Design and Implementation of a Compact 3-D Stacked RF Front-End Module for Micro Base Station

Abstract

In the current 4G Long Term Evolution and the incoming 5G mobile communication technology, as the number of radio frequency (RF) devices in the RF front-end module is increasing fast, miniaturization is essential and significant. The 3-D RF system-in-package (SiP) technology is an excellent miniaturization solution. In this paper, a 700–2900-MHz 3-D stacked RF module with the size of 23 mm $\times$ 23 mm $\times$ 3.3 mm has been designed and implemented, which is used for a micro base station. It is more compact than other reported 3-D RF SiP products used for micro base stations. The 3-D RF module integrates four bare dies, one quad flat no-lead packaged chip, and more than 200 passive devices. Considering the electromagnetic isolation requirement, mechanical performance, and effective interconnection, the detailed structure design is presented in this paper. Simulations are performed for the electrical characterization and the thermal performance evaluation of the stacked module. The simulation results show that the insertion loss ( $S_{21}$ ) and return loss ( $S_{11}$ ) of the RF signal transmission lines are controlled below 0.42 dB and over 15 dB within 3 GHz, respectively. The electromagnetic isolation between different RF and/or intermediate frequency signal transmission lines is no less than 65 dB within 3 GHz. In thermal management simulation, the highest junction temperature of the chips in the 3-D structure is below 94 °C at the severe condition (50 °C ambient temperature and nature air convection). Finally, the assembly flow is presented, and the test results indicate the good electrical performance of the 3-D RF module.