Web-based software speeds IC thermal modelling

Compact thermal models reduced the time required to optimise package design and develop thermal design guidelines for the new Nvidia nForce4 media and communications processor.

Nvidia took advantage of the speed and time savings provided by compact thermal models to reduce the time required to optimise package design and develop thermal design guidelines for their new Nvidia nForce4 media and communications processor.

Nvidia optimises the package design of its products in order to improve thermal performance and minimise real estate and also provides its customers with detailed thermal guidelines that simplify system design.

Nvidia has developed a new process that substantially reduces the amount of time required to simulate the thermal performance of new products.

The new process uses the web-based Flopack software from Flomerics to quickly produce a computationally efficient thermal behavioural model - known as a "compact" model - which accurately represents a component's thermal characteristics in any end-user environment.

"We simply describe the die size and heat dissipation and the package characteristics, such as substrate size and number of balls, in the Flopack website and hit go", said Mark Hemmeyer, Mechanical Engineer for Nvidia.

"Then the website generates a compact thermal model that predicts the temperature of the various elements within the package accurately regardless of the computational environment in which it is placed".

For a typical version of the Nvidia nForce4, Hemmeyer evaluated a number of different packages with the goal of optimising the design by trading off the thermal performance against package size.

"This process used to take at least a week when we modelled the full geometry of the package and die".

"The new approach makes it possible to do a thorough thermal performance evaluation well in advance of first silicon".

"Only minimal physical testing is required to confirm the accuracy of the simulation during the time-sensitive later stages of the development cycle".

Hemmeyer also prepared a thermal design guide that provides answers to questions such as whether or not a heatsink is required under certain ambient temperature and airflow conditions and what type of heatsink provides the best performance.

To obtain this type of detailed thermal performance information, Hemmeyer downloaded both the two-resistor and Delphi compact models for the final package from the Flopack website and imported them into Flotherm thermal simulation software.

In the Flotherm environment, he developed various reference mechanical designs based on chip's target market, which is high-end desktop systems.

"Within Flotherm I can play with a various environments and look at the impact on junction temperatures as the airflow across the chip is reduced", Hemmeyer said.

"In the case of the Nvidia nForce4, I first evaluated a number of different active and passive heatsinks and picked one from each category that provided the best performance".

"Then I evaluated the chip under different operating speeds, airflows, and board conditions with no heatsink, a passive heatsink, and an active heatsink".

"By the time I was done, I was able to provide a detailed engineering document that makes it clear to our customers what is required to keep the chip cool under a wide range of conditions".

Reviewers have lauded the Nvidia nForce4's firsts, including Nvidia ActiveArmor, which provides end users with a hardware-accelerated security firewall solution built directly into the silicon; support for the next-generation SATA 3Gbit/s hard drives; native Gigabit Ethernet networking, and advanced overclocking options through the use of the company's nTune software application.

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