Simplified integrated approaches to thermal modeling of electronics packages call for fast and easy thermal models. However, this is often in contrast with the complexity of the thermal problem to be solved, which prevents the application of simplified approaches. After a review of the available modeling strategies, steady state thermal analysis of a typical stacked ball grid array package based on a thermal resistance network is presented. The physical model is discussed in detail, together with its advantages and limitations. The results have been compared with detailed 3D-simulations performed by means of a commercial code: for thermal design purposes, the accuracy is satisfactorily, leading a prediction error of the junction temperature lower than 10%.