System and Package Level Thermal Optimization of Power Amplifier Modules With Application in Wireless Communication

Increased functionality of microelectronic packages for commercial applications leads to the necessity of identifying packaging solutions with high standards for thermal performance, during its functioning lifetime as well as during various test conditions. A detailed numerical analysis examines the thermal characteristics of a power amplifier module for time division multiple access (TDMA), using commercially available software. The increasing trend in power levels and densities leads to the need of design thermal optimization, either at module level or system level. Under specific test conditions, the thermal performance of the module degrades gradually; therefore, alternative test designs are investigated for thermal performance optimization. Initial study focuses on assessing the thermal performance of a baseline design. The peak temperature reaches 144°C, about 60°C temperature increase over the reference temperature. The peak temperature value is below the limit of 150°C. Further investigation focuses on several systems level designs, by incorporating individual test contactors between the DUT and load board or with conductive elastomers or pedestal solid ground slug for thermal performance enhancement. The peak temperatures are calculated in this case for the system being exposed to the ambient at 85°C. The results indicate that the test design with solid ground slug provides the best thermal performance, ∼ 5% better than the other designs. The small difference between the first two designs (with individual contactors and separate solid ground slug with conductive elastomer) resides in the fact that the elastomer has a small thickness (0.25mm), thus a low thermal resistance (based on thermal conductivity greater than 1W/mK), with minimal impact on the overall thermal performance of the TDMA under current test conditions. The temperature difference between the top section of the contactor designs with the CBC pin/copper block/pedestal is small; in spite of this, the high temperature reached by the individual CBC pins induces possible failures in the elastomer. The designs with pedestal and solid ground slugs have a notable advantage over the design with individual contactors, due to no moving parts within the elastomer, being more robust. The peak temperature reached by the module under the best/worst testing scenarios varies by ∼ 4–5%.