Patent Publication Number: US-9406438-B2

Title: Stack-type inductor element and method of manufacturing the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stack-type inductor element, and particularly to a stack-type inductor element including a stack obtained by stacking a magnetic element layer and a non-magnetic element layer and a conductor pattern located on opposing surfaces of the magnetic element layer which defines a portion of the inductor. 
     The present invention also relates to a manufacturing method of manufacturing such a stack-type inductor element. 
     2. Description of the Related Art 
     Japanese Patent Laying-Open No. 2009-111197 and Japanese Patent Laying-Open No. 2009-231331 disclose one example of a stack-type inductor element of this type and a method of manufacturing the same. According to Japanese Patent Laying-Open No. 2009-111197, an adhesive film is provided on at least one surface of a sintered ferrite substrate. In addition, in order to provide a stack with a bending property, a fracture is formed in the substrate. Here, a fracture lowers permeability, however, permeability varies depending on a state of the fracture. Therefore, grooves are formed in the substrate with regularity and a fracture is formed in this groove portion. Thus, magnetic characteristics after formation of a fracture can be stabilized while a bending property is provided. 
     According to Japanese Patent Laying-Open No. 2009-231331, in order to divide a ceramic substrate into individual pieces of a stack, a division groove is formed in the ceramic substrate. Specifically, the division groove is formed by moving a scribing blade pressed against the other main surface of the ceramic substrate with a desired pressure. In succession, a roller pressed against one main surface of the ceramic substrate with a protection sheet being interposed is moved along the ceramic substrate. Thus, the ceramic substrate deforms to open the division groove, so that the ceramic substrate is divided along the division groove. 
     When a groove is formed in a substrate in a stage prior to firing, warpage is caused due to asymmetry between one main surface and the other main surface forming the substrate. This warpage may impair coplanarity of each element obtained by breakage (division into individual pieces) of the substrate and may become a factor interfering decrease in thickness. 
     SUMMARY OF THE INVENTION 
     Therefore, preferred embodiments of the present invention provide a stack-type inductor element capable of achieving a smaller thickness and a method of manufacturing the same. 
     A stack-type inductor element according to a preferred embodiment of the present invention includes a stack including a magnetic element layer, a coil-shaped conductor pattern provided in the stack, a plurality of first pad electrodes located on one main surface of the stack, and a plurality of second pad electrodes located on the other main surface of the stack and symmetric to the plurality of first pad electrodes, the stack has a rectangular or substantially rectangular shape when viewed in a direction of stack of the stack, and one end and the other end of the coil-shaped conductor pattern are electrically connected to two of the plurality of first pad electrodes, respectively, and the plurality of second pad electrodes are all electrically open. 
     Preferably, the stack has the rectangular or substantially rectangular shape when viewed in the direction of stack of the stack and the plurality of first pad electrodes are arranged in two rows along a longitudinal direction of the stack. 
     Preferably, the number of the first pad electrodes is three or more and a pad electrode not connected to the coil-shaped conductor pattern of the plurality of first pad electrodes is each electrically open. 
     Preferably, the stack includes non-magnetic element layers arranged to be superimposed on opposing main surfaces of the magnetic element layer. 
     A method of manufacturing a stack-type inductor element according to another preferred embodiment of the present invention is a method of manufacturing a stack-type inductor element by dividing into division units, a substrate assembly having a structure that sandwiches a magnetic element layer between a first outermost layer and a second outermost layer, including a first step of forming a plurality of first via holes passing through the first outermost layer, a second step of forming a plurality of first conductor patterns on an upper surface of the first outermost layer or a lower surface of the magnetic element layer, a third step of forming a plurality of second via holes passing through the magnetic element layer, a fourth step of forming a plurality of second conductor patterns on an upper surface of the magnetic element layer or a lower surface of the second outermost layer, a fifth step of performing an operation for forming a plurality of first pad electrodes on a lower surface of the first outermost layer and connecting two first pad electrodes to two respective points of the plurality of first conductor patterns through two first via holes for each division unit, a sixth step of forming a plurality of second pad electrodes on an upper surface of the second outermost layer so as to be symmetric to the plurality of first pad electrodes, and a seventh step of fabricating a plurality of inductors by spirally connecting the plurality of first conductor patterns and the plurality of second conductor patterns through the plurality of second via holes for each division unit. 
     Preferably, a ninth step of applying a blade of a scriber to a line defining the division unit and forming a groove in a longitudinal direction and a direction of a short side of the substrate assembly is further provided. 
     The substrate assembly preferably includes a quadrangular or substantially quadrangular main surface, and the ninth step includes the steps of forming a first groove having a first depth along a long side of the quadrangle and forming a second groove having a second depth smaller than the first depth along a short side of the quadrangle. 
