Radio frequency (RF) channel isolation is one of the important indicators for measuring the performance of system in package (SiP) modules, which directly affects the stability and signal quality of the system. A ball grid array (BGA) solder ball isolation technology for 3D SiP modules has been proposed, which utilizes BGA solder balls connecting the upper and lower substrates in the board level stacking process to form a shielding wall, thereby improving the isolation between RF channels. The common RF space leaks in SiP modules are classified according to their arrangement, and the effectiveness of this isolation technology is verified through simulation calculations and physical testing, providing strong support for improving the RF channel isolation of SiP modules.