JP2016146431A - Coil device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coil device which has a low rate of change of direct current and has high reliability even after heat load has been repeatedly applied thereto.SOLUTION: A coil device 2 has: an insulating substrate 11; internal conductor paths 12 and 13 which are formed in a spiral shape on at least one main surface of the insulating substrate 11; a core element body 10 which is formed of a magnetic power-containing resin and covers one main surface and the other main surface of the insulating substrate 11; and at least a pair of terminal electrodes 4 which are formed on the outer surface of the core element body and are each connected to a pair of contacts 13b for leads formed on both ends of the internal conductor paths. Each of the terminal electrodes has an inner layer 4a in contact with the core element body, and an outer layer 4b formed on the surface of the inner layer. The inner layer is formed of a conductor powder-containing resin, and a thermal expansion coefficient difference between the magnetic powder-containing resin and the conductor powder-containing resin is 14 ppm or less.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a coil device, and more particularly to a coil device that is preferably used as a power supply inductance, such as a choke coil for a power supply smoothing circuit in an electronic device.

  As a coil device that is preferably used as an inductance for a power supply, for example, a coil device shown in Patent Document 1 has been proposed. According to this coil device, it is possible to provide a high-performance coil device that has good direct current superposition characteristics and does not require the formation of a magnetic gap.

  Recently, such coil devices have been used in portable electronic devices such as mobile phones and mobile devices, and further downsizing and thinning of portable electronic devices, and further downsizing and thinning of coil devices are also required. It has been. In addition to the reduction in size and thickness of the coil device, there is a demand for improved reliability in accordance with the usage environment of the portable electronic device.

  For example, in order to increase the number of functions and charge amount of portable electronic devices, a large rated current is required, and an increase in heat generation accompanying an increase in rated current and a high temperature operation accompanying an increase in mounting density are expected. For this reason, even after a thermal load is repeatedly applied as a coil component, there is a demand for a coil device that has a lower rate of change in direct current than the prior art and has high reliability. Moreover, since it is used for a portable electronic device, the coil device is also desired to have improved reliability against a drop impact or the like.

JP 2012-89765 A

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a highly reliable coil device that has a low rate of change in DC current even after a thermal load is repeatedly applied.

In order to achieve the above object, a coil device according to the present invention comprises:
An insulating substrate;
An inner conductor passage formed in a spiral shape on at least one main surface of the insulating substrate;
A core element body made of a magnetic powder-containing resin and covering one main surface and the other main surface of the insulating substrate;
A coil device having at least a pair of terminal electrodes formed on the outer surface of the core body and connected to a pair of lead contacts formed on both ends of the internal conductor passage,
Each of the terminal electrodes has an inner layer in contact with the core body, and an outer layer formed on the surface of the inner layer,
The inner layer is composed of a conductor powder-containing resin,
The difference in thermal expansion coefficient between the magnetic powder-containing resin and the conductor powder-containing resin is 14 ppm or less.

  As a result of intensive studies on a highly reliable coil device that has a low direct current change rate even after repeated thermal loads, the present inventors have found that there is a difference in thermal expansion coefficient between the resin containing the magnetic powder and the resin containing the conductor powder. It was found that the object of the present invention can be achieved by setting the content to 14 ppm or less, and the present invention has been completed.

  Preferably, the lead contact protrudes from the end face of the core body into the inner layer. With such a configuration, variation in direct current resistance (RDC) can be reduced, the thickness of the terminal electrode at the corner of the terminal electrode is not reduced, and the fixing strength between the terminal electrode and the core element is increased. improves.

  Preferably, the conductor powder contained in the conductor powder-containing resin constituting the inner layer has a spherical powder and a flat powder, the content of the spherical powder contained in the conductor powder-containing resin is α, and the conductor When the content of the flat powder contained in the powder-containing resin is β, α / β is in the range of 2 to 3. With such a configuration, the fixing strength between the terminal electrode and the core body is improved, and the resistance of the terminal electrode can be reduced.

