The steady state thermal performance of semiconductor packages has been traditionally reported through the utilization of a single junction-to-ambient thermal resistance constant commonly referred to as theta(ja). This is particularly inadequate for multichip modules where several devices reside within the same package structure. This paper discusses how a central composite design of experiments can be applied to provide a more accurate thermal characterization of a multichip module package. The end product is a series of linear or polynomial equations which can be utilized by the customer to calculate individual device junction temperatures over a,vide variation of convection cooling environments and multiple device power dissipations. A 352 plastic ball grid array package, which encompasses three individual integrated circuit devices, is used as an example. The paper steps through the sensitivity analysis and evaluates the accuracy of the resulting equations. This method of thermal characterization can be easily applied to single chip modules of varying power and cooling regimes, or multiple output devices where several power junctions reside within the same integrated circuit.