     A tenth step of firing the substrate assembly prior to the ninth step preferably is further provided. 
     Preferably, the fifth step includes the step of filling the plurality of first via holes with a first conductive material, and the seventh step includes the step of filling the plurality of second via holes with a second conductive material (PS 2 , PS 2 ′). 
     Preferably, the substrate assembly has a thickness not greater than about 0.6 mm, for example. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view showing a state that a stack-type inductor element according to a preferred embodiment of the present invention is disassembled. 
         FIG. 2A  is a plan view showing one example of a ceramic sheet SH 1  of a stack-type inductor element and  FIG. 2B  is a plan view showing one example of a ceramic sheet SH 3  of the stack-type inductor element. 
         FIG. 3A  is an illustrative diagram showing one example of a pad electrode located on a lower surface of ceramic sheet SH 1  and  FIG. 3B  is a plan view showing one example of a ceramic sheet SH 4  of the stack-type inductor element. 
         FIG. 4  is a perspective view showing an appearance of the stack-type inductor element according to a preferred embodiment of the present invention. 
         FIG. 5  is a cross-sectional view along A-A′ of the stack-type inductor element shown in  FIG. 4 . 
         FIG. 6A  is a process chart showing a portion of a process for manufacturing ceramic sheet SH 1  and  FIG. 6B  is a process chart showing another portion of the process for manufacturing ceramic sheet SH 1 . 
         FIG. 7A  is a process chart showing still another portion of the process for manufacturing ceramic sheet SH 1  and  FIG. 7B  a process chart showing yet another portion of the process for manufacturing ceramic sheet SH 1 . 
         FIG. 8A  is a process chart showing a portion of a process for manufacturing a ceramic sheet SH 2 ,  FIG. 8B  is a process chart showing another portion of the process for manufacturing ceramic sheet SH 2 , and  FIG. 8C  is a process chart showing still another portion of the process for manufacturing ceramic sheet SH 2 . 
         FIG. 9A  is a process chart showing a portion of a process for manufacturing ceramic sheet SH 3  and  FIG. 9B  is a process chart showing another portion of the process for manufacturing ceramic sheet SH 3 . 
         FIG. 10A  is a process chart showing still another portion of the process for manufacturing ceramic sheet SH 3  and  FIG. 10B  is a process chart showing yet another portion of the process for manufacturing ceramic sheet SH 3 . 
         FIG. 11A  is a process chart showing a portion of a process for manufacturing ceramic sheet SH 4  and  FIG. 11B  is a process chart showing another portion of the process for manufacturing ceramic sheet SH 4 . 
         FIG. 12  is a plan view showing one example of a carrier film on which a pad electrode is printed. 
         FIG. 13A  is a process chart showing a portion of a process for manufacturing a stack-type inductor element,  FIG. 13B  is a process chart showing another portion of the process for manufacturing a stack-type inductor element, and  FIG. 13C  a process chart showing still another portion of the process for manufacturing a stack-type inductor element. 
         FIG. 14A  is a process chart showing yet another portion of the process for manufacturing a stack-type inductor element,  FIG. 14B  is a process chart showing another portion of the process for manufacturing a stack-type inductor element,  FIG. 14C  is a process chart showing still another portion of the process for manufacturing a stack-type inductor element, and  FIG. 14D  is a process chart showing yet another portion of the process for manufacturing a stack-type inductor element. 
         FIG. 15A  is a process chart showing a portion of a process for manufacturing ceramic sheet SH 1  in another preferred embodiment of the present invention and  FIG. 15B  is a process chart showing another portion of the process for manufacturing ceramic sheet SH 1  in another preferred embodiment of the present invention. 
         FIG. 16A  is a process chart showing still another portion of the process for manufacturing ceramic sheet SH 1  in another preferred embodiment of the present invention and  FIG. 16B  is a process chart showing yet another portion of the process for manufacturing ceramic sheet SH 1  in another preferred embodiment of the present invention. 
         FIG. 17A  is a process chart showing a portion of a process for manufacturing ceramic sheet SH 2  in another preferred embodiment of the present invention and  FIG. 17B  is a process chart showing another portion of the process for manufacturing ceramic sheet SH 2  in another preferred embodiment of the present invention. 
         FIG. 18A  is a process chart showing still another portion of the process for manufacturing ceramic sheet SH 2  in another preferred embodiment of the present invention and  FIG. 18B  is a process chart showing yet another portion of the process for manufacturing ceramic sheet SH 2  in another preferred embodiment of the present invention. 
         FIG. 19A  is a process chart showing a portion of a process for manufacturing ceramic sheet SH 3  in another preferred embodiment of the present invention and  FIG. 19B  is a process chart showing another portion of the process for manufacturing ceramic sheet SH 3  in another preferred embodiment of the present invention. 