It is a perspective view of a coil device concerning one embodiment of the present invention. FIG. 2 is an exploded perspective view of the coil device shown in FIG. FIG. 3 is a sectional view taken along line III-III shown in FIG. 4 is a cross-sectional view taken along line IV-IV shown in FIG. FIG. 5 is an enlarged cross-sectional view of a main part in the vicinity of the terminal electrode shown in FIG. FIG. 6 is a graph showing the effects of the coil device according to one embodiment of the present invention. FIG. 7A is a graph showing another effect of the coil device according to the embodiment of the present invention. FIG. 7B is a graph showing still another function and effect of the coil device according to the embodiment of the present invention. FIG. 8A is a graph showing still another function and effect of the coil device according to the embodiment of the present invention. FIG. 8B is a graph showing still another function and effect of the coil device according to the embodiment of the present invention.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
A coil device 2 shown in FIG. 1 includes a rectangular plate-shaped core element body 10 and a pair of terminal electrodes 4 and 4 attached to both ends of the core element body 10 in the X-axis direction. The terminal electrodes 4, 4 cover the X-axis direction end face of the core element body 10, and partially cover the upper surface 10 a and the lower surface 10 b of the core element body 10 in the Z-axis direction near the end face in the X-axis direction.

  As shown in FIG. 2, the core body 10 includes an upper core 15 and a lower core 16, and has an insulating substrate 11 at the center in the Z-axis direction. The insulating substrate 11 serves as a lower ground for forming spiral inner conductor passages 12 and 13 to be described later.

  The upper core 15 has a columnar middle leg portion 15a that protrudes downward in the Z-axis direction at the center of a rectangular flat core body. The upper core 15 has plate-like side legs 15b that protrude downward in the X-axis direction at both ends in the Y-axis direction of the rectangular flat core body.

  The lower core 16 has a rectangular flat plate shape similar to the core body of the upper core 15, and the middle leg portion 15 a and the side leg portion 15 b of the upper core 15 are respectively in the center portion and the Y-axis direction of the lower core 16. It is connected and integrated with the end of the. In FIG. 2, the core body 10 is depicted as being separated into an upper core 15 and a lower core 16, but these may be integrally formed with a metal magnetic powder-containing resin. Further, the middle leg portion 15 a and / or the side leg portion 15 b formed on the upper core 15 may be formed on the lower core 16. In any case, the core body 10 forms a complete closed magnetic circuit, and no gap exists in the closed magnetic circuit.

  In the present embodiment, the core body 10 is made of a metal magnetic powder-containing resin. The metal magnetic powder-containing resin is a magnetic material in which metal magnetic powder is mixed into the resin. The metal magnetic powder is not particularly limited, and examples thereof include permalloy, iron, sendust, Fe-Si-Cr alloy, Fe-Si-Cr amorphous alloy, etc., but Fe-Si-Cr amorphous alloy is used. It is preferable. Specifically, an Fe—Si—Cr amorphous alloy having an average particle size of preferably 10 to 50 μm, more preferably 10 to 30 μm is used as the first metal magnetic powder, and the average particle is used as the second metal magnetic powder. Metallic magnetic powder containing carbonyl iron having a diameter of preferably 1 to 10 μm, more preferably 1 to 6 μm, and containing these in a predetermined ratio, for example, 70:30 to 80:20, preferably 75:25. It is preferable to use it.

  The content of the metal magnetic powder is preferably 90 to 99% by weight. If the amount of metal magnetic powder is reduced relative to the resin, the saturation magnetic flux density decreases. Conversely, if the amount of metal magnetic powder is increased, the saturation magnetic flux density increases. Can be adjusted.

  In this embodiment, it is preferable to use two or three to four types of metal magnetic powders having different particle diameters. In that case, a high-density magnetic core is molded under low pressure or non-pressure molding. Therefore, a magnetic core with high permeability and low loss can be realized.

  The resin contained in the metal magnetic powder-containing resin functions as an insulating binder. As the resin material, liquid epoxy resin or powder epoxy resin is preferably used. The resin content is preferably 1 to 10% by weight.

  The upper core 15 and the lower core 16 preferably have the same thickness, and the total thickness T (see FIG. 3) can be reduced to about 0.3 to 1.2 mm. However, if the total thickness T of the upper core 15 and the lower core 16 is too thin, not only the mechanical strength of the parts but also the coil inductance may be reduced.

  In the figure, the X axis, the Y axis, and the Z axis are perpendicular to each other. In this embodiment, the X axis is a direction in which the pair of terminal electrodes 4 and 4 face each other, and the Y axis is the terminal electrode 4. , 4 and the Z axis is a direction perpendicular to the upper surface 10 a and the lower surface 10 b of the core body 10.

  As shown in FIG. 2, an internal electrode pattern including a circular spiral internal conductor passage 12 is formed on the upper surface (one main surface) in the Z-axis direction of the insulating substrate 11.

