Abstract:
A filter includes a first magnetic layer, a second magnetic layer, an insulating layer, a plurality of coils, a first non-magnetic layer and a second non-magnetic layer. The insulating layer is disposed between the first magnetic layer and the second magnetic layer, and the coils are disposed in the insulating layer. The first non-magnetic layer is disposed on one side of the first magnetic layer, which is far away from the insulating layer, and the second non-magnetic layer is disposed on one side of the second magnetic layer, which is far away from the insulating layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 096143387 filed in Taiwan, Republic of China on Nov. 16, 2007, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The invention relates to a filter and a manufacturing method thereof. More particularly, the invention relates to a common mode filter and a manufacturing method thereof. 
         [0004]    2. Related Art 
         [0005]    Recently, applications of power electronic circuits are widely spread and this kind of circuits usually operate in a high-frequency switching state, so electro magnetic interference (EMI) is easily occurred. The high-frequency noises may be conducted through the electromagnetic radiation or power lines to interfere with normal works of other electronic apparatuses. The conductive EMI can be a differential mode (DM) noise or a common mode (CM) noise according to different noise current transferring paths. 
         [0006]    In order to eliminate the EMI effectively, a filter for eliminating a kind of the noises is usually equipped in the electronic apparatus. For example, when the common mode noises are to be eliminated, a common mode filter for eliminating the common mode noises is equipped in the electronic apparatus. 
         [0007]    The common mode filter suppresses the common mode noises and prevents the signals transmitted in the circuit from being distorted. The conventional common mode filter has a magnetic layer serving as a substrate having a thickness of about several hundreds of microns (about 300 microns). 
         [0008]    However, the magnetic layer cannot be easily formed and has the thickness of several hundreds of microns (about 300 microns). Therefore, when the conventional common mode filter operates at the high-frequency band, a lot of transmission loss may occur. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the foregoing, the invention is to provide a filter with a reduced transmission loss and a manufacturing method thereof. 
         [0010]    To achieve the above, the invention discloses a filter including a first magnetic layer, a second magnetic layer, an insulating layer, a plurality of coils, a first non-magnetic layer and a second non-magnetic layer. The insulating layer is disposed between the first magnetic layer and the second magnetic layer. The coils are disposed in the insulating layer. The first non-magnetic layer is disposed on one side of the first magnetic layer, which is opposite to the insulating layer. The second non-magnetic layer is disposed on one side of the second magnetic layer, which is opposite to the insulating layer. 
         [0011]    In addition, the invention also discloses a manufacturing method of a filter. The method includes the following steps of forming a first magnetic layer on a first non-magnetic layer, forming an insulating layer on the first magnetic layer, forming a plurality of coils in the insulating layer, forming a second magnetic layer on a second non-magnetic layer, and combining the insulating layer with the second magnetic layer. 
         [0012]    As mentioned above, the thickness of each of the first magnetic layer and the second magnetic layer ranges from sub-microns to several tens of microns, and the non-magnetic substrate made of, for example, aluminum oxide is adopted in the present invention. Compared with the prior art, when the filter of the present invention operates at a high-frequency band, it has lower transmission loss. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0014]      FIG. 1  is a flow diagram showing a manufacturing method of a common mode filter according to a first embodiment of the present invention; 
           [0015]      FIGS. 2A to 2P  are schematic sectional views showing various partial structures of the common mode filter corresponding to the flow chart of  FIG. 1 ; 
           [0016]      FIG. 3  is a flow diagram showing a manufacturing method of a common mode filter according to a second embodiment of the present invention; and 
           [0017]      FIGS. 4A to 4S  are schematic sectional views showing various partial structures of the common mode filter corresponding to the flow chart of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
       First Embodiment 
       [0019]    Referring to  FIG. 1 , a manufacturing method of a common mode filter  1  according to a first embodiment of the present invention includes steps S 101  to S 120 . Illustrations will be made with reference to  FIG. 1  in view of  FIGS. 2A to 2P . 
         [0020]    As shown in  FIG. 2A , a first magnetic layer  102  is formed on a first non-magnetic layer  101  in the step S 101 . The first non-magnetic layer  101  can be a non-magnetic substrate made of, for example, aluminum oxide. The material of the first magnetic layer  102  includes nickel-zinc ferrite, barium ferrite or any other ferrite suitable for high-frequency operation. 
