Patent Publication Number: US-8988181-B2

Title: Common mode filter with multi-spiral layer structure and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on, and claims priority from, Taiwan Patent Application Serial Number 100134273, filed on Sep. 23, 2011, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a common mode filter and a method of manufacturing the same, and more particularly relates to a multilayer common mode filter and a method of manufacturing the same. 
     2. Background 
     Common mode noise describes the type of noise that is conducted on all lines in the same direction. To suppress common mode noise, common mode filters or chokes can be installed on conducting lines where common mode noise is present. Traditionally, a common mode filter is comprised of components including an iron core and two coils wound around the iron core with the same winding number. When a common mode current flows through the common mode filter, the two coils generate a magnetic flux in the same direction such that the common mode filter exhibits high impedance and can suppress common mode noise. 
     To address the requirement of portable electronic apparatuses, thin film common mode filters have been developed. Japanese Patent Application No. JP2000173824 (A) discloses a thin film common mode filter. The thin film common mode filter has an upper magnetic layer, a lower magnetic layer, a plurality of insulative layers and a plurality of conductive patterns. The plurality of insulative layers and the plurality of conductive patterns are alternatively formed between the upper and lower magnetic layers. 
     Furthermore, U.S. Pat. No. 7,145,427 B2 discloses one type of thin film common mode filter, which includes two coil conductor layers, two lead-out electrode layers, a plurality of insulation layers, and two magnetic layers. Each coil conductor layer includes a coil, and the two lead-out electrode layers are used to extend the inner ends of the two coils to an edge of the thin film common mode filter for achieving an external electrical connection. The insulation layers are used for electrically insulating the coil conductor layers and the lead-out electrode layers. The coil conductor layers, the lead-out electrode layers, and the insulation layers are disposed between two magnetic layers. 
     Limited by dimensions, higher common mode impedance or different cut off frequencies cannot be easily obtained by modifying the coil structure of the above-mentioned thin film common mode filter. If the increase of the common mode impedance is achieved by adding to the number of windings, more space will be needed to install the thin film common mode filter, creating an adverse effect on the application of the thin-film common mode filter to portable electronic products. 
     SUMMARY 
     In one embodiment of the present invention, a common mode filter with a multi-spiral layer structure comprises a first coil, a second coil, a first insulating layer, a third coil, a second insulating layer, a fourth coil, and a third insulating layer. The first insulating layer is configured to separate the first coil from the second coil. The third coil is connected in series with the first coil, wherein the second coil is disposed between the first coil and the third coil. The second insulating layer is configured to separate the second coil from the third coil. The fourth coil is connected in series with the second coil, wherein the third coil is disposed between the second coil and the fourth coil. The third insulating layer is configured to separate the third coil from the fourth coil. At least one of the first, second, and third insulating layers comprises magnetic material. 
     In another embodiment of the present invention, a common mode filter with a multi-spiral layer structure comprises a first coil, a second coil, a third coil, a fourth coil, and a magnetic material portion. The third coil is connected in series with the first coil, wherein the second coil is disposed between the first coil and the third coil. The fourth coil connected in series with the second coil, wherein the third coil is disposed between the second coil and the fourth coil. The magnetic material portion is formed through the first, second, third, and fourth coils. 
     In one embodiment of the present invention, a method of manufacturing a common mode filter with a multi-spiral layer structure comprises the steps of forming a first coil comprising an inner end portion and an outer end portion on a material layer; forming a first insulating layer covering the first coil; forming a second coil comprising an inner end portion and an outer end portion on the first insulating layer; forming a second insulating layer covering the second coil; forming a first contact hole exposing either of the inner and outer end portions of the first coil; filling first metal material in the first contact hole to form a first conductive pillar; forming a third coil comprising an inner end portion and an outer end portion on the second insulating layer, wherein either the inner or outer end portion of the third coil is connected with the first conductive pillar; forming a third insulating layer covering the third coil; forming a second contact hole exposing either the inner or outer end portion of the second coil; filling second metal material in the second contact hole to form a second conductive pillar; forming a fourth coil comprising an inner end portion and an outer end portion on the third insulating layer, wherein either the inner or outer end portion of the fourth coil is connected with the second conductive pillar; forming a fourth insulating layer covering the fourth coil; forming a recess passing through the first, second, third, and fourth coils; and filling magnetic material into the recess. 
     The foregoing has broadly outlined the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, and form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objectives and advantages of the present invention are illustrated with the following description and upon reference to the accompanying drawings in which: 
         FIG. 1  is an exploded view schematically depicting a common mode filter according to one embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the common mode filter of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view schematically illustrating a common mode filter according to another embodiment of the present invention; 
         FIG. 4  is a cross-sectional view schematically demonstrating a common mode filter according to another embodiment of the present invention; 
         FIG. 5  is a cross-sectional view schematically demonstrating a common mode filter according to another embodiment of the present invention; 
         FIG. 6  is a sectional top view showing a common mode filter according to another embodiment of the present invention; 
         FIG. 7  is a cross-sectional view showing a common mode filter according to one embodiment of the present invention; 
         FIGS. 8 through 10  are cross-sectional views schematically depicting the steps of the method of manufacturing a common mode filter according to one embodiment of the present invention; 
         FIG. 11  is a diagram illustrating the relationship between the impedance and frequency of a common mode filter according to one embodiment of the present invention; 
         FIG. 12  is a diagram illustrating the relationship between the impedance and frequency of a current common mode filter; 
         FIG. 13  is a side view schematically demonstrating a heterogeneous substrate according to one embodiment of the present invention; 
         FIG. 14  is a top view schematically demonstrating a heterogeneous substrate according to another embodiment of the present invention; and 
         FIG. 15  is a top view schematically demonstrating a heterogeneous substrate according to yet another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment of the present invention, a common mode filter comprises two coil groups each comprising a plurality of coil members connected in series with each other. Adjacent coils are separated by an insulating layer. The coil members of the two coil groups may be stacked in an alternating manner. Increasing the number of coils in the coil group can increase the common mode impedance of the common mode filter and easily change the differential mode cut off frequency to a desired value. Moreover, the increase of the number of coils in the coil group does not require more area for the installation of the common mode filter. 