         FIG. 20A  is a process chart showing still another portion of the process for manufacturing ceramic sheet SH 3  in another preferred embodiment of the present invention and  FIG. 20B  is a process chart showing yet another portion of the process for manufacturing ceramic sheet SH 3  in another preferred embodiment of the present invention. 
         FIG. 21A  is a process chart showing a portion of a process for manufacturing ceramic sheet SH 4  in another preferred embodiment of the present invention and  FIG. 21B  is a process chart showing another portion of the process for manufacturing ceramic sheet SH 4  in another preferred embodiment. 
         FIG. 22A  is a process chart showing a portion of a process for manufacturing a stack-type inductor element in another preferred embodiment of the present invention,  FIG. 22B  is a process chart showing another portion of the process for manufacturing a stack-type inductor element in another preferred embodiment of the present invention, and  FIG. 22C  a process chart showing still another portion of the process for manufacturing a stack-type inductor element in another preferred embodiment of the present invention. 
         FIG. 23A  is a process chart showing yet another portion of the process for manufacturing a stack-type inductor element in another preferred embodiment of the present invention,  FIG. 23B  is a process chart showing another portion of the process for manufacturing a stack-type inductor element in another preferred embodiment of the present invention, and  FIG. 23C  is a process chart showing still another portion of the process for manufacturing a stack-type inductor element in another preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a stack-type inductor element  10  according to a preferred embodiment includes ceramic sheets SH 1  to SH 4  stacked such that each main surface defines a quadrangular or substantially quadrangular shape and preferably is for use as an antenna element for wireless communication in a 13.56 MHz band. Ceramic sheets SH 1  to SH 4  preferably are equal or substantially equal in size of each main surface. Ceramic sheets SH 1  and SH 4  include a non-magnetic element, whereas ceramic sheets SH 2  to SH 3  include a magnetic element. 
     Consequently, a stack  12  preferably defines a parallelepiped. Ceramic sheets SH 2  to SH 3  define a magnetic element layer  12   a , ceramic sheet SH 1  defines a non-magnetic element layer  12   b , and ceramic sheet SH 4  defines a non-magnetic element layer  12   c . The stack  12  of the stack-type inductor element  10  has a stack structure such that magnetic element layer  12   a  is sandwiched between non-magnetic element layers  12   b  and  12   c . A long side and a short side of the quadrangle defining the main surface (e.g., an upper surface or a lower surface) of stack  12  extend along an X axis and a Y axis respectively, and a thickness of stack  12  increases along a Z axis. 
     As shown in  FIGS. 2A and 2B , a plurality of linear conductors are provided on an upper surface of ceramic sheet SH 1 , and a plurality of linear conductors  18  are provided on an upper surface of ceramic sheet SH 3 . In addition, as shown in  FIGS. 3A and 3B , a plurality of pad electrodes  14   a  are provided on a lower surface of ceramic sheet SH 1 , and a plurality of pad electrodes  14   b  are provided on an upper surface of ceramic sheet SH 4 . It is noted that no linear conductor is present on an upper surface of ceramic sheet SH 2  and a magnetic element appears over the entire upper surface. 
     Referring to  FIG. 2A , linear conductors  16  are aligned at a distance D 1  in a direction of the X axis in a position extending obliquely to the Y axis. Opposing ends in a direction of length of linear conductor  16  remain inside of opposing ends in a direction of the Y axis of the upper surface of ceramic sheet SH 1 . Two linear conductors  16  on opposing sides in the direction of the X axis are arranged inside of the opposing ends in the direction of the X axis of the upper surface of ceramic sheet SH 1 . 
     Referring to  FIG. 2B , linear conductors  18  are aligned at distance D 1  in the direction of the X axis in a position extending along the Y axis. Opposing ends in a direction of length of linear conductor  18  also remain inside of the opposing ends in the direction of the Y axis of the upper surface of ceramic sheet SH 3 . Two linear conductors  18  on opposing sides in the direction of the X axis are also arranged inside of the opposing ends in the direction of the X axis of the upper surface of ceramic sheet SH 3 . 
     A distance in the direction of the X axis from one end to the other end of linear conductor  16  corresponds to “D 1 ”. A position of one end of linear conductor  16  is adjusted to a position coinciding with one end of linear conductor  18  when viewed in a direction of the Z axis, and a position of the other end of linear conductor  16  is adjusted to a position coinciding with the other end of linear conductor  18  when viewed in the direction of the Z axis. The number of linear conductors  16  preferably is smaller by one than the number of linear conductors  18 . 
