JP2023147051A - Inductor and inductor manufacturing method - Google Patents

Abstract

To provide an inductor where an external electrode is composed of a conductive resin layer formed on the surface of an element body, which effectively prevents occurrence of peeling between the element body and the external electrode.SOLUTION: An inductor is composed of an element body including a core containing magnetic particles and a resin and a conductor embedded in the core, a conductive resin layer arranged on the surface of the core so as to come in contact with the end of the conductor exposed from the core, and an external electrode including a plating layer formed on the conductive resin layer, wherein the plating layer has a binding part which exceeds a range where the conductive resin layer is arranged, extends to the surface of the core, and comes in contact with the surface of the core, and the plating layer intrudes into the inside of the core from the surface of the core in the binding part and enters between the magnetic particles.SELECTED DRAWING: Figure 8

Description

The present invention relates to an inductor and a method for manufacturing an inductor.

An inductor is known in which two external electrodes are provided on the surface of an element body in which a coil conductor is embedded in a core that is a molded body (see Patent Document 1). In such an inductor, for example, a conductive resin containing silver powder is coated on two places on the surface of the core so as to connect with the exposed ends, and nickel or tin is coated on the conductive resin. The above-mentioned external electrodes are formed by plating with metals such as.

Japanese Patent Application Publication No. 2010-245473

Under environmental conditions such as in-vehicle applications where the operating temperature range is very wide, peeling of the conductive resin from the element body can be considered as a failure mode of the inductor. Furthermore, if the amount of silver powder contained in the conductive resin is increased for the purpose of reducing the electrical resistance of the external electrode, the adhesion of the external electrode to the element may decrease, and the external electrode may easily peel off from the element. In addition, when the thickness of the nickel plating layer on the conductive resin is increased to reduce solder explosion when external electrodes are soldered to a circuit board, etc., the stress of the nickel plating causes the conductive resin to It is conceivable that the material may be easily peeled off from the element body.

An object of the present invention is to effectively prevent the occurrence of peeling of the external electrode from the core in an inductor in which the external electrode is formed of a conductive resin layer and a plating layer formed on the surface of the core.

One aspect of the present invention includes a core including magnetic particles and a resin, an element body including a conductor embedded in the core, and a surface of the core so as to be in contact with an end of the conductor exposed from the core. An inductor comprising a conductive resin layer disposed on the conductive resin layer and an external electrode including a plating layer formed on the conductive resin layer, wherein the plating layer is formed on the conductive resin layer. The plating layer has a binding portion extending beyond the range to the surface of the core and in contact with the surface of the core, and the plating layer penetrates from the surface of the core into the inside of the core at the binding portion to prevent the magnetic property. It is an inductor that is inserted between particles.
Another aspect of the present invention includes a core including a resin and magnetic particles having an insulating film on the surface, an element body including a conductor embedded in the core, and an element body including a conductor embedded in the core, and an element body that is in contact with an end of the conductor exposed from the core. a conductive resin layer disposed on the core; and an external electrode including a plating layer formed on the conductive resin layer. removing the insulating film of the magnetic particles protruding from the surface of the core and the resin on the surface of the core in the area where the external electrode is to be formed; a conductive resin layer forming step of forming a conductive resin layer; and a plating layer forming step of forming a plating layer on the conductive resin layer within the range of the electrode planned location, the plating layer forming step In the step, the plating layer is formed to have a binding portion extending beyond the range of the conductive resin layer formed in the conductive resin layer forming step to the surface of the core and in contact with the surface of the core. In the method of manufacturing an inductor, the plating layer is formed so as to penetrate from the surface of the core into the interior of the core at the binding portion and to enter between the magnetic particles.

According to the present invention, in an inductor in which the external electrode is formed of a conductive resin layer and a plating layer formed on the surface of the element, it is possible to effectively prevent the occurrence of peeling of the external electrode from the element. can.

