JP5339398B2 - Multilayer inductor - Google Patents

Description

  The present invention relates to a multilayer inductor having a structure in which a coil is embedded in a magnetic body. More specifically, the present invention relates to a conductor in which one or more electrically insulating nonmagnetic layers are disposed over the entire multilayer surface and overlap each other at intervals. The present invention relates to a multilayer inductor having a structure in which an electrically insulating nonmagnetic pattern corresponding to the shape of the conductor pattern is disposed between the patterns in proximity to the conductor pattern. This multilayer inductor is particularly useful as an inductor for a DC-DC converter that requires a high bias.

  Transformers and choke coils used in power supply circuits such as DC-DC converters were once configured to have a coil wound around a magnetic core. However, in recent years, power supply circuit components have become smaller and thinner. In accordance with demands, chip components with a laminated structure have been developed and put into practical use.

  In a laminated inductor, an electrically insulating magnetic layer and a conductor pattern are alternately laminated and the conductor patterns are sequentially connected to form a coil that spirals around the magnetic material while being superimposed in the lamination direction. In this structure, both ends of the coil are drawn to the outer surface of the multilayer chip via lead conductors and connected to electrode terminals. That is, the coil is embedded in a chip-type magnetic body. The magnetic layer and the conductor pattern are formed and stacked using, for example, a screen printing technique.

  Such a multilayer inductor is characterized in that since the coil is surrounded by a magnetic material, there is little magnetic leakage, and a necessary inductance can be obtained with a relatively small number of turns, which is suitable for downsizing and thinning. However, the AC resistance increases at the time of a low DC bias current (DC bias), and even with a small coil current (excitation current), a sudden inductance drop occurs due to magnetic saturation of the magnetic material (that is, the DC superposition characteristics are poor). ) And other problems. In particular, a high AC resistance at a low DC bias current means that a loss due to a standby current is large, which causes a serious problem such as a shortened standby time in a device such as a portable terminal.

  Therefore, by replacing a part of the entire magnetic layer with a nonmagnetic layer, a magnetic gap is interposed in the multilayer inductor, thereby increasing the magnetic saturation level and obtaining a sufficient rated current as a transformer or choke coil. Such a multilayer inductor has been proposed (see Patent Document 1).

Certainly, such a structure has a certain effect in suppressing the increase in AC resistance at the time of a low DC bias current and reducing the deterioration of DC superposition characteristics. However, these effects are not always sufficient, and problems such as a decrease in the effect as the number of coil turns increases have been recognized.
JP-A-2005-45108

  The problem to be solved by the present invention is that it exhibits excellent DC superposition characteristics, can suppress AC resistance at the time of low DC bias current, and the inductance change is relatively gradual in the entire current region where the coil current is within the rated range. It is to obtain a high characteristic.

According to the present invention, an electrically insulating magnetic layer and a conductor pattern are laminated and the conductor patterns are sequentially connected to form a coil that spirals around the magnetic material while overlapping in the lamination direction. In a multilayer inductor in which both ends are led out to the outer surface of the multilayer chip through lead conductors and connected to electrode terminals, one or more electrically insulating magnetic gap layers over the entire multilayer surface are disposed and spaced apart. Between the overlapping conductor patterns, an electrically insulating nonmagnetic pattern having a shape corresponding to the conductor pattern shape is disposed in the vicinity of the conductor pattern, and outside the conductor pattern, the conductor pattern A multilayer inductor for a DC-DC converter, wherein a magnetic layer having a shape excluding a portion is provided.

Here, the electrically insulating nonmagnetic pattern may have a shape matching the conductor pattern, but is preferably a shape slightly larger than or slightly smaller than the conductor pattern. In particular, it is more preferable to make the shape slightly larger than the conductor pattern . Preferably symmetrically disposed with or the electrically insulating magnetic gap layer and the electrically insulating non-magnetic pattern to the central direction of lamination. In the case where there is one electrically insulating magnetic gap layer, the magnetic gap layer is disposed at substantially the center in the stacking direction, and the electrically insulating nonmagnetic pattern is symmetrically formed with respect to the center in the stacking direction. Arrange above. The thickness of the electrically insulating magnetic gap layer may be set smaller than the interval between the conductor patterns that overlap each other. The electrically insulating nonmagnetic pattern is preferably disposed between all overlapping conductor patterns.

