The first simulation often occurs prior to device selection. It can be used to evaluate different device and packaging options to ensure they can operate within their specifications for the given environmental constraints. Omitting this step can lead to difficulties, unforeseen costs, and delays later in the design process. The initial simulation can often be simplified by modeling the devices under simplified boundary conditions with the expected power, allowing for a first pass evaluation. As a specific device is selected and more details are finalized about the system, the thermal modeling should evolve to more accurately represent the board, chassis, and airflow characteristics, thereby increasing confidence and providing thermal margin in the thermal design. As power specifications are refined and as board and system-level modifications and assumptions change, simulation should be reevaluated to ensure adequate thermal margins remain. This process helps to identify any thermal or mechanical issues as early as possible, allowing the most time to resolve them. Omitting this process can lead to the identification of such issues towards the end of the project, potentially resulting in undesirable compromises or missed schedules.