FIG. 1 is a perspective view of an inductor according to an embodiment of the present invention viewed from the top side. FIG. 3 is a perspective view of the inductor viewed from the bottom side. FIG. 2 is a transparent perspective view showing the internal configuration of an inductor. FIG. 3 is a schematic diagram of an inductor manufacturing process. It is an enlarged cross-sectional photograph showing a state in which the element body and the external electrode of a conventional inductor are separated. 1 is an enlarged cross-sectional photograph showing a state in which an element body and an external electrode are in close contact with each other in a conventional inductor. 2 is a diagram showing the positional relationship between a conductive resin layer and a plating layer in the inductor shown in FIG. 1. FIG. FIG. 8 is a perspective view of the conductive resin layer and plating layer shown in FIG. 7, viewed from the bottom side. This is an example of a microscopic photograph of a cross section of a binding part. It is another example of a microscopic photograph of a cross section of a binding part.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a perspective view of the inductor 1 according to the present embodiment viewed from the top surface 12 side, and FIG. 2 is a perspective view of the inductor 1 viewed from the bottom surface 10 side facing the top surface 12.
The inductor 1 of this embodiment is configured as a surface-mounted electronic component, and includes an element body 2 having a substantially rectangular parallelepiped shape, which is one aspect of an approximately hexahedral shape, and a pair of external elements provided on the surface of the element body 2. and an electrode 4.

Hereinafter, in the element body 2, a first main surface facing a mounting board (not shown) during mounting is defined as a bottom surface 10, a second main surface opposite to the bottom surface 10 is called an upper surface 12, and a pair of surfaces perpendicular to the bottom surface 10 are defined as a bottom surface 10. The third main surface is called an end surface 14, and the bottom surface 10 and a pair of fourth main surfaces perpendicular to the pair of end surfaces 14 are called side surfaces 16.
As shown in FIG. 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 the pair of side surfaces 16 is defined as the width W of the element body 2, and the distance between the pair of end surfaces 14 is defined as the width W of the element body 2. The distance between them is defined as the length L of the element body 2. Further, 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.

FIG. 3 is a transparent perspective view showing the internal configuration of the inductor 1.
The element body 2 includes a coil conductor 20 and a substantially hexahedral-shaped 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 core 30 is a molded body that is compression-molded into a substantially hexahedral shape by pressurizing and heating a mixed powder of magnetic powder and resin with the coil conductor 20 included therein.

Furthermore, the magnetic powder of the present embodiment includes particles of two types of particle sizes: large first magnetic particles having a relatively large average particle size and small second magnetic particles having a relatively small average particle size. I'm here. As a result, during compression molding, the second magnetic particles, which are small particles, enter between the first magnetic particles, which are large particles, together with the resin, thereby increasing the filling rate of the core 30 and increasing the magnetic permeability. .

In this embodiment, the average particle diameters of the metal particles of the first magnetic particles and the second magnetic particles are 24.4 μm and 4.0 μm, respectively. The average particle size of the first magnetic particles is preferably 19 μm or more and 30 μm or less, and the average particle size of the second magnetic particles is preferably 3 μm or more and 5 μm or less.

In this embodiment, each of the first magnetic particles and the second magnetic particles is a particle having a metal particle and an insulating film covering the surface thereof and having a thickness of several nm or more and several tens of nm or less. Fe--Si based amorphous alloy powder is used, and zinc phosphate glass is used for the insulating film. By covering the metal particles with an insulating film, insulation resistance and withstand voltage are increased.

In addition, in the first magnetic particles and the second magnetic particles, the metal particles include Fe-Si-Cr alloy powder, Cr-less Fe-Si alloy powder, Fe-Ni-Al alloy powder, and Fe-Cr-Al alloy powder. , Fe-Si-Al alloy powder, Fe-Ni alloy powder, and Fe-Ni-Mo alloy powder may be used. In the second magnetic particles, pure iron such as carbonyl iron powder may be used as the metal particles.

In addition, in the first magnetic particles and the second magnetic particles, the insulating film may contain other phosphates (magnesium phosphate, calcium phosphate, manganese phosphate, cadmium phosphate, etc.) or resin materials (silicone resin, epoxy resin, etc.). resins, phenolic resins, polyamide resins, polyimide resins, polyphenylene sulfide resins, etc.) may also be used.

In the mixed powder of this embodiment, an epoxy resin containing bisphenol A type epoxy resin as a main ingredient is used as the resin material. The resin content in the mixed powder is, for example, 3 wt%.
Note that the epoxy resin may be a phenol novolac type epoxy resin.
Further, the resin material may be other than epoxy resin, and may be not just one type but two or more types. 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.

As shown in FIG. 3, the coil conductor 20 includes a winding part 22 around which a conducting wire is wound, and a pair of lead-out parts 24 drawn out from the winding part 22. The winding portion 22 is formed by spirally winding the conducting wire such that both ends of the conducting wire are located on the outer periphery and are 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 part 22 along the thickness direction DT of the element body 2, and the lead-out part 24 extends from the winding part 22. It is drawn out to each of the pair of end faces 14 and electrically connected to the external electrode 4 .

