Effect of system orientation and cooling mechanism on component thermal impedances in an electronic enclosure

An experimental investigation of the dependence of thermal impedance on a variety of typical design dependencies is discussed. Various thermal impedance formulations at the board, regional, and component levels are applied to the analysis of data derived from a simulated circuit pack array in an air-cooled enclosure. The utility of these measures for performance comparison, data analysis, modeling, and design extrapolation is illustrated. A component-level energy balance which is used to predict measured changes in peak component temperature as a function of power level and location of neighboring components is proposed. Neighboring component effects can increase effective component thermal impedance by more than 25%. Measured heat transfer coefficients are compared to literature values. The design issues of correcting for neighboring component effects and utilizing the concept of regional thermal impedances are explored