JP5720791B2 - Inductor element and manufacturing method thereof - Google Patents

Description

  The present invention relates to an inductor element formed by laminating a plurality of ceramic green sheets by forming a conductor pattern, and a method for manufacturing the inductor element.

  Conventionally, an inductor element in which a conductor pattern is printed and laminated on a ceramic green sheet made of a magnetic material is known (see, for example, Patent Document 1).

  In the inductor element shown in Patent Document 1, punch holes are opened before the ceramic green sheets are laminated, and plating electrodes are formed on the side surfaces of the punch holes after lamination, thereby electrically connecting the top and bottom surfaces of the laminate. A method of forming side electrodes to be connected is employed.

JP-A-11-345713

  However, in the manufacturing method of Patent Document 1, it is necessary to perform plating within a very narrow gap on the side surface of the punch hole in the state of the mother laminated body, and it is difficult to plate (for example, electrodes are connected to each other). There are challenges.

  On the other hand, although it is easy to electrically connect the top surface and bottom surface of the laminated body with via holes, an open magnetic circuit is required because it becomes a closed magnetic circuit (for example, an inductor element is used as an antenna coil). In the case of use), there arises a problem that the propagation distance of the electromagnetic wave is shortened.

  Accordingly, an object of the present invention is to provide an inductor element capable of realizing an open magnetic circuit while performing interlayer connection by via holes, and a manufacturing method thereof.

  In the inductor element of the present invention, a first ceramic green sheet made of a material having a relatively high thermal expansion coefficient is sandwiched between a plurality of second ceramic green sheets made of a material having a relatively low thermal expansion coefficient. A ceramic laminate, a first conductor pattern formed on one second ceramic green sheet sandwiching the first ceramic green sheet, and a second conductor sandwiching the first ceramic green sheet A second conductor pattern formed on the second ceramic green sheet, and a via hole for electrical connection between the first conductor pattern and the second conductor pattern.

  The inductor element according to the present invention is characterized in that a crack exists in the first ceramic green sheet between the via hole and the end portion of the ceramic laminate.

  Such a crack is caused by a stress generated by a difference in thermal expansion coefficient between the first ceramic green sheet, the second ceramic green sheet, and the via-hole conductor in the step of integrally firing the ceramic laminate and the coil conductor. That is, a material having a high coefficient of thermal expansion is sandwiched between materials having a low coefficient of thermal expansion, thereby generating a crack due to a compressive stress due to a shrinkage difference during firing and cooling. Since the via hole conductor has the highest thermal expansion coefficient and is most likely to crack around the via hole, if the via hole conductor is formed at a position close to the end face, the crack is connected to the end face. Then, when the first ceramic green sheet contains a magnetic material, the end face side of the magnetic material can be magnetically invalidated by this crack, and a substantially open magnetic path can be obtained. Therefore, an open magnetic circuit can be realized while performing interlayer connection by via holes.

  Actually, the difference between the thermal expansion coefficient of the first ceramic green sheet and the thermal expansion coefficient of the second ceramic green sheet (made of a non-magnetic material) is within a predetermined range (for example, 1 to 2 ppm / ° C.). Yes, if the via-hole conductor has an extremely high thermal expansion coefficient such as silver (for example, the difference from the thermal expansion coefficient of the second ceramic green sheet is 10 ppm / ° C. or more), cracks occur only around the via hole. It can be an open magnetic path.

  In addition, the inductor element can be impregnated with a resin to prevent a decrease in strength due to cracks.

  According to the present invention, an open magnetic circuit can be realized while performing interlayer connection by via holes.

FIG. 3 is an exploded perspective view schematically showing an inductor element. It is sectional drawing which represented the inductor element typically. 3 is a top view of a magnetic ferrite layer 13. FIG. It is sectional drawing which represented typically the inductor element which concerns on another example.

  FIG. 1 is an exploded perspective view schematically showing an inductor element according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the inductor element. The inductor element has a ceramic laminated body in which magnetic and non-magnetic ceramic green sheets are laminated.

  FIG. 1 shows the state of each ceramic green sheet before firing, and FIG. 2 shows the state of the ceramic laminate after lamination and firing. In the cross-sectional view of FIG. 2, the upper side of the paper is the upper surface side of the multilayer inductor element, and the lower side of the paper is the lower surface side of the multilayer inductor element.

  The multilayer inductor element includes a nonmagnetic ferrite layer 11, a nonmagnetic ferrite layer 12, a magnetic ferrite layer 13, a nonmagnetic ferrite layer 14, and a nonmagnetic material in order from the upper surface side to the lower surface side of the outermost layer. A body ferrite layer 15 is disposed.

