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5 Electrothermal Mechanical Stress Reference Design Flow for Printed Circuit Boards and Electronic Packages // / Stage 3: Power Integrity and DCIR Analyses in SIwave Using such a table as reference, you can very easily assign current sinks and voltage sources to the board in SIwave before running a DCIR simulation. The SIwave workflow wizard lists all the steps you need to set up a board for simulating its electrical characteristics. For this particular board, you can directly configure the DCIR simulation since most of the steps listed in the wizard occur automatically upon translating the geometry into SIwave using the ODB++ directory. The workflow wizard lets you open the DCIR Configuration window where you can multi-select the components and assign voltage sources to them, all at once. Similarly, assign current sinks. Modify the voltages and currents for these reference designators based on the manufacturer's data sheets. At this point, you can run the simulation to compute DC current and voltage distribution across the board and ICs. SIwave employs an automatic adaptive mesh refinement process that accurately computes the DC voltage drop and current density for the entire board. It also calculates the I 2 R-drop and current flow within each element in a PCB model (including resistor, inductor, via, trace, plane, bondwire, source, etc.). The current density plot and the final mesh for our PCB are shown in Figures 8 and 9. SIwave highlights areas of high current density across the board in red. Additionally, you can generate power density and voltage drop plots across the board for all nets. SIwave can analyze DC current distribution return paths. Excessive voltage drop along a line or power delivery network can cause major issues at loads. Accurate DCIR drop analysis f rom SIwave is critical for designing optimal power delivery pathways. "What-if" analyses for DC voltage drop, DC currents and DC power losses are possible. Once the problematic areas on the board are found, you can perform "what-if" tests to determine the best approach for improving the layout. The predictive analysis helps you design power delivery networks to efficiently source the power to ICs and minimize power losses. The analysis identifies regions that bear excessive currents and helps you reduce risk of device failure. Adaptive mesh refinement, specifically developed for planar ECAD geometries, is the main reason for generating accurate solutions in SIwave. The overall accuracy of a finite element method (FEM) solver depends upon how accurately a mesh conforms to the design, and of course upon the accuracy of the numerical solution itself. SIwave starts with a high quality initial mesh, which is a collection of triangular elements. Triangles ensure a tighter fit to the geometry and minimize error. A numerical solution's accuracy relies on the density and distribution of mesh elements and the order of the basis functions used within each mesh element. With more adaptive passes, finer granularity ensues progressively f rom the initial mesh towards the final mesh. Figures 7a, 7b, and 7c show the meshes at various stages of adaptive refinement for a different printed circuit board in SIwave. Figure 6. DCIR configuration window in SIwave Figure 7b. Adaptive mesh after three passes Figure 7c. Final mesh Figure 7a. Meshes due to adaptive refinement after Pass 1 in SIwave

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