inductor

Abstract

Provided is an inductor that can easily ensure the density of a resin electrode region while reducing DC resistance. [Solution] One aspect of the present invention is an inductor comprising: a coil wound with a conducting wire; a base body incorporating the coil and containing resin and magnetic powder; and an external terminal formed on the base body and connected to the coil; the external terminal having a resin electrode region containing metal filler and a plating region formed by plating on the resin electrode region; the metal filler having flat large particles and small particles finer than the large particles; and the ratio of the area occupied by the large particles in the cross section of the resin electrode region to the total area is 5% or more and 40% or less.

Description

[Technical Field]

[0001] The present invention relates to an inductor. [Background technology]

[0002] Patent Document 1 discloses an electronic component in which a conductor portion of a wire is connected to an exposed extraction electrode portion and a resin electrode layer is formed on the outer surface of an element body. This electronic component has a diffusion layer at the interface between the extraction electrode portion and the resin electrode layer, thereby increasing the adhesive strength between the extraction electrode portion and the resin electrode layer.

[0003] Patent Document 2 discloses a coil component including a coil section including a lead section exposed on one surface of a main body, an intermetallic compound disposed on one surface of the main body and disposed on the lead section, and a first electrode layer in contact with the intermetallic compound and including a resin and a conductive connecting section. In this coil component, the intermetallic compound is formed only on the exposed lead section, and the first electrode layer is formed on the first surface other than the lead section, thereby enhancing the bonding strength between the main body and the external electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-44341

[0005] [Patent Document 2] Japanese Patent Application Publication No. 2023-67789 Summary of the Invention [Problem to be solved by the invention]

[0006] However, Patent Documents 1 and 2 did not sufficiently consider ensuring the density of the resin electrode. If the density of the resin electrode is not ensured, the plating solution will easily penetrate into the resin electrode, making it more likely to suffer from a defect known as solder cracking. On the other hand, if the amount of resin in the resin electrode is increased to ensure the density of the resin electrode, the ratio of conductive particles in the filler will decrease, increasing the DC resistance. Thus, there is room for improvement in order to achieve both ensuring the density of the resin electrode and reducing the DC resistance. An object of the present invention is to provide an inductor that can easily ensure the density of the resin electrode region while reducing the DC resistance. [Means for solving the problem]

[0007] One aspect of the present invention is an inductor comprising: a coil wound with a conductive wire; a base body incorporating the coil and containing resin and magnetic powder; and an external terminal formed on the base body and connected to the coil; the external terminal having a resin electrode region containing a metal filler and a plating region formed by plating on the resin electrode region; the metal filler having flat large particles and small particles finer than the large particles; and the ratio of the area occupied by the large particles in a cross section of the resin electrode region to the total area is 5% or more and 40% or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an inductor that can easily ensure the density of the resin electrode region and reduce the DC resistance at the same time. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view of an inductor according to an embodiment of the present invention, viewed from above; [Figure 2] FIG. 2 is a perspective view of the inductor as viewed from the mounting surface side. [Figure 3] FIG. 2 is a perspective view showing the internal configuration of an inductor. [Figure 4] 1A to 1C are schematic diagrams illustrating a manufacturing process of an inductor. [Figure 5] FIG. 2 is a cross-sectional view of an inductor. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of an inductor 1 according to this embodiment as viewed from a top surface 12 side, and FIG. 2 is a perspective view of the inductor 1 as viewed from a bottom surface 10 side. The inductor 1 of this embodiment is configured as a surface-mount electronic component, and includes an element body 2 having a substantially rectangular parallelepiped shape, which is one form of a substantially hexahedral shape, and a pair of external electrodes 4 provided on the surface of the element body 2. The external electrodes 4 correspond to an example of the "external terminals" in the present invention.

[0011] The inductor 1 of this embodiment is a so-called power inductor, and is mainly used in step-up / step-down circuits such as DC-DC converters. Power inductors in DC-DC converters are mainly used in switching regulator type circuits. For example, in a switching regulator type step-down circuit, a power inductor rectifies the square wave output by an IC into direct current in cooperation with a capacitor. It is important that power inductors used in such power supply circuits have low energy loss. For this reason, it is considered desirable for power inductors to have low DC resistance (Rdc) in order to suppress energy loss due to heat generation.

[0012] Hereinafter, in the element body 2, the first main surface that faces the mounting board (not shown) during mounting is defined as the bottom surface 10, the second main surface opposite the bottom surface 10 is called the top surface 12, a pair of third main surfaces that are perpendicular to the bottom surface 10 are called end surfaces 14, and a pair of fourth main surfaces that are perpendicular to the bottom surface 10 and the pair of end surfaces 14 are called side surfaces 16. 1, the distance from the bottom surface 10 to the top surface 12 is defined as the thickness T of the element body 2, the distance between a pair of side surfaces 16 is defined as the width W of the element body 2, and the distance between a pair of end surfaces 14 is defined as the length L of the element body 2. Furthermore, the direction of the thickness T is defined as the thickness direction DT, the direction of the width W is defined as the width direction DW, and the direction of the length distance is defined as the length direction DL. The inductor 1 has dimensions, for example, a length L of 2.0 mm, a width W of 1.2 mm, and a thickness T of 0.7 mm. In this case, the element body 2, excluding the external electrodes 4, has dimensions, for example, a length L of 1.95 mm, a width W of 1.15 mm, and a thickness T of 0.65 mm.

