Issue link: https://resources.pcb.cadence.com/i/1532920
Critical Trace Length Definition: Critical trace length is the length of a trace or transmission line that would cause the signal to reflect if it's too long electrically. Steps: 1. Open Constraint Manager. 2. Navigate to the worksheet Electrical > Routing > Total Etch Length. 3. We have existing Constraint Sets but feel free to make a new one. 4. For an electrical constraint set in the list, set the Maximum Total Etch. For example, USB 2.0 operating at 480 Mbps may see any traces longer than 3500 mils (88.90 mm) electrically long. So we set the max total etch to that value (shown below). 5. Recall that this is just the constraint set. It must be applied to nets in the design. Navigate to the Electrical > Net > Routing > Total Etch Length worksheet. 6. Next right click on the nets you want to analyze then choose Analyze. You will see the results below. 7. The Constraint Manager shows what the total etch length of the traces are, the length of the unrouted parts and even the percent of the routed net over the Manhattan distance (orthogonal position and distance if only routing at 90 degree angles). Impact: Manufacturers have significantly reduced the rise times of chip signal transmissions, and we may not always have enough space on a PCB to slow these signals down. Fortunately, we can shorten trace lengths, which helps create a more compact PCB layout. This reduction minimizes the chances of signal reflections, preserving signal integrity and ensuring effective communication between devices for optimal PCB functionality. It's essential to set maximum trace lengths to avoid critical timing issues and signal degradation, especially for high-speed signals, as longer traces can lead to increased attenu- ation and skew. 11 www.cadence.com OrCAD X Constraint Management Guide