Speed Thermal Design Using Compact Models

Web-based model development means sensitive IC design never leaves the company.

An example of Agilent Technologies’s high-performance ASICs.

Agilent has long used thermal simulation tools to produce detailed models of packages that accurately predict the temperature of various elements within the design for a variety of conditions. More recently, the company has found it can save a considerable amount of time by using Flomerics’s new Internet-based process for developing behavioral compact models. The process helps predict temperatures at critical points such as the junction, case, and board.

Thermal analysis of PQFP compact model in JEDEC wind tunnel.

Compact thermal models interact appropriately with their environment. .

For three decades, Agilent has designed and manufactured complex, high-performance application-specific integrated circuits (ASIC) for applications including networking, computing, and imaging. Agilent offers state-of-the-art hierarchical design methodology and design-for-test capability, and has an outstanding track record of first-pass success in the design and manufacture of these chips. These strengths, combined with an extensive IP portfolio, facilitate rapid integration of quality ASICs.

Burton says that thermal data is required for most of the company’s products because it’s useful for engineers to have access to thermal characterization data based on standard tests such as EIA/JEDEC standard JESD51-6 (the integrated circuit thermal test method of environmental conditions–forced convection).

The JESD51-6 standard specifies the environmental conditions for determining thermal performance of an integrated circuit device in a forced convection environment when mounted on a standard test board. The thermal resistance measured using this standard is RJMA or QJMA, a forced convection environment with a specified air velocity and inlet temperature.

In the past, the majority of Agilent’s networking and computing ASICs were supplied to customers who were involved in the design process from start to finish, and those customers had complete access to component design information and decisions. This close relationship, in many cases, eliminated the need to provide standardized thermal design information. However, Agilent is now addressing a broader group of customers and needs to provide thermal design information in a more universal format. 

Agilent engineers have used Flomerics’s Flotherm simulation for system- and component-level thermal analysis. At Agilent, detailed package models are used to generate simulated standard thermal characteristics and the thermal design information needed by customers integrating Agilent components into their systems.

Detailed thermal model (left) and compact version of the same model (right). .

 

“Creating this design information has its difficulties,” Burton said. “Detailed models can often be difficult for customers to use because the ‘conduction only’ software models cannot be easily integrated into computational fluid dynamics (CFD) system simulations and even when they can, the complexity of detailed models can often computationally overwhelm system simulations. Distilling information from these detailed models into something simple and useful for customers can create its own problems,” Burton continued. “Simple resistor models are not universally useful since each customer may need this information tailored to their own system and boundary condition information.”

So Agilent took a close look at work done by the Delphi Consortium, a publicly funded research project consisting primarily of electronics manufacturers and including one software vendor, Flomerics, that led to the first thorough methodology for the generation of boundary condition-independent compact models. Boundary condition-independent means that the models will predict the temperature of the various elements within the package accurately regardless of the computational environment in which it is placed. A compact model is not constructed to mimic the geometry and material properties of the actual component, but rather is an abstraction of the response of the component to various boundary conditions, such as flows, temperatures, and pressures.

It is important to note that the Delphi methodology is a nonproprietary, open methodology that is under active consideration by the JEDEC JC 15.1 committee on thermal phenomena as the framework for an industry-wide standard for compact modeling.

“Flomerics has introduced a very easy and simple method of creating either detailed or Delphi models from what they call JEDEC Library Wizards,” Burton said. “One can simply select the appropriate JEDEC package outline from a dropdown list, input the power and the die size and occasionally a few additional pieces of information for certain package sizes. The website then generates a compact or detailed thermal model of the component.”

PQFP in still air.