COIL DEVICE

TECHNICAL FIELD

The invention relates to a coil device.

BACKGROUND

As an example of a coil device used such as an inductor, the coil device described in Patent Document 1 is known. The coil device described in Patent Document 1 has a core and a coil embedded inside the core, and a lead-out of the coil is arranged at the bottom of the core. The lead-out is plated so that the lead-out arranged at the bottom of the core can be connected to the mounting substrate. In this way, by allowing the lead-out of the coil to function as a connection with the mounting substrate, it becomes possible to omit the step of forming a terminal electrode, such as a resin electrode electrically connected to the lead-out, on the surface of the core. Thus, the production of the coil device can be facilitated and the production cost can be reduced.

However, according to the coil device described in Patent Document 1, since there is a gap between the lead-out of the coil and the bottom of the core, a plating solution may enter the gap and leave residue of the plating solution. Moreover, when mounting the coil device on the mounting substrate, there is a possibility that flux may enter the gap and corrode the lead-out. An improvement is desired since such situations lead to deterioration in the quality and reliability of the coil device.

[Patent Document 1] Japanese Unexamined Patent Application Publication 2017-510072

SUMMARY

The invention has been made considering the above circumstances, and its object is to provide a coil device having a high quality and a high reliability.

In order to achieve the above object, the coil device according to the invention is

- a coil device having a core,
- a coil having a winding embedded inside the core, and a lead-out led from the winding to a bottom of the core, in which
- the lead-out has a terminal arranged at the bottom of the core,
- the terminal has an embedded part embedded inside the core and an exposed part exposed from the core, and
- a metal layer is formed on a surface of the exposed part.

In the coil device according to the invention, a metal layer is formed on the surface of the exposed part. Therefore, it is possible to mount the coil device on the substrate via the metal layer. Thus, it is not necessary to form a terminal electrode on the surface of the core separately from the metal layer, and it is possible to facilitate the manufacture of the coil device and reduce the manufacturing cost.

In addition, the terminal has an embedded part embedded inside the core and an exposed part exposed from the core. Since the terminal is exposed from the core as an exposed part, the exposed part can contribute to the connection with the substrate. In addition, since the terminal is embedded inside the core as an embedded part, there is no gap, a space in which plating solution, flux, etc. may enter, between the terminal and the bottom of the core. Therefore, it is possible to prevent a generation of plating liquid residues or a corrosion of the lead-out due to flux, and is possible to improve the quality and reliability of the coil device.

In addition, by fixing the embedded part to the core inside the core, the fixing strength between the terminal and the core can be increased, and the terminal can be prevented from peeling off from the bottom of the core.

The metal layer is preferably comprised by a metal film. With such a composition, it is possible to improve the solder wettability of the metal layer, dramatically improve the connection strength between the metal layer and the substrate, and effectively prevent a defective mounting of the coil device.

The exposed part may have a first end, an end of the lead-out, and a second end, located on the opposite side of the first end along an extending direction of the exposed part, and a curved surface that curves toward the bottom of the core may be formed on the surface of the exposed part at the second end. With such a configuration, for example, the solder can be formed thickly on the curved surface when connecting the metal layer to the substrate with solder, and the connection strength between the metal layer and the substrate can be increased.

The metal layer may not exist at a position spaced apart from a bottom surface of the metal layer toward the bottom of the core on the curved surface. With such a configuration, it becomes possible to adjust an area of the metal layer part, an effective metal layer, that substantially contributes to the connection with the substrate according to an area of the metal layer non-formation part where the metal layer does not exist. As a result, the area of the effective metal layer can be adjusted according to an area of a land pattern of the substrate.

Preferably, a thickness of the embedded part maybe one forth or more and less the thickness of the terminal. With such a configuration, it is possible to prevent the terminal from peeling off from the bottom of the core. In addition, the height of the coil device can be reduced since a thickness of the exposed part, a part of the terminal exposed from the core, becomes relatively small.

The core may have a resin and a magnetic material, a resin-rich part having a relatively high resin content and a magnetic material-rich part having a relatively high magnetic material content maybe formed at the bottom of the core, and the exposed part maybe exposed from the magnetic material-rich part. The magnetic material-rich part is formed, for example, by irradiating a predetermined range (the exposed part and its surrounding parts) of the bottom of the core with a laser to blow off the resin component. By irradiating the range with a laser and forming the magnetic material-rich part at the bottom of the core, the exposed part can be irradiated with a laser, and the insulation coat on the surface of the exposed part can be removed as a result. This is when the coil is formed by an insulation coated wire. Thereby, it becomes possible to easily form a metal layer on the surface of the exposed part, which can contribute to facilitate the coil device production.

