Signal Integrity Analysis of Butterfly-Shaped Vias for RF Packages

This paper studies the signal integrity of butterfly-shaped vias in fan-out packages simulations by high frequency. A butterfly-shaped copper pillars are modeled as interconnection wires in a fan-out package. The high frequency structure modelling and simulations are carried out to investigate major signal integrity indicators, such as the impedance, the S parameters, and the Q factor. By optimization of the key design parameters of the interconnection, such as the minimum via diameter, the aspect ratio, and the curvature of the via wall, the impact of butterfly-shaped copper pillar on signal integrity can be determined. The numerical study results have been found that the impedance of the selected interconnection cliff falls around 18GHz and tends to be stable beyond 18GHz. As the Angle $\alpha$ increase from 50° to 90°, it has a significant impact on impedance variance below 18GHz. As the input frequency increases, such an impact becomes negligible. Therefore, the selected structure has a great process margin for high frequency applications. In addition, Angle $\alpha$ has a limited impact on the Q factor, which varies insignificantly as the $\alpha$ increases.