Patent Number: 
Section: description

The present invention is composition and a method by which a composition, formed by combining a polymer base matrix, a thermally and EMI and RF wave absorptive filler, and a thermally conductive and EMI and RF wave reflective coating material is molded into a finished component that has thermally conductive and EMI and RF wave reflective properties. The composition of the present invention employs a base matrix of polymer, for example, with different types of filler material loaded therein. The base matrix is, preferably, liquid crystal polymer; however, it may be other materials. This composition is achieved through the steps of combining the base matrix material with a thermally conductive filler material and molding the composition. This process is known to result in producing polymer compositions with high thermal conductivities as compared to the base matrix alone. The base matrix is loaded with thermally conductive filler. The mix may include, for example, by volume, 40 percent base matrix and 60 percent filler material. Depending on the base matrix and filler, loading can be even higher. One of the primary reasons for employing a thermally conductive plastic composition is that it is moldable into more complex geometries to achieve better heat dissipation. Because of the versatility of the material, applications that would clearly indicate its use are extremely widespread. Many of these applications, however, require both heat dissipating and electrical insulation to be provided concurrently. By way of example, a satellite receiver dish employs a small densely packed circuit package to receive transmissions. The circuits generate a great deal of heat and are continually bombarded with EMI and RF waves. To protect the surrounding device components and satellite dish circuitry from heat buildup and malfunctions resulting from EMI and RF absorption, the circuitry of the satellite dish must be enclosed in an EMI and RF wave reflective case that can also effectively dissipate heat. Traditionally, these cases would be constructed from a metallic material with reflective properties that prevent EMI and RF and also transfer heat. The traditional casings, however, have the traditional drawbacks associated with the fabrication of metal casings as discussed earlier. In these applications, it is logical to attempt to employ thermally conductive polymers as a heat transfer solution. The drawback in the prior art is that although the polymers conduct heat, they also absorb and transfer EMI and RF waves over the same pathways used to transfer the heat. The present invention overcomes the absorption problem of the prior art allowing application of thermally conductive polymers in environments that also require EMI and RF wave shielding. The present invention provides a thermally conductive composite material that is formed by first coating the thermally conductive filler material that is to be employed. The coating of the thermally conductive filler material provides a barrier against the natural properties of the filler to absorb EMI and RF waves while conducting heat to the filler, allowing the heat transfer process to continue. The preferred embodiment of the present invention employs carbon flakes as a thermally conductive filler material. The carbon flakes are then coated with a thermally conductive yet EMI and RF wave reflective material, in the preferred embodiment. This coating is preferably copper but may be other metallic materials, such as aluminum or nickel. The coating provides EMI and RF wave shielding to the naturally conductive filler material preventing transfer of into the filler core and thus preventing EMI and RF waves transfer throughout the final composition. Once coated, the filler material is introduced to the base polymer matrix. The two components are mixed and loaded into the desired molding machine and associated mold in a fashion known in the art which need not be discussed in detail here. Once removed from the mold, the final composition is in its final shape and ready for its end use. As can be understood, the process does not eliminate the localized, introduction of EMI and RF waves into the composition or slight conductivity in localized areas within the material. The composition formed in the process of the present invention, however, prevents conduction and absorption of EMI and RF waves throughout the entire composition by interrupting the pathways within the composition over which the interference would flow. The process of the present invention can be employed for many of the various configurations used in fabricating a thermally conductive composite. Although the preferred embodiment indicates the use of carbon flake filler in a polymer base matrix, many other fillers can be employed to achieve the desired thermally conductive composition. As the type of filler varies, the method of coating the particular material remains the same and EMI reflective metallic material is employed as the coating. In view of the foregoing, a superior moldable thermally conductive composite material with EMI and RF wave reflective properties can be realized. The composition of the present invention, greatly improves over prior art attempts to provide such EMI and RF wave reflective, moldable, thermally conductive materials. In particular, the present invention provides thermal conductivity that is vastly improved over known compositions and provides insulation against the absorption EMI and RF waves that was until now unavailable in the prior art. It would be appreciated by those skilled in the art that various changes and modifications can be made to the illustrated embodiments without departing from the spirit of the present invention. All such modifications and changes are intended to be covered by the appended claims.