     In some embodiments, the common mode filter may further comprise a plurality of insulating layers configured to electrically separate the coils from each other. At least one of the insulating layers can comprise magnetic material such that the magnetic lines generated by the coils can be contained and the impedance and the inductance of the common mode filter can be improved. 
     In other embodiments, the common mode filter can comprise a magnetic material portion that may be formed through the coils. The magnetic material portion can improve the impedance and the inductance of the common mode filter. 
     Moreover, the common mode filter may further comprise two material layers, between which the coil members are disposed. At least one of the two material layers comprises magnetic material such that the common mode filter can provide better filtering performance 
       FIG. 1  is an exploded view schematically depicting a common mode filter  100  according to one embodiment of the present invention. As shown in  FIG. 1 , the common mode filter  100  comprises a first coil layer  3 , a first insulating layer  4 , a second coil layer  5 , a second insulating layer  6 , a third coil layer  7 , a third insulating layer  8 , and a fourth coil layer  9 , wherein the first insulating layer  4  electrically separates the first coil layer  3  from the second coil layer  5 , the second insulating layer  6  electrically separates the second coil layer  5  from the third coil layer  7 , and the third insulating layer  8  electrically separates the third coil layer  7  from the fourth coil layer  9 . 
     The first insulating layer  4 , the second insulating layer  6 , and the third insulating layer  8  may comprise of polyimide, epoxy, or benzocyclobutene (BCB). From the first insulating layer  4 , the second insulating layer  6 , and the third insulating layer  8 , either one, two or all three may comprise of magnetic material such as ferromagnetic material. In one embodiment, the magnetic material layer comprises nickel zinc ferrite or manganese-zinc ferrite. 
     The process for forming the first insulating layer  4 , the second insulating layer  6 , and the third insulating layer  8  may be a spin-coating process, a dipping process, a spraying process, a screen-printing process, or a thin film process. 
     The first coil layer  3  may comprise a first coil  31 . The second coil layer  5  may comprise a second coil  51 . The third coil layer  7  may comprise a third coil  71 . The fourth coil layer  9  may comprise a fourth coil  91 . The second coil  51  is disposed between the first coil  31  and the third coil  71 . The third coil  71  is disposed between the second coil  51  and the fourth coil  91 . The first coil  31  is connected in series with the third coil  71 . The second coil  51  is connected in series with the fourth coil  91 . The serially connected first and third coils  31  and  71  are magnetically coupled with the serially connected second and fourth coils  51  and  91  such that the serially connected first and third coils  31  and  71  and the serially connected second and fourth coils  51  and  91  may be used together to eliminate common mode noise. 
     The first coil  31 , the second coil  51 , the third coil  71 , and the fourth coil  91  may be in the form of a rectangular spiral as shown in  FIG. 1 . Alternatively, they may have other spiral shapes such as the shape of a circular spiral. 
     In one embodiment, the first coil  31 , the second coil  51 , the third coil  71 , and the fourth coil  91  may be overlapped in most portions along a vertical direction. 
     In one embodiment, the first coil  31 , the second coil  51 , the third coil  71 , and the fourth coil  91  may have the same number of coil windings. 
     In one embodiment, the first coil layer  3 , the second coil layer  5 , the third coil layer  7 , and the fourth coil layer  9  may be formed using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. The first coil layer  3 , the second coil layer  5 , the third coil layer  7 , and the fourth coil layer  9  comprise silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. 
     The common mode filter  100  may further comprise a first material layer  1  and a second material layer  11 , wherein the first coil  31 , the second coil  51 , the third coil  71 , and the fourth coil  91  are formed between the first material layer  1  and the second material layer  11 . 
     In one embodiment, either the first material layer  1  or the second material layer  11  may comprise of magnetic material such as ferromagnetic material. Specifically, the first material layer  1  is a magnetic material layer, and the second material layer  11  is a non-magnetic material layer or an insulating layer. Alternatively, the first material layer  1  is a non-magnetic material layer or an insulating layer, and the second material layer  11  is a magnetic material layer. In one embodiment, the afore-mentioned magnetic material layer comprises a magnetic plate member. The afore-mentioned non-magnetic material layer comprises a non-magnetic plate. The afore-mentioned insulating layer comprises an insulating plate. In one embodiment, the magnetic material layer comprises nickel zinc ferrite or manganese-zinc ferrite. In one embodiment, the non-magnetic material layer comprises aluminum oxide, aluminum nitride, glass, or quartz. In one embodiment, the magnetic material layer comprises polymer and magnetic powder. The polymer may comprise of polyimide, epoxy, or benzocyclobutene. The magnetic powder may comprise nickel zinc ferrite or manganese-zinc ferrite. 
