Issue link: https://resources.pcb.cadence.com/i/1533023
Controlling Air Gaps Using OrCAD X and Allegro X Tools The shape of things to come is the dynamic shape. Actually, it's a well established pattern of using the constraint set to directly affect the outcome. The smart copper "sees" other traces, vias and other shapes that have different nets and works around them. What the shape does with a friendly pin or other feature is part of a parallel set of rules regarding Same_Net properties. The exact amount the shape pulls back is entirely up to the user - you. As with the line width parameters, the spacing constraint tab has a default set of air-gap parameters. Other rules may be in effect for various reasons around impedance, magnetic coupling, crosstalk or other isolation goals. The numerical value of the air-gap will always be, "It Depends". The first dependency is the nature of the two features. You'd certainly do everything you could in the placement phase to avoid routing the receive chain next to an external oscillator. Mind the established aggressors and potential victims to keep them organically separated. It takes some finesse to get everything to play well together. Coexistence is pretty easy when you have all the board space you want. Shrinking down to the form factor unleashes the unknown threats. Do that layout and then, find out. Figure 1. The green shape is a partial ground plane on the outer layer. It is a dynamic shape used to isolate the four memory chips from nearby circuits while forming around the existing circuit pattern. A static shape would be used to create an EMI shield or other polygon that did not dodge around the existing circuit. Once you've found out the hard way, (and by that I mean boards come in and there's some issues that were not foreseen) there are two concerns, first is correction of the problem and second is prevention of the problem down the road. The correction path involves separating the annoying parts. The prevention path is partly in the realm of the constraint manager. We may add a new constraint set that restricts those unforeseen things from happening again. 2 www.cadence.com Controlling Air Gaps Using OrCAD X and Allegro X Tools