A surface roughness of the bottom of the core in the magnetic material-rich part maybe larger than the surface roughness of the bottom of the core in the resin-rich part. In order to obtain such a configuration, for example, a predetermined range of the bottom of the core is irradiated with a laser at a predetermined intensity, thereby makes it possible to effectively obtain the above-described effects.

The coil is preferably formed by winding an insulation coated flat wire. The flat wire has a relatively wide face. Therefore, with the configuration as described above, the surface area of the exposed part and the metal layer formed on the surface thereof can be increased, and the connection strength between the metal layer and the substrate can be improved.

Preferably, the terminal extends linearly along the bottom of the core from one end to the other end in its extending direction. With such a configuration, it is possible to prevent the terminal from cutting into the core, secure the volume of the core, and thereby improve the magnetic properties of the coil device. Also, it is possible to prevent deterioration in the quality of the coil device due to bending of the terminal.

Preferably, the extending direction of the terminal is inclined with respect to a first direction, in which sides of the core face each other, or a second direction perpendicular to the first direction in a plane parallel to the bottom of the core. With such a configuration, it is possible to increase a length (a surface area) of the embedded part according to an inclination angle of the terminal, thereby increase a bonding strength between the embedded part and the core. Moreover, the length (the surface area) of the exposed part can be increased according to the inclination angle of the terminal, and the connection strength between the exposed part and the substrate can be improved.

With respect to a direction in which one side of the core and the other side of the core face each other, a first distance between the exposed part and the one side of the core and a second distance between the exposed part and the other side of the core are different. For example, if the second distance is greater than the first distance, a relatively large space is formed between the terminal and the other side of the core. As a result, it is possible to increase the thickness of the core and prevent cracks from occurring in the core.

The lead-out may have a connection embedded inside the core and connects the winding and the terminal, the connection maybe bent from the winding to the terminal, a distance between the terminal and the winding with respect to a winding axial direction of the coil maybe smaller than an inner diameter of a bent part of the connection. With such a configuration, it becomes possible to relatively increase a curvature radius of a curved shape (an R-shape) provided at the connection, and thus, a mechanical load added to the connection can be reduced.

A tip of the embedded part may have a convex shape. With such a configuration, inside the core, the tip of the embedded part can be easily engaged with the core and the fixing strength between the core and the embedded part can be increased.

A tip of the embedded part may have a tapered surface, and inside the core, the tapered surface maybe inclined in a direction away from the bottom of the core.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the coil device according to a first embodiment of the present invention.

FIG. 2A is a perspective view of the coil device shown in FIG. 1 when viewed from a mounting surface side.

FIG. 2B is a perspective view of a modified example of the coil device shown in FIG. 2A.

FIG. 3 is a cross-sectional view of the coil device along line shown in FIG. 1.

FIG. 4A is a cross-sectional view of the coil device along line IVA-IVA shown in FIG. 1.

FIG. 4B is a cross-sectional view of a modified example of the coil device shown in FIG. 4A.

FIG. 4C is a cross-sectional view of another modified example of the coil device shown in FIG. 4A.

FIG. 5A is a partially enlarged cross-sectional view of the coil device shown in FIG. 4A.

FIG. 5B is another partially enlarged cross-sectional view of the coil device shown in FIG. 4A.

FIG. 5C is a partially enlarged cross-sectional view of a modified example of the coil device shown in FIG. 5B.

FIG. 6A is a view showing a producing step of the coil device shown in FIG. 1.

FIG. 6B is a view of the first layer compact shown in FIG. 6A viewed from another angle.

FIG. 6C is a view showing a step subsequent to the step shown in FIG. 6A.

FIG. 6D is a view of the first layer compact shown in FIG. 6C viewed from another angle.

FIG. 6E is a view showing a step subsequent to the step shown in FIG. 6C.

FIG. 6F is a view showing a step subsequent to the step shown in FIG. 6E.

FIG. 6G is a view of the substrate shown in FIG. 6F viewed from another angle.

FIG. 7 is a perspective view of a coil device according to a second embodiment of the invention.

FIG. 8 is a cross-sectional view of the coil device shown in FIG. 7 along line VIII-VIII.

DETAILED DESCRIPTION

Hereinafter, the invention will be described based on the embodiments shown in the drawings.

First Embodiment

As shown in FIG. 1, the coil device 2 according to the first embodiment of the invention functions such as an inductor, and is mounted on various electronic devices. The coil device 2 has a core 4, a coil 6 and a metal layer 8.

