JP5691821B2 - Manufacturing method of multilayer inductor element - Google Patents

Description

  The present invention relates to a method for manufacturing a multilayer inductor element, and more particularly to an improvement for enabling a coil conductor in the multilayer inductor element to be made thicker.

  The multilayer inductor element includes a multilayer body in which a plurality of magnetic layers made of ferrite, for example, are stacked, and an inductor that is at least partially configured by a coil conductor provided between the magnetic layers. In a multilayer inductor element, normally, a plurality of coil conductors are provided in alignment in the stacking direction, and the plurality of coil conductors are sequentially connected by via-hole conductors that penetrate the magnetic layer.

  The multilayer inductor element is used, for example, to configure a coil in a micro DC-DC converter. In the case of a multilayer inductor element intended for such an application, since a larger inductance value and load current value are required, the coil conductor is preferably thicker.

  On the other hand, in manufacturing a multilayer inductor element, a coil conductor is usually formed on a ceramic green sheet to be a magnetic layer using a conductive paste, and then a plurality of ceramic green sheets on which the coil conductor is formed are formed. After obtaining a raw laminate by laminating, each step of firing the raw laminate is performed.

  If the coil conductor is formed thicker while adopting the manufacturing method described above, the difference in thickness between the portion where the coil conductor is located and the portion where the coil conductor is not located becomes larger. It may be deformed as desired, an appropriate contact state may not be obtained between adjacent ceramic green sheets, or misalignment may occur during lamination. This problem becomes more prominent as the number of coil conductors is increased and the thickness of the coil conductor is increased.

  Technologies that can solve the above-described problems are described in, for example, Japanese Patent Application Laid-Open No. 2008-130736 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-164215 (Patent Document 2).

  In Patent Document 1, (1) after forming a coil conductor on a ceramic green sheet to be a non-magnetic layer, a magnetic paste to be a magnetic layer having substantially the same thickness as the coil conductor is printed around the coil conductor. And (2) a magnetic paste serving as a magnetic layer in a region excluding a portion corresponding to a coil conductor pattern on a ceramic green sheet serving as a non-magnetic layer. A second method of laminating a composite sheet is disclosed in which a coil conductor having a thickness substantially the same as that of the magnetic layer is formed after printing.

  In Patent Document 2, a coil conductor is disposed on a magnetic green sheet, and a plurality of ceramic layers having the same thickness as the coil conductor are disposed around the coil conductor. It is disclosed that the electrode-arranged sheets are laminated.

  The techniques described in Patent Documents 1 and 2 will be described more generally with reference to FIGS. 8 and 9.

  First, as shown in FIG. 8, a plurality of ceramic green sheets 1 are prepared. The coil conductor 2 is formed on each ceramic green sheet 1 by printing a conductive paste, and the insulating layer 3 having the same thickness as the coil conductor 2 is printed on the outside of the coil conductor 2. Is formed.

  Next, as shown in FIG. 9, a plurality of ceramic green sheets 1 on which the coil conductor 2 and the insulating layer 3 are formed are laminated and pressure-bonded, whereby a raw laminate 4 is obtained.

  According to this method, even if the coil conductor 2 is thickened, or even when the number of coil conductors 2 is increased, the difference in thickness between the portion where the coil conductor 2 is located and the portion where the coil conductor 2 is not located is the insulating layer. 3, the coil conductor 2 is undesirably deformed in the laminating process, a proper adhesion state cannot be obtained between the ceramic green sheets 1, or misalignment occurs during laminating. It can be relaxed to some extent.

  However, as illustrated in FIGS. 8 and 9, the coil conductor 2 is formed by printing a conductive paste. Therefore, the central portion of the cross-sectional shape of the coil conductor 2 is affected by the surface tension acting on the conductive paste. It tends to be thicker and thinner at the periphery. The insulating layer 3 also tends to have a similar cross-sectional shape.

  Therefore, the problem that the coil conductor 2 is undesirably deformed or misaligned cannot be completely solved in the lamination process.

