Keep out Zone

Routing Constraint

Copper traces and vias are excluded from these regions to avoid short circuits with metallic housings or mounting hardware. Within a keep out zone, the absence of conductive material prevents parasitic capacitance between the signal layers and the chassis. Definition of these areas within the library footprint of a component ensures that the restriction moves with the part during layout.

Overlapping these zones usually triggers a violation in the design rule check software.

Mechanical Clearance

Sufficient space around the board edge or mounting holes allows for the application of assembly tools without damaging delicate circuits. A keep out zone surrounding a press-fit connector provides the necessary room for the support anvil during the insertion process. Without these clearances, the board substrate could crack or the solder joints of adjacent parts could be compromised.

Calculation of the clearance must account for the tolerance of the assembly machinery when sizing these boundaries. Precision during the initial definition of these areas prevents costly rework after the fabrication of the first prototype panels. Using standardized keep out regions across a product line simplifies the design of test fixtures and assembly jigs.

Interference Prevention

Sensitive analog circuits or antennas require isolation from high speed digital signals to minimize noise. A keep out zone around an rf antenna prevents the ground plane from detuning the signal or absorbing radiated power. The dimensions of these zones are often determined by electromagnetic field simulations or specific application notes provided by the chip manufacturer.