  A connection end 12 a is formed at the inner peripheral end of the spiral inner conductor passage 12. A lead contact 12 b is formed at the outer peripheral end of the spiral inner conductor passage 12 so as to be exposed along one end of the core body 10 in the X-axis direction.

  On the lower surface (the other main surface) in the Z-axis direction of the insulating substrate 11, an internal electrode pattern including a spiral internal conductor passage 13 is formed.

  A connection end 13 a is formed at the inner peripheral end of the spiral inner conductor passage 13. A lead contact 13 b is formed at the outer peripheral end of the spiral inner conductor passage 13 so as to be exposed along one end of the core element body 10 in the X-axis direction.

  The connection end 12a and the connection end 13a are formed at the same position with the insulating substrate 11 in between, and as shown in FIG. 3, the through hole embedded in the through hole 11i formed in the insulating substrate 11 It is electrically connected through the electrode 18. That is, the spiral inner conductor passage 12 and the spiral inner conductor passage 13 are electrically connected through the through-hole electrode 18.

  The spiral inner conductor passages 12 and 13 substantially overlap with each other when viewed from the Z-axis direction, but may not completely coincide with each other. That is, the spiral inner conductor passage 12 as viewed from the upper surface 11a side of the insulating substrate 11 forms a counterclockwise spiral from the lead contact 12b at the outer peripheral end toward the connection end 12a at the inner peripheral end.

  On the other hand, the spiral inner conductor passage 13 viewed from the upper surface 11a side of the insulating substrate 11 forms a counterclockwise spiral from the connection end 13a which is the inner peripheral end toward the lead contact 13b which is the outer peripheral end. It is composed. As a result, the directions of the magnetic flux generated by the current flowing through the spiral inner conductor passages 12 and 13 coincide with each other, and the magnetic fluxes generated in the spiral inner conductor passages 12 and 13 are superimposed and strengthened to obtain a large inductance. be able to.

  As shown in FIG. 2, a protective insulating layer 14 is interposed between the upper core 15 and the inner conductor passage 12, and these are insulated. Further, a rectangular sheet-like protective insulating layer 14 is interposed between the lower core 16 and the inner conductor passage 13, and these are insulated. A circular through hole 14 a is formed in the central portion of the protective insulating layer 14. A circular through hole 11 h is also formed in the central portion of the insulating substrate 11. Through these through holes 14 a and 11 h, the middle leg portion 15 a of the upper core 15 extends in the direction of the lower core 16 and is connected to the center of the lower core 16.

  Note that the spiral inner conductor passage 12 and the spiral inner conductor passage 13 have a space larger than the through holes 14a and 11h at the center thereof.

  As shown in FIGS. 4 and 5, in this embodiment, the terminal electrode 4 has an inner layer 4 a that contacts the end surface in the X-axis direction of the core element body 10 and an outer layer 4 b that is formed on the surface of the inner layer 4 a. The inner layer 4a is close to the end surface of the core element body 10 in the X-axis direction, and also covers a part of the upper surface 10a and the lower surface 10b of the core element body 10, and the outer layer 4b covers the outer surface.

  As shown in FIG. 5, the lead contact 13 b is formed so as to protrude from the end surface of the core body 10 in the X-axis direction with a predetermined protrusion length d into the terminal electrode 4 and to be connected to the terminal electrode 4. . The protrusion length d is larger than 0, preferably (1) to 10 μm. As shown in FIG. 7A, the larger the protrusion length d, the smaller the variation (%) of the direct current resistance (RDC). However, when it exceeds 10 μm, the effect of reducing the variation is reduced. Therefore, the above range is preferable.

  Moreover, as shown in FIG. 7B, when the protruding length d exceeds 0, the thickness te of the terminal electrode 4 at the corner of the terminal electrode 4 shown in FIG. 5 can be increased rapidly. By keeping the thickness te of the terminal electrode 4 at the corner of the terminal electrode 4 thick, the fixing strength between the terminal electrode 4 and the core body 10 is improved. However, since the effect of keeping the thickness te of the terminal electrode 4 small when the protrusion length d exceeds 10 μm, the above range is preferable.

  Although not shown in FIG. 5, as shown in FIG. 4, in the terminal electrode 4 located on the opposite side in the X-axis direction, the lead contact 12 b is predetermined from the end surface of the core element body 10 in the X-axis direction. The protrusion length d (see FIG. 5) protrudes into the terminal electrode 4 and is connected to the terminal electrode 4. The other terminal electrode 4 is connected only to the upper internal conductor passage 12. Therefore, two spiral internal conductor passages 12 and 13 are connected in series between one terminal electrode 4 and the other terminal electrode 4.

