Laminated coil component

Abstract

To provide a laminated coil component which has a high resistance to voltage and a small variation of inductance.SOLUTION: A magnetic substance layer 4a of a magnetic body, which is located between coil conductor layers 5 in proximity to each other along a lamination direction of the coil conductor layer 5, includes metal magnetic particles 4α. The average particle diameter of the metal magnetic particles 4α is 0.3 μm or more and is 2.5 μm or less, and the occupancy ratio of the metal magnetic particles 4α is 60% or more and is 82% or less. The average circularity of metal magnetic particles 4α1 located in a predetermined region including the boundary between the coil conductor layer and the magnetic substance layer is 0.80 or more.SELECTED DRAWING: Figure 2B

Description

[Technical Field]

[0001] The present invention relates to a multilayer coil component that can be used as, for example, a multilayer inductor. [Background technology]

[0002] For example, a multilayer inductor is known, as shown in Patent Document 1. In multilayer coil components such as this multilayer inductor, there are cases where it is desirable to thin the magnetic layers between the coil conductor layers in order to meet demands for miniaturization, etc. However, thinning the magnetic layers tends to reduce the withstand voltage characteristics.

[0003] Furthermore, in order to improve the inductance of the coil component, a laminate including a conductor layer and a magnetic layer may be pressed at high pressure to increase the occupancy rate of the metal magnetic particles contained in the magnetic layer. However, the present inventors have found that pressing the laminate at high pressure increases the variation in inductance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-38263 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multilayer coil component that has excellent withstand voltage characteristics and small variations in inductance. [Means for solving the problem]

[0006] As a result of extensive research into multilayer coil components, the inventors have discovered that by setting the average particle size of the metal magnetic particles, the space factor of the metal magnetic particles, and the average circularity of the metal magnetic particles located in a predetermined region of the magnetic layer in contact with the coil conductor layer within predetermined ranges, it is possible to obtain a multilayer coil component that has excellent voltage resistance characteristics and small inductance variation, and have thereby completed the present invention.

[0007] That is, a multilayer coil component according to one aspect of the present invention comprises: A multilayer coil component having a magnetic element and coil conductor layers stacked inside the magnetic element so as to be continuously connected in a spiral shape, a magnetic layer of the magnetic element body located between adjacent coil conductor layers along a stacking direction of the coil conductor layers includes metal magnetic particles, The average particle size of the metal magnetic particles is 0.3 μm or more and 2.5 μm or less, the space factor of the metal magnetic particles is 60% or more and 82% or less, The metal magnetic particles within a predetermined region from the boundary between the coil conductor layer and the magnetic layer have an average circularity of 0.80 or more.

[0008] Preferably, the CV value of the particle size of the metal magnetic particles is 30% or more and less than 50%. By configuring in this way, the withstand voltage characteristics are further improved and the variation in inductance is further reduced.

[0009] Preferably, the average particle size of the metal magnetic particles is 0.3 μm or more and 1.9 μm or less. By configuring in this manner, the voltage resistance characteristics are further improved.

[0010] Preferably, in the SEM observation image, the number frequency of the metal magnetic particles having a particle size of 4.0 μm or more may be 1.2% or less, 1.0% or less, 0.8% or less, or 0.6% or less. By configuring in this way, the voltage resistance characteristics are further improved.

[0011] Preferably, the metal magnetic particles include Fe-based metal magnetic particles, and the Fe-based metal magnetic particles have, on their surfaces, an oxide coating containing an element that is more easily oxidized than Fe. By configuring in this manner, the withstand voltage characteristics are further improved and the variation in inductance is further reduced.

[0012] Preferably, the predetermined region of the magnetic layer where the average of the metal magnetic particles is determined is within a range of 0.2 times the distance between adjacent coil conductor layers along the stacking direction. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view of a multilayer coil component according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Figure 2A] FIG. 2A is an enlarged schematic cross-sectional view of a magnetic layer located between the coil conductors shown in FIG. [Figure 2B] FIG. 2B is an explanatory diagram for explaining metal magnetic particles that belong to a predetermined region from the boundary between the magnetic layer and the coil conductor layer shown in FIG. 2A. [Figure 2C] FIG. 2C is an explanatory diagram of the interface-side particles extracted from the metal magnetic particles shown in FIG. 2B. [Figure 2D] FIG. 2D is an enlarged schematic cross-sectional view of a magnetic layer located between coil conductors according to another embodiment of the present invention. [Figure 3A] FIG. 3A is an explanatory diagram of a method for manufacturing the multilayer coil component shown in FIG. [Figure 3B] FIG. 3B is an explanatory diagram showing a step subsequent to that shown in FIG. 3A. [Figure 3C] FIG. 3C is an explanatory diagram showing a step subsequent to that shown in FIG. 3B. [Figure 3D] FIG. 3D is an explanatory diagram showing a step subsequent to FIG. 3C. [Figure 4] FIG. 4 is a perspective view of a multilayer coil component according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following describes the embodiments.

[0015] First embodiment In the following, a laminated coil component 1 shown in FIG. 1 will be described as an example of a coil-type electronic component according to this embodiment.

[0016] 1, a multilayer coil component 1 according to this embodiment has an element 2 and terminal electrodes 3. The element 2 has a configuration in which a coil conductor layer 5 is embedded three-dimensionally and spirally inside a magnetic base body 4. Terminal electrodes 3 are formed on both ends of the element 2, and these terminal electrodes 3 are connected to the coil conductor layer 5 via lead electrodes 5a1 and 5a2.

[0017] 1 and the drawings described later, the X-axis, Y-axis, and Z-axis are perpendicular to one another. In this embodiment, the "inner side" refers to the side closer to the center of the multilayer coil component 1 (or the axis of the coil conductor layer 5), and the "outer side" refers to the side farther from the center of the multilayer coil component 1.