     Referring to  FIG. 13 , in one embodiment, the first material layer  1  comprises a heterogeneous substrate. In another embodiment, the second material layer  11  comprises a heterogeneous substrate. The heterogeneous substrate comprises an insulating substrate  111  and a magnetic material layer  112 . The insulating substrate  111  and the magnetic material layer  112  may be co-fired together such that the insulating substrate  111  and the magnetic material layer  112  are joined by diffusion bonding. In another embodiment, the insulating substrate  111  and the magnetic material layer  112  can be bonded together by an adhesive. In yet another embodiment, the insulating substrate  111  and the magnetic material layer  112  can be separately formed using a thick film printing process. 
     Either the insulating substrate  111  or the magnetic material layer  112  can be an outside layer. In one embodiment, the magnetic material layer  112  can be formed to fit with the sizes of the coils. The magnetic material layer  112  can also be formed smaller than the insulating substrate  111 , as shown in  FIG. 13 . In another embodiment, the magnetic material layer  112  can be equivalent in area to the insulating substrate  111 . 
     Referring to  FIGS. 14 and 15 , the magnetic material layer  112 ′ and  112 ″ may comprise a plurality of independent magnetic material blocks  1121 ′ or  1121 ″. The independent magnetic material blocks  1121 ′ or  1121 ″ can be arranged in order on a major surface of the insulating substrate  111 . 
     The inclusion of magnetic material in the first material layer  1  and/or the second material layer  11  can confine the magnetic field created by the common mode filter  100 . As a result, the common mode filter  100  can provide a better filtering performance 
     Referring back to  FIG. 1 , the common mode filter  100  may further comprise a lateral insulating layer  2  and a lateral insulating layer  10 . The lateral insulating layer  2  is formed on the first material layer  1 . The first coil layer  3  is formed on the lateral insulating layer  2 . The first insulating layer  4  covers the first coil layer  3 . The second coil layer  5  is formed on the first insulating layer  4 . The second insulating layer  6  covers the second coil layer  5 . The third coil layer  7  is formed on the second insulating layer  6 . The third insulating layer  8  covers the third coil layer  7 . The fourth coil layer  9  is formed on the third insulating layer  8 . The lateral insulating layer  10  covers the fourth coil layer  9 . The second material layer  11  is disposed on the lateral insulating layer  10 . 
     In particular, referring to  FIGS. 1 and 2 , the first coil  31  comprises an inner end portion  32 , the third coil  71  comprises an inner end portion  72 , the first insulating layer  4  comprises a contact hole  41 , and the second insulating layer  6  comprises a contact hole  61 , wherein the contact hole  41  is formed between the inner end portion  32  of the first coil  31  and the inner end portion  72  of the third coil  71  and the contact hole  61  is also formed between the inner end portion  32  of the first coil  31  and the inner end portion  72  of the third coil  71  such that the first coil  31  can be electrically connected with the third coil  71  through the contact holes  41  and  61 . 
     In addition, the common mode filter  100  further comprises a conductive pillar  12 , which is formed through the contact holes  41  and  61  and configured to connect the inner end portion  32  of the first coil  31  and the inner end portion  72  of the third coil  71 . 
     Furthermore, the second coil  51  comprises an inner end portion  52 , the fourth coil  91  comprises an inner end portion  92 , the second insulating layer  6  further comprises a contact hole  62 , and the third insulating layer  8  comprises a contact hole  81 , wherein the contact holes  62  and  81  are formed between the inner end portion  52  of the second coil  51  and the inner end portion  92  of the fourth coil  91  such that the inner end portion  52  of the second coil  51  can be electrically connected with the inner end portion  92  of the fourth coil  91  through the contact holes  62  and  81 . 
     The common mode filter  100  may further comprise a conductive pillar  13 , which is formed through the contact holes  62  and  81  and configured to connect the inner end portion  52  of the second coil  51  and the inner end portion  92  of the fourth coil  91 . 
     In one embodiment, the conductive pillars  12  and  13  can be formed using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. The conductive pillar  12  or  13  may be made of silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. 
     In one embodiment, the lateral insulating layers  2  and  10  may comprise of polyimide, epoxy, or benzocyclobutene (BCB). The lateral insulating layers  2  and  10  may be formed using a spin-coating process, a dipping process, a spraying process, a screen-printing process, or a thin film process. 
     The first coil  31 , the second coil  51 , the third coil  71 , and the fourth coil  91  each comprises an outer end portion ( 33 ,  53 ,  73 , or  93 ) connecting to a corresponding electrode  34 ,  54 ,  74 , or  94  disposed adjacent to the periphery of the common mode filter  100 . The first coil  31 , the second coil  51 , the third coil  71 , or the fourth coil  91  makes an external connection through the respective electrode  34 ,  54 ,  74 , or  94 . 
     In one embodiment, the lateral insulating layer  2  may have a thickness in a range of from 1 micrometer to 20 micrometers. 
     In one embodiment, when the first material layer  1  is an insulating plate, the first coil layer  3  can be directly formed on the first material layer  1 . Under such a circumstance, a lateral insulating layer  2  is not necessarily formed on the first material layer  1 . 
     In one embodiment, the common mode filter  100  may further comprise an adhesive layer, which is configured to bond the lateral insulating layer  10  and the second material layer  11 . 
