Design-based Thermal Performance Evaluation of a GaAs MMIC Device in a Plastic Ball grid Array Package

摘要

Computational Fluid Dynamics (CFD) simulations were conducted to characterize the thermal performance of a gallium arsenide (GaAs) monolitic microwave integrated circuit (MMIC) device in a wire-bonded plastic ball grid array (WB-PBGA) package. Thermal analysis is required to assess the design risks associated with the low thermal conductivity of GaAs compared to silicon and the constraints on package substrate design and boundary conditions in cellular basestation cooling applications. A comprehensive thermal model of the sub-system was developed and implemented for an ambient temperature of 85 deg C. Due to the lower thermal conductivity of GaAs, power dissipation in the 13individual (discrete) areas on the die were modeled instead of uniform surface heat flux or volumetric heat generation rate approximations. A conjugate heat transfer problem, in which radiative loss from the exposed surfaces of the package to the RF enclosure were accounted for, was solved for vertical natural convection cooling of the sub-system. The model was benchmarked with infrared thermography measurements from an unencapsulated package in still air environment. Based on this benchmarking, the accuracy of predicted maximum temperatures from the model was determined to be in the range of +6 to +16