Graphite spreader diffuses thermal woes
By Bill Schweber -- EDN, November 11, 2004
A designer’s challenge is not only to remove heat from the component that is dissipating it, but also to get that heat to where you want it to go. The conventional approach is to employ a copper or aluminum heat spreader, often coupling it with a heat pipe or a fan, but the SpreaderShield from GrafTech International Ltd offers a passive alternative with lower weight plus directed heat flow (Picture).
Made of graphite fibers, this pliable spreader is anisotropic, conducting heat well along its x and y axes but poorly in the z axis. As a result, it conducts the heat longitudinally away from the source. Several laptop PCs and cell phones use the material to spread CPU heat dissipation toward the case corners and thus minimize hot spots, notes Julian Norley, PhD, director of technology at the company, adding that the SpreaderShield conveys the heat to the case over an area much broader than the IC’s footprint alone. Designers can also apply the material to large systems, such as big-screen, plasma TVs, to eliminate hot spots, which the image and color on screen can cause.
The in-plane 2-D thermal conductivity of the material is as high as 500W/m-K (watts per meter Kelvin)—comparable with copper and twice that of aluminum—and the z-axis conductivity is less than 10W/mK. The SpreaderShield material weighs approximately 30% less than aluminum and 80% less than copper, and designers can coat the material with a thin metal layer for EMI shielding, as well. Cost depends on size and final form factor but is typically a few dollars per unit (volume quantities).
GrafTech International Ltd, 1-302-778-8227, www.graftech.com.