       FIG. 3  is a cross-sectional view schematically illustrating a common mode filter  300  according to another embodiment of the present invention. As shown in  FIG. 3 , the common mode filter  300  comprises a first material layer  1 , an outer insulating layer  35 , a first conductor layer  14 , a lateral insulating layer  2 , a first coil layer  3 , a first insulating layer  4 , a second coil layer  5 , a second insulating layer  6 , a third coil layer  7 , a third insulating layer  8 , a fourth coil layer  9 , a lateral insulating layer  10 , a second conductor layer  15 , an outer insulating layer  36 , and a second material layer  11 . 
     The outer insulating layer  35  is formed on the first material layer  1 . The first conductor layer  14  is formed on the outer insulating layer  35 . The lateral insulating layer  2  covers the first conductor layer  14 . The first coil layer  3  is formed on the lateral insulating layer  2 . The first insulating layer  4  covers the first coil layer  3 . The second coil layer  5  is formed on the first insulating layer  4 . The second insulating layer  6  covers the second coil layer  5 . The third coil layer  7  is formed on the second insulating layer  6 . The third insulating layer  8  covers the third coil layer  7 . The fourth coil layer  9  is formed on the third insulating layer  8 . The lateral insulating layer  10  covers the fourth coil layer  9 . The second conductor layer  15  is formed on the lateral insulating layer  10 . The outer insulating layer  36  covers the second conductor layer  15 . The second material layer  11  is disposed on the outer insulating layer  36 . 
     In one embodiment, for the first insulating layer  4 , the second insulating layer  6 , and the third insulating layer  8 , either one, two or all three may comprise of magnetic material such as ferromagnetic material. In one embodiment, the magnetic material may comprise nickel zinc ferrite or manganese-zinc ferrite. 
     In one embodiment, the first material layer  1  and/or the second material layer  11  may comprise of magnetic material. 
     In one embodiment, first material layer  1  and/or the second material layer  11  may comprise of a heterogeneous substrate. 
     The outer insulating layer  35  or  36  may comprise of polyimide, epoxy, or benzocyclobutene, and can be formed by a method comprising a spin-coating process, a dipping process, a spraying process, a screen-printing process, or a thin film process. 
     The first coil layer  3  comprises a first coil  31  comprising an inner end portion  32  and an outer end portion  33 . The second coil layer  5  comprises a second coil  51  comprising an inner end portion  52  and an outer end portion  53 . The third coil layer  7  comprises a third coil  71  comprising an inner end portion  72  and an outer end portion  73 . The fourth coil layer  9  comprises a fourth coil  91  comprising an inner end portion  92  and an outer end portion  93 . 
     The first insulating layer  4  comprises a contact hole  41 . The second insulating layer  6  comprises a contact hole  61 . A conductive pillar  12  is formed through the contact holes  41  and  61 , connecting the inner end portion  32  of the first coil  31  and the inner end portion  72  of the third coil  71  such that the first coil  31  is connected in series with the third coil  71 . The second insulating layer  6  further comprises a contact hole  63 . The third insulating layer  8  comprises a contact hole  82 . A conductive pillar  17  is formed through the contact holes  63  and  82 , connecting the outer end portion  53  of the second coil  51  and the outer end portion  93  of the fourth coil  91  such that the second coil  51  is connected in series with the fourth coil  91 . 
     The conductive pillar  12  or  17  can be formed using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. The conductive pillar  12  or  17  may be made of a material comprising silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. 
     The first conductor layer  14  comprises a conductor  141 . The conductor  141  comprises an end portion extending adjacent to a periphery  301  of the common mode filter  300  for making an external electrical connection and another end portion connected with the inner end portion  52  of the second coil  51  through the contact holes on the lateral insulating layer  2  and the first insulating layer  4 . The second conductor layer  15  comprises a conductor  151 . The conductor  151  comprises an end portion extending adjacent to a periphery  301  of the common mode filter  300  for making an external electrical connection and another end portion connecting with the inner end portion  92  of the fourth coil  91  through the contact hole on the lateral insulating layer  10 . Furthermore, the outer end portion  33  of the first coil  31  extends adjacent to the periphery  301  of the common mode filter  300 , connecting with a corresponding electrode adjacent to the periphery  301  of the common mode filter  300 . The outer end portion  73  of the third coil  71  also extends adjacent to the periphery  301  of the common mode filter  300 , connecting with a corresponding electrode adjacent to the periphery  301  of the common mode filter  300 . 
     The first conductor layer  14 , the first coil layer  3 , the second coil layer  5 , the third coil layer  7 , the fourth coil layer  9 , or the second conductor layer  15  may be formed of material comprising silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. In addition, the first conductor layer  14 , the first coil layer  3 , the second coil layer  5 , the third coil layer  7 , the fourth coil layer  9 , or the second conductor layer  15  may be formed using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. 
     In addition to the connecting manner demonstrated in  FIG. 3 , the first coil  31 , the second coil  51 , the third coil  71 , and the fourth coil  91  may be connected by other connecting manners. In another embodiment, the outer end portion  33  of the first coil  31  is connected with the outer end portion  73  of the third coil layer  7  such that the first coil  31  is connected in series with the third coil  71 . The inner end portion  52  of the second coil  51  is connected with the inner end portion  92  of the fourth coil  91  such that the second coil  51  is connected in series with the fourth coil  91 . Moreover, the inner end portion  32  of the first coil  31  and the inner end portion  72  of the third coil  71  are respectively connected with conductors for making an external electrical connection. 
