Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-02-01
2001-11-13
Thompson, Gregory (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C165S185000, C174S016300, C174S050510, C257S796000, C361S708000, C361S715000
Reexamination Certificate
active
06317324
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to electronic circuit packaging and, more specifically, to an electronic circuit with heat generating components in which a relatively high thermal conductivity molded insert is encapsulated with the components to improve removal of heat from the components.
BACKGROUND OF THE INVENTION
To simplify the assembly of electronic devices, electronic components are frequently furnished to manufacturers in the form of preassembled modules containing whole circuits for performing a given function. The modules can then be advantageously handled in the assembly line as single parts of a larger whole, substantially speeding and simplifying the overall assembly process.
Power supplies adapt well to this preassembled module concept. Manufacturers of electronic systems (such as computers and telephone switches) therefore commonly acquire power supplies as preassembled modules from third party suppliers, rather than build them themselves. To protect the components and interconnections within the preassembled modules from environmental and handling damage, and to render them easier to handle during the assembly process, the modules are frequently encapsulated (or “potted”) prior to further assembly.
Power supplies have shrunk in size and grown in power-handling capability over the years. Unfortunately, the resulting increase in power-handling capacity per unit of circuit volume (power density) has made such power supplies evermore difficult to encapsulate.
In general, encapsulating electronic components that require substantial heat removal has proven to be an intransigent problem. Ordinary potting materials do not have a coefficient of thermal conductivity sufficient to accommodate some of today's high thermal density components. Potting materials that have a high coefficient of thermal conductivity tend to be too viscous, resulting in the formation of cavities in the material. Guaranteeing the absence of cavities requires substantial time and care, resulting in a marked (perhaps four-fold) increase in manufacturing time. Even given the extra time, encapsulating machines tend to jam in their attempts to manage the thicker material, forcing the assembly line to be interrupted so the machines can be cleaned and restarted.
Accordingly, what is needed in the art is an improved way to encapsulate power supplies and heat-producing electronic components in general.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides an encapsulant structure for retaining an electronic circuit having heat-generating components within a case that at least partially surrounds the electronic circuit. In one advantageous embodiment, the encapsulant structure provides for a thermally conductive insert to be located within the case proximate the heat-generating components. The insert increases the heat transfer efficiency from the electronic circuit to the case. In a related embodiment, the encapsulant structure further includes a potting material, having a lower coefficient of thermal conductivity than the insert, that encapsulates both the electronic circuit and the insert.
The present invention therefore, in broad scope, introduces the concept of placing an insert that has a high rate of thermal conductivity in an encapsulated circuit proximate to the heat generating components in such circuit. Because the heat transfer characteristics of the insert are better than the potting material used to encapsulate the circuit, heat generated by the components in the circuit can be more efficiently conducted to the case of the encapsulated circuit, where it can be transferred to the surrounding ambient air.
In one embodiment of the invention, the thermally conductive insert has a general topographical conformity to the electronic circuit, which topographic shape places the insert in closer proximity to the heat generating components. In another embodiment of the invention, the thermally conductive insert is premolded. In still another embodiment, the thermally conductive insert is flexible and compliant, which advantageously permits the insert to be pressed around the encapsulated electronic circuit and eases the assembly process of manufacturing the encapsulant structure. In another embodiment of the invention, a plurality of thermally conductive inserts are located within the case.
Another aspect of the invention provides for the encapsulant structure to have a thermally conductive insert precut from sheets of material having a coefficient of thermal conductivity that is greater than the potting material. In a particularly favorable embodiment the insert can be placed in the case by a machine, such as a pick-and-place machine. In yet another embodiment, the precut thermally conductive insert is compressible. This is also particularly beneficial as the insert can be pressed around the components to assure close proximity between the insert and the heat generating components in the circuit.
The present invention also provides for a method of manufacturing an encapsulated electronic circuit having heat-generating components. The method, in one embodiment, comprises the provision of a case to at least partially surround the electronic circuit. A thermally conductive insert is located within the case proximate to the heat-generating components to increase a heat transfer efficiency from the electronic circuit to the case. In a related embodiment, the method further includes locating potting material, having a lower coefficient of thermal conductivity than the insert, in the case to encapsulate both the electronic circuit and the insert.
A particularly useful embodiment of the method of manufacturing calls for providing a case to at least partially surround the electronic circuit containing heat generating components. An initial layer of potting material is placed within the case and quick-cured. A thermally conductive insert is located within the case proximate the heat-generating components. Potting material, having a lower coefficient of thermal conductivity than the insert, in then located in the case to encapsulate both the electronic circuit and the insert. Another aspect of this method provides for the initial layer of potting material within the case to have a thickness of about 2 to 6 millimeters. Yet another aspect of this method is to quick cure wherein the initial layer of potting material within the case using a process selected from the group of an ultraviolet process and a microwave process.
The present invention also provides for an electronic device, comprised of a substrate adapted to receive electronic components and an encapsulant structure for an electronic circuit mounted on the substrate and having heat generating components. The encapsulant structure includes, in one embodiment, a case at least partially surrounding the electronic circuit and a thermally conductive insert located within the case proximate the heat-generating components. In a related embodiment, the encapsulant structure further includes a potting material, having a lower coefficient of thermal conductivity than the insert, to encapsulate both the electronic circuit and the insert so that the insert may increase the heat transfer efficiency from the electronic circuit to the case.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the pertinent art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the pertinent art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the pertinent art should also realize that such equivalent constructions do not depart from the spirit and scope of the i
Chen Shiaw-Jong Steve
Hooey Roger J.
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