     Therefore, when viewed in the direction of the Z axis, linear conductors  16  and  18  are alternately aligned in the direction of the X axis. In addition, one end of linear conductor  16  coincides with one end of linear conductor  18 , and the other end of linear conductor  16  coincides with the other end of linear conductor  18 . 
     Referring to  FIG. 3A , a plurality of pad electrodes each includes a main surface that is rectangular or substantially rectangular and the pad electrodes are equal or substantially equal to one another in a size of the main surface. Some of the pad electrodes  14   a  extend at an equal or substantially equal interval along the X axis slightly inside of an end portion on a positive side in the direction of the Y axis, and the remaining pad electrodes  14   a  extend at an equal interval along the X axis slightly inside of an end portion on a negative side in the direction of the Y axis. 
     A distance from pad electrode  14   a  present on a most negative side in the direction of the X axis to the end portion on the negative side in the direction of the X axis of ceramic sheet SH 1  is equal or substantially equal to a distance from pad electrode  14   a  present on a most positive side in the direction of the X axis to the end portion on the positive side in the direction of the X axis of ceramic sheet SH 1 . A distance from pad electrode  14   a  present on the most negative side in the direction of the Y axis to the end portion on the negative side in the direction of the Y axis of ceramic sheet SH 1  is equal or substantially equal to a distance from pad electrode  14   a  present on the most positive side in the direction of the Y axis to the end portion on the positive side in the direction of the Y axis of ceramic sheet SH 1 . 
     Therefore, with a straight line extending along the X axis through the center in the direction of the Y axis of the main surface of ceramic sheet SH 1  being defined as the reference, the pad electrodes  14   a  on the negative side in the direction of the Y axis relative to the straight line are in line symmetry to the pad electrodes  14   a  on the positive side in the direction of the Y axis relative to the straight line. 
     With a straight line extending along the Y axis through the center in the direction of the X axis of the main surface of ceramic sheet SH 1  being defined as the reference, the pad electrodes  14   a  on the negative side in the direction of the X axis relative to the straight line are in line symmetry to the pad electrodes  14   a  on the positive side in the direction of the X axis relative to this straight line. 
     Referring to  FIG. 3B , the pad electrodes  14   b  each preferably include a rectangular or substantially rectangular main surface and are equal or substantially equal to one another in a size of the main surface. Among these, some of the pad electrodes  14   b  extend at an equal or substantially equal interval along the X axis slightly inside of an end portion on a positive side in the direction of the Y axis, and the remaining pad electrodes  14   b  extend at an equal or substantially equal interval along the X axis slightly inside of an end portion on a negative side in the direction of the Y axis. 
     A distance from pad electrode  14   b  present on a most negative side in the direction of the X axis to the end portion on the negative side in the direction of the X axis of ceramic sheet SH 4  is equal or substantially equal to a distance from pad electrode  14   b  present on a most positive side in the direction of the X axis to the end portion on the positive side in the direction of the X axis of ceramic sheet SH 4 . A distance from pad electrode  14   b  present on the most negative side in the direction of the Y axis to the end portion on the negative side in the direction of the Y axis of ceramic sheet SH 4  is equal or substantially equal to a distance from pad electrode  14   b  present on the most positive side in the direction of the Y axis to the end portion on the positive side in the direction of the Y axis of ceramic sheet SH 4 . 
     Therefore, with a straight line extending along the X axis through the center in the direction of the Y axis of the main surface of ceramic sheet SH 4  being defined as the reference, the pad electrodes  14   b  on the negative side in the direction of the Y axis relative to the straight line are in line symmetry to six pad electrodes  14   b  on the positive side in the direction of the Y axis relative to the straight line. 
     With a straight line extending along the Y axis through the center in the direction of the X axis of the main surface of ceramic sheet SH 4  being defined as the reference, the pad electrodes  14   b  on the negative side in the direction of the X axis relative to the straight line are in line symmetry to the pad electrodes  14   b  on the positive side in the direction of the X axis relative to the straight line. 
     A size of the main surface of pad electrode  14   b  is also the same as a size of the main surface of pad electrode  14   a , and a manner of arrangement of pad electrodes  14   b  at the main surface of ceramic sheet SH 4  is the same as a manner of arrangement of pad electrodes  14   a  at the main surface of ceramic sheet SH 1 . Therefore, pad electrodes  14   b  are in mirror symmetry with pad electrodes  14   a . When viewed in the direction of the Z axis, opposing ends of each linear conductor  18  coincide with two pad electrodes  14   a  aligned along the Y axis, and further coincide also with two pad electrodes  14   b  aligned along the Y axis. 
