Abstract:
An electronic component comprises an insulator substrate ( 11 ), a layered member composed of a plurality of insulator resin layers ( 12   a-   12   f ) and a plurality of conductor pattern layers ( 13   a-   13   f ) alternately stacked on the insulator substrate to form a first conductor line and a second conductor line each of which comprises at least one conductor layer, first and second external electrode terminal portions connected to opposite ends of the first conductor line and covering first and second areas of side surfaces of said layered member and the insulator substrate, respectively, and a third external electrode terminal portion connected to one end of the second conductor line and covering a third area of the side surfaces of the layered member and the insulator substrate. The second conductor lines have magnetic and electrocapacitive coupling with respect to the first conductor line.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an electronic component and, in particular, to an electronic component as an electronic circuit element of a surface-mounted type or a leaded type such as an inductor (L), a capacitor (C), an electric resistance element (R), a thin film EMI filter, a common mode choke coil, a current sensor, a signal transformer, and a composite electronic component comprising an integral combination of the above-mentioned electronic components. 
     A conventional multilayer interconnection board is disclosed in Japanese Unexamined Patent Publication (JP-A) No. 4-167596 (167596/1992) (Reference 1). As shown in FIG. 1, the multilayer interconnection board comprises a ceramics substrate  51  mainly containing silicon, alumina, and the like, and a conductive interconnection layer  52  comprising Cu formed on a predetermined region of the ceramics substrate  51 . Then, an entire surface of the ceramics substrate  51  and the conductive interconnection layer  52  is coated with an insulator resin layer  53  of benzocyclobutene (BCB). After a photo resist pattern is formed on the insulator resin layer  53 , the insulator resin layer  53  of BCB is etched to form via holes  54 . After the via holes  54  are formed, a Cu film is overlaid an entire surface by sputtering and then etched. Alternatively, after a Cr or Ti film is overlaid the entire surface by sputtering, a Cu sputtered film or a Cu or Au or Al plated film is formed to thereby provide a conductive interconnection layer  55 . 
     On the other hand, Japanese Unexamined Patent Publication (JP-A) No. 3-201417 (201417/1991) (Reference 2) discloses an electronic component of the type illustrated in FIG.  2 . The electronic component comprises an insulator substrate  101  of, for example, alumina. On the insulator substrate  101 , an insulator resin layer  102  of polyimide resin and internal conductor patterns  103  and  104  of Ti, Ti—Ag, or Ag formed by sputtering are alternately stacked. Then, an end portion of the insulator resin layer  102  is removed to expose an end portion of the uppermost conductor pattern  104 . Thus, a high frequency coil  100  is formed as the electronic component. 
     Practically, a terminal underlayer portion is formed on the side surface of the electronic component so as to connect with the end portion of the conductor pattern  104 . The terminal underlayer portion is covered with a conductor layer which extends from an end of the upper surface through the side surface to an end of the lower surface of the component. Thus, an external electrode terminal portion is formed. 
     Reference 1 describes the multilayer interconnection board which is neither an electronic component as a circuit element nor an electronic component having a plurality of circuit elements. 
     On the other hand, when the electronic component of the type disclosed in Reference 2 is manufactured, the insulator layers and the conductor layers for a plurality of the electronic components are alternately stacked on different portions of the insulator substrate of a relatively large size. Thus, a plurality of the electronic components are formed on the single insulator substrate. Thereafter, the insulator substrate is cut to separate the individual electronic components. However, since the insulator substrate comprises a very hard material such as alumina, cutting cost is high in the cutting process. In addition, occurrence of chipping of the insulator substrate results in high fraction defective and low yielding percentage. 
     In the above-mentioned structure, the irregularity of the underlying conductor pattern layer reflects or is reproduced on the surface of the insulator resin layer formed thereon. This results in the unevenness of the overlying conductor pattern layer stacked on the insulator resin layer. In this event, a desired characteristic can not be achieved. 
     Furthermore, the moisture contained in the ambient air enters into the electronic component through a gap between the insulator resin layer and the electrode terminal portion. This brings about corrosion of the conductor pattern and fluctuation of the characteristic. As a result, the quality of the electronic component is considerably deteriorated. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a highly reliable electronic component which can be easily manufactured and reduced in size and which has characteristics desired. 
     It is another object of the present invention to provide a circuit element comprising at least one of a low pass filter, a common choke coil, a transformer, an inductance, a capacitance, and an electric resistance each of which is formed as the above-mentioned electronic component. 
