Impact of Filter Placement on the Shielding Effectiveness of a Board-Level Shield

This paper investigates how low-pass filter placement influences the shielding performance of a board-level shield when input/output traces cross its boundary. The analysis examines how these traces degrade shielding effectiveness and explores how low-pass filters suppress unwanted electromagnetic disturbances to improve shielding performance. Furthermore, the study evaluates the impact of parasitic effects of lumped elements within the filter stopband, highlighting their role in the degradation of shielding effectiveness at higher frequencies. Finite-difference time-domain simulations were performed for five configurations to assess the influence of filter placement, proximity to the board-level shield, routing, and parasitic effects. The SAE ARP 6248 stripline method, adapted for board-level shield characterization, was used to evaluate shielding effectiveness from 1 to 40 GHz. The results indicate that placing the low-pass filter as near as possible to the board-level shield improves shielding effectiveness for both internal and crossing traces. In addition, the findings also confirm that parasitic effects in the filter’s stopband can compromise the enhancement of shielding effectiveness at high frequencies.