# Patent

## Title
Surface-mount inductor and method for manufacturing the same

## Abstract

A surface-mount inductor including a coil formed by winding a rectangular wire and a molded body for accommodating the coil, where the coil includes: a first roll formed by winding a rectangular wire, a second roll formed by winding the rectangular wire in position adjacent to the first roll along the winding axis, and a third roll formed by winding the rectangular wire on the second roll in a partially overlapping manner in a position adjacent to and opposite from the first roll along the winding axis, the ends of the wire being brought out from the outermost turns of the first roll and the third roll as lead ends, and the winding axis is parallel with the mounting face and the lead ends being extended over the surface of the molded body, as well as the method for manufacturing the same.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2014-264165, filed on Dec. 26, 2014, and Japanese Patent Application No. 2014-264166, filed on Dec. 26, 2014, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface-mount inductor and a method for manufacturing the same.
2. Description of the Related Art
Conventionally, surface-mount inductors which coil has been coated with thermoplastic sealants (molding materials) containing magnetic powder and resin are widely used. For example, JP2003-290992 discloses a method for manufacturing surface-mount inductors using metal pieces as external terminals. The surface-mount inductors have external terminals which are metal pieces welded to lead ends which are processed to serve as external terminals.
JP2004-193215 discloses a method for manufacturing surface-mount inductors by coating coils, which is configured by winding a wire having a rectangular section (hereinafter “rectangular wire”), with sealing material. The surface-mount inductor has external terminals which are formed by deforming lead wires of a coil.
SUMMARY OF THE INVENTION
In a surface-mount inductor disclosed in JP2003-290992, since its coil ends are welded to metal pieces, the contact portions of the coil ends and of the metal pieces are exposed to thermal and mechanical stresses.
In the surface-mount inductor of JP2004-193215, since the direction of the winding axis of the coil is orthogonal to the wide surface of the rectangular wire, the inner and outer diameters are exposed to mechanical stress during winding.
Further, the surface-mount inductor in JP 2004-193215 is configured so that one lead end goes from its bottom side to the bottom and the other lead end goes from upper side to the bottom.
In this case, because of the difference in the length of the lead wires, the shape of the coil is asymmetrical. The surface-mount inductor housing an asymmetrical coil requires a step of marking the polarity of the terminals, since the electric characteristics when inputting in one terminal are different from those when inputting in the other terminal.
Consequently, the present invention aims to provide a surface-mount inductor has less mechanical and thermal stresses, and provides a method for manufacturing of the same.
Means for Solving the Problem
A surface-mount inductor according to the present invention is characterized by including a coil formed by winding a rectangular wire and a molded body for accommodating the coil, wherein the coil comprises:
a first roll formed by winding a rectangular wire,
a second roll formed by winding the rectangular wire in position adjacent to the first roll along the winding axis, and
a third roll formed by winding the rectangular wire on the second roll in partially overlapped manner in position adjacent and opposite to the first roll along the winding axis,
wherein the ends of the wire are brought out from the outermost turns of the first roll and the third roll as lead ends, and the winding axis is parallel with the mounting face and the lead ends extend over the surface of the molded body.
A method for manufacturing a surface-mount inductor according to the present invention is characterized in that the inductor includes a coil formed by winding a rectangular wire and a molded body for accommodating the coil, wherein
a step for making a coil, forming a first roll contacting the median portion of a rectangular wire to the spindle of a winding machine to wind, forming a second winding portion at a position adjacent to the first roll along the winding axis, arranging a jig at the first roll side of the second roll, forming a third roll winding the wire on the second roll at a position opposite to the first roll along the winding axis in such a manner that a portion of the third roll partially overlap with the second roll, and forming lead ends brought out from the outermost turn of the first roll and the third roll; and
a step for housing the coil inside the molded body,
whereby the coil is housed in the molded body, arranging the winding axis be parallel with the mounting face of the molded body, and the lead ends extending over the surface of the molded body.