[0018] The material of the terminal electrode 3 is not particularly limited as long as it is an electrical conductor. For example, Ag, Cu, Au, Al, Ag alloy, Cu alloy, etc. can be used. Ag is particularly preferred because it is inexpensive and has low resistance. The terminal electrode 3 may contain glass frit. Alternatively, the terminal electrode 3 may have a multilayer structure formed on the element 2, including a metal layer made of the above metal or the above metal and glass frit, and a resin layer made of a conductive resin formed on the metal layer.

[0019] There are no particular restrictions on the type of metal contained in the conductive resin. For example, Ag can be used. The surfaces of the terminal electrodes 3 may also be plated. For example, Cu plating, Ni plating, Sn plating, Cu-Ni-Sn plating, and / or Ni-Sn plating may be used as appropriate.

[0020] The coil conductor layer 5 and the lead electrodes 5a1 and 5a2 can be made of any electrically conductive material. For example, Ag, Cu, Au, Al, Ag alloys, Cu alloys, etc. are used. Ag is particularly preferred because it is inexpensive and has low resistance. The coil conductor layer 5 may contain glass frit.

[0021] The number of turns around the axis of the coil conductor layer 5 is not particularly limited and is, for example, 1.5 to 15.5. The thickness Te of the coil conductor layer 5 shown in FIG. 2 is also not particularly limited and is, for example, 5 to 60 μm. Note that FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1, and is a cross-sectional view parallel to the YZ axes. That is, FIG. 2 is a cross-sectional view showing the lead electrodes 5a1 and 5a2 and the terminal electrode 3.

[0022] 2, the element 2 can be divided, from bottom to top, into an axial end region 2a, an axial central region 2b, and another axial end region 2a along the winding axis (parallel to the Z-axis) of the coil conductor layer 5. In other words, the element 2 can be divided into an axial central region 2b in which the coil conductor layer 5 is embedded, and axial end regions 2a, 2a located above and below the axial central region 2b in the axial direction (Z-axis direction) and in which the coil conductor layer 5 is not embedded. The axial direction of the coil conductor layer 5 is parallel to the stacking direction of the coil conductor layers 5.

[0023] Specifically, the outer side along the axis is defined as axial end regions 2a, 2a, and the inner side along the axis is defined as axial center region 2b, with a virtual line perpendicular to the axial direction (Z-axis direction) and along the outer side of extraction electrodes 5a1, 5a2 as the boundary. In this embodiment, axial center region 2b is defined as a range that includes extraction electrodes 5a1, 5a2.

[0024] In this embodiment, the region of the element 2 located between axially adjacent coil conductor layers 5 is referred to as the interlayer region 4a. The thickness of the magnetic layer 4a in the Z-axis direction (Ti / same as the interlayer thickness d described later) is not particularly limited, and can be as thin as 100 μm or less, 50 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 7 μm or less, or 4 μm or less, for example.

[0025] 2A, the magnetic layer 4a contains metal magnetic particles 4α. The material of the metal magnetic particles 4α is not particularly limited, and examples include Fe-based metal magnetic particles such as Fe—Si-based alloys, Fe—Si—Cr-based alloys, pure Fe, Fe—Ni-based alloys, Fe—Si—Al-based alloys, and Fe—Co-based alloys, with Fe—Si-based alloys being preferred. The metal magnetic particles 4α may also contain metal particles other than these Fe-based metal magnetic particles.

[0026] When the total content of Fe and Si in metal magnetic particle 4α is taken as 100 mass %, the content of Fe in the particle is preferably 92.0 to 97.0 mass %, and more preferably 92.5 to 96.5 mass %.

[0027] When the total content of Fe and Si in metal magnetic particles 4α is taken as 100 mass%, the Cr content in metal magnetic particles 4α is preferably 5 mass% or less, and more preferably less than 2 mass%, which improves the balance between inductance and DC bias characteristics, improves the evaluation of plating elongation suppression, and reduces the number of short circuits.

[0028] When the total content of Fe and Si in metal magnetic particles 4α is taken as 100 mass %, the content of P in metal magnetic particles 4α may be 10 to 700 ppm, or 40 to 650 ppm, which results in a better balance between inductance and DC bias characteristics, a higher evaluation of plating elongation suppression, and a smaller number of short circuits.

[0029] 2B, the metal magnetic particles 4α can be divided into interface-side particles 4α1 that are within a predetermined region (0.2d) from the boundary C3 between the coil conductor layer 5 and the magnetic layer 4a, and center-side particles 4α2 that are not located between the coil conductor layer 5 and the magnetic layer 4a, which are adjacent along the Z axis. The boundary C3 between the coil conductor layer 5 and the magnetic layer 4a can be determined, for example, as follows.

[0030] For example, when the coil conductor layer 5 is formed by a printing method, during the manufacturing process, a portion of the interface-side particle 4α1 of the metal magnetic particle 4α located in the magnetic layer 4a and close to the conductor layer 5 may be embedded in the conductor layer 5. In such cases, the boundary between the magnetic layer 4a and the conductor layer 5 is difficult to see in a cross-sectional photograph of the magnetic layer 4a, but the boundary C3 can be determined as follows.

[0031] 2A, by performing image analysis of the cross section of the magnetic layer 2a using an SEM, STEM, or the like, a peak line C2 is drawn on the cross section photograph, which is in contact with the particle that is most embedded in the coil conductor layer 5 and is perpendicular to the coil axis (Z-axis) direction, and a valley line C1 is drawn, which is in contact with the point located closest to the interlayer of the coil conductor layer 5 and is perpendicular to the coil axis (Z-axis) direction. An intermediate line between these two lines is obtained, and this intermediate line is designated as the boundary C3.

