JPH08250342A - Chip inductor - Google Patents

Abstract

PURPOSE: To provide a chip inductor of high reliability, wherein the inductor is formed through a continuous winding method by the use of a wound core of continuum. CONSTITUTION: A chip inductor is composed of a bar-like insulating core 1, a winding section composed of a wire 2 wound on the peripheral surface of the core 1 and the start and end terminal of the wire 2 led out to the ends faces of the core 1, a molded resin part 3 which seals up the core 1 wound with the wires 2, electrodes 4 provided coming into close contact with the start and end terminal of the winding section and the end faces of the core, and conductive films 5 larger in area than the cross sections 2A of the start terminal and the end terminal of the winding section. The resin material of the resin molded part 3 is set equal to or smaller than the core 1 in linear expansion coefficient, whereby the chip conductor formed through a continuous winding method by the use of a continuous wound core of continuum can be enhanced in reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire wound type chip inductor.

[0002]

2. Description of the Related Art As a conventional chip inductor of this type, a chip inductor as shown in FIG. 5 is proposed in Japanese Patent Laid-Open No. 60-39814 for the purpose of simplifying the manufacturing method.

In this chip inductor, as shown in FIG. 5, a wire 22 is wound around a long core 21 provided with coil winding grooves dispersed in the length direction, and the wound core is provided. 21 is molded with a resin or a resin 23 containing ferrite, and the obtained long molded body is cut into a desired length to form an individual piece.
No. 4 was formed by the continuous winding method using a continuous winding core.

[0004]

However, the above-described conventional chip inductor has an electrical connection between the starting and terminating cross-sections of the wire 22 and the electrode 24 due to thermal shock when the chip inductor is mounted on the printed wiring board by soldering. Since the mechanical strength of the part is weak, this joint is easily disengaged, and the resin mold part 23 has a problem regarding heat resistance such as cracking.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a highly reliable chip inductor having excellent heat resistance by a continuous winding method using a winding core of a continuous body.

[0006]

In order to solve this problem, a chip inductor according to the present invention comprises a rod-shaped core member made of an insulating material, a wire wound around the peripheral surface of the core member, and the start and end of the wire member. A winding portion whose ends are respectively drawn to the respective end surfaces of the core material, a resin mold portion obtained by molding the outer periphery of the core material on which the winding portion is formed, the start and end of the winding portion and the end surface of the core material. In a chip inductor consisting of an electrode part formed in close contact with the electrode part, a conductive film having an area equal to or larger than the cross-sectional area of the wire is formed between the starting end and the electrode part of the winding part and the resin mold part. The linear expansion coefficient of the core material is set to the same value or smaller than the linear expansion coefficient of the resin material to be formed.

[0007]

With this configuration, the bonding strength is improved by the conductive film formed between the starting and terminating ends of the winding part and the electrode part, and the wire rod end and end due to thermal shock when the chip inductor is soldered and mounted on the printed wiring board. Since it is possible to improve the heat resistance of the chip inductor by reducing problems such as electrical disconnection between the end and the electrode and cracking in the resin mold part, it is possible to use a continuous core that is continuous. High reliability can be ensured in the chip inductor manufactured by the winding method.

[0008]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

1 (a) and 1 (b) are a sectional view and a side view showing the structure of a chip inductor according to the same embodiment. In FIG. 1, 1 is a round bar-shaped core material and 2 is an outer periphery of the core material 1. 2A is a cross section of the wire 2 wound at the beginning and end of the wire.
Is a resin molded portion obtained by molding the core material 1 around which the wire 2 is wound, 4 is an electrode connected to both ends of the resin molded portion 3 in the longitudinal direction and the start and end of the wire 2, and 5 is the electrode 4 and the above. This is a conductive film formed between the starting and ending cross section 2A of the wire 2, and the conductive film 5 is formed larger than the area of the starting and ending cross section 2A of the wire 2.

