JP2022060975A - Inductor and method for manufacturing inductor - Google Patents

Abstract

To provide an inductor that can suppress magnetic saturation even by using a magnetic material that can provide an excellent direct-current overlapping characteristics, and a method for obtaining the inductor.SOLUTION: A core 40 of an inductor includes a first soft magnetic particle 81 with a relatively large average particle diameter and a second soft magnetic particle 82 with a relatively small average particle diameter. An element assembly including a coil and a core has an air gap with a length KL and a width KW extending in a direction in which coil parts 32L are lined, in the outer periphery of the winding part 32 of the coil and within the distance five times as large as the average particle diameter of the first soft magnetic particle 81 of the coil part 32.SELECTED DRAWING: Figure 17

Description

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

Conventionally, a surface mount inductor having a prime field including a coil having a winding portion composed of a plurality of winding portions and a core in which the coil is embedded is known. Some inductors of this type form a core by pressure molding a composite material containing metallic magnetic powder.

For example, in the technique described in Patent Document 1, iron-based metal magnetic powder, other composition-based metal magnetic powder, metal magnetic powder such as amorphous, metal magnetic powder whose surface is coated with an insulator such as glass, and a surface. A modified metal magnetic powder and a nano-level fine metal magnetic powder are used.

Japanese Unexamined Patent Publication No. 2020-07795

In the conventional configuration, by using the soft magnetic material made of the metal magnetic powder, better DC superimposition characteristics are obtained as compared with the case of using a magnetic material such as ferrite. However, if the magnetic flux density in the vicinity of the winding portion of the coil becomes too large, magnetic saturation may occur.

An object of the present invention is to make it possible to suppress magnetic saturation even by using a magnetic material capable of obtaining good DC superimposition characteristics.

One aspect of the present invention is an inductor having an element body including a coil having a winding portion composed of a plurality of winding portions and a core in which the coil is embedded, wherein the core has a relative average particle size. The element body is the outer periphery of the winding portion of the coil and the first from the winding portion. It has an air gap extending in the direction in which the winding portions are lined up within a distance of 5 times the average particle size of the soft magnetic particles.

According to the inductor according to the present invention, the air gap functions as a magnetic gap, and magnetic saturation can be suppressed even by using a magnetic material capable of obtaining good DC superimposition characteristics.

It is a figure which shows typically the structure of the inductor which concerns on embodiment of this invention, and is the perspective view which looked at the top surface side of the inductor. It is a figure which shows the structure of the inductor schematically, and is the perspective view which looked at the side of the mounting surface of the inductor. It is a perspective perspective view which shows the internal structure of the inductor transparently. It is a figure which shows the outline of the manufacturing process of an inductor. It is a figure which shows the mode of the prime body molding using the tablet formed with the mixed powder. It is a schematic diagram which shows the state of the core of the prime field after molding. It is a figure which shows the flow mode of the mixed powder in the peripheral part of a coil in a prime body molding / hardening process. It is a figure which shows the state of the void of the surface region and the central part region of the 1st tablet in the element molding / hardening process. It is a figure explaining the reference plane of an inductor. It is a figure which shows the filling mode of the resin on the side surface of a prime field. It is a figure which shows the measurement result of the surface roughness of a prime field. It is a figure explaining the space between the side surface of a prime field and a coil. It is a figure explaining the relationship between the amount of resin in a mixed powder, and the density of a prime field. (A) is an image showing the lower winding portion of the coil together with the surrounding material, and (B) is an image showing the upper winding portion of the coil together with the surrounding material. It is a figure which provides the explanation of the pressing force at the time of prime body molding. It is a characteristic curve diagram which shows the simulation result of the line magnetic powder structure. It is an image when an air gap which becomes a magnetic gap is provided in the vicinity of a winding part. It is a characteristic curve diagram which shows the simulation result according to the presence or absence of an air gap. It is a figure which shows typically an example of the grinding apparatus used for the element grinding. It is explanatory drawing of the side gap. It is a figure which shows typically an example of the protective film forming apparatus used for forming the element protective film. It is a figure which shows the experimental result of the content of nanosilica and the drying rate. It is a figure which shows the experimental result of the average particle diameter of the silica particle of nano silica, and the sticking occurrence rate. It is an image which shows the crack which occurred in the element protection film. It is a figure which shows the result of having measured the number of "plating skips" by changing the thickness of a prime field protective film.

[Overall inductor configuration]
1 and 2 are views schematically showing the configuration of the inductor 1 according to the present embodiment, FIG. 1 is a perspective view of the top surface 14 of the inductor 1, and FIG. 2 is a mounting surface 12 of the inductor 1. It is a perspective view which looked at the side of.
The inductor 1 of the present embodiment is configured as a surface mount type electronic component, and includes a prime field 10 having a substantially rectangular shape and a pair of external electrodes 20 provided on the surface of the prime field 10. One surface of 10 is configured as a mounting surface 12 (FIG. 2) mounted on the surface of a circuit board (not shown), and the prime field 10 is covered with a prime field protective film 50 except for the external electrode 20.

Hereinafter, in the prime field 10, the facing surface of the mounting surface 12 is referred to as a top surface 14 (FIG. 1), and among the four surface surfaces other than the mounting surface 12 and the top surface 14, the drawer portion 34 described later of the coil 30 is located. The pair of faces to be used is referred to as a first side surface 16, and the remaining pair of faces is referred to as a second side surface 18. The first side surface 16 and the second side surface 18 are also the surfaces of the prime field 10 located in the radial direction of the winding portion 32 included in the coil 30 described later. Hereinafter, the mounting surface 12 and the top surface 14 facing each other are also referred to as a pair of main surfaces.

Further, as shown in FIG. 1, the length from the mounting surface 12 to the top surface 14 is defined as the height H of the prime field 10, and the length of the short side of the top surface 14 is defined as the width W of the prime field 10. Then, the length of the long side is defined as the length L of the prime field 10.

FIG. 3 is a perspective perspective view showing the internal configuration of the inductor 1 according to the present embodiment.
The prime field 10 includes a coil 30 and a core 40 in which the coil 30 is embedded, and is configured as a coil-enclosed magnetic component in which the coil 30 is enclosed in the core 40.
The coil 30 is an air-core coil component in which a conducting wire is wound.
The core 40 is a molded body that is compression-molded into a substantially rectangular parallelepiped shape by compacting a mixed powder in which a soft magnetic powder and a resin are mixed in a state of containing a coil 30.

The coil 30 includes a winding portion 32 around which a conducting wire is wound and a pair of drawing portions 34 drawn from the winding portion 32. The winding portion 32 is formed by winding the conducting wire in a spiral shape so that both ends of the conducting wire are located on the outer periphery and are connected to each other on the inner circumference. Inside the prime field 10, the coil 30 is embedded in the core 40 in a posture in which the central axis K of the winding portion 32 is along the direction of the height H of the prime body 10, and the drawer portion 34 is the winding portion. It is drawn from 32 to each of the pair of first side surfaces 16.

The lead wire used for forming the coil 30 is pre-coated with an insulating coating material 60 having an insulating coating layer having electrical insulating properties and a fusion-bonded coating layer formed on the insulating coating layer. In the coil forming step, the conductive wires of the wound portion 32 are fixed to each other by melting the fused coating layer by winding the conducting wire while heating, and the shape of the wound portion 32 after the coil is formed is suppressed. Further, the coil 30 and the core 40 are surely insulated by the insulating coating layer.

The pair of external electrodes 20 are L-shaped members extending from each of the first side surfaces 16 of the prime field 10 to the mounting surface 12. Each of the external electrodes 20 is connected to the extraction portion 34 of the coil 30 on the first side surface 16, and the portion 20A (FIG. 2) extending to the mounting surface 12 is electrically connected to the wiring of the circuit board by an appropriate mounting means such as solder. Is connected.

The inductor 1 having such a configuration is used, for example, as an impedance matching coil (matching coil) for a high frequency circuit, and is used as an electronic device for personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, car electronics, medical / industrial machines, and the like. Used for equipment. However, the application of the inductor 1 is not limited to this, and it can also be used, for example, in a tuning circuit, a filter circuit, a rectifying smoothing circuit, and the like.

[Overview of inductor manufacturing process]
FIG. 4 is a diagram showing an outline of the manufacturing process of the inductor 1.
As shown in the figure, the manufacturing process of the inductor 1 includes a granulation process, a coil forming process, an element molding / curing process, an element grinding process, an element protective film forming process, and an element protective film. It includes a removal step and an external electrode forming step.

The granulation step is a step of granulating a mixed powder in which the soft magnetic powder contained in the core 40 and the resin are mixed. The soft magnetic powder consists of particles whose surface is covered with an insulating film.

The coil forming step is a step of forming the coil 30 from the conductor wire coated with the insulating coating material 60. In this step, the coil 30 is formed into a shape having the above-mentioned winding portion 32 and a pair of drawer portions 34 by winding the conducting wire in a winding method called "alpha winding". The alpha winding refers to a state in which the lead wire 34 that functions as a conductor is spirally wound in two stages so as to be located on the outer periphery of the lead wire 34 at the beginning and end of the winding. The number of turns of the coil 30 is not particularly limited, but is, for example, 6.5 turns.

The prime field molding / curing step is a step of molding the molded body that is the source of the prime field 10.
As the molding material of the molded body, the mixed powder obtained in the granulation step is used.
In this step, the mixed powder is premolded to prepare a tablet (solid substance having a predetermined shape), and the tablet and the coil 30 are placed in the cavity of the molding die. Next, the molded body containing the coil 30 is compression-molded by pressurizing the cavity while heating it with a punch, and then the cured molded body is taken out from the cavity and the molded body is polished. By using barrel polishing for this polishing, R can be applied to the corners of the molded body.

As shown in FIG. 5, the preformed tablet has an appropriately shaped first tablet 70 having a groove 71 into which the coil 30 enters (for example, an E type) and an appropriately shaped tablet 70 covering the groove 71 of the first tablet 70. Two types of tablets (for example, type I, plate-shaped, etc.) and the second tablet 72 are used. At the time of compression molding, the first tablet 70 in which the coil 30 is fitted in the groove 71 and the second tablet 72 are arranged so as to be overlapped in the cavity 75 of the molding die 74. Then, while applying heat to the first tablet 70 and the second tablet 72, punches are made from the side of the first tablet 70 and / and the second tablet 72 (the side of the second tablet 72 in the example of FIG. 5) in this overlapping direction. By pressurizing with 76, the first tablet 70, the coil 30, and the second tablet 72 are integrated.
In addition, instead of the pre-molded tablet, the mixed powder obtained in the granulation step may be directly put into the cavity and compression-molded.

As shown in FIG. 6, the applied pressure P during compression molding is lower than before so that the individual particles 80 constituting the soft magnetic powder do not collapse after molding of the prime field 10 and maintain the shape before molding. It is preferably pressure. Due to the pressing force P, damage to the insulating film on the surface of the individual particles 80 constituting the soft magnetic powder is suppressed, so that deterioration of the insulating performance (that is, deterioration of the pressure resistance performance) is suppressed.

Further, as shown in FIG. 6, the particles 80 constituting the soft magnetic powder have two or more kinds of particle sizes (in the example of FIG. 6, the first soft magnetic particles 81, which are large particles having a relatively large average particle size, and the average particles). The second soft magnetic particles 82), which are small particles having a relatively small diameter, are preferable. According to the soft magnetic powder, as shown in FIG. 6, the second soft magnetic particles 82, which are small particles, enter between the first soft magnetic particles 81, which are large particles, together with the resin 90 during compression molding. A molded body (elementary body 10) having a high filling rate of the particles 80 can be obtained. The embodiments of the first soft magnetic particles 81 and the second soft magnetic particles 82 constituting the core 40 will be described later.