  In the multilayer inductor according to the present invention, since one or more electrically insulating magnetic gap layers are disposed over the entire multilayer surface, the overall magnetic saturation level is increased, the DC superposition characteristics are increased, and the rated current (inductance above a predetermined value) is increased. Can be increased. In the multilayer inductor according to the present invention, an electrically insulating non-magnetic pattern corresponding to the conductor pattern shape is disposed between conductor patterns that overlap with each other at an interval. Generation of a minute magnetization loop around the coil at the time of bias current is prevented, so that a rapid flow of magnetic flux between the conductor patterns does not occur, a sudden change in inductance can be prevented, and an increase in AC resistance can be suppressed.

  The decrease in inductance due to the increase in the DC superimposed current is caused by increasing the magnetic flux generated from the coil due to the increase in DC current and saturating the magnetic material. In addition, a sudden decrease in inductance and an increase in AC resistance at a low DC bias current are caused by a minute magnetization loop around the conductor pattern. In order to suppress the magnetic saturation of the magnetic material, extend the DC superposition characteristics by minimizing the decrease in inductance, and suppress the increase in AC resistance, the position and shape of the magnetic material and the non-magnetic material with respect to the conductor pattern It is important to arrange them in such a way.

  Therefore, in the multilayer inductor according to the present invention, an electrically insulating magnetic gap layer is disposed over the entire multilayer surface, and between the conductor patterns that overlap with each other at an interval, the conductor pattern is close to the conductor pattern and substantially matches the conductor pattern shape. An insulating nonmagnetic pattern is disposed. Typically, the electrically insulating magnetic gap layer is located at the center in the stacking direction, and the electrically insulating nonmagnetic pattern is disposed between all the overlapping conductor patterns.

  By adopting such a structure, the overall magnetic saturation can be controlled and the DC superposition characteristics can be extended. In addition, it is possible to prevent a magnetic flux from abruptly flowing between the conductor pattern at the time of a low DC bias current, to prevent a sudden decrease in inductance, and to suppress an increase in AC resistance.

  FIG. 1 is an explanatory view showing an embodiment of the multilayer inductor according to the present invention. In FIG. 1, A is an external appearance, B is a see-through state viewed from the top surface of a conductor pattern, C is a longitudinal section, and D is a structure of a conductor pattern and a nonmagnetic pattern.

  The multilayer inductor 10 is a chip component for surface mounting that has a substantially rectangular parallelepiped shape, and most of the coil is embedded in a material made of a magnetic material (for example, a Ni—Zn ferrite material), and both ends of the coil are formed. It is a structure electrically connected to the electrode terminals 12 formed at both ends of the chip (see A in FIG. 1).

  The internal coil structure is formed by printing and laminating a substantially annular (or semi-annular) conductor pattern 20 and an electrically insulating magnetic layer 22 by a screen printing method or the like. The conductor pattern 20 is connected to form a coil in a magnetic body by the magnetic layer 22 so as to circulate spirally while being superimposed in the stacking direction. In FIG. 1B, the conductor pattern 20 is wound in a rectangular shape while being bent at a right angle, but of course, it may be circular or oval. Both ends of the coil are respectively drawn out to opposite end faces of the outer surface of the multilayer chip via the lead conductor 24 and connected to the electrode terminal 12.

