Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
1998-11-20
2001-06-19
Donovan, Lincoln (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S083000, C336S178000
Reexamination Certificate
active
06249205
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of electronic devices, and, more particularly, to the field of ferrite inductors, such as for electromagnetic interference (EMI) suppression or ripple smoothing in low power converters.
BACKGROUND OF THE INVENTION
A typical ferrite surface mount multilayer inductor includes a generally rectangular ferrite body with an electrically conductive path extending therethrough. The electrically conductive path, in turn, is connected to respective conductive coating layers on opposite ends of the ferrite body to facilitate connection to a printed circuit board, for example. Such a ferrite component may commonly be manufactured by printing a plurality of interconnected conductive traces on successive stacked ferrite layers.
U.S. Pat. No. 4,543,553 to Mandai et al. entitled “Chip-Type Inductor” discloses a chip inductor comprising a plurality of laminated magnetic layers. Linear conductive patterns extend between the respective magnetic layers, and these linear conductive patterns are connected successively to define a coil so as to produce an inductance component. The conductive patterns on opposite surfaces of the magnetic layers are connected to each other by through-holes or vias wherein the conductors are deformed to plunge through the holes to establish electrical contact.
Another device is disclosed in U.S. Pat. No. 4,689,594 to Kawabata et al. entitled “Multi-Layer Chip Coil.” In this patent a multi-layer chip coil comprises a stack of intermediate layers of magnetizable material having a through-hole defined therein so as to extend completely through the thickness thereof. First and second patterned electrical conductors are formed on the opposite surfaces of each of the intermediate layers, and a hollow tubular conductive layer extends through the through-hole so as to connect adjacent conductors.
Still another device is disclosed in U.S. Pat. No. 5,302,932 to Person et al. entitled “Monolithic Multilayer Chip Inductor and Method For Making Same.” This patent discloses a monolithic multilayer chip inductor which includes a plurality of subassemblies stacked one above another. Each of the intermediate subassemblies includes a ferrite layer having a coil conductor with a uniform width printed on its upper surface. The intermediate ferrite layers include via holes therein for permitting interconnection of the conductor coils from one layer to the other. In addition, one end of the top coil conductor is exposed adjacent the edge of the chip, and one end of the bottom coil conductor is exposed adjacent another end of the chip so that the conductors can be connected to end terminals. Unfortunately, great accuracy may be required in assembling the layers to provide sufficient electrical contact between each vertical conductor and the relatively narrow lateral conductors.
Pending U.S. patent application Ser. No. 08/445,475) entitled “High Current Ferrite Electromagnetic Interference Suppressor and Associated Method”, and assigned to the assignee of the present invention, discloses a significant improvement in a ferrite inductor having high current handling capability. The laterally extending conductors may be made relatively thick and include enlarged width portions to connect to vertically extending electrical conductors. Unfortunately, the device may still become saturated at high currents, and, thus, be unable to provide a desired relatively high inductance at these higher operating currents as needed in certain applications.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the present invention to provide an inductor, such as for EMI suppression or ripple smoothing, particularly of the surface mount type, for carrying a relatively high current that is readily manufacturable and which provides a relatively high inductance.
It is another object of the present invention to provide a manufacturing method for such an inductor.
These and other objects, features and advantages in accordance with the present invention are provided by an inductor comprising a plurality of ferrite layers arranged in stacked relation and joined together to define a ferrite body. A first electrical conductor extends between a first pair of adjacent ferrite layers. In addition, the inductor includes first respective opposing portions of the first pair of adjacent ferrite layers being sintered together, and second respective opposing portions of the first pair of adjacent ferrite layers being in spaced apart relation to define at least one first air gap therebetween. Moreover, the device includes a sintering blocking material associated with the at least one first air gap. The sintering blocking material selectively causes an air gap to form during sintering of the ferrite layers to thereby create an air gap which will block the magnetic flux path. The resulting inductor can retain a higher inductance than could an ungapped conventional device, even at relatively high currents.
In a surface mounting embodiment of the inductor the ferrite body has a generally rectangular shape. In addition, a pair of end conductors are provided on opposing ends of the ferrite body to facilitate the surface mounting of the inductor.
The sintering blocking material may comprise a non-magnetic material. In particular, the sintering blocking material may comprise titanium-dioxide, for example. The sintering blocking material may be at least partially diffused into adjacent ferrite layer portions during the sintering operation.
In some embodiments of the invention, the first electrical conductor defines at least a portion of a first loop. The first air gap is defined within the first loop.
Of course, the inductor may include multiple ferrite layers and multiple conductors to thereby define a longer coil path through the ferrite body. In particular, the inductor may include a second electrical conductor extending between a second pair of adjacent ferrite layers, and have first respective opposing portions of the second pair of adjacent ferrite layers being sintered together and second respective opposing portions of the second pair of adjacent ferrite layers being in spaced apart relation to define at least one second air gap therebetween. The sintering blocking material is also preferably associated with the at least one second air gap to form the gap during sintering.
In one particularly advantageous embodiment of the inductor, the first electrical conductor and the second electrical conductor are outermost electrical conductors. In this embodiment two gaps are provided at the upper and lowermost electrical conductors, and preferably within the loops defined by each.
At least one of the ferrite layers preferably has at least one via extending therethrough. Accordingly, the inductor preferably further comprises an electrical conductor extending vertically through the at least one via. The vertical conductor can connect the adjacent electrical conductors to define a coil path through the ferrite body. To facilitate manufacturing tolerances and retain high current handling capability, the laterally extending electrical conductors preferably include enlarged width portions aligned in registration with each vertical electrical conductor.
REFERENCES:
patent: 4117588 (1978-10-01), Johnson
patent: 4547961 (1985-10-01), Bokil et al.
patent: 4959631 (1990-09-01), Hasegawa et al.
patent: 5250923 (1993-10-01), Ushino et al.
patent: 5-82736 (1993-04-01), None
Cameron Craig P.
Le Phuong
Meadors Richard W.
Smith James A.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Donovan Lincoln
Nguyen Tuyen T.
Steward, Inc.
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