Effect of the Invention
According to the surface-mount inductor and the manufacturing method of the same as described in the present application, since the lead ends of coil are used as external terminals, the thermal and mechanical stresses are decreased. Further, since the direction of the winding axis and that of the wide surface of the coil are parallel, the mechanical stress caused at the inner and outer diameter portions may be decreased. In addition, since the coil is wound such that the direction of the mounting face of the surface-mount inductor and the direction of winding axis of the coil are parallel, the shape of the coil may be symmetrical.
Therefore, a surface-mount inductor, which serves to decrease the thermal and mechanical stresses, and to solve the issue of polarities of electrical characteristics polarity, as well as a method for manufacturing the same can be provided.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a surface-mount inductor of the first embodiment according to the present invention;
FIGS. 2A through 2F show steps in method of winding a coil which is used in the surface-mount inductor of the first embodiment according to the present invention in sequential manner;
FIG. 3 is a perspective view of the blocks which are used in the first embodiment according to the present invention;
FIG. 4 is a plan view of the mounting face of the blocks which are used in the surface-mount inductor of the first embodiment according to the present invention;
FIGS. 5A, 5B and 5C show steps for manufacturing the surface-mount inductor of the first embodiment according to the present invention, FIG. 5A showing the state before blocks being fitted, FIG. 5B showing the attached blocks, and FIG. 5C showing the state of the mounting face after fitting;
FIG. 6 is a partial perspective view showing the method of manufacturing of the surface-mount inductor of the first embodiment according to the present invention;
FIG. 7 shows the step for fitting the two blocks and the coil of the first embodiment according to the present invention;
FIG. 8 is a perspective view of the blocks used in the second embodiment according to the present invention;
FIG. 9 is a plan view of the blocks used in the surface-mount inductor of the second embodiment according to the present invention;
FIGS. 10A, 10B and 10C show sectional views along the line A-A in FIG. 9 for showing the method for manufacturing the second embodiment of the present invention, FIG. 10A showing the state before connecting the blocks, FIG. 10B showing the connected blocks, and FIG. 10C showing the mounting face after connecting the blocks;
FIG. 11 is a perspective view of the magnetic cores used in the surface-mount inductor of the third embodiment according to the present invention: and
FIG. 12 is a perspective view of the surface-mount inductor of the third embodiment according to the present invention.



DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
The first embodiment of a surface-mount inductor according to the present invention will now be described with reference to FIGS. 1 through 7.
FIG. 1 is a perspective view showing an example of a coil 2 used in the surface-mount inductor according to the present invention, the coil 2 being formed by winding a rectangular wire contacting the wide surface 2a on a winding core (not shown), and processing the ends of the wire to be lead ends 2b. 
As shown in FIG. 1, a coil 2 is a coreless (empty core) coil having symmetrical profile when viewed from a direction orthogonal to the axial line. The coil 2 has a first roll 2c, which is such configured that one end of a rectangular wire is positioned at the outermost turn and the other end of a rectangular wire at the innermost turn is positioned adjacently along the winding axis, and a second roll 2d, which is configured as one roll, is positioned adjacent to the first roll 2c on opposite side along the winding axis of the coil 2, and a third roll 2e, which is configured as one roll, the inner diameter of which is equal to or larger than the outer diameter of the second roll 2d, and the third roll 2e is wound on the second roll 2d in partially overlapping manner at a position adjacent to the second roll 2d and opposite side to the first roll 2c along the winding axis of the coil 2.
From the outermost turn of the third roll 2e, the lead ends 2b, which are the ends of the rectangular wire, are brought to the extending direction of the outer peripheries. The respective lead ends 2b are brought toward opposite directions from the winding axis and the end portions are formed to be U-shaped to shelter the outermost turn of the coil 2.
The coil 2 thus formed does not suffer from mechanical stress around the inner and outer diameter portions when winding, because the direction of the wide surface 2a and the direction of the rectangular wire are parallel.
A method of winding the coil 2 is described in reference to FIGS. 2A through 2F. The coil 2 is formed by winding an insulated rectangular wire using a winding machine (not shown) equipped with a pair of spindles 3. Each spindle 3 has a winding core 3a and a base portion 3b, and is equipped with a jig 3c having a C-shaped mouth at the tip.