     Referring back to  FIG. 1 , via hole conductors  20   a  pass through magnetic element layer  12   a  in the direction of the Z axis at a position of one end of linear conductors  16  (the end portion on the positive side in the direction of the Y axis). Via hole conductors  20   b  pass through magnetic element layer  12   a  in the direction of the Z axis at a position of the other end of linear conductors  16  (the end portion on the negative side in the direction of the Y axis). 
     Linear conductors  16  are arranged as shown in  FIG. 2A , and linear conductors  18  are arranged as shown in  FIG. 2B . Therefore, via hole conductors  20   a  are connected to first ends (the end portion on the positive side in the direction of the Y axis) of linear conductors  18  starting from the negative side in the direction of the X axis at the upper surface of ceramic sheet SH 3 . Via hole conductors  20   b  are connected to second ends (the end portion on the negative side in the direction of the Y axis) of linear conductors  18  starting from the positive side in the direction of the X axis at the upper surface of ceramic sheet SH 3 . 
     Consequently, linear conductors  16  and linear conductors  18  are spirally connected, and thus, a coil conductor (a wound element) having the X axis as an axis of winding is provided. Since a magnetic element is present inside the coil conductor, the coil conductor defines and functions as an inductor. 
     A via hole conductor  22   a  passes through magnetic element layer  12   a  and non-magnetic element layer  12   b  in the direction of the Z axis at a position of one end of linear conductor  18  present on the most positive side in the direction of the X axis. Similarly, a via hole conductor  22   b  passes through magnetic element layer  12   a  and non-magnetic element layer  12   b  in the direction of the Z axis at a position of the other end of linear conductor  18  present on the most negative side in the direction of the X axis. 
     Via hole conductor  22   a  is connected to pad electrode  14   a  present on the most positive side in the direction of the X axis and on the positive side in the direction of the Y axis. Via hole conductor  22   b  is connected to pad electrode  14   a  present on the most negative side in the direction of the X axis and on the negative side in the direction of the Y axis. Thus, two different points of the inductor are connected to two pad electrodes  14   a  and  14   a , respectively. 
     Stack  12 , that is, stack-type inductor element  10 , thus fabricated has an appearance shown in  FIG. 4 . A cross-section along A-A′ of this stack-type inductor element  10  has a structure shown in  FIG. 5 . 
     It is noted that ceramic sheets SH 1  and SH 4  preferably are made of a non-magnetite ferrite material (relative permeability: 1) and exhibit a value for coefficient of thermal expansion in a range from about 8.5 to about 9.0, for example. Ceramic sheets SH 2  to SH 3  preferably are made of a magnetite ferrite material (relative permeability: 100 to 120) and exhibit a value for coefficient of thermal expansion in a range from about 9.0 to about 10.0, for example. Pad electrodes  14   a  and  14   b , linear conductors  16  and  18 , and via hole conductors  20   a  to  20   b  and  22   a  to  22   b  preferably are made of a silver material and exhibit a coefficient of thermal expansion of about 20, for example. 
     Ceramic sheet SH 1  preferably is fabricated in a manner shown in  FIGS. 6A, 6B, 7A and 7B . Initially, a ceramic green sheet made of a non-magnetic ferrite material is prepared as a mother sheet BS 1  (see  FIG. 6A ). Here, a plurality of dashed lines extending in the direction of the X axis and the direction of the Y axis show cutting positions. Each of a plurality of rectangles defined by these dashed lines is defined as a “division unit”. 
     Then, a plurality of through holes HL 1  are formed in mother sheet BS 1  in correspondence with the vicinity of an intersection of the dashed lines (see  FIG. 6B ), and through hole HL 1  is filled with a conductive paste PS 1  (see  FIG. 7A ). Conductive paste PS 1  forms via hole conductor  22   a  or  22   b . When filling with conductive paste PS 1  is completed, a conductor pattern corresponding to linear conductors  16  is printed on an upper surface of mother sheet BS 1  (see  FIG. 7B ). 
     Ceramic sheet SH 2  preferably is fabricated in a manner shown in  FIGS. 8A to 8C . Initially, a ceramic green sheet made of a magnetic ferrite material is prepared as a mother sheet BS 2  (see  FIG. 8A ). Here, a plurality of dashed lines extending in the direction of the X axis and the direction of the Y axis show cutting positions. Then, a plurality of through holes HL 2  are formed in mother sheet BS 2  along the dashed lines extending in the direction of the X axis (see  FIG. 8B ), and through hole HL 2  is filled with a conductive paste PS 2  forming via hole conductors  20   a ,  20   b ,  22   a , or  22   b  (see  FIG. 8C ). 
     Ceramic sheet SH 3  preferably is fabricated in a manner shown in  FIGS. 9A-9C  and  FIGS. 10A and 10B . Initially, a ceramic green sheet made of a magnetic ferrite material is prepared as a mother sheet BS 3  (see  FIG. 9A ). Here, a plurality of dashed lines extending in the direction of the X axis and the direction of the Y axis show cutting positions. 