  Here, in the present invention, as shown in FIG. 1C, the conductive pattern 20 that forms a part of the coil and the other conductive pattern 20 that overlaps with each other are all electrically insulating. It is comprised with the nonmagnetic material (for example, Zn ferrite material). One part is an electrically insulating magnetic gap layer 26 over the entire laminated surface, and the other part is a nonmagnetic pattern 28 (see D in FIG. 1) substantially matching the shape of the conductor pattern. For example, a non-magnetic pattern is printed, and a magnetic layer in a shape excluding that portion is printed (the procedure may be reversed). In addition, a conductor pattern is printed, and a magnetic layer in a shape excluding that portion is printed (the procedure may be reversed). By repeating such operations, printing lamination can be performed. In addition, what is necessary is just to electrically connect between upper and lower conductor patterns using a via hole. In this embodiment, four conductor patterns 20 are provided, and the gap between the second layer and the third layer from the bottom is the magnetic gap layer 26 over the entire laminated surface, the bottom is between the first layer and the second layer, and A nonmagnetic pattern 28 is formed between the third layer and the fourth layer. When the conductor pattern 20 is printed, the boundary between the nonmagnetic pattern 28 and the magnetic material is made larger than the conductor pattern 20 as a whole in order to prevent a short circuit from occurring due to the inflow of the conductor paste. It is preferable to set the magnetic layer so that it can be mounted on the magnetic layer with a sufficient margin.

  The multilayer inductor having the structure of the present invention can satisfy the specifications usually required with a relatively small number of coil turns in applications such as a DC-DC converter. The positions where the magnetic gap layer and the nonmagnetic pattern are inserted are appropriately determined according to the coil shape, the number of turns, and the like.

  Another embodiment of the multilayer inductor according to the present invention is shown in FIG. FIG. 2A shows an example in which the thickness of the electrically insulating magnetic gap layer 26 is set smaller than the interval between the conductor patterns 20 that overlap each other. Since the basic configuration is the same as that shown in FIG. 1, the corresponding parts are denoted by the same reference numerals, and detailed description thereof is omitted. The interval between the conductor patterns 20 that overlap with each other at an interval in the vertical direction is usually required to be about 15 μm in order to ensure electrical insulation. On the other hand, in order to control the magnetic saturation level, it is desirable to be able to freely control the thickness of the magnetic gap layer 26 over the entire laminated surface. Therefore, the thickness of the magnetic gap layer 26 is set to a desired size (for example, about 7.5 μm), and a thin nonmagnetic pattern is additionally arranged with a difference from the distance between the conductor patterns 20 (here 7.5 μm). (In this example, it is provided on the upper side of the magnetic gap layer, but it may be provided on the lower side or may be provided on both upper and lower sides equally). Thus, the magnetic gap layer 26 can be set to a desired thickness while the interval between the conductor patterns 20 is set to a size that can sufficiently ensure electrical insulation (without worrying about a short circuit of the coil).

  2B is a modified example of the multilayer inductor shown in FIG. 2A, and this is also basically the same configuration as that shown in FIG. Detailed description is omitted. In this example, six layers of conductor patterns 20 forming a part of the coil are laminated so as to overlap each other at intervals. The regions between the conductor patterns 20 are all made of an electrically insulating non-magnetic material, and part of them (here, two locations) is an electrically insulating magnetic gap layer 26 over the entire laminated surface. Specifically, the gap between the second layer and the third layer from the bottom, and between the fourth layer and the fifth layer is a magnetic gap layer 26 over the entire laminated surface, and from the bottom between the first layer and the second layer, A nonmagnetic pattern 28 is formed between the third layer and the fourth layer and between the fifth layer and the fifth layer. Also in this case, the thickness of the magnetic gap layer 26 is set to be thin (for example, about 7.5 μm), and a nonmagnetic pattern having a thickness different from the conductor pattern interval (here 7.5 μm) is additionally arranged.

  As described above, according to the present invention, the number of conductor patterns forming a coil can be increased or decreased according to required specifications. The number of magnetic gap layers, the thickness of magnetic gap layers, the number of nonmagnetic patterns, etc. Can be changed. As described above, for example, Ni—Zn based ferrite can be used as the magnetic material, and for example, Zn based ferrite can be used as the nonmagnetic material for forming the magnetic gap layer and the nonmagnetic pattern.

