To get accurate thermal results from a simulator, Xilinx suggests using a CFD simulator that is designed specifically for electronics. For this reason, Xilinx directly supports the use of Siemens (formerly Mentor) FloTHERM and Ansys IcePak simulators, and provides natively compiled models for those tools. While it is suggested to use one of the simulators supported by Xilinx, if another CFD is the only tool available, it is better to use it than to not perform thermal simulation. If the simulator supports the generic ECXML format, Xilinx can provide that model by request. If it is not supported, thermal models of Xilinx devices must be hand built by the user.
There are two methods to build such models: resistor-based (DELPHI) and material-based (Detailed). It is not suggested to build simple 2-resistor (2-R) models based on JEDEC values, because while those are developed using a well-defined method, its primary intention is used to compare the thermal performance of different packages but not necessarily under the operating conditions most users face. A more accurate method is to build a multi-resistor DELPHI based model. For our UltraScale+™ and prior families, the details on the dimensions and resistor values can be found in the appropriate thermal characterization documentation that is either included in the models or available by request. DELPHI models provide a good balance of accuracy and computational speed. If greater accuracy is required, a material detailed model can be built. This will require more computation time. This can be requested from Xilinx. For Versal and later devices, only material detailed models are supported.
For devices that support DELPHI, it is suggested to use the DELPHI models early in the thermal design process for several quick iterations of the design to allow quicker convergence of the thermal system. As the variations of the simulations narrow, a detailed model can be substituted to ensure adequate thermal margin exists when using a more accurate model.