The coil 6 is an air-core coil, and is formed by edgewise winding an insulation coated flat wire. As the insulation coat, such as an epoxy-modified acrylic resin is used. As the materials of the flat wire, copper, silver, alloys thereof, other metals or alloys thereof are used. The coil 6 has a winding 60 and a pair of lead-outs 6a and 6b. The winding 60 is embedded inside the core 4. The number of turns of the winding 60 is five turns, but is not particularly limited, and may be one turn or more.

The lead-out 6a constitutes one end of the coil 6, and the lead-out 6b constitutes the other end of the coil 6. The lead-out 6a is led out from the uppermost turn (hereinafter referred to as the upper end of the winding 60) of the winding 60 in the winding axial direction toward the bottom 4a of the core 4. The lead-out 6b is led out from the lowermost turn (hereinafter referred to as the lower end of the winding 60) of the winding 60 in the winding axial direction toward the bottom 4a of the core 4. A detailed configuration of the lead-outs 6a and 6b will be described later.

The core 4 has a substantially rectangular parallelepiped shape and is formed by combining a first layer 41 and a second layer 42. FIGS. 1, 3, and 4A to 4C clearly show the first layer 41 and the second layer 42 as separate members for an explanatory convenience, however, they are substantially integrated and boundaries thereof are virtually indistinguishable.

The core 4 has a bottom 4a, sides 4b to 4e, and a top 4f. The side 4d and the side 4e face each other in the first direction, the side 4b and the side 4c face each other in the second direction, and the side 4a and the top 4f face each other in the third direction. In the drawings, the X-axis corresponds to the first direction, the Y-axis corresponds to the second direction, and the Z-axis corresponds to the third direction.

Although a size of the core 4 is not particularly limited, its X-axis direction width is such as 1.0 to 7.0 mm, its Y-axis direction width is such as 1.0 to 7.0 mm, and its Z-axis direction width is such as 0.5-5.0 mm.

The core 4 is formed by a material containing a magnetic material and a resin. Examples of the magnetic material forming the core 4 include ferrite grains, metal magnetic grains, etc. Examples of the ferrite grains include Ni—Zn based ferrite and Mn—Zn based ferrite. The metal magnetic grains are not particularly limited, but Fe—Ni alloy powder, Fe—Si alloy powder, Fe—Si—Cr alloy powder, Fe—Co alloy powder, Fe—Si—Al alloy powder, amorphous iron, etc. are exemplified. The resin forming the core 4 is not particularly limited, but examples thereof include an epoxy resin, a phenol resin, a polyester resin, a polyurethane resin, a polyimide resin, other synthetic resins, and other non-magnetic materials. The core 4 may be a sintered body of a metallic magnetic material. Although the first layer 41 and the second layer 42 are preferably formed by the same material, they may be formed by different materials.

The first layer 41 has a support 41a, a winding core 41b, cutouts 41c1 to 41c3, and steps 41d1 and 41d2 (FIG. 3). The support 41a has a substantially flat plate shape and is formed in a substantially cross shape. The winding 60 can be placed on a top surface of the support 41a. That is, the support 41a mainly plays a role of supporting the winding 60. The support 41a has a first side 41a1, a second side 41a2, a third side 41a3, and a fourth side 41a4.

The first side 41a1 is located on the positive side of the X-axis than the winding core 41b. The second side 41a2 is located on the negative side of the X-axis direction than the winding core 41b. The third side 41a3 is located on the positive side of the Y-axis than the winding core 41b. The fourth side 41a4 is located on the negative side of the Y-axis than the winding core 41b. The first side 41a1 and the second side 41a2 are formed to be thinner than the third side 41a3 and the fourth side 41a4. As described below, this is because steps 41d1 and 41d2 (FIG. 3) are formed on the bottom surfaces of the first side 41a1 and the second side 41a2, respectively.

The winding core 41b is integrally formed on the top surface of the support 41a. The core 41b has a columnar shape protruding upward, and the winding 60 can be inserted from the above. The coil 6 can be installed on the winding core 41b by winding a wire around the outer peripheral surface of the winding core 41b.

The cutout 41c1 is formed where a first side 41a1 and a third side 41a3 intersect substantially at right angles. The cutout 41c2 is formed where a second side 41a2 and the third side 41a3 intersect substantially at right angles. The cutout 41c3 is formed where the first side 41a1 and a fourth side 41a4 intersect substantially at right angles. Although a detailed illustration is omitted, a cutout is also formed where the second side 41a2 and the fourth side 41a4 intersect substantially at right angles. These cutouts have a substantially rectangular shape when viewed from above, however, they can be cut into other shapes. Further, instead of these cutouts, through-holes penetrating the support 41a in the vertical direction may be formed at the four corners of the support 41a.

