Abstract:
A thin film type common mode noise filter and its fabrication method are disclosed. There are several electric insulation layers, coil lead layers and main coil layers are formed on an insulation substrate by means of processes of Lithography, Physical Vapor Deposition, etching or other chemical process. After that the structure is covered with an electric insulation gluing layer and a magnetic material layer so as to form a thin film type common mode noise filter with a low production cost but an improved filtering characteristic of the common mode noise.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a structure of thin film type common mode noise filter, and in particular, to a thin film coil formed on an insulation substrate with a less expensive cost yet is capable of eliminating high frequency common mode noise, and also to its fabrication method. 
     2. Description of the Related Art 
     In U.S. Pat. No. 7,145,427B2, there disclosed “Coil Component and Method of manufacturing the Same” in which a common mode noise filtering element forms a coil component on a magnetic substrate and then a cavity is caved by etching process on part of the substrate where no coil component occupies, after that the surface thereof is flattened by filling with the magnetic powder mixed with colloidal substance, and followed by the gluing process to bond with another magnetic material thereby completing the fabrication. 
     In the other U.S. Pat. No. 6,356,181 B1 and 6,618,929 B2, a layered common mode noise filter is disclosed. In both cases, a coil structure is established on a magnetic substrate and then covered by a magnetic substrate. The kernel of both cases lies in that a special wiring skill is employed for the coil to lessen the impedance of the differential signals. 
     However, all the aforementioned fabrication methods have the same shortcomings of complexity, time wasting and high cost in its fabrication. When using a magnetic material as the substrate, the ability to filter the common mode noise can not exceed −20 dB, and the manufacturing cost of the common mode noise filter never comes down under such situations. 
     The inventor of the present invention herein provides a common mode noise filter which is simply constructed and can be fabricated with a low cost, yet having common mode noise filtering characteristic of above −30 dB, and also the fabrication method thereof is to be elucidated. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to provide a structure of thin film type common mode noise filter which is simply constructed and can be fabricated with a low cost, and the method of the fabrication thereof. 
     To achieve the above object, the present invention employs a substrate made of insulation material on which a thin film coil structure and insulation layers are established by spin coating, Lithography process, Physical Vapor Deposition, electroplating and thin film etching process successively, and finally a magnetic material layer is formed on the upper surface by gluing, spin coating or screen printing. 
     In the present invention, Al 2 O 3 , AlN, Glass or Quartz are used as an insulation substrate to achieve the low loss and high insulation properties. By doing so, the fabrication process can be simplified, the cost can be came down, but get a better filtering effect of common mode noises. 
     Further objects and purposes of the present invention will become apparent to persons from the detailed descriptions of the following embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of the thin film type common mode noise filter of the present invention. 
         FIGS. 2A through 2J  are a flow chart showing the fabrication process of the present invention. 
         FIG. 3  is a second embodiment of the present invention. 
         FIG. 4  is a third embodiment of the present invention. 
         FIG. 5  is a fourth embodiment of the present invention. 
         FIG. 6  is a graph comparing the electrical characteristic of the present invention with that of a conventional product. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , the thin film type common mode noise filter of the present invention comprises, from bottom to top: an insulation substrate  1 , a first electric insulation layer  2 , a first coil lead layer  3 , a second electric insulation layer  4 , a first main coil layer  5 , a third electric insulation layer  6 , a second main coil layer  7 , a fourth electric insulation layer  8 , a second coil lead layer  9 , an insulation/gluing layer  10 , and a magnetic material layer  11 . 
     The fabrication process of the aforesaid filter includes the following steps: 
     S 1 : As shown in  FIG. 2A , selecting one of the Al 2 O 3 , AlN, glass or quartz substrate as the insulation substrate  1 , and forming a first electric insulation layer  2  on its top surface, the material of the first electric insulation layer  2  is selected one of the polyimide, epoxy resin, Benzo CycloButene (BCB) or other high molecular polymers. The thickness of the spin coating layer can be used to adjust the impedance. 
     S 2 : As shown in  FIG. 2B , forming a first coil lead layer  3  whose constructive material is selected one of Ag, Pd, Al, Cr, Ni, Ti, Au, Cu, Pt or their alloys. The first coil lead layer  3  includes a first electrode  31 , a second electrode  32  and a conductor line  33  connected therebetween. 
     S 3 : As shown in  FIG. 2C , forming a second electric insulation layer  4  on the first coil lead layer  3  by spin coating, and making a via hole  41  by Lithography or etching process, the position of the via hole  41  is aligned with the first electrode  31  of the first coil lead layer  3 . The material of the second electric insulation layer  4  is also selected one of the polyimide, epoxy resin, BCB or other high molecular polymers. 