     According to this invention, there is provided an electronic component comprising an insulator substrate, a layered member composed of a plurality of insulator resin layers and a plurality of conductor pattern layers alternately stacked on the insulator substrate to form a first conductor line and a second conductor line each of which comprises at least one conductor layer, first and second external electrode terminal portions connected to opposite ends of the first conductor line and covering first and second areas of side surfaces of the layered member and the insulator substrate, respectively, and a third external electrode terminal portion connected to one end of the second conductor line and covering a third area of the side surfaces of the layered member and the insulator substrate. The first and the second conductor lines have magnetic and electrocapacitive coupling with each other. 
     According to this invention, there is also provided a common mode choke coil comprising the above mentioned electronic component. The common mode choke coil further comprises a fourth external electrode terminal connected to the other end of the second conductor line and formed on the side surfaces of the layered member and the insulator substrate at a fourth area different from the first through the third external electrode terminal portions. Each of the first and the second conductor lines have a pattern circulated on different conductor layers, the number of turns in both lines being equal to each other. A pair of the first and the third external electrode terminals and another pair of the second and the fourth external electrode terminals serves as an input terminal pair and an output terminal pair, respectively. 
     According to this invention, there is also provided a transformer comprising the above mentioned electronic component. The transformer further comprises a fourth external electrode terminal connected to the other end of the second conductor line and formed on the side surfaces of the layered member and the insulator substrate at a fourth area different from the first through the third external electrode terminal portions. Each of the first and the second conductor lines have a pattern circulated on different conductor layers. A pair of the first and the second external electrode terminal and another pair of the third and the fourth external connection terminals serves as an input terminal pair and an output terminal pair, respectively. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a conventional multilayer interconnection board; 
     FIG. 2 is a sectional view of a conventional electronic component; 
     FIG. 3 is a perspective view of a low pass filter as an electronic component according to a first embodiment of this invention; 
     FIG. 4 is an exploded perspective view of the electronic component illustrated in FIG. 3; 
     FIGS. 5A through 5D show a first part of a process of forming a layered structure for the electronic component illustrated in FIG. 3; 
     FIGS. 6A through 6D show a second part of the process following the first part illustrated in FIGS. 5A through 5D; 
     FIGS. 7A through 7D show a third part of the process following the second part illustrated in FIGS. 6A through 6D; 
     FIG. 8 is a perspective view of showing a plurality of the layered structures formed on an insulator substrate of a large size before separation into the individual electronic components; 
     FIG. 9 is a sectional view of a terminal structure formed on one of the electronic components cut from the insulator substrate illustrated in FIG. 8; 
     FIG. 10 shows another terminal structure for an electronic component having a three terminal structure; 
     FIG. 11 is an exploded perspective view of conductor patterns of a common mode choke coil as another electronic component according to a second embodiment of this invention; 
     FIG. 12 is a partial sectional view of a terminal structure of the common choke coil illustrated in FIG. 11; and 
     FIG. 13 is an exploded perspective view of conductor patterns of a transformer as still another electronic component according to a third embodiment of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Now, description will be made about preferred embodiments of this invention with reference to the drawing. 
     At first referring to FIG. 3, an electronic component according to a first embodiment of this invention is an EMI filter. As shown in FIG. 3, the electronic component  10  comprises a main body  1  and first through third external electrode terminal portions  2   a ,  2   b , and  2   c  formed on different side surfaces of the main body  1 , respectively, to extend from an end of the upper surface through the side surfaces to an end of the lower surface. Specifically, the first and the second external electrode terminal portions  2   a  and  2   b  cover the side surfaces of the main body  1  opposite to each other in a longitudinal direction. The third external electrode terminal portion  2   c  covers the center area of one of the side surfaces parallel to the longitudinal direction. 
     Referring to FIG. 4, the main body  1  comprises a ceramics substrate  11  as an insulator substrate, a plurality of insulator resin layers  12   a  through  12   d , and a plurality of conductor pattern layers  13   a  through  13   d . As shown in FIG. 4, the insulator resin layers  12   a ,  12   b ,  12   c , and  12   d  and the conductor pattern layers  13   a ,  13   b ,  13   c , and  13   d  are alternately stacked on the ceramics substrate  11 . 
     In order to increase the number of turns of a coil of the EMI filter, an additional conductor pattern layer  13   c ′ may be interposed together with an additional insulator layer. 
     In this embodiment, the ceramics substrate  11  comprises a machinable ceramics material manufactured and sold by Mitsui Mining Material, Co., Ltd. under the trade name “Macerite”. The characteristics of the ceramics material are shown in Table 1 in comparison with alumina. 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Machinable 
                   