  In this embodiment, the insulating substrate 11 is preferably a general printed circuit board material in which a glass cloth is impregnated with an epoxy resin. For example, a BT base material, an FR4 base material, an FR5 base material, or the like can be used. Without being limited thereto, a glass substrate, a ceramic substrate, a polyimide substrate, a ferrite substrate, or the like may be used.

  When a printed board material is used as the insulating substrate 11, the spiral inner conductor passages 12 and 13 can be formed by plating instead of sputtering in a so-called thin film construction method. For this reason, the thickness of the conductor which comprises the internal conductor channel | paths 12 and 13 can be made thick enough.

  In order to avoid an increase in stray capacitance, the dielectric constant of the insulating substrate 11 is preferably 7 or less (ε ≦ 7), but is not particularly limited. In the present embodiment, the shape of the resin substrate 11 is rectangular according to the outer shape of the coil device, but may be other shapes. The thickness of the resin substrate 11 is preferably thin enough to ensure insulation between the internal conductor passages 12 and 13, and is not particularly limited, but is preferably 10 to 100 μm. The resin substrate 11 is formed by, for example, injection molding, a doctor blade method, screen printing, or the like.

  The internal conductor passages 12 and the internal conductor passages 13 formed on the upper surface 11a and the lower surface 11b of the insulating substrate 11 are formed by plating, for example, as follows. By forming by plating, the aspect ratio can be increased, and a coil device having a relatively large cross-sectional area and a small DC resistance can be realized.

  First, an insulating substrate 11 having a metal foil (for example, a copper foil having high conductivity and easy to process) formed on the upper surface 11a and the lower surface 11b is prepared, and the metal foil is etched to a predetermined thickness (for example, 3 to 5 μm). Reduce the thickness of the metal foil. This metal foil becomes a plating seed film in the next step.

  Before and after that, the through hole 11i shown in FIG. 3 is formed in the insulating substrate 11 by drilling or the like. A resist film is laminated on both surfaces of the insulating substrate 11 on which the metal foil and the through hole 11i are formed, and a portion that becomes a space of the circuit pattern is exposed by exposure. An unexposed portion is dissolved (developed) with a developer to form a resist pattern on the surface of the metal foil, leaving only the space portion of the circuit pattern.

  Next, the insulating substrate 11 on which the resist pattern is formed is electroplated to deposit a portion on the portion where the resist pattern is not formed, thereby forming portions that become the conductor wiring of the circuit (the inner conductor passages 12 and 13 are formed). Part) is formed. The thickness of the plating is assumed to be the amount to be etched in the next step in advance, and is formed with a thickness adjusted, for example, to a predetermined thickness after etching of the plating seed film.

  Next, the insulating substrate 11 on which the resist is formed is immersed in a resist stripping solution, and the remaining resist is stripped. Furthermore, the insulating substrate 11 is etched with a plating seed film etching solution to remove the plating seed film in a portion that is not plated.

  Next, the insulating film 11 on which the plating film is formed is thickened by electroplating. In this state, internal conductor passages 12 and 13 having a predetermined thickness are formed on the upper surface 11a and the lower surface 11b of the insulating substrate 11 shown in FIG. At the same time, the through-hole electrode 18 shown in FIG. 3 is also formed.

  Next, in order to form the protective insulating layer 14 on both surfaces of the insulating substrate in which the internal conductor passages 12 and 13 are formed, a resin solution obtained by diluting the insulating substrate 11 with a high boiling point solvent at a predetermined concentration, for example. Soak and dry. In this way, the protective insulating layer 14 having a predetermined thickness is formed.

  Next, in order to form the core body 10 composed of the combination of the upper core 15 and the lower core 16 shown in FIG. 2, a magnetic material is printed on the surface of the insulating substrate 11 on which the protective insulating layer 14 is formed. Apply. As the magnetic material, for example, a paste obtained by kneading a paste material obtained by kneading a main metal magnetic material amount and a fine powder metal magnetic material at a predetermined ratio with a resin solution is used. The effective magnetic permeability is improved by increasing the particle size of the metal magnetic material.