The external electrode 4 is a so-called five-sided electrode that is provided from the entire surface of the end surface 14 to a portion of each of the bottom surface 10, the top surface 12, and a pair of side surfaces 16 adjacent to the end surface 14, and is made of solder or the like. It is electrically connected to the wiring of the circuit board by appropriate mounting means.

The inductor 1 having such a configuration can improve the direct current superposition characteristics by using soft magnetic powder as the magnetic powder, so it can be used as an electronic component in an electric circuit through which a large current flows, or as a choke coil in a DC-DC converter circuit or a power supply circuit. It is also used in electronic components of electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, car electronics, and medical and industrial machines. However, the use of the inductor 1 is not limited to this, and can also be used, for example, in a tuning circuit, a filter circuit, a rectifying and smoothing circuit, and the like.

Note that in the inductor 1, an element protection layer may be formed on the entire surface of the element body 2 except for the area of the external electrode 4. As the material for the element protection layer, for example, thermosetting resins such as epoxy resins, polyimide resins, and phenol resins, or thermoplastic resins such as polyethylene resins and polyamide resins can be used. Note that these resins may further contain fillers containing silicon oxide, titanium oxide, and the like.

FIG. 4 is a schematic diagram of the manufacturing process of the inductor 1.
As shown in the figure, the manufacturing process of the inductor 1 includes a coil conductor forming process, a preform forming process, a thermoforming/hardening process, a barrel polishing process, and an external electrode forming process.

The coil conductor forming step is a step of forming the coil conductor 20 from a conducting wire. In this process, the coil conductor 20 is formed into a shape having the above-described winding portion 22 and a pair of lead-out portions 24 by winding the conductive wire in a winding method called "alpha winding." Alpha winding refers to a state in which the conducting wire functioning as a conductor is spirally wound in two stages such that the lead-out portions 24 at the winding start and winding end are located on the outer periphery. The number of turns of the coil conductor 20 is not particularly limited.

The preform forming step is a step of forming a preform called a tablet.
The preformed body is formed into a solid shape that is easy to handle by pressurizing the mixed powder, which is the material of the element body 2. In this embodiment, the preformed body is formed into an appropriate shape having a groove into which the coil conductor 20 is inserted. Two types of tablets are formed: a first tablet (eg, E-shaped) and a second tablet of an appropriate shape (eg, I-shaped, plate-shaped, etc.) that covers the groove of the first tablet.

In the thermoforming/curing process, the first tablet, coil conductor, and second tablet are set in a mold, and while applying heat, pressure is applied in the overlapping direction of the first tablet and the second tablet to harden them. In this way, the first tablet, the coil conductor, and the second tablet are integrated. As a result, the element body 2 in which the coil conductor 20 is enclosed in the core 30 is molded.

The barrel polishing process is a process of barrel polishing this molded body, and through this process, the corners of the element body 2 are rounded.

The external electrode forming step is a step of forming the external electrode 4 on the core 30, and includes a surface treatment step, a conductive resin layer forming step, and a plating layer forming step.

The surface treatment step is a step in which the surface of the core 30 where the electrodes are scheduled is modified by irradiating the electrodes with laser light. Here, the electrode planned area refers to the area on the surface of the core 30 where the external electrode 4 is to be formed, and includes the area where the lead-out part 24 is exposed. Specifically, by irradiating laser light, the resin on the surface of the core 30 is removed in the area where the electrodes are planned, and the insulating film on the surface of the magnetic particles protruding from the core 30 is removed. As a result, on the surface of the core 30 where the electrodes are scheduled, the exposed area of the metal of the magnetic particles per unit area of the surface of the core 30 is larger than on other surface portions of the core 30 . Note that after the laser irradiation, a cleaning process (for example, an etching process) may be performed to clean the surface of the intended electrode location.

In the conductive resin layer forming step, a conductive resin layer is formed by applying a paste-like conductive resin containing conductive powder and resin to the intended electrode location and drying and curing the paste. Specifically, the core 30 is dipped into the conductive resin paste from the end surface 14 side and pulled up, thereby applying the conductive resin to a desired application range including the end surface 14 .

Since such a conductive resin layer contains conductive powder, it is possible to form a uniform potential distribution at electrode locations in the plating layer formation process described later, so that the plating layer formed on the conductive resin layer The homogeneity of the sample can be improved.