The cutout 41c1 serves as a passage for leading out the lead-out 6a drawn from the winding 60 to the bottom surface of the first side 41a1. The cutout 41c2 serves as a passage for drawing out the lead-out 6b led out from the winding 60 to the bottom surface of the second side 41a2. In addition, the cutouts 41c1 to 41c3 serve as passages for allowing a compacting material forming the second layer 42 to flow from the top surface to the bottom surface of the support 41a.

The step 41d1 is formed on the bottom surface of the first side 41a1 of the support 41a and extends along the Y-axis direction. The step 41d2 (FIG. 3) is formed on the bottom surface of the second side 41a2 of the support 41a and extends along the Y-axis direction. As shown in FIG. 3, the lead-out 6a is arranged at the step 41d1, and the lead-out 6b is arranged at the step 41d2.

The step heights of the steps 41d1 and 41d2 are smaller than the thicknesses of the lead-outs 6a and 6b, respectively. Thus, when the lead-out 6a is arranged on the step 41d1, the lead-out 6a protrudes downward from the bottom 4a of the core 4, and a part of the lead-out 6a is arranged below the bottom 4a. Further, when the lead-out 6b is arranged at the step 41d2, the lead-out 6b protrudes downward from the bottom 4a of the core 4, and a part of the lead-out 6b is arranged below the bottom 4a.

As shown in FIG. 1, the second layer 42 covers the first layer 41. More specifically, the second layer 42 covers the top of the support 41a and fills the cutouts 41c1 to 41c3 and the steps 41d1 and 41d2. Of the bottom surfaces of the support 41a, the bottom surfaces of the third side 41a3 and the fourth side 41a4 may not be covered with the second layer 42.

The bottom surface of the second layer 42 is substantially flush with the bottom surface of the support 41a at the steps 41d1 and 41d2 and the cutouts 41c1 to 41c3. Therefore, as shown in FIG. 2A, parts of each of the lead-outs 6a and 6b are exposed from the bottom surface (the bottom 4a of the core 4) of the second layer 42.

Next, the detailed configuration of the lead-outs 6a and 6b will be described. As shown in FIG. 1, the lead-out 6a has a terminal 61 and a connection 62. Similarly, as shown in FIG. 4A, the lead-out 6b has a terminal 61 and a connection 62.

The terminal 61 is arranged at the bottom 4a of the core 4. More specifically, the terminal 61 (FIG. 1) of the lead-out 6a is arranged at the bottom surface side of the first side 41a1, that is, on the step 41d1. The terminal 61 (FIG. 4A) of the lead-out 6b is arranged at the bottom surface side of the second side 41a2, that is, on the step 41d2.

The terminal 61 extends along the Y-axis direction. The end of the terminal 61 on the Y-axis negative direction side may be arranged on the Y-axis positive direction side than the end of the second side 41a2 on the Y-axis negative direction side. The terminal 61 extends linearly along the bottom 4a of the core 4 from one end to the other end in its extending direction. That is, the terminal 61 does not bend toward the inside of the core 4 and does not cut into the inside of the core 4.

Thereby, a volume of the core 4 can be increased, and the magnetic properties of the coil device 2 can be improved. Also, deterioration in quality of the coil device 2 due to bending of the terminal 61 can be prevented.

A first distance L1 (FIG. 2A) between the terminal 61 (exposed part 611 described later) and the side 4b of the core 4 and a second distance L2 (FIG. 2A) between the terminal 61 (exposed part 611 described later) and the side 4c of the core 4 may be different. For example, the second distance L2 may be longer than the first distance L1. In this case, a relatively large space is formed between the terminal 61 and the side 4c of the core 4. As a result, it is possible to increase the thickness of the core 4 and prevent generation of cracks in the core 4.

The terminal 61 has an embedded part 610 and an exposed part 611. The embedded part 610 is embedded inside the core 4 (the second layer 42) and covered with the second layer 42 at the step 41d2. The top surface of the embedded part 610 may be fixed to the bottom surface of the second side 41a2 of the support 41a. Although FIG. 4A shows the terminal 61 of the lead-out 6b, the configuration of the terminal 61 of the lead-out 6a is similar to the configuration of the terminal 61 of the lead-out 6b, and that the detailed explanation thereof is omitted.

As shown in FIG. 5A, the thickness T1 of the embedded part 610 is thinner than the thickness T2 of the terminal 61, is preferably ¼ or more and less than the thickness T2 of the terminal 61, and is more preferably ½ or more and ⅘ or less.

By setting the range of T1 to the range described above, it is possible to prevent the terminal 61 from peeling off from the bottom 4a of the core 4. In addition, since the thickness of the exposed part 611 (a part of the terminal 61 disposed outside the core 4) becomes relatively small, the height of the coil device 2 can be reduced.