       FIG. 4  is a cross-sectional view schematically demonstrating a common mode filter  400  according to another embodiment of the present invention. As shown in  FIG. 4 , the common mode filter  400  comprises a first material layer  1 , an outer insulating layer  35 , a first conductor layer  14 ′, a lateral insulating layer  2 , a first coil layer  3 , a first insulating layer  4 , a second coil layer  5 , a second insulating layer  6 , a third coil layer  7 , a third insulating layer  8 , a fourth coil layer  9 , a lateral insulating layer  10 , a second conductor layer  15 ′, an outer insulating layer  36 , and a second material layer  11 . 
     The outer insulating layer  35  is formed on the first material layer  1 . The first conductor layer  14 ′ is formed on the outer insulating layer  35 . The lateral insulating layer  2  covers the first conductor layer  14 ′. The first coil layer  3  is formed on the lateral insulating layer  2 . The first insulating layer  4  covers the first coil layer  3 . The second coil layer  5  is formed on the first insulating layer  4 . The second insulating layer  6  covers the second coil layer  5 . The third coil layer  7  is formed on the second insulating layer  6 . The third insulating layer  8  covers the third coil layer  7 . The fourth coil layer  9  is formed on the third insulating layer  8 . The lateral insulating layer  10  covers the fourth coil layer  9 . The second conductor layer  15 ′ is formed on the lateral insulating layer  10 . The outer insulating layer  36  covers the second conductor layer  15 ′. The second material layer  11  is disposed on the outer insulating layer  36 . 
     Regarding the first insulating layer  4 , the second insulating layer  6 , and the third insulating layer  8 , either one, two or all three may comprise of magnetic material such as ferromagnetic material. In one embodiment, the magnetic material may comprise nickel zinc ferrite or manganese-zinc ferrite. 
     The first coil layer  3  comprises a first coil  31  comprising an inner end portion  32  and an outer end portion  33 . The second coil layer  5  comprises a second coil  51  comprising an inner end portion  52  and an outer end portion  53 . The third coil layer  7  comprises a third coil  71  comprising an inner end portion  72  and an outer end portion  73 . The fourth coil layer  9  comprises a fourth coil  91  comprising an inner end portion  92  and an outer end portion  93 . 
     The first insulating layer  4  comprises a contact hole  42  and the second insulating layer  6  comprises a contact hole  64 . A conductive pillar  18  is formed through the contact holes  42  and  64 , connecting the outer end portion  33  of the first coil  31  and the outer end portion  73  of the third coil  71  such that the first coil  31  is connected in series with the third coil  71 . The second insulating layer  6  further comprises a contact hole  65  and the third insulating layer  8  comprises a contact hole  83 . A conductive pillar  19  is formed through the contact holes  65  and  83 , connecting the outer end portion  53  of the second coil  51  and the outer end portion  93  of the fourth coil  91  such that the second coil  51  is connected in series with the fourth coil  91 . 
     The conductive pillars  18  and  19  may be formed using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. The conductive pillar  18  or  19  may be made of material comprising silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. 
     The first conductor layer  14 ′ comprises two conductors  141  and  142 . The conductor  141  comprises one end portion extending to the periphery  301  of the common mode filter  400  for making an external electrical connection and another end portion connected with the inner end portion  52  of the second coil  51  through the contact holes on the lateral insulating layer  2  and the first insulating layer  4 . The conductor  142  comprises an end portion extending adjacent to the periphery  301  of the common mode filter  400  for making an external electrical connection and another end portion connected with the inner end portion  32  of the first coil  31  through the contact hole on the lateral insulating layer  2 . The second conductor layer  15 ′ comprises two conductors  151  and  152 . The conductor  151  comprises an end portion extending to the periphery  301  of the common mode filter  400  for making an external electrical connection and another end portion connected with the inner end portion  72  of the third coil  71  through the contact holes on the lateral insulating layer  10  and the third insulating layer  8 . The conductor  152  comprises an end portion extending adjacent to the periphery  301  of the common mode filter  400  for making an external electrical connection and another end portion connected with the inner end portion  92  of the fourth coil  91  through the contact hole on the lateral insulating layer  10 . 
     The first conductor layer  14 ′, the first coil layer  3 , the second coil layer  5 , the third coil layer  7 , the fourth coil layer  9 , or the second conductor layer  15 ′ can be made of material comprising silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. Moreover, the first conductor layer  14 ′, the first coil layer  3 , the second coil layer  5 , the third coil layer  7 , the fourth coil layer  9 , or the second conductor layer  15 ′ can be formed using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. 
     In one embodiment, the first material layer  1  and/or the second material layer  11  may comprise of magnetic material. 
     In one embodiment, the first material layer  1  and/or the second material layer  11  may comprise of a heterogeneous substrate. 
       FIG. 5  is a cross-sectional view schematically demonstrating a common mode filter  500  according to another embodiment of the present invention. Referring to  FIG. 5 , the common mode filter  500  comprises a first material layer  1 , a first coil layer  3 , a first insulating layer  4 , a second coil layer  5 , a second insulating layer  6 , a third coil layer  7 ′, a third insulating layer  8 , a fourth coil layer  9 ′, a fourth insulating layer  25 , a fifth coil layer  21 , a fifth insulating layer  26 , a sixth coil layer  22 , a sixth insulating layer  27 , a conductor layer  23 , a seventh insulating layer  28 , a conductor layer  24 , and a second material layer  11 , wherein the first insulating layer  4  electrically separates the first coil layer  3  from the second coil layer  5 , the second insulating layer  6  electrically separates the second coil layer  5  from the third coil layer  7 ′, the third insulating layer  8  electrically separates the third coil layer  7 ′ from the fourth coil layer  9 ′, the fourth insulating layer  25  electrically separates the fourth coil layer  9 ′ from the fifth coil layer  21 , the fifth insulating layer  26  electrically separates the fifth coil layer  21  from the sixth coil layer  22 , the sixth insulating layer  27  electrically separates the sixth coil layer  22  from the conductor layer  23 , and the seventh insulating layer  28  electrically separates the conductor layer  23  from the conductor layer  24 . 