         [0021]    In practice, the first magnetic layer  102  is formed on the first non-magnetic layer  101  by coating, printing or spin coating process. 
         [0022]    When the first magnetic layer  102  is formed on the first non-magnetic layer  101  by coating process, the step S 101  includes deposing a first magnetic sub-layer (not shown) on the first non-magnetic layer  101  and forming a second magnetic sub-layer (not shown) on the first magnetic sub-layer. Herein, the material of the first magnetic sub-layer includes an anti-ferromagnetic (AFM) material, and the material of the second magnetic sub-layer includes a ferromagnetic (FM) material. Optionally, only a single magnetic sub-layer can be formed in the step S 101 , and the single magnetic sub-layer includes the AFM material or the FM material. 
         [0023]    As shown in  FIG. 2B , a first insulation sub-layer  103  is formed on the first magnetic layer  102  in the step S 102 . In the step S 103 , a first seed layer  104  is formed on the first insulation sub-layer  103 . In the step S 104 , a first lead-out layer  105  partially covering the first seed layer  104  is formed. 
         [0024]    As shown in  FIG. 2C  and in the step S 105 , a portion of the first seed layer  104 , which is not covered by the first lead-out layer  105 , is removed so that the first insulation sub-layer  103  is partially exposed. 
         [0025]    As shown in  FIG. 2D , a second insulation sub-layer  106  partially covering the first insulation sub-layer  103  and partially covering the first lead-out layer  105  is formed in the step S 106 . The second insulation sub-layer  106  includes a first hole H 1  so that the first lead-out layer  105  is exposed therein. 
         [0026]    As shown in  FIG. 2E , a second seed layer  107  covering the second insulation sub-layer  106 , partially covering the first lead-out layer  105  and covering the first hole H 1  is formed in the step S 107 . In the step S 108 , a first coil  108  is formed on the second seed layer  107  so that the hole H 1  is filled by the first coil  108 . In the step S 109 , the portion of the second seed layer  107  without covered by the first coil  108  is removed to expose the second insulation sub-layer  106 , as shown in  FIG. 2F . 
         [0027]    As shown in  FIG. 2G , a third insulation sub-layer  109  covering the exposed second insulation sub-layer  106  and covering the first coil  108  is formed in the step S 110 . As shown in  FIG. 2H , a third seed layer  110  is formed on the third insulation sub-layer  109  in the step S 111 , and a second coil  111  is formed on the third seed layer  110  in the step S 112 . The materials of the first coil and the second coil include copper or silver. 
         [0028]    As shown in  FIG. 2I , the portion of the third seed layer  110  without covered by the second coil  111  is removed in the step S 113 . As shown in  FIG. 2J , a fourth insulation sub-layer  112  covering the exposed third insulation sub-layer  109  and covering the second coil  111  is formed in the step S 114 . The fourth insulation sub-layer  112  includes a second hole H 2  so that a portion of the second coil  111  is exposed therein. 
         [0029]    As shown in  FIG. 2K , a fourth seed layer  113  is formed on the fourth insulation sub-layer  112  and the second coil  111  exposed in the second hole H 2  in the step S 115 . In the step S 116 , a second lead-out layer  114  partially covering the fourth seed layer  113  and filling the second hole H 2  is formed. 
         [0030]    As shown in  FIG. 2L , the fourth seed layer  113  uncovered by the second lead-out layer  114  is removed by, without limitation to, a lithography process or an etching process in the step S 117 . As shown in  FIG. 2M , a fifth insulation sub-layer  115  partially covering the exposed fourth insulation sub-layer  112  and the second lead-out layer  114  is formed in the step S 118 . 
         [0031]    As shown in  FIG. 2N , a second magnetic layer  117  is formed on a second non-magnetic layer  116  in the step S 119 . The second non-magnetic layer  116  can be a non-magnetic substrate, and the material thereof includes aluminum oxide. In the step S 120 , the fifth insulation sub-layer  115  is combined with the second magnetic layer  117  to form the common mode filter  1 , as shown in  FIG. 2O . 
