Radiative coupling in BGA packaging for mixed-signal and high-speed digital

Abstract

Mixed signal packaging must provide high levels of isolation between analog, RF and digital partitions. This has in the past been done on the subsystem level. Future mixed-signal systems should provide this isolation on the package-level and, possibly even on the chip-level. Here we study package-level isolation, focusing on circuit and radiative coupling mechanisms in the ball-grid-array (BGA) environment. Double printed-wiring-board (PWB) test structures joined with BGA solder balls have been designed and fabricated. We have simulated full-wave coupling using 3D FEM simulation and circuit coupling using circuit simulation with 2D capacitance and inductance matrices. Time-domain coupling measurements on unshielded and shielded coupling structures have been performed and correlated with simulations. Based on this we have developed an understanding of circuit and radiative coupling in the BGA environment. Techniques to manage mixed-signal BGA isolation have been identified.