Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
1997-09-30
2001-05-29
Mai, Anh (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S232000, C336S083000, C336S223000
Reexamination Certificate
active
06239683
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to magnetic devices and, more specifically to an inexpensive, readily mass-producible, post-mountable power magnetic device having a relatively high power density and small footprint.
BACKGROUND OF THE INVENTION
Power magnetic devices, such as inductors and transformers, are employed in many different types of electrical circuits, such as power supply circuits. In practice, most power magnetic devices are fabricated of one or more windings, formed by an electrical member, such as a wire of circular or rectangular cross section, or a planar conductor wound about or mounted to a bobbin composed of dielectric material, such as plastic. In some instances, the electrical member is soldered to terminations on the bobbin. Alternatively, the electrical member may be threaded through the bobbin for connection directly to a metallized area on a circuit board. A magnetic core is typically affixed about the bobbin to impart a greater reactance to the power magnetic device.
As with other types of electronic components, there is a trend in the design of power magnetic devices toward achieving increased power and volumetric density and lower device profile. To achieve higher power, the resistance of the power magnetic device must be reduced, typically by increasing the cross-sectional area of the electrical member forming the device windings. To increase the density of the power magnetic device, the bobbin is usually made relatively thin in the region constituting the core of the device to optimize the electrical member resistance. Conversely, the remainder of the bobbin is usually made relatively thick to facilitate attachment of the electrical member to the bobbin terminals or to facilitate attachment of terminals on the bobbin to a circuit board. As a result of the need to make such a bobbin thin in some regions and thick in others, the bobbin is often subject to stresses at transition points between such thick and thin regions.
Another problem associated with present-day power magnetic devices is the lack of planarity of the device terminations. Because of the need to optimize the winding thickness of the power magnetic device to provide the requisite number of turns while minimizing the winding resistance, the thickness of the electrical member forming each separate winding of the device is often varied. Variation in the winding thickness often results in a lack of planarity of the device terminations, an especially critical deficiency when the device is to be mounted onto a surface of a substrate, such as a printed circuit board (“PCB”) or printed wiring board (“PWB”).
A surface-mounted power magnetic device is disclosed in U.S. Pat. No. 5,345,670, issued on Sep. 13, 1994, to Pitzele, et al., entitled “Method of Making a Surface Mount Power Magnetic Device,” commonly assigned with the present invention and incorporated herein by reference. The power magnetic device of Pitzele, et al. is suitable for attachment to a substrate (such as a PWB) and includes at least one sheet winding having a pair of spaced-apart terminations, each receiving an upwardly rising portion of a lead. The sheet winding terminations and upwardly-rising lead portions, together with at least a portion of the sheet windings, are surrounded by a molding material and encapsulated with a potting material. A magnetic core surrounds at least a portion of the sheet windings to impart a desired magnetic property to the device. Thus, Pitzele, et al. disclose a bobbin-free, encapsulated, surface-mountable power magnetic device that overcomes the deficiencies inherent in, and therefore represents a substantial advance over, the previously-described power magnetic devices. However, several additional opportunities to increase power and volumetric density and lower profile in such power magnetic devices remain.
First, device leads typically extend substantially from the device footprint and therefore increase the area of the substrate required to mount the device. In fact, extended leads can add 30% to the footprint or 50% to the volume of the magnetic device. Second, termination co-planarity requires either the aforementioned devices be molded in a lead frame (requiring additional tooling and tighter tolerances) or the leads be staked in after molding (requiring an additional manufacturing operation). Third, the outer molding compound employed for electrical isolation and thermal conductivity adds both volume and cost and raises device profile.
Accordingly, what is needed in the art is a power magnetic device having an improved termination or lead structure and a structure that attains an acceptable electrical isolation and thermal conductivity without requiring a molding compound. Further, what is needed in the art is a method of manufacture for such devices.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a magnetic device comprising: (1) first and second conductive posts mountable to a substantially planar substrate, (2) a plurality of windings coupled to the first and second conductive posts, each of the plurality of windings having first and second conductive termination apertures at predetermined locations thereon, the first and second conductive termination apertures of the plurality of windings engaging and registering with the first and second conductive posts, respectively, the first and second conductive posts electrically coupling the plurality of windings, the first and second conductive posts therefore substantially within a footprint of the magnetic device and (3) a magnetic core mounted proximate the plurality of windings, the magnetic core adapted to impart a desired magnetic property to the plurality of windings, the plurality of windings and the magnetic core substantially free of a molding material to allow the magnetic device to assume a smaller overall device volume.
In a preferred embodiment, the substantially planar substrate has a window defined therein, the magnetic core at least partially recessed within the window thereby to allow the magnetic device to assume a lower profile. Some applications for the device may not allow portions of the planar substrate to be removed to form a window. In such applications, the device is fully employable, although it will have a higher profile.
In a preferred embodiment, the first and second conductive posts are soldered within the first and second conductive termination apertures. Alternatively, the first and second posts may be interference-fit with or mechanically engage with the first and second conductive posts. In another alternative, the first and second conductive posts may be made to bear resiliently against the plurality of windings to make electrical contact with the first and second termination apertures, respectively.
In a preferred embodiment, the plurality of windings are separate and mechanically joined by the first and second conductive posts. In an alternative embodiment, the plurality of windings are portions of a multi-layer flex circuit.
In a preferred embodiment, the magnetic core surrounds and passes through a central aperture in the plurality of windings. Alternatively, the magnetic core may either surround or pass through the central aperture.
In a preferred embodiment, the first and second conductive posts are mounted to the substantially planar substrate. Alternatively, the first and second posts may be through-hole mounted to the substrate.
In a preferred embodiment, the plurality of windings form primary and secondary windings of a power transformer. The plurality of windings can, however, form windings of an inductor or other magnetic device.
In a preferred embodiment, the device further comprises first and second solder preforms coupled to the first and second conductive posts, respectively, the first and second solder preforms reflowable to solder the first and second conductive posts within the first and second conductive termination apertures. Alternatively, solder flux can be applie
Pitzele Lennart Daniel
Roessler Robert Joseph
Mai Anh
Tyco Electronics Logistics A.G.
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