In the prime field grinding step, the second side surface 18 is scraped off (that is, ground) until the width W becomes a predetermined width by allowing the abrasive grains to act on the second side surface 18 of the molded body obtained in the prime field molding / hardening step. ) It is a process.
By this step, the prime field 10 obtained by downsizing the width W of the molded body to a predetermined width is obtained. Due to such downsizing, the distance (also referred to as a side gap) between the coil 30 in the prime field 10 and the second side surface 18 is shortened, so that the occupancy rate of the coil 30 in the radial direction of the winding portion 32 of the coil 30 is increased. Further, since the molded body obtained by compression molding is ground to a predetermined size to obtain the prime field 10, the dimensional variation of the prime field 10 is reduced as compared with the case where the prime field 10 is controlled to a predetermined size only by compression molding. be able to.
In the prime field grinding step, polishing (for example, barrel polishing) for chamfering the corners generated by grinding the second side surface 18 may be performed.

The prime field protective film forming step is a step of forming the prime field protective film 50 on the entire surface of the prime field 10 ground to a predetermined size in the prime field grinding step.
As the material of the element protective film 50, for example, a thermosetting resin such as an epoxy resin, a polyimide resin or a phenol resin, or a thermoplastic resin such as a polyethylene resin or a polyamide resin is used. In addition, these resins may further contain a filler containing silicon oxide, titanium oxide and the like.
In this step, the material of the prime field protective film 50 is applied to the entire surface of the prime field 10 by an appropriate means such as coating or dipping, and the material is cured to form the prime field protective film 50.

In the prime field protective film removing step, the electrode forming portion where the external electrode 20 is formed by irradiating the prime field 10 whose entire surface is covered with the prime field protective film 50 with a laser (first side surface 16 in this embodiment). This is a step of removing the prime field protective film 50 (at a predetermined portion of the inside) and the insulating coating material 60 of the drawer portion 34 of the coil 30 exposed at the electrode forming portion.
In the prime field protective film removing step, after the insulating coating material 60 is removed by a laser, an etching process may be performed to clean the surface of the electrode forming portion.

The external electrode forming step is a step of forming the external electrode 20 by plating at the electrode forming portion where the prime field protective film 50 is removed in the prime field protective film removing step.
In this step, the external electrode 20 is formed by plating the soft magnetic powder exposed on the surface of the prime field 10 and the drawer portion 34 of the coil 30. In this plating process, the external electrode 20 is formed by forming a layer formed of copper (Cu) by plating growth.
A layer formed of nickel (Ni) and a layer formed of tin (Sn) may be laminated and formed on the copper (Cu) layer by plating growth in this order. Further, instead of the copper (Cu) layer, a layer of aluminum (Al), silver (Ag), gold (Au), or palladium (Pd) may be used.

Further, the external electrode may be formed by using sputtering, a conductive resin, a copper plate, or the like. Further, the external electrode 20 is not limited to the L-shape of the illustrated example, and may have a so-called five-sided electrode structure or a bottom electrode.

According to the inductor 1 manufactured as described above, the ratio of the specific resistance of the core 40 to the soft magnetic metal portion and the like is increased while maintaining the mechanical strength of the core 40, and the reliability is high and the withstand voltage is good. , Magnetic permeability, saturation magnetic flux density, and DC superimposition characteristics are realized.

Next, an embodiment of the inductor 1 will be described below.
In each embodiment, unless otherwise specified, the dimensions of the inductor 1 are 0.7 ± 0.1 mm in height H, 1.2 ± 0.2 mm in width W, and 2.0 ± in length L. It is 0.2 mm and has a withstand voltage of about 20 V.
Further, the inductor 1 will be described later in [A. Mixed powder], [B. Coil], [C. Magnetic circuit], [D. Prime field grinding] and [E. It can be configured by any combination of these examples using any of the examples shown in [Prime field protective film].

[A. Mixed powder]
The mixed powder used to form the core 40 contains a soft magnetic powder and a resin.
[A-1. Soft magnetic powder]
The soft magnetic powder contained in the mixed powder is a soft magnetic material composed of particles of the soft magnetic metal. The soft magnetic powder contains, for example, first soft magnetic particles 81 (large particles) and second soft magnetic particles 82 (small particles) having an average particle size smaller than that of the first soft magnetic particles 81. In the present specification, the "average particle size" means a volume-based median diameter.

The average particle size of each of the first soft magnetic particles 81 and the second soft magnetic particles 82 can be measured using a particle size distribution meter before mixing them with each other. Further, when measuring in the state of the core 40 as a molded body obtained by pressure-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 40. can. For example, the circle-equivalent diameter of each soft magnetic particle cross section is obtained from the electron micrograph, and it is assumed that each soft magnetic particle is a sphere having the circle-equivalent diameter, and the volume of each sphere is obtained, and the volume value distribution thereof is obtained. The average particle size can be calculated from the median value of.

The average particle size of the first soft magnetic particles 81 is 20 μm or more and 28 μm or less, preferably 21.4 μm or more and 27.4 μm or less. The average particle size of the second soft magnetic particles 82 is 1 μm or more and 6 μm or less, preferably 1.5 μm or more and 1.8 μm or less. In this way, by forming the mixed powder with the first soft magnetic particles 81 and the second soft magnetic particles 82 having different average particle sizes, the saturation magnetic flux as the core 40 due to the first soft magnetic particles 81 having a large average particle size. While increasing the density and improving the DC superimposition characteristics, the second soft magnetic particles 82 having a small average particle size are allowed to enter the gaps between the first soft magnetic particles 81, and the filling rate of the soft magnetic particles in the core 40 is increased to increase the ratio. The magnetic permeability can be improved.

The amount of the second soft magnetic particles 82 contained in the mixed powder is 15% by weight or more and 30% by weight or less, preferably 20% by weight or more and 30% by weight or less, based on the total weight of the soft magnetic particles contained in the mixed powder. It is less than% by weight. When the content of the second soft magnetic particles 82 in the soft magnetic material is within the above range, the filling rate of the soft magnetic particles in the core 40, which is a molded body of the mixed powder, can be further increased.

The composition of the soft magnetic metal constituting the second soft magnetic particles 82 may be the same as the composition of the soft magnetic metal constituting the first soft magnetic particles 81, but they have different compositions and have substantially the same hardness as each other. It is preferable to have. The hardness of the first soft magnetic particles 81 and the second soft magnetic particles 82 can be measured by using the nanoindentation method. For example, the hardness of the first soft magnetic particles 81 is 600 HV (kgf / mm ² ) or more and 1200 HV or less, and preferably 800 HV or more and 1000 HV or less. The hardness of the second soft magnetic particles 82 is 900 HV (kgf / mm ² ) or more and 1400 HV or less, and preferably 900 HV or more and 1100 HV or less.

Further, it is desirable that the ratio of the hardness of the second soft magnetic particles 82 to the hardness of the first soft magnetic particles 81 is 0.7 or more and 1.2 or less. As a result, when the mixed powder containing these soft magnetic particles is pressure-molded to form the core 40, one of the soft magnetic particles having a low hardness of the first soft magnetic particles 81 or the second soft magnetic particles 82 is deformed. It is possible to prevent the insulation resistance of the core 40 from being lowered.

[A-2. resin]
The ratio of the resin is 2.0% by weight or more and 3.5% by weight or less based on the total weight of the soft magnetic powder and the resin. Further, the resin contains at least a bisphenol A type epoxy resin and a rubber-modified epoxy resin, and may further contain a phenol novolac type epoxy resin.

Through the evaluation experiments described later, the present inventors have found a first resin compounding ratio which is a suitable compounding ratio of the bisphenol A type epoxy resin and the rubber-modified epoxy resin when the phenol novolac type epoxy resin is not blended in the mixed powder. .. The first resin compounding ratio is 40% by weight or more and 90% by weight or less of the bisphenol A type epoxy resin, and 10% by weight or more and 50% by weight or less of the rubber-modified epoxy resin, based on the total weight of the resins contained in the mixed powder.

Here, the bisphenol A type epoxy resin is the main component of the resin contained in the mixed powder, but if the resin contained in the mixed powder is only the bisphenol A epoxy resin, the formed prime field 10 tends to be hard and brittle. Therefore, by blending the rubber-modified epoxy resin with the resin contained in the mixed powder, the formed prime field 10 can be made tough and the hardness and brittleness of the prime field 10 can be improved. Then, the ratio of the bisphenol A type resin and the rubber-modified epoxy resin in the resin contained in the mixed powder is set by the first resin blending ratio, and the element body 10 in which the coil 30 is sealed by the above-mentioned element body molding / curing step is performed. By molding the above, an inductor 1 having both strength and toughness can be manufactured.

Further, in the evaluation experiment described later, the present inventors have obtained a suitable mixing ratio of the bisphenol A type epoxy resin, the rubber-modified epoxy resin and the phenol novolac type epoxy resin when the phenol novolac type epoxy resin is mixed with the mixed powder. A second compounding ratio was found. The second compounding ratio is based on the total weight of the resin contained in the mixed powder, bisphenol A type epoxy resin 40% by weight or more and 80% by weight or less, rubber-modified epoxy resin 10% by weight or more and 50% by weight or less, and phenol novolac type epoxy. The resin is 1% by weight or more and 30% by weight or less.

Here, in the phenol novolac type epoxy resin, in the above-mentioned prime field molding / curing step, the viscosity when flowing the mixed powder when forming the prime field and the glass transition temperature of the prime field are adjusted. It functions to improve the strength of the prime field when it gets hot. Therefore, by appropriately blending the phenol novolac type epoxy resin with the second blending ratio, the inductor 1 that has both strength and toughness is manufactured while improving the strength of the prime field against heating during molding of the prime field. can do.

Furthermore, the present inventors have an inductor having the following specific configurations 1 to 3 by forming a prime field using a mixed powder in which a resin is blended according to the first blending ratio or the second resin blending ratio. It was found that the product can be manufactured.

Specific configuration 1 ... With respect to the cross section of the element body 10, with respect to the total area of the soft magnetic particles (first soft magnetic particles and the second soft magnetic particles) and the resin in the surface region of 1 μm or more and 100 μm or less from the surface of the element body 10. The ratio of the area of the voids is smaller than the ratio of the area of the voids to the total area of the soft magnetic particles and the resin in the central region of the element body 10, and the surface region is denser than the central region.

Specific configuration 2 ... With reference to FIGS. 1 to 3, the amount of resin in the ridge line portion where the main surfaces 12 and 14 and the second side surface 18 are in contact is the amount of the resin in the ridge line portion where the main surfaces 12 and 14 and the first side surface 16 are in contact with each other. Less than the amount of resin.

Specific Configuration 3 ... With reference to FIGS. 1 to 3, the polished first soft magnetic particles or the polished second soft magnetic particles are exposed from the core, and the first soft magnetic particles exposed from the core or The second soft magnetic particles are covered with the prime field protective film 50. Further, the surface roughness of the second side surface 18 is larger than the surface roughness of the first side surface 16, and the narrower distance between the second side surface 18 and the winding portion 32 of the coil 30 is the diameter of the first soft magnetic particles. Greater than 1 times and less than 4 times.