               
               
                   
                 Ceramics 
                   
               
               
                   
                 (Macerite) 
                 Alumina 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Vickers Hardness 
                 220 
                 about 2000 
               
               
                   
                 (kg/mm 2 ) 
               
               
                   
                 Dielectric 
                 6.5 
                 10 
               
               
                   
                 Constant ε 
               
               
                   
                 Relative 
                 1 
                 1 
               
               
                   
                 Permiability μ 
               
               
                   
                 Resistivity 
                 5 × 10 15   
                 10 14   
               
               
                   
                 (Ω · cm) 
               
               
                   
                 Breakdown 
                 150 
                 150 
               
               
                   
                 Voltage 
               
               
                   
                 (kv/cm) 
               
               
                   
                 Water 
                 0 
                 0 
               
               
                   
                 Absorption 
               
               
                   
                 (%) 
               
               
                   
                 Upper Limit 
                 700 
                 (1500) 
               
               
                   
                 Temperature 
               
               
                   
                 (° C.) 
               
               
                   
                   
               
             
          
         
       
     
     Each of the insulator resin layers  12   a  through  12   d  comprises benzocyclobutene (BCB) as ultraviolet photosensitive resin. The use of BCB as the insulator resin layers achieves an excellent flatness of the insulator resin layers. As a consequence, it is possible to obtain a layered structure having a flat surface without an unevenness. Therefore, the electronic component  10  has excellent electric characteristics. 
     Referring to FIGS.  5 A through SD,  6 A through  6 D, and  7 A through  7 D, a process of forming the layered structure of the insulator resin layers and the conductor pattern layers will be described. 
     Referring to FIGS. 5A through 5D, the insulator resin layer  12   a  is formed on the ceramics substrate  11  (not shown) after the ceramics substrate  11  is cleaned by the use of acetone, methylalcohol, or the like. If necessary, the insulator resin layer  12   a  is cleaned by reverse sputtering, as shown in FIG.  5 A. On the insulator resin layer  12   a , an underlayer  3  comprising a Ti film and a Cu film is deposited by sputtering, as illustrated in FIG.  5 B. In FIG. 5B, the Ti film and the Cu film have a thickness of 0.05 μm and a thickness of 0.25-0.3 μm, respectively, although not separately shown in the figure. 
     Next, as shown in FIG. 5C, a resist  4  is applied on the underlayer  3 . Then, by the use of photolithography, the resist  4  is exposed through a mask  5  and developed, as illustrated in FIG.  5 D. 
     In the above-mentioned manner, a resist pattern  4 ′ is formed as illustrated in FIG.  6 A. Then, surface treatment is carried out by the use of H 2 SO 4 . Subsequently, an electrolytic Cu plated layer  6  is formed by electrolytic Cu plating, as illustrated in FIG.  6 B. 
     Referring to FIG. 6C, the resist pattern  4 ′ is removed to form an intermediate conductor pattern  7 . 
     Then, the intermediate conductor pattern  7  illustrated in FIG. 6C is subjected to wet-etching (or dry-etching) to remove those portions of the underlayer  3  exposed without the electrolytic Cu plated layer  6 . Then, cleaning is carried out by the use of HCl. As a consequence, an isolated conductor pattern layer  13   a  is formed on the insulator resin layer  12   a , as illustrated in FIG.  6 D. Although the upper surface of the Cu plated layer  6  is slightly etched during etching, the intermediate conductor pattern  7  will not be removed because it is thicker than the underlayer  3 . 
