Cast Heatsink Design Advantages

Power dissipation of chips has been raising faster than the technology needed to economically cool them. Especially in the high performance arena. To get high efficiency heatsinks presently, extrusions are machined or entire heatsinks are machined with strategically arranged fins. These methods are not as effective in high component densities or cost sensitive units compared to newer, porosity free castings. Die casting of, low cost materials, especially aluminum doped zinc, creates a porosity free, low cost, efficient heatsink. Hand poured aluminum 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 the airflow as required; this can greatly reduce back pressure by creating turbulence only where needed. Assembly clues such as arrows can be located along with stops and alignment pins. Even turbulence enhancing grooves and attachment points can be added with little per piece cost penalty. Our particular design utilizes a zinc-aluminum material. Its shape was optimized from CFD & FEA thermal simulations for minimum backpressure and even heat distribution. Per piece cost is about $0.50 vs. $2.00 for machined. 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 watts per board. One of these boards is shown in Figure 2. 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 had to be placed sided by side with a spacing of only 50mm between boards. All to be forced air-cooled. The backpressure using standard fin or turned heatsinks was unacceptable. A custom shape heatsink was designed which provided adequate cooling to all 44 processors mounted on both sides of the board while controlling the airflow to minimize backpressure. Because of its unique shape and requirements, much discussion with casters and molders were needed during its development. Figure 1 Die cast heatsink 1. ADVANTAGES TO CASTINGS VERSUS