In this embodiment, a mixture of fine silver (Ag) powder (so-called nanosilver) with a particle size of several tens of nanometers and an acrylic resin is used as the conductive resin. The weight ratio of silver in the mixture is, for example, 88%. By using such fine silver powder, in addition to improving the homogeneity of the plating layer described above, the filling rate of silver in the conductive resin layer is increased and the DC resistance value between the external electrode 4 and the lead-out part 24 is increased. can be reduced.

In the plating layer forming step, a plating layer is formed on the surface of the conductive resin layer. The plating layer includes a first plating layer formed directly on the surface of the conductive resin layer and a second plating layer formed on the first plating layer. In this embodiment, the first plating layer is a nickel (Ni) plating layer with a thickness of 4.0 μm or more and 15 μm or less, and the second plating layer is a tin (Sn) plating layer with a thickness of 4 μm or more and 8 μm or less. The plating layer may be formed by electrolytic plating (for example, barrel plating). Although the plating layer is composed of two layers in this embodiment, it is not limited to this and can be composed of any number of layers.

Through the above external electrode forming process, the external electrode 4 composed of the conductive resin layer and the plating layer is formed.

Generally, in the external electrode formed as described above, by forming a conductive resin layer on the core surface at the intended electrode location, the growth of plating at the intended electrode location is facilitated. Moreover, the external electrode including the conductive resin layer is fixed to the surface of the core due to the adhesion strength between the core surface and the conductive resin layer.

However, for example, if bending stress occurs on a board to which the external electrodes of an inductor are soldered, depending on the magnitude of the bending stress, the conductive resin layer may peel off from the element body due to the tensile stress applied from the board to the external electrodes. may be observed.

FIG. 5 is an enlarged cross-sectional photograph showing a peeling state of the external electrode on the bottom surface of the element body, which can be observed in a conventional inductor. FIG. 6 is an enlarged cross-sectional photograph showing a normal state of external electrodes without peeling on the bottom surface of the element body in a conventional inductor for comparison with FIG. 5 and 6, the external electrode 81 is composed of a conductive resin layer 82 and a plating layer 83.

In the cross-sectional photograph shown in FIG. 6, the element body 80 and the conductive resin layer 82 are in contact with each other, whereas in the cross-sectional photograph of FIG. It can be seen that there is separation between 82 and 82. Such peeling of the conductive resin not only leads to disconnection failures (open failures) between the wiring pattern of the circuit board and the inductor, but also to characteristic fluctuations such as inductance fluctuations. countermeasures are required.

For this reason, in the inductor 1 of the present embodiment, the plating layer has a bonding portion that extends beyond the area where the conductive resin layer is disposed, extends to the surface of the core 30, and is in contact with the surface of the core 30. It is formed like this. Further, the plating layer is formed so as to penetrate into the interior of the core 30 from the surface of the core 30 at the binding portion and to enter between the magnetic particles.

FIG. 7 is a diagram for explaining the positional relationship between the conductive resin layer and the plating layer, and the upper and lower parts of FIG. 7 are plan views of the bottom surface 10 and side surface 16 of the inductor 1, respectively. Moreover, FIG. 8 is a perspective view of the conductive resin layer and the plating layer shown in FIG. 7 as viewed from the bottom surface 10 side. As described above, in this embodiment, the plating layer is composed of a nickel plating layer, which is the first plating layer, and a tin plating layer, which is the second plating layer.

As shown in the upper part of FIG. 7 and in FIG. 8, the conductive resin layer 41 extends on the bottom surface 10 of the substantially rectangular core 30 from two first ends 31 facing each other. In this embodiment, the first end 31 is a ridgeline formed by the bottom surface 10 and the end surface 14. The plating layer 42 is formed to extend to the surface of the core 30 beyond the area where the conductive resin layer 41 is disposed. As a result, the plating layer 42 has a binding portion 44 that covers the edge of the conductive resin layer 41 and is in direct contact with the surface of the core 30 .

Similarly, as shown in the lower part of FIG. 7 and in FIG. do. In this embodiment, the second end portion 32 is a ridgeline formed by the side surface 16 and the end surface 14. The plating layer 42 is formed to extend to the surface of the core 30 beyond the area where the conductive resin layer 41 is disposed. As a result, the plating layer 42 includes a binding portion 45 that covers the edge of the conductive resin layer 41 and is in direct contact with the surface of the core 30 .

The top surface 12 and the opposite side surface 16, which are not shown in FIG. 7, are also configured similarly to the bottom surface 10 and the side surface 16 shown in FIG. 7, respectively.

