Logical Placement
Logical placement of test structures on a manufacturing panel provides a representative sample of the quality across the entire production area. Panel coupon positioning involves deciding where to put these test targets relative to the active circuit boards. Most fabricators place them in the corners or the center of the panel to capture the variations in plating and etching.
Statistical Representation
Copper thickness often varies between the center and the edges of a panel due to the way current flows in the plating bath. By using strategic panel coupon positioning, an engineer can verify that even the most disadvantaged areas meet the minimum specifications. If coupons are only placed in the best areas, the test results will not show the potential defects in other parts of the panel.
These structures are designed to mimic the most difficult features of the actual design, such as small vias or tight spacing. This approach allows the lab to destructively test the coupon instead of the expensive finished boards.
Location Logic
Modern software helps optimize the layout to minimize material waste while still providing enough data for quality assurance. The final location of each coupon is recorded and used to correlate test results with the manufacturing process.
