FIG. 2  is a perspective view of the power inductor according to the present invention; 
           [0020]      FIG. 3  is a perspective view of the power inductor according to the present invention in which end electrodes are formed at both sides of the main body; 
           [0021]    FIG.  4 - 1 ˜ FIG. 4-8  are illustrative views showing the process of fabrication method for manufacturing a single power inductor according to a preferred embodiment of present invention; and 
           [0022]    FIG.  5 - 1 ˜ FIG. 5-9  are illustrative views showing the process of fabrication method for forming a plurality of power inductor according to an embodiment of present invention. 
           [0023]      FIG. 6  is an another embodiment of present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    As shown in  FIG. 2 , the power inductor of present invention comprises a lower substrate  100 , a basic conductive electrode pattern  300  formed on the lower substrate  100 , a coil  200  loaded on the lower substrate  100 , and an enclosing layer  400  enclosing the coil  200 , wherein the lower substrate  100  is selected from a high heat conductive material having a thickness of 1 μm˜500 μm with heat conductive coefficient greater than 0.5 w/mk. It may be a soft magnetic substrate, or a glass fiber substrate, or a plate of conductive material; 
         [0025]    wherein, if the lower substrate is an electric-conductive substrate having high heat conductive coefficient, then the two end points of electric-conductive substrate can be insulated by cutting or etching the substrate. 
         [0026]    The coil  200  is formed of conducting wire wrapped with an insulating layer. The basic conductive electrode pattern  300  is formed of Ag, Sn, Cu, Al, Ni, or other conducting materials. The basic conductive electrode pattern  300  and the coil  200  are electrically connected with each other. The enclosing layer  400  is made of colloidal substance containing the magnetic properties. 
         [0027]    The power inductor of present invention can be manufactured as a single granular element or a plurality of granular elements, wherein the process for manufacturing single granular element is illustrated in Embodiment 1 and the process for manufacturing a plurality of granular elements is illustrated in Embodiment 2. 
       Embodiment 1 
       [0028]    The method for manufacturing a single granular element of power inductor of present invention includes the steps of:
   1. Selecting and obtaining a lower substrate  201  which is a soft magnetic plate or a glass fiber substrate or a plate of conductive material having a thickness of 1 μm˜500 μm with heat conductive coefficient greater than 0.5 w/mk (please refer to  FIG. 4-1 ).   2. Forming a basic conductive electrode pattern  300  having a plurality of separated conductive electrodes  202   a ,  202   b  made of Cu, Ag, Al, Sn, Ni, or other conductive materials, or their alloys stacked one another on the lower substrate  201 . The thickness of basic conductive electrode pattern  300  is 0.1 μm˜1 mm (please refer to  FIG. 4-2 ).   3. Forming a coil  203  on the upper surface of the lower substrate  201 . The two ends of coil  203  are lead wires  203   a   1 ,  203   a   2 , the material of coil is copper or another conductive material, wherein, the copper wire can be coated by an insulated layer such as lacquer (please refer to  FIG. 4-3 , it has to be noticed that the order of step 2 and step 3 can be changed).   4. Making electrical connection between the lead wires  203   a   1 ,  203   a   2  of coil  203  and the corresponding conductive electrodes  202   a ,  202   b  (please refer to  FIG. 4-4 ). This process is performed by welding or heat pressing.   5. Putting a pole  2 A (as shown in  FIG. 4-5 ) into said coil  203 , said pole  2 A is a bar of magnetic or non-magnetic material, such as iron or related alloys and oxides; said pole  2 A is used for adjusting electric properties of power inductor.   6. Coating the surface of coil  203  with a magnetic material colloid  204 , this magnetic material colloid  204  may be a ferrite or iron and its alloy powder (please see  FIG. 4-6 ).   7. Covering an upper substrate  205  on the upper surface of the magnetic material colloid  204  serving as a fixing layer (please refer to  FIG. 4-7 ). The upper and the lower substrates  205 ,  201  may be formed of the same material. After that baking the workpiece at 200° C., so as to harden the magnetic material colloid  204  and stick it to the upper substrate  205  to form a single granular element.   8. After the single granular element is obtained, forming end electrodes  206  on its side surfaces, then the product of power inductor becomes a surface mounting device (as shown in  FIG. 4-8 ).   
 