Here, the plating layer 42 is formed in the area where the electrode is planned, and the electrode area includes the insulating film on the surface of the magnetic particles protruding from the core 30 and the resin on the surface of the core 30 in the above-mentioned surface treatment process. is removed by laser beam irradiation. Therefore, the portions of the surface of the core 30 where the plating layer 42 is formed beyond the range of the conductive resin layer 41, that is, the bonding portions 44 and 45, are smaller than the other portions of the surface of the core 30. The exposed area of the metal of the magnetic particles per unit area on the surface of the magnetic particles is increased.

Furthermore, in this embodiment, in the surface treatment step, the insulating film and resin located between the magnetic particles are not usually removed in consideration of short circuits between the magnetic particles, but the irradiation energy of the laser beam is adjusted. The surface roughness of the core 30 in the area where the electrodes are planned is intentionally made rougher so that the plating layer 42 penetrates from the surface of the core 30 into the inside of the core 30 at the bonding parts 44 and 45 and gets between the magnetic particles. I have to.

FIG. 9 is an example of a microscopic photograph of the bonding portion 44 taken along a cut plane parallel to the side surface 16 of the inductor 1. The plating layer 42 of the binding part 44 is composed of a nickel plating layer 42a, which is a first plating layer formed on the core 30, and a tin plating layer 42b, which is a second plating layer formed thereon. There is. Then, with respect to the surface position of the core 30 indicated by the dashed line in the figure, the plating layer 42 of the binding part 44 is directed toward the inside of the core 30 as illustrated by the downward arrow in the figure. It penetrates further inside than the straight line connecting the outermost ends, and enters between the magnetic particles 50. The intrusion portion of the plating layer 42 corresponds to the portion where the insulating film on the surface of the magnetic particles 50 and the resin 51 filling the spaces between the magnetic particles 50 have been removed by the laser beam irradiation described above.

FIG. 10 is another example of a microscopic photograph of the bonding portion 44 taken along a cut plane parallel to the side surface 16 of the inductor 1. Similarly to FIG. 9, the plating layer 42 of the binding portion 44 penetrates into the core 30 as illustrated by the downward arrow in the figure with respect to the surface position of the core 30 indicated by the dashed line in the figure, and the magnetic particles 50 It can be seen that the magnetic particles are inserted between the magnetic particles 50 and the magnetic particles 50.

In the inductor 1 having the above configuration, the plating layer 42 extends beyond the area where the conductive resin layer 41 is disposed to the surface of the core 30 and forms binding portions 44 and 45 that are in contact with the surface of the core 30. It is formed to have. Furthermore, the plating layer 42 penetrates into the interior of the core 30 from the surface of the core 30 at the binding portions 44 and 45 and enters between the magnetic particles 50. Therefore, in the inductor 1, the binding force of the plating layer 42 to the core 30 is improved due to the anchor effect that may occur when a portion of the plating layer 42 enters between the magnetic particles 50 in the binding portions 44 and 45. As a result, in the inductor 1, peeling of the external electrode 4 from the core 30 due to, for example, mechanical stress from the circuit board on which the inductor 1 is mounted can be suppressed.

Further, in conventional inductors, the peeling of the conductive resin layer from the element body generally starts from the edge of the conductive resin layer and progresses, whereas in the inductor 1, the plating layer 42 is separated from the conductive resin layer. Since the conductive resin layer 41 is formed so as to cover the edges of the conductive resin layer 41, this improves the binding strength of the binding parts 44 and 45 to the core 30, and prevents the conductive resin layer 41 from starting to peel off from the element body 2 at the edge. can be effectively prevented. Therefore, in the inductor 1, even if the thickness of the nickel plating layer 42a is increased, peeling of the conductive resin layer 41 from the element body 2 can be sufficiently suppressed. Therefore, in the inductor 1, by increasing the thickness of the nickel plating layer 42a, it is possible to prevent problems such as solder explosion during mounting on a wiring board. Further, in the inductor 1, since the thickness of the plating layer 42 can be increased as described above, it is possible to suppress the occurrence of electrode breakdown due to thermal diffusion, ion migration, etc. during soldering.

Here, the effect of preventing peeling of the external electrode 4 from the element body 2 is determined by the length of the binding portions 44 and 45 of the plating layer 42 extending beyond the edge of the conductive resin layer 41 onto the core 30; It may also depend on the penetration depth of the plating layer 42 into the core 30 at the bonding parts 44, 45. In terms of the length, if it is too short, the binding force will be reduced, and if it is too long, the distance between the facing external electrodes 4 will be shortened, and the withstand voltage may be reduced. Therefore, in each of the plating layers 42 extending from the first end 31 or the second end 32 of the core 30, the first end of the binding portion 44 on the bottom surface 10 or the binding portion 45 on the side surface 16 is The length Lf of the portion 31 or the second end portion 32 along the normal direction is preferably 30 μm or more and 600 μm or less.

