Computational Fluid Dynamics (CFD) tools are routinely used to get accurate predictions of junction temperatures of Integrated Circuit (IC) packages. However, it is desirable to obtain reasonably accurate junction temperature estimates as early as possible in the design process without having to model the board and flow in large detail. In order to accomplish this, a good estimate of the board side thermal resistance is required. The new method presented here estimates the board side resistance for a standard JEDEC high conductivity board in forced convection. The overall board resistance incorporates the spreading resistance of the board, taking into account the multiple layers of copper and dielectric, also the heat transfer coefficient from the board using established correlations. The results of the calculation method are further compared with a full CFD simulation of a simplified package on a board. Good agreement is obtained between the CFD simulation and the proposed method in predicting the junction and case temperatures. The numerical discrepancies are within 1.5% and 4.2% respectively, over a broad range of airflow speeds typical of forced convection cooled electronics systems. The accuracy of the proposed analytical calculation method recommends it as a potential method of replacement of a full CFD simulation of the board and component with a conduction only analysis. The board-side boundary condition for this analysis could be represented with an equivalent heat transfer coefficient.

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