     The conductor pattern layer  13   a  thus obtained comprises the patterns of underlayer  3  and the electrolytic Cu plated layer  6  and has a thickness of about 3-5 μm and a width of about 30 μm. No trouble or inconvenience has been encountered during cleaning, photolithography, and etching in the manufacturing process. 
     Referring to FIGS. 7A through 7D, formation of another insulator resin layer  12   b  is described. As shown in FIG. 7A, the conductor pattern layer  13   a  formed on the insulator resin layer  12   a  (FIG. 6D) is coated with the ultraviolet photosensitive resin of BCB by spin coating to form an intermediate insulator resin layer  8 . Then, by the use of photolithography, the intermediate insulator resign layer  8  is exposed through a mask  9 , as illustrated in FIG.  7 B. As a result, through holes  14  are formed in the intermediate insulator resin layer  8 , as illustrated in FIG.  7 C. The through holes  14  serve to establish electrical contact between the conductor pattern layer  13   a  and another conductor pattern layer formed above. It is therefore unnecessary to form the through holes  14  over the entire surface of the conductor pattern layer  13   a.    
     Then, half-curing is carried out in the nitrogen atmosphere at 210° C. for 30 minutes to obtain the insulator resin layer  12   b  illustrated in FIG.  7 D. 
     The other conductor layers  13   b ,  13   c , and  13   d  illustrated in FIG. 4 are formed in the manner similar to that described in conjunction with FIGS. 5A through 5D and  6 A through  6 D. The other insulator layers  12   c  and  12 D are formed in the manner similar to that described in conjunction with FIGS. 7A through 7D. 
     By repeating the above-mentioned steps, a plurality of main bodies  1  of the electronic components  10  are formed on the insulator substrate, as shown in FIG.  8 . 
     Next referring to FIG. 9, description proceeds to a step of forming the external electrode terminal portion (simply depicted at  2 ) on the main body  1  of each of the electronic components shown in FIG.  8 . In the state illustrated in FIG. 8, the conductor pattern is exposed in the upper surface of the main body  1 . Before separating the individual main bodies  1  by cutting, an external surface of each main body  1  is covered with an insulator resin layer  12   e . In addition, an electrode extracting portion  16  in the form of a through hole is formed in the manner similar to that described above. Then, the electrode extracting portion  16  is filled with a conductive metal material, for example, Cu, to form an electrode extracting pattern  17 . In addition, a protection layer  12   f  of, for example, polyimide, is formed on a surface region of the insulator resin layer  12   e  which is not covered with the electrode extracting pattern  17 . The protection layer  12   f  may be made of any appropriate material selected from various materials such as those specified in Table 2 in dependence upon the applications. 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Material of 
                   
                   
               
               
                 Insulator 
                   
                   
               
               
                 Layer in 
                   
                   
               
               
                 Multilayer 
                 Protection 
                   
               
               
                 Structure 
                 Layer 
                 Effect 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 BCB (Benzo- 
                 Polyimide 
                 1. 
                 Improvement of Mechanical 
               
               
                 cyclobutene) 
                   
                   
                 Strength → Reduction of 
               
               
                 (Water 
                   
                   
                 Defects upon Mounting 
               
               
                 Absorption 
                   
                   
                 between Steps 
               
               
                 0.25%) 
                   
                 2. 
                 Assurance of Fire 
               
               
                   
                   
                   
                 Proofness 
               
               
                   
                   
                   
                 (Shielding BCB from 
               
               
                   