[0013] FIG. 3 is a perspective view showing the internal configuration of the inductor. The element body 2 includes a coil conductor 20 and a substantially hexahedral core 30 in which the coil conductor 20 is embedded, and is configured as a conductor-enclosed magnetic component in which the coil conductor 20 is enclosed in the core 30. The coil conductor 20 corresponds to an example of the "coil" of the present invention.

[0014] The core 30 is a molded body obtained by compressing and molding a mixture of magnetic powder and resin into a substantially hexahedral shape by applying pressure and heat while the mixture contains the coil conductor 20 .

[0015] The magnetic powder of this embodiment contains particles of two particle sizes: first magnetic particles that are large particles with a relatively large average particle size, and second magnetic particles that are small particles with a relatively small average particle size. As a result, during compression molding, the second magnetic particles, which are small particles, get into the spaces between the first magnetic particles together with the resin, thereby increasing the filling rate of the magnetic particles in the core 30 and also increasing the magnetic permeability. In this embodiment, the average particle size of the first magnetic particles is 20 μm or more and 28 μm or less, and the average particle size of the second magnetic particles is 1 μm or more and 6 μm or less. The average particle size of the first magnetic particles is preferably 21.4 μm or more and 27.4 μm or less, and the average particle size of the second magnetic particles is preferably 1.5 μm or more and 1.8 μm or less. Furthermore, the magnetic powder may contain particles with different average particle sizes from the first magnetic particles and the second magnetic particles, thereby containing particles of three or more different particle sizes.

[0016] In this embodiment, the first and second magnetic particles are both particles having a metal particle and an insulating film covering the surface of the metal particle with a thickness of 10 nm to 50 nm, the metal particle being made of Fe-Si amorphous alloy powder, and the insulating film being made of phosphate glass, and the metal particle being covered with the insulating film increases the insulation resistance and withstand voltage.

[0017] The metal particles of the first and second magnetic particles may be Fe-Si-Cr alloy powder, Fe-C-Si alloy powder, Fe-Ni-Al alloy powder, Fe-Cr-Al alloy powder, Fe-Si-Al alloy powder, Fe-Ni alloy powder, or Fe-Ni-Mo alloy powder.The metal particles of the second magnetic particles may be pure iron, such as carbonyl iron powder.

[0018] In addition, in the first magnetic particles and the second magnetic particles, the insulating film may be made of other phosphates (zinc phosphate, magnesium phosphate, calcium phosphate, manganese phosphate, cadmium phosphate, etc.), phosphoric acid, glass, or resin materials (silicone-based resins, epoxy-based resins, phenol-based resins, polyamide-based resins, polyimide-based resins, polyphenylene sulfide-based resins, etc.).

[0019] In the mixed powder of this embodiment, the resin material is an epoxy resin containing bisphenol A type epoxy resin as a main component, and the resin includes a rubber-modified epoxy resin. The epoxy resin may be a phenol novolac type epoxy resin. The resin material may be other than epoxy resin, and may be two or more types instead of one type. For example, in addition to epoxy resin, thermosetting resins such as phenol resin, polyester resin, polyimide resin, and polyolefin resin can be used as the resin material.

[0020] 3, the coil conductor 20 includes a winding portion 22 around which a conductor wire is wound, and a pair of lead-out portions 24 led out from the winding portion 22. The winding portion 22 is formed by spirally winding the conductor wire so that both ends of the conductor wire are led out to the outer periphery and connected to each other at the inner periphery. Inside the element body 2, the coil conductor 20 is embedded in the core 30 with the central axis of the winding portion 22 aligned along the thickness direction DT of the element body 2, and the lead-out portions 24 are led out from the winding portion 22 to each of a pair of end faces 14 and electrically connected to the external electrodes 4.

[0021] The external electrode 4 is a so-called five-sided electrode that is provided over the entire end face 14 and over a portion of each of the bottom face 10, top face 12, and pair of side faces 16 adjacent to the end face 14, and is electrically connected to the wiring of the circuit board by an appropriate mounting means such as solder.

[0022] Inductors with this configuration can improve DC bias characteristics by using soft magnetic powder for the magnetic powder, and are therefore used as electronic components in electric circuits through which large currents flow, as choke coils in DC-DC converter circuits and power supply circuits, and as electronic components in electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, car electronics, medical and industrial machinery, etc. However, the uses of inductors are not limited to these, and they can also be used in tuning circuits, filter circuits, rectifying and smoothing circuits, etc.

[0023] In the inductor, an element protective layer may be formed on the entire surface of the element body 2 excluding the area of ​​the external electrodes 4. The material for the element protective layer may be, for example, a thermosetting resin such as epoxy resin, polyimide resin, or phenolic resin, or a thermoplastic resin such as novolac resin, phenoxy resin, polyethylene resin, or polyamide resin. These resins may further contain fillers such as silicon oxide or titanium oxide.

[0024] FIG. 4 is a schematic diagram of the inductor manufacturing process. As shown in the figure, the inductor manufacturing process includes a coil conductor forming step, a preform forming step, a thermoforming and hardening step, a barrel polishing step, an element protective film forming step, and an external electrode forming step.

[0025] The coil conductor forming process is a process of forming the coil conductor 20 from a conductive wire. In this process, the coil conductor 20 is formed into a shape having the above-mentioned winding portion 22 and a pair of lead-out portions 24 by winding the conductive wire using a winding method called "alpha winding." Alpha winding refers to a state in which the conductive wire, which functions as a conductor, is wound in two stages in a spiral shape so that the lead-out portions 24 at the beginning and end of the winding are located on the outer periphery. The number of turns of the coil conductor 20 is not particularly limited.

