` ` OptimizeIt ensures optimum thermal design

OptimizeIt ensures optimum thermal design

Dr. Eldad Levy, Engineering Manager, CAS Ltd., Haifa, Israel
CAS internal memo, September 2004

Heat is the major limiter of electronic components and systems. It frustrates engineers trying to squeeze extra watts or even milliwatts of functionality into a design--functionality that can mean the difference between leapfrogging competition and lagging behind.

In order to optimize a thermal design, engineers typically set up and solve multiple cases and then compare the results to find the best performing configuration. This process can be incredibly time-consuming. A designer can spend 40 hours or more setting up test cases and analyzing results, with no assurance that he has picked the correct values to test. This "Value-picking" strategy is often hit-or-miss because design sensitivities are not always intuitive.

To eliminate the guess-work and simultaneously shrink the design cycle, engineers need to automate thermal optimization. Automation transforms thermal analysis into a faster, more effective, more efficient process, and guarantees that engineers will examine all possibilities. With automation, all heat sink dimensions, vent and fan locations, properties, etc. are investigated. If there is a combination of parameters that can make the design goal possible, automated optimization will find it.

OptimizeIt, a module integrated with Coolit CFD thermal and flow analysis software, delivers this automation. Users merely define what design parameters can be varied, their ranges, and the objective of the design optimization. They then click "Start", and walk away; OptimizeIt takes care of the rest. Using a sophisticated optimization algorithm, it sets up and runs multiple Coolit cases and identifies the best design.

Telecom Challenge

While any industry can benefit from thermal optimization, telecommunications, with its NEBS requirements, can profit more than most. NEBS, or Network Equipment Building System, is the universally recognized standard for telecom equipment. It requires equipment to operate in a 55 deg. C ambient while maintaining electronic component case temperatures below the manufacturer-defined maximums, typically 80 - 95 deg. C.

At CAS Ltd, we recently designed a telecom chassis for telecom manufacturer, Actelis Networks. Actelis supplies high-quality, high-bandwidth broadband services over existing copper pairs for a wide range of businesses, utilities, military installations and government agencies.

The chassis was a 1U configuration (1.75 inches high) and 9.5 inches wide, dissipating approximately 35 W. The design goals were to ensure that several temperature sensitive components were within their manufacturer's limits, while at the same time optimizing fan type and location, and the number, sizes, and locations of vents. Standard, commercially available, pin fin heat sinks were chosen. If optimizing the above parameters was insufficient to maintain the required component temperatures, we could have added heat sinks to the optimization process. However, that would have required custom and, hence, more expensive heat sinks, which was undesirable.

To optimize the design we used Coolit's OptimizeIt module. The initial design had one fan and 4 vents. It had several key electronic components on both sides of the PCB whose temperatures were at, or exceeding their manufacturers' limits. The hottest device, a BGA on the component side of the board, was 5 deg. C over its 91 deg. C limit.

In OptimizeIt, we specified the maximum allowed component temperatures as the design constraints and objective functions. We set the number, size, and position of the vents and fans as variable parameters.

OptimizeIt automatically set up and ran 73 cases and reported that the design goals could be accomplished with a single Delta 40mm exhaust fan positioned roughly in the middle of the back wall. It also resized and repositioned the existing vents, and added an additional vent to the front panel. In the optimum design, the BGA temperature dropped from 96 deg. C to 88 deg. C, while the case temperatures of the circuit side components fell from 95 deg. C to 89 deg C.

If we had to perform the optimization manually and solved the same number of cases as OptimizeIt, we would have spent an average of 30 minutes per case setting up and comparing results. In total, it would have added almost a week to our project, and resulted in a correspondingly higher price to the client.

Optimizing At Any Level

OptimizeIt is an effective tool for pinpointing the optimum thermal configuration at any level, from individual heat sinks to complete systems. It frees engineers from the iterative, and potentially tedious process of setting up numerous cases and comparing the results. The iterations still occur, but problem-setup occurs automatically with the results ranked in order of thermal performance. The time savings are huge, amounting to man-weeks of manual inputting and analysis that are off-loaded to a computer, leaving engineers to focus on tasks only they can handle. On top of that, engineers no longer have to worry that they might miss the best configuration. OptimizeIt will always find it.

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This view inside the telecom chassis identifies two hot components that were insufficiently cooled in the original design. OptimizeIt repositioned the existing vents, and added an additional vent to bring temperatures within spec.

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Thermal optimization ensured that this telecom chassis from Actelis meets NEBS requirements for operating in a 55 deg C ambient.

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