                   
                   
                 Atmosphere (oxygen)) 
               
               
                   
                 Epoxy 
                 3. 
                 Easy Application 
               
               
                   
                   
                   
                 (Spin Coater) 
               
               
                   
                   
                   
                 Formation at Low Tempera- 
               
               
                   
                   
                   
                 ture → Low Cost 
               
               
                   
                 SiO 2   
                 1. 
                 Improvement of Mechanical 
               
               
                   
                 (CVD 
                   
                 Strength 
               
               
                   
                 Deposition) 
                 2. 
                 Assurance of Fire 
               
               
                   
                   
                   
                 Proofness 
               
               
                   
                 Si 3 N 4   
                 (3. 
                 Further Improvement of 
               
               
                   
                 (CVD 
                   
                 Anti-Humidity) 
               
               
                   
                 Deposition) 
               
               
                 Polyimide 
                 BCB 
                 1. 
                 Improvement of 
               
               
                 (Water 
                 (Benzo- 
                   
                 Anti-Humidity 
               
               
                 Absorption 
                 cyclobutene) 
                 2. 
                 Low Cost (Spin Coater, 
               
               
                 0.25%) 
                   
                   
                 Formation at Low Tempera- 
               
               
                   
                   
                   
                 ture) 
               
               
                   
                 SiO 2   
                 1. 
                 Improvement of 
               
               
                   
                 (CVD Film) 
                   
                 Anti-Humidity 
               
               
                   
                 Si 3 N 4   
                 (3. 
                 Further Improvement of 
               
               
                   
                 (CVD Film) 
                   
                 Mechanical Strength) 
               
               
                   
               
             
          
         
       
     
