Signal Integrity Analysis of RF Probe Card for WLCSP Testing Using Polyimide-Based Grounded Coplanar Waveguide Transmission Lines

Wafer-level chip-scale packages have been extensively adopted in the electronic packaging industry owing to their ability to enhance device performance. This study proposes a novel radio frequency probe card designed for wafer-level chip-scale package testing for frequency of up to 8 GHz, employing polyimide-based grounded coplanar waveguide transmission lines. A hybrid grounded coplanar waveguide is used, wherein the width of the transmission lines and the shape of the ground design are varied to accommodate the current carrying capacity required for high radio frequency power channels. Based on a hybrid design concept, a hybrid grounded coplanar waveguide circuit is fabricated using polyimide-based multilayers via a one-time built-up process, utilizing three-dimensional Micro electromechanical systems technique. This fabrication ensures a robust structure extending up to the contact tip, thereby providing reliable signal transmission and integrity. Moreover, the design incorporates various factors that are critical to signal integrity including impedance matching, scattering parameters, and jitters. The performance of the proposed probe card is validated via comprehensive simulations and measurements, and the feasibility and effectiveness of the design is demonstrated through suitable experiments. The obtained results confirm exceptional performance of the proposed probe card in Wafer-level chip-scale package testing scenarios and demonstrates its appropriateness for a wide range of Wafer-level chip-scale package testing applications up to 8 GHz. Moreover, its ability to ensure reliable signal transmission, coupled with its consideration of key signal integrity parameters, entails it as a valuable tool in the electronic packaging industry.