Defect Concentration
The percentage of individual printed circuit boards rejected during fabrication on a single production sheet reduces the overall output of a manufacturing run. Tracking panel yield loss allows fabricators to identify specific process steps, such as etching or drilling, that are introducing defects across the panel. This calculation is a primary metric for evaluating manufacturing efficiency and process stability.
A high rate of board rejection on a single sheet indicates that the process window is too narrow or the equipment requires calibration.
Scrap Mechanism
Defects that contribute to this scrap rate include line opens from dust on photolithography masks, solder mask misregistration, and plating voids inside via holes. When a single board on a panel fails automated optical inspection or electrical testing, that board is marked with a non-conforming identifier and discarded after the panel is routed into individual pieces. If the panel yield loss exceeds the planned margin, the fabricator must process additional sheets to meet the customer’s total order quantity.
This overrun delay increases lead times and disrupts delivery schedules.
Financial Impact
Manufacturing runs must absorb the cost of discarded boards, which increases the average unit price for the remaining good units. If the yield is too low, the profit margin on the order disappears for the fabricator. Therefore, engineering teams work to optimize layout spacing and plating balance to keep the scrap rate as low as possible.