A pair of spindles 3 includes a pair of winding cores 3a, a pair of cylindrical base portions 3b which are adjacent and coaxial to the winding cores 3a and have a diameter larger than that of the winding cores 3a. The length of the winding core in the axial direction is larger than the width of the rectangular wire. The spindle tips 3aa are the end faces of the winding cores 3a and are positioned at sides opposite to the base portions 3b. 
Firstly, the two spindles 3 are positioned in a manner that the spindle tips 3aa face each other, as shown in FIG. 2A.
Next, as shown in FIG. 2B, the wide surface 2a of the median portion of the rectangular wire is put in contact with the winding cores 3a. Then, as shown in FIG. 2C, the ends of the rectangular wire are repetitively wound around the winding cores 3a, and the first roll 2c is formed on the winding cores 3a. And then, one end of the rectangular wire at the innermost turn of the first roll 2c is shifted in the opposite direction from the first roll 2c along the winding axes of the spindles 3 to be in contact with the winding cores 3a. And, as shown in FIG. 2D, the rectangular wire is wound on the winding cores 3a to form the second roll 2d. 
Subsequently, as shown in FIG. 2E, a jig 3 having a C-shaped mouth is arranged on the second roll 2d to be in contact with the end of the first roll 2c. In this state, the third roll 2e is formed by winding a rectangular wire on the second roll 2d in partially overlapping manner at a position opposite to the first roll 2c in the direction of the winding axis.
The lead ends 2b are pulled from the outermost turn of the coil 2 in its extended directions oppositely each other and the ends are bent to form U-shaped portions. The coil 2 is heated and solidified, and then is removed thereafter from the spindles 3 as shown in FIG. 2F, thus producing the coil 2 which is symmetrical relative to a direction orthogonal to the winding axis.
The lead ends 2b, which are the ends of the rectangular wire, are brought out in the extending direction thereof from the outermost turns of the first roll 2c and of the third roll 2e, respectively. The lead ends 2b are brought out in opposite directions to each other from the winding axis and the ends are bent in a U shape to surround the outer periphery of the coil 2. The coil 2 is left by heating it and, as shown in FIG. 2F, distancing the spindles 3, which tips are in mutual contact, from the coil 2.
Although the coil 2 is formed by winding, in sequence, the first roll 2c-the second roll 2d-the third roll 2e, the sequence may be varied. A sequence of the second roll 2d-the third roll 2e-the first roll 2c may be employed, and a sequence of the first roll 2c to halfway, the second roll 2d and the first roll 2c to the end and then the third roll 2e, etc., can also be applicable, with the sequences being unlimited.
The shape of the mouth of the jig 3c is not limited to a C shape, other shapes which prevent winding of a rectangular wire at the point of contact of the jig are also applicable.
Further, by varying the thickness of the jig 3c, the width of the second roll 2d, namely the distance between the first roll 2c and the third roll 2e, may be varied, thus the axial length of the coil 2 may be varied. Toward such a purpose, a plurality of jig of the same shape and a certain thickness may be employed.
For example, in the case the thickness of the second roll 2d is superposed 3 mm, three jigs of 1 mm thickness may be used to easily adjust without changing the manufacturing process. The jigs may be shaped to engage with each other so as to be easily superposable and less slippery.
A molded body 4 which includes the coil 2 will be described in reference to FIG. 3. The molded body 4 is formed by assembling two blocks 4a. The block 4a is formed by applying pressure to a sealant consisting of a filler with metallic magnetic powder and epoxy resin.
As shown in FIG. 3, the blocks 4a are rectangular parallelepipeds having one open end surface and a space 4b to accommodate the coil 2 inside. The cylindrical protrusion 4c to pass through the winding axis of the coil 2 extends from the central portion of the inner wall of the end surface opposing the open end surface. The upper and bottom surfaces of the block 4a have the same shape, with one of them serving as the mounting face 4e. In the case shown in FIG. 3, the upper surface is the mounting face 4e. 
As shown in FIG. 4, the mounting faces 4e are rectangular, with the open surface forming the short side and the other surface forming the long side. At both short sides of the mounting face 4e, the elongated slits 4d for bringing out the lead ends 2b therethrough are provided.