  In addition, the magnetic material formed by printing volatilizes the solvent, and improves the density of the core body 10 by, for example, press processing. Further, the upper surface 11a and the lower surface 11b of the core body 10 are ground with, for example, a fixed grindstone, and the core body 10 is made to have a predetermined thickness. Thereafter, the core body 10 is obtained by thermosetting and cross-linking the resin.

  Thereafter, if the insulating substrate 11 on which the core body 10 is formed is cut into individual pieces by, for example, dicing, the core body 10 before the terminal electrode 4 shown in FIG. 1 is formed is obtained. In the state before cutting, the core body 10 is integrally connected in the X-axis direction and the Y-axis direction. After the cutting, an etching process is performed on the separated core body 10. The conditions for the etching process are not particularly limited.

  The purpose of this etching process is to remove metal particles contained in the core body 10 and stretched by dicing, to improve the insulation of the surface of the core body 10 and to suppress the deposition of terminal plating. Further, as shown in FIG. 5, the purpose is to project the X-axis direction end portion of the lead contact 13b (same for 12b) from the X-axis direction end portion of the core body 10 with a predetermined protruding length d, This is to ensure electrical connection with the terminal electrode 4.

  As shown in FIG. 7A, when the protrusion length d is larger than 0, the electrical connection is stable when the RDC is 4% or less, preferably 3% or less. However, if the protrusion length d is 0 or less, the contact resistance increases and the variation in electrical connection increases. This occurs because the electrode material coating process for forming the inner layer 4a of the terminal electrode 4 is processed by DIP immersion, so that it is easy to embrace bubbles when immersed in DIP, and the bubbles are difficult to escape. This is thought to be due to

  As for the thickness te (see FIG. 5) of the electrode edge portion formed by DIP, if the protruding length d is larger than 0, the thickness te is secured to 9 μm or more as shown in FIG. Is also strong. However, when the protruding length d is 0 or less, the fixing strength is weakened, and it has been confirmed that the drop test results in dropping off.

  Next, an electrode material is applied to both ends of the etched core element body 10 in the X-axis direction by a dipping method (DIP) to form the inner layer 4a. The electrode material is a paste material in which a conductor powder such as Ag powder is kneaded with a predetermined content, for example, in a thermosetting resin such as an epoxy resin, in the same manner as the component fixing the magnetic material.

  The conductor powder (for example, Ag powder) contained in the conductor powder-containing resin constituting the inner layer 4a has a spherical powder and a flat powder, the content of the spherical powder contained in the conductor powder-containing resin is α, and the conductor powder When the content of the flat powder contained in the contained resin is β, α / β is preferably in the range of 2-3. With such a configuration, the fixing strength between the terminal electrode 4 and the core body 10 is improved, and the resistance of the terminal electrode 4 can be reduced.

  In addition, the average particle diameter of spherical powder and flat powder is measured by the laser analysis scattering method. In addition, flat powder means that the aspect ratio (aspect ratio) of the powder is 2 or more, and spherical powder means that the outer diameter of the powder is close to a circle. Means close.

  In the DIP dipping method, the electrode material surface is smoothed with a squeegee, and the electrode thickness is dipped and applied. The excessively applied part is removed by contacting the metal surface.

  Next, the outer layer 4b is formed by barrel plating on the product coated with the electrode paste to be the inner layer 4a. The terminal plating for forming the outer layer 4b may be a single plating film or a multilayer plating film. For example, a Ni film and a Sn film are formed.

  In the present embodiment, a thermal load is repeatedly applied by setting the difference in thermal expansion coefficient between the magnetic powder-containing resin constituting the core body 10 shown in FIG. 5 and the conductor powder-containing resin constituting the inner layer 4a to 14 ppm or less. Even after this, the rate of change in direct current is small and a highly reliable coil device can be realized.

  Further, as shown in FIG. 5, the lead contact 12b (same for 12c, 13b, and 13c) protrudes from the end surface in the X-axis direction of the core body 10 into the inner layer 4a. With this configuration, variation in direct current resistance (RDC) can be reduced, and the terminal electrode thickness te at the corners of the terminal electrode 4 is not reduced, and the terminal electrode 4 and the core body 10 This improves the fixing strength.

  Furthermore, in this embodiment, the conductor powder contained in the conductor powder-containing resin constituting the inner layer 4a has spherical powder and flat powder, the content of the spherical powder contained in the conductor powder-containing resin is α, and the conductor When the content of the flat powder contained in the powder-containing resin is β, α / β is in the range of 2 to 3. With such a configuration, the fixing strength between the terminal electrode 4 and the core body 10 is improved, and the resistance of the terminal electrode 4 can be reduced.

