Verification Geometry
Test structures placed on the periphery of a production panel provide a representative area for destructive and non-destructive evaluation without sacrificing functional boards. Effective coupon design follows IPC-2221 requirements to ensure that the trace widths, hole sizes, and plating thicknesses match those found in the active circuit area. These patterns allow for the measurement of impedance, solderability, and registration accuracy across the entire manufacturing lot.
Fabricators use them to confirm that the etch rate was consistent.
Conformance Boundary
Mechanical constraints often dictate where these structures reside on the panel edge because they must not interfere with the routing of individual boards. Because a coupon design must survive the same chemical and thermal environments as the product, it validates the fabrication process through microsectioning. A poorly placed structure fails to capture the plating variation seen in the center of the panel.
Trace Correlation
The layout includes specific targets for automated optical inspection and flying probe testing. By aligning the orientation of the traces with the grain of the laminate, the coupon design accounts for dimensional stability changes during the lamination cycle. This ensures that measured impedance values are valid for the production units.
It provides a permanent record of the lot quality.