The portion of the mounting face 4e bordered by the slits 4d forms the supporting portion 4h which serves to support the lead ends 2b of the coil 2. Namely, the two slits 4d and the supporting portion 4h constitutes the U-shaped supporting structure to fit to the sectional shape of the lead ends 2b. 
Next, the method for sealing the coil is described in reference to FIGS. 5A-5C.
FIGS. 5A and 5B are sectional views along the line A-A in FIG. 4, namely sectional views parallel with the mounting face 4e, while FIG. 5C is a plan view of the mounting face 4e. 
As shown in FIG. 5A, the blocks 4a are arranged on both sides of the axial direction of the coil 2 in a manner that the open sides face each other. In one of the blocks 4a, the protrusion 4c of the block is inserted into the central hole of the coil 2 and the lead ends 2b are pulled out through the slits 4d of the mounting face.
FIG. 5B shows a state where other block 4a is fitted from the direction of the winding axis of the coil 2. The space 4b for accommodating the coil 2 is provided inside the block 4a. The coil 2 is accommodated inside the two blocks 4a with the protrusions 4c being inserted into the central hole of the coil 2. The long sides of the lead end 2b are brought out through the slits 4d so as to be parallel with the short sides of the mounting face and inserted into the other slits 4d to be U-shaped in section.
In this state, the two blocks 4a which house the coil 2 are pressed in a mold and then heated (thermocompressed). Thus, as shown in FIG. 5C, the lead ends 2b of the coil 2 are fixed to the mounting face 4e so as to be visible, and the two blocks 4a are solidified to form a molded body 4 sealing the coil 2 inside.
FIG. 6 shows the step for forming the external terminals by processing the lead ends 2b. FIG. 6 is the sectional view along the line B-B in FIG. 5C.
The lead ends 2b, which are embedded in the mounting face 4e, and the portion of the lead ends 2b exposed are machined by laser beam to remove the insulation cover therefrom. Because of the flatness of the rectangular wire, the settings for laser processing are uncomplicated. As the laser processing is used to remove the insulation off one face, the process does not require to be repeated.
The lead ends 2b are simultaneously sputtered with predetermined ratio of Ni and Cu to form a Ni—Cu layer, subsequently sputtering with Sn to form a Sn layer so as to process the lead ends 2b into the external terminals. Because of using the rectangular wire, the adhesiveness to other components may be improved, compared to the case of using a round wire. In addition, the evenness of the mounting face 4e can be raised.
FIG. 7 shows the steps for fitting the two blocks 4a and the coil 2 according to the first embodiment of the present invention. The left end of the coil 2 is inserted into the block 4a (left side in FIG. 7). For this process, the central hole of the coil 2 is positioned on the protrusion 4c of the block 4a, and the lead ends 2b (left side in FIG. 7) of the coil 2 are positioned to be mounted on the supporting portion 4h of the block 4a. Thus, the coil 2 is pressed toward the left as indicated by the arrow in FIG. 7 so that the coil 2 is fitted with the block 4a on the left in FIG. 7.
Then, the block 4a on the right side in FIG. 7 is fitted with the left side block 4a which is already fitted with the coil 2. For such a process, the central hole of the coil 2 is positioned on the protrusion 4c of the block 4a at the right side in FIG. 7, and the right-side supporting portion 4h is aligned with the right-side lead end 2a, and then the block 4a on the right side in FIG. 7 is pressed toward the left side as shown by the arrow. As a result, the two U-shaped portions of the lead ends 2b are supported by the supporting portions 4h. 
Accordingly, the two blocks 4a are joined via the coil 2 so the three of them are integrated together. As described before referring to FIG. 5, the molded body 4 is formed by thermocompressing.
Since the surface-mount inductor produced as described above has an entirely symmetrical shape, the electric characteristics are the same regardless of which of the input terminals receives an input. Therefore, there is no need for marking so as to discriminate between terminals and manufacturing cost can be thus reduced.
Embodiment 2
The surface-mount inductor and the method for manufacturing the same of the second embodiment according to the present invention are described, referring to FIGS. 8-11. The same reference numbers are used in the case the components are equivalent to those of the first embodiment.