In this way, on the starting and terminating cross section 2A of the wire rod 2,
By bonding and forming the conductive film 5 having an area larger than this cross-sectional area, the chip inductor is soldered to the printed wiring board due to the effects such as the strength and adhesion of the conductive film 5 itself and the increase of the contact area with the electrode 4. It is possible to reduce the problem that the electrical connection between the beginning and the end of the wire 2 and the electrode 4 is disconnected due to the thermal shock at the time of mounting and mounting.

Further, as the constituent material of the chip inductor shown in FIGS. 1A and 1B, the material having the structure shown in Table 1 was used.

[0012]

[Table 1]

Simulation of thermal shock when soldering a chip inductor using these materials and a chip inductor using the same material without the conductive film 5 as shown in FIG. As an experiment, after immersing in solder at 300 ° C. for 10 seconds, the continuity between electrodes at both ends of each chip inductor was confirmed (Table 2).

[0014]

[Table 2]

As described above, it can be seen that by providing the copper plating film of the conductive film 5 shown in FIGS. 1A and 1B, the conduction failure rate during soldering can be greatly improved.

In particular, the effect of improving the soldering heat resistance is greater when the conductive film 5 has a thickness of 5 μm or more and is as thick as possible.
Further, as the material of the conductive film 5, a sprayed film, a sputtered film, an ultrafine particle film or the like may be used in addition to the plated film, and the same effect can be obtained.

Further, like the above-mentioned chip inductor, by adopting a resin material for the core material 1 which has heat resistance to soldering and has a linear expansion coefficient smaller than that of the resin material forming the resin mold portion 3, the chip inductor At the same time, it is possible to prevent the resin mold part 3 from being cracked due to expansion of the core material 1 due to thermal shock when soldering is mounted on the printed wiring board.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings.

The structure of the chip inductor according to the embodiment is the same as that of the chip inductor shown in FIG. 1, except that the insulating material of the resin mold portion 3 has an expansion amount due to a temperature rise from 25 ° C. to 300 ° C. The difference in thermal expansion between the wire rod 2 and the resin mold portion 3 is reduced by using a material having a length close to that of the wire rod 2 having the same length as the resin mold portion 3, and the chip inductor is mounted on the printed wiring board by soldering. It is possible to further enhance the effect of reducing the problem that the electrical connection between the beginning and the end of the wire 2 and the electrode 4 is disconnected due to thermal shock.

For example, as shown in (Table 3), in order to clarify the difference in solder heat resistance due to the difference in insulating material of the resin mold portion 3, the structure without the conductive film 5 as shown in FIG. A comparison will be made between the one having a structure having the conductive film 5 as shown in FIG.

[0021]

[Table 3]

In the chip inductor using the above-mentioned constituent materials, an epoxy resin is adopted as the insulating material of the resin mold parts 3 and 13 and is mounted on the printed wiring board by soldering when the linear expansion coefficient is changed. As a simulation test of thermal shock at that time, after immersing in solder at 300 ° C. for 10 seconds, the result of confirming conduction between both end electrodes of each chip inductor is shown in (Table 4).

[0023]

[Table 4]

FIG. 3 shows a wire rod 2 made of a copper wire and various epoxy resins having different linear expansion coefficients at the same length from 25 ° C. to 3 ° C.
The characteristic of the amount of elongation due to the temperature rise up to 00 ° C is shown.

As is apparent from these, the wire 2 is wound around the core 1 for 3 turns so that the wire length of the wire 2 is the resin mold portion 3.
Although it is more than 3 times the total length of
The improvement in conduction failure can be seen in the epoxy resins B to F whose elongation amount due to the temperature rise up to 0 ° C. is closer to the elongation amount of the wire 2 having the same length as the entire length of the resin mold portion as compared with the epoxy resin A.