[0032] 2D, when the coil conductor layer 5 is formed by plating or the like, the metal magnetic particles 4α tend to sink less into the conductor layer 5, but some sinking still occurs, so the boundary C3 can be determined in the same manner as in Figures 2A and 2B. Alternatively, the boundary C3 can be defined as the center line (perpendicular to the Z axis) of the irregularities on the surface of the conductor layer 5 in contact with the magnetic layer 4a.

[0033] In either case, the interface-side particles 4α1 can be defined as follows. As shown in FIG. 2B, the distance along the Z axis between the boundaries C3, C3 between adjacent conductor layers 5, 5 along the Z axis is defined as the thickness (interlayer thickness) d of the magnetic layer 4a. A distance of 0.2 times the thickness d is defined as a predetermined range of distance 0.2d, and a virtual line C4 parallel to the boundary C3 is obtained at a distance of 0.2d inward from the boundary C3 along the Z axis toward the center of the magnetic layer 4a. Particles touching or contained within a predetermined region between the boundary C3 and the virtual line C4 at the 0.2d position can be extracted as shown in FIG. 2C and defined as interface-side particles 4α1. Furthermore, as shown in FIG. 2B, magnetic particles 4α other than the interface-side particles 4α1 can be defined as center-side particles 4α2.

[0034] In this embodiment, the average circularity of the interface-side particles 4α1 (a part of the metal magnetic particles 4α) within a predetermined region (0.2d) from the boundary C3 between the coil conductor layer 5 and the magnetic layer 4a is preferably 0.80 or more, 0.82 or more, or 0.84 or more. By setting the average circularity in this range, the inductance is maintained high, the inductance variation is reduced, and the withstand voltage characteristics are also improved.

[0035] The circularity can be measured, for example, by the following formula for the interface-side particle 4α1 extracted by the above-described method as shown in FIG. 2C. Circularity = 4πS / L2

[0036] Here, in the above formula, S represents the projected area of the particle 4α1, and L represents the circumferential length of the particle. The number of particles 4α1 (metal magnetic particles 4α) on the interface side near the conductor layer 5 analyzed for circularity is preferably 100 or more. If one field of view is insufficient, it is preferable to analyze multiple fields of view.

[0037] The average circularity near the conductor can be adjusted by the circularity of the metal magnetic powder used as the raw material, the pressing pressure of the laminate before firing, the presence or absence of a resin-rich buffer layer, the presence or absence of heat treatment of the metal magnetic powder before making it into a paste, increasing or decreasing the amount of resin in the magnetic layer paste, increasing or decreasing the amount of resin in the conductor paste, the method for making the metal magnetic powder paste, and whether or not the magnetic sheet is roll-pressed.

[0038] The average particle size of the metal magnetic particles 4α (hereinafter, unless otherwise specified, 4α includes both 4α1 and 4α2) shown in FIG. 2B is preferably 0.3 μm or more and 2.5 μm or less, and more preferably 0.3 μm or more and 1.9 μm or less. By setting the average particle size of the metal magnetic particles 4α in this range, it is possible to increase the inductance, reduce inductance variation, and improve voltage resistance characteristics compared to when the average particle size is 0.3 μm or less. Furthermore, by setting the average particle size of the metal magnetic particles 4α in this range, it is possible to increase the inductance while maintaining a thin magnetic layer 4a (for example, 10 μm or less), reduce inductance variation, and improve voltage resistance characteristics compared to when the average particle size is larger.

[0039] While the method for measuring the average particle size of the metal magnetic particles is not particularly limited, in this embodiment, the area of each metal magnetic particle 4α is calculated by performing image analysis on a cross section of the magnetic layer 2a in the laminated coil component 1 (electronic component) using an SEM, STEM, or the like, and the diameter of a circle corresponding to that area (circle-equivalent diameter) is calculated as the particle size of the metal magnetic particle 4α. The average particle size is determined as the average value of the particle sizes of multiple metal magnetic particles 4α. Note that, when calculating the average value, as shown in FIG. 2A , the magnetic layer 4a located between two adjacent conductor layers 5, 5 is observed, and the average is calculated for those 800 or more metal magnetic particles 4α within the observed range. Note that if there are fewer than 800 particles in one visual field, multiple visual fields may be used for analysis.

[0040] The CV value, which indicates the particle size variation of the metal magnetic particles 4α, is preferably 30% or more and less than 50%, more preferably 35% or more and less than 50%, and particularly preferably 40% or more and less than 50%. If the CV value is too small, the packing property tends to deteriorate and the space factor tends to decrease, while if the CV value is too large, the withstand voltage tends to decrease and the variation in inductance tends to increase. The CV value can be determined by calculating the standard deviation under the same measurement conditions as when determining the average particle size of the particles 4α, dividing the standard deviation by the average particle size, and multiplying the result by 100.

[0041] The metal magnetic particles α may preferably have a particle size of 4.0 μm or more in a number frequency of 1.2% or less, 1.0% or less, 0.8% or less, or 0.6% or less, which further improves the withstand voltage characteristics.

[0042] Furthermore, the space factor of the metal magnetic particles 4α in the magnetic layer 4a is preferably 60% or more and 82% or less. By achieving a space factor within this range, the variation in inductance is reduced without decreasing the inductance, and the withstand voltage characteristics are also improved. However, if the space factor is too low, the inductance tends to decrease. If the space factor is too high, the variation in inductance tends to increase, and the withstand voltage characteristics also tend to deteriorate. This is thought to be because high voltage is applied to the element during the manufacturing process to increase the space factor, which reduces the circularity of the metal magnetic particles located in the magnetic layer, especially those close to the coil conductor layer.

