Inductor devices – Core forms casing
Reexamination Certificate
2001-10-29
2003-06-24
Mai, Anh (Department: 2832)
Inductor devices
Core forms casing
C336S215000, C252S062620, C252S062630
Reexamination Certificate
active
06583699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic material to be used as a core material of an inductance element and an inductor having the core using the magnetic material, and in particular to a ferrite to be suitably used as the core material of a chip inductor of a resin molded type and an inductor using the core.
2. Description of the Related Art
Generally a temperature characteristic of a permeability of the ferrite to be used to the inductance element has conventionally had a positive temperature coefficient. This is because since a capacitance of a condenser used in combination for composing the inductance element and a circuit has normally a negative temperature characteristic, a measure is taken in order that characteristics of the combined substances are changed as least as possible by change in temperature.
However, considering not a simple combination of the inductance element and the condenser, but the temperature coefficient in the whole of the circuit, since temperature coefficients of parts composing the circuit, other than the condenser, are positive, the inductor having a negative temperature coefficient about permeability is needed in order to lessen the temperature coefficient in the whole of the circuit, and such a ferrite has been demanded where the temperature coefficient of the permeability satisfying the need is negative.
On the other hand, recently, in fields of chip inductor, fixed coil and others of resin molded type which have rapidly spread and are used in televisions, video tape recorders or mobile communication machinery, in order to comply with demands concerning small size, light weight and high precision, requirements of narrow tolerance and high reliability with respect to these parts have increased. In elements of the resin molded type, since an inductance value is varied by compression stress caused by molding a resin, it is difficult to obtain parts of high quality having small tolerance of inductance. Therefore, such a ferrite has been demanded which is small in change of the inductance to an external stress, that is, good in an anti-stress characteristic.
Thus, in order to comply with these demands, a magnetic material having the negative temperature coefficient about the permeability and the good anti-stress characteristic will be necessary.
As the ferrite where the temperature coefficient of the permeability is negative, JP-A-59-121803, JP-A-59-121804, JP-A-59-121806, JP-A-59-121155 and JP-A-59-121156 respectively show the ferrite where the temperature coefficient of an initial permeability is similarly negative in range between 0 and 80° C. Further, examples of these publications show that densities of sintered compacts are heightened and are effective for improving strength of products. However, a problem about variances of the inductance when an external stress is effected cannot be settled.
On the other hand, JP-A-1-179402 refers to a core for inductor in which a ferrite material of oxide containing nickel as a necessary component is contained with at least one kind of 1.5 to 5 wt % of Bi
2
O
3
and V
2
O
5
, whereby change of the inductance is small, though the external stress is fluctuated. However, the ferrite material of this composition cannot comply with the demand that the temperature coefficient of the permeability is made negative.
JP-A-3-93667 describes a high frequency magnetic material which has a spinel type composition of Fe
2
O3 of 25 to 40 mol %, ZnO of 0 to 20 mol %, the rest being NiO and CuO, and a mol ratio of NiO being more than a mol ratio of CuO, containing, as components of small amount, Bi
2
O
3
of 0.1 to 12 wt % and SiO
2
of 0.05 to 4.0 wt %, and which is small loss even if being above 1 MHz. Further, Co
3
O
4
of 0.01 to 1.5 wt % or cobalt oxide or cobalt carbide of amounts being equivalent thereto is added to the above high frequency magnetic material as another example. An example of the same measures changes of inductance by applying pressure, and shows that the change of inductance is small to pressure. However, relative temperature coefficients of the initial permeability are both positive, and it is not possible to satisfy the demand that the temperature coefficient of the permeability is made negative.
JP-A-3-91209 sets forth a ferrite composition which is a spinel type composition of Fe
2
O
3
of 25 to 40 mol %, ZnO of 0 to 20 mol %, the rest being NiO and CuO, and a mol ratio of NiO being more than a mol ratio of CuO, containing, as components of small amount, Bi
2
O
3
of 0.1 to 5 wt % and SiO
2
of 0.05 to 4.0 wt %. However, the example shows only the composition where a basic composition of Fe
2
O
3
: 38.2 mol %, NiO: 50.3 mol %, ZnO: 8.4 mol % and CuO: 3.1 mol % is added with Bi
2
O
3
: 3 wt % and SiO
2
: 0.8 wt %. With respect to this example, the change of inductance is measured by applying pressure, and the changing rate thereof is calculated. However, the calculated changing rate is not a rate of change exerted with a predetermined pressure but a value calculated from inductance before and after molting the resin. Therefore, it is not seen whether an inductance at pressure of, for example, 50 kPa is within ±5% or not. Further, a positive value is shown as to the temperature coefficient of inductance, and it is not possible to satisfy the demand that the temperature coefficient of the permeability is made negative.
Further, JP-A-11-87126 discloses that main components containing at least iron oxide and nickel oxide contain as additives one kind or two kinds or more bismuth oxide, vanadium oxide, phosphorus oxide and boron oxide, and are added with a first subcomponent and a second subcomponent. The ratios of the additives such as bismuth oxide to the main components are 0.5 to 15 wt %. The first subcomponent is silicon oxide, and the ratio to the main component is 0.1 to 10.0 wt %. The second subcomponent is one kind or two kinds or more of magnesium oxide, calcium oxide, barium oxide and strontium oxide, and the ratios to the main components are 0.1 to 10.0 wt %. In regard to this ferrite, the changing ratio of the inductance when applying pressure of 50 kPa is within ±5%, and the relative temperature coefficient of the initial permeability in the temperature range of −20 to 60° C. is ±20 ppm/° C. However, in examples of the same, the relative coefficients of the initial permeability are all positive, and it is not possible to satisfy the demand that the temperature coefficient of the permeability is made negative.
SUMMARY OF THE INVENTION
As mentioned above, there has never existed any magnetic material having the negative temperature coefficient about the initial permeability and the excellent anti-stress characteristic. Accordingly, it is an object of the invention to offer such a magnetic material where a relative temperature coefficient of an initial permeability is negative and an anti-stress characteristic is excellent. Another object of the invention is to offer a resin molded typed inductor having a negative temperature coefficient about inductance by use of this magnetic material and having a small tolerance of the inductance.
A magnetic material of a first aspect of the invention is characterized in that main components of 100 wt parts including Fe
2
O
3
of 46.0 to 51.0 mol %, CuO of 0.5 to 15.0 mol % and the rest being NiO are added with additives of bismuth oxide of 4.0 to 10.0 wt part in terms of Bi
2
O
3
, magnesium oxide of 1.0 to 5.0 wt part in terms of MgO, silicon oxide of 2.0 to 8.0 wt part in terms of SiO
2
, and cobalt oxide of 0.2 to 0.5 wt part in terms of CoO.
In the magnetic material of the first aspect, the relative temperature coefficient of the initial permeability is negative, and the excellent anti-stress characteristic can be realized. Accordingly, it is possible to actualize a resin molded type inductor having a negative temperature coefficient about inductance by use of the magnetic material and having a small tolerance of the inductance.
Herein, reasons for specifying the a
Mai Anh
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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