  That is, the ceramic laminate includes a magnetic ferrite layer 13 (first ceramic green sheet in the present invention), a nonmagnetic ferrite layer 12 (one second ceramic green sheet in the present invention), and a nonmagnetic ferrite layer 14. (The other second ceramic green sheet in the present invention).

  Internal wiring is formed on part of the ceramic green sheets constituting the ceramic laminate. In the figure, a conductor pattern 31 (first conductor pattern in the present invention) made of a conductive paste is formed on a magnetic ferrite layer 13. Further, a conductor pattern 32 (second conductor pattern in the present invention) made of a conductive paste is formed on the nonmagnetic ferrite layer 14.

  The conductor pattern 31 and the conductor pattern 32 are electrically connected in the stacking direction by the via hole 21. The via hole 21 is formed by opening a punch hole at a predetermined position for each ceramic green sheet and plating the surface after lamination. As a result, the wiring is formed in a spiral shape with the magnetic ferrite layer 13 interposed therebetween to form a coil conductor. The end portion of the coil conductor is exposed to the lowermost surface by a via hole 21 provided in the nonmagnetic ferrite layer 15. The inductor element functions as a coil antenna by mounting the end portion of the coil conductor exposed on the lowermost surface on the mounting substrate and supplying power to the coil conductor.

  The via hole 21 is formed at a position not exposed to the end face of the ceramic green sheet and as close to the end face as possible. However, the position is set such that it is not exposed to the end face even if process variations are taken into consideration.

  In the example of FIG. 1, the conductor pattern 31 is formed on the upper surface of the magnetic ferrite layer 13, but may be formed on the lower surface of the nonmagnetic ferrite layer 12. The conductor pattern 32 may be formed not on the top surface of the nonmagnetic ferrite layer 14 but on the top surface of the magnetic ferrite layer 13. Further, as shown in FIG. 4, a conductor pattern is formed on the upper surface of the nonmagnetic ferrite layer 12 and the lower surface of the nonmagnetic ferrite layer 14 and connected by via holes to form a parallel line, so that a direct current of the coil conductor is obtained. The resistance component may be lowered.

  Here, the non-magnetic ferrite layer 11, the non-magnetic ferrite layer 12, the non-magnetic ferrite layer 14, and the non-magnetic ferrite layer 15 in this embodiment have a lower thermal contraction rate than the magnetic ferrite layer 13. ing. Therefore, by sandwiching the magnetic ferrite layer 13 having a relatively high heat shrinkage rate between the nonmagnetic ferrite layer 12 and the nonmagnetic ferrite layer 14 having a relatively low heat shrinkage rate, the entire element is obtained by firing. The strength can be improved by compression.

  Further, the inductor element according to the present embodiment includes the thermal expansion coefficients of the nonmagnetic ferrite layer 11, the nonmagnetic ferrite layer 12, the nonmagnetic ferrite layer 14, and the nonmagnetic ferrite layer 15, and the magnetic ferrite layer 13. The difference from the thermal expansion coefficient is within a predetermined range (for example, 1-2 ppm / ° C.), and the conductor (silver) of the via hole 21 has an extremely high thermal expansion coefficient (for example, 10 ppm / ° C. or more than the magnetic ferrite layer 13). By having a high thermal expansion coefficient, cracks are generated only around the via hole 21 during firing, as shown in FIG.

  As described above, this crack is caused by sandwiching the magnetic ferrite layer 13 which is a material having a high thermal expansion coefficient between the nonmagnetic ferrite layer 12 and the nonmagnetic ferrite layer 14 which are materials having a low thermal expansion coefficient. It is generated by the compressive stress due to the shrinkage difference at the time of firing and cooling.

  FIG. 3 is a top view of the magnetic ferrite layer 13. As shown in FIG. 3, since the conductor (silver) of the via hole 21 has the highest thermal expansion coefficient, cracks are most likely to occur around the via hole 21. Therefore, as shown in FIG. 3, if the via hole 21 is formed at a position close to the end face of the magnetic ferrite layer 13, a crack 51 that connects the via hole 21 and the end face of the magnetic ferrite layer 13 is generated.

  Then, the crack 51 can make the end face side of the magnetic ferrite layer 13 magnetically invalid, and a substantial open magnetic path can be obtained.

  However, when the temperature lowering rate is too slow, silver in the conductor pattern 31, the conductor pattern 32, and the via hole 21 may diffuse and the plating may be abnormally deposited. Therefore, a certain temperature lowering rate is ensured (for example, -7 ° C / min). And above).