[0043] The occupancy rate is measured by performing image analysis of the cross section of the magnetic layer 2a using an SEM, STEM, or the like, to calculate the total area of the metal magnetic particles 4α from the black-and-white binarized image, and then calculating the ratio of the area of the metal magnetic particles 4α to the total image area to obtain the space factor. When calculating the space factor, it is preferable to include particles that extend beyond the edge of the cross section image. Furthermore, if multiple fields of view are analyzed in terms of the number of particles analyzed for particle size and circularity, the average space factor may be used. It is preferable to calculate particle size, CV value, and circularity by excluding particles that extend beyond the edge of the cross section image.

[0044] The surfaces of the metal magnetic particles 4α may be covered with a coating film. Specifically, the coating film is preferably an oxide film, and the oxide film is preferably an oxide film containing an element that is more easily oxidized than Fe, and may include a layer made of an oxide containing Si. When the metal magnetic particles 4α are covered with a coating film, the insulation between the metal magnetic particles 4α is improved, thereby improving the Q value. Furthermore, when the oxide film includes a layer made of a compound containing Si, the formation of Fe oxide can be prevented. The metal magnetic particles 4α may be covered with a coating layer other than the oxide film, or together with the oxide film.

[0045] Next, a description will be given of a method for manufacturing the multilayer coil component 1 shown in Fig. 1. First, an example of a method for manufacturing the metal magnetic particles 4α will be described.

[0046] In this embodiment, the raw material for metal magnetic particles 4α can be a single element or an alloy of the constituent elements, such as Fe, Si, Cr, Ni, Co, or Al.

[0047] In this embodiment, the metal magnetic particles 4α can be obtained using a method similar to known methods for producing metal magnetic particles 4α. Specifically, the metal magnetic particles 4α can be produced using a gas atomization method, a water atomization method, a rotating disk method, or the like. Among these, the gas atomization method is preferred because it is easier to obtain metal magnetic particles 4α with a high degree of circularity.

[0048] Next, the obtained metal magnetic particles 4α are slurried with additives such as a solvent and a binder to prepare a magnetic layer paste. This paste is then used to form, for example, magnetic sheet layers 40a-40e shown in FIGS. 3A-3D, which will constitute the magnetic layer 4a in the shaft end region 2a and the central region 2b shown in FIG. 2 after firing. The organic vehicle is a mixture of a binder (e.g., polyvinyl butyral resin, ethyl cellulose resin, acrylic resin, etc.) and a solvent (e.g., terpineol, butyl carbitol, etc.), with a binder-to-solvent ratio of, for example, 5-20:80-95 (by mass), and the ratio can be adjusted to obtain a desired viscosity in the magnetic layer paste. For example, the organic vehicle used in the magnetic layer paste may use polyvinyl butyral resin as the binder and butyl carbitol as the solvent, with a binder-to-solvent ratio of 10:90 (by mass). The magnetic layer paste may contain additives selected from various dispersants, plasticizers, dielectrics, insulators, etc., as needed.

[0049] At the same time, or before or after, a conductor paste for forming the coil conductor layer 5 shown in Figures 1 and 2 is also prepared. The conductor paste contains metals for forming the coil conductor layer 5 together with additives such as a solvent and a binder. For example, the organic vehicle used in the conductor paste may be composed of ethyl cellulose resin as the binder and terpineol as the solvent, with the binder / solvent mixture ratio being 10:90 (mass ratio). The conductor paste may also contain additives selected from various dispersants, plasticizers, dielectrics, insulators, etc., as needed.

[0050] For example, to form the extraction electrode 5a1 shown in Figures 1 and 2, the right half of the magnetic sheet 40b from the dotted line J is printed on the magnetic sheet layer 40a shown in Figure 3A, and the conductive pattern layer 50a1 is formed by a printing method or the like so that it overlaps the step between the magnetic sheets 40a and 40b.

[0051] Next, as shown in Fig. 3B, a magnetic sheet layer 40c is printed and formed in the left half of dotted line L so as to cover most of the conductive pattern layer 50a1 shown in Fig. 3A and expose only the pattern layer 50a1 between dotted line L and dotted line M, and a conductive pattern layer 50b is formed thereon by a printing method or the like. As a result, the pattern layer 50a1 shown in Fig. 3A and the pattern layer 50b shown in Fig. 3B are connected between dotted line L and dotted line M.

[0052] Next, as shown in Fig. 3C, a magnetic sheet layer 40d is printed and formed in the half to the right of dotted line K so as to cover most of the conductive pattern layer 50b shown in Fig. 3B and expose only the pattern layer 50b between dotted line J and dotted line K, and a conductive pattern layer 50c is formed thereon by a printing method or the like. As a result, the pattern layer 50b shown in Fig. 3B and the pattern layer 50c shown in Fig. 3C are connected between dotted line J and dotted line K.

[0053] By repeating the printing shown in Figure 3B and the printing shown in Figure 3C, a conductor pattern layer corresponding to the spiral coil conductor layer 5 wound multiple times as shown in Figure 1 and a sheet layer corresponding to the magnetic layer 4a located therebetween are obtained.

[0054] At the end of the spiraling process, as shown in FIG. 3D, a magnetic sheet layer 40e is printed and formed in the left half of dotted line L so as to cover most of the conductive pattern layer 50C shown in FIG. 3C and expose only the pattern layer 50c between dotted lines L and M, and a conductive pattern layer 50a2 is formed thereon by a printing method or the like. As a result, the pattern layer 50c shown in FIG. 3C and the pattern layer 50a2 shown in FIG. 3D are connected between dotted lines L and M. The pattern layer 50a2 is the portion that will become the extraction electrode 5a2 shown in FIGS. 1 and 2 after firing.

