JP3051534B2 - Chip inductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip inductor, in particular, a type comprising a wound drum core (a drum core having a large-diameter flange at both ends) and a cylindrical or square sleeve core wound around the core. Related to a chip inductor.

[0002]

2. Description of the Related Art Conventionally, there has been known an inductor of a type comprising a drum core such as a high-permeability ferrite provided with a winding and a sleeve core such as a high-permeability ferrite covered around the drum core. Recently, chip inductors have been increasingly miniaturized. For example, small chip inductors having a diameter of about 2 mm and a length of about 2.5 mm are not uncommon. As described above, when the size of the inductor is reduced, it becomes difficult to control the inductance value to a predetermined value even if there is a slight dimensional change and a relative position change in the components of the inductor. The main causes of the variation in the inductance value of this type of inductor are as follows. (A) The gap between the drum core and the sleeve core. (B) Eccentricity of the drum core with respect to the sleeve core. (C) Number of windings. (D) Permeability μ of both cores. (E) Temperature characteristics of both cores. Of these, those that depend on the material are (D) and (E), and research on the material is necessary. However, even if the material is improved, if the mechanical accuracy of (A), (B) and (C) is not improved, the suppression of variation is insufficient. Variations in the material can be significantly suppressed by devising the shape and dimensions.

[0003] The following relationships are established with respect to the above (A), (B) and (C). (A) The larger the gap between the drum core and the sleeve core, the smaller the variation in inductance value. (B) The smaller the eccentricity of the drum core with respect to the sleeve core and the relative displacement in the axial direction, the smaller the variation in inductance value. (C) Variations decrease as the number of windings is controlled more precisely.

As a means for simultaneously satisfying these, there is a method in which about four to twelve ridges are provided at equal intervals in the circumferential direction on the outer peripheral surface of the flange of the drum core or the inner peripheral surface of the sleeve opposed thereto. 64-35720, 6
2-55318). As a result, a predetermined gap can be secured between the drum core and the sleeve core, eccentricity due to the gap can be avoided to some extent. Can be suppressed. According to an experiment performed by the present inventors to quantify this point, the outer diameter of the drum core was 1.08 mm, the inner diameter of the sleeve core was 1.0.
26mm, Material M9N, M5N, T9F-All are TD
As shown in FIG. 13, the eccentric dimension and the change rate of the inductance L are more eccentric for nine ridges than for four ridges (solid line) as shown in FIG. And provide stable characteristics.

Further, in order to facilitate relative positioning between the both ends of the drum core, which are the winding ends, and the contact end of the extraction terminal electrode (lead frame), and to prevent solder from sticking out, a conductive film (Ag-Pd) is used. It is known that the end surface of a drum core to which a paste or the like has been applied is formed in a concave shape (Japanese Utility Model Application Laid-Open Nos. 609-156715 and 59-155).
No. 709, No. 59-152714, No. 58-1531
No. 7, JP-A-62-235706). There is also a technique for inserting a convex circular terminal of a terminal electrode into a concave recess (Japanese Utility Model Application Laid-Open No. 59-152714). However, these techniques use a technique of casting a magnetic resin around a drum core, and are not used for a combination of a drum core and a sleeve core.

The following problems cannot be sufficiently solved by these techniques. (1) The problem of the lengthwise displacement between the two cores, (2) The problem of the protective resin protruding to an undesired portion, and (3) The manufacturing that the terminal electrode may protrude undesirably from the chip inductor. (4) Insufficient area for soldering the exposed portion of the external terminal, (5) Difficulty in bending the external terminal, (6) Cream solder protrusion when attaching the external terminal to the end face of the drum core. Problem, (7)
The problem of insufficient adhesive strength between the sleeve core and the bent portion of the external terminal has not been sufficiently solved. Accordingly, the present invention is directed to overcoming one or more of these problems.

[0006]

The chip inductor according to the present invention has a rectangular parallelepiped soft magnetic sleeve core having a cylindrical through hole, and a flange inserted into the through hole and having a diameter sufficiently smaller than the through hole at both ends. A soft magnetic drum core having a cylindrical portion having a smaller diameter between the flanges, a winding applied to the cylindrical portion, and a solder connection to a winding end drawn out from a concave surface on both end surfaces of the drum core. A terminal electrode extending from the inner end portion to the outer end portion exposed to the both end surfaces or one side surface of the sleeve core, and one of the inner peripheral surface of the through hole and the outer peripheral surface of the flange has a circumferential direction. A chip inductor having a large number of ridges formed at equal intervals has one or more of the following features.

