— David Perlmutter

A wire-frame model of a printedcircuit board shows temperature results after running an analysis. Red nodes indicate heat sources.

A color contour map shows temperatures on the printedcircuit board.

A model of a temperature-sensitive enclosure shows part of a what-if analysis to find an optimal design.

As part of these projects, we are often required to perform thermal analyses. The Sauna thermal-modeling program makes this task easy, allowing us to simulate a wide variety of electronic systems, including heat sinks, circuit boards, semiconductor stackups, and complete enclosures. Sauna has been a solid performer for us, and is moderately priced.

Topping the list, the program is easy to learn. This is important because our company doesn't have a dedicated thermal analyst. A clean and intuitive screen layout helps make the program simple to use. And the manual, which covers all of the situations that Sauna is capable of modeling, is filled with examples to help out beginning and occasional users. The manual steps through actual problems, an easier and more powerful way to learn than trying to follow abstract instructions. The manual clearly delineates steps to be taken and illustrates graphical and textual analysis outputs.

Model definition is straight-forward. A relatively simple model can be quickly created without a lot of planning or cryptic inputs. For circuit-board analysis, users typically only need to specify material type and board dimensions, and the software creates the appropriate configuration based on a library of material properties and the current modeling setup.

Users can "see" models graphically as soon as they are entered, which often eliminates the need for backtracking and error correction. The graphics area provides wire-frame or shaded models for simplified visualization. Also, multicolor temperature profiles make analysis output easy to understand.

In a recent application, the design consisted of a circuit board with several high-heat-dissipating ICs. The customer wanted to know if the suggested thermal planes in the board would be sufficient to maintain acceptable temperatures. Using Sauna, we created a wire-frame model of the board, selected appropriate materials from the library and typed in the board dimensions. Analysis showed that the proposed design achieved project goals.

In addition to circuit boards, the program analyzes models with fins, enclosures with multiple internal boards, and forced-convection models. Users are able to create such complex 3D models by combining "building blocks," including plates, circuit boards, and plates with fins. Sauna also analyzes models of semiconductor-device stackups. This comes in handy for specifying thermal vias when designing boards with surfacemount components.

The program goes beyond static analysis to perform transient and duty-cycle simulation. However, transient and duty-cycle features are available only in the expanded modeling version, not the basic package.

We have been using Sauna for several years and find that the analytically derived temperature profiles are usually quite close to experimental values. Any differences are typically a result of inaccurate modeling or a misunderstanding of the design problem. In fact, all output is accurate — at least as accurate as the inputs — because the software uses accepted analytical techniques.

Customer support is superb and quickly responds to questions. As a design tool aimed only at thermal analysis for electronic products, Sauna doesn't have a huge customer service staff, nor does it need one. The well-designed manual answers most questions.

Of course, no software package is perfect. My problem concerns the depth of the menu tree. Many often-used commands are buried deep within the tree. A good first step to minimize this inconvenience is the new menu button layout on the screen that helps to quickly find the appropriate commands.

The Sauna thermal-modeling package comes from Thermal Solutions Inc., 3135 S. State St., Suite 108, Ann Arbor, MI 48108, (734) 761-1956, thermalsoftware.com

David Perlmutter, a principal of Perl Technologies Inc. (perltech.com), is a degreed mechanical engineer and registered professional engineer in the state of Maryland. He can be reached at (703) 807-2714, davidp@perltech.com