[0055] Furthermore, a magnetic layer paste is used on the printed body shown in Figure 3D to form the portion that will form the shaft end region 2a after firing using a printing method or the like. Note that although the above describes the method for manufacturing the laminate using a printing method, a laminate with the above configuration can also be obtained using a sheet method. Also, in the above embodiment, the coil conductor layer 5 is formed by a printing method, but it may also be formed by a plating method.

[0056] In either case, the resulting laminate is press-formed during or after lamination to increase the density of the metal magnetic particles 4α. In this embodiment, it is preferable to add a step of increasing the hardness of the metal magnetic particles 4α before press-forming. Alternatively, a resin-rich buffer layer may be provided on the front and / or back surfaces of the conductive pattern layers 50a1, 50a2, 50b-50c so that the circularity of the interface-side particles 4α1 located near the conductive layer 5 does not decrease even when the metal magnetic material 4α comes into contact with the conductive layer 5.

[0057] One possible method for increasing the hardness of the metal magnetic particles 4α is to heat treat the metal magnetic particles before they are made into a paste. The conditions for the heat treatment are not particularly limited, but the heat treatment can be carried out, for example, at 250 to 800°C for 5 to 120 minutes in the air, or in an inert gas (e.g., nitrogen) containing a certain amount of oxygen (e.g., an oxygen partial pressure of 1% or less). The heat treatment also forms an oxide film of a suitable thickness.

[0058] Alternatively, a resin-rich buffer layer may be formed by printing or coating a buffer pattern layer containing only the resin and solvent contained in the conductive pattern layers 50a1, 50a2, 50b-50c before and / or after forming the conductive pattern layers 50a1, 50a2, 50b-50c. Alternatively, a buffer pattern layer may be formed by printing or coating using a paste in which the amount of organic vehicle added to the soft magnetic metal powder is adjusted so that the resin content is 1 to 10 wt% higher than that of the conductive paste before and / or after forming the conductive pattern layers 50a1, 50a2, 50b-50c.

[0059] The obtained laminate is subjected to heat treatment (binder removal step and firing step) to remove the binder and obtain a fired body (element 2). The holding temperature in the binder removal step (binder removal temperature) is not particularly limited as long as it is a temperature at which the binder can be decomposed and removed as a gas. For example, it may be 300°C or higher and 450°C or lower. The holding time in the binder removal step (binder removal time) is also not particularly limited. For example, it may be 0.5 hours or higher and 2.0 hours or lower.

[0060] The holding temperature (sintering temperature) in the sintering step is not particularly limited as long as it is a temperature at which the metal magnetic particles that make up the soft magnetic metal powder are bonded to each other. It may be 550°C or higher and 850°C or lower. The holding time (sintering time) in the sintering step is also not particularly limited. It may be 0.5 hours or higher and 3.0 hours or lower.

[0061] After firing, annealing (heat treatment) may be performed. There are no particular restrictions on the conditions for annealing. For example, annealing may be performed at 500 to 800°C for 0.5 to 2.0 hours. There are also no particular restrictions on the atmosphere after annealing.

[0062] Next, the terminal electrodes 3 are formed on the element. There are no particular limitations on the method for forming the terminal electrodes 3, and they are usually produced by forming a slurry of the metal (such as Ag) that will become the terminal electrodes 3 together with additives such as a solvent and a binder.

[0063] The laminated coil component 1 according to this embodiment is obtained by the above-described method, but in this embodiment in particular, it is preferable to employ the above-described measures in order to maintain the circularity of the interface-side particles 4α1 among the metal magnetic particles 4α shown in FIG. 2B.

[0064] Second embodiment The second embodiment will be described below, but unless otherwise specified, it is the same as the first embodiment.

[0065] As shown in FIG. 4, in the multilayer coil component 1 according to this embodiment, the coil conductor layer 5 disposed inside the magnetic base body 4 is embedded in a spiral shape with the Y axis as the winding axis. Terminal electrodes 3 are formed on both ends of the element 2, and these terminal electrodes 3 are connected to the coil conductor layer 5 via lead electrodes 5a. The cross section of the magnetic layer 4a located between the coil conductor layers 5 adjacent along the Y axis inside the element 2 is similar to that shown in FIGS. 2A to 2D. In the first embodiment, the winding axis of the coil is parallel to the Z axis, but in the second embodiment, the winding axis of the coil is parallel to the Y axis. Furthermore, in the first embodiment, the stacking direction of the magnetic layer 4a is parallel to the Z axis, but in the second embodiment, the stacking direction of the magnetic layer 4a is parallel to the Y axis.

[0066] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention.

[0067] For example, in the above-described embodiment, a multilayer coil component is exemplified as an example of a coil-type electronic component, but known coil-type electronic components include transformers, choke coils, coils, etc. Furthermore, the coil-type electronic components according to the above-described embodiments are suitably used in the power supply circuits of various electronic devices such as mobile devices for applications such as inductance and impedance, but can also be used for other applications. [Example]

[0068] More detailed examples will be described below, but the present invention is not limited to these examples.

[0069] Example 1 Ingots, chunks, or shots of elemental Fe and elemental Si were prepared to have a composition of 94Fe-6Si. They were then mixed and placed in a crucible placed in a gas atomizer. Next, in an inert atmosphere, the crucible was heated to over 1600°C by high-frequency induction using an external work coil. The ingots, chunks, or shots in the crucible were melted and mixed to obtain a molten metal. A gas flow of 1–10 MPa was then impinged on the molten metal, which was then injected through a nozzle in the crucible to form a linear, continuous stream. The molten metal was rapidly cooled, dehydrated, dried, and classified. The metal powder obtained by the above process was heat-treated in air at 300°C for 30 minutes to produce soft magnetic metal powder composed of Fe-Si alloy particles. The average circularity of the soft magnetic metal powder was 0.89, as measured by static image analysis.

