Power Output Improvement Of Flip Chip Packaged Power Amplifier

Power Amplifier (PA) is to amplify small signal, and obtain a bigger output signal of mobilephone. Flip Chip is one kind of package mode in which the surface of the packaged chip is faceddown to and connected to the underlying substrate. Using this method, the interconnect distance isshorter, and parasitic inductance, capacitance and resistance of the chip all also smaller. Therefore, RFsignal loss is less, the signal integrity and frequency characteristics become better.The paper focuses on the output power improvement of a flip chip packaged PA product. Throughthe circuit function analysis and Smith chart analysis of similar frequency bands, the theoretical basis ofthe way to improve the output power is obtained.Considering the cost and time-to-market of the PA product, the most feasible way is to add anadditional capacitance. Our experimental data show that power output can be improved by increasingthe effective capacitance. In the optimized condition, the improved output power at a frequency of1710MHz is larger than31.2dBm, meeting the target of the customer.On the other hand, from failure analysis of PA products with different power outputs, we found animportant issue which affects the power output at1710MHz. In the substrate of low output samples, thewidth of metal lines of1710MHz matching inductance coil becomes narrowed and is out ofspecification, resulting in bigger value of the hollow inductance. The correlation between the largerinductance value and smaller power output can be understood based on the circuit analysis.