[0026] The preform forming step is a step of forming a preform called a tablet. The preform is formed by pressing the above-mentioned mixed powder, which is the material of the base body 2, into a solid form that is easy to handle.In this embodiment, two types of tablets are formed: a first tablet of an appropriate shape (e.g., E-shaped) with a groove into which the coil conductor 20 fits, and a second tablet of an appropriate shape (e.g., I-shaped or plate-shaped) that covers the groove of the first tablet.

[0027] In the thermoforming and curing process, the first tablet, the coil conductor, and the second tablet are placed in a molding die, and while applying heat, pressure is applied in the overlapping direction of the first tablet and the second tablet, and they are cured to integrate the first tablet, the coil conductor, and the second tablet, thereby forming the element body 2 in which the coil conductor 20 is enclosed in the core 30.

[0028] The barrel polishing step is a step of barrel polishing this molded body, and by this step, burrs on the element body 2 are removed and the corners of the element body 2 are rounded.

[0029] The element body protective film forming process is a process of forming an element body protective film on the surface of the element body 2. The element body protective film is formed using a rotary spray device that sprays the material for the element body protective film onto multiple element bodies 2 placed in a rotating drum. The element body protective film may also be formed on the element body 2 by spraying, dipping, or the like.

[0030] The external electrode forming step is a step of forming the external electrodes 4 on the core 30, and includes a surface treatment step, a resin electrode region forming step, and a plating region forming step.

[0031] The surface treatment process is a process of modifying the surface of the planned electrode area by irradiating the area with laser light. Here, the planned electrode area refers to the area on the surface of the core 30 where the external electrode 4 is to be formed, including the portion where the lead portion 24 is exposed. Specifically, by irradiating the laser light, the element protective film and the resin on the surface of the core 30 are removed within the planned electrode area, and the insulating film on the surface of the magnetic particles exposed from the core 30 is also removed. As a result, the exposed area of ​​the metal of the magnetic particles per unit area of ​​the surface of the core 30 is larger in the planned electrode area than in other surface areas of the core 30. Note that after the laser irradiation, a cleaning process (e.g., etching process) may be performed to clean the surface of the planned electrode area.

[0032] In the resin electrode region forming step, a conductive resin paste containing a metal filler and resin is applied to the planned electrode location, and then dried and hardened to form the resin electrode region 40 (see FIG. 5). Specifically, the core 30 is dipped from the end face 14 side into the conductive resin paste that is the material for the resin electrode region 40, and then pulled up, so that the conductive resin is applied to a desired application range including the end face 14.

[0033] Since the resin electrode region 40 contains a metal filler, a uniform potential distribution can be formed at the planned electrode location in the plating region forming step described below, which improves the uniformity of the plating region 50 (see FIG. 5) formed on the resin electrode region 40. The resin electrode region 40 will be described in detail later.

[0034] In the plating region forming step, a plating region 50 is formed on the surface of the resin electrode region 40. The plating region 50 is composed of a first plating layer formed directly on the surface of the resin electrode region 40, a second plating layer formed on the first plating layer, and a third plating layer formed on the second plating layer. In this embodiment, the first plating layer is a copper (Cu) plating layer. The second plating layer is a nickel (Ni) plating layer with a thickness of 4 μm to 15 μm. The third plating layer is a tin (Sn) plating layer with a thickness of 4 μm to 8 μm. Each plating layer may be formed by electrolytic plating (e.g., barrel plating). Note that the type of metal constituting each plating layer can be changed or replaced as desired. In this embodiment, the plating region 50 is composed of three layers, but this is not limited to this and the plating region 50 may be composed of any number of layers.

[0035] By the above external electrode forming step, the external electrode 4 composed of the resin electrode region 40 and the plating region 50 is formed. The external electrode 4 is not limited to a five-surface electrode, but may be a so-called L-shaped electrode formed only on both the end surface 14 and the bottom surface 10, or a so-called bottom electrode formed only on the bottom surface 10.

[0036] [External electrode configuration] 5 is a cross-sectional view of the inductor 1, showing the vicinity of the boundary between the core 30 and the external electrode 4. In detail, the cross-section of FIG. 5 is a cross-section of the inductor 1 taken along the length direction DL and the thickness direction DT at the center of the inductor 1 in the width direction DW. As shown in FIG. 5, the external electrode 4 has a resin electrode region 40 formed on the element body 2 and a plating region 50 formed on the resin electrode region 40.

[0037] [Configuration of resin electrode area] As shown in FIG. 5, the resin electrode region 40 has a layered structure formed directly on the electrode portion of the element body 2 of the external electrode 4 .

[0038] Although a portion of the resin electrode region 40 is formed on the lead-out portion 24 of the element body 2, the majority of the resin electrode region 40 is formed directly on the surface 31 of the core 30 of the intended electrode location. For this reason, the adhesion between the element body 2 and the resin electrode region 40 can be affected by the surface roughness of the surface 31 in contact with the resin electrode region 40. In this embodiment, the surface roughness of the surface 31 in contact with the resin electrode region 40 is configured to be 5 μm or more in a cross section equivalent to that of FIG. 5. Note that, according to an experiment conducted by the inventors and described below, it has been confirmed that good adhesion between the resin electrode region 40 and the element body 2 can be ensured if the surface roughness of the surface 31 is 5 μm or more in a cross section equivalent to that of FIG. 5.

[0039] The resin electrode region 40 is composed of resin and metal filler. The resin electrode region 40 is conductive because it contains metal filler. The DC resistance value of the resin electrode region 40 tends to be small when the content of the metal filler in the resin electrode region 40 is large, and tends to be large when the content of the metal filler is small.