[0070] The obtained soft magnetic metal powder (powder that would become the metal magnetic particles 4α contained in the magnetic layer 4a) was slurried with additives such as a solvent and binder to prepare a magnetic layer paste. The magnetic layer paste contained 100 wt% soft magnetic metal powder and 20 wt% organic vehicle. The organic vehicle used in the magnetic layer paste was prepared by mixing a binder (polyvinyl butyral resin) and a solvent (butyl carbitol) in a 10:90 (mass ratio). The magnetic layer paste was then used to form magnetic sheet layers 40a to 40e, for example, as shown in FIGS. 3A to 3D, by printing to form the magnetic layer 4a in the shaft end region 2a and the central region 2b shown in FIG. 2 after firing.

[0071] Simultaneously, or before or after, a conductor paste for forming the coil conductor layer 5 shown in FIGS. 1 and 2 was also prepared. The conductor paste contained Ag for forming the coil conductor layer 5 together with additives such as a solvent and binder. The conductor paste contained 100 wt% Ag particles and 20 wt% organic vehicle. The organic vehicle used in the conductor paste was prepared by mixing a binder (ethyl cellulose resin) and a solvent (ethyl cellulose resin) in a 10:90 (mass ratio). Then, using the conductor paste, conductor pattern layers 50a1, 50b-50c, and 50a2 shown in FIGS. 3A to 3D, for example, for forming the coil conductor layer 5 shown in FIG. 2 after firing, were formed by printing.

[0072] A 0.8 mm green laminate was obtained through the process shown in Figures 3A to 3D. The coil conductor layer 5 was composed of an Ag conductor and had a winding number of 7.5Ts. Furthermore, to prevent a decrease in the circularity of the interface-side particles 4α1 located near the conductor layer 5 even when the metal magnetic material 4α contacts the conductor layer 5 shown in Figure 2A, resin-rich buffer layers were formed on the front and back surfaces of the conductor pattern layers 50a1, 50a2, 50b to 50c by printing. The paste composition for forming the resin-rich buffer layer was 100 wt% Ag particles, with 50 wt% of an organic vehicle containing a binder (ethyl cellulose resin) and a solvent (ethyl cellulose resin) in a mixing ratio of 10:90 (mass ratio). The printing thickness of the resin-rich buffer layer was 1 / 2 to 1 / 20 of the thickness of the conductor paste film.

[0073] The green laminate thus obtained was cut into a shape of 1.6 mm x 0.8 mm to obtain a green chip.

[0074] Next, the obtained green chip was subjected to a binder removal process in an inert atmosphere (N2 gas atmosphere) at 400°C, and then fired in a reducing atmosphere (a mixed gas atmosphere of N2 gas and H2 gas (hydrogen concentration 1.0%)) at 750°C for 1 hour to obtain a fired chip.

[0075] The terminal electrode paste was applied to both end faces of the obtained fired body chip, dried, and baked at 700 °C for 1 hour in an atmosphere with an oxygen partial pressure of 1%. Thereafter, electrolytic plating was performed to form a Ni plating layer and a Sn plating layer on the terminal electrode, and the terminal electrode 3 shown in FIG. 1 was formed to obtain the multilayer coil component 1.

[0076] The internal dimensions of the obtained multilayer coil component were as follows: the thickness (Te) of the coil conductor layer 5 shown in FIG. 2 was 20 μm, and the thickness (Ti) of the magnetic body layer 4a was 10 μm.

[0077] The following analysis was performed on the obtained multilayer coil component.

[0078] <Component analysis> For the multilayer coil component of Example 1, an elemental mapping photograph was obtained and component analysis was performed. As a result, it was confirmed that metal magnetic particles 4α having the same composition as the soft magnetic metal powder used as a raw material were formed in the magnetic body layer 4a. Furthermore, it was confirmed that an oxide film composed of an oxide of Si was observed with a thickness of 5 to 100 nm on the surface of the metal magnetic particles 4α.

[0079] <SEM image analysis> The coil component sample was cut along a plane perpendicular to the internal electrode layer, and the cut surface was wet-polished to obtain a polished surface. Next, ion milling was performed on the polished surface. The SEM image of the polished surface at the center of the chip after ion milling was observed.

[0080] Using image processing software (imageJ), the particle size distribution in terms of the equivalent circle diameter (Heywood diameter) was obtained for at least 800 or more metal magnetic particles 4α. When the number of metal magnetic particles in the visual field was less than 800, observations were made in multiple visual fields. Based on the particle size distribution, the average particle diameter, CV value, and the number ratio of particles of 4.0 μm or more (≧4.0 μm number frequency) were calculated. The results are shown in Table 1.

[0081] Furthermore, the above-mentioned SEM image was subjected to binarization processing or the like to determine the area ratio of the metal magnetic particles 4α to the entire image of the magnetic layer 4a, and this was taken as the space factor. The results are shown in Table 1. The space factor was adjusted by the pressing pressure of the pre-fired laminate and the paste composition (amount of resin), etc. The particle size distribution of the metal magnetic particles was adjusted by classifying the raw material metal magnetic powder, mixing metal magnetic powders with multiple particle size distributions, etc.

