Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-10-26
2002-10-29
Tolin, Gerald (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C174S050510, C361S719000, C361S752000
Reexamination Certificate
active
06473304
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to power electronics and, more specifically, to an encapsulated, board-mountable power supply and a method of manufacture therefor.
BACKGROUND OF THE INVENTION
Electronic devices for the power supplies or other applications are conventionally provided in a protective, heat-dissipating package. Often, the device (e.g., a metal oxide semiconductor field-effect transistor, or “MOSFET” is attached to a lead-frame by a wire bonding technique. The device is then encapsulated or “molded” wherein an encapsulant is formed about the device to yield a unitary, board-mountable package device. One well-known configuration for board-mountable package is a so-called dual in-line package (DIP), wherein electrical leads protrude from opposing sidewalls of the package. The leads are advantageously so arranged to allow the package to be mounted to a circuit board by various conventional soldering processes. DIPs are widely used for packaging integrated circuits, most often in telecommunications or computer-related environments.
In a power electronics environment, the packaged power devices are conventionally mounted directly to a circuit board, using either through-hole or surface-mounting techniques. The devices are then joined with other electronic components to form a circuit, perhaps to function as a power supply such as a DC/DC power converter. As with other types of electronic components, the trend in the design of power supplies has been toward achieving increased power and device density and lower device profile. However, any improvements in power, density and profile cannot be at the expense of the thermal and electrical characteristics of the components and overall power supply.
Analogous to the packaged power devices, the power supply is conventionally encapsulated to form a packaged power supply module. Using the DC/DC power converter as an example, a simplified process of constructing the packaged DC/DC power converter will hereinafter be described. First, the packaged devices (e.g., power switching devices) of the DC/DC power converter that must be thermally managed due to high power dissipation are mounted via an insulator to a five-sided metal enclosure. Next, a printed circuit board including the remaining components (e.g., a transformer, inductor, output filter and control circuitry) of the DC/DC power converter is placed over the packaged switching devices in the metal enclosure. The printed circuit board is then mechanically fastened to the enclosure and the leads of the packaged switching device are soldered to the printed circuit board. Third, an encapsulant is flowed into the enclosure covering the packaged switching devices and circuit board with leads exposed therefrom for connection to a circuit employing the DC/DC power converter to advantage. Finally, the encapsulant is cured (e.g., through exposure to heat) thereby forming a packaged power supply module.
While the aforementioned technique provides a viable alternative for packaging a power supply, it endures several limitations. First, the metal enclosure is electrically conductive thereby creating an environment where the components of the power supply must be individually isolated therefrom. Second, the thermal and electrical characteristics of the devices therein are unacceptable; namely, the thermal resistance of the power devices is high. In conjunction therewith, the power supply module employed discrete devices and did not incorporate planar magnetic devices into the design. Third, the package density of the power supply module is low. Thus, in a period where the trend is toward higher power density power supply modules, the foregoing design for packaging the power supply module is contrary to the present trend and provides a lower power density package. Finally, the design requires several iterative manual steps that do not support a cost effective and mass producible design for power supply modules.
Accordingly, what is needed in the art is a power supply and a technique for packaging power supply circuitry into a packaged power supply module that enhances the power and device density of the power supply without sacrificing the thermal and electrical characteristics of the devices. Preferably, the technique should be cost-effective and suitable for mass production.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a power supply and a method of manufacture therefor. The power supply includes: (1) a circuit board containing conductors for interconnecting electrical components of the power supply; (2) a thermally-conductive case having an integral electrically insulating layer, the thermally-conductive case forming a reservoir to receive the circuit board therein; (3) a power semiconductor device having a body connected in thermal communication with the thermally-conductive case and terminals coupled to the conductors of the circuit board; (4) an encapsulant, located within the reservoir, the encapsulant ensconcing the power semiconductor device and the electrical components and; (5) electrical leads extending from the power supply that allow the power supply to be coupled to a printed wiring board. The present invention, therefore, introduces a highly compact, thermally-conductive package for a power supply (perhaps a DC/DC converter) that is readily manufacturable, durable and easily mounted to the printed wiring board (allowing the power supply to form a portion of a larger piece of equipment). The encapsulant provides environmental protection (e.g., protection from dirt and moisture) for the power semiconductor device and electrical components of the power supply. The encapsulant may also, among other things, provide a path for heat generated by the electrical components of the power supply and a mechanical fixture to resist displacement of the electrical components therein.
In one embodiment of the present invention, the thermally-conductive case further includes an integral electrically conductive circuit layer; portions of the circuit layer are capable of being removed to form electrically conductive traces therein. The power semiconductor devices or other electrical components may be advantageously located within the thermally-conductive case to enhance a flexibility of the design of the power supply. This is not necessary to the broad scope of the present invention, however.
In one embodiment of the present invention, one of the conductors are formed as windings and a core is disposed through apertures of the circuit board proximate the windings. The windings and the core form a power magnetic device. The present invention may take advantage of planar magnetics thereby further enhancing the compactness of the power supply. This is not necessary to the broad scope of the present invention, however. In one embodiment of the present invention, the electrical leads comprise posts extending from the circuit board. In an alternative embodiment of the present invention, portions of an integral electrically conductive circuit layer are capable of being removed to form electrically conductive traces herein; the traces are coupled to a conductor of the circuit board and form the electrical leads. One of the alternatives is set forth in the detailed description that follows. However, those skilled in the art will recognize that other structures for communicating electricity to and from the power supply are within the broad scope of the present invention.
In one embodiment of the present invention, the power semiconductor device is soldered to the thermally-conductive case. In an embodiment to be illustrated and described, a power switching device is soldered to the thermally-conductive case. However, the power semiconductor device may be coupled in any manner that is not inconsistent with the objective of allowing the case to serve as a heat sink for the power semiconductor device.
In one embodiment of the present invention, the encapsulant substantially fills the r
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