Predicting Chip-Package-Board Radiation EMI-EMC Early in the Design Cycle: Can Your EM Solver Do That ?

Consider the following scenario. Switching logic for large on-chip blocks leads to power transients. These transients find their way through solder bumps or bond wires through to the package, and through solder balls into the board. These cause not only IR drop, and voltage and ground bounce, but also cause radiation and electromagnetic interference. This radiation or EMI may couple back into the system, cause undesired interference to other system, cause unacceptable loss and noise, and may also cause the system to violate EMC rules such as those set by the FCC.

Consider a slightly diffferent scenario, associated with signal waveforms rather than switching power waveforms. Consider a differentially designed channel. Unfortunately, common modes are almost always excited due to some assymetry in channels, impedance mismatches, and complexity of geometry and environment in the chip, chip-package interface, package, package-PCB interface or within the board.  This so-called “differential EMI” (i.e. arising in differentially excited and designed systems) can also create undesired crosstalk and radiated fields.

The demands on an EM solver that can be used in such a scenario are extremely challenging. 3D full-wave accuracy is key, because interface and edge-effects, especially for systems with multiple or ill-defined references, are important in EMI. Quasi-static or 2.5D solvers will not cut it in this application. At the same time, this solver needs to scale to the full chip-package-board level to allow RDL and GDS layers, full-packages, and board nets to be simulated. The speed of the solver is critical: if early design is to be enabled, several design choices need to be considered on-chip, at the package, and in the PCB including routing, decap placement, logic switching and turn-off, etc.  Finally, such a solver needs to interface with on-chip noise modeling tools and SPICE, such that noise models from library characterization or worst-case switching noise can be directly integrated.  These are significant challenges of accuracy, compatibility, scale, and speed, where no compromises can be made by making rudimentary assumptions on 3D full-wave EM wave behavior.