     Then, a plurality of through holes HL 3  are formed in mother sheet BS 3  along the dashed lines extending in the direction of the X axis (see  FIG. 9B ), and through hole HL 3  is filled with a conductive paste PS 3  (see  FIG. 10A ). Conductive paste PS 3  forms via hole conductors  20   a ,  20   b ,  22   a , or  22   b . When filling with conductive paste PS 3  is completed, a conductor pattern corresponding to linear conductors  18  is printed on an upper surface of mother sheet BS 3  (see  FIG. 10B ). 
     Ceramic sheet SH 4  preferably is fabricated in a manner shown in  FIGS. 11A and 11B . Initially, a ceramic green sheet made of a non-magnetic ferrite material is prepared as a mother sheet BS 4  (see  FIG. 11A ). Here, a plurality of dashed lines extending in the direction of the X axis and the direction of the Y axis show cutting positions. Then, a conductor pattern corresponding to pad electrodes  14   b  is printed on an upper surface of mother sheet BS 4  (see  FIG. 11B ). 
     The conductor pattern corresponding to pad electrodes  14   a  is printed on a carrier film  24  in a manner shown in  FIG. 12 . A size of a main surface of carrier film  24  is the same as a size of the main surface of mother sheets BS 1  to BS 4 . A plurality of dashed lines extending in the direction of the X axis and the direction of the Y axis correspond to a plurality of dashed lines drawn on mother sheets BS 1  to BS 4 . 
     Mother sheets BS 1  to BS 4  created in the manner described above are stacked and press-bonded in this order (see  FIG. 13A ). Here, a position of stack of each sheet is adjusted such that dashed lines allocated to each sheet coincide when viewed in the direction of the Z axis. In succession, carrier film  24  shown in  FIG. 12  is prepared (see  FIG. 13B ) and a conductor pattern formed on carrier film  24  is transferred to the lower surface of mother sheet BS 1  (see  FIG. 13C ). 
     As transfer of the conductor pattern is completed, carrier film  24  is peeled off (see  FIG. 14A ), and an unprocessed substrate assembly is fabricated. A thickness of the fabricated substrate assembly preferably is reduced to about 0.4 mm or smaller, for example. The fabricated substrate assembly is fired (see  FIG. 14B ) and thereafter subjected to primary scribing and secondary scribing (see  FIGS. 14C and 14D ). 
     In primary scribing, a blade of a scriber  26  is applied along the dashed line extending in the direction of the X axis, and in secondary scribing, the blade of scriber  26  is applied along the dashed line extending in the direction of the Y axis. In any of primary scribing and secondary scribing, a groove is formed in an upper surface of the substrate assembly. It is noted that a groove formed in primary scribing reaches non-magnetic element layer  12   b , whereas a groove formed in secondary scribing reaches only magnetic element layer  12   a . This is a groove made by a prior crack which was caused by adjusting a blade pressure at the time of application of the blade of scriber  26  and intentionally adjusting a depth. As scribing is completed, the substrate assembly is broken into division units, to thus obtain a plurality of stack-type inductor elements  10 . 
     As is clear from the description above, stack  12  includes magnetic element layer  12   a  and non-magnetic element layers  12   b  and  12   c  provided on respective opposing main surfaces thereof. Linear conductors  16  and  18  define a portion of an inductor having a longitudinal direction of stack  12  as an axis of winding and are provided on opposing main surfaces of magnetic element layer  12   a . Pad electrodes  14   a  are provided on the upper surface of stack  12 , and pad electrodes  14   b  are provided on the lower surface of stack  12  so as to be symmetric to pad electrodes  14   a . Two different points of the inductor are electrically connected to two different pad electrodes  14   a  and  14   a , respectively. 
     Stack-type inductor element  10  is manufactured by breaking a substrate assembly having such a structure that magnetic mother sheets BS 2  and BS 3  are sandwiched between non-magnetic mother sheets BS 1  and BS 4  into division units. The substrate assembly is fabricated in a manner below. 
     Initially, through holes HL 1  extending in the direction of the Z axis are formed in mother sheet BS 1  (see  FIG. 6B ), and a conductor pattern corresponding to linear conductors  16  is formed on the upper surface of mother sheet BS 1  (see  FIG. 7B ). In addition, through holes HL 2  extending in the direction of the Z axis are formed in mother sheet BS 2  (see  FIG. 8B ), through holes HL 3  extending in the direction of the Z axis are formed in mother sheet BS 3  (see  FIG. 9B ), and a conductor pattern corresponding to linear conductors  18  is formed on the upper surface of mother sheet BS 3  (see  FIG. 10B ). 
