Issue link: https://iconnect007.uberflip.com/i/1327102
72 DESIGN007 MAGAZINE I JANUARY 2021 rough number to represent the dielectric con- stant, dielectric thickness, and the attributes of the trace thickness and width to establish a solution. However, these are not the attributes of the actual materials used by the fabricator to manufacture the board and are inherently inaccurate. There is no point in employing a field solver if your numbers are wrong. Once the ballpark virtual material num- bers are established, the material needs to be selected for the correct frequency of operation. Choosing the materials that are stocked will result in up to 5% better accuracy. Obviously, what you select is based on what is available at a reasonable price. Figure 5 is a graph of the low loss dielectrics stocked by a particular fab- ricator. One can clearly see which is the best material. B. Incorporating Multiple Technologies The iCD Stackup Planner is the first con- trolled impedance tool to enable field solver computation of multiple differential pair def- initions per layer. This allows you to incor- porate differential 50/100 ohm Digital, 40/80 ohm DDR3/4, 90 ohm USB, etc., sharing the same layers (Figure 6). This is important as it is extremely rare to just have a 50-ohm single ended impedance. Usually, many dif- ferent single-ended and differential imped- ances have to share layers throughout the substrate. And these variations have to be documented. C. Seamless Integration to EDA software For PCB designers, it is also important to be able to transfer the impedance variables and material properties to their EDA tools. Plan- ning the PCB stackup in the early stages of the project reduces unnecessary iterations and optimizes the costs by increasing manufac- turability and electrical performance. Far too many designers leave stackup design, which is critical to signal and power integrity, to the Figure 4: 2D Field Solver used to predict microstrip and stripline impedance (iCD Stackup Planner).