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General Bandwidth taps Coolit for rapid virtual prototyping.

Courtesy of General Bandwidth Inc.

At telecommunications equipment manufacturer, General Bandwidth, tight production schedules make rapid thermal prototyping imperative. Delays can force board layout engineers to proceed without thermal data in order to avoid schedule slips, a costly decision if problems surface later forcing a redesign.

To perform fast design iterations, General Bandwidth simplifies its thermal models. Rather than pinpoint temperatures to within a couple degrees, General Bandwidth quickly identifies preferred component and air mover locations, along with some placement options for maximum layout flexibility. To further speed calculations, initial models are analyzed for parameter sensitivity using a minimum number of grid cells. As models are refined, the number of cells is increased. A typical simplified model, takes about an hour to run. The simplified models demonstrate a strong correlation with test results; for example, a change in chip placement or airflow, that produces a 10% change in the Coolit model temperature, will produce a 10% change in measured results.

There are three to four circuit boards in development at any one time. The designs are evolutionary, so that test results from one generation can be used to refine assumptions for follow-on modules. All components are assumed to operate at maximum power consumption, to guarantee a conservative estimate.

Prior to Coolit, General Bandwidth depended on an outside consultant for its thermal analyses. But the rapid development pace soon created an information bottleneck between the organizations. It took too long to cycle modeling information and test data back and forth.

Once the decision was made to do thermal modeling in-house, General Bandwidth reviewed its options, including the CFD package used by its consultants---a choice that would have made porting of legacy information relatively easily. After a thorough evaluation, Coolit was selected for its unparalleled speed and ease-of-use.

Ramp up for the three member thermal team occurred rapidly; the mechanical engineer was creating models in a day and, within a week, he had three boards ready for layout. The other two team members, who had never used CFD, took two days to get up to speed. Throughout, Daat Technical Support was there to help as required.

Since adopting Coolit for its in-house use, General Bandwidth has significantly shortened its thermal prototyping schedules and saved thousands of dollars in consulting fees. The Coolit graphics have made it easy for thermal engineers to communicate recommendations to non-specialists, who can view in 3D full color and with animation, the impact of various design decisions on thermal performance. In one instance, Coolit proved that relying on intuition can be dangerous. A stack of three components, that should have shown increasing temperature with distance from the fan, instead had a hot spot in the middle of the stack. The culprit proved to be an unexpected airflow pattern that disrupted the seemingly logical temperature variation.

A Coolit thermal model.
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