     Carrier film  24  on which a plurality of pad electrodes  14   a  are printed is prepared on the lower surface of mother sheet BS 1 , and two pad electrodes  14   a  and  14   a  defining each division unit are connected to two points of linear conductors  16  and  16  through two corresponding through holes HL 1  and HL 1 , respectively (see  FIG. 13C ). It is noted that pad electrodes  14   b  are provided on the upper surface of mother sheet BS 4  so as to be symmetric to pad electrodes  14   a  (see  FIG. 11B ). The inductor is formed by spirally connecting linear conductors  16  and  18  for each division unit through through holes HL 2  and HL 3  (see  FIG. 13A ). 
     The substrate assembly thus fabricated is subjected to primary scribing and secondary scribing after firing (see  FIGS. 14B to 14D ), and broken along grooves formed by such scribing. 
     In the fired substrate assembly, residual stress originating from a difference in coefficient of thermal expansion between a material forming pad electrodes  14   a  and  14   b  and linear conductors  16  and  18  and a material forming magnetic element layer  12   a  or non-magnetic element layers  12   b  and  12   c  is caused. It is noted that pad electrodes  14   a  and  14   b  provided on the opposing main surfaces of stack  12  preferably are mirror symmetric to each other in this preferred embodiment. Therefore, warpage of the substrate assembly originating from residual stress is significantly reduced or prevented and stack-type inductor element  10  obtained by breakage is smaller in thickness. 
     It is noted that decrease in thickness is suitable for a case that stack-type inductor element  10  is contained in an SIM card or a micro SIM card together with a secure IC for NFC (Near Field Communication). 
     Since residual stress is generated, a breakage line extends in a direction of thickness of stack  12  so as to go around pad electrodes  14   a  and  14   b . Thus, defective breakage is significantly reduced or prevented. 
     Furthermore, since no groove is present in a stage prior to firing, a magnetic element layer is not exposed and precipitation of plating onto a magnetic element layer is avoided. By making use of dummy pad electrode  14   a  (pad electrode  14   a  not connected to an inductor) during mounting of stack-type inductor element  10  on a printed board, the number of points of contact between stack-type inductor element  10  and the printed board increases. Thus, fall strength or bending strength of stack-type inductor element  10  is significantly improved. 
     A method of manufacturing stack-type inductor element in another preferred embodiment will be described. Ceramic sheet SH 1  is fabricated in a manner shown in  FIGS. 15A, 15B, 16A and 16B . Initially, a ceramic green sheet made of a non-magnetic ferrite material is prepared as a mother sheet BS 1 ′ (see  FIG. 15(A) ). Here, a plurality of dashed lines extending in the direction of the X axis and the direction of the Y axis show cutting positions. 
     Then, a plurality of through holes HL 1 ′ are formed in mother sheet BS 1 ′ in correspondence with the vicinity of an intersection of the dashed lines (see  FIG. 15B ), and through hole HL 1 ′ is filled with a conductive paste PS 1 ′ (see  FIG. 16A ). Conductive paste PS 1 ′ forms via hole conductor  22   a  or  22   b . When filling with conductive paste PS 1 ′ is completed, a conductor pattern corresponding to pad electrodes  14   a  is printed on a lower surface of mother sheet BS 1 ′ (see  FIG. 16B ). 
     Ceramic sheet SH 2  is fabricated in a manner shown in  FIGS. 17A, 17B, 18A, and 18B . Initially, a ceramic green sheet made of a magnetic ferrite material is prepared as a mother sheet BS 2 ′ (see  FIG. 17A ). Here, a plurality of dashed lines extending in the direction of the X axis and the direction of the Y axis show cutting positions. Then, a plurality of through holes HL 2 ′ are formed in mother sheet BS 2 ′ along a dashed line extending in the direction of the X axis (see  FIG. 17B ), and through hole HL 2 ′ is filled with a conductive paste PS 2 ′ forming via hole conductors  20   a ,  20   b ,  22   a , or  22   b  (see  FIG. 18A ). When filling with conductive paste PS 2 ′ is completed, a conductor pattern corresponding to linear conductors  16  is printed on a lower surface of mother sheet BS 2 ′ (see  FIG. 18B ). 
     Ceramic sheet SH 3  preferably is fabricated in a manner shown in  FIGS. 19A, 19B, 20A and 20B . Initially, a ceramic green sheet made of a magnetic ferrite material is prepared as a mother sheet BS 3 ′ (see  FIG. 19A ). Here, a plurality of dashed lines extending in the direction of the X axis and the direction of the Y axis show cutting positions. 