The mechanism for obtaining the specific configurations 1 to 3 will be described. As described above with reference to FIG. 5, the coil 30 is set in the first tablet 70, and the coil 30 is sandwiched between the first tablet 70 and the second tablet 72 to be integrated. By applying heat to the first tablet 70 and the second tablet 72 and pressurizing in the overlapping direction of the first tablet 70 and the second tablet 72, the mixed powder flows and a core in which the coil 30 is embedded is obtained. ..

FIG. 7 is an enlarged image of the peripheral portion of the coil 30 being pressurized in the overlapping direction with the coil 30 sandwiched between the first tablet 70 and the second tablet 72. FIG. 8 is a cross-sectional view of the first tablet 70. As shown in FIG. 7, gaps s1, s2, and s3 are formed in the region beside the coil 30. Therefore, when the pressure is applied in the overlapping direction of the first tablet 70 and the second tablet 72, the mixed powder is filled first from the gap near the outer peripheral portion of the core.

That is, the amount of movement of the mixed powder increases in the vicinity of the outer peripheral portion of the coil 30, and as a result, the gaps are easily filled and the filling density tends to be high. On the other hand, in the region inside the coil 30, since the amount of movement of the mixed powder is small, it is difficult to fill the gap and the filling density tends to be low. Therefore, as shown in FIG. 8, the filling rate of the mixed powder in the outer peripheral portions s10 to s13 of the coil 30 is higher than that in the inner portion s14 of the coil 30. Therefore, the inductor 1 having the specific configuration 1 can be obtained.

If there is a gap in the surface region of the prime field, there is a disadvantage that moisture enters the inside of the prime field from the gap and the moisture resistance of the inductor deteriorates. Further, when forming the external electrode, there is a disadvantage that the plating solution enters the inside of the prime field through the voids and the deterioration of the prime field over time is accelerated. Therefore, by increasing the density of the surface region of the prime field by the above specific configuration, it is possible to prevent these inconveniences from occurring.

Here, FIG. 9 is an explanatory view of an LT surface and a WT surface which are reference surfaces of the inductor 1, and FIG. 10 is an image of a cross section of the LT surface and the WT surface of the inductor 1 shown in FIG. As described above, the second side surface 18 is ground by the element grinding step before the element protective film is formed on the element body 10, but the first side surface 16 is not ground. Therefore, in the ridge line portions s22 and s23 where the main surface (here, the mounting surface) 12 and the second side surface 18 in the cross section of the LT surface are in contact with each other, the metal magnetic powder is ground flush with the second side surface, and the ridge line portion s22, The exposed area of the metallic magnetic powder in s23 is increased, and the amount of resin in the ridge line portions s22 and s23 is smaller than the amount of resin in the ridge line portions s20 and s21 in which the main surface 12 and the second side surface 18 are in contact with each other in the cross section of the WT surface. Become. Thereby, the inductor 1 having the specific configuration 2 can be obtained. According to the specific configuration 2, the vicinity of the ridge line portion where the main surface 12 and the second side surface 18 are in contact is ground, so that the soft magnetic particles protruding from the prime field protective film are reduced, and the insulating property of the inductor is lowered. Can be prevented.

Further, FIG. 11 is a comparison table of the maximum height with the micrographs of the surfaces of the LT surface and the WT surface after the processing by the above-mentioned element molding / hardening process and after the element grinding process. The maximum height Sz is used as an index value of surface roughness. The larger the maximum height Sz, the larger the surface roughness.

The LT surface is ground by the prime field grinding step, and at that time, the first soft magnetic particles or the second soft magnetic particles are shed, so that the surface roughness becomes large. Therefore, the maximum height Sz (50 μm) of the LT surface is larger than the maximum height Sz (43 μm) of the MT surface on which grinding is not performed. By increasing the surface roughness of the LT surface, the bondability between the prime field protective film and the core on the LT surface can be improved. This surface roughness is measured by scanning the center of the surface of the LT surface and the surface of the WT surface along the longitudinal direction using a shape analysis laser microscope (VK-X250 manufactured by KEYENCE CORPORATION) and measuring the maximum height (Sz). I asked for it.

Further, as shown in FIG. 12, of the gaps SG1 and SG2 between the second side surface 18 and the coil 30, the narrower gap is set to a range larger than 1 times and smaller than 4 times the first soft magnetic particles. By doing so, it is possible to obtain an inductor 1 having the above-mentioned specific configuration 3 in which the outer size is reduced while ensuring the moisture resistance of the prime field.

[A-2-1. Embodiment using the resin of the first resin compounding ratio]
Using the mixed powder containing the resin of the first resin compounding ratio, the above-mentioned granulation step → coil forming step → prime field molding / hardening step → prime field grinding step → prime field protective film forming step → prime field protective film A sample of the prime field of the inductor was prepared by the removal step → the external electrode formation step, and the prime field of each sample was evaluated. The manufacturing conditions in the prime field molding / curing process are a temperature of 135 ° C. and a pressing force of 10 MPa.

(Evaluation of body strength)
The strength of each sample was evaluated by the fracture load at the time of 3-point bending using a 3-point bending test device (3-point bending test device AGS-5kNX manufactured by Shimadzu Corporation). When the fracture load was 30 MPa or more, it was regarded as G (pass), and when it was less than 30 MPa, it was regarded as NG (fail).

(Evaluation of toughness)
A three-point bending test was performed on each sample using a three-point bending test device, and the toughness was evaluated by the amount of sample deformation when broken.

(Evaluation of density)
For each sample, image processing was performed on the image of the cross section to extract the image portion of the void, and the ratio of the total area of the image portion of the void to the area of the cross section was calculated to measure the void ratio.
To measure the void ratio, the prime field is cut at 1/2 in the length direction, and on the cut surface, four locations (one location on each surface) in a region of 1 μm or more and 100 μm from the surface of the prime field are each 1000 times. The image was taken with a scanning electron microscope (SEM) set to the magnification of, the voids contained in the cut surface were measured, and the average was calculated. In addition, the prime field was cut at 1/2 in the length direction, and four points in the central region of the prime field were photographed using a scanning electron microscope (SEM) set to a magnification of 1000 times each on the cut surface. Then, the void ratio was measured by measuring the voids contained in the cut surface and calculating the average.
As a result, except for sample numbers b9 to sample number b13, sample number b27, sample number b28, and sample number b32, the average porosity of a total of eight points in the surface region and the central region of the prime field is small, and the surface region of the prime field is small. The proportion of voids in the sample was smaller than the proportion of voids in the central region of the prime field, and the surface region was denser than the central region.

(Ratio of resin in mixed powder)
In FIG. 13, the relationship between the amount of resin in the mixed powder and the density of the prime field is set to the density of the prime field (g / cm ³ ) on the vertical axis and the amount of resin (% by weight) in the mixed powder on the horizontal axis. It is shown by setting to. The molding conditions of the prime field are a temperature of 180 degrees, a pressing force of 30 MPa, and a pressurizing time of 100 seconds. In FIG. 13, when the amount of resin is less than 2.0%, the density of the prime field decreases. It is presumed that this is because the fluidity of the mixed powder is lowered and the filling property of the mixed powder when molding the prime field is deteriorated.

From the evaluation results using the samples in Table 1, bisphenol A type epoxy resin 40% by weight or more and 90% by weight or less was used as a suitable compounding ratio of the resin in the mixed powder for forming an inductor having both strength and toughness of the element body. A rubber-modified epoxy resin of 10% by weight or more and 50% by weight or less (the above-mentioned first resin compounding ratio) was found.

[A-2-2. Embodiment using the resin of the second resin compounding ratio]
Similar to the embodiment shown in A-2-1 above, a sample of the element body of the inductor is prepared using the mixed powder containing the resin of the second resin compounding ratio, and the element body of each sample is evaluated. rice field. The proportion of the resin in the mixed powder is 2.0% by weight or more and 3.5% by weight or less of the mixed powder, as in the embodiment shown in A-2-1.

From the evaluation results using the samples in Table 2, bisphenol A type epoxy resin 40% by weight or more and 80% by weight or less is suitable as a suitable compounding ratio of the resin in the mixing material for forming an inductor having both strength and toughness of the element body. , 10% by weight or more and 50% by weight or less of the rubber-modified epoxy resin, and 1% by weight or more and 30% by weight or less of the phenol novolac type epoxy resin (the above-mentioned second resin compounding ratio) were found. In particular, the toughness of the prime field was excellent in sample numbers b14 to b26 and b29 to b31.

[A-2-3. Embodiment regarding side gap]
In order to evaluate the distance (side gap) SG1 and SG2 between the second side surface 18 and the coil 30 shown in FIG. 12 and the quality of the moisture resistance of the inductor 1, the samples shown in Tables 3 and 4 below were prepared. Then, the moisture resistance was evaluated.

(Evaluation of moisture resistance)
A moisture resistance test was conducted on each sample using a moisture-resistant tank with a temperature of 85 ° C and a humidity of 85%, and when the weight increase of the element due to water absorption was 2% by weight or less, it was regarded as G (pass) and exceeded 2. If it is, it is regarded as NG (failure).
(Specifications of mixed powder)
The ratio of the resin in the mixed powder was 2.0% by weight or more and 3.5% or less, and the compounding of the resin was the above-mentioned first resin compounding ratio. The average particle size of the large soft magnetic particles (first soft magnetic particles) in the mixed powder is 21 μm (sample in Table 3) or 28 μm (sample in Table 4), and the small soft magnetic particles (second soft magnetic particles). The average particle size of the particles) is 2 μm.

（実施例Ａ－２－３－１）
＜実施例Ａ－２－３－１１（試料番号ｂ５４）
サイドギャップ小側２５μｍ、サイドギャップ大側８５μｍである素体を形成した。評価結果…耐湿性Ｇ。
＜実施例Ａ－２－３－１２（試料番号ｂ５５）＞
サイドギャップ小側２９μｍ、サイドギャップ大側８１μｍである素体を形成した。評価結果…耐湿性Ｇ。
＜実施例Ａ－２－３－１３（試料番号ｂ５６）＞
サイドギャップ小側３３μｍ、サイドギャップ大側７７μｍである素体を形成した。評価結果…耐湿性Ｇ。
＜実施例Ａ－２－３－１４（試料番号ｂ５７）＞
サイドギャップ小側４０μｍ、サイドギャップ大側７０μｍである素体を形成した。評価結果…耐湿性Ｇ。
＜実施例Ａ－２－３－１５（試料番号ｂ５８）＞
サイドギャップ小側４５μｍ、サイドギャップ大側６５μｍである素体を形成した。評価結果…耐湿性Ｇ。
＜実施例Ａ－２－３－１６（試料番号ｂ５９）＞
サイドギャップ小側５０μｍ、サイドギャップ大側６０μｍである素体を形成した。評価結果…Ｇ。
＜実施例Ａ－２－３－１７（試料番号ｂ６０）＞
サイドギャップ小側５５μｍ、サイドギャップ大側５５μｍである素体を形成した。評価結果…耐湿性Ｇ。 Hereinafter, the evaluation of the samples b51 to b60 shown in Table 3 will be described. Samples b54 to b60 are examples of the present invention, and samples b51 to b53 are comparative examples.

