Ground guard structure to reduce the crosstalk noise and electromagnetic interference (EMI) in a vertical probe card for wafer-level testing

Wafer-level testing is an important process in integrated circuit (IC) manufacturing to enhance the yield and reduce costs. The development of a vertical probe card enables the testing of low-voltage and high-frequency devices with reduced probe lengths compared to conventional probe cards. Despite these advantages, crosstalk noise and electromagnetic interference (EMI) have alarmingly become a serious problem with smaller pad sizes, higher pad densities, and increased signal input/output frequencies. In this paper, we propose a new ground guard structure of needle in a vertical probe card to reduce crosstalk noise and EMI. The effect of the proposed ground guard structure is analyzed in the frequency- and time-domains. To validate the effect, the original structure and the proposed ground guard structure are compared. The ground guard structure is designed with a 3D electromagnetic solver and the results are visualized by means of S-parameter curves and eye-diagrams. Also, the reduction of the radiated near-field emission is presented through a 3D polar plot. The simulation results successfully confirm that the proposed ground guard structure effectively reduces the crosstalk noise and radiated emission.