     S 4 : As shown in  FIG. 2D , forming a first main coil layer  5  on the second electric insulation layer  4  by thin film metal deposition, Lithography and electroplating alternately, the material of the first main coil layer  5  is also selected one of Ag, Pd, Al, Cr, Ni, Ti, Au, Cu, Pt, or their alloys. The first main coil layer  5  includes a first electrode  51 , a second electrode  52  and a helical coil  53  connected therebetween. The first electrode  51  is connected with the first electrode  31  of the first coil lead layer  3  via the via hole  41  of the second electric insulation layer  4 . 
     S 5 : As shown in  FIG. 2E , forming a second electric insulation layer  6  on the first main coil layer  5  by spin coating, the material of the second electric insulation layer  6  is also selected one of the polyimide, epoxy resin, BCB or other high molecular polymers. 
     S 6 : As shown in  FIG. 2F , forming a second main coil layer  7  on the second electric insulation layer  6  by thin film metal deposition, Lithography and electroplating, the material of the second main coil layer  7  is also selected one of Ag, Pd, Al, Cr, Ni, Ti, Au, Cu, Pt, or their alloys. The second main coil layer  7  includes a first electrode  71 , a second electrode  72  and a helical coil  73  connected therebetween. 
     S 7 : As shown in  FIG. 2G , forming a fourth electric insulation layer  8  on the second main coil layer  7  by spin coating, and caving a via hole  81  by Lithography or etching. 
     S 8 : As shown in  FIG. 2H , forming a second coil lead layer  9  on the fourth electric insulation layer  8  by thin film metal deposition, Lithography and electroplating alternately, the material of the second coil lead layer  9  is one of Ag, Pd, Al, Cr, Ni, Ti, Au, Cu, Pt, or their alloys. The second coil lead layer  9  includes a first electrode  91 , a second electrode  92  and a conductor line  93  connected therebetween. The first electrode  91  is connected with the first electrode  71  of the second main coil layer  7  via the via hole  81  of the fourth electric insulation layer  8 . 
     S 9 : As shown in  FIG. 2I , forming an insulation/gluing layer  10  on the second coil lead layer  9  by spin coating. 
     S 10 : Finally as shown in  FIG. 2J , fabricating an upper lid using a magnetic material layer  11  by gluing, screen printing or spin coating. The magnetic material layer  11  may be a magnetic substrate or a colloidal substance mixed with the magnetic powder, where the colloidal substance may be one of the polyimide, epoxy resin, BCB or other high molecular polymers. 
     The aforesaid etching process may be either dry or wet etching process, RIE is preferable for dry etching, while chemical solution etching is adaptive for wet etching. 
     It is understood that in the present invention, the insulation layer and the coil structure are fabricated sequentially on a low energy loss and high insulation substrate, and a magnetic material layer is formed on the uppermost surface by gluing a magnetic substrate, or screen printing/spin coating a colloidal substance mixed with the magnetic powder, where the colloidal substance may be one of the polyimide, epoxy resin or other high molecular polymers. 
     From the above description, it can be clearly observed that the thin film type common mode noise filter of the present invention can be fabricated with simple steps yet with low production cost. 
     Referring to  FIG. 6 , in the graph measured by the vector network analyzer, a higher common mode noise filtering effect can be achieved in comparison with the conventional one, wherein Scc 21  attains below −30 dB. 
     Referring to  FIG. 3 , in the second embodiment, the magnetic material layers  301  and  302  are each formed on the uppermost and lowermost surface of the structure. In the third embodiment shown in  FIG. 4 , the magnetic material layers  401 .  402 ,  403 ,  404  can respectively be formed on the uppermost, lowermost, left and right surfaces. 
     Referring to  FIG. 5 , in the fourth embodiment, the coil lead layers and the main coil layers are formed in pairs according to the requirements of the electronic products which the filter of the present invention is applied. In this case, the structure comprises, from bottom to top: an insulation substrate  501 , a first electric insulation layer  502 , a first paired coil lead layers  503 , a second electric insulation layer  504 , a first paired main coil layers  505 , a third electric insulation layer  506 , a second paired main coil layers  507 , a fourth electric insulation layer  508 , a second paired coil lead layers  509 , an insulation/gluing layer  600 , and a magnetic material layer  601 . 
     It is understood that the present invention is a high level technical creation, by no means simply utilizes conventional technology or knowledge known prior to the application for patent, or not easily be made by persons skilled in the prior arts, and the invention has neither been published or put to public use, nor displayed in an exhibition. Therefore the present invention is entitled for a patent. 
     Those who are skilled in the arts will readily perceive how to modify the invention. Therefore, the appended claims are to be construed to cover all equivalent structures which fall within the true scope and spirit of the invention.