Cool Your Heels
03/01/2007
Have you ever taken a Latin dance class? At first glance, everyone comes off as shy, and then the movement heats up. An editor rushed into my office this morning to go over the shaking, twisting, gyrating, and swaying of her Zumba class the night before. The instructor didn’t know much English, but her, “Let’s go babies,” got their attention as everyone twisted into nearly unimaginable postures. They danced muy caliente. Some things are just meant to be hot, while others are not.
In electronics, for instance, all goes better when heat responses are controlled. There are many approaches to mitigating excess heat generated by components crowded into denser, smaller packages and devices. In this supplement, “What’s Cool and What’s Hot,” for instance, Jason Brandi of Henkel talks about new classes of phase change thermal interface materials (PC TIMS) that help with inadequate heat transfer associated with thermal greases and pastes. With wax-based materials, changes occur from solid at room temperature to liquid once excess heat from the devices pushes the material past its melting point. Unlike thermal grease, these TIMS do not migrate out of the interface. In the sidebar to this article, Andy Delano of Honeywell looks at the choice of grease or phase change material. He concludes that the decision of whether to use grease or PCM should include looking at the ease of application, re-workability, cost, shelf-life, and reliability. After 500 cycles, grease’s performance begins to degrade, and by 1000 cycles its temperature has increased by 2°C. On the other hand, PCM’s high viscosity allows it to remain in place and performance is stable.
Bob Conner of Nextreme Thermal Solutions talks about hot spots that exceed average die temperature due to designers’ desire to place transistors in close proximity. Packing high-performance circuits together results in a rise in temperature. Conner suggests using an embedded thermoelectric cooler to cool hot spots, and therefore to increase product performance, reliability, and yield.
In the third article of this supplement, Sarang Shidore of Flomerics writes the most readable article on thermal modeling of semiconductor packages available. Really. He begins by looking at a normal detailed thermal model that reconstructs the physical geometry of a package. Constructing the detailed thermal analysis is added by integrating part mechanical CAD data. If done right, it will predict the temperature at various points within the package - which includes junction, case, and leads - regardless of the environment. This type of analysis fits design simulations with a few packages, but doesn’t work as well for simulations of subsystems or system-level computations with numerous semiconductor packages, because the computational resources required for these large problems would be excessive. Lost yet? Next Shidore goes into explaining two models for handling this type of problem: two-resistor compact thermal models and the DELPHI compact thermal model.
There is just no denying that thermal issues surrounding dense packaging are more important now than ever. The heat of a laptop on your lap can point out that fact. Luckily, there are numerous solutions. Keep reading and we will keep supplying this type of valuable information.
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Gail Flower
Editor-in-Chief