Chip-type coil

Details Chip-type coil Chip-type coil

1988-08-22

1991-03-26

Kozma, Thomas J.

Inductor devices

Winding with terminals, taps, or coil conductor end...

439886, H01F 1510

Patent

active

050032798

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a chip-type coil which forms a terminal electrode directly on a magnetic core, and more particularly to a chip-type coil which reduces an eddy current loss at the terminal electrode to prevent Q-deterioration.


BACKGROUND OF THE INVENTION

A chip-type coil as shown in FIG.5 has hitherto been used. The chip-type coil has at both vertical sides of a winding portion 2a flanges 2b and 2c, a winding 4 is wound around the winding portion 2a and a pair of terminal electrodes 6a and 6b for mounting the coil on a printed substrate or the like are formed directly at both lateral sides of the lower flange 2c, the wiring 4 being electrically connected at both ends thereof to both the terminal electrodes 6a and 6b by use of soldering ( not shown ). The terminal electrodes 6a and 6b are formed of electrically conductive paste, such as silver paste or silver-palladium paste, printed on the surface of the flange 2c and baked.
The above-mentioned chip-type coil, however, forms directly on the core 2 the terminal electrodes 6a and 6b Which are superior in conductivity, whereby the problem is created in that the eddy current loss at the terminal electrodes 6a and 6b causes Q-deterioration.
In detail, as shown in FIG.6, the magnetic flux 8 caused at the wiring 4 passes through the terminal electrodes 6a and 6b formed at the flange 2c, at which time an eddy current flows in the terminal electrodes 6a and 6b. The eddy current i can generally be given in rot i=-K(dB/dt), where K is an electrical conductivity: inverse number of specific resistance .rho., and B, flux density. In this case, the conventional terminal electrodes 6a and 6b are formed of silver or silver - palladium and are larger in the conductivity K, so that the eddy current i is larger and an energy loss thereby causes the Q-deterioration.
Also, in order to prevent solder-reaching caused when soldering, it is preferable to apply metal plating of nickel, tin, solder or copper on the surface of the electrode formed of silver or the like. However, the above-mentioned chip-type coil, when metal plating is applied on the surface of terminal electrodes 6a and 6b, further increases in Q-deterioration, thereby creating the problem in that the metal plating is not applicable to the terminal electrodes.


SUMMARY OF THE INVENTION

The chip-type coil of the invention is characterized in that the terminal electrodes formed at a magnetic core each comprise a mixture of a conductive material with an insulating material.
The conductive material is mixed with the insulating material, thereby enabling the specific resistance of each terminal electrode to increase. Hence, the eddy current at the terminal electrode decreases to prevent the Q-deterioration at the chip-type coil.
Moreover, the Q-deterioration at the terminal electrode is prevented, so that the same caused by metal plating is allowable, thereby enabling the terminal electrode to be applied with metal plating.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. l is a longitudinally sectional view of an embodiment of a chip-type coil of the invention,
FIG. 2 is a graph showing the relation between specific resistance at the terminal electrode at the chip-type coil in FIG.1 and Q of the coil,
FIG.3 is a graph showing the relation between the frequency at the chip-type coil in FIG.1 and the Q of the coil,
FIG.4 is a longitudinally sectional view of a modified embodiment of the chip-type coil of the invention,
FIG.5 is a perspective view exemplary of the conventional chip-type coil, and
FIG.6. is a longitudinally sectional view showing the chip-type coil in FIG.5 together with the magnetic flux.


BEST MODE FOR CARRYING OUT THE INVENTION

Next, the present invention will be detailed in accordance with the accompanying drawings. FIG.1 is a longitudinally sectional view of an embodiment of a chip-type coil of the invention, in which reference numeral 2 designates a magnetic core formed of ferrite or the like, which has flanges 2b and 2c at both vertical sides of a winding portio

REFERENCES:
patent: 3517361 (1970-06-01), Reifel et al.
patent: 4204863 (1980-05-01), Schreiner
patent: 4327349 (1982-04-01), Ettinger et al.
patent: 4687515 (1987-08-01), Talento

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