         [0032]    The first insulation sub-layer  103 , the second insulation sub-layer  106 , the third insulation sub-layer  109 , the fourth insulation sub-layer  112  and the fifth insulation sub-layer  115  can be integrated as an insulating layer  118 . The insulation sub-layers  103 ,  106 ,  109 ,  112  and  115  may have the same material or different materials. Herein, the insulation sub-layers  103 ,  106 ,  109 ,  112  and  115  have the same material, for example, to form the common mode filter  1  shown in  FIG. 2P . 
         [0033]    In this embodiment, the thickness of each of the first magnetic layer  102  and the second magnetic layer  117  ranges from about sub-microns to several tens of microns. Compared with the prior art, when the common mode filter  1  of this embodiment operates at the high-frequency band, it has lower transmission loss. 
         [0034]    It is to be noted that the order of the above-mentioned steps is not particularly limited, and can be changed according to the requirement in the manufacturing processes. 
       Second Embodiment 
       [0035]    Referring to  FIG. 3 , a manufacturing method of a common mode filter  2  according to a second embodiment of the present invention includes steps S 201  to S 220 . Illustrations will be made with reference to  FIG. 3  in conjunction with  FIGS. 4A to 4S , wherein the processes in  FIG. 4A to 4L  are the same as those of the first embodiment in  FIGS. 2A to 2L , so detailed descriptions thereof will be omitted. 
         [0036]    As shown in  FIG. 4M , a portion of a fourth insulation sub-layer  112 , a portion of a third insulation sub-layer  109 , a portion of a second insulation sub-layer  106  and a portion of a first insulation sub-layer  103  are removed to form a hole H 3  by, without limitation to, a lithography process or an etching process in the step S 218 . 
         [0037]    In the step S 219 , a second magnetic layer  117  is formed on a second non-magnetic layer  116 , and can have various aspects, as shown in  FIG. 4N  or  4 O. The second non-magnetic layer  116  can be a non-magnetic substrate, and the material thereof includes aluminum oxide. 
         [0038]    As shown in  FIG. 4P , when the second non-magnetic layer  116  and the second magnetic layer  117  are shown in  FIG. 4N , a magnetic material  119  is filled into the hole H 3  to cover a second lead-out layer  114  and the portion of the fourth insulation sub-layer  112 . In the step S 220 , the fourth insulation sub-layer  112  is combined with the second magnetic layer  117  to form the common mode filter  2 , as shown in  FIG. 4Q . 
         [0039]    After the second non-magnetic layer  116  and the second magnetic layer  117  are formed as shown in  FIG. 4O , the step S 220  is also performed. In the step S 220 , the fourth insulation sub-layer  112  is combined with the second magnetic layer  117  to form the common mode filter  2 , as shown in  FIG. 4R . 
         [0040]    The first insulation sub-layer  103 , the second insulation sub-layer  106 , the third insulation sub-layer  109  and the fourth insulation sub-layer  112  can be integrated as an insulating layer  118 . The insulation sub-layers can have the same material or different materials. Herein, the first, second, third and fourth insulation sub-layers  103 ,  106 ,  109 ,  112  have the same material, for example, to form the common mode filter  2  shown in  FIG. 4S . 
         [0041]    The thickness of each of a first magnetic layer  102  and a second non-magnetic layer  117  ranges from about sub-microns to several tens of microns. Compared with the prior art, when the common mode filter  2  of this embodiment operates at the high-frequency band, it has lower transmission loss. In addition, the common mode filter  2  of the embodiment forms a magnetic closed loop through a magnetic material  119 , the first magnetic layer  102  and the second magnetic layer  117 , and thus has larger inductance and better filtering effect. 
         [0042]    It is to be noted that the order of the above-mentioned steps is not particularly limited, and can be changed according to the requirement in the manufacturing processes. 
         [0043]    In summary, the thickness of each of the first magnetic layer and the second magnetic layer ranges from sub-microns to several tens of microns, and the non-magnetic substrate made of, for example, aluminum oxide is adopted in the present invention. Compared with the prior art, when the filter of the present invention operates at a high-frequency band, it has lower transmission loss. 
         [0044]    Although the present invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the present invention.