  Furthermore, in the coil device 2 of the present embodiment, the surface roughness of the outer surface of the core body 10 is 130 μm or less. With such a configuration, it is possible to increase the surface resistance of the core body 10 and effectively prevent a short circuit between the terminal electrodes 4 and 4.

  In the present embodiment, when the core body 10 is composed of a resin containing metal magnetic powder, the resin exists between the metal magnetic powders, and a minute gap is formed, so that the saturation magnetic flux density is reduced. Enhanced. For this reason, magnetic saturation can be prevented without forming an air gap between the upper core 15 and the lower core 16. Therefore, it is not necessary to machine the magnetic core with high accuracy to form the gap.

  Furthermore, in the coil device 2 according to the present embodiment, the magnetic body covering the spiral inner conductor passages 12 and 13 is a resin mold, and the dimensional processing accuracy is very high, and the coil body is formed as an aggregate on the substrate surface. The position accuracy is very high, and it is possible to reduce the size and thickness. Furthermore, in this embodiment, a metal magnetic material is used for the magnetic body, and since the direct current superimposition characteristic is better than that of ferrite, the formation of the magnetic gap can be omitted.

  Furthermore, the coil device 2 according to the present embodiment has a heat generation accompanying an increase in rated current, a high-temperature operation accompanying an increase in mounting density, and a use in a humid environment close to a human body (such as a pocket) (temperature around 40 degrees, humidity 60%). ~ 90%), particularly effective.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

  For example, the spiral inner conductor passage 12 or 13 may be formed only on one surface of the insulating substrate 11. In the above-described embodiment, the spiral inner conductor passages 12 and 13 are connected in series. However, the inner conductor pattern may be formed so as to be connected in parallel. Further, the number of terminal electrodes 4 formed on the outer surface of the core body 10 may be three or more.

Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.
Example 1

  First, an insulating substrate 11 having a copper foil formed on the upper surface 11a and the lower surface 11b was prepared. The dimension of the insulating substrate 11 was 2.5 × 2.0 × 0.06 mm. The copper foil formed on the insulating substrate 11 was etched to a predetermined thickness (for example, 3 to 5 μm) to reduce the thickness of the copper foil. This copper foil becomes a plating seed film in the next step.

  Before and after that, through holes 11i shown in FIG. 3 were formed in the insulating substrate 11 by drilling or the like. A resist film was laminated on both surfaces of the insulating substrate 11 on which the copper foil and the through-holes 11i were formed, and a portion that became a space of the circuit pattern was exposed by exposure. The unexposed portion was dissolved (developed) with a developer, and a resist pattern was formed on the surface of the copper foil leaving only the space portion of the circuit pattern.

  Next, the insulating substrate 11 on which the resist pattern is formed is electroplated to deposit a portion on the portion where the resist pattern is not formed, thereby forming portions that become the conductor wiring of the circuit (the inner conductor passages 12 and 13 are formed). Part). As for the film thickness of the plating, an amount to be etched in the next step was assumed in advance, and a film thickness of 13 μm or more was formed in order to form a film thickness adjusted to 10 μm after etching the plating seed film.

  Next, the insulating substrate 11 on which the resist was formed was immersed in a resist stripping solution, and the remaining resist was stripped. Furthermore, the insulating substrate 11 was etched with an etching solution for a plating seed film, and the plating seed film in a portion not plated was removed.

  Next, the insulating film 11 on which the plating film was formed was thickened by electroplating. In this state, it was confirmed that the inner conductor passages 12 and 13 having a predetermined thickness were formed on the upper surface 11a and the lower surface 11b of the insulating substrate 11 shown in FIG. At the same time, it was confirmed that the through-hole electrode 18 shown in FIG. 3 was also formed. The inner conductor passages 12 and 13 had a width of 70 μm, a height of 120 μm, and a pitch of 10 μm.

  Next, in order to form the protective insulating layer 14 on both surfaces of the insulating substrate on which the internal conductor passages 12 and 13 were formed, the insulating substrate 11 was dipped in an epoxy solution diluted with a solvent and dried. . Thus, the protective insulating layer 14 having a predetermined thickness was formed.