     The ceramics substrate (FIG. 8) with a plurality of the main bodies  1  formed thereon is cut by a dicing saw along a dash-and-dot line. Thus, the individual main bodies  1  are separated. In FIG. 8, one of the main bodies  1  is depicted by the solid line. 
     Then, the main body  1  is cleaned by the use of 5% HCl solution. Thereafter, Ni conductive paste comprising, for example, epoxy resin containing Ni powder is applied to an area from an end portion of the electrode extracting pattern  17  through the side surface to the lower surface of the main body  1  and is subjected to thermosetting or thermal curing. Next, ultrasonic cleaning is carried out by the use of both a KOH solution and a H 2 SO 4  solution as a pretreatment prior to plating. Thereafter, a Ni plated film  18  is formed as an underlayer by electrolytic barrel plating of a nickel sulfanate bath. Herein, Ni is excellent in electrolysis migration and serves to protect the internal diffusion of solder or the like. Thereafter, a solder plated film  19  is formed on the Ni plated film  18  by electrolysis barrel plating of a tin-lead alkanolsulfonate bath. The tin-lead alkanolsulfonate bath prevents the deterioration of the insulator resin layer because no chelating agent is contained. It is noted here that the solder plated film  19  can be formed by a phenolsulfonate plating bath. A tin plated film may be formed instead of the solder plated film. 
     In the above-mentioned terminal structure, the electrode extracting pattern  17  is formed above the insulator resin layer  12  at the interface between the electrode extracting pattern  17  and the insulator resin layer. Therefore, the separation therebetween hardly occurs so that external moisture is effectively prevented from entering. 
     Referring to FIG. 10, another terminal structure of an electronic component according to a second embodiment of this invention will be described. In FIG. 8, a three terminal structure used in the EMI filter, LCR parts, and the like, is illustrated. The electrode extracting pattern  17  is connected to the second conductor pattern layer  13  counted from the topmost conductor pattern layer  13 . The protection film is not shown in the figure. 
     Referring to FIG. 11, a common mode choke coil according to a third embodiment of this invention has first through fourth conductor pattern layers  13   a  through  13   d . Practically, in the manner similar to that illustrated in FIG. 3, the first through the fourth conductor pattern layers  13   a  through  13   d  are successively stacked with the insulator resin layers interposed therebetween although the insulator resin layers are not shown in FIG. 11 for convenience of illustration. In FIG. 11, each of the first through the fourth conductor pattern layers  13   a  through  13   d  has end patterns  15   a  through  15   d . The end patterns  15   a  of the first through the fourth conductor pattern layers  13   a  through  13   d  are overlapped on one another through notches formed in the insulator resin layers to be electrically connected. Likewise, the end patterns  15   b ,  15   c , and  15   d  are respectively overlapped and electrically connected. The end portion of a conductor pattern  21  of the first or the lowest conductor pattern layer  13   a  is connected through a central conductor pattern  23  of the second conductor pattern layer  13   b  to the end portion of an extracting conductor pattern  25  of the third conductor pattern layer  13   c . In this structure, the end portions  15   b  and  15   d  of the conductor patterns serve as opposite ends of a single circulated conductor line. On the other hand, a circulating conductor pattern  24  of the second conductor pattern layer  13   b  is connected to the end portion of an extracting conductor pattern  26  of the third conductor pattern layer  13   c . In this structure, the end portions  15   a  and  15   c  of the conductor patterns serve as opposite ends of another circulated conductor line. These conductor lines have the same number of turns. 
     FIG. 12 shows the structure of the terminal portion of the electronic component illustrated in FIG.  11 . In FIG. 12, the terminal portion has a four terminal structure. The electrode extracting pattern  17  is connected to the uppermost conductor pattern layer  13 . The protection film is not shown in the figure. 
     Referring to FIG. 13, a transformer according to a fourth embodiment of the present invention has first through fourth conductor pattern layers  13   a  through  13   d . Practically, in the manner similar to that illustrated in FIG. 4, the first through the fourth conductor pattern layers  13   a  through  13   d  are successively stacked with the insulator resin layers interposed therebetween. In FIG. 13, each of the conductor pattern layers  13   a  through  13   d  has end patterns  15   a  through  15   d . The end patterns  15   a  are overlapped on one another through notches formed in the insulator resin layers to be electrically connected. Likewise, the end patterns  15   b ,  15   c , and  15   d  are respectively overlapped and electrically connected. The end portion of a circulated conductor pattern  27  of the first conductor pattern layer  13   a  is connected to the end portion of an extracting conductor pattern  28  of the second conductor pattern layer  13   b . In this structure, the end portions  15   a  and  15   b  of the conductor patterns serve as opposite ends of a single circulated conductor line. On the other hand, the end portion of a circulating conductor pattern  30  of the third conductor pattern layer  13   c  is connected to another extracting conductor pattern  29  of the second conductor pattern layer  13   b . In this structure, the end portions  15   c  and  15   d  of the conductor patterns serve as opposite ends of another circulated conductor line. The turn ratio of these conductor lines is 1:n. 
     In the common mode choke coil (FIG. 11) and the transformer (FIG.  13 ), each of the conductor pattern layers is formed in the manner described in conjunction with FIGS. 5A through 5D and  6 A through  6 D. The insulator resin layers which are not shown in FIGS. 11 and 13 are formed in the manner described in conjunction with FIGS. 7A through 7D. In either case, the terminal structure illustrated in FIG. 12 is used. 
     In either case, a plurality of the above-mentioned electronic components are simultaneously formed on the insulator substrate  11  of a large size in the manner similar to that described in conjunction with FIG.  8 . After separation into each individual component, the terminal structure is formed. The cutting operation is easily carried out if the insulator substrate comprises a machinable material, for example, having a Vickers hardness within the range between 100 and 1000. Thus, the cost can be reduced. 
     Although the foregoing embodiments have been directed to the low pass filter, the common mode choke coil, and the transformer, this invention is also applicable to an element such as an inductor, a capacitor, or an electric resistance element. 
     As thus far been described, the electronic component of this invention can be easily manufactured and reduced in size, has desired characteristics, and is highly reliable. 
     Furthermore, a circuit element comprising at least one of the low pass filter, the common mode choke coil, the transformer, the inductance, the capacitance, and the electric resistance each of which is formed as the electronic component is obtained according to the present invention.