A method to predict failure of solder joints caused by thermal shock using finite element analysis for RF power amplifier applications

Due to price competition, low-cost design plays an important role in the power amplifier (PA) market. The cost of new single board design saves about 50% of direct material cost. Other advantages include decreasing direct labor cost, increasing maximum power output, increasing PA efficiency, and decreasing piece part count. For quality and reliability of solder joints, liquid-to-liquid thermal shock test would be considered during the design cycle. It was postulated that the failure is related to the coefficient of thermal expansion (CTE) mismatch between different materials, in the PCB, heat spreader, lead, cast heat sink, and device. The high power RF devices used in power amplifiers for base station applications have pushed the requirements of advanced materials and processes to provide new low-cost packaging solutions. A methodology is presented for design option evaluation and failure possibility prediction for solder joints on single board power amplifier. This method integrates the finite element analysis models and experimental data. The finite element model identifies the displacement at the solder joint locations. Several sets of experimental tests have been conducted and analyzed to evaluate the design improvements. Good correlation has been achieved between finite element analysis (FEA) predictions and experimental tests on design options.