Particularly, the closer the elongation of the resin mold portion is to the elongation amount of the wire rod 2 having the same length as the entire length of the resin mold portion, that is, the closer the characteristic curve of the epoxy resin is to the straight line of the wire rod 2 in FIG. The lower the conduction failure rate, the lower the tendency. However, if the characteristic curve of the epoxy resin is below the straight line of the wire rod 2, the conduction failure rate will be increased, so that the linear expansion coefficient (both before and after the glass transition temperature) of the resin mold portion is preferably the wire rod 2. Of the linear expansion coefficient of 2 or more and the elongation of the resin mold portion due to the temperature rise from 25 ° C. to 300 ° C. is 2.3 times or less than the elongation of the wire 2 having the same length as the entire length of the resin mold portion. It is better to set the material (see (Table 4) and the graph in FIG. 3).

The present invention is particularly effective for a small number of turns of 30 turns or less. (Third Embodiment) A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a sectional view showing the structure of the chip inductor according to the present embodiment. In this embodiment, an electrode of the resin mold portion 3 is formed in addition to the first embodiment or the second embodiment. It is difficult to transfer heat to the inside of the chip inductor by closely forming the heat-resistant coating 6 having an insulating property on the surfaces excluding both end surfaces, and the thermal shock when the chip inductor is mounted on the printed wiring board by the thermal shock of the wire 2 It is possible to further improve the effect of reducing the problem that the electrical connection between the start end and the electrode 4 is disconnected.

For example, as a constituent material of the chip inductor shown in FIG. 4, the materials shown in (Table 5) are adopted and manufactured.

[0030]

[Table 5]

At 300 ° C., as a simulation test of thermal shock when the chip inductor is mounted on a printed wiring board by soldering.
(Table 6) shows the results of confirming the continuity between the electrodes on both ends of the chip inductor after dipping in the solder for 10 seconds.

[0032]

[Table 6]

As described above, the heat resistant film 6 as shown in FIG.
It can be seen that the provision of is greatly improved in the conduction failure rate during soldering.

[0034]

As described above, the chip inductor according to the present invention has the structure shown in the first to third embodiments, so that the chip inductor can be mounted on the printed wiring board by soldering due to thermal shock between the wire rod start and end and the electrode. Since it is possible to reduce problems such as disconnection of electrical connection of, and cracking in the resin mold part, that is, it is possible to improve the heat resistance of the chip inductor, the continuous winding method using the winding core of the continuous body It is possible to secure high reliability in the manufactured chip inductor.

[Brief description of drawings]

FIG. 1A is a sectional view showing a configuration of a chip inductor according to a first embodiment and a second embodiment of the present invention. FIG. 1B is a side view of the same.

FIG. 2 is a sectional view showing a configuration of a chip inductor manufactured as a comparison with the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing elongation characteristics of an epoxy resin used in a chip inductor according to a second embodiment of the present invention due to temperature rise.

FIG. 4 is a sectional view showing the structure of a chip inductor according to a third embodiment of the present invention.

FIG. 5 is a sectional view showing the configuration of a conventional chip inductor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 core material 2 wire material 2A wire material start / end cross section 3 resin mold part 4 electrode 5 conductive film 6 heat resistant film 11 core material 12 wire material 13 resin mold part 14 electrode

Claims (3)

[Claims] 1. A rod-shaped core member made of an insulating material, a wire member wound around the peripheral surface of the core member, and a winding portion in which the starting and terminating ends of the wire member are respectively drawn to respective end faces of the core member, and the winding member. In a chip inductor comprising a resin mold part formed by molding the outer periphery of the core member on which a wire part is formed, and an electrode part formed in close contact with the start and end of the winding part and the end face of the core member, the winding part A conductive film having an area equal to or larger than the cross-sectional area of the wire material between the beginning and end of the wire and the electrode portion, and the linear expansion coefficient of the core material with respect to the linear expansion coefficient of the resin material forming the resin mold portion. A chip inductor with the same value or a smaller value. 2. The resin material forming the resin mold portion is 0.8 times to 3 times based on the elongation amount of the wire having the same length as the resin mold portion due to the temperature rise from 25 ° C. to 300 ° C. The chip inductor according to claim 1, wherein a material having an elongation amount up to twice is used. 3. The chip inductor according to claim 1, wherein a heat resistant coating having an insulating property is formed on the surface of the resin mold portion.