(Example A-2-3-1)
<Example A-2-3-11 (Sample No. b54)
A prime field with a small side gap of 25 μm and a large side gap of 85 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-12 (sample number b55)>
A prime field with a small side gap of 29 μm and a large side gap of 81 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-13 (sample number b56)>
A prime field with a small side gap of 33 μm and a large side gap of 77 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-14 (sample number b57)>
A prime field having a small side gap of 40 μm and a large side gap of 70 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-15 (sample number b58)>
A prime field having a small side gap of 45 μm and a large side gap of 65 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-16 (sample number b59)>
A prime field having a small side gap of 50 μm and a large side gap of 60 μm was formed. Evaluation result ... G.
<Example A-2-3-17 (sample number b60)>
A prime field having a small side gap of 55 μm and a large side gap of 55 μm was formed. Evaluation result ... Moisture resistance G.

(Comparative Example A-2-3-1)
<Comparative Example A-2-3-11 (Sample No. b51)>
A prime field with a small side gap of 0 μm and a large side gap of 110 μm was formed. Evaluation result ... Moisture resistance NG.
<Comparative Example A-2-3-12 (Sample No. b52)>
A prime field having a small side gap of 10 μm and a large side gap of 100 μm was formed. Evaluation result ... Moisture resistance NG.
<Comparative Example A-2-3-13 (Sample No. b53)>
A prime field with a small side gap of 18 μm and a large side gap of 92 μm was formed. Evaluation result ... Moisture resistance NG.

From the evaluation results according to Table 3, for the first soft magnetic particles having an average particle size of 21 μm, the small side gap is a range larger than 1 times and smaller than 4 times the particle size of the first soft magnetic particles. It was found that good moisture resistance was obtained.

Hereinafter, the evaluation of the samples b61 to b70 shown in Table 4 will be described. Samples b54 to b60 are examples of the present invention, and samples b51 to b53 are comparative examples.

(Example A-2-3-2)
<Example A-2-3-21 (Sample No. b65)
A prime field with a small side gap of 29 μm and a large side gap of 81 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-22 (sample number b66)>
A prime field with a small side gap of 33 μm and a large side gap of 77 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-23 (sample number b67)>
A prime field having a small side gap of 40 μm and a large side gap of 70 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-24 (sample number b68)>
A prime field having a small side gap of 45 μm and a large side gap of 65 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-25 (sample number b69)>
A prime field having a small side gap of 50 μm and a large side gap of 60 μm was formed. Evaluation result ... Moisture resistance G.
<Example A-2-3-26 (sample number b70)>
A prime field having a small side gap of 55 μm and a large side gap of 55 μm was formed. Evaluation result ... G.

(Comparative Example A-2-3-2)
<Comparative Example A-2-3-21 (Sample No. b61)>
A prime field with a small side gap of 0 μm and a large side gap of 110 μm was formed. Evaluation result ... Moisture resistance NG.
<Comparative Example A-2-3-22 (Sample No. b62)>
A prime field having a small side gap of 10 μm and a large side gap of 100 μm was formed. Evaluation result ... Moisture resistance NG.
<Comparative Example A-2-3-23 (Sample No. b63)>
A prime field with a small side gap of 18 μm and a large side gap of 92 μm was formed. Evaluation result ... Moisture resistance NG.
<Comparative Example A-2-3-24 (Sample No. b64)>
A prime field with a small side gap of 25 μm and a large side gap of 85 μm was formed. Evaluation result ... Moisture resistance NG.

From the evaluation results according to Table 4, for the first soft magnetic particles having an average particle size of 28 μm, the small side gap is a range larger than 1 times and smaller than 4 times the particle size of the first soft magnetic particles. It was found that good moisture resistance was obtained.

[A-2-4. Other considerations]
In the above embodiment, a bisphenol A type epoxy resin, a rubber-modified epoxy resin, and a phenol novolac type epoxy resin are adopted as the resin to be contained in the mixed powder. The superordinate concept of bisphenol A epoxy resin is epoxy resin, and the superordinate concept of rubber-modified epoxy resin is flexible rubber or resin.

Therefore, examples of the resin that can be considered as an alternative to the bisphenol A type epoxy resin include bisphenol A, F, and S type phenoxy resins. Examples of the resin or rubber for which alternative to the rubber-modified epoxy resin can be considered include urethane modification, NBR (Acrylonityl Butadiene Rubber) rubber modification, CTBN (Carboxyl Terminated Butadiene Acrylonirile) rubber modification, and CTBN rubber. In addition, as the resin for which alternatives to the phenol novolac type epoxy resin can be considered, cresol, dicyclopentadiene, phenol aralkyl, biphenyl, naphthol, xylylene, triphenylmethane, and tetrakisphenol ethane can be mentioned as limited to the novolak type. However, if not limited to the novolak type, naphthalene, biphenyl, and triazine can also be mentioned.

[B. coil]
(Conductor)
In the inductor 1, the conducting wire used for the coil 30 may be either a round wire or a flat wire (flat wire in FIG. 3), but by using a flat wire as the conducting wire, the conducting wire is formed when the winding portion 32 is formed. It becomes easy to wind without creating a gap between them.
The number of turns of the winding portion 32 is appropriately determined according to the characteristics realized by the inductor 1.
Further, as the conducting wire, a copper wire made of copper is preferably used.

For example, in the inductor 1, the dimensions of the winding portion 32 of the coil 30 are preferably 1.17 mm in the width W direction, 0.55 mm in the inner diameter, and 0.4 mm in the height.
Further, in the inductor 1 having dimensions in which only the thickness T is changed to 0.55 ± 0.1 mm, the outer shape is 1.17 ± 0.05 mm, the inner diameter is 0.48 ± 0.05 mm, and the height is 0.30. It is preferably ± 0.05 mm.

Here, when the lead wire of the coil 30 is a flat wire, the thickness of the flat wire is preferably 0.118 mm or less, more preferably 0.113 mm or less. By reducing the thickness of the flat wire, the coil 30 becomes smaller even if the number of turns is the same, which is advantageous for miniaturization of the entire coil component. Further, even if the coils 30 have the same size, the number of turns can be increased.

Further, the thickness of the flat wire may be preferably 0.052 mm or more, more preferably 0.77 mm or more. By setting the thickness of the flat wire to 0.052 mm or more, the resistance of the conductor can be reduced.

The width of the flat wire may be preferably 0.203 mm or less, more preferably 0.183 mm or less.
By reducing the width of the flat wire, the coil 30 can be made smaller, which is advantageous for miniaturization of the entire coil component.

Further, the width of the flat line may be preferably 0.141 mm or more, more preferably 0.162 mm or more. By setting the width of the flat wire to 0.141 mm or more, the resistance of the conductor can be reduced.

The aspect ratio (width / thickness) of the flat line may be between 1: 1.3 and 1: 3.4, preferably 1: 1.3.
In the inductor 1 having dimensions such that only the width W is changed to 0.55 ± 0.1 mm, the conductor has a thickness of 0.113 mm, a width of 0.141 mm, and an aspect ratio (width / thickness) of 1: 1.3. Is used for the coil 30.
The smaller the aspect ratio is, the better the coil 30 (lead wire) occupancy in the width W direction with respect to the height H direction of the inductor 1, and the saturation magnetic flux density Bs is reduced while lowering the Rdc (direct current resistance). Can be improved.

(Insulation coating material)
The material for forming the insulating coating layer of the insulating coating material 60 is not particularly limited, and examples thereof include polyurethane resin, polyester resin, epoxy resin, and polyimide amide resin, and polyimide amide resin is preferable.
The thickness of the insulating coating layer is preferably 4 μm.

Examples of the material for forming the fused coating layer of the insulating coating material 60 include a polyamide resin.
The thickness of the fused coating layer is preferably 1 μm or more and 25 μm or less, more preferably 2 μm or more and 25 μm or less, and further preferably 2 μm or more and 4 μm or less.
By setting the thickness of the fusional coating layer to the above value, the fusion force that sufficiently suppresses the peeling of the conducting wire due to the springback at the outermost periphery of the winding portion 32 while suppressing the increase in size of the winding portion 32 of the coil 30. Can be obtained, and the shape defect of the coil 30 can be prevented.

[C. Magnetic circuit]
[C-1. Magnetic powder between lines]
Since the inductor 1 uses a soft magnetic material made of metal magnetic particles as the magnetic material, better DC superimposition characteristics can be obtained as compared with the case where a magnetic material such as ferrite is used. However, in particular, if the magnetic flux density in the vicinity of the winding portion 32 of the coil 30 becomes too large, magnetic saturation may occur.
Here, FIG. 14A is an image showing the lower winding portion 32L of the coil 30 together with the surrounding material, and FIG. 14B is an image showing the upper winding portion 32L of the coil 30 together with the surrounding material. Is. In FIGS. 14A and 14B, the vertical direction of the paper surface corresponds to the height H direction of the prime field 10, and the horizontal direction of the paper surface corresponds to the radial direction of the winding portion 32. Further, in the figure, the reference numeral CW indicates the winding width of the winding portion 32.

In this configuration, in order to prevent the magnetic flux density from being locally saturated, as shown in FIGS. 14A and 14B, a part of the second soft magnetic particles 82, which are small particles, is wound around a winding portion. It is made to enter between 32L to form a magnetic path between the winding portions 32L. The structure in which the second soft magnetic particles 82 are inserted between the winding portions 32L is referred to as an interline magnetic powder structure.

The line magnetic powder structure will be described.
As shown in FIGS. 14A and 14B, the first soft magnetic particles 81, which are large particles, have a larger diameter than those between the winding portions 32L, and therefore do not enter between the winding portions 32L. On the other hand, the second soft magnetic particles 82 have a smaller diameter than the first soft magnetic particles 81 and are formed to have an average diameter smaller than the thickness of the fused coating layer. Therefore, the second soft magnetic particles 82 enter the region 10S between the first soft magnetic particles 81 and the winding portion 32L, and the second soft magnetic particles 82 can easily enter between the winding portions 32L.

In this configuration, the second soft magnetic particles 82 are the first in the prime field molding / curing step of arranging the coil 30 in the mixed powder containing the first and second soft magnetic particles 81 and 82 and performing compression molding. The pressing force P is adjusted to a higher value than before so as to positively enter between the soft magnetic particles 81 and the winding portion 32L. Moreover, since heating is performed during the compression molding, the fusion-bonded coating layer in the insulating coating material 60 on the surface of the winding portion 32L is melted, and the second soft magnetic particles 82 can be easily put into the melted fusion-coated layer. Become.

More specifically, when the pressing force P is applied from above as shown in FIG. 15, the pressing force P acts on the winding portion 32 of the coil 30 and its surroundings from above, and the action and reaction. According to the law, the pressing force P acts from below and from the left and right. As a result, pressure is applied to the second soft magnetic particles 82 from the outer peripheral side of the coil 30 toward each winding portion 32L, and it becomes easy to fill between the winding portions 32L.
The condition of the pressing force P at this time may include not only the value of the pressing force P but also various parameters related to the pressurization such as the time for applying the pressing force P. By appropriately setting this condition, it becomes easy to appropriately fill the second soft magnetic particles 82 between the winding portions 32L. In this case, the second soft magnetic particles are further adjusted by adjusting the heating conditions and the distance between the winding portion 32 and the peripheral wall (inner surface of the molding die 74 and the punch 76). The 82 may be easier to fill between the winding portions 32L.

As shown in FIGS. 14A and 14B, the magnetic flux density is locally increased in the vicinity of the winding portion 32 by forming a magnetic path composed of the second soft magnetic particles 82 between the winding portions 32L. Saturation can be suppressed and DC superimposition characteristics can be improved.

