ALPHARETTA, GA. - Pitch-based graphite fibers dissipate heat effectively and have the potential to replace metals in automotive and electronics applications, an Amoco Corp. unit manager said. ``We are looking at developing some thermally conductive fibers in the pitch arena,'' said D.J. DeLong, business manager of carbon fibers for Amoco Perform-ance Products Inc. of Alpharetta, a unit of the corporation's Amoco Polymers business group. ``We have existing manufacturing capacity in pitch'' at the plant in Greenville, S.C.
Ultra-high modulus graphite fibers are useful when a material needs thermal dissipation or extreme stiffness, such as in most existing space structures and satellites. These fibers, however, lack the sales volume of polyacrylonitrile-based fibers, widely used in the aerospace and sporting goods markets.
Several Amoco developments in pitch-based fibers are proprietary, but two others are on the market:
Wakefield Engineering Inc. uses high-conductivity carbon fiber-filled Amoco Xydar thermoplastic molding compound for its new generation Deltem II heat sinks. The compound replaces a polyphenylenesulphide resin with an aluminum flake filler in some Wakefield products, said David Saums, program manager, and both are upgrades from aluminum.
The Wakefield, Mass., company injection molds the part with high-volume production tooling and creates an 8.5-gram heat sink for plastic ball grid arrays, quad packs and other common surface-mounted integrated-circuit package types.
In Casa Grande, Ariz., Hexcel Corp. fabricates carbon honeycomb core with Amoco's P-120 pitch-based fiber for use on the inner barrel of Boeing Co. 777 twinjets. As a replacement for the traditional aluminum sandwich structure, the carbon version weighs less and eliminates corrosion concerns, said Clark Smith, Hexcel product manager. The honeycomb acoustic core wraps around, and conducts heat away from, each engine.
Boeing will use the technology in next-generation 737s now in development. In combining material features, Hexcel uses Amoco T300-1K PAN-based fiber for hard points on the inner barrel core and outer cowl panels.
The Amoco Performance Products family of pitch-based graphite fibers and preforms can attain axial thermal conductivity to 1,100 watts per meter degree Kelvin. By comparison, copper's conductivity is about 400 w/mK.
A fiber-polymer compound can achieve a thermal conductivity as high as 25 w/mK, about the same as Inconel alloy or stainless steel. Normal polymers have a conductivity of less than 1 w/mK.
DeLong seeks ``how to make the plastic materials conductive enough and combine them into a metals-replacement opportunity for the injection molding community.'' Amoco, based on its Greenville output, is the world's largest manufacturer of pitch-based fiber, according to the Stanford Research Institute.
``If we can get into the electronics market, it is great business to demonstrate that it works,'' he said, acknowledging that acceptance there is in the preliminary stages. As electronic devices and packages get smaller and more powerful, the material-needs grow.
DeLong sees opportunity.
``If you can find the right match of thermal conductivity and corrosion-resistant plastic resins, then I think there is a whole area that is unexplored,'' he said. ``The automotive environment is a good place to test out these things.''
DeLong compared heat-sink costs. ``After you drill holes and machine three or four times, it becomes an $8 item in brass or copper. You can mold out that of reinforced short fiber for $3,'' said DeLong.
Molding reduces the number of parts and encourages automated assembly. Post shapes can change, an altered geometry may improve heat transfer and some taller posts can spell out the chip maker's name on top.
Bridging the industry gap may take time. ``The heat exchange guy doesn't think plastic; the plastics guy doesn't think heat exchange,'' he said. ``We need missionary work to bring those communities together.''
In March, the Office of Naval Research awarded a $9.7 million contract under which Amoco pursues ways to improve performance, develop fabrication techniques and reduce the cost of thermally conductive pitch-based fibers for electronic, space and other end-use applications.