(A) The inner end of the terminal electrode has a center having a circular and convex (preferably C-shaped bifurcated) end protruding toward the concave surface so as to contact the concave surface of both end surfaces of the drum core. It has a three-pronged structure comprising a piece and two wing pieces on both sides of the center piece and in contact with both end faces of the sleeve core. According to this structure, the inner end of the terminal electrode is positioned at the center of the concave surface of the drum core. In the manufacturing process, the drum core and the sleeve core can be held and correctly positioned. This is because by forming a U-shaped groove between the center piece and the base of the two wing pieces, each piece can act as a spring relatively independently. Further, the two wing pieces act as weirs for a protective resin such as an ultraviolet-curable resin, and the center piece forms a semicircular groove in a cross-section at the joint between the center piece and the base of the two wing pieces, thereby forming an ultraviolet-curable resin or the like. Of the protective coating resin to an undesired portion can be suppressed. Also, if the central piece is C-shaped, escape of the cream solder is given at the central part, so that undesired protruding outside of the solder can be avoided, and the wetting state of the winding inside the C-shaped solder is confirmed. Becomes easier.

(B) A groove is formed by cutting open ends at both ends of the through hole of the sleeve core. This not only facilitates the incorporation of the drum core by the groove, but also prevents the resin from adhering to the exposed portion of the external electrode by trapping a protective resin such as an ultraviolet curable resin in the groove. Can be.

(C) Both sides (corners) of the lower surface of the sleeve core are cut in the length direction to form a step or a groove. Further, both wings at the outer end of the terminal electrode are bent to this step. As a result, it is possible to avoid protrusion (projection) from the chip inductor at both ends of the outer end of the terminal electrode, which cannot be avoided due to difficulties in the manufacturing process, and it is possible to guarantee a small-sized shape with uniform dimensions. Further, the two wings increase the area required for soldering to the printed circuit board, so that reliable soldering is possible.

(D) The terminal electrode is formed by forming one surface facing the drum core from phosphor bronze having low affinity with solder but having high affinity with an adhesive, and plating the opposite surface with solder plating. The adhesiveness between the outer end of the sleeve core and the sleeve core can be enhanced. In addition, the bending strength increases due to the elasticity and bonding strength of the phosphor bronze plate. Furthermore, this configuration of the terminal electrodes prevents the cream solder from flowing between the cores along the terminal electrodes when overheated. As a result, characteristic deterioration due to residual flux can be avoided.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 3 illustrate a chip inductor of the present invention, FIG. 1 is a side view, FIG. 2 is an end view,
And FIG. 3 is a bottom view. The chip inductor has a substantially rectangular parallelepiped outer shape and a cylindrical sleeve core 1 having a through hole 5 therein, a drum core 3 housed in the through hole, and a winding wound around the drum core 3. 11, a pair of terminal electrodes 19, 19 for drawing both ends of the winding drawn to both end faces of the drum core to the end face and one side face 17 of the sleeve core 1, and both ends of the winding 11 to the terminal electrodes 19, 1.
9 are composed of solders 45, 45 electrically connected to 9 and protective resins 29, 29 for protecting these connection portions.

Details of the sleeve core 1 are shown in FIGS.
FIG. 4 is a partially cutaway side view, and FIG. 5 is an end view. The sleeve core 1 is made of soft magnetic ferrite, has a substantially square cross section, and has a planar chamfer 47 along both corners of the upper surface.
47. These chamfers can be used as a guide for accurately positioning the sleeve core at the designated position of the trapezoidal support end of the parts feeder, and the direction of the inductor can be easily determined. Further, the lower surface 17 and both side surfaces 18 of the sleeve core,
Steps or grooves 40, 40 are formed along the ridge line with 20. The faces of these steps are parallel to the sides 18,18. As a result, both wings at the outer end of the terminal electrode, which will be described later, can be bent to these steps to prevent the terminal electrode from protruding and to make the size of the chip inductor constant. On the other hand, grooves or chamfers 31, 31 are formed at the open ends of the through holes 5 of the sleeve core, thereby preventing the ultraviolet curable resin 29 from protruding from a predetermined position as described later.