Next, the length of the magnetic path composed of the second soft magnetic particles 82 will be described.
The line width of the winding portion 32L of the coil 30 is 95 μm, the thickness of the winding portion 32L of the coil 30 is 180 μm, the thickness of the fused coating layer between the winding portions 32L of the coil 30 is 6 μm, and the average grain of the first soft magnetic particles 81. Under the conditions that the diameter is 10 μm or more, the average particle size of the second soft magnetic particles 82 is 5 μm or less, and the pressing force P = 300 kg / cm ² , the magnetic path composed of the second soft magnetic particles 82 between the winding portions 32L is 5%. A study was conducted to calculate the DC superimposition rated current Isat by making them different one by one.
The DC superimposition rated current Isat is a current value when the inductance drops by a certain percentage with respect to the initial characteristic in which the current is not superimposed, and is a guideline for the maximum current that can be passed without magnetic saturation. The current value when the current value is about 30% lower than the initial inductance value is defined as the DC superimposition rated current Isat. The examination results are shown in Table 5.

Comparative Example C1-1 is a case where the length of the magnetic path between the winding portions 32L is zero, that is, the second soft magnetic particles 82 do not exist between the winding portions 232L. In Comparative Example C1-2, the length of the magnetic path between the winding portions 32L is set to 5% of the length at which the winding portions 32L are in contact with each other. The length of contact between the winding portions 32L corresponds to the height of the coil 30.
Example C1-1 shows a case where the length of the magnetic path between the winding portions 32L is set to 10% of the length in which the winding portions 32L are in contact with each other. Example C1-2 shows a case where the length of the magnetic path between the winding portions 32L is set to 50% of the length in which the winding portions 32L are in contact with each other. Comparative Example C1-3 shows a case where the length of the magnetic path between the winding portions 32L is set to 55% of the length in which the winding portions 32L are in contact with each other. The DC superimposition rated current Isat has a value of 100 in the case of Comparative Example C1.

As a result of examination by the inventors, when the length of the magnetic path between the winding portions 32L becomes 10% or more, the DC superimposition rated current Isat is compared with the case where the length of the magnetic path between the winding portions 32L is zero. The length of the magnetic path is preferably 10% or more because the increase in the magnetic path is large. However, if the length of the magnetic path between the winding portions 32L exceeds 55%, cracks may occur in the fusion-bonded coating layer that joins the winding portions 32L, and the winding portions 32L may easily peel off from each other.

Considering these circumstances, from the viewpoint of suppressing magnetic saturation and improving the DC superimposition characteristic, it is preferable that the length of the magnetic path between the winding portions 32L is 10% or more, and the winding portions 32L are connected to each other. Considering the viewpoint of suppressing peeling, it was judged that it is preferable to make it 10% or more and 50% or less. Therefore, it is preferable to set the length of the magnetic path between the winding portions 32L in the range of 10% to 50%.

FIG. 16 is a characteristic curve diagram showing a simulation result of an interline magnetic powder structure.
In FIG. 16, the horizontal axis represents the current value, and the vertical axis represents the inductance value (L value). Further, in FIG. 16, Comparative Example C1-4 shows a case where the interline magnetic powder structure is not provided, that is, the surface between the upper and lower stages of the winding portion 32 wound in the upper and lower two stages. The second soft magnetic particles 82 are not present in either the upper winding portion 32L or the lower winding portion 32L.
In Example C1-3, the second soft magnetic particles 82 are present on the entire circumference of the surface between the upper and lower stages of the winding portion 32, between the winding portions 32L of the upper stage, and between the winding portions 32L of the lower stage. It shows the case of making it.
Example C1-4 shows a case where the second soft magnetic particles 82 are present in the upper half between the upper winding portions 32L and the lower half between the lower winding portions 32L.
Example C1-6 shows a case where the second soft magnetic particles 82 are present on the entire circumference between the upper winding portion 32L and the lower winding portion 32L.

Table 6 shows the simulation results of the initial inductance values (initial L values) and the DC superimposition rated current Isat of Comparative Examples C1-4 and Examples C1-3 to C1-6. The conditions such as the line width and thickness of the coil 30 and the thickness of the fused coating layer are the same as in Table 5.

As shown in FIG. 16, in Examples C1-3 to C1-6, a large inductance value is obtained in a wide current range of 0A to 10A as compared with Comparative Example C1-4, and magnetic saturation is suppressed. It can be confirmed that the DC superimposition characteristics are improved. Further, as shown in Table 6, it is clear that the DC superimposition rated current Isat of Examples C1-3 to C1-6 exceeds that of Comparative Example C1-4.
Further, the characteristics (inductance value and DC superimposition rated current Isat) of Examples C1-3 and C1-6 are almost the same, and the inductance is larger than that of other Examples C1-4 and C1-5. The value is obtained. Examples C1-3 and C1-6 have in common that the second soft magnetic particles 82 are present between the upper winding portion 32L and the lower winding portion 32L, and this point is magnetic. It can be presumed that it is advantageous to suppress saturation and improve the DC superimposition characteristic.

As described above, the core 40 in which the coil 30 is embedded includes the first soft magnetic particles 81 of large particles and the second soft magnetic particles 82 of small particles, and a part of the second soft magnetic particles 82 is the first. Since it enters the region 10S between the soft magnetic particles 81 and the winding portion 32L of the coil 30 and enters between the winding portions 32L to form a magnetic path between the winding portions 32L, good DC superimposition characteristics can be obtained. It is possible to suppress the local saturation of the magnetic flux density even by using the magnetic particles obtained.

Further, since the second soft magnetic particles 82 exist between the winding portions 32L over a length of 10% or more of the length in which the adjacent winding portions 32L are in contact with each other, the magnetic flux is higher than that in the case of less than 10%. Local saturation of density, that is, magnetic saturation can be further suppressed.
Further, the second soft magnetic particles 82 are configured to exist between the winding portions 32L over a length of 50% or less of the length in which the adjacent winding portions 32L are in contact with each other. It becomes easy to avoid a situation in which cracks occur in the fusion-bonded coating layer to which the two wound portions 32L are joined and the winding portions 32L are easily peeled off from each other.

Further, the adjacent winding portions 32L are bonded to each other by a fusion agent made of a fusion coating layer, and the second soft magnetic particles 82 are formed to have a diameter smaller than the thickness of the fusion coating layer, and the second soft magnetic particles are formed. Since a part of 82 enters the fusional coating layer and forms a magnetic path between the winding portions 32L, it is possible to efficiently form a magnetic path between the winding portions 32L while joining the adjacent winding portions 32L to each other. , It becomes easy to effectively suppress magnetic saturation.

Further, when the material of the core 40 (first and second soft magnetic particles 81, 82, etc.) and the material composed of the coil 30 are compression-molded to form the prime field 10, a part of the second soft magnetic particles 82 is formed. At least the pressing force P at the time of compression molding is adjusted so as to enter the region 10S, so that a magnetic path can be easily provided between the winding portions 32L.
The method of inserting a part of the second soft magnetic particles 82 into the winding portion 32L does not have to be limited to the conditions of the pressing force P, the heating conditions, and the like. For example, the second soft magnetic particles may be appropriately combined by adjusting the diameters of the first and second soft magnetic particles 81 and 82, adjusting the slipperiness of the surface layer between the first and second soft magnetic particles 81 and 82, and selecting the resin. The 82 may be easily inserted into the region 10S.

Further, when the coil 30 has a winding portion 32 wound in multiple upper and lower stages (including two or more stages) with the conducting wire connected, the first is between the winding portion 32L of the uppermost stage and / or the lowermost stage. 2 It is preferable that the soft magnetic particles 82 are present. This makes it easier to provide a magnetic path that is effective in suppressing magnetic saturation.
The material of the core 40 may be appropriately increased or decreased or changed as long as a part of the second soft magnetic particles 82 can be inserted between the winding portions 32L, the coil 30 and the like. The shape of the may be changed as appropriate. Further, the present invention is not limited to the case where the second soft magnetic particles 82 are allowed to enter the region 10S during the element molding / curing step, and the second soft magnetic particles 82 may be made to enter the region 10S by another method. good.

Further, the winding method of the coil 30 is not limited to the alpha winding, and may be, for example, edgewise winding. Even in the case of edgewise winding, the magnetic path is formed by the second soft magnetic particles 82 between the adjacent winding portions 32L joined by the fused coating layer, so that magnetic saturation can be effectively suppressed. ..

[C-2. Magnetic gap]
In order to further suppress the saturation of the magnetic flux density in the vicinity of the winding portion 32 of the coil 30 with respect to the inductor 1, a magnetic gap may be provided in the vicinity of the winding portion 32.
FIG. 19 is an image when an air gap 40K, which is a magnetic gap, is provided in the vicinity of the winding portion 32.
The air gap 40K extends in the alignment direction of the winding portions 32L and is substantially orthogonal to the magnetic flux. The air gap 40K is formed during the prime field molding / curing process. More specifically, as shown in FIG. 15, by applying a pressing force P to the top, bottom, left, and right of the coil 30, the first and second soft magnetic particles which are core materials are applied around the winding portion 32 of the coil 30. 81, 82 and the like are compressed. After that, the punch 76 is quickly evacuated, or the prime field 10 is taken out from the mold in a state where the core material is not completely solidified, thereby causing springback (repulsion) of the first and second soft magnetic particles 81, 82 and the like. The force) is used to form an air gap 40K as shown in FIG. 17 around the winding portion 32.

This springback includes at least one repulsion between the first soft magnetic particles 81, the second soft magnetic particles 82, and the first and second soft magnetic particles 81, 82. By appropriately utilizing these repulsions, an air gap 40K that functions as a magnetic gap is formed. The springback may include a repulsion between the coil 30 and the core 40 (first and second soft magnetic particles 81, 82).

That is, by appropriately adjusting various conditions at the time of compression molding such as the pressing force P at the time of compression molding, the pressurizing speed, the pressurizing time, the saving speed of the punch 76, and the take-out timing of the prime field 10, the winding portion 32L An air gap 40K extending in the arrangement direction of the winding portion 32L is formed around the winding portion 32L. As a result, an air gap 40K that functions as a magnetic gap can be easily provided, and the air gap 40K can suppress saturation of the magnetic flux density in the vicinity of the winding portion 32 of the coil 30 and improve the DC superimposition characteristic.

Next, the position, length and width of the air gap 40K will be described.
The wire width of the winding portion 32L of the coil 30 is 95 μm, the thickness of the winding portion 32L of the coil 30 is 180 μm, the thickness of the fused coating layer of the winding portion 32L of the coil 30 is 4 μm, and the average grain of the first soft magnetic particles 81. Under the conditions that the diameter is 10 μm or more, the average particle size of the second soft magnetic particles 82 is 5 μm or less, and the pressing force P = 300 kg / cm ² , the position, length, and width of the air gap 40K are different, and the DC superimposition rated current Isat. Was examined to calculate. The DC superimposition rated current Isat is a current value when the current is about 30% lower than the initial inductance value.

Table 7 shows the results of examining the position of the air gap 40K. The DC superimposition rated current Isat in Table 7 shows the case where the value 100 is the case where the air gap 40K is located at the position of 11 μm from the winding portion 32.