  Further, when the method corresponding to the second method described in Patent Document 1, that is, the method of forming the coil conductor 2 after forming the insulating layer 3 is adopted, the outline of the coil conductor 2 is likely to blur. This is because the insulating layer 3 has a thick cross section at the center and a thin cross section at the periphery. The insulating layer 3 cannot sufficiently serve as a wall that blocks the conductive paste forming the coil conductor 2, and as shown in FIG. 10, the conductive paste forming the coil conductor 2 can easily run on the insulating layer 3, As a result, the outline of the coil conductor 2 tends to blur.

  The blurring of the outline of the coil conductor 2 described above may cause an undesired electrical short-circuit problem with other circuit elements such as other coil conductors disposed close to the coil conductor 2. .

JP 2008-130736 A JP 2002-164215 A

  Therefore, an object of the present invention is to provide a method for manufacturing a multilayer inductor element that can solve the above-described problems.

  The present invention includes a step of forming a coil conductor on a ceramic green sheet, a step of laminating a plurality of ceramic green sheets including the ceramic green sheet on which the coil conductor is formed, thereby obtaining a raw laminate, And a step of forming a coil conductor in order to solve the technical problem described above. It is characterized by.

  That is, in order to form a coil conductor, first, on the ceramic green sheet, a coil peripheral portion that is a part of the coil conductor to be formed and extends along at least a part of the outline of the coil conductor, A first step of forming with a conductive paste is performed. Next, after the first step, a second step is performed in which an insulating layer is formed using a ceramic paste in a region extending outside the outline of the coil conductor to be formed on the ceramic green sheet. Next, after the second step, the coil on the ceramic green sheet surrounded by the insulating layer, which is a portion of the coil conductor to be formed inside the coil peripheral portion, excluding the coil peripheral portion. A third step of forming the main part with a conductive paste is performed.

  When a via-hole conductor is formed in the multilayer inductor element, after the second step, a step of forming a through-hole in the ceramic green sheet, and a step of forming a via-hole conductor by filling the through-hole with a conductor Is preferably implemented.

  In the step of obtaining a raw laminate, when the step of laminating a plurality of ceramic green sheets each having coil conductors is performed, the via-hole conductors are coil conductors formed on different ceramic green sheets, respectively. It is preferable to include a via-hole conductor for connecting in the stacking direction.

  It is preferable that both the ceramic green sheet and the insulating layer on which the coil conductor is formed contain a magnetic ceramic in that the inductance characteristics can be improved.

  Moreover, it is preferable that the material of a coil main part is equal to the material of a coil peripheral part at the point which can reduce material cost.

  Moreover, it is preferable that the heights in the thickness direction of the insulating layer, the coil peripheral portion, and the coil main portion are equal to each other.

  According to this invention, since the coil peripheral portion is formed before the coil main portion, the coil peripheral portion is already formed at the stage of forming the coil main portion. Therefore, even when some blurring occurs in the outline of the coil main part when forming the coil main part, only a part of the conductive paste forming the coil main part can run over the coil peripheral part, Therefore, it is possible to prevent the blurring problem from appearing apparently. As a result, the problem of undesired electrical shorts with other circuit elements, such as other coil conductors, that can be caused by bleeding of the contour of the coil conductor can be made difficult to occur.

  In the present invention, the peripheral edge of the coil is not limited to being formed along the entire contour of the coil conductor, but also includes the case of being formed along only a part of the contour of the coil conductor. In other words, it is sufficient that the coil peripheral edge is formed along the contour of the coil conductor only at a location where the above-described electrical short-circuit problem may occur.

  Further, according to the present invention, the coil peripheral part is formed, and then the insulating layer made of ceramic paste is formed outside the contour of the coil conductor to be formed, and then the coil main part is formed. The thickness of the coil conductor can be easily increased, and it is easy to obtain a cross-sectional shape closer to a rectangle in the coil conductor.

