JPH0782948B2 - Small coil - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small coil used in various electric devices, and more particularly to a small coil in which terminals are directly attached to a ferrite core.

[0002]

[Prior art and its problems] On a base with terminals implanted,
A coil having a structure in which a core formed by winding a wire is attached is generally used. However, in recent years, by removing the base and directly attaching the terminals to the core, a small coil which is further miniaturized has been used. FIG. 1 shows an example of such a coil. The flange 2 of the ferrite core 1 has two plate-like terminals 3 and 4 made of phosphor bronze or the like.
Is bonded and the ends 6 and 7 of the wire 5 wound around the core 1 are connected to the terminals 3 and 4 by soldering or welding. However, since the terminals 3 and 4 and the core 1 are conventionally bonded using an organic adhesive such as an epoxy-based adhesive,
This joint part is weak to heat, and the terminal may peel off from the core due to the heat of the solder near 300 ° C. when mounting on the printed board.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a small coil of the type in which the terminals are directly attached to the core so that the terminals do not peel off from the core due to heat when soldering to the printed circuit board.

[0004]

The present invention was made by paying attention to the fact that the core material ferrite and glass have substantially the same coefficient of thermal expansion. Instead of a conventional organic adhesive, an inorganic material that is difficult to melt at high temperatures is used. Is characterized in that the core and the terminal are joined by the glass, and the terminal is formed of a material having a thermal expansion coefficient substantially the same as that of the glass and the ferrite core.

[0005]

EXAMPLE FIG. 2 shows an example of a small coil of the present invention. Two terminals are provided on the lower surface of a core 20 made of ferrite.
11 and 12 are bonded by glass, and the ends 31 and 32 of the wire 30 wound around the core 20 are connected to the terminals 11 and 12, respectively, by means such as welding. As shown in cross section in FIG. 3, the terminals 11 and 12 are made of a metal plate 8 made of a clad material having a three-layer structure in which copper 8b is adhered on both surfaces of a Kovar 8a which is an alloy of cobalt, nickel and iron. is there. Next, a method for manufacturing this coil will be described with reference to FIGS. First,
As shown in FIG. 3, a strip-shaped metal plate 8 made of a clad material having a three-layer structure, in which copper 8b is coated on both surfaces of Kovar 8a, is prepared. The coefficient of thermal expansion of Kovar alone is around 54 × 10 ^-7 / ° C at 300 ° C, but by applying copper to both sides of Kovar to form a clad material, the coefficient of thermal expansion can be changed to glass or ferrite. You can get closer. In particular,
When the thickness ratio of the three layers of copper, kovar, and copper is 1: 2: 1, the thermal expansion coefficient of the clad material is, for example, about 93 × 10 ⁻⁷ / ° C at 300 ° C. 95 x
The value is extremely close to 10 ^-7 / ° C. The metal plate 8 made of such a clad material is punched out to form the lead frame 10 in which the opposing terminal portions 11 and 12 are provided at predetermined intervals in the longitudinal direction as shown in FIG.

Next, a glass paste made by mixing crystalline glass powder and water and a drum-shaped core 20 made of a ferrite material are prepared, and the glass paste is applied to the tips 11a, 12a of the terminals 11, 12 or the core 20. On the bottom surface or both of the
The tips 11a and 12a are placed on the tips 11a and 12a as shown in FIG. Then, pass the lead frame 10 with the core 20 through a firing furnace,
The glass paste is fired in an atmosphere in which an inert gas such as nitrogen is slightly mixed with oxygen. By this baking treatment, the water content of the glass paste is evaporated, and the core 20 and the terminal portions 11 and 12 of the lead frame 10 are firmly joined by the melted glass.

After this, the wire 30 is wound around the core 20, the ends 31 and 32 thereof are welded or soldered to the terminals 11 and 12, and then the terminals 11 and 12 are separated from the lead frame 10.
A small coil as shown in FIG. 2 is completed in which 11 and 12 are made of a clad material having a three-layer structure in which both sides of Kovar are coated with copper, and the terminals 11 and 12 and the core 20 are joined by glass.

The oxygen concentration in the atmosphere in the firing furnace is 5
It is preferable to have a low value in the range of 0 ppm to 200 ppm. If the oxygen concentration is further increased, the lead frame 10
The copper surface of is oxidized and the solderability of the terminals 11 and 12 deteriorates. On the other hand, if the oxygen concentration is lower than this, the chemical bond between the surfaces of the copper and the glass is not sufficiently performed, and the bonding strength between the lead frame 10 and the glass becomes insufficient. Further, in order to melt the glass component and obtain a sufficient bonding effect, it is preferable to bake at a high temperature of about 600 ° C. for about 10 minutes.

Lead boron-based crystalline glass powder and industrial pure water are mixed to form a glass paste having an oxygen concentration of 100 p.
After firing for 10 minutes at 610 ° C. in a mixed atmosphere of nitrogen and oxygen of pm, a force was applied to the upper brim of the core 20 from the lateral direction, and the limit force value at which the core 20 peels from the lead frame 10 was measured. It was confirmed that the adhesive strength was enough to withstand a force of 300 grams. The glass paste may be made by mixing an organic solvent such as thinner with glass powder instead of water. However, in this case, oxygen for vaporizing the organic solvent is required, so the oxygen concentration during firing must be slightly increased, but the surface of the lead frame 10 is oxidized because it is difficult to strictly control the oxygen concentration. In some cases, the lead frame 10 may need to be cleaned after firing. As a material for the terminal, other iron-based alloy such as 42 alloy may be used instead of Kovar, and another copper-based alloy such as brass may be used instead of copper. Also,
Other metal materials may be used as long as they have the same coefficient of thermal expansion as that of glass. Further, the number and shape of the terminal portions can be modified in various ways.
Can be joined together to form a small coil having four terminals.

[0010]

In the miniature coil according to the present invention, the core and the terminal are adhered by using a glass that does not melt at a temperature of about soldering, so that the terminal is peeled from the core even when a high temperature is applied to the printed board. There is no fear. In addition, since the terminal material that has almost the same coefficient of thermal expansion as ferrite as the core material and glass as the adhesive material is used, even when a large temperature change occurs during cooling immediately after firing or during soldering to the printed circuit board. The terminal does not peel off from the core, and a small coil with high reliability can be obtained.

[0011]

[Brief description of drawings]

FIG. 1 is a perspective view of a conventional coil.

FIG. 2 is a perspective view showing an embodiment of a small coil of the present invention.

FIG. 3 is an enlarged sectional view of a part of the terminal of the coil.

FIG. 4 is a plan view of a lead frame used for manufacturing the coil.

FIG. 5 is a perspective view of the assembly process.

FIG. 6 is a plan view showing another embodiment of the lead frame.

[Explanation of symbols] 11 terminals 12 terminals 20 cores 30 wires

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Utsunomiya 18 Tsurugashima-cho, Iruma-gun, Saitama Omi Gomigaya Toko Co., Ltd. Saitama Works (56) Reference JP-A-57-193019 (JP, A)

Claims (2)

[Claims] 1. A small coil in which a terminal is directly attached to a core made of a ferrite material , wherein copper or copper
Is a clad material with a three-layer structure coated with a copper alloy terminal
Together form a small coil, characterized in that the core and the terminal is bonded with a glass. 2. A clad having copper coated on both sides of Kovar.
The terminal is formed of the material, and the thickness of the copper, kovar, and copper three layers
The miniature coil of claim 1 wherein the ratio is approximately 1: 2: 1 .