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Package Design Heats Up
Hot chips force changes in chassis cooling techniques
Terry Costlow -- Design News, April 26, 2004
The newest generation of processors continues to push speeds to new heights, but their power consumption and heat generation are forcing system developers to look more closely at enclosure designs. As design engineers augment CPUs with faster, hotter graphics chips and other high-wattage parts, enclosure manufacturers are challenged to cool them reliably without adding any cost.
That's an especially big challenge in VME, CompactPCI, and emerging architectures. "There's an incredible need for sophisticated cooling," says Valerie Andrews, marketing manager at ACT/Technico, an Ivyland, PA maker of bus-oriented systems (http://rbi.ims.ca/3848-692).
The hotter chips are only part of the issue. In many platforms there's a growing trend to add functions with PCI Mezzanine cards (PMC). "When you put a PMC on a board, you can greatly increase the pressure drop, making it harder to move air," says Bob Sullivan, vice president of technology at Hybricon Corp. of Ayer, MA (http://rbi.ims.ca/3848-693). Such boards can create air dams, raising the possibility that it will overheat.
That's prompting enclosure makers to add more cooling capability. One technique for minimizing air dams and pressure drops is to switch to impellers instead of fans. "Impellers usually have a higher flow rate and they also handle higher pressure drops," Sullivan says.
Most observers feel that cooling will be a key aspect when system developers run simulations for switched fabric architectures. Most system houses will expect cooling solutions to come from the supplier of the shelf enclosure that holds the cards. "I think the system integrator would expect the shelf manufacturer to specify and qualify the enclosure with the fans," says Wolfgang Poschenrieder, project manager for AdvancedTCA Systems at Force Computers Inc. (http://rbi.ims.ca/3848-697).
The closeness of system designer and enclosure maker is even more evident in high-end military applications, where designers often design their own boxes, farming manufacturing out to enclosure vendors. "We developed a hybrid composite chassis built with carbon fibers and aluminum. It handles over 500W in a small system. Not only does it dissipate heat better, it's three-fourths the weight of an all-aluminum chassis," says Doug Patterson, marketing director at Vista Controls (http://rbi.ims.ca/3848-698). However, he notes that the material is "not inordinately higher" in price than conventional mil-spec cabinetry, but it is too expensive for commercial applications.
Cost remains the driving force in commercial applications, but heat is rising in importance. At contract manufacturer Solectron Corporation (http://rbi.imsca/3848-699), "cost avoidance" is the prime factor for most enclosures, says David Cohoon, marketing manager at Solectron's Shinei USA enclosure subsidiary. But the dangers of overheating are prompting many designers to value effective cooling over cost.
Heating is also changing the look of systems with fairly low performance needs, where the focus on low acoustic noise prohibits fan use. Here, adding more openings such as grilled doors and vented side panels provides sufficient cooling.
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