  In addition, due to the presence of the insulating layer described above, the coil conductor may be deformed undesirably in the stacking process, a proper adhesion state may not be obtained between the ceramic green sheets, or misalignment may occur during stacking. Can be made difficult to occur. In particular, when the height in the thickness direction of each of the insulating layer, the coil peripheral edge portion, and the coil main portion is equal to each other, the above-described inconvenience can be made more difficult to occur.

It is a top view of the ceramic green sheet 52 for demonstrating the manufacturing method of the multilayer inductor element by one Embodiment of this invention, especially the formation method of the coil conductor 51 in order of a process. It is an expanded sectional view which follows the line II-II of Drawing 1 (2). FIG. 3 is an enlarged sectional view taken along line III-III in FIG. FIG. 4 is an enlarged sectional view taken along line IV-IV in FIG. FIG. 5 is an enlarged sectional view taken along line VV in FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing a step-down DC-DC converter 10 configured using the multilayer inductor element 11 while schematically showing the multilayer inductor element 11 manufactured by the manufacturing method according to the present invention. FIG. 7 is an equivalent circuit diagram of the step-down DC-DC converter 10 shown in FIG. 6. FIG. 2 is a cross-sectional view illustrating a state in which a coil conductor 2 and an insulating layer 3 are formed on a plurality of ceramic green sheets 1 for explaining the techniques described in Patent Documents 1 and 2. It is sectional drawing which shows the raw laminated body 4 obtained by laminating | stacking and crimping | bonding the several ceramic green sheet 1 in which the coil conductor 2 and the insulating layer 3 which were shown in FIG. 8 were formed. FIG. 3 is a cross-sectional view illustrating a state where a conductive paste forming a coil conductor 2 rides on an insulating layer 3 in order to explain problems of the techniques described in Patent Documents 1 and 2.

  First, an example of a multilayer inductor element manufactured by the manufacturing method according to the present invention will be described with reference to FIGS. FIGS. 6 and 7 show a step-down DC-DC converter 10 configured using a multilayer inductor element 11.

  As shown in FIG. 6, the multilayer inductor element 11 is formed by laminating a nonmagnetic layer 12, a magnetic layer 13, a nonmagnetic layer 14, a magnetic layer 15 and a nonmagnetic layer 16 in order from the top. A laminated body 17 is provided. The nonmagnetic layers 12, 14 and 16 are made of, for example, nonmagnetic ferrite, and the magnetic layers 13 and 15 are made of, for example, magnetic ferrite. In FIG. 6, for example, each of the magnetic layers 13 and 15 is illustrated as an integral body, but may be composed of a plurality of layers.

  The multilayer inductor element 11 also includes a conductor provided inside or outside the multilayer body 17. As the conductor, there are a plurality of coil conductors 18 provided on the magnetic layers 13 and 15. The plurality of coil conductors 18 are sequentially connected in the stacking direction via via-hole conductors 19 indicated by broken lines to constitute a coil extending in a spiral shape as a whole. This coil corresponds to the coil L shown in FIG.

  In FIG. 6, via-hole conductors 20 to 25 extending in the stacking direction of the multilayer body 17 and internal conductor films 26 and 27 extending in parallel to the main surface of the multilayer body 17 are formed as conductors formed in the multilayer body 17. It is shown in the figure. Via-hole conductors 20, 21, and 24 are exposed on the upper main surface of multilayer body 17 so as to provide connection terminals.

  Further, in FIG. 6, as conductors formed on the outer surface of the multilayer body 17, terminal conductors 28 and 29 formed on the upper main surface of the multilayer body 17 and terminals formed on the lower main surface of the multilayer body 17. Conductors 30, 31, and 32 are shown.

  In the multilayer inductor element 11 shown in FIG. 6, the nonmagnetic material layer 14 is interposed between the magnetic layers 13 and 15 to make it difficult for magnetic saturation to occur and to improve the direct current superposition characteristics. This is because 11 can be used even with a large current.

  The step-down DC-DC converter 10 is configured by mounting the IC chip 33 and the chip capacitor 34 as surface-mounted electronic components on the multilayer inductor element 11 as described above. The IC chip 33 is electrically connected to the exposed ends of the via-hole conductors 20, 21 and 24 through the bumps 35, 36 and 37, respectively. The chip capacitor 34 is electrically connected to the terminal conductors 28 and 29 via solder (not shown).