Note that, on each of the bottom surface 10 and the side surface 16, the edges of the binding portions 44 and 45 are not necessarily straight lines, and the length Lf may vary depending on the measurement location. In this case, the lengths Lf of the binding parts 44 and 45 are, for example, at the center of the width direction DW and the thickness direction DT on the bottom surface 10 and the side surface 16, respectively, and at a predetermined length from the center along the width direction DW and the thickness direction DT. The length Lf can be taken as the average value of the measured values measured at two or more locations separated by a distance of .

If the penetration depth P of the plating layer 42 into the core 30 in the binding parts 44 and 45 (for example, the length of the arrowed part in FIG. 10) is too shallow, the effect of improving the binding force will be small, and if it is too deep. Then, the insulation between the magnetic particles 50 of the inductor 1 as a whole may be reduced, and the withstand voltage may be reduced.
Hereinafter, evaluation results regarding the relationship between the penetration depth of the plating layer 42 into the interior of the core 30 at the binding portion 44 and the like and the adhesion strength of the binding portion 44 and the like will be described.

With the same configuration as the inductor 1 described above, test samples with different penetration depths P of the plating layer 42 into the interior of the core 30 in the binding part 44 were created, and for each test sample, the outer electrode 4 in the binding part 44 was The adhesion strength to the core 30 and withstand voltage were evaluated.

The size of the element body 2 in the test sample is a length L of 3.55 mm, a width W of 2.55 mm, and a thickness T of 1.93 mm. In the first magnetic particles and the second magnetic particles contained in the core 30 of the element body 2 of the test sample, Fe--Si--Cr alloy powder was used as the metal particles. The average particle diameters of the metal particles of the first magnetic particles and the second magnetic particles are 24.4 μm and 4.0 μm, respectively, as described above. The width W of the external electrode 4 is 2.85 mm, and the length L of the conductive resin layer 41 is 210 μm. Further, the length Lf of the test sample at the binding portion 44 was 100 μm.

The average particle diameter of each of the first soft magnetic particles and the second soft magnetic particles can be measured using a particle size distribution meter before mixing them with each other. In addition, when measuring in the state of a core as a molded body obtained by compression molding the mixed powder, the measurement can be performed by analyzing an electron microscope image of a cross section of the soft magnetic particles obtained by polishing the core. For example, the equivalent circle diameter of the cross section of each soft magnetic particle is determined from the above-mentioned electron micrograph, and assuming that each soft magnetic particle is a sphere having the above-mentioned circle equivalent diameter, the volume of each sphere is determined, and the volume value distribution is The average particle size can be calculated from the median value.

Here, as described above, the penetration depth P is controlled by changing the surface roughness of the core 30 by changing the irradiation energy of the laser beam irradiated to the electrode planned location on the surface of the core 30 in the surface treatment process. can. The penetration depth P of the plating layer 42 is measured in the direction perpendicular to the bottom surface 10 along the length direction DL of the element body 2, and at the winding portion of the coil conductor 20 when viewed from the top surface of the element body 2. The test was carried out by cutting the element body 2 in the longitudinal direction through the winding shaft of No. 22 and observing the cross section of the bonding portion 44 of the plating layer 42 of the external electrode 4. Specifically, a cross section of the central part of any one of the four binding sections 44 is photographed using an SEM (scanning electron microscope), and the components of each part of the cross section are analyzed using a component analyzer. The penetration depth of the nickel plating layer was measured by comparing the position where nickel had penetrated with the SEM image. At this time, the SEM image was taken at a magnification of 500 times with the length in the L direction set to such a length that five or more first magnetic particles close to the surface of the core 30 are visible. In the measurement, identify the part where the nickel plating layer enters the photographic field of view, identify the two first magnetic particles that are farthest along the surface of the core 30, and identify the two first magnetic particles that are farthest apart along the surface of the core 30 For the plating layer 42 between the magnetic particles that has penetrated inside the straight line connecting the top surfaces of the two first magnetic particles, measure the depth from the straight line connecting the top surfaces of the two first magnetic particles, and calculate the average value to determine the depth of the plating layer 42 between the magnetic particles. The depth was set to P. The evaluation test results are shown in Table 1.

