RF Low-Pass Design Guiding Rules to Improve PCB to Die Transition Applied to Different Types of Low-Cost Packages

We present in this paper some design rules to improve the signal integrity (SI) of a package transition. The design rules are based on standard low-pass (LP) filter synthesis methodology. This methodology uses the modeling of the package transition by a pi network and is valid as long as the through phase shift of the package transition remains sufficiently small. Based on this pi network approximation, it is possible to add external distributed elements at the package carrier level and lumped elements at the DIE level to build an equivalent low-pass ladder filter. This approach improves significantly the signal integrity properties of the package transition without modifying the package. In some cases the frequency bandwidth for which the return loss (RL) remains higher than 20 dB can be doubled by using this method.