Details of the drum core 3 and the winding 11 are shown in FIGS.
FIG. FIG. 6 is a partially cutaway side view, and FIG. 7 is a left end view thereof. The drum core 3 is made of soft magnetic ferrite and includes a pair of flanges 7 having a substantially circular cross section and a cylindrical portion 9 extending therebetween. The diameter of each flange is designed to be sufficiently smaller than the diameter of the through hole 5 of the sleeve core 1 in order to reduce variations in inductance. Further, at least six, in this example, eight, ridges 21 are formed on the peripheral surface of the flange at regular intervals in the circumferential direction, and the envelope passing through the outer end of the ridge 21 is It is slightly smaller than through hole 5. Therefore, the eccentricity of the drum core 3 with respect to the sleeve core 1 is minimized. The groove 22 between the ridges 21 is a drawing groove at both drawing ends of the winding.
3 can be set at a fixed angle, and variations in the number of turns can be minimized. The winding 11 is held in the cylindrical portion 9, and is drawn out to both end surfaces through the groove 22. A smooth concave surface 2 is provided on each end surface 13 of the drum core.
3 is formed, and an electrode film 2 such as Ag-Pd is formed on its surface.
4 is baked. As shown in the figure, an end of the winding from which the insulating coating has been peeled off is attached to the electrode film 24, and is soldered together with the terminal electrode 19 as described later.

Next, FIGS. 1 to 3 and FIGS.
The structure of the terminal electrode 19 will be described with reference to FIG. Figures 1-3
, The terminal electrode 19 has a concave surface 23 so as to contact the electrode film 24 on the concave surface 23 of each end surface 13 of the drum core 3.
A central piece 33 having a circular, convex (preferably C-shaped bifurcated) inner end 25 projecting toward the center piece, and a pair of wing pieces 3 on both sides of the central piece 33 and in contact with both end faces of the sleeve core 1.
5 and 35, which are united at the base and extend to both end surfaces of the sleeve core 1, and further bent therefrom to form outer end portions 2 along the bottom side surface 17 of the sleeve core 1.
Terminate at 7. According to this three-pronged structure, the inner end 25 of the terminal electrode 19 is easily positioned at the center of the concave surface 23 of the drum core in the manufacturing process. In the manufacturing process, the drum core and the sleeve core can be held and correctly positioned. Further, the two wing pieces 35, 35 act as weirs for a protective resin 29 such as an ultraviolet curable resin, and prevent unnecessary spread of the resin. Further, if the central piece 33 is formed into a C shape having an empty space in the center, escape of cream solder is given,
Unwanted protrusion of the solder to the outside can be avoided. Further, by forming a groove 47 having a semicircular cross section at the joint portion of the center piece 33 and the roots 35, 35, the protrusion of the ultraviolet curable resin 29 and the like can be suppressed. This is because the U-shaped groove between the center piece and the base of the wing pieces traps a protective coating resin 29 such as an ultraviolet-curing resin in this groove so that the resin does not adhere to the exposed portion of the external electrode. This is because it can be done. 8 to 1
As shown at 0, a U-shaped groove 39 is formed at the base of the central piece 33, and each piece can act as a spring relatively independently. Further, the wing pieces 43 on both ends of the outer end portion 27, 43
A U-shaped bent groove 51 is formed on the inner surface of the boundary between the wing piece 43 and the wing piece 43.
Similarly, if a V-shaped cut groove 59 is formed at the tip of the terminal, the terminal electrode can be easily separated from the material.

Next, the terminal electrode 19 is formed of phosphor bronze on one surface facing the drum core 3 and the sleeve core 1 with poor affinity for solder but good affinity for an adhesive, and the other surface is coated with solder plating. I do. The conventional terminal electrode is obtained by plating copper on both surfaces of a phosphor bronze thin plate and further performing solder plating on both surfaces thereof. Leave it alone. Thereby, the outer end portion 2 of the terminal electrode 19 is
7 and the sleeve core 1 can be improved in adhesiveness.
Also, the elasticity of the phosphor bronze plate is utilized to increase the bending strength due to the adhesive strength. Furthermore, this configuration of the terminal electrodes can prevent the cream solder 45 from flowing between the cores along the terminal electrodes when overheated. As a result, characteristic deterioration due to residual flux can be avoided.

The solder plating used is 90% lead-tin 1
It is preferably set to 0%. This gives a melting point of 300 ° C
And the heat stability of the product is improved. For the same reason, it is preferable to use the same solder plating for the cream solder 45.

Next, the assembly of the chip inductor of the present invention will be described with reference to FIGS. First, while supplying the long material thin plate 52 for forming terminal electrodes having the above-mentioned laminated structure, as shown in FIG. Many punches are made along the longitudinal direction. Numerals 55 and 57 are stamped and removed portions. Further, the two wing pieces 4 at the outer end 27 of the terminal electrode
The portions forming 3, 43 remain connected to the thin plate 52. Further, the inner end portion 25 of the C-shape is drawn by a mold so as to have a convex surface toward the near side of the paper of FIG. 8, and the center piece 33 and the two wing pieces 35, 35 are shown in FIGS. 11 and 12, respectively. In this way, the sleeve core 1 and the drum core 2 are folded toward the front side of the paper of FIG. Further, the semicircular groove 47 and the V-shaped grooves 49 and 51 are formed at predetermined positions described above. Reference numeral 53 denotes an automatic feed hole.

