Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-02-19
2001-05-01
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S016300, C174S252000, C361S705000, C361S707000, C361S708000, C165S080200, C165S185000, C165S080300, C257S707000, C257S713000, C257S717000
Reexamination Certificate
active
06225571
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to a heatsink and, more specifically, to a heatsink having an insulating dielectric with a high thermal conductivity.
BACKGROUND OF THE INVENTION
Because of the ever increasing demand placed on electrical components, in general, electronic designers need to be able to pack higher powered components closer together in ever smaller spaces. More power in less space translates to higher watt densities, and therefore, increased heat generation. As temperatures rise, the reliability and functionality of electronic components are impaired dramatically. Experience has shown that more than 50 percent of electronic failures are the result of thermal problems. Traditionally, heatsinks are used to move heat from components generating the heat to an area where the heat can be dissipated to the atmosphere or adequate ventilation can be provided to the heatsink.
Conventional heatsinks use some type of mechanical method to attach the heat-generating component to the heatsink. The most common methods are: adhesives, spring clamping devices, or hold-down brackets with a mechanical fastener such as a machine screw. These methods generally require an assembler to make the mechanical attachment of the component to the heatsink.
Heat-generating electronic devices need to be electrically isolated from the heatsink in many cases. Currently the devices are electrically isolated by a thermal interface pad, which results in a substantial thermal contact resistance. Typically, in a stamped heatsink assembly, the presence of the thermal interface pad can contribute up to 50 percent of the overall thermal resistance, even in the best designs. However, heat generating devices may be directly mounted on the heatsink. In at least one conventional approach, the entire heatsink is covered with a dielectric material prior to mounting the device on an intervening metal foil layer. By covering unnecessary areas of the heatsink with the dielectric, the thermal efficiency of forced convection cooling is significantly reduced. When the device is surface mounted, the contact resistance is very low, because of the metal to metal bond between the tab of the device and the metal foil substrate.
There are additional thermal transfer inefficiencies associated with the way in which components are conventionally attached to the heatsink. Although the component surface and the mating surface appear to be smooth, under adequate magnification it can be shown that they are actually rough. When a heatsink is mated with a heat-generating device by a mechanical means such as a spring clamp or hold-down bracket, microscopic peaks in the surface of the component ride upon corresponding microscopic peaks of the heatsink. Therefore, the two surfaces are not in the close physical proximity that fosters good heat transference by conduction. Of course, this poor thermal conductivity results in higher device temperatures which, in turn, lead to device failures. Alternatively, adhesives are often used to adhere the electrical component to the heatsink; however, these conventional adhesives also bring disadvantages. For example, while these adhesives often have good dielectric characteristics, they are not good thermal conductors, or, if they are good thermal conductors, they tend to have poor dielectric characteristics. Thus, these present day adhesives do have undesirable characteristics.
Accordingly, what is needed in the art is a heatsink with a low thermal impedance between the electronic component and the body of the heatsink while maintaining good dielectric characteristics and eliminating mechanical fasteners.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a heatsink for use with a heat-generating electrical component. The heatsink comprises a spine having opposing sides, cooling fins extending from the spine, and a dielectric layer adhered to at least one of the opposing sides. The dielectric layer has a thermal conductivity of at least about 1 W/m° C. In one embodiment, the heatsink further comprises a metal layer adhered to the exposed surface of the dielectric layer. The metal layer is preferably adhered to exposed surface of the dielectric layer without the use of conventional adhesives that are typically used to adhere electrical components to heatsinks. Thus, the problems associated with the use of such conventional adhesives are avoided. Once attached to the dielectric layer, the metal layer provides a surface to which an electric component can be attached. In another aspect of this embodiment, the heatsink further includes a heat-generating component adhered or attached to the metal layer. In a particularly advantageous embodiment, the heat-generating component is a surface-mount electrical component that is adhered to the metal layer with solder.
In another embodiment, the metal layer is patterned to form concentric patterns on the dielectric layer to provide a mounting location for electrical components having mounting footprints of different sizes. These concentric patterns can be used as a self-aligning mark for easily placing or positioning the electrical components on the metal layer. In one aspect of this embodiment, the metal layer forms at least three concentric patterns to accommodate any of three different sizes of electrical components. In a particularly advantageous embodiment, the concentric patterns provide a self-aligning pattern for adhering a surface-mountable electrical component thereon during a soldering process.
In another embodiment, the electrical component has electrical leads extending therefrom with each of the electrical leads configured to be received in a corresponding contact opening within a printed wiring board. The self-aligning pattern aligns each of the electrical leads with one of the corresponding contact openings, respectively.
In yet another embodiment, the heatsink further includes a heat-generating component adhered to the dielectric layer. The dielectric layer, in particularly advantageous embodiments, comprises material with a thermal conductivity ranging from about 2 W/m° C. to about 15 W/m° C.
The dielectric layers may be adhered to each of the opposing sides with a metal layer being adhered to each of the dielectric layers. In one aspect of this particular embodiment, the heatsink has an electrical component adhered to each of the metal layers.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the 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 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 art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
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Bream Jeffrey L.
Ferranti Stephen A.
Ganesa-Pillai Madhu
Klafter Leon
Lyons Alan M.
Gaffin Jeffrey
Lucent Technologies - Inc.
Patel Ishwar B.
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