The surface of the embedded part 610 is covered with an insulation film, not shown. As described above, the coil 6 is formed by an insulation coated wire, and an insulation coat is left unremoved at the embedded part 610. As a result, it is possible to prevent generation of a short circuit between the embedded part 610 and the core 4 (a magnetic material contained in the core 4).

As shown in FIG. 4A, the exposed part 611 is arranged outside the core 4. The exposed part 611 is exposed downward from the bottom 4a of the core 4. The width of the exposed part 611 in the X-axis direction is substantially equal to the width of the embedded part 610 in the X-axis direction. The width of the exposed part 611 in the Y-axis direction is substantially equal to the width of the embedded part 610 in the Y-axis direction. The exposed part 611 extends along the Y-axis direction and has a substantially rectangular shape when viewed from the bottom 4a side of the core 4 (See FIG. 2A).

As shown in FIG. 2A, a magnetic material-rich part 4a1 containing a relatively large amount of magnetic material is formed around the exposed part 611. The magnetic material rich-part 4a1 is formed around each exposed part 611 of the lead-outs 6a and 6b. In other words, the exposed part 611 is exposed from the magnetic material-rich part 4a1.

Further, in the area between the magnetic material-rich part 4a1 surrounding the exposed part 611 of the lead-out 6a and the magnetic material-rich part 4a1 surrounding the exposed part 611 of the lead-out 6b, a resin-rich part 4a2 having a relatively large resin content is formed. The resin-rich part 4a2 contains more resin than the magnetic material-rich part 4a1. In addition, the magnetic material-rich part 4a1 contains more magnetic material than the resin-rich part 4a2. The magnetic material-rich part 4a1 and the resin-rich part 4a2 are formed at the bottom 4a of the core 4.

Laser irradiation is exemplified as a method for forming the magnetic material-rich part 4a1. By irradiating a predetermined range (the exposed part 611 and its surroundings) of the bottom 4a of the core 4 with laser, the resin around the exposed part 611 (the resin of the core 4 or the insulation coat covering the metal grains) is blown off. As a result, the magnetic material content becomes relatively higher than the resin content in the exposed part 611 and its surroundings (laser irradiation surface), and magnetic material-rich part 4a1 is formed. The insulation coat on the surface of the exposed part 611 is removed by laser irradiation.

The magnetic material-rich part 4a1 has a substantially rectangular shape when viewed from the bottom 4a side of the core 4. The width of the magnetic material-rich part 4a1 in the X-axis direction is longer than the width of the lead-out 6a or 6b in the X-axis direction, and the width of the magnetic material-rich part 4a1 in the Y-axis direction is longer than the width of the lead-out 6a or the exposed part 611 in the Y-axis direction.

A ratio W1/W2 of the width W1 of the magnetic material-rich part 4a1 in the X-axis direction and the width W2 of the core 4 in the X-axis direction is preferably ⅛ to ⅓. By setting the value of the ratio W1/W2 within the above range, it is possible to avoid fluctuations in the magnetic properties of the coil device 2 due to a decrease in the resin content in the core 4.

In the magnetic material-rich part 4a1, the resin of the bottom 4a is blown off by laser irradiation, so the surface roughness of the bottom 4a of the core 4 in the magnetic material-rich part 4a1 is more than the surface roughness of the bottom 4a of the core 4 in the resin-rich part 4a2. The surface roughness (arithmetic mean height) Sa of the bottom 4a in the magnetic material-rich part 4a1 is, for example, 2.3 to 2.9 μm. On the other hand, the surface roughness (arithmetic mean height) Sa of the bottom 4a in the resin-rich part 4a2 is, for example, 1.0 to 2.0 μm. In addition, the difference between the surface roughness of the bottom 4a in the magnetic material-rich part 4a1 and the surface roughness of the bottom 4a in the resin-rich part 4a2 is, for example, 0.9 to 1.7 μm.

The surface roughness Sa is measured by a laser microscope (VK-X1000) manufactured by Keyence Corporation at a magnification of 1000 times to obtain the measured values of the surface roughness at three points in an inner part of the magnetic material-rich part 4a1. Then, the average value thereof was used as the value of the surface roughness Sa of the bottom 4a in the magnetic material-rich part 4a1. Similarly, measured values of surface roughness at three points in the inner part of the resin-rich part 4a2 were obtained, and the average value thereof was used as the value of the surface roughness Sa of the bottom 4a of the resin-rich part 4a2.