The coil and the spindle used in the second embodiment are the same as those in the first embodiment.
As shown in FIG. 8, two blocks 14a are assembled to make the molded body 14. The block 14a are formed by a sealant including metallic magnetic powder and epoxy resin. The blocks 14a is parallelepiped having an aperture at one end, including the space 14b for accommodating the coil 2 inside.
From the center of inside wall of another end surface, a cylindrical protrusion 14c to be inserted into the central hole of the coil 2 is provided toward the surface having the aperture. The upper and the bottom surfaces of the block 4a are the same in shape, anyone of the surfaces being the mounting face 14e (upper surface in FIG. 8).
As shown in FIG. 9, the outline of the mounting face 14e is rectangular, and the surface having the aperture is on the short side and the other surface is on the long side. The long side of the block 14a is larger than that of the clock 4a so that two coils 2 can be accommodated in the assembled two blocks 14a. 
At the ends of the short sides of the respective mounting faces 14e, the elongated slits 14d are provided to bring out the lead ends 12b therethrough. The portion between the two slits 14d is the supporting portion 14h for supporting the lead ends 2b of the coil 2. Namely, the two slits 14d and the supporting portion 14h form a U-shaped supporting structure in side view.
Next, the method for sealing the coil is described in reference to FIGS. 10A through 10C. FIGS. 10A, 10B are views of the section A-A in FIG. 9, namely, sectional views of a surface parallel to the mounting face 14e and FIG. 10C is a plan view of the mounting face 14e. 
As shown in FIG. 10A, the two coils 2 are arranged facing each other in a manner that the first winding portions 3a are coaxial, and arrange the blocks 14a in both axial directions of the coil 2 in a manner that the open ends of the blocks 14a face each other. Thus, in one of the blocks 14a, the protrusion 14c of the block is inserted into the central hole of the coil 2 and the lead ends 2b are pulled out through the slits 14d. The other block 14a is similarly processed.
FIG. 10B shows the state of the assembled blocks 14a. The space 14b for accommodating the coil 2 is provided inside the block 14a. The two coils 2 are accommodated inside the blocks 4a in a manner that the first rolls 2c face each other and the protrusion 14c is inserted into the central hole of the coil 2.
The lead ends 2b are U-shaped to be suitable for being pulled out from one of the slits 14d parallel with the short side of the mounting face 14e and inserted into the other slit 14d. 
Then, the two blocks 4a housing the two coils 2 are pressed in a mold and heated to be formed. Thus, as shown in FIG. 10C, the lead ends 2b of the coil 2 are fixed to the mounting faces 14e partially embedded therein to be exposed therefrom, and the two blocks 14a, 14a are pressed to harden so that a molded body 14, in which the two coils 2 are sealed, is formed. And then, the lead ends 2b are processed in a manner similar to that of the first embodiment so as to be external terminals.
The surface-mount inductor described above, being overall symmetrical in shape, has the same electric characteristics regardless of which of the two terminals is used for input. Therefore, it is unnecessary to mark the coil to indicate the polarity which allows for lower costs.
Embodiment 3
The surface-mount inductor and the method for manufacturing the same according to the third embodiment of the present invention are described in reference to FIGS. 11 and 12. The third embodiment is a surface-mount inductor which has a molded body housing magnetic cores and sealant.
Firstly, the coil 2 (FIG. 1) is formed in the same way as in the first embodiment. Then, a pair of bottomed magnetic cores 6a, 6b, as shown in FIG. 11, is attached to the coil 2. The magnetic cores 6a, 6b have a protrusion P to be inserted into the central hole of the coil 2, slits S to bring out the lead ends 2b to the mounting face, a hole H provided on the open end surface facing the mounting face, and a recess R formed in a surface adjacent to the mounting face.
The pair of bottomed cores 6a, 6b are attached by inserting the protrusion P into the central hole from both sides along the winding axis direction, and passing the lead ends 2b through the slits S.
Further, as shown in FIG. 11, the lead ends 2b of the coil 2 accommodated in the pair of bottomed magnetic cores 6a, 6b are bent along the magnetic cores 6a, 6b to extend over the mounting face of the magnetic cores 6a, 6b and over the surface adjacent to the mounting face.
