Investigation of PWB Stack-Up Using FDTD Modeling

The Electromagnetic Interference (EMI) from multi-layer Printed Wiring Board (PWB) was investigated by Finite-Difference Time-Domain (FDTD) modeling. The modeling was corroborated by a comparison between measurement and modeling for a test board. Two types of noises - simultaneously switch noise (SSN) and shoot-through current as an EMI source were investigated. A method to model SSN is proposed, and applied on a six-layer board with two stack-up structures, e.g., adjacent power and ground plane versus stripline structure. The results indicate that if shoot-through current dominates the noise source, the SSGPSS stack-up is suggested. If SSN is high, the SGSSPS stackup has advantages below the board resonance frequencies, while the SSGPSS stack-up is generally preferable above the board resonance frequencies.