As shown in FIG. 4A, the shapes of the first end 611a (the end in the Y-axis negative direction side) of the exposed part 611 and the second end 611b (the end in the Y-axis positive direction side) of the exposed part 611 may be different. The surface of the exposed part 611 is flat at the first end 611a. On the other hand, as shown in FIG. 5A, the surface of the exposed part 611 at the second end 611b may be formed with a curved surface 612 that curves toward the bottom 4a of the core 4.

As a result, for example, when connecting the exposed part 611 to the mounting substrate by soldering, it is possible to form a thick solder on the curved surface 612 and increase the connection strength between the exposed part 611 and the mounting substrate. A tapered surface may be formed on the surface of the exposed part 611 instead of the curved surface 612.

The thickness of the exposed part 611 is preferably ⅕ or more and ½ or less of the thickness T2 of the terminal 61. By setting the range of the thickness of the exposed part 611 within the above range, it becomes easier to connect the exposed part 611 to the mounting substrate. Also, when producing the coil device 2, it becomes easier to form the metal layer 8 on the surface of the exposed part 611.

As shown in FIG. 4A, the connection 62 is embedded inside the core 4 (the second layer 42) and connects the winding 60 and the terminal 61. The connection 62 has a bent shape (an R shape), and extends from the winding 60 to the terminal 61 while turning about 180 degrees from the Y-axis positive direction side toward the Y-axis negative direction side.

More specifically, as shown in FIGS. 1 and 4A, the connection 62 of the lead-out 6a is led out from the upper end of the winding 60 to the vicinity of the side 4b of the core 4. Also, the connection 62 of the lead-out 6b is led out from the lower end of the winding 60 to the vicinity of the side 4b of the core 4.

In addition, each connection 62 of the lead-outs 6a and 6b is bent in the Z-axis direction near the side 4b of the core 4 and is led out near the bottom 4a of the core 4.

Further, the connection 62 of the lead-out 6a is bent in the Y-axis direction near the bottom 4a of the core 4 (cutout 41c1) and connected to the terminal 61 near the step 41d1. The connection 62 of the lead-out 6b is bent in the Y-axis direction near the bottom 4a of the core 4 (cutout 41c2) and connected to the terminal 61 near the step 41d2.

As shown in FIG. 4A, with respect to the Z-axis direction, the distance L3 between the terminal 61 and the winding 60 is shorter than the inner diameter (a bending diameter) L4 at the bent part (a folded part) of the connection 62. Therefore, it is possible to make the curvature radius of the curved shape provided at the connection 62 relatively large, and reduce the mechanical load applied to the connection 62 when forming the shape.

A metal layer 8 is formed on the surface of the exposed part 611. The metal layer 8 is a part connected to the substrate, and is formed of a plated film. Therefore, the metal layer 8 has a solder wettability and assists the connection between the exposed part 611 and the mounting substrate. Examples of the plated films include metals such as Sn, Au, Ni, Pt, Ag, and Pd, and alloys thereof. Note that the metal layer 8 may be formed by a method such as sputtering. The thickness of the metal layer 8 is preferably 3-30 μm. The thickness of metal layer 8 is preferably thinner than the thickness of the exposed part 611 of the terminal 61.

The width of the metal layer 8 in the Y-axis direction is substantially equal to the width of the exposed part 611 in the Y-axis direction, and the width of the metal layer 8 in the X-axis direction is substantially equal to the width of the exposed part 611 in the X-axis direction. That is, the metal layer 8 preferably covers the whole area of the exposed part 611. However, as shown in FIG. 5A, the metal layer 8 does not have to exist on the curved surface 612 of the exposed part 611 at a position spaced apart from the bottom surface of the metal layer 8 toward the bottom 4a of the core 4. Hereinafter, an area where the metal layer 8 does not exist is referred to as a metal layer non-formed part 613.

The metal layer non-formed part 613 mainly serves to adjust the area of the metal layer 8. That is, by providing the metal layer non-formed part 613 in the exposed part 611, the area (an effective metal layer) of the metal layer 8 that substantially contributes to the connection with the mounting substrate can be adjusted. As a result, the area of the effective metal layer can be adjusted according to the area of the land pattern of the mounting substrate. At the metal layer non-formed part 613, the insulation coat may be formed on the surface of the exposed part 611 (a curved surface 612).

Although the metal layer 8 is formed on the surface of the exposed part 611, it is not formed on the surface of the embedded part 610. This is to prevent a short-circuit failure between the embedded part 610 and the magnetic material inside the core 4.

Next, a producing method for the coil device 2 is described. According to the method of the embodiment, a first layer compact 410 (FIG. 6A) corresponding to the first layer 41 shown in FIG. 1 and a multiple coils 6 wound in an air-core coil shape are firstly prepared.