The portion of the lead ends 2b extending over the surface adjacent to the mounting face of the magnetic cores 6a, 6b is bent upward from the mounting face of the magnetic cores 6a, 6b and arranged in the recess R formed on the surface adjacent to the mounting face of the magnetic cores 6a, 6b. 
Subsequently, as shown in FIG. 12, the ends of the lead ends 2b of the coil 2 are adhered to the recess R formed on the surface adjacent to the mounting face of the magnetic cores 6a, 6b using an adhesive Ad.
Furthermore, the magnetic cores 6a, 6b having the coil 2 inside are placed in a mold, the mounting faces of the magnetic cores 6a, 6b being directed upward, and molding resin is poured in the mold in a manner so as to expose the mounting faces of the magnetic cores 6a, 6b. 
Since the magnetic cores 6a, 6b have the slit S and the hole H, the molding resin poured inside the magnetic cores 6a, 6b suffices to fill them up to the same level of the mounting face in the slit S.
Next, after the molding resin hardens, the molded body is taken out from the mold. The molded body houses the coil 2 whose winding axis is parallel with the mounting face, with the lead ends 2b of the coil 2 extending over the mounting face of the magnetic cores 6a, 6b and over the surface adjacent to the mounting face, and is covered with the molding resin so as to expose the mounting face of the magnetic cores 6a, 6b. In addition, the lead ends 2b of the coil 2 are also covered with the molding resin.
The lead ends 2b of the coil 2 extending over the mounting face 4e of the molded body 4, which consists of the mounting faces of the magnetic cores 6a, 6b, are used as external terminals, the insulation coating being removed. Electrodes covering the portions of lead ends 2b, which are extending over the mounting face 4e of the molded body 4, are provided in order to form the external terminals.
Although the surface-mount inductor and the method for manufacturing the same have been described in relation to the embodiments, the present invention should not be limited thereto. A part of the blocks may be replaced with a magnetic core, and a part of the magnetic cores may be replaced with a block. The mounting face of the magnetic cores may be covered with the molding resin in a manner that the surface of the lead ends 2b is exposed. In addition, the molding resin may include ferrite powder.
The molded body 4, 14 may be equipped with a pair of metal bodies. The pair of metal bodies are so formed to cover the upper and end surfaces and the adjacent surfaces of the molded body, the lower ends of the metal bodies reaching the same level of the external terminals formed on the mounting faces 4e, 14e of the mounting bodies 4, 14.
When mounting and soldering the surface-mount inductor described above on a wiring board, the gaps between the metal bodies and the external terminals may be filled with solder fillet so as to firmly secure the surface-mount inductor to the board securely. In addition, external noise can be shut out.
Further, in the second embodiment, the mounting face of the magnetic cores may be covered with the molding resin to expose the surface of the magnetic cores.
EXPLANATION OF CODES


    1 surface-mount inductor
    2 coil
    2a wide surface
    2b lead end
    2c first roll
    2d second roll
    2e third roll
    3 spindle
    3a winding core
    3aa tip
    3b base portion
    3c jig
    4, 14 molded body
    4a, 14a block
    4b, 14b space
    4c, 14c protrusion
    4d, 14d slit
    4e, 14e mounting face
    5 external terminal
    6a, 6b magnetic core
    P protrusion
    S slit
    H hole
    R recess
    Ad adhesive

## Claims

1. A surface-mount inductor including a coil formed by winding a rectangular wire and a molded body for accommodating the coil,
the coil comprising:
a first roll formed by winding a rectangular wire,
a second roll formed by winding the rectangular wire in a position adjacent to the first roll along the winding axis, and
a third roll formed by winding the rectangular wire on the second roll in partially overlapping manner in a position adjacent to and opposite from the first roll along the winding axis,
wherein the ends of the wire are brought out from the outermost turns of the first roll and of the third roll as lead ends, the winding axis is parallel with the mounting face and the lead ends extend over the surface of the molded body.

2. The surface-mount inductor according to claim 1,
wherein the molded body includes the two coils.