Abstract: Ceramic-based packaging substrates for system-in-package (SiP) have the characteristics of a large number of ball grid array (BGA) pins and good application compatibility, and are widely used in digital circuits, analog circuits, and RF circuit SiP. With the increase in system functionality, ceramic-based packaging substrates for SiP require larger dimensions and a greater number of BGA pins, which leads to an increase in thermal mismatch due to the mismatch in thermal expansion coefficients of different materials between the ceramic-based packaging substrates and the printed circuit board (PCB), thereby significantly affecting the reliability of BGA interconnections. Replacing the PCB with copper column grid array (CCGA) pins increases the distance between the ceramic substrate and the PCB, effectively reducing the impact of thermal mismatch on connection reliability. In this paper, structural and RF performance simulations, and experimental verification were carried out for studying the connection between RF SiP using CCGA and the PCB under thermal load conditions. Simulation and experimental results show that thermal stress is concentrated at the root of the corner positions of the SiP geometric structure. The CCGA-based RF SiP designed in this study demonstrates effective capability of withstanding thermal mismatch-induced structural stress and excellent RF transmission performance.