     Then, a plurality of through holes HL 3 ′ are formed in mother sheet BS 3 ′ along the dashed line extending in the direction of the X axis (see  FIG. 19B ), and through hole HL 3 ′ is filled with a conductive paste PS 3 ′ (see  FIG. 20A ). Conductive paste PS 3 ′ forms via hole conductors  20   a ,  20   b ,  22   a , or  22   b . When filling with conductive paste PS 3 ′ is completed, a conductor pattern corresponding to linear conductors  18  is printed on an upper surface of mother sheet BS 3 ′ (see  FIG. 20B ). 
     Ceramic sheet SH 4  preferably is fabricated in a manner shown in  FIGS. 21A and 21B . Initially, a ceramic green sheet made of a non-magnetic ferrite material is prepared as a mother sheet BS 4 ′ (see  FIG. 21A ). Here, a plurality of dashed lines extending in the direction of the X axis and the direction of the Y axis show cutting positions. Then, a conductor pattern corresponding to pad electrodes  14   b  is printed on an upper surface of mother sheet BS 4 ′ (see  FIG. 21B ). 
     Mother sheets BS 1 ′ and BS 2 ′ are stacked and press-bonded in such a position that a lower surface of mother sheet BS 2 ′ faces the upper surface of mother sheet BS 1 ′ (see  FIG. 22A ). Here, a position of stack of each sheet is adjusted such that dashed lines allocated to each sheet coincide when viewed in the direction of the Z axis. 
     Similarly, mother sheets BS 3 ′ and BS 4 ′ are stacked and press-bonded in such a position that the upper surface of mother sheet BS 3 ′ faces a lower surface of mother sheet BS 4 ′ (see  FIG. 22B ). Here again, a position of stack of each sheet is adjusted such that dashed lines allocated to each sheet coincide when viewed in the direction of the Z axis. 
     In succession, a vertical direction of the stack based on mother sheets BS 1 ′ and BS 2 ′ is inverted, and the stack based on mother sheets BS 3 ′ and BS 4 ′ is additionally stacked and press-bonded (see  FIG. 22C ). Here, a position of stack is adjusted such that the lower surface of mother sheet BS 3 ′ faces the upper surface of mother sheet BS 2 ′ and dashed lines allocated to each sheet coincide when viewed in the direction of the Z axis. Thus, an unprocessed substrate assembly of which thickness preferably is reduced to about 0.4 mm or smaller, for example, is fabricated. The fabricated substrate assembly is fired (see  FIG. 23A ), and thereafter subjected to primary scribing and secondary scribing (see  FIGS. 23B and 23C ). 
     In primary scribing, a blade of scriber  26  is applied along the dashed line extending in the direction of the X axis, and in secondary scribing, the blade of scriber  26  is applied along the dashed line extending in the direction of the Y axis. In any of primary scribing and secondary scribing, a groove is formed in an upper surface of the substrate assembly. It is noted that a groove formed in primary scribing reaches non-magnetic element layer  12   b , whereas a groove formed in secondary scribing reaches only magnetic element layer  12   a . As scribing is completed, the substrate assembly is broken into division units, to thus obtain a plurality of stack-type inductor elements  10 ,  10 . 
     In this preferred embodiment as well, in the fired substrate assembly, residual stress originating from a difference in coefficient of thermal expansion between a material of pad electrodes  14   a  and  14   b  and linear conductors  16  and  18  and a material of magnetic element layer  12   a  or non-magnetic element layers  12   b  and  12   c  is caused. It is noted that pad electrodes  14   a  and  14   b  provided on the opposing main surfaces of stack  12  preferably are mirror symmetric to each other and therefore warpage of the substrate assembly originating from residual stress is significantly reduced or prevented and stack-type inductor element  10  obtained by breakage is smaller in thickness. 
     It is noted that linear conductor  16  preferably extends obliquely to the Y axis, whereas linear conductor  18  preferably extends in the direction of the Y axis in the preferred embodiment described above. So long as linear conductors  16  and  18  are connected like a coil by via hole conductors  20   a  and  20   b , however, a direction of extension of linear conductors  16  and  18  may be different from that in this preferred embodiment. 
     In addition, in the preferred embodiment described above, a conductor pattern corresponding to linear conductors  18  preferably is printed on the upper surface of mother sheet BS 3  or BS 3 ′. The conductor pattern corresponding to linear conductor  18 , however, may be printed on the lower surface of mother sheet BS 4  or BS 4 ′. 
     Moreover, in this preferred embodiment, ceramic sheets SH 2  and SH 3  preferably are stacked to define magnetic element layer  12   a . Magnetic element layer  12   a  may be provided, however, by stacking a plurality of ceramic sheets corresponding to magnetic element layer ceramic sheet SH 2  and ceramic sheet SH 3 . 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.