As shown in FIG. 6A, the first layer compact 410 has a shape in which a plurality of the first layers 41 are connected. The first layer compact 410 can be obtained by green compacting, injection molding, or machining.

As shown in FIGS. 6A and 6B, the first layer compact 410 includes a support 410a, a plurality of winding cores 410b, a plurality of cutouts 410c, a plurality of steps 410d, and a plurality of through holes 410e.

The support 410a has a shape in which a plurality of supports 41a (FIG. 1) are connected. The cutout 410c and the through hole 410e are used as a passage for compacting materials forming the second layer 420 to flow inside the press mold, as will be described later. The step 410d is mainly used for arranging the lead-outs 6a and 6b of the coil 6.

Next, as shown in FIGS. 6C and 6D, the coil 6 is arranged on the winding core 410b. Note that the wire 6 may be wound around the outer peripheral surface of the winding core 410b. Next, the lead-outs 6a and 6b of the coil 6 are led out toward the bottom surface of the first layer compact 410 and placed on the step 410d.

Next, the first layer compact 410 with the coil 6 arranged thereon is placed in a press mold. In addition, the first layer compact 410 is covered with the second layer 420 (FIG. 6E) so that the lead-outs 6a and 6b are partially exposed, and the substrate 400 of the first layer compact 410 and the second layer 420 are formed (FIG. 6F).

The method for compacting the second layer 420 is not particularly limited, however, insert injection molding, in which the first layer compact 410 is placed inside the press mold and pressed thereof, is exemplified. According to this compacting, the compacting material forming the second layer 420 flows from the front surface to the rear surface of the first layer compact 410 through the cutout 410c or the through hole 410e shown in FIG. 6A, and can be distributed inside the step 410d. In addition, as a material constituting the second layer 420, a material having fluidity during compacting is used, and a composite magnetic material using a thermoplastic resin or a thermosetting resin as a binder is used.

Here, the step height of the step 410d shown in FIG. 6B is smaller than the thickness of the wire forming the coil 6. Therefore, when the first layer compact 410 is covered with the second layer 420 (FIG. 6E), a part of each of the lead-outs 6a and 6b is exposed from the bottom surface of the substrate 400 as shown in FIG. 6G. That is, the part exposed from the bottom surface of the substrate 400 becomes the exposed part 611 of the terminal 61 shown in FIG. 4A.

Next, a predetermined range at the bottom surface of the substrate 400 is irradiated with a laser by a predetermined intensity to remove the insulation coat of the exposed parts 611 of the lead-outs 6a and 6b exposed from the bottom surface of the substrate 400. Next, the substrate 400 is cut along the planned cutting lines 10A and 10B shown in FIG. 6F to separate the substrate 400 into pieces. Thereby, a core 4 having a single coil 6 embedded therein as shown in FIG. 1 can be obtained.

Next, a barrel polishing is performed on a plurality of individuated cores 4. Next, by forming metal layer 8 on the surfaces of each exposed part 611 of lead-outs 6a and 6b by plating, coil device 2 shown in FIG. 1 can be obtained.

As described above, according to the embodiment, the metal layer 8 is formed on the surface of the exposed part 611 as shown in FIG. 4A. Therefore, it is possible to mount the coil device 2 on the mounting substrate via the metal layer 8. Therefore, it is not necessary to form a terminal electrode on the bottom 4a of the core 4 separately from the metal layer 8. Thus, the coil device 2 can be easily produced and the production cost can be reduced.

In addition, since the terminal 61 is exposed from the core 4 as the exposed part 611, the exposed part 611 can contribute to connection with the mounting substrate. In addition, since the terminal 61 is embedded inside the core 4 as the embedded part 610. Thus, a gap, a space in which plating solution, flux, or the like may enter, between the terminal 61 and the bottom 4a of the core 4 does not exist. Therefore, it is possible to prevent the lead-outs 6a and 6b from being corroded due to the residue of the plating solution and the flux, and quality and reliability of the coil device 2 can be improved.

In addition, since the embedded part 610 is fixed to the core 4 inside the core 4, the fixing strength between the terminal 61 and the core 4 is increased, and the terminal 61 is prevented from peeling off from the bottom 4a of the core 4.

In addition, since the coil 6 is formed of an insulation coated flat wire, the surface areas of the exposed part 611 and the metal layer 8 formed on the surface thereof are increased, and the connection strength between the metal layer 8 and the mounting substrate can be improved.

