Finding the right balance among test cost, test quality, and data collection for running diagnosis requires consideration of several competing factors. Luckily there are some best practices for creating efficient cost-effective pattern sets and applying them in the best order for detection and diagnosis of defective parts.
Test engineers can improve defect detection and silicon quality by applying a lot of patterns and pattern types, such as gate-exhaustive patterns, but this gets expensive. The more cost-effective way is to target the types of fault models that detect the most silicon defects without over-testing. Do this by creating a sequence such that each pattern set can be fault-simulated against other fault types before additional “top-up” patterns are created to target the remaining undetected faults. This cross-fault simulation is important for test cost reduction.
The challenge is determining the order in which patterns should be created. In general, give priority to creating patterns that have the most strict detection requirements, such as path delay patterns. Figure 1 illustrates a typical pattern generation process.