  In the present embodiment, a ferrite containing iron, nickel, zinc, and copper is used as the magnetic ferrite layer, and a ferrite containing iron, zinc, and copper is used as the nonmagnetic ferrite layer. An example in which a silver material is used as the internal wiring including the conductor pattern 32 and the via hole 21 is shown. When these materials are different or when the blending ratio is different, the difference in thermal expansion coefficient between the magnetic ferrite layer, the nonmagnetic ferrite layer, and the internal wiring is that the via hole 21 and the magnetic ferrite layer are different. It is set each time within a range where cracks 51 connecting the 13 end faces are generated. Even when the thicknesses of the magnetic ferrite layer and the nonmagnetic ferrite layer are changed, the difference in thermal expansion coefficient between the magnetic ferrite layer, the nonmagnetic ferrite layer, and the internal wiring is different from that of the via hole 21 and the magnetic ferrite. It is set each time within a range where a crack 51 connecting the end face of the layer 13 is generated.

  With the above structure, the inductor element can realize an open magnetic circuit while performing interlayer connection by via holes. Since the inductor element is an interlayer connection by via holes, there is no fear that the electrodes are connected at the time of plating, and the productivity is improved. Further, when the inductor element is used as an antenna coil, the propagation distance can be made longer than when the inductor element is a closed magnetic circuit.

  Next, the manufacturing process of the inductor element will be described. The inductor element is manufactured by the following process.

  First, an alloy (conductive paste) containing silver or the like is applied on a ceramic green sheet to be a magnetic ferrite layer or a nonmagnetic ferrite layer, and internal wiring such as the conductor pattern 31 and the conductor pattern 32 is formed. It is formed.

  And about each ceramic green sheet, a punch hole is opened in the location used as the via hole 21. FIG. The conductor pattern 31 and the conductor pattern 32 may be formed after a punch hole to be the via hole 21 is formed.

  Next, each ceramic green sheet is laminated. That is, the nonmagnetic ferrite layer 11, the nonmagnetic ferrite layer 12, the magnetic ferrite layer 13, the nonmagnetic ferrite layer 14, and the nonmagnetic ferrite layer 15 are laminated in this order from the upper surface side, and provisional pressure bonding is performed. . Thereby, the mother laminated body before baking is formed.

  Then, the surface of the via hole 21 of the mother laminate is plated. The plating process is performed, for example, by immersing the mother laminate in a plating solution and swinging it.

  Finally, firing is performed. Thereby, the fired mother laminated body is obtained. During this firing, cracks occur around the via hole 21 in the magnetic ferrite layer 13 due to the difference in thermal expansion coefficient.

  Note that the mother laminate may be impregnated with resin after firing. In this case, strength reduction due to cracks can be prevented.

  In addition, the shape of the punch hole of the via hole 21 is not limited to the circular shape, and may be another shape such as a rectangle or a semicircle.

11, 12, 14, 15 ... non-magnetic ferrite layer 13 ... magnetic ferrite layer 21 ... via hole 31, 32 ... conductor pattern 51 ... crack

Claims (4)

A ceramic laminate in which a first ceramic green sheet made of a material having a relatively high thermal expansion coefficient is sandwiched between a plurality of second ceramic green sheets made of a material having a relatively low thermal expansion coefficient;
A first conductor pattern formed between one second ceramic green sheet sandwiching the first ceramic green sheet and the first ceramic green sheet;
A second conductor pattern formed between the other second ceramic green sheet sandwiching the first ceramic green sheet and the first ceramic green sheet;
Via holes for electrical connection between the first conductor pattern and the second conductor pattern;
An inductor element comprising
There is a crack in the first ceramic green sheet between the via hole and the end of the ceramic laminate ,
The first ceramic green sheet includes a magnetic material;
The second ceramic green sheet is made of a non-magnetic material;
The via hole is made of a conductive paste mainly composed of silver,
The difference between the thermal expansion coefficient of the second ceramic green sheet and the thermal expansion coefficient of the first ceramic green sheet is in the range of 1 to 2 ppm / ° C.
The inductor element , wherein the via hole has a thermal expansion coefficient higher than that of the first ceramic green sheet by 10 ppm / ° C. or more .   The inductor element according to claim 1, wherein the first conductor pattern and the second conductor pattern are made of a conductive paste mainly composed of silver. The inductor element, an inductor element according to claim 1 or claim 2, characterized in that the resin is impregnated. A method for manufacturing an inductor element according to any one of claims 1 to 3 ,
In the step of firing the ceramic laminate , a difference between a thermal expansion coefficient of the first ceramic green sheet and a thermal expansion coefficient of the second ceramic green sheet is set within a range of 1 to 2 ppm / ° C, A method for manufacturing an inductor element, wherein the crack is generated by increasing a thermal expansion coefficient of a via hole by 10 ppm / ° C. or more higher than that of the first ceramic green sheet .

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