  An example of the measurement result is shown in FIGS. The DC superposition characteristics of two types of laminated inductors of the same material, the same dimensions, and different internal structures were measured. The product of the present invention has the same structure as the multilayer inductor shown in FIG. 1, and has an electrically insulating magnetic gap layer formed at the center over the entire multilayer surface, and with a conductor pattern overlapping at intervals. This is a structure in which an electrically insulating non-magnetic pattern is disposed between all the spaces. On the other hand, the comparative example has a structure in which only one electrically insulating magnetic gap layer is formed at the center over the entire laminated surface (there is no electrically insulating nonmagnetic pattern). In any case, the conductor pattern is four layers, and a coil of 4.5 turns is formed.

  FIG. 3 shows the DC bias current characteristics. FIG. 3A shows a change in inductance. When the product of the present invention is compared with the comparative example, the product of the present invention can maintain a relatively high inductance up to a high current, and the change in inductance is small even if the direct current changes. I understand that. FIG. 3B shows the change in AC resistance. Compared with the product of the present invention and the comparative example, the product of the present invention has a particularly low AC resistance at a low current, and the AC resistance changes even when the DC current changes. I understand that there are few. From these measurement results, as in the present invention, an electrically insulating magnetic gap layer is formed over the entire laminated surface, and an electrically insulating nonmagnetic pattern is disposed between conductor patterns overlapping each other at intervals. It can be seen that the DC superposition characteristics can be improved and the AC resistance at the time of a low DC bias current can be reduced.

  FIG. 4 shows frequency characteristics. 4A shows the Q value, B shows the inductance, and C shows the AC characteristics. The product of the present invention has a higher Q value and lower AC resistance. Although the inductance is slightly low, it can be made almost constant regardless of the frequency. At present, the operating frequency of the DC-DC converter is about 1 to 3 MHz, but it is expected to become higher in the future (for example, approaching 10 MHz). Since the product of the present invention has good high frequency characteristics, it is considered that the present invention becomes more advantageous as the frequency increases.

  The number of coil turns can be increased or decreased as appropriate according to the required specifications. However, if the number of coil turns is excessively large, the number of manufacturing steps is increased and the cost is increased. Therefore, the number of coil turns is preferably set to the minimum necessary.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows one Example of the multilayer inductor which concerns on this invention. The longitudinal cross-sectional view which shows the other Example of this invention. The graph which shows the difference of the direct current | flow superimposition characteristic of this invention product and a comparative example. The graph which shows the difference in the frequency characteristic of this invention product and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Multilayer inductor 12 Electrode terminal 20 Conductor pattern 22 Magnetic layer 24 Leader conductor 26 Magnetic gap layer 28 Nonmagnetic pattern

Claims (5)

An electrically insulative magnetic layer and a conductor pattern are laminated and the conductor patterns are sequentially connected to form a coil that spirals around the magnetic material while overlapping in the lamination direction, and both ends of the coil are drawn out. In the multilayer inductor that is drawn to the outer surface of the multilayer chip through the conductor and connected to the electrode terminal,
One or more electrically insulative magnetic gap layers over the entire laminated surface are arranged, and between conductor patterns that overlap with each other at an interval, electrical insulation having a shape corresponding to the conductor pattern shape is provided close to the conductor pattern. A laminated inductor for a DC-DC converter , characterized in that a magnetic non-magnetic pattern is disposed and a magnetic layer having a shape excluding the portion of the conductor pattern is provided outside the conductor pattern. 2. The multilayer inductor for a DC-DC converter according to claim 1, wherein the electrically insulating magnetic gap layer and the electrically insulating nonmagnetic pattern are arranged symmetrically with respect to a center in the stacking direction. 2. The DC− according to claim 1, wherein the electrically insulating magnetic gap layer is located in the center in the stacking direction, and the electrically insulating nonmagnetic pattern is arranged symmetrically with respect to the center in the stacking direction. Multilayer inductor for DC converter . The multilayer inductor for a DC-DC converter according to any one of claims 1 to 3, wherein a thickness of the electrically insulating magnetic gap layer is set to be smaller than an interval between conductor patterns overlapping each other. The multilayer inductor for a DC-DC converter according to any one of claims 1 to 4, wherein the electrically insulating nonmagnetic pattern is disposed between all conductor patterns that overlap with each other at intervals.

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