[0082] <Average circularity near the conductor> For a specific magnetic layer 4a within the observation area, the boundary C3 was determined using the method described above, and the distance between them was defined as the interlayer thickness d. A distance of 0.2d was defined as a predetermined range, 0.2 times the thickness d. A virtual line C4 parallel to the boundary C3 was obtained at a distance of 0.2d inward from the boundary C3 along the Z axis of the magnetic layer 4a toward the center. Particles touching or contained within the specified region between the boundary C3 and the virtual line C4 at the 0.2d position were extracted as shown in Figure 2C and defined as interface-side particles 4α1.

[0083] In the examples, the circularity of the interface-side particles 4α1 within a predetermined region (0.2d) from the boundary C3 between the coil conductor layer 5 and the magnetic layer 4a was determined using image processing software (ImageJ), and the average was taken as the average circularity near the conductor (average circularity of the interface-side particles 4α1). The results are shown in Table 1. The average circularity near the conductor was adjusted by the circularity of the metal magnetic powder used as the raw material, the pressing pressure of the pre-fired laminate, the thickness of the resin-rich buffer layer, the proportion of resin, etc.

[0084] <Inductance variation> The inductance L of 50 inductor samples was measured using an RF impedance analyzer (Keysight Technologies E4991A) and a test fixture (Keysight Technologies 16192A). Measurement conditions were a measurement frequency of 10 MHz and a measurement temperature of 25°C. From the obtained data, the inductance variation (%) was calculated by dividing the maximum value by the minimum value and the average value by 100. In the inductance variation column of each table, a variation of 10% or less was marked as particularly good (VG), a variation of over 10% but not exceeding 15% was marked as good (G), and a variation of over 15% was marked as poor (NG). The results are shown in Table 1.

[0085] <Voltage resistance> In addition to the inductor sample, a capacitor sample was fabricated using the same materials and methods, with the thickness between electrode layers being equivalent to the above-mentioned conductor layer thickness d, and the number of laminated conductor layers being 8 (close to 7.5 turns). The withstand voltage of the capacitor sample was evaluated as follows.

[0086] For five or more capacitor samples, a DC voltage was applied to the sample at a rate of 10 V / sec. The voltage at which a leakage current of 10 mA was observed was measured and divided by the thickness between the conductors to determine the value. The average of these values was taken as the withstand voltage. A withstand voltage of 1.0 V / μm or more was considered good. The results are shown in Table 1.

[0087] Examples 2 to 8 Samples were prepared in the same manner as in Example 1, and evaluations were performed in the same manner as in Example 1, except that the proportion of resin contained in the magnetic layer paste and the molding pressure of the laminate before sintering were adjusted so that the space factor would be the value shown in Table 1. The results are shown in Table 1.

[0088] Comparative Example 1 Samples were prepared and evaluated in the same manner as in Example 1, except that the resin ratio and molding pressure were adjusted so that the space factor was less than 60%. In Comparative Example 1, cracks were generated in the sample after firing, so the withstand voltage and inductance could not be evaluated, and are indicated by "-" in Table 1. The average circularity of the interface-side particles 4α1 was evaluated in the part where no cracks were generated.

[0089] Comparative Example 2

[0090] The resin ratio and molding pressure were adjusted so that the space factor exceeded 82%, and samples were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0091] Example 9 The same samples as in Example 1 were prepared and evaluated in the same manner, except that the raw materials were changed so that the composition of the soft magnetic metal powder was 85Fe-9.5Si-5.5Al and the resin proportion and molding pressure were adjusted so that the space factor was 68%. The results are shown in Table 1.

[0092] Example 10 The same samples as in Example 1 were prepared and evaluated in the same manner, except that the raw materials were changed so that the composition of the soft magnetic metal powder was 49Fe-42Ni-3Si-6Co, and the resin proportion and molding pressure were adjusted so that the space factor was 70%. The results are shown in Table 1.

[0093] [Table 1]

[0094] Rating 1 The results shown in Table 1 show that by setting the space factor to 60% or more and 82% or less, the withstand voltage can be improved and the inductance variation can be reduced. Note that in Comparative Example 2, in which the average circularity of the interface-side particles 4α1 is low, the withstand voltage was reduced and the inductance variation was greater compared to Examples 1 to 8. Furthermore, by comparing Examples 9 and 10 with Examples 1 to 8, it was found that, regardless of the composition of the metal magnetic particles 4α, by setting the space factor to 60% or more and 82% or less and the average circularity of the interface-side particles 4α1 to 0.80 or more, the withstand voltage can be improved and the inductance variation can be reduced.

[0095] Examples 11 to 17 Samples were prepared and evaluated in the same manner as in Example 1, except that the manufacturing conditions and classification conditions of the soft magnetic metal powder used as the raw material were adjusted so as to obtain the average particle size (metal magnetic particle 4α) shown in Table 2, and the proportion of resin and molding pressure were adjusted so as to obtain a space factor of 70%. The results are shown in Table 2.

[0096] Example 18 As shown in Table 2, the manufacturing conditions and classification conditions for the soft magnetic metal powder used as raw material were adjusted so that the average particle size (metal magnetic particle 4α) was 2.5 μm and the CV value was 31%. At this time, the number ratio of metal magnetic particles with a particle size of 4.0 μm or more was 0.3%. Thereafter, samples were prepared in the same manner as in Example 1, and similar evaluations were performed, except that the resin proportion and molding pressure were adjusted so that the space factor was 68%. The results are shown in Table 2.

[0097] Comparative Example 3 Samples were prepared and evaluated in the same manner as in Example 1, except that the manufacturing conditions and classification conditions for the soft magnetic metal powder used as the raw material were adjusted so that the average particle size (metal magnetic particles 4α) would be less than 0.3 μm, and the resin proportion and molding pressure were adjusted so that the space factor would be 62%, as shown in Table 2. The results are shown in Table 2.

