Package Performance Improvement with Counter-Discontinuity and its Effective Bandwidth

This paper discusses a package design technique to enhance high speed signal performance by reducing the large discontinuity effects at the vias and solder ball interfaces. In the technique, an intentional counter-discontinuity in complementary phase to existing discontinuity is inserted to mitigate the existing discontinuity. Transmission line behavior of short multiple discontinuities are analyzed using theoretical approximation and simulation examples to demonstrate the validity of the technique. The techniques are then applied to package via and solder ball transitions of high speed differential nets using 3D simulation to evaluate improvement at target frequencies versus impact in bandwidth.