Thermal evaluation of power amplifier modules and RF packages in a handheld communicator system

The General Packet Radio Service (GPRS) is a non-voice value added service in the handheld communicator system allowing information to be sent and received across a mobile telephone network. It enables networks to offer ´always-on´, higher capacity, and Internet-based content and packet-based data services. With more capabilities and higher duty cycles, the chip set in the handheld system should withstand larger thermal loads, yet maintain high standards for electrical and thermal performance. A detailed Computational Fluid Dynamics (CFD) study was performed to examine the thermal characteristics of a chip set at the system level. This chip set includes the Power Amplifier (PA) module, power management and base-band packages, front-end receiver package and memory. Detailed solid modeling was applied to the PA module with the GaAs (Gallium Arsenide) device bonded to a multi-layer ceramic substrate. Other packages placed on the PCB were simulated as compact thermal models. Several system level variables are investigated, including the PCB thermal via distribution, Power Management package designs, and enclosure convection and thermal interaction among packages. The study focuses on the power management (ball grid array) package and demonstrates the advantage of using thermal simulations to predict the device peak temperatures under realistic operating conditions. The results also demonstrate the minimal impact of thermal via structures and their specific locations underneath the PA module.