JPH0831382B2 - Coil structure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coil, and more particularly to the structure of a coil or transformer suitable for surface mounting on a printed board.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 4, a small coil or transformer mounted on a printed board has been widely used. That is, the bobbin 6 having the conducting wire 5 wound around the central protrusions 3 and 4 of the pair of ferrite cores 1 and 2 having an E-shaped cross section is loosely fitted and protrudes from the base portion 7 of the bobbin 6.
The ends of the lead wires are connected to the terminals 8 and 8--.

In the conventional coil or transformer having such a structure, first, the bobbin 6 having the conductor wire 5 wound on the central protrusion 3 of the E-shaped core 1 is fitted and then the center of the other E-shaped core 2 is fitted. The protrusion 4 is inserted into the central hole of the bobbin 6, and thereafter, the outer circumferences of the E-shaped cores 1 and 2 paired with each other are wound with a tape 9 and then the protrusions on both sides of the E-shaped cores 1 and 2 are wound. Instant adhesives 10 and 11 which can be expected to be sucked in due to capillary action are injected between the contacting end faces to tightly fix the pair of cores, and further, to secure the cores 1 and 2 and the bobbin 6 to the flange of the bobbin 6. A very troublesome manufacturing method of injecting an adhesive 12 having a filling effect, such as an epoxy adhesive, into the gap between the E-shaped core 2 and the projecting portion has been used.

However, since it is difficult to control the winding degree of the tape 9 in the conventional coil having such a structure, a slight difference is maintained in the E-shaped core joint surface gap. Since it is fixed, there is not only a large variation in the inductance between products, but when it is mounted on a printed board, especially when it is subjected to a reflow process as a surface mounting strip, the E-shaped core 1, Since the bonding surfaces of the instant adhesives 10 and 11 that bond 2 are stripped and the close contact between the cores is broken, the inductance of the coil is significantly reduced compared to before mounting, and the electronic circuit does not exhibit desired characteristics. Had a serious flaw: loss of function.

Further, when the coil having such a structure is applied to the one for applying an alternating voltage such as a step-up transformer, chatter vibration occurs due to the mechanical fixation between the cores being broken, and it is difficult to take measures against it. It was one that had both.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned defects of the conventional coil all at once, and can reduce the man-hours for manufacturing, and can improve the machine between cores and between the core and the bobbin even after heating. It is an object of the present invention to provide a coil having a structure capable of ensuring a fixed fixation and suppressing variation in inductance between products.

[0007]

SUMMARY OF THE INVENTION To achieve the above object, a coil according to the present invention is basically heat-resistant between an inner wall of a bobbin around which a conductive wire is wound and an outer periphery including an end face contact portion of an E-shaped core central protrusion. The structure is filled with adhesive.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail with reference to the embodiments shown in the drawings. 1 (a) to 1 (c) are a partially cutaway plan view, a front sectional view and a side sectional view, respectively, showing a basic embodiment of the present invention. In the figure, 1 and 2 are E-shaped ferrite cores forming a pair, and a bobbin 6 having a conducting wire 5 wound around the central projections 3 and 4 thereof is loosely fitted thereto and protrudes from a base portion 7 of the bobbin 6. The basic structure of connecting the ends of the conducting wire 5 to the terminals 8 and 8-- is exactly the same as the conventional coil.

The coil according to the present invention is different from the conventional coil in that the cores 1 and 2 are not tightened by a tape, but instead, the bobbin 6 is loosely fitted to the central protrusion 3 of the core 1. Afterwards, an adhesive 13 having both heat resistance and filling property, such as an acrylic adhesive, is applied to the inner wall space of the bobbin 6.
After injecting a proper amount of the above, the central protrusion 4 of the other core 2 is inserted into the bobbin 6, the center faces of both cores and the end faces of the both side protrusions are aligned, and then clamped at a predetermined pressure and heated for a predetermined time. The manufacturing method is used.

In this way, the heat-resistant adhesive 13 is basically filled between the central projections 3 and 4 of the cores 1 and 2 and the inner wall of the core 6 to mechanically fix these three. become. At this time, an adhesive layer is interposed between the end faces of the central protrusions 3 and 4 which come into contact with each other, and an air layer is interposed between the end faces of both protrusions of the core, which disturb magnetic lines of force penetrating the core. However, it has been empirically proved that such a core does not seriously affect the inductance of the coil because the end surface to be abutted is mirror-finished in the first place.

As is clear from the above description, the coil according to the present invention can make the clamping pressure applied when bonding both cores constant, so that the variation in the inductance between products is reduced and the surface mounting on the printed circuit board is reduced. Since the mechanical fixation between the cores is not broken by the heating of the coil, the inductance of the coil does not change after mounting, and when this structure is applied to a step-up transformer etc., chatter vibration due to peeling of the core joint surface is generated. There is no risk of this occurring. Moreover, it is obvious that the number of man-hours required for manufacturing is drastically reduced, and it can be understood that the cost can be significantly reduced. It should be noted that it may be effective to mix fine ferrite powder in the adhesive in order to reduce the influence of the adhesive layer interposed between the end faces of the central protrusions 3 and 4 of the E-shaped ferrite cores 1 and 2.