  Next, in order to form the core body 10 composed of the combination of the upper core 15 and the lower core 16 shown in FIG. 2, a magnetic material is printed on the surface of the insulating substrate 11 on which the protective insulating layer 14 is formed. Applied. As the magnetic material, for example, a paste material obtained by kneading a main metal magnetic material and a fine powder metal magnetic material at a ratio of 3: 1 with an epoxy resin was used. The ratio of the metal magnetic powder was 97% by weight, the average particle size of the main metal magnetic powder was 30 μm, and the average particle size of the fine metal magnetic powder was 1 to 4 μm. Fe-Si-Cr amorphous alloy was used as the main metal magnetic material, and carbonyl iron was used as the fine metal magnetic material.

  In the magnetic material paste formed by printing, the solvent content was volatilized, for example, at 100 ° C. for 5 hours, and the density of the core body 10 was improved by pressing. Moreover, the upper surface 11a and the lower surface 11b of the core body 10 were ground with, for example, a fixed grindstone, and the core body 10 was aligned to a predetermined thickness. Thereafter, the core body 10 was obtained by thermosetting at 170 ° C. and 90 minutes to crosslink the epoxy resin. The linear expansion coefficient of the core body 15 was measured by TMA analysis (JIS 7197) and found to be 15 ppm.

  Thereafter, the insulating substrate 11 on which the core body 10 was formed was cut into individual pieces by, for example, dicing, and the core body 10 before the terminal electrode 4 shown in FIG. 1 was formed was obtained. . In addition, in the state before cutting | disconnection, the core element | base_body 10 was integrally connected by the X-axis direction and the Y-axis direction.

  After cutting, the core element 10 separated into pieces was etched. The etching process was performed by immersion in an etching solution. After the immersion treatment, the protruding length shown in FIG. 5 was measured, and d = 5.0 μm.

  Next, an electrode material was applied to both ends in the X-axis direction of the etched core element body 10 by a dipping method (DIP) to form an inner layer 4a. The electrode material was, for example, a paste material obtained by kneading 84 wt% of Ag powder in an epoxy resin in the same manner as the component fixing the magnetic material. As the Ag powder, a spherical powder and a flat powder having a spherical powder / flat powder weight ratio of 2.3, for example, were used. The average particle size of the Ag powder was 1 μm for the spherical powder and 10 μm for the flat powder.

  A DIP dipping method was employed. In this method, the surface of the electrode material was smoothed with a squeegee and the electrode thickness was immersed and applied. The excessively applied part was removed by contacting the metal surface. It was 25 ppm when the linear expansion coefficient of the inner layer 4a was measured by TMA analysis (JIS7197).

  Next, the outer layer 4b was formed by barrel plating on the product coated with the electrode paste to be the inner layer 4a. As terminal plating for forming the outer layer 4b, a Ni film of 1 μm and an Sn film of 3 μm were formed to form a terminal electrode 4, and a sample of the coil device 2 shown in FIGS. 1 to 5 was obtained. The size of the coil device 2 was 2.5 mm × 2.0 mm × 1.0 mm.

Example 2
A sample of the coil device was produced in the same manner as in Example 1 except that the Ag content of the electrode material constituting the inner layer 6a was changed and an electrode material having a different linear expansion coefficient was used. Regarding the samples of these coil devices, a difference in linear expansion between the core element 10 and the inner layer 4a (linear expansion coefficient of the inner layer 4a−linear expansion coefficient of the core element 10 made of a magnetic substance) was obtained. Moreover, the heat cycle test was done about these samples and the change rate of direct current RDC before and behind a test was calculated | required. The results are shown in FIG.

  The test conditions of the heat cycle are that the low temperature range is −40 ° C., the keep time is 30 minutes, the high temperature range is 85 ° C., and the keep time is 30 minutes. And one cycle of the high temperature region was 70 minutes, and the total test time was 1000 hours.

  As shown in FIG. 6, it was confirmed that the rate of change in RDC was increased when the difference in linear expansion coefficient was 15 ppm or more. Further, in a reliability test in which a current load was intermittently applied to a sample of a coil device having a linear expansion coefficient difference of 15 ppm or more at 85 ° C. and 85% humidity, the terminal electrode 4 and the lead contacts 12b and 13b The mode of peeling was confirmed. This is probably because when the difference in coefficient of linear expansion is large, if the phenomenon that each material moves due to swelling due to humidity and thermal load is expressed, the difference in the amount of movement is large, resulting in a large stress difference. .

