First simulation often occurs prior to device selection. Simulation can be used to evaluate different device and packaging options to ensure they can operate within its specifications for the given environmental constraints. Omitting this step can lead to difficulties, unperceived costs, and delays later in the design process. First simulation can often be simplified by just modeling the devices in a simplified boundary condition with the expected power to do a first pass evaluation. As a specific device is selected and more is finalized about the system, the thermal modeling should evolve to more accurately represent the board, chassis, and airflow characteristics to bring greater confidence and greater thermal margin to the thermal design. As power is refined and as board and system-level modifications and assumptions change, simulation should be reevaluated to ensure adequate thermal margin remains. This process helps to ensure that any thermal or mechanical issues are identified as early as possible to allow the most time to resolve. Omitting this can lead to identification of such issues towards the end of the project, potentially leading to compromises that can be undesirable or missing schedules.