     In one embodiment, the first insulating layer  4 , the second insulating layer  6 , the third insulating layer  8 , the fourth insulating layer  25 , the fifth insulating layer  26 , the sixth insulating layer  27 , or the seventh insulating layer  28  may comprise of polyimide, epoxy, or benzocyclobutene. At least one of the first insulating layer  4 , the second insulating layer  6 , the third insulating layer  8 , the fourth insulating layer  25 , the fifth insulating layer  26 , the sixth insulating layer  27 , or the seventh insulating layer  28  may comprise of magnetic material such as ferromagnetic material. In one embodiment, the magnetic material comprises nickel zinc ferrite or manganese-zinc ferrite. 
     The first coil layer  3  comprises a first coil  31 . The second coil layer  5  comprises a second coil  51 . The third coil layer  7 ′ comprises a third coil  71 . The fourth coil layer  9 ′ comprises a fourth coil  91 . The fifth coil layer  21  comprises a fifth coil  211 . The sixth coil layer  22  comprises a sixth coil  221 . The first coil layer  3 , the second coil layer  5 , the third coil layer  7 ′, the fourth coil layer  9 ′, the fifth coil layer  21 , and the sixth coil layer  22  are formed in a stacking manner, wherein the first coil  31 , the third coil  71  and the fifth coil  211  are connected in series, and the second coil  51 , the fourth coil  91  and the sixth coil  221  are connected in a series. Further, the first coil  31 , the second coil  51 , the third coil  71 , the fourth coil  91 , the fifth coil  211 , and the sixth coil  221  are disposed between the first material layer  1  and the second material layer  11 . 
     In one embodiment, a lateral insulating layer  2  is formed on the first material layer  1 , and the first coil layer  3  is formed on the lateral insulating layer  2 . In addition, a lateral insulating layer  10  can be formed, covering the conductor layer  24 , and the second material layer  11  is disposed on the lateral insulating layer  10 . 
     The lateral insulating layers  2  and  10  may comprise of polyimide, epoxy, or benzocyclobutene, and can be formed by a method comprising a spin-coating process, a dipping process, a spraying process, a screen-printing process, or a thin film process. 
     A conductive pillar  12  is formed through the contact hole  41  of the first insulating layer  4  and the contact hole  61  of the second insulating layer  6 , connecting the inner end portion  32  of the first coil  31  and the inner end portion  72  of the third coil  71 . The outer end portion  33  of the first coil  31  is connected with an electrode  34 . 
     A conductive pillar  13  is formed through the contact hole  62  of the second insulating layer  6  and the contact hole  81  of the third insulating layer  8 , connecting the inner end portion  52  of the second coil  51  and the inner end portion  92  of the fourth coil  91 . The outer end portion  53  of the second coil  51  is connected with an electrode  54 . 
     A conductive pillar  75  is formed through the contact hole  82  on the third insulating layer  8  and the contact hole  252  on the fourth insulating layer  25 , connecting the outer end portion  73  of the third coil  71  and the outer end portion  213  of the fifth coil  211 . 
     A conductive pillar  95  is formed through the contact hole  251  on the fourth insulating layer  25  and the contact hole  261  on the fifth insulating layer  26 , connecting the outer end portion  93  of the fourth coil  91  and the outer end portion  223  of the sixth coil  221 . 
     A conductive pillar  214  is formed through the contact hole  262  on the fifth insulating layer  26  and the contact hole  271  on the sixth insulating layer  27 , connecting the inner end portion  212  of the fifth coil  211  and one end portion of the conductor  231  of the conductor layer  23 . Another end portion of the conductor  231  is connected with an electrode. 
     A conductive pillar  224  is formed through the contact hole  272  on the sixth insulating layer  27  and the contact hole  281  on the seventh insulating layer  28 , connecting the inner end portion  222  of the sixth coil  221  and one end portion of the conductor  241  of the conductor layer  24 . Another end portion of the conductor  241  is connected with an electrode. 
     The first coil layer  3 , the second coil layer  5 , the third coil layer  7 ′, the fourth coil layer  9 ′, the fifth coil layer  21 , the sixth coil layer  22 , the conductor layer  23 , or the conductor layer  24  may be made of material comprising silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof, and can be formed using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. 
     The conductive pillar  12 ,  13 ,  75 ,  95 ,  214 , or  224  may be made of material comprising silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof, and can be formed using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. 
     In one embodiment, the first material layer  1  and/or the second material layer  11  may comprise of magnetic material. 
     In one embodiment, the first material layer  1  and/or the second material layer  11  may comprise of a heterogeneous substrate. 
