System design heats up

By: 
March 09, 2004

Motherboards with high wattage CPUs like Intel's Prescott Pentium are being
augmented with mezzanine cards that have fast graphics chips and other hot
devices, making heat a key part of system design. These heat-generating boards
often fill cabinets completely, challenging heat sink and enclosure
manufacturers to cool systems reliably without pushing costs skyward.

"The Prescott and other 90 nanometer processors are drawing 100 W and higher.
That's a point where conventional cooling techniques start hitting their
limits," says Andy Keane, marketing vice president at Cooligy Inc. a Mt. View,
CA, startup. Cooligy makes a liquid cooling system with an electrokinetic pump
that replaces conventional metal heat sinks and fanned heat sinks ( http://www.cooligy.com/technology.html).

Even
before the advent of these high-powered processors, cooling has been a challenge
in VME, CompactPCI, and emerging architectures. In many platforms, there's
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://www.hybricon.com/EngWebsite/index.html.These
boards can create air dams where there's dead air over a hot chip, prompting
some enclosure makers to switch from fans to impellers. "Impellers usually have
a higher flow rate and they also handle higher pressure drops," Sullivan
says.

The close link between system designer and enclosure maker is
even more evident in high-end military applications, which often use techniques
used in commercial systems a couple of generations out. "We developed a hybrid
composite chassis built with carbon fibers and aluminum. It handles over 500 W
in a small system," says Doug Patterson, marketing director at Vista Controls of
Santa Clarita, CA ( http://www.vistacontrols.com/products.php).
However, he notes that the material is too expensive for commercial
applications.

Price remains the driving force in commercial applications, but heat is
rising up the list. At contract manufacturer Solectron Corp. ( http://www.solectron.com/svs_products/index.html),
"cost avoidance" is the number one factor for most enclosures, says David
Cohoon, marketing manager at Solectron's Shinei USA enclosure subsidiary in
Hillsboro, OR. But designers are starting to value effective cooling over
cost. "We're seeing more requirements for redundant cooling solutions,"
Cohoon says.

Heating is also changing the look of low performance systems. There, adding
more openings such as grilled doors and vented side panels provides sufficient
cooling without the noise of fans. "We punch away so much metal we need to add
stiffeners. We normally go for about 67 % open space," says Jeff Guenther, sales
manager at Equipto Electronics Corp. of Aurora, IL ( http://www.equiptoelec.com/subrack.htm).





The nickname for Hybricon's RME1221,
CoolSlot, highlights the focus on removing
heat.

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