As shown in Table 7, when the air gap 40K is in the range of 30 μm from the winding portion 32, the value of the DC superimposition rated current Isat increases as the distance from the winding portion 32 increases, and when it exceeds 50 μm, the value of Isat becomes 100. It fell below. According to the studies by the inventors, the range of the air gap 40K within the range of 50 μm from the winding portion 32 is an effective range for suppressing magnetic saturation, in other words, 5 of the average particle size of the first soft magnetic particles 81. Within double the distance was a suitable range for suppressing magnetic saturation. More preferably, the air gap 40K is in the range of 20 μm or more and 30 μm or less from the winding portion 32.

Table 8 shows the examination results of the length KL of the air gap 40K (see FIG. 17). The DC superimposition rated current Isat in Table 8 shows a case where the length KL of the air gap 40K is 10% of the winding width CW (FIG. 17) of the winding portion 32, and the value is 100.

As shown in Table 8, the value of the DC superimposition rated current Isat increased as the air gap 40K became longer up to 110% of the winding width CW of the winding portion 32. According to the study by the inventors, it is effective to suppress magnetic saturation when the length KL of the air gap 40K is equal to or larger than the width of a single winding portion 32L (33% or more of the winding width CW). rice field.
On the other hand, when the length KL of the air gap 40K greatly exceeds the winding width CW, more specifically, when it exceeds 110% of the winding width CW, the region where the air gap 40K is parallel to the winding shaft or the winding shaft of the coil 30. There is a risk that the inductance value will drop significantly.

Therefore, the inventors have stated that the length KL of the air gap 40K is equal to or larger than the width of a single winding portion 32L (corresponding to 33% or more of the winding width CW of the winding portion 32), and the winding width CW of the winding portion 32. 110% or less, more preferably 1.5 times or more the width of a single winding portion 32L (50% or more of the winding width CW of the winding portion 32), and the winding width CW or less of the winding portion 32. It was judged that (100% or less) was good.

Table 9 shows the examination results of the width KW (see FIG. 17) of the air gap 40K. This width KW corresponds to the length of the air gap 40K orthogonal to the arrangement direction of the winding portions 32L. The DC superimposition rated current Isat in Table 9 shows a case where the width KW of the air gap 40K is less than 1 μm, which is less than the diameter of the minimum particle, as a value of 100.

As shown in Table 9, until the width KW of the air gap 40K is 10 μm, the value of the DC superimposition rated current Isat increases as the width KW increases, and the value of the DC superimposition rated current Isat is the same at 10 μm and 11 μm. Further, when the width KW of the air gap 40K exceeds 11 μm, the width KW becomes larger than the average particle size of the first soft magnetic particles 81, and the soft magnetic particle adhesion strength of the resin adhered to the first soft magnetic particles 81. Is weakened, and cracks are likely to occur in the prime field 10 along the extending direction of the air gap 40K.
Therefore, the width KW of the air gap 40K is preferably at least the average particle size (5 μm) of the second soft magnetic particles 82 and at least 11 μm, and more preferably at a value close to 10 μm within a range in which cracks in the prime field 10 can be suppressed. Is preferable.

FIG. 18 is a characteristic curve diagram showing simulation results depending on the presence or absence of an air gap of 40K. In FIG. 18, the horizontal axis shows the current value, the vertical axis shows the inductance value (L value), the characteristic curve K1 shows the case without the air gap 40K, and the characteristic curve K2 shows the upper and lower parts of the winding portion 32. , The case where the air gap 40K extends in both the longitudinal direction and the lateral direction of the winding portion 32 on the inner circumference and the outer circumference is shown.

Table 10 shows the simulation results of the initial inductance value (initial L value) corresponding to each of the characteristic curves K1 and K2 and the DC superimposition rated current Isat. The conditions such as the line width and thickness of the coil 30 and the thickness of the fused coating layer are the same as those in Tables 5 and K2.

As shown in FIGS. 18 and 10, it can be seen from the simulation results that the magnetic saturation can be suppressed when the air gap is 40K, and in particular, the magnetic saturation suppressing effect can be obtained in the range of the current value of 0 A or more and 6 A or less. You can check it.

In this way, in the element body 10, the winding portions 32L are lined up on the outer periphery of the winding portion 32 of the coil 30 and within a distance of 5 times the average particle size of the first soft magnetic particles 81 from the winding portion 32. Since it has an air gap of 40K extending in the direction, it is possible to suppress magnetic saturation even by using magnetic particles that can obtain good DC superimposition characteristics.

Moreover, the air gap 40K has a length equal to or greater than the width of a single winding portion 32L and equal to or less than the winding width CW of the winding portion 32 in the direction in which the winding portions 32L are lined up, and is in the radial direction of the winding portion 32L. Since the width is equal to or more than the average particle size of the second soft magnetic particles 82 and not more than 10 μm, magnetic saturation can be effectively suppressed.

Further, since the air gap 40K is formed by using the springback when the material of the core 40 and the material of the coil 30 are compression-molded to form the prime field 10, the air gap 40K is easily provided. be able to.
The material of the core 40 may be appropriately increased or decreased or changed as long as the air gap 40K can be formed, or the shape of the coil 30 or the like may be appropriately changed. Further, the case is not limited to the case where the air gap 40K is formed during the element molding / curing step, and the air gap 40K may be formed by another method.

[D. Prime field grinding]
In this embodiment, a mixed powder of a soft magnetic powder and a resin composed of large particles having a large average particle size and small particles having an average particle size smaller than the large particles is compression-molded on the element body 10 of the inductor 1. A molded body is used.

In the prime field grinding step shown in FIG. 4, as described above, in the step of applying abrasive grains to the second side surface 18 (FIG. 1) of the prime field 10 after compression molding until the width W becomes a predetermined width. be. By this grinding, the prime field 10 is downsized to a predetermined size, and the occupancy rate of the coil 30 in the prime field 10 is increased. Further, by adopting a method of downsizing the prime field 10 by grinding and processing it to a predetermined size, the size of the prime field 10 is controlled to a predetermined size by adjusting the size of the cavity of the molding die. Dimensional variation can be reduced. After this grinding, for example, barrel polishing may be performed on the second side surface 18 in order to chamfer the corners generated by the grinding.

(Grinding device)
FIG. 19 is a diagram schematically showing an example of a grinding device 101 used for prime field grinding.
The grinding device 101 includes a holder 102 that holds the prime field 10 (work) to be ground, an upper grindstone 103 that sandwiches the prime field 10 held by the holder 102, and a lower grindstone 104. The holder 102 holds the prime field 10 in a posture in which the second side surface 18, which is the grinding surface, is turned up and down.
At the time of element grinding, the grinding device 101 presses the upper grindstone 103 and the lower grindstone 104 against the upper and lower second side surfaces 18 with a predetermined load, and the upper grindstone 103 and the lower grindstone 104 are pressed against the upper and lower second side surfaces 18. By moving relative to each other, the upper and lower second side surfaces 18 are simultaneously ground by the abrasive grains 105 of the upper grindstone 103 and the lower grindstone 104 (so-called double-sided grinding).

(Size of abrasive grains)
The size of the abrasive grains 105 is proportional to the grinding rate, and the inventor's experiment shows that the larger the abrasive grains 105, the more the particles of the soft magnetic powder are shed on the ground surface and the surface roughness becomes larger. Has been confirmed by.
More specifically, when the molded body of the soft magnetic powder is ground, the particles of the soft magnetic powder are not a little deflated by the abrasive grains 105, and dents due to the chipping of the particles are generated on the ground surface. In the soft magnetic powder composed of large particles and small particles, the large particles are easier to degranulate than the small particles, and the larger the abrasive grain 105, the more large particles are degranulated, so that a relatively large dent is formed on the ground surface. It occurs frequently, which increases the surface roughness of the ground surface.
Regarding the surface roughness, it has been confirmed by the inventor's experiment that there is no correlation between the surface roughness and the load.

In this example, the arithmetic mean height was used to evaluate the surface roughness. Specifically, a plurality of measurement areas (for example, 3 to 4 points) having a predetermined size (about 200 μm × 290 μm in this embodiment) are set on the surface to be measured, and the maximum height in each measurement area is determined by a laser microscope. The calculated average height was calculated from the average of these maximum heights. A model VK-X250 manufactured by KEYENCE CORPORATION was used as the laser microscope.

(Grinding speed)
As the grinding speed (moving speed of the upper grindstone 103 and the lower grindstone 104) increases, the particles of the soft magnetic powder are cut and the surface roughness of the ground surface becomes lower, and the grinding speed is proportional to the above-mentioned grinding rate. This has been confirmed by the inventor's experiment.

(Grinding rate)
For the grinding rate, a target value is appropriately set, and the size and grinding speed of the abrasive grains 105 required to realize the target value are determined. As described above, the size of the abrasive grains 105 and the grinding speed are each related to the surface roughness of the ground surface. In this embodiment, the surface roughness after grinding is made larger than that before grinding, and the roughness of the second side surface 18 after grinding is made larger than the top surface 14 and the mounting surface 12 which are the surfaces not to be ground. As described above, the size of the abrasive grains 105 and the grinding speed are set.
By increasing the surface roughness Sa by grinding, the fixing strength of the prime field protective film 50 covering the second side surface 18 of the prime field 10 is increased. The surface of the prime field 10 is covered with the prime field protective film 50 except for the external electrode 20, and the prime field protective film 50 enhances the moisture resistance, rust resistance, and electrical insulation of the prime field 10. There is.

(Grinding time)
The grinding time is defined by the time from the grinding start timing Ts to the grinding end timing Te. Determined based on.
At the time of grinding the prime field, the control device (not shown) controls the grinding operation of the grinding device 101 based on the load profile 106 and the grinding time, so that the width W of the prime field 10 after compression molding becomes a predetermined width. Grinding is performed until it becomes.

(Side gap)
As shown in FIG. 20, the side gap Sg is defined by the thickness of the inductor 1 from the coil 30 inside the prime field 10 to the nearest second side surface 18. When the prime field 10 is covered with the prime field protective film 50, the side gap Sg is the thickness excluding the prime field protective film 50.
Then, in this embodiment, in the prime field 10 in which the width W is ground to a predetermined width, the side gap Sg is larger than the thickness corresponding to the average particle size of the large particles of the soft magnetic powder for one piece, and 4 It is smaller than the thickness corresponding to the average particle size of the large particles of the soft magnetic powder for each piece. In other words, in this embodiment, the predetermined width and the width WLa (FIG. 20) of the winding portion 32 of the coil 30 are set so that the side gap Sg of the prime field 10 ground to a predetermined width has such a thickness. Both or one is pre-adjusted.

In the element body 10 after grinding, the thickness of the side gap Sg is made larger than the thickness corresponding to the average particle size of at least one large particle of the soft magnetic powder, so that the second side surface 18 is threshed by grinding. Even if it occurs, at least one large particle remains between the second side surface 18 and the coil 30, so that the coil 30 is prevented from being exposed.
Further, in the prime field 10 after grinding, the thickness of the side gap Sg is limited to a range smaller than the thickness corresponding to the average particle size of the four large particles of the soft magnetic powder, so that the size of the prime field 10 is increased. It is possible to maintain the occupancy rate of the coil 30 at a sufficiently high value and prevent a decrease in inductance while preventing the above.

Tables 11 and 12 show the maximum and minimum values of the side gap Sg in the inductor 1, the inductance value of the inductor 1, and the measurement results of the moisture resistance.
Table 11 measures the inductor 1 having an average particle size of 21 μm and 2 μm, respectively, for the large particles and the small particles of the soft magnetic powder, and Table 12 shows the average of the large particles and the small particles of the soft magnetic powder. The inductor 1 having a particle size of 28 μm and 2 μm, respectively, was measured.

