Design Constraint
Fabrication clearance establishes the mandatory buffer zone between the physical edge of a printed circuit board array and any active copper features or component footprints. This panel edge keepout prevents mechanical interference between routing equipment and the functional circuit when a board resides within a larger production panel. Copper traces placed inside this clearance zone risk damage during the depaneling process when saws or routers separate individual units from the main frame.
Fabrication Requirement
Solder mask and base copper layers require strict adherence to this buffer to ensure the integrity of the board during automated assembly. Machine fixtures often utilize the exterior space of the panel to register the board accurately under pick and place nozzles or optical inspection sensors. Any intrusion by conductive material into this zone results in short circuits or structural failure when the routing bit cuts through the material at high velocity.
The distance typically matches the mechanical tolerance of the routing equipment, which varies based on the specific mill diameter and the spindle runout of the machine. Manufacturers maintain these gaps to facilitate the extraction of boards without damaging the dielectric material or the internal layers of the substrate.
Assembly Consequence
Effective board extraction relies upon the total absence of structural features within this defined perimeter. Automated depanalization equipment exerts significant force against the carrier frame to move the panel through the station. Excessive copper in the keepout area creates uneven stress concentrations that cause delamination of the laminate during the mechanical severance process.
Reliable circuit performance demands that this keepout zone remains free of conductive material to avoid any risk of exposed copper or burrs affecting the final fit into a housing.
