Polar Instruments Si9000 is one of the most important tools for anyone working on high speed digital designs. The software is aimed at estimating trace impedance and can help simulate loss less trace impedance as well as analyse how trace impedance would change based on the frequency of interest. There are a number of built in PCB layer stack-up configurations available within the tool and all the user needs to do is to enter relevant data for a chosen stack-up and click the calculate button. The calculated database can be saved and retrieved at a later time, making it non-repetitive. Almost all possible trace configurations are built in along with a XFE option which enables hashing of ground planes. Possible trace configurations include both single ended traces and differential traces. The tool allows cross calculation between a few variables. For example, target impedance can be entered and trace spacing or trace width required to achieve that impedance can be calculated. XFE is a very important option while dealing with Flexible printed circuits (FPC). Due to relatively thin buildup it is extremely difficult to achieve 50 ohms impedance for single ended signals with a solid ground reference plane on FPCs and so the ground return paths are generally hashed. XFE helps understand what sort of hash width and spacing is required for the ground layer to achieve required impedance.