[0040] In this embodiment, the resin constituting the resin electrode region 40 is an acrylic resin. However, the resin constituting the resin electrode region 40 may be a resin other than an acrylic resin.

[0041] The metal filler includes small particles. The small particles are particles that are dispersed in the resin that constitutes the resin electrode region 40. The average particle size of the small particles is, for example, 300 nm or more and 2000 nm or less. In this embodiment, the small particles are silver (Ag) particles. However, instead of silver particles, particles of copper (Cu), nickel (Ni), tin (Sn), gold (Au), palladium (Pd), or the like may be used as the small particles.

[0042] The metal filler includes large particles 41. The large particles 41 have a flat shape and are larger than the small particles. In this embodiment, the large particles 41 are silver particles. However, instead of silver particles, particles of copper, nickel, tin, gold, palladium, or the like may be used as the large particles 41.

[0043] In this embodiment, the average longitudinal size L1 of the large particles 41 is set to 5 μm or more in a cross section equivalent to that of Fig. 5. Note that, through experiments conducted by the inventors (described later), it has been confirmed that good adhesion between the resin electrode region 40 and the element body 2 can be ensured if the average longitudinal size L1 of the large particles 41 is 5 μm or more in a cross section equivalent to that of Fig. 5.

[0044] The large particles 41 have a small, flat shape. During the formation of the resin electrode region 40, the large particles 41 adhere to the surface 31 of the core 30 due to the surface tension of the resin surrounding the large particles 41. Therefore, the large particles 41 are likely to be arranged in the resin electrode region 40 with the large surface area of ​​the large particles 41 facing the surface 31 of the core 30. Therefore, in a cross section of the inductor 1 such as that shown in FIG. 5, cross sections of the large particles 41 that are parallel to the thickness direction and the plane direction of the large particles 41 are likely to be exposed. This tends to increase the aspect ratio of the large particles 41, i.e., the ratio of the longitudinal dimension L1 of the large particles 41 divided by the lateral dimension L2 of the large particles 41 in the cross section shown in FIG. 5. The longitudinal direction of the large particles 41 may be the direction along the line connecting the two most distant points of the large particles 41 in a cross section similar to that shown in FIG. 5. Furthermore, the short-side direction of the large particle 41 may be a direction perpendicular to the long-side direction of the large particle 41 in a cross section similar to that of FIG.

[0045] In this embodiment, in a cross section equivalent to that of Fig. 5, the average aspect ratio of the large particles 41 is not less than 5 and not more than 50. Note that, through experiments conducted by the inventors, which will be described later, it has been confirmed that, in a cross section equivalent to that of Fig. 5, if the average aspect ratio of the large particles 41 is not less than 5 and not more than 50, good adhesion between the resin electrode region 40 and the element body 2 can be ensured.

[0046] In this embodiment, the proportion of the volume of the resin electrode region 40 occupied by the large particles 41, i.e., the filling rate of the large particles 41, is set to 5% or more and 40% or less. Furthermore, in a cross section equivalent to that of FIG. 5, the proportion of the area occupied by the large particles 41 to the area occupied by the resin electrode region 40 is set to 5% or more and 40% or less. Note that, according to an experiment conducted by the inventors and described below, it has been confirmed that good adhesion between the resin electrode region 40 and the element body 2 can be ensured when the proportion of the area occupied by the large particles 41 to the area occupied by the resin electrode region 40 is 5% or more and 40% or less in a cross section equivalent to that of FIG. 5.

[0047] In this way, by forming the plating region 50 on the resin electrode region 40 that ensures adhesion with the element body 2, it is possible to ensure the density of the resin electrode region 40. Furthermore, by making the large particles 41 flat, it is possible to easily ensure adhesion between the resin electrode region 40 and the element body 2 even when the content of the large particles 41 is increased, and it is possible to easily suppress the DC resistance of the inductor 1.

[0048] [Plating area configuration] 5, the plating region 50 has a layered structure formed on the resin electrode region 40. As described above, in this embodiment, the plating region 50 has a first plating layer which is a copper plating layer, a second plating layer which is a nickel plating layer, and a third plating layer which is a tin plating layer.

[0049] The plating region 50 is formed on the conductive resin electrode region 40. Therefore, when plating the plating region 50, the potential distribution in the resin electrode region 40 is easily made uniform, and a uniform plating region 50 is easily formed.

[0050] [First experiment] The inventors conducted a first experiment to verify the effect of the filling rate of the large particles 41 in the resin electrode region 40 on the adhesion between the resin electrode region 40 and the element body 2. The details of the first experiment will be described below.

[0051] (Experiment overview) As samples for the first experiment, the inventors created a number of inductors 1 having resin electrode regions 40 with different filling rates of large particles 41. The inventors also examined the adhesion between the resin electrode regions 40 and the element body 2, as well as the DC resistance, for each of the created samples.

[0052] (Sample details) The inventors created an element body 2 similar to that of the above-described embodiment, and formed an external electrode 4 consisting of a resin electrode region 40 and a plating region 50 on the created element body 2. In the external electrode 4, the configuration of the plating region 50 was the same as that of the embodiment.

[0053] The inventors used acrylic resin as the resin in the resin electrode region 40 of each sample, and silver particles as the metal filler for both the small particles and large particles 41 in the resin electrode region 40 of each sample.

[0054] In each sample, the average value of the longitudinal size L1 of the large particles 41, the average value of the aspect ratio of the large particles 41, and the surface roughness of the surface 31 were the same as those in the embodiment.

