Effect of flag design on thermal performance of PBGA packages

In order to meet performance requirements, the package design of the 272 27/spl times/27 mm PBGA package must incorporate the best possible thermal path from the die to the printed circuit board to which the package is attached. Unfortunately, the reliability requirements for passing moisture resistance are more easily passed with a minimum amount of copper under the die. This paper reports finite element thermal simulations predicting the effect of the design options on thermal performance. Switching from a solid flag with a solid spreader pad on the bottom of the substrate to a minimal copper design would cause about 3 to 6/spl deg/C/watt increase in junction temperature.