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FROM EDN EUROPE: Helping gigahertz processors keep their cool
By Graham Prophet -- EDN, 12/7/2000
When you have processors running at gigahertz clock speeds, how do you cool them? The components group of Agilent Technologies believes it answers that question with its ArctiCooler series of fans for direct processor mounting (Picture). Cooling fans might at first sight seem an unlikely market sector for Agilent, but these are not ordinary fans. Apart from catering for Pentium 4 out to a planned 2-GHz operation, these fans also offer operation that Agilent says is significantly quieter than other units. ArctiCooler units use high-specification (dual-ball-race) fans mounted on a solid aluminium heat sink. For less demanding applications, such as Pentium III and Athlon processors running at 1.2 GHz, the model CD uses a cast heat sink with straight fins. A conical transition within the aluminium, from base plate through to fin area, aids even heat flow, and these units come with the mountings for socket-370-style application. The company quotes a thermal resistance of 0.8°C/W junction-to-air at 12V. Higher rated units use a heat sink machined from solid aluminium, with inclined fins and a parabolic transition from the solid base to fins; according to Agilent, this feature helps maintain laminar air flow to increase heat transfer and reduce noise. In both designs, you need minimal clearance above the fan because the air flow first draws in through the fins and then expels out through them. This feature, too, increases heat transfer. Base-plate design conforms to the Pentium 4 requirement. For the CB model, junction-to-air thermal resistance is 0.33°C/W at 12V. Typical acoustic-noise levels are 25 dB against a typical industry-standard fan value around 30 dB; the company adds that there is scope for even more heat transfer by incorporating a copper core in the aluminium.
