This paper demonstrates the advantage of applying Predictive Engineering in thermal assessment of a 279 I/Os, 6-layer, depopulated array flip chip PBGA package. Thermal simulation was conducted using a Computational Fluid Dynamics (CFD) tool to analyze the heat transfer and fluid flow in a free air environment. This study first described the modeling techniques on multilayer substrate, thermal vias, C5 ball, and PCB. For a flip chip package without any thermal enhancement, more than 90% of the total power was conducted from the front surface of the die through the solder ball interconnects to the substrate, then to the board. To enhance the thermal performance of the package, the heat transfer area from the backside of the die needs to increase dramatically. Several thermal enhancing techniques were examined. These methods included copper heat spreader with various thicknesses and with thermal pads, metallic lid, overmolded with and without heat spreader, and with heat sink. With an aluminum lid and a heat sink, it gave the best improvement; followed by a heat spreader with thermal pads. Both methods reduced thermal resistance by an average of 50%. Detailed analyses on heat flow projections are discussed.