       FIG. 6  is a sectional top view showing a common mode filter  100 ′ according to another embodiment of the present invention.  FIG. 7  is a cross-sectional view showing a common mode filter  100 ′ according to one embodiment of the present invention. Referring to  FIGS. 6 and 7 , the common mode filter  100 ′ comprises a first coil layer  3 , a second coil layer  5 , a third coil layer  7 , a fourth coil layer  9 , and a magnetic material portion ( 601 ,  602 ,  603 , or  604 ). The first coil layer  3  comprises a first coil  31 . The second coil layer  5  comprises a second coil  51 . The third coil layer  7  comprises a third coil  71 . The fourth coil layer  9  comprises a fourth coil  91 . The second coil  51  is disposed between the first coil  31  and the third coil  71 . The third coil  71  is disposed between the second coil  51  and the fourth coil  91 . The first coil  31  is connected in series with the third coil  71 . The second coil  51  is connected in series with the fourth coil  91 . The serially connected first and third coils  31  and  71  are magnetically coupled with the serially connected second and fourth coils  51  and  91  such that the serially connected first and third coils  31  and  71  and the serially connected second and fourth coils  51  and  91  may be used together to eliminate common mode noise. The magnetic material portion ( 601 ,  602 ,  603 , or  604 ) is formed through the first, second, third, and fourth coils ( 31 ,  51 ,  71 , and  91 ) such that the common mode filter  100 ′ exhibits higher impedance. 
     In one embodiment, the common mode filter  100 ′ comprises a magnetic material portion  601 , wherein the first, second, third, and fourth coils ( 31 ,  51 ,  71 , and  91 ) are formed surrounding the magnetic material portion  601 . 
     In one embodiment, the common mode filter  100 ′ comprises a magnetic material portion  601 , wherein the magnetic material portion  601  passes through the centers of the first, second, third, and fourth coils ( 31 ,  51 ,  71 , and  91 ). 
     In one embodiment, the common mode filter  100 ′ comprises a magnetic material portion ( 602 ,  603 , or  604 ), wherein the magnetic material portion ( 602 ,  603 , or  604 ) passes through the inter-turn spaces  96  of the first, second, third, and fourth coils ( 31 ,  51 ,  71 , and  91 ). 
     In one embodiment, the common mode filter  100 ′ comprises a magnetic material portion  601  and at least one of the magnetic material portions ( 602 ,  603 , and  604 ). 
       FIGS. 8 through 10  are cross-sectional views schematically depicting the steps of the method of manufacturing a common mode filter  100 ′ according to one embodiment of the present invention. The common mode filter  100 ′ of the embodiment in  FIG. 10  is similar to the common mode filter  100  of the embodiment in  FIG. 1  except that the common mode filter  100 ′ includes a magnetic material portion  601 . As such, the structures of coil layers and the connections between coils can refer to  FIG. 1 . As shown in  FIGS. 1 and 8 , a material layer  1  is provided. In one embodiment, the material layer  1  can be an insulating material layer. In one embodiment, the material layer  1  can be a magnetic material layer. In one embodiment, the material layer  1  can be a heterogeneous substrate as shown in  FIGS. 13 to 15 , wherein the heterogeneous substrate comprises an insulating substrate and a magnetic material layer. The insulating substrate and the magnetic material layer can be co-fired to join or bonded together using an adhesive. The insulating substrate and the magnetic material layer can be separately formed using a thick film printing process. The magnetic material layer may comprise nickel-zinc ferrite or manganese-zinc ferrite. The magnetic material layer may comprise of polymer material and magnetic powder. The polymer may comprise of polyimide, epoxy, or benzocyclobutene and the magnetic powder may comprise of nickel-zinc ferrite or manganese-zinc ferrite. The insulating substrate may comprise aluminum oxide, aluminum nitride, glass, or quartz. 
     Thereafter, a lateral insulating layer  2  is formed on the material layer  1 . The lateral insulating layer  2  may comprise of polyimide, epoxy, or benzocyclobutene. The lateral insulating layer  2  can be formed using a spin-coating process, a dipping process, a spraying process, a screen-printing process, or a thin film process. 
     Referring to  FIGS. 1 and 8 , a first coil layer  3  is formed on the lateral insulating layer  2 . The first coil layer  3  comprises a first coil  31  and an electrode  34 , as shown in  FIG. 1 , wherein an outer end portion  33  of the first coil  31  is connected with the electrode  34 . The first coil layer  3  may comprise metal such as silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. The material for forming the first coil layer  3  can be deposited using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. The patterning of the metal layer can be performed by a lithography process. The metal layer may comprise silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. 
     In particular, the first coil  31  can be formed using a plating process. The plating process initially forms an electrode layer on the lateral insulating layer  2 . The electrode layer can be formed using a sputtering or vapor deposition process. A chromium or titanium film can be formed under the electrode layer for facilitating the adhesion between the electrode layer and the lateral insulating layer  2 . Next, a photoresist layer with a coil pattern is formed on the electrode layer by a lithography process. Thereafter, an electroplated layer is formed using an electroplating process. The photoresist layer is peeled off, then the electrode layer is removed using an etch process, and finally, the first coil  31  can be obtained. 
     Furthermore, a first insulating layer  4  is formed, covering the first coil layer  3 . The first insulating layer  4  may comprise polymer, which may comprises polyimide, epoxy, or benzocyclobutene. The first insulating layer  4  may be formed using a spin-coating process, a dipping process, a spraying process, a screen-printing process, or a thin film process. 
     Thereafter, a second coil layer  5  comprising a second coil  51  and an electrode  74 , as shown in  FIG. 1 , is formed on the first insulating layer  4 , wherein the outer end portion  53  of the second coil  51  is connected with the electrode  54  as shown in  FIG. 1 . The second coil layer  5  may be made of metal comprising silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. The material used to form the second coil layer  5  may be deposited by a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. The patterning of the second coil layer  5  may be performed using a lithography process. In one embodiment, the second coil  51  may be formed using the above-mentioned plating process. 