Second Embodiment

A coil device 2A according to the second embodiment of the invention shown in FIG. 7 has the same configuration as the coil device 2 of the first embodiment except for the followings. In FIG. 7, members that overlap with the coil device 2 of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

The coil device 2A has a coil 6A. The coil 6A is formed by crosswise winding a flat wire. The coil 6A has a winding 60A, and the winding 60A is formed to have a substantially elliptical shape when viewed from above. The lead-outs 6a and 6b are led out toward the bottom 4a of the core 4 in a twisted manner from above and below the winding 60A, respectively.

As shown in FIG. 8, the exposed part 611 of the terminal 61 is exposed from the bottom 4a of the core 4, and the metal layer 8 is formed on the surface of the exposed part 611. Therefore, the same effects as in the first embodiment can be obtained in this embodiment.

The invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the invention.

In the first embodiment described above, as shown in FIG. 4B, the winding 60 may be curved or warped so as to be convex upward. The degree of curvature of the winding 60 increases toward the upper end of the winding 60. Also, the degree of curvature of the winding 60 decreases toward the lower end of the winding 60.

Further, as shown in FIG. 4C, the winding 60 may be curved or warped so as to be convex downward. The degree of curvature of the winding 60 increases toward the upper end of the winding 60. Also, the degree of curvature of the winding 60 decreases toward the lower end of the winding 60.

In each of the above-described embodiments, as shown in FIGS. 5B and 5C, the tip of the embedded part 610 may have a convex shape (convex 610a). With such a configuration, the convex 610a can be easily engaged with the core 4 inside the core 4, and the fixing strength between the core 4 and the embedded part 610 can be increased.

Also, a tapered surface 610b may be formed at the tip of the embedded part 610 (the surface of the convex 610a). Inside the core 4, the tapered surface 610b may be inclined toward the bottom 4a of the core 4. In the example shown in FIG. 5B, the proportion of such a tapered surface is large.

Alternatively, inside the core 4, the tapered surface 610b may be inclined in a direction away from the bottom 4a of the core 4. In the example shown in FIG. 5C, the proportion of such a tapered surface is large. In this case, the tip of the embedded part 610 is arranged at a relatively deep position (the center side of the core 4) of the core 4, effectively preventing the terminal 61 from peeling off from the bottom 4a of the core 4.

In each of the above-described embodiments, as shown in FIG. 2B, the extending direction of the terminal 61 may be inclined with respect to the first direction or the second direction (the X-axis direction or the Y-axis direction) of the core 4. For example, the extending direction of the terminal 61 may be inclined with respect to the Y-axis direction so as to approach the side surface of the core 4 in the X-axis direction. Alternatively, the extending direction of the terminal 61 may be inclined with respect to the Y-axis direction so as to be away from the side surface of the core 4 in the X-axis direction.

With such a configuration, the length (the surface area) of the embedded part 610 can be increased according to the inclination angle of the terminal 61, and the fixing strength between the embedded part 610 and the core 4 can be increased. Moreover, the length (the surface area) of the exposed part 611 can be increased according to the inclination angle of the terminal 61, and the connection strength between the exposed part 611 and the mounting substrate can be improved.

In each of the above embodiments, the metal layer non-formed part 613 shown in FIG. 4A is not essential and may be omitted. That is, the metal layer 8 may also be formed on the curved surface 612 of the exposed part 611. The curved surface 612 may be omitted.

In each of the above embodiments, the distance L3 between the terminal 61 and the winding 60 and the inner diameter L4 of the bent part of the connection 62, shown in FIG. 4A, may be substantially equal.

Although the core 4 include the first layer 41 and the second layer 42 in each of the above embodiments, the core 4 may include one core. For example, the core 4 may be formed by placing the coil 6 inside a press mold, filling the inside of the press mold with a compacting material, and compressing and pressing thereof

2, 2A . . . Coil device
4 . . . Core
4a . . . Bottom
4a1 . . . Magnetic material-rich part
4a2 . . . Resin-rich part
41 . . . First layer
41a . . . Support
41a1 to 41a4 . . . First side to Fourth side
41b . . . Winding core
41c1 to 41c3 . . . Cutouts
41d1, 41d2 . . . Step
42 . . . Second layer
6, 6A . . . Coil
6a, 6b . . . Lead-outs
60, 60A . . . Winding
61 . . . Terminal
610 . . . Embedded part
610a . . . Convex
610b . . . Tapered surface
611 . . . Exposed part
612 . . . Curved surface
613 . . . Metal layer non-formed part
62 . . . Connection
8 . . . Metal layer
400 . . . Substrate
410 . . . First layer compact
410a . . . Support
410b . . . Winding core
410c . . . Cutout
410d . . . Step
410e . . . Through hole
420 . . . Second layer

COIL DEVICE

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CPC

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Priority Claims (1)