Next, the portion of the V-time groove 49 is bent, and FIG.
Both terminal electrodes 19, 19 are erected as shown in FIGS. A cream solder 45 is applied to the inner surface of the terminal electrode facing the inner end 25. In addition, from the intermediate portion of the terminal electrode to the outer end portion 27
To apply a thermosetting adhesive. Next, the drum core 2 is wound in advance, and both ends thereof are drawn out along the concave surfaces 23, 23 formed with the electrode films 24 such as Ag-Pd on both end surfaces, and the drum core 2 is inserted into the through hole 5 of the sleeve core 1. The semi-finished product is sandwiched between the terminal electrodes 19, 19 as shown by a chain line in FIGS. Next, the mixture is passed through a heating furnace to be heated to the melting point of the cream solder, and the inner end 25 and the winding end of the terminal electrode are bonded to the electrode film 24. At the same time, the adhesive 61 is cured, and the terminal electrodes are firmly bonded to the sleeve core 1. Inner end 25 of terminal electrode and wing pieces 35, 3
Numeral 5 holds the cores 1 and 3 at predetermined positions as shown in FIGS. Thus, the relative position in the longitudinal direction of both cores is accurately determined. Also, even if there is a dimensional error between the two cores, the elasticity of the two terminal electrodes ensures reliable holding. Even if the amount of cream solder varies, the inner end 25
Since the extra solder is trapped in the C-shaped opening, there is no danger of the solder field protruding, and the phosphor bronze surface and the plating have poor affinity. Elimination of the risk of characteristic deterioration due to residual flux penetration. Next, an ultraviolet curable resin 29 is preferably applied in a disk shape so as to cover both end surfaces of both cores 1 and 2. The resin 29 is blocked by the two wing pieces 35, 35, and the variation in the resin amount is absorbed to some extent by the U-shaped groove 39. The periphery of the resin 29 is shaped into a disk shape by an annular groove 31 provided at the opening of the through hole 5 of the sleeve core 1, so that unnecessary protrusion to an undesired portion does not occur.

Next, as shown in FIGS. 8 to 10, the terminal electrode is separated from the thin plate 52 by a line 59 and bent by V-shaped grooves 51, 51. The cutting of this portion was conventionally performed in contact with the sleeve core 1, but it was difficult. Therefore, there was a drawback that the portion protruded from the sleeve core. However, in the present invention, the cut portion is far away from the core, so that cutting is easy. Then the two wings 43, 4
3 is bent to the steps 40, 40 of the core 1. In this way, there is an advantage that the protruding portion is eliminated, and the soldering area for connecting to an external circuit as a terminal is increased, so that electrical connection is facilitated.

[0020]

According to the present invention, the following effects can be obtained. (A) The inner end 25 of the terminal electrode 19 is the concave surface 2 of the drum core.
3 is located at the center. Further, the drum core and the sleeve core can be held and correctly positioned in the manufacturing process by the center piece 33 and the two wing pieces 35, 35. In addition, the two wing pieces 35, 35 act as dams for a protective resin such as an ultraviolet curable resin, and prevent adhesion to undesired portions. Further, if the inner end 25 of the central piece 33 is formed in a C-shape, escape of the cream solder is provided at the central portion, so that undesired protrusion of the solder to the outside can be avoided. Further, if a U-shaped groove 39 is formed at the base of the center piece 33, the protection covering resin 29 such as an ultraviolet curing resin can be prevented from protruding. Further, if a groove 47 having a semicircular cross section is formed at the joint portion between the center piece 33 and the two wing pieces 35, 35, each piece can function as a relatively independent spring.

(B) Since the groove 31 is formed by cutting off the open ends of both ends of the through hole 5 of the sleeve core 1, the drum core 3
Not only is facilitated by this groove being guided by this groove, but also by trapping a protective resin 29 such as an ultraviolet curable resin in this groove, it is possible to prevent the resin from adhering to the exposed portion of the external electrode.

(C) Since the two wing pieces 43 of the outer end 27 of the terminal electrode 19 are bent to the step portions or the grooves 40 at both side corners (corners) of the lower surface of the sleeve core,
Extrusion (projection) from both ends of the outer end portion 27 of the terminal electrode from the chip inductor, which cannot be avoided due to difficulties in the manufacturing process, can be avoided, and a small size with uniform dimensions can be guaranteed. Further, since the two wings 43 increase the area required for soldering to the printed circuit board, reliable soldering is possible.