     Subsequently, a second insulating layer  6  is formed, covering the second coil layer  5 . The second insulating layer  6  may comprise polymer comprising polyimide, epoxy, or benzocyclobutene. The second insulating layer  6  may be formed using a spin-coating process, a dipping process, a spraying process, a screen-printing process, or a thin film process. 
     Moreover, as shown in  FIG. 1 , contact holes  41  and  61  are formed on the location of the inner end portion  32  of the first coil  31  using a lithography process to expose the inner end portion  32  of the first coil  31 . Afterwards, metal is deposited into the contact holes  41  and  61  using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process to form a conductive pillar  12 . 
     Referring back to  FIGS. 1 and 8 , a third coil layer  7  is formed on the second insulating layer  6 . The third coil layer  7  comprises a third coil  71  and an electrode  74  ( FIG. 1 ), wherein the outer end portion  73  of the third coil  71  is connected with the electrode  74 , as shown in  FIG. 1 , while the inner end portion  72  of the third coil  71  is connected with the conductive pillar  12 . The third coil layer  7  is formed of metal comprising silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. The material used to form the third coil layer  7  can be deposited using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. The patterning of the third coil layer  7  may be performed using a lithography process. In one embodiment, the third coil  71  may be formed using the above-mentioned plating process. 
     Furthermore, a third insulating layer  8  is formed, covering the third coil layer  7 . The third insulating layer  8  may comprise polymer that may comprise polyimide, epoxy, or benzocyclobutene. The third insulating layer  8  may be formed using a spin-coating process, a dipping process, a spraying process, a screen-printing process, or a thin film process. 
     Thereafter, contact holes  62  and  81  are formed using a lithography process to expose the inner end portion  52  of the second coil  51 . Afterwards, metal material is deposited into the contact holes  62  and  81  using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process to form a conductive pillar  13 . 
     Moreover, a fourth coil layer  9  comprising a fourth coil  91  and an electrode  94  ( FIG. 1 ) is formed on the third insulating layer  8 , wherein the outer end portion  93  of the fourth coil  91  is connected with the electrode  94 , as shown in  FIG. 1 , and the inner end portion  92  of the fourth coil  91  is connected with the conductive pillar  13 . The fourth coil layer  9  is formed of metal comprising silver, palladium, aluminum, chromium, nickel, titanium, gold, copper, platinum, or an alloy thereof. The material used to form the fourth coil layer  9  may be deposited using a plating process or a vacuum film formation process including a vapor deposition process or a sputtering process. The patterning of the fourth coil layer  9  can be carried out using a lithography process. In one embodiment, the fourth coil  91  can be formed using the above-mentioned plating process. 
     Thereafter, a lateral insulating layer  10  is formed, covering the fourth coil layer  9 . The lateral insulating layer  10  may comprise of a polymer that may include polyimide, epoxy, or benzocyclobutene. 
     Further, a recess  605  is formed, passing through the first insulating layer  4 , the second insulating layer  6 , and the third insulating layer  8 , exposing the lateral insulating layer  2 . In one embodiment, the recess  605  can expose the surface that supports the first coil layer  3 . In another embodiment, the recess  605  can be formed through the surface that supports the first coil layer  3 . 
     As shown in  FIG. 9 , magnetic material  606  is disposed to cover the lateral insulating layer  10  and fill into the recess  605 . The magnetic material  606  may comprise of resin. The magnetic material  606  can be printed onto the lateral insulating layer  10  and then the magnetic material  606  is hardened. 
     The hardened magnetic material  606  can then be polished, leaving the necessary portions. In one embodiment, the portion of the hardened magnetic material  606  above the lateral insulating layer  10  is removed. In another embodiment, the portion of the hardened magnetic material  606  above the lateral insulating layer  10  is polished to form a thin layer covering the lateral insulating layer  10 . 
     As shown in  FIG. 10 , a material layer  11  is disposed on the lateral insulating layer  10 . In one embodiment, the material layer  11  is an insulating substrate, which may comprise of polyimide, epoxy, or benzocyclobutene. In one embodiment, the material layer  11  comprises a magnetic plate member. 
     In one embodiment, the material layer  11  can be bonded to the lateral insulating layer  10  by an adhesive layer  701 . 
     The common mode filters in other embodiments of the present invention can be formed using the process demonstrated in  FIGS. 8 through 10 , and the details are not described to avoid redundant description. 
       FIG. 11  is a diagram illustrating the relationship between the impedance and frequency of a common mode filter according to one embodiment of the present invention.  FIG. 12  is a diagram illustrating the relationship between the impedance and frequency of a conventional common mode filter. In comparison of the curves in  FIG. 11  and  FIG. 12 , it can be found that the common mode filter of one embodiment of the present invention exhibits higher impedance, and has a wider rejection bandwidth at the same impedance level. Thus, the common mode filter with a multi-spiral layer structure can have better performance compared to a conventional common mode filter. 
     In the following description, numerous details, such as specific materials, dimensions, and processes, are set forth in order to provide a thorough understanding of the present invention. However, one skilled in the art will realize that the invention may be practiced without these particular details. In other instances, well-known semiconductor equipment and processes have not been described in particular detail so as to avoid obscuring the present invention. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, many of the processes discussed above can be implemented in different methodologies and replaced by other processes, or a combination thereof. 
     Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.