Thermal evaluations of 144 pin plastic flat packs

Experimental thermal evaluation procedures and results for 144-pin plastic flat packs soldered on a circuit board are presented. The board is positioned at the center of a 19-mm-wide air flow duct. Both internal and external thermal resistances are obtained for modules containing 6.7-mm*7.0-mm rectangular and 9.9-mm*9.9-mm square chips. The external thermal resistances at air velocities ranging from 0.5 to 4 m/s at power dissipation levels of 0.5-1.5 W are determined. It is found that external thermal resistances are significantly different for different chip sizes, and the difference is relatively constant in the range of variables covered in this experiment. Data on external thermal resistances are correlated with respect to air velocities. They indicate that air flow becomes turbulent at about 1.5 m/s. The internal thermal resistance increases slightly with respect to the air flow velocity. A numerical solution using a finite-difference method is performed, and the result shows the same trend as the experimental data.<>