[0055] Under the above conditions, the inventors created Samples A1 to A9 while changing the filling rate of the large particles 41 in the resin electrode region 40. Of the created samples, Samples A2 to A6 are examples according to the above-mentioned embodiment, and Sample A1 and Samples A7 to A9 are comparative examples.

[0056] (Verification of adhesion) To verify the adhesion between the resin electrode region 40 and the element body 2, the inventors performed a peel test based on AEC-Q200-006 on the external electrodes 4 of the prepared samples A1 to A9, and then observed each sample. Based on the results of the observations, the inventors determined whether the adhesion between the resin electrode region 40 and the element body 2 was good, based on whether the external electrodes 4 peeled off and the element body 2 was exposed. In the first experiment, the adhesion was determined using three levels: "A," indicating good adhesion; "C," indicating poor adhesion; and "B," which is intermediate between "A" and "C." In more detail, in the first experiment, if the external electrodes 4 did not peel off and the element body 2 was not exposed after the peel test, the result was "A." If the external electrodes 4 peeled off and the element body 2 was exposed, the result was "C."

[0057] (Measurement of DC resistance) The inventors also used a resistance meter to measure the DC resistance of the prepared samples A1 to A9. Specifically, the inventors used a resistance meter (RM3541 manufactured by HIOKI Corporation) to measure the DC resistance between the pair of external electrodes 4 of samples A1 to A9.

[0058] (result) Table 1 below shows the results of the first experiment.

[0059] [Table 1]

[0060] As shown in Table 1, in sample A1 according to the comparative example, the filling rate of the large particles 41 in the resin electrode region 40 was 4%. In sample A1, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "C." The DC resistance value of sample A1 was 100 mΩ. In sample A2 according to the example, the filling rate of the large particles 41 in the resin electrode region 40 was set to 5%. In sample A2, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "A". The DC resistance value in sample A2 was 20 mΩ. In sample A3 according to the example, the filling rate of the large particles 41 in the resin electrode region 40 was 18%. In sample A3, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "A". The DC resistance value in sample A3 was 18 mΩ. In sample A4 according to the example, the filling rate of the large particles 41 in the resin electrode region 40 was 28%. In sample A4, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "A". The DC resistance value in sample A4 was 19 mΩ. In sample A5 according to the example, the filling rate of the large particles 41 in the resin electrode region 40 was 35%. In sample A5, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "A". The DC resistance value in sample A5 was 18 mΩ. In sample A6 according to the example, the filling rate of the large particles 41 in the resin electrode region 40 was 40%. In sample A6, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "A". The DC resistance value in sample A6 was 18 mΩ. In sample A7 according to the comparative example, the filling rate of the large particles 41 in the resin electrode region 40 was 41%. In sample A7, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "B". The DC resistance value in sample A7 was 19 mΩ. In sample A8 according to the comparative example, the filling rate of the large particles 41 in the resin electrode region 40 was 42%. In sample A8, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "B". The DC resistance value in sample A8 was 22 mΩ. In sample A9 according to the comparative example, the filling rate of the large particles 41 in the resin electrode region 40 was set to 45%. In sample A9, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "C". The DC resistance value of sample A9 was 45 mΩ.

[0061] (Conclusions for the first experiment) As shown in Table 1, it was confirmed that when the filling rate of the large particles 41 in the resin electrode region 40 is 5% or more and 40% or less, the adhesion between the resin electrode region 40 and the element body 2 is good. It was also confirmed that when the filling rate of the large particles 41 in the resin electrode region 40 is 5% or more and 40% or less, the DC resistance value is 20 mΩ or less, which is relatively small. For this reason, the inventors have concluded that in order to ensure good adhesion between the resin electrode region 40 and the element body 2, the suitable range for the filling rate of the large particles 41 in the resin electrode region 40 is 5% or more and 40% or less.

[0062] Thus, the reason why the DC resistance value is relatively small when the filling rate of large particles 41 is 5% or more is thought to be because the increased filling rate of large particles 41, which are conductors, makes it easier for DC current to flow through large particles 41. Also, the reason why adhesion is good when the filling rate of large particles 41 is 40% or less is thought to be because the increased filling rate of the resin that bonds large particles 41 to element body 2 and between large particles 41 is used.

[0063] (Additional information about the packing rate of large particles) In the first experiment, the filling rate of the large particles 41 in the resin electrode region 40 may be determined from the mixing ratio of the resin, small particles, and large particles 41 when preparing the conductive resin paste that forms the resin electrode region 40. However, the filling rate of the large particles 41 in the resin electrode region 40 can be determined from the prepared inductor 1, for example, as follows. First, the inductor 1 is cut along the DL and DT directions at the center of the inductor 1 in the DW direction to form a cut surface. Next, an enlarged image of the resin electrode region 40 containing 10 or more large particles 41 is obtained on the cut surface using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Then, the obtained enlarged image is analyzed to calculate the ratio of the area occupied by the large particles 41 to the area occupied by the resin electrode region 40. The ratio calculated in this manner can be considered as the filling rate of the large particles 41 in the resin electrode region 40.

[0064] [Second experiment] The inventors conducted a second experiment to verify the influence of the longitudinal size L1 and aspect ratio of the large particles 41 in the resin electrode region 40 on the adhesion between the resin electrode region 40 and the element body 2. The second experiment will be described in detail below.

[0065] (Experiment overview) As samples for the second experiment, the inventors created a number of inductors 1 having resin electrode regions 40 with different average longitudinal sizes L1 of the large particles 41 and different average aspect ratios of the large particles 41. The inventors also examined the adhesion between the resin electrode regions 40 and the element body 2 for each of the created samples.