  In the equivalent circuit diagram of the step-down DC-DC converter 10 shown in FIG. 7, the reference numerals used in FIG. 6 are attached to corresponding elements. The step-down DC-DC converter 10 includes a coil L provided by a coil conductor 18, a capacitor C provided by a chip capacitor 34, and an IC chip 33.

  The IC chip 33 is provided with functions of first and second switching elements 38 and 39 configured by MOSFETs and the driver 40, for example. The first switching element 38 and the second switching element 39 are controlled by the driver 40 so as to be alternately turned on / off.

  Further, the terminal conductor 30 shown in FIG. 6 functions as the input terminal Vin, the terminal conductor 31 functions as the ground terminal GND, and the terminal conductor 32 functions as the output terminal Vout.

  The step-down DC-DC converter 10 uses a switching technique to convert a certain DC voltage into a lower DC voltage. First, a constant input voltage input from the input terminal Vin is chopped into a rectangular waveform by the first switching element 38 and the second switching element 39 in the IC chip 33, and is configured by the coil L and the capacitor C. The signal is smoothed by the low-pass filter, and the target DC output voltage is taken out from the output terminal Vout.

  For the coil L used in such a step-down DC-DC converter 10, a considerably larger inductance value and load current value than those of a normal one are required. That is, it is desirable that the coil conductor 18 formed inside the multilayer inductor element 11 is made thicker. Therefore, in forming the coil conductor 18, the method described below with reference to FIGS. 1 and 2 is advantageously employed. 1 and 2 show not only the method of forming the coil conductor 18 shown in FIG. 6, but also a more general method of forming the coil conductor. The coil conductor 51 formed by this forming method is shown in FIGS.

  First, as shown in FIG. 1A, a ceramic green sheet 52 is prepared. The ceramic green sheet 52 preferably includes a magnetic ceramic.

  Next, as shown in FIG. 1B and FIG. 2, the coil that is to be formed on the ceramic green sheet 52 and that is a part of the coil conductor 51 that extends along the contour of the coil conductor 51. The peripheral portion 53 is formed by printing a conductive paste.

  Next, as shown in FIGS. 1 (3) and 3, an insulating layer 54 is printed on the ceramic green sheet 52 using ceramic paste in a region extending outside the outline of the coil conductor 51 to be formed. It is formed. This ceramic paste preferably contains a magnetic ceramic, and preferably contains the same ceramic material as the ceramic green sheet 52.

  Next, as shown in FIG. 1 (4) and FIG. 4, through-holes are formed in the ceramic green sheet 52, and several via-hole conductors 55 and 56 are formed by filling the through-holes with a conductor. The For example, a conductive paste is used as the conductor, and the through-hole is filled with the conductive paste in order to form the via-hole conductors 55 and 56. The via-hole conductor 56 formed in the region surrounded by the coil peripheral portion 53 corresponds to the via-hole conductor 19 shown in FIG. 6 and is adjacent to the coil conductor 51 on the ceramic green sheet 52 and the ceramic green sheet 52. And a coil conductor formed on another ceramic green sheet to be laminated in the laminating direction. Further, the through-hole forming the via-hole conductor 55 is provided so as to penetrate not only the ceramic green sheet 52 but also the insulating layer 54.

  Next, as shown in FIGS. 1 (5) and 5, the coil main portion 57 is electrically conductive in the region surrounded by the insulating layer 54 on the ceramic green sheet 52 and inside the coil peripheral portion 53. It is formed by printing a paste. The coil main portion 57 constitutes a portion of the coil conductor 51 to be formed excluding the coil peripheral portion 53.

  As can be seen from FIG. 5, the heights of the insulating layer 54, the coil peripheral edge 53, and the coil main portion 57 in the thickness direction are preferably equal to each other.

