Inductor devices – Winding with terminals – taps – or coil conductor end...
Reexamination Certificate
1997-11-26
2001-06-12
Mai, Anh (Department: 2832)
Inductor devices
Winding with terminals, taps, or coil conductor end...
C336S229000, C336S083000, C336S065000
Reexamination Certificate
active
06246311
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to inductive devices having conductive areas on their surface.
A typical inductive device is formed by winding conductive wire around the body of a magnetic core or around a bobbin supporting a magnetic core. Transformers, for example, have primary and secondary windings surrounding the body of the core. The terminations of the primary and secondary windings are connected to input and output circuits, respectively. When used in an electronic circuit, a transformer performs the function of stepping up or down an input voltage and providing an output with a required voltage, frequency, and phase.
In a typical electronic assembly the winding terminations of inductive devices are inserted into holes in the printed circuit board and soldered. Electronic components in a typical electronic assembly are often mounted on the surface of a printed circuit board by an automated assembly process. To permit surface mounting of an inductive device the core with the windings typically is attached to a structure (e.g. a box or a frame). The winding terminations are attached to features on the exterior of the structure (contacts or leads), which in turn are attached to a printed circuit board. The structure and interposing attachment features occupy additional volume which would otherwise have been available for circuit elements. The shape of the core used for an inductive device also affects the space otherwise available for other circuit components. Typical inductive devices use cylindrical or ring-shaped annular cores. These toroidal structures do not fit well with the other mostly square electronic components on the printed circuit board. Inductive devices with non-toroidal cores exhibit flux leakage and demagnetization due to their geometry. A more rectangular core shape is shown for example in U.S. pat. No. 5,546,065. That patent describes the use of conductive shields on the surface of the magnetic core to control leakage inductance.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention features an inductive device that includes a magnetic core, a first conductive winding surrounding the core, a first conductive element formed on selected portion of a surface of the magnetic core, and a first termination of the winding mechanically attached and electrically connected to the first conductive element.
Implementations of the invention may include one or more of the following features. The device may include a second conductive element electrically isolated from the first and a second termination of the primary winding mechanically attached and electrically connected to the second conductive element. A second conductive winding may also surround the core, and two additional electrically isolated conductive elements may be formed on selected portions of a surface of the magnetic core, to which may be connected the two terminations of the second winding.
In general, in another aspect, the invention features an inductive device assembly that includes a circuit board bearing a first connection pad, a magnetic core, a first conductive winding surrounding the core, and a first conductive element formed on a selected portion of the surface of the magnetic core. The conduction element is mechanically attached to and electrically connected to the connection pad and a first winding termination is mechanically attached and electrically connected to the first conductive element.
Implementations of the invention may include one or more of the following features. The windings may be formed from metallic wire, metallic foil, or metallic film lines deposited on the surface of the magnetic core. The conductive element may include layers of a silver-filled epoxy, copper and tin. The magnetic core may have polygonic outside and/or inside perimeters and flat top and bottom surfaces. The dimensions may be chosen to maintain a generally constant cross-sectional area of the core. The core may be a ferrite or iron powder, and may include an electrical insulation layer. The electrical insulation layer may be a para-xylylene polymer.
In general, in another aspect, the invention features a method of making an inductive device by covering a selected area of a magnetic core surface with a conductive element, winding a conductive winding around the core and attaching a termination of the conductive winding to the conductive element.
In general, in another aspect, the invention features a method of making an inductive device assembly by forming a connection pad on a circuit board, covering a selected area of a magnetic core surface with a conductive element, winding a conductive winding around the core and attaching mechanically and connecting electrically the conductive element to the connection pad on the circuit board. A termination of the winding may also be mechanically attached and electrically connected to the conductive element on the surface of the core.
Implementations of the invention may include one or more of the following features. The winding terminations may be mechanically attached and electrically connected to the conductive areas by soldering or thermal compression bonding. The covering of the selected surface areas of the magnetic core with the conductive element may include gravure printing of a silver epoxy, electroplating of copper and electroplating or immersion plating of tin. The inductive device may be connected to the printed circuit board by soldering the conductive surface areas of the core to the contacts on the board. The inductive device may also be attached and connected to the board connection pads via a conductive adhesive.
Among the advantages of the invention may be one or more of the following. The invention integrates and combines the function of conductive magnetic flux shields, winding terminations and device mounting contacts on the surface of a magnetic core. The device may be mounted on a printed circuit board by attaching the mounting contacts to the board connection pads, a process suitable for automation and compatible with surface mount printed circuit board technology. In another aspect, an inductive device may be provided, which incorporates windings, winding terminations and mounting contacts on the surface of a magnetic core with any desired geometric configuration.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments, and from the claims.
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TDK Inductor Nov. 4, 1997.
Finnemore Fred M.
Montminy Steven N.
Vinciarelli Patrizio
Fish & Richardson P.C.
Mai Anh
VLT Corporation
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