[0066] (Sample details) The inventors created an element body 2 similar to that of the above-described embodiment, and formed an external electrode 4 consisting of a resin electrode region 40 and a plating region 50 on the created element body 2. In the external electrode 4, the configuration of the plating region 50 was the same as that of the embodiment.

[0067] The inventors used acrylic resin as the resin in the resin electrode region 40 of each sample, and silver particles as the metal filler for both the small particles and large particles 41 in the resin electrode region 40 of each sample.

[0068] In each sample, the filling rate of the large particles 41 in the resin electrode region 40 and the surface roughness of the surface 31 were set to the same values ​​as those in the embodiment.

[0069] Under the above conditions, the inventors created samples B1 to B31 while changing the longitudinal size L1 of the large particles 41 in the resin electrode region 40 and the aspect ratio of the large particles 41. Of the created samples, samples B9-B12, B15-B18, B21-24, and B27-30 are examples according to the above-mentioned embodiment, and the other samples are comparative examples.

[0070] (Verification of adhesion) To verify the adhesion between the resin electrode region 40 and the element body 2, the inventors performed a peeling test based on AEC-Q200-006 on the external electrodes 4 of the prepared samples B1 to B31, and then observed each sample. As a result of the observation, the inventors determined whether the adhesion between the resin electrode region 40 and the element body 2 was good based on whether the external electrodes 4 had peeled off and the element body 2 was visible. In the second experiment, as in the first experiment, the determination of whether the adhesion was good was made using three levels: "A" indicating good adhesion, "C" indicating poor adhesion, and "B" which is intermediate between "A" and "C."

[0071] (result) Table 2 below shows the results of the second experiment.

[0072] [Table 2]

[0073] As shown in Table 2, in sample B1 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 2 μm, and the average aspect ratio of the large particles 41 was 1. In sample B1, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "C." In sample B2 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 2 μm, and the average aspect ratio of the large particles 41 was 5. In sample B2, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "C." In sample B3 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 2 μm, and the average aspect ratio of the large particles 41 was 10. In sample B3, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "B."

[0074] In sample B4 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 4 μm, and the average aspect ratio of the large particles 41 was 1. In sample B4, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "C." In sample B5 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 4 μm, and the average aspect ratio of the large particles 41 was 5. In sample B5, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "B." In sample B6 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 4 μm, and the average aspect ratio of the large particles 41 was 10. In sample B6, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "B." In sample B7 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 4 μm, and the average aspect ratio of the large particles 41 was 20. In sample B7, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "B."

[0075] In sample B8 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 5 μm, and the average aspect ratio of the large particles 41 was 1. In sample B8, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "C." In sample B9 according to the example, the average longitudinal size L1 of the large particles 41 was 5 μm, and the average aspect ratio of the large particles 41 was 5. In sample B9, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B10 according to the example, the average longitudinal size L1 of the large particles 41 was 5 μm, and the average aspect ratio of the large particles 41 was 10. In sample B10, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B11 according to the example, the average longitudinal size L1 of the large particles 41 was 5 μm, and the average aspect ratio of the large particles 41 was 20. In sample B11, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B12 according to the example, the average longitudinal size L1 of the large particles 41 was 5 μm, and the average aspect ratio of the large particles 41 was 50. In sample B12, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B13 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 5 μm, and the average aspect ratio of the large particles 41 was 55. In sample B13, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "B."

[0076] In sample B14 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 8 μm, and the average aspect ratio of the large particles 41 was 1. In sample B14, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "C." In sample B15 according to the example, the average longitudinal size L1 of the large particles 41 was 8 μm, and the average aspect ratio of the large particles 41 was 5. In sample B15, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B16 according to the example, the average longitudinal size L1 of the large particles 41 was 8 μm, and the average aspect ratio of the large particles 41 was 10. In sample B16, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B17 according to the example, the average longitudinal size L1 of the large particles 41 was 8 μm, and the average aspect ratio of the large particles 41 was 20. In sample B17, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B18 according to the example, the average longitudinal size L1 of the large particles 41 was 8 μm, and the average aspect ratio of the large particles 41 was 50. In sample B18, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B19 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 8 μm, and the average aspect ratio of the large particles 41 was 55. In sample B19, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "B."

[0077] In sample B20 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 10 μm, and the average aspect ratio of the large particles 41 was 1. In sample B20, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "C." In sample B21 according to the example, the average longitudinal size L1 of the large particles 41 was 10 μm, and the average aspect ratio of the large particles 41 was 5. In sample B21, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B22 according to the example, the average longitudinal size L1 of the large particles 41 was 10 μm, and the average aspect ratio of the large particles 41 was 10. In sample B22, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B23 according to the example, the average longitudinal size L1 of the large particles 41 was 10 μm, and the average aspect ratio of the large particles 41 was 20. In sample B23, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B24 according to the example, the average longitudinal size L1 of the large particles 41 was 10 μm, and the average aspect ratio of the large particles 41 was 50. In sample B24, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B25 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 10 μm, and the average aspect ratio of the large particles 41 was 55. In sample B25, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "B."

[0078] In sample B26 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 15 μm, and the average aspect ratio of the large particles 41 was 1. In sample B26, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "C." In sample B27 according to the example, the average longitudinal size L1 of the large particles 41 was 15 μm, and the average aspect ratio of the large particles 41 was 5. In sample B27, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B28 according to the example, the average longitudinal size L1 of the large particles 41 was 15 μm, and the average aspect ratio of the large particles 41 was 10. In sample B28, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B29 according to the example, the average longitudinal size L1 of the large particles 41 was 15 μm, and the average aspect ratio of the large particles 41 was 20. In sample B29, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B30 according to the example, the average longitudinal size L1 of the large particles 41 was 15 μm, and the average aspect ratio of the large particles 41 was 50. In sample B30, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample B31 according to the comparative example, the average longitudinal size L1 of the large particles 41 was 15 μm, and the average aspect ratio of the large particles 41 was 55. In sample B31, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "B."

