Package and Board Power Integrity Design with ANSYS SIwave-PI

Modern design challenges such as 3-D IC and 2.5-D silicon interposers are excellent examples of how we pack more transistors into a smaller form factor. This is also evident from the trends requiring chip-aware system design with increasing transistor density and higher throughput on device IO interfaces. Smaller gate size requires a reduction in gate voltage, thereby shrinking power noise margins. It’s a huge challenge to stay within the shrinking voltage noise limits and keep pace with increasing current demand, since engineers also have to account for signal transitions occurring due to faster edge rates and more transistors switching simultaneously.

While designing PCB systems, the power distribution system plays an integral role in signal transmission. Unless a PCB is designed properly, all of the careful SI and PI engineering on the components and communication links can be wasted. ANSYS SIwave offers advanced techniques for full-system power integrity including chip–package–system technologies to provide full coverage for PI simulation needs.

SIwave can extract complete designs (which include multiple, arbitrarily shaped power/ground layers, vias, signal traces, wirebonds and circuit elements) while producing highly accurate models very quickly, without requiring potentially laborious layout partitioning by the user. Multiple layout topologies similar to those in this case study are supported, such as PoP, SoC, SiP and PKG on PCB. Integration of ECAD translation enables simple and seamless geometry translation from popular third-party electrical CAD (ECAD) vendors.

Locations of decoupling capacitors are important in PCDB design; generally, they should be placed close to the DUT, allowing enough room for signal net spacing. SIwave-PI includes PI Advisor, a technology that automates decoupling capacitor selection and placement and optimizes the impedance profile for ECAD. SIwave’s capacitor library browser contains over 20,000 capacitor and inductor models from the industry. It is very useful for evaluating lumped capacitor values with mounting inductance and resistance, viewing multiple impedance curves, and calculating their parallel impedance with easy user-defined filtering features to narrow down capacitor selection. Users can create their own user-defined library of capacitors, inductors and resistors from SPICE and Touchstone models.