Effects of package orientation and mixed convection on heat transfer from a PQFP

The thermal resistance of a surface-mount, plastic quad flat package (PQFP) was measured over a range of heating powers, air velocities, and package orientations. The specific package was one developed by a Joint Electronic Device Engineering Council (JEDEC) committee for standardized testing. The package was mounted in a low-speed wind tunnel which could be rotated in a vertical plane, thus changing the orientation of the package with respect to the gravity vector. Results define the limits of mixed convection for a horizontal package, and of orientation effects for package/tunnel orientations from buoyancy-opposing to buoyancy-assisting. For large air velocities greater than 2.5 m/s, for all tunnel orientations, the package thermal resistance shows a steep decrease, which is attributed to restarting of the surface boundary layer on the package