Coverage Metric
Defect-oriented test coverage measures the percentage of physical component pins and traces that are verified for assembly correctness. High structural test coverage guarantees that faults like shorts and open circuits are detected without relying on the circuit’s functional operation. This test metric evaluates the physical integrity of the assembled board.
It helps engineers choose between automatic optical inspection, x-ray inspection and in-circuit testing to maximize fault detection. By tracking this coverage, the manufacturing team ensures that every placed component undergoes at least one form of mechanical or electrical verification, minimizing the risk of latent failures.
Calculation Method
Calculation of this value uses a detailed analysis of which nodes can be accessed by the test hardware. Designers use boundary scan and flying probe testers to reach nodes that are otherwise buried in internal board layers. By using this mathematical metric, the production team can identify untested areas and adjust probe placement or test routines accordingly.
Production Boundary
Production lines use this percentage to estimate the risk of shipping a defective board. In high-density assemblies, achieving complete structural test coverage is difficult due to restricted physical access and the use of ultra-fine-pitch packages. Testing teams must combine complementary methods to compensate for these limits and ensure that every high-risk joint is evaluated.
This strategy ensures that defects are caught in the factory rather than in the field.