  Although it is preferable in terms of cost to use the same material as the conductive paste forming the coil peripheral portion 53 as the conductive paste forming the coil main portion 57, in the case where the thickness of the coil conductor is made thicker, There is also a method of making the thickness and flatness of the coil conductor compatible by making the conductive paste forming the coil peripheral portion 53 highly viscous and making the conductive paste forming the coil main portion 57 low viscosity. obtain.

  As described above, the unsintered coil conductor 51 is formed. Thereafter, a firing step is performed, and a sintered coil conductor 51 is obtained.

  When the coil main portion 57 shown in FIGS. 1 (5) and 5 is formed, even if some blurring occurs in the outline of the coil main portion 57, one of the conductive pastes forming the coil main portion 57 is used. Therefore, it is possible to prevent the bleeding problem from appearing apparently. As a result, it is possible to make it difficult to cause an undesired electrical short-circuit problem with other circuit elements such as other coil conductors, which can be caused by blurring of the outline of the coil conductor 51.

  In this embodiment, the coil peripheral portion 53 is formed along the entire contour of the coil conductor 51, but may be formed along only a part of the contour of the coil conductor. That is, a coil peripheral part may be formed along the outline of a coil conductor only about the place where the problem of the electrical short circuit mentioned above may arise. Referring to FIG. 6, for example, at a location indicated by “A”, the coil conductor 18 and the via-hole conductor 20 are close to each other, and an electrical short-circuit problem is likely to occur. Therefore, for the coil conductor 18, for example, a modification in which the coil peripheral portion is formed only in the vicinity of the via-hole conductor 20 is also possible.

  Further, according to this embodiment, the coil peripheral portion 53 is formed, and then the insulating layer 54 made of ceramic paste is formed outside the contour of the coil conductor 51 to be formed, and then the coil main portion 57 is formed. Thus, the thickness of the coil conductor 51 can be easily increased, and the coil conductor 51 can have a cross-sectional shape closer to a rectangle as shown in FIG.

  Next, a method for manufacturing the multilayer inductor element 11 which is implemented by adopting the method for forming a coil conductor described above will be described with reference to FIG. 6 again.

  First, ceramic green sheets to be the magnetic layers 13 and 15 and the nonmagnetic layers 12, 14 and 16 are prepared. These ceramic green sheets are obtained by adding a binder, a plasticizer, a wetting agent, a dispersant and the like to a desired ceramic raw material powder to form a slurry, which is then formed into a sheet shape.

  Next, by printing a conductive paste on a specific ceramic green sheet, the coil conductor 18, the internal conductor films 26 and 27, and the terminal conductors 28 to 32 are formed, and the through hole is formed in the specific ceramic green sheet. The via-hole conductors 19 to 25 are formed by filling the through holes with a conductive paste.

  Here, the formation method described above with reference to FIGS. 1 and 2 is adopted for forming the coil conductor 18 and the via-hole conductor 19 and forming each of the via-hole conductors 20, 21, 22 and 23.

  The conductive metal contained in the conductive paste for forming the coil conductor 18, the inner conductor films 26 and 27, the terminal conductors 28 to 32, and the via-hole conductors 19 to 25 is mainly composed of silver or silver / palladium. It is preferable that

  Next, in order to form each of the magnetic layers 13 and 15 and the nonmagnetic layers 12, 14 and 16, a predetermined number of ceramic green sheets are stacked in a predetermined order and then pressed to form a stacked body. Seventeen unsintered ones are obtained.

  In the laminating process described above, the thick coil conductor 18 is undesirably deformed due to the presence of the insulating layer 54 shown in FIGS. 1 and 3 to 5, and an appropriate adhesion state is obtained between the ceramic green sheets. Inconveniences such as absence or misalignment during stacking. In particular, as shown in FIG. 5, when the height in the thickness direction of each of the insulating layer 54, the coil peripheral portion 53, and the coil main portion 57 is equal to each other, the above-described inconvenience can be made less likely to occur.

  In the case where the above-described process is performed on an aggregated mother multilayer body for simultaneously manufacturing a plurality of multilayer inductor elements 11, the aggregated mother multilayer body may be divided later. A split groove is formed for ease.

