Cast heatsink design advantages

Abstract

IC power dissipation requirements have been rising faster than the technology needed to economically cool them. Die casting of low cost materials, especially Al doped Zn, creates a porosity free, low cost, efficient heatsink. Hand poured Al and brass alloys are also useful in special circumstances, but with a cost penalty. Airfoil shapes can be made to take full advantage of true 3D casting shapes and direct airflow as required, greatly reducing back pressure by creating turbulence only where needed. Assembly clues such as arrows can be located along with stops and alignment pins, and turbulence enhancing grooves and attachment points can be added with little per piece cost penalty. Our particular design utilizes a Zn-Al material. Its shape was optimized from CFD and FEA thermal simulations for minimum back pressure and even heat distribution. This investigation is based from the work of cooling PXFL, licensed to Hewlett Packard as the Visualize PXFL, the world's fastest graphics computer, dissipating about 450 W per board. The cooling problem in this project stemmed from the electrical design, requiring 3 closely spaced rows of processors 8 to 10 deep. Nine of these double-sided boards were placed side by side with spacing of only 50 mm between boards, all to be forced air-cooled. The back pressure using standard fin or turned heatsinks was unacceptable. A custom shape heatsink was designed to provide adequate cooling to all 44 processors mounted on both sides of the board while controlling airflow to minimize back pressure.