In Table 1, the first column on the leftmost side indicates the penetration depth P of the plating layer 42. The second column shows the penetration depth P with respect to the average particle diameter D (24.4 μm in this embodiment) of the first magnetic particle having a larger particle size among the two types of magnetic particles having different particle sizes included in the magnetic particles 50. The ratio (P/D) is shown. Further, the third column and the fourth column respectively indicate the fixing strength of the binding portion 44 to the core 30 and the withstand voltage. The adhesion strength was evaluated by mounting the test sample on an auxiliary substrate, bending the test sample through the auxiliary substrate, and determining the amount of deflection of the auxiliary substrate when the external electrode of the test sample peeled off. As an evaluation result, a deflection amount of less than 2 mm was graded as "fair," a deflection of 2 mm or more and less than 3 mm was graded as "good," and a deflection of 4 mm or more was graded as "excellent." Further, the withstand voltage was measured by applying an impulse voltage between the external electrodes of the test sample and determining the voltage at which dielectric breakdown occurred between the external electrodes.

As shown in Table 1, when the ratio P/D is less than 1/3, the fixing strength becomes weak, and when the ratio P/D exceeds 3, the withstand voltage becomes lower than those within the range.
Therefore, from the results in Table 1, it can be seen that from the viewpoint of adhesion strength and withstand voltage, the ratio P/D is preferably 1/3 or more and 3 or less. That is, the penetration depth P from the surface of the core 30 into the interior of the core 30 in the binding portion 44 is preferably 1/3 or more and 3 times or less of the average particle diameter of the first magnetic particles included in the core 30.

Note that the above-described embodiment is merely an example of one aspect of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention.

For example, in the embodiment described above, the magnetic powder includes first magnetic particles and second magnetic particles, which are two types of particles with different particle sizes, but the present invention is not limited to this. By including particles having an average particle size different from the average particle size of each of the particles, particles having three or more types of particle sizes may be included. In this case, the first magnetic particles refer to the particles with the largest particle size.

For example, in the embodiment described above, the binding portion 44 or 45 is formed on the bottom surface 10, the top surface 12, and the side surface 16 of the core 30, respectively. It may be formed in a plane. For example, the inductor 1 may be formed at least at a bottom surface 10 that can be soldered to a circuit board as the one surface.

Furthermore, unless otherwise specified, horizontal and vertical directions, various numerical values, shapes, and materials in the embodiments described above refer to ranges that have the same effects as those directions, numerical values, shapes, and materials (so-called equivalent ranges). range).

As described above, the inductor 1 according to the embodiment described above has the element body 2 including the core 30 including the magnetic particles 50 and the resin 51, and the coil conductor 20 embedded in the core 30. The inductor 1 also includes a conductive resin layer 41 disposed on the surface of the core 30 so as to be in contact with the lead-out portion 24 that is the end of the coil conductor 20 exposed from the core 30, and a conductive resin layer 41 formed on the conductive resin layer 41. The external electrode 4 includes a plating layer 42 and a plating layer 42 . The plating layer 42 extends beyond the area where the conductive resin layer 41 is disposed to the surface of the core 30 and has binding portions 44 and 45 that are in contact with the surface of the core 30 . The plating layer 42 penetrates into the interior of the core 30 from the surface of the core 30 at the binding portions 44 and 45 and enters between the magnetic particles 50 . According to this configuration, occurrence of peeling between the element body 2 and the plating layer 42 of the external electrode 4 can be effectively prevented.

Further, in the inductor 1, the magnetic particles include first magnetic particles and second magnetic particles having different average particle sizes, and the average particle size of the first magnetic particles is larger than the average particle size of the second magnetic particles. The penetration depth P of the plating layer 42 from the surface of the core 30 into the interior of the core 30 in the binding parts 44 and 45 is 1/3 or more of the average particle diameter D of the first magnetic particles included in the core 30. It is preferable that it is 3 times or less. According to this configuration, the occurrence of peeling between the element body 2 and the plating layer 42 can be more effectively prevented.

Further, in the inductor 1, the core 30 has a substantially hexahedral shape, and the conductive resin layer 41 and the plating layer 42 are arranged at two opposing first ends 31 of the bottom surface 10, which is at least one main surface of the core 30. Extends onto the bottom surface 10 from either of the above. Then, in each of the plating layers 42 extending on the core 30 beyond the edge of the conductive resin layer 41 extending from the first end 31 of the core 30, the first end of the binding portion 44 on the bottom surface 10 is The length of one end portion 31 along the normal direction is preferably 30 μm or more and 600 μm or less. According to this configuration, the occurrence of peeling between the element body 2 and the plating layer 42 can be more effectively prevented.