[0079] (Conclusions for the second experiment) As shown in Table 2, it was confirmed that the average range of the longitudinal size L1 of the large particles 41 was 5 μm or more when the adhesion between the resin electrode region 40 and the element body 2 was good. It was also confirmed that the average range of the aspect ratio of the large particles 41 was 5 or more and 50 or less when the adhesion between the resin electrode region 40 and the element body 2 was good. For this reason, the inventors concluded that the preferred range for the average longitudinal size L1 of the large particles 41 is 5 μm or more in order to ensure good adhesion between the resin electrode region 40 and the element body 2. The inventors also concluded that the preferred range for the average aspect ratio of the large particles 41 is 5 or more and 50 or less in order to ensure good adhesion between the resin electrode region 40 and the element body 2. The inventors also concluded that it is more preferred for the average longitudinal dimension of the large particles 41 to be 5 μm or more and for the average aspect ratio of the large particles 41 to be 5 or more and 50 or less.

[0080] The reason why the adhesion between the resin electrode region 40 and the element body 2 is good when the aspect ratio of the large particles 41 is 5 or more is thought to be that when the aspect ratio is large, the surface area relative to the volume of the large particles 41 becomes large, making it easier for the large particles 41 to be adhered via the resin.

[0081] (Additional information on the longitudinal size and aspect ratio of large particles) The average longitudinal size L1 and average aspect ratio of the large particles 41 in the resin electrode region 40 can be determined from the fabricated inductor 1, for example, as follows.

[0082] First, the inductor 1 is cut along the DL and DT directions at the center of the inductor 1 in the DW direction to form a cut surface. Next, an enlarged image of the resin electrode region 40 containing 10 or more large particles 41 is obtained using an SEM, TEM, or the like on the formed cut surface. Then, from the enlarged image, 10 large particles 41 are identified in descending order of longitudinal size L1. Furthermore, the longitudinal sizes L1 of the identified 10 large particles 41 are each obtained by image analysis, and the arithmetic mean value of the obtained values ​​can be regarded as the average longitudinal size of the large particles 41. Furthermore, the aspect ratio is calculated using the longitudinal size L1 and the lateral size L2 of the identified 10 large particles 41, and the arithmetic mean value can be regarded as the average aspect ratio of the large particles 41.

[0083] [Third Experiment] The inventors conducted a third experiment to verify the effect of the surface roughness of the surface 31 of the core 30 in contact with the resin electrode region 40 on the adhesion between the resin electrode region 40 and the element body 2. Details of the third experiment will be described below.

[0084] (Experiment overview) As samples for the first experiment, the inventors created a number of inductors 1 each having different surface roughness on the surface 31 of the core 30 that contacts the resin electrode region 40. The inventors also verified the adhesion between the resin electrode region 40 and the element body 2 for each of the created samples.

[0085] (Sample details) The inventors created a plurality of element bodies 2 each having a different surface roughness on the surface 31 of the core 30, and formed an external electrode 4 consisting of a resin electrode region 40 and a plating region 50 on each element body 2. In the external electrode 4 similar to that of the embodiment, the resin electrode region 40 and the plating region 50 had the same configurations as those of the embodiment.

[0086] The inventors used acrylic resin as the resin in the resin electrode region 40 of each sample, and silver particles as the metal filler for both the small particles and large particles 41 in the resin electrode region 40 of each sample.

[0087] In each sample, the average longitudinal size L1 of the large particles 41, the average aspect ratio of the large particles 41, and the filling rate of the large particles 41 in the resin electrode region 40 were the same as those in the embodiment.

[0088] Under the above conditions, the inventors created samples C1 to C5 while changing the surface roughness of surface 31 of core 30. Of the created samples, samples C3 to C5 are examples according to the above-mentioned embodiment, and samples C1 and C2 are comparative examples.

[0089] (Verification of adhesion) To verify the adhesion between the resin electrode region 40 and the element body 2, the inventors performed a peel test based on AEC-Q200-006 on the external electrodes 4 of the prepared samples C1 to C5, and then observed each sample. Based on the results of the observations, the inventors determined whether the adhesion between the resin electrode region 40 and the element body 2 was good, based on whether the external electrodes 4 peeled off and the element body 2 was exposed. In the third experiment, the adhesion was determined using two levels: "A" indicating good adhesion, and "C" indicating poor adhesion. Specifically, in the third experiment, if the external electrodes 4 did not peel off and the element body 2 was not exposed after the peel test, the result was "A." If the external electrodes 4 peeled off and the element body 2 was exposed, the result was "C."

[0090] (result) Table 3 below shows the results of the third experiment.

[0091] [Table 3]

[0092] As shown in Table 3, in sample C1 according to the comparative example, the surface roughness of the surface 31 of the core 30 in the portion in contact with the resin electrode region 40 was set to 1 μm. In sample C1, the evaluation result for the adhesion between the resin electrode region 40 and the element body 2 was "C." In sample C2 according to the comparative example, the surface roughness of the surface 31 of the core 30 in the portion in contact with the large resin electrode region 40 was set to 4 μm. In sample C2, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "C." In sample C3 according to the example, the surface roughness of the surface 31 of the core 30 in the portion in contact with the resin electrode region 40 was set to 5 μm. In sample C3, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample C4 according to the example, the surface roughness of the surface 31 of the core 30 in the portion in contact with the resin electrode region 40 was set to 10 μm. In sample C4, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "A." In sample C5 according to the example, the surface roughness of the surface 31 of the core 30 in the portion in contact with the resin electrode region 40 was set to 20 μm. In sample C3, the judgment result for the adhesion between the resin electrode region 40 and the element body 2 was "A."

