Thermal management concerns are always prevalent in the design of electronics hardware, from DC and power conversion applications, to high-frequency communications applications. Poor thermal management can directly result in degraded device performance, and potentially even catastrophic device failure. Having the ability to accurately predict any thermal concerns prior to hardware assembly will potentially save a great deal of time and money further down the line. Thermal modeling is the most cost-effective means of predicting potential thermal management concerns, as there is no hardware that would need to be scrapped, and modification and optimization of the model can easily be incorporated without impacting any material cost.

There are several thermal modeling software packages that are widely used throughout industry. One of the most accurate, and intuitive, is the COSMOSFloWorks® program. FloWorks is an easy-to-use thermal analysis program that is fully embedded within SolidWorks® solid modeling software program. It provides the capability to simulate and accurately analyze fluid and gas flow, for practically any application. Heat transfer within FloWorks can be modeled using conduction, convection and even radiation. Along with the ease of modifying solid geometries within a model, the boundary conditions can quickly be changed to efficiently optimize the thermal model. Critical boundary conditions that usually require optimization are fluid and gas flow rate, pressure, surface and volume heat generation rates and temperatures.

Figure 3-1 shows a heat exchanger assembly which was designed, built, and tested at the EMPF to simulate the cooling strategy for the power electronic modules. It was designed to simulate the junction temperature of Insulated Gate Bipolar Transistors (IGBTs) so that their steady state, as well as their short duration on demand outputs, could be evaluated. Optimization of the design involved analysis of several thermal interface materials (TIMs), coolants, and cold plate designs. Instead of using actual IGBTs as heat sources, planar 600W 3'W resistors were used to simulate each IGBT. To model a steady state condition where the inner and outer IGBTs are at different heat outputs, two Lambda power supplies (GEN 40-85) were used to provide different power levels to the inner and outer resistors. Attaching the resistors to the cold plate was accomplished using a copper heat spreader designed to minimize thermal loss and to accommodate the different footprints of the resistors and the IGBT. The heat spreader also allowed attachment of thermocouples that were placed directly under each resistor and directly above the coldplate using 0.030" slots and silver epoxy. These thermocouples accurately monitor the heat flow from the resistors into the coldplate, and detect any anomalies.

Optimization of the hardware to the parameters in question proved to be fairly time consuming, as materials had to be swapped, and hardware had to be modified. Conversely, utilization of a solid model allows for much more efficient optimization of the hardware. Model parameters can be quickly changed and results can be achieved in a much more desirable timeframe. Figure 3-2 shows a SolidWorks representation of the heat exchanger assembly described above. The FloWorks software was able to analyze the model and provide temperature gradient data in a very reasonable timeframe. Results for this particular model are also shown in Figure 3-2.

The model simulation results compared very favorably to the hardware assembly measured data. While some experimental data must be obtained to verify and “tweak” the computer model, subsequent modifications to the material properties and thermal conditions can be quickly and easily incorporated, for the same fast, accurate results. The modeling of this particular assembly provided significant insight into the benefits of incorporating modeling software into the design phase of any electronics application.

Thermal modeling can be performed and then verified using real devices in a controlled thermal environment at the EMPF’s Thermal Management Test Facility. More information can be found by visiting the EMPF website, www.empf.org, or by calling the EMPF technical staff at 610.362.1320.