The wide disparity of scales in a typical electronics system makes it difficult to simultaneously evaluate the flow and heat transfer characteristics at the system/board level as well as the component level in a CFD (Computational Fluid Dynamics) simulation. The determination of junction temperatures of individual components necessitates a zoom-in approach, where data obtained from the system level simulation is used as an input for the component level model. This requires the accurate specification of boundary conditions to describe the effects of the local package environment. For conditions involving complex flow situations and heat spreading in the board, this task can be challenging. The present work proposes a method where the flow boundary conditions are obtained from a macroscopic board level model. The junction temperatures are obtained using a superposition approach. The zoom-in model requires fewer grid cells, enabling quicker evaluation of junction temperatures. An additional advantage is that heat sinks can be optimized within the zoom in model and the junction temperatures directly predicted without having to run the complete board model at every stage in the design. The method is verified against experiment.

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