[0093] (Conclusions for the third experiment) As shown in Table 3, it was confirmed that when the adhesion between the resin electrode region 40 and the element body 2 is good, the surface roughness of the surface 31 of the core 30 in the portion in contact with the resin electrode region 40 is 5 μm or more. For this reason, the inventors concluded that the suitable range for the surface roughness of the surface 31 of the core 30 in the portion in contact with the resin electrode region 40 is 5 μm or more in order to ensure good adhesion between the resin electrode region 40 and the element body 2.

[0094] The reason why the adhesion between the resin electrode region 40 and the element body 2 is good when the surface roughness of the surface 31 is 5 μm or more is thought to be because the surface area of ​​the surface 31 is larger, making it easier for the surface 31 to adhere to the resin of the resin electrode region 40.

[0095] (Additional information about surface roughness) In the third experiment, the surface roughness of the surface 31 is determined as follows.

[0096] First, the inductor 1 is cut along the DL and DT directions at the center of the inductor 1 in the DW direction to form a cut surface. Next, an enlarged image of the area of ​​the cut surface, including the boundary between the resin electrode region 40 and the surface 31 of the core 30, is obtained using an SEM, TEM, or the like. Then, the boundary between the surface 31 and the resin electrode region 40 is obtained from the obtained enlarged image by image analysis. Furthermore, the arithmetic mean roughness is calculated from the obtained boundary. The arithmetic mean roughness calculated in this manner may be used as the surface roughness of the surface 31. The reference length when calculating the arithmetic mean roughness may be set to, for example, approximately 20 μm to 100 μm.

[0097] The above-described embodiments are merely examples of aspects of the present invention, and any modifications and applications are possible without departing from the spirit of the present invention.

[0098] Unless otherwise specified, the horizontal, vertical, and other directions, various numerical values, shapes, and materials in the above-described embodiments include a range (so-called equivalent range) that has the same effect as those directions, numerical values, shapes, and materials.

[0099] [Configuration supported by the above embodiment]

[0100] According to this embodiment, the following effects are achieved.

[0101] (Configuration 1) An inductor comprising: a coil wound with a conductive wire; an element body incorporating the coil and containing resin and magnetic powder; and an external terminal formed on the element body and connected to the coil, wherein the external terminal has a resin electrode region containing metal filler and a plating region formed by plating on the resin electrode region, the metal filler having flat large particles and small particles finer than the large particles, and the area ratio occupied by the large particles in the cross section of the resin electrode region is 5% or more and 40% or less. According to the inductor of the first aspect, by using large flat particles as the metal filler, it is possible to reduce the amount of resin used in the resin electrode region while ensuring adhesion in the resin electrode region, which makes it easier to achieve both ensuring the density of the resin electrode region and reducing the DC resistance.

[0102] (Configuration 2) The inductor according to configuration 1, wherein the large particles have a longitudinal size of 5 μm or more. According to the inductor of configuration 2, the surface area of ​​the large particles used as the metal filler can be increased, which makes it easier to ensure adhesion to the resin electrode region. This makes it easier to ensure the density of the resin electrode region and reduce the DC resistance at the same time.

[0103] (Configuration 3) The inductor according to configuration 1 or 2, wherein the large particles have an aspect ratio of 5 or more and 50 or less. According to the inductor of configuration 3, the surface area relative to the volume of the large particles used as the metal filler can be adjusted to an appropriate value, which makes it easier to ensure the density of the resin electrode region while also reducing the DC resistance.

[0104] (Configuration 4) The inductor according to any one of configurations 1 to 3, wherein the metal filler contains any of silver, copper, nickel, tin, gold, and palladium. According to the inductor of configuration 4, it is possible to easily ensure the density of the resin electrode region and reduce the DC resistance at the same time.

[0105] (Configuration 5) The inductor according to any one of configurations 1 to 4, wherein the surface of the element body in contact with the resin electrode region has a surface roughness of 5 μm or more. This allows the resin in the resin electrode region to adhere more easily to the surface of the element body, making it easier to ensure the density of the resin electrode region. [Explanation of symbols]

[0106] 1 inductor 2 Base 4 External terminals 20 Coil conductor 30 cores 31 Surface 40 Resin electrode area 41 Large particles 50 Plating Area

Claims

1. A coil wound with a conductor, an element body that houses the coil and contains resin and magnetic powder; an external terminal formed on the element body and connected to the coil; the external terminal has a resin electrode region containing a metal filler and a plating region formed on the resin electrode region by plating, The metal filler has flat large particles and small particles that are finer than the large particles, In the cross section of the resin electrode region, the ratio of the area occupied by the large particles is 5% or more and 40% or less. Inductor.

2. The large particles have a longitudinal size of 5 μm or more.

10. The inductor of claim 1.

3. The aspect ratio of the large particles is 5 or more and 50 or less.

10. The inductor of claim 1.

4. The metal filler includes any one of silver, copper, nickel, tin, gold, and palladium.

10. The inductor of claim 1.

5. the surface roughness of the surface of the element body in contact with the resin electrode region is 5 μm or more; 10. The inductor of claim 1.

Images