  Next, the unsintered laminate is fired, thereby obtaining a sintered laminate 17.

  Next, the terminal conductors 28 to 32 exposed on the surface of the multilayer body 17 are plated as necessary. For example, electroplating is performed, whereby a nickel plating film and a tin plating film are sequentially formed. The plating process may be performed by electroless plating. In this case, for example, a nickel plating film and a gold plating film are sequentially formed.

  When electroplating is applied in the plating process described above, the surface of the laminate 17 is not the magnetic layers 13 and 15 but the nonmagnetic layers 12 and 16 located on the surface of the laminate 17. It is possible to make it difficult to cause abnormal deposition of the plating film such that the plating film is deposited on portions other than the terminal conductors 28 to 32. This is because the nonmagnetic layers 12 and 16 generally have lower electrical conductivity than the magnetic layers 13 and 15.

  Next, in order to obtain the step-down DC-DC converter 10, an IC chip 33 and a chip capacitor 34 are mounted as shown in FIG. Needless to say, the DC-DC converter using the multilayer inductor of the present invention is not limited to the step-down type, but can be applied to a step-up type, a step-up / step-down type, a polarity inversion type, and the like.

  And when the above process is implemented with respect to the assembled mother laminated body, the process divided | segmented along the division | segmentation groove | channel mentioned above is implemented, and each multilayer inductor element 11 is taken out. Although not shown, the multilayer inductor element 11 is attached with a metal cover as necessary.

  In the above description, the dividing grooves are formed before the firing process. However, without forming the dividing grooves, the assembled mother laminated body is divided before the firing process, and the individual laminated inductor elements 11 are separated. You may make it take out the thing of the raw state of the laminated body 17 of.

11 Laminated Inductor Elements 12, 14, 16 Nonmagnetic Layer 13, 15 Magnetic Layer 17 Laminated Body 18, 51 Coil Conductors 19-25, 55, 56 Via Hole Conductor 52 Ceramic Green Sheet 53 Coil Perimeter 54 Insulating Layer 57 Coil Main part

Claims (6)

Forming a coil conductor on the ceramic green sheet, laminating a plurality of ceramic green sheets including the ceramic green sheet on which the coil conductor is formed, thereby obtaining a raw laminate, and the raw laminate A method of manufacturing a multilayer inductor element comprising:
The step of forming the coil conductor includes:
On the ceramic green sheet, a coil peripheral portion that becomes a part of the coil conductor to be formed and extends along at least a part of the outline of the coil conductor is formed by a conductive paste. Process,
After the first step, a second step of forming an insulating layer on the ceramic green sheet using a ceramic paste in a region extending outside the outline of the coil conductor to be formed;
After the second step, on the ceramic green sheet, a region surrounded by the insulating layer, and a portion of the coil conductor to be formed inside the coil peripheral portion excluding the coil peripheral portion A third step of forming a coil main part to be a conductive paste;
A method for manufacturing a multilayer inductor element.   The laminated mold according to claim 1, further comprising a step of forming a through hole in the ceramic green sheet and a step of forming a via-hole conductor by filling the through hole with a conductor after the second step. Inductor element manufacturing method.   The step of obtaining the raw laminate includes the step of laminating a plurality of the ceramic green sheets each having the coil conductor formed thereon, and the via-hole conductors are formed on the different ceramic green sheets. The method for manufacturing a multilayer inductor element according to claim 2, further comprising a via-hole conductor for connecting the electrodes in the stacking direction.   4. The method of manufacturing a multilayer inductor element according to claim 1, wherein both the ceramic green sheet on which the coil conductor is formed and the insulating layer include a magnetic ceramic. 5.   The method for manufacturing a multilayer inductor element according to claim 1, wherein a material of the coil main part is equal to a material of the coil peripheral part.   The method for manufacturing a multilayer inductor element according to any one of claims 1 to 5, wherein heights of the insulating layer, the coil peripheral portion, and the coil main portion in the thickness direction are equal to each other.

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