As the soft magnetic powder, a magnetic powder composed of chromeless Fe—Si based amorphous alloy powder and crystalline pure iron is used, and the particles of the chromeless Fe—Si based amorphous alloy powder correspond to large particles. , Pure iron corresponds to small particles. The surface of the large particles is covered with an oxide film in which a SiO layer and a Fe ₂ SiO ₄ layer are laminated, and the surface of the small particles is covered with an oxide film of Fe. Have.
Then, the element body 10 of the inductor 1 is molded by compression-molding the mixed powder of the soft magnetic powder and the epoxy resin.
Therefore, a resin, an oxide of Fe or Fe, a phosphate glass, and an alkyl group having a chain length of SiO ₂ and 16 carbon atoms are present on the surface of the prime field.

The inductance value is measured with an LCR meter, and the humidity resistance is tested by exposing the inductor 1 to an environment where the temperature is 85 ° C and the humidity is 85%. Those that do not meet are referred to as "NG".

As shown in Tables 11 and 12, it can be seen that sufficient moisture resistance can be obtained when the minimum value of the side gap Sg is larger than the average particle size of one large particle. Further, it can be seen that the inductance value decreases as the maximum value of the side gap Sg increases.
Further, in the range where the minimum value of the side gap Sg is larger than the average particle size of one large particle and the maximum value of the side gap Sg is smaller than the average particle size of four large particles, the side gap Sg It can be seen that when the ratio of the minimum value to the maximum value is 1: 1, the inductor 1 having good moisture resistance and inductance value can be obtained.

As described above, the inductor 1 of the present embodiment is an inductor 1 in which a pair of external electrodes 20 are provided on a base 10 made of a plate-shaped molded body in which a coil 30 is embedded, and the base 10 is a base 10. The side gap Sg, which is formed from a mixed powder of soft magnetic powder and resin composed of large particles and small particles having different average particle sizes, and has a thickness from the second side surface 18 located in the radial direction of the coil 30 to the coil 30. Is larger than the thickness corresponding to one large particle and smaller than the thickness corresponding to four large particles.

The thickness of the side gap Sg of the prime field 10 is larger than the thickness corresponding to the average particle size of at least one large particle of the soft magnetic powder, so that at least one large particle is coiled with the second side surface 18. It exists between 30 and is in a state where the exposure of the coil 30 is prevented.
Further, the thickness of the side gap Sg of the prime field 10 is limited to a range smaller than the thickness corresponding to the average particle size of the four large particles of the soft magnetic powder, thereby preventing the prime field 10 from becoming large. While maintaining the occupancy rate of the coil 30 at a sufficiently high value, it is possible to prevent a decrease in inductance. As a result, it is possible to realize the inductor 1 which can obtain a practical DC resistance and a saturation magnetic flux density while being compact.

In the inductor 1 of this embodiment, the second side surface 18 of the prime field 10 is covered with the prime field protective film 50, and the surface roughness is higher than that of at least one or more other surfaces (mounting surface 12 and top surface 14). Is big.
As a result, the adhesive strength between the second side surface 18 and the prime field protective film 50 can be increased.

In the inductor 1 of this embodiment, the surface of the prime field 10 is covered with the prime field protective film 50 except for the external electrode 20.
As a result, the moisture resistance, rust resistance, and electrical insulation of the prime field 10 are enhanced, and a high-quality inductor 1 can be obtained.

[E. Prime field protective film]
In this embodiment, a mixed powder of a soft magnetic powder and a resin composed of large particles having a large average particle size and small particles having an average particle size smaller than the large particles is compression-molded on the element body 10 of the inductor 1. A molded body is used.

The prime field protective film 50 is a layer that covers the entire surface of the prime field 10 except for the portion of the external electrode 20 and enhances the electrical insulation and rust resistance of the prime field 10. Even if large particles of soft magnetic powder are deflated on the ground surface (second side surface 18) in the above-mentioned element grinding step, the element body protective film 50 covers the ground surface to provide electrical insulation and rust prevention. It is possible to prevent deterioration of sex.

(Prime field protective film forming process / protective film forming device)
As described with reference to FIG. 4, the prime field protective film 50 is sprayed (sprayed) or dip (immersed) with a protective film material containing a thermosetting resin on the entire surface of the prime field 10 in the prime field protective film forming step. ), Etc., it is formed by applying it by an appropriate method.

FIG. 21 is a diagram schematically showing an example of a protective film forming apparatus 201 used for forming a protective film for a prime field.
The protective film forming device 201 is a device that coats the surface of a large number of elements 10 which are the work 208 by spraying the protective film material. As shown in the figure, the protective film forming apparatus 201 is rotatably provided on the apparatus main body 202, and has a drum 203 into which a large number of elements 10 (work 208) are charged, a heater 204 for supplying heat, and a drum. It includes a duct 205 as an exhaust path of the 203 and a spray nozzle 206 arranged in the drum 203.

At the time of forming the element protective film, the protective film forming apparatus 201 preheats the drum 203 into which a large number of elements 10 are charged to a temperature (for example, 30 to 70 ° C.) at which the heater 204 does not heat cure (preheating step).
Next, the protective film forming apparatus 201 rotates the drum 203 (so-called barrel rotation) to stir the prime field 10, sprays the protective film material from the spray nozzle 206 onto the prime field 10, and uses an air nozzle (not shown). Hot air 207 is sprayed onto the prime field 10 to coat the surface of the prime field 10 with the prime field protective film 50 (coating step). At the final stage of this coating step, the protective film forming apparatus 201 stops spraying the protective film material, while stirring the prime field 10 and blowing hot air 207 onto the prime field 10, so that the prime field 10 is primed. The protective film 50 is appropriately dried (drying step). Then, after the prime field protective film 50 is dried, the prime field 10 is taken out from the drum 203 (work take-out step).

If the drying is insufficient in the drying step, pores (pores) and swelling occur in the prime field protective film 50, and the adhesion of the prime field protective film 50 to the prime field 10 also deteriorates. When the drying is excessive, the element protective film 50 becomes a so-called discontinuous film, and the adhesion of the element protective film 50 to the element 10 also deteriorates. Therefore, it is preferable that the drying is performed to an appropriate degree so that the prime field protective film 50 becomes a so-called continuous film and the adhesion of the prime field protective film 50 to the prime field 10 is well maintained.

(Protective film material)
As the protective film material, a mixed solution of a resin type which is a base material of the prime field protective film 50, a solvent type which dilutes the resin type, and a filler type which is an additive is used.

(Resin type)
As the resin type, a resin containing an epoxy resin as a main component and one or both of a phenoxy resin and a novolak resin added is preferably used. The toughness of the prime field protective film 50 is enhanced by adding the phenoxy resin. The heat resistance of the prime field protective film 50 is enhanced by adding the novolak resin.
It is preferable that the resin of the resin type contains a pigment.
By using a resin containing a pigment, in the prime field protective film forming step and the external electrode forming step shown in FIG. 4, the surface of the prime field 10 is irradiated with laser light to remove the prime field protective film 50 and the external electrode is used. The workability when forming 20 can be improved. For the pigment, for example, carbon black is preferably used.

(Solvent type)
As the solvent type, a solvent that can spray the resin seed in the form of mist in the above coating step and that can obtain appropriate drying property in the drying step is used, for example, methyl ethyl ketone (MEK) used as a diluent for a paste-like resin. A solvent containing the above is preferably used.

(Filler type)
As the filler type, a filler that reduces the gloss of the prime field protective film 50 and improves the film quality of the prime field protective film 50 and is dispersed in a solvent is used.
By reducing the gloss of the prime field protective film 50, it is possible to prevent erroneous determination due to color skipping during an appearance inspection of the inductor 1 using a camera. Silica (SiO ₂ ) powder is preferably used as such a filler.
Further, as for the filler type, the smaller the particle size of the filler, the smaller the size of the filler particles, in order to prevent clogging of the spray nozzle 206 that sprays the protective film material and to reduce damage to the surface of the prime field 10 due to the rotation of the barrel of the drum 203. It is preferable to use nanosilica when silica powder is used as a filler.

(Nano silica)
The inventor has experimentally found that when nanosilica is used as a filler, there is a correlation between the drying rate in the drying step performed at the end of the coating step and the content of nanosilica.

FIG. 22 is a diagram showing experimental results of nanosilica content and drying rate.
In this experiment, a sample of the protective film material was prepared using epoxy resin as the resin type, MEK as the solvent type, and nanosilica as the filler type, and this sample was used to form the prime field protective film 50 on the prime field 10. The external electrode 20 was formed to form the inductor 1. Then, in the drying step of the prime field protective film 50, the relationship between the drying leaving time and the solid content of the prime field protective film 50 was investigated.
Four samples of the protective film material were prepared, in which the content of nanosilica was 0 (no content), 50 phr, 100 prh, and 200 phr. In each sample, nanosilica composed of silica particles having an average particle size of 45 nm is used as a filler.
The average particle size of the silica particles in the inductor 1 intersects the intersections where the four corners of the top surface 14 are diagonally connected, and cuts the prime field 10 in parallel with the second side surface 18, so that the prime field 10 is formed. On the upper and lower second side surfaces 18, the cross section of the prime field protective film 50 is magnified 300,000 times using a transmission electron microscope (TEM) at each of the points where the length L of the prime field 10 is divided into four equal parts. A picture was taken and silica particles were observed. For the transmission electron microscope, measurement was performed using a field emission transmission electron microscope (FE-TEM). This field emission transmission electron microscope is equipped with an energy dispersive X-ray analyzer (EDX) system (model number: NORAN System 7 manufactured by Thermo Fisher Scientific Co., Ltd.), which is manufactured by JEOL Ltd. A functional electron microscope (model number: JEM-F200) was used.

As shown in FIG. 22, it can be seen that the larger the content of nanosilica, the higher the solid content even after a short drying time. That is, by increasing the content of nanosilica in the protective film material, the drying rate can be increased and the process time of the drying step can be shortened.

As a result of observing the prime protective film 50 after drying in this experiment, when the fixed content after drying is 80% or less, "sticking" described later occurs, and when the solid content is about 90%. It was found that although a prime field protective film 50 having a good film quality was obtained, cracks were generated on the surface of the prime field protective film 50.
Therefore, in the drying step, it is preferable to dry so that the fixed content is in the range of 80% to 90%.

(Sticking)
"Adhesion" is a phenomenon in which the element protective films 50 of the element 10 adhere to each other when a plurality of elements are put into the drum 203 and spray-applied in the coating process, and the quality of the element protective film 50 is obtained. It becomes a factor of decline. The inventor has experimentally found that when nanosilica is used as a filler, "sticking" during the coating process can be suppressed by changing the particle size of the silica particles of the nanosilica.

FIG. 23 is a diagram showing the experimental results of the average particle size of the silica particles of nanosilica and the rate of occurrence of sticking.
In this experiment, two samples 1 and 2 were prepared as protective film materials.
Sample 1 is a protective film material using epoxy resin as the resin type, PGM as the solvent type, and nanosilica as the filler type. Sample 2 uses epoxy resin as the resin type, MEK as the solvent type, and nanosilica as the filler type. It is a protective film material. In each of Samples 1 and 2, the content of nanosilica was set to 200 phr.
Then, in the coating step, the prime field protective film 50 is coated on the prime field 10 using the respective samples 1 and 2, and then the prime field 10 is adhered to each other when the prime field 10 is taken out from the drum 203 in the work removal step. By counting the number of prime fields 10 in the state, the sticking occurrence rate was obtained.