[0098] In Comparative Example 3, even when the molding pressure was increased, the space factor only increased to 62%. Furthermore, cracks occurred in the sintered sample, so the withstand voltage and inductance could not be evaluated. These are indicated by "-" in Table 2. The average circularity of the interface-side particles 4α1 was evaluated in the area where no cracks occurred.

[0099] Comparative Example 4 As shown in Table 2, the manufacturing conditions and classification conditions for the soft magnetic metal powder used as raw material were adjusted so that the average particle size (metal magnetic particle 4α) exceeded 2.5 μm and the CV value was 27%. At this time, the number ratio of metal magnetic particles with a particle size of 4.0 μm or more was 0.7%. Thereafter, samples were prepared in the same manner as in Example 18, and similar evaluations were performed, except that the resin proportion and molding pressure were adjusted so that the space factor was 64%. The results are shown in Table 2.

[0100] In Comparative Example 4, the sample after firing had a short circuit, so the withstand voltage and inductance could not be evaluated, and are shown in Table 2 as "-".

[0101] [Table 2]

[0102] Rating 2 The results shown in Table 2 indicate that the withstand voltage can be improved and the inductance variation can be reduced by setting the average particle size of the metal magnetic particles 4α to 0.3 μm or more and 2.5 μm or less. In particular, it was confirmed that the withstand voltage can be improved by setting the average particle size of the metal magnetic particles 4α to 2.2 μm or less, 2.0 μm or less, 1.9 μm or less, 1.5 μm or less, 1.3 μm or less, 1.0 μm or less, or 0.8 μm or less.

[0103] It was found that in Comparative Example 3, which had a small average particle size, the space factor could not be increased and cracks tended to occur during firing, compared to the Examples. It was also found that in Comparative Example 4, which had a large average particle size, the multilayer coil component tended to short-circuit, compared to the Examples.

[0104] Examples 19 to 24 Samples were prepared and evaluated in the same manner as in Example 3, except that the thickness of the resin-rich buffer layer and the resin ratio were changed to change the average circularity of the interface-side particles 4α1 within a range of 0.80 or more. The results are shown in Table 3.

[0105] Comparative Example 5

[0106] Except for not providing a resin-rich buffer layer, a sample was prepared in the same manner as in Example 24 and evaluated in the same manner. The results are shown in Table 3.

[0107] [Table 3]

[0108] Rating 3 The results shown in Table 3 reveal that by setting the average circularity of the interface-side particles 4α1 to 0.80 or more, the withstand voltage is improved and the variation in inductance is reduced.

[0109] Examples 25 to 29

[0110] In order to adjust the proportion of metal magnetic particles having a particle size of 4.0 μm or more, the same samples as in Example 22 were prepared and evaluated in the same manner, except that the classification conditions of the soft magnetic metal powder used as the raw material were changed. The results are shown in Table 4.

[0111] [Table 4]

[0112] Rating 4 From the results shown in Table 4, it was confirmed that by setting the proportion of metal magnetic particles with a particle size of 4.0 μm or more to 1.2% or less, or 1.0% or less, or 0.8% or less, or 0.6% or less, the voltage resistance characteristics are improved even if the CV value is high above a specified value (for example, 37% or more, or 40% or more).

[0113] Examples 30 to 32

[0114] In order to adjust the CV value, the same samples as in Example 3 were prepared and evaluated in the same manner, except that the classification conditions of the soft magnetic metal powder as the raw material were changed. The results are shown in Table 5.

[0115] [Table 5]

[0116] Rating 5 The results shown in Table 5 confirm that the withstand voltage can be improved by lowering the CV value. However, reducing the CV value to less than 30% may increase manufacturing costs due to the need for advanced classification and other processes. [Explanation of symbols]

[0117] 1... Multilayer coil components 2... Element 2a…Shaft end area 2b… Axis center area 3…Terminal electrode 4…Magnetic element 4a... Magnetic layer 4α... Metal magnetic particles 4α1… Interface side particle 4α2… center side particle 40a~40h... Magnetic sheet layer 5... Coil conductor layer 5a1,5a2… Extraction electrode 50a1, 50a2, 50b to 50c... Conductive pattern layers

Claims

1. A multilayer coil component having a magnetic element and coil conductor layers stacked inside the magnetic element so as to be continuously connected in a spiral shape, a magnetic layer of the magnetic element body located between adjacent coil conductor layers along a stacking direction of the coil conductor layers includes metal magnetic particles, The average particle size of the metal magnetic particles is 0.3 μm or more and 2.5 μm or less, the space factor of the metal magnetic particles is 60% or more and 82% or less, A laminated coil component, wherein the metal magnetic particles within a predetermined region from the boundary between the coil conductor layer and the magnetic layer have an average circularity of 0.80 or more.

2. 2. The multilayer coil component according to claim 1, wherein the CV value of the particle size of the metal magnetic particles is 30% or more and less than 50%.

3. 2. The laminated coil component according to claim 1, wherein the average particle size of the metal magnetic particles is 0.3 μm or more and 1.9 μm or less.

4. 2. The multilayer coil component according to claim 1, wherein in the SEM observation image, the number frequency of the metal magnetic particles having a particle size of 4.0 μm or more is 1.2% or less.

5. 2. The laminated coil component according to claim 1, wherein the metal magnetic particles include Fe-based metal magnetic particles, and the Fe-based metal magnetic particles have, on their surfaces, oxide coatings containing elements that are more easily oxidized than Fe.

6. 6. The multilayer coil component according to claim 1, wherein the predetermined region of the magnetic layer in which the average of the metal magnetic particles is obtained is within a range of 0.2 times the distance between the coil conductor layers adjacent to each other along the stacking direction.

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