  It was confirmed that the difference in linear expansion between the core body 10 and the inner layer 4a (the linear expansion coefficient of the inner layer 4a—the linear expansion coefficient of the core body 10 made of a magnetic material) is desirably 14 ppm or less.

Example 3
A coil is formed in the same manner as in Example 1 except that the etching process condition (etching process time) performed on the separated core body 10 is changed and d is changed as shown in FIGS. 7A and 7B. A sample of the device was made. Regarding the samples of these coil devices, RDC variation and (%) and the electrode edge portion thickness te shown in FIG. 5 were measured.

  The lead contacts 12b and 13b with the recessed end portions were prepared by applying epoxy resin to the core body 10 made of a magnetic material so as not to be etched, and etching the Cu of the lead contacts 12b and 13b. .

  As shown in FIG. 7A, when the protrusion length d is larger than 0, it can be confirmed that the electrical connection is stable when the RDC is 4% or less, preferably 3% or less. However, it was confirmed that when the protrusion length d is 0 or less, the contact resistance increases and the variation in electrical connection increases. This occurs because the electrode material coating process for forming the inner layer 4a of the terminal electrode 4 is processed by DIP immersion, so that it is easy to embrace bubbles when immersed in DIP, and the bubbles are difficult to escape. This is thought to be due to

  Further, as shown in FIG. 7B, the thickness te (see FIG. 5) of the electrode edge portion formed by DIP is also secured to a thickness te of 9 μm or more if the protruding length d is greater than 0, and the bonding strength Was also confirmed to be strong. However, when the protruding length d is 0 or less, the fixing strength is weakened, and it has been confirmed that the drop test results in dropping off.

Example 4
When the content of the spherical powder in the Ag powder contained in the conductor powder-containing resin constituting the inner layer 4a is α and the content of the flat powder contained in the conductor powder-containing resin is β, α / β is changed. A sample of the coil device was produced in the same manner as in Example 1 except that. Regarding the samples of these coil devices, the adhesion strength of the terminal electrode 4 to the core body 10 and the electrode resistance component (mΩ) were measured.

  The fixing strength was measured by the following method. That is, when the coil device was soldered to the mounting substrate and the coil device was pushed in parallel with the mounting substrate by the load cell, the force when the coil device was peeled from the mounting substrate was measured.

  The electrode resistance component (mΩ) was measured by the following method. That is, the measurement was carried out by applying a DC resistance meter probe to the terminal electrode.

  As shown in FIG. 8A, when α / β exceeds 3, the fixing strength decreases, and although not shown, it has been confirmed that when α / β is 4 or more, a drop-out failure occurs. It was done. Furthermore, as shown in FIG. 8B, it was confirmed that when α / β is less than 2 or greater than 3, the electrical resistance increases and a conduction failure occurs. From the above results, it was confirmed that the ratio α / β of the spherical powder and the flat powder contained in the conductor powder-containing resin constituting the inner layer 4a is desirably 2 or more and 3 or less.

2 ... Coil device 4 ... Terminal electrode 4a ... Inner layer 4b ... Outer layer 10 ... Core element body 11 ... Insulating substrate 12, 13 ... Internal conductor passages 12a, 13a ... Connection end 12b, 13b ... Lead contact 14 ... Protective insulating layer 15 ... Upper core 15a ... Middle leg 15b ... Side leg 16 ... Lower core 18 ... Through-hole conductor

Claims (3)

An insulating substrate;
An inner conductor passage formed in a spiral shape on at least one main surface of the insulating substrate;
A core element body made of a magnetic powder-containing resin and covering one main surface and the other main surface of the insulating substrate;
A coil device having at least a pair of terminal electrodes formed on the outer surface of the core body and connected to a pair of lead contacts formed on both ends of the internal conductor passage,
Each of the terminal electrodes has an inner layer in contact with the core body, and an outer layer formed on the surface of the inner layer,
The inner layer is composed of a conductor powder-containing resin,
The coil device, wherein a difference in thermal expansion coefficient between the magnetic powder-containing resin and the conductor powder-containing resin is 14 ppm or less.   The coil device according to claim 1, wherein the lead contact protrudes from an end surface of the core body into the inner layer. The conductor powder contained in the conductor powder-containing resin constituting the inner layer has a spherical powder and a flat powder,
When the content of the spherical powder contained in the conductor powder-containing resin is α and the content of the flat powder contained in the conductor powder-containing resin is β, α / β is in the range of 2 to 3. The coil device according to claim 1 or 2.

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