As shown in FIG. 23, it can be seen that the smaller the average particle size of the silica particles, the lower the rate of occurrence of sticking.
Comparing Sample 2 using MEK as the solvent type and Sample 1 using PGM as the solvent type, it can be seen that when the average particle size of the silica particles is the same, the rate of occurrence of sticking is lower in Sample 2.
Further, regarding the sample 2, it can be seen that when the average particle size of the silica particles is 45 nm or less, the sticking occurrence rate is remarkably reduced.

In both Samples 1 and 2, when the average particle size of the silica particles is reduced to about 12 nm, the sticking occurrence rate is suppressed to almost zero.
However, when the average particle size of the silica particles was 12 nm, the occurrence of cracks shown in FIG. 24 was observed on the surface of the element protective film 50 after formation in both Samples 1 and 2. Therefore, the average particle size of the silica particles is preferably larger than 12 nm, and more preferably 15 nm or more in which the generation of cracks is more reliably suppressed.

Further, it was observed that when the average particle size of the silica particles became larger than 75 nm, the filler was significantly precipitated in the protective film material. When this protective film material is used for a coating film, a uniform prime field protective film 50 cannot be obtained even if adhesion does not occur. Therefore, the average particle size of the silica particles is preferably 75 nm or less, which is the particle size at which precipitation does not occur in the protective film material.

When the prime field protective film 50 is formed by using a protective film material containing silica particles (silica powder) having an average particle size of 15 nm to 75 nm only in a content (150 phr to 250 phr) that can obtain a sufficient drying rate. In the prime field protective film 50 after formation, the weight ratio of the silica particles to the resin is approximately 150% to 250%.
In other words, when the prime field protective film 50 having such a weight ratio is formed, it indicates that the prime field protective film 50 is formed at a high drying rate and without "sticking", and is high. It can be said that a high-quality prime field protective film 50 is obtained.

(Plating skip)
FIG. 25 is a diagram showing the results of measuring the number of “plating skips” by changing the thickness of the prime field protective film 50.
“Plating skipping” means that a portion where the prime field protective film 50 is not applied occurs on the surface of the prime field 10, and plating is formed on an unintended portion. For example, if large particles of soft magnetic powder are shed by grinding the prime field and a relatively large dent is formed on the surface of the prime 10, the protective film material cannot sufficiently enter the dent and "plating". It becomes a factor that causes "flying".

In this measurement, it is confirmed whether or not there is "plating skipping" at predetermined measurement intervals on all sides of the ridgeline portion where the top surface 14 and the mounting surface 12 of the prime field 10 and the first side surface 16 and the second side surface 18 intersect. Then, the number of places where "plating skipping" occurred was counted.

As can be seen from the figure, when the thickness of the prime field protective film 50 becomes small, many "plating skips" occur, but when the thickness is 5 μm or more, the number of “plating skips” decreases remarkably and 10 μ or more. If so, it can be seen that "plating skipping" has not occurred.
Therefore, the thickness of the prime field protective film 50 is preferably 10 μm or more, and by setting such a thickness, the occurrence of “plating skipping” is suppressed and the entire surface of the prime field 10 is reliably covered by the prime field protective film 50. Can be protected.

However, when the size of the prime field 10 of the inductor 1 is specified, as the thickness of the prime field protective film 50 increases, the size of the prime field 10 excluding the prime field protective film 50 is reduced by that amount, and the coil. Since 30 becomes smaller, the performance of the inductor 1 deteriorates.
Further, in the inductor 1, since the external electrode 20 is formed at the position where the prime field protective film 50 is removed, if the prime field protective film 50 is thicker than the external electrode 20, the external electrode 20 is the surface of the prime field protective film 50. The contact property between the external electrode 20 and the substrate is deteriorated without protruding from the surface.
Therefore, the thickness of the prime field protective film 50 is preferably at least the thickness of the external electrode 20 or less. In this embodiment, in the case of the inductor 1 having a height H of 0.7 ± 0.1 mm, a width W of 1.2 ± 0.2 mm, and a length L of 2.0 ± 0.2 mm, the external electrode 20 The thickness is in the range of 0.58 mm to 0.75 mm, the height H is 0.55 ± 0.1 mm, the width W is 1.2 ± 0.2 mm, and the length L is 2.0 ± 0.2 mm. In the case of the inductor 1 of the size of, the thickness of the external electrode 20 is 0.58 mm to 0.75 mm, and is in the range of 0.43 to 0.60 mm. The prime field protective film 50 is more preferably 30 μm or less in order to obtain a high-performance inductor 1 even in the range of the thickness or less of the external electrode 20.
The thickness of the external electrode 20 was measured as follows. That is, in the inductor 1, the prime field 10 is cut in parallel with the second side surface 18 by intersecting the intersections connecting the four corners of the top surface 14 diagonally, and formed on the mounting surface 12 of the prime field 10. The film thickness of the point obtained by dividing the length direction of the external electrode 20 into four equal parts was measured by magnifying it 1000 times using a microscope, and the average of each was obtained as the first measured value. Then, the first measured value was obtained for 10 inductors 1, and the average of each first measured value was taken as the thickness of the external electrode 20. The model number VHX-7000 manufactured by KEYENCE CORPORATION is used for the microscope.

(Countermeasures against threshing)
When the surface of the prime field 10 which is a molded body is ground, as described above, not a few particles of soft magnetic powder are shed during grinding. In this embodiment, since a soft magnetic powder composed of large particles having a large average particle size and small particles having a small average particle size is used, a relatively deep dent is formed on the ground surface due to the degraining of the large particles (in this embodiment). It occurs on the second side surface 18).

Table 13 is a diagram showing the experimental results of the thickness of the prime field protective film 50, the depth of the dent caused by the shedding, and the rust prevention performance.
The same sample as in the experiment shown in FIG. 23 was used as the protective film material for this experiment. As the soft magnetic powder used for molding the prime field 10, large particles having an average particle size of 21 μm to 28 μm are used.
The thickness of the prime field protective film 50 was measured as follows. That is, in the inductor 1, the prime field 10 is cut in parallel with the second side surface 18 by intersecting the intersections connecting the four corners of the top surface 14 diagonally, and the upper and lower second side surfaces of the prime field 10 are cut. At 18, the film thickness of the prime field protective film 50 was measured by magnifying 1000 times using a microscope at each of the points where the length L of the prime field 10 was divided into four equal parts, and the average of each was measured as the second measured value. Asked as. Then, the second measured value is obtained for 10 inductors 1, and the average of each second measured value is used as the measured value of the thickness (average thickness). The model number VHX-7000 manufactured by KEYENCE CORPORATION is used for the microscope.
As for the rust resistance, those that do not meet the predetermined product quality standards are "NG", and those that satisfy the rust resistance are "G".

As shown in Table 13, if the thickness of the prime field protective film 50 is small with respect to the depth of the dent due to grain removal, the rust resistance is poor, and it is found that the quality of the prime field protective film 50 is not sufficient. It can be seen that when the ratio of the thickness of the prime field protective film 50 to the rust is 0.4 or more, sufficient rust resistance can be obtained. Since the depth of the dent generally corresponds to the average particle size of the large particles, if the thickness of the prime field protective film 50 is 0.4 times or more the average particle size of the large particles, degranulation occurs on the surface. However, a prime field protective film 50 of sufficient quality can be obtained.

As described above, the inductor 1 of the present embodiment includes a prime field 10 containing soft magnetic powder and a resin, a coil 30 embedded in the prime field 10, and an external electrode 20 provided in the prime field 10. The inductor 1 has a prime field protective film 50 on the surface of the prime field 10, and the prime field protective film 50 has a thickness of 10 μm or more, contains silica particles and a resin, and is an average grain of silica particles. The diameter is 15 to 75 nm, and the weight ratio of the silica particles to the resin is 150 to 250%.

When the thickness of the prime field protective film 50 is 10 μm or more, the occurrence of “plating skipping” can be suppressed and the entire surface of the prime field 10 can be reliably protected by the prime field protective film 50.
Since the prime field protective film 50 contains silica particles, the gloss is reduced and erroneous determination at the time of visual inspection using an optical method can be prevented.
Further, in the prime field protective film 50, the average particle size of the silica particles is 15 to 75 nm, and the weight ratio of the silica particles to the resin is 150 to 250%. A high-quality body protective film 50 that has not been received can be obtained.

In this embodiment, the thickness of the prime field protective film 50 is equal to or less than the thickness of the external electrode 20.
As a result, the external electrode 20 can be in good contact with the circuit of the substrate without being hindered by the thickness of the prime field protective film 50.

In this embodiment, the prime field protective film 50 contains carbon black.
As a result, the workability when the prime field protective film 50 is removed by the laser to form the external electrode 20 is enhanced.

In this embodiment, the prime field protective film 50 contains a phenoxy resin.
This makes it possible to increase the toughness of the prime field 10.

In this embodiment, the prime field protective film 50 contains a novolak resin.
This makes it possible to increase the heat resistance of the prime field 10.

In this embodiment, the thickness of the prime field protective film 50 is 0.4 times or more the average particle size of the large particles.
As a result, the element protective film 50 of sufficient quality can be obtained even if the surface is shed.

In this embodiment, titanium oxide, zirconium oxide, or aluminum oxide may be used as the filler species.

1 Inductor 10 Element 10S Area 12 Mounting surface 14 Top surface 16 1st side surface 18 2nd side surface 20 External electrode 30 Coil 32 Winding part 32L Winding part 34 Drawer part 40 Core 40K Air gap (magnetic gap)
50 Prime field protective film 60 Insulation coating material 81 First soft magnetic particles 82 Second soft magnetic particles H Height W Width L Length P Pressurized CW Winding part winding width KL Air gap length KW Air gap width

Claims (4)

In an inductor having a prime field including a coil having a winding portion composed of a plurality of winding portions and a core in which the coil is embedded.
The core contains first soft magnetic particles having a relatively large average particle size and second soft magnetic particles having a relatively small average particle size.
The prime field extends in the direction in which the winding portions are lined up on the outer periphery of the winding portion of the coil and within a distance of 5 times the average particle size of the first soft magnetic particles from the winding portion. Has an air gap,
Inductor. The air gap has a length equal to or greater than the width of a single winding portion and equal to or less than the winding width of the ticket winding portion in the direction in which the winding portions are lined up, and the first in the radial direction of the winding portions. 2 The width is equal to or more than the average particle size of the soft magnetic particles and not more than 10 μm.
The inductor according to claim 1. The air gap is formed by utilizing a springback when the material of the core and the material of the coil are compression-molded to form the prime field.
The inductor according to claim 1 or 2. In a method for manufacturing an inductor having a prime field including a coil having a winding portion composed of a plurality of winding portions and a core in which the coil is embedded.
The core contains first soft magnetic particles having a relatively large average particle size and second soft magnetic particles having a relatively small average particle size.
By utilizing the springback when the material composed of the core material and the coil is compression-molded to form the prime field, the outer circumference of the winding portion of the coil and the winding are formed on the prime body. An air gap extending in the direction in which the winding portions are lined up is formed within a distance of 5 times the average particle size of the first soft magnetic particles from the portions.
How to make an inductor.

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