The embodiment in which the adhesive layer is allowed to intervene between the central projection contacting end faces of the E-shaped core has been described above. However, if a core having a structure as shown in FIG. An extremely efficient coil can be constructed with no adhesive layer on the surface. That is, a channel 15 for the adhesive is formed from the back surface of the central protrusion 4 of at least one of the E-shaped cores 14 to the outer periphery of the protrusion 4, and after clamping both cores 1 and 14, the adhesive 13 is applied to the channel 15. If is pressed in, the adhesive 13 is filled between the outer circumferences of the central protrusions 3 and 4 of both cores 1 and 14 and the inner wall of the bobbin 6, and the adhesive 13 enters the contact surfaces of the central protrusions 3 and 4. It will be understood that this is not possible.

The adhesive flow path 15 as described above has, for example, two or three forked legs 1 as shown in FIG.
It is not necessary to specifically explain that the wax mold 17 having a shape in which one end of each of 6, 6 and 16 is concentrated can be easily manufactured by baking the wax mold 17 together with the ferrite powder in a mold.

Further, the coil according to the present invention can be modified as shown in FIG. That is, there is a case where the E-shaped core 1 and the flat plate core 18 are combined as a core. In such a case, 2 to 2 are provided in a portion of the flat plate core 1 corresponding to the outer peripheral edge of the central protrusion 3 of the E-shaped core 1. Three through holes 19, 19
By providing a --- and pressing the adhesive 13 through the holes 19 and 19 ---, the cores 1 and 18 and the bobbin 6 can be mechanically fixed to each other. At this time, if an appropriate chamfer 20 is applied to the peripheral edge of the inner wall of the bobbin 6, the adhesive 1
3 will be fully filled and will be effective in strengthening the bond between the cores.

[0015]

Since the coil according to the present invention has the structure as described above, the cost is reduced and the inductance between the products is reduced as the man-hour required for the manufacturing is largely reduced in consideration of the manufacturing process. The unit cost can be further reduced by improving the yield by reducing the variation, and the possibility of the peeling of the joint surface of the core after mounting on the printed board is almost eliminated so that the electronic circuit malfunctions or is lost due to the reduction in inductance. Since there is no fear of this, there is a significant effect in improving the production yield of the electronic device using this coil. In addition, when the structure of the present invention is applied to a step-up transformer or the like, there is no room for chatter vibration due to the peeling of the core joint surface, which often occurs in the conventional case, so it is also necessary to take extra measures on the printed circuit board. It significantly contributes to the cost reduction of electronic circuits.

[0016]

[Brief description of drawings]

1A and 1B are views showing a basic embodiment of the present invention, in which FIG. 1A is a partially cutaway plan view thereof, and FIG.
(C) is a side sectional view.

2A and 2B are views showing a second embodiment of the present invention, in which FIG. 2A is a front sectional view thereof, and FIG. 2B is a view of a mold to be used in manufacturing a core used in this embodiment. The perspective view which shows one Example.

FIG. 3 is a front sectional view showing a third embodiment of the present invention.

FIG. 4 is a diagram showing a structure of a conventional coil (a).
Is a partially cutaway plan view thereof, (b) is a front sectional view, and (c) is a side sectional view.

[0017]

[Explanation of symbols]

1, 2 and 14 --- E-shaped, 3,4 --- central protrusion of core 5 ---- wire ring, 6 --- bobbin, 13 --- adhesive agent 15, 19 --- hole (adhesion Agent channel)

Claims (5)

[Claims] 1. In a coil of the type which is surface-mounted on a printed board by reflow processing, a core consisting of a lower core member having an E-shaped cross section and an upper core member also having an E-shaped cross section, and a conductor wire wound around the core. A bobbin loosely fitted to the central protrusions of the upper core member and the lower core member, wherein the bobbin has a base portion horizontally protruding from a bottom member provided with the central protrusion of the lower core member, Of the bottom core member, a bottom surface of a portion projecting horizontally from the bottom member is flush with the bottom surface of the lower core member, and a side surface of the base has a terminal for connecting an end of the lead wire. The structure of the coil is characterized in that a gap between the inner wall surface of the bobbin and the outer peripheral surface including the end face abutting portions of the core central protrusions of the upper and lower core members is filled with a heat resistant adhesive. 2. The coil structure according to claim 1, wherein no adhesive is applied to the end faces of the central protrusions of the upper core member and the lower core member. 3. An upper core member and a lower core are provided through the holes by providing a predetermined number of holes from the back side of the central projection of at least one of the upper core member and the lower core member toward the outer peripheral surface of the central projection. The structure of the coil according to claim 1 or 2, wherein an adhesive can be injected into a gap between the outer peripheral surface of the central protrusion of the member and the inner wall of the bobbin. 4. The coil structure according to claim 1, wherein the upper core member or the lower core member has an I-shaped cross section. 5. When one of the upper core member and the lower core member is I-shaped, a predetermined number of holes are provided in the periphery of the E-shaped core central projection contact portion of the I-shaped core so that the I-shaped core can be inserted through the holes. The adhesive can be injected into the gap between the inner surface of the I-shaped core and the outer surface of the flange of the bobbin facing the inner surface of the I-shaped core and the inner wall of the bobbin and the outer periphery of the central protrusion of the E-shaped core. Item 4. The coil structure according to Item 4.