       Embodiment 2 
       [0037]    The method for manufacturing a plurality of granular elements of power inductor of present invention includes the steps of:
   1. Selecting and obtaining a lower substrate  401  which is a soft magnetic plate or a glass fiber substrate or a plate of conductive material having a thickness of 1 μm˜500 μm with heat conductive coefficient greater than 0.5 w/mk (please refer to  FIG. 5-1 ).   2. Forming a basic conductive electrode pattern  300  constructed by a plurality of conductive electrodes  402   a ,  402   b ,  402   c  . . . aligned in different arrays. The conductive electrodes  402   a ,  402   b ,  402   c  . . . can be made of Cu, Ag, Al, Sn, Ni, or other conductive materials, or their alloys stacked one another on the lower substrate  401 . The thickness of basic conductive electrode pattern  700  is 0.1 μm˜1 mm (please refer to  FIG. 5-2 ).  3 . Forming a plurality of coil units  403   a ,  403   b  . . . aligned in matrix array, between each two adjacent coil units  403   a ,  403   b  . . . are the lead wires  403   a   1 ,  403   a   2 ,  403   b   1 ,  403   b   2  . . . of each coil unit  403   a ,  403   b  . . . , while the adjacent lead wires  403   a   2 ,  403   b   1  . . . of two adjacent coil units can be the same one. The material of coil can be a copper wire or another conductive material, wherein, the copper wire can be coated by an insulated layer such as lacquer (please refer to  FIG. 5-3 ).   4. Making electrical connection between the lead wires  403   a   1 ,  403   a   2 ,  403   b   1 ,  403   b   2  . . . of coil units  403   a ,  403   b , . . . and the corresponding conductive electrodes  402   a ,  402   b  . . . , such that each of the coil units  403   a ,  403   b  . . . is respectively placed between two separate conductive electrodes  402   a ,  402   b  . . . (please refer to  FIG. 5-4 ). This process is performed by welding or heat pressing.   5. Putting a post  4 A into each of coil unit  403   a ,  403   b , . . . (please refer to  FIG. 5-5 ), said post  4 A is a bar of magnetic or non-magnetic material, such as iron or related alloys and oxides; said post  4 A is used for adjusting electric properties of power inductor.   6. Coating the surface of each coil unit  403   a / 403   b / . . . with a magnetic material colloid  404 , this magnetic material colloid  404  may be a ferrite or iron and its alloy powder mixed with resins (please refer to  FIG. 5-6 ).   7. Covering an upper substrate  405  on the upper surface of the magnetic material  404  serving as a fixing layer (please refer to  FIG. 5-7 ). The upper and the lower substrates  405 ,  401  may be formed of the same material. After that baking the workpiece at 200° C., so as to harden the magnetic material  404  and stick it to the upper substrate  405     8. Using a cutting process to cut the baked substrate into a plurality of granular elements  2000  (as shown in  FIG. 5-8 ).   9. After the single granular element is obtained, forming end electrodes  406  on its side surfaces, then the product of power inductor becomes a surface mounting device (as shown in  FIG. 4-9 ).   
 
         [0046]    In step  8  of the embodiment 2, 200° C. baking temperature is only one exemplary value used in the embodiment 2, and should not be construed as an only one limited value of temperature to be carried out in the fabrication process. 
         [0047]    The steps for manufacturing power inductor described in Embodiments 1 &amp; 2 can be adjusted according to necessities of elements as follows:
   1. Before the coil is formed, as shown in  FIG. 6 , a bottom layer of magnetic material colloid  80  which is able to adjust the electric properties of devices can be formed on the upper surface of the lower substrate  201 ( 401 ), the material forming the bottom layer of colloid can be the same as that of said magnetic material colloid  204 , that is, a ferrite or iron and its alloy powder. After the bottom layer of magnetic material colloid  80  is formed onto the upper surface of lower substrate  201 ( 401 ), the coil  203 ( 403   a ,  403   b ) then is formed onto said bottom layer, such that the electric properties can be adjusted by said bottom layer of magnetic material colloid.   2. The upper substrate can be used according to the demands of electronic devices.   3. The coil can be placed or not placed with the post  2 A( 4 A).   4. The step orders for forming coil and conductive electrode pattern can be exchanged.   5. The coils and conductive electrodes can be connected by welding or heat pressing.   6. The magnetic material colloid can be a mixture of ferrite colloid or iron or its alloy powder mixed with resins.   7. The upper and lower substrates can be formed by a single material or a plurality of materials stacked together, and the surfaces of the upper and lower substrates can be flat or formed with a plurality of grooves.   8. The bottom layer material colloid and the upper layer material colloid having magnetic properties can be injected, pressed or filled onto the conductive electrodes and coils.   
 
         [0056]    It is understood that power inductor and its fabrication method of the present invention is a high level technical creation and, by no means, simply utilizes conventional technology or knowledge known prior to the application for patent or can easily made by persons skilled in the arts. The power inductor according to the present invention has the merits of simple in construction, easy to fabricate, secure to operate. The present invention will surely improve the quality of the traditional power inductor and benefit the present electronic engineering. The invention has neither been published nor put to pubic, therefore it is entitled for patent. 
         [0057]    It is apparent to a person skilled in the art that the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above, but may vary with the scope of the claims.