(D) Since the terminal electrode 19 has a high affinity with the adhesive and a low affinity with the solder, the adhesion with the sleeve core 1 can be enhanced. Further, with this configuration of the terminal electrodes, the cream solder 45 can be prevented from flowing between the two cores along the terminal electrodes when overheated, and the deterioration can be avoided due to the residual flux.

[Brief description of the drawings]

FIG. 1 is a partially broken side view of a chip inductor of the present invention.

FIG. 2 is an end view of the same.

FIG. 3 is a bottom view of the same.

FIG. 4 is a partially broken side view of the sleeve core of the present invention.

FIG. 5 is an end view of the same.

FIG. 6 is a partially broken side view of the drum core of the present invention.

FIG. 7 is an end view of the same.

FIG. 8 is a plan view showing a state where the terminal electrode of the present invention is punched out of a material.

FIG. 9 is a side view in which a pair of terminal electrodes is made upright from a material.

FIG. 10 is an end view in which a pair of terminal electrodes is made upright from a material.

FIG. 11 is a side sectional view showing the relationship between the center piece of the terminal electrode, the drum core and the sleeve core during the assembly.

FIG. 12 is a side cross-sectional view showing a relationship between a blade piece of a terminal electrode, a drum core, and a sleeve core during assembly.

FIG. 13 is a graph showing the relationship between the number of protrusions around the core, the eccentric dimension, and the inductance change rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Soft-magnetic sleeve core 3 Sleeve core 5 Through-hole 7 Flange 9 Cylindrical part 11 Winding 13 Drum core end face 17 Sleeve core 19 Terminal electrode 21 Ridge 22 Groove 23 Concave surface 24 Electrode film 25 Inner end 27 Outer end 29 For protection Resin 31 Annular groove 33 Center piece 35 Wing piece 39 U-shaped groove 40 Step 43 Wing piece 45 Cream solder 46 Chamfer 47 Semicircular groove 49, 51 V-shaped groove 52 Material thin plate 61 Adhesive

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takeshi Suzuki 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References Japanese Utility Model Sho-62-55318 (JP, U) Japanese Utility Model Sho-64 −35720 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 27/29 H01F 17/04

Claims (8)

(57) [Claims] 1. A soft magnetic sleeve core (1) having a rectangular parallelepiped outer shape having a cylindrical through hole (5), and said through hole (5).
A soft magnetic drum core (3) having flanges (7) at both ends which are sufficiently smaller than the through hole (5) and having a cylindrical portion (9) between the flanges; (9) and from the inner end (25) soldered to the ends of the windings drawn out on both end surfaces (13, 15) of the drum core (3), from the end surfaces (25). The outer end (2) exposed on one side (17) of the sleeve core
A plurality of protrusions (21) are formed at equal intervals in the circumferential direction on one of the inner peripheral surface of the through hole (5) and the outer peripheral surface of the flange (7). In the chip inductor, the terminal electrode (19) is connected to both end faces (1) of the drum core (3).
The concave surface (2) is in contact with the concave surface (23) of (3, 13).
A central piece (33) having a circular convex inner end (25) protruding toward 3), and a pair of wing pieces on both sides of the central piece (33) and in contact with both end faces of the sleeve core (1). (3
5. A chip inductor having a three-pronged structure consisting of (5, 35). 2. The chip inductor according to claim 1, wherein the inner end has a C-shape. 3. A center piece (33) and two wing pieces (35, 3).
The chip inductor according to claim 1, wherein a U-shaped groove (39) is formed between the roots of (5). 4. A center piece (33) and two wing pieces (35, 3).
2. The chip inductor according to claim 1, wherein a groove (47) having a semicircular cross section is formed in the joint portion at the root of (5). 5. A sleeve (1) according to claim 1, wherein the opening ends at both ends of the through hole (5) of the sleeve core (1) are cut off to form a groove (31), and a protective resin (29) is trapped therein. Chip inductor. 6. A stepped portion (40, 40) formed by cutting off both side corners of a lower surface of a sleeve core in a longitudinal direction, and both wing pieces (43, 40) of an outer end portion (27) of a terminal electrode (19). 43. The chip inductor according to claim 1, wherein (43) is bent to the step. 7. The terminal electrode (19) includes a drum core (3).
2. The chip inductor according to claim 1, wherein one surface facing the substrate is formed of phosphor bronze having low affinity for solder but good affinity for an adhesive, and the other surface is plated with solder. 8. The number of the plurality of ridges (21) formed at equal intervals in one circumferential direction on one of the inner peripheral surface of the through hole (5) and the outer peripheral surface of the flange (7) is 6 or more. The chip inductor according to claim 1.