Further, the manufacturing method according to the embodiment described above is a manufacturing method of the inductor 1 including the element body 2 and the external electrode 4. The element body 2 includes a core 30 including magnetic particles 50 having an insulating film on the surface and a resin 51, and a coil conductor 20 embedded in the core 30. The external electrode 4 is formed on a conductive resin layer 41 disposed on the core 30 so as to be in contact with the lead-out portion 24 that is the end of the coil conductor 20 exposed from the core 30, and on the conductive resin layer 41. A plating layer 42 is included. In this manufacturing method, the insulating film of the magnetic particles 50 protruding from the surface of the core 30 and the resin on the surface of the core 30 are removed from the area where the external electrode 4 is to be formed on the surface of the core 30. a conductive resin layer forming step of forming a conductive resin layer 41 within the range of the intended electrode location; and a plating layer formation step of forming a plating layer 42 on the conductive resin layer 41 within the range of the intended electrode location. It has a process. Then, in the plating layer forming step, the plating layer 42 extends beyond the range of the conductive resin layer 41 formed in the conductive resin layer forming step to the surface of the core 30, and forms a bond in contact with the surface of the core 30. It is formed to have fitting parts 44 and 45. In the plating layer forming step, the plating layer 42 is formed so as to penetrate from the surface of the core 30 into the interior of the core 30 at the binding portions 44 and 45 and to enter between the magnetic particles 50 . According to this manufacturing method, it is possible to easily manufacture the inductor 1 that can effectively prevent the occurrence of peeling between the element body 2 and the plating layer 42 of the external electrode 4.

DESCRIPTION OF SYMBOLS 1... Inductor, 2, 80... Element body, 4, 81... External electrode, 10... Bottom surface, 12... Top surface, 14... End surface, 16... Side surface, 20... Coil conductor, 22... Winding part, 24... Drawer part, 30... Core, 31... First end, 32... Second end, 41, 82... Conductive resin layer, 42, 83... Plating layer, 42a... Nickel plating layer, 42b... Tin plating layer, 44, 45... Binding portion, 50...Magnetic particles, 51...Resin.

Claims (4)

an element body including a core including magnetic particles and resin and a conductor embedded in the core; a conductive resin layer disposed on the surface of the core so as to be in contact with an end of the conductor exposed from the core; An inductor comprising an external electrode including a plating layer formed on the conductive resin layer,
The plating layer has a binding portion extending beyond the area where the conductive resin layer is disposed to the surface of the core and in contact with the surface of the core,
The plating layer penetrates into the interior of the core from the surface of the core at the binding portion and enters between the magnetic particles,
inductor. The magnetic particles include first magnetic particles and second magnetic particles having different average particle sizes, the average particle size of the first magnetic particles being larger than the average particle size of the second magnetic particles,
The penetration depth of the plating layer from the surface of the core to the inside of the core in the binding portion is 1/3 or more and 3 times or less of the average particle diameter of the first magnetic particles included in the core,
The inductor according to claim 1. The core has a substantially hexahedral shape,
The conductive resin layer and the plating layer extend from one of two opposing ends of the core to the one main surface of the core,
In a plating layer extending on the core beyond the edge of the conductive resin layer extending from the end of the core, the normal to the end of the binding portion on the one main surface; The length along the direction is 30 μm or more and 600 μm or less,
The inductor according to claim 1 or 2. an element body including a core including magnetic particles and resin having an insulating film on the surface and a conductor embedded in the core; and an element body disposed on the core so as to be in contact with an end of the conductor exposed from the core. A method for manufacturing an inductor comprising a conductive resin layer and an external electrode including a plating layer formed on the conductive resin layer,
a step of removing the insulating film of the magnetic particles protruding from the surface of the core and the resin on the surface of the core in a region on the surface of the core where an external electrode is to be formed, where an electrode is to be formed;
a conductive resin layer forming step of forming the conductive resin layer within the range of the planned electrode location;
a plating layer forming step of forming a plating layer on the conductive resin layer within the range of the planned electrode location;
has
In the plating layer forming step,
The plating layer is formed to have a binding portion extending beyond the range of the conductive resin layer formed in the conductive resin layer forming step to the surface of the core and in contact with the surface of the core, and ,
The plating layer is formed to penetrate from the surface of the core into the interior of the core at the binding portion and to enter between the magnetic particles.
A method of manufacturing an inductor.

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